Inhibition of phosphorylation of the colony-stimulating factor-1 receptor (c-Fms) tyrosine kinase in transfected cells by ABT-869 and other tyrosine kinase inhibitors

Pyrrolopyrimidine based CSF1R inhibitors: Attempted departure from Flatland

The colony-stimulating factor 1 receptor (CSF1R) is an attractive target for inflammation disorders and cancers. Based on a series of pyrrolo[2,3-d]pyrimidine containing two carbo-aromatic rings, we have searched for new CSF1R inhibitors having a higher fraction of sp3-atoms. The phenyl unit in the 4-amino group could efficiently be replaced by tetrahydropyran (THP) retaining inhibitor potency. Exchanging the 6-aryl group with cyclohex-2-ene units also resulted in highly potent compounds, while fully saturated ring systems at C-6 led to a loss of activity. The structure-activity relationship study evaluating THP containing pyrrolo[2,3-d]pyrimidine derivates identified several highly active inhibitors by enzymatic studies. A comparison of 11 pairs of THP and aromatic compounds showed that inhibitors containing THP had clear benefits in terms of enzymatic potency, solubility, and cell toxicity. Guided by cellular experiments in Ba/F3 cells, five CSF1R inhibitors were further profiled in ADME assays, indicating the para-aniline derivative 16t as the most attractive compound for further development.

PHDs-seq: a large-scale phenotypic screening method for drug discovery through parallel multi-readout quantification

High-throughput phenotypic screening is a cornerstone of drug development and the main technical approach for stem cell research. However, simultaneous detection of activated core factors responsible for cell fate determination and accurate assessment of directional cell transition are difficult using conventional screening methods that focus on changes in only a few biomarkers. The PHDs-seq (Probe Hybridization based Drug screening by sequencing) platform was developed to evaluate compound function based on their transcriptional effects in a wide range of signature biomarkers. In this proof-of-concept demonstration, several sets of markers related to cell fate determination were profiled in adipocyte reprogramming from dermal fibroblasts. After validating the accuracy, sensitivity and reproducibility of PHDs-seq data in molecular and cellular assays, a panel of 128 signalling-related compounds was screened for the ability to induce reprogramming of keloid fibroblasts (KF) into adipocytes. Notably, the potent ATP-competitive VEGFR/PDGFR inhibitor compound, ABT869, was found to promote the transition from fibroblasts to adipocytes. This study highlights the power and accuracy of the PHDs-seq platform for high-throughput drug screening in stem cell research, and supports its use in basic explorations of the molecular mechanisms underlying disease development.

Targeting CSF-1R represents an effective strategy in modulating inflammatory diseases

Colony-stimulating factor-1 receptor (CSF-1R), also known as FMS kinase, is a type I single transmembrane protein mainly expressed in myeloid cells, such as monocytes, macrophages, glial cells, and osteoclasts. The endogenous ligands, colony-stimulating factor-1 (CSF-1) and Interleukin-34 (IL-34), activate CSF-1R and downstream signaling pathways including PI3K-AKT, JAK-STATs, and MAPKs, and modulate the proliferation, differentiation, migration, and activation of target immune cells. Over the past decades, the promising therapeutic potential of CSF-1R signaling inhibition has been widely studied for decreasing immune suppression and escape in tumors, owing to depletion and reprogramming of tumor-associated macrophages. In addition, the excessive activation of CSF-1R in inflammatory diseases is consecutively uncovered in recent years, which may result in inflammation in bone, kidney, lung, liver and central nervous system. Agents against CSF-1R signaling have been increasingly investigated in preclinical or clinical studies for inflammatory diseases treatment. However, the pathological mechanism of CSF-1R in inflammation is indistinct and whether CSF-1R signaling can be identified as biomarkers remains controversial. With the background information aforementioned, this review focus on the dialectical roles of CSF-1R and its ligands in regulating innate immune cells and highlights various therapeutic implications of blocking CSF-1R signaling in inflammatory diseases.

Diarylureas as Antitumor Agents

The diarylurea is a scaffold of great importance in medicinal chemistry as it is present in numerous heterocyclic compounds with antithrombotic, antimalarial, antibacterial, and anti-inflammatory properties. Some diarylureas, serine-threonine kinase or tyrosine kinase inhibitors, were recently reported in literature. The first to come into the market as an anticancer agent was sorafenib, followed by some others. In this review, we survey progress over the past 10 years in the development of new diarylureas as anticancer agents.

Using in silico modelling and FRET-based assays in the discovery of novel FDA-approved drugs as inhibitors of MERS-CoV helicase

A Förster resonance energy transfer (FRET)-based assay was used to screen the FDA-approved compound library against the MERS-CoV helicase, an essential enzyme for virus replication within the host cell. Five compounds inhibited the helicase activity with submicromolar potencies (IC₅₀, 0.73-1.65 µM) and ten compounds inhibited the enzyme with micromolar potencies (IC₅₀, 19.6-502 µM). The molecular operating environment (MOE) was used to dock the identified inhibitors on the MERS-CoV helicase nucleotide binding. Strong inhibitors docked well in the nucleotide-binding site and established interactions with some of the essential residues. There was a reasonable correlation between the observed IC₅₀ values and the MOE docking scores of the strong inhibitors (r ² = 0.74), indicating the ability of the in silico docking model to predict the binding of strong inhibitors. In silico docking could be a useful complementary tool used with the FRET-based assay to predict new MERS-CoV helicase inhibitors. The identified inhibitors could potentially be used in the clinical development of new antiviral treatment for MERS-CoV and other coronavirus related diseases, including coronavirus disease 2019 (COVID-19).

Small-molecule CSF1R kinase inhibitors; review of patents 2015-present

INTRODUCTION

Colony stimulating factor 1 receptor (CSF-1R, also known as c-FMS kinase) is in the class III receptor tyrosine kinase family, along with c-Kit, Flt3 and PDGFRα. CSF-1/CSF-1R signaling promotes the differentiation and survival of myeloid progenitors into populations of monocytes, macrophages, dendritic cells and osteoclasts, as well as microglial cells and also recruits host macrophages to develop into tumor-associated macrophages (TAMs), which promote tumor progression and metastasis.

AREAS COVERED

In the last 5 years, and recently stimulated by the approval of pexidartinib (Turalio™, Daiichi Sankyo) in 2019 for the treatment of tenosynovial giant cell tumors, there has been a large increase in activity (both journal articles and patent applications) around small molecule inhibitors of CSF1R. Features of this work have been the surprising diversity of chemical classes shown to be potent and selective inhibitors, and the breadth of disease states (cancer, arthritis, and 'cytokine storm' syndromes) covered by CSF1R inhibitors. All these aspects are covered in the following sections.

EXPERT OPINION

The field has developed rapidly from 2014 to the present, with many different chemotypes proving to be potent inhibitors. The range of potential utilities of CSF1R inhibitors has also expanded to include dementia, ulcerative colitis/Crohn's disease, rheumatoid arthritis inflammation, and fibrosis.

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.

Rational Drug Design Approach of Receptor Tyrosine Kinase Type III Inhibitors

Rational drug design is accomplished through the complementary use of structural biology and computational biology of biological macromolecules involved in disease pathology. Most of the known theoretical approaches for drug design are based on knowledge of the biological targets to which the drug binds. This approach can be used to design drug molecules that restore the balance of the signaling pathway by inhibiting or stimulating biological targets by molecular modeling procedures as well as by molecular dynamics simulations. Type III receptor tyrosine kinase affects most of the fundamental cellular processes including cell cycle, cell migration, cell metabolism, and survival, as well as cell proliferation and differentiation. Many inhibitors of successful rational drug design show that some computational techniques can be combined to achieve synergistic effects.

Long-term efficacy of imatinib mesylate in patients with advanced Tenosynovial Giant Cell Tumor

Tenosynovial giant cell tumors (TGCT), are rare colony stimulating factor-1(CSF-1)-driven proliferative disorders affecting joints. Diffuse-type TGCT often causes significant morbidity due to local recurrences necessitating multiple surgeries. Imatinib mesylate (IM) blocks the CSF-1 receptor. This study investigated the long term effects of IM in TGCT. We conducted an international multi-institutional retrospective study to assess the activity of IM: data was collected anonymously from individual patients with locally advanced, recurrent or metastatic TGCT. Sixty-two patients from 12 institutions across Europe, Australia and the United States were identified. Four patients with metastatic TGCT progressed rapidly on IM and were excluded for further analyses. Seventeen of 58 evaluable patients achieved complete response (CR) or partial response (PR). One- and five-year progression-free survival rates were 71% and 48%, respectively. Thirty-eight (66%) patients discontinued IM after a median of 7 (range 1–80) months. Reported adverse events in 45 (78%) patients were among other edema (48%) and fatigue (50%), mostly grade 1–2 (89%). Five patients experienced grade 3–4 toxicities. This study confirms, with additional follow-up, the efficacy of IM in TGCT. In responding cases we confirmed prolonged IM activity on TGCT symptoms even after discontinuation, but with high rates of treatment interruption and additional treatments.

Dovitinib Triggers Apoptosis and Autophagic Cell Death by Targeting SHP-1/p-STAT3 Signaling in Human Breast Cancers

Breast cancer is the most common cancer and the leading cause of cancer deaths in women worldwide. The rising incidence rate and female mortality make it a significant public health concern in recent years. Dovitinib is a novel multitarget receptor tyrosine kinase inhibitor, which has been enrolled in several clinical trials in different cancers. However, its antitumor efficacy has not been well determined in breast cancers. Our results demonstrated that dovitinib showed significant antitumor activity in human breast cancer cell lines with dose- and time-dependent manners. Downregulation of phosphor-(p)-STAT3 and its subsequent effectors Mcl-1 and cyclin D1 was responsible for this drug effect. Ectopic expression of STAT3 rescued the breast cancer cells from cell apoptosis induced by dovitinib. Moreover, SHP-1 inhibitor reversed the downregulation of p-STAT3 induced by dovitinib, indicating that SHP-1 mediated the STAT3 inhibition effect of dovitinib. In addition to apoptosis, we found for the first time that dovitinib also activated autophagy to promote cell death in breast cancer cells. In conclusion, dovitinib induced both apoptosis and autophagy to block the growth of breast cancer cells by regulating the SHP-1-dependent STAT3 inhibition.

Recent advances in colony stimulating factor-1 receptor/c-FMS as an emerging target for various therapeutic implications

Colony stimulating factor-1 (CSF-1) is one of the most common proinflammatory cytokine responsible for various inflammatory disorders. It has a remarkable role in the development and progression of osteoarthritis, cancer and other autoimmune disease conditions. The CSF-1 acts by binding to the receptor, called colony stimulating factor-1 receptor (CSF-1R) also known as c-FMS resulting in the cascade of signalling pathway causing cell proliferation and differentiation. Interleukin-34 (IL-34), recently identified as another ligand for CSF-IR, is a cytokine protein. Both, CSF-1 and IL-34, although two distinct cytokines, follow the similar signalling pathway on binding to the same receptor, CSF-1R. Like CSF-1, IL-34 promotes the differentiation and survival of monocyte, macrophages and osteoclasts. This CSF-1R/c-FMS is over expressed in many cancers and on tumour associated macrophages, consequently, have been exploited as a drug target for promising treatment for cancer and inflammatory diseases. Some CSF-1R/c-FMS inhibitors such as ABT-869, Imatinib, AG013736, JNJ-40346527, PLX3397, DCC-3014 and Ki20227 have been successfully used in these disease conditions. Many c-FMS inhibitors have been the candidates of clinical trials, but suffer from some side effects like cardiotoxicity, vomiting, swollen eyes, diarrhoea, etc. If selectivity of cFMS inhibition is achieved successfully, side effects can be overruled and this approach may become a novel therapy for treatment of various therapeutic interventions. Thus, successful targeting of c-FMS may result in multifunctional therapy. With this background of information, the present review focuses on the recent developments in the area of CSF-1R/c-FMS inhibitors with emphasis on crystal structure, mechanism of action and various therapeutic implications in which c-FMS plays a pivotal role. The review on structure activity relationship of various compounds acting as the inhibitors of c-FMS which gives the selection criteria for the development of novel molecules is also being presented.

Clinical pharmacodynamic/exposure characterisation of the multikinase inhibitor ilorasertib (ABT-348) in a phase 1 dose-escalation trial

Background

Ilorasertib (ABT-348) inhibits Aurora and VEGF receptor (VEGFR) kinases. Patients with advanced solid tumours participated in a phase 1 dose-escalation trial to profile the safety, tolerability, and pharmacokinetics of ilorasertib.

Methods

Ilorasertib monotherapy was administered at 10–180 mg orally once daily (Arm I, n = 23), 40–340 mg orally twice daily (Arm II, n = 28), or 8–32 mg intravenously once daily (Arm III, n = 7), on days 1, 8, and 15 of each 28-day cycle.

Results

Dose-limiting toxicities were predominantly related to VEGFR inhibition. The most frequent treatment-emergent adverse events ( > 30%) were: fatigue (48%), anorexia (34%), and hypertension (34%). Pharmacodynamic markers suggested that ilorasertib engaged VEGFR2 and Aurora B kinase, with the VEGFR2 effects reached at lower doses and exposures than Aurora inhibition effects. In Arm II, one basal cell carcinoma patient (40 mg twice daily (BID)) and one patient with adenocarcinoma of unknown primary site (230 mg BID) had partial responses.

Conclusions

In patients with advanced solid tumours, ilorasertib treatment resulted in evidence of engagement of the intended targets and antitumour activity, but with maximum inhibition of VEGFR family kinases occurring at lower exposures than typically required for inhibition of Aurora B in tissue.

Clinical Trial Registration: NCT01110486

Spectrophotometric and molecular modelling studies on in vitro interaction of tyrosine kinase inhibitor linifanib with bovine serum albumin

Linifanib (LNF) possess antitumor activity and acts by inhibiting receptor tyrosine kinase VEGF and PDGF. The interaction of BSA with the drug can provide valuable information regarding the pharmacokinetic and pharmacodynamics behavior of drug. In our study the spectrophotometric methods and molecular docking studies were executed to understand the interaction behavior of BSA and LNF. BSA has an intrinsic fluorescence and that fluorescence was quenched by LNF. This quenching process was studied at three different temperatures of 288, 300and 308 K. The interaction between LNF and BSA was due to static quenching because the Ksv (Stern-Volmer constant) at 288 K was higher than at 300 and 308 K. Kq (quenching rate constant) behaved in a similar fashion as the Ksv. Several other parameters like binding constants, number of binding sites and binding energy in addition to molecular docking studies were also used to evaluate the interaction process. A decrease in the binding constants was observed with increasing temperatures and the binding site number approximated unity. The decreasing binding constant indicates LNF–BSA complex stability. The site mark competition experiment confirmed the binding site for LNF was located on site II of BSA. UV–visible studies along with synchronous fluorescence confirm a small change in the conformation of BSA upon interaction with LNF. The thermodynamic analysis provided the values for free energy ΔG⁰, ΔH⁰ and ΔS⁰. The ΔG⁰ at the 288, 300 and 308 K ranged in between -21.5 to -23.3 kJ mol-1, whereas the calculated values of ΔH (-55.91 kJ mol^-1) and ΔS⁰ (-111.74 J mol^-1·K^-1). The experimental and molecular docking results suggest that the interaction between LNF and BSA was spontaneous and they exhibited hydrogen bonding and van der Waals force between them.

Development of a protease-resistant reporter to quantify BCR-ABL activity in intact cells

A peptidase-resistant ABL kinase substrate was developed by identifying protease-susceptible bonds on an ABL substrate peptide and replacing flanking amino acids with non-native amino acids. After an iterative design process, the lead, or designed, peptide X-A possesses a six-fold longer life in a cytosolic lysate than that of the starting peptide. The catalytic efficiency (kcat/KM) of purified ABL kinase for the lead peptide (125 s-1 μM-1) is similar to that of the starting peptide (103 s-1 μM-1) demonstrating preservation of the peptide's ability to serve as a kinase substrate. When incubated in cytosolic lysates, the lead peptide is slowly degraded into 4 fragments over time. In contrast, when loaded into intact cells, the peptide is metabolized into 5 fragments, with only 2 of the fragments corresponding to those in the lysate. Thus the two environments possess differing peptidase activities, which must be accounted for when designing peptidase-resistant peptides. In both settings, the substrate is phosphorylated by BCR-ABL providing a readout of BCR-ABL activity. A small panel of tyrosine kinase inhibitors verified the substrate's specificity for BCR-ABL/ABL kinase activity in both lysates and cells in spite of the multitude of other kinases present. The designed peptide X-A acts as a long-lived BCR-ABL kinase reporter in the leukemic cells possessing the BCR-ABL mutation.

Linifanib for treatment of hepatocellular carcinoma: An overview of clinical trials

Linifanib achieves the antitumor activity by inhibiting all vascular endothelial growth factor receptors and platelet-derived growth factor receptors. We aim to review the findings of clinical trials of linifanib for the treatment of hepatocellular carcinoma (HCC). Several phase I clinical trials have confirmed the safety of linifanib in patients with solid malignancy. One phase Ⅱ clinical trial has shown the clinical efficacy of linifanib alone for the treatment of HCC. Recently, a phase Ⅲ randomized controlled trial showed that, compared with sorafenib, linifanib cannot significantly improve the overall survival of HCC patients. Thus, linifanib is not recommended as the first-line therapy for advanced HCC. However, because linifanib could significantly prolong the time-to-progression and progression-free survival time and increase the objective response rate, future studies might be necessary to explore the clinical utility of linifanib as a second-line therapy for advanced HCC.

Review of angiogenesis in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a hypervascular tumor, and its vascularity is unique and greatly different from peripheral parenchyma of liver. Afferent and efferent vessels of HCC lesions come to differ as the lesion develops. The characteristic of the flow regulates the common style of metastasis. The portal tract of the HCC lesion is the first site of the intrahepatic metastasis, because cancer cells roll into the portal vein via efferent flow. On microscopic observation, HCC displays marked vascular abnormalities, arteriogenesis and capillarization. Arteriogenesis is defined as the growth of functional collateral arteries covered with smooth muscle cells from pre-existing arteries. Sinusoidal capillarization involves the transformation of fenestrated hepatic sinusoids into continuous capillaries. Several angiogenic factors have been reported, and some of them are studied as prognostic factors or target molecules of chemotherapeutic reagents. However, the mechanism of neovascularization during HCC development is still unclear. This review discusses the characteristics of angiogenesis in HCC and known angiogenic factors of HCC.

Phase I clinical trial combining imatinib mesylate and IL-2 in refractory cancer patients: IL-2 interferes with the pharmacokinetics of imatinib mesylate

Imatinib mesylate (IM) is a small molecule inhibitor of protein tyrosine kinases. In addition to its direct effect on malignant cells, it has been suggested IM may activate of natural killer (NK) cells, hence exerting immunomodulatory functions. In preclinical settings, improved antitumor responses have been observed when IM and interleukin-2 (IL-2), a cytokine that enhances NK cells functions, were combined. The goals of this study were to determine the maximum tolerated dose (MTD) of IL-2 combined with IM at a constant dose of 400 mg, the pharmacokinetics of IM and IL-2, as well as toxicity and clinical efficacy of this immunotherapeutic regimen in patients affected by advanced tumors. The treatment consisted in 50 mg/day cyclophosphamide from 21 d before the initiation of IM throughout the first IM cycle (from D-21 to D14), 400 mg/day IM for 14 d (D1 to D14) combined with escalating doses of IL-2 (3, 6, 9 and 12 MIU/day) from days 10 to 14. This treatment was administered at three week intervals to 17 patients. Common side effects of the combination were mild to moderate, including fever, chills, fatigue, nausea and hepatic enzyme elevation. IL-2 dose level II, 6 MIU/day, was determined as the MTD with the following dose-limiting toxicities: systemic capillary leak syndrome, fatigue and anorexia. Pharmacokinetic studies revealed that the area under the curve and the maximum concentration of IM and its main metabolite CGP74588 increased significantly when IM was concomitantly administered with IL-2. In contrast, IM did not modulate IL-2 pharmacokinetics. No objective responses were observed. The best response obtained was stable disease in 8/17 (median duration: 12 weeks). Finally, IL-2 augmented the impregnation of IM and its metabolite. The combination of IM (400 mg/day) and IL-2 (6 MIU/day) in tumors that express IM targets warrants further investigation.

Simple, sensitive and rapid determination of linifanib (ABT-869), a novel tyrosine kinase inhibitor in rat plasma by UHPLC-MS/MS

BACKGROUND

Linifanib (ABT-869) is an orally active receptor tyrosine kinase inhibitor, which simultaneously inhibits vascular endothelial and platelet derived growth factor receptor. The aim of the present study was to develop an UHPLC-MS/MS method for the quantification of linifanib in rat plasma to support the pharmacokinetic and toxicokinetic studies.

RESULTS

Linifanib was separated on Acquity UPLC BEH™ C18 column (50 × 2.1 mm, i.d. 1.7 μm) using acetonitrile-10 mM ammonium acetate (60:40, v/v) as an isocratic mobile phase at a flow rate of 0.3 mL/min with sunitinib as internal standard (IS). Detection was performed on tandem mass spectrometer using electrospray ionization source in positive mode by multiple reaction monitoring. The monitored transitions were set at m/z 376.05 > 250.97 for linifanib and m/z 399.12 >283.02 for IS, respectively. Both linifanib and IS were eluted at 0.68 and 0.44 min, respectively with a total run time of 2.0 min only. The calibration curve was found to be linear over the concentration range of 0.40-500 ng/mL. The intra- and inter-day precision value was ≤10.6% and the accuracy ranged from 90.9-108.9%. In addition, all the validation results were within general assay acceptability criteria according to guidelines of bio-analytical method validation.

CONCLUSION

A selective and sensitive UHPLC-MS/MS method was developed and validated for the determination of linifanib in rat plasma for the first time. The developed method is simple, sensitive and rapid in terms of chromatographic separation and sample preparation and was successfully applied in a pilot pharmacokinetic study in rats.

Exposure-response (safety) analysis to identify linifanib dose for a Phase III study in patients with hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is the third most common cause of cancer-related deaths and the fifth most common cancer globally. Hepatocellular carcinoma produces highly vascular tumors that overexpress vascular endothelial growth factor (VEGF), thus making VEGF a promising therapeutic target. The competitive inhibitor linifanib (ABT-869) has selectivity for VEGF and platelet-derived growth factor (PDGF) receptors and minimal activity against unrelated tyrosine and serine and threonine kinases. However, the optimal dosing regimen for linifanib in HCC patients is not yet known.

OBJECTIVE

This study attempts to identify a linifanib dose or dosing regimen with an acceptable safety profile for a Phase III study in HCC patients.

METHODS

The pharmacokinetic (PK) properties of linifanib were characterized from 2 Phase I and 3 Phase II clinical trials. Of the 266 patients evaluated, the median weight was 68 kg (range, 35-177 kg), 64% were male, and 87.6% of patients received an oral solution of linifanib, whereas 12.4% received a tablet formulation. Approximately 95% of patients received drug based on weight, with the remaining on a fixed-dosing regimen. A population PK analysis was conducted to characterize the linifanib exposure for each patient. Linifanib Cmax and AUC derived from the population PK properties were correlated with the rates of adverse events (AEs).

RESULTS

Linifanib PK properties are dose proportional for the 0.10-mg/kg to 0.25-mg/kg once daily dose range and are time independent after repeated oral dosing. The Tmax of linifanib is approximately 3 hours, and the t½ is approximately 1 day. The most common AEs related to linifanib PK were hypertension (P = 0.02 for Cmax and P = 0.01 for AUC), diarrhea (P = 0.001 for Cmax and P = 0.0012 for AUC), proteinuria (P = 0.001 for Cmax and P = 0.002 for AUC), and asthenia (P = 0.03 for AUC). Weight and sex were identified as covariates for Cmax, and sex was identified as a covariate for AUC. The predicted AE range for females was slightly higher compared with males; however, the AE range is tighter for the weight range for fixed dosing compared with weight-based dosing, regardless of sex.

CONCLUSIONS

The PK properties of linifanib support a one-compartment model with first-order absorption and elimination. Comparison of weight-based and fixed dosing revealed predicted AE rates to be similar, with a tighter AE range for fixed dosing. The safety profile of linifanib, therefore, supports a 17.5 mg fixed starting dose for Phase III clinical studies.

Preclinical characterization of ABT-348, a kinase inhibitor targeting the aurora, vascular endothelial growth factor receptor/platelet-derived growth factor receptor, and Src kinase families

ABT-348 [1-(4-(4-amino-7-(1-(2-hydroxyethyl)-1H-pyrazol-4-yl)thieno[3,2-c]pyridin-3-yl)phenyl)-3-(3-fluorophenyl)urea] is a novel ATP-competitive multitargeted kinase inhibitor with nanomolar potency (IC(50)) for inhibiting binding and cellular autophosphorylation of Aurora B (7 and 13 nM), C (1 and 13 nM), and A (120 and 189 nM). Cellular activity against Aurora B is reflected by inhibition of phosphorylation of histone H3, induction of polyploidy, and inhibition of proliferation of a variety of leukemia, lymphoma, and solid tumor cell lines (IC(50) = 0.3-21 nM). In vivo inhibition of Aurora B was confirmed in an engrafted leukemia model by observing a decrease in phosphorylation of histone H3 that persisted in a dose-dependent manner for 8 h and correlated with plasma concentration of ABT-348. Evaluation of ABT-348 across a panel of 128 kinases revealed additional potent binding activity (K(i) < 30 nM) against vascular endothelial growth factor receptor (VEGFR)/platelet-derived growth factor receptor (PDGFR) families and the Src family of cytoplasmic tyrosine kinases. VEGFR/PDGFR binding activity correlated with inhibition of autophosphorylation in cells and inhibition of vascular endothelial growth factor (VEGF)-stimulated endothelial cell proliferation (IC(50) ≤ 0.3 nM). Evidence of on-target activity in vivo was provided by the potency for blocking VEGF-mediated vascular permeability and inducing plasma placental growth factor. Activity against the Src kinase family was evident in antiproliferative activity against BCR-ABL chronic myeloid leukemia cells and cells expressing the gleevec-resistant BCR-ABL T315I mutation. On the basis of its unique spectrum of activity, ABT-348 was evaluated and found effective in representative solid tumor [HT1080 and pancreatic carcinoma (MiaPaCa), tumor stasis] and hematological malignancy (RS4;11, regression) xenografts. These results provide the rationale for clinical assessment of ABT-348 as a therapeutic agent in the treatment of cancer.

Phase 2 trial of linifanib (ABT-869) in patients with unresectable or metastatic hepatocellular carcinoma

BACKGROUND

The efficacy and safety of linifanib (ABT-869), a selective inhibitor of vascular endothelial growth factor and platelet-derived growth factor receptor tyrosine kinases, were assessed in this phase 2, single-arm, open-label, multicenter trial.

METHODS

Eligible patients had unresectable or metastatic hepatocellular carcinoma and had received ≤ 1 prior systemic therapy. Patients received oral linifanib at a fasting dose of 0.25 mg/kg,. The primary endpoint was the progression-free rate at 16 weeks. Tumor response was assessed every 8 weeks. Secondary endpoints included the time to disease progression, overall survival, and objective response rate. Safety was also assessed.

RESULTS

Of the 44 patients enrolled, the majority were Asian (89%), had received no prior systemic therapy (82%), had Child-Pugh class A hepatic function (86%), and had hepatitis B virus infection (61%). The estimated progression-free rate at 16 weeks was 31.8% (34.2% for patients with Child-Pugh class A hepatic function), the estimated objective response rate was 9.1% (10.5% for patients with Child-Pugh class A hepatic function), the median time to disease progression was 3.7 months (3.7 months for patients with Child-Pugh class A hepatic function), and the median overall survival was 9.7 months (10.4 months for patients with Child-Pugh class A hepatic function). The most common linifanib-related adverse events were diarrhea (55%) and fatigue (52%). The most common linifanib-related grade 3/4 adverse events were hypertension (25%) and fatigue (14%). Serum levels of biomarkers cancer antigen (CA) 125, cytokeratin fragment (CYFRA)21.1, and protein induced by vitamin K absence or antagonist II (PIVKA) demonstrated potential as prognostic indicators of patient response or outcome.

CONCLUSIONS

Single-agent linifanib was found to be clinically active in patients with advanced hepatocellular carcinoma, with an acceptable safety profile.

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.

An open-label, phase 1 study evaluating safety, tolerability, and pharmacokinetics of linifanib (ABT-869) in Japanese patients with solid tumors

Purpose

This phase 1 study assessed the safety, tolerability, pharmacokinetics, and preliminary antitumor activity of linifanib in Japanese patients with advanced solid tumors.

Methods

Patients were assigned to one of four sequential cohorts (0.05, 0.10, 0.20, or 0.25 mg/kg) of oral, once-daily linifanib on a 21-day cycle. Adverse events (AEs) were assessed per common terminology criteria for adverse events v3.0; tumor responses were assessed by response evaluation criteria in solid tumors.

Results

Eighteen patients were enrolled. Eleven (61%) received ≥3 prior therapies. Dose-limiting toxicities were Grade 3 ALT increase (0.10 mg/kg linifanib) and Grade 1 T-wave inversion (0.25 mg/kg linifanib) requiring dose interruption for >7 days and discontinuation on day 29. The most common linifanib-related AE was hypertension. Other significant treatment-related AEs included proteinuria, fatigue, and palmar-plantar erythrodysaesthesia. Linifanib pharmacokinetics were dose-proportional across 0.10–0.25 mg/kg. Two patients (11.1%) had confirmed partial responses, 12 had a best response of stable disease (11 had stable disease for ≥12 weeks), and four patients were not evaluable due to incomplete data. Four patients (lung cancer, breast cancer, thymic cancer, sarcoma) have continued linifanib for ≥48 weeks (range, 48–96+ weeks).

Conclusion

Linifanib was well tolerated with promising preliminary clinical activity in Japanese patients. Later-phase global studies examining linifanib efficacy will include Japanese patients.

Phase 2 trial of Linifanib (ABT-869) in patients with advanced non-small cell lung cancer

INTRODUCTION

This study assessed activity and safety of linifanib (ABT-869), a selective inhibitor of vascular endothelial growth factor and platelet-derived growth factor receptors, in patients with locally advanced or metastatic non-small cell lung cancer.

METHODS

In this open-label trial (NCT00517790), patients who received one to two prior lines of systemic therapy were randomized to oral linifanib 0.10 mg/kg (low dose) or 0.25 mg/kg (high dose) once daily. Tumor responses were assessed by independent central imaging review every 8 weeks. The primary end point was progression-free rate at 16 weeks. Secondary end points included objective response rate, time to progression, progression-free survival, and overall survival. Safety was also assessed.

RESULTS

Between August 2007 and October 2008, 139 patients were enrolled; 60% had two or more prior regimens, and 88% had nonsquamous cell carcinoma. The objective response rate (low dose and high dose) was 5.0% (3.1 and 6.8%), progression-free rate at 16 weeks was 33.1% (32.3 and 33.8%), median time to progression was 3.6 months (3.6 and 3.7 months), median progression-free survival was 3.6 months (3.5 and 3.6 months), and median overall survival was 9.0 months (10.0 and 8.3 months). The most common linifanib-related adverse events were fatigue (42%), decreased appetite (38%), hypertension (37%), diarrhea (32%), nausea (27%), palmar-plantar erythrodysesthesia (24%), and proteinuria (22%). These events were more common in the high-dose group. The most common linifanib-related grade 3 or 4 adverse event was hypertension (14%).

CONCLUSIONS

Linifanib is active in advanced non-small cell lung cancer as second- or third-line therapy. Increased adverse event rates were observed at the high dose of linifanib.

Tumor cells and tumor-associated macrophages: secreted proteins as potential targets for therapy

Inflammatory pathways, meant to defend the organism against infection and injury, as a byproduct, can promote an environment which favors tumor growth and metastasis. Tumor-associated macrophages (TAMs), which constitute a significant part of the tumor-infiltrating immune cells, have been linked to the growth, angiogenesis, and metastasis of a variety of cancers, most likely through polarization of TAMs to the M2 (alternative) phenotype. The interaction between tumor cells and macrophages provides opportunities for therapy. This paper will discuss secreted proteins as targets for intervention.

Treatment of tenosynovial giant cell tumor and pigmented villonodular synovitis

PURPOSE OF REVIEW

To review recent developments in the molecular pathogenesis of tenosynovial giant cell tumor (TGCT) or pigmented villonodular synovitis (PVNS) and its therapeutic implications.

RECENT FINDINGS

TGCT or PVNS is a benign clonal neoplastic proliferation arising from the synovium characterized by a minor population of intratumoral cells that harbor a recurrent translocation. These cells overexpress CSF1, resulting in recruitment of CSF1R-bearing macrophages that are polyclonal and make up the bulk of the tumor. Inhibition of CSF1R using small molecule inhibitors such as imatinib, nilotinib or sunitinib can result in clinical, radiological and functional improvement in the affected joint.

SUMMARY

Currently, surgery remains the treatment of choice for patients with TGCT/PVNS. Localized TGCT/PVNS is managed by marginal excision. Recurrences occur in 8-20% of patients and are easily managed by re-excision. Diffuse TGCT/PVNS tends to recur more often (33-50%) and has a much more aggressive clinical course. Patients are often symptomatic and require multiple surgical procedures during their lifetime. For patients with unresectable disease or multiple recurrences, systemic therapy using CSF1R inhibitors may help delay or avoid surgical procedures and improve functional outcomes.

ABT-869, a multitargeted receptor tyrosine kinase inhibitor, reduces tumor microvascularity and improves vascular wall integrity in preclinical tumor models

N-[4-(3-amino-1H-indazol-4-yl)phenyl]-N1-(2-fluoro-5-methyl phenyl)-urea (ABT-869) is a novel multitargeted receptor tyrosine kinase inhibitor that demonstrates single-agent activity in preclinical studies and has undergone phase I and II clinical trials. We characterized the mechanism of action of ABT-869 by examining vascular changes after treatment (25 mg/kg per day) in HT1080 fibrosarcoma and SW620 colon carcinoma cells, using immunohistochemistry, dynamic contrast enhanced-magnetic resonance imaging (DCE-MRI), and hypoxic protein detection. We observed the inhibition of vascular endothelial growth factor receptor 2 and platelet-derived growth factor receptor β phosphorylation in both tumors and changes in tumor vasculature. Reductions in microvessel density and diameter were observed. Vascular-wall integrity was assessed by colocalization of pericytes and basement membrane. Although both microvessel density and total number of pericytes decreased with treatment, the percentage of pericyte coverage on remaining vessels significantly increased. These data suggest the selective ablation of microvessels lacking pericyte coverage. Functional vascular measures DCE-MRI and hypoxia formation were also tested. After 2 days of treatment on the HT1080 model, vascular permeability, K(trans), was reduced by >60% and hypoxic tumor fraction was significantly decreased, which was also seen in the SW620 tumors after 4 days of treatment. Taken together, decreases in vascular permeability and changes in vascular integrity observed in these studies define the mode of action of ABT-869 and may aid in optimizing the timing of therapeutic window for combination therapies.

c-FMS inhibitors: a patent review

INTRODUCTION

Macrophages are key drivers of both the innate and adaptive immune systems. The cellular receptor for CSF-1 and IL-34, c-FMS, is a key component of the mechanism(s) by which macrophages are regulated. Several drug discovery programs aimed at uncovering inhibitors of the tyrosine kinase activity of this receptor are now entering clinical phase, and the prospect of readjusting the behavior of macrophages in a number of pathological situations, such as inflammation and cancer, is now on us.

AREAS COVERED

In this review, we evaluate the available patent literature on the topic of small molecule inhibitors of c-FMS. By way of background, we review the biology of c-FMS and make an analysis of the therapeutic opportunities that a small molecule c-FMS inhibitor might present. In order to place the pharmacology in perspective, we examine the literature concerning the role of the CSF-1-IL-34-c-FMS axis in macrophage function as well as cell types related to macrophages, such as the osteoclast, the dendritic cell and microglia, and provide a background to the understanding of the therapeutic opportunities for c-FMS inhibitors as well as potential obstacles that could limit their use.

EXPERT OPINION

The c-FMS receptor is a hot target for the development of novel regulators of macrophage behavior. Some nice candidates have been developed by a number of groups, and their recent entry into clinical phase testing means that we are now on the cusp of a fuller understanding of the role of these important regulators of the innate and adaptive immune systems in the development of cancer and inflammatory diseases.

ENMD-2076 is an orally active kinase inhibitor with antiangiogenic and antiproliferative mechanisms of action

ENMD-2076 is a novel orally active, small molecule kinase inhibitor with a mechanism of action involving several pathways key to tumor growth and survival: angiogenesis, proliferation, and the cell cycle. ENMD-2076 has selective activity against the mitotic kinase Aurora A, as well as kinases involved in angiogenesis (VEGFRs, FGFRs). ENMD-2076 inhibited the growth in vitro of a wide range of human solid tumor and hematopoietic cancer cell lines with IC(50) values ranging from 0.025 to 0.7 μmol/L. ENMD-2076 was also shown to induce regression or complete inhibition of tumor growth in vivo at well-tolerated doses in tumor xenograft models derived from breast, colon, melanoma, leukemia, and multiple myeloma cell lines. Pharmacodynamic experiments in vivo showed that in addition to inhibiting Aurora A, single doses of ENMD-2076 had sustained inhibitory effects on the activation of Flt3 as well as the angiogenic tyrosine kinases, VEGFR2/KDR and FGFR1 and 2. ENMD-2076 was shown to prevent the formation of new blood vessels and regress formed vessels in vivo at doses equivalent to those that gave substantial activity in tumor xenograft models. These results indicate that ENMD-2076 is a well-tolerated, orally active multitarget kinase inhibitor with a unique antiangiogenic/antiproliferative profile and provides strong preclinical support for use as a therapeutic for human cancers. Several phase 1 studies involving ENMD-2076 have been recently completed, and the compound is currently being evaluated in a phase 2 clinical trial in patients with platinum-resistant ovarian cancer.

Molecular pathways involved in synovial cell inflammation and tumoral proliferation in diffuse pigmented villonodular synovitis

Diffuse-type tenosynovial giant cell tumors, also known as pigmented villonodular synovitis, are unique mesenchymal lesions that arise from the synovial tissue of the joints. They are predominantly intraarticular, aggressive, infiltrative processes, characterized by both inflammatory or neoplastic properties and local destructive progression. The pattern of synovial gene and protein expressions in pigmented villonodular synovitis, similar to those in activated macrophages in rheumatoid arthritis, and the phenotype of multinucleated giant cells, characteristic of osteoclasts, suggest that there is a common autocrine mechanism in osteoclast differentiation in both diseases and indicate the potential utility of tumor necrosis factor (TNF)-alpha blockade. High synovial colony stimulating factor 1 (CSF1) messenger RNA (m RNA) expression in pigmented villonodular synovitis, unrelated to a chromosomal translocation involving CSF1 locus, may indicate that there is a synergic paracrine loop mediated by TNF-alpha and CSF1, as shown in both inflammatory and neoplastic conditions. The effects of a new therapeutic approach consisting in intraarticular TNF-alpha blockade were studied in four pigmented villonodular synovitis knees. Knee injections produced a rapid reduction in clinical and sonographic indexes and immunohistological alterations, confirmed by arthroscopic synovectomy. A delayed relapse in one of the four knees and unaltered synovial CSF1 expression were other important findings. In the light of these observations, CSF1/CSF1R interaction probably represents a more sensible therapeutic target than TNF-alpha blockade in the diffuse form of pigmented villonodular synovitis.

In-silico approaches to multi-target drug discovery : computer aided multi-target drug design, multi-target virtual screening

Multi-target drugs against selective multiple targets improve therapeutic efficacy, safety and resistance profiles by collective regulations of a primary therapeutic target together with compensatory elements and resistance activities. Efforts have been made to employ in-silico methods for facilitating the search and design of selective multi-target agents. These methods have shown promising potential in facilitating drug discovery directed at selective multiple targets.

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.

ABT-869, a promising multi-targeted tyrosine kinase inhibitor: from bench to bedside

Tyrosine Kinase Inhibitors (TKI) have significantly changed the landscape of current cancer therapy. Understanding of mechanisms of aberrant TK signaling and strategies to inhibit TKs in cancer, further promote the development of novel agents.ABT-869, a novel ATP-competitive receptor tyrosine kinase inhibitor is a potent inhibitor of members of the vascular endothelial growth factor (VEGF) and platelet derived growth factor (PDGF) receptor families. ABT-869 showed potent antiproliferative and apoptotic properties in vitro and in animal cancer xenograft models using tumor cell lines that were "addicted" to signaling of kinases targeted by ABT-869. When given together with chemotherapy or mTOR inhibitors, ABT-869 showed at least additive therapeutic effects. The phase I trial for ABT-869 was recently completed and it demonstrated respectable efficacy in solid tumors including lung and hepatocellular carcinoma with manageable side effects. Tumor cavitation and reduction of contrast enhancement after ABT-869 treatment supported the antiangiogenic activity. The correlative laboratory studies conducted with the trial also highlight potential biomarkers for future patient selection and treatment outcome.Parallel to the clinical development, in vitro studies on ABT-869 resistance phenotype identified novel resistance mechanism that may be applicable to other TKIs. The future therapeutic roles of ABT-869 are currently been tested in phase II trials.

Discovery of 2-(alpha-methylbenzylamino) pyrazines as potent Type II inhibitors of FMS

A series of 2-(alpha-methylbenzylamino) pyrazines have shown to be potent inhibitors of the FMS tyrosine receptor kinase. Details of SAR studies, modeling and synthesis of compounds within this series are reported.

ABT-869, a multi-targeted tyrosine kinase inhibitor, in combination with rapamycin is effective for subcutaneous hepatocellular carcinoma xenograft

BACKGROUND/AIMS

Receptor tyrosine kinase inhibitors (RTKIs) and mTOR inhibitors are potential novel anticancer therapies for HCC. We hypothesized that combination targeted on distinctive signal pathways would provide synergistic therapeutics.

METHODS

ABT-869, a novel RTKI, and rapamycin were investigated in HCC pre-clinical models.

RESULTS

Rapamycin, but not ABT-869, inhibited in vitro growth of Huh7 and SK-HEP-1 HCC cells in a dose dependant manner. However, in subcutaneous Huh7 and SK-HEP-1 xenograft models, either ABT-869 or rapamycin can significantly reduce tumor burden. Combination treatment reduced the tumors to the lowest volume (95+/-20mm(3)), and was significantly better than single agent treatment (p<0.05). Immunohistochemical staining of tumor shows that ABT-869 potently inhibits VEGF in HCC in vivo. In addition, the MAPK signaling pathway has been inhibited by significant inhibition of phosphorylation of p44/42 MAP kinase by ABT-869 in vivo. Rapamycin inhibits phosphorylation of p70 S6 kinase and 4E-BP-1, downstream targets of mTOR, and decreases VEGF. Combination treatment showed synergistic effect on expression levels of p27 in vivo. Dramatic inhibition of neo-angiogenesis by ABT-869 was also demonstrated.

CONCLUSIONS

HCC could potentially be treated with the combination treatment of ABT-869 and rapamycin. Clinical trials on combination therapy are warranted.

Tyrosine kinase inhibitors reverse type 1 diabetes in nonobese diabetic mice

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.

In vivo activity of ABT-869, a multi-target kinase inhibitor, against acute myeloid leukemia with wild-type FLT3 receptor

Neoangiogenesis plays an important role in leukemogenesis. We investigated the in vivo anti-leukemic effect of ABT-869 against AML with wild-type FLT3 using RFP transfected HL60 cells with in vivo imaging technology on both the subcutaneous and systemic leukemia xenograft models. ABT-869 showed a five-fold inhibition of tumor growth in comparison with vehicle control. IHC analysis revealed that ABT-869 decreased p-VEGFR1, Ki-67 labeling index, VEGF and remarkably increased apoptotic cells in the xenograft models. ABT-869 also reduced the leukemia burden and prolonged survival. Our study supports the rationale for clinically testing an anti-angiogenesis agent in AML with wild-type FLT3.

Synergistic antileukemic effects between ABT-869 and chemotherapy involve downregulation of cell cycle-regulated genes and c-Mos-mediated MAPK pathway

Internal tandem duplications (ITDs) of fms-like tyrosine kinase 3 (FLT3) receptor play an important role in the pathogenesis of acute myeloid leukemia (AML) and represent an attractive therapeutic target. ABT-869 has demonstrated potent effects in AML cells with FLT3-ITDs. Here, we provide further evidence that ABT-869 treatment significantly downregulates cyclins D and E but increases the expression of p21 and p27. ABT-869 induces apoptosis through downregulation of Bcl-xL and upregulation of BAK, BID and BAD. We also evaluate the combinations of ABT-869 and chemotherapy. ABT-869 demonstrates significant sequence-dependent synergism with cytarabine and doxorubicin in cell lines and primary leukemia samples. The optimal combination was validated in MV4-11 xenografts. Low-density array analysis revealed the synergistic interaction involved in downregulation of cell cycle and mitogen-activated protein kinase pathway genes. CCND1 and c-Mos were the most significantly inhibited targets on both transcriptional and translational levels. Treatment with short hairpin RNAs targeting either CCND1 or c-Mos further sensitized MV4-11 cells to ABT-869. These findings suggest that specific pathway genes were further targeted by adding chemotherapy and support the rationale of combination therapy. Thus, a clinical trial using sequence-dependent combination therapy with ABT-869 in AML is warranted.

ASCO 2006 highlights: targeted therapy for renal cell carcinoma

In the past few years, advances in the understanding of the pathogenesis of renal cell carcinoma (RCC) have resulted in the identification of new therapeutic targets, and ultimately, the development of new targeted agents for the treatment of the disease. This paper reviews latest data in RCC for the recently approved agents sunitinib and sorafenib, as well as other molecularly targeted drugs, presented at the annual meeting of the American Society for Clinical Oncology, held in Atlanta, Georgia, in June 2006. Clinical findings to date show that these new agents are challenging the role of cytokines in this setting, and for some (e.g. sunitinib) a substantially improved efficacy profile (progression-free survival and response) over conventional cytokine therapy has been reported. While challenges remain with regard to optimal use of these agents, the outlook for patients with advanced RCC has improved considerably and there is great hope for continuing progress.

A review of the latest clinical compounds to inhibit VEGF in pathological angiogenesis

Angiogenesis plays an important role in the formation of new blood vessels and is crucial for tumour development and progression. Imbalance between pro- and antiangiogenesis factors regulates the biological process of angiogenesis. The best characterised of the proangiogenic factors and the most potent is vascular endothelial growth factor (VEGF). The binding of VEGF to one of its transmembrane tyrosine kinase receptors, which are predominantly found on endothelial cells, results in receptor dimerisation, activation and autophosphorylation of the tyrosine kinase domain. This triggers a cascade of complex downstream signalling pathways. Several strategies targeting the VEGF signalling pathway have been developed. These include neutralising antibodies to VEGF (bevacizumab) or VEGF receptors (VEGFRs) (DC101), soluble VEGFR/VEGFR hybrids (VEGF-Trap), and tyrosine kinase inhibitors of VEGFRs (BAY43-9006, SU11248, ZD6474, AZD2171, PTK/ZK and others). Several of these agents are now being investigated in clinical trials.

VEGF/VEGFR signalling as a target for inhibiting angiogenesis

VEGFs and a respective family of tyrosine kinases receptors (VEGFRs) are key proteins modulating angiogenesis, the formation of new vasculature from an existing vascular network. There has been considerable evidence in vivo, including clinical observations, that abnormal angiogenesis is implicated in a number of disease conditions, which include rheumatoid arthritis, inflammation, cancer, psoriasis, degenerative eye conditions and others. Antiangiogenic therapies based on inhibition of VEGF/VEGFR signalling were reported to be powerful clinical strategies in oncology and ophthalmology. Current efforts have yielded promising clinical data for several antiangiogenic therapeutics. In this review, the authors elucidate key aspects of VEGFR signalling, as well as clinically relevant strategies for the inhibition of VEGF-induced angiogenesis, with an emphasis on small-molecule VEGFR inhibitors.

A cellular assay for measuring the modulation of glucose production in H4IIE cells

Type II diabetes and its associated complications are a major health concern of the developed world. One of the hallmarks of diabetes is insulin resistance, where secreted insulin no longer has any effect on its target tissues, namely, liver, muscle, and fat. An important therapeutic strategy is to modulate blood glucose levels using pharmacological agents. Glycogen synthase kinase-3 (GSK3) is a serine-threonine protein kinase that plays important roles in regulating glucose metabolism. It is a key negative regulator of insulin action and is an important contributing factor to insulin resistance in liver, muscle, and adipose tissue. We describe the development of a cell-based assay designed to measure glucose production in rat hepatoma cell line H4IIE liver cells in response to treatment with small molecule inhibitors, including GSK3 inhibitors. The assay is set up in a 96-well format, and glucose production is assessed using a convenient fluorescence-based readout. This disease-relevant cellular assay is a valuable tool for the progression of small molecules that modulate glucose production.

Preclinical activity of ABT-869, a multitargeted receptor tyrosine kinase inhibitor

ABT-869 is a structurally novel, receptor tyrosine kinase (RTK) inhibitor that is a potent inhibitor of members of the vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) receptor families (e.g., KDR IC50 = 4 nmol/L) but has much less activity (IC50s > 1 micromol/L) against unrelated RTKs, soluble tyrosine kinases, or serine/threonine kinases. The inhibition profile of ABT-869 is evident in cellular assays of RTK phosphorylation (IC50 = 2, 4, and 7 nmol/L for PDGFR-beta, KDR, and CSF-1R, respectively) and VEGF-stimulated proliferation (IC50 = 0.2 nmol/L for human endothelial cells). ABT-869 is not a general antiproliferative agent because, in most cancer cells, >1,000-fold higher concentrations of ABT-869 are required for inhibition of proliferation. However, ABT-869 exhibits potent antiproliferative and apoptotic effects on cancer cells whose proliferation is dependent on mutant kinases, such as FLT3. In vivo ABT-869 is effective orally in the mechanism-based murine models of VEGF-induced uterine edema (ED50 = 0.5 mg/kg) and corneal angiogenesis (>50% inhibition, 15 mg/kg). In tumor growth studies, ABT-869 exhibits efficacy in human fibrosarcoma and breast, colon, and small cell lung carcinoma xenograft models (ED50 = 1.5-5 mg/kg, twice daily) and is also effective (>50% inhibition) in orthotopic breast and glioma models. Reduction in tumor size and tumor regression was observed in epidermoid carcinoma and leukemia xenograft models, respectively. In combination, ABT-869 produced at least additive effects when given with cytotoxic therapies. Based on pharmacokinetic analysis from tumor growth studies, efficacy correlated more strongly with time over a threshold value (cellular KDR IC50 corrected for plasma protein binding = 0.08 microg/mL, >or=7 hours) than with plasma area under the curve or Cmax. These results support clinical assessment of ABT-869 as a therapeutic agent for cancer.