A Hsp70-dependent bioorthogonal platform for tumor-specific drug release

Here, we present a novel Hsp70-dependent bioorthogonal prodrug platform that integrates tumor-selective accumulation with inverse electron-demand Diels-Alder (IEDDA) chemistry to enable spatiotemporally controlled drug release. We constructed a tetrazine (Tz)-functionalized Hsp70 inhibitor Tz-S1g, along with trans-cyclooctene (TCO)-caged prodrugs TCO-DOX and TCO-MZ1. Tz-S1g selectively accumulates in tumor cells via high-affinity binding to overexpressed and activated Hsp70, which is characteristic of malignant cells. In tumor microenvironments, Tz-S1g rapidly triggers the IEDDA reaction to liberate active DOX and MZ1, and fully restores cytotoxicity, and BRD4 degradation in tumor cells, whereas minimal activation and cytotoxicity occur in normal cells. In vivo studies have shown that this strategy can effectively inhibit tumor growth in both B16 tumor-bearing mice and MDA-MB-231 tumor-bearing mice, while avoiding systemic toxicity. This Hsp70 bioorthogonal strategy offers a general, safe, and efficient platform for the tumor-specific activation of chemotherapeutic agents and PROTACs, significantly improving therapeutic selectivity and safety.