Posters at AACR Annual Meeting

Validation of a MEK/MET-specific NGS panel for early phase trial interrogation‘ and ‘Upregulation of the MET transcript is consistently associated with invasion and tumor budding in colorectal cancer‘ were presented at the AACR Annual Meeting on 18 Apr 2016 in New Orleans. Mariangela Russo from UNITO also presented related work (Abstract 878).

 

Validation of a MEK/MET-specific NGS panel for early phase trial interrogation

Introduction – MErCuRIC is a Phase Ib/II clinical trial study using a combined MEK1/2 – cMET inhibition in RAS MT and RAS WT (with aberrant c[[unable to display character: ‐]]MET) colorectal cancer patients. As part of the discovery efforts on the cases enrolled in Phase I, we aimed to analyze the mutation status of 10 genes that could potentially be associated to the doublet MEK/MET inhibition. This study compared the MEK/MET-specific panel with the Ion Torrent 50 gene panel, aiming to compare: long-established, commercially available panels against this newly developed panel; the Ion Torrent PGM2 platform against Illumina MiSeq v.3 600 bp chemistry; hot-spot-based against full exomes-designed; and to compare the use of different bioinformatics reporter systems. The overlapping genes between the panels were: EGFR (n=3); BRAF (n=4); KRAS (n=8); NRAS (n=1); MET (n=8); PIK3CA (n=6); and ERBB2 (n=5).

Summary of Method – NGS Design – The Multiplicom – MErCuRIC specific MASTR assay includes PTEN, MAP2K1 (MEK), EGFR, KRAS, NRAS, BRAF, PIK3CA, ERBB2, MET and PIK3R1, involving 257 amplicons in 4 plexes covering all coding exons of the 10 genes. Of the 257, 21 are control amplicons to allow for gene deletions/amplifications. The average length of the amplicons is 198 bp ranging from 124 bp to 255 bp.
Validation – From a pool of 120 routine tumour samples characterised with a 50 gene mutation panel (Ion Torrent PGM2) and confirmed by Sanger sequencing and/or COBAS (Roche) QPCR, 24 FFPE cases were selected representing colorectal cancer and 4 other solid tumour types; all included a variety of DNA quality, and DNA concentration was standardized prior to library preparation. Pre-analytical handling was in accordance with established protocols in a laboratory, clinically-accredited in the UK for tissue-based, anatomical pathology testing.

Results – The evaluation of this MEK/MET-specific panel (Illumina MiSeq platform) resulted in 100% coverage of all targets, a higher than 97% on target reads and higher than 99% of all amplicons within 20% of mean coverage. The design minimized the areas of low coverage. A small part of exon 9 of ERBB2 was covered suboptimally: the low covered region is 30 bp in size located at the 5’ end of exon 9. It is unlikely that this low coverage led to false negative results since no mutations are reported in the COSMIC database for this DNA fragment. The results were concordant in relation to mutations involved in the genes stated above. Importantly, the percentages of allele frequency between both methods were similar, with variations ranging from 0.2% to 11.5% with an average variation of 5.2%. Insertion/deletion (Indel) detection however, required alternative bioinformatics pathways.

Conclusion – After combining well-established quality metrics to cover pre-analytical aspects with suitable technologies such as the MiSeq platform (Illumina) and appropriate bioinformatics, we recognize that this MEK/MET-specific NGS panel is fit for purpose.

 

Upregulation of the MET transcript is consistently associated with invasion and tumor budding in colorectal cancer

Background – The c-MET proto-oncogene is frequently overexpressed (50-60%), amplified (1-3%), and mutated (1-3%) in colorectal cancer (CRC). Hepatocyte growth factor (HGF)-dependent and independent activation of c-MET has been associated with increased survival and resistance to targeted therapies. This study aimed to investigate the role of the HGF/c-MET axis in regulating migration/invasion in CRC, using pre-clinical models and clinical samples.

Methods – In order to model CRC tumour cell invasion, we have generated invasive CRC subpopulations using Boyden Invasion chambers. To model the CRC microenvironment, we have used a range of co-culture techniques with CRC cells and colon fibroblasts. Migration/invasion was determined using xCELLigence System (Roche). c-MET expression in parental and invasive cell lines was measured using Western blotting and qRT-PCR. c-MET expression in CRC FFPE tissues was measured using IHC and RNAScope®.

Results – We identified marked upregulated expression of c-MET at both the protein and transcript levels in our invasive CRC cell line models. Importantly, both parental and invasive subpopulations were found to be inherently dependent on c-MET for migration, as RNAi against c-MET abrogated migration/invasion in both parental and invasive models. We also demonstrated that stimulation of CRC cells with rh-HGF resulted in increased CRC cell migration/invasion. In addition, co-culture of CRC cells with colonic myofibroblasts, resulted in marked increases in migratory and invasive capacity, and this was dependent on HGF/c-MET signaling. Interestingly, stimulation with myofibroblast conditioned medium or HGF promotes rapid degradation of c-MET at the protein level, followed by recycling, while METtranscript remains unaltered, illustrating a dynamic expression of c-MET protein in response to activation. We further showed that MET is transcriptionally upregulated in tumour budding foci at the invasive front of a cohort of stage III CRC tumors. Intriguingly, c-MET protein levels do not correlate with the transcript, most likely due to a similar protein degradation process observed in our aforementioned in vitro models.

Conclusions – We show for the first time a key role for transcriptional upregulation of MET as a molecular driver of tumour invasion, both in vitro and in stage III CRC tumours.