The biochemical signature of SB202190 identifies BRAF activating mutations in primary colorectal cancer organoids.

The p38 inhibitor SB202190 is a necessary component of the medium used for normal colorectal mucosa culture. Sato suggested that SB202190 primary activity would be EGFR signaling stabilization, causing an increased phosphorylation of Erk1-2 sustaining organoids proliferation. Although, some colorectal cancer (CRC) derived organoid cultures were inhibited by this molecule.MethodsWe decided to biochemically investigate this phenomenon on a prospective collection of CRC organoids, established by a simplified culture medium devoid of any contamination of animal-derived cytokines or transfected cell-derived supernatants.ResultsThe yield of our culture method was in line with the results obtained from other labs, with a 35.8% of continuously proliferating CRC organoids, that could be expanded and tested. We found that Erk1-2 phosphorylation was induced by SB202190 in 19 and inhibited in 5 organoid cultures. The NGS analysis revealed that the inhibition of p-Erk1-2 signaling corresponded to the cultures with BRAF mutations (with 4 different hits, one being undescribed), while p-Erk1-2 induction was apparently unrelated to other mutations involving the EGFR pathway (Her2, KRAS, NRAS). We found that SB202190 mirrored the biochemical activity of the BRAF inhibitor Dabrafenib, known to induce the paradoxical activation of p-Erk1-2 signaling in BRAF wild type cells. SB202190 inhibited the growth of BRAF-mutated organoids, as did the specific inhibitors Dabrafenib and PLX8394.ConclusionsOur simplified organoid medium, containing only animal-free EGF as added growth factor, is suitable for CRC organoids establishment and culture. SB202190 can predict BRAF activating mutations in primary CRC organoids, also for new variants, preceding and enforcing NGS data.