XWH - 11 - 1 - 0040 TITLE : The Role of IDO in Muc 1 Targeted Immunotherapy

While much advancement has been made in breast cancer treatment, metastatic breast cancer remains an incurable disease. MUC1 is a glycoprotein expressed on normal glandular epithelial but is over-expressed and underglycosylated in over 90% of human breast tumors and 100% of metastatic lesions, which lead to its ranking by NCI as the second most targetable antigen. Vaccines against tumor antigens have several benefits, including the chance to eliminate metastatic lesions that express the vaccinating tumor antigen. To this end, we have proposed vaccinating with peptides from the MUC1 protein core, which is only visible to the immune system on the tumor-associated form of the protein. Previous work from our lab has demonstrated that this vaccine does elicit a MUC1-specific immune response that can only be functional if the immunosuppressive tumor microenvironment is altered to allow efficient killing of tumor cells. Thus, we investigated the effectiveness of MUC1 vaccination in combination with drugs known to inhibit immunosuppression to determine which drug is the most effective. Methods: Mice that are transgenic for human MUC1 (MUC1.Tg) mice were orthotopically injected with a syngenic breast cancer cell line expressing human MUC1 (Mtag.MUC1). Mice were vaccinated after palpable tumor formation with the vaccine cocktail, consisting of two MHC class I-restricted MUC1 tandem repeat peptides and a class II pan helper peptide mixed with GM-CSF and CpG ODN, in incomplete Freund’s adjuvant. Previous work in our lab has shown that blocking the cyclooxygenase pathway (COX) resulted in an inhibition of immunosuppression. Thus we used the following drugs in combination with the MUC1-vaccine therapy: Indomethacin (COX1 and COX2 inhibitor), Celecoxib (COX2 inhibitor), 1-methyl tryptophan (indoleamine 2,3 dioxygenase inihibitor), and AH6809 (EP2 receptor antagonist). Mice were euthanized and tissue was collected post the final vaccination. MUC1 vaccine therapy alone caused a slight reduction in tumor burden, although not significant. The combinational therapy of Indomethacin + Vaccine resulted in a significant reduction in tumor burden, whereas all other treatments resulted in no significant reduction in tumor burden, as measured by caliper measurements. The combination treatment of Vacc+Indomethacin and Vacc+Celecoxib both reduced PGE2 levels compared to vaccine alone. In a repeat experiment, we found that the combination of Vacc+Indomethacin caused a significant reduction in tumor wet weight compared to vaccine alone as well as compared to control. However, Indomethacin alone did not significantly reduce tumor wet weight compared to control, indicating a synergistic effect of vaccine and indomethacin. Since Indomethacin but not Celecoxib reduced tumor burden when given in combination with the MUC1 vaccine, we are further investigated COX-independent pathways involved in this mechanism.