PubMed · 11470939
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M A Whittaker, N J Carr, N Cripps. 2001. Hyperplastic polyposis coli associated with dysplasia.. https://doi.org/10.1136/pmj.77.910.532
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BACKGROUND: In recent years it has become evident that nonsteroidal anti-inflammatory drugs, in particular aspirin represent a potential class of cancer chemotherapeutic agents. Despite the wealth of knowledge gained from epidemiological, clinical and animal studies, the effectiveness of aspirin to treat established gastrointestinal cancer has not been determined. The present study examines the ability of aspirin to treat established polyposis in Min/+ mice. METHODS: Min/+ mice with established polyposis were treated orally once daily from 12-16 weeks of age with either drug vehicle or aspirin (25 mg/kg). Upon completion of treatment, the number, location and size of intestinal tumours was determined. Additional variables examined were the number of apoptotic cells within tumours and COX activity. RESULTS: Administration of aspirin for 4 weeks to Min/+ mice produce no effect on tumour number compared to vehicle-treated Min/+ mice (65 +/- 8 vs. 63 +/- 9, respectively). In addition, aspirin had no effect on tumour size or location. However, aspirin treatment produced a greater than 2-fold (p<0.05) increase in the number of apoptotic positive cells within tumours and significantly decreased hepatic PGE2 content. CONCLUSIONS: Aspirin was found to have no effect on tumour number and size when administered to Min/+ mice with established polyposis. The findings in the present study call in to question the utility of aspirin as a stand-alone treatment for established GI cancer. However, aspirin's ability to significantly promote apoptosis may render it suitable for use in combinatorial chemotherapy.
According to the classical interpretation of Knudson's 'two-hit' hypothesis for tumorigenesis, the two 'hits' are independent mutation events, the end result of which is loss of a tumor suppressing function. Recently, it has been shown that the APC (adenomatous polyposis coli) gene does not entirely follow this model. Both the position and type of the second hit in familial adenomatous polyposis (FAP) polyps depend on the localization of the germline mutation. This non-random distribution of somatic hits has been interpreted as the result of selection for more advantageous mutations during tumor formation. However, the APC gene encodes for a multifunctional protein, and the exact cellular function upon which this selection is based is yet unknown. In this study, we have analyzed somatic APC point mutations and loss of heterozygosity (LOH) in 133 colorectal adenomas from six FAP patients. We observed that when germline mutations result in truncated proteins without any of the seven beta-catenin downregulating 20-amino-acid repeats distributed in the central domain of APC, the majority of the corresponding somatic point mutations retain one or, less frequently, two of the same 20-amino-acid repeats. Conversely, when the germline mutation results in a truncated protein retaining one 20-amino-acid repeat, most second hits remove all 20-amino-acid repeats. The latter is frequently accomplished by allelic loss. Notably, and in contrast to previous observations, in a patient where the germline APC mutation retains two such repeats, the majority of the somatic hits are point mutations (and not LOH) located upstream and removing all of the 20-amino-acid repeats. These results indicate selection for APC genotypes that are likely to retain some activity in downregulating beta-catenin signaling. We propose that this selection process is aimed at a specific degree of beta-catenin signaling optimal for tumor formation, rather than at its constitutive activation by deletion of all of the beta-catenin downregulating motifs in APC.
Germline mutations of the adenomatous polyposis coli ( APC) gene cause familial adenomatous polyposis (FAP), an autosomal, dominantly inherited disease that predisposes patients to colorectal cancer. The APC gene is composed of 15 coding exons and encodes an open reading frame of 8.5 kb. The 3' 6.5 kb of the APCopen reading frame is encoded by a single exon, exon 15. Most identified APC mutations are at the 5' half of the APC open reading frame and are nucleotide substitutions and small deletions or insertions that result in truncation of the APC protein. Very few well-characterized gross alterations of APC have been reported. Patients with FAP typically develop hundreds to thousands of colorectal tumors beginning in their adolescence. A subgroup of patients with FAP who develop fewer tumors at an older age have what is called attenuated FAP (AFAP). Accumulating evidence indicates that patients carrying germline APC mutations in the first four coding exons, in the alternatively spliced region of exon 9, or in the 3' half of the coding region usually develop AFAP. We characterized two germline APC alterations that deleted the entire APC exon 15 as the result of 56-kb and 73-kb deletions at the APC locus. A surprising finding was that one proband had the typical FAP phenotype, whereas the other had a phenotype consistent with that of AFAP.