CLINICAL PHARMACOLOGY
Mechanism Of Action
SIGNIFOR LAR is an injectable cyclohexapeptide,
somatostatin analog. Pasireotide exerts its pharmacological activity via
binding to somatostatin receptors (SSTR). There are 5 known human somatostatin
receptor subtypes: SSTR 1, 2, 3, 4, and 5. These receptor subtypes are
expressed in different tissues under normal physiological conditions.
Somatostatin analogs bind to SSTRs with different potencies. Pasireotide binds
with high affinity to 4 of the 5 SSTRs (see Table 3).
Table 3 : Binding Affinities of Somatostatin (SRIF-14)
Pasireotide to the Five Human SSTR Subtypes (SSTR 1-5)
Compound |
SSTR1 |
SSTR2 |
SSTR3 |
SSTR4 |
SSTR5 |
Somatostatin (SRIF-14) |
0.93 ± 0.12 |
0.15 ± 0.02 |
0.56 ± 0.17 |
1.5 ± 0.4 |
0.29 ± 0.04 |
Pasireotide |
9.3 ± 0.1 |
1.0 ± 0.1 |
1.5 ± 0.3 |
> 100 |
0.16 ± 0.01 |
Results are the mean+SEM of IC50 values expressed as
nmol/l (nM).
Pharmacodynamics
Somatostatin receptors are expressed in many tissues
including neuroendocrine tumors (e.g., growth hormone secreting pituitary
adenomas). Pasireotide binds to SSTR2 and SSTR5 subtype receptors which may be
relevant for inhibition of GH secretion. In vivo studies show that SIGNIFOR LAR
lowers GH and IGF-1 levels in patients with acromegaly.
Cardiac Electrophysiology
Individually corrected QT (QTcI) interval was evaluated
in a randomized, blinded, crossover study in healthy subjects investigating
pasireotide subcutaneous doses of 0.6 mg and 1.95 mg twice daily, respectively.
The maximum mean (95% upper confidence bound) placebo-subtracted QTcI change
from baseline was 12.7 (14.7) ms and 16.6 (18.6) ms, respectively. Both
pasireotide doses decreased heart rate, with a maximum mean (95% lower
confidence bound) placebo-subtracted change from baseline of -10.9 (-11.9)
beats per minute (bpm) observed at 1.5 hours for pasireotide 0.6 mg twice
daily, and -15.2 (-16.5) bpm at 0.5 hours for pasireotide 1.95 mg twice daily.
The predicted peak concentrations for the SIGNIFOR LAR
dose of 60 mg in acromegaly patients are similar to the observed peak
concentration (24.3 mg/mL) of the subcutaneous SIGNIFOR 0.6 mg twice daily dose
and below the observed peak concentration (80.6 ng/mL) of the subcutaneous
SIGNIFOR 1.95 mg twice daily dose.
Pharmacokinetics
Absorption And Distribution
No studies have been conducted to evaluate the absolute
bioavailability of pasireotide in humans. Food effect is unlikely to occur
since SIGNIFOR LAR is administered via a parenteral route.
In healthy volunteers, pasireotide administered as
SIGNIFOR LAR is widely distributed with large apparent volume of distribution
(Vz/F >100 L). Distribution between blood and plasma is
concentration-independent and shows that pasireotide is primarily located in
the plasma (91%). Plasma protein binding is moderate (88%) and independent of
concentration.
Pasireotide has low passive permeability and is likely to
be a substrate of P-gp (P-glycoprotein), but the impact of P-gp on the ADME
(absorption, distribution, metabolism, excretion) of pasireotide is expected to
be low. In clinical testing in healthy volunteers, P-gp inhibition did not
affect the rate or extent of pasireotide availability [see DRUG INTERACTIONS].
At therapeutic dose levels, pasireotide is not expected to be a substrate of
BCRP (breast cancer resistance protein), OCT1 (organic cation transporter 1),
or OATP (organic anion-transporting polypeptides) 1B1, 1B3, or 2B1.
Metabolism And Excretion
Pasireotide was shown to be highly metabolically stable
in human liver and kidney microsomes. In healthy volunteers, pasireotide in its
unchanged form is the predominant form found in plasma, urine and feces.
Somatropin may increase CYP450 enzymes and, therefore, suppression of growth
hormone secretion by somatostatin analogs including pasireotide may decrease
the metabolic clearance of compounds metabolized by CYP450 enzymes.
Pasireotide is eliminated mainly via hepatic clearance
(biliary excretion) with a small contribution of the renal route. In a human
ADME study with subcutaneous SIGNIFOR with a single dose 0.6 mg, 55.9 ± 6.63%
of the radioactivity dose was recovered over the first 10 days post dosing,
including 48.3 ± 8.16% of the radioactivity in feces and 7.63 ± 2.03% in urine.
The apparent clearance (CL/F) of SIGNIFOR LAR in healthy
volunteers is on average 4.5–8.5 liters/hour.
Steady-State Pharmacokinetics
PK steady-state for SIGNIFOR LAR is achieved after 3
months. Following multiple intramuscular doses every 4 weeks (every 28 days), SIGNIFOR
LAR demonstrates approximately dose-proportional PK exposures in the dose range
of 20 mg to 60 mg every 4 weeks in patients with acromegaly.
Special Populations
Population PK analyses of SIGNIFOR LAR suggest that race,
gender and body weight do not have clinically relevant influence on circulating
levels of pasireotide. No dose adjustment is required for demographics.
Pediatric Patients
No studies have been performed in pediatric patients [see
Use In Specific Populations].
Geriatric Patients
Age is not a significant covariate in the population PK
analysis of patients with acromegaly. Therefore age is not expected to
significantly impact circulating levels of pasireotide.
Efficacy and safety data on patients with acromegaly
older than 65 years are limited [see Use In Specific Populations].
Hepatic Impairment
In a clinical study with a single subcutaneous dose of
600 μg pasireotide in subjects with impaired hepatic function (Child-Pugh
A, B and C), subjects with moderate and severe hepatic impairment (Child-Pugh B
and C) showed significantly higher exposures than subjects with normal hepatic
function. Upon comparing with the control group, AUCinf was increased by 12%,
56%, and 42%; and Cmax was increased by 3%, 46%, and 33% respectively, in the
mild, moderate, and severe hepatic impairment groups [see Use In Specific
Populations and DOSAGE AND ADMINISTRATION].
Renal Impairment
Renal clearance has a minor contribution to the
elimination of pasireotide in humans. In a clinical study with a single
subcutaneous dose of 900 μg pasireotide in subjects with impaired renal
function, renal impairment of mild, moderate, or severe degree or end stage
renal failure did not have a significant impact on the pharmacokinetics of pasireotide
[see Use In Specific Populations].
Clinical Studies
Drug-Naïve Patients With Acromegaly
A multicenter, randomized, double-blind study was
conducted to assess the safety and efficacy of SIGNIFOR LAR in patients with
active acromegaly. A total of 358 patients naïve to drugs used to treat
acromegaly were randomized in a 1:1 ratio to SIGNIFOR LAR or another somatostatin
analog active comparator. Randomization was stratified based on previous
pituitary surgical status (e.g., at least 1 prior pituitary surgery versus no
prior pituitary surgery).
In the overall study population, 52% were female and the
average age of patients was 45 years. Sixty percent of patients were Caucasian,
23% Asian, 12% Other, 3% American Indian and 2% were Black. Forty-two percent
of patients had previous pituitary surgery and 1 patient had a history of
pituitary radiation therapy. Median time between diagnosis and trial
participation was 6 months. Median GH was 8.8 mcg/L (range: 0.8–200 mcg/L) and
10.1 mcg/L (range: 0.6–169.6 mcg/L) for SIGNIFOR LAR and active comparator,
respectively at baseline. Median standardized IGF-1, defined as IGF-1 value
divided by the ULN (i.e., fold above the ULN), was 2.9 (range: 0.9–6.9) and 2.9
(range: 0.8–7.3), for SIGNIFOR LAR and active comparator, respectively, at
baseline.
The starting dose of SIGNIFOR LAR was 40 mg. Dose
increase was allowed in both arms, at the discretion of investigators, after 3
and 6 months of treatment if mean GH was greater than or equal to 2.5 mcg/L
and/or IGF-1 was greater than the ULN for age and sex. The maximum allowed dose
for SIGNIFOR LAR was 60 mg. The maximum dose of the active comparator was not
used in this trial because the trial was multi-national and the maximum dose
approved in the US was not approved in all participating countries.
The efficacy endpoint was the proportion of patients with
a mean GH level less than 2.5 mcg/L and a normal IGF-1 levels at month 12 (age-
and sex-adjusted) (see Table 4, Figure 3 and Figure 4). The proportion of
patients achieving this level of control was 31.3% and 19.2% for SIGNIFOR LAR
and active comparator, respectively. The changes in mean GH and IGF-1 levels by
study visits in subjects with a measurement at these visits (observed cases)
are shown in Figures 3 and 4.
Table 4 : Results at Month 12 in Drug-Naïve Patients
Study
|
SIGNIFOR LAR (40-60 mg) %
N=176 |
Active Comparator& %
N=182 |
GH < 2.5mcg/L and normalized IGF-1* |
31.3** |
19.2 |
GH < 2.5mcg/L and IGF-1 ≤ ULN |
35.8 |
20.9 |
Normalized IGF-1 |
38.6** |
23.6 |
GH < 2.5 mcg/L |
48.3 |
51.6 |
*Primary endpoint (patients with IGF-1< lower limit of
normal (LLN) were not considered as “responders”) ULN = Upper limit of normal
**p-value < 0.01 for treatment difference
& The maximum dose approved for use in the United States was not used in
this trial but the majority of patients were receiving the dose most commonly
used in the United States to treat acromegaly |
Figure 3: Mean GH (mcg/L) Levels by Visit in Drug
Naïve Patient Study*
*Numbers of patients with a GH value at the given
timepoint for SIGNIFOR LAR/Active comparator arm are displayed as xxx/xxx on
the x axis.
Figure 4: Mean Standardized IGF-1 Levels* by Visit in
Drug Naïve Patient Study**
**Numbers of patients with an IGF-1 value at the given
timepoint for SIGNIFOR LAR/Active comparator arm are displayed as xxx/xxx on
the x axis.
Biochemical control was achieved by Month 3 in 30.1% of
patients in the SIGNIFOR LAR arm. Ninety-eight percent of patients treated with
SIGNIFOR LAR had either a reduction or no change in tumor volume from baseline
assessed by MRI at month 12. The median (range) change in tumor volume was a
reduction of 39.8% (-97.6% to 16.9%).
Additionally, ring size and acromegaly symptoms score
(i.e. headache, fatigue, perspiration, paresthesia, and osteoarthralgia) were
followed. At month 12, reductions in ring size and in symptom severity scores
in both treatment groups compared to baseline were noted.
Patients With Acromegaly Inadequately Controlled On Other
Somatostatin Analogs
A multicenter, randomized, 3-arm trial was conducted in
patients with acromegaly inadequately controlled on somatostatin analogs.
Patients were randomized to double-blind SIGNIFOR LAR 40 mg (n=65) or SIGNIFOR
LAR 60 mg (n=65) or to continued open-label pretrial somatostatin analog
therapies at maximal or near maximal doses (n=68). A total of 181 patients
completed the 6 month trial.
Inadequate control was defined as a GH concentration of
greater than 2.5 mcg/L (i.e., mean of 5 samples over 2 hours) and a sex- and
age-adjusted IGF-1 level greater than 1.3 times the upper limit of normal.
Patients were required to have been treated with other somatostatin analogs for
at least 6 months prior to randomization. Note that the maximum dose for one of
the active comparators approved for use in the United States was not used in
this multinational trial; approximately 75% of the population in the comparator
group was receiving this active comparator.
In the overall study population, 56% were female and the
average age of patients was 45 years. Eighty-one percent of patients were
Caucasian, 7% Other, 8% Black, 2% American Indian and 2% Asian. The percentage
of patients with previous pituitary surgery in the SIGNIFOR LAR 40 mg and 60 mg
arms and in the active control arm was 77%, 63% and 60%, respectively. Three
percent (3%) of patients in the SIGNIFOR LAR groups and 7% of patients in the
active control arm had prior radiation therapy. Median (range) time from
diagnosis to participation in this trial was 50 (10–337) months, 55 (8–357)
months, and 54 (8–357) months in the SIGNIFOR LAR 40 mg, 60 mg and the pretrial
therapy arms, respectively. At baseline, median (range) GH was 7.1 (1.0–200)
mcg/L, 5.3 (1.4–113.8) mcg/L and 6.1 (1.0–92.4) mcg/L in the SIGNIFOR LAR 40
mg, 60 mg and the pretrial therapy arms, respectively. Baseline median
standardized IGF-1 (defined as IGF-1 value divided by the ULN) values were 2.3,
2.6 and 2.9 in the SIGNIFOR LAR 40 mg, 60 mg and the pretrial therapy arms,
respectively.
The efficacy endpoint was the proportion of patients with
a mean GH level less than 2.5 mcg/L and normal IGF-1 levels at week 24. The
primary analysis compared SIGNIFOR LAR 60 mg and 40 mg to continued pretrial
therapy (i.e., no change in treatment). The proportion of patients achieving
biochemical control was 15.4% and 20.0% for SIGNIFOR LAR 40 mg and 60 mg,
respectively, at 6 months.
Biochemical control was achieved by Month 3 in 15.4% and
18.5% of patients in the SIGNIFOR LAR 40 mg and 60 mg arms, respectively.
Table 5 : Results at 6 Months in Inadequately
Controlled Patient Study
|
SIGNIFOR LAR 40 mg %
N=65 |
SIGNIFOR LAR 60 mg %
N=65 |
Continued Pretrial Therapy Control Arm& %
N=68 |
GH < 2.5 mcg /L and normalized IGF-1* |
15.4 |
20.0 |
0 |
Normalization of IGF-1 |
24.6 |
26.2 |
0 |
GH < 2.5 mcg /L |
35.4 |
43.1 |
13.2 |
*Primary endpoint (patients with IGF-1< lower limit of
normal (LLN) were not considered as “responders”).
&For one of the active comparators, the maximum dose approved for use in
the United States was not used in this trial but the majority of patients were
receiving the dose most commonly used in the United States to treat acromegaly. |
Eighty-one percent and 70 percent of patients treated
with SIGNIFOR LAR 40 mg and 60 mg, respectively, had either a reduction or no
change in tumor volume from baseline assessed by MRI at month 6. The median
(range) change in tumor volume was a reduction of -10.4% (-74.5% to 19.4%) and
-6.3% (-66.7% to 14.5%) from baseline for SIGNIFOR LAR 40 mg and 60 mg,
respectively.