CLINICAL PHARMACOLOGY
Mechanism Of Action
Ruxolitinib, a kinase inhibitor, inhibits Janus Associated Kinases (JAKs) JAK1 and JAK2 which
mediate the signaling of a number of cytokines and growth factors that are important for
hematopoiesis and immune function. JAK signaling involves recruitment of STATs (signal
transducers and activators of transcription) to cytokine receptors, activation and subsequent localization of STATs to the nucleus leading to modulation of gene expression.
MF and PV are myeloproliferative neoplasms (MPN) known to be associated with dysregulated JAK1 and JAK2 signaling. In a mouse model of JAK2V617F-positive MPN, oral administration of ruxolitinib prevented splenomegaly, preferentially decreased JAK2V617F mutant cells in the spleen and decreased circulating inflammatory cytokines (e.g., TNF- α, IL-6).
Pharmacodynamics
Jakafi inhibits cytokine induced STAT3 phosphorylation in whole blood from patients with MF and PV. Jakafi administration resulted in maximal inhibition of STAT3 phosphorylation 2 hours after dosing which returned to near baseline by 10 hours in patients with MF and PV.
Cardiac Electrophysiology
At a dose of 1.25 to 10 times the highest recommended starting dosage, Jakafi does not prolong the QT interval to any clinically relevant extent.
Pharmacokinetics
Mean ruxolitinib maximal plasma concentration (Cmax) and AUC increased proportionally over a single dose range of 5 mg to 200 mg. Mean ruxolitinib Cmax ranged from 205 nM to 7100 nM and AUC ranged from 862 nM*hr to 30700 nM*hr over a single dose range of 5 mg to 200 mg.
Absorption
Ruxolitinib achieves Cmax within 1 hour to 2 hours post-dose. Oral absorption of ruxolitinib is estimated to be at least 95%.
Food Effect
No clinically relevant changes in the pharmacokinetics of ruxolitinib were observed upon administration of Jakafi with a high-fat, high-calorie meal (approximately 800 to 1000 calories of which 50% were derived from fat).
Distribution
The mean volume of distribution at steady-state is 72 L (coefficient of variation [CV] 29%) in patients with MF and 75 L (23%) in patients with PV.
Binding to plasma proteins is approximately 97%, mostly to albumin.
Elimination
The mean elimination half-life of ruxolitinib is approximately 3 hours and the mean half-life of ruxolitinib + metabolites is approximately 5.8 hours.
Ruxolitinib clearance was 17.7 L/h in women and 22.1 L/h in men with MF (39% inter-subject variability).
Ruxolitinib clearance was 12.7 L/h in patients with PV (42% inter-subject variability).
Metabolism
Ruxolitinib is metabolized by CYP3A4 and to a lesser extent by CYP2C9.
Excretion
Following a single oral dose of radiolabeled ruxolitinib, elimination was predominately through metabolism with 74% of radioactivity excreted in urine and 22% excretion via feces. Unchanged drug accounted for less than 1% of the excreted total radioactivity.
Specific Populations
No clinically relevant differences in ruxolitinib pharmacokinetics were observed with regard to age, race, sex, or weight.
Patients With Renal Impairment
The safety and pharmacokinetics of single dose Jakafi (25 mg) were evaluated in a study in healthy subjects [CLcr 72 mL/min to 164 mL/min as estimated using Cockcroft-Gault] and in subjects with mild [CLcr 53 mL/min to 83 mL/min], moderate [CLcr 38 mL/min to 57 mL/min], or severe renal impairment [CLcr 15 mL/min to 51 mL/min]. Additional subjects with ESRD requiring hemodialysis were also enrolled.
The pharmacokinetics of ruxolitinib was similar in subjects with various degrees of renal impairment and in those with normal renal function, but the plasma AUC values of ruxolitinib metabolites increased with increasing severity of renal impairment. This was most marked in the subjects with ESRD requiring hemodialysis. The change in the pharmacodynamic marker, pSTAT3 inhibition, was consistent with the corresponding increase in metabolite exposure. Ruxolitinib is not removed by dialysis; however, the removal of some active metabolites by dialysis cannot be ruled out.
Patients With Hepatic Impairment
The safety and pharmacokinetics of single dose Jakafi (25 mg) were evaluated in a study in healthy subjects and in subjects with mild [Child-Pugh A], moderate [Child-Pugh B], or severe hepatic impairment [Child-Pugh C]. The mean AUC for ruxolitinib was increased by 87% in patients with mild impairment, 28% in patients with moderate impairment and 65% in patients with severe hepatic impairment compared to patients with normal hepatic function. The terminal elimination half-life was prolonged in patients with hepatic impairment compared to healthy subjects (4.1 hours to 5 hours versus 2.8 hours). The change in the pharmacodynamic marker, pSTAT3 inhibition, was consistent with the corresponding increase in ruxolitinib exposure except in the severe hepatic impairment cohort where the pharmacodynamic activity was more prolonged in some subjects than expected based on plasma concentrations of ruxolitinib.
Drug Interactions
Fluconazole
Simulations suggest that fluconazole (a dual CYP3A4 and CYP2C9 inhibitor) increases steady state ruxolitinib AUC by approximately 100% to 300% following concomitant administration of 10 mg of Jakafi twice daily with 100 mg to 400 mg of fluconazole once daily [see DOSAGE AND ADMINISTRATION and DRUG INTERACTIONS].
Strong CYP3A4 Inhibitors
Ketoconazole (a strong CYP3A4 inhibitor) increased ruxolitinib Cmax by 33% and AUC by 91%. Ketoconazole also prolonged ruxolitinib half-life from 3.7 hours to 6 hours [see DOSAGE AND ADMINISTRATION and DRUG INTERACTIONS].
Moderate CYP3A4 Inhibitors
Erythromycin (a moderate CYP3A4 inhibitor) increased ruxolitinib Cmax by 8% and AUC by 27% [see DRUG INTERACTIONS].
Strong CYP3A4 Inducers
Rifampin (a strong CYP3A4 inducer) decreased ruxolitinib Cmax by 32% and AUC by 61%. The
relative exposure to ruxolitinib’s active metabolites increased approximately 100% [see DRUG INTERACTIONS].
In Vitro Studies
Ruxolitinib and its M18 metabolite did not inhibit CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6 or CYP3A4. Ruxolitinib did not induce CYP1A2, CYP2B6 or CYP3A4 at clinically relevant concentrations.
Ruxolitinib and its M18 metabolite did not inhibit the P-gp, BCRP, OATP1B1, OATP1B3, OCT1, OCT2, OAT1 or OAT3 transport systems at clinically relevant concentrations. Ruxolitinib is not a substrate for the P-gp transporter.
Clinical Studies
Myelofibrosis
Two randomized Phase 3 studies (Studies 1 and 2) were conducted in patients with MF (either primary MF, post-polycythemia vera MF or post-essential thrombocythemia-MF). In both studies, patients had palpable splenomegaly at least 5 cm below the costal margin and risk category of intermediate 2 (2 prognostic factors) or high risk (3 or more prognostic factors) based on the International Working Group Consensus Criteria (IWG).
The starting dose of Jakafi was based on platelet count. Patients with a platelet count between 100 and 200 X 109/L were started on Jakafi 15 mg twice daily and patients with a platelet count greater than 200 X 109/L were started on Jakafi 20 mg twice daily. Doses were then individualized based upon tolerability and efficacy with maximum doses of 20 mg twice daily for patients with platelet counts between 100 to less than or equal to 125 X 109/L, of 10 mg twice daily for patients with platelet counts between 75 to less than or equal to 100 X 109/L, and of 5 mg twice daily for patients with platelet counts between 50 to less than or equal to 75 X 109/L.
Study 1
Study 1 (NCT00952289) was a double-blind, randomized, placebo-controlled study in 309 patients who were refractory to or were not candidates for available therapy. The median age was 68 years (range 40 to 91 years) with 61% of patients older than 65 years and 54% were male. Fifty percent (50%) of patients had primary MF, 31% had post-polycythemia vera MF and 18% had post-essential thrombocythemia MF. Twenty-one percent (21%) of patients had red blood cell transfusions within 8 weeks of enrollment in the study. The median hemoglobin count was 10.5 g/dL and the median platelet count was 251 X 109/L. Patients had a median palpable spleen length of 16 cm below the costal margin, with 81% having a spleen length 10 cm or greater below the costal margin. Patients had a median spleen volume as measured by magnetic resonance imaging (MRI) or computed tomography (CT) of 2595 cm3 (range 478 cm3 to 8881 cm3). (The upper limit of normal is approximately 300 cm3).
Patients were dosed with Jakafi or matching placebo. The primary efficacy endpoint was the proportion of patients achieving greater than or equal to a 35% reduction from baseline in spleen volume at Week 24 as measured by MRI or CT.
Secondary endpoints included duration of a 35% or greater reduction in spleen volume and proportion of patients with a 50% or greater reduction in Total Symptom Score from baseline to Week 24 as measured by the modified Myelofibrosis Symptom Assessment Form (MFSAF) v2.0 diary.
Study 2
Study 2 (NCT00934544) was an open-label, randomized study in 219 patients. Patients were randomized 2:1 to Jakafi versus best available therapy. Best available therapy was selected by the investigator on a patient-by-patient basis. In the best available therapy arm, the medications received by more than 10% of patients were hydroxyurea (47%) and glucocorticoids (16%). The median age was 66 years (range 35 to 85 years) with 52% of patients older than 65 years and 57% were male. Fifty-three percent (53%) of patients had primary MF, 31% had post24 polycythemia vera MF and 16% had post-essential thrombocythemia MF. Twenty-one percent (21%) of patients had red blood cell transfusions within 8 weeks of enrollment in the study. The median hemoglobin count was 10.4 g/dL and the median platelet count was 236 X 109/L. Patients had a median palpable spleen length of 15 cm below the costal margin, with 70% having a spleen length 10 cm or greater below the costal margin. Patients had a median spleen volume as measured by MRI or CT of 2381 cm3 (range 451 cm3 to 7765 cm3).
The primary efficacy endpoint was the proportion of patients achieving 35% or greater reduction from baseline in spleen volume at Week 48 as measured by MRI or CT.
A secondary endpoint in Study 2 was the proportion of patients achieving a 35% or greater reduction of spleen volume as measured by MRI or CT from baseline to Week 24.
Study 1 And 2 Efficacy Results
Efficacy analyses of the primary endpoint in Studies 1 and 2 are presented in Table 14 below. A significantly larger proportion of patients in the Jakafi group achieved a 35% or greater reduction in spleen volume from baseline in both studies compared to placebo in Study 1 and best available therapy in Study 2. A similar proportion of patients in the Jakafi group achieved a 50% or greater reduction in palpable spleen length.
Table 14: Percent of Patients with Myelofibrosis Achieving 35% or Greater Reduction
from Baseline in Spleen Volume at Week 24 in Study 1 and at Week 48 in
Study 2 (Intent to Treat)
|
Study 1 |
Study 2 |
Jakafi (N=155) |
Placebo (N=154) |
Jakafi (N=146) |
Best Available Therapy (N=73) |
Time Points |
Week 24 |
Week 48 |
Number (%) of Patients with Spleen Volume Reduction by 35% or More |
65 (42) |
1 (<1) |
41 (29) |
0 |
P-value |
< 0.0001 |
< 0.0001 |
Figure 1 shows the percent change from baseline in spleen volume for each patient at Week 24 (Jakafi N=139, placebo N=106) or the last evaluation prior to Week 24 for patients who did not complete 24 weeks of randomized treatment (Jakafi N=16, placebo N=47). One (1) patient (placebo) with a missing baseline spleen volume is not included.
Figure 1: Percent Change from Baseline in Spleen Volume at Week 24 or Last
Observation for Each Patient (Study 1)
In Study 1, MF symptoms were a secondary endpoint and were measured using the modified
Myelofibrosis Symptom Assessment Form (MFSAF) v2.0 diary. The modified MFSAF is a daily
diary capturing the core symptoms of MF (abdominal discomfort, pain under left ribs, night
sweats, itching, bone/muscle pain and early satiety). Symptom scores ranged from 0 to 10 with 0
representing symptoms “absent” and 10 representing “worst imaginable” symptoms. These
scores were added to create the daily total score, which has a maximum of 60.
Table 15 presents assessments of Total Symptom Score from baseline to Week 24 in Study 1
including the proportion of patients with at least a 50% reduction (ie, improvement in
symptoms). At baseline, the mean Total Symptom Score was 18.0 in the Jakafi group and 16.5 in
the placebo group. A higher proportion of patients in the Jakafi group had a 50% or greater
reduction in Total Symptom Score than in the placebo group, with a median time to response of
less than 4 weeks.
Table 15: Improvement in Total Symptom Score in Patients with Myelofibrosis
|
Jakafi (N=148) |
Placebo (N=152) |
Number (%) of Patients with 50% or Greater Reduction in Total Symptom Score by Week 24 |
68 (46) |
8 (5) |
P-value |
< 0.0001 |
Figure 2 shows the percent change from baseline in Total Symptom Score for each patient at Week 24 (Jakafi N=129, placebo N=103) or the last evaluation on randomized therapy prior to Week 24 for patients who did not complete 24 weeks of randomized treatment (Jakafi N=16, placebo N=42). Results are excluded for 5 patients with a baseline Total Symptom Score of zero, 8 patients with missing baseline and 6 patients with insufficient post-baseline data.
Figure 2: Percent Change from Baseline in Total Symptom Score at Week 24 or Last Observation for Each Patient (Study 1)
Figure 3 displays the proportion of patients with at least a 50% improvement in each of the individual symptoms that comprise the Total Symptom Score indicating that all 6 of the symptoms contributed to the higher Total Symptom Score response rate in the group treated with Jakafi.
Figure 3: Proportion of Patients with Myelofibrosis Achieving 50% or Greater
Reduction in Individual Symptom Scores at Week 24
An exploratory analysis of patients receiving Jakafi also showed improvement in fatigue-related
symptoms (i.e., tiredness, exhaustion, mental tiredness, and lack of energy) and associated
impacts on daily activities (i.e., activity limitations related to work, self-care, and exercise) as
measured by the PROMIS® Fatigue 7-item short form total score at Week 24. Patients who
achieved a reduction of 4.5 points or more from baseline to Week 24 in the PROMIS® Fatigue
total score were considered to have achieved a fatigue response. Fatigue response was reported
in 35% of patients in the Jakafi group versus 14% of the patients in the placebo group.
Overall survival was a secondary endpoint in both Study 1 and Study 2. Patients in the control
groups were eligible for crossover in both studies, and the median times to crossover were
9 months in Study 1 and 17 months in Study 2.
Figure 4 and Figure 5 show Kaplan-Meier curves of overall survival at prospectively planned
analyses after all patients remaining on study had completed 144 weeks on study.
Figure 4: Overall Survival -Kaplan-Meier Curves by Treatment Group in Study 1
Figure 5: Overall Survival -Kaplan-Meier Curves by Treatment Group in Study 2
Polycythemia Vera
Study 3 (NCT01243944) was a randomized, open-label, active-controlled Phase 3 study conducted in 222 patients with PV. Patients had been diagnosed with PV for at least 24 weeks, had an inadequate response to or were intolerant of hydroxyurea, required phlebotomy and exhibited splenomegaly. All patients were required to demonstrate hematocrit control between 40-45% prior to randomization. The age ranged from 33 to 90 years with 30% of patients over 65 years of age and 66% were male. Patients had a median spleen volume as measured by MRI or CT of 1272 cm3 (range 254 cm3 to 5147 cm3) and median palpable spleen length below the costal margin was 7 cm.
Patients were randomized to Jakafi or best available therapy. The starting dose of Jakafi was 10 mg twice daily. Doses were then individualized based upon tolerability and efficacy with a maximum dose of 25 mg twice daily. At Week 32, 98 patients were still on Jakafi with 8% receiving greater than 20 mg twice daily, 15% receiving 20 mg twice daily, 33% receiving 15 mg twice daily, 34% receiving 10 mg twice daily, and 10% receiving less than 10 mg twice daily. Best available therapy (BAT) was selected by the investigator on a patient-by-patient basis and included hydroxyurea (60%), interferon/pegylated interferon (12%), anagrelide (7%), pipobroman (2%), lenalidomide/thalidomide (5%), and observation (15%).
The primary endpoint was the proportion of subjects achieving a response at Week 32, with response defined as having achieved both hematocrit control (the absence of phlebotomy eligibility beginning at the Week 8 visit and continuing through Week 32) and spleen volume reduction (a greater than or equal to 35% reduction from baseline in spleen volume at Week 32). Phlebotomy eligibility was defined as a confirmed hematocrit greater than 45% that is at least 3 percentage points higher than the hematocrit obtained at baseline or a confirmed hematocrit greater than 48%, whichever was lower. Secondary endpoints included the proportion of all randomized subjects who achieved the primary endpoint and who maintained their response 48 weeks after randomization, and the proportion of subjects achieving complete hematological remission at Week 32 with complete hematological remission defined as achieving hematocrit control, platelet count less than or equal to 400 X 109/L, and white blood cell count less than or equal to 10 X 109/L.
Results of the primary and secondary endpoints are presented in Table 16. A significantly larger proportion of patients on the Jakafi arm achieved a response for the primary endpoint compared to best available therapy at Week 32 and maintained their response 48 weeks after randomization. A significantly larger proportion of patients on the Jakafi arm compared to best available therapy also achieved complete hematological remission at Week 32.
Table 16: Percent of Patients with Polycythemia Vera Achieving the Primary and Key Secondary Endpoints in Study 3 (Intent to Treat)
|
Jakafi (N=110) |
Best Available Therapy (N=112) |
Number (%) of Patients Achieving a Primary Response at Week 32 |
25 (23%) |
1 (<1%) |
95% CI of the response rate (%) |
(15%, 32%) |
(0%, 5%) |
P-value |
< 0.0001 |
Number (%) of Patients Achieving a Durable Primary Response at Week 48 |
22 (20%) |
1 (<1%) |
95% CI of the response rate (%) |
(13%, 29%) |
(0%, 5%) |
P-value |
< 0.0001 |
Number (%) of Patients Achieving Complete Hematological Remission at Week 32 |
26 (24%) |
9 (8%) |
95% CI of the response rate (%) |
(16%, 33%) |
(4%, 15%) |
P-value |
0.0016 |
Primary Response defined as having achieved both the absence of phlebotomy eligibility beginning at the Week 8 visit and continuing through Week 32 and a greater than or equal to 35% reduction from baseline in spleen volume at Week 32. |
Additional analyses for Study 3 to assess durability of response were conducted at Week 80 only in the Jakafi arm. On this arm, 91 (83%) patients were still on treatment at the time of the Week 80 data cut-off. Of the 25 patients who achieved a primary response at Week 32, 19 (76% of the responders) maintained their response through Week 80, and of the 26 patients who achieved complete hematological remission at Week 32, 15 (58% of the responders) maintained their response through Week 80.
In an assessment of the individual components that make up the primary endpoint, there were 66 (60%) patients with hematocrit control on the Jakafi arm vs. 21 (19%) patients on best available therapy at Week 32; 51 (77% of hematocrit responders) patients on the Jakafi arm maintained hematocrit control through Week 80. There were 44 (40%) patients with spleen volume reduction from baseline greater than or equal to 35% on the Jakafi arm vs. 1 (<1%) patient on best available therapy at Week 32; 43 (98% of spleen volume reduction responders) patients on the Jakafi arm maintained spleen volume reduction through Week 80.