PLX647

PLX647 is a potent and specific dual inhibitor of FMS and KIT kinases with IC50 values of 28 and 16 nM, respectively [1].

McDonough feline sarcoma viral (v-fms) oncogene homolog (FMS, also known as CSF1R) is a member of the platelet-derived growth factor receptor (PDGFR) family. Macrophage colony-stimulating factor (M-CSF or CSF-1) and interleukin 34 are two known FMS ligands. FMS plays important roles in regulating the survival, proliferation, and differentiation of monocyte/macrophage lineages. The stem cell factor (SCF) receptor v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog (KIT) is also a member of the PDGFR family. Mutational activation of KIT occurs in many cancers [1].

PLX647 is a potent and specific dual inhibitor of FMS and KIT kinases. PLX647 showed aqueous solubility of 14 μM. PLX647 bound to the autoinhibited state of the KIT kinase with the juxtamembrane domain and prevented the activation loop from adopting the DFG-in conformation. In Ba/F3 cells expressing breakpoint cluster region activated kinase (BCR)-FMS and BCR-KIT, PLX647 inhibited cell proliferation with IC50 values of 0.092 and 0.18 μM. Also, PLX647 inhibited osteoclast differentiation with IC50 value of 0.17 μM [1].

In mice, PLX647 (40 mg/kg) significantly reduced LPS-induced TNF-α and IL-6 release by 85% and 75%, respectively. In an acute renal inflammation mouse model, PLX647 (40 mg/kg twice daily) reduced the levels of F4/80+ macrophages by 77% [1].

Reference:
[1].  Zhang C, Ibrahim PN, Zhang J, et al. Design and pharmacology of a highly specific dual FMS and KIT kinase inhibitor. Proc Natl Acad Sci U S A, 2013, 110(14): 5689-5694.

Colony-Stimulating Factor 1 Receptor Antagonists Sensitize Human Immunodeficiency Virus Type 1-Infected Macrophages to TRAIL-Mediated Killing.[Pubmed:27122585]

J Virol. 2016 Jun 24;90(14):6255-6262.

UNLABELLED: Strategies aimed at eliminating persistent viral reservoirs from HIV-1-infected individuals have focused on CD4(+) T-cell reservoirs. However, very little attention has been given to approaches that could promote elimination of tissue macrophage reservoirs. HIV-1 infection of macrophages induces phosphorylation of colony-stimulating factor 1 receptor (CSF-1R), which confers resistance to apoptotic pathways driven by tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), thereby promoting viral persistence. In this study, we assessed whether CSF-1R antagonists (PLX647, PLX3397, and PLX5622) restored apoptotic sensitivity of HIV-1-infected macrophages in vitro PLX647, PLX3397, and PLX5622 at clinically relevant concentrations blocked the activation of CSF-1R and reduced the viability of infected macrophages, as well as the extent of viral replication. Our data show that strategies targeting monocyte colony-stimulating factor (MCSF) signaling could be used to promote elimination of HIV-1-infected myeloid cells and to contribute to the elimination of persistent viral reservoirs. IMPORTANCE: As the HIV/AIDS research field explores approaches to eliminate HIV-1 in individuals on suppressive antiviral therapy, those approaches will need to eliminate both CD4(+) T-cell and myeloid cell reservoirs. Most of the attention has focused on CD4(+) T-cell reservoirs, and scant attention has been paid to myeloid cell reservoirs. The distinct nature of the infection in myeloid cells versus CD4(+) T cells will likely dictate different approaches in order to achieve their elimination. For CD4(+) T cells, most strategies focus on promoting virus reactivation to promote immune-mediated clearance and/or elimination by viral cytopathicity. Macrophages resist viral cytopathic effects and CD8(+) T-cell killing. Therefore, we have explored clearance strategies that render macrophages sensitive to viral cytopathicity. This research helps inform the design of strategies to promote clearance of the macrophage reservoir in infected individuals on suppressive antiviral therapy.

Tyrosine kinase inhibitors reverse type 1 diabetes in nonobese diabetic mice.[Pubmed:19015530]

Proc Natl Acad Sci U S A. 2008 Dec 2;105(48):18895-900.

The recent development of small-molecule tyrosine kinase (TK) inhibitors offers increasing opportunities for the treatment of autoimmune diseases. In this study, we investigated the potential of this new class of drugs to treat and cure type 1 diabetes (T1D) in the NOD mouse. Treatment of prediabetic and new onset diabetic mice with imatinib (Gleevec) prevented and reversed T1D. Similar results were observed with sunitinib (Sutent), an additional approved multikinase inhibitor, suggesting that the primary target of imatinib, c-Abl, was not essential in blocking disease in this model. Additional studies with another TK inhibitor, PLX647 (targeting c-Kit and c-Fms) or an anti-c-Kit mAb showed only marginal efficacy whereas a soluble form of platelet-derived growth factor receptor (PDGFR), PDGFRbetaIg, rapidly reversed diabetes. These findings strongly suggest that inhibition of PDGFR is critical to reverse diabetes and highlight a crucial role of inflammation in the development of T1D. These conclusions were supported by the finding that the adaptive immune system was not significantly affected by imatinib treatment. Finally, and most significantly, imatinib treatment led to durable remission after discontinuation of therapy at 10 weeks in a majority of mice. Thus, long-term efficacy and tolerance is likely to depend on inhibiting a combination of tyrosine kinases supporting the use of selective kinase inhibitors as a new, potentially very attractive approach for the treatment of T1D.