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A critical point in cancer progression is evading recognition by the immune system. Cancer cells accomplish this by stimulating immune checkpoint signals on effector T-cells. In patients with advanced melanoma treated with immune checkpoint inhibitors, 3-year survival increased by 20%. While immune checkpoint therapies are the new first treatment option for advanced melanoma in over a decade, their efficacy is limited because resistance often develops. Understanding the molecular mechanisms of immune checkpoint inhibitor resistance is critical to develop combinatorial drug therapy to potentiate therapeutic responsiveness. The unfolded protein response (UPR) is an endoplasmic reticulum (ER) stress pathway activated when unfolded/misfolded proteins accumulate within the ER. Highly secretory cell types, such as T-cells, have larger ER cell compartments and elevated UPR components to deal with the increased protein synthesis/folding required by these cell types. Therefore, these cell types may be highly sensitive to ER stress. Our data demonstrates elevated UPR signaling components as a driver of T-cell exhaustion/dysfunction. Using a previously established T-cell exhaustion protocol, we stimulated naïve T-cells with antibodies to CD3/CD28 for 5 days and co-cultured them with MDA-MB-231 breast cancer cells, Mun2b melanoma cell line, or CMI patient-derived melanoma cell line. Exhausted T-cells displayed an increased PD-1 and PERK expression, suggesting that UPR signaling is activated during T-cell exhaustion. Treatment of naïve T-cells with DTT, a chemical agent that stimulates ER stress, also induced PD-1 and PERK compared with vehicle-treated T-cells. Gene expression analysis of T-cells indicate that co-culture with cancer cells, not CD3/CD28 activation, elevates T-cell UPR gene expression. Furthermore, induction of ER stress through low-dose DTT treatment decreased cytotoxic T-cell mediated cancer cell death, further supporting our hypothesis of ER stress inducing T-cell exhaustion. Inhibition of PERK by RNAi in TALL-104, a human cytotoxic T-cell line, enhanced T-cell mediated cancer cell clearance when exposed to ER stress-inducing agents, suggesting that PERK may represent a novel target to prevent T-cell exhaustion or restore T-cell effector capabilities. PERK inhibition in the patient-derived melanoma cells did not negatively affect T-cell-mediated killing, suggesting that systemic PERK inhibition may be an effective therapeutic strategy to enhance anti-tumor immune responses. Matched PBMC from melanoma patients before treatment or after ipilimumab therapy resistance indicated increased UPR signaling components in PBMC samples from patients after ipilimumab resistance when compared with PBMC samples before therapy, supporting a novel role UPR signaling in anti-CTLA4 therapy resistance. Citation Format: Yismeilin R. Feliz Mosquea, David R. Soto Pantoja, Adam Wilson, Pierre L. Triozzi, Katherine L. Cook. UPR signaling promotes T-cell dysfunction to prevent immune-mediated cancer cell killing and immune checkpoint therapy resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1704. doi:10.1158/1538-7445.AM2017-1704

According to the National Cancer Institute more than 140,000 people will be diagnosed in the United States with colorectal cancer this year alone. The adenomatus polyposis coli (APC) gene is frequently mutated in colorectal cancer, the APC‐min mouse correspondingly is a widely used model for the study of this type of cancer. Yet, intestinal tumors develop predominately in the small intestine reflecting familial adenomatous polyposis rather than colorectal cancer. Studies indicate that the matricellular protein Thrombospondin 1 (TSP1), a key component in modifying inflammatory processes, is lost during the development of colon cancer. To study the role of TSP1 during inflammation driven colorectal carcinogenesis we developed an APC‐min and TSP−/− APC‐min mouse model. A lack of TSP1 increases tumor size and multiplicity predominately in the large intestine of these mice. Our data indicate that expression of TSP1 in the APC‐min mouse prevents the development of adenomas in the large intestine in mice fed a low fat diet. Moreover, TSP−/− APC‐min mice show 50% reduction in survival when compared to TSP+/+APC‐min mice alone (P<0.05). Our in vitro experiments indicate that this difference may be due to TSP1 regulation of pro‐inflammatory mechanisms. Together this data indicates TSP1 regulates progression of colon carcinogenesis and define cellular and molecular targets of TSP1 in the prevention of colorectal cancer.

According to the National Cancer Institute more than 140,000 people will be diagnosed in the United States with colorectal cancer this year alone. The adenomatus polyposis coli (APC) gene is frequently mutated in colorectal cancer, the APC-min mouse correspondingly is a widely used model for the study of this type of cancer. Studies indictate that the matricellular protein Thrombospondin 1 (TSP1) is lost during progression of colon cancer. To study the role of TSP1 in this disease we generated APC-min and TSP-/- APC-min mice. Our data indicates that expression of TSP1 in the APC-min mouse prevents the development of adenomas in the large intestine in mice fed a low fat diet. On the other hand lack of TSP1 increases tumor multiplicity in these mice, and up-regulates Ki67 in intestinal tissue. Moreover TSP-/- APC-min mice show 50% reduction in survival when compared to TSP+/+APC-min mice alone. Here we show that ADD1/SREBP1 a key transcription factor linking changes in nutritional status of certain genes that regulate systemic energy metabolism is upregulated only in the TSP null APC min/+ animals indicating and association with increased tumor aggressiveness. Together this data indicates that TSP1 regulates progression of colon carcinogenesis and define molecular targets of TSP1 in the prevention of colorectal cancer. Citation Format: David R. Soto Pantoja, Maria E. Torres, J. Michael Sipes, Nicole Morris, David D. Roberts, Nancy J. Emenaker. Thrombospondin-1 regulates carcinogenesis in an in vivo model of colorectal cancer. [abstract]. In: Proceedings of the Thirteenth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2014 Sep 27-Oct 1; New Orleans, LA. Philadelphia (PA): AACR; Can Prev Res 2015;8(10 Suppl): Abstract nr B18.

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