Pharmacotherapeutic group: Antineoplastic agents, protein kinase inhibitors, ATC code: L01EX10
Mechanism of action
Midostaurin inhibits multiple receptor tyrosine kinases, including FLT3 and KIT kinase. Midostaurin inhibits FLT3 receptor signalling and induces cell cycle arrest and apoptosis in leukaemic cells expressing FLT3 ITD or TKD mutant receptors or over-expressing FLT3 wild type receptors. In vitro data indicate that midostaurin inhibits D816V mutant KIT receptors at exposure levels achieved in patients (average achieved exposure higher than IC50). In vitro data indicate that KIT wild type receptors are inhibited to a much lesser extent at these concentrations (average achieved exposure lower than IC50). Midostaurin interferes with aberrant KIT D816V-mediated signalling and inhibits mast cell proliferation, survival and histamine release.
In addition, midostaurin inhibits several other receptor tyrosine kinases such as PDGFR (platelet-derived growth factor receptor) or VEGFR2 (vascular endothelial growth factor receptor 2), as well as members of the serine/threonine kinase family PKC (protein kinase C). Midostaurin binds to the catalytic domain of these kinases and inhibits the mitogenic signalling of the respective growth factors in cells, resulting in growth arrest.
Midostaurin in combination with chemotherapeutic agents (cytarabine, doxorubicin, idarubicin and daunorubicin) resulted in synergistic growth inhibition in FLT3-ITD expressing AML cell lines.
Pharmacodynamic effects
Two major metabolites have been identified in murine models and humans, i.e. CGP62221 and CGP52421. In proliferation assays with FLT3-ITD expressing cells, CGP62221 showed similar potency compared to the parent compound, however CGP52421 was approximately 10-fold less potent.
Cardiac electrophysiology
A dedicated QT study in 192 healthy subjects with a dose of 75 mg twice daily did not reveal clinically significant prolongation of QT by midostaurin and CGP62221 but the study duration was not long enough to estimate the QTc prolongation effects of the long-acting metabolite CGP52421. Therefore, the change from baseline in QTcF with the concentration of midostaurin and both metabolites was further explored in a phase II study in 116 patients with ASM, SM-AHN or MCL. At the median peak Cmin concentrations attained at a dose of 100 mg twice daily, neither midostaurin, CGP62221 nor CGP52421 showed a potential to cause clinically significant QTcF prolongation, since the upper bounds of predicted change at these concentration levels were less than 10 msecs (5.8, 2.4, and 4.0 msecs, respectively). In the ASM, SM-AHN and MCL population, 25.4% of patients had at least one ECG measurement with a QTcF greater than 450 ms and 4.7% greater than 480 ms.
Clinical efficacy and safety
AML
The efficacy and safety of midostaurin in combination with standard chemotherapy versus placebo plus standard chemotherapy and as single agent maintenance therapy was investigated in 717 patients (18 to 60 years of age) in a randomised, double-blind, phase III study. Patients with newly diagnosed FLT3-mutated AML as determined by a clinical study assay were randomised (1:1) to receive midostaurin 50 mg twice daily (n=360) or placebo (n=357) sequentially in combination with standard daunorubicin (60 mg/m2 daily on days 1-3) / cytarabine (200 mg/m2 daily on days 1-7) induction and high-dose cytarabine (3 g/m2 every 12 hours on days 1, 3, 5) consolidation, followed by continuous midostaurin or placebo treatment according to initial assignment for up to 12 additional cycles (28 days/cycle). While the study included patients with various AML-related cytogenetic abnormalities, patients with acute promyelocytic leukaemia (M3) or therapy-related AML were excluded. Patients were stratified by FLT3 mutation status: TKD, ITD with allelic ratio <0.7, and ITD with allelic ratio ≥0.7.
The two treatment groups were generally balanced with respect to the baseline demographics of disease characteristics. The median age of the patients was 47 years (range: 18 to 60 years), a majority of the patients had ECOG performance status of 0 or 1 (88.3%), and most patients had de novo AML (95%). Of the patients with race information reported, 88.1% were Caucasian. The majority of patients (77.4%) had FLT3-ITD mutations, most of them (47.6%) with a low allelic ratio (<0.7), and 22.6% of patients had FLT3-TKD mutations. Forty-eight per cent were male in the midostaurin arm and 41% in the placebo arm.
Patients who proceeded to haematopoietic stem cell transplant (SCT) stopped receiving study treatment prior to the start of the SCT conditioning regimen. The overall rate of SCT was 59.4% (214/360) of patients in the midostaurin plus standard chemotherapy arm versus 55.2% (197/357) in the placebo plus standard chemotherapy arm. All patients were followed for survival.
The primary endpoint of the study was overall survival (OS), measured from the date of randomisation until death by any cause. The primary analysis was conducted after a minimum follow-up of approximately 3.5 years after the randomisation of the last patient. The study demonstrated a statistically significant improvement in OS with a 23% risk reduction of death for midostaurin plus standard chemotherapy over placebo plus standard chemotherapy (see Table 6 and Figure 1).
Figure 1 Kaplan-Meier curve for overall survival, non-censored for SCT
The key secondary endpoint was event-free survival (EFS; an EFS event is defined as a failure to obtain a complete remission (CR) within 60 days of initiation of protocol therapy, or relapse, or death from any cause). The EFS showed a statistically significant improvement for midostaurin plus standard chemotherapy over placebo plus standard chemotherapy (HR: 0.78 [95% CI, 0.66 to 0.93] p = 0.0024), and a median EFS of 8.2 months and 3.0 months, respectively; see Table 5.
Table 5 Efficacy of midostaurin in AML
| Efficacy parameter | Midostaurin n=360 | Placebo n=357 | HR* (95% CI) | P-value¥ |
| Overall survival (OS)1 |
| Median OS in months (95% CI) | 74.7 (31.5, NE) | 25.6 (18.6, 42.9) | 0.77 (0.63, 0.95) | 0.0078 |
| Kaplan-Meier estimates at 5 years (95% CI) | 0.51 (0.45, 0.56) | 0.43 (0.38, 0.49) | | |
| Event-free survival (EFS)2 |
| Median EFS in months, considering CRs within 60 days of treatment start (95% CI) | 8.2 (5.4, 10.7) | 3.0 (1.9, 5.9) | 0.78 (0.66, 0.93) | 0.0024 |
| Median EFS in months, considering CRs any time during induction (95% CI) | 10.2 (8.1, 13.9) | 5.6 (2.9, 6.7) | 0.73 (0.61, 0.87) | 0.0001 |
| Disease-free survival (DFS) |
| Median DFS in months (95% CI) | 26.7 (19.4, NE) | 15.5 (11.3, 23.5) | 0.71 (0.55, 0.92) | 0.0051 |
| Complete remission (CR) |
| within 60 days of treatment start (%) | 212 (58.9) | 191 (53.5) | NE | 0.073§ |
| any time during induction (%) | 234 (65.0) | 207 (58.0) | NE | 0.027§ |
| Cumulative incidence of relapse (CIR) |
| Median (95% CI) | NE (25.7, NE) | 17.6 (12.7, 46.3) | 0.68 (0.52, 0.89) | 0.0023 |
| 1primary endpoint; 2key secondary endpoint; NE: Not Estimated * Hazard ratio (HR) estimated using Cox regression model stratified according to the randomisation FLT3 mutation factor. ¥1-sided p-value calculated using log-rank test stratified according to the randomisation FLT3 mutation factor. §Not significant |
There was a trend favouring midostaurin for CR rate by day 60 for the midostaurin arm (58.9% versus 53.5%; p = 0.073) that continued when considering all CRs during induction (65.0% versus 58.0%; p = 0.027). In addition, in patients who achieved complete remission during induction, the cumulative incidence of relapse at 12 months was 26% in the midostaurin arm versus 41% in the placebo arm.
Sensitivity analyses for both OS and EFS when censored at the time of SCT also supported the clinical benefit with midostaurin plus standard chemotherapy over placebo.
Results for OS by SCT status are shown in Figure 2. For EFS, considering complete remissions within 60 days of study treatment start, the HR was 0.602 (95% CI: 0.372, 0.974) for patients with SCT and 0.827 (95% CI: 0.689, 0.993) for patients without SCT, favouring midostaurin.
Figure 2 Kaplan Meier curve for overall survival by SCT status in AML
In a subgroup analysis, no apparent OS benefit was observed in females, however, a treatment benefit was observed in females in all secondary efficacy endpoints (see Table 6).
Table 6 Overview of OS, EFS, CR, DFS and CIR by gender in AML
| Endpoint | Overall 95% CI | Males 95% CI | Females 95% CI |
| OS (HR) | 0.774 (0.629, 0.953) | 0.533 (0.392, 0.725) | 1.007 (0.757, 1.338) |
| EFS (CR induction) (HR) | 0.728 (0.613, 0.866) | 0.660 (0.506, 0.861) | 0.825 (0.656, 1.037) |
| CR induction (OR) | 0.743* (0.550, 1.005) | 0.675* (0.425, 1.072) | 0.824* (0.552, 1.230) |
| DFS (CR induction) (HR) | 0.663 (0.516, 0.853) | 0.594 (0.408, 0.865) | 0.778 (0.554, 1.093) |
| CIR (CR induction) (HR) | 0.676 (0.515, 0.888) | 0.662 (0.436, 1.006) | 0.742 (0.516, 1.069) |
| *Odds ratio calculated as (No complete remission in treatment/Complete remission in treatment) / (No complete remission in placebo/complete remission in placebo) HR= Hazard ratio; OR=odds ratio |
Efficacy and safety in patients >60-70 years old were evaluated as part of a phase II, single-arm, investigator-initiated study of midostaurin in combination with intensive induction, consolidation including allogenic SCT and single-agent maintenance in patients with FLT3-ITD mutated AML. Based on the final analysis, the EFS rate at 2 years (primary endpoint) was 34% (95% CI: 27, 44) and the median OS was 22.7 months in patients older than 60 years of age (128 out of 440 patients).
ASM, SM-AHN and MCL
The efficacy of midostaurin in patients with ASM, SM-AHN and MCL, collectively referred to as advanced systemic mastocytosis (SM), was evaluated in two open-label, single-arm, multicentre studies (142 patients in total).
The pivotal study was a multicentre, single-arm phase II study in 116 patients with advanced SM (Study CPKC412D2201). Midostaurin was administered orally at 100 mg twice daily until disease progression or intolerable toxicity. Of the 116 patients enrolled, 89 were considered eligible for response assessment and constituted the primary efficacy population. Of these, 73 patients had ASM (57 with an AHN) and 16 patients had MCL (6 with an AHN). The median age in the primary efficacy population was 64 years with approximately half of the patients ≥65 years. Approximately one third (36%) received prior anti-neoplastic therapy for ASM, SM-AHN or MCL. At baseline in the primary efficacy population, 65% of the patients had >1 measurable C finding (thrombocytopenia, hypoalbuminaemia, anaemia, high total bilirubin, transfusion-dependent anaemia, weight loss, neutropenia, high ALT or high AST). The KIT D816V mutation was detected in 82% of patients.
The primary endpoint was overall response rate (ORR). Response rates were assessed based on the modified Valent and Cheson criteria and responses were adjudicated by a study steering committee. Secondary endpoints included duration of response, time to response, and overall survival. Responses to midostaurin are shown in Table 7. Activity was observed regardless of number of prior therapies, and presence or absence of an AHN. Confirmed responses were observed in both KIT D816V mutation positive patients (ORR=63%) and KIT D816V wild type or unknown patients (ORR=43.8%). However, the median survival for KIT D816V positive patients was longer, i.e. 33.9 months (95% CI: 20.7, 42), than for KIT D816V wild type or unknown patients, i.e. 10 months (95% CI: 6.9, 17.4). Forty-six percent of patients had a decrease in bone marrow infiltration that exceeded 50% and 58% had a decrease in serum tryptase levels that exceeded 50%. Spleen volume decreased by ≥10% in 68.9% of patients with at least 1 post-baseline assessment (26.7% of patients had a reduction of ≥35%, which correlates with a 50% decrease by palpation).
The median time to response was 0.3 months (range: 0.1 to 3.7 months). The median duration of follow-up was 43 months.
Table 7 Efficacy of midostaurin in ASM, SM-AHN and MCL: primary efficacy population
| | All | ASM | SM-AHN | MCL |
| N=89 | N=16 | N=57 | N=16 |
| Primary endpoint |
| Overall response, n (%) | 53 (59.6) | 12 (75.0) | 33 (57.9) | 8 (50.0) |
| (95% CI) | (48.6, 69.8) | (47.6, 92.7) | (44.1, 70.9) | (24.7, 75.3) |
| Major response, n (%) | 40 (44.9) | 10 (62.5) | 23 (40.4) | 7 (43.8) |
| Partial response, n (%) | 13 (14.6) | 2 (12.5) | 10 (17.5) | 1 (6.3) |
| Stable disease, n (%) | 11 (12.4) | 1 (6.3) | 7 (12.3) | 3 (18.8) |
| Progressive disease, n (%) | 10 (11.2) | 1 (6.3) | 6 (10.5) | 3 (18.8) |
| Secondary endpoints |
| Median duration of response, months (95% CI) | 18.6 (9.9, 34.7) | 36.8 (5.5, NE) | 10.7 (7.4, 22.8) | NR (3.6, NE) |
| Median overall survival, months (95% CI) | 26.8 (17.6, 34.7) | 51.1 (28.7, NE) | 20.7 (16.3, 33.9) | 9.4 (7.5, NE) |
| Kaplan-Meier estimates at 5 years (95% CI) | 26.1 (14.6, 39.2) | 34.8 (1.7, 76.2) | 19.9 (8.6, 34.5) | 33.7 (12.3, 56.8) |
| NE: Not Estimated, NR: Not Reached Patients who received non-study anti-neoplastic therapy were considered as having progressed at the time of the new therapy. |
Although the study was designed to be assessed with the modified Valent and Cheson criteria, as a post-hoc exploratory analysis, efficacy was also assessed per the 2013 International Working Group - Myeloproliferative Neoplasms Research and Treatment - European Competence Network on Mastocytosis (IWG-MRT-ECNM) consensus criteria. Response to Rydapt was determined using a computational algorithm applied without any adjudication. Out of 116 patients, 113 had a C-finding as defined by IWG response criteria (excluding ascites as a C-finding). All responses were considered and required a 12-week confirmation (see Table 8).
Table 8 Efficacy of midostaurin in ASM, SM-AHN and MCL per IWG-MRT-ECNM consensus criteria using an algorithmic approach
| | All patients evaluated | ASM | SM-AHN | MCL | Subtype unknown |
| N=113 | N=15 | N=72 | N=21 | N=5 |
| Overall response rate, n (%) | 32 (28.3) | 9 (60.0) | 15 (20.8) | 7 (33.3) | 1 (20.0) |
| (95% CI) | (20.2, 37.6) | (32.3, 83.7) | (12.2, 32.0) | (14.6, 57.0) | (0.5, 71.6) |
| Best overall response, n (%) |
| Complete remission | 1 (0.9) | 0 | 0 | 1 ( 4.8) | 0 |
| Partial remission | 17 (15.0) | 5 (33.3) | 8 (11.1) | 3 (14.3) | 1 (20.0) |
| Clinical improvement | 14 (12.4) | 4 (26.7) | 7 (9.7) | 3 (14.3) | 0 |
| Duration of response* |
| n/N (%) | 11/32 (34.4) | 4/9 (44.4) | 4/15 (26.7) | 3/7 (42.9) | 0/1 (0.0) |
| median (95% CI) | NE (27.0, NE) | 36.8 (10.3, 36.8) | NE (17.3, NE) | NE (4.1, NE) | NE |
| Overall survival |
| n/N (%) | 65/113 (57.5) | 4/15 (26.7) | 49/72 (68.1) | 12/21 (57.1) | 0/5 (0.0) |
| median (95% CI) | 29.9 (20.3, 42.0) | 51.1 (34.7, NE) | 22.1 (16.8, 32.2) | 22.6 (8.3, NE) | NE |
| *Confirmation period for responses: 12 weeks Analysis excludes ascites as a C-finding. Patients who received non-study anti-neoplastic therapy were considered as having progressed at the time of the new therapy. |
The supportive study was a single-arm, multicentre, open-label phase II study of 26 patients with ASM, SM-AHN and MCL (CPKC412A2213). Midostaurin was administered orally at 100 mg twice daily in cycles of 28 days. Lack of a major response (MR) or partial response (PR) by the end of the second cycle required discontinuation from the study treatment. Twenty (76.9%) patients had ASM (17 [85%] with AHN) and 6 patients (23.1%) had MCL (2 [33.3%] with AHN). The median age was 64.5 years with half of the patients ≥65 years). At baseline, 88.5% had >1 C finding and 69.2% had received at least one prior anti-neoplastic regimen.
The primary endpoint was ORR evaluated by the Valent criteria during the first two cycles of treatment. Nineteen patients (73.1%; 95% CI = [52.2, 88.4]) achieved a response during the first two cycles of treatment (13 MR; 6 PR). The median duration of follow-up was 73 months, and the median duration of response has not been reached. Median overall survival was 40.0 months (patients were only followed up for one year after treatment discontinuation for survival).
Paediatric population
In a phase II study, midostaurin was investigated in combination with chemotherapy in newly diagnosed paediatric patients with FLT3-mutated AML. Among the three FLT3-mutated AML patients enrolled in the study, two patients (10 and 14 years old) experienced dose limiting toxicities (DLTs) following the second induction cycle with midostaurin (at 30 mg/m2 twice daily) in combination with chemotherapy (containing cytarabine 2 g/m2/day, day 1-5; fludarabine 30 mg/m2/day, day 1-5 and idarubicin 12 mg/m2/day, day 2, 4 and 6). Both patients showed markedly delayed haematological recoveries (i.e. prolonged grade 4 thrombocytopenia lasting for 44 days in the first patient and 51 days in the second patient and grade 4 neutropenia lasting for 46 days in the second patient). In the first induction cycle both patients received midostaurin in combination with cytarabine, etoposide and idarubicin.
The European Medicines Agency has waived the obligation to submit the results of studies with Rydapt in all subsets of the paediatric population in the treatment of malignant mastocytosis and mast cell leukaemia (see section 4.2 for information on paediatric use).
The European Medicines Agency has deferred the obligation to submit the results of studies with Rydapt in one or more subsets of the paediatric population in the treatment of acute myeloid leukaemia (see section 4.2 for information on paediatric use).