Reduced folate carrier 1 (SLC19A1) (RFC1)

The Reduced folate carrier 1 (SLC19A1) is the primary protein responsible for the transport of reduced folates and antifolate drugs across the plasma membrane in mammalian cells. As a member of the solute carrier family, it functions as an organic anion antiporter, facilitating the uptake of 5-methyltetrahydrofolate and 5-formyltetrahydrofolate (folinic acid) in exchange for intracellular organic phosphates (UniProt: P41440). In clinical practice, SLC19A1 is the central site of 'folinic acid competition,' where leucovorin is administered to compete with methotrexate for cellular entry, thereby protecting healthy tissues from the lethal effects of high-dose antifolate therapy (StatPearls: Leucovorin). Beyond its role in drug transport, SLC19A1 is essential for maintaining the one-carbon metabolism cycle, which is critical for DNA synthesis, methylation, and amino acid metabolism (PubMed: 18485975). Dysregulation or genetic variations in SLC19A1 are linked to altered sensitivity to chemotherapy, folate deficiency syndromes, and various malignancies. While other transporters like the Proton-coupled folate transporter (PCFT) and Folate receptors (FOLR1) also contribute to folate homeostasis, SLC19A1 remains the dominant pathway for systemic folate delivery and a key pharmacological target for modulating antifolate toxicity.

Other names

SLC19A1Folate transporter 1Reduced folate carrierRFCSolute carrier family 19 member 1Intestinal folate carrier 1IFC-1

Folinic acid acts as a competitive substrate for folate transporters, primarily the Reduced Folate Carrier 1 (SLC19A1), competing with antifolate drugs like methotrexate for cellular uptake. By increasing the intracellular pool of reduced folates, it bypasses the metabolic block created by dihydrofolate reductase (DHFR) inhibition, thereby 'rescuing' healthy cells from systemic toxicity while potentially enhancing the efficacy of other agents like 5-fluorouracil through stabilization of the thymidylate synthase ternary complex.