DEVELOPMENT OF POSTOPERATIVE LOCAL TUMORS AND DISTANT METASTASES IS DIET, GENETICS, AND MICROBIOME-DEPENDENT IN A MOUSE MODEL OF COLORECTAL CANCER RECURRENCE
Ryan B. Morgan*1, Mason Vierra1, Meejeon Roh1, Andrea Olivas1, Lindsay Alpert1, Kinga S. Olortegui1, Colin W. Steele2, Eugene B. Chang1, Ralph Weichselbaum1, Olga Zaborina1, Benjamin D. Shogan1
1The University of Chicago Medicine, Chicago, IL; 2Glasgow Royal Infirmary, Glasgow, Glasgow, United Kingdom
Introduction: A high-fat diet (HFD) is one of the primary environmental risk factors for the development of a local recurrence or distant metastasis following curative resection for colorectal cancer. Whether the promotion of postoperative recurrence by a HFD is specific to certain genetic mutations or generalizable to all tumors is unknown. Using a validated mouse model of CRC recurrence, we test the hypothesis that only certain genetic profiles exhibit increased tumorigenesis in response to a HFD.
Methods: C57/6BL male mice were fed either a HFD (60% fat) or standard diet (6.5% fat) (SD) for 6 weeks prior to creation of a colonic anastomosis. On post-operative day (POD) 2, mice were given a cancer cell enema (mimicking exfoliated cancer cells) with either AKPT (adenoma-to-carcinoma pathway: Apcfl/fl;KrasG12D/+;Tp53fl/fl;Tgfbr1fl/fl) or KPN (serrated adenoma pathway: KrasG12D/+;Tp53-/-;Rosa26N1icd/+) organoids. Mice were sacrificed on POD 56 and local and distant tumors were identified by gross inspection, H&E, and in-situ hybridization for Lgr5by a blinded pathologist. Tumor burden was evaluated using a 5-point scale (tumor size and dissemination). Rates of tumor formation were compared using binomial probability tests.
Results: Both AKPT and KPN organoids (n=20) formed local tumors and distant metastases, but the effect of a HFD on tumor incidence differed. In AKPT mice, a HFD promoted a significantly higher incidence of both local tumors (100% HFD v. 40% SD; p=0.01) and distant metastases (100% v. 20%; p<0.01). In contrast, KPN mice given a HFD had no significant difference in local tumor formation (20% HFD v. 60% SD; p=0.09) and lower rates of metastasis (0% v. 60%; p=0.01). Importantly, we observed that a HFD significantly increased AKPT tumor burden resulting in enhanced cancer-related mortality (FIG 1); there was no effect of a HFD on tumor burden or mortality in KPN mice.
To confirm that a HFD was responsible for enhanced tumor formation in AKPT mice, we created experiments in which HFD-fed mice are ‘reversed' by switching to a SD for 6 weeks prior to operation. Strikingly, 'reversed' animals had decreased tumor burden and improved survival compared to HFD-fed mice (p=0.04) (FIG 2). Finally, since diet shapes the microbiome, we hypothesized that the effect of a HFD on tumor burden in AKPT mice is mediated by alterations to the microbiome and repeated our anastomotic model using germ-free C57/6BL mice. In a preliminary cohort of GF mice (n=5) that underwent an anastomosis and AKPT enema, only one mouse formed post-operative tumors.
Conclusions: The influence of a HFD in promoting CRC recurrence is dependent upon the interaction of the microbiome and the genetic profile of the CRC. Further research defining the precise mechanism by which a HFD and microbiome co-interact may result in novel strategies to prevent and treat colorectal cancer.
Figure 1: Survival of mice receiving AKPT or KPN organoid cells via enema following colon anastomosis based on pre-operative exposure to a high-fat diet vs a standard diet (N = 5 for all groups. Median survival 32 days for AKPT HFD vs. > 56 days for all other groups; p<0.01)
Figure 2: Survival of mice receiving AKPT organoid cells via enema following colon anastomosis based on pre-operative exposure to a high-fat diet, a standard diet, or a high-fat diet followed by ‘reversal' with a standard diet (N = 9-10 for all groups. Median survival: 38 days for HFD vs. >56 days for ‘reversal' and SD; p=0.04).
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