CLINICAL PHARMACOLOGY
Mechanism Of Action
Eribulin inhibits the growth
phase of microtubules without affecting the shortening phase and sequesters
tubulin into nonproductive aggregates. Eribulin exerts its effects via a
tubulin-based antimitotic mechanism leading to G 2/M cell-cycle block, disruption
of mitotic spindles, and, ultimately, apoptotic cell death after prolonged
mitotic blockage.
In addition, eribulin treatment
of human breast cancer cells caused changes in morphology and gene expression
as well as decreased migration and invasiveness in vitro. In mouse xenograft
models of human breast cancer, eribulin treatment was associated with increased
vascular perfusion and permeability in the tumor cores, resulting in reduced
tumor hypoxia, and changes in the expression of genes in tumor specimens
associated with a change in phenotype.
Pharmacodynamics
Cardiac Electrophysiology
The effect of HALAVEN on the
QTc interval was assessed in an open-label, uncontrolled, multicenter,
single-arm dedicated QT trial. A total of 26 patients with solid tumors
received 1.4 mg/m² of HALAVEN on Days 1 and 8 of a 21-day cycle. A
delayed QTc prolongation was observed on Day 8, with no prolongation observed
on Day 1. The maximum mean QTcF change from baseline (95% upper confidence
interval) was 11.4 (19.5) ms.
Pharmacokinetics
The pharmacokinetics (PK) of
eribulin is linear with a mean elimination half-life of approximately 40 hours,
a mean volume of distribution of 43 L/m² to 114 L/m² and
mean clearance of 1.16 L/hr/m² to 2.42 L/hr/m² over the
dose range of 0.25 mg/m² to 4.0 mg/m² . The human
plasma protein binding of eribulin at concentrations of 100 ng/mL to 1,000
ng/mL ranges from 49% to 65%. Eribulin exposure after multiple dosing is
comparable to that following a single dose. No accumulation of eribulin is
observed with weekly administration.
Elimination
Metabolism
Unchanged eribulin was the major circulating species in
plasma following administration of 14C-eribulin to patients.
Metabolite concentrations represented < 0.6% of parent compound, confirming
that there are no major human metabolites of eribulin. Cytochrome P450 3A4
(CYP3A4) negligibly metabolizes eribulin in vitro.
Excretion
Eribulin is eliminated primarily in feces unchanged.
After administration of 14C-eribulin to patients, approximately 82%
of the dose was eliminated in feces and 9% in urine. Unchanged eribulin
accounted for approximately 88% and 91% of total eribulin in feces and urine,
respectively.
Specific Populations
Age, Sex, and Race/Ethnicity
Based on a
population pharmacokinetic analysis with data collected from 340 patients, sex,
race, and age do not have a clinically meaningful effect on the exposure of
eribulin.
Hepatic Impairment
In a study evaluating the effect of hepatic impairment on
the PK of eribulin, eribulin exposures increased by 1.8-fold in patients with
mild hepatic impairment (Child-Pugh A; n=7) and by 2.5-fold in patients with
moderate (Child-Pugh B; n=5) hepatic impairment as compared to patients with
normal hepatic function (n=6). Administration of HALAVEN at a dose of 1.1 mg/m² to patients with mild hepatic impairment and 0.7 mg/m² to
patients with moderate hepatic impairment resulted in similar exposure to
eribulin at a dose of 1.4 mg/m² to patients with normal hepatic
function [see DOSAGE AND ADMINISTRATION, Use in Specific Populations].
Renal Impairment
In a study evaluating the effect of renal impairment on
the PK of eribulin, patients with moderate (CLcr 30-49 mL/min; n=7) and severe
renal impairment (CLcr 15-29 mL/min; n=6) had 1.5-fold higher eribulin
dose-normalized exposures compared to that in patients with normal renal
function (CLcr ≥ 80 mL/min; n=6). There were no clinically meaningful
changes in patients with mild renal impairment (CLcr 50-79 mL/min; n=27) [see
DOSAGE AND ADMINISTRATION, Use in Specific Populations].
Drug Interaction Studies
Effect of Strong Inhibitors or Inducers of CYP3A4 on
Eribulin: The effect of a strong CYP3A4 inhibitor and a P-gp inhibitor,
ketoconazole, on the PK of eribulin was studied in a crossover trial of 12
patients with advanced solid tumors. No clinically relevant PK interaction was
observed when HALAVEN was administered with or without ketoconazole (the
geometric mean ratio of the AUC: 0.97; 90% CI: 0.83, 1.12).
The effect of a CYP3A4 inducer, rifampin, on the PK of
eribulin was studied in a crossover trial of 14 patients with advanced solid
tumors. No clinically relevant PK interaction was observed when HALAVEN was
administered with or without rifampin (the geometric mean ratio of the AUC:
1.10; 90 CI%: 0.91, 1.34).
Effect of Eribulin on CYP Substrates: Eribulin
shows no induction potential for CYP1A, CYP2B6, CYP2C9, CYP2C19, and CYP3A in
primary human hepatocytes. Eribulin inhibits CYP3A4 activity in human liver
microsomes, but it is unlikely that eribulin will substantially increase the
plasma levels of CYP3A4 substrates. No significant inhibition of CYP1A2,
CYP2C9, CYP2C19, CYP2D6, or CYP2E1 was detected with eribulin concentrations up
to 5 μM in pooled human liver microsomes. In vitro drug interaction
studies indicate that eribulin does not inhibit drugs that are substrates of
these enzymes and it is unlikely that eribulin will affect plasma levels of
drugs that are substrates of CYP enzymes.
Effect of Transporters on Eribulin: In vitro data
suggest that eribulin at clinically relevant concentrations is a substrate of
P-gp, but is not a substrate of breast cancer resistance protein (BCRP),
multidrug resistance proteins (MRP2, MRP4), bile salt extrusion pump (BSEP),
organic anion transporting polypeptides (OATP1B1, OATP1B3), organic anion
transporters (OAT1, OAT3), organic cation transporters (OCT1, OCT2), or
multidrug and toxin extrusion 1 (MATE1).
Effect of Eribulin on Transporters: In vitro data
suggest that eribulin at clinically relevant concentrations may inhibit P-gp,
but does not inhibit BCRP, OATP1B1, OCT1, OAT1, OAT3, or MATE1.
Clinical Studies
Metastatic Breast Cancer
Study 1 was an open-label, randomized, multicenter trial
of 762 patients with metastatic breast cancer who received at least two
chemotherapeutic regimens for the treatment of metastatic disease and
experienced disease progression within 6 months of their last chemotherapeutic
regimen. Patients were required to receive prior anthracycline-and taxane-based
chemotherapy for adjuvant or metastatic disease. Patients were randomized (2:1)
to receive HALAVEN (n=508) or a single agent therapy selected prior to randomization
(control arm, n=254). Randomization was stratified by geographic region, HER2/neu
status, and prior capecitabine exposure. HALAVEN was administered at a dose of
1.4 mg/m² on Days 1 and 8 of a 21-day cycle. HALAVEN-treated
patients received a median of 5 cycles (range: 1 to 23 cycles) of therapy.
Control arm therapy consisted of 97% chemotherapy (26% vinorelbine, 18%
gemcitabine, 18% capecitabine, 16% taxane, 9% anthracycline, 10% other
chemotherapy), and 3% hormonal therapy. The main efficacy outcome was overall
survival.
Patient demographic and baseline characteristics were
comparable between the treatment arms. The median age was 55 (range: 27 to 85
years) and 92% were White. Sixty-four percent of patients were enrolled in
North America/Western Europe/Australia, 25% in Eastern Europe/Russia, and 11%
in Latin America/South Africa. Ninety-one percent of patients had a baseline
ECOG performance status of 0 or 1. Tumor prognostic characteristics, including
estrogen receptor status (positive: 67%, negative: 28%), progesterone receptor
status (positive: 49%, negative: 39%), HER2/neu receptor status (positive: 16%,
negative: 74%), triple negative status (ER, PR-, HER2/neu -:
19%), presence of visceral disease (82%, including 60% liver and 38% lung) and
bone disease (61%), and number of sites of metastases (greater than two: 50%),
were also similar in the HALAVEN and control arms. Patients received a median
of four prior chemotherapy regimens in both arms.
In Study 1, a statistically significant improvement in
overall survival was observed in patients randomized to the HALAVEN arm
compared to the control arm (see Table 5). An updated, unplanned survival
analysis, conducted when 77% of events had been observed (see Figure 1), was
consistent with the primary analysis. In patients randomized to HALAVEN, the
objective response rate by the RECIST criteria was 11% (95% CI: 8.6%, 14.3%)
and the median response duration was 4.2 months (95% CI: 3.8, 5.0 months).
Table 5: Comparison of Overall Survival in HALAVEN and
Control Arm -Study 1
Overall Survival |
HALAVEN
(n=508) |
Control Arm
(n=254) |
Primary survival analysis |
Number of deaths |
274 |
148 |
Median, months (95% CI) |
13.1 (11.8, 14.3) |
10.6 (9.3, 12.5) |
Hazard Ratio (95% CI)a |
0.81 (0.66, 0.99) |
P valueb |
0.041 |
Updated survival analysis |
Number of deaths |
386 |
203 |
Median, months (95% CI) |
13.2 (12.1, 14.4) |
10.6 (9.2, 12.0) |
CI = confidence interval
a Based on Cox proportional hazards model stratified by geographic
region, HER2 status, and prior capecitabine therapy.
b Based on a log-rank test stratified by geographic region, HER2
status, and prior capecitabine therapy. |
Figure 1: Updated Overall
Survival Analysis for Study 1
Liposarcoma
The efficacy and safety of
HALAVEN were evaluated in Study 2, an open-label, randomized (1:1),
multicenter, active-controlled trial. Eligible patients were required to have
unresectable, locally advanced or metastatic liposarcoma or leiomyosarcoma, at
least two prior systemic chemotherapies (one of which must have included an
anthracycline), and disease progression within 6 months of the most recent
chemotherapy regimen. Patients were randomized to HALAVEN 1.4 mg/m² administered
intravenously on Days 1 and 8 of a 21-day cycle or to dacarbazine at a dose of
850 mg/m², 1000 mg/m², or 1200 mg/m² administered
intravenously every 21 days (dacarbazine dose was selected by the investigator
prior to randomization). Treatment continued until disease progression or
unacceptable toxicity. Randomization was stratified by histology (liposarcoma
or leiomyosarcoma), number of prior therapies (2 vs. > 2), and geographic
region (U.S. and Canada vs. Western Europe, Australia, and Israel vs. Eastern
Europe, Latin America, and Asia). The major efficacy outcome measure was
overall survival (OS). Additional efficacy outcome measures were
progression-free survival (PFS) and confirmed objective response rate (ORR) as
assessed by the investigator according to Response Evaluation Criteria in Solid
Tumors (RECIST v1.1). Patients in the dacarbazine arm were not offered HALAVEN
at the time of disease progression.
A total of 446 patients were
randomized, 225 to the HALAVEN arm and 221 to the dacarbazine arm. The median
age was 56 years (range: 24 to 83); 33% were male; 73% were White; 44% had ECOG
performance status (PS) 0 and 53% had ECOG PS 1; 68% had leiomyosarcoma and 32%
had liposarcoma; 39% were enrolled in U.S. and Canada (Region 1) and 46% were
enrolled in Western Europe, Australia, and Israel (Region 2); and 47% received
more than two prior systemic chemotherapies. The most common ( > 40%) prior
systemic chemotherapies were doxorubicin (90%), ifosfamide (62%), gemcitabine
(59%), trabectedin (50%), and docetaxel (48%).
Of the 143 patients with
liposarcoma, the median age was 55 years (range: 32 to 83); 62% were male, 72%
were White; 41% had ECOG PS of 0 and 53% had ECOG PS of 1; 35% were enrolled in
Region 1 and 51% were enrolled in Region 2; and 44% received more than two
prior systemic chemotherapies. The distribution of subtypes of liposarcoma,
based on local histologic assessment, were 45% dedifferentiated, 37%
myxoid/round cell, and 18% pleomorphic.
Study 2 demonstrated a statistically significant
improvement in OS in patients randomized to HALAVEN compared with dacarbazine
(see Table 6). There was no significant difference in progression-free survival
in the overall population. Treatment effects of HALAVEN were limited to
patients with liposarcoma based on pre-planned, exploratory subgroup analyses
of OS and PFS (see Tables 6 and 7 and Figure 2). There was no evidence of
efficacy of HALAVEN in patients with advanced or metastatic leiomyosarcoma in
Study 2 (see Table 7).
Table 6: Efficacy Results for the Liposarcoma Stratum
and All Patients* in Study 2a
|
Liposarcoma Stratum |
All Patients* |
Halaven
(n=71) |
Dacarbazine
(n=72) |
Halaven
(n=225) |
Dacarbazine
(n=221) |
Overall survival |
Deaths, n (%) |
52 (73) |
63 (88) |
173 (77) |
179 (81) |
Median, months |
15.6 |
8.4 |
13.5 |
11.3 |
(95% CI) |
(10.2, 18.6) |
(5.2, 10.1) |
(11.1, 16.5) |
(9.5, 12.6) |
Hazard ratio (HR) |
|
0.51 |
|
|
0.75 |
(95% CI) |
(0.35, 0.75) |
(0.61, 0.94) |
Stratified log-rank p value |
N/A† |
0.011 |
Progression-free survival |
Events, n (%) |
57 (80) |
59 (82) |
194 (86) |
185 (84) |
Disease progression |
53 |
52 |
180 |
170 |
Death |
4 |
7 |
14 |
15 |
Median, months |
2.9 |
1.7 |
2.6 |
2.6 |
(95% CI) |
(2.6, 4.8) |
(1.4, 2.6) |
(2.0, 2.8) |
(1.7, 2.7) |
HR |
|
0.52 |
|
0.86 |
(95% CI) |
(0.35, 0.78) |
(0.69, 1.06) |
Objective response rate |
Objective response rate (%) |
1.4 |
0 |
4.0 |
5.0 |
(95% CI) |
(0, 7.6) |
(0, 4.2) |
(1.8, 7.5) |
(2.5, 8.7) |
a Efficacy data from one study site enrolling
six patients were excluded. *All patients = liposarcoma and leiomyosarcoma.
† N/A = not applicable |
Figure 2: Kaplan-Meier
Curves of Overall Survival in the Liposarcoma Stratum in Study 2
Table 7: Efficacy Results for the Leiomyosarcoma
Stratum in Study 2a
|
Leiomyosarcoma Stratum |
Halaven
(n=154) |
Dacarbazine
(n=149) |
Overall survival |
Deaths, n (%) |
121 (79) |
116 (78) |
Median, months |
12.8 |
12.3 |
(95% CI) |
(10.3, 14.8) |
(11.0, 15.1) |
HR (95% CI) |
0.90 (0.69, 1.18) |
Progression-free survival |
Events, n (%) |
137 (89) |
126 (85) |
Disease progression |
127 |
118 |
Death |
10 |
8 |
Median, months |
2.2 |
2.6 |
(95% CI) |
(1.5, 2.7) |
(2.2, 2.9) |
HR (95% CI) |
1.05 (0.81, 1.35) |
Objective response rate (%) |
5.2 |
7.4 |
(95% CI) |
(2.3, 10) |
(3.7, 12.8) |
a Efficacy data from one study site enrolling
six patients were excluded. |