Clinical Pharmacokinetics and Pharmacodynamics of Rucaparib.

Rucaparib is an oral small-molecule poly(ADP-ribose) polymerase inhibitor indicated for patients with recurrent ovarian cancer in the maintenance and treatment settings and for patients with metastatic castration-resistant prostate cancer associated with a deleterious BRCA1 or BRCA2 mutation. Rucaparib has a manageable safety profile; the most common adverse events reported were fatigue and nausea in both indications. Accumulation in plasma exposure occurred after repeated administration of the approved 600-mg twice-daily dosage. Steady state was achieved after continuous twice-daily dosing for a week. Rucaparib has moderate oral bioavailability and can be dosed with or without food. Although a high-fat meal weakly increased maximum concentration and area under the curve, the effect was not clinically significant. A mass balance analysis indicated almost a complete dose recovery of rucaparib over 12 days, with metabolism, renal, and hepatic excretion as the elimination routes. A population pharmacokinetic analysis of rucaparib revealed no effect of age, sex, race, or body weight. No starting dose adjustments were necessary for patients with mild-to-moderate hepatic or renal impairment; the effect of severe organ impairment on rucaparib exposure has not been evaluated. In patients, rucaparib moderately inhibited cytochrome P450 (CYP) 1A2 and weakly inhibited CYP3As, CYP2C9, and CYP2C19. Rucaparib weakly increased systemic exposures of oral contraceptives and oral rosuvastatin and marginally increased the exposure of oral digoxin (a P-glycoprotein substrate). In vitro studies suggested that rucaparib inhibits transporters MATE1, MATE2-K, OCT1, and OCT2. No clinically meaningful drug interactions with rucaparib as a perpetrator were observed. An exposure-response analysis revealed dose-dependent changes in selected clinical efficacy and safety endpoints. Overall, this article provides a comprehensive review of the clinical pharmacokinetics, pharmacodynamics, drug-drug interactions, effects of intrinsic and extrinsic factors, and exposure-response relationships of rucaparib.

Population pharmacokinetics of rucaparib in patients with advanced ovarian cancer or other solid tumors.

PURPOSE: To develop a population pharmacokinetics (PPK) model for rucaparib, an oral poly(ADP-ribose) polymerase inhibitor. METHODS: The PPK analysis used PK data from patients in Study 1014 (NCT01009190, n = 35), Study 10 (NCT01482715, n = 123), and ARIEL2 (NCT01891344, n = 300), including intensive intravenous data (12-40 mg), intensive and sparse oral data (12-360 mg single-dose, 40-500 mg once daily, and 240-840 mg twice daily [BID]), and intensive single-dose oral data under fasted conditions and after a high-fat meal (40, 300, and 600 mg). RESULTS: Rucaparib PK was well described by a two-compartment model with sequential zero-order release and first-order absorption and first-order elimination. A high-fat meal slightly increased bioavailability at 600 mg but not at lower doses; this is not considered clinically significant, and rucaparib can be taken with or without food. Covariate effects of baseline creatinine clearance and albumin on rucaparib clearance were identified. Despite numerical increases in exposure with renal impairment, no dose adjustment is recommended for patients with mild or moderate renal impairment. No statistically significant relationships were detected for demographics, hepatic function (normal versus mild impairment), CYP1A2 and CYP2D6 phenotypes, or strong CYP1A2 or CYP2D6 inhibitors. Concomitant proton pump inhibitors showed no clinically significant effect on absorption. External validation of the model with data from ARIEL3 (NCT01968213) and TRITON2 (NCT02952534) studies showed no clinically meaningful PK differences across indications or sex. CONCLUSION: The PPK model adequately described rucaparib PK, and none of the covariates evaluated had a clinically relevant effect. CLINICALTRIALS: GOV: Study 1014 (NCT01009190), Study 10 (NCT01482715), ARIEL2 (NCT01891344), ARIEL3 (NCT01968213), and TRITON2 (NCT02952534).

A phase 1, open-label, drug-drug interaction study of rucaparib with rosuvastatin and oral contraceptives in patients with advanced solid tumors.

PURPOSE: This study aimed at evaluating the effect of rucaparib on the pharmacokinetics of rosuvastatin and oral contraceptives in patients with advanced solid tumors and the safety of rucaparib with and without coadministration of rosuvastatin or oral contraceptives. METHODS: Patients received single doses of oral rosuvastatin 20 mg (Arm A) or oral contraceptives ethinylestradiol 30 µg + levonorgestrel 150 µg (Arm B) on days 1 and 19 and continuous doses of rucaparib 600 mg BID from day 5 to 23. Serial blood samples were collected with and without rucaparib for pharmacokinetic analysis. RESULTS: Thirty-six patients (n = 18 each arm) were enrolled and received at least 1 dose of study drug. In the drug-drug interaction analysis (n = 15 each arm), the geometric mean ratio (GMR) of maximum concentration (Cmax) with and without rucaparib was 1.29 for rosuvastatin, 1.09 for ethinylestradiol, and 1.19 for levonorgestrel. GMR of area under the concentration-time curve from time zero to last quantifiable measurement (AUC0-last) was 1.34 for rosuvastatin, 1.43 for ethinylestradiol, and 1.56 for levonorgestrel. There was no increase in frequency of treatment-emergent adverse events (TEAEs) when rucaparib was given with either of the probe drugs. In both arms, most TEAEs were mild in severity and considered unrelated to study treatment. CONCLUSION: Rucaparib 600 mg BID weakly increased the plasma exposure to rosuvastatin or oral contraceptives. Rucaparib safety profile when coadministered with rosuvastatin or oral contraceptives was consistent with that of rucaparib monotherapy. Dose adjustments of rosuvastatin and oral contraceptives are not necessary when coadministered with rucaparib. ClinicalTrials.gov NCT03954366; Date of registration May 17, 2019.

Population exposure-efficacy and exposure-safety analyses for rucaparib in patients with recurrent ovarian carcinoma from Study 10 and ARIEL2.

OBJECTIVE: To evaluate correlations between rucaparib exposure and selected efficacy and safety endpoints in patients with recurrent ovarian carcinoma using pooled data from Study 10 and ARIEL2. METHODS: Efficacy analyses were limited to patients with carcinomas harboring a deleterious BRCA1 or BRCA2 mutation who had received ≥2 prior lines of chemotherapy. Safety was evaluated in all patients who received ≥1 rucaparib dose. Steady-state daily area under the concentration-time curve (AUCss) and maximum concentration (Cmax,ss) for rucaparib were calculated for each patient and averaged by actual dose received over time (AUCavg,ss and Cmax,avg,ss) using a previously developed population pharmacokinetic model. RESULTS: Rucaparib exposure was dose-proportional and not associated with baseline patient weight. In the exposure-efficacy analyses (n = 121), AUCavg,ss was positively associated with independent radiology review-assessed RECIST response in the subgroup of patients with platinum-sensitive recurrent disease (n = 75, p = 0.017). In the exposure-safety analyses (n = 393, 40 mg once daily to 840 mg twice daily [BID] starting doses), most patients received a 600 mg BID rucaparib starting dose, with 27% and 21% receiving 1 or ≥2 dose reductions, respectively. Cmax,ss was significantly correlated with grade ≥2 serum creatinine increase, grade ≥3 alanine transaminase/aspartate transaminase increase, platelet decrease, fatigue/asthenia, and maximal hemoglobin decrease (p < 0.05). CONCLUSION: The exposure-response analyses provide support for the approved starting dose of rucaparib 600 mg BID for maximum clinical benefit with subsequent dose modification only following the occurrence of a treatment-emergent adverse event in patients with BRCA-mutated recurrent ovarian carcinoma.

Evaluation of in vitro absorption, distribution, metabolism, and excretion and assessment of drug-drug interaction of rucaparib, an orally potent poly(ADP-ribose) polymerase inhibitor.

1. The absorption, distribution, metabolism, elimination, and drug-drug interaction (DDI) potential of the poly(ADP-ribose) polymerase (PARP) inhibitor rucaparib was characterised in vitro.2. Rucaparib showed moderate cellular permeability, moderate human plasma protein binding (70.2%), and slow metabolism in human liver microsomes (HLMs). In HLMs, cytochrome P450 (CYP) 1A2 and CYP3A contributed to the metabolism of rucaparib to its major metabolite M324 with estimated fractions of metabolism catalysed by CYP (fm,CYP) of 0.27 and 0.64, respectively. Rucaparib reversibly inhibited CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3As (IC50, 3.55, 12.9, 5.42, 41.6, and 17.2-22.9 µM [2 substrates], respectively), but not CYP2B6 or CYP2C8 (>190 µM). No time-dependent inhibition of any CYP was observed. In cultured human hepatocytes, rucaparib showed concentration-dependent induction of CYP1A2 mRNA and downregulation of CYP3A4 and CYP2B6 mRNA. In transfected cells expressing drug transporters, rucaparib was a substrate for P-gp and BCRP, but not for OATP1B1, OATP1B3, OAT1, OAT3, or OCT2. Rucaparib inhibited P-gp and BCRP (IC50, 169 and 55 µM, respectively) and slightly inhibited OATP1B1, OATP1B3, OAT1, and OAT3 (66%, 58%, 58%, and 42% inhibition, respectively) at 300 µM. Rucaparib inhibited OCT1, OCT2, MATE1, and MATE2-K (IC50, 4.3, 31, 0.63, and 0.19 µM, respectively).3. DDI risk assessment using static models suggested potential CYP-related DDIs, with rucaparib as a perpetrator. Caution is advised when co-administering rucaparib with sensitive substrates of MATEs, OCT1, and OCT2.

Evaluation of absorption, distribution, metabolism, and excretion of [14C]-rucaparib, a poly(ADP-ribose) polymerase inhibitor, in patients with advanced solid tumors.

Rucaparib, a poly(ADP-ribose) polymerase inhibitor, is licensed for use in recurrent ovarian, fallopian tube, or primary peritoneal cancer. We characterized the absorption, distribution, metabolism, and elimination of rucaparib in 6 patients with advanced solid tumors following a single oral dose of [14C]-rucaparib 600 mg (≈140 µCi). Total radioactivity (TRA) in blood, plasma, urine, and feces was measured using liquid scintillation counting. Unchanged rucaparib concentrations in plasma were determined using validated liquid chromatography with tandem mass spectrometry. Maximum concentration (Cmax) of TRA and unchanged rucaparib in plasma was 880 ng Eq/mL and 428 ng/mL, respectively, at approximately 4 h post dose; terminal half-life was >25 h for both TRA and rucaparib. The plasma TRA-time profile was parallel to yet higher than that of rucaparib, suggesting the presence of metabolites in plasma. Mean blood:plasma ratio of radioactivity was 1.0 for Cmax and 0.8 for area under the concentration-time curve from time zero to infinity. Mean postdose recovery of TRA was 89.3% over 12 days (71.9% in feces; 17.4% in urine). Unchanged rucaparib and M324 (oxidative metabolite) were the major components in plasma, contributing to 64.0% and 18.6% of plasma radioactivity, respectively. Rucaparib and M324 were the major rucaparib-related components (each ≈7.6% of dose) in urine, whereas rucaparib was the predominant component (63.9% of dose) in feces. The high fecal recovery of unchanged rucaparib could be attributed to hepatic excretion and/or incomplete oral absorption. Overall, these data suggest that rucaparib is eliminated through multiple pathways, including metabolism and renal and biliary excretion.

Pharmacokinetic Study of Rucaparib in Patients With Advanced Solid Tumors.

The phase 1-2 study CO-338-010 (Study 10; NCT01482715) is evaluating single-agent rucaparib, a poly(ADP-ribose) polymerase inhibitor, administered orally to patients with an advanced solid tumor. In the dose escalation phase (Part 1), we characterized the single-dose and steady-state pharmacokinetic profiles of rucaparib administered once daily (QD; dose range, 40-500 mg; n = 16) or twice daily (BID; dose range, 240-840 mg; n = 30). Across all dosing schedules examined, the plasma exposure of rucaparib was approximately dose proportional; half-life was approximately 17 hours, and median time to maximum concentration (tmax ) ranged from 1.5 to 6.0 hours after a single dose and 1.5 to 4.0 hours following repeated dosing. The steady-state accumulation ratio ranged from 1.60 to 2.33 following QD dosing and 1.47 to 5.44 following BID dosing. No effect of food on rucaparib pharmacokinetics was observed with a single dose of 40 mg (n = 3) or 300 mg (n = 6). In a phase 2 portion of the study (Part 3), the pharmacokinetic profile of rucaparib was further evaluated at the recommended phase 2 dose of 600 mg BID (n = 26). The mean (coefficient of variation) steady-state maximum concentration (Cmax ) and area under the concentration-time curve from time zero to 12 hours (AUC0-12h ) were 1940 ng/mL (54%) and 16 900 ng ⋅ h/mL (54%), respectively. A high-fat meal moderately increased rucaparib exposure. The fed-to-fasted geometric mean ratios (90% confidence interval [CI]) for AUC0-24h and Cmax were 138% (117%-162%) and 120% (99.1%-146%); the median (90%CI) tmax delay was 2.5 (0.5-4.4) hours.

Evaluation of Drug-Drug Interactions of Rucaparib and CYP1A2, CYP2C9, CYP2C19, CYP3A, and P-gp Substrates in Patients With an Advanced Solid Tumor.

This phase I study (CO-338-044; NCT02740712), conducted in patients with advanced solid tumors, evaluated the effect of the poly(ADP-ribose) polymerase (PARP) inhibitor rucaparib on the pharmacokinetics (PK) of caffeine 200 mg, warfarin 10 mg, omeprazole 40 mg, and midazolam 2 mg (cytochrome P450 (CYP) 1A2, CYP2C9, CYP2C19, and CYP3A substrates; dosed as a cocktail) and digoxin 0.25 mg (P-glycoprotein (P-gp) substrate; dosed separately) without rucaparib and following oral rucaparib 600 mg b.i.d. Geometric mean (GM) ratios (90% confidence interval (CI)) of area under the concentration-time curve (AUC) from time zero to last quantifiable measurement with and without rucaparib were: caffeine, 2.26 (1.93-2.65); S-warfarin, 1.49 (1.40-1.58); omeprazole, 1.55 (1.32-1.83); midazolam, 1.39 (1.14-1.68); and digoxin, 1.20 (1.12-1.29). There was limited effect on peak concentration of the substrates (GM ratios, 0.99-1.13). At steady state, rucaparib 600 mg b.i.d. moderately inhibited CYP1A2, weakly inhibited CYP2C9, CYP2C19, and CYP3A, and marginally increased digoxin exposure.

A survey of renal impairment pharmacokinetic studies for new oncology drug approvals in the USA from 2010 to early 2015: a focus on development strategies and future directions.

The US Food and Drug Administration (FDA) issued a guidance document in 2010 on pharmacokinetic (PK) studies in renal impairment (RI) on the basis of observations that substances such as uremic toxins might result in altered drug metabolism and excretion. No specific recommendations for oncology drugs were included. We surveyed the publicly available FDA review documents of 29 small molecule oncology drugs approved between 2010 and the first quarter of 2015. The objectives were as follows: (i) summarize the impact of RI on PK at the time of the initial new drug application; (ii) identify limitations of the guidance; and (iii) outline an integrated approach to study the impact of RI on these drugs. Our survey indicates that the current FDA guidance does not appear to provide clear strategic or decision pathways for RI studies in terms of small molecule oncology drugs. The FDA review documents indicate an individualized approach to the review because of the complex pharmacologic nature of these drugs and patient populations. Overall, the strategy for carrying out a RI study during clinical development or as a postmarketing study requires integration with the totality of data, including mass balance, absolute bioavailability, drug-drug interaction, hepatic dysfunction, population PK, exposure-response analysis, the therapeutic window for best guidance, and determination of the optimal doses for special oncology populations.

Pharmacodynamic Model of Hepcidin Regulation of Iron Homeostasis in Cynomolgus Monkeys.

Hepcidin (H25) is a hormone peptide synthesized by the liver that binds to ferroportin and blocks iron export. In this study, H25 was inhibited by administration of single and multiple doses of an anti-H25 monoclonal antibody Ab 12B9m in cynomolgus monkeys. The objective of this analysis was to develop a pharmacodynamic model describing the role of H25 in regulating iron homeostasis and the impact of hepcidin inhibition by Ab 12B9m. Total serum H25 and Ab 12B9m were determined in each animal. Corresponding measurements of serum iron and hemoglobin (Hb) were obtained. The PD model consisted of iron pools in serum (FeS), reticuloendothelial macrophages (FeM), hemoglobin (FeHb), and liver (FeL). The iron was assumed to be transported between the FeS, FeHb, and FeM unidirectionally at rates k S, k Hb, and k M. H25 serum concentrations were described by the previously developed PK model with the parameters fixed at their estimates. The serum iron and Hb data were fitted simultaneously. The corresponding estimates of the rate constants were k S/Fe0 = 0.113 h(-1), k M = 0.00191 h(-1), and k Hb = 0.00817 h(-1). The model-based IC50 value for the H25 inhibitory effect on ferroportin activity was 0.398 nM. The PD model predicted a negligible effect of Ab 12B9m on Hb levels for the tested doses. The presented PD model adequately described the serum iron time courses following single and multiple doses of Ab 12B9m. Ab 12B9m-induced inhibition of H25 resulted in a temporal increase in serum and liver iron and a decrease in the iron stored in reticuloendothelial macrophages.

Population pharmacokinetic-pharmacodynamic modeling of omecamtiv mecarbil, a cardiac myosin activator, in healthy volunteers and patients with stable heart failure.

Data from 3 clinical trials of omecamtiv mecarbil in healthy volunteers and patients with stable heart failure (HF) were analyzed using a nonlinear mixed-effects model to investigate omecamtiv mecarbil's pharmacokinetics and relationship between plasma concentration and systolic ejection time (SET) and Doppler-derived left ventricular outflow tract stroke volume (LVOTSV). Omecamtiv mecarbil pharmacokinetics were described by a linear 2-compartment model with a zero-order input rate for intravenous administration and first-order absorption for oral administration. Oral absorption half-life was 0.62 hours, and absolute bioavailability was estimated as 90%; elimination half-life was approximately 18.5 hours. Variability in pharmacokinetic parameters was not explained by patient baseline characteristics. Omecamtiv mecarbil plasma concentration was directly correlated with increases in SET and LVOTSV between healthy volunteers and patients with HF. The maximum increase from baseline in SET (delta SET) estimated by an Emax model was 137 milliseconds. LVOTSV increased linearly from baseline by 1.6 mL per 100 ng/mL of omecamtiv mecarbil. Model-based simulations for several immediate-release oral dose regimens (37.5, 50, and 62.5 mg dosed every 8, 12, and 24 hours) showed that a pharmacodynamic effect (delta SET ≥20 milliseconds) could be maintained in the absence of excessive omecamtiv mecarbil plasma concentrations.

Modeling the pharmacokinetic-pharmacodynamic relationship of the monoclonal anti-macaque-IL-15 antibody Hu714MuXHu in cynomolgus monkeys.

Hu714MuXHu is a recombinant chimeric murine-human monoclonal antibody directed against interleukin-15 (IL-15), a proinflammatory cytokine associated with memory CD8+ and natural killer (NK) T-cell activation and implicated in the pathogenesis of inflammatory diseases. A pharmacokinetic-pharmacodynamic (PK/PD) model was developed to describe the NK cell count reduction in cynomolgus monkeys after treatment with Hu714MuXHu. Cynomolgus monkeys were dosed with Hu714MuXHu in three studies: as a single dose at 0.1 or 1 mg·kg(-1) i.v.; weekly for 5 weeks at 0, 30, 60, or 150 mg·kg(-1) i.v. or 150 mg·kg(-1) s.c.; weekly for 13 weeks at 0, 5, 30, or 150 mg·kg(-1) s.c. Serum Hu714MuXHu concentration-time data were analyzed using noncompartmental analysis and the PK/NK cell count relationship was assessed via simultaneous PK/PD modeling. Hu714MuXHu PK was approximately dose-proportional between 0.1-150 mg·kg(-1) for i.v. and 5-150 mg·kg(-1) for s.c. administration with an elimination half-life of 12.7-18 days. Hu714MuXHu administration resulted in rapid and marked reductions in NK cell counts after the first dose which recovered fully after the serum Hu714MuXHu concentrations approached 0.1 µg·mL(-1) (assay limit of quantification). PK/PD modeled Hu714MuXHu effects on NK cells had an EC 50 of 0.09 µg·mL(-1). In summary, weekly i.v. or s.c. doses with Hu714MuXHu for up to 3 months in cynomolgus monkeys demonstrated linear PK and significant NK cell count reduction, which was described using PK/PD modeling. This approach may be used to guide investigative product dose selections for inflammatory diseases where NK cell count alterations are quantifiable.

Pharmacokinetic models for FcRn-mediated IgG disposition.

The objectives were to review available PK models for saturable FcRn-mediated IgG disposition, and to explore an alternative semimechanistic model. Most available empirical and mechanistic PK models assumed equal IgG concentrations in plasma and endosome in addition to other model-specific assumptions. These might have led to inappropriate parameter estimates and model interpretations. Some physiologically based PK (PBPK) models included FcRn-mediated IgG recycling. The nature of PBPK models requires borrowing parameter values from literature, and subtle differences in the assumptions may render dramatic changes in parameter estimates related to the IgG recycling kinetics. These models might have been unnecessarily complicated to address FcRn saturation and nonlinear IgG PK especially in the IVIG setting. A simple semimechanistic PK model (cutoff model) was developed that assumed a constant endogenous IgG production rate and a saturable FcRn-binding capacity. The FcRn-binding capacity was defined as MAX, and IgG concentrations exceeding MAX in endosome resulted in lysosomal degradation. The model parameters were estimated using simulated data from previously published models. The cutoff model adequately described the rat and mouse IgG PK data simulated from published models and allowed reasonable estimation of endogenous IgG turnover rates.

Pharmacodynamics-mediated drug disposition (PDMDD) and precursor pool lifespan model for single dose of romiplostim in healthy subjects.

The objective of this study was to characterize the pharmacokinetics and pharmacodynamics (PK-PD) of romiplostim after single-dose administration in healthy subjects. The mean serum romiplostim concentrations (PK data) and mean platelet counts (PD data) collected from 32 subjects receiving a single intravenous (0.3, 1 and 10 µg/kg) or subcutaneous (0.1, 0.3, 1, and 2 µg/kg) dose were fitted simultaneously to a mechanistic PK-PD model based on pharmacodynamics-mediated drug disposition (PDMDD) and a precursor pool lifespan concept. The two-compartment PK model incorporated receptor-mediated endocytosis and linear mechanisms as parallel elimination pathways. The maximal concentration of receptors (assumed to be proportional to the platelet count), the equilibrium dissociation constant, and the first-order internalization rate constant for endocytosis of the drug-receptor complex were 0.022 fg/platelet, 0.131 ng/mL, and 0.173 h⁻¹, respectively. Romiplostim concentration stimulates the production of platelet precursors via the Hill function, where the SC50 was 0.052 ng/mL and S (max) was 11.2. The estimated precursor cell and platelet lifespans were 5.9 and 10.5 days, respectively. Model-based simulations revealed that the romiplostim exposure and the platelet response are both dependent on the dose administered and the baseline platelet counts. Also, weekly dosing produced a sustained PD response while dosing intervals ≥2 weeks resulted in fluctuating platelet counts. Thus, the mechanistic PK-PD model was suitable for describing the romiplostim PK-PD interplay (PDMDD), the dose-dependent platelet stimulation, and the lifespans of thrombopoietic cell populations.

Pharmacokinetics of anti-hepcidin monoclonal antibody Ab 12B9m and hepcidin in cynomolgus monkeys.

Hepcidin is a key regulator responsible for systemic iron homeostasis. A semi-mechanistic PK model for hepcidin and a fully human anti-hepcidin monoclonal antibody (Ab 12B9m) was developed to describe their total (free + bound) serum concentration-time data after single and multiple weekly intravenous or subcutaneous doses of Ab 12B9m. The model was based on target mediated drug disposition and the IgG-FcRn interaction concepts published previously. Both total Ab 12B9m and total hepcidin exhibited nonlinear kinetics due to saturable Fc-FcRn interaction. Ab 12B9m showed a limited volume of distribution and negligible linear elimination from serum. The nonlinear elimination of Ab 12B9m was attributed to the endosomal degradation of Ab 12B9m that was not bound to the FcRn receptor. The terminal half-life, assumed to be the same for free and total serum Ab 12B9m, was estimated to be 16.5 days. The subcutaneous absorption of Ab 12B9m was described with a first-order absorption rate constant k(a) of 0.0278 h⁻¹, with 86% bioavailability. The model suggested a rapid hepcidin clearance of approximately 800 mL h⁻¹ kg⁻¹. Only the highest-tested Ab 12B9m dose of 300 mg kg⁻¹ week⁻¹ was able to maintain free hepcidin level below the baseline during the dosing intervals. Free Ab 12B9m and free hepcidin concentrations were simulated, and their PK profiles were nonlinear as affected by their binding to each other. Additionally, the total amount of FcRn receptor involved in Ab 12B9m recycling at a given time was calculated empirically, and the temporal changes in the free FcRn levels upon Ab 12B9m administration were inferred.

Population pharmacokinetics of humanized monoclonal antibody HuCC49deltaCH2 and murine antibody CC49 in colorectal cancer patients.

To predict the optimal time for surgery after antibody administration, the population pharmacokinetics of (125)I-HuCC49deltaCH2 and (125)I-CC49 were characterized in 55 patients with colorectal cancers. A 2-compartment linear model was used to fit the pharmacokinetic data. Model stability and performance were assessed using a visual predictive check procedure. Different clinical trial designs were evaluated by simulation in combination with Bayesian estimation method to predict the optimal time for surgery. The results showed that HuCC49deltaCH2 had 65% faster clearance from blood circulation and 24% shorter mean residence time than CC49. Population pharmacokinetic analysis identified body weight as the only covariate to explain between-subject variability in clearance, intercompartmental flow rate, and volume of distribution. Model predictions indicated a wide interval for the optimal time of surgery, suggesting that it would be beneficial to individualize the time of surgery for each patient by measurement of antibody disposition. Clinical trial designs with at least 3 measurements of antibody disposition were found to be better than an empirical direct observation method for the optimal prediction of surgery time.

Discovery of a daunorubicin analogue that exhibits potent antitumor activity and overcomes P-gp-mediated drug resistance.

Anthracyclines are considered to be some of the most effective anticancer drugs for cancer therapy. However, drug resistance and cardiotoxicity of anthracyclines limit their clinical application. We hypothesize that direct modifications of the sugar moiety of anthracyclines avert P-glycoprotein (P-gp) recognition and efflux, increase drug intracellular concentration in cancer cells, and thus overcome P-gp-mediated drug resistance. Daunorubicin (DNR) analogues with sugar modifications were synthesized by directly transforming the amino group of DNR to an azido group or triazole group. Molecular docking showed that the lead compound (3'-azidodaunorubicin, ADNR) averts P-gp binding, while daunorubicin (DNR) extensively interacts with multidrug-resistance (MDR) protein through H-bonds and electrostatic interactions. FACS assay demonstrated that these new compounds abolished P-gp drug efflux and accumulated high intracellular concentration in the drug-resistant leukemia K562/Dox. P-gp inhibition by CsA confirmed that these new analogues are no longer P-gp substrates. ADNR exhibited potent anticancer activity in both drug-sensitive (K562) and drug-resistant leukemia cells (K562/Dox), with a 25-fold lower drug resistance index than DNR. An in vivo xenograft model demonstrated that ADNR showed more than 2.5-fold higher maximum growth inhibition rate against drug-resistant cancers and significant improvement for animal survival rate versus DNR. No significant body weight reduction in mice was observed for ADNR at the maximum tolerable dose, as compared to more than 70% body weight reduction for DNR. These data suggest that sugar modifications of anthracyclines avert P-gp binding, abolish P-gp-mediated drug efflux, increase intracellular drug concentration, and thus overcome P-gp-mediated drug resistance in cancer therapy.

Chemoresistance to depsipeptide FK228 [(E)-(1S,4S,10S,21R)-7-[(Z)-ethylidene]-4,21-diisopropyl-2-oxa-12,13-dithia-5,8,20,23-tetraazabicyclo[8,7,6]-tricos-16-ene-3,6,9,22-pentanone] is mediated by reversible MDR1 induction in human cancer cell lines.

Histone acetylation status, an epigenetic determinant of gene transcription, is controlled by histone acetyltransferases (HATs) and histone deacetylases (HDACs). The potent HDAC inhibitor FK228 [(E)-(1S,4S,10S,21R)-7-[(Z)-ethylidene]-4,21-diisopropyl-2-oxa-12,13-dithia-5,8,20,23-tetraazabicyclo[8,7,6]-tricos-16-ene-3,6,9,22-pentanone] is a substrate for multidrug resistance protein (MDR1) and multidrug resistance-associated protein 1 (MRP1), both of which mediate FK228 resistance. To determine the mechanisms underlying acquired FK228 resistance, we developed four FK228-resistant cell lines from HCT-15, IGROV1, MCF7, and K562 cells by stepwise increases in FK228 exposure. Parent and resistant cells were characterized using a 70-oligomer cDNA microarray, real-time reverse transcription-polymerase chain reaction (RT-PCR), Western blot, and cytotoxicity assays. At both mRNA and protein levels, MDR1, but not MRP1 or other potential resistance genes, was strongly up-regulated in all resistant cell lines. HAT or HDAC activities were unaffected in resistant cells, consistent with a lack of cross-resistance to HDAC inhibitors that are not MDR1 substrates. FK228 was found to reversibly induce MDR1 expression by HDAC inhibition and subsequent histone hyperacetylation at the MDR1 promoter, as shown by real-time RT-PCR, Western blot, and chromatin immunoprecipitation. This study reveals a significant role of histone acetylation in MDR1 transcription, which seems to mediate FK228 resistance.

Efflux of depsipeptide FK228 (FR901228, NSC-630176) is mediated by P-glycoprotein and multidrug resistance-associated protein 1.

Depsipeptide FK228 [(E)-(1S,4S,10S,21R)-7[(Z)-ethylideno]-4,21-diisopropyl-2-oxa-12,13-dithia-5,8,20,23-tetraazabicyclo[8,7,6]-tricos-16-ene-3,6,9,22-pentanone], a novel histone deacetylase (HDAC) inhibitor, previously was reported to be a P-glycoprotein (Pgp) substrate. We now expand the investigation to demonstrate that FK228 is a substrate for Pgp and multidrug resistance-associated protein 1 (MRP1). Transport of FK228 across the Caco-2 cell monolayer in apical to basolateral (AP-->BL) and basolateral to apical (BL-->AP) directions in the absence and presence of Pgp and MRP inhibitors were investigated. An in vitro uptake study in human red blood cells (RBCs) and a cytotoxicity assay in MRP1(-) HL60 and MRP1(+) HL60Adr cells were conducted to show that FK228 is an MRP1 substrate. An FK228-resistant cell line (HCT15R) was developed from HCT15 colon carcinoma and characterized using a 70-oligomer cDNA microarray, reverse transcription-polymerase chain reaction, Western blot analysis, histone acetyltransferase (HAT) and HDAC activity assays, and cytotoxicity assays. FK228 showed a nearly unidirectional flux across the Caco-2 cell monolayer, with the BL-->AP apparent permeability coefficient (P(app)) 32 times that of AP-->BL without apparent saturation. Pgp inhibition decreased the BL-->AP P(app) and increased the AP-->BL P(app). RBC showed a concentration-dependent uptake and saturable efflux of FK228. HL60Adr cells were 4-fold more resistant to FK228 than HL60 cells, and the resistance was reversed by MRP inhibition. Up-regulation of Pgp, but not changes of MRPs or HAT/HDAC enzymatic activities, was the major mechanism for the acquired FK228 resistance. These studies demonstrate that FK228 is a substrate for Pgp and MRP1, and reversible Pgp up-regulation is predominantly involved in FK228 resistance in vitro.

A phase 1 and pharmacodynamic study of depsipeptide (FK228) in chronic lymphocytic leukemia and acute myeloid leukemia.

Preclinical studies with the histone deacetylase (HDAC) inhibitor depsipeptide (FK228) in chronic lymphocytic leukemia (CLL) and acute myeloid leukemia (AML) have demonstrated that it effectively induces apoptosis at concentrations at which HDAC inhibition occurs. We initiated a minimum effective pharmacologic dose study of depsipeptide, targeting an in vivo dose at which acetylation of histone proteins H3 and H4 increased by 100% or more in vitro. Ten patients with CLL and 10 patients with AML were treated with 13 mg/m(2) depsipeptide intravenously days 1, 8, and 15 of therapy. Neither life-threatening toxicities nor cardiac toxicities were noted, although the majority of patients experienced progressive fatigue, nausea, and other constitutional symptoms that prevented repeated dosing. Several patients had evidence of antitumor activity following treatment, but no partial or complete responses were noted by National Cancer Institute criteria. HDAC inhibition and histone acetylation increases of at least 100% were noted, as well as increases in p21 promoter H4 acetylation, p21 protein, and 1D10 antigen expression. We conclude that depsipeptide effectively inhibits HDAC in vivo in patients with CLL and AML, but its use in the current schedule of administration is limited by progressive constitutional symptoms. Future studies with depsipeptide should examine alternative administration schedules.