Person:

Kucherlapati, Melanie

Non-steroidal anti-inflammatory drugs (NSAIDs) appear to be effective cancer chemopreventives. Previous cellular studies demonstrated that aspirin (acetylsalicylic acid: ASA) and nitric oxide-donating ASA (NO-ASA) suppressed microsatellite instability (MSI) in mismatch repair (MMR)-deficient cells linked to the common cancer predisposition syndrome hereditary non-polyposis colorectal cancer or Lynch syndrome (LS/HNPCC), at doses 300-3000-fold less than ASA. Using a mouse model that develops MMR-deficient intestinal tumors that appear pathologically identical to LS/HNPCC we show that ASA (400 mg/kg) and low dose NO-ASA (72 mg/kg) increased life span by 18–21%. We also note a trend where ASA treatment resulted in intestinal tumors with reduced high MSI (H-MSI) and increased low MSI (L-MSI) as defined by the Bethesda Criteria. Low dose NO-ASA had a minimal effect on MSI status. In contrast to previous studies, high dose NO-ASA (720/1500 mg/kg) treatments increased tumor burden, decreased life span and exacerbated MSI uniquely in the LS/HNPCC mouse model. These results suggest that MMR-deficient tissues/mice may be specifically sensitive to intrinsic pharmacokinetic features of this drug. It is likely that long-term treatment with ASA may represent a chemopreventive option for LS/HNPCC patients. Moreover, since low dose NO-ASA demonstrates equivalent life span increase at 10-fold lower doses than ASA, it may have the potential to significantly reduce the gastropathy associated with long-term ASA treatment.

Background & Aims Mutations in the DNA mismatch repair (MMR) gene MSH2 cause Lynch Syndromes I & II, and sporadic colorectal cancers (CRCs). Msh2null mice predominantly develop lymphoma and do not accurately recapitulate the CRC phenotype.

Methods We generated and examined mice with a conditional Msh2 disruption (Msh2LoxP), permitting tissue-specific gene inactivation. ECMsh2LoxP/LoxP mice carried an EIIa-Cre transgene and VCMsh2LoxP/LoxP mice carried a Villin-Cre transgene. We combined the VCMsh2LoxP allele with either Msh2Δ7null (VCMsh2LoxP/null) or Msh2G674D mutations (VCMsh2LoxP/G674D) to create allelic phase mutants. These mice were given cisplatin, or 5-fluorouracil/leucovorin and oxaliplatin (FOLFOX) and their tumors were measured by magnetic resonance imaging.

Results Embryonic fibroblasts from ECMsh2LoxP/LoxP mice do not express MSH2 and are MMR-deficient. Reverse transcription, PCR, and immunohistochemistry from VCMsh2LoxP/LoxP mice demonstrated specific loss of Msh2 mRNA and protein from epithelial cells of the intestinal tract. Microsatellite instability (MSI) was observed in all VCMsh2 strains and limited to the intestinal mucosa. Resulting adenomas and adenocarcinomas had somatic Apc truncation mutations. VCMsh2LoxP/LoxP mice did not develop lymphoma. Comparison of allelic phase tumors revealed significant differences in multiplicity and size. When treated with cisplatin or FOLFOX, tumor size was reduced in VCMsh2LoxP/G674D but not VCMsh2LoxP/null tumors. The apoptotic response to FOLFOX was partially sustained in the intestinal mucosa of VCMsh2LoxP/G674D animals.

Conclusion Msh2LoxP/LoxP mice in combination with appropriate Cre recombinase transgenes have excellent potential for preclinical modeling of Lynch Syndrome, MMR deficient tumors of other tissue types, and use in drug development.