A Bayesian population PK-PD model of ispinesib-induced myelosuppression

Ribociclib Population Pharmacokinetics and Pharmacokinetic/Pharmacodynamic Analysis of Neutrophils in Cancer Patients

The population pharmacokinetics (popPK) of ribociclib and population pharmacokinetic/pharmacodynamic (PK/PD) relationship between ribociclib and absolute neutrophil count (ANC) were characterized in patients with cancer. PopPK and ANC PK/PD modeling were both conducted in 2 rounds per data availability. Initial models were developed based on data sets from early-phase trials and qualified using external data from the phase III MONALEESA-2 trial. The second round of analyses was performed using updated data sets that included 2 more phase III trials (MONALEESA-3 and -7). The popPK and ANC PK/PD models adequately described the data and demonstrated reasonable predictive ability. Covariate analysis showed that ribociclib PK were not affected by age, sex, race, baseline Eastern Cooperative Oncology Group (ECOG) status (grade 1), mild/moderate renal impairment, mild hepatic impairment, or concomitant use of combination partners, including aromatase inhibitors (letrozole, anastrozole) or fulvestrant, proton-pump inhibitors, or weak cytochrome P450 3A4/5 inhibitors. Body weight had no impact on ribociclib clearance to warrant dose adjustment. The ANC PK/PD relationship was not affected by age, weight, sex, race, baseline ECOG status (grade 1), or concomitant use of letrozole, anastrozole, or fulvestrant. The PK/PD analysis confirmed reversibility of ribociclib's effect on ANC; it also suggested that lowering the dose of ribociclib would mitigate ANC decrease and neutropenia risk. The popPK and ANC PK/PD analyses support the use of ribociclib in combination with an aromatase inhibitor or fulvestrant in patients with hormone receptor-positive, human epidermal growth factor receptor-2-negative advanced or metastatic breast cancer without dose adjustment in subpopulations, and the use of dose interruption/reduction to mitigate potential treatment-emergent neutropenia.

Bayesian sequential integration within a preclinical pharmacokinetic and pharmacodynamic modeling framework: Lessons learned

The present manuscript aims to discuss the implications of sequential knowledge integration of small preclinical trials in a Bayesian pharmacokinetic and pharmacodynamic (PK-PD) framework. While, at first sight, a Bayesian PK-PD framework seems to be a natural framework to allow for sequential knowledge integration, the scope of this paper is to highlight some often-overlooked challenges while at the same time providing some guidances in the many and overwhelming choices that need to be made. Challenges as well as opportunities will be discussed that are related to the impact of (1) the prior specification, (2) the choice of random effects, (3) the type of sequential integration method. In addition, it will be shown how the success of a sequential integration strategy is highly dependent on a carefully chosen experimental design when small trials are analyzed.

Evaluation of 4β-Hydroxycholesterol as a Clinical Biomarker of CYP3A4 Drug Interactions Using a Bayesian Mechanism-Based Pharmacometric Model

A Bayesian mechanism–based pharmacokinetic/pharmacodynamic model of cytochrome P450 3A4 (CYP3A4) activity was developed based on a clinical study of the effects of ketoconazole and rifampin on midazolam exposure and plasma 4β-hydroxycholesterol (4βHC) concentrations. Simulations from the model demonstrated that the dynamic range of 4βHC as a biomarker of CYP3A4 induction or inhibition was narrower than that of midazolam; an inhibitor that increases midazolam area under the curve by 20-fold may only result in a 20% decrease in 4βHC after 14 days of dosing. Likewise, an inducer that elevates CYP3A4 activity by 1.2-fold would reduce the area under the curve of midazolam by 50% but would only increase 4βHC levels by 20% after 14 days of dosing. Elevation in 4βHC could be reliably detected with a twofold induction in CYP3A4 activity with study sample sizes (N ~ 6–20) typically used in early clinical development. Only a strong CYP3A4 inhibitor (e.g., ketoconazole) could be detected with similar sample sizes.

Kinesin-5: cross-bridging mechanism to targeted clinical therapy

Kinesin motor proteins comprise an ATPase superfamily that works hand in hand with microtubules in every eukaryote. The mitotic kinesins, by virtue of their potential therapeutic role in cancerous cells, have been a major focus of research for the past 28 years since the discovery of the canonical Kinesin-1 heavy chain. Perhaps the simplest player in mitotic spindle assembly, Kinesin-5 (also known as Kif11, Eg5, or kinesin spindle protein, KSP) is a plus-end-directed motor localized to interpolar spindle microtubules and to the spindle poles. Comprised of a homotetramer complex, its function primarily is to slide anti-parallel microtubules apart from one another. Based on multi-faceted analyses of this motor from numerous laboratories over the years, we have learned a great deal about the function of this motor at the atomic level for catalysis and as an integrated element of the cytoskeleton. These data have, in turn, informed the function of motile kinesins on the whole, as well as spearheaded integrative models of the mitotic apparatus in particular and regulation of the microtubule cytoskeleton in general. We review what is known about how this nanomotor works, its place inside the cytoskeleton of cells, and its small-molecule inhibitors that provide a toolbox for understanding motor function and for anticancer treatment in the clinic.

Assessing the probability of drug-induced QTc-interval prolongation during clinical drug development

Early in the course of clinical development of new non-antiarrhythmic drugs, it is important to assess the propensity of these drugs to prolong the QT/QTc-interval. The current regulatory guidelines suggest using the largest time-matched mean difference between drug and placebo (baseline-adjusted) groups over the sampling interval, thereby neglecting any potential exposure-effect relationship and nonlinearity in the underlying physiological fluctuation in QT values. Thus far, most of the attempted models for characterizing drug-induced QTc-interval prolongation have disregarded the possibility of model parameterization in terms of drug-specific and system-specific properties. Using a database consisting of three compounds with known dromotropic activity, we built a bayesian hierarchical pharmacodynamic (PD) model to describe QT interval, encompassing an individual correction factor for heart rate, an oscillatory component describing the circadian variation, and a truncated maximum-effect model to account for drug effect. The explicit description of the exposure-effect relationship, incorporating various sources of variability, offers advantages over the standard regulatory approach.

Pharmacokinetic and pharmacodynamic analysis of hyperthermic intraperitoneal oxaliplatin-induced neutropenia in subjects with peritoneal carcinomatosis

The objective of this study was to characterize the pharmacokinetics and the time course of the neutropenia-induced by hyperthermic intraperitoneal oxaliplatin (HIO) after cytoreductive surgery in cancer patients with peritoneal carcinomatosis. Data from 30 patients who received 360 mg/m(2) of HIO following cytoreductive surgery were used for pharmacokinetic-pharmacodynamic (PK/PD) analysis. The oxaliplatin plasma concentrations were characterized by an open two-compartment pharmacokinetic model after first-order absorption from peritoneum to plasma. An oxaliplatin-sensitive progenitor cell compartment was used to describe the absolute neutrophil counts in blood. The reduction of the proliferation rate of the progenitor cells was modeled by a linear function of the oxaliplatin plasma concentrations. The typical values of oxaliplatin absorption and terminal half-lives were estimated to be 2.2 and 40 h, with moderate interindividual variability. Oxaliplatin reduced the proliferation rate of the progenitor cells by 18.2% per mg/L. No patient's covariates were related to oxaliplatin PK/PD parameters. Bootstrap and visual predictive check evidenced the model was deemed appropriate to describe oxaliplatin pharmacokinetics and the incidence and severity of neutropenia. A peritoneum oxaliplatin exposure of 65 and 120 mg·L/h was associated with a 20% and 33% incidence of neutropenia grade 4. The time course of neutropenia following HIO administration was well described by the semiphysiological PK/PD model. The maximum tolerated peritoneum oxaliplatin exposure is 120 mg L/h and higher exposures should be avoided in future studies. We suggest the prophylactic use of granulocyte colony stimulating factor for patients treated with HIO exposure higher than 65 mg L/h.

Prediction of neutropenia-related effects of a new combination therapy with the anticancer drugs BI 2536 (a Plk1 inhibitor) and pemetrexed

This study investigated the feasibility of predicting the neutropenia-related effects of a therapy that combines the investigational drug BI 2536 (inhibitor of Polo-like kinase 1) and pemetrexed, an approved anticancer drug. Predictions were arrived at using the pharmacokinetic/pharmacodynamic (PK/PD) parameters of each of the drugs obtained from monotherapy studies and assuming that the neutropenic effect is additive when the drugs are administered as a combination therapy. Subsequently, a PK/PD model was developed to determine whether this assumption of additive effect was reasonable in relation to these two drugs. All analyses and simulations were performed using the population approach in NONMEM, version VI.

Predictive ability of a semi-mechanistic model for neutropenia in the development of novel anti-cancer agents: two case studies

In cancer chemotherapy neutropenia is a common dose-limiting toxicity. An ability to predict the neutropenic effects of cytotoxic agents based on proposed trial designs and models conditioned on previous studies would be valuable. The aim of this study was to evaluate the ability of a semi-mechanistic pharmacokinetic/pharmacodynamic (PK/PD) model for myelosuppression to predict the neutropenia observed in Phase I clinical studies, based on parameter estimates obtained from prior trials. Pharmacokinetic and neutropenia data from 5 clinical trials for diflomotecan and from 4 clinical trials for indisulam were used. Data were analyzed and simulations were performed using the population approach with NONMEM VI. Parameter sets were estimated under the following scenarios: (a) data from each trial independently, (b) pooled data from all clinical trials and (c) pooled data from trials performed before the tested trial. Model performance in each of the scenarios was evaluated by means of predictive (visual and numerical) checks. The semi-mechanistic PK/PD model for neutropenia showed adequate predictive ability for both anti-cancer agents. For diflomotecan, similar predictions were obtained for the three scenarios. For indisulam predictions were better when based on data from the specific study, however when the model parameters were conditioned on data from trials performed prior to a specific study, similar predictions of the drug related-neutropenia profiles and descriptors were obtained as when all data were used. This work provides further indication that modeling and simulation tools can be applied in the early stages of drug development to optimize future trials.

Semi-mechanistic model for neutropenia after high dose of chemotherapy in breast cancer patients

PURPOSE

To describe the absolute neutrophil counts (ANC) profile in breast cancer patients receiving high-dose of chemotherapy and peripheral blood stem-cells (PBSC) transplantation.

METHODS

Data from 41 subjects receiving cyclophosphamide, thiotepa and carboplatin were used to develop the ANC model consisting of a drug-sensitive progenitor cell compartment, linked to the peripheral blood compartment, through three transition compartments. PBSC were incorporated into the first transit compartment following a zero-order process, k(in), and the rebound effect was explained by a feedback mechanism. A 'kinetics of drug action' model was used to quantify the HDC effect on the progenitor cells according to a linear function, with a slope (alpha).

RESULTS

The typical of the ANC at baseline (Circ(0)), mean transit time (MTT), feedback parameter (gamma), k(in) and alpha were estimated to be 5,610 x 10(6)/L, 3.25 days, 0.145, 0.954 cell/kg/day and 2.50 h/U, respectively. rHuG-CSF shortens the MTT by 92% and increases the mitotic activity by 120%. Bootstrap analysis, visual predictive check and numerical predictive checks evidenced accurate prediction of the ANC nadir, time to ANC nadir and time to grade 4 neutropenia recovery.

CONCLUSION

The time course of neutropenia following high-dose of chemotherapy and PBSC transplantation was accurately predicted. Higher amount of CD34+ cells in the PBSC transplantation and earlier administration rHuG-CSF were associated with faster haematological recovery.

Molecular Systems Biology in Drug Development

Molecular systems biology seeks to explain the behavior of complex cellular systems through a multicomponent analysis. We illustrate this approach and its relevance to drug development by reviewing two examples of the interplay between cellular processes and drugs: the internalization and recycling of oncogenic receptors, their ligands and therapeutic antibodies; and strategies for discovering drugs that affect intracellular protein kinase pathways.

Mechanism-based Pharmacokinetic/Pharmacodynamic Meta-analysis of Trabectedin (ET-743, Yondelis) Induced Neutropenia

Myelosuppression was found to be one of the main toxicities of trabectedin (ET-743, Yondelis) during phase I/II studies. Our objective was to develop a pharmacokinetic-pharmacodynamic (PK/PD) model that describes the time course of the absolute neutrophil counts (ANCs) in cancer patients receiving trabectedin. Data from 699 patients who received intravenous trabectedin as monotherapy (dose range: 0.006-1.8 mg/m2) as a 1-, 3-, or 24-h infusion every 21 days; 1- or 3-h infusion on days 1, 8, and 15 every 28 days; or a 1-h infusion daily for 5 consecutive days every 21 days were used to develop (N=405; ANCs=7,291) and validate (N=294; ANCs=5,029) the model. The PK/PD model comprised a trabectedin-sensitive progenitor cell compartment, linked to the peripheral blood compartment, through three transition compartments representing the maturation chain in the bone marrow. To capture the rebound effect due to endogenous growth factors, the model included a feedback mechanism. The model estimated three system-related parameters: ANC at baseline (Circ0), mean transit time in bone marrow (MTT), and a feedback parameter (gamma). A first-order process quantified by the rate constant k(e0) described the trabectedin concentrations at the effect compartment (C(e)), which were assumed to reduce the proliferation rate and/or to increase the killing rate of the progenitor cells according to the function alphaC(e)beta. The model was qualified and simulations were undertaken to evaluate the neutropenia schedule dependency and the effects of selected covariates. NONMEM software was used to perform the modeling and simulation analyses. For a typical man of 70 kg, the mean values (between-subject variability; %) of the Circ0, MTT, gamma, k(e0), alpha, and beta were estimated to be 4.46 x 10(9)/l (37.9%), 4.0 days (37.5%), 0.218 (41.8%), 2.09 h(-1) (77.9%), 2.00 l/microg (85.1%), and 1.26, respectively. Although in women, k(e0) was reduced by 29% and a 25% increase in body weight resulted in a 12.6% reduction in the beta parameter, the clinical relevance of these effects is limited. The model evaluation procedure indicated accurate prediction of the observed incidence of neutropenia grades 3 and 4 across the dosing regimens evaluated. Simulations indicated that trabectedin dose and interdose interval, but not infusion duration, are the main determinants of the neutropenia severity. The model-predicted time course of the ANC and its variability confirmed that neutropenia is reversible, of short duration, and non-cumulative. The extent and time course of neutropenia following six different dosing regimens of trabectedin were well predicted by the semiphysiological PK/PD model.