Transductional Targeting of oncolytic adenoviruses by CARex-pSia adapter molecules improves therapy of pSia-expressing tumors and reduces viral liver load

Polysialic acid (pSia) is a cell surface antigen that plays an important role in neuronal development but is not expressed in most adult tissues. However, expression of pSia is reactivated during oncogenesis of several cancers of neuroendocrine origin including glioblastoma, rhabdomyosarcoma and small cell lung cancer (SCLC). pSia therefore represents an excellent tumor selective target for oncolytic adenovirus-based therapies. In this study, we developed a strategy to retarget oncolytic Adenoviruses (OAV) to pSia-expressing tumors using a recombinant bispecific adapter protein. To generate the adapter molecule CARex-pSia, the soluble CAR ectodomain was fused to a pSia-binding domain linked via a trimerization motif. By infection experiments in CHO and pSia-negative CHO mutant cell, we could show that CARex-pSia treatment of Ad5 efficiently allowed viral cell entry in a pSia-selective manner. Furthermore, CARex-pSia treatment allowed efficient adenoviral infection of normally refractory pSia-expressing human tumor cells. After intravenous injection of CARex-pSia-treated Luciferase-Ad we could observe a significant reduction of adenoviral liver load in mice and could show improved adenoviral infection of s.c. grown pSia-expressing human tumor xenografts. Therapeutic investigations were performed in a syngeneic, murine SCLC model induced by intravenous delivery of transgenic, pSia-expressing CMT64 cells in C57/Bl6 mice. Systemic administration of CARex-pSia pretreated OAV allowed for successful transduction of lung colonies as shown by in vivo imaging and virus qPCR, and finally led to significantly improved survival of mice. Together, we could demonstrate that retargeting OAVs to cell surface pSia via a bispecific adapter represents a promising strategy to improve the oncolytic treatment of clinically relevant pSia-expressing tumors species with reduced virus-mediated side effects on the liver.

oncolytic Adenovirus - polysialic acid - transductional targeting