Clinical investigation: pancreas
Concurrent chemoradiotherapy with gemcitabine and cisplatin for pancreatic cancer: from the laboratory to the clinic

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Abstract

Purpose: We have reported that gemcitabine and concurrent radiation is a promising therapy for patients with pancreatic cancer. We investigated whether the addition of cisplatin, which may increase the systemic efficacy of gemcitabine, would be synergistic with gemcitabine and/or radiation in human pancreatic cancer cell lines.

Methods and Materials: BxPc3 and Panc-1 human pancreatic cancer cells were treated with three different schedules before radiation: (A) a sequential incubation of gemcitabine for 2 h followed by cisplatin for 2 h, (B) gemcitabine for 2 h, followed by washout of drug, replenishment of media for a 24-h incubation, followed by cisplatin for 2 h, and (C) gemcitabine for 24 h with a concurrent incubation of cisplatin for the last 2 h. Cells were assessed for clonogenic survival using a standard assay. Synergism was evaluated by the median effect analysis.

Results: The schedule shown to be maximally synergistic for both cell lines was the consecutive 2-h gemcitabine, 2-h cisplatin exposure, particularly at surviving fractions of <0.5. Cisplatin did not produce radiosensitization nor did it affect gemcitabine-mediated radiosensitization.

Conclusion: Cisplatin produces synergistic cytotoxicity with gemcitabine without compromising gemcitabine-mediated radiosensitization. On the basis of these laboratory and previous clinical observations, we have initiated a Phase I trial of cisplatin plus gemcitabine and radiotherapy in patients with unresectable pancreatic cancer.

Introduction

Concomitant radiation (RT) and 5-fluorouracil has been reported to modestly improve the median survival of patients with unresectable pancreatic cancer in a number of randomized clinical trails 1, 2, 3, 4, 5. Considering the minimal decrease in distant metastases and the relatively low dose of fluorouracil in these studies, it is likely that radiosensitization was responsible for the slight improvement in median survival produced by combined modality therapy. In the adjuvant setting, however, a recent large European randomized trial showed little benefit for the combination of RT and 5-fluorouracil in patients undergoing complete resection (6).

The search for a more effective combined modality therapy led to the evaluation and recognition of 2′2′-diflouro-2′-deoxycytidine (dFdCyd) (gemcitabine) as a potent RT sensitizer of human pancreatic cancer cells (7). The observation that radiosensitization is maximized when cytotoxic concentrations of drug are used has prompted the approach investigated at the University of Michigan using full-dose gemcitabine with concurrent three-dimensional conformal RT to a small field in pancreatic cancer patients (8). It was hypothesized that the use of conformal RT would minimize toxicity and permit the administration of full-dose chemotherapy to maximize the efficacy of systemic treatment. Local control did not appear to be compromised by smaller RT fields, and failures were predominantly systemic, in the liver and peritoneum (8). Compared with strategies combining less chemotherapy with conventional RT 9, 10, this combined modality approach, which emphasizes systemic therapy appears to have an improved therapeutic ratio, with significantly less gastrointestinal toxicity and a favorable median survival.

Given the pattern of failure in our gemcitabine-RT trial, we wished to design a new therapy that would preserve this apparent improvement in local control without increasing toxicity, while offering the potential for more intensive systemic therapy. Cisplatin seemed to be an excellent candidate drug. The combination of cisplatin and gemcitabine has been shown to be synergistic in a number of human cancer cell lines, such as ovarian cancer, head-and-neck cancer, and non-small-cell lung cancer 11, 12, 13, 14, 15. In addition, a Phase II study of gemcitabine and cisplatin in advanced pancreatic cancer (16) has demonstrated increased response rates compared with gemcitabine alone (17). Thus, we set out to study whether gemcitabine and cisplatin are synergistic in human pancreatic cancer cell lines and to determine a rational schedule for their combination with RT in preparation for a clinical study.

Section snippets

Cell culture

Panc-1 and BxPc3 human pancreatic cancer cells were obtained from the American Type Culture Collection and were maintained in Roswell Park Memorial Institute (RPMI) medium containing 10% bovine serum in an atmosphere of 93% air and 7% carbon dioxide. Cells were checked for mycoplasma contamination every 3 months.

Cell survival assay

BxPc3 and Panc-1 cells were trypsinized, plated, incubated for 48 h at 37°C, and then treated with gemcitabine, cisplatin, and RT administered using three different schedules as shown

Results

First, we determined the cytotoxicity of gemcitabine and cisplatin on Panc-1 and BxPc3 cells. For gemcitabine, the cells were incubated for a 2-h period, because the effects of gemcitabine on dNTP pool depletion occur during the first 30 min and plateaued by 2 h (20). For cisplatin, clonogenicity was determined after a 2-h incubation when the levels of platinum-AG adducts, which are thought to be the cytotoxic lesion, have peaked in most cell lines (21). We chose to evaluate 3 different

Discussion

In this study, we demonstrated that the combination of gemcitabine and cisplatin is synergistic in inducing cytotoxicity in 2 human pancreatic cancer cell lines. The schedule shown to be maximally synergistic was a consecutive 2-h gemcitabine, 2-h cisplatin exposure. The mechanism of this synergy is not fully elucidated. Some evidence has demonstrated that the incorporation of 2′2′-difluoro-2′-deoxycytidine triphosphate (dFdCTP) into DNA leads to conformational changes, affecting the binding of

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    Supported by NCI grants CA 78554, Cancer Center Core Grant CA 46592 and AACR/ASCO/FECS workshop at Flims, 1999, CA 82242.

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