Use of pyridoxine to increase anticacner activity of methionine-gammalyase in murine cancer models
We presented results of monotherapy and combination therapy of transplantable murine tumor models using methionine-gamma-lyase (MGL) and pyridoxine hydrochloride. We studied MGL from Clostridium sporogenes and Citrobacter freundii. We used Lewis lung carcinoma (LLC), melanoma B16, leukemias P388 and L1210 and Fisher lymphadenosis L5178y. Neither monotherapy with MGL nor combination of MGL and pyridoxine demonstrated antitumor activity against P388 and L5178y. In the murine L1210 leukemia model, MGL C. sporogenes injected intraperitoneally in the dose of 2000 U/kg, 11 times with a 12-hour interval increased the life span of mice (ILS=22 %, р=0.035). In the LLC model, the combination of MGL C. sporogenes at a dose of 400 U/kg, i.p., 4 times with a 48-hour interval and pyridoxine at a dose of 250 mg/kg led to tumor growth inhibition (TGI=55 %, р<0.001) on the first day after the completion of treatment. Monotherapy with MGL or pyridoxine in the same regimens resulted in a 24 % TGI (р=0.263) or 21 % TGI (р=0.410), respectively. In a pair-wise comparison of treatments, MGL + pyridoxine was more effective compared to MGL used alone (р=0.061) and MGL + pyridoxine was more effective then pyridoxine alone (р=0.031). MGL from C. freundii at a dose of 200 U/kg, 4 times with a 48-hour interval plus pyridoxine at a dose of 500 mg/kg injected on day 9 after the completion of treatment led to 50 % TGI, whereas MGL monotherapy at a single dose of 400 U/kg or pyridoxine monotherapy in the same regimen showed 5 % TGI (р=0.991) and 4 % TGI (р=0.998), respectively. The pair-wise comparison showed that MGL (200 U/kg) + pyridoxine was more effective than MGL (400 U/ kg) alone (р<0.001) and pyridoxine alone (р=0.003). In the B16 model, the combination of MGL injected i.p at a dose of 2000 U/kg and pyridoxine at a dose of 300 mg/kg showed 56 % TGI on day 1after the completion of treatment (р=0.045) and 35 % TGI on day 3 (р=0.038). Pyridoxine significantly increased the anticancer effect of MGL: MGL 1000 U/kg i.p and MGL 1000 U/kg i.p. + pyridoxine 300 mg/kg led to TGI=45 % (р=0.034) on day 3 after the completion of treatment. Single maximum tolerated dose after multiple i.p. administration was defined as 2000 U/kg, simultaneous administration of pyridoxine did not increase the toxicity of MGL. In conclusion, LLC and B16 are sensitive to MGL treatment, and pyridoxine may increase the efficacy of MGL.