Project Summary/ Abstract Light is an exceptional tool in disease treatment, offering precise controllability in treatment time and location. Unlike UV light, longer visible and near infrared (IR) light is not toxic and reaches deeper tissues than UV for clinical applications. However, chemical linkers that are cleavable by such biocompatible light are very scarce. Long term goals are to develop chemical linkers that are cleaved by visible and near IR light for light-controlled drug delivery, and to design and synthesize chemical conjugates that are used for pho-biomodulation. In the previous project, a drug conjugate platform and photo-release strategy for site specific drug delivery were established. Click and photo-unclick chemistry was demonstrated, where singlet oxygen (SO)-cleavable linker is synthesized via amine-yne click reaction and cleaved by SO. The drug conjugates are composed of drug, SO- cleavable linker, photosensitizer and cancer-targeting group. When illuminated with red light (690 nm), the conjugates generate SO and release drug only in the illuminated region and treat the disease locally. In the next 5 years, a bolder photo-biomodulation strategy will be established using the light-responsive drug conjugate platform. Overarching hypothesis is that local photo-biomodulation using visible and near IR light-responsive conjugates can make systemic pharmacological effects via activation of immune system. Main goals in this application are to design and prepare SO-cleavable conjugates of immunostimulant drugs and to prove that this visible-light responsive conjugates can be used for generating systemic and tumor-specific anticancer effects. The conjugates are activated by a focused local illumination, release drugs site-specifically, and stimulate immune system to trigger systemic and tumor-specific immune responses. The systemic antitumor effect is further enhanced by the combination with systemically administered drugs with non-overlapping mechanisms with the local photo-biomodulation. The goals are realized with 3 specific aims: (1) Design and prepare SO- activatable conjugates of immune-stimulating drugs and determine systemic antitumor effects, (2) Determine the mechanisms of systemic effects of the photo-biomodulation and establish the immuno-pharmacodynamics, (3) Determine the enhanced systemic antitumor effect of the local photo-biomodulation by adding clinically available checkpoint inhibitors. Pharmacokinetic and immune-pharmacodynamic modeling is used for analyzing and simulating dynamic changes of conjugates, released drugs, and immune cells in various tissues to gain mechanistic insight at the systemic level. Major deliverables are (i) red-light responsive conjugates of immunostimulant drugs, (ii) immune-pharmacodynamic models following photo-biomodulation, and (iii) validation of our local photo-biomodulation for systemic effects. The strategy is tested using breast and colon cancer animal models but it could be applic...