Solid tumor chemotherapy using injectable gelatin microspheres containing free methotrexate and conjugated methotrexate

Abstract

Biodegradable gelatin microspheres containing free methotrexate (MTX) (GMFM) and gelatin microspheres containing MTX covalently conjugated to gelatin using carbodiimide (GMCM-I) and two types of azide coupling-grafting methods (GMCM-II and GMCM-III) have been prepared and evaluated for their efficacy towards the solid tumor fibrosarcoma in Wistar rats. The tumor was induced by inoculation of a 10% tumor cell suspension in the anterior aspect of the hind limb. Seven groups were studied—untreated control, intratumoral (i.t.) injection of free MTX, i.t. injection of placebo microspheres, i.t. injection of GMFM, i.t. injection of GMCM-I, i.t. injection of GMCM-II and i.t. injection of GMCM-III of mean particle size 10–20 μm. The gelatin-microspheres-entrapped MTX showed an improved antitumor activity over free MTX as evidenced by the gross tumor weight assessments and [ 3H]thymidine incorporation studies in vitro. This was attributed to the slow and controlled release of MTX from gelatin microspheres, which was more effective compared with free MTX given over the same period of treatment. The drug release from microspheres is due to gradual degradation of the spheres and concomitant diffusion of drug into the external medium. GMCM showed higher antitumor activity than GMFM. The antitumor activity of the various GMCM preparations was of the order: GMCM-I > GMCM-II > GMCM-III. The injectable MTX-containing gelatin microspheres can thus be a potential alternative to conventional therapy using free MTX in the treatment of solid tumors such as fibrosarcoma.