Mechanistic Study of Methotrexate-Induced Oxidative Distress in Neurons and the CSF

The neurocognitive side effects of cancer chemotherapy in pediatric patients are heart-breaking; not only must these children deal with the hardship of the disease and harsh treatment, but they often also face neurocognitive impairments that affect their performance in school and their daily life as cancer survivors. These brain toxicities, named “chemobrain”, or Chemotherapy-related Cognitive Impairment (CRCI), include immediate symptoms (confusion, memory impairment, ataxia), as well as prolonged neurocognitive malfunctions. THE GAP IN THE FIELD: Not enough is known about the molecular mechanisms of chemotherapy-induced toxicity. Specifically, metabolic aberrations in the brain that ensue following therapy with metabolic drugs such as the anti-folate MTX, a standard of care for childhood leukemia, is an unexplored field. To be able to offer solutions to chemotherapy-induced neurotoxicity it is critical to first understand the molecular mechanisms of the toxicity caused by common chemotherapies. Therefore, THE GOAL OF THIS PROJECT is to elucidate targetable mechanisms that mediate and modify chemotherapy-induced neurotoxicity with focus on oxidative distress. HYPOTHESIS: A good understanding of the molecular mechanisms of CRCI is required to be able to offer preventive care or treatment. PRELIMINARY DATA: We applied metabolite profiling of MTX-treated mouse and human cerebrospinal fluid (CSF) to study the metabolic impact of the drug and revealed oxidative distress in the CSF and the choroid plexus (ChP), the organ that produces the CSF. We found that in addition to damaging the ChP and CSF, MTX also caused toxicity to neurons in the hippocampus. However, these findings offer some hope: the CSF can serve as a conduit for therapy because it is relatively accessible for clinical intervention and reaches all parts of the brain. Indeed, our discovery that MTX treatment causes reduction in CSF levels of the secreted antioxidant enzyme SOD3, both in mice and in MTX-treated patients, led us to test CSF-based therapy; ChP-targeted gene therapy with exogenous SOD3 expression replenishes CSF's protective capacity, preventing metabolic damage in the hippocampus and even rescues MTX-induced behavioral deficits in mice. APPROACH: We will test our hypothesis that the ChP-CSF system can be harnessed to alter the brain redox environment to reduce adverse effects of chemotherapy on noncancerous brain cells by assessing the mechanisms by which CSF-SOD3 protects the hippocampus from MTX-induced toxicity (Aim 1), by studying the role of nitric oxide (NO) and peroxynitrite in the MTX-induced oxidative damage in ChP cells and neurons (Aim 2), and by testing if resuming oxidative balance in the CSF can be achieved by peripheral and brain-specific injection of antioxidants, and whether these are sufficient to mitigate oxidative damage to ChP and hippocampus (Aim 3). IMPACT: Our study will reveal actionable tools to mitigate the neurological damage induced by MTX, and other chemotherapies, and the immediate potential of antioxidants co-administration with chemotherapy for amelioration of CRCI and improved survivorship.