Delandistrogene moxeparvovec

Delandistrogene moxeparvovec is the recombinant gene therapy product that is comprised of a non-replicating, recombinant, adeno-associated virus (AAV) serotype rh74 (AAVrh74) capsid and a ssDNA expression cassette flanked by inverted terminal repeats (ITRs) derived from AAV2. The cassette contains: 1) an MHCK7 gene regulatory component comprising a creatine kinase 7 promoter and an α-myosin heavy chain enhancer, and 2) the DNA transgene encoding the engineered delandistrogene moxeparvovec micro-dystrophin protein.

Vector/Capsid: Clinical and nonclinical studies have demonstrated AAVrh74 serotype transduction in skeletal muscle cells. Additionally, in nonclinical studies, AAVrh74 serotype transduction has been demonstrated in cardiac and diaphragm muscle cells.

Promoter: The MHCK7 promoter/enhancer drives transgene expression and has been shown in animal models to drive transgenic delandistrogene moxeparvovec micro-dystrophin protein expression predominantly in skeletal muscle (including diaphragm) and cardiac muscle. In clinical studies, muscle biopsy analyses have confirmed delandistrogene moxeparvovec micro-dystrophin expression in skeletal muscle.

Transgene: DMD is caused by a mutation in the DMD gene resulting in lack of functional dystrophin protein. Delandistrogene moxeparvovec carries a transgene encoding a micro-dystrophin protein consisting of selected domains of dystrophin expressed in normal muscle cells.

Delandistrogene moxeparvovec micro-dystrophin has been demonstrated to localize to the sarcolemma.

In 61 subjects who received delandistrogene moxeparvovec in clinical studies, delandistrogene moxeparvovec micro-dystrophin protein expression from muscle biopsies (gastrocnemius) was quantified by western blot and localized by immunofluorescence staining (fiber intensity and percentage delandistrogene moxeparvovec micro-dystrophin).

Delandistrogene moxeparvovec micro-dystrophin expression (expressed as change from baseline) as measured by western blot was the primary objective of Study 1 and Study 2. Muscle biopsies were obtained at baseline prior to delandistrogene moxeparvovec infusion and at Week 12 after delandistrogene moxeparvovec infusion in all subjects. The absolute quantity of delandistrogene moxeparvovec micro-dystrophin was measured by western blot assay, adjusted by muscle content and expressed as a percent of control (levels of wild-type dystrophin in subjects without DMD or Becker muscular dystrophy) in muscle biopsy samples. Results of subjects receiving 1.33 × 10¹⁴ vg/kg delandistrogene moxeparvovec are presented in the followinf table.

Delandistrogene moxeparvovec Micro-Dystrophin Expression in Studies 1 and 2 (Western Blot Assay)^abcd:

^a All patients received 1.33 × 10¹⁴ vg/kg, as measured by ddPCR
^b Muscle biopsies were obtained from the gastrocnemius
^c Change from baseline was statistically significant
^d Adjusted for muscle content. Control was level of wild-type (normal) dystrophin in normal muscle.

For subjects aged 4 through 5 years who received 1.33 × 10¹⁴ vg/kg of delandistrogene moxeparvovec, the mean (SD) delandistrogene moxeparvovec micro-dystrophin expression levels (change from baseline) at Week 12 following delandistrogene moxeparvovec infusion were 95.7% (N=3, SD: 17.9%) in Study 1 Parts 1 and 2 and 51.7% (N=11, SD: 41.0%) in Study 2 Cohort 1.

Assessment of delandistrogene moxeparvovec micro-dystrophin levels can be meaningfully influenced by differences in sample processing, analytical technique, reference materials, and quantitation methodologies. Therefore, valid comparisons of delandistrogene moxeparvovec micro-dystrophin measurements obtained from different assays cannot be made.

Vector Distribution and Vector Shedding

Nonclinical Data

Biodistribution of delandistrogene moxeparvovec was evaluated in tissue samples collected from healthy mice and Dmd ^mdx mice following intravenous administration in toxicology studies. At 12 weeks following delandistrogene moxeparvovec administration at dose levels of 1.33 × 10¹⁴ to 4.02 × 10¹⁴ vg/kg, vector DNA was detected in all major organs with the highest quantities detected in the liver, followed by lower levels in the heart, adrenal glands, skeletal muscle, and aorta. Delandistrogene moxeparvovec was also detected at low levels in the spinal cord, sciatic nerve and gonads (testis). Protein expression of delandistrogene moxeparvovec micro-dystrophin was highest in cardiac tissue, exceeding physiologic dystrophin expression levels in healthy mice, with lower levels in the skeletal muscle and diaphragm. In some studies, micro-dystrophin was also detected at low levels in the liver.

Clinical Data

Following IV administration, delandistrogene moxeparvovec vector genome undergoes distribution via systemic circulation and distributes into target muscle tissues followed by elimination in the urine and feces. Delandistrogene moxeparvovec biodistribution and tissue transduction are detected in the target muscle tissue groups and quantified in the gastrocnemius or biceps femoris biopsies obtained from patients with mutations in the DMD gene. Evaluation of delandistrogene moxeparvovec vector genome exposure in clinical muscle biopsies at Week 12 post-dose expressed as copies per nucleus revealed delandistrogene moxeparvovec drug distribution and transduction with a mean change from baseline of 2.91 and 3.44 copies per nucleus at the recommended dose of 1.33 × 10¹⁴ vg/kg for Study 1 and Study 2 Cohort 1, respectively.

In Study 2 Cohort 1, the biodistribution and vector shedding of delandistrogene moxeparvovec in the serum and excreta were quantified, respectively. The mean maximum concentration (C_max) in the serum was 0.0049 × 10¹³ copies/mL and 4.11 × 10⁵ copies/mL in the urine, 4.72 × 10⁷ copies/mL in the saliva, and 2.32 × 10⁷ copies/μg in the feces. The median time to achieve maximum concentration (T_max) was 5.3 hours post-dose in the serum, followed by 6.7 hours, 6.4 hours and 13.5 days post-dose in the saliva, urine, and feces, respectively. The median time to achieve first below limit of quantification (BLOQ) sample followed by 2 consecutive BLOQ samples were 63 days post-dose for serum. The median time to achieve complete elimination as the first below limit of detection (BLOD) sample followed by 2 consecutive BLOD samples were 49.8 days, 123 days and 162 days post-dose for saliva, urine and feces, respectively. The estimated elimination half-life of delandistrogene moxeparvovec vector genome in the serum is approximately 12 hours, and the majority of the drug is expected to be cleared from the serum by 1-week post-dose. In the excreta, the estimated elimination half-life of delandistrogene moxeparvovec vector genome is 40 hours, 55 hours, and 60 hours in the urine, feces, and saliva, respectively. As an AAV-based gene therapy that consists of a protein capsid containing the transgene DNA genome of interest, delandistrogene moxeparvovec capsid proteins are broken down through proteasomal degradation following AAV entry into target cells. As such, delandistrogene moxeparvovec is not likely to exhibit the drug-drug interaction potential mediated by known drug metabolizing enzymes (cytochrome P450-based) and drug transporters.