Chan Choi

Association Between Recurrent Metastasis From Stage II and III Primary Colorectal Tumors and Moderate Microsatellite Instability

Colorectal cancer cells frequently have low levels of microsatellite instability (MSI-L) and elevated microsatellite alterations at selected tetranucleotide repeats (EMAST), but little is known about the clinicopathologic significance of these features. We observed that patients with stage II or III colorectal cancer with MSI-L and/or EMAST had shorter times of recurrence-free survival than patients with high levels of MSI (P = .0084) or with highly stable microsatellites P = .0415), based on Kaplan-Meier analysis. MSI-L and/or EMAST were independent predictors of recurrent distant metastasis from primary stage II or III colorectal tumors (Cox proportional hazard analysis: hazard ratio, 1.83; 95% confidence interval, 1.06-3.15; P = .0301).

NTRK1 fusions for the therapeutic intervention of Korean patients with colon cancer

The identification and clinical validation of cancer driver genes are essential to accelerate the translational transition of cancer genomics, as well as to find clinically confident targets for the therapeutic intervention of cancers. Here we identified recurrent LMNA-NTRK1 and TPM3-NTRK1 fusions in Korean patients with colon cancer (3 out of 147, 2%) through next-generation RNA sequencing (RNA-seq). NTRK1 fusions were mutually exclusive oncogenic drivers of colon cancer that were accompanied with in vitro potential of colony formation and in vivo tumorigenicity comparable to KM12, a human colon cancer cell line harboring TPM3-NTRK1 fusion. NTRK1-encoded TrkA protein was prevalent in 11 out of 216 Korean (5.1%) and 28 out of 472 Chinese patients (5.9%) from independent cohorts, respectively. The expression level of TrkA was significantly correlated with NTRK1 fusion (p = 0.0192), which was verified by a fluorescence in situ hybridization (FISH). Korean patients with TrkA-positive colon cancer had a marginal but significant shorter overall survival time than TrkA-negative colon cancer [hazard ratio (HR) = 0.5346, 95% confidential interval (CI) = 0.2548-0.9722, p = 0.0411]. In addition, KM12 cell line was sensitive to selective TrkA inhibitors. These results demonstrate that NTRK1 fusion is granted as a clinically relevant target for therapeutic intervention of colon cancer.

Sa1991 Metastasis Candidate Genes on 9p24.2 in Colorectal Cancers

cancers with different mitochondrial DNA (mtDNA) genetics including mutations, the number of noncoding variants, the number of synonymous variants, the number of non-synonymous variants and the number of total variants. (A) Basal oxygen consumption rate (OCR) of polyps with different mtDNA genetics. (B) Basal OCR of cancers with different mtDNA genetics

39 Identification of Gene Loci With Microsatellite Repeats Frequently Altered in Liver Metastasis Exhibiting Moderate Levels of Microsatellite Instability From Primary CRC

Background and Aims. Elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) is a genetic signature observed in up to 60% of sporadic colorectal cancers (CRCs). Unlike microsatellite unstable colorectal cancers, where hypermethylation of the major mismatch repair (MMR) gene hMLH1 drives multiple target gene mutations, the cause of EMAST is unknown but was recently associated with reduced expression of the minor MMR protein hMSH3 in CRCs. We assessed experimentally whether hMSH3 deficiency is a cause of EMAST.Methods. We constructed plasmids containing D8S321 and D20S82 tetranucleotide loci (12 and 16 repeats of AAAG respectively) that are used to define EMAST. Sequences were cloned +1 bp out of frame immediately after the start codon of the EGFP gene. A -4 bp frameshift deletion of one AAAG unit would allow in-frame expression of EGFP. Mutationresistant counterpart plasmids were constructed by changing 2 nucleotide sequences in every 3 units of AAAG, preventing frameshift mutations. First, we created MMR proficient, hMLH1, hMSH6, and hMSH3 stable cell lines carrying the plasmids. Subsequently, we reduced hMSH3 expression via RNAi in MMR proficient cells harboring the EMAST constructs. Non-fluorescent cells were sorted and cultured for flow cytometry analysis. Mutations were examined by DNA-sequencing. Results. Sequencing confirmed frameshift mutations in fluorescent cells containing D8S321 and D20S82. Such mutations included contraction and expansion of microsatellites. D8S321 mutations occurred 31-and 40-fold higher in hMLH1 and hMSH3 cells compared to hMSH6 cells, respectively. D20S82 mutations occurred 82-and 49-fold higher in hMLH1 and hMSH3 cells compared to hMSH6 cells, respectively. When hMSH3 expression levels were reduced in MMR proficient cells upon hMSH3 shRNA transfection, significantly higher mutation rates were detected in hMSH3 knockdown cells for D8S321 (18.14 x 10-4) and D20S82 (11.14 x 10-4) compared to their individual scramble control cells (0 and 0.26 x 10-4 separately). Conclusions. EMAST is dependent upon MMR background, with hMSH3 more prone to frameshift mutations than hMSH6, opposite to frameshift mutation observed at mononucleotide repeats. hMSH3 mimics complete MMR failure (hMLH1) in inducing EMAST. Furthermore, knock down of hMSH3 expression alone was able to elicit EMAST. Given the observed heterogeneous expression of hMSH3 in CRCs with EMAST, loss of hMSH3 function appears to be the cause of EMAST.