Expression of p53, or targeting towards EGFR, enhances the oncolytic potency of conditionally replicative adenovirus against neuroblastoma

Background: Advanced stage and relapsing neuroblastoma (NB) has a poor prognosis with frequent treatment failures, warranting new treatment options and enhanced local tumor control. Treatment with conditionally replicative adenoviruses (CRAds) has shown effectiveness in various preclinical cancer models, but has not yet been evaluated for local control of NB. Here, we tested the efficacy of the CRAd AdΔ24 and of two AdΔ24 derivatives against NB. Derivative AdΔ24-425S11 infects cells deficient in coxsackie/adenovirus receptor (CAR) via the epidermal growth factor receptor (EGFR). Derivative AdΔ24-p53 expresses the tumor suppressor protein p53 to promote oncolysis. Methods: Expression of CAR and EGFR, and p53 pathway and DNA damage responses were analyzed in six NB cell lines and two xenografts derived from primary NB using immunohistochemistry, reporter gene transactivation, Western blot and fluorescence-activated cell sorting (FACS) analysis. Efficacy of AdΔ24, AdΔ24-425S11 and AdΔ24-p53 against NB was evaluated in vitro by cell viability analysis and in vivo by monitoring subcutaneous xenograft tumor growth in mice and by histological analysis of treated tumors. Results: Neuroblastoma cell lines were sensitive to oncolysis by AdΔ24, with a higher susceptibility of those with functional p53 and intact DNA damage responses. Compared to AdΔ24, AdΔ24-p53 exhibited enhanced oncolytic potency on all NB cell lines independent of their p53 status and AdΔ24-425S11 was more effective against CAR-low IGR-NB8 cells. Moreover, five daily intratumoral injections of 10⁸ plaque-forming units (pfu) of AdΔ24-p53 or AdΔ24-425S11 into subcutaneous IGR-NB8 and IGR-N91 xenografts at an advanced tumor stage yielded significant tumor growth delays (TGD). In contrast, at this dose, AdΔ24 did not cause significant TGD of neuroblastoma xenografts. Injection of AdΔ24-p53 was associated with extensive cell lysis, apoptotic cell death, and fibrous fascicles in the tumors. Conclusion. CRAds expressing p53 and targeted towards EGFR appear promising new agents for local control in the treatment of neuroblastoma.