A successful drug development program requires a complete understanding of the clinical pharmacology of the agents being evaluated. The Clinical Pharmacology Program (CPP) has as its primary interest the use of pharmacokinetic (PK) and pharmacodynamic (PD) concepts in the development of novel anticancer agents. The CPP is directly responsible for the PK/PD analysis of numerous Phase I and II clinical trials conducted within the NCI and also provides direct PK support for many studies performed elsewhere in the extramural community. We utilize compartmental and noncompartmental approaches to define the disposition of agents. We also often characterize the plasma protein binding properties and metabolism of new agents through in vitro techniques. Several of our clinical trials have used adaptive control with a feedback mechanism to target particular plasma concentrations (e.g., suramin, CAI). The drugs with which the CPP has had its greatest experience include: suramin, phenylacetate, phenylbutyrate, TNP-470, CAI, DAB486IL2, IgG-RFB4-SMPT-dgA CD22, IgG-HD37-SMPT-dgA CD19, ormaplatin, UCN-01, docetaxel, flavopiridol, thalidomide, lenalidomide, intraperitoneal cisplatin, intraperitoneal carboplatin, paclitaxel, 17-DMAG, imatinib, sorafenib, nelfinavir, bevacizumab, romidepsin, clopidrogrel, bortezomib, TRC-105, vandetanib, olaparib, topotecan, irinotecan, AZD7451 (tropomyosin-receptor kinase inhibitor), 7-hydroxystaurosporine and fludararbine phosphate. The CPP participates in several preclinical pharmacology projects in order to study drug metabolism, PK, drug formulation and bioavailability, as well as efficacy in preclinical models of drug development. The CPP has validated assays for such compounds as 3-deazaneplanocin (DZ-Nep), PV1162, schweinfurthin G, englerin A, aza-englerin, and XZ-419. The CPP also provided full PK analysis for DZ-Nep and PV1162, and bioavailability data for schweinfurthin G, englerin A, and aza-englerin. Such projects allow for more accurate dosing estimates for first-in-human studies, if the compound progresses to that stage. We are involved in the preclinical development of several compounds. In collaboration with the Molecular Targets Laboratory (MTL) and the Natural Products Branch (NPB), the CPP provided preclinical PK support to study the bioavailability of englerin A (extracted from the Tanzanian plant Phyllanthus engleri Pax on the basis of its high potency and selectivity for inhibiting renal cancer cell growth) and its aza-derivative, aza-englerin analogues. Niemann-Pick type C (NPC) disease is a neurodegenerative lysosomal storage disease caused by mutations in either the NPC1 or NPC2 genes. NPC is characterized by storage of multiple lipids in the late endosomal/lysosomal compartment, resulting in cellular and organ system dysfunction. The underlying molecular mechanisms that lead to the range of clinical presentations in NPC are not fully understood. While evaluating small molecule therapies in the Npc1-/- mouse, Dr. Forbes Porter (NICHHD, NIH) observed a consistent pattern of toxicity associated with drugs metabolized by cytochrome P450s, suggesting a potential drug metabolism defect in NPC1 disease. In collaboration with Dr. Porter, the CPP evaluated these pharmacological changes. We investigated the P450 system and found that NPC1 dysfunction is associated with a significant reduction in the expression and activity of cytochrome P450 reductase and multiple cytochrome P450 catalyzed dealkylation reactions, in the NPC1 mouse and cat models, as well as in NPC1 patients. In vivo drug metabolism studies using a prototypic P450 metabolized drug, midazolam, confirmed dysfunctions in drug clearance in the Npc1-/- mouse. Expression of the Phase II enzyme uridine diphosphate glucuronosyltransferase was also significantly reduced in the Npc1-/- mouse. Interestingly, reduced activity within the P450 system was also observed in heterozygous Npc1+/- mice. The reduced activity of P450 enzymes is likely caused by bile acid deficiency/imbalance in the Npc1-/- mice as bile acid treatment significantly rescued P450 gene expression/enzyme activity in Npc1-/- mice and has the potential to be an adjunctive therapy for NPC disease patients. The carrier frequency is 0.6%, thus, the data for heterozygous raises concerns about altered pharmacokinetics (and increased toxicity) in this patient population. During the FY2016, the CPP provided PK support for several phase I/II clinical studies, including carfilzomib, sorafenib combined with cetuximab, TRC-105, birinapant, ISIS 183750 and belinostat. We provided the PK support for a trial evaluating the treatment with carfilzomib-lenalidomide-dexamethasone with lenalidomide extension in patients with smoldering or newly diagnosed multiple myeloma. To characterize the PK, the CPP developed an analytical assay to simultaneously measure plasma concentrations of carfilzomib and 3 metabolites (PR-389, PR-413, and PR-519) using an ultra HPLC-MS/MS assay. At 20mg/m2, the PK results include a mean Cmax of 284 ng/mL, AUC of 112 hr*ng/mL, half-life of 0.3 hr, CL of 663 L/hr and VSS of 236 L. Based on carfilzomib clearance, there was significant stratification based on albumin levels, as more albumin (in healthier patients) led to a faster carfilzomib clearance, hence lower albumin (in sicker patients) had a slower clearance, and subsequently better progression-free survival. In further support, our ex vivo experiments confirmed that albumin addition to plasma potentiated carfilzomib metabolism, and the potentiation was reversible using nonspecific protease inhibitor; studies are ongoing to characterize potential leads involved in its metabolism. We also provided PK support for trials on TRC105, is a chimeric immunoglobulin G1 monoclonal antibody that binds endoglin (CD105). In a phase I open-label study evaluating the safety, pharmacokinetics and pharmacodynamics of TRC105 in patients with metastatic castration-resistant prostate cancer, we determined the maximum tolerated dose was 20 mg/kg every 2 weeks. Significant plasma CD105 reduction was observed at the higher dose levels. An exploratory analysis showed a tentative correlation between the reduction of CD105 and a decrease in PSA velocity, suggestive of potential activity of TRC105 in the patients with mCRPC. We conducted the PK assessement in a phase I/II translational clinical trial of ISIS 183750, an antisense oligonucleotide against eIF4E, in combination with irinotecan in solid tumors and irinotecan-refractory colorectal cancer. There were no statistically significant differences between C1D1 and C1D15 for any PK parameter, except for half-life of ISIS 183750, which was 28% longer in the presence of irinotecan (2.55 hr vs. 3.19 hr). There is no physiological basis for a drug-drug interaction based on metabolism, transport and elimination pathways between ISIS 183750 and irinotecan, so difference in half-life may be related to small numbers and interpatient variability. The 28% longer half-life of the ASO with irinotecan could be related to the 12% larger volume of distribution vs. ASO alone. We found that the combination of ISIS 183750 and irinotecan at full doses was moderately well tolerated. The PK data suggested an interaction between the two drugs which resulted in a prolonged half-life and therefore increased AUC of irinotecan and its metabolites (SN38, SN38-G) compared to historically reported data, and this was consistent with the clinical experience as reported by the patients of increased chronic low-grade toxicities (predominantly fatigue). For the phase 2 portion we reduced the dose of the irinotecan. No dose-limiting toxicities were seen but based on PK data and tolerability, the dose of irinotecan was reduced to 160 mg/m(2) biweekly.
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