Abstract 152: Gene expression and mutational load in colon tumors from African American patients

Colorectal cancer (CRC) is the third most common cancer among African Americans (AA) and when compared to Caucasian Americans (CA), they present with more advanced disease and lower survival rates. Our previous findings suggest that this may be related to the differential expression of genes linked to cell recruitment and immune response. Therefore, we aimed to investigate if differences in the cellular anti-tumor immune activity in AA and CA patients play a role in the disparate cancer progression observed between these populations. Our approach includes examining gene expression and immune cell recruitment at the tumor site and secretion of cytokines characteristic of effector T helper cells (Th) subsets in plasma. Lastly, we observed the expression of several proteins involved in apoptosis, stress, and drug resistance in response to treatment with 5-FU in two microsatellite unstable (MSI) CRC cell lines, one from an AA and one from a CA patient, and a microsatellite stable (MSS) CA colon cancer cell line. Methods: We performed whole transcriptome sequencing in colon tumors, utilizing the NextSeq 500/550 High Output Kit v2.5 (Illumina). ELISA assays (RayBiotech) were used to examine the secretion of cytokines linked to Th subsets (Th1, Th2, Th17) and inflammation in plasma. Using IHC we evaluated the cell recruitment and activation of T and Natural Killer cells in colon tumors and by MetaCore we correlated gene expression to immune-oncology pathways. Western blots were used to evaluate the expression of cleaved caspase 3, phospho-JNK and RRM1 in the in-vitro models. Results: ELISAs of plasma from CA and AA patients revealed a differential Th cytokines production patterns between early stage (I, II) and late stage (III) disease. Our gene expression results indicate that the immune profiles of AA patients differ from CA in the expression of 36 key genes and cytokines related to cellular anti-tumor activity, including FOXP3, Granzyme B and IL-17A, suggestive of more favorable prognosis in the CA tumors. Lastly, the MSI AA cell line showed sensitivity to 5-FU in terms of protein expression when compared to the CA cell lines. Conclusions: Our gene expression findings demonstrated the differential expression of immunological pathways involved in immune-surveillance, cancer progression and antigen presentation in colon tumors from these two ethnicities. These results were in accordance with the systemic cytokines’ expression patterns observed in plasma and cell recruitment to the tumor sites. Importantly, our data indicates that treatment with 5-FU chemotherapy promotes apoptosis and stress in the MSI AA cell line but fails to produce the same effect in the CA cell lines at the same concentrations. Taken together, the differences in the immunological profiles in AA when compared to CA suggests a deficiency of the appropriate immune defense mechanisms in this population that may contribute to the cancer disparities among CRC patients. Citation Format: Jenny Paredes, Jone Garai, Ping Ji, Sayed Imtiaz, Marzia Spagnardi, Maria Munoz-Sagastibelza, Mubarak Akadri, Raavi Gupta, Mohamed Alshal, Maksim Agaronov, Henry Talus, Ellen Li, Jennie Williams, Jovanny Zabaleta, Laura Martello-Rooney. Gene expression and mutational load in colon tumors from African American patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 152.