Augmentation of tumor immunity by 6-MPG, a water-soluble derivative of 6-mercaptopurine, in mice

A new lanostane-type triterpene from the fruiting bodies of Ganoderma lucidum

A new lanostane-type triterpene, named ganoderic acid LM2 (5), was isolated from the fruiting bodies of Ganoderma lucidum. Its structure was characterized as (23S) 7beta, -dihydroxy-3, 11, 15-trioxo-5alpha-lanosta-8, 24-dien-26-oic acid by 1D- and 2D-NMR spectra. In addition, a known triterpene, ganoderic acid epsilon (4), was obtained. Both of them exhibited potent enhancement of ConA-induced mice splenocytes proliferation in vitro.

Study on the mechanism of immunopotentiating antitumor effect of 6-MPG, a water-soluble derivative of 6-mercaptopurine

We investigated possible mechanisms of the antitumor action of gamma-(9H-purine-6-yl) thiomethyl L-glutamate (6-MPG), a water-soluble derivative of 6-MP. In the double grafted tumor system, BALB/c mice were inoculated intradermally with 10(6) cells of MethA fibrosarcoma at the right inguinal region on day 0 (the primary tumor) and later with 3 x 10(6) cells at the left on day 10 (the secondary tumor). Intraperitoneal administration of 6-MPG at a dose of 100 mg/kg/day from day 3 through 7 completely prevented growth of the secondary tumor. 6-MPG showed no effect on growth of colon 26 adenocarcinoma cells inoculated in place of the secondary MethA cells (antigen specificity). 6-MPG did not inhibit the secondary MethA growth in the BALB/c (nu/nu) mouse. The inhibitory effect of 6-MPG on the secondary tumor growth was diminished by prior treatment of the primed animals with cyclosporin A and anti-Thy antibody. Spleen cells from the tumor-bearing mice treated with 6-MPG showed a tumor-neutralizing activity (Winn assay). Treatment of the spleen cells with anti-CD8 antibody plus complement diminished the tumor-neutralizing effect but that with anti-CD4 antibody plus complement did not, indicating that CD8-positive cells are responsible for potentiation of the tumor immunity. These results suggest that the antitumor effect of 6-MPG against the secondary tumor is elicited by augmenting tumor specific T-cell production.