CLINICAL PHARMACOLOGY
Mechanism Of Action
Emapalumab-lzsg is a monoclonal antibody that binds to
and neutralizes interferon gamma (IFNγ). Nonclinical data suggest that
IFNγ plays a pivotal role in the pathogenesis of HLH by being
hypersecreted.
Pharmacodynamics
IFNγ Inhibition
Emapalumab-lzsg reduces the plasma concentrations of
CXCL9, a chemokine induced by IFNγ.
Cardiac Electrophysiology
At a dose of 3 mg/kg GAMIFANT does not prolong the QT
interval to any clinically relevant extent.
Pharmacokinetics
The pharmacokinetics of emapalumab-lzsg were evaluated in
healthy adult subjects and in patients with primary HLH.
Following a 1 mg/kg emapalumab-lzsg dose, median steady
state peak concentration was 44 mcg/mL, which was 2.9 times higher than after
the first dose. The median steady state trough concentration was 25 mcg/mL,
which was 4.3 times higher than after the first dose. Emapalumab-lzsg AUC
increases slightly more than proportionally between 1 and 3 mg/kg doses, and
less than proportionally at 3, 6, and 10 mg/kg doses.
Emapalumab-lzsg exhibits target-mediated clearance
dependent on IFNγ production, which can vary between and within patients
as a function of time and can affect the recommended dosage [see DOSAGE AND
ADMINISTRATION]. Emapalumab-lzsg steady state is achieved by the 7th
infusion when the IFNγ production is moderate. At high IFNγ
production, steady-state is reached earlier due to a shorter half-life.
Distribution
The central and peripheral volumes of distribution in a
subject with body weight of 70 kg are 4.2 and 5.6 L, respectively.
Elimination
Emapalumab-lzsg elimination half-life is approximately 22
days in healthy subjects, and ranged from 2.5 to 18.9 days in HLH patients.
Emapalumab-lzsg clearance is approximately 0.007 L/h in
healthy subjects.
In patients, the total clearance of emapalumab-lzsg was
significantly influenced by the production of IFNγ, demonstrating target
mediated clearance of emapalumab-lzsg.
Metabolism
The metabolic pathway of emapalumab-lzsg has not been
characterized. Like other protein therapeutics, GAMIFANT is expected to be
degraded into small peptides and amino acids via catabolic pathways.
Specific Populations
Body weight (2 to 82 kg) was a significant covariate of
emapalumab-lzsg pharmacokinetics, supporting body weight-based dosing.
No clinically significant differences in the
pharmacokinetics of emapalumab-lzsg were observed based on age (0.02 to 56
year), sex (53% Females), race (71.4% Caucasian, 12.2% Asian and 8.2% Black),
renal impairment including dialysis, or hepatic impairment (mild, moderate, and
severe).
Drug Interaction Studies
No drug-drug interaction studies have been conducted with
GAMIFANT.
Clinical Studies
The efficacy of GAMIFANT was evaluated in a multicenter,
open-label, single-arm trial NI-0501-04 (NCT01818492) in 27 pediatric patients
with suspected or confirmed primary HLH with either refractory, recurrent, or
progressive disease during conventional HLH therapy or who were intolerant of
conventional HLH therapy.
Patients were required to fulfill the following criteria
for enrollment: primary HLH based on a molecular diagnosis or family history
consistent with primary HLH or five out of the 8 criteria fulfilled: fever,
splenomegaly, cytopenias affecting 2 of 3 lineages in the peripheral blood
(hemoglobin < 9 , platelets < 100 x 109/L, neutrophils < 1 x 109/L),
hypertriglyceridemia (fasting triglycerides > 3 mmol/L or ≥ 265 mg/dL)
and/or hypofibrinogenemia (≤ 1.5 g/L), hemophagocytosis in bone marrow,
spleen, or lymph nodes with no evidence of malignancy, low or absent NK-cell
activity, ferritin ≥ 500 mcg/L, soluble CD25 ≥ 2400 U/mL. Patients
had to have evidence of active disease as assessed by treating physician.
Patients had to fulfill one of the following criteria as assessed by the
treating physician: having not responded or not achieved a satisfactory
response or not maintained a satisfactory response to conventional HLH therapy,
or intolerance to conventional HLH treatments. Patients with active infections
caused by specific pathogens favored by IFNγ neutralization were excluded
from the trial (e.g., mycobacteria and Histoplasma Capsulatum). Patients
received prophylaxis for Herpes Zoster, Pneumocystis jirovecii, and
fungal infections.
Twenty-seven patients enrolled and received treatment in
the study and twenty patients (74%) completed the study. Seven patients (26%)
were prematurely withdrawn. Twenty-two patients (81%) enrolled onto the
open-label extension study which monitored patients for up to 1 year after HSCT
or after the last GAMIFANT infusion (NI-0501-05; NCT02069899).
The study treatment duration was up to 8 weeks after
which patients could continue treatment on the extension study. All patients
received an initial starting dose of GAMIFANT of 1 mg/kg every 3 days.
Subsequent doses could be increased to a maximum of 10 mg/kg based on clinical
and laboratory parameters interpreted as unsatisfactory response. Forty-four
percent of patients remained at a dose of 1 mg/kg, 30% of patients increased to
3-4 mg/kg and 26% of patients increased to 6-10 mg/kg. The median time to dose
increase was 27 days (range: 3-31 days) with 22% of patients requiring a dose
increase in the first week of treatment.
All patients received dexamethasone as background HLH
treatment with doses between 5 to 10 mg/m²/day. Cyclosporine A was continued if
administered prior to screening. Patients receiving methotrexate and
glucocorticoids administered intrathecally at baseline could continue these
treatments.
In Study NI-0501-04, the median patient age was 1 year
(0.2 to 13). Fifty-nine percent of the patients were female, 63% were
Caucasian, 11% were Asian, and 11% were Black.
A genetic mutation known to cause HLH was present in 82%
of patients. The most frequent causative mutations were FHL3-UNC13D (MUNC 13-4)
(26%), FHL2-PRF1 (19%), and Griscelli Syndrome type 2 (19%).
The HLH mutations in the population enrolled are
described in Table 3.
Table 3: HLH Mutations in Patients with Primary HLH
with Prior Therapy
|
GAMIFANT (N=27) |
HLH Genetic Confirmation |
22 (82) |
FHL3 - UNC13D |
7 (26) |
FHL2 - PRF1 |
5 (19) |
Griscelli Syndrome type 2 (RAB27A) |
5 (19) |
FHL5 - STXBP2 (UNC18B) |
2 (7.4) |
FHL4 - STX11 |
1 (3.7) |
X-linked Lymphoproliferative Disorder 1 |
1 (3.7) |
X-linked Lymphoproliferative Disorder 2 |
1 (3.7) |
All patients received previous HLH treatments. Patients
received a median of 3 prior agents before enrollment into the trial. Prior
regimens included combinations of the following agents: dexamethasone,
etoposide, cyclosporine A, and anti-thymocyte globulin.
At baseline entry into the study, 78% of patients had
elevated ferritin levels, thrombocytopenia (70% with platelet count of < 100
x 109cells/L), hypertriglyceridemia (67%) with triglyceride level > 3
mmol/L. Central nervous system findings were present in 37% of patients.
Forty-one percent of patients had active infections not due to specific
pathogens favored by IFNγ neutralization at the time of GAMIFANT
initiation.
The efficacy of GAMIFANT was based upon overall response
rate (ORR) at the end of treatment, defined as achievement of either a complete
or partial response or HLH improvement. ORR was evaluated using an algorithm
that included the following objective clinical and laboratory parameters:
fever, splenomegaly, central nervous system symptoms, complete blood count,
fibrinogen and/or D-dimer, ferritin, and soluble CD25 (also referred to as
soluble interleukin-2 receptor) levels. Complete response was defined as
normalization of all HLH abnormalities (i.e., no fever, no splenomegaly,
neutrophils > 1x109/L, platelets > 100x109/L, ferritin < 2,000 μg/L,
fibrinogen > 1.50 g/L, D-dimer < 500 μg/L, normal CNS symptoms, no
worsening of sCD25 > 2-fold baseline). Partial response was defined as
normalization of ≥ 3 HLH abnormalities. HLH improvement was defined as
≥ 3 HLH abnormalities improved by at least 50% from baseline.
Table 4: Overall Response Rate at End of Treatment
|
GAMIFANT
(N=27) |
Overall Response Rate |
N (%) |
17 (63) |
(95% CI) |
(0.42, 0.81) |
p-value† |
0.013 |
Overall Response by Category |
Complete response, n (%) |
7 (26) |
Partial response |
8 (30) |
HLH improvement |
2 (7.4) |
†p-value based on Exact Binomial Test at a one-sided
significance level of 2.5% comparing proportion of patients with overall
response to hypothesized null hypothesis of 40%.
CI = confidence interval |
The median duration of first response, defined as time
from achievement of first response to loss of first response, is not reached
(range: 4-56+ days). Seventy percent (19/27) of patients proceeded to HSCT.