Positive allosteric modulator of SERCA pump NDC-1171 attenuates cardiac functional decline in mouse model of Duchenne muscular dystrophy

The novel SERCA pump positive allosteric modulator NDC-1171 significantly attenuates cardiac functional decline in a mouse model of Duchenne muscular dystrophy without improving skeletal muscle function.

The Gist

Imagine your body's muscles are like a high-performance race car. To keep that engine running smoothly, it needs a perfect system for managing fuel and exhaust. In our muscles, that "exhaust" is a tiny particle called calcium.

When a muscle contracts (like when you lift a box), calcium floods the engine. To relax and get ready for the next move, the engine needs a pump to suck that calcium back up and clear it out. This pump is called SERCA.

The Problem: A Broken Pump in Duchenne Muscular Dystrophy (DMD)

In people with Duchenne Muscular Dystrophy (DMD), the "engine block" is damaged. Because of this damage, the SERCA pump gets clogged and slows down. It can't clear the calcium fast enough.

• The Result: The muscle stays tense, gets tired quickly, and eventually, the heart muscle (which is also a muscle) starts to fail. In fact, heart failure is the biggest danger for people with DMD.

The Solution: A New "Tuner" Called NDC-1171

Scientists at Purdue University wanted to fix this broken pump. They had previously found a chemical (CDN-1163) that acted like a wrench to tighten the pump, but it didn't work very well when taken by mouth—it got broken down by the body before it could reach the muscles.

They created a new, improved version called NDC-1171. Think of this new molecule as a high-performance turbocharger for the SERCA pump. It's designed to:

1. Stick better to the pump.
2. Survive the journey through the stomach and bloodstream.
3. Rev up the pump's speed, helping it clear calcium much faster.

The Experiment: Testing on "Mini-Muscle" Mice

The researchers tested this new turbocharger on mice that have a version of DMD (called D2.mdx mice).

• The Setup: They gave one group of sick mice the new drug (NDC-1171) via a small tube in their mouth (oral gavage) for 8 weeks. Another group got a fake treatment (a "sugar pill" or vehicle), and a third group of healthy mice got the fake treatment to act as a control.
• The Checks: They used ultrasound machines (like a sonogram for babies) to check the heart's pumping power. They also made the mice run on tiny treadmills and squeeze a metal bar to test their muscle strength.

The Results: A Heart Hero, But Not a Muscle Miracle

Here is where it gets interesting, and a bit surprising:

1. The Heart Got a Boost (The Good News)
The drug worked like magic on the heart.

• The sick mice that got the drug kept their heart pumping much stronger than the sick mice that didn't.
• Analogy: Imagine two old, rusty pumps. One is left alone, and it starts sputtering and failing. The other gets the new turbocharger, and even though it's still an old pump, it keeps chugging along at a much better speed. The drug preserved the heart's ability to pump blood.

2. The Limbs Didn't Change (The Mixed News)
However, when they tested the arms and legs (skeletal muscles), the drug didn't help at all.

• The mice with the drug were just as weak and tired on the treadmill as the mice without it.
• Analogy: It's like putting a super-turbo on the car's engine (the heart), but the tires (the limbs) are still bald and worn out. The engine runs great, but the car still can't drive fast on the road.

Why Did This Happen?

The scientists have a few theories:

• Different Rules for Different Muscles: The heart and the limbs use slightly different versions of the pump. The drug might be a perfect fit for the heart's version but gets blocked by a "guard" in the limb muscles (called sarcolipin) that stops the drug from working.
• Delivery Issues: Maybe the drug gets to the heart easily but doesn't reach the deep muscles in the legs in high enough concentrations.

The Bottom Line

This study is a promising first step.

• What it means: We found a way to protect the heart in DMD, which is the most critical organ to save. Even if the drug doesn't fix the walking or running yet, keeping the heart strong buys time and saves lives.
• What's next: Scientists need to figure out how to get the drug into the limbs too, or perhaps find a way to remove the "guard" in the legs so the drug can work there as well.

In short: NDC-1171 is a new tool that successfully tunes the heart's engine in DMD mice, preventing it from stalling, even though it hasn't fixed the car's tires yet. It's a big win for heart health, and a clue for how to fix the rest of the body in the future.

Technical Summary

1. Problem Statement

Duchenne muscular dystrophy (DMD) is a fatal X-linked genetic disorder affecting 1 in 5,000 male births. While skeletal muscle weakness is the hallmark of the disease, progressive cardiomyopathy is the leading cause of death. A central driver of DMD-associated cardiac and skeletal muscle dysfunction is impaired calcium ($Ca^{2+}$) handling, specifically the reduced reuptake of cytosolic calcium into the sarcoplasmic reticulum (SR) by the SERCA pump.

Previous research identified CDN-1163, a quinoline amide positive allosteric modulator of SERCA, which showed efficacy in attenuating neurodegenerative and metabolic disorders. However, CDN-1163 had suboptimal pharmacokinetic (PK) properties, including low oral bioavailability and rapid clearance, limiting its systemic exposure and therapeutic potential. There was a need for a next-generation analogue that retained SERCA activation efficacy while meeting stricter PK criteria for effective oral administration.

2. Methodology

The study employed a multi-faceted approach combining medicinal chemistry, pharmacokinetics, and in vivo efficacy testing in a murine model.

• Compound Design & Synthesis:

  • Researchers synthesized NDC-1171, a novel analogue of CDN-1163.
  • The synthesis involved activating a substituted benzoic acid (2-chloro-4-methylbenzoic acid) to an acid chloride and coupling it with 2-methylquinolin-8-amine to form a benzamide scaffold.
  • The goal was to achieve oral bioavailability >30%, clearance <100 mL/min/kg, half-life ($t_{1/2}$) $\ge$ 1 hour, and plasma $C_{max}$ > 1 $\mu$M.

• In Vitro Characterization:

  • Ca-ATPase Assay: Measured ATP hydrolysis rates in cardiac SR membrane vesicles from pig hearts to determine $V_{max}$ shifts at various concentrations (1, 3, 10 $\mu$M).
  • Pharmacokinetics (PK): Conducted in male CD-1 mice (IV and oral dosing) to measure AUC, $C_{max}$, clearance, and bioavailability using LC-MS/MS.

• In Vivo Efficacy Study:

  • Animal Model: Male D2.mdx mice (a severe DMD model) were used, alongside DBA/2J mice as background controls.
  • Groups: Three groups ($n=9$ each): DBA/2J (Control), D2.mdx + Vehicle, D2.mdx + NDC-1171.
  • Dosing: NDC-1171 was administered via oral gavage at 40 mg/kg, 3 times weekly for 8 weeks (ages 6–14 weeks).
  • Assessments:
    • Cardiac Function: Transthoracic echocardiography (Vevo 3100) at baseline, midpoint, endpoint, and post-behavior to measure Left Ventricular Ejection Fraction (LVEF), volumes, and cardiac output.
    • Skeletal Muscle Function: Treadmill exhaustion test and 4-paw grip strength test.
    • Histology: Hearts were collected at week 17, stained with H&E and Masson's trichrome to assess fibrosis and necrosis.

3. Key Contributions

• Development of NDC-1171: Successfully engineered a next-generation SERCA modulator with superior pharmacokinetic properties compared to its predecessor, CDN-1163.
• Mechanistic Validation: Demonstrated that NDC-1171 acts as a potent positive allosteric modulator of SERCA, increasing $V_{max}$ in a dose-dependent manner.
• Organ-Specific Efficacy: Provided the first evidence that a SERCA activator can selectively preserve cardiac function in DMD without necessarily improving skeletal muscle function in the same treatment window, highlighting a potential "cardiac-dominant" therapeutic window.

4. Key Results

• Pharmacokinetics:

  • NDC-1171 showed significantly improved exposure compared to CDN-1163.
  • AUC: 583 ng·h/mL (vs. 283 for CDN-1163).
  • $C_{max}$: 1.7 $\mu$M (vs. 0.3 $\mu$M).
  • Oral Bioavailability (F): 30.8% (vs. 13.2%).
  • Clearance: Reduced to 89 mL/min/kg (vs. 251 mL/min/kg).

• Cardiac Function (Echocardiography):

  • At 16 weeks, the Vehicle-treated D2.mdx group showed significant cardiac decline (LVEF: 50.7 ± 0.9%).
  • The NDC-1171 treated group showed significant attenuation of this decline (LVEF: 57.7 ± 0.5%, $p < 0.05$ vs. Vehicle).
  • While still lower than healthy DBA/2J controls (62.4 ± 0.6%), the treatment preserved systolic function effectively.

• Skeletal Muscle Function:

  • No significant improvement was observed in the treated group compared to the vehicle group.
  • Grip Strength: No difference ($p=0.90$).
  • Treadmill Exhaustion: No difference ($p=0.64$).
  • Both D2.mdx groups (Vehicle and NDC-1171) performed significantly worse than the healthy DBA/2J controls.

• Histology:

  • No significant differences in myocardial fibrosis were detected between groups. Fibrosis was minimal in all groups, suggesting the cardiac benefit is functional (calcium handling) rather than structural (fibrosis prevention) at this stage.

5. Significance and Discussion

• Therapeutic Potential: NDC-1171 represents a promising candidate for treating DMD-associated cardiomyopathy. By improving SERCA-mediated calcium cycling, it preserves left ventricular systolic function during a critical window of disease progression.
• Tissue Specificity: The dissociation between cardiac preservation and skeletal muscle failure suggests that SERCA activation may have organ-specific windows of efficacy. The authors hypothesize this may be due to:
  • Differences in SERCA isoforms (SERCA2a in heart vs. SERCA1 in skeletal muscle).
  • Upregulation of sarcolipin (SLN) in dystrophic skeletal muscle, which uncouples calcium transport from ATP hydrolysis, potentially blunting the drug's effect in skeletal muscle.
  • Differences in drug distribution or target engagement between tissues.
• Clinical Implications: Since cardiomyopathy is the primary cause of death in DMD patients, a therapy that specifically targets cardiac function could significantly extend life expectancy, even if skeletal muscle weakness persists.
• Limitations & Future Work: The study notes limitations including small sample sizes for echocardiography, lack of diastolic function assessment, and the short duration of the study. Future work should investigate dose-response relationships, longer treatment durations, and the use of stressors (e.g., exercise or isoproterenol) to better reveal structural remodeling and fibrosis.

Conclusion: The study establishes NDC-1171 as a potent, orally available SERCA modulator that effectively attenuates cardiac functional decline in DMD mice, offering a viable path forward for developing targeted therapies for Duchenne-associated cardiomyopathy.