Folate transporter dynamics and therapy with classic and tumor-targeted antifolates

Area of Science:

• Biochemistry
• Molecular Biology
• Pharmacology

Background:

• Human cells rely on three primary folate uptake systems: reduced folate carrier (RFC), folate receptors (FRs), and proton-coupled folate transporter (PCFT).
• Understanding the functional relationships between these transporters is crucial for optimizing antifolate drug delivery and efficacy, especially for novel tumor-targeted agents.

Purpose of the Study:

• To investigate the functional interrelationships among RFC, FRs, and PCFT in the context of various antifolate drugs.
• To determine how transporter expression levels and extracellular pH affect cellular folate accumulation and antifolate drug activity.

Main Methods:

• Engineered HeLa cell models with inducible expression of FRα or RFC, and constitutive PCFT.
• Assessed cellular folate accumulation and cell proliferation in the presence of different antifolates (AGF94, AGF102, pemetrexed, methotrexate, PT523) under varying conditions.

Main Results:

• Cellular folate uptake is dictated by the type and expression levels of folate transporters, with PCFT and RFC often dominating over FRα.
• Transport redundancy was observed for pemetrexed (RFC/PCFT) and AGF94 (PCFT/FRα), with PCFT and FRα predominating, respectively.
• PCFT antagonized the anti-proliferative effects of classic and FRα-targeted antifolates by enhancing folate accumulation.

Conclusions:

• A complex interplay exists among RFC, FRs, and PCFT, influenced by transporter expression and pH.
• This interplay significantly impacts the uptake and anti-tumor efficacy of both targeted and non-targeted antifolates.
• Findings reveal previously unrecognized mechanisms governing antifolate drug action based on folate transporter dynamics.