Gene therapy for pretreated ovarian cancer via a novel fiber modified mdr1 targeting conditionally replicating adenovirus

Abstract

e16513 Background: Ovarian cancer (OC) is a leading cause of death from gynecologic malignancies. Oncolytic adenoviruses (CRAd) are a new approach for cancer treatment. In this study, we constructed a fiber-modified CRAd containing the multi drug resistance gene (mdr) 1 promoter to control viral replication (Ad5/3MDR1). Antineoplastic agents induce mdr1-gene expression triggering chemoresistance. Methods: RT-PCR was performed for expression of mdr1 in cell lines and primary patient samples. We constructed Ad5/3MDR1luc1 to determine relative activity in a variety of cell lines, patient samples, and normal control cells. Replication and oncolysis of Ad5/3MDR1 were assessed in naïve and pretreated OC cell lines. The specificity of viral replication was analyzed in co-culture of pretreated OC cell lines and human fibroid cells. A mouse model of peritoneal carcinomatosis was used to evaluate the efficacy of a combined chemo- and gene therapy for OC. Results: RT-PCR reveals a significantly (p < 0.05) increased expression of the mdr1 gene in OC cell lines and patient samples. Compared to the ubiquitous cmv promoter, mdr1 showed a high level of activity in chemoresistant OC cell lines (7.3%-11.5 %) and OC patient samples (8.8%-12.4%), whereas activity in normal fibroblasts (<1%) was low. Ad5/3MDR1 shows highly selective replication in chemoresistant OC cells in a co-culture with fibroblast cells. Cell killing of Ad5/3MDR1 was comparable to Ad5/3Δ24, a CRAD that replicates in cancer cells inactive in the Rb/p16 pathway, in chemotherapy naïve OC cells but displayed significantly (1.5 log; p < 0.05) higher oncolytic potency in pretreated OC cell lines and primary cells from pretreated OC patients. Moreover, in a therapeutic orthotopic mouse model of peritoneal carcinomatosis, dramatically enhanced survival was noted with Ad5/3MDR1. Conclusions: Ad5/3MDR1 is a promising candidate for gene therapy of metastatic chemoresistant OC with great potential for clinical testing. No significant financial relationships to disclose.