Formulation Development, Pharmacokinetic and Pharmacodynamic Assessments of a Combination regimen of Paclitaxel and Calcipotriol in a KrasG12D Mouse Model of Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a human health challenge whose solution remains elusive. Advancement in our understanding of PDAC has uncovered significant stroma-tumor crosstalk, the disruption of which may improve treatment outcome. Genetic deletion of stroma has led to increased T-cell and chemotherapy infiltration into the tumor bed, but these approaches are characterized by complete stroma depletion which leads to more aggressive PDAC phenotypes. An alternative strategy that maintains a balance between stroma depletion and excess was pursued. In this study, a pharmacological approach using the synthetic vitamin D analog calcipotriol (Cal) to achieve stroma reprogramming while simultaneously delivering a chemotherapeutic agent, paclitaxel (PTX), into the tumor was pursued. To facilitate the studies, an LC-MS/MS method with improved sensitivity was developed to simultaneously measure Cal and PTX in biological samples. To improve the efficacy and safety profiles of Cal and PTX, a polymeric micellar drug delivery system (MDDS) was developed and optimized using the response surface methodology to reduce free Cal exposure as well as facilitate tumor accumulation of both agents. Pharmacokinetic (PK) and biodistribution studies confirmed the MDDS extended the half-lives of both Cal and PTX, reduced systemic exposure of Cal and facilitated tumor accumulation of Cal and PTX. A potential drug-drug interaction (DDI) between Cal and PTX was discovered. Co-administering Cal and PTX resulted in increased clearance of Cal but decreased PTX clearance. The involvement of transporters is speculated. Significant differential PK of Cal between healthy and tumor bearing mice was observed, but less so for PTX. Cal elimination half-life in healthy mice was at least 16 times longer than that in the diseased mice. Cal clearance was also > 5 times faster in the diseased mice compared to the healthy ones. Unsurprisingly, this resulted in a significantly diminished exposure in the diseased mice. A reduction in PTX exposure and an increase in clearance was observed in the diseased mice. PTX clearance was 1.5x faster and exposure (AUClast) 1.5x lower in the diseased animals compared to the healthy ones. While the potential clinical impact of these differences is unknown, the combination regimen remained effective at the doses tested. Population PK analyses revealed the diseased status to be a significant covariate of Cal PK. Increased expression of CYP24A1 in the diseased mice was postulated to be the underlying factor for the PK difference. Further, a population PK approach was used to understand the metabolic profile of Cal and its major metabolites MC1046 and MC1080. The analyses showed that although Cal is metabolized to MC1046 by CYP24A1, this clearance pathway only accounted for 23% of the total Cal clearance. CYP24A1-mediated Cal metabolism to metabolites other than MC1046, or the involvement of other enzymes in the metabolism of Cal could not be ruled out. Moreover, the analyses suggested that the immediate metabolite of Cal, MC1046, was predominantly further metabolized by another enzyme which accounted for 94% of MC1046 elimination. In vivo, it was demonstrated that the micellar formulation of Cal and PTX had no negative impact on the body weights of mice, as well as the markers of liver and kidney functions. Additionally, this combination regimen deactivated the PDAC stroma and inhibited tumor cell proliferation that led to the extended survival of diseased animals. Overall, the study demonstrated the potential merits of micellar co-delivery of Cal and PTX for PDAC treatment which warrants further development.