Macropinocytic Uptake and pH‐Responsive Endolysosomal Processing Drive Sustained Chemotherapeutic Efficacy of High‐Load Core@Shell Nanocarriers in Colorectal Cancer

Poor tumor targeting, strong toxic side effects, and high drug resistance remain clinical challenges for conventional chemotherapy. Here, it is reported that drug-cocktail core@shell nanocarriers are developed for the codelivery of lipophilic irinotecan (ITC) and the hydrophilic 5-fluorouracil (5-FU) metabolite (FdUMP), a commonly used combination in chemotherapy regimens for colorectal cancer. With a drug loading of 57% by mass, these nanocarriers achieve one of the highest reported drug payloads for a chemotherapeutic drug cocktail. Crucially, using a probe-based imaging strategy with mechanistically responsive fluorescent reporters, we found that after slow uptake predominantly via macropinocytosis, the nanocarriers rapidly traffic to endolysosomal compartments, where the acidic environment triggers sustained drug release. In alignment with the slow uptake and trafficking behavior, these nanocarriers induce a delayed yet prolonged cytotoxic effect in colorectal cancer cells. These findings provide the first direct evidence linking slow uptake, intracellular trafficking, and progressive nuclear delivery of nanocarrier cargo to the delayed yet sustained cytotoxic response. Together, this work highlights both the therapeutic potential of these nanocarriers and the broad applicability of the probe-based imaging approach to elucidate the mechanistic intracellular trafficking and nuclear delivery of different types of nanoparticles delivering cargoes beyond cancer chemotherapy in various cellular models.