A comparative study of the distribution in the male rat of platinum-labelled cis-dichlorodiammine platinum (II), cis-trans-dichlorodihydroxy-bis-(isopropylamine) platinum (I), and cis-dichloro-bis-cyclopropylamine platinum (II)

Schedule dependent tumour growth delay, DNA cross-linking and pharmacokinetic parameters in target tissues with cis-diamminedichloroplatinum(II) and etanidazole with or without hyperthermia or radiation

It has been reported previously that striking increases in tumour growth delay and cytotoxicity are seen when cis-diamminedichloroplatinum(II) (CDDP) is combined with mild local hyperthermia (43 degrees C, 30 min) and/or etanidazole (ETA). This paper reports a study of CDDP pharmacology and the in vivo tumour DNA cross-linking produced by these combinations. In C3H mice bearing the FSaIIC murine fibrosarcoma, Pt plasma pharmacokinetics were not significantly altered by any of the combination of treatments. Although ETA caused no significant change in CDDP tissue pharmacokinetics, treatment of the tumour-bearing limb with hyperthermia immediately following an i.p. injection of CDDP (10 mg/kg) resulted in an increased peak Pt concentration (3.5 versus 2.8 micrograms Pt/g tumour wet weight) and doubled the t1/2 elimination of Pt (15 to 30 h) from the tumour. Similar heat-induced changes were observed in the Pt pharmacokinetics in skin. There was about a three-fold increase in the Pt area under the curve (AUC) for the tumour, a 1.5-fold increase in the AUC for skin and little change in the AUC for muscle with hyperthermia. When the tumour DNA cross-linking factor (CLF) was determined, it was found that local hyperthermia treatment (43 degrees C, 30 min) increased the CLF of CDDP from 1.7 to 2.7 and hyperthermia (43 degrees C, 1 h) further increased the CLF to 6.1. Misonidazole (MISO) (1 g/kg) increased the CDDP CLF to 2.0, 6.3 and 15.1 in conjunction with 37, 43 (30 min) and 43 degrees C (1 h), respectively. ETA (1 g/kg) was more effective than MISO at increasing the CDDP CLF, producing CLFs of 2.8, 9.1 and 21.5 at 37, 43 (30 min) and 43 degrees C (1 h), respectively. These changes in CLF were reflected in an increased tumour growth delay in the FSaIIC murine fibrosarcoma with CDDP (5 mg/kg) alone from 4.4 to 5.9 days with 43 degrees C (30 min) and then to 11.9 days with ETA (1 g/kg) and 20.9 days with both ETA and local hyperthermia (43 degrees C, 30 min). When CDDP, ETA and hyperthermia were added to a radiation schedule of 300 cGy daily for five days, it was found that giving ETA (1 g/kg), CDDP (5 mg/kg) and hyperthermia (43 degrees C, 30 min) together on day 1 produced the largest tumour growth delay (43 days) and that other schedules which divided the dose of ETA over the other days of the radiation treatment (including one schedule with a second heat treatment on day 4) were significantly inferior.(ABSTRACT TRUNCATED AT 400 WORDS)

Cisplatin pharmacokinetics: applications of a physiological model

A physiological pharmacokinetic model for the disposition of the antineoplastic drug cis-diamminedichloroplatinum(II) (cisplatin or DDP) in several mammalian species is reviewed. The significance of the model's key parameters and of their interspecies relationships is discussed. Methods for estimating two of these parameters (the rate constants for formation of the fixed and mobile metabolites) from in vitro experiments are presented. Fixed and mobile metabolites are formed by the irreversible binding of cisplatin to macromolecules and low molecular weight nucleophiles, respectively. Use of the model to simulate and predict the pharmacokinetic behavior of cisplatin and its metabolites in different animal species following intravenous and intraperitoneal administration is illustrated. Fixed metabolite formation rate constants can be used in conjunction with mass transport parameters to estimate tissue exposures to cisplatin following systemic or regional drug administration. The model logically can serve as the basis for a pharmacodynamic model that incorporates cisplatin reactions with DNA. The model also provides a means for comparing the pharmacokinetic characteristics of cisplatin analogs and for assisting in rational analog development.

An autoradiographic study of the intrarenal localisation and retention of cisplatin, iproplatin and paraplatin

The intrarenal localisation of platinum following the intravenous administration of platinum-195m-labelled cisplatin, iproplatin and paraplatin was studied using autoradiography. Following injection of cisplatin, platinum was distributed throughout the kidney even up to 14 days after treatment. In the case of iproplatin and paraplatin rapid platinum clearance was noted from the glomeruli, blood vessels and renal medulla within 2 h of administration. Relative cortical and medullary platinum radionuclide concentrations for all three agents were determined by Chalkley grid analysis. This showed greater relative concentrations of platinum in the cortex at increasing times following iproplatin and paraplatin compared with cisplatin. It is suggested that the lower renal toxicity of iproplatin and paraplatin than of cisplatin may be due to reduced platinum retention within the pars recta.

The comparative tissues distribution of platinum and 14C in mice receiving 14C-labelled carboplatin

Since the reactivity of carboplatin depends on the rate of removal of the 1,1-cyclobutanedicarboxylate ligand, the time course of this dissociation has been determined in various tissue and body fluids using 14C-labelled carboplatin (cis-diammine[1,1-cyclobutane-1-14C-dicarboxylate]platinum II). Mice received 14C-carboplatin (80 mg/kg; 1.1 mCi/kg, i.v.), and tissue was removed at times ranging from 5 min to 5 days posttreatment. Following solubilization, tissue aliquots were analyzed for platinum and 14C contents. Carboplatin remained intact for up to 2 h posttreatment, since the ratio of 14C: Pt in tissues (nmol/g) was unity. Thereafter, the 14C ligand was released from the molecule and preferentially removed from tissues, indicated by decreasing 14C: Pt ratios. The elimination half-lives for Pt varied between tissues (40-156 h). In contrast, the corresponding half-lives for the 14C species were similar in most types of tissue (18-35 h), although those in the liver and spleen were exceptional (210 and 90 h, respectively). At 5 days a maximum of 4%-24% of the total Pt in tissue might exist as intact drug. Thus, the metabolic handling of carboplatin varies according to the tissue, since the elimination of the 14C cyclobutane dicarboxylate species from most tissue was similar and Pt elimination was slower and tissue-dependent.

Microscale syntheses of anti-tumour platinum compounds labelled with 191Pt

Several compounds of platinum have been found to have significant anti-tumour activity and are in various stages of clinical trials. Four such compounds: cis-PtCl2(NH3)2, cis PtCl2(cyclopropylamine)2, cis,trans-PtCl2(OH)2(isopropylamine)2 and cis-Pt(1,1-cyclobutanedicarboxylate) (NH3)2 were synthesised with radioactive platinum-191 as a label for the study of animal organ distribution, patient blood clearance, urinary excretion and renal uptake and clearance. This paper describes the microscale synthesis of these compounds. Purification and quality control procedures are also described.

Physiological model for the pharmacokinetics of cis-dichlorodiammineplatinum (II) (DDP) in the tumored rat

A physiological model has been developed to describe the disposition of cis-dichlorodiammine-platinum(II) (DDP) following i.v. dosing in the female rat bearing the Walker 256 carcinoma. The model simulates concentrations of DDP and its mobile and fixed metabolites in plasma, liver, gut, skin, muscle, tumor, carcass, and kidney, and DDP and mobile metabolite excretion following a 4 mg/kg dose. In the kinetic model, DDP binds irreversibly to low MW nucleophiles and macromolecules (largely proteins) within the plasma and tissue compartments to form mobile and fixed metabolites, respectively. Reaction rates for the formation of each metabolite are tissue/organ specific. The rate constant for the biotransformation of DDP to fixed metabolite in plasma (k2P = 0.0082 min-1) was determined from in vitro incubation studies. This rate was used as the basis for estimating the biotransformation rate constants for DDP to fixed and mobile metabolites in other compartments. Both DDP and mobile metabolite are assumed to follow flow-limited transport, to freely traverse compartmental barriers, and to partition equally in all compartments. Both are excreted in the urine, the major route of Pt elimination. Urinary excretion is modeled as a linear process involving filtration only; an assumption based on a calculated renal clearance of 1.1 ml/min, a value very similar to the estimated GFR. Biliary excretion is a minor route of mobile metabolite elimination and is modeled as a linear process occurring in the liver. Four hours after dosing, approximately 60% of the administered Pt remains in the tissues and plasma. Of this, over 75% of the plasma Pt and 90% of the metal ion in every other compartment is fixed (protein bound). Fixed Pt can be eliminated from a compartment only after its biotransformation to mobile metabolite. In most compartments this rate of elimination corresponds closely to the average rate of protein turnover in that compartment.