This multicenter, open-label, randomized Phase 2 portion of clinical trial PROTECTIVE-2 (NCT04227990 registered January 14, 2020, BPI-2358-106) enrolled adult women with Stage I, II, or III breast cancer who were candidates for at least four cycles of TAC chemotherapy. Eligible patients did not have previous chemotherapy, had Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 with adequate hematologic and organ function, and were recruited from the clinical populations of the study centers. Exclusion criteria included concurrent administration of chemotherapy or radiation therapy, active infection, or the use of strong cytochrome P4503A4 inhibitors.
All patients received docetaxel 75 mg/m2, doxorubicin 50 mg/m2, and cyclophosphamide 500 mg/m2 (TAC) on Day 1 by intravenous infusion (IV), repeated every three weeks for four cycles. We evaluated patients in two separate, sequential cohorts with parallel randomization schemes. In the monotherapy cohort, patients were randomized to pegfilgrastim 6 mg by subcutaneous injection (SQ) on Day 2 or plinabulin IV at either 10, 20, or 30 mg/m2, 30 minutes after docetaxel on Day 1, with no Day 2 treatment. (Online Resource Fig. 1a). Based on the results of the single-agent plinabulin study, a superiority objective would not be met. We amended the protocol to evaluate an additional combined therapy cohort: plinabulin 20 mg/m2 with pegfilgrastim 1.5, 3, or 6 mg on Day 2, compared with monotherapy pegfilgrastim 6 mg (Online Resource Fig. 1b). Randomization was by the Medidata electronic data capture (EDC) system.
Complete blood count and absolute neutrophil count (ANC) were collected during Cycle 1 on Days 1 (pre-dose), 2, 3, 6, 7, 8, 9, 10, 11, 12, 13, and 15, and during subsequent cycles on Days 1 (predose), 8, and 15, and measured at a central laboratory (Covance, Shanghai and Covance, Geneva). Ambulatory blood pressure (AMBP) was measured at 15minute intervals on Day 1 of Cycle 1, starting 15 minutes preplinabulin until 3 hours after plinabulin completion.
At investigator discretion, doxorubicin could be omitted (that is, TAC converted to TC) during Cycles 2 through 4 or continued for more than four cycles. Docetaxel premedication with corticosteroids and rescue medications to treat FN was pre-specified.
2.1 Trial Outcomes
The primary objective was to establish the recommended Phase 3 dose (RP3D) of plinabulin based on pharmacokinetic (PK) and pharmacodynamic (PD) analyses. The primary efficacy PD endpoint was DSN (Grade 4; defined as ANC <0.5 × 109/L). The primary safety endpoint was blood pressure on Day 1 of Cycle 1 within 3.5 hours after the docetaxel infusion. PK of plinabulin, pegfilgrastim and the TAC components, and the plinabulin PK and PD for CIN prevention was modeled with a nonlinear mixed effects approach (NONMEM, ICON Development, Ellicott City, MD) using a sequential PK/PD approach for plinabulin CIN prevention. Separate population PK models were developed for plinabulin, docetaxel, doxorubicin, cyclophosphamide, and pegfilgrastim (Online Resource Supplemental Material).
Secondary endpoints included the frequency of patients with at least one day of Grade 4 neutropenia, Grade 3 or 4 neutropenia, ANC nadir, change in bone pain between pretreatment during cycle 1, relative dose intensity, safety, and tolerability. Bone pain was evaluated by using the Brief Pain Inventory[19, 20] before trial drug infusion on Day 1 compared with Days 1–8 of Cycle 1. Tolerability is defined as the number of patients who received >85% of the planned chemotherapy dose.
Exploratory endpoints included FN incidence, CD34+ stem cell mobilization, health-related quality of life (QOL), and thrombocytopenia. The European Organization for Research and Treatment of Cancer Quality of Life Questionnaire C30 (EORTCQLQ-C30) was used to evaluate QOL [21–23]. Changes from baseline in platelet count were used to investigate the incidence of thrombocytopenia during the trial. The frequency of patients with thrombocytopenia was analyzed for each treatment group in the combined therapy cohort.
2.2 Statistical Methods
Patients were stratified by region: China versus the rest of the world. The pegfilgrastim 6 mg monotherapy data served as the comparator arm for both cohorts, and hypotheses testing used a significance level of 0.05. In the monotherapy cohort, with an 80% power to detect an event rate ratio of 0.3 and a significance level of 0.05, up to 18 patients in each arm were required. In the combined therapy cohort, two sequential tests were made by using the O'Brien-Fleming spending function to determine the test boundaries. During an interim analysis, if a statistically significantly superior outcome with respect to DSN was reached when comparing pegfilgrastim alone to any of the combination treatments, or an indication that superiority could not be achieved, then no further patients were allocated to the combination arms.
All randomized patients were included in the intent-to-treat (ITT) analysis set, and the safety analysis set included all randomized patients who received at least one dose of any trial medication. Stata v11.0 or later generalized Poisson model procedures were used to assess Cycle 1 DSN. Barnard’s method was used to evaluate the difference in proportions of Grade 4 and Grade 3/4 neutropenia between the treatment arms. For the assessment of bone pain, the mean change from pre-dose (Day 1) bone pain score to Days 2 through 8 in Cycle 1 were analyzed by using repeated measures mixed linear model with the predose (Day 1) value and treatment arm as covariates. The method was used to construct point estimates and confidence intervals (CIs). Post-hoc analyses of mean bone pain score by visit and treatment group were performed by using a repeated measure mixed linear model, with the baseline value and treatment arm as covariates. Continuous variables were summarized with counts, means, standard deviations, medians, CIs, minimums, and maximums. Categorical variables were summarized by counts and by the percentage of patients. Descriptive summaries were also provided. Missing or invalid data were not imputed. The PK/PD modeling approach adopted to estimate the population PK of plinabulin and the TAC drugs and to characterize the plinabulin PK and PD in preventing CIN is summarized in Online Resource Supplemental Material.
All patients provided written informed consent. The trial was conducted following International Council for Harmonization Good Clinical Practice guidelines and ethical principles and approved by the relevant Independent Ethics Committee or Institutional Review Board at each site. The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request