Effects of the Moderate CYP3A4 Inhibitor Erythromycin on the Pharmacokinetics of Palbociclib: A Randomized Crossover Trial in Patients With Breast Cancer

Palbociclib is an oral inhibitor of cyclin-dependent kinases 4 and 6 used in the treatment of locally advanced and metastatic breast cancer, and is extensively metabolized by cytochrome P450 enzyme 3A4 (CYP3A4). A pharmacokinetic/pharmacodynamic relationship between palbociclib exposure and neutropenia is well known. This study aimed to investigate the effects of the moderate CYP3A4 inhibitor erythromycin on the pharmacokinetics of palbociclib. We performed a randomized crossover trial comparing the pharmacokinetics of palbociclib monotherapy 125 mg once daily (q.d.) with palbociclib 125 mg q.d. plus oral erythromycin 500 mg three times daily for seven days. Pharmacokinetic sampling was performed at steady-state for both dosing schedules. Eleven evaluable patients have been enrolled. For palbociclib monotherapy, geometric mean area under the plasma concentration-time curve from zero to infinity (AUC_0-24h ), maximum plasma concentration (C_max ), and minimum plasma concentration (C_min ) were 1.46 × 10³  ng•h/mL (coefficient of variation (CV) 45.0%), 80.5 ng/mL (CV 48.5%), and 48.4 ng/mL (CV 38.8%), respectively, compared with 2.09 × 10³  ng•h/mL (CV 49.3%, P = 0.000977), 115 ng/mL (CV 53.7%, P = 0.00562), and 70.7 ng/mL (CV 47.5%, P = 0.000488) when palbociclib was administered concomitantly with erythromycin. Geometric mean ratios (90% confidence intervals) of AUC_0-24h , C_max , and C_min for palbociclib plus erythromycin vs. palbociclib monotherapy were 1.43 (1.24-1.66), 1.43 (1.20-1.69), and 1.46 (1.30-1.63). Minor differences in adverse events were observed, and only one grade ≥ 3 toxicity was observed in this short period of time. To conclude, concomitant intake of palbociclib with the moderate CYP3A4 inhibitor erythromycin resulted in an increase in palbociclib AUC_0-24h and C_max of both 43%. Therefore, a dose reduction of palbociclib to 75 mg q.d. is rational, when palbociclib and moderate CYP3A4 inhibitors are used concomitantly.

ABCB1 and ABCG2 Control Brain Accumulation and Intestinal Disposition of the Novel ROS1/TRK/ALK Inhibitor Repotrectinib, While OATP1A/1B, ABCG2, and CYP3A Limit Its Oral Availability

Repotrectinib shows high activity against ROS1/TRK/ALK fusion-positive cancers in preclinical studies. We explored the roles of multidrug efflux transporters ABCB1 and ABCG2, the OATP1A/1B uptake transporter(s), and the CYP3A complex in pharmacokinetics and tissue distribution of repotrectinib in genetically modified mouse models. In vitro, human ABCB1 and ABCG2, and mouse Abcg2 efficiently transported repotrectinib with efflux transport ratios of 13.5, 5.6, and 40, respectively. Oral repotrectinib (10 mg/kg) showed higher plasma exposures in Abcg2-deficient mouse strains. Brain-to-plasma ratios were increased in Abcb1a/1b^−/− (4.1-fold) and Abcb1a/1b;Abcg2^−/− (14.2-fold) compared to wild-type mice, but not in single Abcg2^−/− mice. Small intestinal content recovery of repotrectinib was decreased 4.9-fold in Abcb1a/1b^−/− and 13.6-fold in Abcb1a/1b;Abcg2^−/− mice. Intriguingly, Abcb1a/1b;Abcg2^−/− mice displayed transient, mild, likely CNS-localized toxicity. Oatp1a/1b deficiency caused a 2.3-fold increased oral availability and corresponding decrease in liver distribution of repotrectinib. In Cyp3a^−/− mice, repotrectinib plasma AUC_0–h was 2.3-fold increased, and subsequently reduced 2.0-fold in humanized CYP3A4 transgenic mice. Collectively, Abcb1 and Abcg2 restrict repotrectinib brain accumulation and possibly toxicity, and control its intestinal disposition. Abcg2 also limits repotrectinib oral availability. Oatp1a/1b mediates repotrectinib liver uptake, thus reducing its systemic exposure. Systemic exposure of repotrectinib is also substantially limited by CYP3A activity. These insights may be useful to optimize the therapeutic application of repotrectinib.

IHC-based Ki67 as response biomarker to tamoxifen in breast cancer window trials enrolling premenopausal women

Window studies are gaining traction to assess (molecular) changes in short timeframes. Decreased tumor cell positivity for the proliferation marker Ki67 is often used as a proxy for treatment response. Immunohistochemistry (IHC)-based Ki67 on tissue from neo-adjuvant trials was previously reported to be predictive for long-term response to endocrine therapy for breast cancer in postmenopausal women, but none of these trials enrolled premenopausal women. Nonetheless, the marker is being used on this subpopulation. We compared pathologist assessed IHC-based Ki67 in samples from pre- and postmenopausal women in a neo-adjuvant, endocrine therapy focused trial (NCT00738777), randomized between tamoxifen, anastrozole, or fulvestrant. These results were compared with (1) IHC-based Ki67 scoring by AI, (2) mitotic figures, (3) mRNA-based Ki67, (4) five independent gene expression signatures capturing proliferation, and (5) blood levels for tamoxifen and its metabolites as well as estradiol. Upon tamoxifen, IHC-based Ki67 levels were decreased in both pre- and postmenopausal breast cancer patients, which was confirmed using mRNA-based cell proliferation markers. The magnitude of decrease of Ki67 IHC was smaller in pre- versus postmenopausal women. We found a direct relationship between post-treatment estradiol levels and the magnitude of the Ki67 decrease in tumors. These data suggest IHC-based Ki67 may be an appropriate biomarker for tamoxifen response in premenopausal breast cancer patients, but anti-proliferative effect size depends on estradiol levels.

ABCB1 and ABCG2, but not CYP3A4 limit oral availability and brain accumulation of the RET inhibitor pralsetinib

BACKGROUND AND PURPOSE

Pralsetinib is an FDA-approved oral small-molecule inhibitor for treatment of rearranged during transfection (RET) proto-oncogene fusion-positive non-small cell lung cancer. We investigated how the efflux transporters ABCB1 and ABCG2, the SLCO1A/1B uptake transporters and the drug-metabolizing enzyme CYP3A influence pralsetinib pharmacokinetics.

EXPERIMENTAL APPROACH

In vitro, transepithelial pralsetinib transport was assessed. In vivo, pralsetinib (10 mg/kg) was administered orally to relevant genetically modified mouse models. Pralsetinib concentrations in cell medium, plasma samples and organ homogenates were measured using liquid chromatography-tandem mass spectrometry.

KEY RESULTS

Pralsetinib was efficiently transported by human (h)ABCB1 and mouse (m)Abcg2, but not hACBG2. In vivo, mAbcb1a/1b markedly and mAbcg2 slightly limited pralsetinib brain penetration (6.3-and 1.8-fold, respectively). Testis distribution showed similar results. Abcb1a/1b;Abcg2-/- mice showed 1.5-fold higher plasma exposure, 23-fold increased brain penetration, and 4-fold reduced recovery of pralsetinib in the small intestinal content. mSlco1a/1b deficiency did not affect pralsetinib oral availability or tissue exposure. Oral coadministration of the ABCB1/ABCG2 inhibitor elacridar boosted pralsetinib plasma exposure (1.3-fold) and brain penetration (19.6-fold) in wild-type mice. Additionally, pralsetinib was a modest substrate of mCYP3A, but not of hCYP3A4, which did not noticeably restrict the oral availability or tissue distribution of pralsetinib.

CONCLUSIONS AND IMPLICATIONS

SLCO1A/1B and CYP3A4 are unlikely to affect the pharmacokinetics of pralsetinib, but ABCG2 and especially ABCB1 markedly limit its brain and testis penetration, as well as oral availability. These effects are mostly reversed by oral coadministration of the ABCB1/ABCG2 inhibitor elacridar. These insights may be useful in the further clinical development of pralsetinib.

The suitability of oral diacetylmorphine in treatment-refractory patients with heroin dependence: A scoping review

OBJECTIVE

To review the scientific literature on the pharmacokinetics, pharmacodynamics and clinical efficacy and safety of (supervised) oral diacetylmorphine for patients with severe heroin dependence.

METHODS

The PubMed, Embase, Web of Science and PsycINFO databases were searched. Eleven published studies were identified and selected based on defined eligibility and exclusion criteria.

RESULTS

Four pharmacokinetic studies reported negligible plasma concentrations of diacetylmorphine and its active metabolite 6-monacetylmorphine. Among six pharmacodynamic studies, three trials showed that oral diacetylmorphine reduced opioid withdrawal symptoms, one open-label pilot study reported that two patients experienced a modest 'rush' after oral diacetylmorphine and two studies found that patients could not distinguish between oral diacetylmorphine, methadone, or morphine. Regarding the clinical studies, a Swiss prospective cohort study in patients with heroin dependence showed high retention rates of oral diacetylmorphine treatment with few serious adverse events, whereas in the Canadian SALOME trial, oral diacetylmorphine treatment was prematurely discontinued because treatment retention of oral diacetylmorphine was lower than injectable diacetylmorphine maintenance treatment. Finally, two case studies illustrate the limitations and potential problems of oral diacetylmorphine in the treatment of treatment-refractory heroin dependent patients.

CONCLUSIONS

Based on all published data, it is unlikely that oral diacetylmorphine produces a substantial 'rush'. Prescription of oral diacetylmorphine might therefore be effective only for treatment-refractory patients with heroin dependence (i) as maintenance treatment for those who never injected or inhaled opioids; (ii) as maintenance treatment for those who want to switch from injection to oral administration of diacetylmorphine; and/or (iii) to reduce opioid withdrawal symptoms.

Population Pharmacokinetic Modelling to Support the Evaluation of Preclinical Pharmacokinetic Experiments with Lorlatinib

The effect of transporters and enzymes on drug pharmacokinetics is increasingly evaluated using genetically modified animals that have these proteins either knocked-out or their human orthologues transgenically expressed. Analysis of pharmacokinetic data obtained in such experiments is typically performed using non-compartmental analysis (NCA), which has limitations such as not being able to identify the PK parameter that is affected by the genetic modification of the enzymes or transporters and the requirement of intense and homogeneous sampling of all subjects. Here we used a compartmental population pharmacokinetic modeling approach using PK data from a series of genetically modified mouse experiments with lorlatinib to extend the results and conclusions from previously reported NCA analyses. A compartmental population pharmacokinetic model was built and physiologically plausible covariates were evaluated for the different mouse strains. With the model, similar effects of the strains on the area under the concentration-time curve (AUC) from 0 to 8 hours were found as for the NCA. Additionally, the differences in AUC between the strains were explained by specific effects on clearance and bioavailability for the strain with human expressing CYP3A4. Finally, effects of multidrug efflux transporters ATP-binding cassette (ABC) sub-family B member 1 (ABCB1) and G member 2 (ABCG2) on brain efflux were quantified. Use of compartmental population PK modeling yielded additional insight into the role of drug-metabolizing enzymes and drug transporters in mouse experiments compared to the NCA. Furthermore, these models allowed analysis of heterogeneous pooled datasets and the sparse organ concentration data in contrast to classical NCA analyses.

A Review of CYP3A Drug-Drug Interaction Studies: Practical Guidelines for Patients Using Targeted Oral Anticancer Drugs

Many oral anticancer drugs are metabolized by CYP3A. Clinical drug-drug interaction (DDI) studies often only examine the effect of strong CYP3A inhibitors and inducers. The effect of moderate or weak inhibitors or inducers can be examined using physiologically based pharmacokinetic simulations, but data from these simulations are not always available early after approval of a drug. In this review we provide recommendations for clinical practice on how to deal with DDIs of oral anticancer drugs if only data from strong CYP3A inhibitors or inducers is available. These recommendations were based on reviewed data of oral anticancer drugs primarily metabolized by CYP3A and approved for the treatment of solid tumors from January 1st, 2013 to December 31st, 2015. In addition, three drugs that were registered before the new EMA guideline was issued (i.e., everolimus, imatinib, and sunitinib), were reviewed. DDIs are often complex, but if no data is available from moderate CYP3A inhibitors/inducers, a change in exposure of 50% compared with strong inhibitors/inducers can be assumed. No a priori dose adaptations are indicated for weak inhibitors/inducers, because their interacting effect is small. In case pharmacologically active metabolites are involved, the metabolic pathway, the ratio of the parent to the metabolites, and the potency of the metabolites should be taken into account.

Tumor infiltrating lymphocytes (TIL) therapy in metastatic melanoma: boosting of neoantigen-specific T cell reactivity and long-term follow-up

Treatment of metastatic melanoma with autologous tumor infiltrating lymphocytes (TILs) is currently applied in several centers. Robust and remarkably consistent overall response rates, of around 50% of treated patients, have been observed across hospitals, including a substantial fraction of durable, complete responses.

PURPOSE

Execute a phase I/II feasibility study with TIL therapy in metastatic melanoma at the Netherlands Cancer Institute, with the goal to assess feasibility and potential value of a randomized phase III trial.

EXPERIMENTAL

Ten patients were treated with TIL therapy. Infusion products and peripheral blood samples were phenotypically characterized and neoantigen reactivity was assessed. Here, we present long-term clinical outcome and translational data on neoantigen reactivity of the T cell products.

RESULTS

Five out of 10 patients, who were all anti-PD-1 naïve at time of treatment, showed an objective clinical response, including two patients with a complete response that are both ongoing for more than 7 years. Immune monitoring demonstrated that neoantigen-specific T cells were detectable in TIL infusion products from three out of three patients analyzed. For six out of the nine neoantigen-specific T cell responses detected in these TIL products, T cell response magnitude increased significantly in the peripheral blood compartment after therapy, and neoantigen-specific T cells were detectable for up to 3 years after TIL infusion.

CONCLUSION

The clinical results from this study confirm the robustness of TIL therapy in metastatic melanoma and the potential role of neoantigen-specific T cell reactivity. In addition, the data from this study supported the rationale to initiate an ongoing multicenter phase III TIL trial.

A physiologically based pharmacokinetic (PBPK) model to describe organ distribution of 68Ga-DOTATATE in patients without neuroendocrine tumors

Background

Physiologically based pharmacokinetic (PBPK) models combine drug-specific information with prior knowledge on the physiology and biology at the organism level. Whole-body PBPK models contain an explicit representation of the organs and tissue and are a tool to predict pharmacokinetic behavior of drugs. The aim of this study was to develop a PBPK model to describe organ distribution of ⁶⁸Ga-DOTATATE in a population of patients without detectable neuroendocrine tumors (NETs).

Methods

Clinical ⁶⁸Ga-DOTATATE PET/CT data from 41 patients without any detectable somatostatin receptor (SSTR) overexpressing tumors were included. Scans were performed at 45 min (range 30–60 min) after intravenous bolus injection of ⁶⁸Ga-DOTATATE. Organ (spleen, liver, thyroid) and blood activity levels were derived from PET scans, and corresponding DOTATATE concentrations were calculated. A whole-body PBPK model was developed, including an internalization reaction, receptor recycling, enzymatic reaction for intracellular degradation and renal clearance. SSTR2 expression was added for several organs. Input parameters were fixed or estimated using a built-in Monte Carlo algorithm for parameter identification.

Results

⁶⁸Ga-DOTATATE was administered with a median peptide amount of 12.3 µg (range 8.05–16.9 µg) labeled with 92.7 MBq (range 43.4–129.9 MBq). SSTR2 amounts for spleen, liver and thyroid were estimated at 4.40, 7.80 and 0.0108 nmol, respectively. Variability in observed organ concentrations was best described by variability in SSTR2 expression and differences in administered peptide amounts.

Conclusions

To conclude, biodistribution of ⁶⁸Ga-DOTATATE was described with a whole-body PBPK model, where tissue distribution was mainly determined by variability in SSTR2 organ expression and differences in administered peptide amounts.

Low antileishmanial drug exposure in HIV-positive visceral leishmaniasis patients on antiretrovirals: an Ethiopian cohort study

Background

Despite high HIV co-infection prevalence in Ethiopian visceral leishmaniasis (VL) patients, the adequacy of antileishmanial drug exposure in this population and effect of HIV-VL co-morbidity on pharmacokinetics of antileishmanial and antiretroviral (ARV) drugs is still unknown.

Methods

HIV-VL co-infected patients received the recommended liposomal amphotericin B (LAmB) monotherapy (total dose 40 mg/kg over 24 days) or combination therapy of LAmB (total dose 30 mg/kg over 11 days) plus 28 days 100 mg/day miltefosine, with possibility to extend treatment for another cycle. Miltefosine, total amphotericin B and ARV concentrations were determined in dried blood spots or plasma using LC–MS/MS.

Results

Median (IQR) amphotericin B C_max on Day 1 was 24.6 μg/mL (17.0–34.9 μg/mL), which increased to 40.9 (25.4–53.1) and 33.2 (29.0–46.6) μg/mL on the last day of combination and monotherapy, respectively. Day 28 miltefosine concentration was 18.7 (15.4–22.5) μg/mL. Miltefosine exposure correlated with amphotericin B accumulation. ARV concentrations were generally stable during antileishmanial treatment, although efavirenz C_min was below the 1 μg/mL therapeutic target for many patients.

Conclusions

This study demonstrates that antileishmanial drug exposure was low in this cohort of HIV co-infected VL patients. Amphotericin B C_max was 2-fold lower than previously observed in non-VL patients. Miltefosine exposure in HIV-VL co-infected patients was 35% lower compared with adult VL patients in Eastern Africa, only partially explained by a 19% lower dose, possibly warranting a dose adjustment. Adequate drug exposure in these HIV-VL co-infected patients is especially important given the high proportion of relapses.

Development and Validation of a Stability-indicating HPLC Method for the Analysis of Cabazitaxel in Jevtana® Concentrate-solvent Leftover Samples

Aim/Background:

In this study, a stability-indicating method of the anticancer agent cabazitaxel was developed and validated. This method will be used to determine the chemical stability of commercially available concentrate-solvent mixture cabazitaxel (Jevtana®) to examine the possibility of multi-dosing from the same product vial after storage. The impossibility to re-use leftovers today is contributing to an unnecessary and significant financial waste.

Methods:

A forced degradation study of cabazitaxel was performed under different conditions to produce degradation products. Acidic, basic, oxidation, heat, and ultraviolet (UV) light conditions were tested. The method to determine the stability was developed so that potential degradation products would be shown in the UV spectra after separation from cabazitaxel with a C18 column in a high-performance liquid chromatography (HPLC) system. The only degradation product occurring during storage in room temperature and ambient light was identified by accurate mass Orbitrap Mass Spectrometry.

Results:

A stability-indicating method for cabazitaxel (Jevtana®) concentrate-solvent mixture has been developed. We demonstrated that this method can be applied to stability studies with the purpose of multi-dosing cabazitaxel from a chemical/physical stability perspective within the tested period of time and conditions.

Conclusion:

As an addition, the only naturally occurring degradation product found has been identified and a degradation reaction has been suggested.

Characterizing the non-linear pharmacokinetics of miltefosine in paediatric visceral leishmaniasis patients from Eastern Africa

Background

Conventional miltefosine dosing (2.5 mg/kg/day) for treatment of visceral leishmaniasis (VL) is less effective in children than in adults. A higher allometric dose (median 3.2 mg/kg/day) was therefore investigated in paediatric VL patients in Eastern Africa. Results of this trial showed an unforeseen, lower than dose-proportional increase in exposure_. Therefore, we performed a pooled model-based analysis of the paediatric data available from both dosing regimens to characterize observed non-linearities in miltefosine pharmacokinetics (PK).

Methods

Fifty-one children with VL were included in this analysis, treated with either a conventional (n = 21) or allometric (n = 30) miltefosine dosing regimen. PK data were analysed using non-linear mixed-effects modelling.

Results

A two-compartment model following first-order absorption and linear elimination, with two separate effects on relative oral bioavailability, was found to fit these data best. A 69% lower bioavailability at treatment start was estimated, presumably due to initial malnourishment and malabsorption. Stagnation in miltefosine accumulation in plasma, hampering increased drug exposure, was related to the increase in cumulative dose (mg/kg/day). However, the allometric regimen increased exposure 1.7-fold in the first treatment week and reduced the time to reach the PK target by 17.4%.

Conclusions

Miltefosine PK in children suffering from VL are characterized by dose-dependent non-linearities that obstruct the initially expected exposure levels. Bioavailability appeared to be affected by the cumulative dose, possibly as a consequence of impaired absorption. Despite this, allometric dosing led to a faster target achievement and increased exposure compared with conventional dosing.

Simultaneous quantification of abemaciclib and its active metabolites in human and mouse plasma by UHPLC-MS/MS

Abemaciclib is the third cyclin-dependent kinase 4 and 6 inhibitor approved for the treatment of advanced or metastatic breast cancer. In humans, abemaciclib is extensively metabolized by CYP3A4 with the formation of three active metabolites: N-desethylabemaciclib (M2), hydroxyabemaciclib (M20) and hydroxy-N-desethylabemaciclib (M18). These metabolites showed similar potency compared to the parent drug and were significantly abundant in plasma circulation. Thus, M2, M20, and M18 may contribute to the clinical activity of abemaciclib. For this reason, an UHPLC-MS/MS method for the simultaneous quantification of abemaciclib and its active metabolites in human and mouse plasma was developed and validated to support further clinical or preclinical investigations on this drug. Samples were processed by protein precipitation with acetonitrile, followed by supernatant dilution and filtration. Chromatographic separation was performed on a Kinetex C₁₈ column (150 × 2.1 mm ID, 2.6 μm) using gradient elution with 10 mM ammonium bicarbonate in water (eluent A) and in methanol-water (9:1, v/v, eluent B). This method was selective, linear, accurate and precise within the range of 1-600 ng/mL for abemaciclib, 0.5-300 ng/mL for M2 and M20, and 0.2-120 ng/mL for M18. Furthermore, stability of the analytes in human and mouse plasma samples in several conditions was demonstrated. Finally, this assay was successfully used in a preclinical pharmacokinetic study, where abemaciclib and its active metabolites were identified and quantified. Inter-species differences between human and mouse samples were encountered, especially in the formation of M20, where isomers of this compound were detected in mouse plasma, but not in human plasma. This was confirmed by high resolution-mass spectrometry (HR-MS) measurements.

Geographical Variability in Paromomycin Pharmacokinetics Does Not Explain Efficacy Differences between Eastern African and Indian Visceral Leishmaniasis Patients

Introduction

Intramuscular paromomycin monotherapy to treat visceral leishmaniasis (VL) has been shown to be effective for Indian patients, while a similar regimen resulted in lower efficacy in Eastern Africa, which could be related to differences in paromomycin pharmacokinetics.

Methods

Pharmacokinetic data were available from two randomized controlled trials in VL patients from Eastern Africa and India. African patients received intramuscular paromomycin monotherapy (20 mg/kg for 21 days) or combination therapy (15 mg/kg for 17 days) with sodium stibogluconate. Indian patients received paromomycin monotherapy (15 mg/kg for 21 days). A population pharmacokinetic model was developed for paromomycin in Eastern African and Indian VL patients.

Results

Seventy-four African patients (388 observations) and 528 Indian patients (1321 observations) were included in this pharmacokinetic analysis. A one-compartment model with first-order kinetics of absorption and elimination best described paromomycin in plasma. Bioavailability (relative standard error) was 1.17 (5.18%) times higher in Kenyan and Sudanese patients, and 2.46 (24.5%) times higher in Ethiopian patients, compared with Indian patients. Ethiopian patients had an approximately fourfold slower absorption rate constant of 0.446 h^–1 (18.2%). Area under the plasma concentration-time curve for 24 h at steady-state (AUC_τ,SS) for 15 mg/kg/day (median [interquartile range]) was higher in Kenya and Sudan (172.7 µg·h/mL [145.9–214.3]) and Ethiopia (230.1 µg·h/mL [146.3–591.2]) compared with India (97.26 µg·h/mL [80.83–123.4]).

Conclusion

The developed model provides detailed insight into the pharmacokinetic differences among Eastern African countries and India, however the resulting differences in paromomycin exposure do not seem to explain the geographical differences in paromomycin efficacy in the treatment of VL patients.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40262-021-01036-8.

Transtympanic Sodium Thiosulfate for Prevention of Cisplatin-Induced Ototoxicity: A Randomized Clinical Trial

OBJECTIVES

To determine safety, feasibility, and preliminary activity of transtympanic injection of sodium thiosulfate (STS) against cisplatin-induced hearing loss (CIHL).DESIGN Randomized controlled trial.SETTING Tertiary cancer hospital.PATIENTS Adults to be treated with high-dose cisplatin (≥ 75 mg/m2).INTERVENTION Selected by randomization, 0.1 M STS gel on one side and placebo gel on the other side was transtympanically applied to the middle ear 3 hours before cisplatin administration. After amendment, the placebo ear was left untreated.

MAIN OUTCOME MEASURE

Primary outcome was safety and feasibility. Secondary outcomes included pharmacokinetic analysis of systemic cisplatin and preliminary activity of STS. Clinically relevant CIHL was defined as a ≥ 10 dB threshold shift at pure-tone average 8-10-12.5 kHz (PTA8-12.5). Response to STS was defined as a threshold shift at PTA8-12.5 in the STS-treated ear of ≥ 10 dB smaller than the untreated ear.

RESULTS

Twelve patients were treated. Average CIHL at PTA8-12.5 was 12.7 dB in untreated ears and 8.8 dB SPL in STS-treated ears (p = 0.403). Four patients did not develop CIHL. Four out of eight patients with CIHL responded to STS: CIHL at PTA8-12.5 in STS-treated ears was 18.4 dB less compared to untreated ears (p = 0.068). Grade 1 adverse events were reported. Pharmacokinetic results were available for 11 patients.

CONCLUSION

Transtympanic application of STS was safe and feasible. Based on our pharmacokinetic analysis, we postulate that transtympanic STS does not interfere with the systemically available cisplatin. Our results provide a preliminary proof of concept for transtympanic application of STS in preventing CIHL and warrants further evaluation on a larger scale.

A Semi-Mechanistic Population Pharmacokinetic/Pharmacodynamic Model of Bortezomib in Pediatric Patients with Relapsed/Refractory Acute Lymphoblastic Leukemia

INTRODUCTION

The pharmacokinetics (PK) of the 20S proteasome inhibitor bortezomib are characterized by a large volume of distribution and a rapid decline in plasma concentrations within the first hour after administration. An increase in exposure was observed in the second week of treatment, which has previously been explained by extensive binding of bortezomib to proteasome in erythrocytes and peripheral tissues. We characterized the nonlinear population PK and pharmacodynamics (PD) of bortezomib in children with acute lymphoblastic leukemia.

METHODS

Overall, 323 samples from 28 patients were available from a pediatric clinical study investigating bortezomib at an intravenous dose of 1.3 mg/m² twice weekly (Dutch Trial Registry number 1881/ITCC021). A semi-physiological PK model for bortezomib was first developed; the PK were linked to the decrease in 20S proteasome activity in the final PK/PD model.

RESULTS

The plasma PK data were adequately described using a two-compartment model with linear elimination. Increased concentrations were observed in week 2 compared with week 1, which was described using a Langmuir binding model. The decrease in 20S proteasome activity was best described by a direct effect model with a sigmoidal maximal inhibitory effect, representing the relationship between plasma concentrations and effect. The maximal inhibitory effect was 0.696 pmol AMC/s/mg protein (95% confidence interval 0.664-0.728) after administration.

CONCLUSION

The semi-physiological model adequately described the nonlinear PK and PD of bortezomib in plasma. This model can be used to further optimize dosing of bortezomib.

Cortisol as biomarker for CYP17 inhibition in mCRPC patients treated with abiraterone acetate

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Background: Abiraterone acetate is an effective metastatic castration resistant prostate cancer (mCRPC) treatment, however, there is a high variability in response. It inhibits CYP17, thereby preventing the production of androgens. Abiraterone trough concentrations (Cmin) > 8.4 ng/mL have been associated with an increased progression free survival (PFS) (Eur J Cancer. 2017;72:54-61; Prostate Cancer Prostatic Dis. 2020;23(2):244-251). However, plasma levels do not directly provide information on the level of CYP17 inhibition. Ideally, testosterone levels should be measured, but these levels are below the detection limit of available assays. The synthesis of cortisol is also inhibited by abiraterone via CYP17 inhibition and might therefore be a biomarker for CYP17 inhibition. The objective of this study was to investigate if cortisol levels are related to abiraterone levels and to clinical response. Methods: An observational study was performed in mCRPC patients treated with abiraterone acetate. At the outpatient clinic, plasma samples were collected for pharmacokinetic (PK) monitoring at each hospital visit. Reference populations of healthy volunteers and mCRPC patients using enzalutamide were included to investigate the influence of mCRPC and abiraterone treatment on the circadian rhythm of cortisol. Abiraterone and cortisol levels were measured using validated liquid chromatography-mass spectrometry (LC-MS/MS) assays. Clinical (prostate specific antigen (PSA) independent) PFS and PSA response were evaluated. Results: In total, 117 mCRPC patients using abiraterone acetate, 100 mCRPC patients using enzalutamide and 12 healthy volunteers were included. A clear circadian rhythm of cortisol was described in healthy volunteers and unaffected in mCRPC patients using enzalutamide. Contrarily, a circadian rhythm of cortisol could not be identified in mCRPC patients using abiraterone acetate, due to continuous suppression throughout the day. Patients with an abiraterone Cmin > 8.4 ng/mL (n = 77) had a median cortisol concentration of 1.03 ng/mL vs. 2.59 ng/mL in patients with an abiraterone Cmin ≤8.4 ng/mL (n = 40) (p = 0.020). The median cortisol concentration in PSA responders (n = 63) was 1.02 ng/mL vs. 2.59 ng/mL for PSA non responders (n = 54) (p = 0.037). Patients in the highest cortisol tertile ( > 3.03 ng/mL) had a median PFS of 3.7 months (n = 39) vs. 13.8 months in patients with cortisol levels ≤3.03 ng/mL (n = 78) (p = 0.007). The median PFS was 16.3 months in patients with an abiraterone Cmin > 8.4 ng/mL and cortisol concentration < 3.03 ng/ml vs. 5.3 months in patients with an abiraterone Cmin > 8.4 ng/mL and cortisol concentration > 3.03 ng/ml (p = 0.02). Conclusions: This study demonstrates that cortisol levels are of additional value to abiraterone concentrations as a marker for abiraterone acetate efficacy. This might help be helpful to assess efficacy of abiraterone treatment.

The development and validation of a high performance liquid chromatography method to determine the radiochemical purity of [177Lu]Lu-HA-DOTA-TATE in pharmaceutical preparations

Lutetium-177 [¹⁷⁷Lu] tetra-azacyclododecanetetra-acetic acid [DOTA]-(Tyr3)-octreotate [TATE] ([¹⁷⁷Lu]Lu-DOTA-TATE) is a radiopeptide used for peptide receptor radionuclide therapy in patients with neuroendocrine tumours (NETs). This radiopeptide is made by labelling the ligand octreotate with Lutetium-177 using the linker DOTA. After labelling, and before clinical application quality control of the radiopeptide is needed and the radiochemical purity is assessed. Acceptance limits for radiochemical purity should be within 90-110% of the label claim for radiopharmaceuticals for diagnostic use and within 95-105% of the label claim for radiopharmaceuticals for therapeutic use. Moreover, the amount of unlabelled [¹⁷⁷Lu]LuCl₃ cannot exceed 2% of the radioactive dose. Since no monograph is available for [¹⁷⁷Lu]Lu-DOTA-TATE in the European Pharmacopeia (Ph Eur), this article describes the development and validation of a high-performance liquid chromatography (HPLC) method with ultraviolet (UV) detection and radiodetection. A Waters Acquity Arc UHPLC system equipped with a Waters 2998 photodiode array (PDA) detector was used coupled to a Berthold Lb 514 Flowstar detector equipped with a BGO-X gamma measuring cell. A reversed phase Symmetry Shield C18 column (4.6 mm × 250 mm, 5 µm) was used for chromatographic separation. A flow of 1.5 mL/min was maintained during analysis, using 0.1% TFA in water as mobile phase A and 0.1% TFA in ACN as mobile phase B. The retention time was around 1.7 min and 13.5 min for [¹⁷⁷Lu]LuCl₃ and [¹⁷⁷Lu]Lu-HA-DOTA-TATE, respectively. Stock solutions of [¹⁷⁷Lu]LuCl₃ were made by serial dilution and were injected to test for linearity, accuracy and precision, carry over and signal-to-noise ratio. A [¹⁷⁷Lu]Lu-HA-DOTA-TATE sample was prepared and injected to determine the carry over. The results showed that the method is linear over a range of 0.300-130 MBq/mL, which covers the range for clinical samples, provided that the clinical sample is diluted ten times before analysis. The LLOQ can be measured accurately even after dilution, with a signal-to-noise ratio of at least 5. In short, the method is accurate, precise and sensitive and can be implemented as part of the quality control of [¹⁷⁷Lu]Lu-HA-DOTA-TATE.

Quantification of KRAS inhibitor sotorasib in mouse plasma and tissue homogenates using liquid chromatography-tandem mass spectrometry

Sotorasib is a KRAS inhibitor with promising anticancer activity in phase I clinical studies. This compound is currently under further clinical evaluation as monotherapy and combination therapy against solid tumors. In this study, a liquid chromatography-tandem mass spectrometric method to quantify sotorasib in mouse plasma and eight tissue-related matrices (brain, liver, spleen, kidney, small intestine, small intestine content, lung, and testis homogenates) was developed and validated. Protein precipitation using acetonitrile was utilized in 96-well format to extract sotorasib and erlotinib (internal standard) from mouse plasma and tissue homogenates. Separation of the analytes was performed on an Acquity UPLC® BEH C18 column by gradient elution of methanol and 0.1% formic acid in water at a flow rate of 0.6 ml/min. Sotorasib was detected by a triple quadrupole mass spectrometer with positive electrospray ionization in selected reaction monitoring mode. A linear calibration range of 2-2,000 ng/ml of sotorasib was achieved during the validation. Accuracy values were in the range of 90.7-111.4%, and precision values (intra- and interday) were between 1.7% and 9.2% for all tested levels in all investigated matrices. The method was successfully applied to investigate the plasma pharmacokinetics and tissue accumulation of sotorasib in female wild-type mice.

ABCB1 and ABCG2 Restrict Brain and Testis Accumulation and, Alongside CYP3A, Limit Oral Availability of the Novel TRK Inhibitor Selitrectinib

Selitrectinib (BAY2731954; LOXO-195) is a promising oral tropomyosin receptor kinase (TRK) inhibitor currently in phase I/II clinical trials for the treatment of histology-agnostic cancers positive for TRK fusions. With therapeutic resistance eventually developing with first-generation TRK inhibitors, selitrectinib was designed to overcome resistance mediated by acquired kinase domain mutations. Using genetically modified mouse models and pharmacological inhibitors, we investigated the roles of the multidrug efflux transporters ABCB1 and ABCG2, and the drug-metabolizing CYP3A enzyme complex in selitrectinib pharmacokinetics. In vitro, selitrectinib was markedly transported by mouse Abcg2 and human ABCB1, and modestly by human ABCG2. Following oral administration at 10 mg/kg, selitrectinib brain-to-plasma ratios were increased in Abcb1a/1b^-/- (twofold) and Abcb1a/1b;Abcg2^-/- (5.8-fold) compared with wild-type mice, but not in single Abcg2^-/- mice. Testis distribution showed similar results. mAbcb1a/1b and mAbcg2 each restricted the plasma exposure of selitrectinib: With both systems absent oral availability increased by 1.7-fold. Oral administration of the ABCB1/ABCG2 inhibitor elacridar boosted plasma exposure and brain accumulation in wild-type mice to the same levels as seen in Abcb1a/1b;Abcg2^-/- mice. In Cyp3a^-/- mice, plasma exposure of selitrectinib over 4 hours was increased by 1.4-fold and subsequently reduced by 2.3-fold upon transgenic overexpression of human CYP3A4 in liver and intestine. The relative tissue distribution of selitrectinib remained unaltered. Thus, selitrectinib brain accumulation and oral availability are substantially restricted by ABCB1 and ABCG2, and this can be reversed by pharmacological inhibition. Moreover, oral availability of selitrectinib is limited by CYP3A activity. These insights may be useful to optimize the clinical application of selitrectinib.

Pharmacokinetics of docetaxel and ritonavir after oral administration of ModraDoc006/r in patients with prostate cancer versus patients with other advanced solid tumours

PURPOSE

ModraDoc006 is a novel oral formulation of docetaxel. The clearance of intravenous docetaxel is higher in medically castrated prostate cancer patients as compared to patients with other types of solid tumours. Oral docetaxel requires co-administration ritonavir (r), which might further impact the pharmacokinetics (PK). We now compare the PK of docetaxel and ritonavir between patients with Hormone Sensitive Prostate Cancer (HSPC), metastatic Castration-Resistant Prostate Cancer (mCRPC) and other metastatic solid tumours, treated on the same dose and weekly schedule of ModraDoc006/r.

METHODS

The docetaxel and ritonavir PK were compared between four patient groups from three clinical phase I trials, including eight male and eight female patients with different types of solid tumours (study 1), seven patients with HSPC (study 2) and five patients with mCRPC (study 3). All patients were treated with ModraDoc006 30 mg and ritonavir 100 mg in the morning, followed by ModraDoc006 20 mg and ritonavir 100 mg in the evening (ModraDoc006/r 30-20/100-100). For comparative purposes, the PK of six mCRPC patients that received 30-20/200-100 in study 3 were also evaluated.

RESULTS

The maximum plasma concentration (C_max) was significantly lower for both docetaxel and ritonavir in the prostate cancer patients as compared to the patients with other types of solid tumours treated at ModraDoc006/r 30-20/100-100. The docetaxel area under the plasma concentration versus time curve (AUC) was significantly different at this dose, with a mean AUC_0-48 of 1359 ± 374 ng/mL*h (N = 8) in female patients and 894 ± 223 ng/mL*h (N = 8) in male patients with different solid tumours (study 1), 321 ± 81 (N = 7) in HSPC (study 2) and 367 ± 182 ng/mL*h (N = 5) in mCRPC (study 3). A similar pattern was observed for ritonavir. ModraDoc006/r 30-20/200-100 in six mCRPC patients led to a comparable ritonavir exposure as compared to the patients at 30-20/100-100 in study 1 and increased the docetaxel AUC_0-48 to 1266 ± 473 ng/mL*h (N = 6).

CONCLUSION

The exposure to docetaxel and ritonavir was significantly lower in prostate cancer patients as compared to patients with other types of solid tumours, treated on ModraDoc006/r 30-20/100-100. An increase of the ritonavir dose increased the docetaxel exposure in mCRPC patients. Therefore, a different RP2D of ModraDoc006/r is pursued in castrated prostate cancer patients as compared to patients with other types of solid tumours.

TRIAL REGISTRATION

Study 1: ClinicalTrials.gov Identifier NCT01173913, date of registration August 2, 2010. Study 2: ClinicalTrials.gov Identifier NCT03066154, date of registration February 28, 2017. Study 3: ClinicalTrials.gov Identifier NCT03136640, date of registration May 2, 2017.

ModraDoc006, an oral docetaxel formulation in combination with ritonavir (ModraDoc006/r), in metastatic castration-resistant prostate cancer patients: A phase Ib study

BACKGROUND

ModraDoc006 is an oral formulation of docetaxel, which is co-administered with the cytochrome P450 3A4 and P-glycoprotein inhibitor ritonavir (r): ModraDoc006/r. Weekly treatment with ModraDoc006/r had been evaluated in phase I trials in patients with different types of advanced solid tumors, but up to this point in time not in patients with metastatic castration-resistant prostate cancer (mCRPC).

AIM

We assessed safety and pharmacokinetics (PK) of ModraDoc006/r to establish the recommended phase 2 dose (RP2D) in patients with mCRPC.

METHODS

mCRPC patients, treatment naïve or following abiraterone or enzalutamide treatment, were included. Dose-escalation of ModraDoc006/r was based on safety and docetaxel PK. Antitumor activity was assessed by serum prostate-specific antigen (PSA) and radiological evaluation.

RESULTS

Cohort 1 (n = 5) received once weekly ModraDoc006 30 mg with ritonavir 100 mg in the morning, and ModraDoc006 20 mg with ritonavir 100 mg in the evening (30-20/100-100). The mean docetaxel area under the plasma concentration-time curve (mAUC0-inf) was 461 ng/mL × h with 1 dose limiting toxicity (DLT); grade 3 alanine transferase increase. In cohort 2 (n = 6, ModraDoc006/r 30-20/200-200), the mAUC0-inf was 1687 ng/mL × h with 2 DLTs; grade 3 diarrhea and mucositis. In cohort 3A (n = 6, ModraDoc006/r 30-20/200-100), the mAUC0-inf was 1517 ng/mL × h with 1 DLT; grade 3 diarrhea. In cohort 3B (n = 3, ModraDoc006/r 20-20/200-100), the mAUC0-inf was 558 ng/mL × h without DLTs. The mAUC0-inf exceeded estimated exposures of intravenous docetaxel in cohort 2 and 3A, was lower in cohort 1 and was in range in cohort 3B. PSA decreases of >50% occurred in 6/10 evaluable patients throughout the various cohorts. In five radiological evaluable patients, two confirmed partial responses were observed.

CONCLUSION

The RP2D was established at weekly ModraDoc006/r 30-20/200-100. Observed PSA and radiological responses suggest promising clinical activity. These results have led to an ongoing randomized Phase 2b study, comparing weekly ModraDoc006/r with 3-weekly IV docetaxel in patients with mCRPC.

Development and validation of a combined liquid chromatography tandem-mass spectrometry assay for the quantification of aprepitant and dexamethasone in human plasma to support pharmacokinetic studies in pediatric patients

A pharmacokinetic study was set up to investigate the pharmacokinetics of the anti-emetic agents aprepitant and dexamethasone and the drug-drug interaction between these drugs in children. In order to quantify aprepitant and dexamethasone, a liquid chromatography-tandem mass spectrometry assay was developed and validated for the simultaneous analysis of aprepitant and dexamethasone. Protein precipitation with acetonitrile-methanol (1:1, v/v) was used to extract the analytes from plasma. The assay was based on reversed-phase chromatography coupled with tandem mass spectrometry detection operating in the positive ion mode. The assay was validated based on the guidelines on bioanalytical methods by the US Food and Drug Administration and European Medicines Agency. The calibration model was linear and a weighting factor of 1/concentration² was used over the range of 0.1-50 ng/mL for aprepitant and 1-500 ng/mL for dexamethasone. Intra-assay and inter-assay bias were within ±20% for all analytes at the lower limit of quantification and within ±15% at remaining concentrations. Dilution integrity tests showed that samples exceeding the upper limit of quantification can be diluted 100 times in control matrix. Stability experiments showed that the compounds are stable in the biomatrix for 25 h at room temperatures and 89 days at -20 °C. This assay is considered suitable for pharmacokinetic studies and will be used to study the drug-drug interaction between aprepitant and dexamethasone in pediatric patients.

Investigating the influence of relevant pharmacogenetic variants on the pharmacokinetics and pharmacodynamics of orally administered docetaxel combined with ritonavir

The anticancer drug docetaxel exhibits large interpatient pharmacokinetic and pharmacodynamic variability. In this study, we aimed to assess the functional significance of 14 polymorphisms in the CYP3A, CYP1B1, ABCB1, ABCC2, and SLCO1B3 genes for the pharmacokinetics and pharmacodynamics of oral docetaxel, co-administered with ritonavir. None of the tested CYP3A, ABCB1, ABCC2, and SLCO1B3 genotypes and diplotypes showed a significant relation with an altered bioavailability or clearance of either docetaxel or ritonavir. Similarly, no clear effect of CYP1B1 genotype on clinical outcomes was observed in a subgroup of non-small cell lung cancer (NSCLC) patients. Our post hoc power analysis indicated that our pharmacogenetic-pharmacokinetic analysis was only powered for relatively high effect sizes, which were to be expected given the high interpatient variability. This makes it unlikely that future studies will explain the high observed interpatient variability in oral docetaxel pharmacokinetics as a result of any of these separate polymorphisms and diplotypes.