Colorectal Cancers from Distinct Ancestral Populations Show Variations in BRAF Mutation Frequency

It has been demonstrated for some cancers that the frequency of somatic oncogenic mutations may vary in ancestral populations. To determine whether key driver alterations might occur at different frequencies in colorectal cancer, we applied a high-throughput genotyping platform (OncoMap) to query 385 mutations across 33 known cancer genes in colorectal cancer DNA from 83 Asian, 149 Black and 195 White patients. We found that Asian patients had fewer canonical oncogenic mutations in the genes tested (60% vs Black 79% (P = 0.011) and White 77% (P = 0.015)), and that BRAF mutations occurred at a higher frequency in White patients (17% vs Asian 4% (P = 0.004) and Black 7% (P = 0.014)). These results suggest that the use of genomic approaches to elucidate the different ancestral determinants harbored by patient populations may help to more precisely and effectively treat colorectal cancer

Colon cancer-derived oncogenic EGFR G724S mutant identified by whole genome sequence analysis is dependent on asymmetric dimerization and sensitive to cetuximab

Background: Inhibition of the activated epidermal growth factor receptor (EGFR) with either enzymatic kinase inhibitors or anti-EGFR antibodies such as cetuximab, is an effective modality of treatment for multiple human cancers. Enzymatic EGFR inhibitors are effective for lung adenocarcinomas with somatic kinase domain EGFR mutations while, paradoxically, anti-EGFR antibodies are more effective in colon and head and neck cancers where EGFR mutations occur less frequently. In colorectal cancer, anti-EGFR antibodies are routinely used as second-line therapy of KRAS wild-type tumors. However, detailed mechanisms and genomic predictors for pharmacological response to these antibodies in colon cancer remain unclear. Findings: We describe a case of colorectal adenocarcinoma, which was found to harbor a kinase domain mutation, G724S, in EGFR through whole genome sequencing. We show that G724S mutant EGFR is oncogenic and that it differs from classic lung cancer derived EGFR mutants in that it is cetuximab responsive in vitro, yet relatively insensitive to small molecule kinase inhibitors. Through biochemical and cellular pharmacologic studies, we have determined that cells harboring the colon cancer-derived G719S and G724S mutants are responsive to cetuximab therapy in vitro and found that the requirement for asymmetric dimerization of these mutant EGFR to promote cellular transformation may explain their greater inhibition by cetuximab than small-molecule kinase inhibitors. Conclusion: The colon-cancer derived G719S and G724S mutants are oncogenic and sensitive in vitro to cetuximab. These data suggest that patients with these mutations may benefit from the use of anti-EGFR antibodies as part of the first-line therapy

p85 Associates with Unphosphorylated PTEN and the PTEN-Associated Complex ▿ † ‡

The lipid phosphatase PTEN functions as a tumor suppressor by dephosphorylating the D3 position of phosphoinositide-3,4,5-trisphosphate, thereby negatively regulating the phosphoinositide 3-kinase (PI3K)/AKT signaling pathway. In mammalian cells, PTEN exists either as a monomer or as a part of a >600-kDa complex (the PTEN-associated complex [PAC]). Previous studies suggest that the antagonism of PI3K/AKT signaling by PTEN may be mediated by a nonphosphorylated form of the protein resident within the multiprotein complex. Here we show that PTEN associates with p85, the regulatory subunit of PI3K. Using newly generated antibodies, we demonstrate that this PTEN-p85 association involves the unphosphorylated form of PTEN engaged within the PAC and also includes the p110β isoform of PI3K. The PTEN-p85 association is enhanced by trastuzumab treatment and linked to a decline in AKT phosphorylation in some ERBB2-amplified breast cancer cell lines. Together, these results suggest that integration of p85 into the PAC may provide a novel means of downregulating the PI3K/AKT pathway

Loss of Tuberous Sclerosis Complex 2 (TSC2) Confers Sensitivity to mTOR Inhibitor Everolimus in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the third leading cause of cancer deaths worldwide and hyper-activation of mammalian target of rapamycin (mTOR) signaling plays a pivotal role in HCC tumorigenesis. Tuberous Sclerosis Complex (TSC), a heterodimer of TSC1 and TSC2, functions as a negative regulator of mTOR signaling. In the present study, we discovered that TSC2 loss of function is common in HCC. TSC2 loss was found in 4 of 8 HCC cell lines and 8 of 28 (28.5%) patient-derived HCC xenografts. TSC2 mutations and deletions are likely to be the underlying cause of TSC2 loss in HCC cell lines, xenografts and tumors for most cases. We further demonstrated that TSC2-null HCC cell lines and xenografts have elevated mTOR signaling and, more importantly, were significantly more sensitive to RAD001 (everolimus), an mTOR inhibitor. These preclinical findings led to the analysis of TSC2 status in HCC samples collected in the EVOLVE-1 clinical trial of everolimus. Using an optimized IHC assay we developed, 15 samples with low to undetectable levels of TSC2 (10.8%) were identified (5 in the placebo arm and 10 in the everolimus arm). Although the sample size lacked power to demonstrate statistical significance, TSC2-null/low tumor patients who received everolimus had noticeably longer overall survival than those who received placebo. We also observed that TSC2 loss is rare in Caucasian samples compared to Asian samples. Therefore, we performed an epidemiology survey of more than 239 Asian HCC tumors. The frequency of TSC2 loss is estimated to be around 20% in Asian HBV+ HCC, which accounts for nearly half of HCC malignancies in the world. Taken together, our data strongly argue that TSC2 loss is a predictive biomarker for the sensitivity to everolimus in HCC patients and can be applied as a robust selection biomarker for mTOR inhibitor clinical trials

RAS/RAF family mutations by tumor and gene.

<p>A summary chart of all RAS/RAF mutations in each patient group displays genes across in rows and tumors down in columns. The bottom row of each represents the total number of mutations per tumor as a heat map (0-5 mutations). Chart A displays Asian patients, chart B, Black patients and chart C, White patients.</p

Mutation spectrum by tumor and gene.

<p>A summary chart of all mutations in each group displays genes across in rows and patient tumors down in columns. The bottom row of each represents the total number of mutations per tumor as a heat map (0-5 mutations). Chart A displays Asian patients, chart B, Black patients and chart C, White patients. Chart D displays the distribution of all mutations for each cohort.</p

Hyper-mutated samples.

<p>Represented here are the genes mutated in the 7 patient samples that each have four or more mutations. A, W and B represent tumors from Asian, Black or White tumors, respectively.</p