Person:

Kucherlapati, Melanie

Objective Lynch syndrome is caused by germline mutations in DNA mismatch repair genes leading to microsatellite instability (MSI) and colorectal cancer. Mesalazine, commonly used for the treatment of UC, reduces MSI in vitro. Here, we tested natural compounds for such activity and applied mesalazine and thymoquinone in a Msh2loxP/loxP Villin-Cre mouse model for Lynch syndrome.

Design Flow cytometry was used for quantitation of mutation rates at a CA13 microsatellite in human colon cancer (HCT116) cells that had been stably transfected with pIREShyg2-enhanced green fluorescent protein/CA13, a reporter for frameshift mutations. Mice were treated for 43 weeks with mesalazine, thymoquinone or control chow. Intestines were analysed for tumour incidence, tumour multiplicity and size. MSI testing was performed from microdissected normal intestinal or tumour tissue, compared with mouse tails and quantified by the number of mutations per marker (NMPM).

Results Besides mesalazine, thymoquinone significantly improved replication fidelity at 1.25 and 2.5 µM in HCT116 cells. In Msh2loxP/loxP Villin-Cre mice, tumour incidence was reduced by mesalazine from 94% to 69% (p=0.04) and to 56% (p=0.003) by thymoquinone. The mean number of tumours was reduced from 3.1 to 1.4 by mesalazine (p=0.004) and to 1.1 by thymoquinone (p<0.001). Interestingly, MSI was reduced in normal intestinal tissue from 1.5 to 1.2 NMPM (p=0.006) and to 1.1 NMPM (p=0.01) by mesalazine and thymoquinone, respectively. Thymoquinone, but not mesalazine, reduced MSI in tumours.

Conclusions Mesalazine and thymoquinone reduce tumour incidence and multiplicity in Msh2loxP/loxP Villin-Cre mice by reduction of MSI independent of a functional mismatch repair system. Both substances are candidate compounds for chemoprevention in Lynch syndrome mutation carriers.

Blood-based biomarkers for early detection of colorectal cancer (CRC) could complement current approaches to CRC screening. We previously identified the APC-binding protein MAPRE1 as a potential CRC biomarker. Here we undertook a case-control validation study to determine the performance of MAPRE1 in detecting early CRC and colon adenoma and to assess the potential relevance of additional biomarker candidates. We analyzed plasma samples from 60 patients with adenomas, 30 with early CRC, 30 with advanced CRC, and 60 healthy controls. MAPRE1 and a set of 21 proteins with potential biomarker utility were assayed using high-density antibody arrays, and CEA was assayed using ELISA. The biologic significance of the candidate biomarkers was also assessed in CRC mouse models. Plasma MAPRE1 levels were significantly elevated in both patients with adenomas and patients with CRC compared with controls (P < 0.0001). MAPRE1 and CEA together yielded an area under the curve of 0.793 and a sensitivity of 0.400 at 95% specificity for differentiating early CRC from controls. Three other biomarkers (AK1, CLIC1, and SOD1) were significantly increased in both adenoma and early CRC patient plasma samples and in plasma from CRC mouse models at preclinical stages compared with controls. The combination of MAPRE1, CEA, and AK1 yielded sensitivities of 0.483 and 0.533 at 90% specificity and sensitivities of 0.350 and 0.467 at 95% specificity for differentiating adenoma and early CRC, respectively, from healthy controls. These findings suggest that MAPRE1 can contribute to the detection of early-stage CRC and adenomas together with other biomarkers.