Permeability and Metabolic Stability of ALK2 Inhibitors

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Diffuse Intrinsic Pontine Glioma (DIPG) is a rare and aggressive pediatric brain cancer with few effective treatment options. M4K Pharma is developing selective ALK2 inhibitors as potential therapies for DIPG through an open science approach, with the goal of accelerating the discovery of safe and effective treatments for children affected by this devastating disease. As part of preclinical development, candidate compounds undergo comprehensive absorption, distribution, metabolism, and excretion (ADME) studies to evaluate their pharmacokinetic properties, optimize drug-like characteristics, and support the selection of compounds with favorable profiles before advancing toward clinical studies. Permeability Permeability is a key determinant of drug absorption, tissue distribution, and therapeutic efficacy. For treatments targeting central nervous system diseases such as DIPG, evaluating membrane permeability and blood-brain barrier (BBB) penetration is important to determine whether candidate compounds can reach therapeutic concentrations within the brain. In vitro permeability assays are therefore routinely used during preclinical development to predict in vivo drug disposition and optimize lead compounds. The following entries summarize permeability studies performed for a number of ALK2 inhibitor compounds developed by M4K Pharma. These datasets include MDCK-MDR1 permeability assays, comparative analyses with Caco-2 and SwissADME predictions, and assessments of apparent permeability, efflux ratios, and MDR1 substrate status. Together, these studies evaluate the potential for gastrointestinal absorption and BBB penetration while supporting in vitro-in vivo correlation (IVIVC) during lead optimization. The results provide a comprehensive assessment of compound permeability and transporter-mediated efflux, helping identify ALK2 inhibitors with favourable brain penetration profiles. These datawere used to prioritize the selection of candidate compounds with favourable permeability and efflux profiles for further preclinical development as potential therapies for DIPG. Microsomal Stability Microsomal stability studies evaluate how readily a compound is metabolized by enzymes present in liver microsomes, making it an important component for preclinical ADME characterization. Measuring the remaining parent compound after incubation provides insight into metabolic stability and can help identify compounds susceptible to hepatic metabolism. Furthermore, assessing microsomal stability across species also helps identify interspecies differences in metabolism and supports the selection of compounds with favourable pharmacokinetic properties for further development. The following data summarize microsomal stability studies conducted for the ALK2 inhibitor compounds in mouse and human liver microsomes. These data were used to compare the relative metabolic stability of the compounds and support the selection of candidates for further preclinical development. Metabolism Drug metabolism is a critical component of preclinical drug development, as it influences a compound's pharmacokinetic properties, efficacy, safety, and potential for drug-drug interactions. Characterizing metabolic pathways and identifying metabolites across preclinical species and humans supports the selection of compounds with favourable metabolic stability and translational potential before clinical evaluation. As a representative example of an ALK2 inhibitor, the metabolism of M4K2281 was evaluated in hepatocytes from multiple species, including mouse, rat, dog, minipig, monkey, and human. , including identification of major metabolites. The predominant metabolite of M4K2281 was M17, formed by mono-oxygenation, observed in rat, dog, minipig, monkey, and human hepatocytes and accounted for approximately 52% of the human metabolite profile. N-Demethylation to M4K2308 (M14), was also a significant metabolite, accounting for approximately 13% in human hepatocytes and 30% in monkey hepatocytes. Several minor metabolites arising from N-/O-demethylation, oxygenation, and sulfation were identified, generally at low levels. Overall, the results demonstrate extensive metabolism of M4K2281, with no apparent human-specific major metabolite, and demonstrate the major human metabolite M17 is also formed extensively cross-species. The results provide a comprehensive pharmacokinetic and metabolic characterization of these ALK2 inhibitors, enabling assessment of species differences, biotransformation pathways, and exposure profiles to support the translational development of ALK2 inhibitor candidates. Keyword Definition ALK2 Activin receptor-like kinase 2, the therapeutic target of the compounds evaluated. ACVR1 Gene encoding the ALK2 receptor; frequently altered in DIPG. ADME Absorption, distribution, metabolism, and excretion properties used to characterize drug candidates. Drug Metabolism Enzymatic biotransformation of compounds and formation of metabolites. Metabolic Stability Measure of how readily a compound is metabolized over time. Microsomal Stability Assessment of compound stability and metabolic turnover using liver microsomes. Caco-2 Assay In vitro cell-based model commonly used to assess intestinal permeability and drug transport. MDR1 / P-glycoprotein (P-gp) Efflux transporter that can restrict intracellular accumulation and brain penetration of drug compounds. In Vitro–In Vivo Correlation (IVIVC) Relationship between laboratory measurements and observed drug behaviour in vivo.

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