Phase 2 Study of Flonoltinib Maleate Oral Regimens in Patients With Myelofibrosis

Flonoltinib Maleate (FM) is a triple-targeted inhibitor of JAK2/FLT3/cyclin-dependent kinase 6 (CDK6). Cocrystal structure of JAK2-JH2 domain in complex with FM revealed that FM binds both to the pseudokinase domain (JH2) and kinase domain (JH1) of JAK2 and achieves high selectivity for the JAK family. FM has potent inhibitory activity against JAK family. The concentration required for 50% inhibition (IC50) of FM against JAK2 kinase is 0.8 nM, while the inhibitory IC50 of FM against JAK1, JAK3, and TYK2 kinases are 690 nM, 557 nM, and 65 nM, respectively, with a selective multiplicity of 862.5-fold, 696.3-fold, and 81.3-fold. FM has moderate inhibitory activity against FLT3 and CDK6, with IC50 values of 15 nM and 35 nM, respectively.

The Phase 2 FMF-02 study (NCT06457425) was a multi-center, open-label, randomized, controlled, parallel-cohort evaluating the efficacy and safety of FM compared to ruxolitinib in patients with intermediate-2 or high-risk MF. Key hematologic criteria for inclusion included PLT ≥50×109/L and HGB >60 g/L. A total of 75 patients were enrolled in three cohorts: (i) 25 patients in the FM low-dose cohort receiving 50 mg of FM once daily, (ii) 26 patients in the FM high-dose cohort receiving 100 mg of FM once daily, and (iii) 24 patients in the ruxolitinib twice daily cohort, with the starting dose determined based on the patient's baseline platelet levels. The study met its primary endpoint at week 24, demonstrating superior ≥ 35% reduction in spleen volume (SVR35) rates for both FM high (100mg qd) (FMH) and low dose (50mg qd) (FML) cohorts versus the ruxolitinib cohort (RUX). Patients in the RUX arm who completed 24 weeks of therapy or had progressive disease due to splenomegaly could cross over to FML or FMH group. Efficacy and safety endpoints were assessed at week 48, included SVR35, TSS50, bone marrow fibrosis improvement, and safety. With a median follow up of 60 weeks, 68 patients (90%) entered the extension phase, including 12 and 10 patients crossing over from RUX to FML and FMH respectively. At week 48, among evaluable patients on treatment, SVR35 was achieved/maintained in 74% (17/23) in FML and 95% (20/21) in FMH, compared with 80% (8/10) in RUX FML and 100% (9/9) in RUX FMH. Among the 19 crossover patients, 3 of 5 (60%) who had suboptimal responses to RUX at week 24 achieved SVR35 by week 48, with most crossovers showing deeper responses over time. At week 48, TSS50 response rates were 96% (22/23) in FML and 81% (17/21) in FMH, versus 60% (6/10) in RUX FML and 78% (7/9) in RUX FMH, with continued durability of symptom improvement observed through long-term follow-up. Durable dual SVR35 and TSS50 responses were observed in FML and FMH arms, with consistent benefit across subgroups through week 48, including patients with baseline platelet counts <100 × 10⁹/L (3/3 in FML and 1/1 in FMH achieved dual response at week 48). Bone marrow fibrosis grade was stable or improved in 86% (19/22), 84% (16/19), 100% (9/9), and 100% (9/9) in FML, FMH, RUX FML and RUX FMH cohorts, respectively, among patients with evaluable week 48 biopsies. JAK2 V617F mutation variant allele frequency, was assessed at the end of treatment versus baseline, 2 of the 3 patients in the FMH group showed a reduction from baseline, with 1 patient achieving a 30% decrease. The most common Grade ≥3 hematologic treatment-emergent adverse event (TEAE) was anemia, with incidences of 4%, 14%, 8%, and 20% in extension period, respectively-markedly lower than rates observed during the initial 24 week period. No Grade ≥3 non hematologic TEAEs were reported in any of the four arms. Dose reductions due to TEAEs occurred in 13% (3/24), 27% (6/22), 8% (1/12), and 30% (3/10) of patients in the respective arms during the extension period, consistent with improved tolerability on long term treatment. Thus at week 48, spleen volume and TSS improvements were sustained in both FM cohorts. Patients who switched from RUX to FM after week 24 experienced additional benefits. These findings provided a compelling rationale for the continued development of FM for patients with MF including the conduct of this FM-MF-02 study.

This study is designed to characterize dose-response and support Recommended Phase 3 Dose (RP3D) selection for an intended randomized study of FM versus JAKi in patients with advanced refractory MF. This study will enroll 105 fully evaluable patients, including 42 JAKi-naïve and 63 JAKi-resistant patients randomized to 3 dose cohorts (50 mg, 75 mg, 100 mg), with 35 patients per cohort. The study will is characterize the dose-response relationship of FM in patients with MF by evaluation of efficacy, safety and tolerability, pharmacokinetic (PK) profile, and pharmacodynamic (PD) effects. After signing the informed consent form (ICF), patients will undergo a 2-week screening period to confirm eligibility, followed by baseline assessments before entering the clinical study.

Participants in the 50 mg, 75 mg and 100 mg cohorts are concurrently enrolled and randomized. One stratification factor will be applied: intermediate-1 vs. intermediate-2/high for JAKi-naïve participants and JAKi-resistant participants.

Participants will be dosed for 28 consecutive days (a cycle) in a fasting state starting on the morning of Day 1. Blood samples from 20 participants in each cohort will be collected according to the PK and biomarker sample collection time points. Participants will undergo safety evaluations (conducted on Days 14 and 28 of Cycles 1 to 2, Day 28 of Cycles 3, 4, 5, and 6, and every 3 treatment cycles [12 weeks] of subsequent dosing therapy). Participants will receive continuous treatment until unacceptable toxicities, progressive disease or meeting other stopping criteria. The key safety endpoints and clinical efficacy endpoints in this trial will be evaluated at the end of 6 cycles (24 weeks). Other efficacy and safety evaluations will be conducted every 3-6 cycles. Safety follow-up will be conducted 30 days after the last dose and all participants will be followed up for adverse events, serious adverse events (SAEs), and concomitant medication (including any new therapy) for 30 days following last FM dose. Dose adjustment shall be implemented based on hematologic/non-hematologic toxicities observed during treatment. Dose escalation may be considered for suboptimal response.

Cardiac safety will be monitored using a structured QTc Monitoring Plan. ECGs will be performed at baseline and at prespecified on-treatment time points, with additional assessments as clinically indicated. Predefined QTc thresholds will guide clinical management, including repeat ECG evaluation, assessment of electrolyte abnormalities and concomitant medications (other assessments such as cardiac biomarker, echocardiogram may be needed per institutional guideline), and implementation of dose interruption, modification, or discontinuation as appropriate. Clinically significant QTc prolongation or related cardiac events will trigger Safety Review Committee (SRC) review. Persistent or clinically significant QTc abnormalities may result in treatment discontinuation in accordance with Participant-level stopping criteria.

Study or cohort-level stopping decisions will be based on an integrated assessment of safety and efficacy by the SRC. An interim futility assessment will be performed at the earlier of 75% of participants enrolled, or after approximately 50% of participants in each dose cohort have completed the Week 12 evaluation. If the observed response rate (SVR35) is below 30%, the SRC may recommend discontinuation of that cohort.

Safety-based stopping criteria include:

• Treatment-related Grade 3 or higher adverse events leading to discontinuation in approximately ≥30% of patients
• Treatment-related hematologic SAEs in approximately ≥30% of patients
• Recurrent treatment-related fatal adverse events
• Clustering of QTcF ≥500 ms events Final decisions will be based on the totality of available safety and efficacy data.

Detailed study-level stopping criteria and patient-level discontinuation criteria are provided in the protocol.

The statistical analysis framework is based on dose-response characterization and an estimand-based approach, including predefined handling of intercurrent events and missing data. Statistical analyses will be conducted using SAS software version 9.4 (or above). Continuous variables will be summarized using the number of observations, mean, standard deviation, median, first quartile, third quartile, minimum, maximum, and, for outcomes, CIs. Categorical variables will be summarized using counts, percentages and, for outcomes, CIs. Time to Event variables will be summarized by number of observed events, median and associated CI. Comparisons between treatment doses will be based on normal regression for continuous variables, and logistic regression for categorical variables. Mixed Models with Repeated Measures will be used to assess the average treatment effect post-baseline on continuous variables. Dose will be fitted as a categorical variable, and models adjusted for baseline values. The 95% CIs for treatment effects will be presented, and for categorical variables, converted to risk differences for the observed population risk.

No adjustment will be made for multiple comparisons between treatment cohorts since this is a Phase 2 study, and no formal conclusions of efficacy will be drawn. Methods of statistical analysis of tolerance and safety The study will statistically analyze the tolerability data at different time points and doses. The tolerability analysis will be primarily descriptive. Safety statistical analysis includes statistical analysis of the incidence of adverse events/adverse reactions, list of adverse events, vital signs, laboratory tests, physical examination results, ECG examination, etc.

PK statistical analysis methodology Plasma PK concentrations will be summarized by nominal sample time and by dose cohort. The PK data will also be displayed graphically. For the intensively sampled data, PK parameters including but not limited to Cmax, Tmax, t1/2, and AUC will be determined from the concentration-time profile using standard noncompartmental approaches. Dose proportionality may also be evaluated.

The PK data may also be included in population PK modelling analysis and exposure-response analysis, and the results will be reported separately

Inclusion criteria

All participants must:

• Have signed the current relevant ICF prior to any study related procedures;
• Understand and commit to comply with study requirements;
• Be ≥18 years of age;
• Be able to swallow and retain oral medications;
• Be diagnosed with PMF according to the 2016 WHO criteria, or PPV-MF or PET-MF according to International Working Group for Myelofibrosis Research and Treatment (IWG-MRT) criteria;
• Have Intermediate-1 to high-risk myelofibrosis (as per Dynamic International Prognostic Scoring System [DIPSS] risk categories) and be either JAKi-naïve or JAKi-resistant. JAKi-naïve patients include those with JAKi exposure of no more than 14 days. The JAKi-resistant patients need to meet 1 of the following criteria: a) Treatment with JAKi for 3 months with inadequate efficacy response defined as < 10% spleen volume reduction (SVR) by Magnetic Resonance Imaging (MRI) or <30% decrease from baseline in spleen size by palpation or regrowth to these parameters following an initial response; b) Treatment with JAKi for ≥28 days complicated by any of the following: development of a red blood cell transfusion requirement (at least 2 units/month for 2 months) or cytopenia-related intolerance requiring ≥2 dose reductions or discontinuation of a JAKi; c) Persistent MF-related symptoms defined as less than 50% reduction in TSS (MFSAF V 4.0) after 3 months of JAKi therapy;
• Not be intended to undergo stem cell transplantation for at least 6 months;
• Have life expectancy per investigator assessment ≥ 12 weeks;
• Have Eastern Cooperative Oncology Group (ECOG) score ≤ 2;
• Have splenomegaly: palpable spleen extending at least 5 cm below the costal margin or unpalpable due to body habitus (obesity), but confirmed to be ≥450 cm³ by MRI (or computed tomography [CT] scan) at screening;
• Have at least 2 symptoms with an average score ≥3 over the 7-day period prior to randomization or an average total score of ≥10 over the 7-day period prior to randomization using the Myelofibrosis Symptom Assessment Form (MFSAF) v4.0;
• Have bone marrow blast cells ≤10% and peripheral blood blast cells ≤10%;
• Have PLT ≥50 × 109 /L and absolute neutrophil count (ANC) ≥ 1.0 × 109 /L and hemoglobin (HGB) >60 g/L without the assistance of CSF, EPO, TPO, or component blood transfusions. Have discontinued growth factors and platelets transfusions for more than 2 weeks before screening tests;
• Have no overt significant disease involving heart, lungs, liver, kidneys, or pancreas (left ventricular ejection fraction ≥ 45%; serum direct bilirubin ≤2 × upper limit of normal [ULN]; serum creatinine ≤1.5 × ULN or Estimated Glomerular Filtration Rate [eGFR] by the 2021 chronic kidney disease-Epidemiology Collaboration formula ≥ 45 mL/min/1.73 m2; alanine aminotransferase [ALT] and aspartate aminotransferase [AST] ≤2.5 × ULN) or ≤5 × ULN if associated with liver MF involvement;
• Have no severe coagulation dysfunction (prothrombin time [PT] or thrombin time [TT] ≤2 × ULN; activated partial thromboplastin time [APTT] ≤2 × ULN);
• Have a normal thiamine level at the time of study entry;
• Agree to comply with the relevant regulations of the treating institution and the research organization.

Exclusion criteria

Participants must not:

• Have failure to recover from toxic effects of prior anticancer therapy to Grade 1 or below (except alopecia), or failure to fully recover from prior surgery (major surgery within 4 weeks);
• Have known hypersensitivity to the investigational product or its excipients;
• Have any significant clinical or laboratory abnormality that would interfere with accurate safety evaluation on study, including:

• Uncontrolled diabetes with fasting blood glucose >250 mg/dL (13.9 mmol/L);
• Hypertension not controlled by one or two antihypertensive drugs to the following range: systolic <160 mmHg, diastolic <100 mmHg;
• Peripheral neuropathy of Grade 2 or higher according to Common Terminology Criteria for Adverse Events (CTCAE) v6.0;
• Thyroid dysfunction of Grade 2 or higher per CTCAE v6.0;
• Any other relevant abnormality in the opinion of the investigator;
• Have a history of congestive heart failure, unstable angina, myocardial infarction, cerebrovascular accident, or pulmonary embolism within the 6 months prior to screening;
• Have impaired cardiac function including any of the following conditions as determined by echocardiogram or electrocardiogram (ECG): left ventricular ejection fraction less than 45%, or complete left bundle branch block with ST-segment depression greater than 1 mm or T-wave inversion across 2 or more leads. Other criteria include congenital ventricular arrhythmias, clinically significant tachycardia (greater than 100 beats per minute), bradycardia (less than 50 beats per minute) with accompanying clinical symptoms, heart rate less than 60 beats per minute with symptoms, an ECG Corrected QT Interval (QTc) interval greater than 450 ms, or clinically significant cardiac conditions such as unstable angina, congestive heart failure, or myocardial infarction occurring within the last 6 months. Patients with heart failure who meet New York Heart Association class III and IV definitions are ineligible for this study;
• Have an active serious infection requiring treatment at the time of screening;
• Have undergone splenectomy or who have received splenic irradiation within 6 months prior to screening;
• Have Human Immunodeficiency Virus (HIV) positive, active Hepatitis B (Hepatitis B Surface Antigen [HBsAg] positive and Hepatitis B Virus [HBV]-DNA ≥1000 copies/mL), or positive for Hepatitis C Virus (HCV) antibodies or HCV-RNA at screening;
• Have epilepsy or are taking psychotropic or sedative medications at screening;
• Be women of childbearing potential (WOCBP): who are unwilling or unable to practice highly effective contraception before the initial dose/start of the first treatment, during the study, and for at least 6 months after the last dose. Highly effective contraceptive measures include:

i) Stable use of combined (estrogen and progestogen-containing) hormonal contraception (oral, intravaginal, transdermal) or progestogen-only hormonal contraception (oral, injectable, implantable) associated with inhibition of ovulation initiated 2 or more menstrual cycles before screening; ii) Intrauterine device; intrauterine hormone-releasing system; iii) Sexual abstinence; iv) Intercourse with a vasectomized partner (the male vasectomized partner is the sole sexual partner of the WOCBP study patient, the vasectomized partner has obtained medical assessment of surgical success for the procedure);

• Be sexually active male patients with WOCBP partners who are unwilling to use 1 of the following forms of medically acceptable birth control at the start of the first treatment, during the study, and for at least 6 months after the last dose:

i) Vasectomy with medical assessment of surgical success or consistent use of a condom; ii) Male Participants must also agree not to donate sperm while receiving the investigational product and for at least 6 months after the last dose;

• Have a history of malignancy within the 3 years prior to study screening (except for successfully treated basal cell carcinoma of the skin or carcinoma in situ of the cervix);
• Have any other severe illnesses that the investigator feels may jeopardize Participant safety or compliance;
• Have participated in an investigational agent or medical device study within 1 month prior to screening;
• Have prior or concomitant treatment with any of the following: any myelofibrosis therapy (except hydroxyurea that may be stopped one day before first dose; prior JAKi is allowed with a ≥14 day washout); any immunomodulators (e.g., thalidomide); any immunosuppressants; androgenic steroids systemic corticosteroids ≥10 mg/day prednisone equivalent; or any growth factor (e.g., EPO) within 5 half lives or 2 weeks before enrollment (whichever is longer);
• Have received potent or moderate cytochrome P450 (CYP)3A4 inhibitors (including but not limited to ketoconazole, clarithromycin, itraconazole, nefazodone, telithromycin) or potent CYP3A4 inducers (including but not limited to rifampin and St. John's wort) within 2 weeks before the first dose;
• Have received concomitant QT-prolonging medications that cannot be discontinued or appropriately managed in accordance with the QTc Monitoring Plan;
• Have received concomitant strong inhibitors/inducers of P-gp or Breast Cancer Resistance Protein (BCRP)；
• Have congenital or acquired bleeding disorders;
• Be alcohol dependent or drug abusers;
• Consume grapefruit, starfruit, or their products within 48 hours of the first dose of study medication, or be unwilling to abstain from such products while on study as these substances may affect drug absorption, distribution, metabolism, or excretion;
• Have any other severe and/or uncontrolled concomitant medical condition that in the opinion of the investigator could compromise participation in the study or analysis of study data.

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