ATG16L1 isoforms and CRC health disparities

Compared to non-Hispanic Whites (NHW), African Americans (AAs) are 20% more likely to get colorectal cancer (CRC) and 40% more likely to die from CRC. The negative impacts of health inequity on CRC incidence and mortality are undeniable, though it is becoming clear that ancestry-specific tumor biology also plays a significant

role. A greater understanding of ancestry specific biology on CRC etiology is required if we are to fully elucidate its true contribution to cancer disparity, ATG16L1 is critical for LC3 lipidation and autophagosome formation. ATG16L1 isoforms show ancestry specific expression in CRC tissue. Alanine homozygosity at residue 300 of

ATG16L1 (A300A) is more predominant in NHWs and threonine homozygosity at the same residue (T300T) is more predominant in AA’s. In CRC, the A300A genotype is associated with reduced metastasis and increased overall survival and the T300T genotype is associated with increased risk of CRC. Using isogenic CRC cells, we

found that chemotherapies that enhance autophagy show more therapeutic efficacy in T300T cells than more established cytotoxic based chemotherapies which have more cell killing efficacy in the A300A isoform. Collectively, these data suggest that isoform status of ATG16L1 promote aggressive CRC and represent a key

pivotal biomarker to stratify CRC treatment response in relation to autophagic function. Our hypothesis is “that the ATGL16L T300T isoform is a prognostic indicator of response in AA CRC patients and represents a predictive treatment biomarker for treatment decisions and help to reduce disparate outcomes.”

Specific Aim 1. Determine whether ATG16L1 isoforms differentially promote aggressive CRC growth and metastasis in vivo. Using isogenic male and female ATG16L1 T300T and ATG16L1 A300A mice we will chemically induce colitis-associated tumors using azoxymethane (AOM) and dextran sodium sulfate (DSS).10

Following AOM / DSS exposure, we will determine tumor number, size, and location in T300T and A300A mice. Male and female Apc min/+ mice that are ATG16L1 T300T will be cross-bred with ATG16L1 A300A mice.11 We will isolate tumor epithelial cells and stromal fibroblasts from tumors arising from transgenic mice over time,

define alterations in their molecular biology and establish novel cell lines.12,13 This aim will inform on the biological mechanisms promoting aggressive tumor growth and metastasis in patients with the different ATG16L1 isoforms. Specific Aim 2. Determine whether the T300T isoform predicts tumor response and improves outcome

to combination-treatment regimens that target autophagy in pre-clinical isogenic mouse tumor models. The response of male and female murine colorectal tumors using cells isolated from Aim 1 will be defined in either T300T or A300A mice, to drug combinations that utilize autophagy to kill, or where autophagy reduces

drug efficacy. This will define the importance of T300T or A300A isoform expression with respect to both the tumor epithelial cells and to the autophagic competency of the tumor microenvironment. This aim will inform on why AA CRC patients have poorer responses to standard of care therapies resulting in worse outcomes.