Published online Dec 20, 2018. doi: 10.5306/wjco.v9.i8.188
Peer-review started: June 17, 2018
First decision: July 19, 2018
Revised: August 24, 2018
Accepted: November 4, 2018
Article in press: November 4, 2018
Published online: December 20, 2018
Tumor cells often develop immune evasion mechanisms, thus combination of tumor antigens may be used to counteract immune resistance. Survivin is a tumor antigen exclusively expressed on tumor cells, essential for cancer cell survival, and its overexpression is associated with aggressiveness of the disease. Similarly, many tumor cells from breast, prostate, ovary or endometrial origin are hormone dependent for their survival. Immunization against hormones such as luteinizing hormone-releasing hormone (LHRH) using LHRH based peptide vaccines have shown efficacy as vaccine antigens in preclinical models of hormone dependent cancers such as breast and prostate cancer. This communication describes the studies undertaken to determine the optimum dose of Survivin antigen for maximum tumor suppressive effect and the synergy between Survivin and LHRH as vaccine antigens for immunotherapy of murine model of breast cancer, 4T-1.
We undertook the prophylactic approach for two reasons: (1) to investigate if the immunization induces a tumor protective response in vivo and (2) this prophylactic approach also closely mimics the clinical situation where primary tumors have been removed or adjuvant treatment for cancer patients has been initiated. Major issues in cancer treatment are the recurrence of tumor after surgery and chemoresistance. Our study was aimed at targeting these issues and developing a strategy, which may prevent tumor spread and recurrence and can overcome resistance. Generating immune response in the body against the tumor antigens will be a safer way of treatment. Anti-Survivin approach may help in overcoming the problem of resistance to therapy.
The aim of this study was to evaluate the possibility of using an immunotherapy based on a combination of Survivin and LHRH fusion protein in 4T-1 murine model of breast cancer. LHRH(6leu)-LTB was used as an immunogen in combination with Survivin along with an immunomodulator, Mycobacterium indicus pranii (MIP). It was observed that efficacy of the combination was marginally better than the Survivin alone but significantly better when only LHRH(6leu)-LTB was used along with MIP. More importantly, combination was best at preventing metastasis of primary tumors to lungs. In most cancer cases, the patients undergo surgery. Though patients are rendered free of tumor, chances of recurrence are very high. If translation of LHRH fusion protein and Survivin based combination approach is successful, it may find applications in such clinical scenario.
Survivin and LHRH fusion protein were used as vaccine antigens. These antigens were expressed as recombinant proteins using E. coli based host-vector systems. Purified proteins were adsorbed on alum before administration as immunogens in mice. MIP was used as immunomodulator along with the recombinantly made vaccine antigens. Inbred Balb/c mice were used for conducting the immunogenicity and efficacy studies of the Survivin vaccine in vivo. Tumor volume was measured bi-dimensionally with digital vernier calipers and results are expressed as mean ± SD of tumor volume for each group. Anti-tumor efficacy of combination of Survivin and LHRH fusion protein in comparison to Survivin and LHRH fusion protein alone was also determined. Sera were collected from mice and assayed for Interferon gamma levels using ELISA kit. ELISA was also performed for the analysis of immunogenicity of the recombinant proteins in mice.
We have shown that Survivin (+ MIP) at a dose of 20 µg is most effective in preventing the growth of 4T-1 breast tumor cells in mice and incorporation of anti-LHRH vaccine exercises a synergistic effect. The study is limited by the fact that the results need to be validated in other tumor models and further translational development needs to be undertaken for appropriate human application. The combination will be effective in immune competent organisms and has to be supplemented with other therapies for use in immune compromised individuals. Furthermore, investigating the molecular mechanism of action of the combination leading to tumor inhibition may also lead to development of novel targeted therapies for cancer.
Our results show the protective role of combination immunotherapy with Survivin and LHRH antigens in murine tumor model. Though it did not lead to much benefit in preventing the growth of primary tumor, it was highly effective in blocking the pulmonary metastasis. Combination of Survivin and LHRH fusion protein may hold immense promise for further development of immunotherapeutic approaches in management of breast cancers.