Abstract 5024: Implications of MAPK pathway inhibition on monocytes and tumor-associated macrophages in melanoma

Plasticity in T-cell populations during response and onset of resistance to targeted therapy has been well documented. More recently, macrophage-derived tumor necrosis factor has been described to drive resistance to MAPK pathway inhibition, yet little is known on the adaptation of tumor-associated macrophage populations to treatment and disease progression in human melanoma. To test for alterations in macrophage abundance following resistance to MAPK pathway inhibition, we applied a fluorescence-based co-staining strategy on melanoma specimens, representing tissue collected from patients before treatment and at relapse. In addition, we established in vitro co-culture systems to study the paracrine effects of melanoma cells on various aspects of monocyte differentiation and macrophage activation in the background of MAPK inhibition and resistance. Resistance to targeted therapy was found to be associated with an increase in the number of tumor-resident macrophages. In vitro co-culture of melanoma cell lines with monocytes isolated from the peripheral blood of healthy donors or with CSF1-differentiated macrophages in the presence or absence of MAPK inhibition led to profound changes in monocyte/macrophage marker expression, indicating a direct interplay between the two cell populations upon MAPK pathway inhibition. Our data show that macrophages play an integral role in the changing immune-microenvironment during the course of MAPK pathway inhibition. Elucidation of mechanisms driving these processes will result in strategies to optimize treatment combinations and consecutive treatment outcomes for melanoma patients. Note: This abstract was not presented at the meeting. Citation Format: Gabriela Gremel, Maria Romina Girotti, Amaya Viros, Garry Ashton, Helen Bradley, Elena Galvani, Rebecca Lee, Alberto Fusi, Paul Lorigan, Richard Marais. Implications of MAPK pathway inhibition on monocytes and tumor-associated macrophages in melanoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5024. doi:10.1158/1538-7445.AM2015-5024