Functional differences drive the selection of NRAS mutants in melanoma

ABSTRACTDistinct NRAS mutants are enriched in various tumor types. Here, we generated a suite of fully congenic, conditional, Nras knock-in mouse models (LSL-Nras Q61R, -K, -L, -H, -P, -Q; G12D and G13D, -R) to test the hypothesis that melanocyte transformation requires functions specific to the NRAS mutants enriched in human melanoma (Q61R and Q61K). Consistent with the rarity of NRAS codon 12 and 13 mutants in human melanoma, spontaneous melanomas were rare or absent in mice expressing NRAS G12D, G13D or G13R. Mice expressing less common codon 61 alleles (Q61H, Q61P) also developed few or no tumors. NRAS Q61R, Q61K, or Q61L expression, by contrast, induced rapid melanoma onset with high penetrance. Cohorts of heterozygous mice containing one LSL-Nras Q61R and one LSL-Nras Q61K, -L, -H, -P, or -Q allele were generated to assess potential interactions between NRAS mutants. The ability of each Nras variant to substitute for an Nras Q61R allele was consistent with its own ability to drive spontaneous melanoma formation. However, LSL-Nras Q61Q/Q61R mice rarely developed tumors. In vitro experiments in mouse embryonic fibroblasts (MEFs) highlighted activation of the MAPK pathway as a defining difference between tumorigenic and non-tumorigenic NRAS mutants. Enhanced MAPK activation was associated with the promotion of BRAF-BRAF and BRAF-CRAF dimers. These results support the development of cancer preventative strategies specific to the properties of the commonly observed RAS mutants in each tumor type.

Comprehensive Validation of Snapback Primer-Based Melting Curve Analysis to Detect Nucleotide Variation in the Codon 12 and 13 of KRAS Gene

Background. KRAS genotyping in tumor samples is a decisive clinical test for the anti-EGFR therapy management. However, the complexity of KRAS mutation landscape across different cancer types and the mosaic effect caused by cancer cellularity and heterogeneity make the choice of KRAS genotyping method a challenging topic in the clinical practice. Methods. We depicted the landscape of somatic KRAS mutation in 7,844 primary tumors and 10,336 metastatic tumors across over 30 types of cancer using the Cancer Genome Atlas (TCGA) and Integrated Mutation Profiling of Actionable Cancer Targets (MSKCC-IMPACT) databases, respectively. A snapback primer assay based on melting curve analysis was developed to detect the most common somatic mutations in KRAS codons 12 and 13. The sensitivity and accuracy of the method was validated by genotyping 100 colorectal cancer (CRC) samples, in comparison with Sanger sequencing and T-A cloning sequencing. Results. Pancreas adenocarcinoma (somatic mutation frequency 90.6%), colorectal adenocarcinoma (42.5%), and lung adenocarcinoma (32.6%) are the top three most KRAS mutant primary cancer types. The metastatic tumors showed a higher prevalence (90.99% versus 66.31%) and diversity of KRAS mutation compared with the primary tumors. Mutations in codons 12 and 13 are the predominant genetic alteration in KRAS (84.15% for TCGA and 86.13% for MSK-IMPACT). Moreover, KRAS mutation is highly correlated with the overall survival of patients with metastatic cancer. The snapback primer assay showed a more favorable performance in enriching and detecting the KRAS codon 12 and 13 mutation (1% mutation load) compared with Sanger sequencing (20% mutation load and 7% false-negative rate). Conclusions. KRAS mutation pattern is highly diverse among different cancer types and is associated with the survival of patients with metastatic cancers. The snapback primer assay is a reliable, sensitive method to detect the major mutant KRAS alleles, which might facilitate the effective cancer treatment decisions.

THE MUTATION STATUS OF KRAS GENE CODON 12 AND 13 IN COLORECTAL ADENOCARCINOMA (Status Mutasi Gen Kras Kodon 12 dan 13 di Adenocarcinoma Kolorektal)

Kanker kolorektum merupakan salah satu kanker yang tersering di dunia. Target molekuler untuk pengobatan kanker kolorektumyaitu Epidermal Growth Factor Receptor (EGFR) dengan pemberian antibodi monoklonal anti-EGFR. Pemberian pengobatan ini tidakdapat memberikan efek dampak di pasien dengan status gen KRAS bentuk mutan, sehingga perlu dilakukan pemeriksaan status mutasigen KRAS. Telitian berupa deskriptif dengan pendekatan potong lintang yang bertujuan untuk mendapatkan data status mutasi genKRAS kodon 12 dan 13 di pasien adenocarcinoma colorectal. Deteksi mutasi KRAS dilakukan dengan teknik Polymerase Chain ReactionRestriction Fragment Length Polymorphism (PCR RFLP) yang dikonfirmasi dengan sekuensing. Sampel telitian adalah 30 blok parafinyang diperoleh dari Rumah Sakit Dr.Soetomo Surabaya masa waktu Januari-Desember 2013. Setelah dilakukan ekstraksi DNA terdapat21 sampel yang dapat digunakan untuk pemeriksaan lanjutan. Hasil PCR RFLP menunjukkan terdapat 7/21 mutasi pada kodon12 dan tidak terdapat mutasi gen KRAS pada kodon 13. Mutasi pada kodon 12 yaitu GGT>GCT, GGT>GGA dan GGT>GAT yangmenyebabkan perubahan asam amino Gly12Ala, Gly12Gly dan Gly12Asp. Simpulan telitian ini adalah mutasi gen KRAS kodon 12 padaadenocarcinoma colorectal di Rumah Sakit Dr. Soetomo Surabaya sebanyak 33%.

Impact of consensus molecular subtyping (CMS) on overall survival (OS) and progression free survival (PFS) in patients (pts) with metastatic colorectal cancer (mCRC): Analysis of CALGB/SWOG 80405 (Alliance).

3511 Background: CALGB 80405 was a randomized Ph3 trial showing no OS or PFS difference in mCRC pts treated with Bevacizumab (BV) or Cetuximab (Cet) in the first line. A Nanostring platform was used to determine the CMS classification of 392 KRAS wt (codon 12 and 13) primary tumors and correlated it with OS and PFS in patients enrolled in 80405. Methods: CMS for 392 of 431tumors were defined using a custom CRC Nanostring panel (39 CMS classification not possible). Stratified Cox proportional hazard model was used to evaluate the effect of CMS classification stratified by prior radiation, prior chemotherapy, adjusting for age, sex, race, primary in place, liver met only, and sidedness. Results: We found CMS1 (14%), CMS2 (47%), CMS3 (2%), CMS4 (29%), NonConsensus (8%). Results are shown in Table 1. Patients with CMS1 who received BV had significantly longer OS than those who received Cet (HR 0.47, 95% CI [0.24, 0.92]). Patients with CMS2 who received BV tended to have shorter OS than those who received Cet (HR 1.41, CI [0.95, 2.08]). Conclusions: Our data suggest that CMS is associated with OS and PFS in first line therapy in mCRC patients. Preliminary data suggest that certain CMS may be associated with efficacy of Bev and Cet based chemotherapy. CMS classification should be explored as a stratification factor in future trials. Support: U10CA180821, U10CA180830, U10CA180882 Clinical trial information: NCT00265850. [Table: see text]