Yuichiro Kido

Thermal enhancement of drug uptake and DNA adducts as a possible mechanism for the effect of sequencing hyperthermia on cisplatin-induced cytotoxicity in L1210 cells

An optimal scheduling of hyperthermia andcis-diammine-dichloroplatinum(II) (cisplatin) may increase the therapeutic gain of the combination of these two modalities. In this study, intracellular platinum accumulation, total platinum binding to DNA, and DNA interstrand crooslinks (ISC) were assayed to investigate the molecular mechanisms responsible for the effect of sequencing hyperthermia on the thermal enhancement of cisplatin-induced cytotoxicity in mouse leukemia L1210 cells. Simultaneous treatment with heat (41.5°C, 60 min) and cisplatin produced maximal cell killing with a 4-fold decrease in the 50% growth-inhibitory concentration (IC50) of the platinum complex. Super-additive cell killing was also shown when cells were exposed to heat before cisplatin treatment, whereas no thermal enhancement in cisplatin-mediated cytotoxicity was observed in cells given heat after exposure to cisplatin. These results correlated with the degree of formation of ISC observed in cells following various treatments. A 2-to 3-fold increase in ISC formation was observed in cells given heat before or during cisplatin exposure, whereas heat after cisplatin treatment did not alter either the formation or the reversal of ICC as compared with cisplatin alone. The increased ISC formation was associated with an increase in intracellular platinum accumulation and total platinum binding to DNA in cells given heat before or during cisplatin exposure. These data, showing that hyperthermia potentiates cisplatin cytotoxicity by increasing drug uptake and the formation of DNA adducts without inhibiting the repair of DNA lesions, demonstrate the potential utility of sequencing hyperthermia combined with cisplatin as a clinical anticancer therapy.

Differential cytotoxicity, uptake and DNA binding of tetraplatin and analogous isomers in sensitive and resistant cancer cell lines

Some platinum complexes contain 1,2-diaminocyclohexane (DACH) as a stable carrier ligand, which can exist as the R,R-, S,S- and cis-isomers. Tetraplatin, for instance, is a mixture of R,R- and S,S-DACH-Cl4-Pt(IV). We have examined each of the three individual isomers of DACH-Cl4-Pt(IV) with respect to cytotoxicity, uptake of platinum and total DNA-platinum in three murine leukemia L1210 (cisplatin-sensitive L1210/0, 50-fold cisplatin-resistant L1210/DDP and 36-fold tetraplatin-resistant L1210/DACH) and human ovarian carcinoma A2780 (cisplatin-sensitive) and A2780cp (8-fold cisplatin-resistant) cell lines. Against A2780, A2780cp and L1210/DDP cell lines, the R,R-isomer was the most potent followed by the S,S-isomer and then the cis-isomer. However, the three isomers demonstrated similar IC50 values against the L1210/0 and L1210/DACH cell lines. The cis-isomer demonstrated cross-resistance (9- to 20-fold) to cisplatin in L1210/DDP and A2780cp cell lines. On the other hand, R,R- and S,S-isomers demonstrated minimal (2- to 4-fold) cross-resistance against these tumor models. Intracellular platinum accumulation over a 2 h period at 40 microM drug concentration was significantly (p < 0.05) greater for the R,R-isomer than the cis-isomer in L1210/0 (122 versus 101 ng Pt/mg protein) and L1210/DDP (73 versus 50) cell lines, while no difference was observed in L1210/DACH cells (55 versus 56). In L1210/DDP cells, total DNA-bound platinum was significantly (p < 0.05) greater for the R,R-isomer compared with the cis-isomer (10.3 versus 7.5 ng Pt/mg DNA).(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation of total and interstrand DNA adducts in tumor and kidney with antitumor efficacies and differential nephrotoxicities of cis-ammine/cyclohexylamine-dichloroplatinum(II) and cisplatin

Mixed amine platinum complexes have been identified as a new class of antitumor agents with activity in some cisplatin-resistant tumor models. cis-Ammine/cyclohexylamine-dichloroplatinum(II) is one such analog that we have evaluated in vivo and found it to have antitumor activity that was comparable to that of cisplatin in a solid murine fibrosarcoma tumor model. In contrast to the nephrotoxicity observed with cisplatin, the analog was free from inducing this side-effect. Pharmacokinetics of the two compounds administered i.v. at equitoxic dose levels to tumor-bearing mice indicated similar decay kinetics of total platinum in plasma, kidney and the tumor. Furthermore, DNA-platinum adducts of the two agents were similar in the tumor. Total adduct levels in the kidney, on the other hand, were significantly greater (P < 0.5) by up to 4-fold for cisplatin compared with the mixed amine analog. Likewise, the levels of interstrand cross-links of the two platinum complexes were comparable in the tumor, but significantly greater (P < 0.05) in the kidney for cisplatin. The data indicate that the greater renal levels of total and interstrand DNA-platinum adducts formed by cisplatin correlate with renal damage associated with this agent, and suggest that adduct levels, and not total tissue platinum levels, provide a more useful correlation with pharmacodynamic observations.

Synthesis, Characterization, and Antitumor Activity of New Chloroethylamine Platinum Complexes

A series of cis-bis-(2-chloroethylamine)platinum(II) and platinum(IV) complexes were synthesized and characterized by elemental analysis, IR, and 1H and 195Pt NMR spectroscopic techniques. Complexes were tested in vitro against murine L1210 leukemia and human ovarian A2780 cell lines and in vivo against the L1210 leukemia model. Some of these complexes showed excellent antitumor activity in both systems. However, all were inactive against cisplatin-resistant A2780/CP cells.

Screening test for hormone sensitivity by the autoradiographic method using cell mats.

We developed an autoradiographic screening test for hormone sensitivity of single cell suspensions of tumor tissues on cell mats, which inhibited the growth of normal cells alone. We applied this method to our newly established KSE-1 line derived from esophageal carcinoma and compared this method with well-established cytoplasmic and nuclear assays. Our assay, though taking longer to implement and providing only qualitative information, requires significantly smaller specimens than the current biochemical assay and will predict the hormone sensitivity of only viable neoplastic cells.