Advanced ovarian cancer has the highest mortality rate among patients with cancers of the female reproductive system in the United States. Existing therapies for ovarian cancer, such as surgery and chemotherapy, have significant side effects and rarely result in long-term cures for patients with locally advanced or metastatic disease. The lack of curative treatments and high proportion of patients diagnosed with advanced disease underscores the urgent need to develop innovative and targeted therapies to control advanced stage ovarian cancer. In the current proposal, we aim to overcome major limitations of current therapies by employing human papillomavirus (HPV) pseudovirions (psVs) to deliver a therapeutic DNA construct to ovarian tumor cells in order to control infected and uninfected ovarian tumor cells through cell-mediated and humoral immune responses. Recently, we demonstrated that HPV psV is able to preferentially infect ovarian tumors in vivo. Furthermore, we have shown that a chimeric protein containing a tumor-homing molecule, NKG2D, fused to the Fc fragment of immunoglobulin G (IgG2a) was capable of coating tumor cells and generating antitumor effects (see preliminary data). The tumor-homing molecule, NKG2D, binds with high affinity to NKG2D ligand, which is overexpressed on the majority of ovarian tumor cells, compared to normal cells. NKG2D fused to the Fc fragment (NKG2D-Fc) enables the binding of effector cells exhibiting Fc receptor, such as macrophages and natural killer cells, to the tumor cells for the induction of antibody-dependent and complement-dependent cytotoxicity. We propose to further fuse NKG2D-Fc, with an MHC class I-restricted immunogenic CTL epitope for influenza virus, separated by a furin cleavage site. This will bypass immune tolerance by exploiting pre-existing cytotoxic T lymphocytes (CTLs) against a common foreign viral epitope, which is found in the vast majority of individuals. We have previously demonstrated that intraperitoneal injection of a similar chimeric protein containing model immunogenic CTL antigenic peptide, OVA, flanked with a furin cleavage site, led to the targeted delivery of the chimeric protein and the presentation of OVA CTL peptide on MHC class I molecules of tumor cells in tumor-bearing mice. Therefore, we reason that from the chimeric protein (NKG2D-Fc-RM), the NKG2D portion will make the chimeric protein bind specifically to HPV psV infected and uninfected ovarian cancer cells, where the immunogenic CTL epitopes will be released through cleavage by furin and coat the tumor cells for recognition by pre-existing CTLs. In addition, the presence of Fc renders the bound tumor cell susceptible to attack by humoral immunity. Overall, our proposed therapeutic chimeric protein delivered by HPV psV has the advantages of targeted tumor delivery, specific furin cleavage at the tumor site, and potent tumor-targeted killing through existing CTL immunity and Fc-mediated killing, representing a novel strategy with high translational value. The successful implementation of the proposed study would serve as an innovative strategy that may be applied to the treatment of other types of late stage cancers.
This project will exploit preexisting host immunity to control ovarian tumor cells. We plan to use HPV psuedovirions to facilitate the targeted delivery of an innovative chimeric protein that will coat both infected and uninfected tumor cells with a common foreign viral epitope as well as the Fc portion of the immunoglobulin G to induce adaptive and innate immune responses, respectively. The successful implementation of this project may result in the generation of a novel therapy for the control of ovarian tumors.
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