Uptake and cytotoxicity of novel nitroimidazole-polyamine conjugates in Ehrlich ascites tumour cells.
A number of tumour cells, including Ehrlich ascites tumour cells (EATC), possess a polyamine uptake system which selectively accumulates endogenous polyamines and structurally related compounds by an active energy dependent system(s). We suggest that it may be possible to utilize this uptake system to target certain cytotoxic agents to those tumour cells possessing this system. In an initial attempt to determine the feasibility of this suggestion, we have synthesized a series of 2- and 5-nitroimidazoles linked to polyamines and determined their ability to utilize the polyamine uptake system. Within the limited series of compounds synthesized, 2-nitroimidazole-polyamine conjugates were more potent inhibitors of spermidine uptake into EATC than the 5-nitroimidazole conjugates. It has been assumed partly based on the competitive nature of this inhibition, that the ability of these compounds to inhibit spermidine uptake is also a measure of their ability to be accumulated by EATC. A greater than 700-fold variation was observed in the ability of different analogues to inhibit spermidine uptake. The most potent inhibitors retained certain structural characteristics similar to those of spermidine. Those compounds linked to polyamines were much more potent inhibitors of polyamine uptake than the parent nitroimidazoles i.e. metronidazole and misonidazole. The toxicity of the parent compounds and their polyamine conjugates in control and polyamine-depleted EATC was assessed by measuring inhibition of tritiated thymidine incorporation. Polyamine depletion, by prior exposure to difluoromethylornithine, results in a compensatory increase in the uptake of polyamines and related structures which may result in an increase in toxicity. Whilst many of the novel conjugates showed only little or moderate toxicity to control cells, the toxicity of several of the conjugates but not the parent nitroimidazoles increased in the polyamine-depleted cells. A clear distinction was also observed between the ability to inhibit spermidine uptake (and hence affinity for the uptake system) and toxicity, e.g. compound 430, a dinitroimidazole-polyamine conjugate, was the best inhibitor of spermidine uptake studied but showed no toxicity. These results support the hypothesis that linking polyamines to nitroimidazoles facilitates the entry of the latter into cells, such as EATC, which possess the polyamine uptake system and may therefore have therapeutic application in the delivery of polyamine-linked cytotoxics to certain tumours.
Holley
J
J
Department of Pharmacology, School of Pharmacy, University of London, U.K.
Mather
A
A
Cullis
P
P
Symons
M R
MR
Wardman
P
P
Watt
R A
RA
Cohen
G M
GM
D000818:Animals; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism*; D004337:Drug Carriers; D015195:Drug Design; D008920:Misonidazole / Q000494:pharmacology*; D009593:Nitroimidazoles / Q000138:chemical synthesis / Q000378:metabolism* / Q000494:pharmacology; D011073:Polyamines / Q000138:chemical synthesis / Q000378:metabolism* / Q000494:pharmacology; D013095:Spermidine / Q000378:metabolism; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism
D004337:Drug Carriers; D009593:Nitroimidazoles; D011073:Polyamines; D008920:Misonidazole; D013095:Spermidine