IDO1 and cancer: designed a caspase‐activatable, multifunctional, prodrug nanoplatform for inhibiting cancer metastasis and recurrence.[156] The caspase‐responsive multifunctional prodrug (PpIX‐1MT) was synthesized by a caspase‐responsive peptide sequence modified with IDO inhibitor (1MT) and photosensitizer (PpIX), and the PpIX‐1MT self‐assembled into nanoparticles without the addition of any other excipients (Figure 17a).