The DART Study: Results from the Dose-Escalation and Expansion Cohorts Evaluating the Combination of Dalantercept plus Axitinib in Advanced Renal Cell Carcinoma

Bone Morphogenetic Protein Signaling in Cancer; Some Topics in the Recent 10 Years

Bone morphogenetic proteins (BMPs), members of the transforming growth factor-β (TGF-β) family, are multifunctional cytokines. BMPs have a broad range of functions, and abnormalities in BMP signaling pathways are involved in cancer progression. BMPs activate the proliferation of certain cancer cells. Malignant phenotypes of cancer cells, such as increased motility, invasiveness, and stemness, are enhanced by BMPs. Simultaneously, BMPs act on various cellular components and regulate angiogenesis in the tumor microenvironment. Thus, BMPs function as pro-tumorigenic factors in various types of cancer. However, similar to TGF-β, which shows both positive and negative effects on tumorigenesis, BMPs also act as tumor suppressors in other types of cancers. In this article, we review important findings published in the recent decade and summarize the pro-oncogenic functions of BMPs and their underlying mechanisms. The current status of BMP-targeted therapies for cancers is also discussed.

Novel Pathways for Targeting Tumor Angiogenesis in Metastatic Breast Cancer

Breast cancer is the most common cancer affecting women and is the second leading cause of cancer related death worldwide. Angiogenesis, the process of new blood vessel development from pre-existing vasculature, has been implicated in the growth, progression, and metastasis of cancer. Tumor angiogenesis has been explored as a key therapeutic target for decades, as the blockade of this process holds the potential to reduce the oxygen and nutrient supplies that are required for tumor growth. However, many existing anti-angiogenic approaches, such as those targeting Vascular Endothelial Growth Factor, Notch, and Angiopoietin signaling, have been associated with severe side-effects, limited survival advantage, and enhanced cancer regrowth rates. To address these setbacks, alternative pathways involved in the regulation of tumor angiogenesis are being explored, including those involving Bone Morphogenetic Protein-9 signaling, the Sonic Hedgehog pathway, Cyclooxygenase-2, p38-mitogen-activated protein kinase, and Chemokine Ligand 18. This review article will introduce the concept of tumor angiogenesis in the context of breast cancer, followed by an overview of current anti-angiogenic therapies, associated resistance mechanisms and novel therapeutic targets.

From Bench to Bedside: How the Tumor Microenvironment Is Impacting the Future of Immunotherapy for Renal Cell Carcinoma

Immunotherapy has revolutionized the treatment landscape for many cancer types. The treatment for renal cell carcinoma (RCC) has especially evolved in recent years, from cytokine-based immunotherapies to immune checkpoint inhibitors. Although clinical benefit from immunotherapy is limited to a subset of patients, many combination-based approaches have led to improved outcomes. The success of such approaches is a direct result of the tumor immunology knowledge accrued regarding the RCC microenvironment, which, while highly immunogenic, demonstrates many unique characteristics. Ongoing translational work has elucidated some of the mechanisms of response, as well as primary and secondary resistance, to immunotherapy. Here, we provide a comprehensive review of the RCC immunophenotype with a specific focus on how preclinical and clinical data are shaping the future of immunotherapy.

Clinical Results and Biomarker Analyses of Axitinib and TRC105 versus Axitinib Alone in Patients with Advanced or Metastatic Renal Cell Carcinoma (TRAXAR)

LESSONS LEARNED

The combination of carotuximab with axitinib did not provide a benefit over axitinib monotherapy in patients with metastatic clear cell renal cell carcinoma who had previously progressed on one or more vascular endothelial growth factor (VEGF)-targeted therapies. Exploratory evaluation of pretreatment circulating biomarkers suggested the combination might benefit patients who have low baseline VEGF levels.

BACKGROUND

Endoglin is an angiogenic receptor expressed on proliferating tumor vessels and renal cell carcinoma (RCC) stem cells that is implicated as a mechanism of resistance to vascular endothelial growth factor receptor (VEGFR) inhibitors. This study evaluated an antiendoglin monoclonal antibody (carotuximab, TRC105) combined with axitinib in patients with advanced or metastatic clear cell renal cell carcinoma (mccRCC) who had progressed following one or more prior VEGF inhibitors.

METHODS

TRAXAR was a multicenter, international randomized 1:1 (stratified by ECOG, 0 vs. 1), phase II study of carotuximab combined with axitinib versus axitinib alone in mccRCC patients who had progressed following one or more prior VEGF inhibitors. The primary endpoint was progression-free survival (PFS) assessed by independent central review (ICR) per RECIST 1.1 RESULTS: A total of 150 patients were randomized. The combination therapy resulted in shorter median PFS by RECIST 1.1 than axitinib monotherapy (6.7 vs. 11.4 months). The combination was tolerated similarly to axitinib monotherapy, and there were no treatment related deaths. Exploratory evaluation of pretreatment circulating biomarkers suggested the combination might benefit patients who have low baseline VEGF levels.

CONCLUSION

The combination of carotuximab with axitinib did not demonstrate additional efficacy over single agent axitinib in patients with mccRCC who progressed following one or more prior VEGF inhibitor treatment.

Targeting the HIF2-VEGF axis in renal cell carcinoma

Insights into the role of the tumor suppressor pVHL in oxygen sensing motivated the testing of drugs that target the transcription factor HIF or HIF-responsive growth factors, such as VEGF, for the treatment of cancers caused by VHL inactivation, such as clear-cell renal cell carcinoma (ccRCC). Multiple VEGF inhibitors are now approved for the treatment of ccRCC, and a HIF2α inhibitor has advanced to phase 3 development for this disease. These inhibitors are now also increasingly combined with immune-checkpoint blockers. In this Perspective, we describe the understanding of the mechanisms of oxygen sensing and hypoxia signaling that resulted in the development of HIF2α-targeted therapies for patients with VHL-associated tumors. We also present future directions for extending the use of these therapies to other cancers.

A phase 2, randomized trial evaluating the combination of dalantercept plus axitinib in patients with advanced clear cell renal cell carcinoma

BACKGROUND

In a prior open-label study, the combination of dalantercept, a novel antiangiogenic targeting activin receptor-like kinase 1 (ALK1), plus axitinib was deemed safe and tolerable with a promising efficacy signal in patients with advanced renal cell carcinoma (RCC).

METHODS

In the current phase 2, randomized, double-blind, placebo-controlled study, patients with clear cell RCC previously treated with 1 prior angiogenesis inhibitor were randomized 1:1 to receive axitinib plus dalantercept versus axitinib plus placebo. Randomization was stratified by the type of prior therapy. The primary endpoint was progression-free survival (PFS). Secondary endpoints were PFS in patients with ≥2 prior lines of anticancer therapy, overall survival, and the objective response rate.

RESULTS

Between June 10, 2014, and February 23, 2017, a total of 124 patients were randomly assigned to receive axitinib plus dalantercept (59 patients) or placebo (65 patients). The median PFS was not found to be significantly different between the treatment groups (median, 6.8 months vs 5.6 months; hazard ratio, 1.11 [95% CI, 0.71-1.73; P = .670]). Neither group reached the median overall survival (hazard ratio, 1.39 [95% CI, 0.70-2.77; P = .349]). The objective response rate was 19.0% (11 of 58 patients; 95% CI, 9.9%-31.4%) in the dalantercept plus axitinib group and 24.6% (15 of 61 patients; 95% CI, 14.5%-37.3%) in the placebo plus axitinib group. At least 1 treatment-emergent adverse event of ≥grade 3 was observed in 59% of patients (34 of 58 patients) in the dalantercept group and 64% of patients (39 of 61 patients) in the placebo group. One treatment-related death occurred in the placebo plus axitinib group.

CONCLUSIONS

Although well tolerated, the addition of dalantercept to axitinib did not appear to improve treatment-related outcomes in previously treated patients with advanced RCC.

A Phase Ib, Open-Label Study of Dalantercept, an Activin Receptor-Like Kinase 1 Ligand Trap, plus Sorafenib in Advanced Hepatocellular Carcinoma

Lessons Learned.

Patients with hepatocellular carcinoma (HCC) often have limited therapeutic responses to the vascular endothelial growth factor (VEGF) tyrosine kinase inhibitor sorafenib, which is standard of care in advanced HCC. Targeting the activin receptor‐like kinase 1 (ALK1) and VEGF pathways simultaneously by combining the ALK1 ligand trap dalantercept with sorafenib may result in more effective angiogenic blockade and delay tumor progression in patients with advanced HCC.

Although the combination was generally well tolerated, there was no additive antitumor activity with the combination of dalantercept plus sorafenib in patients with advanced HCC. No complete or partial responses were observed, and overall survival ranged from 1.9 to 23.3 months.

These results suggest that, in this patient population, further development of the possible limited benefits of combination therapy with dalantercept plus sorafenib is not warranted.

Background.

Targeting the activin receptor‐like kinase 1 (ALK1) and vascular endothelial growth factor (VEGF) pathways may result in more effective angiogenic blockade in patients with hepatocellular carcinoma (HCC).

Methods.

In this phase Ib study, patients with advanced HCC were enrolled to dose‐escalation cohorts, starting at 0.6 mg/kg dalantercept subcutaneously every 3 weeks plus 400 mg sorafenib orally once daily, or to a dose expansion cohort. The primary objective was to determine the safety and tolerability and the dalantercept maximum tolerated dose (MTD) level. Secondary objectives were to assess the preliminary activity and the association of pharmacodynamic biomarkers with tumor response.

Results.

A total of 21 patients were enrolled in the study. Five patients received 0.6 mg/kg dalantercept in the first dose escalation cohort. Based on the initial safety results, the dose level was de‐escalated to 0.4 mg/kg in the second cohort (n = 6). The MTD was identified as 0.4 mg/kg and used for the dose expansion cohort (n = 10). At this dose level, the combination was generally well tolerated. Overall survival ranged from 1.9 to 23.3 months, and the best overall response was stable disease.

Conclusion.

The addition of dalantercept to sorafenib did not improve antitumor activity in patients with HCC. The dalantercept program in this population was discontinued.

An Open Label Phase Ib Dose Escalation Study of TRC105 (Anti-Endoglin Antibody) with Axitinib in Patients with Metastatic Renal Cell Carcinoma

BACKGROUND

TRC105 is an IgG1 endoglin monoclonal antibody that potentiates VEGF inhibitors in preclinical models. We assessed safety, pharmacokinetics, and antitumor activity of TRC105 in combination with axitinib in patients with metastatic renal cell carcinoma (mRCC).

SUBJECTS, MATERIALS, AND METHODS

Heavily pretreated mRCC patients were treated with TRC105 weekly (8 mg/kg and then 10 mg/kg) in combination with axitinib (initially at 5 mg b.i.d. and then escalated per patient tolerance to a maximum of 10 mg b.i.d.) until disease progression or unacceptable toxicity using a standard 3 + 3 phase I design.

RESULTS

Eighteen patients (median number of prior therapies = 3) were treated. TRC105 dose escalation proceeded to 10 mg/kg weekly without dose-limiting toxicity. Adverse event characteristics of each drug were not increased in frequency or severity when the two drugs were administered concurrently. TRC105 and axitinib demonstrated preliminary evidence of activity, including partial responses (PR) by RECIST in 29% of patients, and median progression-free survival (11.3 months). None of the patients with PR had PR to prior first-line treatment. Lower baseline levels of osteopontin and higher baseline levels of TGF-β receptor 3 correlated with overall response rate.

CONCLUSION

TRC105 at 8 and 10 mg/kg weekly was well tolerated in combination with axitinib, with encouraging evidence of activity in patients with mRCC. A multicenter, randomized phase II trial of TRC105 and axitinib has recently completed enrollment (NCT01806064).

IMPLICATIONS FOR PRACTICE

TRC105 is a monoclonal antibody to endoglin (CD105), a receptor densely expressed on proliferating endothelial cells and also on renal cancer stem cells that is implicated as a mediator of resistance to inhibitors of the VEGF pathway. In this Phase I trial, TRC105 combined safely with axitinib at the recommended single agent doses of each drug in patients with renal cell carcinoma. The combination demonstrated durable activity in a VEGF inhibitor-refractory population and modulated several angiogenic biomarkers. A randomized Phase II trial testing TRC105 in combination with axitinib in clear cell renal cell carcinoma has completed accrual.

Targeting Endoglin to Treat Metastatic Renal Cell Carcinoma: Lessons from Osler-Weber-Rendu Syndrome

This commentary reviews the novel mechanism of action of TRC105 in the context of treatments currently available for metastatic renal cell carcinoma, highlighting the recent findings of Choueiri and colleagues.

Activin receptor-like kinase 1 is associated with immune cell infiltration and regulates CLEC14A transcription in cancer

Cancer cells sustain their metabolic needs through nutrients and oxygen supplied by the bloodstream. The requirement for tumor angiogenesis has been therapeutically exploited in the clinical setting mainly by means of inhibition of the vascular endothelial growth factor family of ligands and receptors. Despite promising results in preclinical models, the benefits for patients proved to be limited. Inadequate efficacy similarly halted the development of agents impinging on the activity of the activin receptor-like kinase (ALK)1, a member of the transforming growth factor-β superfamily. Notwithstanding its characterization as an endothelial cell marker, the full spectrum of biological processes associated with ALK1 is essentially unexplored. Here, we present data revealing the genetic network associated with ACVRL1 (the gene encoding for ALK1) expression in human cancer tissues. Computational analysis unveiled a hitherto unknown role for ACVRL1 in relation to genes modulating the functionality of the immune cell compartment. Moreover, we generated a signature of 8 genes co-expressed with ACVRL1 across different tumor types and characterized the c-type lectin domain containing protein (CLEC)14A as a potential downstream target of ACVRL1. Considering the lack of reagents for ALK1 detection that has hampered the field to date, our work provides the opportunity to validate the 8-gene signature and CLEC14A as biomarkers for ALK1 activity. Ultimately, this may help revisit the clinical development of already existing ALK1-blocking compounds as precision medicines for cancer.

Phase II evaluation of dalantercept in the treatment of persistent or recurrent epithelial ovarian cancer: An NRG Oncology/Gynecologic Oncology Group study

OBJECTIVE

To determine the efficacy of dalantercept, a soluble ALK1 inhibitor receptor fusion protein, in patients with persistent or recurrent ovarian carcinoma and related malignancies.

METHODS

Eligibility criteria included measurable disease, 1-2 prior cytotoxic regimens and GOG performance status (PS) ≤2. Dalantercept was administered subcutaneously at 1.2 mg/kg every 3 weeks until disease progression or development of unacceptable toxicity. The primary null hypothesis was the probability of response ≤0.10 and the probability of 6-month progression-free survival without receipt of non-protocol therapy (event-free survival at 6 months, EFS6) ≤0.15, using RECIST 1.1 criteria.

RESULTS

The first stage was closed after enrollment of 30 participants with median age of 56.5 years, high-grade serous histology in 76.7%, 2 prior regimens in 46.7%, and platinum-free interval <6 months in 73.3%. All participants discontinued dalantercept, 24 (80.0%), 5 (16.7%) and 1 (3.3%) due to progression, toxicity, and other reason, respectively. The median number of treatment cycles per patient was 2 (range 1-29). There were six treatment-related grade 3 AEs and no grade ≥4 AEs. There were no objective responses. EFS6 was reached in 20% (6 out of 30 participants, 90% CI 9.1% to 35.7%).

CONCLUSIONS

Though safe, dalantercept as administered had limited efficacy in this patient population overall.

Current and Emerging Therapeutic Targets for Metastatic Renal Cell Carcinoma

PURPOSE OF REVIEW

The treatment of advanced renal cell carcinoma has evolved dramatically over recent years. In this review, we will summarize current and emerging therapies based on molecular targets and provide insight into treatment strategy for metastatic renal cell carcinoma.

RECENT FINDINGS

We have witnessed a paradigm shift in the therapeutic landscape as treatment was formerly reliant on cytokine-based agents which have now been replaced with therapies targeting angiogenesis, mammalian target of rapamycin pathways, and immune responses. These dramatic changes are primarily due to our improved understanding of the underlying mutations and molecular mechanisms leading to tumorigenesis and progression. We now have targeted agents in the form of small-molecule tyrosine kinase inhibitors, monoclonal antibodies, and mTOR inhibitors. Moreover, immunotherapy-targeting checkpoints of T-lymphocyte activity has provided increased overall survival and a new class of agents with potential to radically change the treatment options. With these agents and their combination, durable responses are increasingly seen even though treatment resistance remains a huge challenge. New treatment strategies are rapidly developing and the therapeutic landscape is expected for further evolution.

Compound genetically engineered mouse models of cancer reveal dual targeting of ALK1 and endoglin as a synergistic opportunity to impinge on angiogenic TGF-β signaling

Angiogenesis occurs early in tumor development, sustains primary tumor growth and provides a route for metastatic escape. The TGF-β family receptors modulate angiogenesis via endothelial-cell specific pathways. Here we investigate the interaction of two such receptors, ALK1 and endoglin, in pancreatic neuroendocrine tumors (PanNET). Independently, ALK1 and endoglin deficiencies exhibited genetically divergent phenotypes, while both highly correlate to an endothelial metagene in human and mouse PanNETs. A concurrent deficiency of both receptors synergistically decreased tumor burden to a greater extent than either individual knockdown. Furthermore, the knockout of Gdf2 (BMP9), the primary ligand for ALK1 and endoglin, exhibited a mixed phenotype from each of ALK1 and endoglin deficiencies; overall primary tumor burden decreased, but hepatic metastases increased. Tumors lacking BMP9 display a hyperbranching vasculature, and an increase in vascular mesenchymal-marker expression, which may be implicit in the increase in metastases. Taken together, our work cautions against singular blockade of BMP9 and instead demonstrates the utility of dual blockade of ALK1 and endoglin as a strategy for anti-angiogenic therapy in PanNET.

The FDA approved PI3K inhibitor GDC-0941 enhances in vitro the anti-neoplastic efficacy of Axitinib against c-myc-amplified high-risk medulloblastoma

Aberrant receptor kinase signalling and tumour neovascularization are hallmarks of medulloblastoma development and are both considered valuable therapeutic targets. In addition to VEGFR1/2, expression of PDGFR α/β in particular has been documented as characteristic of metastatic disease correlating with poor prognosis. Therefore, we have been suggested that the clinically approved multi‐kinase angiogenesis inhibitor Axitinib, which specifically targets these kinases, might constitute a promising option for medulloblastoma treatment. Indeed, our results delineate anti‐neoplastic activity of Axitinib in medulloblastoma cell lines modelling the most aggressive c‐myc‐amplified Non‐WNT/Non‐SHH and SHH‐TP53‐mutated tumours. Exposure of medulloblastoma cell lines to Axitinib results in marked inhibition of proliferation and profound induction of cell death. The differential efficacy of Axitinib is in line with target expression of medulloblastoma cells identifying VEGFR 1/2, PDGFR α/β and c‐kit as potential markers for drug application. The high specificity of Axitinib and the consequential low impact on the haematopoietic and immune system render this drug ideal multi‐modal treatment approaches. In this context, we demonstrate that the clinically available PI3K inhibitor GDC‐0941 enhances the anti‐neoplastic efficacy of Axitinib against c‐myc‐amplified medulloblastoma. Our findings provide a rational to further evaluate Axitinib alone and in combination with other therapeutic agents for the treatment of most aggressive medulloblastoma subtypes.

Evolving Treatment Paradigm in Metastatic Renal Cell Carcinoma

The treatment paradigm for advanced and metastatic renal cell carcinoma (mRCC) has evolved rapidly since the arrival of targeted therapies and novel immunotherapies. mRCC was previously treated only with cytokines. However, discoveries of mutations affecting the von Hippel-Lindau tumor suppressor gene (leading to increased expression of VEGF and hypoxia inducible factor/HIF-1) and of deregulations in the phosphatidylinositol-3 kinase/AKT/mTOR pathway (resulting in tumor angiogenesis, cell proliferation, and tumor growth) have led to the development of numerous targeted therapies. The U.S. Food and Drug Administration (FDA) has thus approved a total of nine targeted therapies since 2005, including VEGF tyrosine kinase inhibitors (sunitinib, pazopanib, axitinib, sorafenib, and lenvatinib), a monoclonal antibody targeting VEGF (bevacizumab), mTOR inhibitors (temsirolimus and everolimus), and a multityrosine kinase inhibitor (cabozantinib). Furthermore, the development of immune checkpoint inhibitors has again shifted the mRCC therapeutic landscape with the FDA's approval of nivolumab. Herein, we discuss the unprecedented changes in the field of clear cell histology mRCC in both the first-line and salvage settings, and we also discuss future therapies and recommend a treatment paradigm on sequencing of these agents.

ALK1 signaling in development and disease: new paradigms

Activin A receptor like type 1 (ALK1) is a transmembrane serine/threonine receptor kinase in the transforming growth factor-beta receptor family that is expressed on endothelial cells. Defects in ALK1 signaling cause the autosomal dominant vascular disorder, hereditary hemorrhagic telangiectasia (HHT), which is characterized by development of direct connections between arteries and veins, or arteriovenous malformations (AVMs). Although previous studies have implicated ALK1 in various aspects of sprouting angiogenesis, including tip/stalk cell selection, migration, and proliferation, recent work suggests an intriguing role for ALK1 in transducing a flow-based signal that governs directed endothelial cell migration within patent, perfused vessels. In this review, we present an updated view of the mechanism of ALK1 signaling, put forth a unified hypothesis to explain the cellular missteps that lead to AVMs associated with ALK1 deficiency, and discuss emerging roles for ALK1 signaling in diseases beyond HHT.

Systematic Review: Perioperative Systemic Therapy for Metastatic Renal Cell Carcinoma

Background: Approximately 16% of patients with renal cell carcinomas (RCC) present with stage IV disease at time of diagnosis. Treatment options for metastatic clear cell RCC, the most common histologic subtype, have proliferated over the past decade and include a combination of surgery and systemic therapy. The selection of systemic agent and best timing of systemic therapy in relation to nephrectomy is an area of active research. Objective: To evaluate the evidence for perioperative systemic therapy, including presurgical and postsurgical, for metastatic RCC. Methods: A systematic literature search using PubMed and MEDLINE databases was performed in January 2017 for articles related to perioperative systemic therapy in metastatic RCC using key word search terms. The authors screened the search results and identified selected publications by predetermined inclusion criteria and consensus. Expert opinion was obtained to assess for publications missed by search. Results: Early phase clinical trials of antiangiogenic tyrosine kinase inhibitors prior to cytoreductive nephrectomy in select patients show that these systemic agents are safe and effective in the presurgical setting. There are no randomized data evaluating pre- or post-surgical systemic therapy in metastatic RCC. Conclusions: Retrospective and early-phase prospective studies on the use and timing of systemic therapy in relation to cytoreductive nephrectomy in metastatic RCC show that standard of care antiangiogenic agents are safe and effective in the perioperative setting, though randomized data are still lacking. Pre-surgical immune checkpoint therapy for metastatic RCC has strong biologic rationale and holds promise. Sequential tumor sampling in neoadjuvant and presurgical trials is necessary to determine biomarkers of response and resistance.