CLINICAL PHARMACOLOGY
Mechanism Of Action
Enasidenib is a small molecule
inhibitor of the isocitrate dehydrogenase 2 (IDH2) enzyme. Enasidenib targets
the mutant IDH2 variants R140Q, R172S, and R172K at approximately 40-fold lower
concentrations than the wild-type enzyme in vitro. Inhibition of the mutant
IDH2 enzyme by enasidenib led to decreased 2-hydroxyglutarate (2-HG) levels and
induced myeloid differentiation in vitro and in vivo in mouse xenograft models
of IDH2 mutated AML. In blood samples from patients with AML with mutated IDH2,
enasidenib decreased 2-HG levels, reduced blast counts and increased
percentages of mature myeloid cells.
Pharmacodynamics
Cardiac Electrophysiology
The potential for QTc
prolongation with enasidenib was evaluated in an open-label study in patients
with advanced hematologic malignancies with an IDH2 mutation. Based on the QTc
data for a single dose of 30 mg to 650 mg and multiple doses of 100 mg daily in
the fasted state, no large mean changes in the QTc interval (>20 ms) were
observed following treatment with enasidenib.
Pharmacokinetics
The peak plasma concentration
(Cmax) is 1.3 mcg/mL [% coefficient of variation (CV%) 56.4] after a single
dose of 100 mg, and 13 mcg/mL (CV% 46.3) at steady state for 100 mg daily. The
area under concentration time curve (AUC) of enasidenib increases in an
approximately dose proportional manner from 50 mg (0.5 times approved
recommended dosage) to 450 mg (4.5 times approved recommended dosage) daily
dose. Steady-state plasma levels are reached within 29 days of once-daily
dosing. Accumulation is approximately 10-fold when administered once daily.
Absorption
The absolute bioavailability after 100 mg oral dose of
enasidenib is approximately 57%. After a single oral dose, the median time to Cmax
(Tmax) is 4 hours.
Distribution
The mean volume of distribution (Vd) of enasidenib is
55.8 L (CV% 29). Human plasma protein binding of enasidenib is 98.5% and of its
metabolite AGI-16903 is 96.6% in vitro.
Enasidenib is not a substrate for P-glycoprotein or BCRP,
while AGI-16903 is a substrate of both Pglycoprotein and BCRP. Enasidenib and
AGI-16903 are not substrates of MRP2, OAT1, OAT3, OATP1B1, OATP1B3, and OCT2.
Elimination
Enasidenib has a terminal half-life of 137 hours (CV% 41)
and a mean total body clearance (CL/F) of 0.74 L/hour (CV% 71).
Metabolism
Enasidenib accounted for 89% of the radioactivity in
circulation and AGI-16903, the N-dealkylated metabolite, represented 10% of the
circulating radioactivity.
In vitro studies suggest that metabolism of enasidenib is
mediated by multiple CYP enzymes (e.g., CYP1A2, CYP2B6, CYP2C8, CYP2C9,
CYP2C19, CYP2D6, and CYP3A4), and by multiple UGTs (e.g., UGT1A1, UGT1A3,
UGT1A4, UGT1A9, UGT2B7, and UGT2B15). Further metabolism of the metabolite
AGI-16903 is also mediated by multiple enzymes (e.g., CYP1A2, CYP2C19, CYP3A4,
UGT1A1, UGT1A3, and UGT1A9).
Excretion
Eighty-nine percent (89%) of enasidenib is eliminated in
feces and 11% in the urine. Excretion of unchanged enasidenib accounts for 34%
of the radiolabeled drug in the feces and 0.4% in the urine.
Specific Populations
No clinically meaningful effect on the pharmacokinetics
of enasidenib was observed for the following covariates: age (19 years to 100
years), race (White, Black, or Asian), mild hepatic impairment [defined as
total bilirubin ≤ upper limit of normal (ULN) and aspartate transaminase
(AST) >ULN or total bilirubin 1 to 1.5 times ULN and any AST], renal
impairment (defined as creatinine clearance ≥ 30 mL/min by Cockcroft-Gault
formula), sex, body weight (39 kg to 136 kg), and body surface area.
Drug Interaction Studies
In vitro studies suggest that enasidenib inhibits the
activity of CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4, and
UGT1A1. Enasidenib inhibits P-gp, BCRP, OAT1, OATP1B1, OATP1B3, and OCT2, but
not MRP2 or OAT3. Enasidenib induces CYP2B6 and CYP3A4.
In vitro studies suggest that the metabolite AGI-16903
inhibits the activity of CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, and CYP2D6.
AGI-16903 inhibits BCRP, OAT1, OAT3, OATP1B1, and OCT2, but not P-gp, MRP2, or
OATP1B3.
Coadministration of IDHIFA may increase or decrease the
concentrations of combined hormonal contraceptives. The clinical significance
of this potential drug interaction is unknown at this time.
Clinical Studies
Acute Myeloid Leukemia
The efficacy of IDHIFA was evaluated in an open-label,
single-arm, multicenter, two-cohort clinical trial (Study AG221-C-001,
NCT01915498) of 199 adult patients with relapsed or refractory AML and an IDH2
mutation, who were assigned to receive 100 mg daily dose. Cohort 1 included 101
patients and Cohort 2 included 98 patients. IDH2 mutations were identified by a
local diagnostic test and retrospectively confirmed by the Abbott RealTime™
IDH2 assay, or prospectively identified by the Abbott RealTime™ IDH2 assay,
which is the FDA-approved test for selection of patients with AML for treatment
with IDHIFA. IDHIFA was given orally at starting dose of 100 mg daily until
disease progression or unacceptable toxicity. Dose reductions were allowed to
manage adverse events.
The baseline demographic and disease characteristics are
shown in Table 4. The baseline demographics and disease characteristics were
similar in both study cohorts.
Table 4: Baseline Demographic and Disease
Characteristics in Patients with Relapsed or Refractory AML
Demographic and Disease Characteristics |
IDHIFA (100 mg daily)
N=199 |
Demographics |
Age (Years) Median (Min, Max) |
68 (19, 100) |
Age Categories, n (%) |
<65 years |
76 (38) |
≥ 65 years to <75 years |
74 (37) |
≥ 75 years |
49 (25) |
Sex, n (%) |
Male |
103(52) |
Female |
96 (48) |
Race, n (%) |
White |
153 (77) |
Black |
10 (5) |
Asian |
1 (1) |
Native Hawaiian/Other Pacific Islander |
1 (1) |
Other / Not Provided |
34 (17) |
Disease Characteristics, n (%) |
ECOG PSa, n (%) |
0 |
46 (23) |
1 |
124 (62) |
2 |
28 (14) |
Relapsed AML, n (%) |
95 (48) |
Refractory AML, n (%) |
104 (52) |
IDH2 Mutationb, n (%) |
R140 |
155(78) |
R172 |
44 (22) |
Time from Initial AML Diagnosis (months) |
Median (min, max) (172 patients) |
11.3 (1.2, 129.1) |
Cytogenetic Risk Status, n (%) |
Intermediate |
98 (49) |
Poor |
54 (27) |
Missing /Failure |
47 (24) |
Prior Stem Cell Transplantation for AML, n (%) |
25 (13) |
Transfusion Dependent at Baselinec, n (%) |
157 (79) |
Number of Prior Anticancer Regimens, n (%)d |
1 |
89 (45) |
2 |
64 (32) |
≥ 3 |
46 (23) |
Median number of prior therapies (min, max) |
2 (1, 6) |
ECOG PS: Eastern Cooperative Oncology Group Performance
Status.
a 1 patient had missing baseline ECOG PS.
b For 3 patients with different mutations detected in bone marrow
compared to blood, the result of blood is reported.
c Patients were defined as transfusion dependent at baseline if they
received any red blood cell or platelet transfusions within the 8-week baseline
period.
d Includes intensive and/or nonintensive therapies. |
Efficacy was established on the
basis of the rate of complete response (CR)/complete response with partial
hematologic recovery (CRh), the duration of CR/CRh, and the rate of conversion
from transfusion dependence to transfusion independence. The efficacy results
are shown in Table 5 and were similar in both cohorts. The median follow-up was
6.6 months (range, 0.4 to 27.7 months). Similar CR/CRh rates were observed in
patients with either R140 or R172 mutation.
Table 5: Efficacy Results in
Patients with Relapsed or Refractory AML
Endpoint |
IDHIFA (100 mg daily)
N=199 |
CRa n (%) |
37 (19) |
95% CI |
(13, 25) |
Median DORb (months) |
8.2 |
95% CI |
(4.7, 19.4) |
CRhc n (%) |
9 (4) |
95% CI |
(2, 8) |
Median DOR (months) |
9.6 |
95% CI |
(0.7, NA) |
CR/CRh n (%) |
46 (23) |
95% CI |
(18, 30) |
Median DOR (months) |
8.2 |
95% CI |
(4.3, 19.4) |
CI: confidence interval, NA: not available.
a CR (complete remission) was defined as <5% of blasts in the
bone marrow, no evidence of disease, and full recovery of peripheral blood
counts (platelets >100,000/microliter and absolute neutrophil counts [ANC]
>1,000/microliter).
b DOR (duration of response) was defined as time since first
response of CR or CRh to relapse or death, whichever is earlier.
c CRh (complete remission with partial hematological recovery) was
defined as <5% of blasts in the bone marrow, no evidence of disease, and
partial recovery of peripheral blood counts (platelets >50,000/microliter
and ANC >500/microliter). |
For patients who achieved a CR/CRh, the median time to
first response was 1.9 months (range, 0.5 to 7.5 months) and the median time to
best response of CR/CRh was 3.7 months (range, 0.6 to 11.2
months). Of the 46 patients who achieved a best response of CR/CRh, 39 (85%)
did so within 6 months of initiating IDHIFA.
Among the 157 patients who were
dependent on red blood cell (RBC) and/or platelet transfusions at baseline, 53
(34%) became independent of RBC and platelet transfusions during any 56-day
post baseline period. Of the 42 patients who were independent of both RBC and platelet
transfusions at baseline, 32 (76%) remained transfusion independent during any
56-day post baseline period.