Size-adaptable and ligand (biotin)-sheddable nanocarriers equipped with avidin scavenging technology for deep tumor penetration and reduced toxicity.

The conventional active-targeting nano-chemotherapy suffers from poor tumor tissue penetration and non-negligible toxicity due to the size/ligand dilemmas and insufficient target selectivity. In this report, a stimuli-responsive size-adaptable and ligand (biotin)-sheddable drug delivery system (DDS) combined with two-step strategy of biotin-avidin system was designed to seek a balance between tumor targeting and penetration as well as to self-scavenge the nonresponsive nanocarriers in normal tissues. This DDS was composed of 'multi-seed' polymeric liposomes (ASL-BIO-MPL) with asulacrine-loaded micelles as seeds in their aqueous cavities. The shell of such liposomes was modified with MMP-9 cleavable polymer-polypeptide functionalized with the tumor targeting ligand biotin. ASL-BIO-MPL could disintegrate into mixture of irregularly-shaped liposomes (~200 nm) and scattered tiny micelles (~40 nm) after incubation with MMP-9. The fluorescence-labeled BIO-MPL could travel to the center of the 4T1 breast tumor spheroids under the action of MMP-9, possibly benefited from the relay of released tiny micelles. Conversely, neither the biotin-modified micelles nor non-MMP-9-responsive multi-seed liposomes could penetrate into the spheroids possibly due to the potent binding-site barrier of biotin and large size, respectively. In tumor-bearing mice, ASL-BIO-MPL exhibited the strongest drug penetrability and thus the optimal inhibition of tumor growth compared to other formulations. Following administration of avidin with a rational dosage regimen, the number of apoptotic cells in normal tissues induced by ASL-BIO-MPL reduced without affecting their targeting effect, suggesting the followed administration of adivin could scavenge the DDS in non-target site. Overall, the size/ligand adapting MPL system combined with two-step strategy of biotin-avidin may provide potential avenues for nanocarriers to enhance deep tumor tissue targeting and protect normal tissues.