Mechanisms Contributing to Acquired Activated Protein C Resistance in Patients Treated with Thalidomide: A Molecular Dynamics Study

Introduction: There is a high incidence of venous thromboembolism (VTE) in patients with Multiple Myeloma (MM), however; until now, the exact mechanisms behind VTE in MM are unknown, and some of the elements that may play a significant role are the treatment with an immunomodulator (IMiD) and acquired resistance to activated protein C (APC). Objective: The study aims to reveal the possible mechanisms linked to the reduced antithrombotic activity of APC associated with thalidomide. Methods: The molecular docking approach was used to ascertain the in silico inhibitory potential of thalidomide on the APC protease domain in the architecture of the catalytic triad and its interaction with major substrate binding sites. Results: The coupling showed that the inhibitory activity of thalidomide depends on the induction of structural changes in the protease domain of APC, at the level of the Ser/His/Asp catalytic triad, as a result of a significant increase between the distances of CαAsp102 and Cα Ser195 (11.175 angstroms, increase 14.83%) and between CαSer195 and CαHis57 (9.478 angstroms, increase 13.78 %). This can result in an inefficient transfer of the proton between these residues, the other possible mechanism of inhibition, is a potential reduced binding of the substrate as a result of a direct interaction through a carbon-hydrogen bond on His57, an H-bond on Arg306, and a carbon hydrogen bond on Arg506. Conclusion: We demonstrate the in silico inhibitory potential of thalidomide on APC, through two possible inhibition mechanisms, a pathophysiologically relevant finding to understand the factors that can affect the stability and functions of APC in vivo.