Pexidartinib

Abstract: BackgroundExpression of the colony-stimulating factor 1 (CSF1) gene is elevated in most tenosynovial giant-cell tumors. This observation has led to the discovery and clinical development of therapy targeting the CSF1 receptor (CSF1R). MethodsUsing x-ray co-crystallography to guide our drug-discovery research, we generated a potent, selective CSF1R inhibitor, PLX3397, that traps the kinase in the autoinhibited conformation. We then conducted a multicenter, phase 1 trial in two parts to analyze this compound. In the first part, we evaluated escalations in the dose of PLX3397 that was administered orally in patients with solid tumors (dose-escalation study). In the second part, we evaluated PLX3397 at the chosen phase 2 dose in an extension cohort of patients with tenosynovial giant-cell tumors (extension study). Pharmacokinetic and tumor responses in the enrolled patients were assessed, and CSF1 in situ hybridization was performed to confirm the mechanism of action of PLX3397 and that the pattern of CSF1 ex...

Abstract: Summary Background Diffuse-type tenosynovial giant cell tumour (dt-GCT) of the soft tissue (alternatively known as pigmented villonodular synovitis), an orphan disease with unmet medical need, is characterised by an overexpression of colony-stimulating factor 1 (CSF1), and is usually caused by a chromosomal translocation involving CSF1. CSF1 receptor (CSF1R) activation leads to the recruitment of CSF1R-expressing cells of the mononuclear phagocyte lineage that constitute the tumor mass in dt-GCT. Emactuzumab (RG7155) is a novel monoclonal antibody that inhibits CSF1R activation. We have assessed the safety, tolerability and activity of emactuzumab in patients with Dt-GCT of the soft tissue. Methods In this phase 1, first-in-human dose-escalation and dose-expansion study, eligible patients were aged 18 years or older with dt-GCT of the soft tissue with locally advanced disease or resectable tumours requiring extensive surgery, an Eastern Cooperative Oncology Group performance status of 1 or less, measurable disease according to Response Evaluation Criteria In Solid Tumors version 1.1, and adequate end-organ function. Patients with GCT of the bone were not eligible. Patients received intravenous emactuzumab at 900 mg, 1350 mg, or 2000 mg every 2 weeks in the dose-escalation phase and at the optimal biological dose in a dose-expansion phase. The primary objective was to evaluate the safety and tolerability of emactuzumab, and to determine the maximum tolerated dose or optimal biological dose. All treated patients were included in the analyses. Expansion cohorts are currently ongoing. This study is registered with ClinicalTrials.gov, number NCT01494688. Findings Between July 26, 2012, and Oct 21, 2013, 12 patients were enrolled in the dose-escalation phase. No dose-limiting toxicities were noted in the dose-escalation cohort; on the basis of pharmacokinetic, pharmacodynamic, and safety information, we chose a dose of 1000 mg every 2 week for the dose-expansion cohort, into which 17 patients were enrolled. Owing to different cutoff dates for safety and efficacy readouts, the safety population comprised 25 patients. Common adverse events after emactuzumab treatment were facial oedema (16 [64%] of 25 patients), asthenia (14 [56%]), and pruritus (14 [56%]). Five serious adverse events (periorbital oedema, lupus erythematosus [occurring twice], erythema, and dermohypodermitis all experienced by one [4%] patient each) were reported in five patients. Three of the five serious adverse events—periorbital oedema (one [4%]), lupus erythematosus (one [4%]), and dermohypodermitis (one [4%])—were assessed as grade 3. Two other grade 3 events were reported: mucositis (one [4%]) and fatigue (one [4%]). 24 (86%) of 28 patients achieved an objective response; two (7%) patients achieved a complete response. Interpretation Further study of dt-GCT is warranted and different possibilities, such as an international collaboration with cooperative groups to assure appropriate recruitment in this rare disease, are currently being assessed. Funding F Hoffmann-La Roche.

Abstract: BACKGROUND: Pigmented villonodular synovitis (PVNS) (also known as diffuse-type giant cell tumor) and tenosynovial giant cell tumors (TGCT) are rare, usually benign neoplasms that affect the synovium and tendon sheaths in young adults. These tumors are driven by the overexpression of colony stimulating factor-1 (CSF1). CSF1 is expressed by a minority of tumor cells, which, in turn attract non-neoplastic inflammatory cells that express CSF1 receptor (CSF1R) through a paracrine effect. METHODS: Imatinib mesylate (IM) blocks CSF1R, and previous case reports indicated that it also exerts antitumor activity in PVNS. The authors conducted a multi-institutional retrospective study to assess the activity of IM in patients with locally advanced/metastatic PVNS/TGCT. RESULTS: Twenty-nine patients from 12 institutions in Europe, Australia, and the United States were included. There were 13 men, the median age was 41 years, and the most common site of disease was the knee (n = 17; 59%). Two patients had metastatic disease to the lung and/or bone. Five of 27 evaluable patients had Response Evaluation in Solid Tumor (RECIST) responses (overall response rate, 19%; 1 complete response and 4 partial responses), and 20 of 27 patients (74%) had stable disease. Symptomatic improvement was noted in 16 of 22 patients (73%) who were assessable for symptoms. Despite a high rate of symptomatic improvement and a favorable safety profile, 6 patients discontinued because of toxicity, and 4 patients decided to discontinue IM for no clear medical reason. CONCLUSIONS: IM displayed interesting activity in patients with PVNS/TGCT, providing proof of concept for targeting CSF1R in this disease. The authors concluded that the benefits of alleviating morbidity in patients with localized PVNS/TGCT must be balanced against the potential toxicity of chronic drug therapy.

Abstract: We recently demonstrated that CSF1, the ligand of the tyrosine kinase receptor, CSF1R, can be translocated in pigmented villonodular synovitis (PVNS) and tenosynovial giant cell tumor (TGCT). In this study, we evaluated the staining characteristics of PVNS/TGCT and reactive synovitides for CSF1 and CSF1R by in situ hybridization and immunohistochemistry on tissue microarrays and correlated these findings with the recently described translocation. We collected specimens of TGCT/PVNS from 60 patients and of rheumatoid arthritis and other reactive synovitides from 74 patients. We identify 2 groups of PVNS and TGCT cases by the presence of CSF1 translocation and CSF1 expression. The first group (35 of 57 cases; 61%) had both the CSF1 translocation and high expression of CSF1 RNA, confirming our previous findings. Interestingly, a second group (22 of 57 cases; 39%) was identified that showed high expression of CSF1 RNA or CSF1 protein but did not have the translocation. The rheumatoid arthritis and reactive synovitis specimens showed localization of CSF1 RNA and protein to the synovial lining cells, implying a possible role for CSF1 in the pathogenesis of these lesions. As the CSF1 translocation is postulated to play an important role in the biology of PVNS/TGCT, the consistent presence of CSF1 expression in translocation-negative cases implies that other mechanisms can lead to CSF1 up-regulation. The consistent presence of CSF1 overexpression in all cases of PVNS/TGCT and reactive synovitides suggests both an important role for CSF1 in the spectrum of synovial pathologies and the possibility of targeting the CSF1/CSF1R interaction therapeutically.