¹³¹I Induced In Vivo Proteolysis by Photoswitchable azoPROTAC Reinforces Internal Radiotherapy

Photopharmacology, incorporating photoswitches such as azobenezes into drugs, is an emerging therapeutic method to realize spatiotemporal control of pharmacological activity by light. However, most photoswitchable molecules are triggered by UV light with limited tissue penetration, which greatly restricts the in vivo application. Here, this study proves that ¹³¹I can trigger the trans-cis photoisomerization of a reported azobenezen incorporating PROTACs (azoPROTAC). With the presence of 50 µCi mL^{-1 131}I, the azoPROTAC can effectively down-regulate BRD4 and c-Myc levels in 4T1 cells at a similar level as it does under light irradiation (405 nm, 60 mW cm^-2). What's more, the degradation of BRD4 can further benefit the ¹³¹I-based radiotherapy. The in vivo experiment proves that intratumoral co-adminstration of ¹³¹I (300 µCi) and azoPROTC (25 mg kg^-1) via hydrogel not only successfully induce protein degradation in 4T1 tumor bearing-mice but also efficiently inhibit tumor growth with enhanced radiotherapeutic effect and anti-tumor immunological effect. This is the first time that a radioisotope is successfully used as a trigger in photopharmacology in a mouse model. It believes that this study will benefit photopharmacology in deep tissue.