European School of Oncology Task Force Report. New approaches in cancer pharmacology: drug design and development (Part 2).
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Animals↗
Biomedical subjects
K R Harrap
Publications and source records attributed to K R Harrap.
Mechanism of action of an orally administered platinum complex [ammine bis butyrato cyclohexylamine dichloroplatinum (IV) (JM221)] in intrinsically cisplatin-resistant human ovarian carcinoma in vitro.
Intrinsic resistance to existing clinical platinum drugs is a major cause of treatment failure; moreover, these agents have the drawbacks of cross-resistance and intravenous administration. The mechanism of intrinsic cisplatin resistance and the mechanism of circumvention of intrinsic resistance by a member (JM221) of the ammine/amine platinum (IV) dicarboxylate class of platinum complex was studied in intrinsically resistant (SKOV-3) and sensitive (41M) human ovarian carcinoma cell lines. JM221 reduced the cisplatin resistance factor nine- to 2.7-fold, was more potent than cisplatin and showed marked time-dependent cytotoxicity. Cellular platinum accumulation was 20- to 40-fold greater (P < 0.001), and DNA platination was fourfold greater (P < 0.02), immediately following 2 h equimolar exposure to JM221, compared with cisplatin. DNA platinum levels decreased following cisplatin exposure with a half-life approximating 48 h in both lines, while no net removal of DNA-bound platinum was recorded following JM221 exposure. JM221 caused DNA interstrand cross-linking, but this was 10-20% less frequent with JM221 than with cisplatin when expressed as a proportion of total DNA platinum lesions. Cisplatin DNA interstrand cross-linking was twofold greater in the intrinsically sensitive line (41M) than in the resistant line (SKOV-3) over a range of concentrations and time-points. Neither cellular platinum accumulation, levels of DNA platination nor the rate of removal of DNA-bound platinum in the two cell lines related to their ninefold difference in cisplatin sensitivity. Intrinsic cisplatin resistance appears to be attributable to the inhibition of formation of bifunctional DNA lesions, while the circumvention of intrinsic resistance by JM221 seems to be the result of both improved transport properties and circumvention of DNA repair mechanisms.
Antineoplastic Agents↗
Evaluation of novel ammine/amine platinum (IV) dicarboxylates in L1210 murine leukaemia cells sensitive and resistant to cisplatin, tetraplatin or carboplatin.
Seventeen alkylamine ammine dicarboxylatodichloroplatinum(IV) complexes of general structure c,t,c-[PtCl2(OCOR1)2NH3(RNH2)], where R = aliphatic or alicyclic and R1 = aliphatic or aromatic, have been evaluated against L1210 cell lines with acquired resistance to cisplatin (10-fold), tetraplatin (34-fold) or carboplatin (14-fold) using an in vitro growth-delay assay. All of these compounds overcame cisplatin, tetraplatin and carboplatin resistance. Potency increased as the number of carbon atoms in the axial aliphatic ligands (R1) increased, for example comparing JM216 (R = cyclohexyl, R1 = CH3, IC50 = 1.2 microM) with JM274 (R = cyclohexyl, R1 = n-C4H9, IC50 = 0.05 microM) against the parent sensitive line (L1210/S). The most active compounds were those possessing aromatic ligands at R1, regardless of whether R = aliphatic or alicyclic, for example JM244 (R = n-C3H7, R1 = C6H5, IC50 = 0.028 microM) and JM2644 (R = c-C6H11, R1 = C6H5, IC50 = 0.031 microM) against L1210/S. For an alicyclic alkylamine series in which R is varied from c-C3H7 to C-C7H13, with R1 = n-C3H7 for each compound, cytotoxic potency was maximised at c-C6H11 (JM221, IC50 = 0.06 microM against L1210/S). Preliminary biochemical studies, at equitoxic doses, comparing JM221 (0.1 microM) with cisplatin (0.6 microM) identified five times more platinum associated with JM221 treated cells and 1.5 times more platinum bound to the DNA of JM221-treated cells. The lipophilic properties of some of these platinum(IV) dicarboxylates may contribute to both the potency and circumvention of resistance by these compounds.
Animals↗
Effect of buthionine sulfoximine on PtII and PtIV drug accumulation and the formation of glutathione conjugates in human ovarian-carcinoma cell lines.
Glutathione (GSH) has often been implicated in the mechanism of resistance to platinum anti-cancer drugs. It has been suggested that GSH may reduce the cytotoxicity of these drugs by forming inactive conjugates and by enhancing the repair of DNA-platinum crosslinks. In the present study we have examined the effect of D,L-buthionine-S,R-sulfoximine (BSO) pretreatment on the accumulation of platinum in a sensitive (CHI) and 2 relatively resistant (SKOV-3, HX/62) human ovarian-carcinoma cell lines following exposure to PtII- (cisplatin, carboplatin) and PtIV-drugs (tetraplatin). The metabolism of cisplatin and tetraplatin (particularly the extent of platinum-GSH conjugate formation) in the presence and absence of BSO pre-treatment was also examined in these cell lines. BSO pre-treatment reduced the accumulation of PtII but not that of PtIV drugs in the relatively resistant SKOV-3 and HX/62 cell lines. It had no effect on the accumulation of either class of drugs in the sensitive CHI cells. Metabolism studies with cisplatin showed that the SKOV-3 and HX/62 cells, which contained 2- to 3-fold higher levels of GSH, were able to inactivate a greater proportion of cellular cisplatin, by the formation of platinum-GSH conjugates, than the CHI cells. A significant inhibition in formation of these conjugates, by BSO-induced depletion of cellular GSH (over 80%), did not, however, increase cisplatin concentration in the resistant cells. In contrast, a small increase in cisplatin concentration was observed in the sensitive cells following BSO pre-treatment. Comparison of cisplatin and tetraplatin metabolism in the SKOV-3 cells indicated that a greater proportion of the latter drug was inactivated by formation of GSH conjugates. BSO-induced depletion of cellular GSH in this cell line significantly reduced the formation of such conjugates from both drugs. However, concomitant increases in intracellular levels of reactive species were observed only after tetraplatin exposure. Our data suggest that the greater potentiation of PtIV- compared with PtII-drug cytotoxicity in the relatively resistant cell lines following 24 hr BSO pre-treatment may be caused by a differential effect of BSO on the metabolism and cellular distribution of these drugs. A BSO-induced reduction in PtII- but not PtIV-drug accumulation in these cells may also partially contribute to the differential potentiation of cytotoxicity of these drugs.
Antimetabolites, Antineoplastic↗
Preclinical antitumor evaluation of bis-acetato-ammine-dichloro-cyclohexylamine platinum(IV): an orally active platinum drug.
The cytotoxicity of a novel platinum(IV) complex, bis-acetato-amminedichloro-cyclohexylamine platinum(IV) (JM216), has been evaluated in vitro against a panel of human tumor cell lines (predominantly ovarian) representative of models of intrinsic and acquired to cisplatin. In addition, the activity of JM216 administered by the p.o. route has been determined in vivo using the murine ADJ/PC6 plasmacytoma and four human ovarian carcinoma xenograft lines. In vitro, against seven human ovarian carcinoma cell lines, JM216 showed similar cytotoxicity and pattern of cytotoxicity to cisplatin (mean 50% inhibitory concentrations of 3.5 microM for cisplatin and 1.7 microM for JM216). The cytotoxicity of JM216 was more dependent on the time of drug exposure than that of cisplatin, suggesting that extended split-dosing rather than a single bolus administration might be a more appropriate schedule in patients. Using six pairs of acquired cisplatin-resistant and parent human tumor cell lines (four ovarian, one testicular, and one cervical) JM216 exhibited non-cross-resistance (resistance factor of < 1.5) in three whereas tetraplatin exhibited partial or full cross-resistance in all six pairs. Notably, in two of the acquired cisplatin-resistant lines (41McisR and HX/155cisR) where JM216 retained activity, resistance has previously shown to be due primarily to reduced platinum uptake. In vivo, following p.o. administration using the cisplatin-sensitive murine ADJ/PC6 plasmacytoma, JM216 showed antitumor selectivity far superior to that observed for either cisplatin, carboplatin, or tetraplatin. Across four human ovarian carcinoma xenografts of widely differing sensitivity to cisplatin and carboplatin, JM216 exhibited p.o. activity, broadly comparable to that observed for i.v. administered cisplatin and carboplatin and markedly superior to i.p. administered tetraplatin. These antitumor properties suggest that JM216 provides a structural lead to platinum complexes which may circumvent transport-determined acquired resistance to cisplatin and is a suitable candidate as an p.o. administrable platinum complex for phase I clinical trial.
Animals↗
Gamma-linked dipeptide analogues of 2-desamino-2-methyl-N10-propargyl-5,8- dideazafolate as antitumour agents.
Our search for water-soluble quinazoline TS inhibitors that are transported into cells via the RFC, but are not substrates for FPGS, led us to the synthesis of dipeptide analogues of ICI 198583 diglutamate. Although a number of dipeptide analogues were active against isolated TS and L1210 cells in vitro, lack of in vivo stability was a problem. This was circumvented by the synthesis of modified dipeptides where either the alpha-carboxyl of the second amino acid was removed (alpha'-COOH) e.g. -L-glu-GABA or where the second amino acid was the unnatural D-enantiomer e.g.-L-glu-D-glu. Further studies were performed with the -L-glu-D-glu and its 7-CH3, 2'F modified analogue, demonstrating that they use the RFC for cell entry but are not active through polyglutamate formation. The latter compound was tested against experimental tumour models and found to have good activity.
Animals↗
Lack of nephrotoxicity of oral ammine/amine platinum (IV) dicarboxylate complexes in rodents.
The comparative nephrotoxicity of i.v. cisplatin, i.v. carboplatin and six p.o. ammine/amine Pt(IV) dicarboxylates was studied in rodents following single MTD treatments. In mice, i.v. cisplatin caused proteinuria (1 g l-1), glycosuria (16.7 mM) and decreased GFR at 4 days, and histological kidney damage with onset at 6 days. In contrast, mice treated with i.v. carboplatin or p.o. ammine/amine Pt(IV) dicarboxylates had urinary glucose, urinary protein, GFR and kidney histology within the control range. In rats, i.v. cisplatin caused 5-fold elevations in plasma creatinine (188 +/- 33 microM) and urea (30.4 +/- 8.9 mM), a 10-fold fall in creatinine clearance (0.54 +/- 0.31 ml min-1 kg-1), a 25-fold elevation in urine/plasma glucose concentration ratio (3.28 +/- 0.17), a 20% increase in kidney weight (7.9 +/- 0.56 mg gm-1 body weight) and extensive histological damage 4 days after treatment. In contrast, i.v. carboplatin and p.o. JM216 (the lead compound of this series) caused neither abnormalities in renal function nor histological damage in rats. The nephrotoxicity of single MTD treatments of p.o. ammine/amine Pt(IV) dicarboxylate complexes appears less than i.v. cisplatin and comparable to i.v. carboplatin.
Administration, Oral↗
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 microM (2 h 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 microM (2 h 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 microM for 2 h) 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 microM (2 h exposure). In contrast, after JM216 exposure (1-100 microM for 2 h), no significant difference in intracellular platinum levels between HX/155 and HX/155cisR was observed.(ABSTRACT TRUNCATED AT 400 WORDS)
Antineoplastic Agents↗
Acquisition of platinum drug resistance and platinum cross resistance patterns in a panel of human ovarian carcinoma xenografts.
In vivo models of acquired resistance to the platinum-based agents cisplatin (CDDP), carboplatin (CBDCA), iproplatin (CHIP) and tetraplatin have been established using a panel of six parent human ovarian carcinoma lines, two (HX/110 and PXN/87) being derived from previously untreated patients. Resistance has been generated to CDDP (three lines), CBDCA (one line), CHIP (three lines) and tetraplatin (one line) either by treatment in vivo or (for one line to CDDP) through exposure in vitro and subsequent transfer to mice. With the four tumours where resistance was generated using CDDP or CBDCA, a complete cross-resistance to the remaining platinum agents studied was observed. In contrast, in one of three lines with derived resistance to the platinum (IV) agent, CHIP, (PXN/951) a retention in sensitivity was observed with CDDP and CBDCA. Only one of the six parent tumour lines (PXN/100) was markedly sensitive to tetraplatin. Where resistance was generated to tetraplatin (PXN/100T) there was some retention of activity by CDDP. For the CDDP-resistant line established in vitro, there was a close agreement between the cross-resistance profile obtained in vitro vs that obtained in vivo. This tumour panel may be useful in the elucidation of cellular and molecular resistance mechanisms to platinum drugs operative in vivo. Moreover, as they appear to mimic the clinical observations of shared cross-resistance between CDDP, CBDCA and CHIP, they may represent valuable preclinical evaluation models for the discovery of drugs capable of conferring responses in CDDP-refractory ovarian cancer.
Animals↗
Synthesis and antiviral activity of some new S-adenosyl-L-homocysteine derivatives.
A series of new S-adenosyl-L-homocysteine (AdoHcy) analogues with modifications to amino acid and nucleoside moieties was prepared via condensation of appropriate nucleoside precursors and suitably protected L-homocystine derivatives. The AdoHcy derivatives as well as the nucleoside precursors were evaluated for their antiviral activity. Some of the compounds, in particular S-tubercidinyl-L-homocysteine propyl ester (36), N-(trifluoroacetyl)-S-tubercidinyl-L-homocysteine isopropyl ester (27), S-3'-deoxytubercidinyl-L-homocysteine (58), N-(trifluoracetyl)-S-tubercidinyl-L-homocysteine propyl ester (26), and N-(methoxyacetyl)-S-tubercidinyl-L-homocysteine ethyl ester (31) showed potent and selective activity against HSV, VV, and VSV. It is likely that they exert their antiviral effect via selective inhibition of the methyltransferases which are required for the maturation of viral mRNAs.
Animals↗
Comparison of cellular accumulation and cytotoxicity of cisplatin with that of tetraplatin and amminedibutyratodichloro(cyclohexylamine)platinum(IV) (JM221) in human ovarian carcinoma cell lines.
We have compared the cellular accumulation and cytotoxicity of three platinum compounds in a panel of five human ovarian carcinoma cell lines. The cell lines, which were established from both untreated and pretreated patients, showed a wide range in sensitivity to cisplatin and other platinum drugs. The panel consisted of two sensitive (41M, CH1), one in vivo acquired resistant (PXN/94) with moderate sensitivity, and two intrinsically resistant (SKOV-3, HX/62) cell lines. The cisplatin 2-h concentration of drug required to inhibit cell growth by 50% compared with vehicle treated control cells (IC50 values) for these cell lines were in the following order: CH1 < 41M < PXN/94 < SKOV-3 < HX/62. None of the cell lines showed saturation of platinum accumulation (per mg protein) at 2 h after exposure to cisplatin concentrations of up to 500 microM. The highest cellular platinum accumulation was observed in the sensitive 41M cell line which was established from an untreated patient. The lowest accumulation was found in the intrinsically resistant HX/62 cell line. The rate of platinum accumulation at an equimolar concentration of cisplatin was 41M > SKOV-3 > CH1 > PXN/94 > HX/62. The relationship between drug accumulation and cytotoxicity was evaluated by comparing 2-h IC50 values with platinum accumulation following exposure to both equimolar and equitoxic doses of the agent. The results suggest that reduced drug accumulation may play a partial role in the mechanism of intrinsic resistance to cisplatin in one cell line (SKOV-3) and a major role in another (HX/62), where reduced accumulation is attributable to reduced uptake rather than enhanced efflux. Decreased drug accumulation may also contribute significantly to the lower sensitivity of the PXN/94 cell line to cisplatin. Interestingly, both the PXN/94 and the sensitive CH1 cell lines, which were established from patients pretreated with platinum drugs, showed reduced drug accumulation relative to the 41M cell line. Cellular accumulation of tetraplatin and JM221 [(ammine)dibutyratodichloro(cyclohexylamine)platinum(IV)], a novel platinum(IV) dicarboxylate complex exhibiting enhanced cytotoxicity compared to cisplatin, was also examined. Comparison with platinum accumulation from cisplatin suggests that the increased cytotoxicity of tetraplatin and JM221 may be related to their increased accumulation. Significantly both agents are more lipophilic than cisplatin, which may account partially for their improved uptake in cisplatin resistant cells.
Antineoplastic Agents↗
Mechanism-related circumvention of acquired cis-diamminedichloroplatinum(II) resistance using two pairs of human ovarian carcinoma cell lines by ammine/amine platinum(IV) dicarboxylates.
Acquired resistance to cisplatin has been generated in vitro in two human ovarian carcinoma cell lines: 41M, established from a previously untreated patient; and CH1, from a patient previously treated with cisplatin and cis-diammine-1,1-cyclobutane dicarboxylatoplatinum(II) (carboplatin). In neither cell line with acquired resistance did intracellular detoxification (via increased glutathione or metallothioneins) appear to be a major determinant of resistance. Resistance in 41McisR (resistance factor of 4.7) appeared to be due predominantly to a reduced platinum accumulation (levels were only 23.8% in 41McisR versus 41M). This was also reflected at the DNA level by a similar level of reduced DNA interstrand cross-links and total platinum-DNA adducts measured immediately after a 2-h exposure to cisplatin in 41McisR versus 41M. Conversely, for CH1cisR (resistance factor of 6.5), platinum accumulation, and initial numbers of DNA-interstrand cross-links and total DNA-platinum adducts were not significantly different from the parent CH1 line. This is suggestive of a resistance mechanism involving increased DNA repair or tolerance to platinum-DNA adducts operating in the CH1cisR/CH1 pair of lines. Cross-resistance to carboplatin and partial cross-resistance to the 1,2-diaminocyclohexane-containing agent, (trans-d,l)-1,2-diaminocyclohexane tetrachloroplatinum(IV) (tetraplatin), was observed in both pairs. However, two novel platinum(IV) ammine/amine dicarboxylates, ammine dibutyratodichloro(cyclohexylamine)platinum(IV) (JM221) and ammine dibenzoatodichloro(propylamine)platinum(IV) (JM244), completely circumvented resistance in 41McisR to produce some collateral sensitivity (resistance factors of 0.67 and 0.54, respectively) but showed cross-resistance in CH1cisR (resistance factors of 3.7 and 4.6). In contrast to the data for cisplatin, intracellular platinum levels were not significantly different between the 41M and 41McisR pair of cell lines after exposure to JM244. These results suggest that the ammine/amine platinum(IV) dicarboxylates, which show considerably greater in vitro cytotoxicity than cisplatin, are capable of circumventing acquired cisplatin resistance which is due to decreased intracellular accumulation but are not able to overcome resistance at the level of DNA platination and removal.
Antineoplastic Agents↗
Establishment and characterization of an in vitro model of acquired resistance to cisplatin in a human testicular nonseminomatous germ cell line.
Clinically, human testicular nonseminomatous germ cell tumors exhibit remarkable sensitivity to platinum-based chemotherapy. To define better the mechanistic basis for this unusual sensitivity, the biochemical determinants of platinum-induced cytotoxicity have been investigated in a human testicular tumor cell line (GCT27) established from a previously untreated patient and in an in vitro derived 5.6-fold cisplatin-resistant stable variant (GCT27cisR). Compared to 12 ovarian and 5 cervical human tumor cell lines, the parent GCT27 line was among the most sensitive to the cytotoxic effects of both cisplatin (dosage producing 50% inhibition, 0.2 microM) and carboplatin (dosage producing 50% inhibition, 2.9 microM), thus reflecting clinical data. A 4-day exposure sulforhodamine B-staining assay was used to determine that GCT27cisR was cross-resistant to carboplatin and iproplatin and the classical bifunctional alkylating agents melphalan and chlorambucil. Partial cross-resistance was observed to tetraplatin, methotrexate, and mitomycin C. No cross-resistance was observed to Adriamycin, etoposide, vinblastine, bleomycin, 1-beta-D-arabinofuranosylcytosine, and 5-fluorouracil. Intracellular cisplatin accumulation across the dose range 2.5-100 microM (for 2 h) was 1.6 +/- 0.39-fold (mean +/- SD) greater for the parent line. There was no significant difference in glutathione levels between the two lines. The acquired resistance line was 1.9-fold more resistant than the parent line to the cytotoxic effects of cadmium chloride. There was no significant difference between the two lines, however, in the total amounts of platinum bound to DNA after cisplatin exposure (25, 50, or 100 microM for 2 h). The removal of total platinum adducts from DNA was significantly faster for GCT27cisR compared to the parent line (half-times of removal, 32 and 67 h, respectively). These data suggest that the abnormal sensitivity of the parent testicular tumor cell line to platinum-containing anticancer drugs may be due predominantly to an inherent defect in the ability of these cells to remove platinum from their DNA. This defect is apparently lost in the acquired resistance counterpart. Reduced intracellular accumulation and increased cytoplasmic concentrations of metallothionein may also contribute, in part, to the acquisition of cisplatin resistance in this model.
Antineoplastic Agents↗
Ammine/amine platinum(IV) dicarboxylates: a novel class of platinum complex exhibiting selective cytotoxicity to intrinsically cisplatin-resistant human ovarian carcinoma cell lines.
Using a panel of six human ovarian carcinoma cell lines varying by two orders of magnitude in terms of cisplatin cytotoxicity, we have investigated the in vitro antitumor activity of a series of novel alkylamine ammine dicarboxylatodichloroplatinum(IV) complexes of the general formula c,t,c-[PtCl2(OCOR1)2NH3(RNH2)]. A clear relationship existed between increasing the number of carbons in the R1 substituent and increasing cytotoxicity up to R1 = C5H11. In terms of changing the R group, maximum cytotoxic effects were conferred by alicyclic substituents. Furthermore, increasing the alicyclic ring size from cyclobutane through to cycloheptane resulted in increasing cytotoxicity. The agents with longer axial chains (e.g., JM300, R = cyclohexyl, R1 = C6H13) were significantly more cytotoxic than cisplatin and, moreover, exhibited a selective cytotoxic effect against the most intrinsically cisplatin-resistant cell lines (e.g., for HX/62, cisplatin 50% inhibitory concentration, 12.6 microM; SKOV-3, cisplatin 50% inhibitory concentration, 4.4 microM and 41 M; cisplatin 50% inhibitory concentration, 0.23 microM; JM300 was 840-, 440-, and only 34-fold more active, respectively). The dicarboxylates JM221 (R = cyclohexyl, R1 = C3H7) and JM244 (R = n-propyl, R1 = C6H5) also retained activity against a 4-fold cisplatin-acquired resistant variant of the 41M cell line. At least part of the increased cytotoxicity of the dicarboxylate, JM221, over cisplatin appeared to be attributable to an increased intracellular accumulation. This novel class of platinum compound represents a valuable lead in the development of a "third-generation" agent capable of exhibiting activity against clinical disease currently resistant to cisplatin.
Antineoplastic Agents↗
Human ovarian-carcinoma cell lines and companion xenografts: a disease-oriented approach to new platinum anticancer drug discovery.
A disease-oriented approach to the discovery of novel platinum anticancer drugs has been established through the setting up of parallel human ovarian-carcinoma cell lines and xenografts. The correlation between in vitro and in vivo antitumour activity was determined for four reference platinum agents (cisplatin, carboplatin, iproplatin and tetraplatin) in eight companion lines. Two methods of assessing antitumour effect were used in vitro (tritiated thymidine incorporation and sulforhodamine B staining) and three were applied in vivo [28-day treated/control (T/C) ratio, growth delay and specific growth delay]. In vitro, large differences in cytotoxicity across the cell lines were observed for each drug. This was also reflected in the xenografts for cisplatin and carboplatin and, to a lesser extent, for iproplatin. A correlation analysis of in vitro vs in vivo data revealed a high, statistically significant positive correlation for cisplatin and a strong positive correlation for carboplatin. However, for the two platinum(IV) drugs, the correlation was less good. In particular, tetraplatin was markedly less active in vivo (showing a general lack of activity against all of the tumour lines) than its in vitro potency against the cell lines predicted, resulting in poor correlation coefficients. These human tumour panels may be valuable for the elucidation of both cellular/molecular and corresponding in vivo pharmacological mechanisms of platinum drug resistance. Moreover, the HX/62 and SKOV-3 tumour lines, which exhibit a level of intrinsic resistance to the four reference agents both in vitro and in vivo (and which were derived from patients who had not received prior platinum therapy), represent particularly useful evaluation models for the discovery of novel broad-spectrum platinum drugs.
Antineoplastic Agents↗
Reduced drug accumulation as a major mechanism of acquired resistance to cisplatin in a human ovarian carcinoma cell line: circumvention studies using novel platinum (II) and (IV) ammine/amine complexes.
Acquired resistance to cisplatin (cis-diamminedichloroplatinum (II)) has been generated in vitro in the 41M human ovarian carcinoma cell line, established from a previously untreated patient. Three cisplatin-resistant variants were selected at approximately 2, 4 and 6-fold resistance (in terms of 50% inhibitory concentrations), in order to study the underlying mechanisms of acquired cisplatin resistance. Compared to the parent line, platinum accumulation following exposure to equimolar concentrations of cisplatin was on average (across the entire concentration range) 2.9, 3.6 and 4.8-fold lower in the 41McisR2, 41McisR4 and 41McisR6 cell lines, respectively. Thus the difference in uptake corresponded closely with their resistance factor in the three resistant variants. Moreover, a significant reduction in platinum accumulation was observed as early as 5 min after exposure to cisplatin in the 41M vs 41McisR6 cell lines. Platinum accumulation was similar in all cell lines following exposure to equitoxic concentrations (2 h IC50) of cisplatin. Enhanced efflux of drug was not observed between the 41M and 41McisR6 cells. In addition, there was no difference in intracellular glutathione (GSH) levels. Our previous studies have shown no indication of metallothionein involvement and the decrease in cisplatin uptake in the 41McisR6 cells was reflected by a similar reduction in DNA interstrand cross-links (ISC) formation. These results suggest that the mechanism of acquired resistance to cisplatin in the 41McisR6 cell line may be predominantly due to reduced drug uptake. The 41McisR6 cells were not found to be cross-resistant to ouabain, a postulated specific inhibitor of sodium-potassium adenosine triphosphatase (Na+, K(+)-ATPase), suggesting that decreased cisplatin accumulation in these cells is probably not regulated by alterations in their Na+, K(+)-ATPase levels, and Na+ potential across the plasma membrane. Cellular accumulation of a novel class of platinum (IV) ammine/cyclohexylamine dicarboxylates, which exhibit enhanced cytotoxicity over cisplatin and completely circumvent resistance to cisplatin in the 41McisR line, was also examined. The data suggests that increased accumulation of these compounds, as a result of their enhanced lipophilicity, could account for the dramatic increase in their potency over cisplatin.
Carcinoma↗
The role of platinum uptake and glutathione levels in L1210 cells sensitive and resistant to cisplatin, tetraplatin or carboplatin.
Three L1210 murine leukemia variants resistant to cisplatin, tetraplatin or carboplatin were compared with their sensitive parent line for differences in platinum accumulation, efflux and glutathione (GSH) content. All three resistant lines had reduced platinum accumulation compared with the sensitive line following exposure to each of the three drugs. There was no difference in the efflux of platinum between the sensitive and resistant lines indicating that reduced platinum accumulation was due to impaired uptake mechanisms. However, in cell survival experiments it was apparent that the resistant lines could tolerate higher intracellular platinum levels than the sensitive line. Intracellular GSH measurements revealed comparable levels in all but the L1210/carboplatin line which had a 2-fold elevation during the first 24 hours of culture. However, depletion of intracellular GSH with buthionin sulphoximine over a 72 hour period did not sensitize the resistant lines to the drugs. These studies have demonstrated that impaired platinum uptake is one of the mechanisms contributing to platinum drug resistance, while perturbations in GSH levels do not appear to play a role in these cell lines.
Animals↗
Antimetabolites in cancer chemotherapy.
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Antimetabolites, Antineoplastic↗