Library

Notes: [Auszug] Cytochrome P450 3A4 is an important mediator of drug catabolism that can be regulated by the steroid and xenobiotic receptor (SXR). We show here that SXR also regulates drug efflux by activating expression of the gene MDR1, which encodes the protein P-glycoprotein (ABCB1). Paclitaxel (Taxol), a ...

Notes: Abstract Purpose: The triphenylethylenes tamoxifen and toremifene have been reported to enhance the cytotoxicity of cisplatin by inhibition of protein kinase C (PKC) signal transduction pathways. However, the concentrations of tamoxifen and toremifene required for chemosensitization in preclinical models are generally ≥5 μM, at least tenfold higher than plasma levels observed in patients receiving these agents as antiestrogenic therapy. As part of a translational phase II trial investigating the efficacy and potential molecular mechanism of high-dose toremifene as a cisplatin modulator in metastatic non-small-cell lung cancer, plasma concentrations of toremifene and its active metabolite N-desmethyltoremifene were measured to determine whether targeted levels could be achieved clinically. Methods: Treatment consisted of toremifene, 600 mg orally on days 1–7, and cisplatin, 50 mg/m2 intravenously on days 4 and 11, repeated every 28 days. Toremifene and N-desmethyltoremifene were measured by reverse-phase HPLC assay on days 4 and 11 prior to cisplatin infusion. Results: In the initial 14 patients, the mean total plasma concentrations of toremifene plus its N-desmethyl metabolite on days 4 and 11 were 14.04 (±8.6) μM and 9.8 (±4.4) μM, respectively. Variability in concentrations achieved did not correlate with renal or hepatic function, gender, or body surface area. Levels of N-desmethyltoremifene were higher on day 11 relative to toremifene concentrations. Conclusions: We conclude that plasma levels achieved compare favorably with the levels required for cisplatin chemosensitization and PKC modulation in vitro. Targeted toremifene levels can be achieved clinically with 600 mg orally daily in combination with cisplatin and are well tolerated.

Notes: Abstract Purpose: In recognition of the variety of available chemotherapeutic modulating agents and their potential to enhance the efficacy of platinum-based therapy, we embarked upon a phase I study to investigate the feasibility of combining fixed doses of carboplatinum (CBDCA) and etoposide (VP-16) with 24-h concurrent infusions of dipyridamole (DP), prochlorperazine (PCZ) and cyclosporine A (CSA) administered in escalating doses. Methods: Patients received intravenous VP-16 (200 mg/m2) and CBDCA (300 mg/m2), each over 30 min, starting at hour 6 of the modulator infusions. Resistance modulators were escalated sequentially to determine their respective maximally tolerated doses (MTDs). The pharmacokinetics (PK) of VP-16, CBDCA, and the three drug resistance (DR) modifiers were studied in eight patients. Results: A total of 59 patients were entered on study. The MTD was established at DP 5 mg/kg per day, PCZ 24 mg/h, and CSA 9.5 mg/kg per day. Dose-limiting toxicities included hypotension and severe sedation, presumably related to PCZ. No objective responses were seen. PK studies were performed when PCZ and DP doses were 24 mg/h and 3.3 mg/kg, and the CSA dose was either 8.5 mg/kg (five patients) or 9.5 mg/kg (three patients). The median clearance of VP-16 was 0.96 l/h per m2 (range 0.8–1.5 l/h per m2), which is lower than for VP-16 alone and similar to previously reported effects of CSA on VP-16 elimination. The median measured CBDCA AUC was 3.0 mg/ml · min (range 2.4–4.8 mg/ml · min). CBDCA AUC predicted by the Calvert formula using measured creatinine clearance underestimated the actual AUC in seven of the eight patients, in one case by as much as twofold. The median end of infusion PCZ and total DP plasma concentrations were 1.2 μM (range 0.5–2.2 μM) and 4.4 μM (range 1.3–5.9 μM), respectively, consistent with in vitro resistance modulatory levels. However, free DP was only 0.02 μM (range 0.004–0.04 μM). The median CSA level at 24 h of 1450 μg/l (range 1075–1640 μg/l) is in agreement with concentrations required for partial DR reversal in vitro, although it is much lower than levels achieved in our previous phase I study of CBDCA + CSA alone using similar doses of CSA. The CSA dose on the current trial was escalated beyond the MTD for the previous phase I study, suggesting that there may be an interaction between CSA and one of the other modulators. Conclusion: These results demonstrate that in vitro DR- reversing levels of two of the three agents used in this study can be achieved in vivo, and that this combination of DR modulators has significant effects on the pharmacokinetics of VP-16.

Notes: Abstract The topoisomerase I inhibitor 9-dimethylaminomethyl-10-hydroxycamptothecin (topotecan) was evaluated against a panel of xenografts comprising four lines of adult colon adenocarcinoma, three colon tumors derived from adolescents, six childhood rhabdomyosarcomas from previously untreated patients as well as sublines selected in vivo for resistance to vincristine and melphalan, and three lines of childhood osteogenic sarcoma. Efficacy was determined at maximal tolerated dose levels using intermittent i.p. administration [every 4 days for 4 doses (q4d×4)] or daily p.o. or i. p. administration 5 days per week for up to 20 courses. On a q4d×4 schedule, the maximum tolerated dose (MTD) was 12.5 mg/kg per administration, which caused marked weight loss and lethality in ≈5% of the tumor-bearing mice. This schedule caused significant growth inhibition (but no tumor regression) in advanced adult colon adenocarcinomas. The minimal treated/control (T/C) ratios were 0.49, 0.54, and 0.3 for three of the tumor lines and were achieved at 18–21 days after the initiation of treatment. In contrast, rhabdomyosarcomas were considerably more sensitive, with T/C ratios being 〈0.1 for three lines, whereas topotecan was less active against two other rhabdomyosarcoma xenografts (minimal T/C ratios, 0.17 and 0.14). As inhibitors of topoisomerase I have been demonstrated to have activity in the replication phase of the cell cycle (S-phase-specific), prolonged administration schedules were examined. Mice received topotecan 5 days per week for 3 weeks either by i.p. injection or by oral gavage (p.o.). In selected experiments, p.o. administration was continued for up to 20 weeks. Oral administration for 3 weeks (2 mg/kg per dose) resulted in complete regression of all six lines of rhabdomyosarcoma, with two lines demonstrating no regrowth during the period of observation (≥84 days). Similar results were obtained after i.p. administration, suggesting significant schedule dependency for these tumors. For colon tumors, the daily administration schedule (i.p. or p.o.) demonstrated some advantage over the intermittent schedule, resulting in partial regressions and significant inhibition of the growth of several colon adenocarcinoma lines. In rhabdomyosarcoma Rh 12 and VRC5 colon adenocarcinoma, both of which demonstrated intermediate sensitivity to topotecan, and in osteosarcoma OS33, protracted p.o. administration for 13–20 weeks (1.0–1.5 mg/kg per dose given daily x 5 days) caused complete regression without regrowth in Rh12 and OS33 tumors and partial regression of all VRC5 tumors. No toxicity was observed using this schedule of administration. Topotecan demonstrated significant activity against all three osteosarcoma xenografts examined, with optimal schedules causing complete regression in two lines. Topotecan demonstrated similar activity against KB 3-1 and KB 8-5 multidrug-resistant cells in culture, and the Rh 12/VCR an Rh 18/VCR xenografts selected for vincristine (VCR) resistance in vivo were as sensitive as their parental lines. However, Rh 28/L-PAM, selected for resistance to melphalan, was cross-resistant to topotecan. Plasma pharmacokinetics studies were carried out at the respective MTD for oral (2 mg/kg) or i.p. (1.75 mg/kg) administration. During oral administration the maximal plasma concentration (of the active lactone) was achieved at 0.25 h (Cmax 41.7 ng/ml) and thet 1/2α andt 1/2β values were 0.55 and 2.8 h, respectively. Administration i.p. resulted in peak plasma levels of 523 ng/ml, witht 1/2α andt 1/2β elimination rates being 0.29 and 2.5 h, respectively. Although i.p. administration resulted in a 3-fold increase in AUC as compared with oral dosing, similar antitumor activity was observed against most xenograft lines. These results suggest that topotecan may have significant activity against several human cancers and that its efficacy may be schedule-dependent. Topotecan may have a particular role to play in the treatment of childhood solid tumors such as rhabdomyosarcoma and osteosarcoma.

Notes: Abstract Purpose: Lometrexol [(6R)-5,10-dideaza-5,6,7,8-tetrahydrofolate] is the prototype folate antimetabolite that targets the de novo purine synthesis pathway. Early phase I trials were confounded by cumulative myelosuppression that prevented repetitive administration. Subsequent preclinical and clinical studies suggested that coadministration of folic acid might favorably modulate lometrexol toxicity without eliminating potential antitumor activity. We set out to determine if concurrent folic acid would allow administration of lometrexol on a weekly schedule, and, if so, to identify an appropriate dose combination for phase II trials. Pharmacokinetic and metabolism studies were undertaken in an attempt to improve our understanding of lometrexol pharmacodynamics. Methods: Patients with advanced cancer received daily oral folic acid beginning 7 days before lometrexol and continuing for 7 days beyond the last lometrexol dose. Lometrexol was administered by short i.v. infusion weekly for 8 weeks. Scheduled lometrexol doses were omitted for toxicity of more than grade 2 present on the day of treatment, and dose-limiting toxicity was prospectively defined in terms of frequency of dose omission as well as the occurrence of severe toxic events. Plasma and whole blood total lometrexol contents (lometrexol plus lometrexol polyglutamates) were measured in samples taken just prior to each lometrexol dose. Results: A total of 18 patients were treated at five lometrexol dose levels. The maximum tolerated dose was identified by frequent dose omission due to thrombocytopenia and mucositis. The recommended phase II dose combination is lometrexol 10.4 mg/m2 per week i.v. with folic acid 3 mg/m2 per day orally. One patient with melanoma experienced a partial response, and three patients, two with melanoma and one with renal cell carcinoma, experienced stable disease. Lometrexol was not detectable in any predose plasma sample tested. The total red blood cell content of lometrexol increased over several weeks and then appeared to plateau. Conclusions: Weekly administration of lometrexol is feasible and well-tolerated when coadministered with daily oral folic acid. The nature of the interaction between natural folates and lometrexol that renders this schedule feasible remains unclear. A definition of dose-limiting toxicity that incorporated attention to dose omissions allowed efficient identification of a recommended phase II dose that reflects the maximum feasible dose intensity for a weekly schedule. Lometrexol is a promising, anticancer agent.