An in vitro study comparing the cytotoxicity of three platinum complexes with regard to the effect of thiol depletion

Allantoin reduces cell death induced by cisplatin: possible implications for tumor lysis syndrome management

Massive lysis of tumor mass in cancer patients under chemotherapy regimens generates high levels of uric acid, leading to what is known as tumor lysis syndrome (TLS). Rasburicase, a recombinant urate oxidase, converts urate to allantoin, which is readily excreted by the kidneys. Even though there is a high production of allantoin from urate in cancer patients following rasburicase treatment, there are no studies on how allantoin excess could interfere with chemotherapy. We have evaluated allantoin interference with cisplatin efficiency on the lung cancer cell line H460 in vitro. The cells were treated with cisplatin (33 µM), with or without allantoin, for 48 h, in the presence or absence of UV light, and N-acetyl-L-cysteine (NAC) for 24 h. Cell viability, cell cycle, ROS production, apoptosis and immunoblot assays were performed. We showed that allantoin reduced the apoptosis induced by cisplatin in the H460 cell line. However, the activity of carboplatin and oxaliplatin, betulinic acid, TIBA, UV and H₂O₂ was not affected by allantoin. NMR spectroscopy showed that allantoin reduces cisplatin activity through direct interaction with cisplatin.

Recent insights into platinum drug resistance in cancer

Cisplatin and its analogs have become important components of chemotherapeutic regimens for the treatment of solid tumors, however, their overall effectiveness is limited by the emergence of drug-resistant tumor cells. Resistance to the platinum drugs is multifactorial consisting of mechanisms that prevent the formation of lethal platinum-DNA adducts and mechanisms that operate downstream of the drug/target interaction to promote cell survival. Continued progress in the study of the drug resistance phenotype as well as the development of new platinum analogs may eventually lead to improved therapies and increased survival rates.

Characterization of carboplatin-resistant sublines derived from human larynx carcinoma cells

In human larynx carcinoma cells, resistance to carboplatin (CBDCA) was induced by continuous five-day exposure of parental lines to the increasing CBDCA concentrations in culture medium, reaching the clinical level of 9.23 micrograms/ml. Three clones were selected and characterized: CBP-3, CBP-6 and CBP-7, CBP-3 clone was 2.0-fold, CBP-6 2.1-fold, and CBP-7 2.9-fold more resistant to carboplatin. The response of these sublines to different cytostatics was compared to the response of the parental cell lines to the same drug. CBP-7 and CBP-6 clones exhibited cross-resistance to cisplatin (cis-DDP), CBP-7 clone became markedly more sensitive and CBP-3 slightly more sensitive to 5-fluorouracil (5-FU), CBP-6 became sensitive to etoposide (Et), CBP-6 became sensitive and CBP-7 resistant to vinblastine (VBL). Other clones did not change change their sensitivity to cis-DDP, 5-FU, Et or VBL. None of the three clones did alter the sensitivity to mitomycin C, doxorubicin (Dox) or vincristine (VCR). There was no change in the growth rate. Glutathione (GHS) levels were elevated in all three clones, but the increase was significant only for CBP-7 clone. Similarly, the activity of glutathione transferase (GST) was elevated in all clones, but this increase was not significant for CBP-7 clone. The analysis of the of c-myc, c-Ha-ras and c-fos genes reveal no change in the c-myc expression, induction of the c-Ha-ras oncogene in CBP-6 and CBP-7 cells, and biochemistry and oncogene expression indicate that the acquired resistance to carboplatin is a complex, multifactorial process in these cells.

Intracellular glutathione and cytotoxicity of platinum complexes

Although there have been a number of reports correlating cellular GSH levels with cytotoxicity of platinum agents, none has examined the relationship between GSH concentrations and cytotoxicity. In this study, using a highly specific HPLC method for measuring GSH and expressing GSH as concentration and also per cell number, we evaluated the correlation between GSH levels and the cytotoxicity to five agents in ten human tumor cell lines. The five platinum agents included the platinum(II) complexes cisplatin, carboplatin and oxaliplatin and platinum(IV) complexes iproplatin and tetraplatin. The correlation between intracellular GSH concentration and cytotoxicity was highly significant only for iproplatin (P = 0.002) followed by tetraplatin, which demonstrated a trend toward statistical significance (P = 0.06). Cytotoxicity of the other platinum complexes showed no relation to GSH concentration, cisplatin itself showing a P-value of 0.09. In contrast, the GSH levels normalized to cell number showed a statistically significant correlation with the cytotoxicity of four of the five platinum agents, the exception being carboplatin; the strongest correlation observed was that for iproplatin and tetraplatin. Glutathione-S-transferase (GST) activity in these cell lines showed no correlation with cytotoxicity of any of the platinum complexes. Our results, from the analyses of both GSH concentration as well as GSH per cell number, suggest a significantly higher interaction between GSH and iproplatin compared with the other platinum agents. Moreover, our data suggest that relationships between cytotoxicity and GSH levels on a per-cell basis may not persist when differences in cell volume are taken into account.

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.

Ultrastructural alterations and DNA synthesis of renal cell nuclei following cisplatin or carboplatin injection in rats

To clarify the difference in nephrotoxicity between cisplatin and carboplatin, ultrastructural alterations and DNA synthesis of renal cell nuclei were studied in Sprague-Dawley rats which had received intravenously either cisplatin or carboplatin at an equitoxic dose. Twelve hours after cisplatin injection, nucleolar segregation accompanied by aggregated nuclear heterochromatin was observed in the third segment of the proximal tubules. Seventy-two hours after cisplatin injection, nuclear damage was more widespread while regenerative cells were also observed. Nuclear damage was not observed in the carboplatin-treated rats. Nuclear DNA synthesis of renal cells was suppressed at 8, 12 and 24 h and was accelerated at 72 h after cisplatin injection. Carboplatin did not suppress nuclear DNA synthesis at any time. The results indicate that cisplatin, but not carboplatin, can affect the renal cell nuclei. Cisplatin-induced nephrotoxicity is related to its effects on renal cell nuclei.

Cell cycle perturbations of platinum derivatives on two ovarian cancer cell lines

Cisplatin continues to be one of the most commonly used cytotoxic agent. Problems of drug resistance and nephrotoxicity have generated interest in new platinum derivatives. In this study, we used flow cytometry to study their effects on cell kinetics and to see if the extent of cell cycle perturbations can be used to determine relative potency. The following four platinum derivatives were tested: cisplatin, carboplatin, 254S, and NK121 on two human ovarian cancer cell lines: BG1 and CAOV3. Flow cytometric analysis revealed a dynamic spectrum of cell kinetic perturbations, which included sequential S-G2 block, concomitant S-G2 block, and a dominant S block with abolition of G2 block. Platinum derivatives NK121, 254S, and CARBO induced an average of 54.5 +/- 5.6, 21.2 +/- 5.5, and 2.5 +/- 2.8% more S-G2 blocks than cisplatin, respectively. When comparing the severity of S-G2 blocks and requiring a p-value of 0.05, the order of increasing potency was: cisplatin, carboplatin, 254S, and NK121.

Comparative study of cisplatin and carboplatin on pharmacokinetics, nephrotoxicity and effect on renal nuclear DNA synthesis in rats

To clarify the difference in nephrotoxicity between cisplatin and carboplatin, the pharmacokinetics of platinum, renal function and nuclear DNA synthesis in renal cortical and outer medullary cells were studied in rats which had received cisplatin or carboplatin. Male Sprague-Dawley rats were given either cisplatin or carboplatin intravenously at an equi-toxic dose (LD10 or LD50) and were killed at various times within 7 days after the injection. Cisplatin bound to plasma proteins more avidly than carboplatin. Much more platinum was detectable in the renal nuclei after cisplatin injection than after carboplatin injection. BUN and serum creatinine levels in the rats treated with 8.5 mg/kg of cisplatin were significantly higher than in those treated with 100 mg/kg of carboplatin. Cisplatin markedly suppressed the renal nuclear DNA synthesis both in vivo and in vitro, when compared with carboplatin. It is concluded that the differences in nephrotoxicity between cisplatin and carboplatin are related to their different inhibitory effects on nuclear DNA synthesis in the renal cells.

The relationships between glutathione, glutathione-S-transferase and cytotoxicity of platinum drugs and melphalan in eight human ovarian carcinoma cell lines

The role of glutathione (GSH) and GSH-S-transferase (GST) activity in modulating the cytotoxicity of four platinum drugs and melphalan was evaluated in eight human ovarian carcinoma cell lines. The cell lines were established from solid and ascitic tumours from pretreated and untreated patients, and showed a wide spectrum of sensitivity to several platinum II and platinum IV drugs; cisplatin, carboplatin, CHIP and tetraplatin. Intracellular glutathione concentration measured in the cell lines showed a significant (P = 0.05) correlation with IC50 values for cisplatin (r = 0.91), carboplatin (r = 0.87) and CHIP (r = 0.88). The correlation between GSH levels and IC50 values for melphalan (r = 0.76) or tetraplatin (r = 0.60) was not as significant. GST activity showed no correlation with IC50 values, for the four platinum drugs. To determine the significance of the elevated GSH concentration in the refractory cell lines, the effect of D,L-buthionine-S, R-sulfoximine (BSO) mediated GSH depletion on platinum drug cytotoxicity was examined in one of the most sensitive (CH1) and two of the least sensitive (relatively resistant; SKOV-3, HX/62) cell lines. Comparison was made with the effect of GSH depletion on melphalan cytotoxicity in these three lines. These lines were differentially sensitive to BSO, with the two most platinum drug resistant lines being more tolerant to BSO than the sensitive CH1 line. Depletion of cellular GSH, ranging between 61 and 88%, had a differential effect on the sensitivity to PtII vs PtIV drugs in the three cell lines: cytotoxicity of the PtIV drugs, tetraplatin and CHIP, was substantially enhanced in both the resistant and sensitive cell lines; in contrast, the cytotoxicity of the PtII drugs, cisplatin and carboplatin, was only significantly increased in one of the two relatively resistant lines (SKOV-3) and in the sensitive (CH1) line after GSH depletion. Moreover the dose modification factor (DMF) for the PtII agents were lower than those for PtIV agents in the three cell lines. The dose modification factor for tetraplatin after BSO treatment was similar to that observed for melphalan in all three cell lines. In the SKOV-3 cell line extending the BSO pretreatment period to 48 h from 24 h marginally reduced the cytotoxicity of cisplatin, whereas the cytotoxicity of the other three drugs remained similar to that observed after 24 h BSO pretreatment. In contrast, extending the BSO treatment to 24 h after drug exposure potentiated the cytotoxicity of cisplatin, CHIP and tetraplatin.(ABSTRACT TRUNCATED AT 400 WORDS)

The relative nephrotoxicity of cisplatin, cis-[Pt(NH3)2(guanosine)2]2+, and the hydrolysis product of cisplatin in the rat

An examination of the comparative nephrotoxicity in the rat of cisplatin, its hydrolysis product (mostly cis-[Pt(NH3)2Cl(H2O)]+ under the conditions applied), and cis-[Pt(NH3)2(guanosine)2]2+ revealed that these compounds differed significantly in the extent of renal damage they produced following their i.v. injection in Sprague-Dawley rats. The hydrolysis product was found to be the most toxic of the three complexes studied and produced nephrotoxicity at doses lower than those at which cisplatin was nephrotoxic. Under the conditions used, the i.v. administration of cis-[Pt(NH3)2(guanosine)2]2+ resulted in no observable signs of nephrotoxicity at levels at which an equimolar dose of cisplatin produces clear evidence of renal function impairment and morphological alterations. The nephrotoxicity of these complexes appears to be generally related to the ease with which they undergo nucleophilic substitution reactions. The lack of substantial nephrotoxicity found for cis-[Pt(NH3)2(guanosine)2]2+ suggests that the products resulting from the action of the DNA repair processes on platinated DNA do not contribute significantly to the nephrotoxicity of cisplatin. Renal platinum levels found following the administration of these compounds correlated with the degree of nephrotoxicity produced by each compound, but no general correlation of nephrotoxicity and renal platinum levels was found. The nephrotoxicity of cis-[Pt(NH3)2Cl(H2O)+ on a molar basis was estimated to be approximately 3 times as great as that of cisplatin itself.

Historical aspects of glutathione and cancer chemotherapy

This presentation sets in historical context the impact of glutathione and its metabolism upon the efficacy of several anticancer drugs. The basic biochemistry of the tripeptide is reviewed briefly, highlighting its role in oxido-reduction and in the gamma-glutamyl cycle. The ability of selective modulators of glutathione metabolism, such as buthionine sulfoximine, as adjuncts to chemotherapy is also discussed.

Protective effect of reduced glutathione against cisplatin-induced renal and systemic toxicity and its influence on the therapeutic activity of the antitumor drug

Reduced glutathione has been shown to be an effective protector against cisplatin-induced nephrotoxicity of potential clinical value, since it does not reduce antitumor activity of the cytotoxic drug. This paper extends previous observations on the protective potential of reduced glutathione against cisplatin-induced nephrotoxicity, in different rodent models. Following i.v. administration, glutathione protection against cisplatin-induced nephrotoxicity was found to be critically dependent on timing of thiol administration. Whereas the sulfhydryl compound provided almost complete protection in CD rats, the protective effect against toxic renal damage was only partial in mice of different strains. In spite of the modest protection against kidney toxicity, glutathione reduced lethal toxicity in the mouse. Under the same experimental conditions at protective dose levels, the tripeptide thiol did not interfere with the antitumor effectiveness of cisplatin, in any of the tumor models examined. The kidney content of non-protein sulfhydryls of CD rats produced by the effective dose of glutathione was markedly higher than that found in the mouse treated with the same dose. This finding is consistent with a differential protection provided by glutathione against cisplatin-induced renal toxicity in these species.