CLINICAL PHARMACOLOGY
Mechanism Of Action
Lapatinib is a 4-anilinoquinazoline kinase inhibitor of
the intracellular tyrosine kinase domains of both Epidermal Growth Factor
Receptor (EGFR [ErbB1]) and of Human Epidermal Receptor Type 2 (HER2 [ErbB2])
receptors (estimated Kiapp values of 3nM and 13nM, respectively) with a
dissociation half-life of greater than or equal to 300 minutes. Lapatinib
inhibits ErbB-driven tumor cell growth in vitro and in various animal models.
An additive effect was demonstrated in an in vitro study
when lapatinib and 5-FU (the active metabolite of capecitabine) were used in
combination in the 4 tumor cell lines tested. The growth inhibitory effects of lapatinib
were evaluated in trastuzumab-conditioned cell lines. Lapatinib retained
significant activity against breast cancer cell lines selected for long-term
growth in trastuzumab-containing medium in vitro. These in vitro findings
suggest non-cross-resistance between these two agents.
Hormone receptor-positive breast cancer cells (with ER
[Estrogen Receptor] and/or PgR [Progesterone Receptor]) that coexpress the HER2
tend to be resistant to established endocrine therapies. Similarly, hormone receptor-positive
breast cancer cells that initially lack EGFR or HER2 upregulate these receptor
proteins as the tumor becomes resistant to endocrine therapy.
Pharmacodynamics
Cardiac Electrophysiology
The effect of lapatinib on the QT-interval was evaluated
in a single-blind, placebo-controlled, single sequence (placebo and active
treatment) crossover study in patients with advanced solid tumors (N = 58).
During the 4- day treatment period, three doses of matching placebo were
administered 12 hours apart in the morning and evening on Day 1 and in the
morning on Day 2. This was followed by three doses of lapatinib 2000 mg (1.3 – 1.6
times the recommended dosage) administered in the same way. Measurements,
including ECGs and pharmacokinetic samples were done at baseline and at the
same time points on Day 2 and Day 4. In the evaluable population of subjects
who had complete dosing and ECG assessments (N = 37), the maximum mean ΔΔQTcF
(90% CI) of 8.75 ms (4.08, 13.42) was observed 10 hours after ingestion of the
third dose of lapatinib 2000 mg. The ΔΔQTcF exceeded the 5 ms
threshold and the upper bound 90% CIs exceeded the 10 ms threshold at multiple
time points.
There was a concentration-dependent increase in QTcF
effects [see WARNINGS AND PRECAUTIONS].
Pharmacokinetics
Absorption
Absorption following oral administration of TYKERB is
incomplete and variable. Serum concentrations appear after a median lag time of
0.25 hours (range 0 to 1.5 hours). Peak plasma concentrations (Cmax) of
lapatinib are achieved approximately 4 hours after administration. Daily dosing
of TYKERB results in achievement of steady state within 6 to 7 days, indicating
an effective half-life of 24 hours.
At the dose of 1,250 mg daily, steady-state geometric
mean [95% confidence interval (CI)] values of Cmax were 2.43 mcg/mL (1.57 to
3.77 mcg/mL) and AUC were 36.2 mcg.h/mL (23.4 to 56 mcg.h/mL).
Divided daily doses of TYKERB resulted in approximately
2-fold higher exposure at steady state (steady-state AUC) compared to the same
total dose administered once daily.
Systemic exposure to lapatinib is increased when
administered with food. Lapatinib AUC values were approximately 3- and 4-fold
higher (Cmax approximately 2.5- and 3-fold higher) when administered with a
lowfat (5% fat-500 calories) or with a high-fat (50% fat-1,000 calories) meal,
respectively.
Distribution
Lapatinib is highly bound (greater than 99%) to albumin
and alpha-1 acid glycoprotein. In vitro studies indicate that lapatinib is a
substrate for the transporters breast cancer-resistance protein (BCRP, ABCG2)
and P-glycoprotein (P-gp, ABCB1). Lapatinib has also been shown to inhibit
P-gp, BCRP, and the hepatic uptake transporter OATP 1B1, in vitro at clinically
relevant concentrations.
Metabolism
Lapatinib undergoes extensive metabolism, primarily by
CYP3A4 and CYP3A5, with minor contributions from CYP2C19 and CYP2C8 to a
variety of oxidated metabolites, none of which accounts for more than 14% of
the dose recovered in the feces or 10% of lapatinib concentration in plasma.
Elimination
At clinical doses, the terminal phase half-life following
a single dose was 14.2 hours; accumulation with repeated dosing indicates an
effective half-life of 24 hours.
Elimination of lapatinib is predominantly through
metabolism by CYP3A4/5 with negligible (less than 2%) renal excretion. Recovery
of parent lapatinib in feces accounts for a median of 27% (range 3% to 67%) of
an oral dose.
Effects Of Age, Gender, Or Race
Studies of the effects of age, gender, or race on the
pharmacokinetics of lapatinib have not been performed.
Pharmacogenomics
The HLA alleles DQA1*02:01 and DRB1*07:01 were associated
with hepatotoxicity reactions in a genetic substudy of a monotherapy trial with
TYKERB (n = 1,194). Severe liver injury (ALT greater than 5 times the upper
limit of normal, NCI CTCAE Grade 3) occurred in 2% of patients overall; the
incidence of severe liver injury among DQA1*02:01 or DRBI*07:01 allele carriers
was 8% versus 0.5% in non-carriers. These HLA alleles are present in
approximately 15% to 25% of Caucasian, Asian, African, and Hispanic populations
and 1% in Japanese populations. Liver function should be monitored in all
patients receiving therapy with TYKERB regardless of genotype.
Animal Toxicology And/Or Pharmacology
In 104-week repeat-dose studies in rodents, severe skin
lesions that led to lethality were seen at the highest doses tested (300
mg/kg/day) in male mice and female rats. There was also an increase in renal
infarcts and papillary necrosis in female rats at greater than or equal to 60
mg/kg/day and greater than or equal to 180 mg/kg/day, respectively
(approximately 7 and 10 times the expected human clinical exposure based on AUC,
respectively). The relevance of these findings for humans is uncertain.
Clinical Studies
HER2-Positive Metastatic Breast Cancer
The efficacy and safety of TYKERB in combination with
capecitabine in breast cancer were evaluated in a randomized, Phase 3 trial.
Patients eligible for enrollment had HER2 (ErbB2) overexpressing (IHC 3+ or IHC
2+ confirmed by FISH), locally advanced or metastatic breast cancer, progressing
after prior treatment that included anthracyclines, taxanes, and trastuzumab.
Patients were randomized to receive either TYKERB 1,250
mg once daily (continuously) plus capecitabine 2,000 mg/m²/day on Days 1-14
every 21 days, or to receive capecitabine alone at a dose of 2,500 mg/m²/day on
Days 1-14 every 21 days. The endpoint was time to progression (TTP). TTP was
defined as time from randomization to tumor progression or death related to
breast cancer. Based on the results of a pre-specified interim analysis,
further enrollment was discontinued. Three hundred and ninety-nine (399)
patients were enrolled in this study. The median age was 53 years and 14% were
older than 65 years. Ninety-one percent  (91%) were Caucasian. Ninety-seven
percent (97%) had stage IV breast cancer, 48% were estrogen receptor+ (ER+) or
progesterone receptor+ (PR+), and 95% were ErbB2 IHC 3+ or IHC 2+ with FISH
confirmation. Approximately 95% of patients had prior treatment with
anthracyclines, taxanes, and trastuzumab.
Efficacy analyses 4 months after the interim analysis are
presented in Table 6, Figure 1, and Figure 2.
Table 6. Efficacy Results
|
Independent Assessmenta |
Investigator Assessment |
TYKERB 1,250 mg/day + Capecitabine 2,000 mg/m²/day
(N = 198) |
Capecitabine 2,500 mg/m²/day
(N = 201) |
TYKERB 1,250 mg/day + Capecitabine 2,000 mg/m²/day
(N = 198) |
Capecitabine 2,500 mg/m²/day
(N = 201) |
Number of TTP events |
82 |
102 |
121 |
126 |
Median TTP, weeks (25th, 75th, Percentile), weeks |
27.1 (17.4, 49.4) |
18.6 (9.1, 36.9) |
23.9 (12.0, 44.0) |
18.3 (6.9, 35.7) |
Hazard Ratio (HR) (95% CI) |
0.57 (0.43, 0.77) |
0.72 (0.56, 0.92) |
P value |
0.00013 |
0.00762 |
Response Rate (%)(95% CI) |
23.7 (18.0, 30.3) |
13.9 (9.5, 19.5) |
31.8 (25.4, 38.8) |
17.4 (12.4, 23.4) |
TTP = Time to Progression
CI = Confidence Interval
a The time from last tumor assessment to the data cut-off date was
greater than 100 days in approximately 30% of patients in the independent
assessment. The pre-specified assessment interval was 42 or 84 days. |
Figure 1: Kaplan-Meier Estimates for Independent
Review Panel-evaluated Time to Progression
Figure 2: Kaplan-Meier Estimates for Investigator
Assessment Time to Progression
At the time of above efficacy analysis, the overall
survival data were not mature (32% events). However, based on the TTP results,
the study was unblinded and patients receiving capecitabine alone were allowed
to cross over to treatment with TYKERB plus capecitabine. The survival data
were followed for an additional 2 years to be mature and the analysis is
summarized in Table 7.
Table 7: Overall Survival Data
|
TYKERB 1,250 mg/day + Capecitabine 2,000 mg/m²/day
(N = 207) |
Capecitabine 2,500 mg/m²/day
(N = 201) |
Overall Survival |
Died |
76% |
82% |
Median Overall Survival (weeks) |
75.0 |
65.9 |
Hazard ratio, 95% CI |
0.89 (0.71, 1.10) |
(P value) |
0.276 |
CI = Confidence Interval |
Clinical Studies Describing Limitations Of Use
In two randomized trials, TYKERB-based chemotherapy regimens
have been shown to be less effective than trastuzumab-based chemotherapy
regimens. The first randomized, open-label study compared the safety and
efficacy of TYKERB in combination with capecitabine relative to trastuzumab in
combination with capecitabine in women with HER2-positive metastatic breast cancer
(N = 540). The study was stopped early based on the findings of a pre-planned
interim analysis showing a low incidence of CNS events (primary endpoint) and
superior efficacy of the trastuzumab plus capecitabine. The median
progression-free survival was 6.6 months in the group receiving TYKERB in
combination with capecitabine compared with 8.0 months in the group receiving
the trastuzumab combination [HR = 1.30 (95% CI: 1.04, 1.64)]. Overall survival
was analyzed when 26% of deaths occurred in the group receiving TYKERB in
combination with capecitabine and 22% in the group receiving the trastuzumab
combination [HR = 1.34 (95% CI: 0.95, 1.92)].
The second randomized, open-label study compared the
safety and efficacy of taxane-based chemotherapy plus TYKERB to taxane-based
chemotherapy plus trastuzumab as first-line therapy in women with
HER2-positive, metastatic breast cancer (N = 652). The study was stopped early
based on findings from a pre-planned interim analysis. The median
progression-free survival was 11.3 months in the trastuzumab combination
treatment arm compared to 9.0 months in patients treated with TYKERB in the
combination arm for the intent-to-treat population [HR = 1.37 (95% CI: 1.13,
1.65)].
Hormone Receptor-Positive, HER2-Positive Metastatic
Breast Cancer
The efficacy and safety of TYKERB in combination with
letrozole were evaluated in a double-blind, placebocontrolled, multi-center
study. A total of 1,286 postmenopausal women with hormone receptor-positive (ER
positive and/or PgR positive) metastatic breast cancer, who had not received
prior therapy for metastatic disease, were randomly assigned to receive either
TYKERB (1,500 mg once daily) plus letrozole (2.5 mg once daily) (n = 642) or
letrozole (2.5 mg once daily) alone (n = 644). Of all patients randomized to
treatment, 219 (17%) patients had tumors overexpressing the HER2 receptor,
defined as fluorescence in situ hybridization (FISH) greater than or equal to 2
or 3+ immunohistochemistry (IHC). There were 952 (74%) patients who were HER2-negative
and 115 (9%) patients did not have their HER2 receptor status confirmed. The
primary objective was to evaluate and compare progression-free survival (PFS)
in the HER2-positive population. Progression-free survival was defined as the
interval of time between date of randomization and the earlier date of first
documented sign of disease progression or death due to any cause.
The baseline demographic and disease characteristics were
balanced between the two treatment arms. The median age was 63 years and 45%
were 65 years of age or older. Eighty-four percent (84%) of the patients were white.
Approximately 50% of the HER2-positive population had prior
adjuvant/neo-adjuvant chemotherapy and 56% had prior hormonal therapy. Only 2
patients had prior trastuzumab.
In the HER2-positive subgroup (n = 219), the addition of
TYKERB to letrozole resulted in an improvement in PFS. In the HER2-negative
subgroup, there was no improvement in PFS of the combination of TYKERB plus letrozole
compared to the letrozole plus placebo. Overall response rate (ORR) was also
improved with the combination of TYKERB plus letrozole. The overall survival
(OS) data were not mature. Efficacy analyses for the hormone receptor-positive,
HER2-positive and HER2-negative subgroups are presented in Table 8 and Figure
3.
Table 8: Efficacy Results
|
HER2-Positive Population |
HER2-Negative Population |
TYKERB 1500 mg/day + Letrozole 2.5 mg/day
(N = 111) |
Letrozole 2.5 mg/day
(N = 108) |
TYKERB 1500 mg/day + Letrozole 2.5 mg/day
(N = 478) |
Letrozole 2.5 mg/day
(N = 474) |
Median PFSa, weeks |
35.4 |
13.0 |
59.7 |
58.3 |
(95% CI) |
(24.1, 39.4) |
(12.0, 23.7) |
(48.6, 69.7) |
(47.9, 62.0) |
Hazard Ratio (95% CI) |
0.71 (0.53, 0.96) |
0.90 (0.77, 1.05) |
P value |
0.019 |
0.188 |
Response Rate (%) |
27.9 |
14.8 |
32.6 |
31.6 |
(95% CI) |
(19.8, 37.2) |
(8.7, 22.9) |
(28.4, 37.0) |
(27.5, 36.0) |
PFS = Progression-free survival;
CI = Confidence Interval.
a Kaplan-Meier estimate |
Figure 3: Kaplan-Meier Estimates for Progression-Free
Survival for the HER2-Positive Population
The efficacy and safety of TYKERB, in combination with an
aromatase inhibitor (AI), were confirmed in another randomized Phase 3 trial.
Patients enrolled were post-menopausal women who had hormone receptorpositive (HR+)/HER2-positive,
metastatic breast cancer, which had progressed after prior
trastuzumabcontaining chemotherapy and endocrine therapies. A total of 355
patients were randomized in a 1:1:1 ratio to TYKERB 1000 mg + trastuzumab + AI
(N = 120), or trastuzumab + AI arm (N = 117), or TYKERB 1500 mg + AI (N = 118).
In the trastuzumab-containing arms, trastuzumab was administered with a loading
dose of 8 mg/kg IV followed by the maintenance dose of 6 mg/kg every 3 weeks.
In the AI-containing arms, the AIs were administered at doses of letrozole 2.5
mg once daily, or exemestane 25 mg once daily, or anastrozole 1 mg once daily.
The study was designed to evaluate a potential benefit in
Progression Free Survival (PFS) when double versus single HER2 targeted therapy
was administered in combination with an AI (letrozole, exemestane, or anastrozole).
The major efficacy outcome measure was PFS based on local
radiology/investigator’s assessment comparing TYKERB + trastuzumab + AI versus
trastuzumab + AI.
The median age was 56 years (range 30-84). The majority
of the patients treated on this trial (70%) were Caucasian.
Efficacy results are presented in Table 9 and Figure 4.
The overall survival (OS) data were not mature (23% of patients had died).
Table 9: Efficacy Results
|
TYKERB (1000 mg) + Trastuzumab + AI
(N = 120) |
Trastuzumab + AI
(N = 117) |
TYKERB (1500 mg) + AI
(N = 118) |
Median PFSa, months (95% CI) |
11.0 (8.3, 13.8) |
5.6 (5.4, 8.3) |
8.3 (5.8, 11.1) |
Hazard Ratio (95% CI) |
0.62 (0.45, 0.88) |
— |
P valueb |
0.0040 |
|
-- |
0.85 (0.62, 1.17) |
|
0.2921c |
Response Rate (%)d(95% CI) |
22.5 (15.4, 31.0) |
8.5 (4.2, 15.2) |
12.7 (7.3, 20.1) |
PFS = Progression-free survival
CI = Confidence Interval
a Kaplan-Meier estimate
b Stratified log-rank test
c Nominal p-value. No multiplicity adjustment
d CR+PR; subjects with unknown or missing response were treated as
non-responders |
Figure 4: Kaplan-Meier Estimates for Progression-Free
Survival