# The colloidal stability of albumin-based drug delivery systems has a profound effect on tumoricidal activity

## TL;DR

This paper shows how improving the stability of albumin-based drug delivery systems can significantly enhance their effectiveness in treating tumors.

## Contribution

The study reveals that pharmaceutical HSA is structurally denatured and introduces HSA-PLA nanoparticles with improved colloidal stability and antitumor efficacy.

## Key findings

- Pharmaceutical HSA is structurally denatured compared to native HSA, leading to rapid clearance and poor drug delivery.
- HSA-PLA nanoparticles exhibit improved colloidal stability and reduced premature drug release compared to Abraxane.
- HSA-PLA nanoparticles show greater tumor exposure and superior antitumor efficacy in tumor models.

## Abstract

Human serum albumin (HSA) has attracted significant attention in drug delivery since the approval of Abraxane in 2005. Abraxane is a nanoparticle albumin-bound paclitaxel (nab-PTX) formulation. Although HSA offers advantages such as prolonged circulation time (half-life ~19 days) and intrinsic hydrophobic pockets, the translation of other HSA-based nanomedicines remains limited. In fact, the significant differences between native and pharmaceutical HSA in protein structure and biological interactions could hinder their translational use in drug delivery. In this study, we demonstrate that pharmaceutical HSA (α-helix = 17%) is structurally denatured compared with native HSA (α-helix = 68%), leading to rapid clearance (<1 h) from the circulation and that drug loading is driven by pharmaceutical HSA’s amphiphilicity rather than by its hydrophobic pockets. Here, we revealed that Nab-PTX is composed of protein-coated PTX solid cores. These nanosystems have insufficient surface charge (ζ = −13.7 mV), leading to aggregation, and low colloidal stability, resulting in premature drug release upon dilution (<0.1  mg/mL). To address these shortcomings, we developed HSA-polylactic acid (HSA-PLA) nanoparticles with enhanced negative surface charge (ζ = −27.4 mV) and improved colloidal stability to reduce the premature release of encapsulated PTX upon dilution (<0.01  mg/mL). In tumor models, comparative pharmacokinetics, biodistribution, and efficacy studies demonstrated that HSA-PLA (PTX) nanoparticles reduce premature drug release, resulting in greater tumor exposure (129 ± 3 vs. 90 ± 12 µg·h/g, p < 0.01) and superior antitumor efficacy compared with Abraxane. These improvements further suggest that optimization may require only a simple modification when guided by proper theoretical principles.

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