Abstract 980: Intrathecal methotrexate induces focal cognitive deficits and alters CNS folate physiology in rats

Background: In order to reduce the persistent neurologic toxicity of therapy for childhood acute lymphoblastic leukemia (ALL), many treatment protocols avoid cranial radiation, relying instead on intrathecal chemotherapy to prevent central nervous system relapses. Nevertheless a significant subset of survivors treated without radiation manifest persistent focal deficits in cognitive function. The folate antagonist methotrexate (MTX), a key component of prophylactic intrathecal therapy, is suspected to contribute to treatment-induced cognitive dysfunction. Our goal was to establish a rodent model to isolate the cognitive and neurotoxic effects of MTX after direct administration into cerebrospinal fluid (CSF). Methods: Adult Long-Evans rats were given either intrathecal MTX 0.5mg/kg or artificial CSF via transcutaneous puncture at the level of the cisterna magna. Three days later, all rats subsequently underwent a battery of behavioral tests designed to assess cognitive domains frequently impaired among children treated for ALL, including spatial memory, visual memory, and motor coordination. Indicators of folate physiology (folate and homocysteine) in CSF and serum were measured using high performance liquid chromatography. Concentrations of interleukin-1β, IL-6, and tumor necrosis factor-α were measured in CSF to assess whether intrathecal MTX induces an inflammatory response. Results: Intrathecal MTX administration reliably produced both visual and spatial memory deficits, without altering general activity or motor coordination. MTX administration was associated with a significant reduction in both CSF and serum folate concentrations, along with an increase in CSF homocysteine. At 24 hours post-injection of MTX, CSF folate decreased by 75% and CSF homocysteine was increased 4-fold, relative to baseline. Intrathecal injection of both MTX and artificial CSF was associated with a significant rise in CSF IL-6 within 6 hours, which then returned to baseline by 24h. Conclusion: We have established an animal model in which intrathecal MTX induces cognitive dysfunction that mimics clinically observed toxicity, in association with a rapid fall in CSF folate and increase in CSF homocysteine. A non-specific, transient increase was seen in the proinflammatory cytokine IL-6 within CSF. This proinflammatory response does not appear sufficient to cause cognitive deficits, as it was observed among both groups of rats, while toxicity was demonstrated among only those who received MTX. This model will allow us both to further investigate the pathophysiology of treatment-induced cognitive dysfunction and to test protective interventions. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 980.