Cancer Therapy: Preclinical Concurrent and Sequential Administration of Chemotherapy and the Mammalian Target of Rapamycin Inhibitor Temsirolimus in Human Cancer Cells and Xenografts

Purpose: Optimal scheduling of cycle-active chemotherapy with (initially cytostatic) molecular-targeted agents is important to maximize clinical benefit. Concurrent scheduling might allow up-regulation of cell death pathways at the time of chemotherapy, whereas sequential treatments might maximize inhibition of repopulation and avoid putting tumor cells out of cycle when administering cycle-active chemotherapy. We compared the effects of concurrent and sequential administration of chemotherapy and the mammalian target of rapamycin (mTOR) inhibitor temsirolimus (CCI-779) on tumor cells and xenografts. Experimental Design: Human prostate cancer PC-3 and LnCaP, and human breast cancer MDA-468 cells and xenografts were treated with chemotherapy (docetaxel and 5-fluorouracil, respectively) and temsirolimus, using concurrent and sequential treatment schedules. Cell killing and repopulation were evaluated by clonogenic assays. Cell cycle analysis was done using flow cytometry. Effects on xenografts were assessed by tumor growth delay. Results: The proliferation of all cell lines was inhibited by temsirolimus in a dosedependent manner; PTEN negative PC-3 and mutant LnCaP cells were more sensitive than PTEN-negative MDA-468 cells. Temsirolimus inhibited cell cycle progression from G1 to S phase in all cell lines. Combined treatment had greater effects than temsirolimus or chemotherapy alone: for PC-3 and LnCaP xenografts, concurrent treatment seemed superior to sequential scheduling, whereas MDA-468 cells and xenograft tumors did not show schedule dependence. Conclusions: Combined treatment with temsirolimus and chemotherapy had a greater therapeutic effect than monotherapy; concurrent scheduling was more effective for PC-3 and LnCaP cells and xenografts that were sensitive to temsirolimus. (Clin Cancer Res 2009;15(17):5389–95) Clinical benefit from chemotherapy is limited by systemic toxicity and by drug resistance. Most studies of drug resistance have concentrated on cellular and molecular mechanisms operating at the level of a single cell (reviewed in ref. 1), but limited drug distribution within tumors and repopulation of surviving tumor cells between cycles of chemotherapy are important and neglected causes of clinical drug resistance (2–5). Repopulation of tumor cells between successive courses of chemotherapy may accelerate, and may lead to acquired resistance in the absence of changes in the intrinsic sensitivity of the tumor cells (2, 3, 6). Many molecular-targeted agents are being introduced in the clinic; their initial effects are usually cytostatic, and these agents have considerable potential for inhibiting repopulation. For example, cetuximab, an inhibitor of the epidermal growth factor receptor, has been shown to increase survival of patients receiving radiotherapy for head and neck cancer (7), and the most likely mechanism is inhibition of repopulation during the course of radiotherapy. Inhibition of repopulation by cytostatic agents between cycles of chemotherapy is more complex because most chemotherapy drugs are more active against cycling cells, and the outcome may depend markedly on schedule. Concurrent scheduling might allow up-regulation of cell death pathways at the time of chemotherapy, whereas sequential treatments might maximize inhibition of repopulation and avoid putting tumor cells out of cycle when administering cycle-active chemotherapy. Temsirolimus (CCI-779), an inhibitor of the mammalian target of rapamycin (mTOR), is a molecular-targeted agent that Authors' Affiliation:Division of AppliedMolecular Oncology andDepartment of Medical Oncology and Hematology, Princess Margaret Hospital and University of Toronto, Toronto, Canada Received 11/17/08; revised 6/5/09; accepted 6/9/09; published OnlineFirst 8/25/09. Grant support: Canadian Institutes of Health Research. The costs of publication of this articlewere defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Note: A. Fung and L. Wu contributed equally to this work. Current address for L. Wu: Division of Thoracic Surgery, Toronto Medical Discovery Tower, Toronto, Canada. Requests for reprints: Ian F. Tannock, PrincessMargaret Hospital, Suite 5-208, 610 University Avenue, Toronto, ON M5G 2M9, Canada. Phone: 416-9462245; Fax: 416-946-4563; E-mail: [email protected]. F 2009 American Association for Cancer Research. doi:10.1158/1078-0432.CCR-08-3007 5389 Clin Cancer Res 2009;15(17) September 1, 2009 www.aacrjournals.org Research. on May 1, 2017. © 2009 American Association for Cancer clincancerres.aacrjournals.org Downloaded from Published OnlineFirst August 25, 2009; DOI: 10.1158/1078-0432.CCR-08-3007