Colorectal Cancers with the Uncommon Findings of KRAS Mutation and Microsatellite Instability

Investigating the Pathogenicity of Uncommon KRAS Mutations and Their Association with Clinicopathologic Characteristics in Patients with Colorectal Cancer

Kirsten rat sarcoma viral oncogene homolog (KRAS) somatic mutations occur in 30% to 40% of patients with colorectal cancer (CRC). These were thought to equally affect prognosis and resistance to anti-epidermal growth factor receptor agents; however, recent data show the activity of KRAS-G12C and pan-RAS inhibitors. The effects of uncommon KRAS (uKRAS) variants are largely unexplored. The distribution and pathogenicity of uKRAS mutations and their relationship with patients' clinicopathologic features were assessed. A total of 2427 CRCs were profiled for KRAS using next-generation sequencing (NGS). The study and control groups included patients with uKRAS (<1% frequency in CRC data sets on cBioPortal) and canonical KRAS mutations, respectively. In silico protein structure modifications and prediction analyses were performed by using PyMOL, trRosetta, and PolyPhen-2. uKRAS mutations affected 35 cases (1.5%), with G13C (28.6%), G12R (20%), and V14I (8.6%) being most common. Missense mutations (D33E, G12W, G12F, Q22H, Q61L, and L19F) occurred in nine cases (25.7%). Duplications (G10dup and L52_G60dup) affected two cases. Pathogenicity analyses showed that G12W, Q22R, L56V, and A130I mutations are probably damaging, with scores between 0.928 and 1.000. No differences were seen in clinicopathologic features. uKRAS mutants had lower event-free survival but no difference in overall survival compared with controls. Although these data are hypothesis generating and need further confirmation, they highlight the importance of NGS-based profiling to identify CRC patients with uKRAS mutations as candidates for personalized therapy.

SIRT1: a novel regulator in colorectal cancer

The class-III histone deacetylase SIRT1 is the most extensively investigated sirtuin deacetylase. It is resistant to the broad deacetylase inhibitor trichostatin A and depends on oxidized nicotinamide adenine nucleotide (NAD+). SIRT1 plays a crucial role in the tumorigenesis of numerous types of cancers, including colorectal cancer (CRC). Accumulating evidence indicates that SIRT1 is a therapeutic target for CRC; however, the function and underlying mechanism of SIRT1 in CRC still need to be elucidated. Herein, we provide a detailed and updated review to illustrate that SIRT1 regulates many processes that go awry in CRC cells, such as apoptosis, autophagy, proliferation, migration, invasion, metastasis, oxidative stress, resistance to chemo-radio therapy, immune evasion, and metabolic reprogramming. Moreover, we closely link our review to the clinical practice of CRC treatment, summarizing the mechanisms and prospects of SIRT1 inhibitors in CRC therapy. SIRT1 inhibitors as monotherapy in CRC or in combination with chemotherapy, radiotherapy, and immune therapies are comprehensively discussed. From epigenetic regulation to its potential therapeutic effect, we hope to offer novel insights and a comprehensive understanding of SIRT1's role in CRC.

K-ras Mutations as the Earliest Driving Force in a Subset of Colorectal Carcinomas

K-ras oncogene is a key factor in colorectal cancer. Based on published and our data we propose that K-ras could be the oncogene responsible for the inactivation of the tumor-suppressor gene APC, currently considered as the initial step in colorectal tumorigenesis. K-ras fulfills the criteria of the oncogene-induced DNA damage model, as it can provoke well-established causes for inactivating tumor-suppressors, i.e. DNA double-strand breaks (causing allele deletion) and ROS production (responsible for point mutation). The model we propose is a variation of the currently existing model and hypothesizes that, in a subgroup of colorectal carcinomas, K-ras mutation may precede APC inactivation, representing the earliest driving force and, probably, an early biomarker of colorectal carcinogenesis. This observation is clinically useful, since it may modify the preventive colorectal cancer strategy, restricting numerically patients undergoing colonoscopies to those bearing K-ras mutation in their colorectum, either in benign polyps or the normal accompanying mucosa.