Mukherjee, Pinku

Abstract Cyclooxygenase-2 (COX-2) inhibitors are rapidly emerging as a new generation of therapeutic drug in combination with chemotherapy or radiation therapy for the treatment of cancer. The mechanisms underlying its antitumor effects are not fully understood and more thorough preclinical trials are needed to determine if COX-2 inhibition represents a useful approach for prevention and/or treatment of breast cancer. The purpose of this study was to evaluate the growth inhibitory mechanism of a highly selective COX-2 inhibitor, celecoxib, in an in vivo oncogenic mouse model of spontaneous breast cancer that resembles human disease. The oncogenic mice carry the polyoma middle T antigen driven by the mouse mammary tumor virus promoter and develop primary adenocarcinomas of the breast. Results show that oral administration of celecoxib caused significant reduction in mammary tumor burden associated with increased tumor cell apoptosis and decreased proliferation in vivo. In vivo apoptosis correlated with significant decrease in activation of protein kinase B/Akt, a cell survival signaling kinase, with increased expression of the proapoptotic protein Bax and decreased expression of the antiapoptotic protein Bcl-2. In addition, celecoxib treatment reduced levels of proangiogenic factor (vascular endothelial growth factor), suggesting a role of celecoxib in suppression of angiogenesis in this model. Results from these preclinical studies will form the basis for assessing the feasibility of celecoxib therapy alone or in combination with conventional therapies for treatment and/or prevention of breast cancer.

Cancer vaccines have often failed to live up to their promise, although recent results with checkpoint inhibitors are reviving hopes that they will soon fulfill their promise. Although mutation-specific vaccines are under development, there is still high interest in an off-the-shelf vaccine to a ubiquitous antigen, such as MUC1, which is aberrantly expressed on most solid and many hematological tumors, including more than 90% of breast carcinomas. Clinical trials for MUC1 have shown variable success, likely because of immunological tolerance to a self-antigen and to poor immunogenicity of tandem repeat peptides. We hypothesized that MUC1 peptides could be optimized, relying on heteroclitic optimizations of potential anchor amino acids with and without tumor-specific glycosylation of the peptides. We have identified novel MUC1 class I peptides that bind to HLA-A*0201 molecules with significantly higher affinity and function than the native MUC1 peptides. These peptides elicited CTLs from normal donors, as well as breast cancer patients, which were highly effective in killing MUC1-expressing MCF-7 breast cancer cells. Each peptide elicited lytic responses in greater than 6/8 of normal individuals and 3/3 breast cancer patients. The CTLs generated against the glycosylated-anchor modified peptides cross reacted with the native MUC1 peptide, STAPPVHNV, suggesting these analog peptides may offer substantial improvement in the design of epitope-based vaccines.

Abstract Genetically modified mice with spontaneous development of mammary carcinoma provide a powerful tool to study the efficacy of tumor vaccines, since they mimic breast cancer development in humans. We used a transgenic murine model expressing polyomavirus middle T oncogene and mucin 1 tumor-associated Ag to determine the preventive effect of a dendritic/tumor fusion cell vaccine. The MMT (a transgenic murine model) mice developed mammary carcinoma between the ages of 65–108 days with 100% penetrance. No spontaneous CTL were detected. However, prophylactic vaccination of MMT mice with dendritic/tumor fusion cells induced polyclonal CTL activity against spontaneous mammary carcinoma cells and rendered 57–61% of the mice free of the disease at the end of experiment (180 days). Furthermore, the level of CTL activity was maintained with multiple vaccinations. The antitumor immunity induced by vaccination with dendritic/tumor fusion cells reacted differently to injected tumor cells and autochthonous tumor. Whereas the injected tumor cells were rejected, the autochthonous tumor evaded the attack and was allowed to grow. Collectively these results indicate that prophylactic vaccination with dendritic/tumor fusion cells confers sufficient antitumor immunity to counter the tumorigenesis of potent oncogenic products. The findings in the present study are highly relevant to cancers in humans.

Abstract Pancreatic cancer is a highly aggressive, treatment refractory cancer and is the fourth leading cause of death in the United States. In humans, 90% of pancreatic adenocarcinomas overexpress altered forms of a tumor-specific Ag, mucin 1 (MUC1; an epithelial mucin glycoprotein), which is a potential target for immunotherapy. We have established a clinically relevant animal model for pancreatic cancer by developing a double transgenic mouse model (called MET) that expresses human MUC1 as self molecule and develops spontaneous tumors of the pancreas. These mice exhibit acinar cell dysplasia at birth, which progresses to microadenomas and acinar cell carcinomas. The tumors express large amounts of underglycosylated MUC1 similar to humans. Tumor-bearing MET mice develop low affinity MUC1-specific CTLs that have no effect on the spontaneously occurring pancreatic tumors in vivo. However, adoptive transfer of these CTLs was able to completely eradicate MUC1-expressing injectable tumors in MUC1 transgenic mice, and these mice developed long-term immunity. These CTLs were MHC class I restricted and recognized peptide epitopes in the immunodominant tandem repeat region of MUC1. The MET mice appropriately mimic the human condition and are an excellent model with which to elucidate the native immune responses that develop during tumor progression and to develop effective antitumor vaccine strategies.

Abstract We report that administration of celecoxib, a specific cyclooxygenase-2 (COX-2) inhibitor, in combination with a dendritic cell-based cancer vaccine significantly augments vaccine efficacy in reducing primary tumor burden, preventing metastasis, and increasing survival. This combination treatment was tested in MMTV-PyV MT mice that develop spontaneous mammary gland tumors with metastasis to the lungs and bone marrow. Improved vaccine potency was associated with an increase in tumor-specific CTLs. Enhanced CTL activity was attributed to a significant decrease in levels of tumor-associated IDO, a negative regulator of T cell activity. We present data suggesting that inhibiting COX-2 activity in vivo regulates IDO expression within the tumor microenvironment; this is further corroborated in the MDA-MB-231 human breast cancer cell line. Thus, a novel mechanism of COX-2-induced immunosuppression via regulation of IDO has emerged that may have implications in designing future cancer vaccines.

Abstract MUC1, a membrane tethered mucin glycoprotein, is overexpressed and aberrantly glycosylated in >80% of human ductal pancreatic adenocarcinoma. However, the role of MUC1 in pancreatic cancer has been elusive, partly due to the lack of an appropriate model. We report the characterization of a novel mouse model that expresses human MUC1 as a self molecule (PDA.MUC1 mice). Pancreatic tumors arise in an appropriate MUC1-tolerant background within an immune-competent host. Significant enhancement in the development of pancreatic intraepithelial preneoplastic lesions and progression to adenocarcinoma is observed in PDA.MUC1 mice, possibly due to increased proliferation. Tumors from PDA.MUC1 mice express higher levels of cyclooxygenase-2 and IDO compared with PDA mice lacking MUC1, especially during early stages of tumor development. The increased proinflammatory milieu correlates with an increased percentage of regulatory T cells and myeloid suppressor cells in the pancreatic tumor and tumor draining lymph nodes. Data shows that during pancreatic cancer progression, MUC1-mediated mechanisms enhance the onset and progression of the disease, which in turn regulate the immune responses. Thus, the mouse model is ideally suited for testing novel chemopreventive and therapeutic strategies against pancreatic cancer.

Abstract With a 5-year survival rate of <5%, pancreatic cancer is one of the most rapidly fatal malignancies. Current protocols for the treatment of pancreas cancer are not as effective as we desire. In this study, we show that a novel Mucin-1 (MUC1)-based vaccine in combination with a cyclooxygenase-2 inhibitor (celecoxib), and low-dose chemotherapy (gemcitabine) was effective in preventing the progression of preneoplastic intraepithelial lesions to invasive pancreatic ductal adenocarcinomas. The study was conducted in an appropriate triple transgenic model of spontaneous pancreatic cancer induced by the KRASG12D mutation and that expresses human MUC1 as a self molecule. The combination treatment elicited robust antitumor cellular and humoral immune responses and was associated with increased apoptosis in the tumor. The mechanism for the increased immune response was attributed to the down-regulation of circulating prostaglandin E2 and indoleamine 2, 3,-dioxygenase enzymatic activity, as well as decreased levels of T regulatory and myeloid suppressor cells within the tumor microenvironment. The preclinical data provide the rationale to design clinical trials with a combination of MUC1-based vaccine, celecoxib, and gemcitabine for the treatment of pancreatic cancer.