Tumor Site-Dependent Transport Properties Determine Nanotherapeutics Delivery and Its Efficacy.

Insufficient delivery of systemically administered anticancer drugs to tumors can compromise therapeutic efficacy and develop drug delivery-based therapeutic resistance. Nanotherapeutics such as PEGylated liposomal doxorubicin (PLD) are designed to preferentially accumulate in tumors utilizing enhanced permeation and retention effect. However, their antitumor effects and resulting clinical outcomes are modest and heterogeneous among tumors. Here, we aimed to investigate whether the amount and efficacy of PLD delivered to tumors are tumor site dependent. We established orthotopic primary tumor or liver metastases models of murine breast cancer using 4 T1 cells. PLD showed significant therapeutic effects against tumors that grew in primary mammary sites but not in the liver. We found that differences in therapeutic efficacy were not because of the intrinsic biological resistance of cancer cells but rather were associated with tumor site-dependent differences in transport properties, such as the amount of PLD delivery, blood vessel function, relative vascular permeability, and mechanical pressure in tumors. Thus, transport properties in tumor is site dependent and can be used as phenotypic surrogate markers for tumor drug delivery and therapeutic efficacy.