Synthesis and biological activity of novel thymidine derivatives of podophyllotoxin and 4'-demethylepipodophyllotoxin
Derry, W.B.; Pamidi, C.C.; Gupta, R.S.
Anti-Cancer Drug Design 8(3): 203-221
1993
ISSN/ISBN: 0266-9536 PMID: 8517914 Document Number: 418442
We have synthesized a number of novel derivatives of podophyllotoxin (POD) and 4'-demethylepipodophyllotoxin (DMEP) in which the nucleoside thymidine has been conjugated at the C4 position. To investigate the structure-activity relationship among these compounds, the cross-resistance patterns of these derivatives towards a set of either POD-resistant (Pod-R) or VP16/VM26-resistant (Vpm-R) mutants of Chinese hamster ovary (CHO) cells were determined. These mutants exhibit highly specific cross-resistance patterns towards compounds that show either POD- or VP16/VM26-like activity. The observed cross-resistance patterns of the thymidine derivatives suggests that these compounds display POD-like activity in vivo and show no VP16/VM26-like activity. Further, treatment of Chinese hamster cells with these compounds caused a dose-dependent increase in the mitotic index similar to the patterns observed with POD and DMEP, supporting the data from the cross-resistance assay. Most thymidine derivatives exhibited much lower activity in comparison to POD or DMEP, suggesting that the thymidine moiety interferes with the interaction of these compounds with the receptor site on the tubulin molecule. One of these derivatives which was most active in the aforementioned assays was also found to be a competitive inhibitor of radiolabelled POD binding to purified bovine brain tubulin. All other compounds were insoluble at concentrations required to perform the competition assay. Molecular modelling studies provide valuable insight regarding the three-dimensional structural requirements that distinguish POD-like compounds from their VP16/VM26-like counterparts. There appears to be a very limited spatial and electrostatic requirement for the bulky glycosidic moiety at C4 which is essential for VP16/VM26-like activity.