New C-19-modified geldanamycin derivatives: synthesis, antitumor activities, and physical properties study.

Thiazinogeldanamycin (2) was identified from Streptomyces hygroscopicus 17997 at the late stage of the fermentation. The pH was firstly proposed as an important factor in the biosynthesis of it. It was verified that 2 was produced by direct chemical reactions between geldanamycin (1, GDM) and cysteine or aminoethanethiol hydrochloride at pH > 7 in vitro. The proposed synthesis pathway for compound 2 was also discussed. Eleven new C-19-modified GDM derivatives, including five stable hydroquinone form derivatives, were synthesized, most of which exhibited desirable properties such as lower cytotoxicity, increased water solubility, and potent antitumor activity. Especially, compounds 5 and 8 showed antitumor activities against HepG2 cell with IC50 values of 2.97-6.61 µM, lower cytotoxicity and at least 15-fold higher water solubility compared with 1 in pH 7.0 phosphate buffer.

Conjugation of toll-like receptor-7 agonist to gastric cancer antigen MG7-Ag exerts antitumor effects.

AIM: To investigate the effects of our tumor vaccines on reversing immune tolerance and generating therapeutic response. METHODS: Vaccines were synthesized by solid phase using an Fmoc strategy, where a small molecule toll-like receptor-7 agonist (T7) was conjugated to a monoclonal gastric cancer 7 antigen mono-epitope (T7-MG1) or tri-epitope (T7-MG3). Cytokines were measured in both mouse bone marrow dendritic cells and mouse spleen lymphocytes after exposed to the vaccines. BALB/c mice were intraperitoneally immunized with the vaccines every 2 wk for a total of three times, and then subcutaneously challenged with Ehrlich ascites carcinoma (EAC) cells. Three weeks later, the mice were killed, and the tumors were surgically removed and weighed. Serum samples were collected from the mice, and antibody titers were determined by ELISA using an alkaline phosphate-conjugated detection antibody for total IgG. Antibody-dependent cell-mediated cytotoxicity was detected by the lactate dehydrogenase method using natural killer cells as effectors and antibody-labeled EAC cells as targets. Cytotoxic T lymphocyte activities were also detected by the lactate dehydrogenase method using lymphocytes as effectors and EAC cells as targets. RESULTS: Vaccines were successfully synthesized and validated by analytical high performance liquid chromatography and electrospray mass spectrometry, including T7, T7-MG1, and T7-MG3. Rapid inductions of tumor necrosis factor-α and interleukin-12 in bone marrow dendritic cells and interferon γ and interleukin-12 in lymphocytes occurred in vitro after T7, T7-MG1, and T7-MG3 treatment. Immunization with T7-MG3 reduced the EAC tumor burden in BALB/c mice to 62.64% ± 5.55% compared with PBS control (P < 0.01). Six or nine weeks after the first immunization, the monoclonal gastric cancer 7 antigen antibody increased significantly in the T7-MG3 group compared with the PBS control (P < 0.01). As for antibody-dependent cell-mediated cytotoxicity, antisera obtained by immunization with T7-MG3 were able to markedly enhance cell lysis compared to PBS control (31.58% ± 2.94% vs 18.02% ± 2.26%; P < 0.01). As for cytotoxic T lymphocytes, T7-MG3 exhibited obviously greater cytotoxicity compared with PBS control (40.92% ± 4.38% vs 16.29% ± 1.90%; P < 0.01). CONCLUSION: A successful method is confirmed for the design of gastric cancer vaccines by chemical conjugation of T7 and multi-repeat-epitope of monoclonal gastric cancer 7 antigen.