Platelet-activating factor receptor (PAF-R)-dependent pathways control tumour growth and tumour response to chemotherapy

Abstract

BackgroundPhagocytosis of apoptotic cells by macrophages induces a suppressor phenotype. Previous data from our group suggested that this occurs via Platelet-activating factor receptor (PAF-R)-mediated pathways. In the present study, we investigated the impact of apoptotic cell inoculation or induction by a chemotherapeutic agent (dacarbazine, DTIC) on tumour growth, microenvironmental parameters and survival, and the effect of treatment with a PAF-R antagonist (WEB2170). These studies were performed in murine tumours: Ehrlich Ascitis Tumour (EAT) and B16F10 melanoma.MethodsTumour growth was assessed by direct counting of EAT cells in the ascitis or by measuring the volume of the solid tumour. Parameters of the tumour microenvironment, such as the frequency of cells expressing cyclo-oxygenase-2 (COX-2), caspase-3 and galectin-3, and microvascular density, were determined by immunohistochemistry. Levels of vascular endothelium growth factor (VEGF) and prostaglandin E2 (PGE2) were determined by ELISA, and levels of nitric oxide (NO) by Griess reaction. PAF-R expression was analysed by immunohistochemistry and flow cytometry.ResultsInoculation of apoptotic cells before EAT implantation stimulated tumour growth. This effect was reversed by in vivo pre-treatment with WEB2170. This treatment also reduced tumour growth and modified the microenvironment by reducing PGE2, VEGF and NO production. In B16F10 melanoma, WEB2170 alone or in association with DTIC significantly reduced tumour volume. Survival of the tumour-bearing mice was not affected by WEB2170 treatment but was significantly improved by the combination of DTIC with WEB2170. Tumour microenvironment elements were among the targets of the combination therapy since the relative frequency of COX-2 and galectin-3 positive cells and the microvascular density within the tumour mass were significantly reduced by treatment with WEB2170 or DTIC alone or in combination. Antibodies to PAF-R stained the cells from inside the tumour, but not the tumour cells grown in vitro. At the tissue level, a few cells (probably macrophages) stained positively with antibodies to PAF-R.ConclusionsWe suggest that PAF-R-dependent pathways are activated during experimental tumour growth, modifying the microenvironment and the phenotype of the tumour macrophages in such a way as to favour tumour growth. Combination therapy with a PAF-R antagonist and a chemotherapeutic drug may represent a new and promising strategy for the treatment of some tumours.

Emerging targets for combination therapy in melanomas

“…Interestingly, differential effects observed in vivo and in vitro, indicate that heterotypic interactions (between tumor and microenvironmental cells) are PAFR‐dependent [107]. Similar results were also observed with another chemotherapeutic agent, dacarbazine [108].…”

“…In fact, studies have shown that in a melanoma model, the co‐injection of a large number of apoptotic cells can promote tumor growth from a subtumorigenic dose of melanoma cells and this combination induces an inflammatory response, recruiting neutrophils and macrophages [110]. Further studies have related that this process is in part mediated by PAFR [108,111]. Besides, the suppressive phenotype of macrophages induced by the clearance of apoptotic cells depends on PAFR and CD36 expressed by macrophages [112,113].…”

Clearance of Apoptotic Cells by Macrophages Induces Regulatory Phenotype and Involves Stimulation of CD36 and Platelet-Activating Factor Receptor

“…The concentration of WEB (50  μ M) and CV (10  μ M) used here was based on previous works by our group [8, 17]. CD36 was blocked by a specific anti-CD36 blocking antibody (monoclonal IgA anti-CD36, clone CRF D-2712, BD Biosciences, Franklin Lakes, NJ, USA) at 1  μ g/mL, added 30 min before the addition of AC.…”

Platelet-activating factor (PAF) receptor expression is associated with histopathological stage and grade and patients’ survival in gastric adenocarcinoma

“…Animals co-treated with cisplatin and the PAFR antagonist, WEB2086, presented significantly decreased tumor growth compared to the control group and those treated with only one agent, supporting evidence that PAFR accumulation and signalling may be part of a prosurvival program of melanoma cells [43]. In Ehrlich Ascitis Tumor (EAT) and B16F10 melanoma, PAFR-dependent pathways were activated during experimental tumor growth, modifying the microenvironment and the phenotype of the tumor macrophages, supporting evidence that combination therapy with a PAFR antagonist and a chemotherapeutic drug may represent a new and promising strategy for the treatment of some tumors [56].…”