Low-dose methotrexate exposure induced long-term cognitive deficits in mice

Purpose: Chemotherapy-related cognitive impairment (CRCI) remains a mysterious morbidity that threatens the quality of life of up to 70% cancer survivors in the United States. Longitudinal studies of CRCI highlighted deficits in memory, learning, attention, motor, and executive functions for up to 20 years after the completion of chemotherapy paradigm. These deficits, especially if happened during childhood, can negatively impact educational achievement, employment, self-independence, and life expectancy of approximately 500,000 adult survivors currently living in the U.S. Given that acute lymphoblastic leukemia (ALL) is the most common diagnosis of childhood cancers worldwide, the folate-inhibitor methotrexate (MTX) has been at the backbone of ALL-treatment with a substantial risk of neurotoxicity. The purpose of this study was to establish a tumor-free mouse model representative of MTX-induced CRCI in childhood ALL survivors and study the long-term effects of chemotherapy treatment on brain function. We hypothesized that MTX administration at a very young age will induce long-term cognitive impairments. Methods: At post-natal day 15, male and female C57BL6/J pups received intraperitoneal injections of either saline (n=12) or MTX (2 mg/kg; n=12) once a day for 3 days. The pups were weaned at post-natal day 21 and allowed to age. At 8-month-old, animals underwent behavioral tests to assess motor, affective and cognitive functions. Results: MTX administration impaired cognitive flexibility in males and impaired spatial learning and memory in females, indicating potential sex- and test-dependent behavioral outcomes. MTX increased performance in coordinated-running test, and increased swimming speed. Anxiety-like behaviors were not affected by the treatment. Conclusions: These preliminary results suggested that low dose MTX-treatment induced sex-dependent cognitive deficits while affective and motor functions were not negatively affected. This study will be repeated, and behaviors will be assessed at other time points to establish complete neurobehavioral profiles of mice affected by MTX chemotherapy.