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The objective of this study was to determine the utility of (99m)Tc-3P-Arg-Gly-Asp (RGD2) single photon emission computed tomography (SPECT)/computed tomography (CT) for noninvasive monitoring of integrin αvβ3-expression response to antiangiogenic treatment with linifanib. Linifanib or vehicle therapy was carried out in female athymic nu/nu mice bearing U87MG glioma (high αvβ3 expression) or PC-3 prostate (low αvβ3 expression) tumors at 12.5 mg/kg twice daily. The average tumor volume was 180 ± 90 mm(3) the day prior to baseline SPECT/CT. Longitudinal (99m)Tc-3P-RGD2 SPECT/CT imaging was performed at baseline (-1 day) and days 1, 4, 11, and 18. Tumors were harvested at all imaging time points for histopathological analysis with H&E and immunohistochemistry. A significant difference in tumor volumes between vehicle- and linifanib-treated groups was observed after 4 days of linifanib therapy in the U87MG model. The percent injected dose (%ID) tumor uptake of (99m)Tc-3P-RGD2 peaked in the vehicle-treated group at day 11, while the %ID/cm(3) tumor uptake decreased slowly over the whole study period. During the first 2 days of linifanib treatment, a rapid decrease in both %ID/cm(3) tumor uptake and tumor/muscle ratios of (99m)Tc-3P-RGD2 was observed, followed by a slow decrease until day 18. No decrease in tumor uptake of (99m)Tc-3P-RGD2 or tumor volume was observed for either treatment group in the PC-3 model. Changes in tumor vasculature were confirmed by histopathological H&E analysis and immunohistochemistry. Longitudinal imaging using (99m)Tc-3P-RGD2 SPECT/CT may be a useful tool for monitoring the downstream biologic effects of linifanib therapy.

Linifanib, a potent oral inhibitor of fms-like tyrosine kinase 3 (FLT3) and vascular endothelial growth factor receptor tyrosine kinases, has demonstrated promising preclinical single-agent and synergistic anti-leukemic activity in combination with cytarabine. In this phase 1, multicenter, open-label, dose-escalation study, 45 adults with relapsed/refractory acute myeloid leukemia (AML) received linifanib alone in arm A (n = 29) and linifanib plus intermediate-dose cytarabine in arm B (n = 16). Median treatment duration was 21 days (range 5-110). Linifanib was well tolerated overall. The most common grade 3/4 events were fatigue (arm A) and febrile neutropenia (arm B). The recommended phase 2 dose was 15 mg (alone), and 10 mg (with cytarabine). Evidence of on-target kinase inhibition in patients with FLT3-mutant and wild-type AML was seen. Decreased phosphorylated FLT3 was seen in 3/3 patients with FLT3-internal tandem duplication (ITD) with peripheral blast reductions and in 8/24 (33%) patients with wild-type, D835 or unknown FLT3 mutation. Eight/29 (28%) patients had decreased phosphorylated extracellular signal-regulated kinase (ERK).

Linifanib (ABT-869) is a multitargeted receptor tyrosine kinase inhibitor. This work aims to evaluate F-fluorodeoxyglucose-positron emission tomography (FDG-PET) as a pharmacodynamic (PD) biomarker for linifanib treatment utilizing the Calu-6 model of human non-small cell lung (NSCLC) cancer in SCID-beige mice. Animals received either vehicle or 12.5 mg/kg linifanib orally twice a day for the duration of the study. Imaging was performed at -1, 1, 3, and 7 days after beginning treatment (n = 12-14 per group). Linifanib inhibited tumor growth and suppressed tumor metabolic activity. Changes in tumor FDG uptake were observed as early as 1 day after beginning linifanib treatment and were sustained for the duration of the study. This study confirms that linifanib is efficacious in this xenograft model of human NSCLC and confirms FDG-PET is a potential PD biomarker strategy for linifanib therapy.

Tyrosine kinase inhibitors represent a class of targeted therapy that has proven to be successful for cancer treatment. Linifanib is a novel, orally active multi-targeted receptor tyrosine kinase (RTK) inhibitor that exhibits potent antitumor and antiangiogenic activities against a broad spectrum of experimental tumors and malignancies in patients. The compound is currently being evaluated in phase 2 and 3 clinical trials. To investigate the effectiveness of linifinib against gliomas and the mechanism of drug action, we characterized treatment-induced antitumor and antiangiogenic responses to linifanib in an orthotopic rat glioma model. The effect of linifanib treatment on tumor growth was determined by tumor volume assessment using anatomical magnetic resonance imaging (MRI). Changes in tumor microvessel function were evaluated with dynamic contrast-enhanced MRI (DCE-MRI). Immunohistochemistry (IHC) was applied to excised tumor samples to examine underlying changes in vascular structures and target receptor expression. Linifanib (10 mg/kg) given twice daily inhibited tumor growth following treatment for 7 days with tumor volumes being 149 ± 30 and 66 ± 7 mm(3) for vehicle-and linifanib-treated groups, respectively. A significant reduction of 37 ± 13% in tumor perfusion and microvessel permeability (measured by K (trans)) was observed as early as 2 h after administration compared with vehicle treatment. Continuous linifanib administration further reduced K (trans) at later time points until the end of the study (7 days post-treatment). At day 7, K (trans) was reduced by 75 ± 32% for linifanib treatment compared with vehicle treatment. Significant reduction in total blood vessel density and improved vessel wall integrity were observed, and staining for target receptor expression confirmed inhibition of phospho VEGFR-2 and PDGFR-β by linifanib treatment. These results demonstrate significant antitumor and antiangiogenic activity against gliomas by linifanib, a property that may result from the inhibition of VEGFR-2 and PDGFR-β-mediated vascular changes. DCE-MRI measured K (trans) changes at early treatment stages may be a useful pharmacodynamic marker for linifanib activity in clinical trials, and basal K (trans) may provide predictive value for tumor progression.

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.

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.

ABT-869 [N-(4-(3-amino-1H-indazol-4-yl)phenyl)-N'-(2-fluoro-5-methylphenyl)urea] is a novel multitargeted inhibitor of the vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) receptor tyrosine kinase family members. ABT-869 demonstrates tumor growth inhibition in multiple preclinical animal models and in early clinical trials. VEGF receptor inhibition is also associated with reversible hypertension that may limit its benefit clinically. To evaluate optimal therapeutic approaches to prevent hypertension with VEGF receptor inhibition, we characterized the dose-dependent effects of seven antihypertensive agents from three mechanistic classes [angiotensin-converting enzyme inhibitors (ACEis), angiotensin receptor blockers (ARBs), calcium channel blockers (CCBs)] on hypertension induced by ABT-869 in conscious telemetry rats. We report that ABT-869-induced hypertension can be prevented and reversed with subtherapeutic or therapeutic doses of antihypertensive drugs with a general rank order of ACEi > ARB > CCB. In SCID mice, the ACE inhibitor, enalapril (C(20)H(28)N(2)O(5) x C(4)H(4)O(4)) at 30 mg/kg, prevented hypertension, with no attenuation of the antitumor efficacy of ABT-869. These studies demonstrate that the adverse cardiovascular effects of the VEGF/PDGF receptor tyrosine kinase inhibitor, ABT-869, are readily controlled by conventional antihypertensive therapy without affecting antitumor efficacy.

ABT-869 is a novel multitargeted inhibitor of vascular endothelial growth factor and platelet-derived growth factor receptor tyrosine kinases (RTKs) with potent antiangiogenic properties that slow tumor progression. Vascular endothelial growth factor receptor blockade has been shown to produce hypertension. Atrasentan is a potent and selective endothelin (ETA) receptor antagonist that lowers blood pressure and affects tumor growth. To assess the utility of ETA receptor blockade in controlling hypertension with RTK inhibition, we evaluated the ability of atrasentan to block hypertension with ABT-869 in conscious, telemetry-instrumented rats. Changes in mean arterial pressure (MAP) and heart rate (HR) were evaluated using mean values and the area under the curve (AUC). Atrasentan (0.5, 1.5, and 5.0 mg kg(-1) d(-1) for 5 days) elicited dose-dependent decreases in MAP-AUC (-16.7 +/- 1.3, -20.94 +/- 3.68, and -30.12 +/- 3.57 mm Hg x day, respectively) compared with vehicle. ABT-869 (1, 3, 10, 30 mg kg(-1) d(-1) for 5 days) increased MAP compared with vehicle (MAP-AUC values of -5.52 +/- 3.75, 12.7 +/- 8.4, 37.5 +/- 4.4, and 63.8 +/- 3.3 mm Hg x day, respectively). Pretreatment with atrasentan (5 mg/kg for 5 days) prevented and abolished the hypertensive effects of ABT-869. Thus, ETA receptor blockade effectively alleviated hypertension with RTK inhibition and may serve a dual therapeutic role by preventing hypertension and slowing tumor progression.

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.

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.

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.

In 15% to 30% of patients with acute myeloid leukemia (AML), aberrant proliferation is a consequence of a juxtamembrane mutation in the FLT3 gene (FMS-like tyrosine kinase 3-internal tandem duplication [FLT3-ITD]), causing constitutive kinase activity. ABT-869 (a multitargeted receptor tyrosine kinase inhibitor) inhibited the phosphorylation of FLT3, STAT5, and ERK, as well as Pim-1 expression in MV-4-11 and MOLM-13 cells (IC(50) approximately 1-10 nM) harboring the FLT3-ITD. ABT-869 inhibited the proliferation of these cells (IC(50) = 4 and 6 nM, respectively) through the induction of apoptosis (increased sub-G(0)/G(1) phase, caspase activation, and PARP cleavage), whereas cells harboring wild-type (wt)-FLT3 were less sensitive. In normal human blood spiked with AML cells, ABT-869 inhibited phosphorylation of FLT3 (IC(50) approximately 100 nM), STAT5, and ERK, and decreased Pim-1 expression. In methylcellulose-based colony-forming assays, ABT-869 had no significant effect up to 1000 nM on normal hematopoietic progenitor cells, whereas in AML patient samples harboring both FLT3-ITD and wt-FLT3, ABT-869 inhibited colony formation (IC(50) = 100 and 1000 nM, respectively). ABT-869 dose-dependently inhibited MV-4-11 and MOLM-13 flank tumor growth, prevented tumor formation, regressed established MV-4-11 xenografts, and increased survival by 20 weeks in an MV-4-11 engraftment model. In tumors, ABT-869 inhibited FLT3 phosphorylation, induced apoptosis (transferase-mediated dUTP nick-end labeling [TUNEL]) and decreased proliferation (Ki67). ABT-869 is under clinical development for AML.

In our continued efforts to search for potent and novel receptor tyrosine kinase (RTK) inhibitors as potential anticancer agents, we discovered, through a structure-based design, that 3-aminoindazole could serve as an efficient hinge-binding template for kinase inhibitors. By incorporating an N,N'-diaryl urea moiety at the C4-position of 3-aminodazole, a series of RTK inhibitors were generated, which potently inhibited the tyrosine kinase activity of the vascular endothelial growth factor receptor and the platelet-derived growth factor receptor families. A number of compounds with potent oral activity were identified by utilizing an estradiol-induced mouse uterine edema model and an HT1080 human fibrosarcoma xenograft tumor model. In particular, compound 17p (ABT-869) was found to possess favorable pharmacokinetic profiles across different species and display significant tumor growth inhibition in multiple preclinical animal models.

Purpose: Inhibiting hypoxia-inducible factor-1 (HIF-1) represents a unique mechanism for cancer therapy. It is conceived that HIF-1 inhibitors may synergize with many classes of cancer therapeutic agents, such as angiogenesis inhibitors and cytotoxic drugs, to achieve a more robust tumor response. However, these hypotheses have not been rigorously tested in tumor models in vivo. The present study was carried out to evaluate the antitumor efficacy of combining HIF-1 inhibition with angiogenesis inhibitors or cytotoxic agents., Experimental Design: Using a D54MG-derived tumor model that allows knockdown of HIF-1alpha on doxycycline treatment, we examined the tumor responses to chemotherapeutic agents, including the angiogenesis inhibitor ABT-869 and cytotoxic agents 1,3-bis(2-chloroethyl)-1-nitrosourea and temozolomide, in the presence or absence of an intact HIF-1 pathway., Results: Surprisingly, inhibiting HIF-1 in tumors treated with the angiogenesis inhibitor ABT-869 did not produce much added benefit compared with ABT-869 treatment alone, suggesting that the combination of an angiogenesis inhibitor with a HIF-1 inhibitor may not be a robust therapeutic regimen. In contrast, the cytotoxic drug temozolomide, when used in combination with HIF-1alpha knockdown, exhibited a superadditive and likely synergistic therapeutic effect compared with the monotherapy of either treatment alone in the D54MG glioma model., Conclusions: Our results show that the DNA alkylating agent temozolomide exhibits robust antitumor efficacy when used in combination with HIF-1 inhibition in D54MG-derived tumors, suggesting that the combination of temozolomide with HIF-1 inhibitors might be an effective regimen for cancer therapy. In addition, our results also show that the RNA interference-based inducible knockdown model can be a valuable platform for further evaluation of the combination treatment of other cancer therapeutics with HIF-1 inhibition.

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.