IN-VITRO PLATINUM DRUG CHEMOSENSITIVITY OF HUMAN CERVICAL SQUAMOUS-CELL CARCINOMA CELL-LINES WITH INTRINSIC AND ACQUIRED-RESISTANCE TO CISPLATIN

The platinum drug chemosensitivity of five human cervical squamous cell carcinoma cell lines (HX/151, HX/155, HX/156. HX/160 and HX/171) derived from previously untreated patients has been determined. Compared to our data obtained previously using human ovarian carcinoma cell lines, all five lines were relatively resistant to cisplatin, carboplatin, iproplatin and tetraplatin. One of the lines (HX/156) was exceptionally sensitive to the novel platinum (IV) ammine/amine dicarboxylates JM216 (bis-acetatoammine dichloro (cyclohexylamine) platinum (IV)) and JM221 (ammine dibutyrato dichloro (cyclohexylamine) platinum (IV)). The range in IC50 values across the five lines was approximately 2.5-fold, for cisplatin, carboplatin and iproplatin, 13-fold for tetraplatin and JM216, and 25-fold for JM221. No significant correlation (P>0.05) was observed between platinum drug chemosensitivity and either glutathione levels or cadmium chloride sensitivity, an indicator of metallothionein levels. In addition, there was no significant correlation (P>0.05) between cisplatin cytotoxicity and intracellular cisplatin accumulation or JM216 cytotoxicity and intracellular JM216 accumulation over the dose range 5-100 mum (2h exposure). The exceptional sensitivity of HX/156 to JM216 appears, at least partially, to be a result of enhanced accumulation of JM216. An 8.6-fold acquired cisplatin resistant stable variant of HX/155 has been generated in vitro. Intracellular cisplatin accumulation was reduced by 2.4+/-0.3-fold (mean+/-s.d.) in HX/155cisR across the dose range 1-100 muM (2h exposure). Glutathione levels in HX/155cisR were elevated by 1.3-fold in terms of protein content and by 1.6-fold in terms of cell number. HX/155cisR was 1.9-fold resistant to cadmium chloride. Total platinum bound to DNA after cisplatin exposure (10, 25, 50 or 100 muM for 2h) was 3.6 +/- 0.6-fold (mean +/- s.d.) lower in HX/155cisR. Hence the mechanism of acquired cisplatin resistance in HX/155cisR appears to be multifocal, with reduced intracellular drug accumulation and elevated glutathione and metallothionein levels combining to reduce DNA platination levels. While HX/155cisR was cross-resistant to tetraplatin and carboplatin, novel platinum (II) and (IV) ammine/amine complexes, including JM216 and JM221, partially circumvented resistance (resistance factors of 1.5-2). Non cross-resistance was observed to iproplatin and nine non-platinum anticancer agents. Intracellular tetraplatin accumulation was reduced by 1.8 +/- 0.1-fold (mean +/- s.d.) in HX/155cisR across the dose range 1-100 muM (2 h exposure). In contrast, after JM216 exposure (1-100 muM for 2 h), no significant difference in intracellular platinum levels between HX/155 and HX/155cisR was observed. Hence the reduction in intracellular drug accumulation by HX/155cisR is similar for cisplatin and tetraplatin, resulting in cross-resistance to tetraplatin. HX/155cisR appears to be unable to retard the accumulation of JM216 which is therefore capable of partially circumventing resistance.