(194a) Nanoparticle-Assisted, Mechanism-Based Combination Photodynamic and Irinotecan Therapy for Pancreatic Cancer

The purpose of this study is to strategically combine two clinical-relevant, nanotechnology-based therapies to facilitate rapid clinical translation and immediately improve on the dismal statistics of pancreatic cancer (PanCa) patients. We hypothesized that benzoporphyrin derivative (BPD)-based photodynamic therapy (PDT) (Phase I/II study, solid PanCa) destroys tumor efflux transporters, which may help maintain high intracellular concentrations of Irinotecan (CPT-11) (Phase III study, metastatic PanCa) to reduce tumor burden and prolong survival. We test our hypothesis in orthotopic PanCa models.

Two types of liposomes were fabricated by adapting procedures from literature. They are: (i) Liposome with BPD in lipid bilayer (LBPD) and (ii) Liposome encapsulating CPT-11 in aqueous core (LCPT-11). Lipids (DPPC, DOTAP, Cholesterol, DSPE-mPEG at a molar ratio of 2:0.2:1.0:0.2) were mixed in chloroform (for LBPD, dissolve with 0.2 mM BPD), and the chloroform was evaporated. Lipid films were rehydrated for 2h in an aqueous solution (for LCPT-11, contain 7 mM CPT-11) with freeze thaw cycles. The resulting dispersion was extruded through polycarbonate membranes (100 nm pore size) to form unilamellar vesicles. Liposome size and polydispersity were measured by dynamic light scattering. BPD (or CPT-11) concentration was determined by UV-Vis spectroscopy. Human pancreatic cancer cells (MIA PaCa-2 or AsPC-1, ATCC) were implanted orthotopically in Swiss Nu/Nu mice (4-6 weeks old, ~25 mg) on day 0. Animals were anesthetized with Ketamine/Xylazine and the pancreas was exteriorized. Cells (1 x 10⁶ in 50 μL of Matrigel-containing media) were injected into the pancreas using a 301/2-gauge needle, and the incision was closed with 4-0 sutures. Treatments were initiated when the tumors reach ~35 mm³ on day 9 (determined by ultrasound imaging). Tumor bearing mice were intravenously (tail vein) injected with LBPD (0.25 mg/kg) and LCPT-11 (20 mg/kg) 1h before light administration. Interstitial PDT (690 nm laser, 100mW/cm², 75 J/cm²) was performed on the exteriorized pancreas of the anesthetized animal, and then followed by wound closure with sutures.

We have delivered reproducible LBPDs (137±9 nm) and LCPT-11s (122±5 nm), with a polydispersity index less than 0.05, were found stable for up to 3 weeks of storage. The BPD and CPT-11 loading efficiency in liposomes were found to be ~75% and ~50%, respectively. The longitudinal ultrasound monitoring of orthotopic tumor volume in response to combination LBPD-PDT and LCPT- 11 was carried out with appropriate controls. We observed that LBPD-PDT significantly enhances the tumoricidal efficacy of LCPT-11 and significantly inhibited tumor growth up to at least 3 weeks post-treatment (p < 0.05). Tumor volumes for the combination group on day 30 were ~3 fold and ~5 fold less than single treatments and no treatment groups, respectively.

Photodynamic therapy (and Irinotecan chemotherapy) alone has already shown promise in treatment of PanCa in clinical studies. This study recognizes that the genetic complexity and heterogeneity of PanCa make it extremely difficult for any single treatment to impact outcome. To overcome therapy resistance, it is critical to understand the limitations of single treatment and develop new combination regimens based on interactive mechanisms. We performed pilot studies in orthotopic PanCa models that demonstrated LBPD-PDT could improve the efficacy of liposomal Irinotecan treatment. We anticipate the findings of this study, based on two clinically relevant treatments, will form the basis for rapid translation of a novel combination regimen for PanCa patients.