Abstract 1237: Mechanism of action of L-BLP25 in preclinical pancreatic tumor models.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Background. L-BLP25 is an investigational antigen-specific cancer immunotherapeutic agent targeting human mucin 1 (MUC1). A single low dose of cyclophosphamide (CPA) is known to be immunostimulatory and may enhance the anti-tumor effects of L-BLP25 when given 3 days before treatment initiation. Here we report the immune and anti-tumor efficacy of L-BLP25 with CPA pretreatment in subcutaneous (s.c.) and orthotopic models of murine pancreatic cancer. These models allow for reproduction of the clinical scenario, where 8 weekly doses of L-BLP25 are administered. Methods. Murine pancreatic tumor cells Panc02 transfected with human MUC1 were injected for comparison s.c. or orthotopically into human MUC1 transgenic mice. Mice received either vehicle control (PBS), CPA (100 mg/kg), L-BLP25 (100 μg), or L-BLP25 (100 μg) + CPA (100 mg/kg). CPA was administered intravenously (i.v.) 3 days prior to initiation of 8 weekly intradermal (i.d.) or s.c. L-BLP25 injections. Tumor volume was monitored and splenic cell populations were quantified by FACS. In the s.c. tumor model, the contribution of CD4+ and CD8+ T cell subsets to the inhibition of tumor growth was studied. In the orthotopic model, antigen-specific IFN-γ secretion was assessed via ex vivo T cell re-stimulation with antigen alone. Results. In the s.c. model of pancreatic cancer, tumor volume was reduced compared to vehicle at day 49 after i.d. administration of L-BLP25 (41.4%, p<0.02) and L-BLP25 + CPA (55.5%, p<0.02). In multiple studies, tumor volume was consistently lower in mice treated with L-BLP25 + CPA vs. L-BLP25 alone. L-BLP25 + CPA s.c. treatment was effective at day 49 with 44% greater inhibition of tumor growth and more pronounced extended survival compared to i.d. treatment, supporting the route of administration in the clinic. Various splenic immune cell populations were increased by s.c. L-BLP25 + CPA treatment compared to vehicle and L-BLP25 alone, including the CD8+ effector memory/Treg ratio. Mice treated with s.c. L-BLP25 + CPA after CD8+ T cell depletion had a greater tumor volume compared to T cell-sufficient mice, while CD4+ T cell depletion had no effect. In the orthotopic model of pancreatic cancer, median survival was improved with s.c. L-BLP25 + CPA treatment vs. vehicle (p<0.05) and vs. L-BLP25 alone (non-significant). When stimulated ex vivo with the BP25 peptide, the frequency of IFN-γ producing CD4+ T cells isolated from the spleens of mice treated with L-BLP25 + CPA was significantly higher than in all other treatment groups (p<0.001). CD8+ T cells were found to produce no IFN-γ after in vitro re-stimulation. Conclusions. When administered after a single, low-dose pre-treatment of CPA, L-BLP25 immunotherapy exhibits anti-tumor activity, immune activation and prolonged survival in murine pancreatic cancer models. T cell depletion data indicate a CD8+ T cell-mediated anti-tumor response, whilst IFN-γ production by CD4+ helper T cells may contribute to prolonged survival. Citation Format: Kenneth Hance, Bo Marelli, Jin Qi, Guozhong Qin, Huakui Yu, Hong Wang, Xiaomei Xu, Robert Tighe, Beatrice Brunkhorst, Yan Lan, Robert Hofmeister, Helen Sabzevari, Michael Wolf. Mechanism of action of L-BLP25 in preclinical pancreatic tumor models. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1237. doi:10.1158/1538-7445.AM2013-1237