TISSUE DISTRIBUTION OF METHOTREXATE FOLLOWING ADMINISTRATION AS A SOLUTION AND AS A MAGNETIC MICROSPHERE CONJUGATE IN RATS BEARING BRAIN-TUMORS

A novel magnetic microsphere-methotrexate (MM-MTX) drug delivery syste m was synthesized and evaluated in rats bearing rat glioma-2 (RG-2) tu mors. Methotrexate was linked to the surface of the magnetic particle via an aminohexanol linker that would release free drug following hydr olysis. Male Fischer 344 rats bearing RG-2 tumors were administered 3 mg/kg of methotrexate (MTX) either as MM-MTX or as a solution (MTX-S) over 5 min. A 6000 gauss magnetic field was applied for 15 min from th e end of MM-MTX administrations. Serial sacrifices were conducted at 1 5 min, 30 min and 45 min after drug administrations, organs collected, and analyzed for total MTX by a radioassay. At all times, MTX right b rain (ipsilateral), brain tumor, and left brain concentrations were ap proximately 3.5 to 5-fold greater in the MM-MTX group compared to the MTX-S group. MTX concentrations in all other organs were less followin g administration of MM-MTX than MTX-S except in lung at 30 and 45 min. The targeting efficacy, an index for site-specificity, for both MM-MT X and MTX-S were similar and indicated some enhancement in MTX localiz ation in brain tumor. Confocal and conventional light microscopic anal yses demonstrated a diffuse distribution of MM-MTX in tumor consistent with extravascular uptake, whereas a predominant capillary distributi on of MM-MTX was observed in normal brain. Following 45 min, the anima ls treated with MM-MTX died possibly due to redistribution of particle s to the lung. This toxicity was dose-dependent. High brain MTX concen trations coupled with extravascular uptake of MM-MTX provide a basis f or further investigations with this novel drug delivery system.