Hormone replacement therapy and adenoma recurrence: implications for its role in colorectal cancer risk

Potentially functional SNPs (pfSNPs) as novel genomic predictors of 5-FU response in metastatic colorectal cancer patients

5-Fluorouracil (5-FU) and its pro-drug Capecitabine have been widely used in treating colorectal cancer. However, not all patients will respond to the drug, hence there is a need to develop reliable early predictive biomarkers for 5-FU response. Here, we report a novel potentially functional Single Nucleotide Polymorphism (pfSNP) approach to identify SNPs that may serve as predictive biomarkers of response to 5-FU in Chinese metastatic colorectal cancer (CRC) patients. 1547 pfSNPs and one variable number tandem repeat (VNTR) in 139 genes in 5-FU drug (both PK and PD pathway) and colorectal cancer disease pathways were examined in 2 groups of CRC patients. Shrinkage of liver metastasis measured by RECIST criteria was used as the clinical end point. Four non-responder-specific pfSNPs were found to account for 37.5% of all non-responders (P<0.0003). Five additional pfSNPs were identified from a multivariate model (AUC under ROC = 0.875) that was applied for all other pfSNPs, excluding the non-responder-specific pfSNPs. These pfSNPs, which can differentiate the other non-responders from responders, mainly reside in tumor suppressor genes or genes implicated in colorectal cancer risk. Hence, a total of 9 novel SNPs with potential functional significance may be able to distinguish non-responders from responders to 5-FU. These pfSNPs may be useful biomarkers for predicting response to 5-FU.

Sex modulates intestinal transformation by the tumor-suppressor GCC

BACKGROUND AND AIMS

Ovarian hormones oppose colorectal cancer, although mechanisms remain undefined. Similarly, the most commonly lost gene products in intestinal neoplasia include guanylin and uroguanylin, paracrine hormones for guanylyl cyclase C (GCC), which recently emerged as a tumor suppressor. However, the molecular intersection between intestinal paracrine and systemic sex hormones opposing intestinal neoplasia has not been explored.

METHODS

Intestinal tumorigenesis was quantified in wild type (Gcc(+/+)) and GCC-deficient (Gcc(-/-)) mice carrying mutations in adenomatous polyposis coli (Apc) (Apc(Min/+)) or exposed to the carcinogen azoxymethane (AOM). Proliferation of epithelial cells was examined employing cell cycle markers.

RESULTS

Deletion of Gcc increased tumor multiplicity and growth in colons and small intestines, respectively, of Apc(Min) (/+) mice. While changes in multiplicity and growth increased tumor burden, females exhibited approximately 60% (p= 0.040) of the burden in males. Similarly, female Gcc(-/-) mice treated with AOM exhibited approximately 40% (p= 0.048) of the burden in males. Moreover, Gcc deletion promoted epithelial cell proliferation, quantified by increases in beta-catenin, cMyc, cyclin D1, and phosphorylated retinoblastoma protein (pRb), in males but not females.

CONCLUSION

There is a previously unappreciated interaction between sex and GCC signaling restricting crypt cell proliferation. Thus, the invariable loss of guanylin and uroguanylin resulting in tumorigenesis is mitigated in females by hormonal components of the ovarian axis. In the context of the universal overexpression of GCC by tumors, these observations highlight the combination of GCC paracrine and ovarian hormones for targeted prevention and therapy of colorectal cancer.

Folate fortification, plasma folate, homocysteine and colorectal adenoma recurrence

In 1996, the US Food and Drug Administration mandated the fortification of grain products with folic acid, a nutrient that has been associated with lower risk of colorectal neoplasia. We assessed the relation of plasma folate and homocysteine and colorectal adenoma recurrence separately in 2 studies: the first involved an intervention of a cereal supplement that contained folic acid, wheat bran fiber (WBF), and the second was conducted primarily during postfortification of the food supply using ursodeoxycholic acid (UDCA). Analyses were stratified for multivitamin use. Results show that plasma folate and homocysteine concentrations were associated with adenoma recurrence among nonusers of multivitamins only. Among nonmultivitamin users, the odds ratio [OR] (95% confidence interval [CI]) for those in the highest versus the lowest folate quartile was 0.65 (0.40-1.06) for the WBF study and 0.56 (0.31-1.02) for the UDCA; likewise, individuals in the highest versus the lowest quartile of homocysteine had higher odds of adenoma recurrence, in both the WBF (OR = 2.25; 95% CI = 1.38-3.66) and UDCA (OR = 1.93; 95% CI = 1.07-3.49) populations. Analyses comparing multivitamin users to different plasma folate concentrations among nonusers show that odds of recurrence for supplement users was lower only when compared to nonusers who had lower concentrations. Our results show that higher plasma folate or lower homocysteine levels are associated with lower odds of recurrence among nonusers of multivitamins in both studies. Our finding, suggesting that multivitamins or supplemental folate only benefit individuals with lower plasma folate concentrations, should be taken into consideration when designing and interpreting results of intervention studies.

Pronounced reduction in adenoma recurrence associated with aspirin use and a polymorphism in the ornithine decarboxylase gene

Most sporadic colon adenomas acquire mutations in the adenomatous polyposis coli gene (APC) and show defects in APC-dependent signaling. APC influences the expression of several genes, including the c-myc oncogene and its antagonist Mad1. Ornithine decarboxylase (ODC), the first enzyme in polyamine synthesis, is a transcriptional target of c-myc and a modifier of APC-dependent tumorigenesis. A single-nucleotide polymorphism exists in intron 1 of the human ODC gene, which lies between two myc-binding domains. This region is known to affect ODC transcription, but no data exist on the relationship of this polymorphism to risk of colorectal neoplasia in humans. We show that individuals homozygous for the minor ODC A-allele who reported using aspirin are approximately 0.10 times as likely to have an adenoma recurrence as non-aspirin users homozygous for the major G-allele. Mad1 selectively suppressed the activity of the ODC promoter containing the A-allele, but not the G-allele, in a human colon cancer-derived cell line (HT29). Aspirin (>or=10 microM) did not affect ODC allele-specific promoter activity but did activate polyamine catabolism and lower polyamine content in HT29 cells. We propose that the ODC polymorphism and aspirin act independently to reduce the risk of adenoma recurrence by suppressing synthesis and activating catabolism, respectively, of colonic mucosal polyamines. These findings confirm the hypothesis that the ODC polymorphism is a genetic marker for colon cancer risk, and support the use of ODC inhibitors and aspirin, or other nonsteroidal antiinflammatory drugs (NSAIDs), in combination as a strategy for colon cancer prevention.