Carboplatin dosage: prospective evaluation of a simple formula based on renal function.

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.

Retention of activity by the new generation platinum agent AMD0473 in four human tumour cell lines possessing acquired resistance to oxaliplatin.

Four models of acquired resistance to the clinically-used platinum drug, oxaliplatin, have been established using human tumour cell lines in vitro; two colon (HCT116 and HT29) and two ovarian (A2780 and CH1). Levels of acquired resistance ranged from 3.0- to 15.8-fold with levels of resistance higher in the colon relative to the ovarian carcinoma cell lines. Notably, the platinum analogue, AMD0473, currently undergoing clinical evaluation, exhibited superior circumvention of acquired oxaliplatin resistance in comparison to either cisplatin or the trinuclear platinum BBR3464. Resistance in the two colon cell lines was unique to oxaliplatin itself among the platinum drugs studied. Acquired oxaliplatin resistance was not due to either reduced drug membrane transport or increased levels of glutathione in any of the four resistant lines. Following exposure to oxaliplatin, a lower level of platinum-DNA adducts was present in acquired oxaliplatin-resistant HT29 cells. In the remaining resistant lines, there was no change in the levels of platinum-DNA adducts relative to the parent lines. There was no change in hMLH1 DNA mismatch repair gene status in any of the four cell line pairs. However, in an A2780 subline where loss of hMLH1 and a p53phe172 mutation occurred, 5-fold resistance to cisplatin was observed, but only 1.7-fold resistance to oxaliplatin and no resistance to AMD0473 were observed. Re-introduction of hMLH1 into these cells caused no significant change in the sensitivity to cisplatin, oxaliplatin or AMD0473. These data show that acquired resistance to oxaliplatin may occur in cell lines (and therefore probably in the clinic) and in the four independent cell lines studied this was circumvented by AMD0473. Alongside previously described models of acquired resistance to cisplatin, these oxaliplatin-resistant cell line models may be useful in the evaluation of further novel platinum agents.

Sequence-dependent synergism between the new generation platinum agent ZD0473 and paclitaxel in cisplatin-sensitive and -resistant human ovarian carcinoma cell lines.

ZD0473 is a new generation hindered platinum agent currently undergoing worldwide Phase II clinical studies. The in vitro cytotoxicity of ZD0473 either alone or in combination with the anticancer drugs paclitaxel, gemcitabine, vinorelbine, topotecan and doxorubicin was determined using four human ovarian carcinoma cell lines and by the sulphorhodamine B assay (SRB). The lines included one model of acquired cisplatin resistance and one isogenic pair differing only in their p53 status. Notably, the simultaneous exposure to ZD0473 and paclitaxel for 96 h resulted in synergy (as defined by a median effect analysis) in all four cell lines (i.e. independent of cisplatin resistance and p53 status). In addition, synergy was observed in 3/4 lines and 2/4 lines following concomitant exposure to topotecan or gemcitabine, respectively. Sequencing studies with ZD0473 and paclitaxel revealed that, for three of the four cell lines, the combination of ZD0473 administered for 24 h prior to paclitaxel for 24 h conferred a greater growth inhibitory effect than the reverse sequential combination. This scheduling effect was particularly marked for the acquired cisplatin-resistant A2780CisR cell line; synergy being observed with ZD0473/paclitaxel, but antagonism with paclitaxel/ZD0473. This effect did not appear to be correlated with changes in drug-induced cell cycle checkpoints. These data suggest that ZD0473 may be usefully combined with various cytotoxics in the clinic, including paclitaxel, topotecan and gemcitabine.

Mechanisms of drug resistance to the platinum complex ZD0473 in ovarian cancer cell lines.

Acquired drug resistance to the sterically hindered platinum drug ZD0473 (formerly known as JM473 and AMD473) and currently being tested in phase I clinical trials, has been studied in two human ovarian carcinoma cell lines (CH1 and A2780) where previously, acquired cisplatin resistance has been described. Common mechanisms of resistance were observed in A2780 acquired cisplatin and ZD0473R (resistant) lines (including reduced drug transport and DNA platination, increased glutathione (GSH) and loss of the MLH1 DNA mismatch repair gene). However, contrasting mechanisms were observed in the CH1 sublines. While ZD0473 retained activity against the acquired cisplatin resistant sublines, cisplatin did not circumvent acquired ZD0473 resistance. The trans platinum complex JM335 circumvented resistance in CH1cisR and A2780ZD0473R lines, but not in A2780cisR or CH1ZD0473R cells. Overexpression of metallothionein (MT) in A2780 cells by stable gene transfection resulted in protection from the growth-inhibitory effects of cadmium chloride (3. 8-fold) and a range in protection with platinum drugs (from 7-fold with cisplatin, but only 1.3-fold with ZD0473). Overall, the results show that some mechanisms of resistance to ZD0473 are shared with those previously described in the same parental lines for cisplatin (e.g. in A2780), but in the CH1 lines, differing mechanisms were apparent. Moreover, ZD0473 possesses distinct cellular pharmacological properties in comparison with cisplatin with respect to reduced interactions with MTs, a thiol-containing species associated with tumour resistance to cisplatin.

cis-Amminedichloro(2-methylpyridine) platinum(II) (AMD473), a novel sterically hindered platinum complex: in vivo activity, toxicology, and pharmacokinetics in mice.

A novel sterically hindered platinum complex, AMD473 [cis-amminedichloro(2-methylpyridine) platinum(II)], designed primarily to be less susceptible to inactivation by thiols, has shown in vitro activity against several ovarian carcinoma cell lines. Notably, AMD473 has shown activity in vitro in human carcinoma cells that have acquired cisplatin resistance due to reduced drug transport (41M/41McisR) or enhanced DNA repair/increased tolerance of platinum-DNA adducts (CH1/CH1cisR). In this study, we show that AMD473, at its maximum tolerated dose of 35-40 mg/kg i.p. administration, produced marked in vivo antitumor activity against a variety of murine (ADJ/PC6 plasmacytoma, L1210 leukemia) and human ovarian carcinoma xenograft models, including several possessing acquired resistance to cisplatin [ADJ/PC6cisR, L1210cisR, CH1cisR, and HX110 (carboplatin-resistant)]. In the ADJ/PC6 model, an increased therapeutic index was noted following oral as opposed to i. p. administration. In a head-to-head comparison using CH1cisR xenografts and equitoxic doses (q7dx4 schedule), comparative growth delays were as follows: AMD473, 34 days; cisplatin, 10.4 days; carboplatin, 6.4 days; and JM216 (p.o. administration), 3.5 days (in a previous experiment, the trans-platinum complex JM335 induced a growth delay of 5.4 days against this model). In this model, oral activity was also noted with a growth delay of 34 days at 400 mg/kg every 7 days (total of four doses). In addition, AMD473 showed promising activity against CH1 xenografts that had regrown following initial treatment with cisplatin (additional growth delay of 30 days over that observed for retreatment with cisplatin). Across the whole panel of cisplatin-sensitive to cisplatin-resistant human ovarian carcinoma xenografts, AMD473 showed improved or at least comparable activity to that observed for an equitoxic dose (4 mg/kg) and schedule of cisplatin. Platinum pharmacokinetics showed that following i.v. administration of 20 mg/kg AMD473 in saline to Balb/c- mice bearing murine plasmacytoma (ADJ/PC6), a biexponential decay was observed in the plasma with a rapid distribution t1/2alpha of 24 min followed by a slow elimination t1/2beta of 44 h. Platinum accumulated in various organs with platinum tissue to plasma area under the curve ratios of 8.6 for liver and kidney, 5.7 for spleen, 3.7 for heart, 5.2 for lung, and 5 for tumor. The plasma and tissue concentration time curve following i.p. administration was similar to that observed following i.v. administration, with a bioavailability of 89%. When AMD473 was given p.o., the platinum absorption was rapid (K01 of 30 min) and the bioavailability was 40%. A less than proportional increase in area under the curve and Cmax was noted in tissue, plasma, and plasma ultrafiltrate following increasing oral doses of AMD473. In vitro, with AMD473, the rate of binding to different plasma proteins was approximately half of that of cisplatin. Following administration of 45 mg/kg i.p. in oil, 33% of the administered platinum was eliminated in the urine after 24 h, and 40% was eliminated after 72 h. Fecal recovery represented 13% of the administered dose after 3 days. Similar results were observed following oral and i.v. administration of 20 mg/kg, but significantly more was excreted in the feces (over 50% of the administered dose) following oral administration of 400 mg/kg, showing that absorption might be a limiting factor by this route of administration. The dose-limiting toxicity for AMD473 in mice was myelosuppression, and no renal toxicity was observed. The promising antitumor activity of AMD473, together with its lack of nephrotoxicity and favorable pharmacokinetic profile, suggests that AMD473 is a good candidate for clinical development. AMD473 is entering Phase I clinical trials under the auspices of the United Kingdom Cancer Research Campaign in 1997.

Metabolism, protein binding and in vivo activity of the oral platinum drug JM216 and its biotransformation products.

This study evaluates the metabolism of the oral platinum drug JM216 [bis(acetato) amminedichloro (cyclohexylamine)platinum (IV)] following oral administration to Balb C- mice. JM216 was detectable 1 h post administration in mice but not in patients. Also, a late eluting metabolite observed in patients was not detected in mice. JM118 [amminedichloro(cyclohexylamine) platinum (II)], the platinum II species which is the major metabolite in patients was rapidly converted following i.v. administration to a compound having the same retention time as JM383 [bis(acetato)ammine(cyclohexylamine)dihydroxo platinum(IV)] indicating that the levels of JM383 following JM216 administration have probably been overestimated. The metabolite D observed in patients for which a structure has not been assigned, was also detected in mice. However, it did not originate from any of the identified biotransformation products. The protein binding evaluated in plasma, and buffer with physiological levels of albumin and globulin showed that only Platinum (II) species have significant binding and that Jm118 showed the same affinity to albumin and globulin (t 1/2 of 4.2 and 4.8 h) while cisplatin bound more readily to albumin (t 1/2 3.4 h) than globulin IV (t 1/2 8.2 h). JM216 itself failed to bind to either of the proteins tested indicating extensive reduction in patients, animals or plasma incubation medium. JM118 and JM518 [bis(acetato)amminechloro(cyclohexylamine) hydroxoplatinum (IV)] were significantly more active than the platinum IV complexes JM216 and JM383 when given i.p. to ADJ/PC6 plasmacytoma bearing mice (ED90 of 1.0 and 0.4 versus 5.7 and 4.2 mg/kg, TI (therapeutic index) of 14 and 37 versus 5.3 and 4.2). When given orally, JM216 was the most potent drug (ED90 of 5.8 versus 11,12 and 42 mg/kg and TI of 57 versus 12 12 and 16) for JM118 and JM383. There data indicates that JM216 biotransformation products are potent but that the levels of JM383 determined in our analytical conditions could have been overestimated.

A phase I and pharmacology study of an oral platinum complex, JM216: dose-dependent pharmacokinetics with single-dose administration.

JM216 [bis-acetato-ammine-dichloro-cyclo-hexylamine-platinum (IV)] is an oral platinum complex with in vivo activity against murine and human tumor models and a lack of nephro- and neurotoxicity in rodents. During a phase I study of a single-dose schedule, JM216 was given in dry-filled hard gelatin capsules by mouth without hydration or diuresis. In all, 37 patients were given a total of 88 courses at doses ranging from 60 to 700 mg/m2. The study was stopped before the MTD was reached because of nonlinear pharmacokinetics. Myelosuppression was manifest by leucopenia or thrombocytopenia and showed marked variability at 420-700 mg/m2. Vomiting was mild and controllable by antiemetics in approximately 50% of courses. The onset of vomiting was delayed to 4 h after during ingestion. There was no nephro-, oto- or neuro-toxicity. A partial response was recorded in a patient with recurrent ovarian cancer, and significant falls in plasma tumour markers (CA125) were seen in two further cases. Plasma pharmacokinetics were linear and showed moderate interpatient variability at dose levels of < or = 120 mg/m2. At dose levels of > or = 200 mg/m2, Cmax and AUC increased less than proportionally to dose. This was associated with greater interpatient pharmacokinetic variability and reduced urinary platinum recovery. A significant sigmoidal relationship existed between ultrafilterable plasma AUC and the percentage of reduction in platelet count (r2 = 0.78). Nonlinear absorption was a limitation to this single-dose schedule of oral NM216; however, little non-haematological toxicity was seen at doses associated with myelosuppression and antitumour activity. Clinical studies of divided dose schedules using doses within the range of pharmacokinetic linearity (< or = 120 mg/m2) are now being investigated.

Schedule dependency of orally administered bis-acetato-ammine-dichloro-cyclohexylamine-platinum(IV) (JM216) in vivo.

JM216 is a novel antitumor platinum(IV) complex displaying oral activity, dose-limiting myelosuppression, and a lack of nephro- and neurotoxicity in rodents. It has been selected for clinical evaluation. The schedule dependency of its antitumor action against a murine (ADJ/PC6 plasmacytoma) and a human tumor model (PXN109T/C ovarian carcinoma xenograft) was studied in vivo. Single dose (q21d), once a day dosing for 5 consecutive days (q21d or q28d), and once a day dosing indefinitely (chronic daily dosing) administration schedules were compared. Against the murine ADJ/PC6 plasmacytoma, daily x5 administration improved the tolerance, antitumor potency, and therapeutic index of oral JM216, compared to single dose administration, whereas no advantage was found for fractionating cisplatin dosages. Against the PXN109T/C human ovarian carcinoma xenograft, oral JM216, given at dose levels delivering a equivalent total dose on single dose (200 mg/kg q21d), daily x5 (40 mg/kg/day q21d) and chronic daily dosing (9.5 mg/kg/d) schedules, showed superior tumor growth delays (55 +/- 15 days; P < 0.05) and maximal tumor regression (10 +/- 11% of initial tumor volume; P < 0.001) with the daily x5 schedule. Gastrointestinal toxicity (P < 0.05) and mild nephrotoxicity (P < 0.01) complicated the chronic daily dosing schedule, while leukopenia (P < 0.02) and thrombocytopenia (P < 0.01) were dose-limiting for the single dose and daily x5 administration, respectively. Peak plasma ultrafiltrate (PUF) platinum levels were below cytotoxic levels (PUF Cmax, 0.11 +/- 0.066 mg/l) at the maximally tolerable dose for the chronic dosing schedule (9.5 mg/kg). Peak PUF platinum levels did not increase significantly with a 5-fold increase in dosage from 40 mg/kg (PUF Cmax 1.5 +/- 0.11 mg/l) to 200 mg/kg (PUF Cmax, 2.4 +/- 0.44 mg/l; P > 0.05). In conclusion, these data demonstrate antitumor schedule dependency for oral JM216 in vivo, independently in two tumor model systems, and with nonlinear pharmacokinetics after its oral administration to mice. Optimal antitumor activity, tolerance, and pharmacokinetics occurred with daily x5 dosing, and this has prompted the clinical evaluation of this administration schedule.

Lack of neurotoxicity of oral bisacetatoamminedichlorocyclohexylamine-platinum(IV) in comparison to cisplatin and tetraplatin in the rat.

This study compared the effect on sensory nerve conduction velocity in the hind limb of chronically treated age-matched rats of a novel lipophilic p.o. platinum complex [bisacetatoamminedichlorocyclohexylamine-platinum(IV)], with that of neurotoxic platinum complexes cisplatin and tetraplatin. Tetraplatin (i.p.) first caused slowing of sensory nerve conduction (-14.4% of controls; P < 0.05) at a dose (1 mg/kg) that was free of constitutional toxicity. Cisplatin (i.p.) first caused slowing of sensory nerve conduction (-17.5% of control; P < 0.05) at a dose (2 mg/kg) approximating the maximal tolerated dose. Bisacetatoamminedichlorocyclohexylamineplatinum(IV) (p.o.) showed no slowing of sensory nerve conduction either after 20.5 weeks of treatment at a dose (25 mg/kg) approximating the maximal tolerated dose or after 6 weeks of treatment at a dose (50 mg/kg) which eventually proved intolerable. In conclusion, p.o. bisacetatoamminedichlorocyclohexylamineplatinum(IV) shows a lack of neurotoxicity compared to parenterally administered cisplatin and tetraplatin at the maximal tolerated dose in rats.

Preclinical toxicology and tissue platinum distribution of novel oral antitumour platinum complexes: ammine/amine platinum(IV) dicarboxylates.

The preclinical toxicology and tissue platinum distribution of a series of six orally given antitumour platinum complexes [ammine/amine platinum(IV) dicarboxylates] with structural variations of their alicyclic amine (c-C5, c-C6 or c-C7), axial dicarboxylate (CH3, C3H7 or NHC2H5) or leaving substituents (Cl2 or OCOOCO) was studied in the mouse. Platinum tissue levels measured at 48 h after a single oral dose at 0.5 of the MTD were highest in the liver (6.0-19 micrograms/g) and second highest in the kidney (2.8-12 micrograms/g), and these levels were up to 5 times higher than those reported with equi-toxic doses of i.v. cisplatin and i.v. carboplatin. Platinum levels in the lung, heart, spleen, skin, skeletal muscle and brain were all < or = 3.1 micrograms/g at this dose level. Liver platinum levels measured at 2 h, 2 days, 6 days and 10 days after a single oral dose at the MTD ranged widely (from 15 to 109 micrograms platinum/g), were related to the number of carbon atoms in the axial dicarboxylate and alicyclic amine groups (r = 0.9389) and showed a diversity of time-course profiles. Elevations of plasma ALT activity were recorded with single oral doses of JM225 and JM256 at the MTD. Accumulation of platinum in the liver with repeated oral dosing weekly for 4 consecutive weeks at 0.5 of the MTD occurred with JM269 (3.3-fold increase, P < 0.05) and JM225 (2.4-fold increase, P < 0.05), and elevated plasma ALT activity (44 +/- 33 IU/l) was recorded with repeated oral doses of JM269. JM216 was selected from this series of analogues for further study on the basis of the elevated plasma ALT activity (JM225, JM256 and JM269), liver platinum accumulation (JM269 and JM225), poor activity against human ovarian carcinoma xenografts (JM291) or severe emetogenesis (JM221) of other examples. Following a single oral dose of JM216 at the MTD, transient reductions in the WBC (nadir, 1.6 x 10(9)/l, 2 days, 74% reduction), platelet count (nadir, 613 x 10(9)/l, 10 days, 33% reduction) and bone marrow cellularity (nadir, 0.5 x 10(7) nucleated cells/femur, 4 days, 75% reduction) were found, and these had recovered by 21 days after treatment. Jejunal mucosal disaccharidase activity following single MTDs indicated that small-intestinal mucosal damage was less severe for oral JM216 (nadir maltase activity, 68% +/- 16% of control, NS) than for i.v. cisplatin (nadir maltase activity).(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Carboplatin dosage: prospective evaluation of a simple formula based on renal function.

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.

Carboplatin and etoposide pharmacokinetics in patients with testicular teratoma.

The pharmacokinetics of carboplatin and etoposide were studied in four testicular teratoma patients receiving four courses each of combination chemotherapy consisting of etoposide (120 mg/m2 daily x 3); bleomycin (30 mg weekly) and carboplatin. The carboplatin dose was calculated so as to achieve a constant area under the plasma concentration vs time curve (AUC) of 4.5 mg carboplatin/ml x min by using the formula: dose = 4.5 x (GFR + 25), where GFR is the absolute glomerular filtration rate measured by 51Cr-EDTA clearance. Carboplatin was given on either day 1 or day 2 of each course and pharmacokinetic studies were carried out in each patient on two courses. Etoposide pharmacokinetics were also studied on two separate courses in each patient on the day on which carboplatin was given and on a day when etoposide was given alone. The pharmacokinetics of carboplatin were the same on both the first and second courses, on which studies were carried out with overall mean +/- SD values (n = 8) of 4.8 +/- 0.6 mg/ml x min, 94 +/- 21 min, 129 +/- 21 min, 20.1 +/- 5.41, 155 +/- 33 ml/min and 102 +/- 24 ml/min for the AUC, beta-phase half-life (t 1/2 beta), mean residence time (MRT), volume of distribution (Vd) and total body (TCLR) and renal clearances (RCLR), respectively. The renal clearance of carboplatin was not significantly different from the GFR (132 +/- 32 ml/min). Etoposide pharmacokinetics were also the same on the two courses studied, with overall mean values +/- SD (n = 8) of: AUC = 5.1 +/- 0.9 mg/ml x min, t 1/2 alpha = 40 +/- 9 min, t 1/2 beta = 257 +/- 21 min, MRT = 292 +/- 25 min, Vd = 13.3 +/- 1.31, TCLR = 46 +/- 9 ml/min and RCLR = 17.6 +/- 6.3 ml/min when the drug was given alone and AUC = 5.3 +/- 0.6 mg/ml x min, t 1/2 alpha = 34 +/- 6 min, t 1/2 beta = 242 +/- 25 min, MRT = 292 +/- 25 min, Vd = 12.5 +/- 1.81, TCLR = 43 +/- 6 ml/min and RCLR = 13.4 +/- 3.5 ml/min when it was given in combination with carboplatin. Thus, the equation used to determine the carboplatin accurately predicted the AUC observed and the pharmacokinetics of etoposide were not altered by concurrent carboplatin administration. The therapeutic efficacy and toxicity of the carboplatin-etoposide-bleomycin combination will be compared to those of cisplatin, etoposide and bleomycin in a randomised trial.

Comparative distribution and excretion of carboplatin and cisplatin in mice.

The comparative distribution and excretion of Carboplatin (cis-diammine-1,1-cyclobutane dicarboxylate platinum II, CBDCA, JM8) and cisplatin have been investigated in Balb C- mice following i.v. administration of the maximally tolerated doses (MTDs) of the compounds. Although the concentrations of platinum in the plasma and tissues during the alpha-phase were much higher for Carboplatin than for cisplatin, reflecting the difference in the doses used (4 vs 80 mg/kg), the tissue-to-plasma ratios were similar. During the beta-phase (1-10 days), however, both the platinum concentrations and the ratios were found to be similar for most tissues when cisplatin and Carboplatin were compared. The platinum concentrations and the tissue-to-plasma ratios of the spleen, brain, muscle, testes, ovary and bile, on the other hand, were consistently higher (two- to sixfold) after Carboplatin than after cisplatin. The highest ratios (greater than 20) were found in the kidney, liver, spleen (after Carboplatin only) and skin at 6 days after treatment. Comparison of the two compounds showed that the half-lives of platinum in the plasma and tissues during both the alpha- and beta-phases were similar, except for the spleen, in which a nine-fold greater t1/2 beta was recorded for Carboplatin than for cisplatin. The main route of excretion for the two complexes is via the kidneys, with 52% of cisplatin and 93% of Carboplatin being excreted during the first 3 days. The major part of this, however, is excreted within the 1st day. These results indicate that, although there are quantitative differences, the distribution and excretion profiles are similar for Carboplatin and cisplatin.

Plasma free platinum pharmacokinetics in patients treated with high dose carboplatin.

Plasma free platinum (less than 50,000 mol. wt) pharmacokinetics have been studied in eight patients treated with high-dose (800-1600 mg/m2) carboplatin as a 1 h infusion with moderate hydration. Following the infusion, levels decayed biphasically with half-lives (means +/- S.D.) of 83 +/- 15 min and 6.1 +/- 2.8 h. The plasma free platinum area under the concentration vs. time curve (AUC) at 1600 mg/m2 in five patients was 23 +/- 2 mg carboplatin/ml.min. Comparison with data at conventional doses (less than or equal to 500 mg/m2) gave no indication of non-linear kinetics. Total body clearance of free platinum was found to correlate with glomerular filtration rate (r = 0.769, P = 0.03), and haematological toxicity, white cell nadir and duration of thrombocytopenia, correlated with plasma free platinum AUC (r = 0.784, P = 0.02 and r = 0.885, P = 0.01, respectively). Persistence of platinum was demonstrated in tissues removed at autopsy from a patient who had received carboplatin 14 days earlier. Highest platinum levels were found in the liver, kidney, skin and small cell lung tumour.

The effect of diethyldithiocarbamate on the haematological toxicity and antitumour activity of carboplatin.

Carboplatin has recently been established as an effective agent in cancer chemotherapy. The dose limiting toxicity of this platinum complex is myelosuppression and, in this study, we have shown that through the use of diethyldithiocarbamate (DDTC), a protective thiol compound, the toxicity in rodents can be ameliorated and lethality prevented. DDTC protected against carboplatin-induced leucopoenia and anaemia when administered as a single bolus or as a multiple schedule incorporating three injections. With the single bolus, the effectiveness of this protection decreased as the lag time between carboplatin and DDTC administrations increased. Thrombocytopoenia was unaffected by DDTC. The growth profile of ADJ/PC6A tumour in mice was dependent on the timing of DDTC administration when given in combination with the platinum complex. The tumour growth delay, however, was unaffected by DDTC at any schedule. Multiple injections of DDTC increased the ED90 for carboplatin from 5.0 to 7.5 mg/kg. The LD50 value was increased from 115 to 216 mg/kg with the same DDTC schedule. Thus, DDTC improved the therapeutic index of carboplatin by 25%. A clinical role for the use of DDTC as a protective agent for carboplatin-induced toxicities is suggested.

The comparative pharmacokinetics of carboplatin and cisplatin in mice and rats.

The plasma, urinary and biliary clearances of cisplatin and its non-nephrotoxic analogue, Carboplatin (cis-diammine-1,1-cyclobutane dicarboxylate platinum II, CBDCA, JM8) have been determined in mice and rats following intravenous administration of the compounds. The plasma concentration-time curves were biphasic during the time period studied (0-60 min), with t1/2 alpha of 2-3 min for both platinum complexes and t1/2 beta of 10-15 min for cisplatin and 25-26 min for Carboplatin. The kinetic rate constants, k12 and k21, were similar for both Carboplatin and cisplatin, indicating that there was no appreciable net accumulation of the compounds in the peripheral tissues. Immediately after administration, Carboplatin became reversibly bound to plasma proteins in vivo to the extent of about 20%. Appreciable irreversible binding appeared after the first 60 min and increased steadily, so that by 4 hr only 34% of the compound was present in the plasma as the free drug. In comparison, binding of cisplatin to plasma was exclusively irreversible and, after the first 10 min, free drug disappeared rapidly, such that by 60 min free platinum was not detectable. The plasma clearance of free cisplatin (26.1 ml/min/kg) was significantly greater than that of either Carboplatin (10.3 ml/min/kg) or insulin (10.1 ml/min/kg). The main route of excretion of the two platinum complexes was via the urine, with 80-90% of Carboplatin and 43-48% of cisplatin being excreted within 4 hr. In the rat, the Carboplatin excreted in the urine was predominantly as the unchanged compound. The renal clearance of cisplatin (12.3 ml/min/kg) was significantly greater than that of either Carboplatin (9.3 ml/min/kg) or insulin (9.6 ml/min/kg), suggesting that cisplatin was excreted by an active renal secretory mechanism whilst Carboplatin was eliminated by glomerular filtration alone. Biliary excretion of the two compounds was only 0.4-1.2% of the administered dose in 6 hr, with biliary clearance of cisplatin (0.27 ml/min/kg) being fivefold greater than that of Carboplatin (0.053 ml/min/kg). The results indicate that the major pharmacokinetic differences between Carboplatin and cisplatin relate to their renal handling and their reactivity with macromolecules. These differences may well underline the substantial lack of Carboplatin nephrotoxicity in comparison with cisplatin.

Flameless atomic absorption spectrophotometric determination of platinum in tissues solubilized in hyamine hydroxide.

Processing biological samples by solubilization in Hyamine hydroxide (methylbenzethonium hydroxide) as an alternative to wet ashing with concentrated nitric acid for atomic absorption determination of platinum has been explored. The concentrations of platinum in tissues removed from rats 2 h after they had received the antitumor drug Carboplatin (60 mg/kg, iv) were comparable using either of the procedures, indicating the utility of tissue solubilization. Limits of detection were also comparable between the Hyamine hydroxide (0.25 microgram platinum/g) and nitric acid (0.15 microgram/g) procedures. The solubilization method, however, has advantages over wet digestion because of its simplicity and greater safety.

Haematological toxicity of carboplatin in rats.

In rats a maximal tolerated dose of carboplatin (60 mg kg-1, i.v.) caused severe anaemia, leucopenia and thrombocytopenia. These indices of haematological toxicity were also observed with a maximal tolerated dose of cis-platin (6.5 mg kg-1, i.v.), but reductions in blood cell counts were less than those observed with carboplatin. Anaemia was deduced to be the dose-limiting toxicity of carboplatin, since red cell transfusions afforded protection to rats receiving a lethal dose of this compound (80 mg kg-1, i.v.). Anaemia did not appear to be due to an increase in the susceptibility of cis-platin- or carboplatin-exposed red cells to lysis, as concluded from results of osmotic fragility tests. These red cells, when tagged with 51Cr, also did not exhibit reductions in survival time. Administration of 51Cr-labelled control red cells to rats, which had been treated with carboplatin 3 days earlier, resulted in substantial loss of the radiolabel from the circulation, indicating that internal haemorrhaging, as a result of thrombocytopenia, is probably the principle cause of drug-induced anaemia.