Methotrexate-induced biochemical alterations of the folate and methyl-transfer pathway in the CNS

Abstract

Methotrexate (MTX), administered as high-dose infusion (3-5 g/m²) and/or intrathecally (3-12 mg) has been associated with neurotoxicity of unclear pathogenesis. It was investigated if the biochemical alterations of the folate and methyl-transfer pathway in the CSF of cancer patients following MTX treatment may play a role in neurotoxicity. Firstly, analytical methods using HPLC with UV and/or fluorescence detection for the measurement of reduced folates, MTX, S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) were developed and validated.<br /> Secondly, CSF samples from adult patients with primary central nervous system lymphoma (PCNSL) and two pediatric ALL populations were collected and analysed. From four PCNSL patients CSF samples were obtained on four or five subsequent days. A massive depletion of the CSF 5-methyl-THF concentration was observed at the end of the high-dose MTX infusion. A repletion occured following the administration of rescue. After intracerebroventricular MTX a gradual decrease of the reduced folate concentrations was observed from day to day. There was no significant alteration of the SAM and SAH concentration in the same time-period. One of the patients had clinical signs of neurotoxicity and lower 5-methyl-THF and SAM concentrations compared to others. <br /> In the pediatric ALL collectives sampling was performed one to three weeks after the last MTX therapy. It was observed that the concentrations of 5-methyl-THF and SAM were in the normal range two weeks after treatment with high-dose and intrathecal (i.th.) MTX followed by rescue. In contrast, in protocols with i.th. MTX only the 5-methyl-THF concentrations were significantly decreased 12 days after the first i.th. MTX administration whereas SAM was significantly decreased throughout the protocols. Three ALL patients manifested signs of neurotoxicity and had low levels of 5-methyl-THF and SAM during or shortly after toxicity. In conclusion, the results suggest that the biochemical alterations of the folate and methyl-transfer pathway may play an important role in the genesis of MTX-associated neurotoxicity.