CSF1/CSF1R Signaling Inhibitor Pexidartinib (PLX3397) Reprograms Tumor-Associated Macrophages and Stimulates T-cell Infiltration in the Sarcoma Microenvironment.

Colony-stimulating factor 1 (CSF1) is a primary regulator of the survival, proliferation, and differentiation of monocyte/macrophage that sustains the protumorigenic functions of tumor-associated macrophages (TAMs). Considering current advances in understanding the role of the inflammatory tumor microenvironment, targeting the components of the sarcoma microenvironment, such as TAMs, is a viable strategy. Here, we investigated the effect of PLX3397 (pexidartinib) as a potent inhibitor of the CSF1 receptor (CSF1R). PLX3397 was recently approved by the Food and Drug Administration (FDA) to treat tenosynovial giant cell tumor and reprogram TAMs whose infiltration correlates with unfavorable prognosis of sarcomas. First, we confirmed by cytokine arrays of tumor-conditioned media (TCM) that cytokines including CSF1 are secreted from LM8 osteosarcoma cells and NFSa fibrosarcoma cells. The TCM, like CSF1, stimulated ERK1/2 phosphorylation in bone marrow-derived macrophages (BMDMs), polarized BMDMs toward an M2 (TAM-like) phenotype, and strikingly promoted BMDM chemotaxis. In vitro administration of PLX3397 suppressed pERK1/2 stimulation by CSF1 or TCM, and reduced M2 polarization, survival, and chemotaxis in BMDMs. Systemic administration of PLX3397 to the osteosarcoma orthotopic xenograft model significantly suppressed the primary tumor growth and lung metastasis, and thus improved metastasis-free survival. PLX3397 treatment concurrently depleted TAMs and FOXP3+ regulatory T cells and, surprisingly, enhanced infiltration of CD8+ T cells into the microenvironments of both primary and metastatic osteosarcoma sites. Our preclinical results show that PLX3397 has strong macrophage- and T-cell-modulating effects that may translate into cancer immunotherapy for bone and soft-tissue sarcomas.

Fujiwara T ，Yakoub MA ，Chandler A ，Christ AB ，Yang G ，Ouerfelli O ，Rajasekhar VK ，Yoshida A ，Kondo H ，Hata T ，Tazawa H ，Dogan Y ，Moore MAS ，Fujiwara T ，Ozaki T ，Purdue E ，Healey JH ... -  《-》

Disruption of tumour-associated macrophage trafficking by the osteopontin-induced colony-stimulating factor-1 signalling sensitises hepatocellular carcinoma to anti-PD-L1 blockade.

In the tumour microenvironment, critical drivers of immune escape include the oncogenic activity of the tumour cell-intrinsic osteopontin (OPN), the expression of programmed death ligand 1 (PD-L1) and the expansion of tumour-associated macrophages (TAMs). We investigated the feasibility of targeting these pathways as a therapeutic option in hepatocellular carcinoma (HCC) mouse models. We analysed the number of tumour-infiltrating immune cells and the inflammatory immune profiles in chemically induced liver tumour isolated from wild-type and OPNknockout (KO) mice. In vitro cell cocultures were further conducted to investigate the crosstalk between TAMs and HCC cells mediated by OPN, colony stimulating factor-1 (CSF1) and CSF1 receptor (CSF1R). The in vivo efficacy of anti-PD-L1 and CSF1/CSF1R inhibition was evaluated in OPN overexpressing subcutaneous or orthotopic mouse model of HCC. The numbers of TAMs, as well as the expression levels of M2 macrophage markers and PD-L1 were significantly decreased, but the levels of cytokines produced by T-helper 1 (Th1) cells were upregulated in tumour tissues from OPN KO mice compared with that from the controls. In addition, we observed a positive association between the OPN and PD-L1 expression, and OPN expression and TAM infiltration in tumour tissues from patients with HCC. We further demonstrated that OPN facilitates chemotactic migration, and alternative activation of macrophages, and promotes the PD-L1 expression in HCC via activation of the CSF1-CSF1R pathway in macrophages. Combining anti-PD-L1 and CSF1R inhibition elicited potent antitumour activity and prolonged survival of OPNhigh tumour-bearing mice. Histological, flow cytometric and ELISA revealed increased CD8+ T cell infiltration, reduced TAMs and enhanced Th1/Th2 cytokine balance in multiple mouse models of HCC. OPN/CSF1/CSF1R axis plays a critical role in the immunosuppressive nature of the HCC microenvironment. Blocking CSF1/CSF1R prevents TAM trafficking and thereby enhances the efficacy of immune checkpoint inhibitors for the treatment of HCC.

Zhu Y ，Yang J ，Xu D ，Gao XM ，Zhang Z ，Hsu JL ，Li CW ，Lim SO ，Sheng YY ，Zhang Y ，Li JH ，Luo Q ，Zheng Y ，Zhao Y ，Lu L ，Jia HL ，Hung MC ，Dong QZ ，Qin LX ... -  《-》

PLX3397 treatment inhibits constitutive CSF1R-induced oncogenic ERK signaling, reduces tumor growth, and metastatic burden in osteosarcoma.

Osteosarcoma (OSA) is a heterogeneous and aggressive solid tumor of the bone. We recently identified the colony stimulating factor 1 receptor (Csf1r) gene as a novel driver of osteosarcomagenesis in mice using the Sleeping Beauty (SB) transposon mutagenesis system. Here, we report that a CSF1R-CSF1 autocrine/paracrine signaling mechanism is constitutively activated in a subset of human OSA cases and is critical for promoting tumor growth and contributes to metastasis. We examined CSF1R and CSF1 expression in OSAs. We utilized gain-of-function and loss-of-function studies (GOF/LOF) to evaluate properties of cellular transformation, downstream signaling, and mechanisms of CSF1R-CSF1 action. Genetic perturbation of CSF1R in immortalized osteoblasts and human OSA cell lines significantly altered oncogenic properties, which were dependent on the CSF1R-CSF1 autocrine/paracrine signaling. These functional alterations were associated with changes in the known CSF1R downstream ERK effector pathway and mitotic cell cycle arrest. We evaluated the recently FDA-approved CSF1R inhibitor Pexidartinib (PLX3397) in OSA cell lines in vitro and in vivo in cell line and patient-derived xenografts. Pharmacological inhibition of CSF1R signaling recapitulated the in vitro genetic alterations. Moreover, in orthotopic OSA cell line and subcutaneous patient-derived xenograft (PDX)-injected mouse models, PLX3397 treatment significantly inhibited local OSA tumor growth and lessened metastatic burden. In summary, CSF1R is utilized by OSA cells to promote tumorigenesis and may represent a new molecular target for therapy.

Smeester BA ，Slipek NJ ，Pomeroy EJ ，Laoharawee K ，Osum SH ，Larsson AT ，Williams KB ，Stratton N ，Yamamoto K ，Peterson JJ ，Rathe SK ，Mills LJ ，Hudson WA ，Crosby MR ，Wang M ，Rahrmann EP ，Moriarity BS ，Largaespada DA ... -  《-》

Colony-Stimulating Factor 1 Receptor Blockade Inhibits Tumor Growth by Altering the Polarization of Tumor-Associated Macrophages in Hepatocellular Carcinoma.

Colony-stimulating factor-1 (CSF-1) and its receptor, CSF-1R, regulate the differentiation and function of macrophages and play an important role in macrophage infiltration in the context of hepatocellular carcinoma. The therapeutic effects of CSF-1R blockade in hepatocellular carcinoma remain unclear. In this study, we found that CSF-1R blockade by PLX3397, a competitive inhibitor with high specificity for CSF-1R tyrosine kinase, significantly delayed tumor growth in mouse models. PLX3397 inhibited the proliferation of macrophages in vitro, but intratumoral macrophage infiltration was not decreased by PLX3397 in vivo Gene expression profiling of tumor-associated macrophages (TAM) showed that TAMs from the PLX3397-treated tumors were polarized toward an M1-like phenotype compared with those from vehicle-treated tumors. In addition, PLX3397 treatment increased CD8+ T-cell infiltration, whereas CD4+ T-cell infiltration was decreased. Further study revealed that tumor cell-derived CSF-2 protected TAMs from being depleted by PLX3397. In conclusion, CSF-1R blockade delayed tumor growth by shifting the polarization rather than the depletion of TAMs. CSF-1R blockade warrants further investigation in the treatment of hepatocellular carcinoma. Mol Cancer Ther; 16(8); 1544-54. ©2017 AACR.

Ao JY ，Zhu XD ，Chai ZT ，Cai H ，Zhang YY ，Zhang KZ ，Kong LQ ，Zhang N ，Ye BG ，Ma DN ，Sun HC ... -  《-》

Pexidartinib and Immune Checkpoint Inhibitors Combine to Activate Tumor Immunity in a Murine Colorectal Cancer Model by Depleting M2 Macrophages Differentiated by Cancer-Associated Fibroblasts.

Shimizu D ，Yuge R ，Kitadai Y ，Ariyoshi M ，Miyamoto R ，Hiyama Y ，Takigawa H ，Urabe Y ，Oka S ... -  《INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES》