Biochemical and pharmacologic rationale for high-dose methotrexate.

Area of Science:

• Pharmacology
• Oncology
• Biochemistry

Background:

• High-dose methotrexate (HDMTX) regimens aim to overcome drug resistance by achieving high intracellular drug concentrations.
• Leucovorin (LV) is essential for mitigating HDMTX toxicity but requires selective action in normal versus tumor cells.
• The hypothesis for selective LV rescue was based on impaired transport in MTX-resistant cells.

Purpose of the Study:

• To re-evaluate the rationale behind selective leucovorin (LV) rescue in high-dose methotrexate (HDMTX) therapy.
• To investigate alternative mechanisms of methotrexate (MTX) resistance beyond defective drug transport.
• To explore new strategies for enhancing the therapeutic index of HDMTX.

Main Methods:

• Review of experimental models and recent findings on MTX resistance mechanisms.
• Analysis of DHFR activity, MTX polyglutamate metabolism, and thymidylate synthase activity in resistant cells.
• Examination of LV rescue mechanisms beyond selective cellular uptake.

Main Results:

• MTX resistance can arise from mechanisms other than defective transport, including altered DHFR, reduced polyglutamylation, or decreased thymidylate synthase.
• These alternative resistance mechanisms may not be overcome by higher MTX concentrations.
• Recent studies suggest impaired MTX polyglutamate metabolism and thymidylate synthase activity are common in human tumors.

Conclusions:

• The traditional rationale for selective LV rescue may be insufficient due to diverse MTX resistance mechanisms.
• Alternative resistance pathways necessitate a re-evaluation of HDMTX treatment strategies and LV rescue protocols.
• Further research is needed to understand and exploit novel mechanisms for selective rescue and improved therapeutic outcomes.