FMS receptor for M-CSF (CSF-1) is sensitive to the kinase inhibitor imatinib and mutation of Asp-802 to Val confers resistance

Treatment Modalities for Refractory-Recurrent Tenosynovial Giant Cell Tumor (TGCT): An Update

Background and Objectives: Tenosynovial giant cell tumor (TGCT) is a rare, locally aggressive, benign neoplasm arising from the synovium of joints, tendon sheaths, and bursa. There are two main subtypes of TGCT: localized-type TGCT(L-TGCT) and diffuse-type TGCT (D-TGCT). While surgical excision is still considered the gold standard of treatment, the high recurrence rate, especially for D-TGCT, may suggest the need for other treatment modalities. Materials and Methods: This study reviews current literature on the current treatment modalities for refractory-relapsed TGCT disease. Results: The gold standard of treatment modality in TGCT remains surgical excision of the tumor nevertheless, the elevated recurrence rate and refractory disease, particularly in D-TGCT indicates and underscores the necessity for additional treatment alternatives. Conclusions: TGCT is a benign tumor with inflammatory features and a potential destructive and aggressive course that can lead to significant morbidity and functional impairment with a high impact on quality of life. Surgical resection remains the gold standard current treatment and the optimal surgical approach depends on the location and extent of the tumor. Systemic therapies have been recently used for relapsed mainly cases.

Mcl-1 Protein and Viral Infections: A Narrative Review

MCL-1 is the prosurvival member of the Bcl-2 family. It prevents the induction of mitochondria-dependent apoptosis. The molecular mechanisms dictating the host cell viability gain importance in the context of viral infections. The premature apoptosis of infected cells could interrupt the pathogen replication cycle. On the other hand, cell death following the effective assembly of progeny particles may facilitate virus dissemination. Thus, various viruses can interfere with the apoptosis regulation network to their advantage. Research has shown that viral infections affect the intracellular amount of MCL-1 to modify the apoptotic potential of infected cells, fitting it to the "schedule" of the replication cycle. A growing body of evidence suggests that the virus-dependent deregulation of the MCL-1 level may contribute to several virus-driven diseases. In this work, we have described the role of MCL-1 in infections caused by various viruses. We have also presented a list of promising antiviral agents targeting the MCL-1 protein. The discussed results indicate targeted interventions addressing anti-apoptotic MCL1 as a new therapeutic strategy for cancers as well as other diseases. The investigation of the cellular and molecular mechanisms involved in viral infections engaging MCL1 may contribute to a better understanding of the regulation of cell death and survival balance.

Impact of adjuvant imatinib on bone and muscle density in patients with resected gastrointestinal stromal tumors

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By its action on macrophage-colony stimulating factor, imatinib can act on bone microenvironment.

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Imatinib can influence bone mineral density in patients with chronic myeloid leukemia.

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The role of imatinib on bone health in GIST patients has not been investigated so far.

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Imatinib can increase bone mineral density in patients with resected GIST.

Adjuvant treatment with Imatinib is the standard of care for high-risk resected GISTs. Imatinib is known to have an impact on bone mineral density in patients affected by chronic myeloid leukemia, however this effect has never been investigated in GISTs.

We retrospectively evaluated, on CT scans, the effect of adjuvant Imatinib (400 mg/die) on bone mineral density and muscle composition in 14 patients with surgically resected GISTs and in a control group of 8 patients who did not received any treatment. The effect of bone and muscle composition on Imatinib-tolerance was assessed as well.

Overall patients receiving Imatinib experienced an increase in bone mineral density during treatment (p = 0.021); with higher increase in patients with basal values < 120 mg/cm³ (p = 0.002). No changes were observed in the control group (p = 0.918).

Skeletal muscle index and lean body mass did not change over time during Imatinib therapy; however, patients with lower lean body mass and lower body mass index experienced more grade 3 treatment related toxicities (p = 0.024 and p = 0.014 respectively). We also found a non-significant trend between basal BMD and grade 3 toxicities (p = 0.060)

Glycosylated Nanoparticles Derived from RAFT Polymerization for Effective Drug Delivery to Macrophages

The functional group tolerance and simplicity of reversible addition fragmentation chain transfer (RAFT) polymerization enable its use in the preparation of a wide range of functional polymer architectures for a variety of applications, including drug delivery. Given the role of tumor-associated macrophages (TAMs) in cancer and their dependence on the tyrosine kinase receptor FMS (CSF-1R), the key aim of this work was to achieve effective delivery of an FMS inhibitor to cells using a polymer delivery system. Such a system has the potential to exploit biological features specific to macrophages and therefore provide enhanced selectivity. Building on our prior work, we have prepared RAFT polymers based on a poly(butyl methacrylate-co-methacrylic acid) diblock, which were extended with a hydrophilic block, a cross-linker, and a mannose-based monomer scaffold, exploiting the abundance of macrophage mannose receptors (MMRs, CD206) on the surface of macrophages. We demonstrate that the prepared polymers can be assembled into nanoparticles and are successfully internalized into macrophages, in part, via the MMR (CD206). Finally, we showcase the developed nanoparticles in the delivery of an FMS inhibitor to cells, resulting in inhibition of the FMS receptor. As such, this study lays the groundwork for further drug-delivery studies aimed at specifically targeting TAMs with molecularly targeted therapeutics.

The effect of Imatinib Mesylate in diffuse-type Tenosynovial Giant Cell Tumours on MR imaging and PET-CT

INTRODUCTION

Recurrence rates remain high after surgical treatment of diffuse-type Tenosynovial Giant Cell Tumour (TGCT). Imatinib Mesylate (IM) blocks Colony Stimulating Factor1 Receptor (CSF1R), the driver mechanism in TGCT. The aim of this study was to determine if IM reduces the tumour metabolic activity evaluated by PET-CT and to compare this response with the response seen on MR imaging.

MATERIALS AND METHODS

25 Consecutive patients treated with IM (off label use) for locally advanced (N = 12) or recurrent (N = 13) diffuse-type TGCT were included, 15 male and median age at diagnosis 39 (IQR 31-47) years. The knee was most frequently affected (n = 16; 64%). The effect of IM was assessed pre- and post-IM treatment by comparing MR scans and PET-CT. MR scans were assessed by Tumour Volume Score (TVS), an estimation of the tumour volume as a percentage of the total synovial cavity. PET-CT scans were evaluated based on maximum standardized uptake value (SUV-max). Partial response was defined as more than 50% tumour reduction with TVS and a decrease of at least 30% on SUV-max.

RESULTS

Median duration of IM treatment was 7.0 (IQR 4.2-11.5) months. Twenty patients (80%) discontinued IM treatment for poor response or intended surgery. Twenty patients experienced an adverse event grade 1-2, three patients grade 3 (creatinine increment, neutropenic sepsis, liver dysfunction). MR assessment of all joints showed 32% (6/19) partial response and 63% (12/19) stable disease, with a mean difference of 12% (P = 0.467; CI -22.4-46.0) TVS between pre- and post-IM and a significant mean difference of 23% (P = 0.021; CI 4.2-21.6) in all knee lesions. PET-CT, all joints, showed a significantly decreased mean difference of 5.3 (P = 0.004; CI 1.9-8.7) SUV-max between pre- and post-IM treatment (58% (11/19) partial response, 37% (7/19) stable disease). No correlation between MR imaging and PET-CT could be appreciated in 15 patients with complete radiological data.

CONCLUSION

This study confirms the moderate radiological response of IM in diffuse-type TGCT. PET-CT is a valuable additional diagnostic tool to quantify response to tyrosine kinase inhibitor treatment. Its value should be assessed further to validate its efficacy in the objective measurement of biological response in targeted systemic treatment of TGCT.

Small-Molecule CSF1R Inhibitors as Anticancer Agents

Persuasive evidence has been presented linking the infiltration of Tumor-Associated Macrophages (TAMs) with the driving force of tumorigenesis and in the suppression of antitumor immunity. In this context CSF1R, the cellular receptor for Colony Stimulating Factor-1 (CSF1) and Interleukin 34 (IL-34), occupies a central role in manipulating the behavior of TAMs and the dysregulation of CSF1R signaling has been implicated in cancer progression and immunosuppression in many specific cancers. Consequently, CSF1R kinase has been a target of great interest in cancer treatment and significant research efforts have focused on the development of smallmolecule CSF1R inhibitors. In this review, we highlight current progress on the development of these small molecule CSF1R inhibitors as anticancer agents. Special attention is paid to the compounds available in advanced clinical trials.

A phase II study of the combination of gemcitabine and imatinib mesylate in pemetrexed-pretreated patients with malignant pleural mesothelioma

OBJECTIVES

Second-line chemotherapy is not a standard of care in patients with malignant pleural mesothelioma (MPM) that progresses after first-line treatment with cisplatin and pemetrexed. In pre-clinical models, the combination of gemcitabine (GEM) and imatinib mesylate (IM), compared with GEM alone, led to a further tumor growth inhibition and improved survival. This phase II study evaluates the antitumor activity of a combination of IM and GEM in platinum-pemetrexed-pretreated MPM patients expressing PDGFR-β and/or cKIT by immunohistochemistry (IHC).

PATIENTS AND METHODS

GEM (1000 mg/m²) was given on days 3 and 10; IM (400 mg) was taken orally on days 1-5 and 8-12 of a 21-day cycle. The primary endpoint was the 3-month progression-free survival (PFS) rate. The study follows the optimal two-stage design of Simon. A 3-month PFS target of 75 % was required. With a probability error α = 10 % and a power of 80 %, the calculated sample size was 22 patients. In particular, in the first step, six out of nine patients and globally 14/22 patients free from progressive disease at 3 months were required. Secondary endpoints included response rate, duration of response, toxicity and overall survival (OS).

RESULTS

In total, 23 patients were enrolled (ECOG PS 0-1/2: 9/13; one previous line/≥two previous lines: 10/13). Partial response was achieved in four patients (17.4 %) and stable disease in 11 (47.8 %) with a disease control rate of 65.3 %. After a median follow-up of 34.5 months, median PFS and OS were 2.8 and 5.7 months, respectively. The 3-month PFS rate was 39.1 % (9/23 patients). All-grade drug-related adverse events occurred in 17 (73.9 %) patients. Grade 3 treatment-related adverse events were observed in four (17 %) patients.

CONCLUSIONS

The combination of IM and GEM is well tolerated in platinum-pemetrexed-pretreated MPM patients expressing PDGFR-β and/or cKIT by IHC, but it does not show a significant PFS benefit.

Clinical characteristics and treatment outcomes in six cases of malignant tenosynovial giant cell tumor: initial experience of molecularly targeted therapy

Background

Although tenosynovial giant cell tumor (TGCT) is classified as a benign tumor, it may undergo malignant transformation and metastasize in extremely rare occasions. High aberrant expression of CSF1 has been implicated in the development of TGCT and recent studies have shown promising activity of several CSF1R inhibitors against benign diffuse-type TGCT; however, little is known about their effects in malignant TGCT.

Case presentation

Information from six consenting patients (3 men, 3 women) with malignant TGCT presenting to Dana-Farber Cancer Institute for initial or subsequent consultation was collected. Median age at initial diagnosis of TGCT was 49.5 years (range 12–55), and median age at diagnosis of malignant TGCT was 50 years (range 34–55). Two patients developed malignant TGCT de novo, while four other cases showed metachronous malignant transformation. All tumors arose in the lower extremities (3 knee, 2 thigh, 1 hip). Five patients underwent surgery for the primary tumors, and four developed local recurrence. All six patients developed lung metastases, and four of five evaluable tumors developed inguinal and pelvic lymph node metastases. All six patients received systemic therapy. Five patients were treated with at least one tyrosine kinase inhibitor with inhibitory activity against CSF1R; however, only one patient showed clinical benefit (SD or PR). Five patients were treated with conventional cytotoxic agents. Doxorubicin-based treatment showed clinical benefit in all four evaluable patients, and gemcitabine/docetaxel showed clinical benefit in two patients. All six patients died of disease after a median of 21.5 months from diagnosis of malignant TGCT.

Conclusions

This study confirms that TGCT may transform into an aggressive malignant tumor. Lymph node and pulmonary metastases are common. Local recurrence rates are exceedingly high. Conventional cytotoxic chemotherapy showed clinical benefit, whereas tyrosine kinase inhibitors against CSF1R showed limited activity. Given its rarity, a prospective registry of malignant TGCT patients is needed to further understand the entity and to develop effective strategies for systemic treatment.

Imatinib inhibits CSF1R that stimulates proliferation of rheumatoid arthritis fibroblast-like synoviocytes

In this study, we aimed to explore the effects of imatinib on the proliferation of rheumatoid arthritis synovial cell (RA-FLS) and inflammatory responses by regulating CSF1R. Differential genes were screened via microarray analysis, followed by being analysed through the weighted co-expression network (WGCNA) network, that included module and cluster analysis. The relationship between imatinib and genes was visualized using the Search Tool for the Retrieval of Interacting Genes (STITCH) database. Expressions of mRNA and protein were determined by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot, respectively. Cell viability was examined via clone formation assay, while cell cycle and apoptosis were analysed through flow cytometry analysis. The hub gene CSF1R was ultimately determined by microarray analysis and WGCNA analysis. Colony-stimulating-factor receptor-1 (SF1R) was highly expressed in rheumatoid arthritis tissues and cells, and CSF1R over-expression could promote inflammatory responses. Moreover, CSF1R could promote RA-FLS proliferation, inhibit apoptosis and accelerate the cell cycle. The targeting relationship between imatinib and CSF1R was also validated in this study. Imatinib attenuated RA-FLS inflammation in a concentration-dependent manner. Meanwhile, imatinib could inhibit RA-FLS proliferation and promote apoptosis, ultimately reducing the damage of RA-FLS. Over-expression of CSF1R accelerated the cell cycle and proliferation of RA-FLS, while inhibiting cell apoptosis. Conversely, imatinib could significantly restrain the cell cycle and viability of RA-FLS and accelerated apoptosis via suppression of CSF1R expression. Further, histological and serological assay investigated and proved the proinflammatory effects of CSF1R in RA rabbits.

Imatinib and Nilotinib Off-Target Effects on Human NK Cells, Monocytes, and M2 Macrophages

Tyrosine kinase inhibitors (TKIs) are used in the clinical management of hematological neoplasms. Moreover, in solid tumors such as stage 4 neuroblastomas (NB), imatinib showed benefits that might depend on both on-target and immunological off-target effects. We investigated the effects of imatinib and nilotinib on human NK cells, monocytes, and macrophages. High numbers of monocytes died upon exposure to TKI concentrations similar to those achieved in patients. Conversely, NK cells were highly resistant to the TKI cytotoxic effect, were properly activated by immunostimulatory cytokines, and degranulated in the presence of NB cells. In NB, neither drug reduced the expression of ligands for activating NK receptors or upregulated that of HLA class I, B7-H3, PD-L1, and PD-L2, molecules that might limit NK cell function. Interestingly, TKIs modulated the chemokine receptor repertoire of immune cells. Acting at the transcriptional level, they increased the surface expression of CXCR4, an effect observed also in NK cells and monocytes of patients receiving imatinib for chronic myeloid leukemia. Moreover, TKIs reduced the expression of CXCR3 (in NK cells) and CCR1 (in monocytes). Monocytes also decreased the expression of M-CSFR, and low numbers of cells underwent differentiation toward macrophages. M0 and M2 macrophages were highly resistant to TKIs and maintained their phenotypic and functional characteristics. Importantly, also in the presence of TKIs, the M2 immunosuppressive polarization was reverted by TLR engagement, and M1-oriented macrophages fully activated autologous NK cells. Our results contribute to better interpreting the off-target efficacy of TKIs in tumors and to envisaging strategies aimed at facilitating antitumor immune responses.

Current Systemic Treatment Options for Tenosynovial Giant Cell Tumor/Pigmented Villonodular Synovitis: Targeting the CSF1/CSF1R Axis

OPINION STATEMENT

Adequate surgical resection remains the treatment of choice for tenosyovial giant cell tumor (TGCT). However, diffuse type TGCT (D-TGCT) is more difficult to resect and has a higher rate of recurrence (up to 50 %), which is often multiple. D-TGCT is rarely lethal and only rare cases of metastases have been described. Nevertheless, patients might have a significant decline in their quality of life due to multiple operations, which may sometimes result in a partial loss of function of the affected joint and may also be associated with perioperative morbidity and secondary arthrosis. As of today, no systemic treatment is approved for this rare disease. The aims of systemic therapy in the context of a non-lethal tumor are to reduce surgical morbidity and to preserve function and patient quality of life. Because TGCT is associated with characteristic cytogenetic abnormalities resulting in the overexpression of CSF1, systemic therapies targeting the CSF1/CSF1R axis (imatinib, nilotinib, emactuzumab, and PLX3397) have been tested in patients with locally advanced or relapsed D-TGCT. The more recent and more specific CSF1R inhibitors have shown a very interesting clinical activity with acceptable toxicity in early phase trials. These results will need to be confirmed in larger, ideally randomized, trials. But the high rate of clinical and functional improvement seen in some patients with advanced D-TGCT, often after multiple operations, suggests that these inhibitors will likely have a role in the management of patients with an inoperable disease; the definition of "inoperable TGCT" still requires refinement to reach a consensus. Another point that will need to be addressed is that of "the optimal duration of therapy" for these patients. Indeed, we and others have observed often prolonged clinical benefit and symptomatic relief even after treatment was stopped, with both monoclonal antibodies and tyrosine kinase inhibitors. Responses were observed very early on with emactuzumab and PLX3397, and patients experienced significant symptom improvement within a few weeks of starting therapy (2-4 weeks). Another possible application of CSF1R inhibitors could be used either as a preoperative or postoperative therapy for patients with operable TGCT. However, we currently lack sufficient follow-up to adequately address these questions which will each require specific trial designs. Overall, the striking clinical activity of CSF1R specific inhibitors in TGCT has created great enthusiasm among clinicians, and further development of these agents is clearly medically needed. Nevertheless, further investigations are necessary to validate those treatments and assess how to best incorporate them among other treatment modalities into the overall therapeutic strategy for a given patient.

Insight on Mutation-Induced Resistance from Molecular Dynamics Simulations of the Native and Mutated CSF-1R and KIT

The receptors tyrosine kinases (RTKs) for the colony stimulating factor-1, CSF-1R, and for the stem cell factor, SCFR or KIT, are important mediators of signal transduction. The abnormal function of these receptors, promoted by gain-of-function mutations, leads to their constitutive activation, associated with cancer or other proliferative diseases. A secondary effect of the mutations is the alteration of receptors' sensitivity to tyrosine kinase inhibitors, compromising effectiveness of these molecules in clinical treatment. In particular, the mutation V560G in KIT increases its sensitivity to Imatinib, while the D816V in KIT, and D802V in CSF-1R, triggers resistance to the drug. We analyzed the Imatinib binding affinity to the native and mutated KIT (mutations V560G, S628N and D816V) and CSF-1R (mutation D802V) by using molecular dynamics simulations and energy calculations of Imatinib•target complexes. Further, we evaluated the sensitivity of the studied KIT receptors to Imatinib by measuring the inhibition of KIT phosphorylation. Our study showed that (i) the binding free energy of Imatinib to the targets is highly correlated with their experimentally measured sensitivity; (ii) the electrostatic interactions are a decisive factor affecting the binding energy; (iii) the most deleterious impact to the Imatinib sensitivity is promoted by D802V (CSF-1R) and D816V (KIT) mutations; (iv) the role of the juxtamembrane region, JMR, in the imatinib binding is accessory. These findings contribute to a better description of the mutation-induced effects alternating the targets sensitivity to Imatinib.

Structural and biochemical studies of the PDGFRA kinase domain

Platelet-derived growth factor receptor α (PDGFRA) is a Type III receptor tyrosine kinase, and this kinase is a target for treatment of gastrointestinal stromal tumors (GIST) as it is frequently mutated in these cancers. Most of the mutations that cause constitutive activation of PDGFRA occur in either the activation loop (A-loop) or in the juxtamembrane (JM) domain, such as the mutations D842V or V561D respectively. Treatment of PDGFRA-mutated GIST with imatinib is successful in some cases, but the D842V mutation is imatinib-resistant. To better understand the mechanism of PDGFRA drug-resistance, we have determined the crystal structure of the PDGFRA kinase domain in the auto-inhibited form, and studied the kinetics of the D842V mutation. Auto-inhibited PDGFRA is stabilized by the JM domain, which inserts into the active site of the kinase. The conserved residue Asp842 makes extensive contacts with several A-loop residues to maintain PDGFRA in the "DFG out" conformation, which stabilizes the kinase in the inactive state and facilitates the binding of imatinib. The D842V mutation would therefore be expected to activate the kinase and hinder the binding of drug through destabilizing the "DFG out" conformation. Furthermore, our kinetic data show that drug resistance in the D842V mutation may also in part result from its increased affinity for ATP. The PDGFRA kinase domain structure we report in this study has potential to facilitate development of new agents which can inhibit this kinase, including both its activating and drug-resistant mutations.

Current Systemic Treatment Options for Tenosynovial Giant Cell Tumor/Pigmented Villonodular Synovitis: Targeting the CSF1/CSF1R Axis

OPINION STATEMENT

Adequate surgical resection remains the treatment of choice for tenosyovial giant cell tumor (TGCT). However, diffuse type TGCT (D-TGCT) is more difficult to resect and has a higher rate of recurrence (up to 50 %), which is often multiple. D-TGCT is rarely lethal and only rare cases of metastases have been described. Nevertheless, patients might have a significant decline in their quality of life due to multiple operations, which may sometimes result in a partial loss of function of the affected joint and may also be associated with perioperative morbidity and secondary arthrosis. As of today, no systemic treatment is approved for this rare disease. The aims of systemic therapy in the context of a non-lethal tumor are to reduce surgical morbidity and to preserve function and patient quality of life. Because TGCT is associated with characteristic cytogenetic abnormalities resulting in the overexpression of CSF1, systemic therapies targeting the CSF1/CSF1R axis (imatinib, nilotinib, emactuzumab, and PLX3397) have been tested in patients with locally advanced or relapsed D-TGCT. The more recent and more specific CSF1R inhibitors have shown a very interesting clinical activity with acceptable toxicity in early phase trials. These results will need to be confirmed in larger, ideally randomized, trials. But the high rate of clinical and functional improvement seen in some patients with advanced D-TGCT, often after multiple operations, suggests that these inhibitors will likely have a role in the management of patients with an inoperable disease; the definition of "inoperable TGCT" still requires refinement to reach a consensus. Another point that will need to be addressed is that of "the optimal duration of therapy" for these patients. Indeed, we and others have observed often prolonged clinical benefit and symptomatic relief even after treatment was stopped, with both monoclonal antibodies and tyrosine kinase inhibitors. Responses were observed very early on with emactuzumab and PLX3397, and patients experienced significant symptom improvement within a few weeks of starting therapy (2-4 weeks). Another possible application of CSF1R inhibitors could be used either as a preoperative or postoperative therapy for patients with operable TGCT. However, we currently lack sufficient follow-up to adequately address these questions which will each require specific trial designs. Overall, the striking clinical activity of CSF1R specific inhibitors in TGCT has created great enthusiasm among clinicians, and further development of these agents is clearly medically needed. Nevertheless, further investigations are necessary to validate those treatments and assess how to best incorporate them among other treatment modalities into the overall therapeutic strategy for a given patient.

CSF1R inhibition with emactuzumab in locally advanced diffuse-type tenosynovial giant cell tumours of the soft tissue: a dose-escalation and dose-expansion phase 1 study

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.

Impact of long-term exposure to the tyrosine kinase inhibitor imatinib on the skeleton of growing rats

The tyrosine kinase (TK) inhibitor imatinib provides a highly effective therapy for chronic myeloid leukemia (CML) via inhibition of the oncogenic TK BCR-ABL1. However, off-target TKs like platelet-derived growth factor receptors (PDGF-R) and colony-stimulating factor-1 receptor (c-fms), involved in bone remodeling, are also inhibited. Thus, pediatric patients with CML on imatinib exhibit altered bone metabolism, leading to linear growth failure. As TKI treatment might be necessary for a lifetime, long-term effects exerted on bone in children are of major concern. Therefore, we studied the skeletal long-term effects of continuous and intermittent imatinib exposure in a juvenile rat model. Four-weeks-old male Wistar rats were chronically exposed to imatinib via drinking water over a period of 10 weeks. Animals were exposed to a standard and high imatinib dosage continuously and to the high imatinib dose intermittently. Bone mass and strength were assessed using pQCT, micro-computed tomography (μCT), and biomechanical testing at the prepubertal, pubertal, and postpubertal age. Bone length and vertebral height as well as biochemical markers of bone turnover were analyzed. Femoral and tibial bone length were dose-dependently reduced by up to 24% (p<0.0001), femoral and tibial trabecular bone mass density (BMD) were reduced by up to 25% (p<0.01), and femoral breaking strength was lowered by up to 20% (p<0.05). Intermittent exposure mitigated these skeletal effects. Long-term exposure resulted in reduced vertebral height by 15% and lower trabecular BMD by 5%. Skeletal changes were associated with suppressed serum osteocalcin (p<0.01) and non-significantly elevated serum CTX-I and PINP levels. In conclusion, imatinib mainly impaired longitudinal growth of long bones rather than the vertebrae of growing rats. Interestingly, intermittent imatinib exposure has less skeletal side effects, which may be beneficial in pediatric patients taking imatinib.

Nonsurgical giant cell tumour of the tendon sheath or of the diffuse type: are MRI or 18F-FDG PET/CT able to provide an accurate prediction of long-term outcome?

PURPOSE

To investigate whether MRI (RECIST 1.1, WHO criteria and the volumetric approach) or (18)F-FDG PET/CT (PERCIST 1.0) are able to predict long-term outcome in nonsurgical patients with giant cell tumour of the tendon sheath or of the diffuse type (GCT-TS/DT).

METHODS

Fifteen "nonsurgical" patients with a histological diagnosis of GCT-TS/DT were divided into two groups: symptomatic patients receiving targeted therapy and asymptomatic untreated patients. All 15 patients were evaluated by MRI of whom 10 were treated, and a subgroup of 7 patients were evaluated by PET/CT of whom 4 were treated. Early evolution was assessed according to MRI and PET/CT scans at baseline and during follow-up. Cohen's kappa coefficient was used to evaluate the degree of agreement between PERCIST 1.0, RECIST 1.1, WHO criteria, volumetric approaches and the reference standard (long-term outcome, delay 505 ± 457 days). The response rate in symptomatic patients with GCT-TS/DT receiving targeted therapy was also assessed in a larger population that included additional patients obtained from a review of the literature.

RESULTS

The kappa coefficients for agreement between RECIST/WHO/volumetric criteria and outcome (15 patients) were respectively: 0.35 (p = 0.06), 0.26 (p = 0.17) and 0.26 (p = 0.17). In the PET/CT subgroup (7 patients), PERCIST was in perfect agreement with the late symptomatic evolution (kappa = 1, p < 0.05). In the treated symptomatic group including the additional patients from the literature the response rates to targeted therapies according to late symptomatic assessment, and PERCIST and RECIST criteria were: 65 % (22/34), 77 % (10/13) and 26 % (10/39).

CONCLUSION

(18)F-FDG PET/CT with PERCIST is a promising approach to the prediction of the long-term outcome in GCT-TS/DT and may avoid unnecessary treatments, toxicity and costs. On MRI, WHO and volumetric approaches are not more effective than RECIST using the current thresholds.

Targeting tumor-associated macrophages with anti-CSF-1R antibody reveals a strategy for cancer therapy

Macrophage infiltration has been identified as an independent poor prognostic factor in several cancer types. The major survival factor for these macrophages is macrophage colony-stimulating factor 1 (CSF-1). We generated a monoclonal antibody (RG7155) that inhibits CSF-1 receptor (CSF-1R) activation. In vitro RG7155 treatment results in cell death of CSF-1-differentiated macrophages. In animal models, CSF-1R inhibition strongly reduces F4/80(+) tumor-associated macrophages accompanied by an increase of the CD8(+)/CD4(+) T cell ratio. Administration of RG7155 to patients led to striking reductions of CSF-1R(+)CD163(+) macrophages in tumor tissues, which translated into clinical objective responses in diffuse-type giant cell tumor (Dt-GCT) patients.

Differential effects of CSF-1R D802V and KIT D816V homologous mutations on receptor tertiary structure and allosteric communication

The colony stimulating factor-1 receptor (CSF-1R) and the stem cell factor receptor KIT, type III receptor tyrosine kinases (RTKs), are important mediators of signal transduction. The normal functions of these receptors can be compromised by gain-of-function mutations associated with different physiopatological impacts. Whereas KIT D816V/H mutation is a well-characterized oncogenic event and principal cause of systemic mastocytosis, the homologous CSF-1R D802V has not been identified in human cancers. The KIT D816V oncogenic mutation triggers resistance to the RTK inhibitor Imatinib used as first line treatment against chronic myeloid leukemia and gastrointestinal tumors. CSF-1R is also sensitive to Imatinib and this sensitivity is altered by mutation D802V. Previous in silico characterization of the D816V mutation in KIT evidenced that the mutation caused a structure reorganization of the juxtamembrane region (JMR) and facilitated its departure from the kinase domain (KD). In this study, we showed that the equivalent CSF-1R D802V mutation does not promote such structural effects on the JMR despite of a reduction on some key H-bonds interactions controlling the JMR binding to the KD. In addition, this mutation disrupts the allosteric communication between two essential regulatory fragments of the receptors, the JMR and the A-loop. Nevertheless, the mutation-induced shift towards an active conformation observed in KIT D816V is not observed in CSF-1R D802V. The distinct impact of equivalent mutation in two homologous RTKs could be associated with the sequence difference between both receptors in the native form, particularly in the JMR region. A local mutation-induced perturbation on the A-loop structure observed in both receptors indicates the stabilization of an inactive non-inhibited form, which Imatinib cannot bind.

S-Fms signalobody enhances myeloid cell growth and migration

Since receptor tyrosine kinases (RTKs) control various cell fates in many types of cells, mimicry of RTK functions is promising for artificial control of cell fates. We have previously developed single-chain Fv (scFv)/receptor chimeras named signalobodies that can mimic receptor signaling in response to a specific antigen. While the RTK-based signalobodies enabled us to control cell growth and migration, further extension of applicability in another cell type would underlie the impact of the RTK-based signalobodies. In this study, we applied the scFv-c-Fms (S-Fms) signalobody in a murine myeloid progenitor cell line, FDC-P1. S-Fms transduced a fluorescein-conjugated BSA (BSA-FL)-dependent growth signal and activated downstream signaling molecules including MEK, ERK, Akt, and STAT3, which are major constituents of Ras/MAPK, PI3K/Akt, and JAK/STAT signaling pathways. In addition, S-Fms transduced a migration signal as demonstrated by the transwell-based migration assay. Direct real-time observation of the cells further confirmed that FDC/S-Fms cells underwent directional cell migration toward a positive gradient of BSA-FL. These results demonstrated the utility of the S-Fms signalobody for controlling growth and migration of myeloid cells. Further extension of our approach includes economical large-scale production of practically relevant blood cells as well as artificial control of cell migration for tissue regeneration and immune response.

Abl family kinases regulate FcγR-mediated phagocytosis in murine macrophages

Phagocytosis of Ab-coated pathogens is mediated through FcγRs, which activate intracellular signaling pathways to drive actin cytoskeletal rearrangements. Abl and Arg define a family of nonreceptor tyrosine kinases that regulate actin-dependent processes in a variety of cell types, including those important in the adaptive immune response. Using pharmacological inhibition as well as dominant negative and knockout approaches, we demonstrate a role for the Abl family kinases in phagocytosis by macrophages and define a mechanism whereby Abl kinases regulate this process. Bone marrow-derived macrophages from mice lacking Abl and Arg kinases exhibit inefficient phagocytosis of sheep erythrocytes and zymosan particles. Treatment with the Abl kinase inhibitors imatinib and GNF-2 or overexpression of kinase-inactive forms of the Abl family kinases also impairs particle internalization in murine macrophages, indicating Abl kinase activity is required for efficient phagocytosis. Further, Arg kinase is present at the phagocytic cup, and Abl family kinases are activated by FcγR engagement. The regulation of phagocytosis by Abl family kinases is mediated in part by the spleen tyrosine kinase (Syk). Loss of Abl and Arg expression or treatment with Abl inhibitors reduced Syk phosphorylation in response to FcγR ligation. The link between Abl family kinases and Syk may be direct, as purified Arg kinase phosphorylates Syk in vitro. Further, overexpression of membrane-targeted Syk in cells treated with Abl kinase inhibitors partially rescues the impairment in phagocytosis. Together, these findings reveal that Abl family kinases control the efficiency of phagocytosis in part through the regulation of Syk function.

FMS Kinase Inhibitors: Current Status and Future Prospects

FMS, first discovered as the oncogene responsible for Feline McDonough Sarcoma, is a type III receptor tyrosine kinase that binds to the macrophage or monocyte colony-stimulating factor (M-CSF or CSF-1). Signal transduction through that binding results in survival, proliferation, and differentiation of monocyte/macrophage lineage. Overexpression of CSF-1 and/or FMS has been implicated in a number of disease states such as the growth of metastasis of certain types of cancer, in promoting osteoclast proliferation in bone osteolysis, and many inflammatory disorders. Inhibition of CSF-1 and/or FMS may help treat these pathological conditions. This article reviews FMS gene, FMS kinase, CSF-1, IL-34, and their roles in bone osteolysis, cancer biology, and inflammation. Monoclonal antibodies, FMS crystal structure, and small molecule FMS kinase inhibitors of different chemical scaffolds are also reviewed.

Efficacy of imatinib mesylate for the treatment of locally advanced and/or metastatic tenosynovial giant cell tumor/pigmented villonodular synovitis

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.

The skeletal effects of the tyrosine kinase inhibitor nilotinib

Nilotinib is a tyrosine kinase inhibitor (TKI) developed to manage imatinib-resistance in patients with chronic myeloid leukemia (CML). It inhibits similar molecular targets to imatinib, but is a significantly more potent inhibitor of Bcr-Abl. Nilotinib exhibits off-target effects in other tissues, and of relevance to bone metabolism, hypophosphataemia has been reported in up to 30% of patients receiving nilotinib. We have assessed the effects of nilotinib on bone cells in vitro and on bone metabolism in patients receiving nilotinib for treatment of CML. We firstly investigated the effects of nilotinib on proliferating and differentiating osteoblastic cells, and on osteoclastogenesis in murine bone marrow cultures and RAW264.7 cells. Nilotinib potently inhibited osteoblast proliferation (0.01-1uM), through inhibition of the platelet-derived growth factor (PDGFR). There was a biphasic effect on osteoblast differentiation such that it was reduced by lower concentrations of nilotinib (0.1-0.5uM), with no effect at higher concentrations (1uM). Nilotinib also potently inhibited osteoclastogenesis, predominantly by stromal-cell dependent mechanisms. Thus, nilotinib decreased osteoclast development in murine bone marrow cultures, but did not affect osteoclastogenesis in RAW264.7 cells. Nilotinib treatment of osteoblastic cells increased expression and secretion of OPG and decreased expression of RANKL. In 10 patients receiving nilotinib, levels of bone turnover markers were in the low-normal range, despite secondary hyperparathyroidism, findings that are similar to those in patients treated with imatinib. Bone density tended to be higher than age and gender-matched normal values. These data suggest that nilotinib may have important effects on bone metabolism. Prospective studies should be conducted to determine the long-term effects of nilotinib on bone density and calcium metabolism.

Role of tyrosine kinase inhibitors in tumor immunology

Various immune cells are involved in both innate and acquired immunity against tumors. NK cells and cytotoxic T lymphocytes play a role as effector cells to directly kill tumor cells. On the other hand, antigen-presenting cells, particularly dendritic cells, control tumor-specific immune responses. In addition, much focus has been paid on the immune regulatory cells in tumor sites, including CD4(+)CD25(+) regulatory T cells and myeloid-derived suppressor cells. The recent advances in molecular-targeted therapy for cancer have provided small-molecule kinase inhibitors, which are effective for several hematopoietic malignancies as well as solid tumors in the clinical setting. Most drugs generally have inhibitory effects on several kinases, including tyrosine kinases, which are critical molecules for the survival, proliferation, migration and invasion of tumor cells. Since the host immune surveillance against tumors affects tumor progression, it is of interest to understand how these molecular-targeted drugs affect immune function in the tumor-bearing host. Besides this, there are emerging findings that myeloid cells could be involved in tumor angiogenesis. In this article, we address the role of tyrosine kinase inhibitors in tumor immunology by summarizing their effects on myeloid cells, such as antigen-presenting cells and regulatory cells, and their role in tumor immunity and angiogenesis.

Imatinib mesylate does not increase bone volume in vivo

Imatinib mesylate is a tyrosine kinase inhibitor used in the management of disorders in which activation of c-Abl, PDGFR, or c-Kit signaling plays a critical role. In vitro, imatinib stimulates osteoblast differentiation, inhibits osteoblast proliferation and survival, and decreases osteoclast development. Patients treated with imatinib exhibit altered bone and mineral metabolism, with stable or increased bone mass. However, recovery from the underlying disease and/or weight gain might contribute to these effects. We therefore investigated the skeletal effects of imatinib in healthy rats. We evaluated the effects of imatinib on bone volume, markers of bone turnover, and bone histomorphometry in mature female rats treated for 5 weeks with either vehicle, imatinib 40 mg/kg daily, or imatinib 70 mg/kg daily. Compared to vehicle, imatinib reduced trabecular bone volume/tissue volume (mean [SD]: vehicle 26.4% [5.4%], low-dose imatinib 24.8% [4.9%] [P = 0.5], high-dose imatinib 21.1% [5.7%] [P = 0.05]), reduced osteoblast surface (mean [SD]: vehicle 12.8% [5.8%], low-dose 6.8% [1.9%] [P < 0.01], high-dose 7.8 [3.1%] [P < 0.05]), and reduced serum osteocalcin (mean change from baseline [95% CI]: vehicle -8.2 [-26.6 to 10.2] ng/ml, low dose -79.7 [-97.5 to -61.9] ng/ml [P < 0.01 vs. vehicle], high-dose -66.0 [-82.0 to -50.0] ng/ml [P < 0.05 vs. vehicle]). Imatinib did not affect biochemical or histomorphometric indices of bone resorption. These results suggest that, in healthy animals, treatment with imatinib does not increase bone mass and that the improvements in bone density reported in patients receiving imatinib may not be a direct effect of the drug.

Therapeutic Antibodies Targeting CSF1 Impede Macrophage Recruitment in a Xenograft Model of Tenosynovial Giant Cell Tumor

Tenosynovial giant cell tumor is a neoplastic disease of joints that can cause severe morbidity. Recurrences are common following local therapy, and no effective medical therapy currently exists. Recent work has demonstrated that all cases overexpress macrophage colony-stimulating factor (CSF1), usually as a consequence of an activating gene translocation, resulting in an influx of macrophages that form the bulk of the tumor. New anti-CSF1 drugs have been developed; however there are no preclinical models suitable for evaluation of drug benefits in this disease. In this paper, we describe a novel renal subcapsular xenograft model of tenosynovial giant cell tumor. Using this model, we demonstrate that an anti-CSF1 monoclonal antibody significantly inhibits host macrophage infiltration into this tumor. The results from this model support clinical trials of equivalent humanized agents and anti-CSF1R small molecule drugs in cases of tenosynovial giant cell tumor refractory to conventional local therapy.

Anti-inflammatory M2 type macrophages characterize metastasized and tyrosine kinase inhibitor-treated gastrointestinal stromal tumors

We have made a detailed inventory of the immune infiltrate of gastrointestinal stromal tumors (GISTs), which originate from mesenchymal cells in the intestinal tract. These sarcomas are heavily infiltrated with macrophages and T cells, while immune cells of other lineages were much less abundant. Dissecting the functional subtypes of T cells with multicolor fluorescent microscopy revealed substantial populations of cytotoxic T cells, helper T cells and FoxP3(+) regulatory T cells. The balance of cytotoxic T cells and FoxP3(+) T cells was toward immune suppression. Analysis of the macrophage population also showed a dominance of anti-inflammatory cells, as the M2 type scavenger receptor CD163 was abundantly present. Other subsets of macrophages (CD14(+)CD163(-)) were occasionally detected. M2 type CD163(+) macrophages were associated with the number of infiltrating FoxP3(+) regulatory T cells and twice as many macrophages were found in metastatic GIST compared to primary lesions. Most metastatic GISTs had been treated with the tyrosine kinase inhibitors imatinib and sunitinib, but the high macrophage infiltrate was not related to this treatment. However, imatinib and sunitinib did induce secretion of anti-inflammatory IL-10 in macrophage cultures, indicating that treatment with these inhibitors might contribute to an immune suppressive microenvironment in GIST. Overall, our data reveal a picture of GIST as an active site of tumor-immune interaction in which suppressive mechanisms overrule potential antitumor responses. Tyrosine kinase inhibitors might promote this negative balance.

PU.1-mediated upregulation of CSF1R is crucial for leukemia stem cell potential induced by MOZ-TIF2

Leukemias and other cancers possess self-renewing stem cells that help to maintain the cancer. Cancer stem cell eradication is thought to be crucial for successful anticancer therapy. Using an acute myeloid leukemia (AML) model induced by the leukemia-associated monocytic leukemia zinc finger (MOZ)-TIF2 fusion protein, we show here that AML can be cured by the ablation of leukemia stem cells. The MOZ fusion proteins MOZ-TIF2 and MOZ-CBP interacted with the transcription factor PU.1 to stimulate the expression of macrophage colony-stimulating factor receptor (CSF1R, also known as M-CSFR, c-FMS or CD115). Studies using PU.1-deficient mice showed that PU.1 is essential for the ability of MOZ-TIF2 to establish and maintain AML stem cells. Cells expressing high amounts of CSF1R (CSF1R(high) cells), but not those expressing low amounts of CSF1R (CSF1R(low) cells), showed potent leukemia-initiating activity. Using transgenic mice expressing a drug-inducible suicide gene controlled by the CSF1R promoter, we cured AML by ablation of CSF1R(high) cells. Moreover, induction of AML was suppressed in CSF1R-deficient mice and CSF1R inhibitors slowed the progression of MOZ-TIF2-induced leukemia. Thus, in this subtype of AML, leukemia stem cells are contained within the CSF1R(high) cell population, and we suggest that targeting of PU.1-mediated upregulation of CSF1R expression might be a useful therapeutic approach.

Platelet-derived growth factor and transforming growth factor beta synergistically potentiate inflammatory mediator synthesis by fibroblast-like synoviocytes

Introduction

The objective of this study was to model the effects of transforming growth factor beta (TGF-β) and platelet-derived growth factor (PDGF), both present in rheumatoid arthritis (RA) synovia, on the behavior of fibroblast-like synoviocytes (FLS) in response to pro-inflammatory cytokine (interleukin (IL)1β, tumor necrosis factor-alpha (TNFα)) challenge.

Methods

Gene and protein expression by fibroblast-like synoviocytes in vitro was studied by quantitative Polymerase Chain Reaction (qPCR), ELISA and multiplex bead cytokine assays. Intracellular signaling pathway activation was determined by Western blot for phospho-kinases and the use of specific inhibitors.

Results

In combination, TGF-β and PDGF (2GF) synergistically augmented TNFα- or IL1β-induced matrix metalloproteinase 3 (MMP3), IL6, IL8, and macrophage inflammatory protein 1 alpha (MIP1α) secretion by FLS. Other FLS-derived mediators remained unaffected. Individually, neither growth factor significantly potentiated TNFα or IL1β-induced MMP3 secretion, and only slightly enhanced IL6. The effect of 2GF on TNFα-induced gene expression was transcriptionally mediated; blocked by imatinib mesylate; and occurred even if 2GF was added as much as four hours prior to TNFα. In addition, a 15-minute pulse of 2GF four hours prior to TNFα stimulation yielded a synergistic response. The extracellular-signal-regulated kinase (ERK) and phosphoinositide 3-kinase (PI3K) signaling pathways were induced for at least four hours by 2GF, as demonstrated by persistently upregulated levels of phospho-Akt and phospho-ERK. However, pharmacologic inhibitor studies demonstrated that the potentiating action of 2GF was dependent on PI3 kinase only, and not on ERK.

Conclusions

The combination of PDGF and TGF-β dramatically potentiates FLS response to cytokines in a receptor-mediated and PI3 kinase-dependent fashion. These data suggest that 2GF contribute to synovitis by directing synovial fibroblasts toward a more aggressive phenotype in response to TNFα. Therefore, inhibition of growth factor signaling may constitute a complementary therapeutic approach to cytokine-targeted treatments for RA.

Arterial colony stimulating factor-1 influences atherosclerotic lesions by regulating monocyte migration and apoptosis

Previous studies have shown that colony stimulating factor-1 (CSF-1) deficiency dramatically reduced atherogenesis in mice. In this report we investigate this mechanism and explore a therapeutic avenue based on inhibition of CSF-1 signaling. Lesions from macrophage colony stimulating factor-1 (Csf1)+/- mice showed increased numbers of apoptotic macrophages, decreased overall macrophage content, and inflammation. In vitro studies indicated that CSF-1 is chemotactic for monocytes. Bone marrow transplantation studies suggested that vascular cell-derived, rather than macrophage-derived, CSF-1 is responsible for the effect on atherosclerosis. Consistent with previous studies, CSF-1 affected lesion development in a dose-dependent manner, suggesting that pharmacological inhibition of CSF-1 might achieve similar results. Indeed, we observed that treatment of hyperlipidemic mice with a CSF-1 receptor kinase inhibitor inhibited plaque progression. This observation was accompanied by a reduction in the expression of adhesion factors (ICAM-1), macrophage markers (F4/80), inflammatory cytokines (Il-6, Il-1beta), and macrophage matrix degradation enzymes (MMP-9). We conclude that the M-CSF pathway contributes to monocyte recruitment and macrophage survival and that this pathway is a potential target for therapeutic intervention.

A potential role for colony-stimulating factor 1 in the genesis of the early endometriotic lesion

OBJECTIVE

To investigate the role(s) of colony-stimulating factor 1 (CSF-1) on the development of early endometriosis in a murine model by comparing rate of lesion formation in mice [1] homozygous for a CSF-1 mutation versus syngeneic controls and [2] after treatment with imatinib, a commercially available tyrosine kinase inhibitor that alters interaction(s) between CSF-1 and its receptor, c-fms.

DESIGN

Prospective, placebo-controlled animal study.

SETTING

Academic medical center.

ANIMALS

Six- to 8-week old female FVB, wild-type C57BL/6, and CSF-1 op/op mice.

INTERVENTION(S)

Endometrial tissue from donor mice was used to induce endometriosis in murine recipients. In some experiments, mice homozygous for a CSF-1 mutation (CSF-1 op/op) were donors or recipients. In other experiments, donor and/or recipient mice received imatinib.

MAIN OUTCOME MEASURE(S)

Histologic confirmation of endometriosis, rate of lesion formation.

RESULT(S)

By 40 hours, recipient mice developed a mean of 7.2 +/- 0.9 endometriotic lesions that had invaded host surfaces, and mesothelial cells had proliferated over the entire surface of the implants. The CSF-1 op/op mice developed significantly fewer (mean 0.9 +/- 0.3) endometriotic lesions versus syngeneic controls. Imatinib treatment resulted in significantly fewer lesions when compared with sham-treated controls.

CONCLUSION(S)

Colony-stimulating factor 1 has a role in establishing early endometriotic lesions. Agents targeting CSF-1 or its actions have therapeutic potential for treating endometriosis.

Dysregulation of bone remodeling by imatinib mesylate

Imatinib mesylate is a rationally designed tyrosine kinase inhibitor that has revolutionized the treatment of chronic myeloid leukemia and gastrointestinal stromal tumors. Although the efficacy and tolerability of imatinib are a vast improvement over conventional chemotherapies, the drug exhibits off-target effects. An unanticipated side effect of imatinib therapy is hypophosphatemia and hypocalcemia, which in part has been attributed to drug-mediated changes to renal and gastrointestinal handling of phosphate and calcium. However, emerging data suggest that imatinib also targets cells of the skeleton, stimulating the retention and sequestration of calcium and phosphate to bone, leading to decreased circulating levels of these minerals. The aim of this review is to highlight our current understanding of the mechanisms surrounding the effects of imatinib on the skeleton. In particular, it examines recent studies suggesting that imatinib has direct effects on bone-resorbing osteoclasts and bone-forming osteoblasts through inhibition of c-fms, c-kit, carbonic anhydrase II, and the platelet-derived growth factor receptor. The potential application of imatinib in the treatment of cancer-induced osteolysis will also be discussed.

Imatinib mesylate enhances therapeutic effects of gemcitabine in human malignant mesothelioma xenografts

PURPOSE

Platelet-derived growth factor receptor beta (PDGFRbeta), frequently activated in malignant mesothelioma, is a promising cancer therapeutic target. Imatinib mesylate (STI571; Glivec) is a selective inhibitor of tyrosine kinases as bcr-abl, c-kit, c-fms, and PDGFRbeta and enhances tumor drug uptake by reducing the interstitial fluid pressure. We previously showed that imatinib mesylate synergizes with gemcitabine and pemetrexed in PDGFRbeta-positive mesothelioma cells. Here, we aimed at investigating these combined treatments in a novel mesothelioma model.

EXPERIMENTAL DESIGN

REN mesothelioma cells, infected with a lentiviral vector carrying the luciferase gene, were injected in the peritoneum of severe combined immunodeficient mice. This model allowed imaging of live animals treated with pemetrexed or gemcitabine chemotherapeutics, or with imatinib mesylate alone, as well as with a combination of gemcitabine and imatinib mesylate.

RESULTS

We show here that, consistent with our previous in vitro studies, gemcitabine inhibited tumor growth, whereas pemetrexed was ineffective, even at the highest dosage tested. Compared with monotreatment, the combination of gemcitabine with imatinib mesylate led to a further tumor growth inhibition and improved mice survival, by a decrease rate of tumor cell proliferation and an increase in number of apoptotic tumor cells.

CONCLUSIONS

Imatinib mesylate enhances the therapeutic response to gemcitabine, in accordance with our previous in vitro data. These in vivo results validate imatinib mesylate and gemcitabine as a combination treatment of malignant mesothelioma, also in view of its known positive effects on tumor drug uptake. These evidences provide the rationale for the currently ongoing clinical trials.

Multiple myeloma cells directly stimulate bone resorption in vitro by down-regulating mature osteoclast apoptosis

Multiple myeloma (MM) is characterized by devastating bone destruction mainly due to stimulation of osteoclastogenesis. However, whether MM cells can directly influence osteoclast apoptosis, a mechanism that would contribute to increase the number of active osteoclasts, has not been addressed yet. Herein, using authentic mature rabbit osteoclasts, we demonstrated that conditioned media (CM) prepared from U266 and RPMI8226 cells but not from LP-1 and OPM-2 cells, stimulated bone resorption and inhibited osteoclast apoptosis in a dose-dependent manner. The MM cells which exerted an anti-apoptotic effect secreted high amounts of M-CSF and addition of a neutralizing antibody against M-CSF reversed the CM effects. Imatinib mesylate, a tyrosine kinase inhibitor that can target the M-CSF receptor, also prevented the effect of CM. These findings suggest that M-CSF originating from MM cells may play a critical role in MM bone disease by decreasing osteoclast apoptosis.

Imatinib promotes osteoblast differentiation by inhibiting PDGFR signaling and inhibits osteoclastogenesis by both direct and stromal cell-dependent mechanisms

Several lines of evidence suggest that imatinib may affect skeletal tissue. We show that inhibition by imatinib of PDGFR signaling in osteoblasts activates osteoblast differentiation and inhibits osteoblast proliferation and that imatinib inhibits osteoclastogenesis by both stromal cell-dependent and direct effects on osteoclast precursors.

INTRODUCTION

Imatinib mesylate, an orally active inhibitor of the c-abl, c-kit, and platelet-derived growth factor receptor (PDGFR) tyrosine kinases, is in clinical use for the treatment of chronic myeloid leukemia (CML) and gastrointestinal stromal cell tumors. Interruption of both c-kit and c-abl signaling in mice induces osteopenia, suggesting that imatinib might have adverse effects on the skeleton. However, biochemical markers of bone formation increase in patients with CML starting imatinib therapy, whereas bone resorption is unchanged, despite secondary hyperparathyroidism. We assessed the actions of imatinib on bone cells in vitro to study the cellular and molecular mechanism(s) underlying the skeletal effects we observed in imatinib-treated patients.

MATERIALS AND METHODS

Osteoblast differentiation was assessed using a mineralization assay, proliferation by [(3)H]thymidine incorporation, and apoptosis by a TUNEL assay. Osteoclastogenesis was assessed using murine bone marrow cultures and RAW 264.7 cells. RT and multiplex PCR were performed on RNA prepared from human bone marrow samples, osteoblastic cells, and murine bone marrow cultures. Osteoprotegerin was measured by ELISA.

RESULTS

The molecular targets of imatinib are expressed in bone cells. In vitro, imatinib increases osteoblast differentiation and prevents PDGF-induced inhibition of this process. Imatinib inhibits proliferation of osteoblast-like cells induced by serum and PDGF. In murine bone marrow cultures, imatinib inhibits osteoclastogenesis stimulated by 1,25-dihydroxyvitamin D(3) and partially inhibits osteoclastogenesis induced by RANKL and macrophage-colony stimulating factor. Imatinib partially inhibited osteoclastogenesis in RANKL-stimulated RAW-264.7 cells. Treatment with imatinib increases the expression of osteoprotegerin in bone marrow from patients with CML and osteoblastic cells.

CONCLUSIONS

Taken together with recent in vivo data, these results suggest a role for the molecular targets of imatinib in bone cell function, that inhibition by imatinib of PDGFR signaling in osteoblasts activates bone formation, and that the antiresorptive actions of imatinib are mediated by both stromal cell-dependent and direct effects on osteoclast precursors.

Harnessing the tumour-derived cytokine, CSF-1, to co-stimulate T-cell growth and activation

Aberrant growth factor production is a prevalent mechanism in tumourigenesis. If T-cells responded positively to a cancer-derived cytokine, this might result in selective enhancement of function within the tumour microenvironment. Here, we have chosen colony-stimulating factor-1 (CSF-1) as a candidate to test this concept. CSF-1 is greatly overproduced in many cancers but has no direct effects upon T-lymphocytes, which do not express the c-fms-encoded CSF-1 receptor. To confer CSF-1-responsiveness, we have expressed the human c-fms gene in immortalized and primary T-cells. Addition of soluble CSF-1 resulted in synergistic enhancement of IL-2-driven T-cell proliferation. CSF-1 also co-stimulated the production of interferon (IFN)-gamma by activated T-cells. These effects required Y809 of the CSF-1R and activation of the Ras-MEK-MAP kinase cascade, but were independent of PI3K signalling. T-cells that express c-fms are also responsive to membrane-anchored CSF-1 (mCSF-1) which, unlike its soluble counterpart, could co-stimulate IL-2 production. CSF-1 promoted chemotaxis of c-fms-expressing primary human T-cells and greatly augmented proliferation mediated by a tumour-targeted chimeric antigen receptor, with preservation of tumour cytolytic activity. Taken together, these data establish that T-cells may be genetically modified to acquire responsiveness to CSF-1 and provide proof-of-principle for a novel strategy to enhance the effectiveness of adoptive T-cell immunotherapy.

Apoptotic killing of HIV-1-infected macrophages is subverted by the viral envelope glycoprotein

Viruses have evolved strategies to protect infected cells from apoptotic clearance. We present evidence that HIV-1 possesses a mechanism to protect infected macrophages from the apoptotic effects of the death ligand TRAIL (tumor necrosis factor–related apoptosis-inducing ligand). In HIV-1–infected macrophages, the viral envelope protein induced macrophage colony-stimulating factor (M-CSF). This pro-survival cytokine downregulated the TRAIL receptor TRAIL-R1/DR4 and upregulated the anti-apoptotic genes Bfl-1 and Mcl-1. Inhibition of M-CSF activity or silencing of Bfl-1 and Mcl-1 rendered infected macrophages highly susceptible to TRAIL. The anti-cancer agent Imatinib inhibited M-CSF receptor activation and restored the apoptotic sensitivity of HIV-1–infected macrophages, suggesting a novel strategy to curtail viral persistence in the macrophage reservoir.

Much of our understanding regarding mechanisms of HIV-1 persistence has been derived from studies with lymphocytes. However, mechanisms governing persistent infection of macrophages are less well understood. We investigated whether HIV-1 modulates macrophage function in a way that promotes their persist infection. We focused on a cytokine called macrophage colony-stimulating factor (M-CSF), because this pro-survival factor is induced upon infection by HIV-1. We found that the viral envelope gene was necessary for M-CSF induction of macrophages. M-CSF upregulated anti-apoptotic genes in macrophages and restricted the expression of the death receptor (tumor necrosis factor–related apoptosis-inducing ligand [TRAIL]-R1). As a consequence, HIV-1–infected macrophages were resistant to the apoptotic effects of TRAIL. If M-CSF was blocked by antibody or if the anti-apoptotic genes were silenced by RNA interference, the apoptotic sensitivity of HIV-1–infected macrophages was restored. Also, the anti-cancer drug Imatinib, which impairs activation of the M-CSF receptor, promoted the death of HIV-1–infected macrophages but not of uninfected macrophages. We believe that HIV-1 regulates M-CSF to extend macrophage survival and promote viral persistence in the host. Agents that interfere with M-CSF signaling, such as Imatinib, warrant further examination for activity against macrophage reservoirs in vivo.

Imatinib mesylate (IM)-induced growth inhibition is associated with production of spliced osteocalcin-mRNA in cell lines

It has been suggested that imatinib mesylate (IM) influences osteogenesis and bone turnover in treated patients. Here we show that the inhibitory effect of IM on cell multiplication is associated with an increased proportion of spliced osteocalcin (OCNs) in leukemia (HL-60) and osteosarcoma cells (MG-63, U-2 OS), despite a lower mRNA synthesis rate. In mouse osteoblastic MC3T3-E1 cells only OCNs is present, independently of treatment. As the stimulatory effect of IM on OCNs is also observed upon treatment with vitamin D, common regulatory processes may be considered.

Molecular mechanisms underlying FIP1L1-PDGFRA-mediated myeloproliferation

An interstitial deletion on chromosome 4q12 resulting in the formation of the FIP1L1-PDGFRA fusion protein is involved in the pathogenesis of imatinib-sensitive chronic eosinophilic leukemia. The molecular mechanisms underlying the development of disease are largely undefined. Human CD34(+) hematopoietic progenitor cells were used to investigate the role of FIP1L1-PDGFRA in modulating lineage development. FIP1L1-PDGFRA induced both proliferation and differentiation of eosinophils, neutrophils, and erythrocytes in the absence of cytokines, which could be inhibited by imatinib. Whereas expression of FIP1L1-PDGFRA in hematopoietic stem cells and common myeloid progenitors induced the formation of multiple myeloid lineages, expression in granulocyte-macrophage progenitors induced only the development of eosinophils, neutrophils, and myeloblasts. Deletion of amino acids 30 to 233 in the FIP1L1 gene [FIP1L1(1-29)-PDGFRA] gave rise to an intermediate phenotype, exhibiting a dramatic reduction in the number of erythrocytes. FIP1L1-PDGFRA and FIP1L1(1-29)-PDGFRA both induced the activation of p38 and extracellular signal-regulated kinase 1/2 (ERK1/2) in myeloid progenitors, whereas signal transducers and activators of transcription 5 (STAT5) and protein kinase B/c-akt were only activated by FIP1L1-PDGFRA. Dominant-negative STAT5 partially inhibited FIP1L1-PDGFRA-induced colony formation, whereas combined inhibition of phosphatidylinositol-3-kinase and ERK1/2 significantly reversed FIP1L1-PDGFRA-induced colony formation. Taken together, these results suggest that expression of FIP1L1-PDFGRA in human hematopoietic progenitors induce a myeloproliferative phenotype via activation of multiple signaling molecules including phosphatidylinositol-3-kinase, ERK1/2, and STAT5.

C3G is required for c-Abl-induced filopodia and its overexpression promotes filopodia formation

The Rap1 guanine nucleotide exchange factor, C3G (also known as Rap1GEF-1) is involved in signaling from growth factors, cytokines and integrins and plays a role in cell adhesion and migration, but the mechanism by which C3G regulates various cellular functions is poorly understood. We, therefore, investigated the ability of C3G to affect actin cytoskeleton-dependent morphological changes in cells. Using RNA interference, we provide evidence that C3G is required for c-Abl-induced filopodia during cell spreading on fibronectin. C3G expression induces actin cytoskeletal reorganization and promotes filopodia formation independent of its catalytic activity. It showed enrichment at filopodia tips characteristic of molecules involved in filopodia dynamics. C3G-induced filopodia were not inhibited by dominant negative mutants of Rho, Rac and Cdc42, but required Abl catalytic activity. Coexpression of N-Wasp-Crib inhibited C3G induced as well as c-Abl-induced filopodia and wiskostatin, a pharmacological inhibitor of N-Wasp attenuates C3G-induced filopodia. Cellular C3G interacts with c-Abl and C3G expression results in enhanced localization of endogenous c-Abl in the cytoplasm. We suggest that C3G and c-Abl function in an interdependent manner, in linking external signals to remodeling the cytoskeleton to induce filopodia.

A novel fusion of RBM6 to CSF1R in acute megakaryoblastic leukemia

Activated tyrosine kinases have been frequently implicated in the pathogenesis of cancer, including acute myeloid leukemia (AML), and are validated targets for therapeutic intervention with small-molecule kinase inhibitors. To identify novel activated tyrosine kinases in AML, we used a discovery platform consisting of immunoaffinity profiling coupled to mass spectrometry that identifies large numbers of tyrosine-phosphorylated proteins, including active kinases. This method revealed the presence of an activated colony-stimulating factor 1 receptor (CSF1R) kinase in the acute megakaryoblastic leukemia (AMKL) cell line MKPL-1. Further studies using siRNA and a small-molecule inhibitor showed that CSF1R is essential for the growth and survival of MKPL-1 cells. DNA sequence analysis of cDNA generated by 5'RACE from CSF1R coding sequences identified a novel fusion of the RNA binding motif 6 (RBM6) gene to CSF1R gene generated presumably by a t(3;5)(p21;q33) translocation. Expression of the RBM6-CSF1R fusion protein conferred interleukin-3 (IL-3)-independent growth in BaF3 cells, and induces a myeloid proliferative disease (MPD) with features of megakaryoblastic leukemia in a murine transplant model. These findings identify a novel potential therapeutic target in leukemogenesis, and demonstrate the utility of phosphoproteomic strategies for discovery of tyrosine kinase alleles.

The 2.7 Å Crystal Structure of the Autoinhibited Human c-Fms Kinase Domain

c-Fms, a member of the Platelet-derived Growth Factor (PDGF) receptor family of receptor tyrosine kinases (RTKs), is the receptor for macrophage colony stimulating factor (CSF-1) that regulates proliferation, differentiation and survival of cells of the mononuclear phagocyte lineage. Abnormal expression of c-fms proto-oncogene is associated with a significant number of human pathologies, including a variety of cancers and rheumatoid arthritis. Accordingly, c-Fms represents an attractive therapeutic target. To further understand the regulation of c-Fms, we determined the 2.7 A resolution crystal structure of the cytosolic domain of c-Fms that comprised the kinase domain and the juxtamembrane domain. The structure reveals the crucial inhibitory role of the juxtamembrane domain (JM) that binds to a hydrophobic site immediately adjacent to the ATP binding pocket. This interaction prevents the activation loop from adopting an active conformation thereby locking the c-Fms kinase into an autoinhibited state. As observed for other members of the PDGF receptor family, namely c-Kit and Flt3, three JM-derived tyrosine residues primarily drive the mechanism for autoinhibition in c-Fms, therefore defining a common autoinhibitory mechanism within this family. Moreover the structure provides an understanding of c-Fms inhibition by Gleevec as well as providing a platform for the development of more selective inhibitors that target the inactive conformation of c-Fms kinase.

Preliminary data suggestive of a novel translational approach to mesothelioma treatment: imatinib mesylate with gemcitabine or pemetrexed

BACKGROUND

Malignant mesothelioma is a cancer which is refractory to current treatments. Imatinib mesylate is a selective inhibitor of tyrosine kinases such as bcr-abl, c-Kit, c-Fms and platelet derived growth factor receptor beta (PDGFRbeta). PDGFRbeta is often overexpressed in mesothelioma cells and is a therapeutic target for imatinib in some solid tumours. A study was undertaken to assess whether imatinib alone or combined with chemotherapeutic agents may be effective for treating mesothelioma.

METHODS

Cultures from mesothelioma MMP, REN and ISTMES2 cell lines were treated with imatinib alone or in combination with a chemotherapeutic agent.

RESULTS

Imatinib induced cytotoxicity and apoptosis selectively on PDGFRbeta positive mesothelioma cells via blockade of receptor phosphorylation and interference with the Akt pathway. Of the chemotherapeutic agents tested in combination with imatinib, a synergistic effect was obtained with gemcitabine and pemetrexed.

CONCLUSIONS

This study provides a rationale for a novel translational approach to the treatment of mesothelioma which relies on enhancement of tumour chemosensitivity by inhibition of Akt.

Results of a multicenter phase II trial for older patients with c-Kit-positive acute myeloid leukemia (AML) and high-risk myelodysplastic syndrome (HR-MDS) using low-dose Ara-C and Imatinib

BACKGROUND

Imatinib (IM) is a potent tyrosine kinase inhibitor of c-Kit. c-Kit is expressed in the majority of patients with acute myeloid leukemia (AML). Whereas clinical trials evaluating monotherapy with IM in AML revealed low response rates, Ara-C and IM showed synergistic effects in vitro. This suggested evaluation of a combination treatment.

METHODS

Low-dose Ara-C (LDAC) combined with IM was tested to determine the efficacy and safety of this regimen. Forty patients from 4 centers with c-Kit-positive AML (n = 34) and high-risk myelodysplastic syndrome (HR-MDS) (n = 6) with a median age of 73 years were enrolled. They were either not eligible for myelosuppressive therapy and/or had recurring/refractory disease.

RESULTS

Thirty-eight patients were evaluable for analysis. In 6 of 38 patients a blast response was observed. Eight of 38 patients showed stable disease for more than 2 months. The objective hematologic response rate was low (11%), with 2 patients showing hematologic improvement and 1 each with a partial response (PR) or complete response (CR). Median overall survival was 138 days, with 20% of patients alive after an observation period of 600 days. Study medication was applied in an ambulatory setting with minimal hospitalization time, an early mortality rate of only 18.9%, and a low toxicity rate.

CONCLUSIONS

LDAC plus IM does not appear to be inferior in older AML patients incomparison with historic controls receiving myelosuppressive therapy. However, this trial also shows that LDAC/IM does not appear to be more effective than LDAC monotherapy in a patient population not selected for appropriate molecular markers.