SBIR-STTR Award

Ovarian cancer causes the highest mortality rate among women with gynecologic malignancy, approximately 14,000 cancer deaths per year. Women with late-stage disease have a 2-year relapse rate of more than 50%, and a 5-year survival rate of less than 50%. The goal of this proposal is to identify the optimal configuration of a Listeria monocytogenes-based cancer vaccine encoding the tumor antigen mesothelin, for application as a targeted immunotherapy for ovarian cancer. Listeria is an intracellular bacterium that primes robust CD4+/CD8+ T-cell mediated responses, has striking potency in animal models of both infectious disease and cancer, and has been tested in healthy human volunteers. Mesothelin is a differentiation antigen that is expressed in 95% of ovarian cancers and lower levels in other cancers, but other than mesothelial cells, is not detected in diverse normal tissues, including normal ovaries. A panel of recombinant Listeria that express mesothelin fused to elements that augment antigen presentation will be derived, and tested for therapeutic efficacy in a newly-developed syngeneic mouse model that expresses mesothelin and recapitulates human ovarian cancer. Accomplishing these goals will set the stage in a Phase II SBIR for moving the project toward a clinical trial in women with advanced ovarian cancer

Pancreatic and ovarian cancers are among the most aggressive and lethal malignancies, and represent a major unmet medical need. To wit: (1) pancreatic cancer patients have a 5-year survival rate of less than 5% and the 32,000 new cases per year in the U.S. is close to the number of annual deaths; and, (2) ovarian cancer represents about 25% of gynecologic malignancies but accounts for over 50% of gynecologic cancer deaths, an estimated 14,000 per annum in the U.S. The overall goal of this SBIR phase II proposal is to continue development of our Listeria monocytogenes (Lm)-based immunotherapy to target Mesothelin and codon 12-mutated activated K-ras antigens in patients with pancreatic and ovarian cancers. Two significant developments have occurred since the SBIR Phase I grant was submitted: (1) We generated (and documented) a live-attenuated Lm vaccine platform strain deleted of ActA and InIB virulence determinants that is greater that 1000-fold attenuated, yet retains immunogenicity that is indistinguishable from wild-type Lm; and, (2) Mesothelin-targeted T-cells from pancreatic cancer patients have been shown by our collaborator, Dr. Elizabeth Jaffee, to target and destroy pancreatic tumor cells, and patient T-cell responses correlate with long-term disease-free survival. Under Phase I funding and continued work, we developed proprietary and unique means for expression and secretion of tumor antigens. By utilizing both codon optimization and signal peptides from distinct Gram+ bacteria, we constructed Lm vaccines that efficiently synthesize and secrete Mesothelin. Overlapping peptide libraries were used to map human Mesothelin- and Lm (LLO)-specific cellular responses in mice immunized with prototype vaccines. We extended the use of the LLO peptide library to measure Lm cellular immunity in humans. Additionally, we demonstrated that Lm vaccines efficiently deliver tumor antigens into human dendritic cells for MHC class I presentation in vitro-a critical proof of concept for studies proposed in Phase II. With this application, we propose to: (1) select the Lm-Mesothelin/ras vaccine strain for clinical trials based on immunogenicity in syngeneic and HLA-A2 transgenic mice, and activation of established HLA-A2-, A3-, and A24-restricted human Mesothelin specific Tcell lines; (2) establish clinical monitoring methods to evaluate Mesothelin- and K-ras-specific T-cell responses in vaccinated patients; (3) establish manufacturing and process methods for the selected Lm Mesothelin/ras vaccine; and, (4) perform IND-enabling murine toxicology studies. Each of these activities is on the critical path to enabling a Phase I clinical trial. To accomplish these goals, we have assembled a team with a history of productive collaboration consisting of scientists and external consultants with documented expertise in Gram-positive bacterial genetics, murine and human immunology, novel cancer vaccine platform development, and translational medicine