Paclitaxel (Taxol), an antitubulin agent with a unique mechanism of action, is a highly active drug when used as first- or second-line therapy in the treatment of advanced breast cancer. Moreover, it produces response rates of 20% to 40% in patients who have not responded to prior anthracycline therapy.[2,3] As a result of the high level of activity and incomplete cross-resistance in vivo, several attempts have been made to combine paclitaxel and anthracyclines.
The combination of doxorubicin with paclitaxel, when given as a prolonged infusion, is complicated by schedule- and sequence-dependent toxicities, pharmacokinetic and/or pharmacodynamic interactions, and possible subadditive activity.[5,6] The combination of doxorubicin with a 3-hour infusion of paclitaxel has demonstrated extremely high activity, but initially had a high incidence of cardiotoxic events.[7,8a] It was then showed that by limiting the cumulative dose of doxorubicin to 360 mg/m² or administering the two drugs with a more prolonged interval, the cardiac toxicity of the combination was limited to an incidence of 5%.[8b,8c].
In an attempt to maintain cytotoxic activity and reduce cardiotoxicity, we performed a phase I-II study of paclitaxel, infused over 3 hours, plus epirubicin, an anthracycline analog that is as active as doxorubicin with reduced cardiotoxicity. The objectives of this study were to:
- Define the maximum tolerated dose (MTD) and dose-limiting toxicities (DLTs) of paclitaxel, given over 3 hours, combined with a fixed dose of epirubicin;
- Investigate the pharmacokinetics of the combination of paclitaxel and epirubicin;
- Evaluate the activity and the toxicities of this combination in previously untreated metastatic breast cancer patients; and
- Investigate the ability of this regimen plus granulocyte colony-stimulating factor (G-CSF, filgrastim) or granulocyte-macrophage colony-stimulating factor (GM-CSF, sargramostim) to mobilize peripheral blood stem cells (PBSCs).
Patients with histologically confirmed breast cancer and metastatic disease with at least one bidimensionally measurable lesion were eligible for the study. They could have undergone prior adjuvant therapy if it had been stopped at least 6 months before study entry. Patients who had received adjuvant anthracycline-based therapy were included if the total cumulative dose of doxorubicin or epirubicin was less than 180 or 360 mg/m², respectively.
Epirubicin was administered as an IV bolus at a fixed dose of 90 mg/m² before the 3-hour infusion of paclitaxel. The initial dose of paclitaxel was 135 mg/m² and was increased by 20-mg/m² steps in subsequent cohorts of three patients until dose-limiting toxicity occurred. Either a standard or rapid IV premedication schedule for paclitaxel was administered. Courses were repeated every 3 weeks.
Dose-limiting toxicity was defined, according to the World Health Organization (WHO) criteria, by the occurrence of one of the following: absolute neutrophil count (ANC) < 500/
mL for more than 7 days; ANC < 100/
mL for more than 3 days; febrile neutropenia (ANC < 500/
mL and fever > 38°C); grade 4 thrombocytopenia; failure to recover to neutrophils >1,500/
mL and/or platelets >100,000/
mL by day 28; and/or any grade 3 nonhematologic toxicity (except nausea, vomiting, and alopecia).
Maximum tolerated dose was defined as the next lower dose than that causing dose-limiting toxicities during the first two courses in at least two of six patients. Filgrastim was not used prophylactically.
A total of 32 patients entered this phase of the study. The most frequent toxicity was transient neutropenia. The dose-limiting toxicity of the combination was febrile neutropenia occurring in two of eight patients who received 225 mg/m² of paclitaxel. Therefore, the maximum tolerated dose and recommended dose for phase II of the study was epirubicin, 90 mg/m², plus paclitaxel, 200 mg/m².
An additional 18 patients with metastatic breast cancer received epirubicin, 90 mg/m², plus paclitaxel, 200 mg/m². The most frequent toxicity in this phase was grade 4 neutropenia, which occurred during 49% of the courses; febrile neutropenia was observed in 22% of patients.
Nonhematologic toxicity was mild. Grade 3 cardiotoxicity occurred in only 6% of the patients and was reversible with appropriate therapy.
Phase I-II Study Efficacy Results
Overall, 50 patients were included in this phase I-II study, 49 of whom were evaluable for response. The overall response rate was 84% (95% confidence interval [CI], 70% to 92%); 9 patients (19%) had a complete response and 32 a partial response (65%). Response rates did not differ between patients who received
£ 175 mg/m² of paclitaxel and those given > 175 mg/m². The median duration of response in partial responders was 10 months (range, 3 to 27+ months).
At a median follow-up of 14 months (including the nine complete responders), 19 of 49 patients were progression-free and 33 of 50 were alive.
Blood samples for measurement of plasma levels of paclitaxel, epirubicin, and its major metabolite epirubicinol were obtained at cycle 1 from at least two patients per dose level of paclitaxel, from 175 to 225 mg/m². Blood samples were obtained from the antecubital vein opposite to the site of drug injection at baseline; 15, 30, and 45 minutes after drug administration; and 1, 2, 3, 4, 6, 8, 12, 18, and 24 hours thereafter. Measurements of plasma epirubicin, epirubicinol, and paclitaxel concentrations were performed using reversed-phase high-performance liquid chromatography.
Pharmacokinetic analysis was performed by nonlinear least-square regression modeling.[14,15] The following plasma pharmacokinetic parameters were calculated: maximum concentration (Cmax), time to Cmax (Tmax), elimination half-life (t1/2), area under the concentration-time curve (AUC), volume of distribution (Vd), and systemic clearance (Cl). Plasma concentrations of paclitaxel, epirubicin, and epirubicinol were available in patients treated with 175 mg/m² (N = 2), 200 mg/m² (N = 5), and 225 mg/m² (N = 4) of paclitaxel.
Mean peak plasma concentrations of paclitaxel were 5.1, 5.7, and 6.2
mM at doses of 175, 200, and 225 mg/m², respectively. Distribution t1/2 values for the three doses were 0.46, 0.63, and 0.76 hours, respectively, whereas elimination t1/2 values were 2.6, 6.8, and 8.6 hours, respectively. The mean AUC (0-24h) values calculated from the concentration-time data were 20.4
´ h at 175 mg/m² of paclitaxel, 22.2
´ h at 200 mg/m², and 34.2
´ h at 225 mg/m² of paclitaxel. Mean Cl values were 13.9, 16.7, and 12.9 L/h for 175, 200, and 225 mg/m² of paclitaxel, respectively, whereas mean Vd values were 170.3, 133.5, and 122.8 L, respectively.
The Cmax values of epirubicin were 109.7 ± 1.1 ng/mL in patients receiving 175 mg/m² of paclitaxel, 99.1 ± 2.7 ng/mL in patients receiving 200 mg/m², and 114.1 ± 15.5 ng/mL in patients receiving 225 mg/m² of paclitaxel, with no significant differences among subjects. The Tmax of epirubicinol was reached at 3.45 + 0.9 hours in all patients, and the concentration of this metabolite decreased from 47.3 ± 9.4 ng/mL in patients treated with 175 mg/m² of paclitaxel to 44.1 ± 11.2 ng/mL in those given 200 mg/m² and to 37.9 ± 7.5 ng/mL in those given 225 mg/m² of paclitaxel. These differences are not significant. The pharmacokinetic data of paclitaxel, in particular, the time above the threshold level of 0.05
mM, were not significantly related to myelosuppression.
After two to eight courses of cytoreductive chemotherapy, 21 patients received an additional course of chemotherapy followed by recombinant human G-CSF (filgrastim [Neupogen]) or recombinant human granulocyte-macrophage CSF (sargramostim [Leukine, Prokine] to mobilize PBSCs. Filgrastim or sargramostim were given at a dose of 5 mg/kg/day from day +1 until the last leukapheresis or the white blood cell (WBC) count was > 50
´ 109/L. The analysis of hematopoietic progenitors was performed on peripheral blood in all patients and on leukapheresis products in patients who underwent apheresis.
From day +6 to day +16, a sample of peripheral blood was collected daily from each patient. A sample of each apheresis product was also collected. Total and differential WBC counts and an analysis for CD34 and CD33 antigen expression were performed on each peripheral blood sample. Cell surface immunophenotyping of PBSCs (by flow cytometry using direct immunofluorescence) was done on the product of leukapheresis.
Mobilization of CD34+ cells was assessed by leukapheresis starting from day +6. The median peak of circulating CD34+ cells occurred on day +11 (range, day +9 to day +16) and the median number of CD34+ cells at peak was 69.5 cells/mL (range, 1.4 to 251 cells/mL). The peak of circulating CD34+/CD33 cells occurred on day +11 (range, day +8 to day +16) and their median number was 14.3 cells/mL (range, 1.74 to 195 cells/mL).
In the group of patients who received fewer than six courses of induction chemotherapy before mobilization, the peak of CD34+ cells in peripheral blood occurred on day +11 (range, day +9 to day +13) and the median number of CD34+ cells at peak was 106.7 cells/mL (range, 2.26 to 251 cells/mL). Patients who were more heavily pretreated before mobilization (six or more courses) showed a significantly lower number of CD34+ cells at peak (median, 7.3 cells/mL; range, 1.41 to 64.7 cells/mL), as well as a significantly longer time to reach peak number (median, day +14; range, day +11 to day +16), as compared with those who received fewer courses of induction therapy (both comparisons, P = .02).
The mean number of cells collected per apheresis procedure were: 2.7
´ 108 of mononuclear leukocytes/kg (range, 0.15 to 13.5
´ 108 cells/kg), 6.3
´ 106 of CD34+ cells/kg (range, 0.52 to 20.4
´ 106 cells/kg), 2.0
´ 106 of CD34+/33 cells/kg (range, 0.8 to 11
´ 106 cells/kg), and 0.18
´ 106 CD34+/CD38 cells/kg (range, 0 to 44
´ 106 cells/kg). A target level of 2.0
´ 106 CD34+ cells/kg was achieved with two apheresis procedures in 90% of the patients and with a single apheresis in 70%.
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