Functional inactivity and mutations of p53 differentially affect sensitivity to 5-fluorouracil and antifolate inhibitors of thymidylate synthase (TS) by altering TS levels in colorectal cancer cells.
ABSTRACT The role of p53 in altering TS expression and chemosensitivity was studied in colorectal cancer cells with wildtype, mutated, or functionally inactive p53. Cytotoxicity of TS inhibitors was studied by MTT, while PCR, Western blot, and activity assays assessed whether p53 status influenced TS expression. Lovo-175X2 cells showed increased resistance to TS inhibitors and significantly greater than wildtype expression and activity of TS. In contrast, Lovo-273X17 and Lovo-li were more sensitive to TS inhibitors and had reduced TS expression, due either to reduced TS mRNA or altered regulation of TS activity. Thus, functional inactivity and mutations of p53 differentially affect TS, potentially influencing response to TS inhibitor-based treatment.
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ABSTRACT: Based on their different mechanisms of action, non-overlapping side effects and radiosensitising potential, combining the antimetabolites pemetrexed (multitargeted antifolate, MTA) and gemcitabine (2',2'-difluorodeoxycytidine, dFdC) with irradiation (RT) seems promising. This in vitro study, for the first time, presents the triple combination of MTA, dFdC and irradiation using various treatment schedules. The cytotoxicity, radiosensitising potential and cell cycle effect of MTA were investigated in A549 (NSCLC) and CAL-27 (SCCHN) cells. Using simultaneous or sequential exposure schedules, the cytotoxicity and radiosensitising effect of 24 h MTA combined with 1 h or 24 h dFdC were analysed. Including a time interval between MTA exposure and irradiation seemed favourable to MTA immediately preceding or following radiotherapy. MTA induced a significant S phase accumulation that persisted for more than 8 h after drug removal. Among different MTA/dFdC combinations tested, the highest synergistic interaction was produced by 24 h MTA followed by 1 h dFdC. Combined with irradiation, this schedule showed a clear radiosensitising effect. Results from our in vitro model suggest that the sequence 24 h MTA --> 1 h dFdC --> RT is the most rational design and would, after confirmation in an in vivo setting, possibly provide the greatest benefit in the clinic.BMC Cancer 01/2010; 10:441. · 3.33 Impact Factor
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ABSTRACT: INTRODUCTION: The folate-dependent enzyme thymidylate synthase (TS) plays a pivotal role in DNA replication/repair and cancer cell proliferation, and represents a valid target for the treatment of several tumor types, including NSCLC. NSCLC is the leading cause of cancer-related mortality, and several TS inhibitors have gone into preclinical and clinical testing, with pemetrexed emerging for its approval and widespread use as first-/second-line and maintenance therapy for this disease. AREAS COVERED: This review summarizes the therapeutic options in NSCLC, as well as the background and rationale for targeting TS. The authors also review recent pharmacogenetic studies and data from clinical trials evaluating novel TS inhibitors, hoping that the reader will gain a comprehensive overview of the field of TS inhibition, specifically relating to drugs used or being developed for lung cancer patients. EXPERT OPINION: TS is a validated target in NSCLC. However, benefits from conventional chemotherapy in NSCLC have plateaued, and more cost-effective results should be obtained with individualized treatment. Accordingly, the clinical success for TS inhibitors may depend on our ability to correctly administer these agents following biomarker-driven patient selection, including TS genotype and expression, and using the right combination therapy.Expert Opinion on Investigational Drugs 10/2011; 20(10):1343-56. · 4.74 Impact Factor