A mechanism-based population pharmacokinetic model for characterizing time-dependent pharmacokinetics of midostaurin and its metabolites in human subjects

Physiologically based pharmacokinetic modeling of midostaurin and metabolites at steady-state to bridge drug interaction scenarios in lieu of clinical trials

Midostaurin and its active metabolites are substrates, mixed inhibitors/inducers of cytochrome P450 (CYP)3A4. The main objective of this study was to develop/refine a physiologically based pharmacokinetic (PBPK) model that incorporated recent clinical drug-drug interaction (DDI) data with midazolam after multiple dosing, to qualify the pharmacokinetic (PK) model simulations of midostaurin and its metabolites, and to apply it to predict untested clinical DDI scenarios with potential comedications. In this study, Simcyp PBPK model of midostaurin and its 2 metabolites was refined from a previously published model associated with endogenous biomarker 4β-hydroxycholesterol data through further optimization of CYP3A4 inhibition/induction potency and was qualified to simulate midostaurin steady-state PK. The incorporation of these parameters enabled DDI predictions of high midostaurin doses on the PK of midazolam and oral contraceptives containing ethinyl estradiol. Additionally, scaling factors for in vitro breast cancer resistance protein and the organic anion transporting polypeptide (OATP1B) inhibition were applied to account for the observed single-dose DDI with rosuvastatin and further extrapolated to predict steady-state DDI with other OATP1B drug substrates. The overall prediction results showed minimal impact of midostaurin at high doses on CYP3A substrates or an effect on the exposure of OATP1B substrates. In summary, the midostaurin PBPK model was retrospectively refined, requalified, and used to simulate the steady-state perpetrator DDI of midostaurin and its metabolites. This PBPK modeling approach and the resulting model predictions were implemented into the midostaurin product label (up to 100 mg twice a day) without the need for confirmatory clinical studies. SIGNIFICANCE STATEMENT: The manuscript describes how a midostaurin PBPK model was updated, verified, and applied to untested scenarios by a predict-learn-confirm cycle as new clinical data become available. It also provides a learning experience of prospective prediction by utilizing endogenous biomarker 4β-hydroxycholesterol to evaluate a complex CYP3A4-mediated drug interaction.

Antiproliferative and Morphological Analysis Triggered by Drugs Contained in the Medicines for Malaria Venture COVID-Box Against Toxoplasma gondii Tachyzoites

Toxoplasma gondii is a protozoan, and the etiologic agent of toxoplasmosis, a disease that causes high mortality in immunocompromised individuals and newborns. Despite the medical importance of toxoplasmosis, few drugs, which are associated with side effects and parasite resistance, are available for its treatment. Here, we show a screening of molecules present in COVID-Box to discover new hits with anti-T. gondii activity. COVID-Box contains 160 molecules with known or predicted activity against SARS-CoV-2. Our analysis selected 23 COVID-Box molecules that can inhibit the tachyzoite forms of the RH strain of T. gondii in vitro by more than 70% at 1 µM after seven days of treatment. The inhibitory curves showed that most of these molecules inhibited the proliferation of tachyzoites with IC50 values below 0.80 µM; Cycloheximide and (-)-anisomycin were the most active drugs, with IC50 values of 0.02 μM. Cell viability assays showed that the compounds are not toxic at active concentrations, and most are highly selective for parasites. Overall, all 23 compounds were selective, and for two of them (apilimod and midostaurin), this is the first report of activity against T. gondii. To better understand the effect of the drugs, we analyzed the effect of nine of them on the ultrastructure of T. gondii using transmission electron microscopy. After treatment with the selected drugs, the main changes observed in parasite morphology were the arrestment of cell division and organelle alterations.

Quantification of midostaurin in plasma and serum by stable isotope dilution liquid chromatography-tandem mass spectrometry: Application to a cohort of patients with acute myeloid leukemia

OBJECTIVES

Midostaurin is an oral multitargeted tyrosine kinase inhibitor for the treatment of acute myeloid leukemia (AML). Therapeutic drug monitoring of midostaurin may support its safe use when suspecting toxicity or combined with strong CYP3A4 inhibitors.

METHODS

A stable isotope dilution liquid chromatography-tandem mass spectrometry method was developed and validated for the determination and quantification of midostaurin in human plasma and serum. Midostaurin serum concentrations were analyzed in 12 patients with FMS-like tyrosine kinase 3 (FLT3)-mutated AML during induction chemotherapy with cytarabine, daunorubicin, and midostaurin. Posaconazole was used as prophylaxis of invasive fungal infections.

RESULTS

Linear quantification of midostaurin was demonstrated across a concentration range of 0.01-8.00 mg/L. Inter- and intraday imprecisions of the proposed method were well within ±10%. Venous blood samples were taken in nine and three patients in the first and second cycle of induction chemotherapy. Median (range) midostaurin serum concentration was 7.9 mg/L (1.5-26.1 mg/L) as determined in 37 independent serum specimens.

CONCLUSION

In a real-life cohort of AML patients, interindividual variability in midostaurin serum concentrations was high, highlighting issues concerning optimal drug dosing in AML patients. A personalized dosage approach may maximize the safety of midostaurin. Prospective studies and standardization of analytical methods to support such an approach are needed.

Posaconazole and midostaurin in patients with FLT3-mutated acute myeloid leukemia: Pharmacokinetic interactions and clinical facts in a real life study

Midostaurin is used in combination with chemotherapy to treat patients with newly diagnosed FLT3-mutated acute myeloid leukemia. Chemotherapy-induced neutropenia exposes these patients to a significant risk of invasive fungal infections (IFIs). International guidelines recommend primary antifungal prophylaxis with posaconazole (PCZ) but nested analysis of a phase III trial showed that strong PCZ inhibition of CYP3A4 diminished midostaurin metabolism and increased midostaurin plasma levels; however, midostaurin-related adverse events (AEs) were only moderately exacerbated. We conducted a prospective multicenter real-life study to evaluate (i) how often concerns around PCZ-midostaurin interactions made the hematologist prescribe antifungals other than PCZ, (ii) how remarkably PCZ increased midostaurin plasma levels, and (iii) how significantly PCZ-midostaurin interactions influenced hematologic and safety outcomes of induction therapy. Although the hematologists were blinded to pharmacokinetic findings, as many as 16 of 35 evaluable patients were prescribed antifungal prophylaxis with micafungin, weak CYP3A4 inhibitor, in place of PCZ (p < 0.001 for deviation from guidelines). In the 19 patients managed as per guidelines, PCZ-midostaurin interactions were more remarkable than previously characterized, such that at the end of induction therapy midostaurin minimum plasma concentration (Cmin ) was greater than three times higher than reported; moreover, midostaurin Cmin , maximum plasma concentration, and area under the curve were more than or equal to four times higher with PCZ than micafungin. Hematologic outcomes (complete remission and duration of severe neutropenia) and safety outcomes (midostaurin-related any grade or grade ≥3 AEs) were nonetheless similar for patients exposed to PCZ or micafungin, as was the number of breakthrough IFIs. In waiting for randomized phase III trials of new prophylaxis regimens, these findings show that PCZ should remain the antifungal of choice for the midostaurin-treated patient.

Effect of flavonoids and CYP3A4 variants on midostaurin metabolism

The objective of this study was to determine the effect of flavonoids on midostaurin disposition considering co-administration and metabolic enzyme gene polymorphism. Enzymatic incubation assays were performed in vitro, while in vivo experiments were conducted in Sprague-Dawley rats. The analytes were determined via UPLC-MS/MS. We found that myricetin was the most potent among the investigated 10 flavonoids in suppressing the metabolism of midostaurin, with an IC₅₀ at a low μM level. After co-administration of midostaurin and myricetin, the plasma concentration of midostaurin's primary metabolite CGP62221 was reduced corresponding to myricetin exposure. Furthermore, CYP3A4 homologous rat protein CYP3A2 was reduced significantly in the co-administration group. Thereafter, the kinetic parameters of 23 recombinant human CYP3A4 variants were determined using midostaurin. The relative intrinsic clearance varied from 269.63% in CYP3A4.29-8.95% in CYP3A4.17. In addition, the inhibitory potency of myricetin was substantially different for CYP3A4.29 and CYP3A4.17 compared with wild type, with IC₅₀ values of 9.85 ± 0.27 μM and 90.99 ± 16.13 μM, respectively. Collectively, our data demonstrated that flavonoids, particularly myricetin, can inhibit the metabolism of midostaurin. Additionally, CYP3A4 genetic polymorphism may contribute to stratification of midostaurin blood exposure.

Effect of autoinduction and food on the pharmacokinetics of furmonertinib and its active metabolite characterized by a population pharmacokinetic model

Furmonertinib (AST2818) is a novel third-generation irreversible EGFR TKI and recently has been approved in China for the treatment of non-small cell lung cancer (NSCLC) with EGFR-sensitizing and T790M resistance mutations. In the current study, we developed a semi-mechanistic population pharmacokinetic model to characterize the nonstationary pharmacokinetics (PK) of the furmonertinib and its active metabolite AST5902 simultaneously. The PK data of furmonertinib and AST5902 were obtained from 38 NSCLC patients and 16 healthy volunteers receiving 20-240 mg furmonertinib in three clinical trials. A nonlinear mixed-effects modeling approach was used to describe the PK data. The absorption process of furmonertinib was described by a transit compartment model. The disposition of both furmonertinib and AST5902 was described by a two-compartment model. An indirect response model accounted for the autoinduction of furmonertinib metabolism mediated by CYP3A4. The model-based simulation suggested that furmonertinib clearance was increased in one cycle of treatment (orally once daily for 21 days) compared to baseline, ranging from 1.1 to 1.8 fold corresponding to the dose range of 20-240 mg. The concentration of furmonertinib was decreased over time whereas that of AST5902 was increased. Interestingly, the concentration of the total active compounds (furmonertinib and AST5902) appeared to be stable. The food intake, serum alkaline phosphatase and body weight were identified as statistically significant covariates. The mechanism of food effect on PK was investigated, where the food intake might increase the bioavailability of furmonertinib via increasing the splanchnic blood flow. Overall, a population PK model was successfully developed to characterize the nonstationary PK of furmonertinib and AST5902 simultaneously. The concentrations of total active compounds were less affected by the autoinduction of furmonertinib metabolism.

A semimechanistic population pharmacokinetic and pharmacodynamic model incorporating autoinduction for the dose justification of TAS-114

TAS-114 is a dual deoxyuridine triphosphatase (dUTPase) and dihydropyrimidine dehydrogenase (DPD) inhibitor expected to widen the therapeutic index of capecitabine. Its maximum tolerated dose (MTD) was determined from a safety perspective in a combination study with capecitabine; however, its inhibitory effects on DPD activity were not assessed in the study. The dose justification to select its MTD as the recommended dose in terms of DPD inhibition has been required, but the autoinduction profile of TAS-114 made it difficult. To this end, an approach using a population pharmacokinetic (PPK)/pharmacodynamic (PD) model incorporating autoinduction was planned; however, the utility of this approach in the dose justification has not been reported. Thus, the aim of this study was to demonstrate the utility of a PPK/PD model incorporating autoinduction in the dose justification via a case study of TAS-114. Plasma concentrations of TAS-114 from 185 subjects and those of the endogenous DPD substrate uracil from 24 subjects were used. A two-compartment model with first-order absorption with lag time and an enzyme turnover model were selected for the pharmacokinetic (PK) model. Moreover, an indirect response model was selected for the PD model to capture the changes in plasma uracil concentrations. Model-based simulations provided the dose justification that DPD inhibition by TAS-114 reached a plateau level at the MTD, whereas exposures of TAS-114 increased dose dependently. Thus, the utility of a PPK/PD model incorporating autoinduction in the dose justification was demonstrated via this case study of TAS-114.

Therapeutic drug monitoring of oral targeted antineoplastic drugs

PURPOSE

This review provides an overview of the current challenges in oral targeted antineoplastic drug (OAD) dosing and outlines the unexploited value of therapeutic drug monitoring (TDM). Factors influencing the pharmacokinetic exposure in OAD therapy are depicted together with an overview of different TDM approaches. Finally, current evidence for TDM for all approved OADs is reviewed.

METHODS

A comprehensive literature search (covering literature published until April 2020), including primary and secondary scientific literature on pharmacokinetics and dose individualisation strategies for OADs, together with US FDA Clinical Pharmacology and Biopharmaceutics Reviews and the Committee for Medicinal Products for Human Use European Public Assessment Reports was conducted.

RESULTS

OADs are highly potent drugs, which have substantially changed treatment options for cancer patients. Nevertheless, high pharmacokinetic variability and low treatment adherence are risk factors for treatment failure. TDM is a powerful tool to individualise drug dosing, ensure drug concentrations within the therapeutic window and increase treatment success rates. After reviewing the literature for 71 approved OADs, we show that exposure-response and/or exposure-toxicity relationships have been established for the majority. Moreover, TDM has been proven to be feasible for individualised dosing of abiraterone, everolimus, imatinib, pazopanib, sunitinib and tamoxifen in prospective studies. There is a lack of experience in how to best implement TDM as part of clinical routine in OAD cancer therapy.

CONCLUSION

Sub-therapeutic concentrations and severe adverse events are current challenges in OAD treatment, which can both be addressed by the application of TDM-guided dosing, ensuring concentrations within the therapeutic window.

Towards better combination regimens of cytarabine and FLT3 inhibitors in acute myeloid leukemia

BACKGROUND

AML patients with FLT3/ITD mutations have poor response to cytarabine-based chemotherapy. FLT3 inhibitors (FLT3i) may resensitize cells to cytarabine (CYT). Improving treatment outcome of this combination may benefit from a mechanistic extrapolation approach from in vitro data.

METHODS

The effects of CYT and several FLT3i on cell proliferation and cell cycle kinetics were examined in AML cell lines. The effect of FLT3i (quizartinib, midostaurin, sorafenib) on cell proliferation and cell cycle kinetics was assessed in AML cell lines with differing FLT3 status; HEL (negligible expression of wild-type FLT3), EOL1 (wild-type FLT3), MV4-11 (FLT3-ITD resulting in constitutively active isoform). Semi-mechanistic cell cycle models for CYT and FLT3i were developed. Clinical CYT and quizartinib pharmacokinetic dosage regimens were modeled. Survival of AML patients was described via a hazard model. Simulations exploring different CYT/quizartinib regimens were conducted with the goal of improving treatment outcome.

RESULTS

FLT3 status was associated with sensitivity to CYT (HEL cells most sensitive > EOL1 > MV4-11 cells). This order of sensitivity is reversed for FLT3i. Cytarabine induced apoptosis in the S-phase while all FLT3i induced apoptosis and cell cycle arrest at G1 phase. Simulations of candidate clinical regimens predict better cell kill upon adding quizartinib simultaneously with or immediately after CYT exposure. Overall survival was predicted to be significantly better with quizartinib 200 mg administered every 48 h vs every 24 h in patients with FLT3 aberrations.

CONCLUSION

Simultaneous administration of quizartinib and CYT every other day is a promising combination regimen for AML patients with FLT3 mutations.

Discovery of benzo[d]oxazole derivatives as the potent type-I FLT3-ITD inhibitors

Fms-like tyrosine kinase 3 (FLT3) has been considered as a potential drug target for the treatment of acute myeloid leukemia (AML), because of its high and aberrant expression in AML patients, especially the patients with FLT3-ITD mutation. Initiating from a hit compound (IC₅₀: 500 nM against FLT3-ITD), a series of compounds were designed and synthesized based on benzo[d]oxazole-2-amine scaffold to discover new potent FLT3-ITD inhibitors. During the medicinal chemistry works, flexible molecular docking was used to provide design rationale and study the binding modes of the target compounds. Through the mixed SAR exploration based on the enzymatic and cellular activities, compound T24 was identified with potent FLT3-ITD inhibitory (IC₅₀: 0.41 nM) and anti-proliferative (IC₅₀: 0.037 μM against MV4-11 cells) activities. And the binding mode of T24 with "DFG-in" FLT3 was simulated by a 20-ns molecular dynamics run, providing some insights into further medicinal chemistry efforts toward novel FLT3 inhibitors in AML therapy.

Clinical Studies on Drug-Drug Interactions Involving Metabolism and Transport: Methodology, Pitfalls, and Interpretation

Many drug-drug interactions (DDIs) are based on alterations of the plasma concentrations of a victim drug due to another drug causing inhibition and/or induction of the metabolism or transporter-mediated disposition of the victim drug. In the worst case, such interactions cause more than tenfold increases or decreases in victim drug exposure, with potentially life-threatening consequences. There has been tremendous progress in the predictability and modeling of DDIs. Accordingly, the combination of modeling approaches and clinical studies is the current mainstay in evaluation of the pharmacokinetic DDI risks of drugs. In this paper, we focus on the methodology of clinical studies on DDIs involving drug metabolism or transport. We specifically present considerations related to general DDI study designs, recommended enzyme and transporter index substrates and inhibitors, pharmacogenetic perspectives, index drug cocktails, endogenous substrates, limited sampling strategies, physiologically-based pharmacokinetic modeling, complex DDIs, methodological pitfalls, and interpretation of DDI information.

FLT3 Inhibitors in Acute Myeloid Leukemia: Current Status and Future Directions

The receptor tyrosine kinase fms-like tyrosine kinase 3 (FLT3), involved in regulating survival, proliferation, and differentiation of hematopoietic stem/progenitor cells, is expressed on acute myeloid leukemia (AML) cells in most patients. Mutations of FLT3 resulting in constitutive signaling are common in AML, including internal tandem duplication (ITD) in the juxtamembrane domain in 25% of patients and point mutations in the tyrosine kinase domain in 5%. Patients with AML with FLT3-ITD have a high relapse rate and short relapse-free and overall survival after chemotherapy and after transplant. A number of inhibitors of FLT3 signaling have been identified and are in clinical trials, both alone and with chemotherapy, with the goal of improving clinical outcomes in patients with AML with FLT3 mutations. While inhibitor monotherapy produces clinical responses, they are usually incomplete and transient, and resistance develops rapidly. Diverse combination therapies have been suggested to potentiate the efficacy of FLT3 inhibitors and to prevent development of resistance or overcome resistance. Combinations with epigenetic therapies, proteasome inhibitors, downstream kinase inhibitors, phosphatase activators, and other drugs that alter signaling are being explored. This review summarizes the current status of translational and clinical research on FLT3 inhibitors in AML, and discusses novel combination approaches. Mol Cancer Ther; 16(6); 991-1001. ©2017 AACR.

Time-dependent pharmacokinetics of dexamethasone and its efficacy in human breast cancer xenograft mice: a semi-mechanism-based pharmacokinetic/pharmacodynamic model

Dexamethasone (DEX) is the substrate of CYP3A. However, the activity of CYP3A could be induced by DEX when DEX was persistently administered, resulting in auto-induction and time-dependent pharmacokinetics (pharmacokinetics with time-dependent clearance) of DEX. In this study we investigated the pharmacokinetic profiles of DEX after single or multiple doses in human breast cancer xenograft nude mice and established a semi-mechanism-based pharmacokinetic/pharmacodynamic (PK/PD) model for characterizing the time-dependent PK of DEX as well as its anti-cancer effect. The mice were orally given a single or multiple doses (8 mg/kg) of DEX, and the plasma concentrations of DEX were assessed using LC-MS/MS. Tumor volumes were recorded daily. Based on the experimental data, a two-compartment model with first order absorption and time-dependent clearance was established, and the time-dependence of clearance was modeled by a sigmoid E_max equation. Moreover, a semi-mechanism-based PK/PD model was developed, in which the auto-induction effect of DEX on its metabolizing enzyme CYP3A was integrated and drug potency was described using an E_max equation. The PK/PD model was further used to predict the drug efficacy when the auto-induction effect was or was not considered, which further revealed the necessity of adding the auto-induction effect into the final PK/PD model. This study established a semi-mechanism-based PK/PD model for characterizing the time-dependent pharmacokinetics of DEX and its anti-cancer effect in breast cancer xenograft mice. The model may serve as a reference for DEX dose adjustments or optimization in future preclinical or clinical studies.

Simultaneous Physiologically Based Pharmacokinetic (PBPK) Modeling of Parent and Active Metabolites to Investigate Complex CYP3A4 Drug-Drug Interaction Potential: A Case Example of Midostaurin

Midostaurin (PKC412) is being investigated for the treatment of acute myeloid leukemia (AML) and advanced systemic mastocytosis (advSM). It is extensively metabolized by CYP3A4 to form two major active metabolites, CGP52421 and CGP62221. In vitro and clinical drug-drug interaction (DDI) studies indicated that midostaurin and its metabolites are substrates, reversible and time-dependent inhibitors, and inducers of CYP3A4. A simultaneous pharmacokinetic model of parent and active metabolites was initially developed by incorporating data from in vitro, preclinical, and clinical pharmacokinetic studies in healthy volunteers and in patients with AML or advSM. The model reasonably predicted changes in midostaurin exposure after single-dose administration with ketoconazole (a 5.8-fold predicted versus 6.1-fold observed increase) and rifampicin (90% predicted versus 94% observed reduction) as well as changes in midazolam exposure (1.0 predicted versus 1.2 observed ratio) after daily dosing of midostaurin for 4 days. The qualified model was then applied to predict the DDI effect with other CYP3A4 inhibitors or inducers and the DDI potential with midazolam under steady-state conditions. The simulated midazolam area under the curve ratio of 0.54 and an accompanying observed 1.9-fold increase in the CYP3A4 activity of biomarker 4β-hydroxycholesterol indicated a weak-to-moderate CYP3A4 induction by midostaurin and its metabolites at steady state in patients with advSM. In conclusion, a simultaneous parent-and-active-metabolite modeling approach allowed predictions under steady-state conditions that were not possible to achieve in healthy subjects. Furthermore, endogenous biomarker data enabled evaluation of the net effect of midostaurin and its metabolites on CYP3A4 activity at steady state and increased confidence in DDI predictions.

Midostaurin/PKC412 for the treatment of newly diagnosed FLT3 mutation-positive acute myeloid leukemia

INTRODUCTION

Acute myeloid leukemia (AML) is an aggressive hematologic malignancy with inadequate treatment options. Approximately one-third of cases have a FLT3-ITD or FLT3-TKD mutation which leads to constitutive tyrosine kinase activation which contributes to leukemogenesis. The FLT3-ITD mutation is associated with a particularly poor prognosis. Midostaurin is a multi-kinase inhibitor active against the FLT3 receptor. Midostaurin was approved by the US FDA in April 2017 for treatment of newly diagnosed FLT3-mutant AML in combination with chemotherapy. Areas covered: Standard treatment of FLT3-mutant AML and outcomes. Early clinical development of midostaurin including pharmacokinetics and metabolism. The development of midostaurin in FLT3-mutant AML is then outlined including review of the phase I, II, and III trials of midostaurin as a single agent and in combination with chemotherapy. Expert commentary: The approval of midostaurin represents the first new therapy for AML in several decades. It is also the first targeted therapy approved for AML. Future studies will focus on defining mechanisms of resistance to midostaurin as well as establishing the role of midostaurin in combination with hypomethylating agents and as maintenance therapy. Second generation, more potent and selective FLT3 inhibitors are also in development; these agents need to be compared to midostaurin.

Midostaurin for the treatment of acute myeloid leukemia

Midostaurin is a multikinase tyrosine kinase inhibitor acting against targets known to be expressed in hematologic malignancies, especially acute myeloid leukemia. Midostaurin combined with chemotherapy followed by single-agent maintenance therapy elicited statistically significant and clinically meaningful improvement in overall survival versus placebo in patients with newly diagnosed FLT3-mutant acute myeloid leukemia. Although gastrointestinal events were more common with midostaurin, overall the drug was relatively well tolerated. Of note, midostaurin is metabolized by cytochrome P450–3A4 (CYP3A4); therefore, concomitant strong CYP3A4 inhibitors should be used with caution. Preliminary safety results from an ongoing trial evaluating midostaurin as a single agent in the post-transplant setting are encouraging. In addition, studies have evaluated its safety and efficacy in advanced systemic mastocytosis.

Midostaurin: an emerging treatment for acute myeloid leukemia patients

Acute myeloid leukemia (AML) is a hematologic malignancy that carries a poor prognosis and has garnered few treatment advances in the last few decades. Mutation of the internal tandem duplication (ITD) region of fms-like tyrosine kinase (FLT3) is considered high risk for decreased response and overall survival. Midostaurin is a Type III receptor tyrosine kinase inhibitor found to inhibit FLT3 and other receptor tyrosine kinases, including platelet-derived growth factor receptors, cyclin-dependent kinase 1, src, c-kit, and vascular endothelial growth factor receptor. In preclinical studies, midostaurin exhibited broad-spectrum antitumor activity toward a wide range of tumor xenografts, as well as an FLT3-ITD-driven mouse model of myelodysplastic syndrome (MDS). Midostaurin is orally administered and generally well tolerated as a single agent; hematologic toxicity increases substantially when administered in combination with standard induction chemotherapy. Clinical trials primarily have focused on relapsed/refractory AML and MDS and included single- and combination-agent studies. Administration of midostaurin to relapsed/refractory MDS and AML patients confers a robust anti-blast response sufficient to bridge a minority of patients to transplant. In combination with histone deacetylase inhibitors, responses appear comparable to historic controls, while the addition of midostaurin to standard induction chemotherapy may prolong survival in FLT3-ITD mutant patients. The response of some wild-type (WT)-FLT3 patients to midostaurin therapy is consistent with midostaurin’s ability to inhibit WT-FLT3 in vitro, and also may reflect overexpression of WT-FLT3 in those patients and/or off-target effects such as inhibition of kinases other than FLT3. Midostaurin represents a well-tolerated, easily administered oral agent with the potential to bridge mutant and WT-FLT3 AML patients to transplant and possibly deepen response to induction chemotherapy. Ongoing studies are investigating midostaurin’s role in pretransplant induction and posttransplant consolidation therapy.

Vatalanib population pharmacokinetics in patients with myelodysplastic syndrome: CALGB 10105 (Alliance)

AIMS

Vatalanib is an oral anti-angiogenesis agent that inhibits vascular endothelial growth factor receptor tyrosine kinases, which in patients showed auto induction of metabolism and variability in pharmacokinetic (PK) disposition. The objective was to characterize the population PK and time-dependent change in vatalanib clearance and assess exposure-toxicity relationship in patients with myelodysplastic syndrome (MDS).

METHODS

This was an open-label phase II study of vatalanib in MDS patients receiving 750-1250 mg once daily in 28-day cycles. Serial blood samples were obtained and plasma vatalanib concentrations measured by HPLC. Population PK analysis was performed using nonmem 7.2 with FO estimation since FOCE failed. The final model was evaluated using goodness-of-fit plots, bootstrap analysis, and visual predictive check.

RESULTS

Pharmacokinetic data were complete for 137 patients (86 M, 51 F), of median age 70 years (range 20-91). A one-compartment model with lagged first-order absorption and time-dependent change in oral clearance was fitted to the vatalanib plasma concentration versus time data. The population means for pre-induction and post-induction oral clearance were 24.1 l h(-1) (range: 9.6-45.5) and 54.9 l h(-1) (range: 39.8-75.6), respectively. The apparent oral clearance increased 2.3-fold, (range: 1.7-4.1-fold) from first dose to steady state. Our data did not identify a significant relationship of the predefined covariates with vatalanib pharmacokinetics, although power to detect such a relationship was limited.

CONCLUSIONS

Vatalanib pharmacokinetics were highly variable and the extent of auto induction was not determined to correlate with any of the pre-defined covariates.

The Biology and Targeting of FLT3 in Pediatric Leukemia

Despite remarkable improvement in treatment outcomes in pediatric leukemia over the past several decades, the prognosis for high-risk groups of acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL), as well as for relapsed leukemia, remains poor. Intensification of chemotherapy regimens for those at highest risk has improved success rates, but at the cost of significantly increased morbidity and long-term adverse effects. With the success of imatinib in Philadelphia-chromosome-positive leukemia and all-trans retinoic acid in acute promyelocytic leukemia, the quest to find additional molecularly targeted therapies has generated much excitement over recent years. Another such possible target in pediatric acute leukemia is FMS-like tyrosine kinase 3 (FLT3). FLT3 aberrations are among the most frequently identified transforming events in AML, and have significant clinical implications in both high-risk pediatric AML and in certain high-risk groups of pediatric ALL. Therefore, the successful targeting of FLT3 has tremendous potential to improve outcomes in these subsets of patients. This article will give an overview of the molecular function and signaling of the FLT3 receptor, as well as its pathogenic role in leukemia. We review the discovery of targeting FLT3, discuss currently available FLT3 inhibitors in pediatric leukemia and results of clinical trials to date, and finally, consider the future promise and challenges of FLT3 inhibitor therapy.

Liquid chromatography-tandem mass spectrometry assay for therapeutic drug monitoring of the tyrosine kinase inhibitor, midostaurin, in plasma from patients with advanced systemic mastocytosis

We developed and validated quantitative bioanalytical liquid chromatography-tandem mass spectrometry assay for the protein kinase inhibitor, midostaurin. Plasma samples were pre-treated using a protein precipitation with methanol containing midostaurin-d5 as an internal standard. After centrifugation, 5μL of the supernatant was injected into the chromatographic system. The system consisted of a 3.5μm particle bonded octadecyl silica column, with gradient elution using a mixture of 0.1% (v/v) formic acid in acetonitrile and 10mM ammonium formate in water with 0.1% formic acid. The analyte was quantified using the selected reaction-monitoring mode of a triple quadrupole mass spectrometer equipped with a heated electrospray interface. The assay was validated in a 75-2500ng/mL calibration range. For quality control, within-day and between-day precisions were 1.2-2.8%, and 1.2-6.9%, respectively. The β-expectation tolerance limit (accuracy) met the limits of acceptance ±15% (±20% for the LLQ). The drug was sufficiently stable under all relevant analytical conditions. The assay has successfully been used to assess drug levels for therapeutic drug monitoring in patients presenting advanced systemic mastocytosis and treated with the promising midostaurin.

Investigation into CYP3A4-mediated drug-drug interactions on midostaurin in healthy volunteers

PURPOSE

Midostaurin (PKC412), a multitargeted tyrosine kinase inhibitor that targets FMS-related tyrosine kinase 3 and KIT, is in clinical trials for the treatment for acute myeloid leukemia and advanced systemic mastocytosis. In vitro studies showed that midostaurin is predominantly metabolized by cytochrome P450 3A4 (CYP3A4) and that midostaurin inhibits and/or induces the same enzyme. Here, we address the clinical relevance of CYP3A4-related drug-drug interactions with midostaurin as either a "victim" or "perpetrator."

METHODS

Three phase I studies in healthy volunteers evaluated the effects of a CYP3A4 inhibitor (ketoconazole 400 mg daily for 10 days) or CYP3A4 inducer (rifampicin 600 mg daily for 14 days) on concentrations of midostaurin and its metabolites following a single 50-mg dose of midostaurin and the effects of midostaurin as a single dose (100 mg) and multiple doses (50 mg twice daily) on midazolam (a sensitive CYP3A4 probe) concentration. The plasma concentrations of midostaurin and its 2 active metabolites, CGP62221 and CGP52421, were determined using a sensitive liquid chromatography/tandem mass spectrometry method.

RESULTS

Inhibition of CYP3A4 by ketoconazole increased midostaurin exposure more than tenfold, and induction of CYP3A4 by rifampicin decreased midostaurin exposure by more than tenfold. Midostaurin did not appreciably affect the concentrations of midazolam or its metabolite, 1'-hydroxymidazolam, at single or multiple doses.

CONCLUSION

The pharmacokinetics of midostaurin and its metabolites was affected substantially by ketoconazole and rifampicin, suggesting that midostaurin is a sensitive CYP3A4 substrate. Midostaurin did not appear to inhibit or induce CYP3A4 in vivo.

FLT3 inhibitors for acute myeloid leukemia: a review of their efficacy and mechanisms of resistance

Since the Food and Drug Administration approval of imatinib for treatment of chronic myeloid leukemia in 2001, tyrosine kinase inhibitors (TKIs) have become a mainstay in the care of many malignancies. In acute myeloid leukemia (AML), activating mutations in the FMS-like tyrosine kinase 3 (FLT3) gene result in survival and proliferation of leukemic blasts and are associated with adverse prognosis. Therefore, the FLT3 receptor is an appealing target for inhibition. Multiple small molecule TKIs are currently in development for FLT3-mutated AML, and agents are beginning to show promising efficacy. In other malignancies, the development of resistance to TKIs during the course of therapy has proven to be a challenge, and thus far, in clinical trials of FLT3 TKIs, resistance to inhibition represents a significant barrier to successful FLT3 inhibition. Understanding the mechanisms of resistance and overcoming these obstacles to target inhibition will be central to the success of these agents.

Phase IIB trial of oral Midostaurin (PKC412), the FMS-like tyrosine kinase 3 receptor (FLT3) and multi-targeted kinase inhibitor, in patients with acute myeloid leukemia and high-risk myelodysplastic syndrome with either wild-type or mutated FLT3

PURPOSE

Mutations leading to constitutive activation of the FMS-like tyrosine kinase 3 receptor (FLT3) occur in blasts of 30% of patients with acute myeloid leukemia (AML). Midostaurin (PKC412; N-benzoylstaurosporin) is a multitargeted tyrosine kinase inhibitor, with demonstrated activity in patients with AML/myelodysplastic syndrome (MDS) with FLT3 mutations.

PATIENTS AND METHODS

Ninety-five patients with AML or MDS with either wild-type (n = 60) or mutated (n = 35) FLT3 were randomly assigned to receive oral midostaurin at 50 or 100 mg twice daily. The drug was discontinued in the absence of response at 2 months, disease progression, or unacceptable toxicity. Response was defined as complete response, partial response (PR), hematologic improvement, or reduction in peripheral blood or bone marrow blasts by ≥ 50% (BR).

RESULTS

The rate of BR for the population in whom efficacy could be assessed (n = 92) was 71% in patients with FLT3-mutant and 42% in patients with FLT3 wild-type. One PR occurred in a patient with FLT3-mutant receiving the 100-mg dose regimen. Both doses were well-tolerated; there were no differences in toxicity or response rate according to the dose of midostaurin.

CONCLUSION

These results suggest that midostaurin has hematologic activity in both patients with FLT3-mutant and wild-type. The degree of clinical activity observed supports additional studies that combine midostaurin and other agents such as chemotherapy especially in FLT3-mutant AML.