335 Background: Liposomal irinotecan (nal-IRI, ONIVYDE) is approved in the US, EU and other countries in combination with 5-fluorouracil/leucovorin for treatment of patients with metastatic pancreatic cancer after disease progression following gemcitabine-based therapy. We report pharmacokinetic and extended pharmacodynamic effects of nal-IRI in pancreatic tumor models compared to non-liposomal irinotecan HCl. Methods: AsPC-1, BxPC-3 and CFPAC-1 tumors were grown in NOD-SCID mice. For efficacy animals were dosed q7d with 25-50 mg/kg irinotecan HCl or at 5x lower doses of nal-IRI. For PK-PD studies doses of 10-50 mg/kg of fluorescently-labeled nal-IRI were used; samples were collected up to 72 hr for irinotecan HCl and up to 168 hr for nal-IRI. Tumor samples were evaluated for liposome localization, macrophage and tumor markers, vessels, DNA damage and apoptosis. Results: nal-IRI yields sustained circulation and delivery of its payload to tumors compared to irinotecan HCl. This results in improved control of growth rates across a range of pancreatic tumor models even at 5x lower doses. DNA damage in BxPC-3 tumors has a comparable extent with both formulations, but is maximal at 6 hr after irinotecan HCl (50 mg/kg) and at 72 hr after nal-IRI (10 mg/kg). Liposomes deposit in tumors heterogeneously around functional vessels. Accumulation peaks at 6 - 24 hr with similar deposition patterns in cell- or patient-derived xenografts. Liposomes are predominantly taken up by macrophages and to a lesser extent by tumor or other stromal cells. DNA damage is mostly confined to tumor cells, a majority of which have not internalized liposomes. DNA damage and apoptosis are seen only minimally in non-tumor cells even when displaying high liposome uptake. Conclusions: nal-IRI improves tumoral deposition of its payload in pancreatic tumor models. Deposition is heterogeneous and restricted to perivascular areas. DNA damage predominantly in tumor cells outside of the liposomal deposition area suggests sufficient intratumoral levels of the SN-38 active metabolite, possibly after payload release by stromal macrophages and concomitant conversion. Effects of repeated dosing cycles should be explored.
In vivo bioluminescence tomography-guided radiation research platform for pancreatic cancer: an initial study using subcutaneous and orthotopic pancreatic tumor models