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Clinical Pharmacology

Commentary: A Case for Minimizing Folate Supplementation in Clinical Regimens with Pemetrexed Based on the Marked Sensitivity of the Drug to Folate Availability

Departments of Medicine and Molecular Pharmacology, The Albert Einstein College of Medicine Cancer Center, Bronx, New York, New York

Key Words. Antifolates • Folate pools • Folic acid • Pemetrexed

Correspondence: I. David Goldman, M.D., Departments of Medicine and Molecular Pharmacology, The Albert Einstein College of Medicine Cancer Center, Bronx, New York 10461, USA. Telephone: 718-430-2302; Fax: 718-430-8550; e-mail: igoldman{at}aecom.yu.edu

Pemetrexed is a novel antifolate recently approved for the treatment of pleural mesothelioma and non-small cell lung cancer. In clinical regimens, pemetrexed is administered in conjunction with folic acid to minimize toxicity. However, excessive folate supplementation may also diminish the activity of this agent. The current study demonstrates, in several human solid tumor cell lines, that when extracellular 5-formyltetrahydrofolate levels are increased in vitro, within the range of normal human blood levels, there is a substantial decrease in pemetrexed activity upon continuous exposure to the drug. This was accompanied by a comparable lower level of trimetrexate activity consistent with an expansion of tumor cell folate pools. Likewise, when cells were exposed to pemetrexed with a schedule that simulates in vivo pharmacokinetics, there was markedly less cell killing with higher extracellular folate levels. Data are provided to indicate that 5-formyltetrahydrofolate is an acceptable surrogate for 5-methyltetrahydrofolate, the major blood folate, for this type of in vitro study. These observations and other reports suggest that, in view of the rise in serum folate and fall in serum homocysteine that has accompanied folic acid supplementation of food in the U.S., the addition of folic acid to regimens with pemetrexed should be limited to the lowest recommended level that provides optimal protection from pemetrexed toxicity.

Disclosure of potential conflicts of interest is found at the end of this article.

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