Paclitaxel Treatment and Proprotein Convertase 1/3 (PC1/3) Knockdown in Macrophages is a Promising Antiglioma Strategy as Revealed by Proteomics and Cytotoxicity Studies

Abstract

<jats:p>High grade gliomas are the most common brain tumors in adult. These tumors are characterized by a high infiltration in microglial cells and macrophages. The immunosuppressive tumor environment is known to orient immune cells toward a pro-tumoral and anti-inflammatory phenotype. Therefore, the current challenge for cancer therapy is to find a way to reorient macrophages toward an antitumoral phenotype. Previously, we demonstrated that macrophages secreted antitumoral factors when they were invalidated for the proprotein converstase 1/3 (PC1/3) and treated with LPS. However, achieving an activation of macrophages via LPS/TLR4/Myd88-dependent pathway appears yet unfeasible in cancer patients. On the contrary, the antitumor drug Paclitaxel is also known to activate the TLR4 MyD88-dependent signaling pathway and mimics LPS action. Therefore, we evaluated if PC1/3 knock-down (KD) macrophages could be activated by Paclitaxel and efficient against glioma. We report here that such a treatment of PC1/3 KD macrophages drove to the overexpression of proteins mainly involved in cytoskeleton rearrangement. In support of this finding, we found that these cells exhibited a Ca<jats:sup>2+</jats:sup> increase after Paclitaxel treatment. This is indicative of a possible depolymerization of microtubules and may therefore reflect an activation of inflammatory pathways in macrophages. In such a way, we found that PC1/3 KD macrophages displayed a repression of the anti-inflammatory pathway STAT3 and secreted more pro-inflammatory cytokines. Extracellular vesicles isolated from these PC1/3 KD cells inhibited glioma growth. Finally, the supernatant collected from the coculture between glioma cells and PC1/3 KD macrophages contained more antitumoral factors. These findings unravel the potential value of a new therapeutic strategy combining Paclitaxel and PC1/3 inhibition to switch macrophages toward an antitumoral immunophenotype.</jats:p>

PC1/3 KD Macrophages Exhibit Resistance to the Inhibitory Effect of IL-10 and a Higher TLR4 Activation Rate, Leading to an Anti-Tumoral Phenotype

“…Most importantly, after TLR4 stimulation, PC1/3 KD macrophages released killing factors that exerted a strong antitumor effect on breast (SKBR3) and ovarian (SKOV3) cancer cells [11]. We also found that extracellular vesicles isolated from PC1/3 KD cells challenged with the antitumor drug paclitaxel, a TLR4 sterile ligand, inhibited glioma growth [13]. Moreover, the supernatant collected from the co-culture between glioma cells and PC1/3KD macrophages also contained more anti-tumoral factors.…”

“…In this context, we found that the endopeptidase proprotein convertase 1/3 (PC1/3) is a relevant target for anti-tumoral immunotherapy [11][12][13][14]. Indeed, PC1/3 knockdown macrophages (PC1/3 KD) present all the characteristics of activated pro-inflammatory macrophages [11][12][13][14][15][16]. These cells spontaneously secrete more pro-inflammatory cytokines and chemokines [11].…”

“…These cells spontaneously secrete more pro-inflammatory cytokines and chemokines [11]. This effect was more prevalent after toll-like receptor 4 (TLR4) and toll-like receptor 9 (TLR9) stimulation [11][12][13]. It has been linked to a stronger activation of the pro-inflammatory pathway nuclear factor-kappa B (NFKB) and repression of the anti-inflammatory pathway signal transducer and activator of transcription 3 (STAT3) [11][12][13].…”

“…This effect was more prevalent after toll-like receptor 4 (TLR4) and toll-like receptor 9 (TLR9) stimulation [11][12][13]. It has been linked to a stronger activation of the pro-inflammatory pathway nuclear factor-kappa B (NFKB) and repression of the anti-inflammatory pathway signal transducer and activator of transcription 3 (STAT3) [11][12][13]. Noteworthy, this effect persisted even in the presence of an anti-inflammatory environment mimicked by interleukin-10 treatment [11,13].…”

“…It has been linked to a stronger activation of the pro-inflammatory pathway nuclear factor-kappa B (NFKB) and repression of the anti-inflammatory pathway signal transducer and activator of transcription 3 (STAT3) [11][12][13]. Noteworthy, this effect persisted even in the presence of an anti-inflammatory environment mimicked by interleukin-10 treatment [11,13]. The secretome from PC1/3 KD cells treated with lipopolysaccharides (LPS), a TLR4 ligand, exerted a strong chemotactic effect on human naïve CD4+T cells [11].…”