Increased Gene-Specific Repair of Cisplatin Interstrand Cross-Links in Cisplatin-Resistant Human Ovarian Cancer Cell Lines

Abstract

We have studied several aspects of DNA damage formation and repair in human ovarian cancer cell lines which have become resistant to cisplatin through continued exposure to the anticancer drug. The resistant cell lines A2780/cp70 and 2008/c13*5.25 were compared with their respective parental cell lines, A2780 and 2008. Cells in culture were treated with cisplatin, and the two main DNA lesions formed, intrastrand adducts and interstrand cross-links, were quantitated before and after repair incubation. This quantitation was done for total genomic lesions and at the level of individual genes. In the overall genome, the initial frequency of both cisplatin lesions assayed was higher in the parental than in the derivative resistant cell lines. Nonetheless, the total genomic repair of each of these lesions was not increased in the resistant cells. These differences in initial lesion frequency between parental and resistant cell lines were not observed at the gene level. Resistant and parental cells had similar initial frequencies of intrastrand adducts and interstrand cross-links in the dihydrofolate reductase (DHFR) gene and in several other genes after cisplatin treatment of the cells. There was no increase in the repair efficiency of intrastrand adducts in the DHFR gene in resistant cell lines compared with the parental partners. However, a marked and consistent repair difference between parental and resistant cells was observed for the gene-specific repair of cisplatin interstrand cross-links. DNA interstrand cross-links were removed from three genes, the DHFR, multidrug resistance (MDR1), and delta-globin genes, much more efficiently in the resistant cell lines than in the parental cell lines. Our findings suggest that acquired cellular resistance to cisplatin may be associated with increased gene-specific DNA repair efficiency of a specific lesion, the interstrand cross-link.

Synthesis and in Vitro and in Vivo Antitumor Activity of a Series of Trans Platinum Antitumor Complexes

“…However, not all of the dihydroxo-Pt(IV) complexes were active; generally, where R = a short aliphatic chain, there was a loss of in vivo activity (e.g., 19 R = methyl; 20 R = ethyl; 24 R = diethyl). In addition, activity was lost where R = morpholino (23), pyridine (26), and quinuclidine (31). From Tables 3 and 4, a total of 14 active trans complexes has been described; those possessing alicyclic R substituents (cyclopentyl, 25; cyclohexyl, 18, 36; and cycloheptyl, 29) were most active (ED90 of <3 mg/kg and a therapeutic index >5).…”

“…Our previous mechanism-based studies have revealed that resistance to cisplatin in 41McisR is mediated predominantly through reduced platinum accumulation21•24 and in CHlcisR through enhanced removal of platinum-DNA adducts combined with an increased tolerance to such DNA adducts.21 resistance in A2780cisR appears to be multifocal, having been ascribed to reduced drug accumulation and increased levels of glutathione14 and increased DNA sequence-specific repair of platinum-DNA adducts. 26 Thus, it appears that the trans complexes exhibiting potent in vitro growth inhibitory properties may be capable of circumventing acquired cisplatin resistance due to reduced drug accumulation and, interestingly, exert some effects against acquired cisplatin resistance due to enhanced DNA repair/enhanced tolerance. Although all of the novel trans complexes except two platinum(II) complexes (7, R = diethyl; 12, R = quinuclidine) were potent inhibitors of at least some human ovarian carcinoma cell lines in vitro, clear structureactivity requirements for in vivo antitumor activity were apparent.…”

Current Status of Platinum-Based Antitumor Drugs

“…A few compounds currently in clinical trials show promise but are still several years away from approval. In recent years, much has been elucidated concerning the mechanisms underlying tumor resistance to cisplatin. − Studies have revealed that a combination of reduced platinum transport, increased cytoplasmic detoxification via elevated glutathione and/or metallothionein levels, enhanced DNA repair, and increased cellular tolerance to Pt−DNA adducts are the major mechanisms underlying resistance. A number of cisplatin resistance cell lines with known resistance mechanisms have been used for the evaluation of new complexes.…”

Combined NMR and Molecular Mechanics Study of the Isomers Formed in the Reaction of Dichloro(1,4-diazacycloheptane)platinum(II) with the Dinucleotide d(GpG)

“…3,[9][10][11][12][13] However, there is also evidence implicating the lower frequency GG interstrand adducts. [14][15][16] We have designed a series of complexes to interact stereospecifically with DNA and so give rise to an adduct profile different from that formed by cis-DDP. [17][18][19][20][21] The long-term aim of these studies is to investigate any correlation between anticancer activity and adduct profile and so contribute to an understanding of the mechanism of action of Pt anticancer drugs.…”