Flt3 ligand delivered in a pluronic formulation prolongs the survival of mice with orthotopic pancreatic adenocarcinoma.

Pancreatic adenocarcinoma is a devastating disease, characterized by asymptomatic development and extremely poor prognosis. Given the resistance of pancreatic cancer to standard chemo- and radiotherapy, we have focused on the development of immunotherapies for this disease. The number of dendritic cells (DCs), natural killer (NK) cells, and T-cells in the blood and secondary lymphoid organs is regulated by a group of hematopoietic growth factors, which includes fms-like tyrosine kinase-3 ligand (Flt3L). We have demonstrated previously that the bioavailability and in vivo half-life of Flt3L are increased by Flt3L formulation in the pluronic ProGelzx. In this study, we first examined the effectiveness of Flt3L delivered in ProGelz against subcutaneous (s.c.) pancreatic adenocarcinomas in mice. We found that an intramuscular (i.m.) injection of Flt3L in ProGelz significantly increased the survival of mice bearing s.c. pancreatic tumors, compared to the administration of phosphate-buffered saline (PBS) in ProGelz. We then tested Flt3L in ProGelz in an orthotopic pancreatic tumor model, and demonstrated that it significantly enhanced the survival of tumor-bearing mice, compared to PBS in ProGelz. Overall, these observations suggest that Flt3L formulated in ProGelz may have potential clinical utility as a treatment for pancreatic cancer.

Hematopoietic progenitor cell mobilization in mice by sustained delivery of granulocyte colony-stimulating factor.

The objective of these studies was to determine the effect of sustained delivery of growth factors (GFs) on hematopoietic progenitor cells (HPCs) in mice. In these studies, granulocyte colony-stimulating factor (G-CSF) was administered using the poloxamer-based matrix, ProGelz (PG) and G-CSF, and pharmacokinetics (PKs) and HPC mobilization was assessed. A single injection of G-CSF formulated in PG (17% poloxamer-407 and 5% hydroxypropyl methylcellulose [HPMC]) administered to BALB/c mice mobilized HPC significantly more rapidly to the spleen, but not the blood, than multiple injections of saline-formulated G-CSF. Two days after a single injection of PG G-CSF, the frequency of colony-forming unit-culture (CFU-c) in the spleen was increased 289-fold compared with an 8-fold increase after 2 days of twice-daily injections of saline-formulated G-CSF. Indeed, 4 days of twice-daily G-CSF injections were required to achieve the same level of HPC mobilization. In contrast, a similar mobilization of HPC to the blood was observed between PG and saline-formulated G-CSF. The mechanism for the accelerated and increased mobilization to the spleen by the PG-formulation of G-CSF is due, in part, to its increased bioavailability (>1.5-fold), T(max) (6-fold), and prolonged elimination (Tbeta) half-life (>3-fold) as compared with a saline formulation. In addition, we observed a more rapid trafficking of the PG G-CSF to the marrow, which could also facilitate mobilization.

Pluronic F127-based systemic vaccine delivery systems.

We have developed a vaccine delivery system based on the non-ionic block copolymer, Pluronic F127 (F127), combined with selected immunomodulators. F127-based matrices are characterized by a phenomenon known as reverse thermogelation, whereby the formulation undergoes a phase transition from liquid to gel upon reaching physiological temperatures. Protein antigens (tetanus toxoid (TT), diphtheria toxoid (DT) and anthrax recombinant protective antigen (rPA)) were formulated with F127 in combination with CpG motifs or chitosan, as examples of immunomodulators, and were compared to more traditional adjuvants in mice. IgG antibody responses were significantly enhanced by the F127/CpG and F127/chitosan combinations compared to antigens mixed with CpGs or chitosan alone. In addition, the responses were significantly greater than those elicited by aluminum salts. Furthermore, the functional activity of these antibodies was demonstrated using either in vivo tetanus toxin challenge or an anthrax lethal toxin neutralization assay. These studies suggest that a block-copolymer approach could enhance the delivery of a variety of clinically useful antigens in vaccination schemes.