Synergistic effect between intraneoplastic methotrexate and radiation on experimental intracerebral rat gliosarcoma

Methotrexate (MTX) alone has a limited effect against malignant brain tumors, but we previously demonstrated a beneficial synergism between MTX and radiation therapy (XRT) against RT-9 gliosarcoma. Because the beneficial effects of that study were limited by systemic toxicity and poor brain penetration of MTX, we have continued our studies using direct intracerebral MTX therapy. Male CD-Fisher rats with intracerebrally implanted RT-9 gliosarcoma and indwelling brain tumor catheters were treated with intracerebral injections of MTX, whole-brain XRT, or a combination of both. MTX was given either as one of two "high-dose" treatments, on the basis of whole-body doses, or two "low-doses," on the basis of average brain weight. MTX alone at lower doses and XRT alone each prolonged survival moderately. High-dose MTX was highly toxic, but low-dose MTX was well tolerated. Combined MTX and XRT caused a significant prolongation of survival in all animals that survived treatment long enough to die from tumor growth.