Research Papers:

Co-existence of BRAF and NRAS driver mutations in the same melanoma cells results in heterogeneity of targeted therapy resistance

Marieke I.G. Raaijmakers, Daniel S. Widmer, Apurva Narechania, Ossia Eichhoff, Sandra N. Freiberger, Judith Wenzina, Phil F. Cheng, Daniela Mihic-Probst, Rob Desalle, Reinhard Dummer and Mitchell P. Levesque _

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Oncotarget. 2016; 7:77163-77174. https://doi.org/10.18632/oncotarget.12848

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Marieke I. G. Raaijmakers1, Daniel S. Widmer1, Apurva Narechania2, Ossia Eichhoff1, Sandra N. Freiberger1,4, Judith Wenzina1,4, Phil F. Cheng1, Daniela Mihic-Probst3, Rob Desalle2, Reinhard Dummer1, Mitchell P. Levesque1

1Department of Dermatology, University of Zurich, University Hospital Zürich, Switzerland

2American Museum of Natural History, New York, New York, USA

3Department of Pathology, University of Zurich, University Hospital Zürich Switzerland

4Department of Dermatology, Skin and Endothelium Research Division, Medical University of Vienna, Austria

Correspondence to:

Mitchell P. Levesque, email: [email protected]

Keywords: melanoma, targeted therapy resistance, MAPK pathway, heterogeneity, mutation

Received: July 04, 2016     Accepted: October 13, 2016     Published: October 24, 2016


Acquired chemotherapeutic resistance of cancer cells can result from a Darwinistic evolution process in which heterogeneity plays an important role. In order to understand the impact of genetic heterogeneity on acquired resistance and second line therapy selection in metastatic melanoma, we sequenced the exomes of 27 lesions which were collected from 3 metastatic melanoma patients treated with targeted or non-targeted inhibitors. Furthermore, we tested the impact of a second NRAS mutation in 7 BRAF inhibitor resistant early passage cell cultures on the selection of second line therapies.

We observed a rapid monophyletic evolution of melanoma subpopulations in response to targeted therapy that was not observed in non-targeted therapy. We observed the acquisition of NRAS mutations in the BRAF mutated patient treated with a BRAF inhibitor in 1 of 5 of his post-resistant samples. In an additional cohort of 5 BRAF-inhibitor treated patients we detected 7 NRAS mutations in 18 post-resistant samples. No NRAS mutations were detected in pre-resistant samples. By sequencing 65 single cell clones we prove that NRAS mutations co-occur with BRAF mutations in single cells. The double mutated cells revealed a heterogeneous response to MEK, ERK, PI3K, AKT and multi RTK - inhibitors.

We conclude that BRAF and NRAS co-mutations are not mutually exclusive. However, the sole finding of double mutated cells in a resistant tumor is not sufficient to determine follow-up therapy. In order to target the large pool of heterogeneous cells in a patient, we think combinational therapy targeting different pathways will be necessary.

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