A Phase I clinical study of cisplatin-incorporated polymeric micelles (NC-6004) in patients with solid tumours.

BACKGROUND: On the basis of preclinical studies of NC-6004, a cisplatin-incorporated micellar formulation, we hypothesised that NC-6004 could show lower toxicity than cisplatin and show greater anti-tumour activity in phase I study. METHODS: A total of 17 patients were recruited in a range of advanced solid tumour types. NC-6004 was administered intravenously (i.v.) every 3 weeks. The dose escalation started at 10 mg m(-2) and was increased up to 120 mg m(-2) according to the accelerated titration method and modified Fibonacci method. RESULTS: One dose-limiting toxicity (DLT) occurred in a patient who was given 90 mg m(-2) of NC-6004, otherwise any significant cisplatin-related toxicity was not observed or generally mild toxicity was observed. Despite the implementation of post-hydration and pre-medication regimen, renal impairment and hypersensitivity reactions still developed at 120 mg m(-2), which led to the conclusion that the maximum tolerated dose was 120 mg m(-2), and the recommended dose was 90 mg m(-2), although DLT was not defined as per protocol. Stable disease was observed in seven patients. The maximum concentration and area under the concentration-time curve of ultrafilterable platinum at 120 mg m(-2) NC-6004 were 34-fold smaller and 8.5-fold larger, respectively, than those for cisplatin. CONCLUSION: The delayed and sustained release of cisplatin after i.v. administration contributes to the low toxicity of NC-6004.

Contribution of HIF-1 and drug penetrance to oxaliplatin resistance in hypoxic colorectal cancer cells.

BACKGROUND: Hypoxia is as an indicator of poor treatment outcome. Consistently, hypoxic HCT116 colorectal cancer cells are resistant to oxaliplatin, although the mechanistic basis is unclear. This study sought to investigate the relative contribution of HIF-1 (hypoxia-inducible factor-1)-mediated gene expression and drug penetrance to oxaliplatin resistance using three-dimensional spheroids. METHODS: Hypoxia-inducible factor-1alpha function was suppressed by the stable expression of a dominant-negative form in HCT116 cells (DN). Cells were drug exposed as monolayer or multicellular spheroid cultures. Cells residing at differing oxygenation status were isolated from Hoechst 33342-treated spheroids using flow cytometry. Sub-populations were subjected to clonogenic survival assays and to Inductively-Coupled Plasma Mass Spectroscopy to determine oxaliplatin uptake. RESULTS: In spheroids, a sensitivity gradient (hypoxic

Adaptive dosing and platinum-DNA adduct formation in children receiving high-dose carboplatin for the treatment of solid tumours.

A pharmacokinetic-pharmacodynamic study was carried out to investigate the feasibility and potential importance of therapeutic monitoring following high-dose carboplatin treatment in children. High-dose carboplatin was administered over 3 or 5 days, with the initial dose based on renal function, to achieve target area under the plasma concentration-time curve (AUC) values of 21 or 20 mg ml(-1).min, respectively. Dose adjustment was carried out based on observed individual daily AUC values, to obtain the defined target exposures. Platinum-DNA adduct levels were determined in peripheral blood leucocytes and toxicity data were obtained. Twenty-eight children were studied. Based on observed AUC values, carboplatin dose adjustment was performed in 75% (21 out of 28) patients. Therapeutic monitoring resulted in the achievement of carboplatin exposures within 80-126% of target AUC values, as compared to estimated exposures of 65-213% of target values without dose adjustment. The carboplatin AUC predicted with no dose modification was positively correlated with pretreatment glomerular filtration rate (GFR) values. Higher GFR values were observed in those patients who would have experienced AUC values >25% above the target AUC than those patients attaining AUC values >25% below the target AUC, following renal function-based dosing. Platinum-DNA adduct levels correlated with observed AUC values on day 1 of carboplatin and increased over a 5-day course of treatment. Real-time monitoring of carboplatin pharmacokinetics with adaptive dosing is both feasible and necessary for the attainment of consistent AUC values in children receiving high-dose carboplatin treatment. Pharmacodynamic data suggest a strong correlation between carboplatin pharmacokinetics and the drug-target interaction.

Pharmacokinetics and metabolism of ifosfamide in relation to DNA damage assessed by the COMET assay in children with cancer.

The degree of damage to DNA following ifosfamide (IFO) treatment may be linked to the therapeutic efficacy. The pharmacokinetics and metabolism of IFO were studied in 19 paediatric patients, mostly with rhabdomyosarcoma or Ewings sarcoma. Ifosfamide was dosed either as a continuous infusion or as fractionated doses over 2 or 3 days. Samples of peripheral blood lymphocytes were obtained during and up to 96 h after treatment, and again prior to the next cycle of chemotherapy. DNA damage was measured using the alkaline COMET assay, and quantified as the percentage of highly damaged cells per sample. Samples were also taken for the determination of IFO and metabolites. Pharmacokinetics and metabolism of IFO were comparable with previous studies. Elevations in DNA damage could be determined in all patients after IFO administration. The degree of damage increased to a peak at 72 h, but had returned to pretreatment values prior to the next dose of chemotherapy. There was a good correlation between area under the curve of IFO and the cumulative percentage of cells with DNA damage (r2=0.554, P=0.004), but only in those patients receiving fractionated dosing. The latter patients had more DNA damage (mean+/-s.d., 2736+/-597) than those patients in whom IFO was administered by continuous infusion (1453+/-730). The COMET assay can be used to quantify DNA damage following IFO therapy. Fractionated dosing causes a greater degree of DNA damage, which may suggest a greater degree of efficacy, with a good correlation between pharmacokinetic and pharmacodynamic data.

Schedule-dependent response of neuroblastoma cell lines to combinations of etoposide and cisplatin.

The growth inhibitory effects of cisplatin and etoposide on neuroblastoma cell lines were investigated in several scheduled combinations. Results were analyzed using median effect and combination index analyses. In all schedules in which cisplatin was administered prior to etoposide a synergistic effect was observed. Conversely, an antagonistic effect was seen in all schedules where etoposide was administered before cisplatin.

Decreased telomerase activity is not a reliable indicator of chemosensitivity in testicular cancer cell lines.

Telomere stabilisation is a critical step in tumorigenesis and telomerase, an enzyme which counteracts telomeric DNA loss, is active in most tumours. Conflicting evidence has been published concerning the potential use of telomerase activity as a measurement of drug-induced tumour cell killing. In this study, the time courses of telomerase loss and induction of apoptosis were investigated in two testicular cell lines, Susa CP and 833 K, following 4-h exposure to cisplatin, melphalan or doxorubicin. Telomerase activity was only affected in both cell lines at 20 h following exposure to high concentrations of cisplatin (100x the drug concentrations causing 50% growth inhibition (IC(50) values)). The time course of melphalan-induced telomerase loss, which was again only apparent at 100x IC(50) concentrations, varied between the cell lines and doxorubicin (100x IC(50)) did not induce telomerase loss in either of the cell lines. Importantly, the levels and rates of appearance of apoptotic cells (nuclear morphology and annexin V staining) were similar for all three drugs in both cell lines; i.e. cisplatin, melphalan and doxorubicin (100x IC(50)) caused similar frequencies of apoptosis in Susa CP cells at 24 h whereas telomerase activities were 65, 123 and 96% of the control, respectively. The possibility that telomerase activity was lost following cisplatin treatment through a direct interaction of cisplatin with telomerase was discounted. Additionally, the relative levels of the RNA component of telomerase (hTR) and mRNA for the telomerase catalytic subunit (hTERT) were not related to the observed decreases in telomerase activity. These data indicate that telomerase activity is not a reliable indicator of chemosensitivity in human testicular cancer cells. Furthermore, cisplatin-induced loss of telomerase activity is not due to a direct reaction with the enzyme or decreased hTR levels.

Influence of cellular factors and pharmacokinetics on the formation of platinum-DNA adducts in leukocytes of children receiving cisplatin therapy.

The formation of platinum (Pt)-DNA adducts is thought to be crucial to the antitumor activity of cisplatin, and relationships between adduct formation in peripheral blood leukocytes (PBLs) and response to cisplatin therapy have been reported. The current study directly tests, for the first time, whether pharmacokinetic or other factors predominantly determine the drug-target interaction of cisplatin in a pediatric patient population. Cisplatin pharmacokinetics and Pt-DNA adduct formation in PBLs were determined in 10 children in parallel with measurement of adduct levels after incubation of pretreatment blood samples with cisplatin in vitro. Total and unbound plasma Pt concentrations were determined by atomic absorption spectrophotometry and adduct measurements performed by competitive ELISA. Pt-DNA adduct levels determined after cisplatin treatment showed considerable interindividual variation (peak levels at 24 h ranged from 0.15 to 1.31 nmol/g DNA) and correlated strongly with adduct levels determined after incubation of pretreatment whole blood with cisplatin (r = 0.92; P = 0.0002). No significant correlation was observed between in vivo adduct formation and either unbound or total cisplatin plasma concentrations (r = 0.14 and 0.18, respectively). A correlation was also observed between the degree of myelosuppression, as determined by WBC nadirs measured over a 14-day period after cisplatin treatment, and the extent of adduct formation, with greater WBC toxicity observed in patients with higher levels of Pt-DNA adducts (P = 0.010). These preliminary results provide evidence that interpatient variation in formation of Pt-DNA adducts in PBLs of children is determined by host-specific factors other than cisplatin pharmacokinetics. These results imply that analysis of adducts in PBLs after incubation of pretreatment blood samples with cisplatin may be used to predict in vivo adduct levels, leukopenia, and, potentially, response to cisplatin therapy.

Antibody recognition of melphalan adducts characterized using immobilized DNA: enhanced alkylation of G-Rich regions in cells compared to in vitro.

The bifunctional alkylating agent, melphalan, forms adducts on DNA that are recognized by two previously described monoclonal antibodies, MP5/73 and Amp4/42. Immunoreactivity to MP5/73 was lost when alkylated DNA was exposed to alkaline pH, while Amp4/42 only recognized the structures formed after the alkali treatment. Competitive enzyme-linked immunoadsorbent assays (ELISAs) indicated that in 0.01 and 0.1 M NaOH, loss of immunoreactivity to MP5/73 occurred with half-lives that were at least 2-fold longer than half-lives for gain of immunoreactivity to Amp4/42. This supported previously published evidence that Amp4/42 did not simply recognize all the products formed by alkali treatment of adducts that were initially recognized by MP5/73. Adducts recognized by MP5/73 on RNA were considerably more stable at 100 degrees C and pH 7 than adducts on DNA. This was consistent with the hypothesis that immunorecognition involved N7 guanine adducts and ruled out the involvement of phosphotriesters in immunoreactivity. Synthetic oligodeoxyribonucleotides, covalently immobilized onto 96-well plates, were reacted with melphalan and incubated for various periods with alkali, and then the levels of adducts recognized by each antibody in replicate wells were assayed by a direct binding ELISA. Adducts formed on oligodeoxyguanylic acid were recognized very weakly by Amp4/42, unlike other DNA sequences that were tested. Retention of immobilized DNA during alkali treatment was confirmed by immunoassay of cisplatin adducts. Poor recognition by Amp4/42 of adducts in oligodeoxyguanylic acid was confirmed by a competitive ELISA. Amp4/42, unlike MP5/73, efficiently recognized adducts resulting from alkylation of DNA with chlorambucil. It is concluded that the two antibodies recognized melphalan adducts in different DNA sequence environments and that this explains (a) the different alkali stability of immunoreactive adducts and (b) previous results which showed that, in DNA from melphalan-treated cells, adducts recognized by Amp4/42 formed a smaller proportion of total adducts compared to DNA alkylated in vitro. The results presented here indicate that this was caused by a marked cellular influence on the overall sequence-dependent pattern of DNA alkylation or repair.

Distinct properties of fenretinide and CD437 lead to synergistic responses with chemotherapeutic reagents.

The RARbeta/gamma-selective retinoids fenretinide and CD437 induce caspase-dependent apoptosis but generate free radicals independently of caspases. Apoptosis, but not free radical generation, induced by these retinoids is inhibited by RARbeta/gamma-specific antagonists. Both fenretinide and CD437 induce apoptosis synergistically with cisplatin, carboplatin, or etoposide. However, antioxidants inhibit this synergy to the level obtained with chemotherapeutic drugs alone, and this implies that free radical generation is important in the synergistic response. Since apoptosis induced by fenretinide or CD437 is mediated by apoptotic pathways involving RARs and/or mitochondria and differs from mechanisms of chemotherapy-induced apoptosis this may explain the strong synergistic response seen between these synthetic retinoids and chemotherapeutic drugs. These results suggest that fenretinide or CD437 may be useful adjuncts to neuroblastoma therapy.

Synergistic induction of apoptosis of neuroblastoma by fenretinide or CD437 in combination with chemotherapeutic drugs.

Retinoic acid therapy improves the survival of children with neuroblastoma and 13-cis retinoic acid now forms an important component of treatment for residual disease of stage IV neuroblastoma after chemotherapy. However, although 13-cis retinoic acid induces differentiation, other retinoids are effective at inducing apoptosis of neuroblastoma in vitro, including the novel compounds fenretinide and CD437 and these may be alternative retinoids for neuroblastoma therapy. The aim of our study was to evaluate the ability of fenretinide, CD437 (6-¿3-(1-adamantyl)-4-hydroxyphenyl¿ -2-naphthalene carboxylic acid) and different retinoic acid isomers to induce apoptosis of neuroblastoma in conjunction with the chemotherapeutic drugs, cisplatin, etoposide and carboplatin. Neuroblastoma cell lines were treated with retinoids prior to treatment with chemotherapeutic agents and flow cytometry used to measure apoptosis and free radical generation. Pre-treatment of neuroblastoma cell lines with fenretinide or CD437 prior to treatment with cisplatin, etoposide or carboplatin synergistically increased apoptosis, an effect not seen with 13-cis, all-trans or 9-cis retinoic acid. Contrary to retinoic acid isomers or chemotherapeutic drugs, apoptosis of neuroblastoma cells induced by fenretinide or CD437 was accompanied by the generation of intracellular free radicals. Quenching of fenretinide- or CD437-induced free radicals with antioxidants abolished the synergistic response seen with the subsequent addition of chemotherapeutic agents. Therefore, the generation of free radicals by fenretinide or CD437 may be the key property of these retinoids leading to synergistic responses with chemotherapeutic drugs. Clearly, these synthetic retinoids provide new opportunities for novel neuroblastoma therapy.

An investigation into the formation of N- [2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA) and 6-[2-(dimethylamino)ethylamino]- 3-hydroxy-7H-indeno[2, 1-C]quinolin-7-one dihydrochloride (TAS-103) stabilised DNA topoisomerase I and II cleavable complexes in human leukaemia cells.

The antitumour agents DACA (XR5000; N-[2-(dimethylamino)ethyl]acridine-4-carboxamide) and TAS-103 (6-[2-(dimethylamino)ethylamino]-3-hydroxy-7H-indeno[2, 1-c]quinolin-7-one dihydrochloride) have been shown to inhibit two essential nuclear enzymes in vitro, DNA topoisomerase I and DNA topoisomerase (topo) II. To examine whether DACA or TAS-103 stabilise topo I, topo IIalpha, and topo IIbeta cleavable complexes in human leukaemia CCRF-CEM cells, the TARDIS assay (trapped in agarose DNA immunostaining) was used. This assay can reveal drug-stabilised topo-DNA complexes formed in situ in individual cells. The results showed that both DACA and TAS-103 can stabilise topo IIalpha cleavable complexes in these cells. Topo IIbeta cleavable complexes were also formed, but only at high concentrations of DACA and TAS-103. The effect on topo I was less clear, with TAS-103 showing only low levels of cleavable complex formation and DACA having no detectable effect under these assay conditions. This is in contrast to the purified enzyme cleavable complex assay, where both DACA and TAS-103 poisoned topo I. Although both DACA and TAS-103 show a preference for topo IIalpha in whole cells using the TARDIS assay, the formation of low levels of topo I or topo IIbeta cleavable complexes may still play a role in cell death.

Camptothecin-stabilised topoisomerase I-DNA complexes in leukaemia cells visualised and quantified in situ by the TARDIS assay (trapped in agarose DNA immunostaining).

We have shown that the TARDIS assay (trapped in agarose DNA immunostaining) can be used to detect DNA-topoisomerase I (topo I) cleavable complexes in situ in individual cells following treatment with topo I-targeting drugs. This assay is a modification of the assay for DNA-topoisomerase II (topo II) cleavable complexes (Willmore et al., Mol Pharmacol 53: 78-85, 1998). Drug-stabilised topo I-DNA complexes were detected in situ by topo I-specific primary antibodies and then visualised using fluorescein isothiocyanate conjugated second antibodies. Immunofluorescence was then quantified using a cooled slow-scan coupled device camera and image analysis procedures. Camptothecin (CPT) was shown to stabilise topo I-DNA cleavable complexes in whole cells in a dose-dependent manner in both CCRF-CEM and K562 cells and in lymphoblasts from an adult with newly diagnosed acute myeloid leukaemia treated ex vivo with CPT. In K562 cells, cleavable complexes were found to be maximal between 30 and 90 minutes continuous exposure of CPT, and approximately 78% of cleavable complexes formed in these cells were found to be reversed within 5 minutes of drug removal. It has also been shown that the immunofluorescence detected by the TARDIS assay was specific for topo I-targeting agents. Hence, the TARDIS assay provides a powerful tool to determine the levels of drug-stabilised cleavable complexes in whole cells and thereby aid in the understanding of the mechanism of interaction between topo I-targeting drugs and their target.

Murine transgenic cells lacking DNA topoisomerase IIbeta are resistant to acridines and mitoxantrone: analysis of cytotoxicity and cleavable complex formation.

Murine transgenic cell lines lacking DNA topoisomerase II (topo II)beta have been used to assess the importance of topo IIbeta as a drug target. Western blot analysis confirmed that the topo IIbeta -/- cell lines did not contain topo IIbeta protein. In addition, both the topo IIbeta +/+ and topo IIbeta -/- cell lines contained similar levels of topo IIalpha protein. The trapped in agarose DNA immunostaining assay (TARDIS) was used to detect topo IIalpha and beta cleavable complexes in topo IIbeta -/- and topo IIbeta +/+ cells. These results show that both topo IIalpha and beta are in vivo targets for etoposide, mitoxantrone, and amsacrine (mAMSA) in topo IIbeta +/+ cells. As expected, only the alpha-isoform was targeted in topo IIbeta -/- cells. Clonogenic assays comparing the survival of topo IIbeta -/- and topo IIbeta +/+ cells were carried out to establish whether the absence of topo IIbeta caused drug resistance. Increased survival of topo IIbeta -/- cells compared with topo IIbeta +/+ cells was observed after treatment with amsacrine (mAMSA), methyl N-(4'-[9-acridinylamino]-2-methoxyphenyl) carbamate hydrochloride (AMCA), methyl N-(4'-[9-acridinylamino]-2-methoxyphenyl)carbamate hydrochloride (mAMCA), mitoxantrone, and etoposide. These studies showed that topo IIbeta -/- cells were significantly more resistant to mAMSA, AMCA, mAMCA, and mitoxantrone, than topo IIbeta +/+ cells, indicating that topo IIbeta is an important target for the cytotoxic effects of these compounds.

Pharmacokinetically guided dose escalation of carboplatin in epithelial ovarian cancer: effect on drug-plasma AUC and peripheral blood drug-DNA adduct levels.

BACKGROUND: Platinum based drugs are active agents in epithelial ovarian cancer and increased platinum drug dose intensity is thought to lead to improved survival, because of the largely untested assumption that increased dose intensity results in an increased interaction of the platinum drug with its target, DNA. In a previously reported phase I trial (Lind et al., J Clin Oncol 1996; 14: 800-5), carboplatin dose intensity was increased by the use of G-CSF to support the bone marrow and using pharmacokinetically-guided carboplatin dosing. The objectives of this study were to validate the carboplatin dosing formula during high dose intensity therapy and evaluate the relationship between systemic carboplatin exposure and Pt-DNA adduct levels in peripheral blood leucocytes. PATIENTS AND METHODS: A total of 17 patients were studied over four levels of dose intensification. The carboplatin dose was calculated using the 'Calvert formula'. Levels of drug-target interaction in peripheral blood leukocytes were measured using an immunoassay based on a monoclonal antibody that recognises DNA-platinum adducts. Pharmacokinetic measurements were carried out using a previously validated single sample method. RESULTS: The area under the curve of concentration of unbound carboplatin in plasma versus time (AUC) for target AUC values of 5, 7 and 9 mg/ml x min were: 5.6 +/- 1.0, 7.3 +/- 0.7 and 9.8 +/- 0.5 mg/ml x min (mean +/- S.D.). There was a good correlation between target and achieved dose intensities (r2 = 0.899) and the slope of the linear regression line was 0.95 (+/- 0.09 SD) not significantly different to 1.0 (P > 0.6). The levels of immunoreactive DNA adducts were not detectable at a target AUC of 5 mg/ml x min but increased progressively at the higher AUC levels. Accumulation of adducts between courses was not detected. CONCLUSIONS: Pharmacokinetically-based carboplatin dosing during high intensity therapy accurately predicted the dose required to achieve a target AUC and resulted in consistent patient exposure to active drug. During the dose escalation study, peripheral blood leucocyte DNA platinum-DNA adduct levels were positively related to drug dose and drug AUC.

Measuring DNA adducts by immunoassay (ELISA).

A large proportion of anti-cancer drugs act by causing chemical modifications to DNA, often involving the addition of part of the drug molecule to DNA to form DNA adducts. As discussed in Chapter 1 , resistance mechanisms can act to diminish the extent of drug-target access or to alter the responses of cells to a given level of target modification. Measurement of the extent of drug-DNA interaction permits direct analysis of the contribution of the former type of mechanisms. Measurement of drug-DNA adduct levels can also be important for experiments focused on cellular responses because, first, it may be necessary to prove that observed differences in response are not owing to variation in drug-DNA access. Second, such measurements can be used to measure directly the rate of DNA repair processes, and hence, the influence on these processes of other variables, such as expression of specific genes. Finally, a knowledge of the DNA adducts levels formed in patients during therapy permits direct assessment of the clinical relevance of the levels of DNA modification employed in in vitro experiments. This could be important because the nature and significance of the various types of cellular responses will be dependent on the level of drug-target interaction initiating those responses.

A monofunctional derivative of melphalan: preparation, DNA alkylation products, and determination of the specificity of monoclonal antibodies that recognize melphalan-DNA adducts.

Bifunctional alkylating agents, such as those based on nitrogen mustard, form important parts of many anti-cancer chemotherapy protocols and are responsible for increased incidences of secondary tumors in successfully treated patients. These drugs generally form a majority of monofunctional DNA adducts, although the bifunctional adducts appear to be necessary for their powerful cytotoxic and antitumor effects. The relative importance of bifunctional as opposed to monofunctional adducts in the varied biological consequences of drug exposure has not been studied in detail, particularly in relation to the role and specificity of biochemical responses to therapy-related DNA damage. A simple method is described for the preparation of useful quantities of a pure monofunctional derivative of the nitrogen mustard-based drug melphalan. Monohydroxymelphalan was prepared by partial hydrolysis, purified by reversed phase chromatography, and characterized by MS, NMR, and HPLC. Contamination with melphalan was

Etoposide targets topoisomerase IIalpha and IIbeta in leukemic cells: isoform-specific cleavable complexes visualized and quantified in situ by a novel immunofluorescence technique.

We have shown that both DNA topoisomerase (topo) IIalpha and beta are in vivo targets for etoposide using a new assay which directly measures topo IIalpha and beta cleavable complexes in individual cells after treatment with topo II targeting drugs. CCRF-CEM human leukemic cells were exposed to etoposide for 2 hr, then embedded in agarose on microscope slides before cell lysis. DNA from each cell remained trapped in the agarose and covalently bound topo II molecules from drug-stabilized cleavable complexes remained associated with the DNA. The covalently bound topo II was detected in situ by immunofluorescence. Isoform-specific covalent complexes were detected with antisera specific for either the alpha or beta isoform of topo II followed by a fluorescein isothiocyanate-conjugated second antibody. DNA was detected using the fluorescent stain Hoechst 33258. A cooled slow scan charged coupled device camera was used to capture images. A dose-dependent increase in green immunofluorescence was observed when using antisera to either the alpha or beta isoforms of topo II, indicating that both isoforms are targets for etoposide. We have called this the TARDIS method, for trapped in agarose DNA immunostaining. Two key advantages of the TARDIS method are that it is isoform-specific and that it requires small numbers of cells, making it suitable for analysis of samples from patients being treated with topo II-targeting drugs. The isoform specificity will enable us to extend our understanding of the mechanism of interaction between topo II-targeting agents and their target, the two human isoforms.

Platinum-DNA adduct formation in leucocytes of children in relation to pharmacokinetics after cisplatin and carboplatin therapy.

Platinum (Pt)-DNA adducts were measured in peripheral blood leucocytes (PBLs) from 24 children with solid tumours after standard cisplatin and/or carboplatin treatment. The relationship between Pt-DNA adduct levels and pharmacokinetics of cisplatin and carboplatin was investigated. Adduct measurements were performed by competitive enzyme-linked immunosorbent assay (ELISA) and plasma unbound Pt concentrations were measured by atomic absorption spectrophotometry (AAS). There was considerable interindividual variation in Pt-DNA adduct level that was weakly correlated (r2 = 0.32) with the area under the unbound drug concentration vs time curve (AUC) at 6 h after the start of cisplatin infusion, indicating that the variation in Pt-DNA adduct levels was primarily determined by factors other than AUC. No clear relationship between AUC and adduct levels was seen at 24 and 48 h after cisplatin or at 6, 24 or 48 h after carboplatin. Carboplatin produced lower levels of immunoreactive adducts than did cisplatin (1.3 +/- 0.6 nmol Pt g-1 DNA vs 3.2 +/- 1.7 nmol Pt g-1 DNA), despite a 20-fold higher unbound drug AUC for carboplatin (8.0 +/- 3.5 mg ml-1 min vs 0.4 +/- 0.2 mg ml-1 min). This study demonstrates that, after cisplatin and carboplatin treatment the drug-target interaction is determined by both pharmacokinetic and, predominantly, cellular factors. Intrinsic differences between the two complexes, primarily reactivity, probably explain the lower adduct levels observed after carboplatin treatment.

Cisplatin pharmacokinetics in children with cancer.

Cisplatin is an important drug in the treatment of a number of paediatric cancers yet, despite widespread use, there are only very limited data on the pharmacokinetics of the drug in children. Cisplatin pharmacokinetics were studied in 21 patients following a 24 h infusion of 50-120 mg/m2 cisplatin. Total and free platinum (Pt) levels in plasma and Pt in urine, were measured by atomic absorption spectrophotometry. Pharmacokinetic parameters were determined by non-compartmental and compartmental analyses. There was 3-fold interpatient variability in free drug exposure (area under the plasma concentration versus time curve--AUC) for a given surface area-based dose of cisplatin. The mean (+/- SD) pharmacokinetic parameters for free Pt were: AUC 0.47 +/- 0.13 mg/ml.min/100 mg/m2, Vdss 12.5 +/- 2.7 l/m2, t1/2 39 +/- 9 min, Ke 0.019 +/- 0.006 min-1, Clrenal 62 ml/min/m2, Cltotal 233 +/- 455 ml/min/m2, Cpss 0.31 +/- 0.09 microgram/ml. The total free Pt clearance was 1.5-5.8-fold higher (3.4 +/- 1.0) than the glomerular filtration rate (GFR). The renal clearance of cisplatin was not related to GFR and cisplatin was subject to only limited urinary excretion (27% administered dose 0-48 h), indicating that there are other important pathways of clearance beside renal elimination. Patient and treatment heterogeneity precluded the investigation of pharmacokinetic-pharmacodynamic relationships; however, the degree of interpatient pharmacokinetic variability observed suggests that body surface area-based dosing of cisplatin in children is not satisfactory.