HER2-targeted star polymer conjugates for improved tumor distribution and efficacy

Actively targeted nanoparticle systems have the potential to improve delivery to tumors over untargeted systems however the design rules to achieve this have not been fully elucidated. A HER2-targeted polymer drug delivery system composed of a 32-arm star polymer (SD) conjugated with the TOP1 inhibitor molecule SN-38, with a trastuzumab antigen binding fragment (HER2-Fab), has been used to target cancer cells overexpressing this receptor. The HER2-Fab was attached to the SD at two different densities (average of 1 or 3 Fabs per star polymer) and compared to the native star polymer without Fab. In vitro experimentation showed that both the targeted star polymers (HER2-SDs) had better binding and uptake in HER2-positive cell lines (SK-BR3 and HEK293) compared to the non-targeted SD. In vivo biodistribution studies showed enhanced accumulation of HER2-targeted SDs in tumors, but not normal tissues, particularly at the later (96 h post-dose) timepoint. The HER2-SDs demonstrated increased localization with tumor cells rather than in stromal regions, greater penetration into the tumor core and a more homogenous distribution in the tumor section than the untargeted SD. The targeted star polymer conjugated to SN-38 was tested for anti-tumor activity in a HER2-positive gastric cancer xenograft in mice and showed significantly greater efficacy compared to untargeted SDs.