Pemetrexed: biochemical and cellular pharmacology, mechanisms, and clinical applications

Pemetrexed is a new-generation antifolate, approved for the treatment of mesothelioma and non-small cell lung cancer, currently being evaluated for the treatment of a variety of other solid tumors. This review traces the history of antifolates that led to the development of pemetrexed and describes the unique properties of this agent that distinguish it from other antifolates. These include (a) its very rapid conversion to active polyglutamate derivatives in cells that build to high levels and are retained for long intervals to achieve prolonged and potent inhibition of its major target enzyme thymidylate synthase, (b) its high affinity for three folate transporters, and (c) its marked sensitivity to the level of physiologic folates in cells. The latter results in the unique and paradoxical finding that when transport mediated by the major folate transporter (the reduced folate carrier) is impaired, pemetrexed activity is preserved. This is due to concurrent contraction of competing cellular physiologic folates and utilization of a novel second transport carrier for which pemetrexed has high affinity, recently identified as the proton-coupled folate transporter (PCFT). Laboratory studies are reviewed that raise the possibility of new approaches to the use of folic acid supplementation in clinical regimens with pemetrexed.

Antimetabolites in the management of non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related death in the United States. Although chemotherapy has been shown to increase survival for patients with advanced-stage disease, survival benefits have been modest and come at the cost of significant toxicity. Treatment options in the second-line setting have been limited. Pemetrexed, a multitargeted antifolate, has activity as a single agent and as part of combination chemotherapy against NSCLC. As reported in a recent phase III clinical trial, survival outcomes in the second-line setting for patients treated with pemetrexed or docetaxel are similar. More importantly, major toxicity with the use of pemetrexed with vitamin B(12) and folate supplementation is far less than with docetaxel. Based on its single agent activity, ease of administration, and favorable toxicity profile, pemetrexed has the potential to be incorporated in various settings against NSCLC, including metastatic disease, as adjuvant therapy, and for locally advanced disease.