WO2014152600A2

WO2014152600A2 - Measurement of cellular fmrp levels for high throughput drug screening and diagnosis of fragile x syndrome

Info

Publication number: WO2014152600A2
Application number: PCT/US2014/027517
Authority: WO
Inventors: Wei Zheng; Daman KUMARI; Karen Pearl USDIN; Manju SWAROOP
Original assignee: The United States Of America, As Represented By The Secretary, Department Of Health And Human Services
Priority date: 2013-03-15
Filing date: 2014-03-14
Publication date: 2014-09-25
Also published as: WO2014152600A3

Abstract

Kits and methods for the measurement of the FMR1 gene product, FMRP, are disclosed. The present kits include highly selective fluorophore-labeled antibodies that enable Förster (Fluorescence) resonance energy transfer (FRET) assays for the quantification of FMRP, which can in turn be used in methods for treating patients with underlying CCG-repeat mutations and for screening therapeutic moieties.

Description

MEASUREMENT OF CELLULAR FMRP LEVELS FOR HIGH THROUGHPUT DRUG SCREENING AND DIAGNOSIS OF FRAGILE X SYNDROME

TECHNICAL FIELD

[0001] The present disclosure pertains to the assessment of cellular Fragile X Mental Retardation- 1 protein (FMRP) for diagnosis, characterization, and treatment of Fragile X syndrome or other conditions that are related to abnormal levels of cellular FMRP.

BACKGROUND

[0002] Fragile X syndrome (FXS) is an X-linked disorder that produces intellectual disability that ranges from mild learning disabilities to severe mental retardation. In addition to cognitive impairment, patients with FXS also have epilepsy, depression and anxiety.

[0003] FXS is caused by mutations in the Fragile X Mental Retardation- 1 (FMR1) gene that result in the absence or a loss of function of its protein product, FMRP. FMRP is an R A binding protein that is ubiquitously expressed during early embryonic development, and highly expressed in adult brain and testes, the two organs that are most affected in FXS. FMRP regulates the translation of RNAs specifically at the synapse and is also involved in the regulated transport of RNAs in the dendrites.

[0004] The most common mutation in FXS is the expansion of a CGG-repeat sequence in the 5'- untranslated region of the FMR1 gene to >200 repeats (referred to as full mutation). Full mutation alleles show aberrant DNA methylation and histone modifications that result in heterochromatin formation on the FMR1 promoter. The net result is that the FMR1 gene is silenced that greatly reduces the synthesis of FMRP. In addition, even when gene is not fully silenced, it is not translated as well as normal alleles, further reducing the amount of FMRP that is produced. This phenomenon is also apparent in carriers of alleles with 55-200 repeats, the so- called pre-mutation alleles, where it is thought to be responsible for various cognitive and behavioral symptoms.

[0005] Research regarding therapeutic intervention for Fragile X syndrome is ongoing. Various targets for potential intervention to treat FXS have been identified, such as the family of metabotropic glutamate receptors (mGluRl-R8), or the gamma-aminobutyric (GAB A) receptor pathway. See, e.g., Pirozzi F, et ah, 2011. The FRAXopathies: Definition, overview, and update. Am J Med Genet Part A 155:1803-1816. Therapeutic intervention to date also addresses alleviating symptoms of FXS, such as stimulants to assist with attention and hyperactivity and selective serotonin reuptake inhibitors for reduction of aggression associated with anxiety. See id. Behavioral therapy has also proven useful for addressing speech and emotional problems associated with Fragile X patients. In addition, numerous U.S. clinical trials are presently ongoing for the purpose of testing therapeutic moieties for their efficacy in alleviating symptoms of Fragile X syndrome. See, e.g., ClinicalTrials.gov Identifier: NCT01253629 ("Safety and Efficacy of AFQ056 in Adult Patients With Fragile X Syndrome"); ClinicalTrials.gov Identifier: NCT01053156 ("Trial of Minocycline to Treat Children With Fragile X Syndrome");

ClinicalTrials.gov Identifier: NCT01329770 ("Safety and Efficacy Study of Antioxidants for the Treatment of the Fragile X Syndrome"); ClinicalTrials.gov Identifier: NCT01725152

("Ganaxolone Treatment in Children With Fragile X Syndrome"). Recently, improved insight into the molecular pathways involved in the pathogenesis of Fragile X symptoms have strengthened the prospects for targeted therapeutic strategies that effectively address the underlying gene defect or underproduction of FMRP.

[0006] Identification and characterization of Fragile X in a subject have the potential to enhance the tailoring of therapeutic intervention to that subject's needs, and highly sensitive assays that detect FMRP would enable screening of drug candidates for increasing FMRP production. A variety of different assays are presently available for the quantification of FMRP. See, e.g., Iwahashi, C et al. (2009) A Quantitative ELISA Assay for the Fragile X Mental Retardation 1 Protein. Journal of Molecular Diagnostics 11(4): 281-289 (ELISA assay that makes use of a combination of avian and murine antibodies to quantify FMRP); U.S. Pat. No. 8,084,220, issued December 27, 201 1; Kenneson A, et al. (2001) Reduced FMRP and increased FMR1 transcription is proportionally associated with CGG repeat number in intermediate- length and premutation carriers, Hum. Mol. Genet. 10 (14): 1449-1454 (western blot analysis to quantify FMRP levels in cultured lymphoblastoid cells); Lessard M et al. (2012) Quantitative measurement of FMRP in blood platelets as a new screening test for fragile X syndrome.

Clinical Genetics 82: 472-477 (assay for quantifying FMRP using blood platelets).

[0007] However, the existing assay types lack the sensitivity and simplicity required for certain applications, such as quantification of cellular FMRP (which requires precise

measurement of FMRP in an environment that may contain homologues of FMRP or other proteins that cross-react with existing detection mechanisms), or high throughput screening for diagnostic purposes or drug discovery, for example, in a 96-, 384-, or 1536-well plate format.

[0008] Accordingly, there remains an ongoing need for FMRP-detection assays that are highly specific to the target and are compatible with high throughput applications. SUMMARY

[0009] The present disclosure pertains to kits for quantifying FMRP in cells from a subject using a TR-FRET assay. Such kits may include a buffer for lysing said cells, a first antibody labeled with a FRET donor fluorophore, and a second antibody labeled with a FRET acceptor fluorophore.

[0010] Also disclosed are methods of treating a subject having an FMR1 gene CCG- repeat sequence mutation comprising quantifying cellular FMRP from the subject using a TR- FRET assay that employs a first antibody labeled with a FRET donor fluorophore and a second antibody labeled with a FRET acceptor fluorophore, using the quantification to characterize the FMR1 CCG repeat sequence mutation as to the degree of repetition of said CCG sequence, and, based on the characterization, administering a therapeutic agent to the subject for treating said subject.

[0011] The present disclosure also provides methods for evaluating the efficacy of a drug candidate for treatment of a condition resulting from an FMR1 gene CCG-repeat sequence mutation comprising quantifying cellular FMRP from said subject using a TR-FRET assay that employs a first antibody labeled with a FRET donor fluorophore and a second antibody labeled with a FRET acceptor fluorophore, administering the drug candidate to the subject, quantifying cellular FMRP from the subject following administration of said drug candidate using a TR- FRET assay that employs a first antibody labeled with a FRET donor fluorophore and a second antibody labeled with a FRET acceptor fluorophore, comparing the results of quantifying cellular FMRP from the subject prior to administration of the drug candidate with the results of quantifying cellular FMRP from the subject following the administration of the drug candidate, and, based on the comparison, determining the efficacy of the drug candidate for increasing production of FMRP in the subject.

[0012] Also provided are methods for quantifying cellular FMRP in a biological sample derived from a subject comprising obtaining the biological sample, and, subjecting the sample to a TR-FRET assay that employs a first antibody labeled with a FRET donor fluorophore and a second antibody labeled with a FRET acceptor fluorophore, thereby quantifying cellular FMRP in the sample.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0013] The present inventions may be understood more readily by reference to the following detailed description taken in connection with the accompanying figures and examples, which form a part of this disclosure. It is to be understood that these inventions are not limited to the specific products, methods, conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of the claimed inventions.

[0014] In the present disclosure the singular forms "a," "an," and "the" include the plural reference, and reference to a particular numerical value includes at least that particular value, unless the context clearly indicates otherwise. Thus, for example, a reference to "a reagent" may be a reference to one or more of such reagents and equivalents thereof known to those skilled in the art, and so forth. When values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another embodiment. As used herein, "about X" (where X is a numerical value) preferably refers to ±10% of the recited value, inclusive. For example, the phrase "about 8" preferably refers to a value of 7.2 to 8.8, inclusive; as another example, the phrase "about 8%" preferably (but not always) refers to a value of 7.2% to 8.8%, inclusive. Where present, all ranges are inclusive and combinable. For example, when a range of "1 to 5" is recited, the recited range should be construed as including ranges "1 to 4", "1 to 3", "1-2", "1-2 & 4-5", "1-3 & 5", "2-5", and the like. In addition, when a list of alternatives is positively provided, such listing can be interpreted to mean that any of the alternatives may be excluded, e.g., by a negative limitation in the claims. For example, when a range of "1 to 5" is recited, the recited range may be construed as including situations whereby any of 1, 2, 3, 4, or 5 are negatively excluded; thus, a recitation of "1 to 5" may be construed as "1 and 3-5, but not 2", or simply "wherein 2 is not included." It is intended that any component, element, attribute, or step that is positively recited herein may be explicitly excluded in the claims, whether such components, elements, attributes, or steps are listed as alternatives or whether they are recited in isolation.

[0015] Unless otherwise specified, any component, element, attribute, or step that is disclosed with respect to one embodiment of the present methods and products may apply to any other method or product that is disclosed herein.

[0016] The disclosures of each patent, patent application, and publication cited or described in this document are hereby incorporated herein by reference, in their entirety.

[0017] Precise measurement of cellular FMRP levels in patients can provide critical information for the diagnosis and assessment of the severity of disease. The pathogenesis of

Fragile X syndrome, pre-mutation Fragile X, and, as has been more recently reported, schizophrenia (see Kovdcs T, et al. Psychiatry Res. 2013 Jan 17. pii: S0165-1781 (12)00845-1. doi: 10.1016/j.psychres.2012.12.022. [Epub ahead of print]), are tied to the underproduction of

FMRP. Additionally, the quantitative measurement of cellular FMRP levels can be used to screen a compound collection for identification of lead compounds that alleviate the FMRP- related disease state. Western blot and ELISA represent conventional methods for measurements of FMRP levels. The Western blot is not suitable for precise quantification of cellular FMRP levels due to its imprecision. Although the ELISA method can be used in 96-well plate format, it requires a complicated assay procedure including plate coating, multiple plate washes and reagent addition steps, low screening throughput, and high sample-to-sample variability.

Accordingly, neither of the conventional assays are suitable for precise measurement of cellular FMRP, or for high throughput screening for drug discovery.

[0018] The present disclosure relates, inter alia, to discoveries that enable the use of F5rster (Fluorescence) resonance energy transfer (FRET) assays, including time-resolved FRET (TR-FRET, also referred to as HTRF), for the quantification of cellular FMRP. Whether a FRET assay can be used against a particular protein target is at the outset highly uncertain. FRET assays require the precise spatial arrangement of donor and acceptor fluorophores in order to provide the radius of interaction that is necessary for producing a signal from the acceptor fluorophore. In particular, Ro values are generally in the range of 60-100 A (6-10 nm) where Ro is defined as a distance providing 50% energy transfer (ET) efficiency. Thus, the efficiency of FRET, E, depends on the distance, r, separating the donor and acceptor fluorophores, and is given by E = (Ro)⁶/[(Ro)⁶ + (r)⁶]. Improper arrangement between the moieties bearing the donor and acceptor fluorophores will produce an inefficient or undetectable signal. Therefore, when the assay target is a protein, it is necessary to develop means not only for associating the donor and acceptor fluorophores with the protein, but ensuring that the spatial arrangement of the donor and acceptor are within the functional radius for producing a detectable signal.

[0019] There are numerous commercially available antibodies that are specific to FMRP. Accordingly, anti-FMRP antibodies that are respectively labeled with donor and acceptor fluorophores could theoretically be used to produce a useful FRET signal as to FMRP in a sample. This assumes that there is sufficient knowledge regarding the binding locations of the first and second antibodies on the FRET protein, such that the appropriate spatial arrangement of donor and acceptor fluorophores results. However, in some instances, the precise epitope for a particular anti-FMRP antibody is not known. Even in instances where the epitope for an anti- FMRP antibody is documented, one cannot simply select two antibodies having epitopes that are known to be within an acceptable FRET radius in two-dimensional space, at least because the conformation of each separate component (i.e., the first antibody, its fluorophore, the second antibody, its fluorophore, and the FMRP protein) in three dimensions may not give rise to the proper spatial arrangement among the respective moieties. This unpredictability is compounded by the fact that the full three-dimensional structure of FMRP is not known. Accordingly, the use of antibodies to a single protein target in order to produce a useful FRET signal is highly unpredictable.

[0020] The present inventors have, however, identified certain pairs of anti-FMRP antibodies can be used to produce a functional FRET signal when incubated against cellular FMRP. The signal that the inventive process produces is highly precise, reliable, and is characterized by reduced noise, thereby representing an advantageous detection tool as compared with conventional ELISA and Western assays, which, as described above, are not compatible with precise measurement of cellular FMRP.

[0021] This discovery enables a TR-FRET-based FMRP assay that has very high measurement specificity. Furthermore, the use of TR-FRET based HTRF detection (by labeling HTRF detection pair to the two antibodies) enables a homogenous (reproducible) measurement of cellular FMRP levels in 96-, 384- and 1536-well plate formats. These characteristics mean that, unlike previously existing techniques for measuring FMRP, the presently disclosed subject matter is compatible with high throughput screening.

[0022] Accordingly, the present disclosure pertains to kits for quantifying FMRP in cells from a subject using a TR-FRET assay. Such kits may include, for example, a buffer for lysing said cells, a first antibody labeled with a FRET donor fluorophore, and a second antibody labeled with a FRET acceptor fluorophore.

[0023] The first and second fluorophores, respectively, may be any fluorophores that are suitable for use in a FRET assay, i.e., fluorophores are so chosen that the emission spectrum of one overlaps significantly with the excitation spectrum of the other. Non-limiting examples of donor and acceptor FRET pairs for labeling antibodies include Europium chelate donors and acceptors (such as, for example, Tb+ or Eu+ and D2 dye or XL665); fluorescent protein donors and acceptors (such as, for example, CFP and YFP, BFP and GFP, GFP and orange/red fluorescent proteins), standard fluorescent dye donors and acceptors (such as, for example, coumarin derivatives and fluorescein derivatives, and other blue and green fluorophore pairs;

Cy3 and Cy5, and other green and red fluorophore dye pairs such as fluorescein derivatives and rhodamine derivatives, e.g., tetramethylrhodamine); Bioluminescence donors and acceptors ( such as, for example, luciferase); particle or bead based FRET donors and acceptors (such as, for example, AlphaScreen donor beads and acceptor beads); other known commercially-available

FRET donors and acceptors; and combinations of donors and acceptors therein. Exemplary donor fluorophores include Eu³⁺cryptate or Tb²⁺cryptate (Cisbio Bioassays, Bedford, MA; hereafter, "Cisbio"). Exemplary acceptor fluorophores include d2 (Cisbio), XL665 (Cisbio). [0024] The labeling of antibodies with fluorophores represents subject matter that is within the ordinary skill of those working in the field of biochemical assays.

[0025] The first and second antibodies of the present kits may be selected from a rabbit monoclonal antibody raised against a synthetic peptide corresponding to residues surrounding Gly552 of human FMRP protein; anti-FMRl mouse monoclonal antibody raised against immunogen sequence of

ATKDTFHKIK LDVPEDLRQM CAKEAAHKDF KKAVGAFSVT YDPENYQLVI

LSINEVTSKR AHMLIDMHFR SLRTKLSLIM RNEEASKQLE SSRQLASRFH;

rabbit polyclonal antibody raised against the synthetic peptide conjugated to KLH derived from within residues 550 to the C-terminus of Human FMRP; a rabbit polyclonal antibody raised against a synthetic peptide corresponding to the sequence of human FMRP; a rabbit monoclonal antibody or a rabbit polyclonal antibody raised against a synthetic peptide surrounding Glycine 552 and optionally capable of detecting all 8 isoforms of FMRP; and, a mouse monoclonal antibody raised against a human recombinant protein fragment corresponding to amino acids 36- 279 of human FMR1 produced in is. coli.

[0026] For example, the first and second antibodies of the present kits may be selected from anti-FMRP D14F4 rabbit monoclonal antibody (Cell Signaling Technology catalogue number 7104, clone d2), anti-FMRl mouse monoclonal antibody (Sigma catalogue number WH0002332M1, clone k), anti-FMRP rabbit polyclonal antibody (Abeam catalogue number ab 17722, clone k), anti-FMRl mouse monoclonal antibody (Sigma catalogue number

WH0002332M1, clone d2), anti-FMRP rabbit polyclonal antibody (Cell Signaling Technology catalogue number 4317, clone d2), anti-FMRP rabbit polyclonal antibody (Cell Signaling Technology catalogue number 4317, clone k), and anti-FMRP rabbit polyclonal antibody (Abeam catalogue number ab 17722, clone d2).

[0027] In certain embodiments, the first and second antibodies are selected from anti- FMRP D14F4 rabbit monoclonal antibody (Cell Signaling Technology catalogue number 7104 and clone d2) and anti-FMRl mouse monoclonal antibody (Sigma catalogue number

WH0002332M1, clone k). In some embodiments, the first and second antibodies are selected from a mouse monoclonal antibody raised against a human recombinant protein fragment corresponding to amino acids 36-279 of human FMR1 produced in E.coli and a rabbit monoclonal antibody that was raised against a synthetic peptide surrounding Glycine 552 and will detect all 8 isoforms of FMRP. In other embodiments, the first and second antibodies are selected from anti-FMRl mouse monoclonal antibody (Sigma catalogue number

WH0002332M1, clone k) and anti-FMRP rabbit polyclonal antibody (Cell Signaling Technology catalogue number 4317, clone d2). In yet other embodiments, the first and second antibodies are selected from anti-FMRP rabbit polyclonal antibody (Abeam catalogue number ab 17722, clone k) and anti-FMRl mouse monoclonal antibody (Sigma catalogue number WH0002332M1, clone d2). The first and second antibodies may also be selected from anti-FMRP rabbit polyclonal antibody (Cell Signaling Technology catalogue number 4317, clone k) and anti-FMRl mouse monoclonal antibody (Sigma catalogue number WH0002332M1, clone d2). The first and second antibodies may also be selected from clone d2) and anti-FMRl mouse monoclonal antibody (Sigma catalogue number WH0002332M1, clone k) and anti-FMRP rabbit polyclonal antibody (Abeam catalogue number ab 17722, clone d2).

[0028] The first and second antibodies may be any antibodies that, when each are bound to FMRP, are positioned such that the distance between the fluorophores that are respectively bound to the first and second antibodies is compatible with the distance required for a FRET -type of energy transfer between the fluorophores. For example, the first and second antibodies may be any antibodies that, when each are bound to FMRP, are positioned such that the distance between the fluorophores that are respectively bound to the first and second antibodies is less than about 10 nm, between about 2 to about 10 nm, or between about 6 to about 10 nm.

[0029] In certain embodiments, the first and second antibodies are pre-labeled with the donor and acceptor fluorophores. In other embodiments, the kits are such that the fluorophores are provided separately from the antibodies, optionally with instructions for labeling the antibodies with respective fluorophores. In other instances, the present kits comprise the first and second antibodies, and the fluorophores are not included within the kits and must be acquired separately.

[0030] The present kits may also include one or more antibodies that are in addition to the first and second antibodies. The additional antibody or antibodies may be, for example, selected from anti-FMRP D14F4 rabbit monoclonal antibody (Cell Signaling Technology catalogue number 7104, clone d2), anti-FMRl mouse monoclonal antibody (Sigma catalogue number WH0002332M1, clone k), anti-FMRP rabbit polyclonal antibody (Abeam catalogue number ab 17722, clone k), anti-FMRl mouse monoclonal antibody (Sigma catalogue number WH0002332M1, clone d2), anti-FMRP rabbit polyclonal antibody (Cell Signaling Technology catalogue number 4317, clone d2), anti-FMRP rabbit polyclonal antibody (Cell Signaling Technology catalogue number 4317, clone k), and anti-FMRP rabbit polyclonal antibody (Abeam catalogue number ab 17722, clone d2). [0031] The lysis buffer for inclusion in the present kits may be any suitable buffer for lysing human cells. Those of ordinary skill in the art can readily identify examples suitable lysis buffers. Lysis buffers may be characterized by the presence of suitable detergent. For example, the buffer may be, for example, PBS + detergent (such as Triton- 100), or dH₂02 + detergent. The detergent may be provided in any suitable amount, for example, at about 0.5 to about 1.0%.

[0032] The present kits may also include any other reagents that can be used in carrying out the TR-FRET assay in a desired manner. Those of ordinary skill in the art can readily identify other such reagents.

[0033] The present kits may include one or more aliquots of first and second antibodies that are each suitable for performing a single TR-FRET assay. For example, the kits may include two separate sets of first and second antibodies, wherein the amounts of each of the first and second antibodies in each set are sufficient to permit the performance of two separate TR-FRET assays. In other embodiments, the kits may include more than two separate sets of first and second antibodies, such as five sets, ten sets, 20 sets, 25 sets, 50 sets, 100 sets, 500 sets, or any other number of sets. If the first and second antibodies of a particular set are not pre-labeled with donor and acceptor fluorophores, then in addition to each set of first and second antibodies, the kits may include an aliquot of FRET donor fluorophore, and an aliquot of FRET acceptor fluorophore. Each reagent may be provided in aliquots that are divided according to the amount required for use in a single TR-FRET assay. Alternatively, one or more of the reagents of the kit for use in a FRET assay may be provided in bulk so that the user may meter out a desired amount as needed.

[0034] The kits may also include an instruction print for carrying out a TR-FRET assay using the provided reagents and for using any additional reagents not included with the kits.

[0035] Also disclosed are methods of treating a subject having an FMR1 gene CCG- repeat sequence mutation comprising quantifying cellular FMRP from the subject using a TR- FRET assay that employs a first antibody labeled with a FRET donor fluorophore and a second antibody labeled with a FRET acceptor fluorophore, using the quantification to characterize the FMR1 CCG repeat sequence mutation as to the degree of repetition of said CCG sequence, and, based on the characterization, administering a therapeutic agent to the subject for treating said subject

[0036] An exemplary method for quantifying cellular FMRP in a subject is provided in Example 1, infra.

[0037] The reagents and materials for use in any of the methods disclosed herein may, for example, be selected from any of the embodiments previously described with respect to the presently disclosed kits. Thus, the antibodies, fluorophores, buffers, or other materials that are used to perform a FRET assay pursuant to any of the presently disclosed methods may respectively be chosen from any of the embodiments for these components disclosed pursuant to the description for the present kits.

[0038] As provided supra, individuals with a certain number of CCG repeat sequences in the 5' untranslated region of the FMRl gene may manifest various conditions along the Fragile X disorder spectrum. Subjects with 55-200 CCG repeats are considered pre-mutation carriers, and those with 200 to about 1000 CCG repeats bear the full mutation. The present methods employ the inventive TR-FRET assays to quantify FMRP in a sample from a subject, and use the results of the quantification to characterize the severity of the alteration of the subjects FMRl gene from the wild-type, which normally includes no more than 55 repeats of the CCG sequence in the 5' untranslated region. It is known that, among individuals with the premutation allele (55-200 CCG repeats), while FMRl transcription is above normal with correspondingly elevated levels of mRNA, translation appears to be less efficient than normal, thus producing lower amounts of FMRP. See Pirozzi F, Tabolacci E, Neri G. 2011. The

FRAXopathies: Definition, overview, and update. Am J Med Genet Part A 155:1803-1816 (internal citations omitted). By contrast, among individuals bearing the full mutation allele, the transcription of the FMRl gene is silenced, leading to absence of FMRP. Id.

[0039] Quantification of FMRP using the presently disclosed methods, which permit uniquely precise measurement to such a degree that they enable hierarchical categorization of FMRP levels among various subjects, can be used to classify the degree of severity of the CCG- repeat sequence mutation in a particular subject. For example, a subject with levels of FMRP that are slightly less than the amount normally observed in individuals bearing wild-type FMRl can be classified as representing the mild pre-mutation state, while a subject with levels of FMRP that are appreciably less than the amount normally observed in individuals bearing wild-type FMRl but more than the amount normally observed in full-mutation individuals can be classified as possessing a severe pre-mutation allele. Once it is known, for example, that an individual possesses a mild pre-mutation allele (for example, corresponding to a number of CCG repeats in the FMRl gene that is closer to 55 than to 200), treatment options may be limited to addressing symptoms, rather than deploying more drastic intervention, such as pharmaceutical or gene therapy designed to ramp up FMRP production. By contrast, a subject with a severe pre-mutation allele, because such individual possesses an FMRl gene that is still capable of producing FMRP, may benefit from therapeutic measures that are designed to increase the activity of FMRl gene. Such measures may include, for example, intervention as to metabotropic glutamate receptors (mGluRl-R8), or the gamma-aminobutyric (GABA) receptor pathway.

[0040] The present disclosure also provides methods for evaluating the efficacy of a drug candidate for treatment of a condition resulting from an FMR1 gene CCG-repeat sequence mutation comprising quantifying cellular FMRP from said subject using a TR-FRET assay that employs a first antibody labeled with a FRET donor fluorophore and a second antibody labeled with a FRET acceptor fluorophore, administering the drug candidate to the subject, quantifying cellular FMRP from the subject following administration of said drug candidate using a TR- FRET assay that employs a first antibody labeled with a FRET donor fluorophore and a second antibody labeled with a FRET acceptor fluorophore, comparing the results of quantifying cellular FMRP from the subject prior to administration of the drug candidate with the results of quantifying cellular FMRP from the subject following the administration of the drug candidate, and, based on the comparison, determining the efficacy of the drug candidate for increasing production of FMRP in the subject.

[0041] Research regarding therapeutic intervention for FMR1 mutation conditions, such as Fragile X syndrome, is ongoing. Because options for drug or gene therapy are presently limited, there exists a pressing need for the identification of such therapies that are effective for increasing FMRP production. Furthermore, because even small increases in FMRP production have potential therapeutic benefit, a highly sensitive assay, such as are enabled using the kits disclosed herein represents a valuable tool for assessing the utility of a drug candidate that may provide only facially marginal benefit in terms of increasing FMRP production, but could be of more significance in terms of the phenotypic results that it provides.

[0042] Pursuant to the present methods for evaluating the efficacy of a drug candidate, a subject, for example, a subject possessing a pre-mutation of full mutation FMR1 gene, may be administered a candidate drug. A "drug" or "therapeutic agent" as used herein may refer to any moiety or interventional measure with potential therapeutic efficacy vis-a-vis the FMR1 gene / FMRP pathway, such as a small molecule, a biochemical, or a gene therapy vector. Dosing of the drug may be determined using standard pharmacological techniques with which those of ordinary skill in the pharmaceutical field will be familiar.

[0043] Prior to the administration of the candidate drug to the subject, the presently disclosed, highly sensitive assays are used to quantify in a precise manner the amount of cellular FMRP in a sample from the subject. The pre-drug quantification step may be performed one or more times as desired, in order to yield a control FMRP value or an average control value. The measured amount of FMRP is noted for future comparison with values obtained after administration of the candidate drug.

[0044] Administration of the candidate drug to the subject may be according to any desired protocol that is assessed to be appropriate given the properties of the candidate drug. Protocol factors may include dosage, dosing profile (such as sustained release, ascending release, etc.), frequency per unit time, and whether the drug is administered as the sole form of therapy or is co-administered with another agent or is administered at the same time as some other type of therapeutic intervention, such as behavioral or psychological therapy, or any type of non-drug therapy, such as electro-shock, acupuncture, or therapy of another variety. Each of such factors may be determined, for example, by application of standard pharmacological technique.

[0045] Following administration of the candidate drug to the subject, cellular FMRP from the subject is quantified using a TR-FRET assay that employs a first antibody labeled with a FRET donor fluorophore and a second antibody labeled with a FRET acceptor fluorophore. The characteristics of the TR-FRET assay and the reagents used in such assay (e.g., antibodies, fluorophores, buffers, and other reagents) may be in accordance with any of the parameters described above or below in connection with the present kits or methods of treatment.

Quantification of FMRP may occur at any time after drug administration at which there is believed to be a high probably that an effect, if any, of the drug has taken place. For example, quantification of FMRP may be performed at about one hour, two hours, four hours, six hours, 12 hours, 18 hours, 24 hours, 2 days, 5 days, 10 days, two weeks, three weeks, a month, two months, or six months following one or more episodes of drug administration. Quantification of FMRP following drug administration may be performed one time or multiple times as desired in order to obtain an FMRP value or an average FMRP value. Quantification may also be performed and recorded at multiple intervals in order to determine if there is a drug effect that changes over time. To similar ends, alternating episodes of drug administration and

quantification may be performed.

[0046] Following quantification of FMRP following administration of a candidate drug to the subject, the results of quantifying cellular FMRP from the subject prior to administration of the drug candidate are compared with the results of quantifying cellular FMRP from the subject following the administration of the drug candidate, and, based on the comparison, the efficacy of the drug candidate for increasing production of FMRP in the subject is determined.

Preferably, a statistical analysis is performed in order to determine whether the administration of the drug candidate - using whatever protocol had been deemed appropriate, including whether or not the drug was co-administered with another drug or was administered at the same time as some other non-drug therapeutic intervention - resulted in a statistically significant change in FMRP production.

[0047] Also provided are methods for quantifying cellular FMRP in a biological sample derived from a subject comprising obtaining the biological sample, and, subjecting the sample to a TR-FRET assay that employs a first antibody labeled with a FRET donor fluorophore and a second antibody labeled with a FRET acceptor fluorophore, thereby quantifying cellular FMRP in the sample. The characteristics of the TR-FRET assay and the reagents used in such assay (e.g., antibodies, fluorophores, buffers, and other reagents) may be in accordance with any of the parameters described above or below in connection with the present kits or methods of treatment. As described supra, the detection of FMRP levels can be used to characterize the disease condition of a subject or to assess the efficacy of a candidate drug. The present methods permit quantification of cellular FMRP under any circumstances, and to accomplish any purpose, even if only for record-keeping purposes or for purposes of statistical analysis of the subject or a cohort of subjects. The subject may be one that possesses a pre- or full-mutation FMR1 allele, the subject may be free of FMR1 gene mutations, or may possess some other genetic condition or disease state that gives rise to a desire, even if for research purposes only, to determine FMRP levels in the subject. For example, determination of FMRP levels may be used for reproductive planning purposes, to assess the underpinnings of a chronic, intermittent, or temporary psychological or behavioral state, or for educational purposes (e.g., as a demonstration of proof- of-concept of a TR-FRET assay generally or an FMRP assay in particular). Thus, the utility of the present methods for quantifying cellular FMRP is far-ranging and is intended to embrace any therapeutic, investigational, statistical, psychological, behavioral, or educational purpose.

[0048] In some embodiments of the presently disclosed methods for quantifying cellular FMRP in a biological sample derived from a subject, the subject is an infant, a child, a young adult, or a mature adult. The present methods can be used to measure changes in FMRP in a single subject over time (e.g., as an infant, child, or young adult grows older), by acquiring multiple biological samples from the subject, performing the instantly disclosed TR-FRET assays for the measurement of FMRP with respect to each sample, and then comparing the results of the measurements over time to each other. Thus, the present methods may comprise performing multiple times over a period of time the steps of obtaining a biological sample from the subject and subjecting the sample to the TR-FRET assay, thereby providing multiple measurements of FMRP over a period of time. The methods may further comprise comparing at least one of the measurements acquired at a first point in time during the period of time to at least one other of the measurements that was acquired at a second point in time during the period of time in order to determine whether the amount of FMRP in the subject has changed over the period of time.

[0049] For example, a biological sample may be obtained at t = 0 and subjected to the TR-FRET assay in order to obtain a measured FMRP value for t = 0. Subsequently, on one or more future occasions, further biological samples may be obtained and each subjected to the TR- FRET assay in order to obtain measured FMRP values for each point in time. The amount of time that elapse between each measurement may be a matter of hours, days, weeks, months, or years, and may occur at regular or irregular intervals, as desired. Thus, for example, a biological sample may be obtained from an infant aged six months and subjected to FMRP measurement, after which time a further sample can be obtained from the subject at the age of, for example, nine months, and at regular or irregular intervals thereafter until a desired endpoint has been reached, such as early childhood, young adulthood, or mature adulthood. Any progressive change in FMRP levels in the subject may thereby be determined using the presently disclosed methods.

[0050] The disclosed methods for measuring FMRP values in a subject over time can therefore provide valuable information concerning whether the subject is suffering from a disease state that results in decreased FMRP production, whether measured decreases in FMRP continue at a detectable rate, whether decreases in FMRP stop and level off at a particular point in time, or any other pattern in FMRP decrease, increase, or stabilization. Such information can yield useful insight regarding the progression of disease and the relationship between the passage of time / patient age and disease severity, as well as concerning appropriate therapeutic intervention.

[0051] Importantly, such methods can also be used to measure FMRP levels in a subject over time when such subject has received or is receiving a therapeutic agent that is intended to stabilize or increase FMRP production. The methods can also be used, for example, to test various dosages of a therapeutic agent. Accordingly, provided herein are methods for treating a condition resulting from an FMR1 gene CCG-repeat sequence mutation in a subject comprising: obtaining a biological sample from the subject; subjecting the sample to a TR-FRET assay that employs a first antibody labeled with a FRET donor fluorophore and a second antibody labeled with a FRET acceptor fluorophore, thereby quantifying cellular FMRP in the sample; administering a therapeutic agent to the subject at a predetermined dosage; obtaining a further biological sample that is acquired from said subject following administration of the therapeutic agent to the subject; subjecting the further sample to a TR-FRET assay that employs a first antibody labeled with a FRET donor fluorophore and a second antibody labeled with a FRET acceptor fluorophore, thereby quantifying cellular FMRP in the further sample; and, comparing the results of quantifying cellular FMRP from the subject prior to administration of the therapeutic agent with the results of quantifying cellular FMRP from the subject following the administration; based on the comparison, determining whether to provide a further dosage that is increased or decreased relative to the initial dosage for administration to the subject.

[0052] For example, measurements of FMRP levels that follow administration of the therapeutic agent may indicate that higher dosage strength is required in order to provide the desired degree of increase in FMRP production. Dosages can be increased or decreased and the timing of measurements relative to one another according to standard pharmacological practice.

[0053] Pursuant to the presently disclosed methods of treatment, e.g., for determining a therapeutically effective dosage of a therapeutic agent, it is the case that, prior to the

administration of the therapeutic agent to the subject, the presently disclosed, highly sensitive assays are used to quantify in a precise manner the amount of cellular FMRP in a sample from the subject. The pre-drug quantification step may be performed one or more times as desired, in order to yield a control FMRP value or an average control value. The measured amount of FMRP is noted for future comparison with values obtained after administration of the therapeutic agent.

[0054] Administration of the therapeutic agent to the subject may be according to any desired protocol that is assessed to be appropriate given the properties of the therapeutic agent. Protocol factors may include initial dosage, dosing profile (such as sustained release, ascending release, etc.), frequency per unit time, and whether the drug is administered as the sole form of therapy or is co-administered with another agent or is administered at the same time as some other type of therapeutic intervention, such as behavioral or psychological therapy, or any type of non-drug therapy, such as electro-shock, acupuncture, or therapy of another variety. Each of such factors may be determined, for example, by application of standard pharmacological technique.

[0055] Following administration of the therapeutic agent to the subject, cellular FMRP from the subject is quantified using a TR-FRET assay that employs a first antibody labeled with a FRET donor fluorophore and a second antibody labeled with a FRET acceptor fluorophore.

The characteristics of the TR-FRET assay and the reagents used in such assay (e.g., antibodies, fluorophores, buffers, and other reagents) may be in accordance with any of the parameters described above in connection with the present kits or methods of treatment. Quantification of

FMRP may occur at any time after therapeutic agent administration at which there is believed to be a high probably that an effect, if any, of the therapeutic agent has taken place. For example, quantification of FMRP may be performed at about one hour, two hours, four hours, six hours, 12 hours, 18 hours, 24 hours, 2 days, 5 days, 10 days, two weeks, three weeks, a month, two months, or six months following one or more episodes of therapeutic agent administration. Quantification of FMRP following therapeutic agent administration may be performed one time or multiple times as desired in order to obtain an FMRP value or an average FMRP value.

Quantification may also be performed and recorded at multiple intervals in order to determine if there is a drug effect that changes over time. To similar ends, alternating episodes of drug administration and quantification may be performed.

[0056] Following quantification of FMRP following administration of a therapeutic agent to the subject, the results of quantifying cellular FMRP from the subject prior to administration of the therapeutic agent are compared with the results of quantifying cellular FMRP from the subject following the administration of the therapeutic agent, and, based on the comparison, the efficacy of the therapeutic agent for increasing production of FMRP in the subject at the initial dosage is determined. Preferably, a statistical analysis is performed in order to determine whether the administration of the therapeutic agent - using whatever protocol had been deemed appropriate, including whether or not the therapeutic agent was co-adminstered with another therapeutic agent or was administered at the same time as some other non-drug therapeutic intervention - resulted in a statistically significant change in FMRP production, so that any appropriate alterations in dosage can be implement during subsequent administrations of the therapeutic agent.

Example 1 - Method of Performing TR-FRET Assay for Quantifying Cellular FMRP

[0057] A method was performed using a kit containing reagents for the quantitative measurement of FMRP in cell lysates. The assay was designed for use with cell lysates in 384 well plates, utilized HTRF (homogenous time-resolved fluorescence) technology, and consisted of a sandwich assay using two antibodies, one labeled with europium cryptate (K*) donor and the other with a d2 acceptor dye. However, the assay may be performed using different cell lines (for example, lymphoblastoid, fibroblasts, NSCs, and neurons) in either the 384 or 1536 well format. Cell number, lysis buffer volume, incubation time and cell lysis temperature, plus time course after addition of antibodies were optimized and validated. The specific FRET signal was proportional to the amount of FMRP in the sample. Table 1

Reagents

[0058] Working solution preparation:

- Anti-FMRP-d2 [make a 2x stock, e.g., 480 μΐ. detection buffer plus 20 μΐ. Anti-FMRP - d2 stock]

- Anti-FMRP-K* [make a 2x stock, e.g., 480 μΐ. detection buffer plus 20 μΐ. Anti-FMRP- K* stock]

- 4x Lysis buffer - 4x lysis stock used instead of diluting four-fold

[0059] Assay protocol for 384 well low volume, solid white Greiner # 784075 - total volume 16 μΐ., instead of 20 μΐ,; or 1536 Greiner white # 789173-F - total volume 8 μ Cells are incubated overnight.

Table 2

Comparison of 384-well and 1536-well protocols

[0060] Plates are covered with plate sealer and incubated overnight at 4°C (not room temperature). Plate sealers are removed and samples were read using an EnVision instrument (serial number 1040842).

Example 2 -Alternative Method of Performing TR-FRET Assay for Quantifying Cellular FMRP

[0061] A method was performed using a kit containing reagents for the quantitative measurement of FMRP in cell lysates. The assay was designed for use with cell lysates in 384 well plates, utilized HTRF (homogenous time-resolved fluorescence) technology, and consisted of a sandwich assay using two antibodies, one labeled with europium cryptate (K*) donor and the other with a d2 acceptor dye. The specific FRET signal is proportional to the amount of FMRP in the sample.

Table 4

Reagents

Anti-FMRP-d2 1 vial frozen - 80°C 50x lOOul

Anti-FMRP-K* 1 vial frozen - 80°C 50x lOOul

Lysis buffer #1 2 bottles frozen or at 4° C 4x 8ml

Detection buffer I bottle / frozen or at 4°C l x 10ml

[0062] Working Solution preparation:

- Anti-FMRP-d2 [make a 50 fold dilution, e.g., 980 detection buffer plus 20 Anti- FMRP-d2 stock]

- Anti-FRMP-K [make a 50 fold dilution, e.g., 980 ul detection buffer plus 20 Anti- FMRP-K* stock]

- Lysis buffer - diluted 4-fold with distilled water [1 mL lysis stock plus 3 mL water]

[0063] Assay protocol for 384 well, low volume, solid white (Greiner # 784075) plates and 20 μΐ_^ final volume (1536 Greiner white # 789173 -F). Reagents are dispensed in the following order

1. 10 μΐ_^ of cell lysate

2. 5 μΐ, of Anti-FMRP-d2 (solution A)

3. 5 μΙ, of Anti- FMRP-K* (solution B)

Plates are covered with plate sealer and incubated overnight at room temperature. Plate sealers are removed and samples are read using an EnVision instrument. Example 3 - Method of Assessing a Drug Candidate

[0064] A subject that is pre-determined to have a condition that gives to lower than wild-type levels of cellular FMRP (for example, as determined by measurement of cellular FMRP levels using the presently disclosed methods for quantifying cellular FMRP in a biological sample), and that has volunteered for participation in a clinical study to test the efficacy of a drug candidate, is selected. The subject is advised as to the procedures that will be carried out in order to test the drug candidate, regarding the identity of the drug candidate, and regarding possible outcomes of the study. Over the course of three weeks, and on a once-weekly basis, cell samples are obtained from the patient and are subjected to lysing and other appropriate processing conditions in order to prepare them for measurement of FMRP levels. Each cell sample is subjected to a TR-FRET assay that is carried out in accordance with the process described in Example 1, and the observed FMRP levels are used to obtain an average FMRP value for the three week period.

[0065] The subject is administered a drug candidate, which is hypothesized to stimulate production of FMRP by FMR1 pre-mutation alleles, on a twice-daily basis at a dosage of 1 mg/kg over the course of one month. At the end of each week during and at the end of the one month course of treatment, a cell sample is obtained and FMRP levels are measured in each cell sample. The results of each FMRP measurement that is obtained during and after the drug administration regimen is compared with the average FMRP value that was obtained from the three week measurement period that preceded the initiation of drug administration. A statistical analysis is performed in order to determine whether FMRP values changed at any point during the drug administration period. For the next three months following cessation of the drug administration regimen, the subject supplies additional cell samples on a once-monthly basis so that each can be subjected to a post-drug FMRP assessment.

[0066] The same protocol is performed with respect to other subjects with a similar FMRP production profile, in order to provide additional study data. The results of this cohort study for investigation of the candidate drug is assessed using a statistical analysis.

[0067] The various features and processes described above may be used independently of one another, or may be combined in various ways. All possible combinations and

subcombinations are intended to fall within the scope of this disclosure. In addition, certain method or process blocks may be omitted in some implementations. The methods and processes described herein are also not limited to any particular sequence, and the blocks or states relating thereto can be performed in other sequences that are appropriate. For example, described blocks or states may be performed in an order other than that specifically disclosed, or multiple blocks or states may be combined in a single block or state. The example blocks or states may be performed in serial, in parallel, or in some other manner. Blocks or states may be added to or removed from the disclosed example embodiments. The example systems and components described herein may be configured differently than described. For example, elements may be added to, removed from, or rearranged compared to the disclosed example embodiments.

[0068] Conditional language used herein, such as, among others, "can," "could," "might," "may," "e.g.," and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements, and/or steps. Thus, such conditional language is not generally intended to imply that features, elements and/or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or steps are included or are to be performed in any particular embodiment. The terms "comprising," "including," "having," and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term "or" is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term "or" means one, some, or all of the elements in the list.

[0069] While certain example embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions disclosed herein. Thus, nothing in the foregoing description is intended to imply that any particular feature, characteristic, step, module, or block is necessary or indispensable.

Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions disclosed herein. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of certain of the inventions disclosed herein.

Claims

What is Claimed:

1. A kit for quantifying FMRP in cells from a subject using a TR-FRET assay comprising:

a buffer for lysing said cells;

a first antibody labeled with a FRET donor fluorophore; and,

a second antibody labeled with a FRET acceptor fluorophore.

2. The kit according to claim 1 wherein said first and second antibodies are selected from anti-FMRP D14F4 rabbit monoclonal antibody (Cell Signaling Technology catalogue number 7104, clone d2), anti-FMRl mouse monoclonal antibody (Sigma catalogue number

WH0002332M1, clone k), anti-FMRP rabbit polyclonal antibody (Abeam catalogue number ab 17722, clone k), anti-FMRl mouse monoclonal antibody (Sigma catalogue number

WH0002332M1, clone d2), anti-FMRP rabbit polyclonal antibody (Cell Signaling Technology catalogue number 4317, clone d2), and anti-FMRP rabbit polyclonal antibody (Abeam catalogue number ab 17722, clone d2).

3. The kit according to claim 2 wherein said first and second antibodies are selected from anti-FMRP D 14F4 rabbit monoclonal antibody (Cell Signaling Technology catalogue number 7104, clone d2) and anti-FMRl mouse monoclonal antibody (Sigma catalogue number

WH0002332M1, clone k).

4. The kit according to claim 1 wherein said donor fluorophore is Cisbio Europium- cryptate.

5. The kit according to claim 1 wherein said acceptor fluorophore is Cisbio d2.

6. A method of treating a subject having an FMR1 gene CCG-repeat sequence mutation comprising:

quantifying cellular FMRP from said subject using a TR-FRET assay that employs a first antibody labeled with a FRET donor fluorophore and a second antibody labeled with a FRET acceptor fluorophore;

using said quantification to characterize the FMR1 CCG repeat sequence mutation as to the degree of repetition of said CCG sequence;

and, based on said characterization, administering a therapeutic agent to said subject for treating said subject.

7. The method according to claim 6, wherein the characterization of the FMR1 CCG repeat sequence mutation identifies said mutation as pre-mutation or full mutation.

8. The method according to claim 6, further comprising selecting the dosage of the therapeutic agent for administration to said subject based on said characterization.

9. The method according to claim 6 wherein said first and second antibodies are selected from anti-FMRP D14F4 rabbit monoclonal antibody (Cell Signaling Technology catalogue number 7104, clone d2), anti-FMRl mouse monoclonal antibody (Sigma catalogue number WH0002332M1, clone k), anti-FMRP rabbit polyclonal antibody (Abeam catalogue number ab 17722, clone k), anti-FMRl mouse monoclonal antibody (Sigma catalogue number

10. The method according to claim 8 wherein said first and second antibodies are selected from anti-FMRP D14F4 rabbit monoclonal antibody (Cell Signaling Technology catalogue number 7104, clone d2) and anti-FMRl mouse monoclonal antibody (Sigma catalogue number WH0002332M1, clone k).

1 1. A method of evaluating the efficacy of a drug candidate for treatment of a condition resulting from an FMR1 gene CCG-repeat sequence mutation comprising:

administering said drug candidate to said subject;

following administration of said drug candidate, quantifying cellular FMRP from said subject using a TR-FRET assay that employs a first antibody labeled with a FRET donor fluorophore and a second antibody labeled with a FRET acceptor fluorophore; comparing the results of quantifying cellular FMRP from said subject prior to administration of said drug candidate with the results of quantifying cellular FMRP from said subject following said administration;

based on said comparison, determining the efficacy of said drug candidate for increasing production of FMRP in said subject.

12. The method according to claim 1 1 wherein said first and second antibodies for use in quantifying FMRP in said subject prior to and following administration of said drug candidate are selected from anti-FMRP D14F4 rabbit monoclonal antibody (Cell Signaling Technology catalogue number 7104, clone d2), anti-FMRl mouse monoclonal antibody (Sigma catalogue number WH0002332M1, clone k), anti-FMRP rabbit polyclonal antibody (Abeam catalogue number ab 17722, clone k), anti-FMRl mouse monoclonal antibody (Sigma catalogue number WH0002332M1, clone d2), anti-FMRP rabbit polyclonal antibody (Cell Signaling Technology catalogue number 4317, clone d2), and anti-FMRP rabbit polyclonal antibody (Abeam catalogue number ab 17722, clone d2).

13. The method according to claim 12 wherein said first and second antibodies are selected from anti-FMRP D14F4 rabbit monoclonal antibody (Cell Signaling Technology catalogue number 7104, clone d2) and anti-FMRl mouse monoclonal antibody (Sigma catalogue number WH0002332M1, clone k).

14. A method for quantifying cellular FMRP in a biological sample derived from a subject comprising:

obtaining the biological sample; and,

subjecting said sample to a TR-FRET assay that employs a first antibody labeled with a FRET donor fluorophore and a second antibody labeled with a FRET acceptor fluorophore,

thereby quantifying cellular FMRP in said sample.

15. The method according to claim 14 wherein said biological sample is a cell lysate.

16. The method according to claim 14 wherein said first and second antibodies for use in quantifying FMRP in said subject prior to and following administration of said drug candidate are selected from anti-FMRP D14F4 rabbit monoclonal antibody (Cell Signaling Technology catalogue number 7104, clone d2), anti-FMRl mouse monoclonal antibody (Sigma catalogue number WH0002332M1, clone k), anti-FMRP rabbit polyclonal antibody (Abeam catalogue number ab 17722, clone k), anti-FMRl mouse monoclonal antibody (Sigma catalogue number WH0002332M1, clone d2), anti-FMRP rabbit polyclonal antibody (Cell Signaling Technology catalogue number 4317, clone d2), and anti-FMRP rabbit polyclonal antibody (Abeam catalogue number ab 17722, clone d2).

17. The method according to claim 14 wherein said first and second antibodies are selected from anti-FMRP D14F4 rabbit monoclonal antibody (Cell Signaling Technology catalogue number 7104, clone d2) and anti-FMRl mouse monoclonal antibody (Sigma catalogue number WH0002332M1, clone k).

18. The method according to claim 14 wherein said subject is an infant, a child, a young adult, or a mature adult.

19. The method according to claim 18 comprising performing multiple times over a period of time said steps of obtaining a biological sample from the subject and subjecting the sample to said TR-FRET assay, thereby providing multiple measurements of FMRP over a period of time.

20. The method according to claim 19 further comprising comparing at least one of said measurements acquired at a first point in time during said period of time to at least one other of said measurements that was acquired at a second point in time during said period of time in order to determine whether the amount of FMRP in said subject has changed over said period of time.

21. A method for treating a condition resulting from an FMR1 gene CCG-repeat sequence mutation in a subject comprising:

obtaining a biological sample from said subject;

subjecting said sample to a TR-FRET assay that employs a first antibody labeled with a FRET donor fluorophore and a second antibody labeled with a FRET acceptor fluorophore, thereby quantifying cellular FMRP in said sample;

administering a therapeutic agent to said subject at a predetermined dosage;

obtaining a further biological sample that is acquired from said subject following administration of the therapeutic agent to the subject; subjecting said further sample to a TR-FRET assay that employs a first antibody labeled with a FRET donor fluorophore and a second antibody labeled with a FRET acceptor fluorophore, thereby quantifying cellular FMRP in said further sample; and,

comparing the results of quantifying cellular FMRP from said subject prior to administration of said therapeutic agent with the results of quantifying cellular FMRP from said subject following said administration;

based on said comparison, determining whether to provide a further dosage that is increased or decreased relative to said initial dosage for administration to said subject.