Mavacamten, known by its brand name Camzyos, is a targeted medication for a specific heart condition. It represents a newer class of therapy designed to address the underlying molecular cause of the disease, unlike previous treatments that focused on managing symptoms. This drug marks a shift toward precision medicine for certain inherited cardiac disorders.
Understanding Hypertrophic Cardiomyopathy
Hypertrophic cardiomyopathy (HCM) is a condition characterized by the thickening of the heart muscle. This hypertrophy most often affects the interventricular septum, the wall separating the left and right ventricles. A thickened septum can stiffen the left ventricle, making it harder for the heart to relax and fill with blood, and in some cases, it can obstruct blood flow out of the heart.
The cause of HCM often lies within the heart’s smallest functional units: the sarcomeres. Located inside muscle cells, sarcomeres are the microscopic engines that drive every heartbeat. In individuals with HCM, genetic mutations cause these engines to become overactive, leading to excessive contraction force.
This overactivity results in a state known as hypercontractility, where the heart muscle squeezes more forcefully than necessary. This excessive contraction contributes to the muscle thickening over time and increases the heart’s energy consumption. This state is a primary driver of the physical changes and symptoms associated with HCM.
The Role of Cardiac Myosin in Heart Contraction
The heart’s ability to pump blood relies on the contraction of its muscle cells, a process powered by the sarcomere. Within this structure, two main proteins, actin and myosin, are responsible for this action. Actin filaments provide a track for movement, while myosin is the motor protein that generates force.
Each myosin molecule has a “head” region that acts as a movable lever. During a heartbeat, these myosin heads bind to actin filaments, forming cross-bridges. The heads then pivot in a “power stroke,” pulling the actin filaments inward and shortening the sarcomere to cause muscle contraction.
This process requires energy from adenosine triphosphate (ATP). The myosin head uses ATP to detach from actin, reset, and prepare for the next contraction cycle. The number of myosin heads actively engaged with actin determines the force of the heart’s contraction.
Mavacamten’s Direct Action on Myosin
Mavacamten is a cardiac myosin inhibitor that directly targets the source of muscle contraction. As a selective and reversible inhibitor, it modulates the function of the myosin motor protein. The drug works by binding directly to a specific subset of myosin heads.
The medication stabilizes myosin heads in a “super-relaxed,” energy-sparing state. In this conformation, the myosin heads are folded back and unavailable to interact with actin. By promoting this inhibited state, mavacamten reduces the number of myosin heads able to form cross-bridges and generate force.
This action does not stop the heart’s contractile process but rather fine-tunes it. By decreasing the probability of cross-bridge formation, mavacamten dials down the excessive contractility seen in hypertrophic cardiomyopathy. This leads to a less forceful, more efficient contraction, and the effect is reversible, depending on the drug’s concentration in the body.
Physiological Outcomes of Myosin Inhibition
Mavacamten’s action on myosin leads to significant physiological changes. By reducing hypercontractility, the medication addresses a primary problem in obstructive HCM, where the thickened septum bulges into the left ventricular outflow tract (LVOT). The forceful contraction of the heart worsens this blockage, an effect that is lessened by inhibiting myosin.
Reducing the contraction force decreases the LVOT pressure gradient, a measure of the obstruction, allowing blood to be ejected more easily. This can alleviate symptoms like shortness of breath and chest pain. Patients treated with mavacamten show measurable reductions in this gradient, indicating improved blood flow.
In addition to reducing obstruction, myosin inhibition enhances the heart’s ability to relax between beats, a process known as diastolic function. The hypercontractile state in HCM impairs this relaxation. By promoting the energy-sparing state of myosin, mavacamten helps the heart muscle relax more completely, improving cardiac filling pressures and overall efficiency.