The mutagenic effect of the antineoplastic drugs VP16 (etoposide; 4'-demethylepipodophyllotoxin-ethylidene-beta-D-glucopyranoside) and VM26 (teniposide; 4'-demethylepipodophyllotoxin-thenylidene-beta-D-glucopyr ano side) in mammalian and prokaryotic test systems have been compared. Both VP16 and VM26 which interact with mammalian DNA topoisomerase II, are strongly mutagenic in Chinese hamster ovary cells as indicated by the induction of mutations at the hypoxanthine-guanine phosphoribosyl transferase and adenosine kinase loci, and production of DNA strand breaks and sister-chromatid exchanges. Mouse L cells treated with these drugs also show a large dose-dependent (0.05-0.2 microgram/ml for VM26 and 0.5-1.5 micrograms/ml for VP16) increase in the frequency of 6-thioguanine-resistant mutants and extensive fragmentation of cellular DNA. In contrast to the results obtained with mammalian cells, VP16, which was extensively investigated, showed no increase in revertant frequencies in the Salmonella typhimurium strains TA98 and TA100 at concentrations up to greater than 500 micrograms/plate, in either the absence or presence of an exogenous rat liver activation system. However, a very weak mutagenic response to VP16 and VM26 (less than 2-fold increase in revertant frequency) at very high drug concentrations was observed in the strain TA102. VP16 also failed to show any mutagenic response (up to greater than 500 micrograms/ml) in an excision repair-proficient Escherichia coli strain 113/143 employing two different forward mutation detection systems [viz. ability to grow in galactose (Gal+) or in presence of 5-methyltryptophan], which are capable of detecting various types of genetic lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

Newcastle disease virus (NDV) and chikungunya virus (CV) replicated in monolayers of human umbilical vein endothelium to peak titres of 104.5 TCD50 per ml in 24 and 48 hours respectively following inoculation of 106 TCD50/ml of virus. The cultures demonstrated no cytopathic effects after 6 days incubation. Analysis of intracellular protein from virus-infected endothelial cells by polyacrylamide gel electrophoresis of 35s-methionine labelled extracts of infected and uninfected cells indicated that at 22 hours after infection, normal cellular protein synthesis was shut down and virus-specific protein was found inside the cells. In contrast, Influenza A viruses (HK and PR 8) did not replicate in endothelial cells. Endothelial cells exposed to a high dose of NDV were severely damaged as illustrated by rounding and stranding. Influenza A and CV did not exhibit this toxic effect. Although both NDV and CV demonstrated replication, they showed contrasting thrombo- genic effects in virus endothelium platelet reactions. Larger amounts of radioactivity were associated with endothelial cells when washed suspensions of 51Cr-labelled human platelets were added 24 hours after infection with NDV than when exposed to heat inactivated NDV or allantoic fluid. Platelets added to cultures infected with non-toxic doses of NDV or influenza virus adhered singly and in clumps to the surface of the endothelial cells, but not to those infected with CV. Identical results were attained when platelets, pre-incubated with virus, were placed on uninfected endothelial cell monolayers, then washed with buffer. The mechanism by which this adhesion takes place may be due to virus bridging or modification of endothelial cell membranes by viral neuraminidase leading to a depression of endothelial cell properties responsible for antiadhesiveness.

Newcastle disease virus (NDV) which aggregates washed suspensions of human or rabbit platelets in vitro was compared to non-aggregating viruses such as influenza A and chikungunya virus (CV) in their capacities to induce thrombocytopenia in rabbits previously infused with 5lCr- labelled platelets. NDV and influenzavirus induced a dramatic drop in platelet and radioactive counts. Five minutes after the injection of NDV, platelet counts fell to 78% of preinjection levels and only 40% of the radioactivity was recoverable. Platelet numbers returned to normal by 30 min. but label never responded past 55% of preinjection. Influenza virus demonstrated a similar pattern of platelet and radioactive counts but the responses were approximately 65% of those induced by NDV. Magnitude of thrombocytopenia was dependent upon the strength of virus injected. CV did not induce a significant drop in platelet counts. Plotting radioactive counts against a constant number of platelets in the circulation suggested that during thrombocytopenia the radioactive label may have been removed from the platelets which could be cleared from the circulation. Return to preinjection numbers may have been due to subsequent removal of platelet- free radioactivity or a movement of platelets from sequestration or storage pools. A second series of rabbits were injected with 51Cr-labelled platelets previously reacted in vitro with virus or purified neuraminidase. Approximately 80% of the platelets pretreated with NDV or influenzavirus were cleared from the circulation within 10 minutes. Only 3.6% of radioactivity was present in the rabbit circulation 10 min. after the injection of platelets which had had 8.65 nanograms of NANA/ml cleaved from their surface by neuraminidase. A mechanism for virus-induced thrombocytopenia may involve platelet aggregation and/or enzymatic platelet membrane modification, which may result in immunological clearance in the animal.