KPKQ

Photodynamic therapy (PDT) holds potential in cancer treatment, but the development of photosensitizers with high-efficient PDT remains a challenge. Herein, we designed and synthesized a series of novel tricyclic carbazole/quinolinium hybrids-KNKQ, KAKQ, and KPKQ-as photosensitizers, and subsequently evaluated their photodynamic anticancer activities and the associated mechanisms. Among them, KPKQ exhibited the most prominent one-/two-photon activated photodynamic characteristics, generating •O₂^-, •OH, and ¹O₂. Particularly, the ¹O₂ quantum yield of KPKQ was 3∼9-fold stronger than KNKQ and KAKQ. Most interestingly, KPKQ demonstrated nanomolar-level and hypoxic-overcoming single-photon phototoxicities with IC₅₀ values of 27∼43 nM (PIs = 46-54), significantly surpassing existing tricyclic carbazole photosensitizers, and also exerted potent photodynamic therapeutic effects (IC₅₀s = 0.13-0.20 μM) via two-photon excitation at 808 nm. Furthermore, KPKQ significantly promoted mitochondrial damage, cell apoptosis, and DNA lesion via reducing Bcl-2 level and increasing the levels of Bax, cleaved-Caspase-3, and γ-H2AX. Concurrently, KPKQ lowered GSH/GPX4 levels and elevated malondialdehyde to trigger ferroptosis. Additionally, KPKQ powerfully promoted autophagy through boosting LC3-II and Beclin-1 expression, thereby demonstrating a multiple anti-tumor mechanism. Ultimately, KPKQ achieved a 90.7 % tumor-inhibitory rate through in vivo PDT. Our findings may provide a promising framework for the discovery of novel tricyclic carbazole photosensitizers with high PDT efficacy.