Dr. Anindita Debnath

Anticancer drug development from natural resources are ventured throughout the world. Animal venoms and toxins a potential bio resource and a therapeutic tool were known to man for centuries through folk and traditional knowledge. The biodiversity of venoms and toxins made it a unique source of leads and structural templates from which new therapeutic agents may be developed. Venoms of several animal species (snake, scorpion, toad, frog etc) and their active components (protein and non protein toxins, peptides, enzymes, etc) have shown therapeutic potential against cancer. In the present review, the anticancer potential of venoms and toxins from snakes, scorpions, toads and frogs has been discussed. Some of these molecules are in the clinical trials and may find their way towards anticancer drug development in the near future. The implications of combination therapy of natural products in cancer have been discussed.

The amphibian skin contains various bioactive molecules (peptides, proteins, steroids, alkaloids, opiods) that possess potent therapeutic activities like antibacterial, antifungal, antiprotozoal, antidiabetic, antineoplastic, analgesic and sleep inducing properties. Research on amphibian skin derived biomolecules can provide potential clue towards newer drug development to combat various pathophysiological conditions. An overview on the bioactive molecules of various amphibian skins has been discussed.

A lethal cardiotoxic-cytotoxic protein (mol. wt. 6.76 kDa) has been purified from the Indian monocellate cobra (Naja kaouthia) venom by ion-exchange chromatography and HPLC. CD spectra indicated the presence of 23% alpha helix, 19% beta sheets and 35% coil. Complete amino acid sequence was determined by MALDI, which showed similar homology with cardiotoxins/cytotoxins isolated from venom of other Naja species. Intraperitoneal LD(50) was 2.5 mg kg(-1) in BalbC male mice. In vitro cardiotoxicity studies on isolated guinea pig auricle showed that the molecule produced auricular blockade that was abolished after trypsin treatment. Cytotoxicity studies on human leukemic U937 and K562 cells showed that it significantly inhibited cell proliferation in a dose and time dependent manner, as observed by trypan blue exclusion method and tetrazolium bromide reduction assay. IC(5)(0) on U937 and K562 cells were 3.5 microg/ml and 1.1 microg/ml respectively. Morphometry and cell sorting studies indicated apoptosis induction in toxin treated leukemic cells. Apoptosis was caspase 3 and 9 dependent and the treated leukemic cells were arrested in sub-G1 stage. There was an increase in Bax-Bcl2 ratio, decrease in HSP (Heat shock protein) 70 and HSP90 and induction of PARP cleavage after NK-CT1 treatment. The toxin showed low cytotoxic effect on normal human leukocytes as compared with imatinib mesylate. Further detailed cytotoxic and cardiotoxic effects at the molecular level are in progress.

Venoms are rich source of several bioactive compounds that possess therapeutic potentials. The different constituents of scorpion venom can modulate cell proliferation, cell growth and cell cycle. In the present communication, the cytotoxic activity of Indian black scorpion (Heterometrus bengalensis) venom was explored on human leukemic U937 and K562 cells. Scorpion venom induced U937 and K562 cell growth inhibition and the IC(50) value calculated to be 41.5 microg/ml (U937) and 88.3 microg/ml (K562). The scorpion venom showed characteristic features of apoptosis such as membrane blebbing, chromatin condensation and DNA degradation in both the cells as evidenced by confocal, fluorescence, scanning electron microscopy. Scorpion venom (IC(50) dose, 48 h) induced DNA fragmentation as evidenced by comet formation. Flow-cytometric assay revealed a significant amount of apoptotic cells (early and late) due to scorpion venom treatment. The venom induced cell cycle arrest was observed with maximum cell accumulation at sub-G(1) phase. Thus, the Indian scorpion (H. bengalensis) venom possessed antiproliferative, cytotoxic and apoptogenic activity against human leukemic cells.