Search

Purpose: Axitinib (AG-013736) is a potent and selective inhibitor of vascular endothelial growth factor (VEGF) receptor tyrosine kinases 1 to 3 that is in clinical development for the treatment of solid tumors. We provide a comprehensive description of its in vitro characteristics and activities, in vivo antiangiogenesis, and antitumor efficacy and translational pharmacology data.Experimental Design: The potency, kinase selectivity, pharmacologic activity, and antitumor efficacy of axitinib were assessed in various nonclinical models.Results: Axitinib inhibits cellular autophosphorylation of VEGF receptors (VEGFR) with picomolar IC50 values. Counterscreening across multiple kinase and protein panels shows it is selective for VEGFRs. Axitinib blocks VEGF-mediated endothelial cell survival, tube formation, and downstream signaling through endothelial nitric oxide synthase, Akt and extracellular signal-regulated kinase. Following twice daily oral administration, axitinib produces consistent and dose-dependent antitumor efficacy that is associated with blocking VEGFR-2 phosphorylation, vascular permeability, angiogenesis, and concomitant induction of tumor cell apoptosis. Axitinib in combination with chemotherapeutic or targeted agents enhances antitumor efficacy in many tumor models compared with single agent alone. Dose scheduling studies in a human pancreatic tumor xenograft model show that simultaneous administration of axitinib and gemcitabine without prolonged dose interruption or truncation of axitinib produces the greatest antitumor efficacy. The efficacious drug concentrations predicted in nonclinical studies are consistent with the range achieved in the clinic. Although axitinib inhibits platelet-derived growth factor receptors and KIT with nanomolar in vitro potencies, based on pharmacokinetic/pharmacodynamic analysis, axitinib acts primarily as a VEGFR tyrosine kinase inhibitor at the current clinical exposure.Conclusions: The selectivity, potency for VEGFRs, and robust nonclinical activity may afford broad opportunities for axitinib to improve cancer therapy.

Supplementary Figures S1-S7 from Nonclinical Antiangiogenesis and Antitumor Activities of Axitinib (AG-013736), an Oral, Potent, and Selective Inhibitor of Vascular Endothelial Growth Factor Receptor Tyrosine Kinases 1, 2, 3

Supplementary Methods, Figures 1-6, Tables A-C from Targeting Activin Receptor-Like Kinase 1 Inhibits Angiogenesis and Tumorigenesis through a Mechanism of Action Complementary to Anti-VEGF Therapies

PURPOSE: PF-00337210 is an oral, highly selective vascular endothelial growth factor receptor (VEGFR) inhibitor. We evaluated a composite of biomarkers in real time to identify the recommended phase 2 dose (RP2D) and preliminary anticancer activity of PF-00337210. PATIENTS AND METHODS: Patients (Pts) with advanced cancers were treated once (QD) or twice daily (BID) with escalating doses. Acute effects on tumor perfusion and vascularity were assessed using DCE-MRI, weekly BP readings, soluble VEGFR-2, and hemoglobin levels. RESULTS: Forty-six pts were treated with 0.67–9 mg QD and 4–6 mg BID of PF-00337210. Nineteen pts (41 %) previously received VEGF/VEGFR inhibitors. Two pts had dose-limiting toxicity (DLT) at 9 mg QD (troponin I increase and hypertension). The MTD at QD dose was 8 mg. Common drug-related adverse events were hypertension, fatigue, proteinuria, and nausea. Hypertension incidence and intensity corresponded with dose, but was well controlled with medication. Two confirmed partial responses and minor regressions (>10 to

Purpose Rucaparib is a potent Poly (ADP-ribose) Polymerase (PARP) inhibitor currently under clinical development. The objectives of this analysis were to establish population PK and PK/PD models for rucaparib, and to evaluate the predictability of PARP activity in PBL for PARP activity in tumor tissues. Experimental Design Rucaparib concentrations and PARP activity in human PBLs and tumor issues were obtained from 32 patients with solid tumors in a Phase 1 First-in-Patient study. Simulations were conducted to evaluate different dosing regimens. Results A 3-compartment PK model best described the PK of rucaparib. An Emax model best described the exposure and PARP inhibition relationship. The maximum PARP inhibition (Imax) achieved in PBLs and in tumors were 90.9% and 90.0% of the baseline PARP activity, and the IC50 values were 1.05 ng/mL and 1.10 ng/mL, respectively. PAR polymer baseline value was found to be a covariate of Emin. Conclusion Population PK and PK/PD models have been established to describe population PK of rucaparib and the relationship between rucaparib plasma concentration and PARP inhibition in both PBLs and tumor issues. Results from this trial indicated that PARP inhibition in PBLs can be used as a substitute for PARP inhibition in melanoma tumor tissues.

We report a comparison between tumor perfusion estimates acquired using contrast-enhanced MRI and motion-corrected contrast-enhanced ultrasound before and after treatment with AG-028262, a potent vascular endothelial growth factor receptor tyrosine kinase inhibitor. Antiangiogenic activity was determined by assessing weekly ultrasound and MRI images of rats with bilateral hind flank mammary adenocarcinomas before and after treatment with AG-028262. Images were acquired with a spoiled gradient, 1.5T magnetic resonance sequence and a destruction-replenishment ultrasound protocol. For ultrasound, a time to 80% contrast replenishment was calculated for each tumor voxel; for MR imaging, a measure of local flow rate was estimated from a linear fit of minimum to maximum intensities. AG-028262 significantly decreased tumor growth and increased the time required to replenish tumor voxels with an ultrasound contrast agent from 2.66 to 4.54 seconds and to fill with an MR contrast agent from 29.5 to 50.8 seconds. Measures of flow rate derived from MRI and ultrasound demonstrated a positive linear correlation of r2=0.86.

Purpose: Antigenic overlap among circulating endothelial cells (CEC) and progenitors (CEP), platelets, and other blood cells led to the need to develop a reliable standardized method for CEC and CEP quantification. These cells are emerging as promising preclinical/clinical tools to define optimal biological doses of antiangiogenic therapies and to help stratify patients in clinical trials. Experimental Design: We report the experimental validation of a novel flow cytometry method that precisely dissects CEC/CEP from platelets and other cell populations and provides information about CEC/CEP viability. Results: Sorted DNA/Syto16+CD45−CD31+CD146+ CECs, investigated by electron microscopy, were found to be bona fide endothelial cells by the presence of Weibel-Palade bodies. More than 75% of the circulating mRNAs of the endothelial-specific gene, VE-cadherin, found in the blood were present in the sorted population. CECs were 140 ± 171/mL in healthy subjects (n = 37) and 951 ± 1,876/mL in cancer patients (n = 78; P < 0.0001). The fraction of apoptotic/necrotic CECs was 77 ± 14% in healthy subjects and 43 ± 23% in cancer patients (P < 0.0001). CEPs were 181 ± 167/mL in healthy donors and 429 ± 507/mL in patients (P = 0.00019). Coefficients of variation were 4 ± 4% (intrareader), 17 ± 4% (interreader), and 17 ± 7% (variability over 0-72 h), respectively. Parallel samples were frozen by a standardized protocol. After thawing, coefficients of variation were 12 ± 8% (intrareader), 16 ± 10% (interreader), and 26 ± 16% (variability over 0-14 days of frozen storage), respectively. Conclusions: This procedure enumerates a truly endothelial cell population with limited intrareader and interreader variability. It appears possible to freeze samples for large-scale CEC enumeration during clinical trials. This approach could be enlarged to investigate other angiogenic cell populations as well.

Dynamic contrast-enhanced MRI (DCE-MRI) was used to noninvasively evaluate the effects of AG-03736, a novel inhibitor of vascular endothelial growth factor (VEGF) receptor tyrosine kinases, on tumor microvasculature in a breast cancer model. First, a dose response study was undertaken to determine the responsiveness of the BT474 human breast cancer xenograft to AG-013736. Then, DCE-MRI was used to study the effects of a 7-day treatment regimen on tumor growth and microvasculature. Two DCE-MRI protocols were evaluated: (1) a high molecular weight (MW) contrast agent (albumin-(GdDTPA)(30)) with pharmacokinetic analysis of the contrast uptake curve and (2) a low MW contrast agent (GdDTPA) with a clinically utilized empirical parametric analysis of the contrast uptake curve, the signal enhancement ratio (SER). AG-013736 significantly inhibited growth of breast tumors in vivo at all doses studied (10-100 mg/kg) and disrupted tumor microvasculature as assessed by DCE-MRI. Tumor endothelial transfer constant (K(ps)) measured with albumin-(GdDTPA)(30) decreased from 0.034+/-0.005 to 0.003+/-0.001 ml min(-1) 100 ml(-1) tissue (P

Inhibitors of VEGF signaling can block angiogenesis and reduce tumor vascularity, but little is known about the reversibility of these changes after treatment ends. In the present study, regrowth of blood vessels in spontaneous RIP-Tag2 tumors and implanted Lewis lung carcinomas in mice was assessed after inhibition of VEGF receptor signaling by AG-013736 or AG-028262 for 7 days. Both agents caused loss of 50%-60% of tumor vasculature. Empty sleeves of basement membrane were left behind. Pericytes also survived but had less alpha-SMA immunoreactivity. One day after drug withdrawal, endothelial sprouts grew into empty sleeves of basement membrane. Vessel patency and connection to the bloodstream followed close behind. By 7 days, tumors were fully revascularized, and the pericyte phenotype returned to baseline. Importantly, the regrown vasculature regressed as much during a second treatment as it did in the first. Inhibition of MMPs or targeting of type IV collagen cryptic sites by antibody HUIV26 did not eliminate the sleeves or slow revascularization. These results suggest that empty sleeves of basement membrane and accompanying pericytes provide a scaffold for rapid revascularization of tumors after removal of anti-VEGF therapy and highlight their importance as potential targets in cancer therapy.

Photodynamic therapy (PDT) clinical results are promising; however, tumor recurrences can occur and, therefore, methods for improving treatment efficacy are needed. PDT elicits direct tumor cell death and microvascular injury as well as expression of angiogenic, inflammatory, and prosurvival molecules. Preclinical studies combining antiangiogenic drugs or cyclooxygenase-2 inhibitors with PDT show improved treatment responsiveness (A. Ferrario et al., Cancer Res 2000;60:4066–9; A. Ferrario et al., Cancer Res 2002;62:3956–61). In the present study, we evaluated the role of Photofrin-mediated PDT in eliciting expression of matrix metalloproteinases (MMPs) and modulators of MMP activity. We also examined the efficacy of a synthetic MMP inhibitor, Prinomastat, to enhance tumoricidal activity after PDT, using a mouse mammary tumor model. Immunoblot analysis of extracts from PDT-treated tumors demonstrated strong expression of MMPs and extracellular MMP inducer along with a concomitant decrease in expression of tissue inhibitor of metalloproteinase-1. Gelatin zymography and enzyme activity assays performed on protein extracts from treated tumors confirmed the induction of both latent and enzymatically active forms of MMP-9. Immunohistochemical analysis indicated that infiltrating inflammatory cells and endothelial cells were primary sources of MMP-9 expression after PDT, whereas negligible expression was observed in tumor cells. Administration of Prinomastat significantly improved PDT-mediated tumor response (P = 0.02) without affecting normal skin photosensitization. Our results indicate that PDT induces MMPs and that the adjunctive use of an MMP inhibitor can improve PDT tumor responsiveness.

Advanced stages of neuroblastoma show increased expression of matrix metalloproteinases MMP-2 and MMP-9 (Y. Sugiura et al., Cancer Res., 58: 2209–2216, 1998) that have been implicated in many steps of tumor progression, suggesting that they play a contributory role. Using pharmacological and genetic approaches, we have examined the role of these MMPs in progression of SK-N-BE (2).10 human neuroblastoma tumors orthotopically xenotransplanted into immunodeficient mice. Mice treated with Prinomastat, a synthetic inhibitor of MMPs, showed an inhibition of tumor cell proliferation in implanted tumors and a prolonged survival (50 versus 39 days in control group, P < 0.035). Treatment with Prinomastat did not affect formation of liver metastases (P = 0.52) but inhibited intravascular colonization by the tumor cells in the lung by 73.8% (P = 0.03) and angiogenesis in both primary tumors and experimental liver metastases. The primary tumors from Prinomastat-treated mice showed a 39.3% reduction in endothelial area detected by PECAM/CD31 staining in tumor sections (P < 0.001), primarily due to the presence of smaller vessels (P = 0.004). MMP-2 is expressed by neuroblastoma tumor cells and stromal cells, whereas MMP-9 is exclusively expressed by stromal cells, particularly vascular cells. To examine the contribution of MMP-9 to tumor angiogenesis, we generated RAG1/MMP-9 double-deficient mice. We observed a significant inhibition of angiogenesis in the immunodeficient RAG1/MMP-9 double-deficient mice orthotopically implanted with tumor cells (P = 0.043) or implanted s.c. with a mixture of tumor cells and Matrigel (P < 0.001). Using an FITC-labeled lectin, we demonstrated an inhibition in the architecture of the tumor vasculature in MMP-9-deficient mice, resulting in fewer and smaller blood vessels. These changes were associated with a 48% decrease in pericytes present along microvessels. Taken together, the data demonstrate that in neuroblastoma, stromally derived MMP-9 contributes to angiogenesis by promoting blood vessel morphogenesis and pericyte recruitment.

We studied the synthetic matrix metalloproteinase inhibitor (MMPI) prinomastat (AG3340) in a well-established NCI-H460 orthotopic lung cancer model that exhibits highly predictable regional and systemic metastatic patterns. Both primary and metastatic tumors express the matrix metalloproteinases (MMP-2), MT1-MMP (MMP-14) and tissue inhibitor of metalloproteinases (TIMP-2). The anti-tumor activity of prinomastat was investigated both as a single agent and in combination therapy with carboplatin. Treatment with both carboplatin (at two dose levels) and prinomastat commenced when the primary lung cancer was approximately 200-300 mg in size and without gross or microscopic evidence of metastases. As single agents, prinomastat significantly reduced the incidence of kidney metastasis, but had no effect on metastatic frequency to other organs. As single agents neither drug enhanced length of survival over control animals, although microvessel counts in prinomastat-treated tumors were lower than in tumors from control animals (P

Preclinical research has provided a strong rationale for employing PARP inhibitors (PARPi) as chemosensitisers in combination with cytotoxic agents, radiosensitisers in combination with radiation, as well as monotherapy to induce synthetic lethality in human malignancies. The primary aim of this chapter is to describe the rationale and preclinical pharmacology of potent PARPi (such as veliparib, rucaparib and olaparib) as chemosensitisers studied in cytotoxic combination regimens. Additional aims are to review: (1) emerging strategies for employing PARPi as monotherapy to induce synthetic lethality; and (2) potentially novel mechanisms by which PARPi may enhance antitumour therapy.

The release of potentially neurotoxic molecules by HIV-infected brain macrophages is accompanied by neuronal injury and death that results in the development of HIV-associated dementia (HAD). Among the potential neurotoxins implicated in the development of HAD is the HIV-1 transactivating protein, Tat. To investigate the mechanism by which Tat causes neurotoxicity, brain-derived Tat sequences from nondemented (Tat-ND) and demented (Tat-HAD) AIDS patients, which differed primarily in the augmenting region of Tat, were expressed in U937 monoblastoid cells and primary human macrophages. Cells expressing Tat-HAD protein exhibited elevated matrix metalloproteinase (MMP)-2 and -7 release and activation, but cells expressing Tat-ND did not exhibit enhanced MMP expression. Conditioned media from Tat-HAD-transfected cells caused significantly greater neuronal death (15.4 +/- 4.3%) than did Tat-ND (4.4 +/- 2.1%) or nontransfected (2.1 +/- 0.8%) cell-derived conditioned media. The neurotoxicity induced by Tat-HAD was inhibited by anti-MMP-2 or -7 antibodies (p < 0.005) but not by antibodies against MMP-9 or Tat. Similarly, scid/nod mice receiving striatal implants of Tat-HAD-transfected cells exhibited greater neurobehavioral abnormalities and neuronal loss (p < 0.005) than did animals receiving Tat-ND or nontransfected cells, which were reduced by treatment with the MMP inhibitor prinomastat (p < 0.005). These findings indicate that Tat causes neuronal death through an indirect mechanism that is Tat sequence dependent and involves the induction of MMPs.

9-cis retinoic acid (9-cis RA) is a retinoid receptor pan-agonist that binds with high affinity to both retinoic acid receptors (RARs) and retinoid X receptors (RXRs). Using a variety of in vivo and in vitro cancer models, we present experimental data that 9-cis RA has activity as a potential chemotherapeutic agent. Treatment of the human promyelocytic leukemia cell line HL-60 with 9-cis RA decreases cell proliferation, increases cell differentiation, and increases apoptosis. Induction of apoptosis correlates with an increase in tissue transglutaminase (type II) activity. In vivo, 9-cis RA induces complete tumor regression of an early passage human lip squamous cell carcinoma xenograft. Finally, 9-cis RA inhibits the anchorage-independent growth of the human breast cancer cell lines MCF-7 and LY2 (an antiestrogen-resistant MCF-7 variant). Transient co-transfection assays indicate that 9-cis RA inhibits estrogen receptor transcription of an ERE-tk-LUC reporter through RAR or RXR receptors. These data suggest that retinoid receptors can antagonize estrogen-dependent transcription and provides one possible mechanism for the inhibition of cell growth by 9-cis RA in breast cancer cell lines. In summary, these findings present evidence that 9-cis RA has a wide range of activities in human cancer models.

Rucaparib is a potent Poly (ADP-ribose) Polymerase (PARP) inhibitor currently under clinical development. The objectives of this analysis were to establish population PK and PK/PD models for rucaparib, and to evaluate the predictability of PARP activity in PBL for PARP activity in tumor tissues.Rucaparib concentrations and PARP activity in human PBLs and tumor issues were obtained from 32 patients with solid tumors in a Phase 1 First-in-Patient study. Simulations were conducted to evaluate different dosing regimens.A 3-compartment PK model best described the PK of rucaparib. An Emax model best described the exposure and PARP inhibition relationship. The maximum PARP inhibition (Imax) achieved in PBLs and in tumors were 90.9% and 90.0% of the baseline PARP activity, and the IC50 values were 1.05 ng/mL and 1.10 ng/mL, respectively. PAR polymer baseline value was found to be a covariate of Emin.Population PK and PK/PD models have been established to describe population PK of rucaparib and the relationship between rucaparib plasma concentration and PARP inhibition in both PBLs and tumor issues. Results from this trial indicated that PARP inhibition in PBLs can be used as a substitute for PARP inhibition in melanoma tumor tissues.

Purpose: This multicenter, open-label, phase II study evaluated the safety and clinical activity of axitinib, a potent and selective second-generation inhibitor of vascular endothelial growth factor receptors (VEGFR)–1, 2, and 3, in patients with metastatic melanoma. Experimental Design: Thirty-two patients with a maximum of one prior systemic therapy received axitinib at a starting dose of 5 mg twice daily. The primary endpoint was objective response rate. Results: Objective response rate was 18.8% [95% confidence interval (CI), 7.2–36.4], comprising one complete and five partial responses with a median response duration of 5.9 months (95% CI, 5.0–17.0). Stable disease at 16 weeks was noted in six patients (18.8%), with an overall clinical benefit rate of 37.5%. Six-month progression-free survival rate was 33.9%, 1-year overall survival rate was 28.1%, and median overall survival was 6.6 months (95% CI, 5.2–9.0). The most frequently (>15%) reported nonhematologic, treatment-related adverse events were fatigue, hypertension, hoarseness, and diarrhea. Treatment-related fatal bowel perforation, a known class effect, occurred in one patient. Axitinib selectively decreased plasma concentrations of soluble VEGFR (sVEGFR)-2 and sVEGFR-3 compared with soluble stem cell factor receptor (sKIT). No significant association was noted between plasma levels of axitinib and response. However, post hoc analyses indicated potential relationships between efficacy endpoints and diastolic blood pressure of 90 mm Hg or higher as well as baseline serum lactate dehydrogenase levels. Conclusions: Axitinib was well tolerated, showed a selective VEGFR-inhibitory profile, and showed single-agent activity in metastatic melanoma. Further evaluations of axitinib, alone and combined with chemotherapy, are ongoing. Clin Cancer Res; 17(23); 7462–9. ©2011 AACR.

Genetic and molecular studies suggest that activin receptor-like kinase 1 (ALK1) plays an important role in vascular development, remodeling, and pathologic angiogenesis. Here we investigated the role of ALK1 in angiogenesis in the context of common proangiogenic factors [PAF; VEGF-A and basic fibroblast growth factor (bFGF)]. We observed that PAFs stimulated ALK1-mediated signaling, including Smad1/5/8 phosphorylation, nuclear translocation and Id-1 expression, cell spreading, and tubulogenesis of endothelial cells (EC). An antibody specifically targeting ALK1 (anti-ALK1) markedly inhibited these events. In mice, anti-ALK1 suppressed Matrigel angiogenesis stimulated by PAFs and inhibited xenograft tumor growth by attenuating both blood and lymphatic vessel angiogenesis. In a human melanoma model with acquired resistance to a VEGF receptor kinase inhibitor, anti-ALK1 also delayed tumor growth and disturbed vascular normalization associated with VEGF receptor inhibition. In a human/mouse chimera tumor model, targeting human ALK1 decreased human vessel density and improved antitumor efficacy when combined with bevacizumab (anti-VEGF). Antiangiogenesis and antitumor efficacy were associated with disrupted co-localization of ECs with desmin+ perivascular cells, and reduction of blood flow primarily in large/mature vessels as assessed by contrast-enhanced ultrasonography. Thus, ALK1 may play a role in stabilizing angiogenic vessels and contribute to resistance to anti-VEGF therapies. Given our observation of its expression in the vasculature of many human tumor types and in circulating ECs from patients with advanced cancers, ALK1 blockade may represent an effective therapeutic opportunity complementary to the current antiangiogenic modalities in the clinic. Cancer Res; 71(4); 1362–73. ©2011 AACR.

Purpose: Axitinib (AG-013736) is a potent and selective inhibitor of vascular endothelial growth factor (VEGF) receptor tyrosine kinases 1 to 3 that is in clinical development for the treatment of solid tumors. We provide a comprehensive description of its in vitro characteristics and activities, in vivo antiangiogenesis, and antitumor efficacy and translational pharmacology data.Experimental Design: The potency, kinase selectivity, pharmacologic activity, and antitumor efficacy of axitinib were assessed in various nonclinical models.Results: Axitinib inhibits cellular autophosphorylation of VEGF receptors (VEGFR) with picomolar IC50 values. Counterscreening across multiple kinase and protein panels shows it is selective for VEGFRs. Axitinib blocks VEGF-mediated endothelial cell survival, tube formation, and downstream signaling through endothelial nitric oxide synthase, Akt and extracellular signal-regulated kinase. Following twice daily oral administration, axitinib produces consistent and dose-dependent antitumor efficacy that is associated with blocking VEGFR-2 phosphorylation, vascular permeability, angiogenesis, and concomitant induction of tumor cell apoptosis. Axitinib in combination with chemotherapeutic or targeted agents enhances antitumor efficacy in many tumor models compared with single agent alone. Dose scheduling studies in a human pancreatic tumor xenograft model show that simultaneous administration of axitinib and gemcitabine without prolonged dose interruption or truncation of axitinib produces the greatest antitumor efficacy. The efficacious drug concentrations predicted in nonclinical studies are consistent with the range achieved in the clinic. Although axitinib inhibits platelet-derived growth factor receptors and KIT with nanomolar in vitro potencies, based on pharmacokinetic/pharmacodynamic analysis, axitinib acts primarily as a VEGFR tyrosine kinase inhibitor at the current clinical exposure.Conclusions: The selectivity, potency for VEGFRs, and robust nonclinical activity may afford broad opportunities for axitinib to improve cancer therapy.

Purpose Patients with advanced, incurable thyroid cancer not amenable to surgery or radioactive iodine (131I) therapy have few satisfactory therapeutic options. This multi-institutional study assessed the activity and safety of axitinib, an oral, potent, and selective inhibitor of vascular endothelial growth factor receptors (VEGFR) 1, 2, and 3 in patients with advanced thyroid cancer. Patients and Methods Patients with thyroid cancer of any histology that was resistant or not appropriate for 131I were enrolled onto a single-arm phase II trial to receive axitinib orally (starting dose, 5 mg twice daily). Objective response rate (ORR) by Response Evaluation Criteria in Solid Tumors was the primary end point. Secondary end points included duration of response, progression-free survival (PFS), overall survival, safety, and modulation of soluble (s) VEGFR. Results Sixty patients were enrolled. Partial responses were observed in 18 patients, yielding an ORR of 30% (95% CI, 18.9 to 43.2). Stable disease lasting ≥ 16 weeks was reported in another 23 patients (38%). Objective responses were noted in all histologic subtypes. Median PFS was 18.1 months (95% CI, 12.1 to not estimable). Axitinib was generally well tolerated, with the most common grade ≥ 3 treatment-related adverse event being hypertension (n = 7; 12%). Eight patients (13%) discontinued treatment because of adverse events. Axitinib selectively decreased sVEGFR-2 and sVEGFR-3 plasma concentrations versus sKIT, demonstrating its targeting of VEGFR. Conclusion Axitinib is a selective inhibitor of VEGFR with compelling antitumor activity in all histologic subtypes of advanced thyroid cancer.

Purpose: There is an unmet need for noninvasive markers to measure the biological effects of targeted agents, particularly those inhibiting the vascular endothelial growth factor (VEGF) receptor (VEGFR) pathway, and identify patients most likely to benefit from treatment. In this study, we investigated potential blood-based biomarkers for SU11248 (sunitinib malate), a multitargeted tyrosine kinase inhibitor, in patients with metastatic imatinib-refractory gastrointestinal stromal tumors. Experimental Design: Patients (n = 73) enrolled in a phase I/II trial received SU11248 daily for 14 or 28 days followed by 14 days without treatment per cycle. Clinical benefit was defined as progression-free survival of >6 months. We assessed plasma markers, including VEGF and soluble VEGFR-2 (sVEGFR-2), and two cellular populations bearing VEGF receptors: monocytes and, in a subset of patients, mature circulating endothelial cells (CEC). Results: Compared to patients with progressive disease, patients with clinical benefit had significantly greater increases in CECs (0.52 versus −−0.01 CEC/μL/d, P = 0.03) and smaller decreases in monocyte levels (47% versus 60%, P = 0.007) during cycle 1. VEGF increased by 2.2-fold and sVEGFR-2 decreased 25% during the first 2 weeks of treatment. Neither plasma marker correlated with clinical outcome although a modest inverse correlation was observed between sVEGFR-2 changes and plasma drug levels. Monocytes, VEGF, and sVEGFR-2 all rebounded towards baseline off treatment. Conclusions: Monocytes, VEGF, and sVEGFR-2 were consistently modulated by treatment, suggesting that they may serve as pharmacodynamic markers for SU11248. Changes in CECs and monocytes, but not the plasma markers, differed between the patients with clinical benefit and those with progressive disease. These end points merit further investigation in future trials to determine their utility as markers of SU11248 activity and clinical benefit in gastrointestinal stromal tumors and other tumor types.

Antibodies and other macromolecular therapeutics can gain access to tumor cells via leaky tumor vessels. Inhibition of vascular endothelial growth factor (VEGF) signaling can reduce the vascularity of tumors and leakiness of surviving vessels, but little is known about how these changes affect the distribution of antibodies within tumors. We addressed this issue by examining the distribution of extravasated antibodies in islet cell tumors of RIP-Tag2 transgenic mice and implanted Lewis lung carcinomas using fluorescence and confocal microscopic imaging. Extravasated nonspecific immunoglobulin G (IgG) and antibodies to fibrin or E-cadherin accumulated in irregular patchy regions of stroma. Fibrin also accumulated in these regions. Anti-E-cadherin antibody, which targets epitopes on tumor cells of RIP-Tag2 adenomas, was the only antibody to achieve detectable levels within tumor cell clusters at 6 hours after i.v. injection. Treatment for 7 days with AG-013736, a potent inhibitor of VEGF signaling, reduced the tumor vascularity by 86%. The overall area density of extravasated IgG/antibodies decreased after treatment but the change was less than the reduction in vascularity and actually increased when expressed per surviving tumor vessel. Accumulation of anti-E-cadherin antibody in tumor cell clusters was similarly affected. The patchy pattern of antibodies in stroma after treatment qualitatively resembled untreated tumors and surprisingly coincided with sleeves of basement membrane left behind after pruning of tumor vessels. Together, the findings suggest that antibody transport increases from surviving tumor vessels after normalization by inhibition of VEGF signaling. Basement membrane sleeves may facilitate this transport. Antibodies preferentially distribute to tumor stroma but also accumulate on tumor cells if binding sites are accessible. (Cancer Res 2006; 66(3): 1434-45)

PURPOSE: To investigate the heterogeneity in the angiogenic response of a human breast cancer xenograft to a novel vascular endothelial growth factor (VEGF)-receptor tyrosine kinase inhibitor, AG-013736, using dynamic contrast-enhanced MR imaging (DCE-MRI). MATERIALS AND METHODS: Changes in pharmacokinetic parameters in a seven-day interval were compared between AG-treated and control groups, using Gd-DTPA and albumin-(Gd-DTPA)(30). A voxel-by-voxel analysis was performed to produce parametric spatial pharmacokinetic parametric maps and histograms. Histogram segmentation was used to quantify the heterogeneity in tumor response to therapy, and compared with conventional descriptive measures of distribution in terms of their capacity to separate control from AG-treated tumors. RESULTS: The albumin-(Gd-DTPA)(30) endothelial transfer constant, K(ps), showed changes with AG-013736 treatment and tumor growth. The changes were highly heterogeneous for individual segments of the histogram with different K(ps) values, and the overall patterns in which the frequency distribution changed differed significantly between the two groups. A change in the number of voxels with K(ps) rangingfrom 0.03 to 0.14 mL/min/(100 mL tissue) was the most sensitive variable for separating control from AG-treated tumors (P = 0.0008). Parametric maps of the kinetic parameters also showed spatial heterogeneity in tumor response to treatment. The K(ps) maps depicted rapid development of central necrosis as a result of AG-013736 treatment. Maps of v(p) demonstrated a marked increase at peripheral regions of necrotic areas. Similar trends were noted in the Gd-DTPA rate constant K(trans) distribution. CONCLUSION: This study demonstrates the value of histogram analysis of maps of pharmacokinetic parameters for assessing heterogeneity in tumor response to antiangiogenic therapy. Changes in the number of voxels within certain segments of the K(ps) histogram were the most sensitive variable for separating control from AG-treated tumors. J. Magn. Reson. Imaging 2005. (c) 2005 Wiley-Liss, Inc.

Macromolecular contrast medium-enhanced magnetic resonance imaging was applied to monitor the effect of matrix metalloprotease (MMP) inhibition on microvascular characteristics of human breast cancers implanted in athymic rats. Twice-daily intraperitoneal administration of Prinomastat over 1.5 days induced significant declines in MRI-assayed microvascular permeabilities (pth day of MMP treatment using the same dose and time schedule. Results demonstrate that Prinomastat produces a rapid but transient decrease in tumor vascular permeability. Contrast-enhanced MRI using macromolecular contrast medium may prove useful as a biomarker for the dynamic MMP biological effect in cancers.

Angiogenesis inhibitors are receiving increased attention as cancer therapeutics, but little is known of the cellular effects of these inhibitors on tumor vessels. We sought to determine whether two agents, AG013736 and VEGF-Trap, that inhibit vascular endothelial growth factor (VEGF) signaling, merely stop angiogenesis or cause regression of existing tumor vessels. Here, we report that treatment with these inhibitors caused robust and early changes in endothelial cells, pericytes, and basement membrane of vessels in spontaneous islet-cell tumors of RIP-Tag2 transgenic mice and in subcutaneously implanted Lewis lung carcinomas. Strikingly, within 24 hours, endothelial fenestrations in RIP-Tag2 tumors disappeared, vascular sprouting was suppressed, and patency and blood flow ceased in some vessels. By 7 days, vascular density decreased more than 70%, and VEGFR-2 and VEGFR-3 expression was reduced in surviving endothelial cells. Vessels in Lewis lung tumors, which lacked endothelial fenestrations, showed less regression. In both tumors, pericytes did not degenerate to the same extent as endothelial cells, and those on surviving tumor vessels acquired a more normal phenotype. Vascular basement membrane persisted after endothelial cells degenerated, providing a ghost-like record of pretreatment vessel number and location and a potential scaffold for vessel regrowth. The potent anti-vascular action observed is evidence that VEGF signaling inhibitors do more than stop angiogenesis. Early loss of endothelial fenestrations in RIP-Tag2 tumors is a clue that vessel phenotype may be predictive of exceptional sensitivity to these inhibitors.

Mechanical ventilation has become an indispensable therapeutic modality for patients with respiratory failure. However, a serious potential complication of MV is the newly recognized ventilator-induced acute lung injury. There is strong evidence suggesting that matrix metalloproteinases (MMPs) play an important role in the development of acute lung injury. Another factor to be considered is extracellular matrix metalloproteinase inducer (EMMPRIN). EMMPRIN is responsible for inducing fibroblasts to produce/secrete MMPs. In this report we sought to determine: (1) the role played by MMPs and EMMPRIN in the development of ventilator-induced lung injury (VILI) in an in vivo rat model of high volume ventilation; and (2) whether the synthetic MMP inhibitor Prinomastat (AG3340) could prevent this type of lung injury. We have demonstrated that high volume ventilation caused acute lung injury. This was accompanied by an upregulation of gelatinase A, gelatinase B, MT1-MMP, and EMMPRIN mRNA demonstrated by in situ hybridization. Pretreatment with the MMP inhibitor Prinomastat attenuated the lung injury caused by high volume ventilation. Our results suggest that MMPs play an important role in the development of VILI in rat lungs and that the MMP-inhibitor Prinomastat is effective in attenuating this type of lung injury.

We studied AG3340, a potent metalloproteinase (MMP) inhibitor with pM affinities for inhibiting gelatinases (MMP-2 and -9), MT-MMP-1 (MMP-14), and collagenase-3 (MMP-13) in many tumor models. AG3340 produced dose-dependent pharmacokinetics and was well tolerated after intraperitoneal (i.p.) and oral dosing in mice. Across human tumor models, AG3340 produced profound tumor growth delays when dosing began early or late after tumor implantation, although all established tumor types did not respond to AG3340. A dose-response relationship was explored in three models: COLO-320DM colon, MV522 lung, and MDA-MB-435 breast. Dose-dependent inhibitions of tumor growth (over 12.5-200 mg/kg given twice daily, b.i.d.) were observed in the colon and lung models; and in a third (breast), maximal inhibitions were produced by the lowest dose of AG3340 (50 mg/kg, b.i.d.) that was tested. In another model, AG3340 (100 mg/kg, once daily, i.p.) markedly inhibited U87 glioma growth and increased animal survival. AG3340 also inhibited tumor growth and increased the survival of nude mice bearing androgen-independent PC-3 prostatic tumors. In a sixth model, KKLS gastric, AG3340 did not inhibit tumor growth but potentiated the efficacy of Taxol. Importantly, AG3340 markedly decreased tumor angiogenesis (as assessed by CD-31 staining) and cell proliferation (as assessed by bromodeoxyuridine incorporation), and increased tumor necrosis and apoptosis (as assessed by hematoxylin and eosin and TUNEL staining). These effects were model dependent, but angiogenesis was commonly inhibited. AG3340 had a superior therapeutic index to the cytotoxic agents, carboplatin and Taxol, in the MV522 lung cancer model. In combination, AG3340 enhanced the efficacy of these cytotoxic agents without altering drug tolerance. Additionally, AG3340 decreased the number of murine melanoma (B16-F10) lesions arising in the lung in an intravenous metastasis model when given in combination with carboplatin or Taxol. These studies directly support the use of AG3340 in front-line combination chemotherapy in ongoing clinical trials in patients with advanced malignancies of the lung and prostate.

ABT-414 is an antibody-drug conjugate (ADC) comprised of an anti-EGFR antibody (ABT-806) conjugated to the potent cytotoxic monomethylauristatin F. ABT-414 binds a unique epitope of EGFR which is largely inaccessible when EGFR is expressed at physiological levels but is accessible in tumors that express EGFRde2-7 [also referred to as EGFR variant III (EGFRvIII)] and in tumors with wild-type amplified EGFR or excessive wild-type EGFR activation. These properties of ABT-414 should limit the effects of the toxin on normal tissues. ABT-414 is highly effective in both mutant and wild-type EGFR-positive human tumor xenografts in mice producing complete regressions and cures observed in the most sensitive models. Squamous cell tumors display a relatively high expression of EGFR. Immunohistochemical analysis reveals >70% of squamous lung and esophageal cancers and >90% of oral cavity tumors show moderate to strong staining for EGFR. Given the high unmet need in these patients and the in vivo data supporting improved ABT-414 efficacy in tumors with high EGFR expression, a Phase I/IIa study evaluating the safety, pharmacokinetics and efficacy of ABT-414 in subjects with EGFR-positive, refractory solid tumors has been initiated with a phase IIa expansion at the MTD in squamous NSCLC. Additionally, this study will evaluate the use of SPECT imaging with an indium-111-labeled parental antibody (ABT-806i) as a predictive tool for patient response. Tumor uptake by ABT-806i SPECT imaging correlates with antitumor response in xenograft models, and ABT-806i has been shown to effectively target tumor sites in select cancer patients. A fluorescent in situ hybridization (FISH) probe to detect EGFR amplification and EGFR IHC are also being evaluated with the goal of identifying patients who are most likely to respond to ABT-414 treatment. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A250. Citation Format: Andrew C. Phillips, Erwin R. Boghaert, Kedar S. Vaidya, Peter J. Ansell, David R. Shalinsky, Yumin Zhang, Martin J. Voorbach, Sarah Mudd, Kyle D. Holen, Rod A. Humerickhouse, Edward B. Reilly. ABT-414: An anti-EGFR antibody-drug conjugate as a potential therapeutic for the treatment of patients with squamous cell tumors. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A250.

3054 Background: PARP activity in PBLs or PBMs, measured as poly(ADP-ribose) (PAR) levels, has been used as a biomarker in the development of PARP inhibitors for dose selection. Results of a phase ...

3033 Background: PF-00337210 is a highly potent and selective ATP-competitive inhibitor of VEGFR2 TK with a cellular IC50 of 0.8 nM. In vivo, it inhibits tumor angiogenesis and human xenograft grow...

Effectively personalizing medicine depends upon selecting patients (pts) amenable to targeted therapies. We report the development of a custom immunohistochemistry (IHC) assay to identify P-cadherin positive expression in the archival biopsy of pts with solid malignancies. Validated reagents including a mAB to P-cadherin were incorporated into a custom IHC kit standardized across three Phase I sites (Seoul National University, Royal Melbourne Hospital, and Fox Chase Cancer Center). Pts with a P-cadherin positive archival biopsy are being enrolled into an ongoing trial. Clinical results will be reported separately. P-cadherin positivity is defined by a scoring index (SI) [product of the Tumor Area Positive for P-cad x Staining Intensity]. Based on the literature, a SI ≥ 4 is associated with poor clinical outcome and was therefore required for pt entry into the trial. The IHC protocol was standardized across sites using positive and negative controls run in a masked fashion at each site and cross-examined and repeated by a central lab that had final decision-making authority (ApoCell, Inc., Houston, TX). Each site ran independent IHC assays and analyses by board-certified pathologists, and provided stained and unstained archival biopsy slides for independent, masked analysis by ApoCell. The turn-around time for central IHC analysis was ≤ 48 h. Forty-four of 67 pts (65.7%) were found to be P-cadherin positive and eligible for entry into the trial. The distribution of enrolled patients by site is as follows: Australia (SI ≥ 4, n = 20), Korea (SI ≥ 4, n = 15), and USA (SI ≥ 4, n = 9). Median and mean SI values for the P-cadherin SI were 6 and 5.3 ± 2.9 (SD), respectively, with a range of 0 – 9. Clinical sites produced a SI equal to ApoCell in 56 of 67 pts (85.6% concordance rate). Among solid malignancies tested, a majority of gastric, colon and rectal cancers have demonstrated P-cadherin SI values ≥ 4. Successful execution of this IHC study demonstrates the feasibility of prospectively selecting pts based on IHC expression of P-cadherin using a custom standardized scoring index analysis across multiple clinical sites. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C16.

3519 Background: PF-00337210 potently inhibits VEGFR2 phosphorylation and is >10-fold more selective, based on IC50, for VEGFR2 than other kinases (eg, KIT and PDGFRs). In vitro, PF-00337210 inhibits VEGF-mediated HUVEC survival (IC50 = 0.53 nM). In vivo, it inhibits tumor angiogenesis and human xenograft growth. Methods: The primary objectives were to determine the safety profile and MTD of PF-00337210. PK and PD (DCE-MRI at baseline and cycle [C] 1, day [D] 2) were also evaluated. The volume rate transfer constant (Ktrans) assessed VEGFR inhibitory effects on vascular permeability and perfusion. Results: To date, 29 patients (pts) with advanced solid tumors were treated with PF-00337210 at doses of 0.67–9 mg QD, 13 of whom (45%) had received prior VEGF/VEGFR inhibitors. No dose-limiting toxicities (DLTs) occurred at 0.67–8 mg QD. Two DLTs occurred at 9 mg QD: one pt had chest pain, G3 troponin I, and G3 myocardial ischemia; a second pt had significant hypertension (HTN) at the anticipated Tmax after the first dose (systolic ≥180 mmHg over 3 hrs). HTN and fatigue were the most common treatment-related adverse events (AEs). HTN occurred in 8 pts (28%); incidence and intensity corresponded with dose, but was well controlled with antihypertensive agents. Fatigue was reported in 9 pts (31%) and occurred most frequently in pts receiving ≥6 mg QD. Other AEs included nausea, anorexia, proteinuria, and diarrhea. PK data indicated that mean (%CV) t1/2 at 8 mg QD was 8.60 (81) h (n=4) and AUC0–24 was 309 (45) ng.h/mL at steady-state (SS) on C1D15. Exposures (AUC0–24) were generally linear and variability ranged from 21 to 44% across doses. The observed accumulation ratio (Rac) at SS was 1.22 (15) (n=21), which was predicted by t1/2. PF-00337210 decreased mean Ktrans (1/min) values by 22.5±11.8 (n=2), 15.2 (n=1), 5.4±4.8 (n=3), and 25.3±8.5% (n=4) at 4, 6, 8, and 9 mg QD, respectively. No objective responses were observed but 7/29 pts (24%) had stable disease. Conclusions: PF-00337210 was well tolerated with the DLTs being HTN and myocardial ischemia. The QD MTD was determined to be 8 mg. Preliminary evidence of VEGFR inhibition was shown by DCE-MRI at ≥4 mg QD. The trial is now evaluating BID dosing which may allow increased drug exposures and fewer hypertensive effects that may be related to Cmax. [Table: see text]

3573 Background: ALK-1 is a member of the TβRI family & a novel target for antiangiogenic therapy (Rx). PF- 03446962 (PF) is a fully human mAB (IgG2, κ) generated against ALK-1 with dose-dependent preclinical antiangiogenic activities (Hu-Lowe et al, Proc AACR, 2009). This study's objectives were to determine whether: 1) CECs in cancer patients express ALK-1; and 2) whether therapy with PF against ALK-1 will modulate ALK-1 expression or CEC function in an ongoing Ph I trial. Methods: The human mAb was conjugated with alexa fluor 647. ALK-1 expression was assayed by a standardized multicolor flow cytometry assay (Mancuso et al, CCR 2009). Results: ALK-1 expression was characterized on human vascular (HUVEC) & lymphatic (HDLC) endothelial cells; HUVEC & HDLC cells highly express ALK-1 (>99% of these cells are ALK- 1+). ALK-1 expression was assessed in healthy controls (n=17) & cancer patients after normalizing for CEC viability. Patients with advanced malignancies had increased numbers of ALK-1+ CECs: Patients with breast ca (n=12), melanoma (n=8), NSCLC (n=11), & CRC (n=4) had 16±12, 39±23, 50±30, & 62±25 ALK-1+ CECs/mL, respectively, vs 7±6 ALK-1+ CECs/mL in controls. In contrast, ALK-1 expression was minimally or not expressed in pts with hematologic malignancies; ALK-1 was absent in CD117+ or CD34+ bone marrow cells. In the Ph I trial, preliminary evidence suggests that PF may alter CEC function; ALK-1+ CECs were markedly reduced in the 1st two pts studied at EIO after 22 days on Rx. Conclusions: ALK-1 is expressed in CECs. Flow cytometry enables rapid assay of ALK-1 expression in cancer patient blood. ALK-1 is expressed in an increased number of CECs/mL in cancer pts with solid malignancies vs controls. ALK-1 expression in CECs in pts with NSCLC & CRC may correspond to high ALK-1 expression observed in corresponding nonmatched tumor microarrays in addition to other malignancies such as sarcoma, SCLC & neuroendrocine pancreatic ca (Fiedler, Proc ASCO, 2009). Additional preliminary Ph I results will be reported as part of assessing whether CECs may have any role as biomarkers to potentially detect patients with ALK-1+ solid malignancies or monitor anti-ALK-1 therapy. [Table: see text]

9006 Background: No treatment has extended survival in stage IV melanoma. Melanomas are highly angiogenic and metastatic, express high levels of vascular endothelial growth factor receptors (VEGFRs...

9036 Background: Clinical testing of targeted agents can be accelerated by non-invasive biomarkers to assess relevant drug actions. SU11248 is an oral multitargeted tyrosine kinase inhibitor of VEGFR-1, 2, and 3, PDGFR, KIT, and FLT-3 with antiangiogenic and antitumor activities. To identify potential pharmacodynamic markers of its activity, we investigated changes in monocytes, which express VEGFR1, and CECs, which express VEGFR2. By targeting tumor vasculature, VEGFR-2 inhibition may increase the release of mature CECs (CD45- CD31+ CD146+ CD133-). Methods: Pts enrolled in a phase 1/2 trial of SU11248 for metastatic imatinib-resistant GIST received SU11248 orally once daily for 14 or 28 days (d) followed by 14d without treatment per cycle. CBC and differential were assessed pre- and post-treatment in 73 pts; CECs were assessed serially by 4-color flow cytometry in 16 pts. Clinical benefit (CB) was defined as PR or SD >6 months. Results: Monocyte levels decreased by 54% from 770 cells/μl at baseline to 35...

The synthesis of 3H-labelled azidothymidine (AZT) from [methyl-3H]thymidine is described. Purification of labelled AZT was accomplished by column chromatography. The purity of the labelled compound was determined by high performance liquid chromatography connected with a radioactive flow detector. The labelled AZT was found to be stable at pH ranging from 2.3 to 7.4 at 37°C and at hyperthermic temperature of 42°C.

We have reported that allicin, a constituent of garlic oil, has no effect on the activities of platelet cyclooxygenase or thromboxane synthase, or vascular PGI2 synthase. The effect of allicin on glutathione (GSH) dependent PGH2 to PGE2 isomerase is unknown. We therefore studied the effect of allicin on PGE2 biosynthesis in a murine mammary adenocarcinoma cell line (No 4526). Intact or sonicated cells were incubated with either 14C-arachidonic acid (AA) or 14C-PGH2, respectively. Following metabolism, products were extracted, separated by TLC and analyzed by radiochromatographic scan. PGE2 was predominantly formed with minimal amounts of PGF2 alpha and PGD2. Formation of 6-keto-PGF1 alpha or TXB2 was not detected indicating the absence of TXA2 and PGI2 synthase activity. Indomethacin and ibuprofen inhibited the PGE2 formation (p less than 0.05). The enzymatic PGE2 formation in sonicates was blocked by depletion of the cellular non-protein thiols by buthionine sulfoximine and was shown to be dependent on GSH. Allicin, over the range of 10-1000 microM, inhibited the formation of PGE2 in cells exposed to 2.0 microM 14C-AA for 20 min. and in sonicated cells incubated with 20.0 microM 14C-PGH2 for 2 min (p less than 0.05). Allicin did not alter cyclooxygenase-mediated oxygen utilization in ram seminal vessicle microsomes, suggesting that allicin selectively inhibits the GSH-dependent PGH2 to PGE2 isomerase in this adenocarcinoma cell line.