Cisplatin DNA adducts

Structure, recognition, and processing of cisplatin-DNA adducts 99CRV2467. 

Further experiments focused therefore on [RuCl(en)(r 6-tha)]+ (12) and [RuCl(rj6-p-cym)(en)]+ (22), which represent the two different classes, and their conformational distortion of short oligonucleotide duplexes. Chemical probes demonstrated that the induced distortion extended over at least seven base pairs for [RuCl(rj6-p-cym)(en)]+ (22), whereas the distortion was less extensive for [RuCl(en)(rj6-tha)]+ (12). Isothermal titration calorimetry also showed that the thermodynamic destabilization of the duplex was more pronounced for [RuCl(r 6-p-cym)(en)]+ (22) (89). DNA polymerization was markedly more strongly inhibited by the monofunctional Ru(II) adducts than by monofunctional Pt(II) compounds. The lack of recognition of the DNA monofunctional adducts by HMGB1, an interaction that shields cisplatin-DNA adducts from repair, points to a different mechanism of antitumor activity for the ruthenium-arenes. DNA repair activity by a repair-proficient HeLa cell-free extract (CFE) showed a considerably lower level of damage-induced DNA repair synthesis (about six times) for [RuCl(en)(rj6-tha)] + compared to cisplatin. This enhanced persistence of the adduct is consistent with the higher cytotoxicity of this compound (89). 

Iyer VN, Szybalski W (1963) A molecular mechanism of mitomycin action Linking of complementary DNA strands. Proc Natl Acad Sci U S A 50 355-362 Jamieson ER, Lippard SJ (1999) Structure, recognition, and processing of cisplatin-DNA adducts. Chem... 

Shellard SA, Fichtinger-Schepman AMJ, Lazo JS, Hill BT. Evidence of differential cisplatin DNA adduct formation, removal and tolerance of DNA damage in three human lung carcinoma cell lines. Anti-Cancer Drugs 1993 4 491-500. 

Schehens JH, Ma J, Planting AS, et al. Relationship between the exposure to cisplatin, DNA-adduct formation in leukocytes and tumorresponse inpatients with sohd tumors. BrJ Cancer1996 73 1569-1575. 

Studies of cisplatin bound to DNA have also been reported by others. Eastman111,112) has used radiolabeled PtCl2(en) to detect and quantify the adducts after enzymatic hydrolysis. Johnson113,114) has used an acid-catalyzed depurination followed by electrophoresis. Rahn115) used radiolabeled platinum compounds for detection, whereas Olinsky and Walter116) have used the SnCl2 method to quantify the amounts of the various cisplatin-DNA adducts. 

The purpose of this chapter is to review the types of proteins that interact with or respond to cisplatin-damaged DNA, and to discuss how these proteins can modulate cellular sensitivity to the drug through their participation in various biochemical pathways (Fig. 2). Included are proteins dedicated to dealing with genotoxic stress, such as components of the DNA repair and p53-regulated pathways, but also proteins affected by the DNA structural distortions induced by cisplatin adduct formation, such as transcription factors and architectural proteins. The manner by which such proteins affect the processing of cisplatin-DNA adducts can determine wheth-... 

Fig. 2. Effects of cisplatin-DNA adducts on some of the proteins in the nucleus that interact...

Table 2. Site-Specific Cisplatin-DNA Adducts Repaired by Mammalian NER...

A reduced capacity to repair cisplatin-DNA adducts may be responsible for the clinical effectiveness of the drug in the treatment of certain types of cancer. Cell lines derived from human testicular tumors are hypersensitive... 

By using leukocytes from chemotherapy patients with squamous-cell carcinoma of the head and neck region, it was demonstrated that damage removal from DNA was related to cisplatin resistance [83], This type of study assumes the profile of adduct formation and repair to be the same in peripheral and tumor tissue. The hypothesis was supported by several early studies which employed either atomic absorption spectroscopy or immunochemical techniques to demonstrate a relationship between DNA adduct formation in blood cells and disease response [84-89]. Subsequent work revealed, however, that cisplatin-DNA adduct levels do not always correlate with survival [90] and can vary substantially between individuals [91]. 

Fig. 4. Possible role of mismatch repair in the cytotoxicity of cisplatin. A) During replicative bypass, a mismatch is incorporated across from the cisplatin-DNA adduct. This compound lesion is bound by the mismatch repair proteins, which cut the DNA on the strand opposite the platinum. Repair synthesis would reproduce the same mismatch, resulting in a futile cycle and possibly the accumulation of DNA strand breaks which would activate apoptosis. B) Alternatively, the mismatch repair complex can recognize the cisplatin-DNA adduct alone and generate a signal that triggers apoptosis.

Cellular sensitivity to different platinum compounds and the recognition of the platinum DNA adducts by mismatch repair protein complexes appear to be linked [103]. It may also be significant that hMSH2 is expressed to higher levels in testicular and ovarian tissue than in other organs such as heart, liver and colon [109], Whether or not mismatch repair plays a general role in the anticancer activity of cisplatin still remains debatable, however. Mismatch repair proteins bind to cisplatin-DNA adducts in vitro with weak specificity [109][113]. Although specificity is enhanced when aplat-inum lesion is combined with a mutation [113], it is still less than the affinity of these proteins for the unplatinated mutation [63] [108]. 

Table 3. HMG-Domain Protein-Binding Constants for Cisplatin-DNA Adducts...

The endogenous HMG-domain proteins in HeLa cell free extracts do not seem to affect the relative rates of repair of cisplatin-DNA adducts [54] [62], Nevertheless, the hypothesis that HMG-domain proteins can enhance cellular sensitivity to cisplatin by blocking repair of the DNA adducts is still viable. Several HMG-domain proteins are specifically expressed in the testes ([146] and references cited therein), two of which, tsHMG and hSRY, inhibit the in vitro excision of cisplatin-DNA adducts at lower protein concentrations than any of the other HMG-domain proteins tested [54] [146], Selective expression of these or other such proteins in testicular tumors would provide an explanation for the unusual cisplatin sensitivity of this tumor type and the reduced repair of cisplatin-DNA adducts observed in testicular cell lines (discussed above). 

Accordingly, some effort has been devoted to studying the effects of cisplatin on transcription. In vitro experiments with RNA polymerases demonstrated that productive elongation activity was prematurely terminated by the whole spectrum of cisplatin-DNA adducts, but not by the /ran.y-DDP 1,3-intrastrand adducts [150-152], Selective bypass of trans-DDP adducts was also demonstrated in XPA cells, suggesting that repair of the DNA lesions did not contribute to differential transcription inhibition by the platinum compounds [153], In vivo, hormone-induced chromatin remodeling and subsequent transcription from the MMTV promoter was specifically inhibited by cisplatin [154], In this case, platinum adducts seemed to cause a decrease in the DNA binding of one of the transcription factors, NF1. Several chromatin-associated proteins, such as the linker histone protein HI or... 

The purpose of this work is to review recent research dealing with both the effect of cisplatin on DNA replication and the mutagenic consequences of translesion synthesis of cisplatin-DNA adducts. Our review will cover both studies performed in prokaryotes (or with prokaryotic proteins) and with eukaryotes (or eukaryotic proteins). 

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