Poster Presentation 28th Lorne Cancer Conference 2016

Prevention of MAPK pathway-driven proliferation of RAS-mutated colorectal cancers with new generation BRAF inhibitors (#117)

Andreas Behren 1 2 , Candani SA Tutuka 1 2 , Miles C Andrews 1 2 3 4 , John M Mariadason 1 2 , Paul Ioannidis 1 2 , Christopher Hudson 1 2 , Jonathan Cebon 1 2 3 4
  1. Olivia Newton-John Cancer Research Institute, Heidelberg, VIC, Australia
  2. School of Cancer Medicine, LaTrobe University, Melbourne, VIC, Australia
  3. Department of Medicine, University of Melbourne, Parkville, VIC, Australia
  4. Medical Oncology, Austin Health, Heidelberg, VIC, Australia

It is now well-established that mutation-selective BRAF inhibitors as used to treat BRAFmtmelanoma can lead to paradoxical activation of the mitogen-activated protein kinase (MAPK) signalling pathway in cells lacking BRAF mutations, but harbouring RAS mutations and other MAPK pathway signalling drivers. This raises concerns about treatment-promoted secondary malignancies. We previously reported a patient whose metastatic colon cancer (BRAFwt/KRASG12D) was promoted in-vivo and in-vitro by BRAF inhibitor therapy. Here we compare the effect of the “classical” BRAF inhibitor PLX4032 (vemurafenib) with that of a new class of BRAF inhibitors lacking the paradoxical activation potential and hence are termed “paradox breakers” on a variety of colorectal cancer cells.

We used western-blotting and proliferation assays to determine if the paradox breakers retain activity against BRAFmtmelanoma cells while not paradoxical activating MAPK-signalling in RASmt colorectal cancer cells.

Paradox Breakers effectively inhibit mutated BRAF in melanoma cells similarly to vemurafenib. Vemurafenib induced hyper-phosphorylation in MEK and ERK and led to an increase in cell proliferation in colorectal cancer cell lines with mutant RAS (LM-COL-1, ALA and LS513). PLX8394, the paradox breaker drug in clinical development, did not result in MAPK activation or increased proliferation. Neither the EGFR pathway nor AKT play any role in the observed differences. These results demonstrate that the new class of BRAF inhibitors can effectively block mutant BRAF without promoting growth of RASmt colorectal cancer cells, potentially offering a safer alternative for patients that are long-term treated with these drugs. 

Classical BRAF inhibitors can promote secondary malignancies by paradoxical activation of MAPK signalling and may promote the growth of cancer precursor lesions. Based on our in-vitro results the paradox-breakers are a safer alternative to classical BRAF-inhibitors and further investigations and clinical trials are warranted.