Abstract
Purpose: To enhance the systemic exposure to oral docetaxel by coadministration of ritonavir, an efficacious inhibitor of CYP 3A4 with minor P-glycoprotein inhibiting effects, in patients with cancer.
Experimental Design: A proof-of-concept study was carried out in 12 patients with solid tumors. The first cohort of patients (n = 4) received 10 mg and the subsequent cohort (n = 8) 100 mg of oral docetaxel, coadministered with 100 mg oral ritonavir randomized simultaneously or ritonavir given 60 minutes before docetaxel on days 1 and 8. On day 15 or 22, patients received 100 mg i.v. docetaxel.
Results: The area under the plasma concentration-time curve in patients who received 10 mg oral docetaxel in combination with ritonavir was low, and the dose could safely be increased to 100 mg. The area under the plasma concentration-time curve in patients who received 100 mg oral docetaxel combined with ritonavir simultaneously or ritonavir given 60 minutes before docetaxel was 2.4 ± 1.5 and 2.8 ± 1.4 mg/h/L, respectively, compared with 1.9 ± 0.4 mg/h/L after i.v. docetaxel. The apparent oral bioavailability of docetaxel combined with ritonavir simultaneously or ritonavir given 60 minutes before docetaxel was 131% ± 90% and 161% ± 91%, respectively. The oral combination of docetaxel and ritonavir was well tolerated.
Conclusion: Coadministration of ritonavir significantly enhanced the apparent oral bioavailability of docetaxel. These data are promising and form the basis for further development of a clinically applicable oral formulation of docetaxel combined with ritonavir.
- docetaxel
- oral bioavailability
- ritonavir
Translational Relevance
Docetaxel was initially developed as an i.v. formulation, but in this study it is under review for oral application in patients with solid tumors. Oral administration of drugs has several advantages over i.v. administration. However, low and variable oral bioavailability has limited the development of oral treatment regimens. This is due to proficient P-glycoprotein and metabolism by CYP3A in the gut wall and/or liver. This study shows one of the first clinical examples that concomitant use of transporter and/or CYP enzyme inhibitors with oral anticancer drugs is an effective and safe strategy. Coadministration of ritonavir, a CYP3A/P-glycoprotein inhibitor, strongly enhanced the apparent oral bioavailability of docetaxel in patients. These data are promising and form the basis for further development of a clinically applicable oral formulation of docetaxel combined with ritonavir.
There is an increasing interest in the development of oral treatment regimens of anticancer drugs. Patient convenience, practicality, and pharmacoeconomics are major arguments in favor of oral therapy (1–3). In addition, weekly schedules of docetaxel are increasingly being used (4, 5). The oral route facilitates the use of more chronic treatment regimens, which result in more frequent exposure of tumor cells to the cytotoxic agent while lower maximal plasma concentration values are reached (6). For the taxane docetaxel, an anticancer agent widely applied against numerous tumors, the low and variable oral bioavailability has limited the development of oral treatment regimens. This is, at least in part, due to the high affinity of docetaxel for the multidrug efflux pump P-glycoprotein (7). Preclinical and clinical studies in our group showed that coadministration of oral cyclosporine, a strong inhibitor of P-glycoprotein and a substrate for the cytochrome P450 (CYP) 3A4 metabolic enzyme, significantly enhanced the oral bioavailability of docetaxel (8, 9). However, the development of this combination was terminated because preclinical and clinical research showed that first-pass elimination by CYP3A4 in the liver and/or gut wall contributed much more to the low oral bioavailability of docetaxel than blockade by P-glycoprotein (10–12). Clinical studies have shown that <10% of docetaxel given is excreted unchanged in the urine, suggesting an important role for hepatic metabolism (9). This has been supported by in vivo experiments in mice (12). Preclinical experiments, conducted in P-glycoprotein knockout and wild-type mice, have shown a significant increase in systemic exposure when docetaxel was coadministered orally with ritonavir (12, 13). The preclinical dosages (docetaxel, 10-30 mg/kg; ritonavir, 12.5 mg/kg) were, however, far higher than those normally used in humans. Ritonavir is a HIV protease inhibitor, with strong CYP3A4-inhibiting properties and with only minor P-glycoprotein–inhibiting effects (14, 15). Furthermore, the enhancement of the systemic exposure of CYP3A4 substrates by ritonavir is already a standard practice in the treatment of HIV patients with protease inhibitors (16, 17). Recently, van Herwaarden et al. (18) showed that the absence of Cyp3a activity in mice alone increased the systemic exposure of docetaxel after oral administration in vivo by 17.7-fold. They also indicated that ritonavir most likely is highly efficacious in inhibiting CYP3A and has high specificity for CYP3A4. We hypothesized that the systemic exposure of orally given docetaxel could be increased by coadministration of ritonavir in patients, although the preclinically used dosages were far higher than those considered safe in humans. To investigate this, we initiated a proof-of-concept study with low dosages of docetaxel in patients with solid tumors.
Patients and Methods
Patient population. Patients for whom no standard therapy of proven benefit existed and with a histologically confirmed cancer refractory to current therapies were eligible for the study. Other eligibility criteria included the following: age ≥18 y; life expectancy ≥3 mo; previous radiotherapy or chemotherapy was allowed, provided that the last treatment was at least 3 wk before study entry and any resulting toxicities were resolved; hormonal therapy should be stopped at least 1 wk before the start of the study. Eligibility criteria included acceptable bone marrow function (WBC count >3.0 × 109/L; platelet count >100 × 109/L), liver function (serum bilirubin level ≤20 μmol/L; serum albumin level ≥25 g/L), and renal function (serum creatinine level ≤160 μmol/L or clearance ≥50 mL/min); and a WHO performance status of ≤2. Patients were not eligible if they suffered from uncontrolled infectious disease, neurologic disease, or bowel obstructions; symptomatic brain metastases, alcoholism, drug addiction, or psychotic disorders leading to inadequate follow-up; or pregnancy. Other exclusion criteria were concomitant use of known P-glycoprotein inhibitors and chronic use of H2-receptor antagonists or proton pump inhibitors. The study protocol was approved by the medical ethics committee of the institute, and all patients had to give written informed consent before the start of the study.
Study design. A proof-of-concept study was carried out in 12 patients with advanced solid malignancies. In the first part of the study, four patients were randomized to receive 10 mg of oral docetaxel coadministered with a 100-mg oral dose of ritonavir simultaneously or ritonavir given 60 min before docetaxel on days 1 and 8 of cycle one. On day 15 of cycle one, patients received 100 mg i.v. docetaxel. In the second part of the study, eight patients were randomized to receive 100 mg of oral docetaxel coadministered with a 100-mg oral dose of ritonavir simultaneously or ritonavir given 60 min before docetaxel on days 1 and 8 of cycle one. On day 22 of cycle one, patients received 100 mg i.v. docetaxel. If it was considered to be in their best interest, patients continued on a 3-weekly schedule of i.v. docetaxel (100 mg/m2) (cycles two, three, etc.). In the first part, an oral docetaxel dose of 10 mg was selected for safety reasons because nonclinical data in mice revealed that coadministration of ritonavir resulted in a 50-fold increase in the systemic exposure to orally applied docetaxel (12). In the second cohort, a dose increase to 100 mg of oral docetaxel was considered justified, based on the pharmacokinetic and safety data obtained in the first part of this study and an earlier study conducted by Malingré et al. (9).
Drug administration. The i.v. formulation of docetaxel (Taxotere; Rhone-Poulenc Rorer/Aventis) was used for both i.v. and oral administration. Ritonavir (Abbott) was given immediately before or 60 min before oral docetaxel administration. Oral drugs were taken with 100 mL of tap water after an overnight fast. Patients remained fasted until 1.5 h after docetaxel administration. Standard docetaxel pretreatment was given during all cycles and consisted of oral dexamethasone, 4 mg 1 h before drug administration and 4 mg every 12 h (twice) after drug administration. One hour before oral docetaxel administration, patients received 1 mg of oral granisetron.
Patient evaluation. Pretreatment evaluation included a complete medical history and complete physical examination. Before each course, an interim history, including concomitant drugs taken, toxicities, and performance status, were registered, and a physical examination was done. Hematology, blood chemistries, including liver and renal function, serum electrolytes, and total protein, albumin, and glucose levels, were checked weekly. All toxicities observed were graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events version 3.0. Dose-limiting toxicity was defined as grade 4 granulocytopenia lasting >5 d, grade 4 thrombocytopenia of any duration, or any grade 3 or 4 nonhematologic toxicity, except alopecia, and untreated nausea and vomiting.
Pharmacokinetic sample collection and sample analysis. Pharmacokinetic monitoring was done during cycle one days 1, 8, and 15 or 22 for docetaxel and on days 1 and 8 for ritonavir. For plasma docetaxel and ritonavir concentrations, blood samples of 5 mL each were collected in heparinized tubes. After oral or i.v. administration, samples were obtained before dosing and at 15, 30, 45, 60, 75, and 90 min, and 2, 3, 4, 6, 8, 10, 24, 36, and 48 h after docetaxel. Blood samples were centrifuged, plasma was separated, and docetaxel and ritonavir samples were immediately stored at -20°C until analysis. Docetaxel and ritonavir concentrations in plasma were determined with the use of validated liquid chromatography coupled with tandem mass spectrometry methods (19, 20).
Pharmacokinetic and statistical analysis. Pharmacokinetic variables were calculated by the noncompartmental trapezoidal method with the use of the software package WinNonlin Professional (version 5.0; Pharsight). The area under the plasma concentration-time curve (AUC) was calculated from time 0 to 48 h and with extrapolation to infinity with the use of the terminal rate constant k. The apparent oral bioavailability (F) was calculated by the formula F = (AUCoral × dosei.v.)/(AUCi.v. × doseoral) × 100%. Other variables to be assessed were the maximal plasma concentration, the time to maximal plasma concentration, the plasma clearance after i.v. administration, and the volume of distribution during the elimination phase. Statistical analysis of the data was done with the use of nonparametric Mann-Whitney U test. The level of significance was set at P < 0.05.
Results
Patient characteristics. A total of 12 patients (11 males and 1 female) were enrolled (Table 1 ). At study entry, the median age of the patients was 51 years (range, 37 to 69 years), and the median WHO performance status was 1 (range, 0 to 2). Primary tumor types included bladder carcinoma (n = 2), non–small cell lung cancer (n = 3), esophagus cancer (n = 1), penis cancer (n = 1), colorectal cancer (n = 2), cardia carcinoma (n = 2), and gastric carcinoma (n = 1). Patients had received prior surgical therapy (n = 8), radiotherapy (n = 7), and/or chemotherapy (n = 12).
Patient characteristics
Pharmacokinetics. The mean plasma pharmacokinetic variables of orally given docetaxel (10 or 100 mg) with oral ritonavir (100 mg) simultaneously or ritonavir given 60 minutes before docetaxel and i.v. docetaxel (100 mg) are presented in Table 2 . Systemic exposure to 10 mg docetaxel was 0.11 ± 0.05 mg/h/L given simultaneously and 0.15 ± 0.07 mg/h/L with ritonavir given 60 minutes before docetaxel. Compared with the systemic exposure to docetaxel after administration of a dose of 100 mg i.v. docetaxel, which was 1.9 ± 0.4 mg/h/L, this was considered very low (Table 2 and Fig. 1 ). The apparent oral bioavailability of docetaxel, calculated as the ratio of the AUC after oral and after i.v. administration with a correction for the difference in dose, was relatively high, 47.3 ± 22.4% in combination with 100 mg ritonavir coadministered simultaneously and 62.8 ± 34.4% with ritonavir given 60 minutes before docetaxel. The very low plasma concentrations of docetaxel may have limited optimal assessment of the AUC and, specifically, may have underestimated the oral AUC. Based on these pharmacokinetic and safety data, a dose increase to 100 mg oral docetaxel in combination with 100 mg ritonavir was considered justified in the second part of this study. The data showed a pronounced increase in the mean AUC value of orally given docetaxel of 2.4 ± 1.5 mg/h/L (n = 7) with ritonavir coadministered simultaneously and 2.8 ± 1.4 mg/h/L with ritonavir given 60 minutes before docetaxel compared with i.v. docetaxel (1.9 ± 0.4 mg/h/L; Table 2; Fig. 1). There was no significant difference between the mean oral AUC value of docetaxel coadministered with ritonavir simultaneously or ritonavir given 60 minutes before docetaxel. The apparent oral bioavailability of docetaxel was strongly enhanced to 131% ± 90% (n = 8) with ritonavir coadministered simultaneously and to 161% ± 91% (n = 8) with ritonavir given 60 minutes before docetaxel. The coefficient of variation of the AUC after oral docetaxel administration in combination with ritonavir simultaneously or ritonavir given 60 minutes before docetaxel was 62.5% and 50%, respectively, (n = 8) and 22% after i.v. administration (n = 8). Overall, these data are promising and form the basis for further development of a clinically useful oral formulation of docetaxel in combination with ritonavir.
Main pharmacokinetic variables of docetaxel after oral administration (10 or 100 mg) with or without ritonavir (100 mg) and i.v. administration of docetaxel (100 mg)
Plasma concentration-time curves of i.v. docetaxel (100 mg) and oral docetaxel (10 or 100 mg) with ritonavir (RTV) simultaneously (sim) or with a 60-min time interval (60 min) represented as mean ± SD.
Hematologic and nonhematologic toxicities. Docetaxel given orally was well tolerated. In one of the patients, no toxicity data was available. In 0 of the 11 patients was any grades 1 to 4 hematologic toxicity (anemia, leukocytopenia, neutropenia, and thrombocytopenia) observed after oral docetaxel administration in combination with ritonavir. Table 3 summarizes the nonhematologic toxicities that were observed after oral docetaxel combined with ritonavir and after the first i.v. administration on day 15 or 22. The main nonhematologic toxicities after oral intake of docetaxel were diarrhea (seven patients), vomiting (five patients), fatigue (five patients), abdominal pain (three patients), and nausea (two patients). Most of the toxicities did not exceed grade 2 in severity, except in five patients in whom short-lasting grade 3 events were observed (Table 3). Three patients developed grade 3 diarrhea after oral docetaxel, which was considered to be probably related to oral docetaxel combined with ritonavir. Furthermore, one patient developed grade 3 stomatitis and one patient a grade 3 allergic reaction (Table 3). The principal nonhematologic toxicities during the first cycle of i.v. docetaxel were nausea (one patient), alopecia (one patient), diarrhea (2 patients), anorexia (one patient), and elevated alkaline phosphatase (one patient; Table 3). The nonhematologic toxicities were mild (grade 1 or 2). In the next i.v. cycles, the principal nonhematologic toxicities were grade 1 or 2 fatigue, alopecia, myalgia, nausea, diarrhea, infections, and skin reactions. In none of the patients treated with i.v. docetaxel was any grades 1 to 4 hematologic toxicity observed.
Nonhematologic toxicities observed after oral docetaxel administration in combination with ritonavir and the first i.v. course of docetaxel
Discussion
The results presented here show that coadministration of oral ritonavir, an effective inhibitor of CYP3A4, strongly enhanced the systemic exposure to orally given docetaxel in patients. Oral docetaxel dosed at 100 mg in combination with ritonavir resulted in an apparent bioavailability of 131% ± 90% or 161% ± 91% when given simultaneously or when ritonavir is given 60 minutes before docetaxel, respectively. No significant differences were found between simultaneous docetaxel and ritonavir administration and ritonavir given 60 minutes before docetaxel, and the interpatient variability in the systemic exposure after oral docetaxel was higher than after i.v. docetaxel but comparable with other clinical studies with oral docetaxel (9).
Preclinical data obtained in wild-type mice, P-glycoprotein knockout mice, and Cyp3a knockout mice combined with these first clinical data indicate that ritonavir reduced the elimination of orally given docetaxel by effectively blocking docetaxel metabolism by CYP3A4 in the gut wall and/or liver (9, 12, 18). This is the major explanation for the substantially increased apparent oral bioavailability (>100%) of docetaxel with ritonavir in patients. This indicates that ritonavir also inhibited the elimination of docetaxel after oral administration. An alternative explanation to those suggested by CYP inhibition could be that ritonavir acts through blocking the orphan nuclear receptor pregnenolone X-receptor that regulates CYP3A and P-glycoprotein at the transcriptional level. Some groups have shown that other CYP3A4 inhibitors, like ketoconazole, have blocking effects on the activated pregnenolone X-receptor (21, 22).
The apparent oral bioavailability after administration of 10 mg of oral docetaxel was much lower compared with the 100 mg dose. The very low plasma concentrations of docetaxel after treatment with 10 mg of oral docetaxel may have limited optimal assessment of the AUC and, specifically, may have underestimated the oral AUC. In addition, at low-dose docetaxel, possibly other elimination pathways with a high affinity for docetaxel, such as drug transporters (23) and drug metabolizing enzymes (9), may be important in the disposition of docetaxel. Recently, van Herwaarden et al. (18) illustrated in transgenic mice, with human CYP3A4 expression in intestine or liver, a dominant effect of intestinal CYP3A4 on the first-pass metabolism of docetaxel over liver CYP3A4. In addition, ritonavir inhibition of P-glycoprotein in the gastrointestinal tract may contribute to a minor extent to the increased systemic exposure.
Preclinical and clinical studies showed that the metabolism of docetaxel by CYP3A4 was the main factor for the low oral bioavailability of docetaxel; thus, oral docetaxel in combination with ritonavir could be an advantage over cyclosporine because ritonavir inhibits efficiently CYP3A4 and, to a minor extent, P-glycoprotein. Moreover, boosting with ritonavir may even reduce the costs of therapy because lower doses of docetaxel can be used. No significant immunosuppressive effects of cyclosporine are to be expected at the applied schedule (9); however, the drug was considered unfavorable compared with ritonavir because a high number of seven capsules of cyclosporine need to be taken. At this moment in our institute, a dose-escalation study in patients with oral docetaxel and ritonavir is being done to determine the maximum tolerated dose, dose limiting toxicities, and optimal dose of docetaxel that can safely be given in combination with ritonavir on a weekly schedule.
The time span between docetaxel and ritonavir given simultaneously or with a 60-minute time interval was also investigated. There was no significant difference between the two treatment methods; thus, simultaneous intake seems to be feasible. The maximal plasma concentration of oral docetaxel in combination with ritonavir was significantly lower than after i.v. docetaxel. The coefficient of variation of the AUC after oral docetaxel administration in combination with ritonavir simultaneously or ritonavir given 60 minutes before docetaxel was 62.5% and 50%, respectively, (n = 8) and 22% after i.v. administration (n = 8). Based on these data, pharmacokinetic variability actually increases by at least 2-fold with docetaxel-ritonavir compared with docetaxel i.v. However, oral treatment is known to have more interpatient variability than i.v. treatment (24); the pharmacokinetic variability could be also due to interpatient variability in CYP3A expression levels. Mathias et al. showed a dose-response relationship of ritonavir for inhibition of CYP3A activity and elvitegravir oral exposure in humans (25). Maximum inhibition of elvitegravir apparent oral clearance was achieved with ritonavir doses of 50 to 100 mg. These results support our selected ritonavir dose. As mentioned above, a dose-escalation study in patients to establish an optimal combination regimen is currently ongoing. An optimal combination regimen can possibly decrease the pharmacokinetic variability with oral docetaxel and ritonavir. Recently, long-term usage of ritonavir (steady-state ritonavir) was shown to be associated with mild enzyme and transporter induction (15); however, net inhibition still predominated. In our study setup, we used acute ritonavir weekly instead of steady-state treatment; thus, no enzyme and/or transporter induction is expected. The obtained results so far have shown efficient drug inhibitory effects of ritonavir on CYP3A.
The oral combination of docetaxel and ritonavir was well tolerated. However, some of the patients complained of an unpalatable and unpleasant taste of the drinking docetaxel solution, probably due to the polysorbate and ethanol excipients. The main side effects were diarrhea, vomiting, fatigue, abdominal pain, and nausea, which were mild to moderate for most of the toxicities, except for diarrhea (grade 3) in 3 of 12 patients. CYP3A4/P-glycoprotein inhibition could cause an increase in the docetaxel levels in the liver and intestinal wall, and may therefore enhance the risk of liver/intestinal toxicities (18, 26). However, we did not observe any signs or symptoms of liver toxicities in our study and only short-lasting grade 3 diarrhea in 3 of the 11 patients. After the first i.v. course of docetaxel, a similar pattern of toxicities was observed as after oral drug administration. However, diarrhea seemed to occur more often after oral administration in combination with ritonavir than after i.v. administration. This may be related to the inhibition of CYP3A4 in the gastrointestinal tract by ritonavir or unabsorbed docetaxel.
In summary, coadministration of oral ritonavir strongly enhanced the apparent oral bioavailability of docetaxel. The safety of the combination of docetaxel and ritonavir was good. These data are promising for the further development of this combination. Population pharmacokinetic analysis to evaluate the influence of ritonavir on the absorption and elimination of docetaxel, and a dose-escalation study in patients to establish an optimal combination regimen are currently ongoing. This pharmacokinetic model and clinical trial can be used for further development of this combination and will support the design of further studies and schedules.
Disclosure of Potential Conflicts of Interest
No potential conflicts of interest were disclosed.
Acknowledgments
We thanks Brigitte Dufourny for data management, the medical and nursing staff of The Netherlands Cancer Institute, and the patients who took part in this study.
Footnotes
-
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
- Received November 11, 2008.
- Revision received February 28, 2009.
- Accepted March 19, 2009.
References
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