A pH-responsive stellate mesoporous silica based nanophotosensitizer for in vivo cancer diagnosis and targeted photodynamic therapy

Development of a photosensitizer that can achieve tumor specificity, improve therapeutic efficacy, and reduce side effects remains a challenge for photodynamic therapy (PDT). In this work, a pH-sensitive activatable nanophotosensitizer (SMSN-ZnPc1) has been elaborately designed, which could be readily prepared by using a functionalized zinc(ii) phthalocyanine (ZnPc) to conjugate with stellate mesoporous silica nanoparticles (SMSNs) through an acid-sensitive hydrazone bond. Meanwhile, a non-activatable analogue SMSN-ZnPc2 has also been prepared as a negative control. The fluorescence emission and singlet oxygen generation of the photosensitizer are essentially quenched in the intact nanophotosensitizer. However, these properties of SMSN-ZnPc1 can be restored greatly both in acidic solutions and at the cellular level. More importantly, after intravenous administration, SMSN-ZnPc1 can also be selectively activated at the tumor site and exhibit efficient tumor growth inhibition in S180 rat ascitic tumor-bearing KM mice with negligible systemic toxicity. It thus may serve as a promising nanoplatform for cancer diagnosis and targeted PDT.