Cisplatin is one of the most potent antitumor agents known, displaying clinical activity against a wide variety of solid tumors. Its cytotoxic mode of action is mediated by its interaction with DNA to form DNA adducts, primarily intrastrand crosslink adducts, which activate several signal transduction pathways, including those involving ATR, p53, p73, and MAPK, and culminate in the activation of apoptosis. DNA damage-mediated apoptotic signals, however, can be attenuated, and the resistance that ensues is a major limitation of cisplatinbased chemotherapy. The mechanisms responsible for cisplatin resistance are several, and contribute to the multifactorial nature of the problem. Resistance mechanisms that limit the extent of DNA damage include reduced drug uptake, increased drug inactivation, and increased DNA adduct repair. Origins of these pharmacologicbased mechanisms, however, are at the molecular level. Mechanisms that inhibit propagation of the DNA damage signal to the apoptotic machinery include loss of damage recognition, overexpression of HER-2/neu, activation of the PI3-K/Akt (also known as PI3-K/PKB) pathway, loss of p53 function, overexpression of antiapoptotic bcl-2, and interference in caspase activation. The molecular signature defining the resistant phenotype varies between tumors, and the number of resistance mechanisms activated in response to selection pressures dictates the overall extent of cisplatin resistance.

A dosage formula has been derived from a retrospective analysis of carboplatin pharmacokinetics in 18 patients with pretreatment glomerular filtration rates (GFR) in the range of 33 to 136 mL/min. Carboplatin plasma clearance was linearly related to GFR (r = 0.85, P less than .00001) and rearrangements of the equation describing the correlation gave the dosage formula dose (mg) = target area under the free carboplatin plasma concentration versus time curve (AUC) x (1.2 x GFR + 20). In a prospective clinical and pharmacokinetic study the formula was used to determine the dose required to treat 31 patients (GFR range, 33 to 135 mL/min) with 40 courses of carboplatin. The target AUC was escalated from 3 to 8 mg carboplatin/mL/min. Over this AUC range the formula accurately predicted the observed AUC (observed/predicted ratio 1.24 +/- 0.11, r = 0.886) and using these additional data, the formula was refined. Dose (mg) = target AUC x (GFR + 25) is now the recommended formula. AUC values of 4 to 6 and 6 to 8 mg/mL. min gave rise to manageable hematological toxicity in previously treated and untreated patients, respectively, and hence target AUC values of 5 and 7 mg/mL min are recommended for single-agent carboplatin in these patient groups. Pharmacokinetic modeling demonstrated that the formula was reasonably accurate regardless of whether a one- or two-compartment model most accurately described carboplatin pharmacokinetics, assuming that body size did not influence nonrenal clearance. The validity of this assumption was demonstrated in 13 patients where no correlation between surface area and nonrenal clearance was found (r = .31, P = .30). Therefore, the formula provides a simple and consistent method of determining carboplatin dose in adults. Since the measure of carboplatin exposure in the formula is AUC, and not toxicity, it will not be influenced by previous or concurrent myelosuppressive therapy or supportive measures. The formula is therefore applicable to combination and high-dose studies as well as conventional single-agent therapy, although the target AUC for carboplatin will need to be redefined for combination chemotherapy.

The efficacy of cisplatin in cancer chemotherapy is limited by the development of resistance. Although the molecular mechanisms involved in chemoresistance are poorly understood, cellular response to cisplatin is known to involve activation of MAPK and other signal transduction pathways. An understanding of early signal transduction events in the response to cisplatin could be valuable for improving the efficacy of cancer therapy. We compared cisplatin-induced activation of three MAPKs, JNK, p38, and ERK, in a cisplatin-sensitive human ovarian carcinoma cell line (2008)

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cis-Diammine-1,1-cyclobutane dicarboxylate platinum II (CBDCA, JM8), an analogue of cisplatin showing reduced toxicity in preclinical studies, was evaluated in 60 patients. Doses were given initially every 3 weeks and escalated from 20 to 520 mg/m2. Following this, doses were given every 4 weeks and escalated from 300 to 500 mg/m2. The dose-limiting toxicity, thrombocytopoenia, occurred in four-fifths of patients treated at 520 mg/m2, with the nadir occurring 3 weeks after treatment. Leucopoenia and anaemia also occurred but were less severe. Vomiting occurred in all patients receiving over 120 mg/m2 but seldom persisted beyond 24 h. Serial measurements of 51Cr-EDTA clearances, urinary N-acetylglucosaminidase, urinary leucine aminopeptidase, and beta 2-microglobulin did not reveal significant evidence of nephrotoxicity. Detriment to the audiogram has not been seen in the first 13 patients studied. Pharmacological studies showed that most of the dose of platinum was excreted in the urine, and that impairment of renal function may be associated with drug retention and an increased risk of myelosuppression. The previous therapy and age of the patient also affected the tolerance of the drug. Clinical responses were seen in patients with ovarian carcinoma receiving greater than 120 mg/m2. A further dose escalation was performed on a 4-week schedule in patients under 65 with good renal function. The maximum dose it was possible to administer repeatedly without incurring myelosuppression was in the range 400-500 mg/m2. JM8 is not significantly nephrotoxic and is less emetic than cisplatin. It has antitumour activity in man and deserves wider evaluation, along with the other analogues under study in various centres, as an alternative to cisplatin.