Mavacamten is shown to have selectivity of >4-fold for cardiac myosin, with IC50 values of 490 nM in the bovine system, 711 nM in the human system, and 2140 nM in the rabbit system[1].

Mavacamten treatment lowers FS from 52±3% to 38±7%. Mavacamten treatment lowers FS from 81±7% to 60±13%, which is a 25% relative reduction. There is a linear relationship between FS and Mavacamten plasma concentrations across all assays; for every 100 ng/mL rise in Mavacamten concentration, FS is lowered by 4.9%[2]. By lowering the cardiac myosin heavy chain's adenosine triphosphatase activity, mavacamten decreases contractility. In mice with heterozygous human mutations in the myosin heavy chain, chronic Mavacamten treatment inhibits the development of ventricular hypertrophy, cardiomyocyte disarray, and myocardial fibrosis and attenuates hypertrophic and profibrotic gene expression[3].

Steady-state characterization [1]
ATPase measurements were conducted using a coupled enzyme system utilizing pyruvate kinase and lactate dehydrogenase. Unless otherwise stated, the buffer system used in all experiments was 12 mm Pipes, 2 mm MgCl2, 1 mm DTT at pH 6.8 (PM12 buffer). All steady-state experiments were carried out at 20 °C using a SpectraMax 384Plus plate reader, and rates were recorded using the SoftMax Pro software package. For all steady-state experiments, data were collected in triplicate and averaged, with n = 3. The value for n refers to the number of individual experiments performed. All data analysis of the steady-state systems were conducted using GraphPad Prism.

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Transient kinetic characterization[1]
Transient kinetic experiments were performed using a stopped-flow apparatus (Hi-Tech Scientific, SF-61 DX2) to determine the effects of mavacamten on myosin association and dissociation from actin filaments, phosphate (Pi) release, and 2′-(or-3′)-O-(N-methylanthraniloyl)-ADP (mant-ADP/ATP) release by myosin. For each data point, transient traces were collected in triplicate and averaged for each experiment, with n = 3. All transient experiments were performed with either varying amounts of mavacamten or single concentrations of mavacamten at varying substrate concentrations to determine a concentration-dependent change in each kinetic parameter, and control experiments were carried out with 2% DMSO final. For mant-ATP or mant-ADP experiments, fluorescence emission was measured through a 400-nm cutoff filter with excitation at 365 nm. The increase in fluorescence upon myosin binding mant-ATP or decrease in fluorescence after release of mant-ADP was monitored as previously described.[1]
The rates of Pi release were measured using the bacterial phosphate-binding protein (PBP) modified with 7-diethyl-amino-3-[[[2-(maleimidyl)ethyl]amino]carbonyl] coumarin (MDCC) dye prepared according to Brune et al. The stopped flow instrument was set up in double mix mode. In this configuration nucleotide free myosin-S1 was mixed with ATP at a 1:1 molar ratio and aged for 2 s to allow for complete hydrolysis. The myosin-nucleotide complex was then rapidly mixed with actin plus MDCC-PBP, and the fluorescence increase due to phosphate binding was measured through a 455-nm cutoff filter with excitation at 425 nm. This system was used to measure the effect of mavacamten by varying the concentration of compound in all syringes and comparing the data to a DMSO control. Before data collection, contaminating phosphate was removed from the system by soaking with a “Pi-mop,” which consisted of purine nucleoside phosphorylase and 7-methylguanosine at concentrations of 1 units/ml and 0.5 mm, respectively. This Pi-mop was also present in all solutions at concentrations of 0.1 units/ml purine nucleoside phosphorylase and 0.25 mm 7-methylguanosine to remove any residual phosphate.[1]
Myosin-S1 association to pyrene-actin filaments was monitored by the quenching of pyrene fluorescence that occurs upon S1 binding to pyrene-actin. The kinetics of ATP-induced acto-S1 dissociation was measured by monitoring the increase in pyrene fluorescence upon mixing pyrene-acto-S1 with increasing concentrations of ATP. Pyrene fluorescence was measured using a 400-nm cutoff filter with excitation at 360 nm. This interaction was also used to monitor the transition from the weakly to strongly bound state of myosin to actin. Briefly, bovine cardiac myosin-S1 and ATP were mixed under single turnover conditions and allowed to age for 2 s to hydrolyze the ATP to ADP-Pi. This mixture was then mixed with pyrene actin in a 1:1 ratio with myosin and 1 mm ADP to shift the equilibrium to the strongly bound state. The quenching of pyrene actin was monitored with varying concentrations of mavacamten, and the reaction amplitudes were analyzed.[1]

Cardiac myofibrils were prepared as previously described. Bovine cardiac tissue was harvested, placed immediately on wet ice, and shipped overnight, and the left ventricle and septum were dissected, frozen in liquid nitrogen, and stored at −80 °C. Human tissue was procured from BioReclamations IVT, and myofibrils were prepared on the day of receipt. Cardiac and skeletal myosin S1 was prepared using a chymotryptic digestion of full-length myosin prepared from bovine cardiac left ventricle and rabbit psoas muscle, respectively. Bovine cardiac HMM was prepared according to Margossian and Lowey. Human cardiac myosin subfragment-1 was expressed in differentiated murine C2C12 myotubes using an adenovirus infection method. The recombinant product utilized a 6×-histidine tag on the essential light chain for initial purification on Ni2+-resin with further purification by anion exchange and size exclusion chromatography. All myofibril and myosin-S1 preparations were brought to 10% sucrose, snap-frozen in liquid nitrogen, and stored at −80 °C. Actin was prepared from a bovine cardiac acetone powder (Pel Freez Biologicals) according to the method of Spudich and Watt. Pyrene actin was prepared according to the method of Criddle et al.[1]

Absorption, Distribution and Excretion
Mavacamten has an estimated oral bioavailability of at least 85% and Tmax of 1 hour. Mavacamten exposures (AUC) increased up to 220% in patients with mild (Child-Pugh A) or moderate (Child-Pugh B) hepatic impairment. The effect of severe (Child-Pugh C) hepatic impairment is unknown.
Following a single 25 mg dose of radiolabeled mavacamten, 7% of the dose was recovered in feces (1% unchanged) and 85% in urine (3% unchanged).
Through the use of a simple 4-species (mouse, rat, dog, and cynomolgus monkey) allometric scaling of unbound blood steady-state volume of distribution, the human volume of distribution of mavacamten is predicted to be 9.5 L/kg.
Mavacamten demonstrates a long terminal half-life and thus low clearance, with an estimated plasma clearance using human hepatocytes of less than 4.9 mL/min/kg. Assuming a one-compartment model, using simple allometric scaling of unbound blood clearance of mouse, rat, dog, and cynomolgus monkey, human plasma clearance of mavacamten is estimated to be 0.51 mL/min/kg.

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Metabolism / Metabolites
Mavacamten is extensively metabolized, primarily through CYP2C19 (74%), CYP3A4 (18%), and CYP2C9 (8%).

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Biological Half-Life
Mavacamten has a variable terminal t1/2 that depends on CYP2C19 metabolic status. Mavacamten's terminal half-life is 6-9 days in CYP2C19 normal metabolizers (NMs), which is prolonged in CYP2C19 poor metabolizers (PMs) to 23 days.

Protein Binding
Plasma protein binding of mavacamten is between 97 and 98%.

[1]. A small-molecule modulator of cardiac myosin acts on multiple stages of the myosin chemomechanical cycle. J Biol Chem. 2017 Oct 6;292(40):16571-16577.

[2]. A Small Molecule Inhibitor of Sarcomere Contractility Acutely Relieves Left Ventricular Outflow Tract Obstruction in Feline Hypertrophic Cardiomyopathy. PLoS One. 2016 Dec 14;11(12):e0168407.

[3]. A small-molecule inhibitor of sarcomere contractility suppresses hypertrophic cardiomyopathy in mice. Science. 2016 Feb 5;351(6273):617-21.

Mavacamten is a myosin inhibitor indicated for the treatment of adults with symptomatic New York Heart Association (NYHA) class II-III obstructive hypertrophic cardiomyopathy (HCM). It received initial US FDA approval in 2022, and it is one of the first myosin inhibitors to be used in humans. Mavacamten was also approved by Health Canada in October 2022 and by EMA in July 2023 for the same indication.
Mavacamten is a Cardiac Myosin Inhibitor. The mechanism of action of mavacamten is as a Cardiac Myosin Inhibitor.

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Drug Indication
Mavacamten is indicated for the treatment of adults with symptomatic New York Heart Association (NYHA) class II-III obstructive hypertrophic cardiomyopathy (HCM) to improve functional capacity and symptoms by the FDA, Health Canada, and the EMA.
Treatment of symptomatic obstructive hypertrophic cardiomyopathy.
Treatment of hypertrophic cardiomyopathy

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Mechanism of Action
Myosin is a family of enzymes that can produce mechanical output by an ATP-mediated cyclic interaction with actin. When ATP is bound to the myosin head, it is hydrolyzed into ADP and organophosphate by myosin ATPase activity, and the energy produced from the reaction is stored in the myosin head. As the organophosphate dissociates from myosin, it shifts myosin into a strong binding state to actin, thus creating a myosin-actin complex otherwise known as "cross-bridging".Dissociation of the organophosphate also causes a conformation change in myosin that creates strain in the actin-myosin bridge that can only be released once the actin and myosin filaments slide past each other, thus shortening the sarcomere and create a muscle contraction. Once the sliding is completed, ADP is released to create further movement of the myosin head. Although this ADP release-induced movement is minor and unlikely to contribute to the sarcomere movement, researchers have hypothesized that this movement is likely essential in limiting the sliding velocity of actin.Finally, myosin then bind to a new ATP molecule to initiate the chemomechanical cycle again. Mavacamten reduces sarcomere hypercontractility by acting as an allosteric and reversible modulator of the beta-cardiac isoform of myosin to reduce its ATPase activity, thus reducing actin-myosin cross bridging. Specifically, mavacamten inhibits the phosphate release, the cycle's rate-limiting step, without affecting the ADP release rate in actin-bound myosin.Also, mavacamten inhibits binding of ADP-bound myosin to actin as well as ADP release to prime the myosin head to initiate turnover.Recently, it was also discovered when myosin is not in its active state to interact with actin, it exists in equilibrium between 2 energy sparing states: a disordered relaxed state, where interaction between actin and myosin by the thin filament regulatory proteins, and a super relaxed state, where significant myosin head-to-head interaction lengthen ATP turnover rate.. Mavacamten's binding to myosin can shift the equilibrium toward the super relaxed state, effectively exerting both a basal and actin-activated ATP inhibition.

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Pharmacodynamics
Mavacamten is a myosin inhibitor to prevent muscle hypercontractility. It binds to myosin and inhibits myosin interaction with actin at various stages of the thermomechanical cycle. Mechanistic studies show that mavacamten can inhibit myosin in both its active and relaxed form, thus effectively alleviating excess sarcomere power, a hallmark of hypertrophic cardiomyopathy. In the EXPLORER-HCM trial, patients achieved reductions in mean resting and provoked (Valsalva) LVOT gradient by Week 4 which were sustained throughout the 30-week trial. At Week 30, the mean (SD) changes from baseline in resting and Valsalva LVOT gradients were -39 (29) mmHg and -49 (34) mmHg, respectively, for the CAMZYOS group and -6 (28) mmHg and -12 (31) mmHg, respectively, for the placebo group. The reductions in the Valsalva LVOT gradient were accompanied by decreases in LVEF, generally within the normal range. Eight weeks after discontinuation of CAMZYOS, mean LVEF and Valsalva LVOT gradients were similar to baseline. Echocardiographic measurements of the cardiac structure showed a mean (SD) reduction from baseline at Week 30 in left ventricular mass index (LVMI) in the mavacamten group (-7.4 [17.8] g/m2) versus an increase in LVMI in the placebo group (8.9 [15.3] g/m2). There was also a mean (SD) reduction from baseline in left atrial volume index (LAVI) in the mavacamten group(-7.5 [7.8] mL/m2) versus no change in the placebo group (-0.1 [8.7] mL/m2). The clinical significance of these findings is unknown. A reduction in a biomarker of cardiac wall stress, NT-proBNP, was observed by Week 4 and sustained through the end of treatment. At Week 30 compared with baseline, the reduction in NT-proBNP after mavacamten treatment was 80% greater than for placebo (proportion of geometric mean ratio between the two groups, 0.20 [95% CI: 0.17, 0.24]). The clinical significance of these findings is unknown. In healthy volunteers receiving multiple doses of mavacamten, a concentration-dependent increase in the QTc interval was observed at doses up to 25 mg once daily. No acute QTc changes have been observed at similar exposures during single-dose studies. The mechanism of the QT prolongation effect is not known. A meta-analysis across clinical studies in HCM patients does not suggest clinically relevant increases in the QTc interval in the therapeutic exposure range. In HCM, the QT interval may be intrinsically prolonged due to the underlying disease, in association with ventricular pacing, or in association with drugs with the potential for QT prolongation commonly used in the HCM population. The effect of coadministration of mavacamten with QT-prolonging drugs or in patients with potassium channel variants resulting in a long QT interval has not been characterized.

C15H19N3O2

273.336

273.147

C, 65.91; H, 7.01; N, 15.37; O, 11.71

1642288-47-8

Mavacamten-d6;2453251-18-6;Mavacamten-d1;2453251-02-8;Mavacamten-d5;2453251-00-6

117761397

White to off-white solid powder

1.2±0.1 g/cm3

1.591

2.65

2

3

4

20

411

1

O=C1NC(=CC(N1C(C)C)=O)N[C@@H](C)C1C=CC=CC=1

RLCLASQCAPXVLM-NSHDSACASA-N

InChI=1S/C15H19N3O2/c1-10(2)18-14(19)9-13(17-15(18)20)16-11(3)12-7-5-4-6-8-12/h4-11,16H,1-3H3,(H,17,20)/t11-/m0/s1

(S)-3-isopropyl-6-((1-phenylethyl)amino)pyrimidine-2,4(1H,3H)-dione

MYK 461; SAR-439152; MYK-461; SAR 439152; SAR439152; Camzyos; MYK-461; SAR-439152; 6-[[(1S)-1-phenylethyl]amino]-3-propan-2-yl-1H-pyrimidine-2,4-dione; Mavacamten [INN]; Mavacamten [USAN]; MYK461; Mavacamten

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ~83.33 mg/mL (~304.87 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (9.15 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.08 mg/mL (7.61 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)