Axel R. Hanauske, MD, PhD

Pemetrexed (Alimta) is a novel folate antimetabolite that primarilyinhibits the enzymes thymidylate synthase (TS), dihydrofolate reductase(DHFR), and glycinamide ribonucleotide formyl transferase(GARFT), all of which are involved in pyrimidine and purine synthesis.In a phase II trial of patients with T3/4, N0–2 breast cancer, expressionof thymidylate synthase (TS), dihydrofolate reductase (DHFR),glycinamide ribonucleotide formyltransferase (GARFT), p53, andc-erb-B2 (at the mRNA or protein level) was examined in tumor biopsyspecimens before and 24 hours after the first dose of pemetrexed andafter three cycles of single-agent treatment to establish correlations ofbiomarker levels and changes with clinical outcome and toxicity. Althoughfinal data are not available, initial indications are that clinicalresponse may correlate with decreased or low TS expression. The resultsobtained from clinical data are supported by laboratory results inthree cell lines (MDA-231, MCF-7, and ZR-75). These results suggestthat in vitro transcript profiling to identify which genes are importantpredictors of successful cytotoxic chemotherapy, followed by a focusedclinical trial to confirm the in vitro results, may be the best approachfor translational research.

Pemetrexed (Alimta) is an antifolate that is effective in the inhibitionof multiple enzyme targets including thymidylate synthase,dihydrofolate reductase, and glycinamide ribonucleotide formyl transferase.The compound has been evaluated in several phase I trials, bothas single agent and in combination with other cytotoxic agents. Theinitial schedule selected for further investigation in phase II trials waspemetrexed 600 mg/m2 as a 10-minute infusion on day 1 every 21 days.During the subsequent phase II development, the dose of pemetrexedwas adjusted to 500 mg/m2 due to bone marrow and gastrointestinaltoxicities. The adjusted dose of pemetrexed was well tolerated throughoutthe late-phase drug development program. Preclinical evidencesuggests that pemetrexed has additive or synergistic activity when combinedwith many other clinically important anticancer agents, includinggemcitabine (Gemzar), fluorouracil, carboplatin (Paraplatin),oxaliplatin (Eloxatin), paclitaxel, and vinorelbine (Navelbine). Doselimitingtoxicities in these studies were primarily hematologic, and therewas no evidence of cumulative hematologic toxicity. During the drugdevelopment program it was discovered that supplementation with folicacid and vitamin B12 profoundly increased the tolerability ofpemetrexed. The studies discussed in this review demonstrate thatpemetrexed is well tolerated as a single agent and will be an importantcontribution to combination chemotherapy regimens.

Locally advanced or metastatic adenocarcinoma of the stomach still carries a poor prognosis, with 5-year survival rates of < 15%. Palliative chemotherapeutic regimens for this disease are largely 5-FU–based. We

Despite recent progress in surgery and chemotherapy, advanced gastric cancer carries a poor prognosis. Although several antitumor agents have some clinical activity, responses are usually of short duration and fail to