Human Serum Albumin Nanoparticles as 3,6-Diazaphenothiazine Delivery System: Preparation and Interaction Studies

Plasma proteins are becoming more and more popular among researchers due to their minimal toxicity and immunogenicity. The largest percentage of plasma proteins is human serum albumin (HSA). HSA is widely used as a drug carrier due to its biocompatibility and specific affinity to cancer cells. 10H-3,6-diazaphenothiazine (DAPT) is a newly synthesized phenothiazine derivative with promising anticancer activity. The main aim of this study was to encapsulate the DAPT into human serum albumin nanoparticles (DAPT-HSA-NPs) as well as to study DAPT interaction with HSA based on spectroscopic, microscopic, and calorimetric techniques. HSA nanoparticles with DAPT (DAPT-HSA-NPs) were prepared using the desolvation method, and this reaction was accompanied by a thermal transition. High encapsulation efficiency of DAPT into the HSA-NPs (DAPT-HSA-NPs) was obtained (~100%) and its release kinetics from the DAPT-HSA-NP system followed the zero-order kinetic model. Both nanoparticle preparation (HSA-NPs) and HSA interaction with DAPT (DAPT-HSA) resulted in changes in the HSA secondary structure. Moreover, the process of DAPT binding to HSA was exothermic (ΔH [kcal·mol^-1] < 0), and DAPT probably formed a static complex with HSA (kq [L·mol^-1·s^-1] > 10¹²) with moderate affinity (K_a [L·mol^-1] of the order of 10⁴). Despite reports on human serum albumin nanoparticles (HSA-NPs) and 10H-3,6-diazaphenothiazine (DAPT), no studies on DAPT encapsulation into HSA-NPs have been published. Therefore, HSA-NPs as a 3,6-diazaphenothiazine delivery system, including preparation methods and interaction analysis, have been evaluated.