bims-pimaco Biomed News
on PI3K and MAPK signalling in colorectal cancer
Issue of 2021‒09‒05
six papers selected by
Lucas B. Zeiger
Beatson Institute for Cancer Research

  1. Mol Cancer Res. 2021 Aug 30. pii: molcanres.0248.2021. [Epub ahead of print]
      KRAS gene somatic point mutations is one of the most prominently mutated proto-oncogenes known to date, and accounts for approximately 60% of all colorectal cancer cases. One of the most exciting drug development areas against colorectal cancer is the targeting of undruggable kinases and kinase-substrate molecules, although whether and how they can be integrated with other therapies remains a question. Current clinical trial data have provided supporting evidence on the use of combination treatment involving MEK inhibitors and either one of the PI3K inhibitors for metastatic colorectal cancer patients to avoid the development of resistance and provide effective therapeutic outcome rather than using a single agent alone. Many clinical trials are also ongoing to evaluate different combinations of these pathway inhibitors in combination with immunotherapy for colorectal cancer patients whose current palliative treatment options are limited. Nevertheless, continued assessment of these targeted cancer therapies will eventually allow colorectal cancer patients to be treated using a personalized medicine approach. In this review, the most recent scientific approaches and clinical trials targeting KRAS mutations directly or indirectly for the management of colorectal cancer are discussed.
  2. Mol Clin Oncol. 2021 Oct;15(4): 197
      Large prospective clinical trials have demonstrated that colorectal cancers (CRCs) with wild-type KRAS respond favorably to anti-epidermal growth factor receptor treatment, thus making mutational analysis obligatory prior to treatment. In our study, frozen CRC tissues from Libyan patients were analyzed for KRAS and HRAS mutations in codons 12/13 by direct sequencing and the correlations with clinical and pathological parameters were investigated. A total of 34 CRC cases, comprising 19 men and 15 women (age range, 24-87 years), were subjected to systematic analysis for RAS mutations. Although HRAS mutations were not detected in any of the patients in the study group, KRAS codon 12/13 mutations were present in 38.2% (13/34) of the patients. The frequent types of codon 12 mutations were glycine to aspartate (G12D, 46.1%); glycine to valine (G12V, 30.8%) and glycine to cysteine (G12C, 15.4%), while the codon 13 mutations were glycine to aspartate (G13D, 7.7%). G→A mutations occurred in 53.8% (7/13) of the patients, while G→T mutations occurred in 46.2% (6/13) of the patients. Mutations occurred at the first base of codon 12 or 13 in 2/13 (15.4%) and at the second base in 11/13 (84.6%) patients. There was no significant association between clinicopathological characteristics and KRAS mutation status, except the site of the tumors harboring KRAS mutations, which was as follows: The frequency was higher among tumors located in the left colon (8/13, 61.5%) compared to other sites (P=0.027). KRAS mutations were correlated with advanced age, with 10/13 being aged >50 years and affected 8/15 female patients (53%) compared with 5/19 male patients (26%). The highest frequency of KRAS mutations was observed in highly differentiated CRCs (8/13).
    Keywords:  DNA sequencing; HRAS; KRAS; colorectal cancer; mutation
  3. Cell Oncol (Dordr). 2021 Aug 30.
      PURPOSE: We hypothesised that plasticity in signal transduction may be a mechanism of drug resistance and tested this hypothesis in the setting of cetuximab resistance in patients with KRAS/NRAS/BRAFV600 wild-type colorectal cancer (CRC).METHODS: A multiplex antibody-based platform was used to study simultaneous changes in signal transduction of 55 phospho-proteins in 12 KRAS/NRAS/BRAFV600 wild-type CRC cell lines (6 cetuximab sensitive versus 6 cetuximab resistant) following 1 and 4 h in vitro cetuximab exposure. We validated our results in CRC patient samples (n = 4) using ex vivo exposure to cetuximab in KRAS/NRAS/BRAFV600 cells that were immunomagnetically separated from the serous effusions of patients with known cetuximab resistance.
    RESULTS: Differences in levels of phospho-proteins in cetuximab sensitive and resistant cell lines included reductions in phospho-RPS6 and phospho-PRAS40 in cetuximab sensitive, but not cetuximab resistant cell lines at 1 and 4 h, respectively. In addition, phospho-AKT levels were found to be elevated in 3/4 patient samples following ex vivo incubation with cetuximab for 1 h. We further explored these findings by studying the effects of combinations of cetuximab and two PI3K pathway inhibitors in 3 cetuximab resistant cell lines. The addition of PI3K pathway inhibitors to cetuximab led to a significantly higher reduction in colony formation capacity compared to cetuximab alone.
    CONCLUSION: Our findings suggest activation of the PI3K pathway as a mechanism of cetuximab resistance in KRAS/NRAS/BRAFV600 wild-type CRC.
    Keywords:  Cetuximab; Colorectal cancer; Phospho-proteomics; Proteomics; Resistance mechanisms; Signalling adaptations
  4. Proc Natl Acad Sci U S A. 2021 Sep 07. pii: e2107207118. [Epub ahead of print]118(36):
      The RAF/MEK/ERK pathway is central to the control of cell physiology, and its dysregulation is associated with many cancers. Accordingly, the proteins constituting this pathway, including MEK1/2 (MEK), have been subject to intense drug discovery and development efforts. Allosteric MEK inhibitors (MEKi) exert complex effects on RAF/MEK/ERK pathway signaling and are employed clinically in combination with BRAF inhibitors in malignant melanoma. Although mechanisms and structures of MEKi bound to MEK have been described for many of these compounds, recent studies suggest that RAF/MEK complexes, rather than free MEK, should be evaluated as the target of MEKi. Here, we describe structural and biochemical studies of eight structurally diverse, clinical-stage MEKi to better understand their mechanism of action on BRAF/MEK complexes. We find that all of these agents bind in the MEK allosteric site in BRAF/MEK complexes, in which they stabilize the MEK activation loop in a conformation that is resistant to BRAF-mediated dual phosphorylation required for full activation of MEK. We also show that allosteric MEK inhibitors act most potently on BRAF/MEK complexes rather than on free active MEK, further supporting the notion that a BRAF/MEK complex is the physiologically relevant pharmacologic target for this class of compounds. Our findings provide a conceptual and structural framework for rational development of RAF-selective MEK inhibitors as an avenue to more effective and better-tolerated agents targeting this pathway.
    Keywords:  BRAF; MEK; MEK inhibitor; X-ray crystallography; allosteric kinase inhibitor
  5. Cancer Gene Ther. 2021 Sep 01.
      Although it has long been deemed "undruggable", with the development of drugs specifically binding the KRAS-G12C mutant protein, clinical trials that directly inhibit oncogenic RAS have recently made promising improvements. In particular, the covalent KRAS-G12C inhibitors sotorasib and adagrasib are used to treat patients with advanced non-small cell lung cancer (NSCLC) carrying KRAS-G12C mutations. Unfortunately, the vast majority of patients do not respond to KRAS-G12C inhibitor therapy, mainly due to intrinsic or acquired resistance caused by cellular, molecular, and genetic mechanisms. Improving the understanding of drug response in the tumor microenvironment may continue to promote the design, testing, and clinical application of KRAS-G12C inhibitors.
  6. ESMO Open. 2021 Aug 31. pii: S2059-7029(21)00191-5. [Epub ahead of print]6(5): 100230
      BACKGROUND: Oncogenic mutations in PIK3CA are prevalent in diverse cancers and can be targeted with inhibitors of the phosphoinositide-3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway. Analysis of circulating tumor DNA (ctDNA) provides a minimally invasive approach to detect clinically actionable PIK3CA mutations.PATIENTS AND METHODS: We analyzed PIK3CA hotspot mutation frequency by droplet digital PCR (QX 200; BioRad) using 16 ng of unamplified plasma-derived cell-free DNA from 68 patients with advanced solid tumors (breast cancer, n = 41; colorectal cancer, n = 13; other tumor types, n = 14). Results quantified as variant allele frequencies (VAFs) were compared with previous testing of archival tumor tissue and with patient outcomes.
    RESULTS: Of 68 patients, 58 (85%) had PIK3CA mutations in tumor tissue and 43 (74%) PIK3CA mutations in ctDNA with an overall concordance of 72% (49/68, κ = 0.38). In a subset analysis, which excluded samples from 26 patients known not to have disease progression at the time of sample collection, we found an overall concordance of 91% (38/42; κ = 0.74). PIK3CA-mutated ctDNA VAF of ≤8.5% (5% trimmed mean) showed a longer median survival compared with patients with a higher VAF (15.9 versus 9.4 months; 95% confidence interval 6.7-17.1 months; P = 0.014). Longitudinal analysis of ctDNA in 18 patients with serial plasma collections (range 2-22 time points, median 5) showed that those with a decrease in PIK3CA VAF had a longer time to treatment failure (TTF) compared with patients with an increase or no change (10.7 versus 2.6 months; P = 0.048).
    CONCLUSIONS: Detection of PIK3CA mutations in ctDNA is concordant with testing of archival tumor tissue. Low quantity of PIK3CA-mutant ctDNA is associated with longer survival and a decrease in PIK3CA-mutant ctDNA on therapy is associated with longer TTF.
    Keywords:  PIK3CA; cancer; circulating tumor DNA; droplet digital PCR