Potential Drug–Drug Interactions with Combination Volasertib + Itraconazole: A Phase I, Fixed-Sequence Study in Patients with Solid Tumors
This drug–drug interaction study determined whether the metabolism and distribution of the Polo-like kinase 1 inhibitor, volasertib, is affected by co-administration of the P-glycoprotein and cytochrome P-450 3A4 inhibitor, itraconazole.
This was an uncontrolled, open-label, fixed-sequence trial of two 21-day treatment cycles in patients with various solid tumors. In cycle 1 (test), eligible patients were administered volasertib (day 1) plus itraconazole (days −3 to 15). In cycle 2 (reference), patients received volasertib monotherapy. The primary end point was the influence of co-administration of itraconazole on the pharmacokinetic profile (AUC0–tz; Cmax) of volasertib and its main metabolite, CD 10899, compared with that of volasertib monotherapy. Other end points included tolerability and preliminary therapeutic efficacy.
Concurrent administration of itraconazole resulted in a slight reduction in the AUC0–tz (geometric mean ratio, 93.6%; 90% CI, 82.1%–106.8%) and a 20% reduction in Cmax (geometric mean ratio, 79.4%; 90% CI, 64.9%–97.1%) of volasertib compared with monotherapy. Of note, concurrent administration of itraconazole + volasertib had no effect on the AUC0–∞ of volasertib. More patients reported at least one drug-related adverse event in cycle 1 than in cycle 2 (75% vs 71%). The most commonly reported drug-related adverse events (cycles 1 and 2) were thrombocytopenia (68% and 33%, respectively), leukopenia (50% and 46%), and anemia (36% and 33%). No objective responses were observed. Stable disease was observed in 25 of 28 patients (89%).
While there was no clear evidence of a pharmacokinetic interaction between volasertib and itraconazole, co-administration reduced the tolerability of volasertib. Clinicaltrials.gov identifier: NCT01772563.
In vitro studies have shown that volasertib is a potent and selective inhibitor of PLK1 (IC50, 0.87 nmol/L [0.54 μg/L]), and, to a lesser extent, the closely related kinases PLK2 (IC50, 5 nmol/L [3.1 μg/L]) and PLK3 (IC50, 56 nmol/L [34.7 μg/L]), and induces mitotic arrest and apoptosis.
CD 10899 is a hydroxylated metabolite of volasertib (Figure 1) and is pharmacologically active against PLK1 (IC50, 6 nmol/L [3.8 μg/L]). PLK1 is overexpressed in a number of human cancers, and the level of expression has been associated with prognosis
; thus, it represents a valid target for anticancer therapy.
) in patients with solid tumors or acute myeloid leukemia.
Across studies, volasertib has demonstrated similar pharmacokinetic (PK) properties, with generally low interpatient variability.
In vitro analyses undertaken in human liver microsomes expressing cytochrome P450 (CYP) enzymes and human hepatocytes, have demonstrated that volasertib is metabolized to CD 10899 by CYP3A4, with no relevant contribution of other CYPs (data on file, Boehringer Ingelheim). Further in vitro studies conducted in Caco-2 cells and human P-glycoprotein (P-gp)-expressing LLC-PK1 cells have demonstrated that volasertib is a substrate of P-gp but not of breast cancer resistance protein or multidrug-resistance protein 2 (data on file, Boehringer Ingelheim). As volasertib is a substrate of CYP3A4 and P-gp, its distribution may be influenced by P-gp inhibitors, and its metabolism may be affected by CYP3A4 inhibitors. Therefore, a drug–drug interaction study was conducted to evaluate the effects of the potent CYP3A4 and P-gp inhibitor itraconazole on the PK properties and tolerability of volasertib. We report here the results of this open-label, Phase I trial.
Materials and Methods
Study Design and Treatment
the recommended Phase II dose of 300 mg of volasertib administered in a 120-min IV infusion every 21 days was chosen as the starting dose. Patients received volasertib + itraconazole in cycle 1 (test) and volasertib monotherapy in cycle 2 (reference), followed by repeated cycles of volasertib monotherapy in patients with clinical benefit.
In cycle 1, itraconazole was administered at 200 mg PO once daily, starting 3 days before the first infusion of volasertib (day −3). Itraconazole dosing continued for another 14 days (to day 15; 18 days in total). All patients were admitted to hospital for volasertib infusions in cycles 1 and 2, and remained for 72 h after the start of the infusion. In subsequent cycles, volasertib was administered on an outpatient basis at the discretion of the investigator. Blood samples for PK analyses were taken from a forearm vein contralateral to the infusion site at defined times until 21 days after the second volasertib infusion. Patients could receive further treatment with volasertib in case of clinical benefit from treatment and acceptable tolerability.
The study enrolled patients aged 18–70 years, with an Eastern Cooperative Oncology Group performance status of ≤2 and a confirmed diagnosis of advanced, nonresectable, and/or metastatic solid tumor. Patients had either failed conventional treatment, had no therapy of proven efficacy available, or were not amenable to established forms of treatment, based on the investigator’s assessment.
Exclusion criteria included: active brain metastasis or leptomeningeal disease; life expectancy of ≤12 weeks; use of a potent CYP3A4 or P-gp inhibitor other than the study drugs between 1 week prior to first drug administration and when the last PK sample was collected. The study was conducted and reported in accordance with the Declaration of Helsinki and the International Conference on Harmonisation Good Clinical Practice guidelines. The study protocol was approved by the Medical Research Council Ethics Committee for Clinical Pharmacology (Budapest, Hungary). All patients provided written informed consent.
End Points and Assessments
The primary end point was the influence of the co-administration of itraconazole + volasertib on the PK profile of volasertib and CD 10899 compared with that of volasertib monotherapy, as assessed using the AUC from time zero to the last actual measurement (AUC0–tz) and the Cmax. A secondary end point was the AUC0–∞ values of volasertib and CD 10899. Other PK end points included the Tmax, t1/2, total plasma clearance (CL), and volume of distribution at steady state (Vss). Plasma concentrations of volasertib and CD 10899 were determined by a validated HPLC-MS/MS assay.
Briefly, volasertib and CD 10899 were analyzed simultaneously by HPLC-MS/MS using [D3]volasertib and [D3]CD 10899 as internal standards. Samples were extracted by solid-phase extraction in the 96-well plate format, followed by chromatography on an analytical reversed-phase HPLC column (Hypersil Gold; Thermo Scientific, Waltham, MA; 50 × 2.1 mm; internal diameter, 3 μm) with gradient elution (eluent A, 0.01 mol/L ammonium formate, pH 4; eluent B, acetonitrile; 10%–90% gradient, 600 μL/min). The substances were detected and quantified by MS/MS using electrospray ionisation in the positive ion mode (transition volasertib, m/z 619.3 → 479.2; [2H3]volasertib, m/z 622.3 → 482.3; transition CD 10899, m/z 635.5 → 495.5; transition [2H3]CD 10899, m/z 638.5 → 498.5). Assay performance during the study was assessed by back-calculation of calibration standards, tabulation of the standard curve-fit function parameters, and measurement of quality-control samples. No relevant interference of endogenous compounds was observed in the human plasma samples. The lower limit of quantification of both volasertib and CD 10899 was 0.2 ng/mL. The calibration curves of undiluted samples were linear over the range of volasertib and CD 10899 concentrations from 0.2 to 200 ng/mL using a plasma volume of 50 μL. Plasma concentrations of itraconazole were analyzed by HPLC-MS/MS using a proprietary method provided by Covance Laboratories Ltd (Harrogate, UK). The lower limit of quantification was 2 ng/mL. The calibration curve of undiluted samples was linear over the range of concentrations from 2 to 1000 ng/mL using a plasma volume of 100 μL. The accuracy values of the calibration standards used in the calibration curves were within 85%–115% of the nominal concentration at all levels for itraconazole. Volasertib and CD 10899 did not affect the quantification of itraconazole. The method was validated for the determination of metabolite hydroxy-itraconazole, and data on both analytes were acquired, but only those on itraconazole were quantified.
Tolerability was analyzed based on the occurrence of adverse events (AEs), AEs leading to dose reduction, AEs leading to permanent treatment discontinuation, and serious AEs. Dose-reducing toxicity (DRT) (ie, unacceptable volasertib toxicity) was defined as the occurrence of any drug-related nonhematologic AE, as defined in the Common Terminology Criteria for Adverse Events (CTCAE), of grade ≥3 (except emesis or diarrhea responding to supportive treatment); drug-related CTCAE-defined neutropenia of grade 4 and lasting ≥7-days; or drug-related CTCAE-defined thrombocytopenia of grade 4. Tolerability was also monitored using physical examinations, including vital sign measurements, laboratory tests, and ECGs.
Preliminary therapeutic effects (clinical benefit) (eg, tumor response, stable disease, or symptom improvement) were assessed by the investigator after each cycle; radiologic and other assessments were performed at the investigator’s discretion.
The PK parameters AUC0–tz and Cmax were log-transformed prior to fitting an ANOVA mode that included treatment and subject as effects. The difference between the expected means of logT and logR, where T was test and R was reference, was estimated by the difference in the corresponding least squares means (point estimates). With regard to the primary and secondary end points, 2-sided 90% CIs based on the t distribution were calculated. These quantities were then back-transformed to the original scale to obtain the point estimator and interval estimates for the intrasubject geometric mean ratio (GMR) between response to test and response to reference. Descriptive statistics for all other parameters and end points were calculated. The relationships of each AE to the study drug treatments were assessed by the investigator. Tolerability end points were analyzed descriptively.
Patients and Exposure
Table IPatient baseline disease and demographic characteristics (N = 28).
BMI = body mass index; ECOG = Eastern Cooperative Oncology Group.
In cycle 1, all 28 patients received volasertib + itraconazole, and 24 received volasertib monotherapy in cycle 2. Two patients discontinued prior to cycle 2 due to toxicities, and 2 discontinued due to disease progression. Three patients received volasertib 300 mg + itraconazole in cycle 1; however, 2 of these patients had DRTs and were discontinued from the study medication before starting cycle 2. As a result, the dose of volasertib was reduced to 250 mg in all subsequent patients (n = 25) (data not shown).
Of the 24 patients who were treated with volasertib in cycle ≥2, 23 patients were permanently discontinued from the study medication, most frequently due to disease progression (17 patients; 71%). Four patients (17%) refused to continue study medication, and 2 (8%) were discontinued for other reasons. As of November 2019, 1 patient was still enrolled in the trial with stable disease and had undergone >100 treatment cycles. With volasertib monotherapy (cycle ≥2), the median duration of therapy was 211 days (range, 1–1334 days), and the median number of cycles was 10 (range, 1–61) at the June 2017 data cutoff (data not shown).
Table IIPharmacokinetic parameters during cycles 1 and 2.
AUC0–tz = area under the plasma concentration–time curve from 0 to the time of the last quantifiable data point; CL = clearance; GM = geometric mean; GMR = geometric mean ratio; Vss = volume of distribution at steady state; Vz = volume of distribution at terminal phase.
Table IIIPharmacokinetic parameters of itraconazole.
Cpre,ss = predose plasma concentration at steady state; GM = geometric mean.
More patients reported at least 1 AE in cycle 1 than in cycle 2 (79% vs 71%); most AEs were considered drug related (cycle 1, 75%; cycle 2, 71%). The natures of the drug-related AEs observed in cycles ≥2 were similar to those in cycle 1. Two in 3 patients (67%) treated with volasertib 300 mg in cycle 1 had DRTs during cycle 1 (grade 4 thrombocytopenia; grade 4 neutropenia for ≥7 days) and were discontinued from the study medication before starting cycle 2. Two of 25 patients (8%) treated with volasertib 250 mg in cycle 1 had DRT during cycle 1 (grade 4 thrombocytopenia) and continued with a reduced dose (200 mg) in cycle 2. None of the patients had AEs leading to dose reduction or discontinuation in cycle ≥2. In cycles ≥2, 92% of patients had at least 1 AE, and 83% had at least 1 drug-related AE (data not shown).
Table IVAdverse events (as defined by the investigator) in cycles 1, 2, and ≥2.
Of the 28 treated patients, 27 were assessable for tumor response. The best overall response observed in any patient was stable disease (25 of 28 patients; 89%); no objective responses were observed. Approximately half of patients (14 of 27; 52%) were discontinued from volasertib treatment by the end of cycle 9, 13 of 27 patients (48%) received ≥10 cycles, and 4 patients (15%) received ≥25 cycles (1 patient each with a diagnosis of colon cancer [no metastases], cancer of the maxilla [metastases to pleura and lymph nodes], cancer of the palate [no metastases], and cancer of the parotid gland [no metastases]).
This drug–drug interaction study in patients with solid tumors demonstrated that the concurrent administration of itraconazole, a dual inhibitor of P-gp and CYP3A4, had no meaningful effect on the systemic exposure (measured in plasma) of intravenously administered volasertib. However, the co-administration of itraconazole clearly had an impact on the tolerability of volasertib.
and displays moderate plasma clearance. Based on these data, it is assumed that volasertib also shows low hepatic clearance. The blood-to-plasma ratio of volasertib is 1.92 (data on file, Boehringer Ingelheim), giving a hepatic blood clearance rate of ∼250 mL/min, indicating that volasertib is a low-clearance drug.
The effects of strong CYP3A4 inhibitors on high-clearance compounds that are primarily metabolized by CYP3A4 are more pronounced. Furthermore, although CYP3A4 is considered to be the major metabolic enzyme of volasertib, itraconazole had only a limited effect on the plasma concentration of CD 10899, supporting the theory that volasertib is a low-clearance drug. Also, the effect of itraconazole as a P-gp inhibitor would have little effect on systemic exposure to volasertib, a P-gp substrate.
Itraconazole was the chosen CYP3A4/P-gp inhibitor based on a protocol proposed by the US PharmA initiative.
Moreover, given that volasertib has the potential to prolong the QT interval, ketoconazole, clarithromycin, and cobicistat could not be used because of their association with QT-interval prolongations as well as hepatotoxic AEs.
Based on guidance from the US Food and Drug Administration, long-term dosing of ritonavir was not an option for drug–drug interaction studies in patients with advanced cancer.
However, the effect of itraconazole on the exposure of volasertib was consistent, with similar effects on AUC0–336h and AUC0–∞. A study with a more potent inhibitor of CYP3A4 may be warranted for assessing the effects of CYP3A4 on the metabolism of volasertib.
and were more frequent and severe with volasertib + itraconazole combination therapy than with volasertib alone. Accordingly, the tolerable dose of volasertib monotherapy identified in previous studies in patients with solid tumors (300 mg every 21 days as monotherapy
or in combination with other anticancer agents
) was not tolerable when combined with itraconazole, and was reduced to 250 mg. These results suggest that itraconazole could affect the distribution of volasertib in tissues that express P-gp. This possibility requires further investigation.
The best overall response was stable disease; no objective responses were observed. Of the 27 patients who received volasertib monotherapy, 14 (52%) had been discontinued from treatment by the completion of cycle 9, and 9 patients were treated for 10 to 24 cycles. Of note, 4 patients received 25 or more cycles of volasertib. No similarities in the type of cancer were apparent among the 4 patients who had prolonged stable disease on volasertib, although most did not have metastatic disease.
Conflicts of Interest
This research, and writing and editorial support, were funded by Boehringer Ingelheim , the manufacturer of volasertib. D. Liu, H. Fritsch, T. Taube, and E. Chizhikov are employees of Boehringer Ingelheim. The sponsor played a role in the collection, management, analysis and interpretation of data. They reviewed and approved the manuscript and the decision to submit, and, as such, are included in the authorship list. The authors have indicated that they have no other conflicts of interest with regard to the content of this article.