The role of l-leucovorin uptake and metabolism in the modulation of 5-fluorouracil efficacy and antifolate toxicity.

in Frontiers in pharmacology by Godefridus J Peters, Ietje Kathmann, Elisa Giovannetti, Kees Smid, Yehuda G Assaraf, Gerrit Jansen

TLDR

  • The study investigates the best way to use a medicine called l-Leucovorin (l-LV) to help cancer cells respond better to a medicine called 5-fluorouracil (5FU). The study found that l-LV is better at helping cancer cells respond to 5FU than a mixture of l-LV and its d-LV stereoisomer. The study also found that l-LV is better at protecting cancer cells from a medicine called methotrexate than d-LV. The study suggests that l-LV is the best way to use this medicine to help cancer cells respond better to 5FU and protect them from other medicines.

Abstract

L-Leucovorin (l-LV; 5-formyltetrahydrofolate, folinic acid) is a precursor for 5,10-methylenetetrahydrofolate (5,10-CH-THF), which is important for the potentiation of the antitumor activity of 5-fluorouracil (5FU). LV is also used to rescue antifolate toxicity. LV is commonly administered as a racemic mixture of its l-LV and d-LV stereoisomers. We compared dl-LV with l-LV and investigated whether d-LV would interfere with the activity of l-LV. Using radioactive substrates, we characterized the transport properties of l-LV and d-LV, and compared the efficacy of l-LV with d-LV to potentiate 5FU-mediated thymidylate synthase (TS) inhibition. Using proliferation assays, we investigated their potential to protect cancer cells from cytotoxicity of the antifolates methotrexate, pemetrexed (Alimta), raltitrexed (Tomudex) and pralatrexate (Folotyn). l-LV displayed an 8-fold and 3.5-fold higher substrate affinity than d-LV for the reduced folate carrier (RFC/SLC19A1) and proton coupled folate transporter (PCFT/SLC46A1), respectively. In selected colon cancer cell lines, the greatest enhanced efficacy of 5FU was observed for l-LV (2-fold) followed by the racemic mixture, whereas d-LV was ineffective. The cytotoxicity of antifolates in lymphoma and various solid tumor cell lines could be protected very efficiently by l-LV but not by d-LV. This protective effect of l-LV was dependent on cellular RFC expression as corroborated in RFC/PCFT-knockout and RFC/PCFT-transfected cells. Assessment of TS activityshowed that TS inhibition by 5FU could be enhanced by l-LV and dl-LV and only partially by d-LV. However, protection from inhibition by various antifolates was solely achieved by l-LV and dl-LV. In general l-LV acts similar to the dl-LV formulations, however disparate effects were observed when d-LV and l-LV were used in combination, conceivably by d-LV affecting (anti)folate transport and intracellular metabolism.

Overview

  • The study investigates the comparative efficacy of l-Leucovorin (l-LV) and its d-LV stereoisomer in potentiating the antitumor activity of 5-fluorouracil (5FU) and protecting cancer cells from antifolate toxicity. The study compares the transport properties of l-LV and d-LV and their ability to enhance 5FU-mediated thymidylate synthase (TS) inhibition and protect cells from antifolate toxicity. The study aims to determine the optimal formulation of l-LV for enhancing the efficacy of 5FU and protecting cells from antifolate toxicity.

Comparative Analysis & Findings

  • The study found that l-LV displayed an 8-fold and 3.5-fold higher substrate affinity than d-LV for the reduced folate carrier (RFC/SLC19A1) and proton coupled folate transporter (PCFT/SLC46A1), respectively. In selected colon cancer cell lines, the greatest enhanced efficacy of 5FU was observed for l-LV (2-fold) followed by the racemic mixture, whereas d-LV was ineffective. The cytotoxicity of antifolates in lymphoma and various solid tumor cell lines could be protected very efficiently by l-LV but not by d-LV. The protective effect of l-LV was dependent on cellular RFC expression as corroborated in RFC/PCFT-knockout and RFC/PCFT-transfected cells. Assessment of TS activity showed that TS inhibition by 5FU could be enhanced by l-LV and dl-LV and only partially by d-LV. However, protection from inhibition by various antifolates was solely achieved by l-LV and dl-LV.

Implications and Future Directions

  • The study highlights the importance of l-LV in enhancing the efficacy of 5FU and protecting cells from antifolate toxicity. The study suggests that l-LV is the optimal formulation for enhancing the efficacy of 5FU and protecting cells from antifolate toxicity. The study also identifies the importance of cellular RFC expression in the protective effect of l-LV. Future research should focus on developing l-LV-based formulations with improved pharmacokinetics and reduced toxicity. Additionally, future research should investigate the use of l-LV in combination with other antifolates and targeted therapies to enhance their efficacy and reduce toxicity.
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