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.

The role of folate receptor alpha (FRalpha) in the response of malignant pleural mesothelioma to pemetrexed-containing chemotherapy

Background:

The standard treatment of choice for malignant pleural mesothelioma is chemotherapy with pemetrexed and platinum, but the clinical outcome is poor. This study investigates the response to pemetrexed in a panel of eight mesothelioma cell lines and the clinical outcome for patients treated with pemetrexed in relation to folate receptor alpha (FRα).

Methods:

Cell lines were treated with pemetrexed to determine the concentration that reduced growth to 50% (GI₅₀). FRα expression was determined by western blotting and that of FRα, reduced folate carrier (RFC) and proton-coupled folate transporter (PCFT) by real-time quantitative RT–PCR. Immunohistochemistry for FRα was carried out on 62 paraffin-embedded samples of mesothelioma from patients who were subsequently treated with pemetrexed.

Results:

A wide range of GI₅₀ values was obtained for the cell lines, H2452 cells being the most sensitive (GI₅₀ 22 nM) and RS5 cells having a GI₅₀ value greater than 10 μM. No FRα protein was detected in any cell line, and there was no relationship between sensitivity and expression of folate transporters. FRα was detected in 39% of tumour samples, generally in a small percentage of cells. There was no correlation between the presence of FRα and the outcome of pemetrexed treatment, and no significant difference between histological subtypes.

Conclusion:

Response to treatment with pemetrexed does not depend on the presence of FRα.

Abstract B149: Phase I, open-label, dose-escalating clinical and pharmacokinetic study of PM00104 administered weekly resting every fourth week, intravenously, over 1 hour to patients with advanced malignant solid tumors or lymphoma

Background: PM00104 (Zalypsis®) is a new synthetic alkaloid related to jorumycin. Preliminary data on mechanism of action suggested DNA-binding properties acting at minor groove and effects on the cell cycle (phase S). PM00104 shows a broad spectrum of activity against solid tumors both in vitro (bladder, gastric, kidney, melanoma, pancreas, prostate, sarcoma, thyroid, leukemia and lymphoma cell lines) and in vivo (xenografts of breast, gastric, prostate, and renal tumor).

Methods: Patients (n=49) with metastatic or advanced solid tumors were enrolled in a phase I, open-label, dose-escalating clinical and pharmacokinetic study of PM00104 administered weekly resting every fourth week, intravenously, over 1 hour. The starting dose was 0.75 mg/m2 and the study followed an accelerated escalation design from 0.75 to 3.037 mg/m2 distributed in 9 dose levels

Results: Median age of patients (pts) was 58 (range, 22–76 y), 29 pts were males. The median ECOG was 1 (0–2). The most frequent cancer types were colorectal, gastric, esophageal and melanoma tumors (n=15/5/4/4). Most patients were heavily pretreated with a median of 3 (1–9) prior lines. A median of 2 cycles of Zalypsis (1–8) were given to each pt. Common mild (G1–2) toxicities were asthenia, anorexia, nausea/emesis, stomatitis, weight decreased, headache and hypotension. The highest dose achieved was 3.035 mg/m2, where 2 pts had DLTs: one had G4 asthenia and G3 nausea, and the other had G4 neutropenia and thrombopenia. At the next lowest level (2.5 mg/m2) 3 pts had DLTs (G3 asthenia and nausea in one pt; febrile neutropenia, G4 thrombopenia and G3 anemia in one pt, and G1 neutropenia and thrombopenia that resulted in two skipped doses in the third pt). Thus, this dose level was declared the MTD. The RD was 2 mg/m2, at which 24 pts were treated and only one pt had DLT (G4 asymptomatic lipase increase). Preliminary PK data showed a relatively prolonged half-life (up to 60 h, with a median value at the RD of 21 h), a wide distribution and high inter-patient variability. Efficacy data showed prolonged stabilization > 3 months in 12 pts, mostly with gastrointestinal tumors (colon, pancreas, esophageal and gastroesophageal junction, n=1 each)

Conclusions: PM00104 shows acceptable safety and tolerability profile and prolonged stabilization (SD ≥3 months) in different tumor types. DLTs were manageable hematological and gastrointestinal toxicities. The RD for phase II studies is 2 mg/m2 weekly.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B149.

Expression of gonadotrophin releasing hormone receptor I is a favorable prognostic factor in epithelial ovarian cancer

The majority of epithelial ovarian cancers originate in the ovarian surface epithelium. The ovarian surface epithelium is a hormonally responsive tissue, and hormones are thought to play a key role in the development of this type of cancer. Gonadotrophin releasing hormone II is one of 2 isoforms which are thought to act through gonadotrophin releasing hormone receptor I, and gonadotrophin releasing hormone II has been shown to cause growth inhibition of cultured ovarian surface epithelium. The aim of this study was to investigate the expression levels and prognostic significance of gonadotrophin releasing hormone II and the gonadotrophin releasing hormone receptor I in epithelial ovarian cancer. Gonadotrophin releasing hormone II and gonadotrophin releasing hormone receptor I messenger RNA expression was examined in 23 cancers and 7 normal ovarian surface epithelium samples by quantitative real time polymerase chain reaction. An ovarian cancer tissue microarray containing 139 cases was constructed and immunohistochemical analysis of gonadotrophin releasing hormone II and gonadotrophin releasing hormone receptor I protein expression was performed and correlated with clinical outcome data. Gonadotrophin releasing hormone II messenger RNA expression was lower in cancer samples compared to normal ovarian surface epithelium samples (P < .05). Gonadotrophin releasing hormone II protein expression correlated with histologic subtype (25% serous versus 45% nonserous, P < .05) but not with overall survival. Gonadotrophin releasing hormone receptor I messenger RNA expression was highest in serous tumors when compared to non serous (P < .05) and normal tissue (P < .001). Expression of the gonadotrophin releasing hormone receptor I protein was also found to correlate with patient survival (P < .05). We have demonstrated gonadotrophin releasing hormone II and its receptor, gonadotrophin releasing hormone receptor I, are present in clinical ovarian samples, and that gonadotrophin releasing hormone receptor I protein expression is a favorable prognostic factor, suggesting these proteins play an important role in the development of epithelial ovarian cancer.

Phase I study of temozolomide plus paclitaxel in patients with advanced malignant melanoma and associated in vitro investigations

The purpose of this study was to determine activity of temozolomide combined with paclitaxel or epothilone B in vitro, and to investigate the combination of temozolomide with paclitaxel in a Phase I clinical trial. Melanoma cell lines A375P and DX3 were treated with temozolomide and either paclitaxel or epothilone B. Combination indices were determined to assess the degree of synergism. In a clinical study, 21 patients with malignant melanoma were treated with increasing doses of temozolomide (orally, days 1–5), in combination with a fixed dose of paclitaxel (i.v. infusion day 1), followed by dose escalation of the latter drug. Cycles of treatment were repeated every 3 weeks. Pharmacokinetics of both agents were determined on day 1, with temozolomide pharmacokinetics also assessed on day 5. All three compounds were active against the melanoma cell lines, with epothilone B being the most potent. There was a strong degree of synergism between temozolomide and either paclitaxel or epothilone B. In the clinical study, no pharmacokinetic interaction was observed between temozolomide and paclitaxel. Dose escalation of both drugs to clinically active doses was possible, with no dose-limiting toxicities observed at 200 mg m⁻² day⁻¹ temozolomide and 225 mg m⁻² day⁻¹ paclitaxel. There were two partial responses out of 15 evaluable patients. One patient remains alive and symptom-free at 4 years after treatment. Temozolomide and paclitaxel may be administered safely at clinically effective doses. Further evaluation of these combinations in melanoma is warranted.

A phase IIA study of the topoisomerase I inhibitor, exatecan mesylate (DX-8951f), administered at two different dose schedules in patients with platinum- and taxane-resistant/refractory ovarian cancer

OBJECTIVES

There is an urgent need for new agents with activity in platinum- and taxane-resistant epithelial ovarian cancer. Exatecan mesylate is a novel topoisomerase I inhibitor with potent activity against ovarian cancer in vitro. A multicentre phase IIA study was conducted in patients with platinum- and taxane-resistant epithelial ovarian cancer.

PATIENTS AND METHODS

Fifty-seven patients with bidimensionally measurable ovarian cancer, previously exposed to platinum and taxanes, whose disease had relapsed within 6 months of platinum-containing chemotherapy were randomised to one of two intravenous schedules of exatecan mesylate; 0.3 mg/m(2) daily for 5 days every 3 weeks (Arm A) or 2.1 mg/m(2) weekly for 3 weeks out of 4 (Arm B).

RESULTS

There were no responses in the weekly arm and a radiological response rate of 5.3% (95% CI 0.3-21.8%) in the daily arm. Principal toxicities were myelosuppression and emesis. Grade 3/4 neutropenia occurred in 29% of patients in Arm A and 6% patients in Arm B. Seventy-one percent of patients in Arm A required red cell transfusions while on treatment.

CONCLUSIONS

Exatecan is well tolerated in this poor prognosis group of patients but only has modest single agent activity when administered in a daily regimen.

Clinical outcome of breast cancer patients with liver metastases alone in the anthracycline-taxane era: a retrospective analysis of two prospective, randomised metastatic breast cancer trials

Liver metastases have long been known to indicate an unfavourable disease course in breast cancer (BC). However, a small subset of patients with liver metastases alone who were treated with pre-taxane chemotherapy regimens was reported to have longer survival compared with patients with liver and metastases at other sites. In the present study, we examined the clinical outcome of breast cancer patients with liver metastases alone in the context of two phase III European Organisation for Research and Treatment of Cancer (EORTC) trials which compared the efficacy of doxorubicin (A) versus paclitaxel (T) (trial 10923) and of AC (cyclophosphamide) versus AT (trial 10961), given as first-line chemotherapy in metastatic BC patients. The median follow-up for the patients with liver metastases was 90.5 months in trial 10923 and 56.6 months in trial 10961. Patients with liver metastases alone comprised 18% of all patients with liver metastases, in both the 10923 and 10961 trials. The median survival of patients with liver metastases alone and liver plus other sites of metastases were 22.7 and 14.2 months (log rank test, P=0.002) in trial 10923 and 27.1 and 16.8 months (log rank test, P=0.19) in trial 10961. The median TTP (time to progression) for patients with liver metastases alone was also longer compared with the liver plus other sites of metastases group in both trials: 10.2 versus 8.8 months (log rank test, P=0.02) in trial 10923 and 8.3 versus 6.7 months (log rank test, P=0.37) in trial 10961. Most patients with liver metastases alone have progression of their disease in their liver again (96 and 60% of patients in trials 10923 and 10961, respectively). Given the high prevalence of breast cancer, improved detection of liver metastases, encouraging survival achieved with currently available cytotoxic agents and the fact that a significant portion of patients with liver metastases alone have progression of their tumour in the liver again, a more aggressive multimodality treatment approach through prospective clinical trials seems worth exploring in this specific subset of women.

Identification of potent nontoxic poly(ADP-Ribose) polymerase-1 inhibitors: chemopotentiation and pharmacological studies

The nuclear enzyme poly(ADP-ribose) polymerase (PARP-1) facilitates DNA repair, and is, therefore, an attractive target for anticancer chemo- and radio-potentiation. Novel benzimidazole-4-carboxamides (BZ1-6) and tricyclic lactam indoles (TI1-5) with PARP-1 K(i) values of <10 nM have been identified. Whole cell PARP-1 inhibition, intrinsic cell growth inhibition, and chemopotentiation of the cytotoxic agents temozolomide (TM) and topotecan (TP) were evaluated in LoVo human colon carcinoma cells. The acute toxicity of the inhibitors was investigated in PARP-1 null and wild-type mice. Tissue distribution and in vivo chemopotentiation activity was determined in nude mice bearing LoVo xenografts. At a nontoxic concentration (0.4 micro M) the PARP-1 inhibitors potentiated TM-induced growth inhibition 1.0-5.3-fold and TP-induced inhibition from 1.0-2.1-fold. Concentrations of the PARP-1 inhibitors that alone inhibited cell growth by 50% ranged from 8 to 94 micro M. Maximum potentiation of TM activity was achieved at nongrowth inhibitory concentrations (</=1 micro M) of potent PARP-1 inhibitors BZ5 and TI4. Whole cell PARP-1 inhibition by BZ3, BZ5, BZ6, TI1, and TI4 was confirmed by attenuation of DNA damage-induced NAD(+) depletion. Selected inhibitors (TI1, TI3, and TI4), in contrast to the benchmark compound PD128763, caused only mild hypothermia in both PARP-1 null and wild-type mice. Excellent distribution of BZ5, TI1, and TI3 into tumor tissue was observed, and TI3 enhanced TM antitumor activity in vivo. These studies have identified potent nontoxic PARP-1 inhibitors with structural modifications that promote aqueous solubility, tolerability, and tissue distribution. These compounds are important leads in the development of clinically viable PARP-1 inhibitors.

Induction of thymidylate synthase as a 5-fluorouracil resistance mechanism

Thymidylate synthase (TS) is a key enzyme in the de novo synthesis of 2'-deoxythymidine-5'-monophosphate (dTMP) from 2'-deoxyuridine-5'-monophosphate (dUMP), for which 5,10-methylene-tetrahydrofolate (CH(2)-THF) is the methyl donor. TS is an important target for chemotherapy; it is inhibited by folate and nucleotide analogs, such as by 5-fluoro-dUMP (FdUMP), the active metabolite of 5-fluorouracil (5FU). FdUMP forms a relatively stable ternary complex with TS and CH(2)THF, which is further stabilized by leucovorin (LV). 5FU treatment can induce TS expression, which might bypass dTMP depletion. An improved efficacy of 5FU might be achieved by increasing and prolonging TS inhibition, a prevention of dissociation of the ternary complex, and prevention of TS induction. In a panel of 17 colon cancer cells, including several variants with acquired resistance to 5FU, sensitivity was related to TS levels, but exclusion of the resistant variants abolished this relation. For antifolates, polyglutamylation was more important than the intrinsic TS level. Cells with low p53 levels were more sensitive to 5FU and the antifolate raltitrexed (RTX) than cells with high, mutated p53. Free TS protein down-regulates its own translation, but its transcription is regulated by E2F, a cell cycle checkpoint regulator. Together, this results in low TS levels in stationary phase cells. Although cells with a low TS might theoretically be more sensitive to 5FU, the low proliferation rate prevents induction of DNA damage and 5FU toxicity. TS levels were not related to polymorphisms of the TS promoter. Treatment with 5FU or RTX rapidly induced TS levels two- to five-fold. In animal models, 5FU treatment resulted in TS inhibition followed by a two- to three-fold TS induction. Both LV and a high dose of 5FU not only enhanced TS inhibition, but also prevented TS induction and increased the antitumor effect. In patients, TS levels as determined by enzyme activity assays, immunohistochemistry and mRNA expression, were related to a response to 5FU. 5FU treatment initially decreased TS levels, but this was followed by an induction, as seen with an increased ratio of TS protein over TS-mRNA. The clear retrospective relation between TS levels and response now forms the basis for a prospective study, in which TS levels are measured before treatment in order to determine the treatment protocol.

Doxorubicin and paclitaxel versus doxorubicin and cyclophosphamide as first-line chemotherapy in metastatic breast cancer: The European Organization for Research and Treatment of Cancer 10961 Multicenter Phase III Trial

PURPOSE

To compare the efficacy and tolerability of the combination of doxorubicin and paclitaxel (AT) with a standard doxorubicin and cyclophosphamide (AC) regimen as first-line chemotherapy for metastatic breast cancer.

PATIENTS AND METHODS

Eligible patients were anthracycline-naive and had bidimensionally measurable metastatic breast cancer. Two hundred seventy-five patients were randomly assigned to be treated with AT (doxorubicin 60 mg/m(2) as an intravenous bolus plus paclitaxel 175 mg/m(2) as a 3-hour infusion) or AC (doxorubicin 60 mg/m(2) plus cyclophosphamide 600 mg/m(2)) every 3 weeks for a maximum of six cycles. A paclitaxel (200 mg/m(2)) and cyclophosphamide (750 mg/m(2)) dose escalation was planned at cycle 2 if no grade >or= 3 neutropenia occurred in cycle 1. The primary efficacy end point was progression-free survival (PFS). Secondary end points were response rate (RR), safety, overall survival (OS), and quality of life.

RESULTS

A median number of six cycles were delivered in the two treatment arms. The relative dose-intensity and delivered cumulative dose of doxorubicin were lower in the AT arm. Dose escalation was only possible in 17% and 20% of the AT and AC patients, respectively. Median PFS was 6 months in the two treatments arms. RR was 58% versus 54%, and median OS was 20.6 versus 20.5 months in the AT and AC arms, respectively. The AT regimen was characterized by a higher incidence of febrile neutropenia, 32% versus 9% in the AC arm.

CONCLUSION

No differences in the efficacy study end points were observed between the two treatment arms. Treatment-related toxicity compromised doxorubicin-delivered dose-intensity in the paclitaxel-based regimen

Population pharmacokinetics of adjuvant cyclophosphamide, methotrexate and 5-fluorouracil (CMF)

Despite the success of adjuvant cyclophosphamide, methotrexate (MTX), 5-fluouracil (5-FU) (CMF) treatment for early stage breast cancer, more than 35% of patients die within 5 years of diagnosis. Optimisation of the dose of each component drug may improve survival and reduce toxicity. In this study, the pharmacokinetics of intravenous (i.v.) cyclophosphamide (600 mg/m(2)), MTX (40 mg/m(2)) and 5-FU (600 mg/m(2)) were determined in 46 women, with data on two consecutive courses available for 41 patients. A population analysis using NONMEM was performed to investigate the effect of patient covariates on pharmacokinetics (PK), and to estimate the relative magnitude of interindividual and interoccasion variability. Patient weight had a significant influence on the clearance of cyclophosphamide and on the volume of central compartment for MTX, whose clearance was dependent on renal function. For all three drugs, interoccasion variability was of the same order (20-40%) as that between individuals, suggesting a limited potential for dose-optimisation of this regimen.

Syntheses and thymidylate synthase inhibitory activity of the poly-.gamma.-glutamyl conjugates of N-[5-[N-(3,4-dihydro-2-methyl-4-oxoquinazolin-6-ylmethyl)-N-methylamino]-2-thenoyl]-L-glutamic acid (ICI D1694) and other quinazoline antifolates

Thirteen poly-gamma-glutamates derived from several novel antifolates have been synthesized by a convergent route. The syntheses of poly-gamma-glutamyl conjugates of N-[5-[N-(3,4-dihydro-2- methyl-4-oxoquinazolin-6-ylmethyl)-N-methylamino]-2-theno yl]-L-glutamic acid (8) (ICI D1694), 2-desamino-N10-propargyl-5,8-dideazafolic acid (6), 2-desamino-2-methyl-N10-propargyl-5,8-dideazafolic acid (7), 2-desamino-2-methyl-N10-propargyl-2'-fluoro-5,8-dideazafolic acid (9), and 2-desamino-2-methyl-4-chloro-N10-propargyl-2'-fluoro-3,5,8-trideazafo lic acid (11) are described. A key step in the route involves coupling of an alpha-tert-butyl-protected poly-gamma-glutamate of the required chain length to the appropriate 5,8-dideazapteroic acid, obtained by carboxypeptidase G2 cleavage of the parent monoglutamate, if available, or by chemical synthesis. Deprotection with trifluoroacetic acid in the final step gave the desired poly-gamma-glutamyl antifolates as their trifluoroacetate salts. As inhibitors of thymidylate synthase, these polyglutamates were more potent in every case than the corresponding non-polyglutamylated drug.

Effect of temozolomide on central nervous system relapse in patients with advanced melanoma

Temozolomide has shown efficacy in the treatment of metastatic melanoma similar to that of dacarbazine (DTIC), the standard chemotherapy, but with the added benefit of penetration into the central nervous system (CNS). Isolated CNS relapse is increasingly a problem for patients who respond to biochemotherapy. By replacing DTIC with temozolomide in treatment regimens, the incidence of CNS relapse might be reduced. This hypothesis is difficult to test in a prospective randomized controlled trial because of the large number of patients that would be required. We have examined this question in a retrospective case control study, observing the rates of CNS relapse in advanced metastatic melanoma patients responding to DTIC- or temozolomide-based chemotherapy in three institutions. Twenty-one DTIC and 20 temozolomide responders were identified, and have been followed up for a median of 19.0 months (range 6.0-74.3 months). CNS relapse occurred in nine DTIC- and two temozolomide-treated patients, a statistically significant difference in favour of the new agent (P = 0.03). These results support the investigation of temozolomide as a replacement for DTIC in systemic treatment regimens for melanoma.

Topotecan in combination with carboplatin: phase I trial evaluation of two treatment schedules

BACKGROUND

Topotecan and cisplatin combinations have shown schedule-dependent toxicity, which may in part be due to cisplatin nephrotoxicity. As carboplatin is less nephrotoxic and increasingly replacing cisplatin in clinical practice, the aim of this study was to define the optimal sequence and dose for topotecan in combination with carboplatin.

PATIENTS AND METHODS

Two parallel phase I trials, with pharmacokinetic studies, were conducted administering carboplatin on day 1 with topotecan on days 1-5 (schedule A) or days 8-12 (schedule B). repeated every 3 weeks.

RESULTS

Twenty-one patients were treated over two dose levels, carboplatin AUC 4 [glomerular filtration rate (GFR) calculated from 51Cr-EDTA clearance] with topotecan 0.5 or 0.75 mg/m2. At the first dose level, six patients were evaluable for each schedule. With schedule A, from 34 cycles, there were two dose reductions and 10 treatment delays due to myelosuppression. With schedule B from 25 cycles, there was one reduction and 10 delays. At dose level 2, both patients in schedule A had dose-limiting neutropenia. In contrast, there was no dose-limiting toxicity with schedule B in six patients, although the majority of cycles were delayed.

CONCLUSION

The combination of topotecan and carboplatin using these 3-weekly schedules lead to significant myelotoxicity with attendant dose reductions and delays; the optimal scheduling of these agents remains to be defined.

Pharmacological study of paclitaxel duration of infusion combined with GFR-based carboplatin in the treatment of ovarian cancer

PURPOSE

To determine the effect on systemic pharmacology and clinical toxicity of dose and mode of administration of paclitaxel combined with carboplatin in the treatment of ovarian cancer.

PATIENTS AND METHODS

A total of 18 patients were treated with a dose of carboplatin determined by GFR, to attain a target AUC of 6 or 7 mg/ml x min. The paclitaxel dose was 175 or 200 mg/m2 administered over approximately 1 or 3 h. The duration of infusion was randomized, crossing over to the alternative treatment for the second course. Blood samples were analysed for carboplatin, paclitaxel and for the excipients of the paclitaxel formulation, ethanol and Cremophor.

RESULTS

Overall the three-weekly schedule of administration of the combination of carboplatin and paclitaxel was well tolerated. There were no clinical differences in the toxicities observed between courses where a 1-h infusion was used compared with those with a 3-h infusion. The target AUC of carboplatin was achieved (mean +/- SD 114 +/- 20% of target). Analysis of paclitaxel pharmacokinetics did not show a difference in the AUC or time above a pharmacological threshold for the two infusion durations. The peak concentration of paclitaxel obtained at the end of the infusion (9.1 vs 4.5 microg/ml), and the plasma ethanol concentration (40.0 vs 20.5 mg/dl) were higher following the shorter duration infusion. Peak concentrations of Cremophor were not different.

CONCLUSION

The combination of paclitaxel at a dose of 175 mg/m2 and carboplatin at a target AUC of 6-7 mg/ml min can safely be administered every 3 weeks. Also, a 1-h infusion of paclitaxel has no acute clinical disadvantage over a 3-h infusion and these durations of administration are pharmacologically equivalent.

A phase II study of pemetrexed disodium (LY231514) in patients with locally recurrent or metastatic breast cancer

A phase II study was conducted to evaluate the activity of pemetrexed in patients with locally recurrent or metastatic breast cancer. 38 patients, median age 52 years (range 36-71 years), were given pemetrexed 600 mg/m(2) as a 10-min intravenous (i.v.) infusion every 3 weeks. Median time from diagnosis to study entry was 48 months (range 14.7-310 months). 33 of 38 patients had prior chemotherapy; 16 adjuvant, 12 metastatic and 5 in both settings. Sites of disease included skin and soft tissue (19/38) nodes (18/38), lung (17/38), liver (13/38) and bone (3/38). An overall response rate of 28% (95% confidence interval (CI): 14.2-45.2%) in 10/36 evaluable patients (1 complete response (CR), 9 partial responses (PR)), included reductions in hepatic and pulmonary metastases. 5 of 10 responders had received taxoid or anthracycline therapy for metastatic disease; 3 of these 5 had also received adjuvant chemotherapy. Median duration of response was 8 months (range 1.6-14+ months), and median survival was 13 months (95% CI 9.56-17.38 months). 167 courses were given (median five per patient; range 1-9), with 37 reductions and 33 delays. Reasons for reduction included neutropenia (11%) and mucositis (5%), with delays due to raised LFTs (21%), neutropenia (12%) and other non-treatment related events. The major haematological toxicities (Common Toxicity Criteria) (CTC) were grade 3/4 neutropenia (47%) and thrombocytopenia (15.7%) of patients. There was one report of a grade 3 infection. Non-haematological toxicities (all grades 2/3) included elevated transaminases (92%), vomiting (34%), nausea (34%) and mucositis (32%). One episode of grade 4 diarrhoea was reported. Other toxicities included a skin rash, grade 2 (42%), 3 (5%) and 4 (13%), which was ameliorated by the use of prophylactic dexamethasone. These results suggest that pemetrexed has significant antitumour activity in advanced breast cancer with responses in patients who had previously received anthracyclines and taxoids.

In vitro and in vivo properties of novel nucleoside transport inhibitors with improved pharmacological properties that potentiate antifolate activity

The activity of antimetabolite inhibitors of de novo deoxyribonucleotide biosynthesis can be compromised by the salvage of extracellular preformed nucleosides and nucleobases. Dipyridamole (DP) is a nucleoside transport inhibitor that has been used clinically in an attempt to increase antimetabolite activity; however, DP binds tightly to the serum protein alpha1-acid glycoprotein (AGP) thereby rendering this therapeutic strategy largely ineffective. Four novel DP analogues (NU3076, NU3084, NU3108, and NU3121) have been developed with substitutions at the 2,6- and 4,8-positions of the pyrimidopyrimidine ring. The novel DP analogues inhibit thymidine (dThd) uptake into L1210 cells in vitro (NU3076 IC(50), 0.25 microM; NU3084 IC(50), 0.27 microM; NU3108 IC(50), 0.31 microM; NU3121 IC(50), 0.26 microM; and DP IC(50), 0.37 microM), but, unlike DP, their activity remains largely unaffected in the presence of 5 mg/ml AGP. The four DP analogues inhibit dThd and hypoxanthine rescue from Alimta (multitargeted antifolate)-induced growth inhibition in A549 and COR L23 human lung carcinoma cell lines in the presence of 2.5 mg/ml AGP, whereas the activity of DP is completely abolished. i.p. administration of 10 mg/kg NU3108, NU3121, and DP produced peak plasma concentrations of 4.4, 2.1, and 6.7 microM, respectively, and levels were sustained above 1 microM for approximately 45 min (DP) and 120 min (NU3108 and NU3121). [3H]thymidine incorporation into COR L23 xenografts grown in CD1 nude mice was reduced by 64% (NU3108), 44% (NU3121), and 65% (DP) 2 h after administration of the nucleoside transport inhibitors. In conclusion, two novel DP analogues (NU3108 and NU3121) have been identified that do not bind to AGP and that display superior pharmacokinetic profiles in comparison to DP and inhibit [3H]thymidine incorporation into human tumor xenografts in vivo.

Pharmacokinetics of carboplatin administered in combination with the bradykinin agonist Cereport (RMP-7) for the treatment of brain tumours

INTRODUCTION

Cereport (RMP-7) is a novel bradykinin agonist which is being developed as a modulator of the blood-brain barrier (BBB). In order to investigate the pharmacokinetics of carboplatin in combination with Cereport, we performed pharmacological studies in conjunction with early clinical trials.

METHODS

Pharmacokinetic samples were collected from eight patients in a phase I study (Cereport 100-300 ng/ kg) and ten patients in a phase II study (Cereport 300 ng/kg). Pharmacokinetic parameters for carboplatin were compared with respect to the dose of Cereport and with historical controls.

RESULTS

Cereport combined with carboplatin was well-tolerated, with mild haematological toxicities consistent with the target area under the concentration time curve (AUC) of 7 mg/ml x min. Although the clearance of carboplatin was within the range reported for this drug alone, the addition of Cereport resulted in a higher than expected carboplatin AUC. This effect was related to the dose of Cereport in the phase I study (AUC values 104-133% of target, Spearman rank correlation coefficient = 0.71, P < 0.001). The higher than expected AUC value was confirmed in the phase II study (AUC values 106-189% of target).

CONCLUSIONS

Co-administration of Cereport with carboplatin may result in a greater than predicted AUC. The mechanism of this possible interaction remains to be determined, although this did not result in any increased toxicity. Thus, the clinical potential of this combination in the treatment of brain tumours warrants further investigation.

Estimation of glomerular filtration rate in cancer patients

The frequent need to obtain an estimate of renal function in cancer patients, not least for targeting carboplatin dose, has led to a number of approaches to estimate glomerular filtration rate (GFR). This study aimed to develop a simple and reliable method to estimate GFR using readily-available patient characteristics. Data from 62 patients with estimates of 51Cr-EDTA clearance were analysed to determine the most appropriate formula relating this method of measuring GFR to patient characteristics. The population pharmacokinetics of 51Cr-EDTA were analysed using NONMEM to evaluate the influence of each covariate. The formulae derived were then validated using a further 38 patients and compared with those obtained using existing formulae. 51Cr-EDTA clearance (GFR) was positively related to Dubois surface area, negatively related to age, and inversely related to serum creatinine (SCr). Females had lower 51Cr-EDTA clearance than males. The enzymatic method of SCr assay gave more reliable results than the Jaffe colorimetric method. A measure of creatine kinase significantly improved the estimation of GFR. The new formula produced estimates of GFR which were less biased (Mean Prediction Error = -3%) and more precise (Mean Absolute Prediction Error = 12%) than Cockcroft and Gault (-8% and 16%) or Jelliffe (-15% and 19%) estimates. The formulae developed here can be used to provide reliable estimates of GFR, particularly in regard to targeted dosing of carboplatin.

Differential effects of the poly (ADP-ribose) polymerase (PARP) inhibitor NU1025 on topoisomerase I and II inhibitor cytotoxicity in L1210 cells in vitro

The potent novel poly(ADP-ribose) polymerase (PARP) inhibitor, NU1025, enhances the cytotoxicity of DNA-methylating agents and ionizing radiation by inhibiting DNA repair. We report here an investigation of the role of PARP in the cellular responses to inhibitors of topoisomerase I and II using NU1025. The cytotoxicity of the topoisomerase I inhibitor, camptothecin, was increased 2.6-fold in L1210 cells by co-incubation with NU1025. Camptothecin-induced DNA strand breaks were also increased 2.5-fold by NU1025 and exposure to camptothecin-activated PARP. In contrast, NU1025 did not increase the DNA strand breakage or cytotoxicity caused by the topoisomerase II inhibitor etoposide. Exposure to etoposide did not activate PARP even at concentrations that caused significant levels of apoptosis. Taken together, these data suggest that potentiation of camptothecin cytotoxicity by NU1025 is a direct result of increased DNA strand breakage, and that activation of PARP by camptothecin-induced DNA damage contributes to its repair and consequently cell survival. However, in L1210 cells at least, it would appear that PARP is not involved in the cellular response to etoposide-mediated DNA damage. On the basis of these data, PARP inhibitors may be potentially useful in combination with topoisomerase I inhibitor anticancer chemotherapy.

Resistance-modifying agents. 9. Synthesis and biological properties of benzimidazole inhibitors of the DNA repair enzyme poly(ADP-ribose) polymerase

The nuclear enzyme poly(ADP-ribose) polymerase (PARP) facilitates the repair of DNA strand breaks and is implicated in the resistance of cancer cells to certain DNA-damaging agents. Inhibitors of PARP have clinical potential as resistance-modifying agents capable of potentiating radiotherapy and the cytotoxicity of some forms of cancer chemotherapy. The preclinical development of 2-aryl-1H-benzimidazole-4-carboxamides as resistance-modifying agents in cancer chemotherapy is described. 1H-Benzimidazole-4-carboxamides, particularly 2-aryl derivatives, are identified as a class of potent PARP inhibitors. Derivatives of 2-phenyl-1H-benzimidazole-4-carboxamide (23, K(i) = 15 nM), in which the phenyl ring contains substituents, have been synthesized. Many of these derivatives exhibit K(i) values for PARP inhibition < 10 nM, with 2-(4-hydroxymethylphenyl)-1H-benzimidazole-4-carboxamide (78, K(i) = 1.6 nM) being one of the most potent. Insight into structure-activity relationships (SAR) for 2-aryl-1H-benzimidazole-4-carboxamides has been enhanced by studying the complex formed between 2-(3-methoxyphenyl)-1H-benzimidazole-4-carboxamide (44, K(i) = 6 nM) and the catalytic domain of chicken PARP. Important hydrogen-bonding and hydrophobic interactions with the protein have been identified for this inhibitor. 2-(4-Hydroxyphenyl)-1H-benzimidazole-4-carboxamide (45, K(i) = 6 nM) potentiates the cytotoxicity of both temozolomide and topotecan against A2780 cells in vitro (by 2.8- and 2.9-fold, respectively).

Resistance-modifying agents. 8. Inhibition of O(6)-alkylguanine-DNA alkyltransferase by O(6)-alkenyl-, O(6)-cycloalkenyl-, and O(6)-(2-oxoalkyl)guanines and potentiation of temozolomide cytotoxicity in vitro by O(6)-(1-cyclopentenylmethyl)guanine

A series of O(6)-allyl- and O(6)-(2-oxoalkyl)guanines were synthesized and evaluated, in comparison with the corresponding O(6)-alkylguanines, as potential inhibitors of the DNA-repair protein O(6)-alkylguanine-DNA alkyltransferase (AGT). Simple O(6)-alkyl- and O(6)-cycloalkylguanines were weak AGT inactivators compared with O(6)-allylguanine (IC(50) = 8.5 +/- 0.6 microM) with IC(50) values ranging from 100 to 1000 microM. The introduction of substituents at C-2 of the allyl group of O(6)-allylguanine reduced activity compared with the parent compound, while analogous compounds in the O(6)-(2-oxoalkyl)guanine series exhibited very poor activity (150-1000 microM). O(6)-Cycloalkenylguanines proved to be excellent AGT inactivators, with 1-cyclobutenylmethylguanine (IC(50) = 0.55 +/- 0.02 microM) and 1-cyclopentenylmethylguanine (IC(50) = 0.39 +/- 0.04 microM) exhibiting potency approaching that of the benchmark AGT inhibitor O(6)-benzylguanine (IC(50) = 0.18 +/- 0.02 microM). 1-Cyclopentenylmethylguanine also inactivated AGT in intact HT29 human colorectal carcinoma cells (IC(50) = 0.20 +/- 0.07 microM) and potentiated the cytotoxicity of the monomethylating antitumor agent Temozolomide by approximately 3- and 10-fold, respectively, in the HT29 and Colo205 tumor cell lines. The observation that four mutant AGT enzymes resistant to O(6)-benzylguanine also proved strongly cross-resistant to 1-cyclopentenylmethylguanine indicates that the O(6)-substituent of each compound makes similar binding interactions within the active site of AGT.

Identification of novel purine and pyrimidine cyclin-dependent kinase inhibitors with distinct molecular interactions and tumor cell growth inhibition profiles

Substituted guanines and pyrimidines were tested as inhibitors of cyclin B1/CDK1 and cyclin A3/CDK2 and soaked into crystals of monomeric CDK2. O6-Cyclohexylmethylguanine (NU2058) was a competitive inhibitor of CDK1 and CDK2 with respect to ATP (Ki values: CDK1, 5 +/- 1 microM; CDK2, 12 +/- 3 microM) and formed a triplet of hydrogen bonds (i.e., NH-9 to Glu 81, N-3 to Leu 83, and 2-NH2 to Leu 83). The triplet of hydrogen bonding and CDK inhibition was reproduced by 2,6-diamino-4-cyclohexylmethyloxy-5-nitrosopyrimidine (NU6027, Ki values: CDK1, 2.5 +/- 0.4 microM; CDK2, 1.3 +/- 0.2 microM). Against human tumor cells, NU2058 and NU6027 were growth inhibitory in vitro (mean GI50 values of 13 +/- 7 microM and 10 +/- 6 microM, respectively), with a pattern of sensitivity distinct from flavopiridol and olomoucine. These CDK inhibition and chemosensitivity data indicate that the distinct mode of binding of NU2058 and NU6027 has direct consequences for enzyme and cell growth inhibition.

Potentiation of temozolomide and topotecan growth inhibition and cytotoxicity by novel poly(adenosine diphosphoribose) polymerase inhibitors in a panel of human tumor cell lines

Potent poly(ADP-ribose) polymerase (PARP) inhibitors have been developed that potentiate the cytotoxicity of ionizing radiation and anticancer drugs. The biological effects of two novel PARP inhibitors, NU1025 (8-hydroxy-2-methylquinazolin-4-[3H]one, Ki = 48 nM) and NU1085 [2-(4-hydroxyphenyl)benzamidazole-4-carboxamide, Ki = 6 nM], in combination with temozolomide (TM) or topotecan (TP) have been studied in 12 human tumor cell lines (lung, colon, ovary, and breast cancer). Cells were treated with increasing concentrations of TM or TP +/- NU1025 (50, 200 microM) or NU1085 (10 microM) for 72 h. The potentiation of growth inhibition by NU1025 and NU1085 varied between the cell lines from 1.5- to 4-fold for TM and 1- to 5-fold for TP and was unaffected by p53 status. Clonogenic assays undertaken in two of the cell lines confirmed that the potentiation of growth inhibition reflected the potentiation of cytotoxicity. NU1025 (50 microM) was about as effective as 10 microM NU1085 at potentiating growth inhibition and cytotoxicity, consistent with the relative potencies of the two molecules as PARP inhibitors. Potentiation of cytotoxicity was obtained at concentrations of NU1025 and NU1085 that were not toxic per se; however, NU1085 alone was 3-fold more cytotoxic (LC50 values ranged from 83 to 94 microM) than NU1025 alone (LC50 > 900 microM). These data demonstrate that PARP inhibitors are effective resistance-modifying agents in human tumor cell lines and have provided a comprehensive assessment protocol for the selection of optimum combinations of anticancer drugs, PARP inhibitors, and cell lines for in vivo studies.

Clinical pharmacokinetic and in vitro combination studies of nolatrexed dihydrochloride (AG337, Thymitaq) and paclitaxel

A clinical study of nolatrexed dihydrochloride (AG337, Thymitaq) in combination with paclitaxel was performed. The aims were to optimize the schedule of administration and determine any pharmacokinetic (PK) interactions between the two drugs. In vitro combination studies were performed to assist with schedule optimization. Three patients were entered on each of three different schedules of administration of the two drugs: (1) paclitaxel 0-3 h, nolatrexed 24-144 h; (2) nolatrexed 0-120 h, paclitaxel 48-51 h; (3) nolatrexed 0-120 h, paclitaxel 126-129 h. Paclitaxel was administered at a dose of 80 mg m(-2) over 3 h and nolatrexed at a dose of 500 mg m(-2) day(-1) as a 120-h continuous intravenous infusion. Plasma concentrations of both drugs were determined by high performance liquid chromatography. In vitro growth inhibition studies using corresponding schedules were performed using two head and neck cancer cell lines. In both HNX14C and HNX22B cell lines, synergistic growth inhibition was observed on schedule 2, whereas schedules 1 and 3 demonstrated antagonistic effects. In the clinical study, there was no effect of schedule on the pharmacokinetics of nolatrexed. However, patients on schedules 1 and 3 had a higher clearance of paclitaxel (322-520 ml min(-1) m(-2)) than those on schedule 2 (165-238 ml min(-1) m(-2)). Peak plasma concentrations (1.66-1.93 vs. 0.86-1.32 microM) and areas under the curve (392-565 vs. 180-291 microM min(-1)) of paclitaxel were correspondingly higher on schedule 2. The pharmacokinetic interaction was confirmed by studies with human liver microsomes, nolatrexed being an inhibitor of the major routes of metabolism of paclitaxel. Toxicity was not schedule-dependent. Nolatrexed and paclitaxel may be safely given together when administered sequentially at the doses used in this study. Studies in vitro suggest some synergy, however, due to a pharmacokinetic interaction, paclitaxel doses should be reduced when administered during nolatrexed infusion.

Resistance-modifying agents. Part 7: 2,6-disubstituted-4,8-dibenzylaminopyrimido[5,4-d]pyrimidines that inhibit nucleoside transport in the presence of alpha1-acid glycoprotein (AGP)

The synthesis and biological evaluation of potent 4,8-dibenzylaminopyrimidopyrimidine nucleoside transport inhibitors, with reduced binding to alpha1-acid glycoprotein, is reported.

Potentiation of the cytotoxicity of thymidylate synthase (TS) inhibitors by dipyridamole analogues with reduced alpha1-acid glycoprotein binding

Dipyridamole has been shown to enhance the in vitro activity of antimetabolite anticancer drugs through the inhibition of nucleoside transport. However, the clinical potential of dipyridamole has not been realized because of the avid binding of the drug to the plasma protein alpha1-acid glycoprotein (AGP). Dipyridamole analogues that retain potent nucleoside transport inhibitory activity in the presence of AGP are described and their ability to enhance the growth inhibitory and cytotoxic effects of thymidylate synthase (TS) inhibitors has been evaluated. Three dipyridamole analogues (NU3026, NU3059 and NU3060) were shown to enhance the growth inhibitory activity of the TS inhibitor CB3717 and block thymidine rescue in L1210 cells. The extent of potentiation at a fixed analogue concentration (10 microM) was related to the potency of inhibition of thymidine uptake. A further analogue, NU3076, was identified, which was more potent than dipyridamole with a Ki value for inhibition of thymidine uptake of 0.1 microM compared to 0.28 microM for dipyridamole. In marked contrast to dipyridamole, inhibition of thymidine uptake by NU3076 was not significantly affected by the presence of AGP (5 mg ml(-1)). NU3076 and dipyridamole produced equivalent potentiation of the cytotoxicity of the non-classical antifolate TS inhibitor, nolatrexed, in L1210 cells with both compounds significantly reducing the LC90, by > threefold in the absence of salvageable thymidine. Thymidine rescue of L1210 cells from nolatrexed cytotoxicity was partially blocked by both 1 microM NU3076 and 1 microM dipyridamole. NU3076 also caused a significant potentiation of FU cytotoxicity in L1210 cells. These studies demonstrate that nucleoside transport inhibition can be maintained in the absence of AGP binding with the dipyridamole pharmacophore and that such analogues can enhance the cytotoxicity of TS inhibitors.

Prevention of thymidine and hypoxanthine rescue from MTA (LY231514) growth inhibition by dipyridamole in human lung cancer cell lines

The novel multitargeted antifolate, MTA (N-[4[2-(2-amino-3,4-dihydro-4-oxo-7H-pyrrolo[2,3-d]pyrimidin-5-yl)-ethy l]-benzoyl]-L-glutamic acid; LY23 1514) inhibits thymidylate synthase, dihydrofolate reductase, and glycinamide ribonucleotide formyltransferase. The resultant inhibition of the de novo thymidylate and purine biosynthesis can be circumvented by salvage of extracellular thymidine and hypoxanthine. The first step in the salvage pathway is the transport of nucleosides and bases across the cell membrane. Dipyridamole inhibits nucleoside transport and in vitro studies have demonstrated that dipyridamole can prevent thymidine salvage rescue from antifolate thymidylate synthase inhibitors. More recently, dipyridamole also has been shown to prevent hypoxanthine rescue from antipurine antifolates in some cell lines but not others. The effects of dipyridamole on MTA growth inhibition and end product reversal by thymidine and hypoxanthine was investigated in two lung cancer cell lines with (A549) and without (COR L23) dipyridamole-sensitive hypoxanthine rescue. The IC50 values for MTA-induced growth inhibition were 28 and 640 nmol/L for COR L23 and A549 cells, respectively. End product reversal studies show that thymidine can completely reverse growth inhibition by IC50 concentration of MTA but only partially rescue cells from 10 times the IC50 concentration of MTA. The combination of thymidine and hypoxanthine was required for complete reversal from MTA at 10 times the IC50 concentration. Dipyridamole blocked the partial rescue from MTA-induced growth inhibition by thymidine alone as well as the complete rescue by thymidine plus hypoxanthine not only in A549 cells, which have dipyridamole-sensitive hypoxanthine transport, but also in COR L23 cells, in which hypoxanthine uptake is insensitive to dipyridamole. These studies demonstrate that nucleoside and base salvage can compromise the activity of MTA in human tumor cell lines, but that dipyridamole can readily prevent salvage and restore growth inhibition.

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.

Carboplatin and paclitaxel, alone and in combination: dose escalation, measurement of renal function, and role of the p53 tumor suppressor gene

In this pharmacokinetic and dose-escalation study of the carboplatin/paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) combination, patients were randomly assigned to receive paclitaxel either as a 1-hour or a 3-hour infusion. The 1-hour infusion was feasible, with maximum tolerated doses similar to those previously reported for a 3-hour infusion. Using patients' age, height, plasma creatinine, and plasma creatine kinase provided an improved estimate of the glomerular filtration rate compared with the more traditional creatinine-based formulas according to population analysis of data derived from glomerular filtration rate estimates performed by an isotope method. Studies of the p53 gene sequence of ovarian tumors at diagnosis suggest that p53 mutations are a potent predictor of response to subsequent treatment with carboplatin.

Phase I studies with the nonclassical antifolate nolatrexed dihydrochloride (AG337, THYMITAQ) administered orally for 5 days

Phase I studies of p.o. administered nolatrexed dihydrochloride (AG337, THYMITAQ), a nonclassical thymidylate synthase inhibitor, were performed to establish the maximum tolerated dose and a recommended dose for Phase II studies. The bioavailability and pharmacokinetic and pharmacodynamic properties of oral nolatrexed were also studied. Forty-five patients were treated with oral nolatrexed every 6 h for 5 days at doses of 288-1000 mg/m2/day. The bioavailability of the oral preparation was determined, and the effect of a standard meal on nolatrexed absorption was investigated at a dose of 800 mg/m2/day. Nolatrexed plasma concentrations were analyzed by high-performance liquid chromatography. Nolatrexed was rapidly absorbed with a median bioavailability of 89% (range 33-116%), with 88% of patients above 70%. The dose-limiting toxicities were gastrointestinal, and the recommended Phase II oral dose was 800 mg/m2/day. After a standard meal, the peak plasma nolatrexed concentration achieved was lower (median, 8.3 microg/ml versus 15.0 microg/ml; P = 0.001), and the time taken to reach the peak was longer (median, 180 min versus 45 min; P = 0.00003), but the trough concentration was higher (median, 3.6 microg/ml versus 2.1 microg/ml; P = 0.004) when compared with the fasted state. The area under the nolatrexed plasma concentration versus time curve was not affected by food. Average trough nolatrexed concentration, but not dose, was significantly related to the % decrease in both thrombocytes (r2 = 0.58; C50 = 6.0 microg/ml, where C50 is the plasma concentration associated with a 50% decrease in thrombocytes) and neutrophils (r2 = 0.63; C50 = 0.6 microg/ml). Nolatrexed can be safely administered as an oral preparation at a dose of 800 mg/m2/day for 5 days. Bioavailability was close to 100% and, because inhibition of thymidylate synthase by nolatrexed is rapidly reversible, the slower absorption after a standard meal may result in a shorter duration of noninhibitory concentrations between doses.

Resistance-modifying agents. 5. Synthesis and biological properties of quinazolinone inhibitors of the DNA repair enzyme poly(ADP-ribose) polymerase (PARP)

Clinical studies concerning the role of poly(ADP-ribose) polymerase (PARP) in the repair of drug- and radiation-induced DNA damage have been impeded by the poor solubility, lack of potency, and limited specificity of currently available inhibitors. A series of 2-alkyl- and 2-aryl-substituted 8-hydroxy-, 8-methoxy-, and 8-methylquinazolin-4(3H)-ones has been synthesized and evaluated for PARP inhibitory activity in permeabilized L1210 murine leukemia cells. 8-Methoxy- and 8-methylquinazolinones (14-34) were readily prepared by acylation of 3-substituted anthranilamides with the appropriate acid chloride, followed by base-catalyzed cyclization. The requisite 8-hydroxyquinazolinones (6, 35-39) were synthesized by demethylation of the corresponding 8-methoxyquinazolinones with BBr3. N-Methylation of 8-methoxy-2-methylquinazolinone (15) with MeI, followed by O-demethylation by BBr3, afforded the control N3-methylquinazolinones 42 and 43, respectively. In general, an 8-hydroxy or 8-methyl substituent enhanced inhibitory activity in comparison with an 8-methoxy group. 2-Phenylquinazolinones were marginally less potent than the corresponding 2-methylquinazolinones, but the introduction of an electron-withdrawing or electron-donating 4'-substituent on the 2-aryl ring invariably increased potency. This was particularly evident in the 8-methylquinazolinone series (IC50 values 0.13-0.27 microM), which are among the most potent PARP inhibitors reported to date. N3-Methylquinazolinones 42 and 43 were essentially devoid of activity (IC50 values > 100 microM). In studies with L1210 cells in vitro, a concentration of 200 microM 8-hydroxy-2-methylquinazolinone (6, NU1025) (IC50 value 0.40 microM) potentiated the cytotoxicity of the monomethylating agent 5-(3-methyltriazen-1-yl)imidazole-4-carboxamide and gamma-radiation 3.5- and 1.4-fold, respectively, at the 10% survival level.

O6-methylguanine-DNA methyltransferase in pretreatment tumour biopsies as a predictor of response to temozolomide in melanoma

Resistance of tumour cells to methylating and monochloroethylating agents in vitro and in vivo has been linked to levels of the DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT). In a clinical trial of temozolomide in advanced malignant melanoma, the relationship between pretreatment MGMT levels in biopsies of cutaneous tumours and involved lymph nodes and clinical response to the drug has been studied. Among 50 evaluable patients, there were three complete responses (CR), four partial responses (PR), six with stable disease (SD) and 37 with progressive disease (PD), with an overall response rate of 14%. In 33 patients in whom MGMT level and clinical response could be evaluated, the tumour MGMT levels (fmol mg(-1) protein) were: CR, 158 +/- 119; PR, 607 +/- 481; NC, 171 +/- 101; PD, 185 +/- 42.3. Thus, measurements of pretreatment levels of MGMT in melanoma did not predict for response to temozolomide.

Dipyridamole potentiates antipurine antifolate activity in the presence of hypoxanthine in tumor cells but not in normal tissues in vitro

The cytotoxicity of the antifolate inhibitors of de novo purine biosynthesis, lometrexol (LTX) and LY309887, can be abolished by hypoxanthine (HPX) salvage. The nucleoside transport inhibitor, dipyridamole (DP) can prevent HPX rescue from LTX growth inhibition in a cell line-specific manner. The studies described here have shown that, excluding colon and hematological malignancies, DP prevents HPX rescue from LTX growth inhibition in approximately one-third of cell lines with otherwise limited tissue specificity. The clinical dose-limiting toxicities of antipurine antifolates are to the bone marrow and gastrointestinal tract. In vitro models of these normal tissues were established, and the effect of DP on HPX rescue from LY309887 treatment was studied. Growth inhibition assays are not feasible in these primary cultures; therefore, an alternative assay, cellular ATP depletion, was validated in four tumor cell lines as a marker of de novo and salvage purine synthesis. In LY309887-treated cells, DP prevented HPX-mediated maintenance of ATP levels only in cell lines in which DP inhibited HPX rescue from antifolate cytotoxicity. Hence, ATP depletion is a reliable indicator of sensitivity of HPX transport to DP when direct cell growth measurement is impractical. In primary cultures of human hematopoetic progenitor cells and mouse small intestine, coincubation with HPX prevented LY309887-mediated ATP depletion, which was not blocked by DP. These data suggest that DP would not prevent HPX rescue from antipurine antifolate growth inhibition in sensitive normal tissues, whereas activity against certain solid human tumors would be maintained.

A phase I and pharmacokinetic study of LY231514, the multitargeted antifolate

LY231514 is a novel antifolate that principally inhibits thymidylate synthase, but with additional folate-dependent enzyme targets. A Phase I study of single-agent LY231514 administered as a daily i.v. infusion over 10 minutes for 5 days, repeated every 3 weeks, was conducted to evaluate the maximum tolerated dose, pharmacokinetic profile, and antitumor activity of the drug using this schedule. Thirty-eight patients with advanced malignancies that were refractory or not amenable to standard therapy were treated with a total of 116 courses of LY231514, escalating treatment doses through 10 dose levels, from 0.2-5.2 mg/m2/day. No objective clinical responses were observed, although minor antitumor activity not fulfilling the response criteria was seen in three patients. A maximum tolerated dose of 4.0 mg/m2/day was determined, with neutropenia as the predominant dose-limiting toxicity. Reversible disturbances of liver biochemistry, fulfilling the protocol definitions of dose-limiting toxicity, were also observed. Other toxicities included diarrhea, mucositis, skin rash, and fatigue. Pharmacokinetic studies were performed at all treatment levels. Analysis showed a linear relation between administered dose and both maximum plasma concentration (Cmax) and area under the plasma concentration/time curve. The drug was cleared with a day 1 total body clearance of 108.9 +/- 38.8 ml/min/m2, with plasma concentrations declining with a mean harmonic terminal half-life of 1.4 +/- 0.98 h. When given by this schedule, LY231514 is tolerable, and Phase II studies are in progress.

Preclinical and phase I clinical studies with the nonclassical antifolate thymidylate synthase inhibitor nolatrexed dihydrochloride given by prolonged administration in patients with solid tumors

PURPOSE

A phase I, multicenter trial of the thymidylate synthase (TS) inhibitor THYMITAQ (nolatrexed dihydrochloride; Agouron Pharmaceuticals, Inc, San Diego, CA) given by 5-day continuous infusion was performed to establish the maximum-tolerated dose (MTD) and to investigate pharmacokinetics, pharmacodynamics, and antitumor effects.

METHODS

In vitro and in vivo preclinical studies demonstrated increased activity with prolonged nolatrexed exposure. In 32 patients, nolatrexed was given as a 5-day infusion at 96 to 1,040 mg/m2/d for 5 days. Pharmacokinetics were determined from high-performance liquid chromatography (HPLC) analyses of plasma and urine. In addition to studying toxicity, plasma deoxyuridine (UdR) elevations were measured as a marker of TS inhibition.

RESULTS

The MTD was 904 mg/m2/d for 5 days and the recommended phase II dose is 800 mg/m2/d for 5 days. The dose-limiting toxicity was neutropenia with clinically significant thrombocytopenia and mucositis. These antiproliferative toxicities of nolatrexed were predictable and reversible. A partial response that lasted 3 months occurred in a patient with metastatic colorectal cancer. Pharmacokinetics were nonlinear, with the median plasma clearance (CI) decreasing from 151 mL/min/m2 (range, 124 to 211) at 96 mg/m2/d for 5 days to 49 mL/min/m2 (range, 30 to 84) at 768 mg/ m2/d for 5 days. The half-life (t1/2) was 173 minutes (range, 43 to 784) and 18% (range, 9% to 35%) of the dose was excreted unchanged in the urine. Plasma UdR increased, but returned to pretreatment levels after the end of infusion. Hematologic toxicity was significantly related to nolatrexed plasma concentrations and dose.

CONCLUSION

Nolatrexed can be safely administered to patients at a dose of 800 mg/m2/d over 5 days by continuous intravenous infusion and this schedule is associated with antitumor effects. The phase II evaluation of nolatrexed is ongoing.

Clinical studies with MTA

MTA (LY231514), a multi-targeted antifolate, is a classical antifolate undergoing intracellular polyglutamation. Polyglutamated MTA is a potent thymidylate synthase (TS) inhibitor and inhibits other folate-dependent enzymes, including dihydrofolate reductase and glycinamide ribonucleotide formyl transferase. Multifocal antifolates may overcome antifolate resistance, but it is not known whether the anti-tumour activity of MTA depends on its TS inhibition, its primary locus of action, or whether other loci contribute. MTA was examined in three phase I trials using different schedules: a 10-min i.v. infusion given once every 3 weeks, once weekly for 4 weeks every 6 weeks or daily for 5 days every 3 weeks. Dose-limiting toxicities were neutropenia and thrombocytopenia. Other consistently seen side-effects, which were manageable, included mucositis, skin rashes and transient elevations of transaminases. Toxicity was highly schedule dependent: the recommended dose for the 3-weekly schedule (600 mg m(-2)) was 30 times that for the daily x 5 schedule (4 mg m(-2)day(-1)). The 3-weekly dosing schedule was chosen for phase II evaluation. Phase II trials are underway to investigate the activity and toxicity of MTA in several tumour types, including colorectal, pancreas, breast, bladder and non-small-cell lung cancer (NSCLC) Further phase I trials will investigate MTA in combination with other agents, including gemcitabine, cisplatin, 5-fluorouracil and folate. Preliminary phase II trials results are encouraging; responses were seen in colorectal, pancreas, NSCLC and breast cancer.

A review of the pharmacokinetics and pharmacodynamics of combination carboplatin/paclitaxel

The combination of carboplatin and paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) has been found to be highly active, to offer convenience of administration and better potential for dose escalation, and to produce less nonhematologic toxicity than standard therapy with cisplatin plus paclitaxel. Increased myelosuppression was anticipated to be a disadvantage of the carboplatin/paclitaxel combination, although it was expected to affect mainly platelets. Studies to date of the paclitaxel/carboplatin combination suggest the combination has a relatively benign effect on platelets compared with single-agent carboplatin. Previous pharmacokinetic studies have suggested that the measured area under the plasma carboplatin concentration-time curve is significantly less than that predicted by dosing formulas based on glomerular filtration rates. Newer evidence, however, contradicts these findings. This review examines the evidence of both a pharmacodynamic and a pharmacokinetic interaction between carboplatin and paclitaxel that has a sparing effect on platelets. It further assesses methodologic differences in methods used to estimate glomerular filtration. Paclitaxel appears to offer some protective effect for carboplatin-induced thrombocytopenia, although the two drugs do not interact pharmacokinetically. The apparent deviations of the achieved carboplatin area under the plasma concentration-time curve from that predicted by a dosing formula are thought to be due to differences in the methodology used to estimate renal function and measure creatinine. Any interaction between the two drugs most likely occurs at the level of the megakaryocyte.

The relationship between intrinsic thymidylate synthase expression and sensitivity to THYMITAQ in human leukaemia and colorectal carcinoma cell lines

Thymidylate synthase (TS) expression has been characterized for a panel of eight human colorectal carcinoma and five human leukaemia cell lines, to relate differences in intrinsic TS activity, protein and mRNA levels to growth inhibition caused by continuous exposure to THYMITAQ, a specific non-classical antifolate TS inhibitor. Although a 20-fold variation in sensitivity to THYMITAQ was found within the colorectal cell line panel (IC50 0.12-2.7 microM), sensitivity was not related to TS activity, TS protein or TS mRNA levels. For the leukaemic cell lines, only a twofold range in sensitivity to THYMITAQ was observed (IC50 0.87-2.3 microM), and this did not correlate with TS activity, TS protein or TS mRNA levels. Across all of the cell lines, TS activity was linearly related to TS protein levels (r2 = 0.87, P < 0.0001). However, for both the colorectal and leukaemia cell line panels, no relationship was found between TS mRNA/18S rRNA ratios and either TS activity or TS protein, consistent with the importance of post-transcriptional mechanisms in regulating TS activity. Two of the colorectal cell lines (BE and HCT116) and one of the human leukaemic cell lines (HL60), were intrinsically resistant to THYMITAQ (IC50 > 2 microM) in the absence of TS overexpression, suggesting that, subsequent to TS inhibition, events such as DNA repair and tolerance to apoptotic stimuli are also important determinants of sensitivity to THYMITAQ.

A clinical and pharmacokinetic study of the combination of carboplatin and paclitaxel for epithelial ovarian cancer

The aim of this phase I study was to determine the maximum tolerated dose of a 3-h infusion of paclitaxel, combined with carboplatin at a fixed AUC of 7 mg ml-1 min every 4 weeks for up to six cycles and to evaluate any possible pharmacokinetic interaction. Twelve chemonaive patients with ovarian cancer were treated with paclitaxel followed by a 30-min infusion of carboplatin. Paclitaxel dose was escalated from 150 mg m-2 to 225 mg m-2 in cohorts of three patients. Carboplatin dose was based on renal function. Pharmacokinetic studies were performed in nine patients (at least two at each dose level). A total of 66 courses were evaluable for assessment. Grade 3 or 4 neutropenia was seen in 70% of the courses, however hospitalization was not required. Grade 3 or 4 thrombocytopenia occurred in 24% of the courses. Alopecia, myalgia and peripheral neuropathy were common but rarely severe. The pharmacokinetics of paclitaxel was non-linear and did not appear to be influenced by co-administration of carboplatin. The AUC of carboplatin was 7.0 +/- 1.4 mg ml-1 min, indicating that there was no pharmacokinetic interaction. The combination of carboplatin and paclitaxel may be administered as first-line treatment for advanced ovarian cancer. Although myelosuppression is the dose-limiting toxicity of the component drugs, the severity of thrombocytopenia was less than anticipated. The results of this study, with only a small number of patients, need to be confirmed in future investigations.

Etoposide phosphate infusion with therapeutic drug monitoring in combination with carboplatin dosed by area under the curve: a cancer research campaign phase I/II committee study

The area under the plasma concentration-time curve (AUC) following an intravenous dose of etoposide varies considerably among patients, which in part contributes to the unpredictability of toxicity and response seen in individual patients. This study evaluated the utility of therapeutic drug monitoring of etoposide in reducing the interpatient variability of etoposide steady-state concentrations during prolonged infusion. The etoposide prodrug etoposide phosphate (Etopophos; Bristol-Myers Squibb Company, Princeton, NJ) was administered by infusion using an adaptive dosing strategy. It was given in combination with carboplatin, which was dosed on an AUC basis. Patients with histologically or cytologically proven small cell lung cancer were treated with etoposide phosphate by continuous 120-hour infusion and carboplatin at a dose calculated by the Calvert formula to give an AUC of 5 mg/ mL.min. Blood samples were taken on days 2 through 5 of each treatment cycle, and high-performance liquid chromatography was used to measure the plasma etoposide concentration. The resultant concentrations were compared with target concentrations of 1 or 2 micrograms/mL and these data were used to calculate the rate of infusion for the following 24 hours. In the first cohort, the target etoposide concentration was 1 microgram/mL, and this was achieved (mean +/- SD = 1.05 +/- 0.24 micrograms/mL) by infusing etoposide phosphate doses of 21 to 109 mg (15 to 68 mg/m2) per day. In the second cohort, the target concentration of 2.0 micrograms/mL was achieved (mean +/- SD = 2.05 +/- 0.31 micrograms/mL) with infused etoposide phosphate doses of 69 to 193 mg (41 to 114 mg/m2) per day. This technique reduced the variation in plasma levels and resulted in predictable hematologic toxicity. Cumulative hematologic toxicity necessitated an extension of the treatment cycle from 3 to 4 weeks, however. Of six evaluable patients, two had a complete response and one had a partial response. Therapeutic drug monitoring was shown to reduce the interpatient variation in the plasma etoposide concentration by half and shows promise for individualizing treatment with combination chemotherapy. Exploiting the known relationships between the pharmacokinetics and pharmacodynamics of these two drugs by using therapeutic drug monitoring may lead to better therapeutic safety and efficacy.

A phase I clinical study of the antipurine antifolate lometrexol (DDATHF) given with oral folic acid

Lometrexol is an antifolate which inhibits glycinamide ribonucleotide formyltransferase (GARFT), an enzyme essential for de novo purine synthesis. Extensive experimental and limited clinical data have shown that lometrexol has activity against tumours which are refractory to other drugs, notably methotrexate. However, the initial clinical development of lometrexol was curtailed because of severe and cumulative antiproliferative toxicities. Preclinical murine studies demonstrated that the toxicity of lometrexol can be prevented by low dose folic acid administration, i.e. for 7 days prior to and 7 days following a single bolus dose. This observation prompted a Phase I clinical study of lometrexol given with folic acid supplementation which has confirmed that the toxicity of lometrexol can be markedly reduced by folic acid supplementation. Thrombocytopenia and mucositis were the major toxicities. There was no clear relationship between clinical toxicity and the extent of plasma folate elevation. Associated studies demonstrated that lometrexol plasma pharmacokinetics were not altered by folic acid administration indicating that supplementation is unlikely to reduce toxicity by enhancing lometrexol plasma clearance. The work described in this report has identified for the first time a clinically acceptable schedule for the administration of a GARFT inhibitor. This information will facilitate the future evaluation of this class of compounds in cancer therapy.

Bioequivalence assessment of etoposide phosphate and etoposide using pharmacodynamic and traditional pharmacokinetic parameters

The bioequivalence of etoposide phosphate, a prodrug of etoposide, to etoposide was assessed in a randomized, crossover study in 29 patients with histologically established solid tumors that had failed conventional treatment. Cohorts of patients received one treatment course each of etoposide and etoposide phosphate which consisted of a 100 mg/m2 per day etoposide equivalent dose infused i.v. over 1 hr on a Day 1 to 5 schedule of treatment. The second course was administered 21 days later or on recovery of blood cell counts. Plasma and urine samples were collected over 24 hr on Day 1 of each course and assayed for etoposide content by a validated HPLC/UV method. Resulting data were subjected to noncompartmental pharmacokinetic analysis. Hematology profiles were obtained by collecting blood samples prior to the first course and twice a week after each course. The pharmacodynamics and pharmacokinetics of etoposide were virtually identical after the two treatments. The point estimates (90% confidence intervals) for nadir WBC, granulocytes, hemoglobin, and platelets expressed as % decrease from the baseline, and for the pharmacokinetic parameters, Cmax, and AUC0 infinity, after intravenous etoposide phosphate relative to etoposide were 100% (96%, 105%), 97% (91%, 103%), 95% (82%, 109%), 95% (84%, 106%), 107% (101%, 113%), and 113% (107%, 119%), respectively. Therefore, etoposide phosphate is bioequivalent to etoposide based on pharmacokinetic and pharmacodynamic assessments.

Alternatively spliced mdm2 transcripts with loss of p53 binding domain sequences: transforming ability and frequent detection in human cancer

The mdm2 oncogene encodes a 90-kilodalton nuclear phosphoprotein that binds and inactivates the p53 tumor suppressor protein. Here we report the observation of five alternatively spliced mdm2 gene transcripts in a range of human cancers and their absence in normal tissues. Transfection of NIH 3T3 cells with each of these forms gave foci of morphologically transformed cells. A higher frequency of splice variants lacking p53 binding domain sequences was found in late-stage and high-grade ovarian and bladder carcinomas. Four of the splice variants show loss of p53 binding, consistent with partial deletion of sequences encoding the p53 binding domain, but retain carboxyterminal zinc-finger domains. These observations suggest a reassessment of the transforming mechanisms of mdm2 and its relation to p53.

The relationship between tumour glutathione concentration, glutathione S-transferase isoenzyme expression and response to single agent carboplatin in epithelial ovarian cancer patients

There is evidence to suggest that glutathione (GSH) and glutathione-S-transferases (GST) are important factors in determining sensitivity to cytotoxic drugs in vitro and in preclinical in vivo model systems. To define the relationship between tumour GSH concentration, GST isoenzyme expression and response to carboplatin in epithelial ovarian cancer (EOC), tumour samples from 39 patients with assessable disease after primary surgery were analyzed for GSH content and GST expression. Response was assessed after completing six courses of single agent carboplatin therapy. GSH was measured by high performance liquid chromatography (HPLC) in fresh tumour samples taken at primary laparatomy. GST isoenzyme expression was assessed by immunohistochemistry of fixed tumour material using antibodies specific for pi, alpha and mu classes. GST isoenzyme expression was defined as positive if the staining intensity was strong and more than 10% of tumour cells were involved. The mean GSH concentrations were: 8351 +/- 4496, 7211 +/- 5026, 6559 +/- 4573 and 3758 +/- 1885 (nmol g-1 tissue dry weight mean +/- s.d.) for tumours from patients who subsequently achieved a complete response (CR, n = 18), partial response (PR, n = 10) or who had static disease (SD, n = 7) or progressive disease (PD, n = 4) respectively. There was no relationship between GSH concentration and response (ANOVA, P = 0.32). There were also no relationship between GST isoenzyme expression and response (P Fisher's exact test 0.51-0.55 and chi-squared test 0.98-0.99). In conclusion, there was no association between the concentration of GSH or expression of GST isoenzymes and response to single agent carboplatin in primary previously untreated EOC.

A single-sample assay for the estimation of the area under the free carboplatin plasma concentration versus time curve

The aim of this study was to develop and validate a simple and rapid method for the estimation of the area under the free carboplatin plasma concentration versus time curve (AUC). The relationship between the carboplatin AUC and the total plasma platinum (Pt) concentration 24 h after treatment was studied using data from 49 patients treated with 20-1600 mg/m2 carboplatin as a 60-100 min infusion (median 60 min). The relationship was confirmed by the in vitro incubation of carboplatin in human plasma and prospectively validated in 13 ovarian cancer patients. Free carboplatin was separated by ultrafiltration (MW cut off 30,000), and free and total Pt measured by atomic absorption spectrophotometry. There was a linear relationship in vivo between the 24 h (median 24.4; range 16.3-27.3 h) total plasma Pt concentration (microM) and free carboplatin AUC (mg/ml.min): AUC=(24 h Pt+0.3)/0.82 (r2=0.93, AUC median 5.8 (0.13-28)mg/ml.min, 24h Pt median 4.4 (0.1-23) microM). A similar relationship was observed in vitro [AUC =(24h Pt +0.1)/0.93 (r2=0.98, AUC median 7.9 (2.0-17) mg/ml.min, 24 h Pt median 7.1 (1.8-15) microM)]. The relationship derived from the in vivo data gave an unbiased and reasonably accurate estimate of the measured carboplatin AUC in 13 patients (AUC =5.1-8.7 mg/ml.min, GFR=59-129 ml/min, infusion time 30-45 min, 24 h sampling time 22.9-24.5 h), giving a percentage mean error of -4.2% and root mean squared percentage error of 11.5%. These results show that the analysis of a single blood sample taken 24 h after carboplatin administration can be used to produce an unbiased and reasonably accurate measure of the free carboplatin AUC. Unlike published limited sampling strategies, this method is not complicated by the need to accurately control the duration of the carboplatin infusion or the time at which the sample is taken.

Phase I study of pharmacologically based dosing of carboplatin with filgrastim support in women with epithelial ovarian cancer

PURPOSE

The aim of this study was to increase the dose intensity of carboplatin in women with International Federation of Gynecology and Obstetrics (FIGO) Stage Ic-IV epithelial ovarian cancer with the use of granulocyte colony-stimulating factor (G-CSF; filgrastim; Amgen, Thousand Oaks, CA).

PATIENTS AND METHODS

A phase I study of escalating target area under the curves (AUCs) of carboplatin with G-CSF (filgrastim) ws undertaken. The target AUCs were 5 mg/mL.min every 21 days for four cycles, 5 mg/mL.min every 14 days for four cycles, 7 mg/mL.min every 14 days for four cycles, 9 mg/mL.min every 14 days for four cycles, and 11 mg/mL.min every 14 days for four cycles. G-CSF was given at a dose of 5 microg/kg/d starting 24 hours after carboplatin administration and lasting until 24 hours before the next cycle and until day 14 after the last cycle.

RESULTS

We were able to escalate to an AUC level of 9 mg/mL.min every 14 days for four cycles. At this dose, severe thrombocytopenia, that necessitated dosage delays, and failure to give subsequent cycles of carboplatin were observed. We then reduced the AUC level to 8 mg/mL.min every 14 days for four cycles. However, severe thrombocytopenia was also observed at this level.

CONCLUSION

An AUC of 7 mg/mL.min every 14 days for four cycles is the maximum tolerated AUC level that can be achieved with G-CSF. Further escalations may be possible using either combinations of cytokines or peripheral stem-cell collections.

Clinical pharmacokinetics of the antipurine antifolate (6R)-5,10- dideaza-5,6,7,8-tetrahydrofolic acid (Lometrexol) administered with an oral folic acid supplement

(6R)-5,10-Dideaza-5,6,7,8-tetrahydrofolic acid (lometrexol) is an antipurine antifolate which selectively inhibits glycinamide ribonucleotide formyltransferase. Lometrexol pharmacokinetics were evaluated in 17 patients (32 courses) as part of a Phase I study in which folic acid supplementation was used to improve tolerance to the drug, its clinical utility being previously limited by severe cumulative toxicity. Lometrexol was administered as an i.v. bolus every 4 weeks at a starting dose of 12 mg/m2, with subsequent interpatient dose escalation to 16, 30, and 45 mg/m2. p.o. folic acid (5 mg/day) was given for 7 days before and 7 days after lometrexol administration. The disposition of total lometrexol in plasma was best described by a biexponential model for data acquired up to 12 h after drug administration, although triexponential plasma pharmacokinetics were often found to give a more adequate description when data were available at later time intervals (24 h and greater). Mean plasma half-lives (+ SD) for model-dependent analysis were t1/2alpha 19 +/- 7 min, t1/2beta 256 +/- 96 min, and t1/2gamma (where measurable) 1170 +/- 435 min. Lometrexol area under plasma concentration versus time curve was proportional to the dose administered. Moderate plasma protein binding of lometrexol was evident (78 +/- 3%) with an inverse linear relationship between fraction of unbound lometrexol and the concentration of serum albumin. The volume of distribution of lometrexol at steady state was between 4.7 and 15.8 l/m2. Renal elimination of lometrexol, studied in 19 patients (21 courses), was considerable, accounting for 56 +/- 17% of the total dose administered within 6 h of treatment, and 85 +/- 16% within 24 h of treatment. These recoveries of unchanged lometrexol indicate that the drug does not appear to undergo appreciable systemic metabolism at the range of concentrations studied. Lometrexol pharmacokinetics were also examined in seven patients who received 45 or 60 mg/m2 lometrexol as part of a separate study of the drug given with folinic acid rescue 5-7 days after treatment. No marked differences were evident in lometrexol plasma half-lives, plasma clearance, or the extent of plasma protein binding, indicating that there is not a pronounced pharmacokinetic interaction between lometrexol and folic acid.