A mouse anti-myostatin antibody increases muscle mass and improves muscle strength and contractility in the mdx mouse model of Duchenne muscular dystrophy and its humanized equivalent, domagrozumab (PF-06252616), increases muscle volume in cynomolgus monkeys

Abstract

Background: The treatments currently approved for Duchenne muscular dystrophy (DMD), a progressive skeletal muscle wasting disease, address the needs of only a small proportion of patients resulting in an urgent need for therapies that benefit all patients regardless of the underlying mutation. Myostatin is a member of the transforming growth factor-β (TGF-β) family of ligands and is a negative regulator of skeletal muscle mass. Loss of myostatin has been shown to increase muscle mass and improve muscle function in both normal and dystrophic mice. Therefore, myostatin blockade via a specific antibody could ameliorate the muscle weakness in DMD patients by increasing skeletal muscle mass and function, thereby reducing patients' functional decline.

Methods: A murine anti-myostatin antibody, mRK35, and its humanized analog, domagrozumab, were developed and their ability to inhibit several TGB-β ligands was measured using a cell-based Smad-activity reporter system. Normal and mdx mice were treated with mRK35 to examine the antibody's effect on body weight, lean mass, muscle weights, grip strength, ex vivo force production, and fiber size. The humanized analog (domagrozumab) was tested in non-human primates (NHPs) for changes in skeletal muscle mass and volume as well as target engagement via modulation of circulating myostatin.

Results: Both the murine and human antibodies are specific and potent inhibitors of myostatin and GDF11. mRK35 is able to increase body weight, lean mass, and muscle weights in normal mice. In mdx mice, mRK35 significantly increased body weight, muscle weights, grip strength, and ex vivo force production in the extensor digitorum longus (EDL) muscle. Further, tibialis anterior (TA) fiber size was significantly increased. NHPs treated with domagrozumab demonstrated a dose-dependent increase in lean mass and muscle volume and exhibited increased circulating levels of myostatin demonstrating target engagement.

Conclusions: We demonstrated that the potent anti-myostatin antibody mRK35 and its clinical analog, domagrozumab, were able to induce muscle anabolic activity in both rodents, including the mdx mouse model of DMD, and non-human primates. A Phase 2, potentially registrational, clinical study with domagrozumab in DMD patients is currently underway.

Keywords: Duchenne muscular dystrophy; Hypertrophy; Monoclonal antibody; Myostatin; Skeletal muscle; mdx.

Fig. 1

Effects of mRK35 on body weight and skeletal muscle mass in C57BL/6 and C57Bl/10 mice. a Weekly body weights following weekly intraperitoneal (IP) administration of 10 mg/kg mRK35 or vehicle (PBS) in 8-week-old male C57Bl/6 mice. b Weekly whole body lean mass measured by NMR. c Tissue wet weights of the gastrocnemius bundle (Gastroc) and quadriceps (Quad) muscles harvested after 4 weeks of treatment. Both groups (mRK35 and vehicle) contained eight mice. d Tissue wet weights of the tibialis antirior (TA), gastrocnemius bundle, and quadriceps of 1-year old male C57Bl/10 mice following weekly IP administration of 10 mg/kg mRK35 or vehicle (PBS) for 4 weeks. Data plotted are means ± SEM. *p < 0.05 versus vehicle as measured by two tailed Student’s t test

Fig. 2

Effect of mRK35 in mdx mice. a Weekly body weights following intraperitoneal administration of 10 mg/kg/week mRK35 or vehicle (PBS) in 8-week-old male mdx mice. b Forelimb grip strength measured after 8 weeks of treatment. c Tissue wet weights of the TA, gastrocnemius, and quadriceps muscles. d Tissue wet weight of the EDL. e EDL maximum tetanic force from resting length. f EDL cross-sectional area. g EDL specific force. Treatment groups contained 9 (vehicle) or 10 (mRK35) treated mice. Data plotted are means ± SEM. *p < 0.05 versus vehicle as measured by two-tailed Student’s t test

Fig. 3

Effect of mRK35 on skeletal muscle fiber size in mdx mice. a Fiber area count at the mid-belly of the TA muscle harvested from mdx mice following 4 weeks of treatment with 10 mg/kg mRK35 or vehicle (n = 4 per treatment). b Representative cross-sectional images of the TA from vehicle-treated mice. c Representative cross-sectional images of the TA from mRK35-treated animals. Muscle fibers are stained with wheat germ agglutinin in green and counterstained with DAPI, which stains the nuclei, in blue

Fig. 4

Effect of domagrozumab on skeletal muscle in cynomolgus monkeys. a Percent change in leg lean muscle mass over vehicle (PBS), measured by DXA, following 8 weeks of treatment with 10 and 30 mg/kg domagrozumab. b Myostatin levels in serum collected from all monkeys. c Percent change from baseline (start of study) in axial muscle volume after 8 weeks of treatment. d Percent change from baseline in appendicular muscle volume after 8 weeks of treatment. N = 5 animals for vehicle and 10 mg/kg groups and 3 animals for 30 mg/kg group. Data plotted are means ± SEM. * denotes p < 0.05 via ANOVA with Fisher’s LSD post-test versus vehicle; # denotes p < 0.05 versus 10 mg/kg domagrozumab; denotes time of dosing