Dinesh P. de Alwis

Pharmacokinetics/pharmacodynamics and the stages of drug development: Role of modeling and simulation

Pharmacokinetic (PK) and pharmacodynamic (PD) modeling and simulation (M&S) are well-recognized powerful tools that enable effective implementation of the learn-and-confirm paradigm in drug development. The impact of PK/PD M&S on decision making and drug development risk management is dependent on the question being asked and on the availability and quality of data accessible at a particular stage of drug development. For instance, M&S methodologies can be used to capture uncertainty and use the expected variability in PK/PD data generated in preclinical species for projection of the plausible range of clinical dose; clinical trial simulation can be used to forecast the probability of achieving a target response in patients based on information obtained in early phases of development. Framing the right question and capturing the key assumptions are critical components of the “learn-and-confirm” paradigm in the drug development process and are essential to delivering high-value PK/PD M&S results. Selected works of PK/PD modeling and simulation from preclinical to phase III are presented as case examples in this article.

A Phase I Trial of a Potent P-Glycoprotein Inhibitor, Zosuquidar.3HCl Trihydrochloride (LY335979), Administered Orally in Combination with Doxorubicin in Patients with Advanced Malignancies

Purpose: Our intention was to (a) to investigate the safety and tolerability of a potent P-glycoprotein modulator, zosuquidar trihydrochloride (LY335979), when administered i.v. alone or in combination with doxorubicin, (b) to determine the pharmacokinetics of zosuquidar and correlate exposure to inhibition of P-glycoprotein function in a surrogate assay, and (c) to compare the pharmacokinetics of doxorubicin in the presence and absence of zosuquidar. Patients and Methods: Patients with advanced malignancies who provided written informed consent received zosuquidar and doxorubicin administered separately during the first cycle of therapy and then concurrently in subsequent cycles. Zosuquidar was given i.v. over 48 h in a cohort-dose escalation manner until the occurrence of dose-limiting toxicity or protocol specified maximum exposure. Doxorubicin doses of 45, 60, 75 mg/m2 were administered during the course of the trial. Results: Dose escalation proceeded through 9 cohorts with a total of 40 patients. The maximal doses administered were 640 mg/m2 of zosuquidar and 75 mg/m2 of doxorubicin. No dose-limiting toxicity of zosuquidar was observed. Pharmacokinetic analysis revealed that, in the presence of zosuquidar at doses that exceeded 500 mg, there was a modest decrease in clearance (17–22%) and modest increase in area under the curve (15–25%) of doxorubicin. This change was associated with an enhanced leukopenia and thrombocytopenia but was without demonstrable clinical significance. The higher doses of zosuquidar were associated with maximal P-glycoprotein inhibition in natural killer cells. Conclusion: Zosuquidar can be safely coadministered with doxorubicin using a 48 h i.v. dosing schedule.

Considerations in the design and development of transport inhibitors as adjuncts to drug therapy.

With the realization of the importance of drug efflux transporters in disease processes and treatment, development of inhibitors to these transporters has been sought for use as adjuncts to therapy. To date, inhibitors that have been best studied are modulators of P-glycoprotein, a transporter important in the removal of anticancer agents from cells and overexpression of this transporter results in multidrug resistance. There is a delicate balance between efficacy and toxicity. This review summarizes key learning points in the development of P-glycoprotein inhibitors. Topics covered include specificity of the inhibitor for the target transporter, effect on metabolism of coadministered drugs, pharmacokinetic interactions, toxicity and the salient features needed for efficacy. These points will have general application to the development of inhibitors of transporters.

Phase I Study of Docetaxel in Combination with the P-Glycoprotein Inhibitor, Zosuquidar, in Resistant Malignancies

Purpose: To determine the maximum tolerated dose, dose-limiting toxicity, and pharmacokinetics of docetaxel infused over 1 hour when given in combination with oral zosuquidar to patients with resistant solid tumors. Experimental Design: In cycle 1, patients received docetaxel alone. In subsequent cycles, zosuquidar was administered with docetaxel, which was escalated from 75 to 100 mg/m2. Zosuquidar was escalated from 100 to 300 mg/m2 every 8 hours on days 1 to 3 for a total of 7 doses, or from 400 to 500 mg every 12 hours for 2 doses administered 2 hours before docetaxel. The pharmacokinetics of docetaxel with and without zosuquidar administration were obtained. Results: Thirty-six of 41 patients completed at least one cycle of docetaxel and zosuquidar. The maximum tolerated dose was docetaxel 100 mg/m2 and zosuquidar 500 mg every 12 hours for 2 doses. The most common toxicity was neutropenia. In 35 patients, zosuquidar produced minimal increases in the docetaxel peak plasma concentrations and area under the curve. Dosing over 3 days with zosuquidar (7 doses) did not show benefit over the 1-day dosing. Of the 36 patients, one patient had a partial response, and 14 patients had disease stabilization. Conclusions: Docetaxel at 75 or 100 mg/m2 and zosuquidar 500 mg 2 hours before docetaxel and 12 hours later is well tolerated. Zosuquidar minimally alters the pharmacokinetics of docetaxel, allowing full dose docetaxel to be given with this P-glycoprotein modulator. A Phase II study with this combination in advanced breast carcinoma is underway.

Population pharmacokinetic-pharmacodynamic modeling of moxonidine using 24-hour ambulatory blood pressure measurements

To develop a model for 24‐hour ambulatory blood pressure measurements (ABPM) that can be applied in a pharmacokinetic‐pharmacodynamic model.

A phase 2 study of tasisulam sodium (LY573636 sodium) as second-line treatment for patients with unresectable or metastatic melanoma†‡

Tasisulam sodium (hereafter, tasisulam) is a novel anticancer agent that induces apoptosis through the intrinsic pathway and has antiangiogenic activity in preclinical models. Tasisulam demonstrated activity across a broad range of tumors, including melanoma. The primary objective of this phase 2 study was to determine the objective response rate (ORR) in patients who had received 1 previous systemic chemotherapy for unresectable/metastatic melanoma; secondary objectives were to evaluate the clinical response rate (CRR), progression‐free survival (PFS), overall survival (OS), duration of response, safety, and pharmacokinetics.

Comparison of manual versus ambulatory blood pressure measurements with pharmacokinetic-pharmacodynamic modeling of antihypertensive compounds: Application to moxonidine

To compare the results of the pharmacokinetic‐pharmacodynamic analyses of 24‐hour ambulatory blood pressure measurements and manual blood pressure data in patients receiving moxonidine.

Tasisulam Sodium (LY573636 Sodium) as Third-Line Treatment in Patients With Unresectable, Metastatic Non–Small-Cell Lung Cancer: A Phase-II Study

Introduction: Tasisulam sodium (hereafter referred to as tasisulam) is a novel anticancer compound that induces apoptosis and exhibits antiangiogenesis activity in a broad range of cancer models, including non–small-cell lung cancer (NSCLC). Methods: Tasisulam was administered as a 2-hour infusion every 21 days as third-line treatment in patients with advanced (stage IIIB/IV) NSCLC. Results: Thirty-two patients received a Cmax target dose of 420 µg/ml. Median time to progression was 3.12 months, median progression-free survival was 2.69 months, and median overall survival was 8.48 months. There were no objective responses; 43.8% of patients achieved stable disease. A high rate of grade-4 hematologic toxicity in the first 30 patients led to exploration of a lower Cmax target dose of 380 µg/ml. The rate of grade-4 hematologic toxicity (thrombocytopenia and/or neutropenia) at the 380-µg/ml dose (n = 20) was 20% versus 34% at the 420-µg/ml dose. Conclusions: Tasisulam has only modest activity as a third-line treatment of patients with unresectable/metastatic NSCLC. The high rate of grade-4 hematologic toxicity observed with this highly albumin– bound compound in this patient population provided challenges for fixed Cmax-based dosing. Alternative dosing methods, including varying the Cmax target dose by predose albumin, are under investigation in other studies.

Drug Transporters and Their Role in Tissue Distribution

Publisher Summary Transporters are critical for the movement of hydrophilic and hydrophobic drugs across membranes. In clinical studies, transporters have been shown to be important in the oral absorption and tissue distribution of a number of very successful marketed drugs. The human genome initiative has estimated that humans possess 2000 or more transporters and ion channels. Functionally, three classes of transporters exist: influx transporters facilitate the movement of compounds into the cell, efflux transporters remove cytosolic substances from the cell, and exchangers permit the simultaneous movement of solutes across the membrane in opposite directions. A second major group of drug transporters are members of the ABC transporter superfamily that are responsible for the efflux of many drugs and drug conjugates. These ABC membrane proteins are ATP-dependent transporters that contain a highly conserved ATP signature domain and multiple transmembrane spanning domains. Humans possess ∼50 members of this superfamily which are divided into seven families (designated ABCA–ABCG) and to date four families contain drug efflux transporters.

Getting Innovative Therapies Faster to Patients at the Right Dose: Impact of Quantitative Pharmacology Towards First Registration and Expanding Therapeutic Use

Quantitative pharmacology (QP) applications in translational medicine, drug‐development, and therapeutic use were crowd‐sourced by the ASCPT Impact and Influence initiative. Highlighted QP case studies demonstrated faster access to innovative therapies for patients through 1) rational dose selection for pivotal trials; 2) reduced trial‐burden for vulnerable populations; or 3) simplified posology. Critical success factors were proactive stakeholder engagement, alignment on the value of model‐informed approaches, and utilizing foundational clinical pharmacology understanding of the therapy.