Elucidating the Solvent-Dependent Solvation and Structural Stability of Irinotecan: A Molecular Simulation Study

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Drug Discovery

Background:

• The clinical use of irinotecan, a chemotherapeutic agent, is significantly limited by its poor and inconsistent solubility.
• Understanding the fundamental physicochemical factors governing irinotecan's solubility is crucial for optimizing its formulation and therapeutic efficacy.

Purpose of the Study:

• To elucidate the solvation thermodynamics of irinotecan using advanced computational methods.
• To identify key molecular interactions and solvent properties that influence irinotecan solubility.
• To develop a predictive framework for optimizing drug formulations.

Main Methods:

• Molecular dynamics (MD) simulations were performed to investigate irinotecan's behavior in various solvents.
• Free energy calculations were employed to quantify solvation thermodynamics.
• Structural analyses (connection matrices, radial distribution functions) and the macroscopic solubility parameter (MOSCED) framework were used for validation.

Main Results:

• Irinotecan's solvation is determined by a balance between Lennard-Jones (cavity formation/dispersion) and electrostatic interactions.
• Polar protic solvents, despite strong electrostatics, are unfavorable due to high cavity formation costs.
• Polar aprotic solvents (e.g., DMSO, pyridine) provide favorable solvation by optimizing this balance.
• Solvent reorganization energy significantly impacts irinotecan's solution-phase behavior, explaining its higher solubility in nonpolar solvents like cyclohexane compared to water.

Conclusions:

• A comprehensive physicochemical framework for understanding irinotecan solvation has been established.
• The findings highlight the critical role of solvent properties in drug solubility and formulation.
• This study provides insights for designing and optimizing formulations of irinotecan and similar complex drug molecules.