Abstract 1692: Dalantercept, an ALK1 inhibitor of angiogenesis, in combination with cisplatin inhibits tumor growth in a xenograft model of squamous cell carcinoma of the head and neck

Activin receptor-like kinase 1 (ALK1) is a key regulator of angiogenesis and vascular morphogenesis. ALK1 and its co-receptor endoglin are selectively expressed on the surface of activated endothelial cells during angiogenesis. Bone morphogenetic proteins (BMP) 9 and 10 are ligands that bind to ALK1 and induce activation of the heteromeric receptor complex, phosphorylation of SMAD1/5/8, and upregulation of specific genes involved in the maturation stage of angiogenesis, such as Id-1 and TMEM100. In particular, BMP9 expression is upregulated in a majority of squamous cell carcinomas of the head and neck (SCCHN).

Dalantercept is an ALK1 extracellular domain-Fc fusion protein that binds BMP9 and BMP10 with high affinity and antagonizes ALK1 signaling in vivo resulting in defective vascular maturation and inhibition of tumor growth in preclinical models. In a completed Phase 1 trial in patients with advanced, refractory solid tumors dalantercept demonstrated signs of clinical activity in a variety of patients, including two of three patients with SCCHN who achieved either an objective response or prolonged stable disease. A Phase 2 trial of dalantercept as monotherapy in recurrent/metastatic SCCHN patients who have had prior platinum-based chemotherapy is currently ongoing.

Based upon the single agent activity of both dalantercept and cisplatin in SCCHN, we tested the feasibility of the combination of cisplatin plus dalantercept in a mouse model of SCCHN. Combination treatment of dalantercept plus cisplatin showed significant tumor growth inhibition (TGI) in the RPMI2650 xenograft model (59% TGI on day 30) which was significantly better than either cisplatin (35% TGI, p= 0.0077) or dalantercept (32% TGI, p=0.0002) alone. No additional toxicity was observed in the combination treatment group compared to cisplatin monotherapy group.

These data suggest that combination of dalantercept plus cisplatin may result in enhanced clinical activity and supports prospective evaluation in patients with SCCHN.

Citation Format: Marat Alimzhanov, Michael Lee, Nicolas Solban, Scott Pearsall, Susan Pandya, Matthew L. Sherman, Ravindra Kumar. Dalantercept, an ALK1 inhibitor of angiogenesis, in combination with cisplatin inhibits tumor growth in a xenograft model of squamous cell carcinoma of the head and neck. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1692. doi:10.1158/1538-7445.AM2014-1692

Differential muscle hypertrophy is associated with satellite cell numbers and Akt pathway activation following activin type IIB receptor inhibition in Mtm1 p.R69C mice

X-linked myotubular myopathy is a congenital myopathy caused by deficiency of myotubularin. Patients often present with severe perinatal weakness, requiring mechanical ventilation to prevent death from respiratory failure. We recently reported that an activin receptor type IIB inhibitor produced hypertrophy of type 2b myofibers and modest increases of strength and life span in the severely myopathic Mtm1δ4 mouse model of X-linked myotubular myopathy. We have now performed a similar study in the less severely symptomatic Mtm1 p.R69C mouse in hopes of finding greater treatment efficacy. Activin receptor type IIB inhibitor treatment of Mtm1 p.R69C animals produced behavioral and histological evidence of hypertrophy in gastrocnemius muscles but not in quadriceps or triceps. The ability of the muscles to respond to activin receptor type IIB inhibitor treatment correlated with treatment-induced increases in satellite cell number and several muscle-specific abnormalities of hypertrophic signaling. Treatment-responsive Mtm1 p.R69C gastrocnemius muscles displayed lower levels of phosphorylated ribosomal protein S6 and higher levels of phosphorylated eukaryotic elongation factor 2 kinase than were observed in Mtm1 p.R69C quadriceps muscle or in muscles from wild-type littermates. Hypertrophy in the Mtm1 p.R69C gastrocnemius muscle was associated with increased levels of phosphorylated ribosomal protein S6. Our findings indicate that muscle-, fiber type-, and mutation-specific factors affect the response to hypertrophic therapies that will be important to assess in future therapeutic trials.

Phase II study of dalantercept, a novel inhibitor of ALK1-mediated angiogenesis, in patients with recurrent or metastatic squamous cell carcinoma of the head and neck

TPS6098

Background: Despite advances in the treatment of recurrent or metastatic squamous cell carcinoma of the head and neck (SCCHN), the prognosis remains poor with a need to develop novel therapeutic strategies. Targeting angiogenesis in SCCHN is an active area of clinical research. Activin receptor-like kinase 1 (ALK1) is a type 1 receptor in the TGF-ß superfamily which is selectively expressed on activated endothelial cells. ALK1 binds bone morphogenetic proteins (BMP) 9 and 10 (ligands for ALK1) and is primarily involved in the maturation stage of angiogenesis. Dalantercept is a human ALK1-Fc receptor fusion protein that binds BMP9/10 and acts as a ligand trap. In preclinical tumor models, dalantercept demonstrated a decrease in tumor vascularization and delayed tumor growth. In a completed phase I study, dalantercept demonstrated anti-tumor activity in patients with advanced solid tumors including SCCHN. Methods: An open label, multi-center, multiple dose, phase II study to evaluate dalantercept in patients with advanced SCCHN is ongoing. Dalantercept is being administered every three weeks via SC injection in a total of 45 patients to assess safety, tolerability, and efficacy. 13 patients were enrolled at the 0.6 mg/kg dose level. To date, 6 out of 30 planned patients have received dalantercept at the 1.2 mg/kg dose level. Key inclusion criteria are tumors arising from the oral cavity, oropharynx, hypopharynx, or larynx, at least one prior platinum-containing regimen, ECOG performance status </= 1, and measurable disease. Exclusion criteria include prior anti-angiogenesis therapy, significant pulmonary, cardiovascular, or bleeding risk. The primary efficacy endpoint is RR. Secondary endpoints include PFS, OS, TTP, DOR, DCR, and PD biomarkers on tumor and serum specimens including BMP9/10 and ALK1 expression. Clinical trial information: NCT01458392.

Inhibition of tumor growth in a VEGFR TKI-resistant model of renal cell carcinoma using dalantercept combined with sunitinib

370

Background: Antagonists of VEGF/VEGFR pathway have demonstrated clinical utility in patients with metastatic renal cell carcinoma (RCC); however, the therapeutic responses tend to be short-lived. Thus, there is a need for new treatments to overcome the acquired resistance to the current standards of care. Methods: We have used a murine xenograft model of RCC to study the relationship of the bone morphogenetic protein (BMP)/transforming growth factor-β (TGF-β) superfamily pathways and the VEGF pathways. Additionally, we have studied the effects of BMP9/10 inhibition on RCC tumor growth and performed MRI based tumor blood flow analyses to study antiangiogenic activity of the treatments. To explore the role of BMP9/10/ALK1 signaling in resistance to VEGFR inhibition, we used dalantercept (human ALK1-Fc fusion protein) as a ligand trap for BMP9 and 10. Results: We have found evidence of upregulation of BMP10 in A498 RCC xenograft tumors that have developed resistance to sunitinib. In tumors that had developed resistance to sunitinib, addition of ALK1-Fc to sunitinib led to prolonged tumor stabilization compared to either agent alone. Imaging of tumors revealed that addition of ALK1-Fc to sunitinib prevented the resumption in blood flow that is generally seen with continued sunitinib. Conclusions: These murine xenograft model data demonstrate that inhibition of ALK1 receptor pathway in combination with inhibition of VEGFR pathway may be a useful strategy for the treatment of RCC. A phase II randomized study of dalantercept in combination with axitinib in patients with metastatic RCC after progression on VEGFR/TKI therapy is ongoing.

BMP9 as a potential biomarker for dalantercept efficacy against ALK1-mediated angiogensis in head and neck cancer

30

Background: Activin receptor-like kinase 1 (ALK1) is a type 1 receptor in the TGF-β superfamily. The ALK1 pathway plays a role in vascular development and pathological angiogenesis. Mutations affecting this pathway result in hereditary hemorrhagic telangiectasia, a disease characterized by failed vascular development and arteriovenous malformations. Therefore, disruption of this pathway in adults may help in conditions with pathological angiogenesis. Bone morphogenetic protein 9 (BMP9) is a ligand that binds with high affinity to ALK1 and stimulates endothelial cell sprouting during vessel maturation. BMP9 is upregulated in the RIP1-Tag2 murine model of vascular invasive carcinoma; treatment with a murine version of dalantercept (RAP-041) can inhibit tumor growth. Methods: Dalantercept (ACE-041) is a soluble receptor protein comprising the extracellular domain of ALK1 linked to an IgG1 Fc region, which functions as a ligand trap to inhibit endogenous BMP9 signaling. Results: In a phase I study of dalantercept in advanced solid tumors, three patients with squamous cell carcinoma of the head and neck (SCCHN) were enrolled. One SCCHN patient received 10 cycles (30 weeks) at 0.4 mg/kg and had a partial response (32.5% decrease in target lesion size). A second SCCHN patient received 11 cycles (33 weeks) at 1.6 mg/kg and had a 28.9% decrease in lesion size. A third SCCHN patient had progressive disease after 1 cycle at 0.8 mg/kg. Dalantercept was generally well-tolerated. Common AEs included fatigue, peripheral edema, nausea, anemia, headache, anorexia, and dyspnea. Analysis of archived tumor samples from SCCHN patients demonstrated that 25% had high BMP9 expression and 44% had medium levels of expression. Conclusions: A phase II study to evaluate the efficacy, safety and pharmacodynamics (PD) of dalantercept in SCCHN is ongoing. The primary objective is ORR. Secondary objectives include PFS, OS, safety, tolerability and pharmacokinetics. Exploratory analyses in this study will examine BMP9 expression in archived and fresh tumor biopsies as well as serum levels of BMP9 and other markers; association of biomarkers with response to therapy will be examined as potential companion diagnostics.

Inhibiting activin-A signaling stimulates bone formation and prevents cancer-induced bone destruction in vivo

Cancers that grow in bone, such as myeloma and breast cancer metastases, cause devastating osteolytic bone destruction. These cancers hijack bone remodeling by stimulating osteoclastic bone resorption and suppressing bone formation. Currently, treatment is targeted primarily at blocking bone resorption, but this approach has achieved only limited success. Stimulating osteoblastic bone formation to promote repair is a novel alternative approach. We show that a soluble activin receptor type IIA fusion protein (ActRIIA.muFc) stimulates osteoblastogenesis (p < .01), promotes bone formation (p < .01) and increases bone mass in vivo (p < .001). We show that the development of osteolytic bone lesions in mice bearing murine myeloma cells is caused by both increased resorption (p < .05) and suppression of bone formation (p < .01). ActRIIA.muFc treatment stimulates osteoblastogenesis (p < .01), prevents myeloma-induced suppression of bone formation (p < .05), blocks the development of osteolytic bone lesions (p < .05), and increases survival (p < .05). We also show, in a murine model of breast cancer bone metastasis, that ActRIIA.muFc again prevents bone destruction (p < .001) and inhibits bone metastases (p < .05). These findings show that stimulating osteoblastic bone formation with ActRIIA.muFc blocks the formation of osteolytic bone lesions and bone metastases in models of myeloma and breast cancer and paves the way for new approaches to treating this debilitating aspect of cancer.

A soluble activin receptor type IIb prevents the effects of androgen deprivation on body composition and bone health

Androgen deprivation, a consequence of hypogonadism, certain cancer treatments, or normal aging in men, leads to loss of muscle mass, increased adiposity, and osteoporosis. In the present study, using a soluble chimeric form of activin receptor type IIB (ActRIIB) we sought to offset the adverse effects of androgen deprivation on muscle, adipose tissue, and bone. Castrated (ORX) or sham-operated (SHAM) mice received either TBS [vehicle-treated (VEH)] or systemic administration of ActRIIB-mFc, a soluble fusion protein comprised of a form of the extracellular domain of ActRIIB fused to a murine IgG2aFc subunit. In vivo body composition imaging demonstrated that ActRIIB-mFc treatment results in increased lean tissue mass of 23% in SHAM mice [19.02 +/- 0.42 g (VEH) versus 23.43 +/- 0.35 g (ActRIIB-mFc), P < 0.00001] and 26% in ORX mice [15.59 +/- 0.26 g (VEH) versus 19.78 +/- 0.26 g (ActRIIB-mFc), P < 0.00001]. Treatment also caused a decrease in adiposity of 30% in SHAM mice [5.03 +/- 0.48 g (VEH) versus 3.53 +/- 0.19 g (ActRIIB-mFc), NS] and 36% in ORX mice [7.12 +/- 0.53 g (VEH) versus 4.57 +/- 0.28 g (ActRIIB-mFc), P < 0.001]. These changes were also accompanied by altered serum levels of leptin, adiponectin, and insulin, as well as by prevention of steatosis (fatty liver) in ActRIIB-mFc-treated ORX mice. Finally, ActRIIB-mFc prevented loss of bone mass in ORX mice as assessed by whole body dual x-ray absorptiometry and micro-computed tomography of proximal tibias. The data demonstrate that treatment with ActRIIB-mFc restored muscle mass, adiposity, and bone quality to normal levels in a mouse model of androgen deprivation, thereby alleviating multiple adverse consequences of such therapy.