Assembly and stability of trastuzumab-conjugated and unmodified poly(L-histidine)-poly(ethylene glycol) micelles for targeting HER2-positive cells

• Poly(L-histidine)-poly(ethylene glycol) micelles with dual functionality for fluorescent tracing and targeted properties. • Investigation of micelle stability, influenced by covalent or physical loading and targeted moiety attachment (trastuzumab). • Efficacy of covalent trastuzumab conjugation versus free trastuzumab against HER2+ was assessed. • The findings may influence cancer therapeutics, aiding the development of targeted treatments for HER2+ breast cancer cells. Micelles have emerged as promising nanocarriers in biomedical research, offering a versatile platform for targeted drug delivery. In this study, we designed and investigated a poly(L-histidine)-poly(ethylene glycol) (PHis-PEG) micelle system capable of incorporating a fluorophore tag within its core through covalent binding, while simultaneously facilitating the surface attachment of the monoclonal antibody trastuzumab. Our investigation highlighted the critical aspect of micelle stability, particularly at concentrations below the critical micelle concentration (CMC), essential for ensuring efficacy in in vivo applications. We observed that covalent or physical loading of hydrophobic molecules into the micelle core enhances stability below the CMC, albeit with destabilization upon trastuzumab conjugation at investigated concentrations. Furthermore, stability studies conducted in the presence of bovine serum albumin, simulating the protein-rich environment of blood, provided insights into the behaviour of PHis-PEG micelles under physiological conditions. Our findings revealed the time-based stability of unmodified micelles versus trastuzumab-functionalized micelles loaded with hydrophobic molecules, underlining their potential for targeted drug delivery. Additionally, functional efficacy assessment post-covalent conjugation of trastuzumab in comparison to free trastuzumab demonstrated substantial efficacy against two HER2 receptor-overexpressing cell lines, highlighting the clinical relevance of our developed PHis-PEG micelle system in targeted cancer therapy. This study elucidates the advantages and limitations of PHis-PEG micelles, emphasizing their potential as pH-responsive targeted carriers and advancing the understanding of stimuli-responsive cancer drug delivery systems.