Justin C. Earp

Impact of Pharmacometric Analyses on New Drug Approval and Labelling Decisions

Pharmacometric analyses have become an increasingly important component of New Drug Application (NDA) and Biological License Application (BLA) submissions to the US FDA to support drug approval, labelling and trial design decisions. Pharmacometrics is defined as a science that quantifies drug, disease and trial information to aid drug development, therapeutic decisions and/or regulatory decisions. In this report, we present the results of a survey evaluating the impact of pharmacometric analyses on regulatory decisions for 198 submissions during the period from 2000 to 2008. Pharmacometric review of NDAs included independent, quantitative analyses by FDA pharmacometricians, even when such analysis was not conducted by the sponsor, as well as evaluation of the sponsor’s report. During 2000–2008, the number of reviews with pharmacometric analyses increased dramatically and the number of reviews with an impact on approval and labelling also increased in a similar fashion. We also present the impact of pharmacometric analyses on selection of paediatric dosing regimens, approval of regimens that had not been directly studied in clinical trials and provision of evidence of effectiveness to support a single pivotal trial. Case studies are presented to better illustrate the role of pharmacometric analyses in regulatory decision making.

U.S. Food and Drug Administration Approval: Ofatumumab for the Treatment of Patients with Chronic Lymphocytic Leukemia Refractory to Fludarabine and Alemtuzumab

Purpose: To describe the data and analyses that led to the U.S. Food and Drug Administration (FDA) approval of ofatumumab (Arzerra, GlaxoSmithKline) for the treatment of patients with chronic lymphocytic leukemia (CLL) refractory to fludarabine and alemtuzumab. Experimental Design: The FDA reviewed the results of a planned interim analysis of a single-arm trial, enrolling 154 patients with CLL refractory to fludarabine, and a supportive dose-finding, activity-estimating trial in 33 patients with CLL. Patients in the primary efficacy study received ofatumumab weekly for eight doses, then every 4 weeks for an additional four doses; patients in the supportive trial received four weekly doses. In the primary efficacy study, endpoints were objective response rate and response duration. Results: For regulatory purposes, the primary efficacy population consisted of 59 patients with CLL refractory to fludarabine and alemtuzumab. In this subgroup, the investigator-determined objective response rate was 42% [99% confidence interval (CI), 26–60], with a median duration of response of 6.5 months (95% CI, 5.8–8.3); all were partial responses. The most common adverse reactions in the primary efficacy study were neutropenia, pneumonia, pyrexia, cough, diarrhea, anemia, fatigue, dyspnea, rash, nausea, bronchitis, and upper respiratory tract infections. Infusion reactions occurred in 44% of patients with the first infusion (300 mg) and 29% with the second infusion (2,000 mg). The most common serious adverse reactions were infections, neutropenia, and pyrexia. Conclusions: On October 26, 2009, the FDA granted accelerated approval to ofatumumab for the treatment of patients with CLL refractory to fludarabine and alemtuzumab, on the basis of demonstration of durable tumor shrinkage. Clin Cancer Res; 16(17); 4331–8. ©2010 AACR.

Modeling Corticosteroid Effects in a Rat Model of Rheumatoid Arthritis I: Mechanistic Disease Progression Model for the Time Course of Collagen-Induced Arthritis in Lewis Rats

A mechanism-based model was developed to describe the time course of arthritis progression in the rat. Arthritis was induced in male Lewis rats with type II porcine collagen into the base of the tail. Disease progression was monitored by paw swelling, bone mineral density (BMD), body weights, plasma corticosterone (CST) concentrations, and tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and glucocorticoid receptor (GR) mRNA expression in paw tissue. Bone mineral density was determined by PIXImus II dual energy X-ray densitometry. Plasma CST was assayed by high-performance liquid chromatography. Cytokine and GR mRNA were determined by quantitative real-time polymerase chain reaction. Disease progression models were constructed from transduction and indirect response models and applied using S-ADAPT software. A delay in the onset of increased paw TNF-α and IL-6 mRNA concentrations was successfully characterized by simple transduction. This rise was closely followed by an up-regulation of GR mRNA and CST concentrations. Paw swelling and body weight responses peaked approximately 21 days after induction, whereas bone mineral density changes were greatest at 23 days after induction. After peak response, the time course in IL-1β, IL-6 mRNA, and paw edema slowly declined toward a disease steady state. Model parameters indicate TNF-α and IL-1β mRNA most significantly induce paw edema, whereas IL-6 mRNA exerted the most influence on BMD. The model for bone mineral density captures rates of turnover of cancellous and cortical bone and the fraction of each in the different regions analyzed. This small systems model integrates and quantitates multiple factors contributing to arthritis in rats.

FDA Approval Summary: Vemurafenib for Treatment of Unresectable or Metastatic Melanoma with the BRAFV600E Mutation

On August 17, 2011, the U.S. Food and Drug Administration (FDA) approved vemurafenib tablets (Zelboraf, Hoffmann-LaRoche Inc.) for the treatment of patients with unresectable or metastatic melanoma with the BRAFV600E mutation as detected by an FDA-approved test. The cobas 4800 BRAF V600 Mutation Test (Roche Molecular Systems, Inc.) was approved concurrently. An international, multicenter, randomized, open-label trial in 675 previously untreated patients with BRAFV600E mutation–positive unresectable or metastatic melanoma allocated 337 patients to receive vemurafenib, 960 mg orally twice daily, and 338 patients to receive dacarbazine, 1,000 mg/m2 intravenously every 3 weeks. Overall survival was significantly improved in patients receiving vemurafenib [HR, 0.44; 95% confidence interval (CI), 0.33–0.59; P < 0.0001]. Progression-free survival was also significantly improved in patients receiving vemurafenib (HR, 0.26; 95% CI, 0.20–0.33; P < 0.0001). Overall response rates were 48.4% and 5.5% in the vemurafenib and dacarbazine arms, respectively. The most common adverse reactions (≥30%) in patients treated with vemurafenib were arthralgia, rash, alopecia, fatigue, photosensitivity reaction, and nausea. Cutaneous squamous cell carcinomas or keratoacanthomas were detected in approximately 24% of patients treated with vemurafenib. Other adverse reactions included hypersensitivity, Stevens–Johnson syndrome, toxic epidermal necrolysis, uveitis, QT prolongation, and liver enzyme laboratory abnormalities. Clin Cancer Res; 20(19); 4994–5000. ©2014 AACR.

Modeling corticosteroid effects in a rat model of rheumatoid arthritis II: Mechanistic pharmacodynamic model for dexamethasone effects in Lewis rats with collagen-induced arthritis

A mechanism-based model for pharmacodynamic effects of dexamethasone (DEX) was incorporated into our model for arthritis disease progression in the rat to aid in identification of the primary factors responsible for edema and bone loss. Collagen-induced arthritis was produced in male Lewis rats after injection of type II porcine collagen. DEX was given subcutaneously in single doses of 0.225 or 2.25 mg/kg or 7-day multiple doses of 0.045 or 0.225 mg/kg at 21 days postdisease induction. Effects on disease progression were measured by paw swelling, bone mineral density (BMD), body weights, plasma corticosterone (CST), and tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and glucocorticoid receptor (GR) mRNA expression in paw tissue. Lumbar and femur BMD was determined by PIXImus II dual-energy X-ray absorptiometry. Plasma CST was assayed by high-performance liquid chromatography. Cytokine and GR mRNA were assayed by quantitative real-time polymerase chain reaction. Indirect response models, drug interaction models, transduction processes, and the fifth-generation model of corticosteroid dynamics were integrated and applied using S-ADAPT software to describe how dexamethasone binding to GR can regulate diverse processes. Cytokine mRNA, GR mRNA, plasma CST, and paw edema were suppressed after DEX administration. TNF-α mRNA expression and BMD seemed to increase immediately after dosing but were ultimately reduced. Model parameters indicated that IL-6 and IL-1β were most sensitive to inhibition by DEX. TNF-α seemed to primarily influence edema, whereas IL-6 contributed the most to bone loss. Lower doses of corticosteroids may be sufficient to suppress the cytokines most relevant to bone erosion.

Assessment of Drug Interactions Relevant to Pharmacodynamic Indirect Response Models

The assessment of drug interactions for a simple turnover system when the basic pharmacodynamic response is governed by indirect mechanisms was explored. This report describes a diverse array of possible in vivo pharmacodynamic effects from a combination of two drugs acting by similar or different indirect mechanisms. Various conditions of pharmacodynamic drug combinations were explored mathematically and by simulation: (a) interactions of two drugs acting simultaneously either on the production (kin) or on the dissipation (kout) processes controlling the in vivo response by competitive (four cases) or non-competitive interaction (six cases); and (b) combinations of two drugs acting on separate kin and kout processes simultaneously (four cases). A range of different combinations of drug doses was used. Plasma concentration time profiles were generated according to monoexponential disposition. Pharmacodynamic response profiles were simulated using the above conditions and characterized by descriptors such as Area Between Effect (and Baseline) Curve (ABEC) values. The interaction of agents by competitive mechanisms produced net responses that were additive in nature. Response profiles for non-competitive interactions on the same process were both antagonistic (for two drugs with effects that oppose each other) and synergistic (for two drugs that produce the same response). On the other hand, response signatures for agents acting non-competitively on the production and dissipation factors by opposing mechanisms (e.g. inhibiting kin plus stimulating kout) showed dramatic changes in net effects and produced apparent drug synergy. Net indirect response profiles for joint use of two or more drugs measured by ABEC values may look “additive”, “antagonistic”, or “synergistic” depending on doses, their intrinsic potencies, the nature of interaction (competitive or non-competitive) as well as their mechanisms of action. These models may help explain changes in pharmacologic responses to two agents in a more rational and mechanistic fashion than older empirical methods.

Therapeutic protein drug-drug interactions: navigating the knowledge gaps-highlights from the 2012 AAPS NBC Roundtable and IQ Consortium/FDA workshop.

The investigation of therapeutic protein drug–drug interactions has proven to be challenging. In May 2012, a roundtable was held at the American Association of Pharmaceutical Scientists National Biotechnology Conference to discuss the challenges of preclinical assessment and in vitro to in vivo extrapolation of these interactions. Several weeks later, a 2-day workshop co-sponsored by the U.S. Food and Drug Administration and the International Consortium for Innovation and Quality in Pharmaceutical Development was held to facilitate better understanding of the current science, investigative approaches and knowledge gaps in this field. Both meetings focused primarily on drug interactions involving therapeutic proteins that are pro-inflammatory cytokines or cytokine modulators. In this meeting synopsis, we provide highlights from both meetings and summarize observations and recommendations that were developed to reflect the current state of the art thinking, including a four-step risk assessment that could be used to determine the need (or not) for a dedicated clinical pharmacokinetic interaction study.

Synergism between Arsenic Trioxide and Heat Shock Protein 90 Inhibitors on Signal Transducer and Activator of Transcription Protein 3 Activity—Pharmacodynamic Drug-Drug Interaction Modeling

Purpose: Constitutive signal transducer and activator of transcription 3 (STAT3) activity, observed in ∼50% of acute myelogenous leukemia cases and associated with adverse treatment outcome, is down-regulated by arsenic trioxide (ATO). Heat shock protein (HSP) 90 is a molecular chaperone involved in signal transduction pathways. We hypothesized that HSP90 inhibitors will potentiate ATO effect on constitutive STAT3 activity and cell killing. One concern was that the effect of ATO and HSP90 inhibitors will result in up-regulation of HSP70, a protein known to inhibit apoptosis. Experimental Design: We have used a semimechanistic pharmacodynamic model to characterize concentration-effect relationships of ATO and HSP90 inhibitors on constitutive STAT3 activity, HSP70 expression, and cell death in a cell line model. Results: Pharmacodynamic interaction of ATO and three HSP90 inhibitors showed synergistic interactions in inhibiting constitutive STAT3 activity and inducing cell death, in spite of a concurrent synergistic up-regulation of HSP70. Conclusions: These preliminary results provide a basis for studying the combined role of ATO with HSP90 inhibitors in acute myelogenous leukemia with constitutive STAT3 activity.

Pharmacokinetics of dexamethasone in a rat model of rheumatoid arthritis

Dexamethasone (DEX) is often given for the treatment of rheumatoid arthritis and clinical dosing regimens of DEX have often been based empirically. This study tests whether the inflammation processes in a rat model of rheumatoid arthritis alters the clearance and volume of distribution of DEX when compared with healthy controls. Groups of healthy and arthritic male Lewis rats received either a low (0.225 mg/kg) or high (2.25 mg/kg) intramuscular dose of DEX. Arthritis was induced by intradermal injection of type II porcine collagen in incomplete Freunds adjuvant emulsion at the base of the tail. DEX was dosed in the arthritic animals 22 days post arthritis induction. Plasma DEX concentrations were determined by HPLC. Plasma concentration versus time data were analysed by non‐compartmental analysis and pharmacokinetic model fitting using the population pharmacokinetic software NONMEM V. A linear bi‐exponential pharmacokinetic model with extravascular input described the data for both healthy and arthritic animals. Clearance was the only parameter determined statistically different between both groups (healthy=1.05 l/h/kg, arthritic=1.19 l/h/kg). The steady‐state volume of distribution for both groups was 4.85 l/kg. The slight difference in clearance was visibly undetectable and unlikely to produce meaningful changes in DEX disposition in arthritic rats. Copyright

Targeting 11q23 positive acute leukemia cells with high molecular weight-melanoma associated antigen-specific monoclonal antibodies

BackgroundAcute leukemia with 11q23 aberrations is associated with a poor outcome with therapy. The lack of efficacy of conventional therapy has stimulated interest in developing novel strategies. Recent studies have shown that 11q23-positive acute leukemia cells express the high molecular weight-melanoma associated antigen (HMW-MAA). This tumor antigen represents a useful target to control growth of human melanoma tumors in patients and in severe combined immunodeficient (SCID) mice, utilizing antibody-based immunotherapy. This effect appears to be mediated by inhibition of the HMW-MAA function such as triggering of the focal adhesion kinase/proline-rich tyrosine kinase 2 (Pyk2) pathways. Therefore, in this study we tested whether HMW-MAA-specific monoclonal antibodies (mAb) could inhibit growth of 11q23-positive leukemia cells in SCID mice.MethodsHMW-MAA-specific mAb were tested for their ability to inhibit the in vitro proliferation of an 11q23-positive acute myeloid leukemia (AML) cell line and blasts from four patients with 11q23 aberrations and their in vivo growth in subcutaneous and disseminated xenograft models.ResultsThe HMW-MAA-specific mAb did not affect in vitro proliferation although they down-regulated phosphorylated (P) Pyk2 expression. Furthermore, the mAb enhanced the in vitro anti-proliferative effect of cytarabine. In vivo the mAb inhibited the growth of leukemic cells in a dose-dependent fashion. However, the difference did not reach statistical significance. No effect was detected on P-Pyk2 expression. Furthermore, HMW-MAA-specific mAb in combination with cytarabine did not improve tumor inhibition. Lastly, the combination of two mAb which recognize distinct HMW-MAA determinants had no detectable effect on survival in a disseminated xenograft model.ConclusionsHMW-MAA-specific mAb down-regulated P-Pyk2 expression and enhanced the anti-proliferative effect of cytarabine in vitro, but had no detectable effect on survival or growth of leukemia cells in vivo. Whether the HMW-MAA-specific mAb can be used as carriers of toxins or chemotherapeutic agents against 11q23-acute leukemia remains to be determined.