Daniel C. Rabe

Targeting the HGF/Met signalling pathway in cancer.

Under normal conditions, hepatocyte growth factor (HGF)-induced Met tyrosine kinase (TK) activation is tightly regulated by paracrine ligand delivery, ligand activation at the target cell surface, and ligand activated receptor internalisation and degradation. Despite these controls, HGF/Met signalling contributes to oncogenesis and tumour progression in several cancers and promotes aggressive cellular invasiveness that is strongly linked to tumour metastasis. The prevalence of HGF/Met pathway activation in human malignancies has driven rapid growth in cancer drug development programmes. Pathway inhibitors can be divided broadly into biologicals and low molecular weight synthetic TK inhibitors; of these, the latter now outnumber all other inhibitor types. We review here the basic properties of HGF/Met pathway antagonists now in preclinical and clinical development as well as the latest clinical trial results. The main challenges facing the effective use of HGF/Met-targeted antagonists for cancer treatment include optimal patient selection, diagnostic and pharmacodynamic biomarker development, and the identification and testing of optimal therapy combinations. The wealth of basic information, analytical reagents and model systems available concerning HGF/Met oncogenic signalling will continue to be invaluable in meeting these challenges and moving expeditiously toward more effective disease control.

Phase II study evaluating 2 dosing schedules of oral foretinib (GSK1363089), cMET/VEGFR2 inhibitor, in patients with metastatic gastric cancer.

Purpose The receptors for hepatocyte and vascular endothelial cell growth factors (MET and VEGFR2, respectively) are critical oncogenic mediators in gastric adenocarcinoma. The purpose is to examine the safety and efficacy of foretinib, an oral multikinase inhibitor targeting MET, RON, AXL, TIE-2, and VEGFR2 receptors, for the treatment of metastatic gastric adenocarcinoma. Patients and Methods Foretinib safety and tolerability, and objective response rate (ORR) were evaluated in patients using intermittent (240 mg/day, for 5 days every 2 weeks) or daily (80 mg/day) dosing schedules. Thirty evaluable patients were required to achieve alpha = 0.10 and beta = 0.2 to test the alternative hypothesis that single-agent foretinib would result in an ORR of ≥25%. Up to 10 additional patients could be enrolled to ensure at least eight with MET amplification. Correlative studies included tumor MET amplification, MET signaling, pharmacokinetics and plasma biomarkers of foretinib activity. Results From March 2007 until October 2009, 74 patients were enrolled; 74% male; median age, 61 years (range, 25–88); 93% had received prior therapy. Best response was stable disease (SD) in 10 (23%) patients receiving intermittent dosing and five (20%) receiving daily dosing; SD duration was 1.9–7.2 months (median 3.2 months). Of 67 patients with tumor samples, 3 had MET amplification, one of whom had SD. Treatment-related adverse events occurred in 91% of patients. Rates of hypertension (35% vs. 15%) and elevated aspartate aminotransferase (23% vs. 8%) were higher with intermittent dosing. In both patients with high baseline tumor phospho-MET (pMET), the pMET:total MET protein ratio decreased with foretinib treatment. Conclusion These results indicate that few gastric carcinomas are driven solely by MET and VEGFR2, and underscore the diverse molecular oncogenesis of this disease. Despite evidence of MET inhibition by foretinib, single-agent foretinib lacked efficacy in unselected patients with metastatic gastric cancer. Trial Registration ClinicalTrials.gov NCT00725712

Targeting the HGF/Met signaling pathway in cancer therapy.

Introduction: Under normal conditions, hepatocyte growth factor (HGF)-induced activation of its cell surface receptor, the Met tyrosine kinase (TK), is tightly regulated by paracrine ligand delivery, ligand activation at the target cell surface, and ligand-activated receptor internalization and degradation. Despite these controls, HGF/Met signaling contributes to oncogenesis and tumor progression in several cancers and promotes aggressive cellular invasiveness that is strongly linked to tumor metastasis. Area covered: The prevalence of HGF/Met pathway activation in human malignancies has driven rapid growth in cancer drug development programs. The authors review Met structure and function, the basic properties of HGF/Met pathway antagonists now in preclinical and clinical development, as well as the latest clinical trial results. Expert opinion: Clinical trials with HGF/Met pathway antagonists show that as a class these agents are well tolerated. Although widespread efficacy was not seen in several completed Phase II studies, promising results have been reported in lung, gastric, prostate and papillary renal cancer patients treated with these agents. The main challenges facing the effective use of HGF/Met-targeted antagonists for cancer treatment are optimal patient selection, diagnostic and pharmacodynamic biomarker development, and the identification and testing of optimal therapy combinations. The wealth of basic information, analytical reagents, and model systems available concerning HGF/Met oncogenic signaling will continue to be invaluable in meeting these challenges and moving expeditiously toward more effective disease control.

Metastasis Suppressors Regulate the Tumor Microenvironment by Blocking Recruitment of Prometastatic Tumor-Associated Macrophages

Triple-negative breast cancer (TNBC) patients have the highest risk of recurrence and metastasis. Because they cannot be treated with targeted therapies, and many do not respond to chemotherapy, they represent a clinically underserved group. TNBC is characterized by reduced expression of metastasis suppressors such as Raf kinase inhibitory protein (RKIP), which inhibits tumor invasiveness. Mechanisms by which metastasis suppressors alter tumor cells are well characterized; however, their ability to regulate the tumor microenvironment and the importance of such regulation to metastasis suppression are incompletely understood. Here, we use species-specific RNA sequencing to show that RKIP expression in tumors markedly reduces the number and metastatic potential of infiltrating tumor-associated macrophages (TAM). TAMs isolated from nonmetastatic RKIP(+) tumors, relative to metastatic RKIP(-) tumors, exhibit a reduced ability to drive tumor cell invasion and decreased secretion of prometastatic factors, including PRGN, and shed TNFR2. RKIP regulates TAM recruitment by blocking HMGA2, resulting in reduced expression of numerous macrophage chemotactic factors, including CCL5. CCL5 overexpression in RKIP(+) tumors restores recruitment of prometastatic TAMs and intravasation, whereas treatment with the CCL5 receptor antagonist Maraviroc reduces TAM infiltration. These results highlight the importance of RKIP as a regulator of TAM recruitment through chemokines such as CCL5. The clinical significance of these interactions is underscored by our demonstration that a signature comprised of RKIP signaling and prometastatic TAM factors strikingly separates TNBC patients based on survival outcome. Collectively, our findings identify TAMs as a previously unsuspected mechanism by which the metastasis-suppressor RKIP regulates tumor invasiveness, and further suggest that TNBC patients with decreased RKIP activity and increased TAM infiltration may respond to macrophage-based therapeutics.

Erratum to: A Phase 1 dose-escalation study of the safety and pharmacokinetics of once-daily oral foretinib, a multi-kinase inhibitor, in patients with solid tumors

Foretinib is an oral multi-kinase inhibitor targeting MET, vascular endothelial growth factor receptor (VEGFR)-2, RON, KIT, and AXL kinases. In this Phase 1, open-label, non-randomized study, foretinib was administered once daily at doses of 60 mg, 80 mg, 100 mg, or 120 mg for 28 days. The primary objectives were to determine the maximum tolerated dose (MTD) and assess the safety and tolerability of the daily oral administration schedule. Secondary objectives included pharmacokinetics, pharmacodynamics, and assessment of tumor response. Patients had histologically confirmed metastatic or unresectable solid tumors for which no standard treatments existed and all received oral foretinib once daily. Dose escalation was planned as a conventional “3 + 3” design with an expansion at the MTD for collection of additional safety and pharmacokinetic information. Thirty-seven patients were treated across four dose levels. The MTD was established as 80 mg foretinib. Dose-limiting toxicities were hypertension, dehydration, and diarrhea. The most common adverse events included fatigue, hypertension, nausea, and diarrhea. Twenty-three of 31 patients (74 %) had a best response of stable disease. No patient had a confirmed partial or complete response. At the MTD, steady state was achieved by approximately 2 weeks, with average post-dose time to maximum concentration, peak concentration, and trough concentration of 4 h, 46 ng/mL, and 24 ng/mL, respectively. In patients treated at the MTD, soluble MET and VEGF-A plasma levels significantly increased (P < 0.003) and soluble VEGFR2 plasma levels significantly decreased from baseline (P < 0.03). The MTD of foretinib bisphosphate salt was determined to be 80 mg once daily.

Targeted Disruption of Heparan Sulfate Interaction with Hepatocyte and Vascular Endothelial Growth Factors Blocks Normal and Oncogenic Signaling

Hepatocyte growth factor (HGF) and vascular endothelial cell growth factor (VEGF) regulate normal development and homeostasis and drive disease progression in many forms of cancer. Both proteins signal by binding to receptor tyrosine kinases and heparan sulfate (HS) proteoglycans on target cell surfaces. Basic residues comprising the primary HS binding sites on HGF and VEGF provide similar surface charge distributions without underlying structural similarity. Combining three acidic amino acid substitutions in these sites in the HGF isoform NK1 or the VEGF isoform VEGF165 transformed each into potent, selective competitive antagonists of their respective normal and oncogenic signaling pathways. Our findings illustrate the importance of HS in growth factor driven cancer progression and reveal an efficient strategy for therapeutic antagonist development.

Identification and evaluation of soft coral diterpenes as inhibitors of HIF-2α induced gene expression

Kidney cancer was the cause of almost 13,000 deaths in the United States in 2009. Loss of function of the VHL tumor suppressor gene (von Hippel-Lindau disease) dramatically increases the risk of developing clear cell kidney cancer. The VHL protein is best understood for its regulation of hypoxia inducible factor (HIF). HIF responds to changes in oxygen levels in the cell and is responsible for mediating the transcriptional response to hypoxia. Of the three known HIFα gene products, HIF-2α appears to play a fundamental role in renal carcinoma. A high throughput screen was developed to identify small molecule inhibitors of HIF-2 gene expression. The screen was performed and yielded 153 confirmed active natural product extracts. Three of the active extracts were from marine soft corals of the order Alcyonacea: Sarcophyton sp., Lobophytum sarcophytoides and Asterospicularia laurae. Bioassay-guided fractionation led to the isolation of two new cembrane diterpenes, (4Z,8S*,9R*,12E,14E)-9-hydroxy-1-(prop-1-en-2-yl)-8,12-dimethyl-oxabicyclo[9.3.2]-hexadeca-4,12,14-trien-18-one (1), and (1E,3E,7R*,8R*,11E)-1-(2-methoxypropan-2-yl)-4,8,12-trimethyloxabicyclo[12.1.0]-pentadeca-1,3,11-triene (7), as well as eight known compounds, 2-6 and 8-10.

The Hepatocyte Growth Factor Receptor: Structure, Function and Pharmacological Targeting in Cancer

Under normal conditions, hepatocyte growth factor (HGF)-induced activation of its cell surface receptor, the Met tyrosine kinase (TK), is tightly regulated by paracrine ligand delivery, ligand activation at the target cell surface, and ligand activated receptor internalization and degradation. Despite these controls, HGF/Met signaling contributes to oncogenesis and tumor progression in several cancers and promotes aggressive cellular invasiveness that is strongly linked to tumor metastasis. The prevalence of HGF/Met pathway activation in human malignancies has driven rapid growth in cancer drug development programs. Pathway inhibitors can be divided broadly into biologicals and low molecular weight synthetic TK inhibitors; of these, the latter now outnumber all other inhibitor types. We review here Met structure and function, the basic properties of HGF/Met pathway antagonists now in preclinical and clinical development, as well as the latest clinical trial results. The main challenges facing the effective use of HGF/Met-targeted antagonists for cancer treatment include optimal patient selection, diagnostic and pharmacodynamic biomarker development, and the identification and testing of optimal therapy combinations. The wealth of basic information, analytical reagents and model systems available concerning HGF/Met oncogenic signaling will continue to be invaluable in meeting these challenges and moving expeditiously toward more effective disease control.

Abstract A8: Final results of a phase I dose escalation study of the safety and pharmacokinetics of foretinib administered orally daily to patients with solid tumors

Foretinib is a potent, orally available, small‐molecule inhibitor of MET and VEGFR2. Significant tumor cell growth inhibition was observed preclinically following treatment in multiple tumor models. Antitumor activity was observed in a previous phase I study in which foretinib was dosed intermittently on days 1–5 every 14 days. This phase I dose‐escalation study to evaluate daily oral administration of foretinib was conducted in adults with solid tumors. Foretinib was orally administered until disease progression or toxicity mandated removal from the study. Dose‐limiting toxicities (DLTs) that occurred during the first 28 days of treatment were used to determine the maximum tolerated dose (MTD). Safety, tolerability, pharmacodynamics (PD), and pharmacokinetics (PK) were evaluated. Tumor volume was assessed every 8 weeks by RECIST. A total of 37 patients (pts) were treated across 4 dose levels in the following order: 60 mg/d (6 pts), 80 mg/d (12 pts), 120 mg/d (3 pts), 100 mg/d (3 pts), and 80 mg/d (13 pts, PK expansion). Reported DLTs were hypertension and dehydration at 120 mg/d and diarrhea at 100 mg/d. The MTD of foretinib was determined to be 80 mg. With chronic dosing, 12 of 25 pts (48%) on 80 mg required a dose reduction to 60 mg between 21 days and 4 months on treatment. Frequent AEs associated with foretinib were hypertension (62%), fatigue (51%), nausea (43%), diarrhea (41%), proteinuria (30%), increased lactate dehydrogenase (27%), vomiting (24%), anorexia (22%), increased aspartate transaminase (19%), rash (16%), increased GGT (16%), and increased lipase (16%), primarily CTCAE grades 1 and 2. The foretinib plasma PK (at MTD) was characterized by a t max of ≈4 hours, a steady‐state oral clearance (CL/F) of ≈83 L/h, and ≈3.8‐fold accumulation at steady state (achieved by ≈day 15). At steady state, values of C max and AUC 0–24 were ≈45.7 ng/mL and ≈805 h · ng/mL, respectively, and the C min was ≈52% of C max . Plasma PD markers were measured during cycle 1 in 19 pts treated at the MTD. Shed Met (sMET) and VEGF showed increases, whereas sVEGFR2 showed a decrease. No pts had confirmed partial response or complete response, but stable disease (SD) (range, 2.1–18.1 months) was seen in 23 pts (74.2%). 11 pts had tumor regression from baseline, with tumor shrinkage ranging from 1%–21%. Disease progression was seen in 8 pts (25.8%). Overall, 35.5% of pts were event‐free at 6 months, and 12.9% of pts (diagnoses included medullary thyroid, hepatocellular, and papillary renal cell carcinomas, and alveolar soft part sarcoma) were event‐free at 12 months. 62% percent of pts withdrew due to progressive disease, 8% due to AEs, 5% due to death, and 24% due to consent withdrawal/investigator discretion/other. Foretinib can be safely administered at the oral daily dose of 80 mg (MTD); however, with chronic administration, dose reductions were not uncommon. The safety profile observed with daily dosing of foretinib is similar to that seen with intermittent dosing. Plasma PK results indicate that exposure to foretinib was well maintained over the daily dosing interval. PD results are similar to that seen with intermittent dosing and indicate that sMET, VEGF, and sVEGFR2 are promising markers for monitoring biological activity of foretinib. Prolonged SD and tumor regression in pts with various cancers suggest that foretinib has promise as an anticancer therapy. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A8.

Gene expression in local stroma reflects breast tumor states and predicts patient outcome

The surrounding microenvironment has been implicated in the progression of breast tumors to metastasis. However, the degree to which metastatic breast tumors locally reprogram stromal cells as they disrupt tissue boundaries is not well understood. We used species-specific RNA sequencing in a mouse xenograft model to determine how the metastasis suppressor RKIP influences transcription in a panel of paired tumor and stroma tissues. We find that gene expression in metastatic breast tumors is pervasively correlated with gene expression in local stroma of both mouse xenografts and human patients. Changes in stromal gene expression elicited by tumors better predicts subtype and patient survival than tumor gene expression, and genes with coordinated expression in both tissues predict metastasis-free survival. These observations support the use of stroma-based strategies for the diagnosis and prognosis of breast cancer.