Co-inhibition of colony stimulating factor-1 receptor and BRAF oncogene in mouse models of BRAFV600E melanoma

SF Ngiow, KM Meeth, K Stannard… - …, 2016 - Taylor & Francis
SF Ngiow, KM Meeth, K Stannard, DS Barkauskas, G Bollag, M Bosenberg, MJ Smyth
Oncoimmunology, 2016Taylor & Francis
The presence of colony stimulating factor-1 (CSF1)/CSF1 receptor (CSF1R)-driven tumor-
infiltrating macrophages and myeloid-derived suppressor cells (MDSCs) is shown to
promote targeted therapy resistance. In this study, we demonstrate the superior effect of a
combination of CSF1R inhibitor, PLX3397 and BRAF inhibitor, PLX4720, in suppressing
primary and metastatic mouse BRAFV600E melanoma. Using flow cytometry to assess
SM1WT1 melanoma-infiltrating leukocytes immediately post therapy, we found that …
Abstract
The presence of colony stimulating factor-1 (CSF1)/CSF1 receptor (CSF1R)-driven tumor-infiltrating macrophages and myeloid-derived suppressor cells (MDSCs) is shown to promote targeted therapy resistance. In this study, we demonstrate the superior effect of a combination of CSF1R inhibitor, PLX3397 and BRAF inhibitor, PLX4720, in suppressing primary and metastatic mouse BRAFV600E melanoma. Using flow cytometry to assess SM1WT1 melanoma-infiltrating leukocytes immediately post therapy, we found that PLX3397 reduced the recruitment of CD11b+ Gr1lo and CD11b+ Gr1int M2-like macrophages, but this was accompanied by an accumulation of CD11b+ Gr1hi cells. PDL1 expression on remaining myeloid cells potentially dampened the antitumor efficacy of PLX3397 and PLX4720 in combination, since PD1/PDL1 axis blockade improved outcome. We also reveal a role for PLX3397 in reducing tumor-infiltrating lymphocytes, and interestingly, this feature was rescued by the co-administration of PLX4720. Our findings, from three different mouse models of BRAF-mutated melanoma, support clinical approaches that co-target BRAF oncogene and CSF1R.
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