Intravesical drug delivery by cationic liposomes (Cat-LPs) represents a potent nanotechnology for enhancing therapeutic effects against bladder disorders. However, preventing the aggregation of Cat-LPs in urine poses a significant barrier. We report on an examination of the effect of modifying liposomes with polyethylene glycol (PEG) lipids to prevent Cat-LPs from aggregating in human urine. Although Cat-LPs underwent significant aggregation in human urine, introducing 5 mol% of PEG2k lipid or 2 mol% of PEG5k lipid completely inhibited the aggregation of the Cat-LPs. When 2 mol% of PEG2k lipids were introduced, the lipid structures of 1,2-distearoly-sn-glycero-3-phosphoethanolamine (DSPE) and 1,2-distearoyl-snglycerol (DSG) greatly prevented aggregation compared with cholesterol. By contrast, when Cat-LPs, after incubation in urine, were exposed to bladder cancer cells, only introducing cholesteryl-PEG into the CatLPs showed a significant enhancement in cellular uptake. These results offer the potential for incorporating cholesteryl-PEG into Cat-LPs for achieving both stability in urine and effective cellular uptake.

The intravesical instillation of live Bacillus Calmette-Guerin (BCG) for treating bladder cancer is a powerful cancer immunotherapy. The BCG cell wall skeleton (BCG-CWS) is the main component of the adjuvant, leading to the induction of antitumor immunity. However, the use of live BCG and BCG-CWS is currently limited to local administration because of the infectiousness of live BCG and the insolubility of BCG-CWS. We previously developed a water-dispersible nanoparticle (NP) formulation of BCG-CWS (CWS-NP), which could be used to apply BCG components for use as a systemically injected adjuvant for the treatment of cancers other than bladder cancer. In the present study, we examined the possible use of CWS-NP for cancer immunotherapy, when intravenously administered. The CWS-NP was a highly uniform dispersion and showed no aggregation in serum. The intravenously injected CWS-NP accumulated in the spleen and was efficiently taken up by dendritic cells, leading to their maturation. The coadministration of CWS-NP and ovalbumin (OVA) loaded NP resulted in the generation of OVA-specific cytotoxic T cells and inhibited the growth of E.G7-OVA tumors. These results represent the first findings related to the use of systemically injected CWS-NP as an adjuvant for cancer immunotherapy.