Carbamate analogues of amsacrine active against non-cycling cells: relative activity against topoisomerases II alpha and beta

Purpose: Methyl N-(4'-(9-acridinylamino)phenyl)carbamate hydrochloride (AMC A) and methyl N-(4'-(9-acridinylamino)-2-methoxyphenyl)carbamate hydrochlor ide (mAMCA) are analogues of the topo-isomerase II (topo II) poison amsacri ne, and are distinguished from amsacrine by their high cytotoxicity towards non-cycling cells. Since mammalian cells contain two forms (alpha and beta ) of topo II and the alpha isoform is down-regulated in non-cycling cells, we have considered whether these carbamate analogues target topo II beta se lectively. Methods: A drug permeable yeast strain (JN394 top2-4) was transf ormed using a shuttle vector containing either human top2 alpha, human top2 alpha or yeast top2 under the control of a GAL1 promoter. The strain was a nalysed at a non-permissive temperature, where only the plasmid-borne topo II was active. Results: AMCA and mAMCA produced comparable levels of cell k illing with human DNA topo II alpha, human DNA topo II beta and yeast DNA t opo II. Two other acridine derivatives N-[2-(dimethylamino)ethyl]acridine-4 -carboxamide (DACA) and its 7-chloro derivative, which like AMCA and mAMCA are able to overcome multidrug resistance mechanisms, were much more active against human DNA topo II alpha than against human DNA topo II beta and ye ast DNA topo II. A series of mutant Chinese hamster and human lines with de fined topo lesions, including the HL60/MX2 line that lacks topo II beta exp ression, was also used to compare resistance to amsacrine, AMCA and etoposi de. Loss of topo II beta activity had a greater effect on amsacrine and AMC A than on etoposide. Resistance of murine Lewis lung cultures in exponentia l and plateau phase was also measured. Loss of topo II alpha activity, as m easured in both mutant cells expressing lower amounts of enzyme and in cell s in plateau phase, resulted in concomitant acquisition of resistance that was greatest for etoposide and least for AMCA. Conclusion: We conclude that the carbamate analogues of amsacrine recognize both topo II alpha and beta in cells.