CAT and neoplasm: As both 5-ALA and CAT are co-loaded into CCPCA NPs, we hypothesized that continuous O2 generation by catalytic endogenous H2O2 decomposition will alter the physiological environment of PpIX biosynthesis and alleviate tumor hypoxia and mediate the cascaded downregulation of HIF-1α and FECH to ultimately shutdown the outflow door of PpIX.