Toxicity of the novel animal-derived anticancer agent, VRCTC-310: acute and subchronic studies in beagle dogs.

Acute and subchronic toxicities of VRCTC-310, a combination product of crotoxin (CT) and cardiotoxin (CD), which has shown antitumor activity in vivo, have been studied in Beagle dogs. Single i.m. doses of 0.25, 0.5 and 1.0 mg/kg resulted in dose-dependent local muscular toxicity consisting of myofiber atrophy, interstitial edema and macrophage infiltration. Also, AST, ALT and LDH levels increased on day 2, returning to normal values on days 6-8. Local lesions were absent after recovery on day 45. At 2.0 mg/kg, signs of neurotoxicity (ataxia) appeared, in addition to vomitus, salivation, hematuria and myotoxicity in tongue and diaphragm on day 8. Local lesions healed with fibrosis at the site of injection on day 45. Administration of fixed (0.025 and 0.05 mg/kg) or escalating (0.025-0.1 mg/kg) daily doses for 30 days also produced local muscular damage, which was absent at day 75. The increases in AST, ALT and LDH serum activities on days 2-4 were independent of dosing schedule and sharply decreased on day 8, despite continuation of treatment. An escalating dose schedule of 0.025-2.0 mg/kg showed local muscle damage at the site of injection on day 31, however, there were no lesions of myotoxicity in the tongue or diaphragm and no clinical signs of neurotoxicity were observed. Animals tolerated the subchronic treatment better than the acute. The resolution of serum enzymes to normal values during treatment may be attributed to a decrease of sensitivity to VRCTC-310-mediated myotoxic effects.

VRCTC-310--a novel compound of purified animal toxins separates antitumor efficacy from neurotoxicity.

Two purified animal venom toxins, crotoxin and cardiotoxin, have been combined to produce a unique natural product (VRCTC-310) currently under investigation as an antitumor agent by the National Cancer Institute. In vitro, it has demonstrated cytotoxic disease specificity and a unique mechanism of action when submitted to COMPARE analysis. In vivo, tolerance was developed to the neurotoxic properties of crotoxin which allowed comparison of several schedules of fixed and escalating daily i.m. doses to mice bearing s.c. Lewis Lung carcinoma. An 83% inhibition of tumor growth was achieved using an escalating dose schedule starting at 1.8 mg/kg and reaching 6.3 mg/kg/day on day 20. Although some irritation around the sites of i.m. injection was noted, animal weight loss was negligible and there were no other signs of adverse toxicity. This natural product represents a new, membrane interactive anticancer agent which produces a unique spectrum of cytotoxicity in vitro and which has demonstrated interesting in vivo antitumor efficacy.

Cytotoxicity of crotoxin on murine erythroleukemia cells in vitro.

The cytotoxic effect of crotoxin, a heterodimeric phospholipase A2 from the venom of Crotalus durissus terrificus, was examined on murine erythroleukemia cells in vitro. Crotoxin cytocidal effect on cell growth had an EC50 of approximately 0.1-0.2 microM (3.0-5.0 micrograms/ml) in serum-free medium. Cytotoxicity was independent of cell growth since both quiescent and proliferating cells had similar sensitivities to the toxin. Dissociation of the crotoxin complex and phospholipase A2 activity of its subunit B are required for cytotoxicity, since the covalently linked crotoxin complex or the specific alkylation of the active site on the subunit B abolish the cytotoxic activity on murine erythroleukemia cells. Specific interaction between crotoxin and murine erythroleukemia cells appears to be required since the homologous phospholipase A2 from Crotalus atrox venom, with a higher phospholipase A2 specific activity than crotoxin, was 86-fold less potent than crotoxin. The data in this report show that the cytotoxic effect of crotoxin on murine erythroleukemia cells is consistent with the specific binding of the toxin resulting in cytocidal action mediated by the phospholipase A2 activity of crotoxin subunit B.