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. 2025 Aug 29.
doi: 10.1007/s13346-025-01950-5. Online ahead of print.

Mesoporous silica nanoparticles with an azobenzene gatekeeper as hypoxia-responsive nanocarriers for targeted doxorubicin delivery

Paula Rodrigo-Martínez  1 , Mariana Barros  1 , María Carmen Terencio  1   2 , Eva Garrido  1   3 , Pau Arroyo  1   4 , Jose A Sáez  1   4 , Margarita Parra  1   4   3 , Pablo Gaviña  5   6   7
Affiliations

Mesoporous silica nanoparticles with an azobenzene gatekeeper as hypoxia-responsive nanocarriers for targeted doxorubicin delivery

Paula Rodrigo-Martínez et al. Drug Deliv Transl Res. .

Abstract

Hypoxia is a key feature of solid tumors, contributing to therapeutic resistance and poor prognosis. Targeting hypoxic environments presents an opportunity to enhance drug delivery selectivity and improve treatment outcomes. Among nanocarriers, mesoporous silica nanoparticles (MSNs) have demonstrated great potential for drug delivery; however, achieving precise control over drug release remains a challenge. In this work, we develop an enzyme-responsive MSN system for targeted drug delivery in hypoxic tumors. MSNs were loaded with the chemotherapeutic drug doxorubicin (Dox) and capped with an azobenzene (Azo) gatekeeper. The bulky Azo group acts as a responsive molecular gate that remains closed under normoxic conditions but undergoes enzymatic cleavage by azoreductases, which are overexpressed in hypoxic tumor microenvironment. This cleavage triggers the uncapping of the pores, inducing the release of Dox specifically in the hypoxic region, minimizing premature drug leakage and off-target toxicity. In vitro studies with A549 cells (which overexpress azoreductase) and THP-1 cells (with low expression of azoreductases) under normoxic and hypoxic conditions, demonstrated a significant increase in Dox release and cytotoxicity in the A549 cells compared with the THP-1, which was more pronounced under hypoxia. These findings highlight the potential of enzyme-responsive MSNs as a promising strategy for selective drug delivery in hypoxic tumors.

Keywords: Azobenzene gatekeeper; Azoreductases; Controlled delivery; Doxorubicin; Hypoxia-responsive; Mesoporous silica nanocarriers.

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Conflict of interest statement

Declarations. Ethics approval and consent to participate: Not applicable. Consent for publication: All the authors gave their consent for publication of this manuscript in this journal and the work has not been publishedand is not being considered for publication elsewhere. Competing interests: The authors have no financial interests to disclose.

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