Profiling the Interaction between Human Serum Albumin and Clinically Relevant HIV Reverse Transcriptase Inhibitors

Area of Science:

• Biochemistry
• Pharmacology
• Molecular Biophysics

Background:

• Tenofovir (TFV), tenofovir disoproxil fumarate (TDF), and tenofovir alafenamide (TAF) are crucial HIV reverse transcriptase inhibitors.
• Human serum albumin (HSA) is the primary carrier for exogenous compounds, yet its interactions with TFV, TDF, and TAF are not fully understood.
• Understanding these interactions is vital for predicting drug pharmacokinetics and efficacy.

Purpose of the Study:

• To characterize the biophysical interactions between HSA and TFV, TDF, and TAF.
• To elucidate the binding mechanisms, thermodynamics, and potential binding sites.
• To correlate binding characteristics with the drugs' pharmacokinetic profiles.

Main Methods:

• Utilized UV-Vis, steady-state, and time-resolved fluorescence spectroscopy.
• Employed isothermal titration calorimetry (ITC) for thermodynamic analysis.
• Performed in silico calculations, including cross-docking, and experimental drug-displacement assays.

Main Results:

• Identified weak, spontaneous binding interactions between HSA and TFV, TDF, and TAF.
• Determined that HSA/TFV and HSA/TDF binding are enthalpically and entropically driven, while HSA/TAF is entropically dominated.
• Site I is the likely binding pocket for TFV, whereas sites II and III accommodate TAF, with binding affinity potentially affected by co-administered drugs.

Conclusions:

• The weak binding of HSA to TFV, TDF, and TAF contributes to their short residence time in the bloodstream.
• Positive cooperativity observed for TAF and TDF with other drugs may enhance their pharmacokinetic profiles.
• These findings provide crucial insights into the pharmacodynamics of key antiretroviral therapies.