Tumour micro-environment elicits innate resistance to RAF inhibitors through HGF secretion


Drug resistance presents a challenge to the treatment of cancer patients. Many studies have focused on cell-autonomous mechanisms of drug resistance. By contrast, we proposed that the tumour micro-environment confers innate resistance to therapy. Here we developed a co-culture system to systematically assay the ability of 23 stromal cell types to influence the innate resistance of 45 cancer cell lines to 35 anticancer drugs. We found that stroma-mediated resistance is common, particularly to targeted agents. We characterized further the stroma-mediated resistance of BRAF-mutant melanoma to RAF inhibitors because most patients with this type of cancer show some degree of innate resistance1,2,3,4. Proteomic analysis showed that stromal cell secretion of hepatocyte growth factor (HGF) resulted in activation of the HGF receptor MET, reactivation of the mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3-OH kinase (PI(3)K)–AKT signalling pathways, and immediate resistance to RAF inhibition. Immunohistochemistry experiments confirmed stromal cell expression of HGF in patients with BRAF-mutant melanoma and showed a significant correlation between HGF expression by stromal cells and innate resistance to RAF inhibitor treatment. Dual inhibition of RAF and either HGF or MET resulted in reversal of drug resistance, suggesting RAF plus HGF or MET inhibitory combination therapy as a potential therapeutic strategy for BRAF-mutant melanoma. A similar resistance mechanism was uncovered in a subset of BRAF-mutant colorectal and glioblastoma cell lines. More generally, this study indicates that the systematic dissection of interactions between tumours and their micro-environment can uncover important mechanisms underlying drug resistance.

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Figure 1: The effect of stromal cells on the chemoresistance of cancer cell lines.
Figure 2: HGF rescues melanoma cancer cell lines from RAF and MEK inhibitors.
Figure 3: HGF is present in the stromal cells of melanoma and correlates with a poor response to therapy.
Figure 4: Characterizing the molecular mechanism of HGF-induced primary resistance.


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We thank all members of the Golub laboratory for discussions. We thank C. M. Johannessen, I. Rabinowitch, N. Shoresh and A. Goren for critical reading of the manuscript, and L. Gaffney for expert assistance with the graphics. This work was supported by the Howard Hughes Medical Institute, National Cancer Institute grants P50CA093683 and U54CA112962 (T.R.G.) and a Melanoma Research Alliance Team Science Award.

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R.S. and T.R.G. conceived and designed the experiments. R.S. performed the primary cancer–stroma–drugs screen with help from K.S., M.B.-R. and A.D. R.S. carried out the protein array experiments. R.S., K.S., M.B.-R., A.D. and M.M.M. carried out the secondary screens, western blot analysis and enzyme-linked immunosorbent assays (ELISAs). J.D. performed tyrosine kinase phosphorylation profiling. Clinical samples and clinical data were collected by J.A.W., K.T.F., D.T.F., P.B.C., D.B.S., A.R. and R.S.L. The immunohistochemistry experiments were carried out and analysed by S.O., T.M. and Z.R.Q. The immunofluorescence experiments were carried out by J.A.W. and Z.A.C. R.S. and T.R.G. produced the text and figures, including the Supplementary Information. K.S. helped to produce some of the text and figures. All authors discussed the results and contributed to the final manuscript.

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Correspondence to Todd R. Golub.

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Straussman, R., Morikawa, T., Shee, K. et al. Tumour micro-environment elicits innate resistance to RAF inhibitors through HGF secretion. Nature 487, 500–504 (2012). https://doi.org/10.1038/nature11183

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