Pegamotecan

Purpose: To determine the maximal tolerated dose and dose-limiting toxicities (DLT) of pegamotecan (polyethylene glycol-camptothecin) in patients with advanced malignancies when administered in cycles of once weekly for 3 of 4 weeks.Experimental Design: Eligible patients had advanced solid tumors that failed to respond to standard therapy or for which no standard therapy was available, including also the following criteria: measurable disease, Eastern Cooperative Oncology Group performance status of ≤2, and acceptable organ function. Pegamotecan was administered as a 60-minute infusion, with successive patient cohorts receiving escalating doses from 800 to 4,300 mg/m2. The primary end point was to determine the maximal tolerated dose. Other end points were toxicity, pharmacokinetics, pharmacodynamics, and efficacy. Pharmacokinetic analysis measured free camptothecin. Pharmacodynamic analysis correlated drug effects with pegamotecan dose and pharmacokinetic variables.Results: Twenty-seven patients were enrolled. The maximal tolerated dose was 3,240 mg/m2. Grade 4 neutropenia, the DLT, was noted in two of four patients treated at 4,300 mg/m2. Other grade 3 and 4 toxicities were anemia, thrombocytopenia, fatigue, prolonged partial thromboplastin time, hemorrhagic cystitis, dysuria, and urinary frequency. Pharmacokinetic analysis showed the apparent terminal elimination half-life to be 46 ± 12.8 hours. Pharmacodynamic analysis showed that hematuria occurred in 8 of 15 patients with an area under the curve extrapolated to infinity (AUC0-∞) > 20 ng h/mL and 0 of 10 patients with an AUC0-∞ ≤ 20 ng h/mL. Unconfirmed partial responses were observed in two patients, one with metastatic small bowel adenocarcinoma and the other with metastatic esophageal cancer.Conclusions: The maximal tolerated dose of pegamotecan when administered weekly for 3 of 4 weeks is 3,240 mg/m2. The DLT was neutropenia. Among nonhematologic toxicities, the incidence of gastrointestinal toxicity was low, but genitourinary toxicity seems to occur in the same effective dose range as noted with native camptothecin in earlier trials (27-43 mg/m2). The observed antitumor activity suggests that pegamotecan has single-agent activity and merits further investigation in phase 2 studies.

The primary purpose of this study was to screen individual amino acid spacers in polyethylene glycol (PEG) conjugated camptothecin for their impact on the conjugates' antitumor activity. Secondly, an active member of this series was used to assess the PEG-camptothecin conjugate's efficacy against a battery of solid tumor types. PEG-camptothecin is a novel water soluble transport form (macromolecular prodrug) of the naturally derived antitumor drug, 20-(S)-camptothecin (CPT). Rates of hydrolysis were studied in phosphate buffered saline (PBS) and the plasma of both rats and humans. In vivo efficacy screens were performed against P388/0 murine leukemia and LS174T human colon solid tumor xenograft models. The results showed that while all the derivatives had considerable stability in PBS, their rates of hydrolysis varied in both rat and human plasma according to the amino acid spacer employed. Not surprisingly, changing the amino acid also affected in vivo toxicity and efficacy in the treatment of ascites and solid tumors. A representative of this amino acid series, PEG-alanine-CPT, which showed moderate activity in the solid tumor screen, was chosen for evaluation of efficacy across a wide range of solid tumor types and demonstrated significant antitumor activity (% T/C < 30%) in all tested xenograft models (colon, ovarian, mammary, lung, pancreatic and prostate). Therefore, this study showed that the use of specific amino acid spacers affected both the PEG-camptothecin conjugates' breakdown and biological activity. We anticipate that using these insights, this soluble macromolecular transport technology could be successfully employed with a number of antitumor drugs.