Cetuximab, intensity-modulated radiotherapy (IMRT), and twice-weekly gemcitabine for pancreatic adenocarcinoma

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Background: Epidermal growth factor receptor (EGFR) is over expressed in pancreatic cancer. Cetuximab is an EGFR-antagonist which has synergy with gemcitabine (gem) and radiation. Gem is a potent radiosensitizer. We are conducting a Phase II trial of cetuximab with IMRT and twice-weekly gem. Eligibility includes stage I-III adenocarcinoma, with EGFR staining by immunohistochemistry. Pretreatment evaluation includes chest/abdomen CT scan and laparoscopy. Methods: Cetuximab 400 mg/m2 IV load was given over two hours. One week later, treatment continued with weekly cetuximab 250mg/m2 IV over one hour, and gem 50mg/m2 IV twice-weekly for twelve doses, concurrent with IMRT given in 28 daily fractions to 54Gy. Cetuximab/gem was given prior to that day’s IMRT. GI prophylaxis was with a proton pump inhibitor. Patients were considered for resection 4–8 weeks following therapy. Results: Ten patients enrolled to date, median age 70 years (range 54–83). Ninety percent of tumors were EGFR positive (range 1+ to 3+). At presentation, three tumors were unresectable, three borderline resectable and four resectable. One patient was removed from study following cetuximab anaphylaxis. Eight patients experienced grade III-IV hematotoxicity. Two patients had ischemic stroke in the backdrop of infection, one from stent obstruction/cholangitis, the other during neutropenic fever. One of these patients (age 81) died. Autopsy revealed severe atherosclerotic disease and evidence of prior strokes. Eight patients were evaluable for response. No patient had local progression. One patient had liver metastases post treatment. Two patients (25%) exhibited partial response. All others had stable disease. EGFR over expression did not predict response. Six patients went on to margin (−) resection, including one patient each with borderline resectable and unresectable disease prior to therapy. At median follow up of 8.5 months, there were no recurrences. Conclusions: Therapy yields modest efficacy and high resectability rates in patients with pancreatic cancer. Downstaging of tumor can occur in some patients. Toxicity may in part reflect the elderly patient demographic. Planned accrual is 48 patients.

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Dual role of glutathione in modulating camptothecin activity: depletion potentiates activity, but conjugation enhances the stability of the topoisomerase I-DNA cleavage complex

Depletion of glutathione (GSH) in MCF-7 and MDA-MB-231 cell lines by pretreatment with the GSH synthesis inhibitor buthionine sulfoximine potentiated the activity of 10,11-methylenedioxy-20(S)-camptothecin, SN-38 [7-ethyl-10-hydroxy-20(S)-camptothecin], topotecan, and 7-chloromethyl-10,11-methylenedioxy-20(S)-camptothecin (CMMDC). The greatest potentiation was observed with the alkylating camptothecin CMMDC. Buthionine sulfoximine pretreatment also increased the number of camptothecin-induced DNA-protein crosslinks, indicating that GSH affects the mechanism of action of camptothecin. We also report that GSH interacts with CMMDC to form a stable conjugate, 7-(glutathionylmethyl)-10,11-methylenedioxy-20(S)-camptothecin (GSMMDC), which is formed spontaneously in buffered solutions and in MCF-7 cells treated with CMMDC. GSMMDC was synthesized and found to be nearly as active as 10,11-methylenedioxy-20(S)-camptothecin in a topoisomerase (topo) I-mediated DNA nicking assay. The resulting topo I cleavage complexes were remarkably stable. In cell culture, GSMMDC displayed potent growth-inhibitory activity against U937 and P388 leukemia cell lines. GSMMDC was not active against a topo I-deficient P388 cell line, indicating that topo I is its cellular target. Peptide-truncated analogues of GSMMDC were prepared and evaluated. All three derivatives [7-(gamma-glutamylcysteinylmethyl)-10,11-methylenedioxy-20(S)-camptothecin, 7-(cysteinylglycylmethyl)-10,11-methylenedioxy-20(S)-camptothecin, and 7-(cysteinylmethyl)-10,11-methylenedioxy-20(S)-camptothecin] displayed topo I and cell growth-inhibitory activity. These results suggest that 7-peptidyl derivatives represent a new class of camptothecin analogues.