Pre-clinical Formulation Development of an in situ Meglumine Salt of AZD5991: A Novel Macrocyclic Mcl-1 Inhibitor

Purpose: AZD5991 is a potent and selective macrocyclic inhibitor of Mcl-1 in clinical development. Developing an intravenous solution formulation for AZD5991 proved to be challenging primarily due to the poor intrinsic solubility of AZD5991. In this article are described studies performed to select a suitable crystalline form and to assess physicochemical properties of AZD5991 to aid in the design of a solution formulation for preclinical studies.

Methods: It is preferable that the preclinical formulation has a line of sight for clinical formulation. For AZD5991, a concentration of at least 20 mg/ml was required for toxicology studies. Toward this goal, extensive pre-formulation characterization of AZD5991 including solid form analysis, pH-solubility profiling and solubility determination in cosolvents and other solubilizing media were carried out.

Results & discussion: Crystalline Form A, which is more stable in aqueous solution and possesses acceptable thermal stability, was selected for preclinical and clinical development of AZD5991. Extensive solubility evaluation revealed an interesting pH-solubility profile that significantly enhances solubilization at pH > 8.5 to allow solution concentrations of at least 30 mg/ml by in situ meglumine salt formation.

Conclusion: Developing pre-clinical formulations to support in vivo studies requires a good understanding of the physicochemical properties of the drug candidates. Candidates with challenging pharmaceutic properties like the novel macrocycle molecule AZD5991, demand extensive characterization in its polymorph landscape, solubility profile and suitability evaluation of the excipients. Meglumine, a pH-adjusting and solubilizing agent, was found to be the best choice for formulating AZD5991 into an intravenous product to support preclinical studies.