A randomized, placebo-controlled study of the pharmacokinetics, pharmacodynamics, and tolerability of the oral JAK2 inhibitor fedratinib (SAR302503) in healthy volunteers

Fedratinib in 2025 and beyond: indications and future applications

ABSTRACT

Dysregulated JAK/STAT signaling underlies the pathogenesis of myelofibrosis, a myeloproliferative neoplasm characterized by cytopenias, splenomegaly, and constitutional symptoms. JAK inhibitors, such as fedratinib, are the primary therapeutic option for patients with high-risk or symptomatic myelofibrosis. Fedratinib has characteristics that distinguish it from other commercially available JAK inhibitors, such as its preferential inhibition of JAK2 and its inhibitory effects on kinases such as Fms-like tyrosine kinase 3 and BRD4. Fedratinib is most often used in the second-line setting after intolerance or resistance to other JAK inhibitors, but there is substantial evidence that it is an effective first-line option in the appropriate patient population. Prevention and early treatment of fedratinib-related gastrointestinal toxicity is key to maintaining adequate drug exposure, and clinicians must remain vigilant for Wernicke encephalopathy during treatment. Fedratinib's JAK2 selectivity and kinome profile make it an appealing agent for alternative indications, such as myelodysplastic/myeloproliferative neoplasms and maintenance after bone marrow transplantation, which are under active investigation.

Advancements in physiologically based pharmacokinetic modeling for fedratinib: updating dose guidance in the presence of a dual inhibitor of CYP3A4 and CYP2C19

PURPOSE

A physiologically based pharmacokinetic (PBPK) model for fedratinib was updated and revalidated to bridge a gap between the observed drug-drug interaction (DDI) of a single sub-efficacious dose in healthy participants and the potential DDI in patients with cancer at steady state. The study aimed to establish an appropriate dose for fedratinib in patients coadministered with dual CYP3A4 and CYP2C19 inhibitors, providing quantitative evidence to inform dosing guidance.

METHODS

The original minimal PBPK model was developed using Simcyp® Simulator v17. The model was updated by substituting a single distribution rate (Qsac) with 2 separate rates (CLin/CLout) and transitioning to v20. Model parameter updates were further informed with 3 clinical studies, and 3 more studies served as independent validation data. The validated model was applied to simulate potential DDIs between fedratinib and a known dual inhibitor of CYP3A4 and CYP2C19 (fluconazole).

RESULTS

Coadministration of fedratinib with fluconazole in patients was predicted to increase fedratinib exposure by < 2-fold in all simulated scenarios. For patients with cancer receiving the approved dose of fedratinib 400 mg once daily along with fluconazole 200 mg daily, the model predicted an approximate 50% increase in fedratinib exposure at steady state.

CONCLUSIONS

The updated PBPK model improved description of the observed pharmacokinetics and predicted a low risk of clinically significant DDIs between fedratinib and fluconazole. The quantitative evidence serves as a primary foundation for providing dose guidance in clinical practice for the coadministration of fedratinib with dual CYP3A4 and CYP2C19 inhibitors.

Synthesis and clinical application of small-molecule inhibitors of Janus kinase

Janus kinase (JAK) plays a crucial role in intracellular signaling pathways, particularly in cytokine-mediated signal transduction, making them attractive therapeutic targets for a wide range of diseases, including autoimmune disorders, myeloproliferative neoplasms, and inflammatory conditions. The review provides a comprehensive overview of the development and therapeutic potential of small-molecule inhibitors targeting JAK family of proteins in various clinical trials. It also discusses the mechanisms of action, specificity, and selectivity of these inhibitors, shedding light on the challenges associated with achieving target selectivity while minimizing off-target effects. Moreover, the review offers insights into the clinical applications of JAK inhibitors, summarizing the ongoing clinical trials and the Food and Drug Administration (FDA)-approved JAK inhibitors currently available for various diseases. Overall, this review provides a thorough examination of the synthesis and clinical use of typical small-molecule JAK inhibitors in different clinical stages and offers a bright future for the development of novel small-molecule JAK inhibitors.

Ten years after ruxolitinib approval for myelofibrosis: a review of clinical efficacy

Myelofibrosis (MF) is a chronic myeloproliferative neoplasm characterized by splenomegaly, abnormal cytokine expression, cytopenias, and progressive bone marrow fibrosis. The disease often manifests with burdensome symptoms and is associated with reduced survival. Ruxolitinib, an oral Janus kinase (JAK) 1 and JAK2 inhibitor, was the first agent approved for MF. As a first-in-class targeted treatment, ruxolitinib approval transformed the MF treatment approach and remains standard of care. In addition, targeted inhibition of JAK1/JAK2 signaling, a key molecular pathway underlying MF pathogenesis, and the large volume of literature evaluating ruxolitinib, have led to a better understanding of the disease and improved management in general. Here we review ruxolitinib efficacy in patients with MF in the 10 years following approval, including demonstration of clinical benefit in the phase 3 COMFORT-I/II trials, real-world evidence, translational studies, and expanded access data. Lastly, future directions for MF treatment are discussed, including ruxolitinib-based combination therapies.

An evaluation of fedratinib for adult patients with newly diagnosed and previously treated myelofibrosis

INTRODUCTION

Myelofibrosis (MF) is a life-shortening myeloproliferative neoplasm that has multiple features such as clonal proliferation, fibrosis and splenomegaly. Until recently, ruxolitinib, a Janus Kinase (JAK) 1/2 inhibitor was the only targeted therapy approved for transplant-ineligible patients with MF and who require treatment for symptoms and/or splenomegaly. However, the discontinuation rate with ruxolitinib at 3 to 5 years is high and mostly due to loss of response or toxicity, and these patients had no subsequent treatment.

AREAS COVERED

Fedratinib, a selective JAK2 inhibitor, was approved by the Food and Drug Administration (FDA) in August 2019 for the treatment of intermediate-2 or high-risk primary or secondary MF, regardless of prior JAK inhibitor treatment for the management of symptoms and splenomegaly. We discuss herein the development of fedratinib and its pharmacology and pharmacokinetics as well as the clinical development and the future directions. We used PubMed for the search of articles related to fedratinib and myelofibrosis.

EXPERT OPINION

Fedratinib provided a second-line treatment for patients with MF who failed or discontinued ruxolitinib. New combinations of JAK inhibitors with other targeted therapies are a must in order to improve the management of MF.

STAT3 Activation as a Predictive Biomarker for Ruxolitinib Response in Head and Neck Cancer

PURPOSE

Increased activity of STAT3 is associated with progression of head and neck squamous cell carcinoma (HNSCC). Upstream activators of STAT3, such as JAKs, represent potential targets for therapy of solid tumors, including HNSCC. In this study, we investigated the anticancer effects of ruxolitinib, a clinical JAK1/2 inhibitor, in HNSCC preclinical models, including patient-derived xenografts (PDX) from patients treated on a window-of-opportunity trial.

EXPERIMENTAL DESIGN

HNSCC cell lines were treated with ruxolitinib, and the impact on activated STAT3 levels, cell growth, and colony formation was assessed. PDXs were generated from patients with HNSCC who received a brief course of neoadjuvant ruxolitinib on a clinical trial. The impact of ruxolitinib on tumor growth and STAT3 activation was assessed.

RESULTS

Ruxolitinib inhibited STAT3 activation, cellular growth, and colony formation of HNSCC cell lines. Ruxolitinib treatment of mice bearing an HNSCC cell line-derived xenograft significantly inhibited tumor growth compared with vehicle-treated controls. The response of HNSCC PDXs derived from patients on the clinical trial mirrored the responses seen in the neoadjuvant setting. Baseline active STAT3 (pSTAT3) and total STAT3 levels were lower, and ruxolitinib inhibited STAT3 activation in a PDX from a patient whose disease was stable on ruxolitinib, compared with a PDX from a patient whose disease progressed on ruxolitinib and where ruxolitinib treatment had minimal impact on STAT3 activation.

CONCLUSIONS

Ruxolitinib exhibits antitumor effects in HNSCC preclinical models. Baseline pSTAT3 or total STAT3 levels in the tumor may serve as predictive biomarkers to identify patients most likely to respond to ruxolitinib.

Fedratinib: a pharmacotherapeutic option for JAK-inhibitor naïve and exposed patients with myelofibrosis

INTRODUCTION

Ruxolitinib is the most commonly used JAK-inhibitor (JAKi) for the management of symptoms related to splenomegaly and cytokine-mediated inflammation in patients with myelofibrosis (MF), but is limited by variable durability of response with most patients experiencing failure after 2-3 years. Long-term data on other approved JAKi, fedratinib and pacritinib, are not available due to the clinical hold put on pivotal trials for toxicity concerns.

AREAS COVERED

Following the initial hold for concern of Wernicke's encephalopathy, fedratinib was approved by the Food and Drug Administration (FDA) in 2019 for MF. We review the data available from early, and late phase critical trials, outline a role for fedratinib in the current treatment landscape of MF, and highlight the knowledge gaps in optimizing use of fedratinib.

EXPERT OPINION

The JAKARTA and JAKARTA2 trials established efficacy in spleen volume response (SVR) and symptom reduction in JAKi-naïve and ruxolitinib-exposed MF patients, respectively. Further trials, FREEDOM and FREEDOM2, are in progress to understand long-term effects of fedratinib; and include strategies to mitigate gastrointestinal toxicity, monitor thiamine levels and surveil for encephalopathy. We use fedratinib for symptomatic MF following ruxolitinib failure in patients without significant cytopenias; with practical strategies for monitoring and managing potential toxicity.

Effect of fluconazole on the pharmacokinetics of a single dose of fedratinib in healthy adults

Purpose

Fedratinib is an orally administered Janus kinase (JAK) 2–selective inhibitor for the treatment of adult patients with intermediate-2 or high-risk primary or secondary myelofibrosis. In vitro, fedratinib is predominantly metabolized by cytochrome P450 (CYP) 3A4 and to a lesser extent by CYP2C19. Coadministration of fedratinib with CYP3A4 inhibitors is predicted to increase systemic exposure to fedratinib. This study evaluated the effect of multiple doses of the dual CYP3A4 and CYP2C19 inhibitor, fluconazole, on the pharmacokinetics of a single dose of fedratinib.

Methods

In this non-randomized, fixed-sequence, open-label study, healthy adult participants first received a single oral dose of fedratinib 100 mg on day 1. Participants then received fluconazole 400 mg on day 10 and fluconazole 200 mg once daily on days 11–23, with a single oral dose of fedratinib 100 mg on day 18. Pharmacokinetic parameters were calculated for fedratinib administered with and without fluconazole.

Results

A total of 16 participants completed the study and were included in the pharmacokinetic population. Coadministration of fedratinib with fluconazole increased maximum observed plasma concentration (C_max) and area under the plasma concentration–time curve from time 0 to the last quantifiable concentration (AUC_0–t) of fedratinib by 21% and 56%, respectively, compared with fedratinib alone. Single oral doses of fedratinib 100 mg administered with or without fluconazole were well tolerated.

Conclusions

Systemic exposure after a single oral dose of fedratinib was increased by up to 56% when fedratinib was coadministered with fluconazole compared with fedratinib alone.

Trial registry: Clinicaltrials.gov

NCT04702464.

Fedratinib, the first selective JAK2 inhibitor approved for treatment of myelofibrosis - an option beyond ruxolitinib

Introduction: Myelofibrosis, a life shortening clonal disorder, presents with a constellation of features: bone marrow fibrosis, abnormal blood counts, extramedullary hematopoiesis, splenomegaly, thrombohemorrhagic complications and constitutional symptoms. Until recently Ruxolitinib, a JAK1 and 2 inhibitor, has been the only targeted therapy available for transplant-ineligible patients requiring treatment for splenomegaly and disease related symptoms. However, most patients discontinue Ruxolitinib after 3-5 years, mostly due to loss of response. There has been an unmet need for this patient group. In August 2019 Fedratinib (INREBIC® capsules, Impact Biomedicines, Inc., a wholly owned subsidiary of Bristol Meyer Squibb), a JAK2 inhibitor, was approved by US FDA for treatment of myelofibrosis in both JAK inhibitor naïve and pre-treated patients for the management of symptoms and splenomegaly.Areas covered: Here, we discuss the development, evidence base to date for Fedratinib. Including early and late phase, and ongoing trials, safety issues, potential role and current position of Fedratinib in the treatment of myelofibrosis, as well as future direction of targeted therapy in myelofibrosis.Expert opinion: Fedratinib presents a much needed option of treatment, particularly, for patients failing Ruxolitinib, with response rates that are quite similar. Nonetheless, there remain important questions including sequencing and options for combining therapy.

JAK Inhibition as a New Treatment Strategy for Patients with COVID-19

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) epidemic continues to spread globally. The rapid dispersion of coronavirus disease 2019 (COVID-19) caused by SARS-CoV-2 drives an urgent need for effective treatments, especially for patients who develop severe pneumonia. The excessive and uncontrolled release of pro-inflammatory cytokines has proved to be an essential factor in the rapidity of disease progression, and some cytokines are significantly associated with adverse outcomes. Most of the upregulated cytokines signal through the Janus kinase-signal transducer and activator of transcription (JAK/STAT) pathway. Therefore, blocking the exaggerated release of cytokines, including IL-2, IL-6, TNF-α, and IFNα/β/γ, by inhibiting JAK/STAT signaling will, presumably, offer favorable pharmacodynamics and present an attractive prospect. JAK inhibitors (JAKi) can also inhibit members of the numb-associated kinase (NAK) family, including AP2-associated kinase 1 (AAK1) and cyclin G-associated kinase (GAK), which regulate the angiotensin-converting enzyme 2 (ACE-2) transmembrane protein and are involved in host viral endocytosis. According to the data released from current clinical trials, JAKi treatment can effectively control the dysregulated cytokine storm and improve clinical outcomes regarding mortality, ICU admission, and discharge. There are still some concerns surrounding thromboembolic events, opportunistic infection such as herpes zoster virus reactivation, and repression of the host's type-I IFN-dependent immune repair for both viral and bacterial infection. However, the current JAKi clinical trials of COVID-19 raised no new safety concerns except a slightly increased risk of herpes virus infection. In the updated WHO guideline, Baricitinb is strongly recommended as an alternative to IL-6 receptor blockers, particularly in combination with corticosteroids, in patients with severe or critical COVID-19. Future studies will explore the application of JAKi to COVID-19 treatment in greater detail, such as the optimal timing and course of JAKi treatment, individualized medication strategies based on pharmacogenomics, and the effect of combined medications.

Role of JAK inhibitors in myeloproliferative neoplasms: current point of view and perspectives

Classic Philadelphia-negative myeloproliferative neoplasms (MPN) include polycythemia vera (PV), essential thrombocythemia (ET), and myelofibrosis (MF), classified as primary (PMF), or secondary to PV or ET. All MPN, regardless of the underlying driver mutation in JAK2/CALR/MPL, are invariably associated with dysregulation of JAK/STAT pathway. The discovery of JAK2V617F point mutation prompted the development of small molecules inhibitors of JAK tyrosine kinases (JAK inhibitors-JAKi). To date, among JAKi, ruxolitinib (RUX) and fedratinib (FEDR) are approved for intermediate and high-risk MF, and RUX is also an option for high-risk PV patients inadequately controlled by or intolerant to hydroxyurea. While not yet registered, pacritinib (PAC) and momelotinib (MMB), proved to be effective particularly in thrombocytopenic and anemic MF patients, respectively. In most cases, JAKi are effective in reducing splenomegaly and alleviating disease-related symptoms. However, almost 50% lose response by three years and dose-dependent toxicities may lead to suboptimal dosing or treatment discontinuation. To date, although not being disease-modifying agents, JAKi represent the therapeutic backbone particularly in MF patient. To optimize therapeutic strategies, many trials with drug combinations of JAKi with novel molecules are ongoing. This review critically discusses the role of JAKi in the modern management of patients with MPN.

Impact of fedratinib on the pharmacokinetics of transporter probe substrates using a cocktail approach

INTRODUCTION

Fedratinib, an oral, selective Janus kinase 2 inhibitor, has been shown to inhibit P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), organic anion transporting polypeptide (OATP) 1B1, OATP1B3, organic cation transporter (OCT) 2, and multidrug and toxin extrusion (MATE) 1 and MATE2-K in vitro. The objective of this study was to evaluate the influence of fedratinib on the pharmacokinetics (PK) of digoxin (P-gp substrate), rosuvastatin (OATP1B1/1B3 and BCRP substrate), and metformin (OCT2 and MATE1/2-K substrate).

METHODS

In this nonrandomized, fixed-sequence, open-label study, 24 healthy adult participants received single oral doses of digoxin 0.25 mg, rosuvastatin 10 mg, and metformin 1000 mg administered as a drug cocktail (day 1, period 1). After a 6-day washout, participants received oral fedratinib 600 mg 1 h before the cocktail on day 7 (period 2). An oral glucose tolerance test (OGTT) was performed to determine possible influences of fedratinib on the antihyperglycemic effect of metformin.

RESULTS

Plasma exposure to the three probe drugs was generally comparable in the presence or absence of fedratinib. Reduced metformin renal clearance by 36% and slightly higher plasma glucose levels after OGTT were observed in the presence of fedratinib. Single oral doses of the cocktail ± fedratinib were generally well tolerated.

CONCLUSIONS

These results suggest that fedratinib has minimal impact on the exposure of P-gp, BCRP, OATP1B1/1B3, OCT2, and MATE1/2-K substrates. Since renal clearance of metformin was decreased in the presence of fedratinib, caution should be exercised in using coadministered drugs that are renally excreted via OCT2 and MATEs.

TRIAL REGISTRATION

Clinicaltrials.gov NCT04231435 on January 18, 2020.

Clinical Utility of Fedratinib in Myelofibrosis

Myelofibrosis (MF) is a clonal hematologic malignancy characterized by bone marrow fibrosis, extramedullary hematopoiesis, splenomegaly, and constitutional symptoms with a propensity towards leukemic transformation. Constitutive activation of the JAK/STAT pathway is a well-described pathogenic feature of MF. Allogeneic stem cell transplant is the only curative therapy, but due to high morbidity and mortality this option is not available for most patients. There are two approved targeted therapy options for MF, ruxolitinib and fedratinib. In this review, we discuss the clinical utility of fedratinib in the myelofibrosis treatment paradigm. Fedratinib has shown impressive pre-clinical and clinical efficacy in patients with untreated MF as well as in those with ruxolitinib intolerance and those with relapsed/refractory MF. Here, we review the pre-clinical and clinical trials that led to the approval of fedratinib, and the ongoing late-phase trials. We highlight several areas regarding the clinical utility of fedratinib that remain unanswered. We discuss the limitations of fedratinib and address areas that are understudied and require further clinical evaluation and research. The approval of fedratinib has provided a significant expansion to the very limited treatment armamentarium available to patients with MF.

Current Status of Baricitinib as a Repurposed Therapy for COVID-19

The emergence of the COVID-19 pandemic has mandated the instant (re)search for potential drug candidates. In response to the unprecedented situation, it was recognized early that repurposing of available drugs in the market could timely save lives, by skipping the lengthy phases of preclinical and initial safety studies. BenevolentAI’s large knowledge graph repository of structured medical information suggested baricitinib, a Janus-associated kinase inhibitor, as a potential repurposed medicine with a dual mechanism; hindering SARS-CoV2 entry and combatting the cytokine storm; the leading cause of mortality in COVID-19. However, the recently-published Adaptive COVID-19 Treatment Trial-2 (ACTT-2) positioned baricitinib only in combination with remdesivir for treatment of a specific category of COVID-19 patients, whereas the drug is not recommended to be used alone except in clinical trials. The increased pace of data output in all life sciences fields has changed our understanding of data processing and manipulation. For the purpose of drug design, development, or repurposing, the integration of different disciplines of life sciences is highly recommended to achieve the ultimate benefit of using new technologies to mine BIG data, however, the final say remains to be concluded after the drug is used in clinical practice. This review demonstrates different bioinformatics, chemical, pharmacological, and clinical aspects of baricitinib to highlight the repurposing journey of the drug and evaluates its placement in the current guidelines for COVID-19 treatment.

Effects of strong and moderate CYP3A4 inducers on the pharmacokinetics of fedratinib in healthy adult participants

PURPOSE

Fedratinib is an oral and selective Janus kinase 2 inhibitor that is indicated for treatment of adults with intermediate-2 or high-risk primary or secondary myelofibrosis. Fedratinib is metabolized by cytochrome P450s (CYPs), primarily CYP3A4. The objective of this study was to determine the effects of the strong CYP3A4 inducer rifampin and moderate CYP3A4 inducer efavirenz on the pharmacokinetics of single doses of fedratinib.

METHODS

This Phase 1, open-label, two-part study (Part 1 for rifampin and Part 2 for efavirenz) was conducted in healthy adult men and women. A single dose of fedratinib (500 mg) was administered on Day 1. Participants received rifampin 600 mg daily or efavirenz 600 mg daily on Days 9-18. On Day 17, a single dose of fedratinib (500 mg) was coadministered with rifampin or efavirenz. Plasma fedratinib concentrations were measured using validated liquid chromatography-tandem mass spectrometry.

RESULTS

Maximum observed plasma fedratinib concentrations were lowered by approximately 70% and 30% during coadministration with rifampin or efavirenz, respectively, compared with fedratinib alone. Geometric means of fedratinib area under the plasma concentration-time curve from 0 to infinity were decreased by 81% (90% confidence interval [CI], 77-83%) and 47% (90% CI, 40-53%) during coadministration with rifampin or efavirenz, respectively. Fedratinib was generally well tolerated when administered alone or in combination with rifampin or efavirenz.

CONCLUSION

Significant reductions in fedratinib exposure were observed in the presence of strong or moderate CYP3A4 inducers. These results suggest that agents that are strong or moderate inducers of CYP3A4 should be avoided when coadministered with fedratinib.

TRIAL REGISTRATION NUMBER

NCT03983239 (Registration date: June 12, 2019).

Fedratinib in myelofibrosis

Following the discovery of the JAK2V617F mutation in myeloproliferative neoplasms in 2005, fedratinib was developed as a small molecular inhibitor of JAK2. It was optimized to yield low-nanomolar activity against JAK2 (50% inhibitory concentration = 3 nM) and was identified to be selective for JAK2 relative to other JAK family members (eg, JAK1, JAK3, and TYK2). It quickly moved into clinical development with a phase 1 clinical trial opening in 2008, where a favorable impact on spleen and myelofibrosis (MF) symptom responses was reported. A phase 3 trial in JAK2 inhibitor treatment-naive MF patients followed in 2011 (JAKARTA); a phase 2 trial in MF patients resistant or intolerant to ruxolitinib followed in 2012 (JAKARTA-2). Clinical development suffered a major setback between 2013 and 2017 when the US Food and Drug Administration (FDA) placed fedratinib on clinical hold due to the development of symptoms concerning for Wernicke encephalopathy (WE) in 8 of 608 subjects (1.3%) who had received the drug. It was ultimately concluded that there was no evidence that fedratinib directly induces WE, but clear risk factors (eg, poor nutrition, uncontrolled gastrointestinal toxicity) were identified. In August 2019, the FDA approved fedratinib for the treatment of adults with intermediate-2 or high-risk MF. Notably, approval includes a "black box warning" on the risk of serious and fatal encephalopathy, including WE. FDA approval was granted on the basis of the JAKARTA studies in which the primary end points (ie, spleen and MF symptom responses) were met in ∼35% to 40% of patients (JAKARTA) and 25% to 30% of patients (JAKARTA-2), respectively.

A Highly Sensitive LC–MS/MS Method Development and Validation of Fedratinib in Human Plasma and Pharmacokinetic Evaluation in Healthy Rabbits

Background:

A simple and sensitive quantitation analytical technique by liquid chromatography–tandem mass spectrometry (LC-MS/MS) is essential for fedratinib in biological media with kinetic study in healthy rabbits.

Objective:

The main objectives of the present research work are to LC-MS/MS method development and validate procedure for the quantitation of fedratinib and its application to kinetic study in rabbits.

Methods:

Separation of processed samples were employed on zorbax SB C18 column (50mm×4.6 mm) 3.5µm with a movable phase of methanol, acetonitrile and 0.1% formic acid in the ratio of 30:60:10. The movable phase was monitored through column at 0.8 ml/min flow rate. The drug and ibrutinib internal standard (IS) were evaluated by monitoring the transitions of m/z -525.260/57.07 and 441.2/55.01 for fedratinib and IS respectively in multiple reaction monitoring mode.

Results:

The linear equation and coefficient of correlation (R2) results were y =0.00348x+0.00245 and 0.9984, respectively. Intra and inter-day precision RSD findings of the developed technique were found in the range of 2.4 - 5.3% for the quality control (QC)-samples (252.56, 1804.0 and 2706 ng/ml). The proposed method was subjected to pharmacokinetic study in healthy rabbits and the kinetic study, fedratinib showed mean AUClast 13190±18.1 hr*ng/ml and Cmax was found to be 3550±4.31 ng/ml in healthy rabbits.

Conclusion:

The validated method can be applicable for the pharmacokinetic and toxicokinetic studies in the clinical and forensic analysis of fedratinib in different kinds of biological matrices successfully.

Therapeutic drug monitoring of oral targeted antineoplastic drugs

PURPOSE

This review provides an overview of the current challenges in oral targeted antineoplastic drug (OAD) dosing and outlines the unexploited value of therapeutic drug monitoring (TDM). Factors influencing the pharmacokinetic exposure in OAD therapy are depicted together with an overview of different TDM approaches. Finally, current evidence for TDM for all approved OADs is reviewed.

METHODS

A comprehensive literature search (covering literature published until April 2020), including primary and secondary scientific literature on pharmacokinetics and dose individualisation strategies for OADs, together with US FDA Clinical Pharmacology and Biopharmaceutics Reviews and the Committee for Medicinal Products for Human Use European Public Assessment Reports was conducted.

RESULTS

OADs are highly potent drugs, which have substantially changed treatment options for cancer patients. Nevertheless, high pharmacokinetic variability and low treatment adherence are risk factors for treatment failure. TDM is a powerful tool to individualise drug dosing, ensure drug concentrations within the therapeutic window and increase treatment success rates. After reviewing the literature for 71 approved OADs, we show that exposure-response and/or exposure-toxicity relationships have been established for the majority. Moreover, TDM has been proven to be feasible for individualised dosing of abiraterone, everolimus, imatinib, pazopanib, sunitinib and tamoxifen in prospective studies. There is a lack of experience in how to best implement TDM as part of clinical routine in OAD cancer therapy.

CONCLUSION

Sub-therapeutic concentrations and severe adverse events are current challenges in OAD treatment, which can both be addressed by the application of TDM-guided dosing, ensuring concentrations within the therapeutic window.

JAK2 Inhibition by Fedratinib Reduces Osteoblast Differentiation and Mineralisation of Human Mesenchymal Stem Cells

Several signalling pathways, including the JAK/STAT signalling pathway, have been identified to regulate the differentiation of human bone marrow skeletal (mesenchymal) stem cells (hBMSCs) into bone-forming osteoblasts. Members of the JAK family mediate the intracellular signalling of various of cytokines and growth factors, leading to the regulation of cell proliferation and differentiation into bone-forming osteoblastic cells. Inhibition of JAK2 leads to decoupling of its downstream mediator, STAT3, and the subsequent inhibition of JAK/STAT signalling. However, the crucial role of JAK2 in hBMSCs biology has not been studied in detail. A JAK2 inhibitor, Fedratinib, was identified during a chemical biology screen of a small molecule library for effects on the osteoblastic differentiation of hMSC-TERT cells. Alkaline phosphatase activity and staining assays were conducted as indicators of osteoblastic differentiation, while Alizarin red staining was used as an indicator of in vitro mineralised matrix formation. Changes in gene expression were assessed using quantitative real-time polymerase chain reaction. Fedratinib exerted significant inhibitory effects on the osteoblastic differentiation of hMSC-TERT cells, as demonstrated by reduced ALP activity, in vitro mineralised matrix formation and downregulation of osteoblast-related gene expression, including ALP, ON, OC, RUNX2, OPN, and COL1A1. To identify the underlying molecular mechanisms, we examined the effects of Fedratinib on a molecular signature of several target genes known to affect hMSC-TERT differentiation into osteoblasts. Fedratinib inhibited the expression of LIF, SOCS3, RRAD, NOTCH3, TNF, COMP, THBS2, and IL6, which are associated with various signalling pathways, including TGFβ signalling, insulin signalling, focal adhesion, Notch Signalling, IL-6 signalling, endochondral ossification, TNF-α, and cytokines and inflammatory response. We identified a JAK2 inhibitor (Fedratinib) as a powerful inhibitor of the osteoblastic differentiation of hMSC-TERT cells, which may be useful as a therapeutic option for treating conditions associated with ectopic bone formation or osteosclerotic metastases.

Inhibition of cytokine signaling by ruxolitinib and implications for COVID-19 treatment

Approximately 15% of patients with coronavirus disease 2019 (COVID-19) experience severe disease, and 5% progress to critical stage that can result in rapid death. No vaccines or antiviral treatments have yet proven effective against COVID-19. Patients with severe COVID-19 experience elevated plasma levels of pro-inflammatory cytokines, which can result in cytokine storm, followed by massive immune cell infiltration into the lungs leading to alveolar damage, decreased lung function, and rapid progression to death. As many of the elevated cytokines signal through Janus kinase (JAK)1/JAK2, inhibition of these pathways with ruxolitinib has the potential to mitigate the COVID-19-associated cytokine storm and reduce mortality. This is supported by preclinical and clinical data from other diseases with hyperinflammatory states, where ruxolitinib has been shown to reduce cytokine levels and improve outcomes. The urgent need for treatments for patients with severe disease support expedited investigation of ruxolitinib for patients with COVID-19.

Excretion balance and pharmacokinetics following a single oral dose of [14C]-fedratinib in healthy subjects

PURPOSE

Fedratinib is an oral and selective kinase inhibitor with activity against wild type and mutationally activated Janus kinase 2 and FMS-like tyrosine kinase 3, for the treatment of adult patients with intermediate-2 or high-risk primary or secondary myelofibrosis. This open-label mass balance study in healthy subjects investigated the excretion balance and systemic exposure of radioactivity after oral administration of [¹⁴C]-fedratinib; and the pharmacokinetics of fedratinib and its contribution to overall exposure of radioactivity.

METHODS

Six healthy males received a single oral dose of 200 mg [¹⁴C]-fedratinib base (2.775 MBq, 75 μCi) as a solution. Blood, urine and feces samples were collected for up to 35 day postdose. Urine and feces samples were collected until the 24-h excretion of radioactivity fell below 0.5% of administered dose (at least 14 day postdose). Expired air was collected up to 8-h postdose. Total radioactivity (blood, plasma, urine, feces, and expired air) and fedratinib concentrations (plasma) were measured.

RESULTS

Approximately 77% (23% unchanged) of fedratinib derived radioactivity was excreted in feces and 5% (3% unchanged) was excreted in urine. Excretion via expired air was negligible. The time to maximum concentration for both total radioactivity and parent drug was similar, with unchanged drug representing the majority of the circulating radioactivity. The ratio of blood to plasma concentration of radioactivity ranged from 0.615 to 0.753 indicating limited distribution of fedratinib and/or its metabolites into red blood cells.

CONCLUSIONS

Fedratinib derived radioactivity was primarily excreted in feces following a single oral dose of radiolabeled fedratinib to healthy subjects.

Evaluation of the Potential for QTc Prolongation With Repeated Oral Doses of Fedratinib in Patients With Advanced Solid Tumors

The impact of repeated daily 500-mg fedratinib (an oral selective Janus kinase [JAK] 2 inhibitor) on QTc and other electrocardiogram (ECG) parameters was assessed in 60 patients with advanced solid tumors. Patients received placebo on day 1 and fedratinib 500 mg daily for 14 days. Concentration-QTc analysis was performed with change-from-baseline QTc corrected by Fridericia's formula (ΔQTcF) as the dependent variable. Fedratinib median time to maximum plasma concentration (C_max ) was observed 3 hours postdose on day 15. The largest difference between means for fedratinib and placebo was 0.5 bpm (90%CI, -2.75 to 3.72 bpm) for heart rate (3 hours postdose) and 4.3 milliseconds (90%CI, 1.04-7.60 milliseconds) for QTcF (4 hours postdose). The estimated slope of the fedratinib concentration-QTcF relationship was shallow and not statistically significant: -0.0005 milliseconds per ng/mL (90%CI, -0.00145 to 0.00050 milliseconds per ng/mL). Predicted fedratinib placebo-corrected ΔQTcF was 0.6 milliseconds (90%CI, -1.80 to 2.93 milliseconds) at the geometric mean of the observed C_max (3615 ng/mL). Fedratinib did not affect PR or QRS intervals. No patients had QTcF > 60 milliseconds, and no patients experienced QTcF ≥ 500 milliseconds. Fedratinib did not cause clinically relevant ECG effects or QTc prolongation. Safety findings were consistent with the known safety profile.

Fedratinib, a newly approved treatment for patients with myeloproliferative neoplasm-associated myelofibrosis

Myeloproliferative neoplasm (MPN)-associated myelofibrosis (MF) is characterized by cytopenias, marrow fibrosis, constitutional symptoms, extramedullary hematopoiesis, splenomegaly, and shortened survival. Constitutive activation of the janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway in MF leads to cell proliferation, inhibition of cell death, and clonal expansion of myeloproliferative malignant cells. Fedratinib is a selective oral JAK2 inhibitor recently approved in the United States for treatment of adult patients with intermediate-2 or high-risk MF. In mouse models of JAK2V617F-driven myeloproliferative disease, fedratinib blocked phosphorylation of STAT5, increased survival, and improved MF-associated disease features, including reduction of white blood cell counts, hematocrit, splenomegaly, and fibrosis. Fedratinib exerts off-target inhibitory activity against bromodomain-containing protein 4 (BRD4); combination JAK/STAT and BRD4 inhibition was shown to synergistically block NF-kB hyperactivation and inflammatory cytokine production, attenuating disease burden and reversing bone marrow fibrosis in animal models of MPNs. In patients, fedratinib is rapidly absorbed and dosed once daily (effective half-life 41 h). Fedratinib showed robust clinical activity in JAK-inhibitor-naïve patients and in patients with MF who were relapsed, refractory, or intolerant to prior ruxolitinib therapy. Fedratinib is effective regardless of JAK2 mutation status. Onset of spleen and symptom responses are typically seen within the first 1–2 months of treatment. The most common adverse events (AEs) with fedratinib are grades 1–2 gastrointestinal events, which are most frequent during early treatment and decrease over time. Treatment discontinuation due to hematologic AEs in clinical trials was uncommon (~3%). Suspected cases of Wernicke’s encephalopathy were reported during fedratinib trials in ~1% of patients; thiamine levels should be monitored before and during fedratinib treatment as medically indicated. Phase III trials are ongoing to assess fedratinib effects on long-term safety, efficacy, and overall survival. The recent approval of fedratinib provides a much-needed addition to the limited therapeutic options available for patients with MF.

Assessment of effects of repeated oral doses of fedratinib on inhibition of cytochrome P450 activities in patients with solid tumors using a cocktail approach

PURPOSE

Fedratinib, an oral selective kinase inhibitor with activity against both wild type and mutationally activated Janus kinase 2, has been approved for the treatment of adult patients with intermediate-2 or high-risk myelofibrosis by the US Food and Drug Administration. In vitro studies indicated that fedratinib was an inhibitor of several cytochrome P450 (CYP) enzymes. The primary objective of this study was to evaluate the effects of repeated doses of fedratinib on the activity of CYP2D6, CYP2C19, and CYP3A4 in patients with solid tumors using a CYP probe cocktail.

METHODS

An open-label, one-sequence, two-period, two-treatment crossover study was conducted. Patients were administered a single oral dose cocktail of metoprolol (100 mg), omeprazole (20 mg), and midazolam (2 mg) used as probe substrates for CYP2D6, CYP2C19, and CYP3A4 enzyme activities, respectively, without fedratinib on Day -1 or with fedratinib on Day 15.

RESULTS

Coadministration of 500 mg once-daily doses of fedratinib for 15 days increased the mean area under the plasma concentration-time curve from time zero to infinity following a single-dose cocktail containing metoprolol (CYP2D6 substrate), omeprazole (CYP2C19 substrate), and midazolam (CYP3A4 substrate) by 1.77-fold (90% confidence interval [CI] 1.27-2.47) for metoprolol, 2.82-fold (90% CI 2.26-3.53) for omeprazole, and 3.84-fold (90% CI 2.62-5.63) for midazolam, respectively. The mean plasma Day 14/Day 1 ratio of 4β-hydroxycholesterol, an endogenous biomarker of CYP3A4 activity, was 0.59 (90% CI 0.54-0.66), suggesting a net inhibition of CYP3A4 by fedratinib.

CONCLUSION

Fedratinib is a weak inhibitor of CYP2D6, and a moderate inhibitor of CYP2C19 and CYP3A4. These results serve as the basis for dose modifications of these CYP substrate drugs when co-administered with fedratinib.

Pharmacokinetics and tolerability of fedratinib, an oral, selective Janus kinase 2 inhibitor, in subjects with renal or hepatic impairment

PURPOSE

Fedratinib is an oral, selective Janus kinase 2 inhibitor that is approved in the United States for the treatment of patients with intermediate-2 or high-risk myelofibrosis. Pharmacokinetics and tolerability of fedratinib in subjects with renal impairment (RI) and hepatic impairment (HI) were evaluated in two separate studies.

METHODS

In the renal study, male and female subjects with stable, chronic mild, moderate, and severe RI, as well as those with end-stage renal disease, were included. The hepatic study included subjects with stable, chronic mild HI. Both were phase 1, multicenter, open-label, single-dose studies, and included matched healthy subjects. Subjects received a single oral dose of fedratinib 300 mg on day 1, were discharged on day 4, returned for clinical visits on days 5-12, and had their end-of-study visit between days 14 and 16.

RESULTS

Thirty-six and 17 subjects were included in the renal and hepatic studies, respectively. In the renal study, fedratinib area under the plasma concentration-time curve from time 0 to infinity (AUC_inf) was 1.9- and 1.5-fold higher in subjects with severe and moderate RI, respectively, than in matched healthy subjects. In the hepatic study, fedratinib AUC_inf did not appreciably differ between subjects with mild HI and matched healthy subjects. Overall, most treatment-emergent adverse events were gastrointestinal and mild.

CONCLUSION

Mild RI and HI do not necessitate fedratinib dosage adjustments. Subjects with moderate RI should be monitored (with dosage adjustments made as necessary), whereas those with severe RI should receive a daily dose of 200 mg, reduced from the indicated dose of 400 mg.

A phase I study of the effect of repeated oral doses of pantoprazole on the pharmacokinetics of a single dose of fedratinib in healthy male subjects

PURPOSE

Fedratinib, an oral, selective Janus kinase 2 inhibitor with activity against both wild-type and mutant Janus kinase 2, has pH-dependent solubility, with free solubility at pH 1. Concomitant administration of drugs that reduce gastric acid secretion, such as pantoprazole, may decrease the absorption of fedratinib and affect patient outcomes. The aim of this study was to evaluate the impact of 7-day repeated 40-mg doses of pantoprazole on the pharmacokinetic (PK) properties of a single 500-mg dose of fedratinib in healthy male subjects.

METHODS

In this phase I, single-center, open-label, two-period, two-treatment, fixed-sequence crossover study, healthy male subjects were administered a single dose of fedratinib 500 mg on day 1 in Period 1, followed by pantoprazole 40 mg daily for 7 days (day 1 to day 7) and a single dose of fedratinib 500 mg on day 7 in Period 2. After the discontinuation of nine subjects due to vomiting, the protocol was amended to provide ondansetron as antiemetic prophylaxis to an additional ten enrolled subjects.

RESULTS

Twenty-six subjects were included. Repeated doses of pantoprazole 40 mg resulted in clinically insignificant increases in fedratinib exposure. Maximum plasma concentration increased by 1.09-fold and area under the plasma concentration-time curve from time 0 to infinity increased by 1.15-fold. All treatment-emergent adverse events were mild or moderate, except for one instance of neutropenia, which was considered unrelated to study intervention.

CONCLUSION

Coadministration with pantoprazole did not have clinically meaningful effects on fedratinib PK. No new or unexpected safety signals were observed with fedratinib.

Fedratinib: First Approval

Fedratinib (INREBIC^®) is a JAK2-selective inhibitor that has been developed as an oral treatment for myelofibrosis. In August 2019, fedratinib received its first global approval in the USA for the treatment of adult patients with intermediate-2 or high-risk primary or secondary (post-polycythemia vera or post-essential thrombocythemia) myelofibrosis. Phase III clinical development for myelofibrosis is ongoing worldwide. This article summarizes the milestones in the development of fedratinib leading to this first approval for myelofibrosis.

Effects of repeated oral doses of ketoconazole on a sequential ascending single oral dose of fedratinib in healthy subjects

PURPOSE

Fedratinib is an orally administered Janus kinase 2-selective inhibitor that is indicated for the treatment of adult patients with intermediate-2 or high-risk myelofibrosis in the United States. Fedratinib is metabolized by multiple cytochrome P450s (CYPs) in vitro, with the predominant contribution from CYP3A4. The primary objective of this study was to evaluate the effects of 14-day repeated 200 mg twice daily (BID) oral doses of a strong CYP3A4 inhibitor, ketoconazole, on a sequential ascending single oral dose of fedratinib in healthy male subjects.

METHODS

An open-label, fixed-sequence, two-treatment cross-over study was conducted. Two cohorts of healthy adult males received two single doses of fedratinib (50 mg in Cohort 1 and 300 mg in Cohort 2) with one dose administered alone on Day 1 of Period 1 and the other dose coadministered with ketoconazole in the morning of Day 6 of Period 2. Subjects in both cohorts received 200-mg BID (Days 1-14) ketoconazole during Period 2.

RESULTS

Coadministration of repeated 200-mg BID oral doses of ketoconazole for 14 days increased fedratinib exposure by 3.85- and 3.06-fold for area under the plasma concentration-time curve from time zero to infinity following a single oral dose of fedratinib of 50 and 300 mg, respectively. Oral administration of a single dose of 50 or 300 mg of fedratinib, administered alone or coadministered with steady-state ketoconazole, was safe and tolerable in the healthy male subjects.

CONCLUSIONS

These results serve as the basis for fedratinib dose reduction when fedratinib is coadministered with strong CYP3A4 inhibitors.

Beyond Ruxolitinib: Fedratinib and Other Emergent Treatment Options for Myelofibrosis

Myelofibrosis (MF) is a myeloproliferative neoplasm characterized by clonal proliferation of differentiated myeloid cells leading to bone marrow fibrosis, cytopenias and extramedullary hematopoiesis. In late 2019, the FDA approved the highly selective JAK2 inhibitor, fedratinib, for intermediate-2 or high-risk primary or secondary MF, making it the second drug approved for MF after ruxolitinib, a JAK1/2 inhibitor, which was approved for MF in 2011. The approval of fedratinib was based on phase II trials and the phase III JAKARTA trial, in which the drug significantly reduced splenomegaly and symptom burden compared to placebo, including some patients previously treated with ruxolitinib. The main side effects of fedratinib include anemia, gastrointestinal symptoms, and elevations in liver transaminases. Fedratinib also has ablack box warning for encephalopathy, although this occurred only in about 1% of the treated patients, most of which were ultimately felt not to represent Wernicke’s encephalopathy. Nonetheless, monitoring of thiamine levels and supplementation are recommended especially in high-risk patients. This concern has led to a prolonged clinical hold and delayed the drug approval by several years during which the drug exchanged manufacturers, highlighting the need for meticulous investigation and adjudication of serious, but rare, adverse events in drug development that could end up preventing drugs with favorable risk/benefit ratio from being approved. In this review, we discuss the pharmacokinetic data and efficacy, as well as the toxicity results of clinical trials of fedratinib. We also review ongoing trials of JAK inhibitors in MF and explore future treatment options for MF patients who are refractory to ruxolitinib.

Population pharmacokinetics of fedratinib in patients with myelofibrosis, polycythemia vera, and essential thrombocythemia

PURPOSE

Fedratinib (SAR302503, TG101348) is an orally administered Janus kinase (JAK) 2-selective inhibitor that is being developed for the treatment of patients with myelofibrosis (MF). The objectives of this analysis were to develop a population pharmacokinetic (PK) model to characterize fedratinib concentration-time profiles in patients with MF, polycythemia vera (PV) and essential thrombocythemia (ET) following oral fedratinib administration; and to investigate the effects of selected covariates on fedratinib PK parameters.

METHODS

Nonlinear mixed effects modeling was employed in developing a population PK model for fedratinib. Intensive or sparse fedratinib concentration data collected in adult subjects with MF, PV or ET from six studies were pooled, and a total of 452 subjects and 3442 plasma concentration observations were included in the final model.

RESULTS

Fedratinib PK in patients with MF/PV/ET was adequately described by a two-compartment structural PK model with first-order absorption incorporating a lag time and first-order elimination. Following oral administration, fedratinib undergoes biphasic disposition and exhibits linear, time-invariant PK at doses of 200 mg and above. Compared to MF/ET patients, PV patients had higher apparent clearance (CL/F) and apparent central volume of distribution. Creatinine clearance was a statistically significant covariate on CL/F, and patients with mild and moderate renal impairment had 10% and 37% increases in fedratinib exposure as compared to patients with normal renal function. No clinically meaningful effect on fedratinib exposure was observed regarding age, body weight, sex, race and liver function.

CONCLUSIONS

These results should serve as the basis for dose adjustment of fedratinib for special populations.

STAT3 as a potential therapeutic target in triple negative breast cancer: a systematic review

Triple negative breast cancer (TNBC), which is typically lack of expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), represents the most aggressive and mortal subtype of breast cancer. Currently, only a few treatment options are available for TNBC due to the absence of molecular targets, which underscores the need for developing novel therapeutic and preventive approaches for this disease. Recent evidence from clinical trials and preclinical studies has demonstrated a pivotal role of signal transducer and activator of transcription 3 (STAT3) in the initiation, progression, metastasis, and immune evasion of TNBC. STAT3 is overexpressed and constitutively activated in TNBC cells and contributes to cell survival, proliferation, cell cycle progression, anti-apoptosis, migration, invasion, angiogenesis, chemoresistance, immunosuppression, and stem cells self-renewal and differentiation by regulating the expression of its downstream target genes. STAT3 small molecule inhibitors have been developed and shown excellent anticancer activities in in vitro and in vivo models of TNBC. This review discusses the recent advances in the understanding of STAT3, with a focus on STAT3’s oncogenic role in TNBC. The current targeting strategies and representative small molecule inhibitors of STAT3 are highlighted. We also propose potential strategies that can be further examined for developing more specific and effective inhibitors for TNBC prevention and therapy.

How I treat myelofibrosis after failure of JAK inhibitors

The introduction of JAK inhibitors, leading to regulatory approval of ruxolitinib, represents a major therapeutic advance in myelofibrosis (MF). Most patients experience reduction in splenomegaly and improved quality of life from symptom improvement. It is a paradox, however, that, despite inhibition of signaling downstream of disease-related driver mutations, JAK inhibitor treatment is not associated with consistent molecular or pathologic responses in MF. Furthermore, there are important limitations to JAK inhibitor therapy including development of dose-limiting cytopenias and/or nonhematological toxicities such as neuropathy or opportunistic infections. Over half of the patients discontinue treatment within 3 years of starting treatment. Although data are sparse, clinical outcome after JAK inhibitor "failure" is likely poor; consequently, it is important to understand patterns of failure to select appropriate salvage treatment(s). An algorithmic approach, particularly one that incorporates cytogenetics/molecular data, is most helpful in selecting stem cell transplant candidates. Treatment of transplant-ineligible patients relies on a problem-based approach that includes use of investigational drugs, or consideration of splenectomy or radiotherapy. Data from early phase ruxolitinib combination studies, despite promising preclinical data, have not shown clear benefit over monotherapy thus far. Development of effective treatment strategies for MF patients failing JAK inhibitors remains a major unmet need.

Quantifying the relationship between inhibition of VEGF receptor 2, drug-induced blood pressure elevation and hypertension

BACKGROUND AND PURPOSE

Several anti-angiogenic cancer drugs that inhibit VEGF receptor (VEGFR) signalling for efficacy are associated with a 15-60% incidence of hypertension. Tyrosine kinase inhibitors (TKIs) that have off-target activity at VEGFR-2 may also cause blood pressure elevation as an undesirable side effect. Therefore, the ability to translate VEGFR-2 off-target potency into blood pressure elevation would be useful in development of novel TKIs. Here, we have sought to quantify the relationship between VEGFR-2 inhibition and blood pressure elevation for a range of kinase inhibitors.

EXPERIMENTAL APPROACH

Porcine aortic endothelial cells overexpressing VEGFR-2 (PAE) were used to determine IC₅₀ for VEGFR-2 phosphorylation. These IC₅₀ values were compared with published reports of exposure attained during clinical use and the corresponding incidence of all-grade hypertension. Unbound average plasma concentration (C_av,u ) was selected to be the most appropriate pharmacokinetic parameter. The pharmacokinetic-pharmacodynamic (PKPD) relationship for blood pressure elevation was investigated for selected kinase inhibitors, using data derived either from clinical papers or from rat telemetry experiments.

KEY RESULTS

All-grade hypertension was predominantly observed when the C_av,u was >0.1-fold of the VEGFR-2 (PAE) IC₅₀ . Furthermore, based on the PKPD analysis, an exposure-dependent blood pressure elevation >1 mmHg was observed only when the C_av,u was >0.1-fold of the VEGFR-2 (PAE) IC₅₀ .

CONCLUSIONS AND IMPLICATIONS

Taken together, these data show that the risk of blood pressure elevation is proportional to the amount of VEGFR-2 inhibition, and a margin of >10-fold between VEGFR-2 IC₅₀ and C_av,u appears to confer a minimal risk of hypertension.

Treatment of rats with the JAK-2 inhibitor fedratinib does not lead to experimental Wernicke's encephalopathy

Recent clinical trials suggest that patients with myelofibrosis can develop Wernicke's encephalopathy (WE) when treated with fedratinib, a specific Janus kinase-2 (JAK-2) inhibitor. To investigate this issue, we have examined (1) if fedratinib can produce or alter the course of this disorder, (2) its effects on thiamine-dependent enzyme activity and thiamine status, and (3) its influence on the uptake of thiamine. Animals administered fedratinib for 28days at a comparable dose used to treat human cases of myelofibrosis showed no evidence of clinical signs of thiamine deficiency (TD). Rats treated with a combination of fedratinib and TD exhibited no neurological differences in their progress to the symptomatic stage when compared to thiamine-deficient animals only. Treatment with the JAK-2 inhibitor did not compromise erythrocyte transketolase activity, and thiamine status was not affected in a major way unlike animals with TD. In addition, treatment of cultured astrocytes with fedratinib did not diminish the uptake of thiamine into these cells. Our findings suggest that treatment with fedratinib does not lead to or alter the progress of TD, and do not support the notion that administration of this JAK-2 inhibitor directly results in the development of WE due to inhibition of thiamine transport. Known adverse effects of fedratinib involving compromised gastrointestinal function may be an important indirect contributing factor to previously reported cases of WE in patients with myelofibrosis.

Interaction of 2,4-Diaminopyrimidine-Containing Drugs Including Fedratinib and Trimethoprim with Thiamine Transporters

Inhibition of thiamine transporters has been proposed as a putative mechanism for the observation of Wernicke's encephalopathy and subsequent termination of clinical development of fedratinib, a Janus kinase inhibitor (JAKi). This study aimed to determine the potential for other JAKi to inhibit thiamine transport using human epithelial colorectal adenocarcinoma (Caco-2) and thiamine transporter (THTR) overexpressing cells and to better elucidate the structural basis for interacting with THTR. Only JAKi containing a 2,4-diaminopyrimidine were observed to inhibit thiamine transporters. Fedratinib inhibited thiamine uptake into Caco-2 cells (IC50 = 0.940 µM) and THTR-2 (IC50 = 1.36 µM) and, to a lesser extent, THTR-1 (IC50 = 7.10 µM) overexpressing cells. Two other JAKi containing this moiety, AZD1480 and cerdulatinib, were weaker inhibitors of the thiamine transporters. Other JAKi-including monoaminopyrimidines, such as momelotinib, and nonaminopyrimidines, such as filgotinib-did not have any inhibitory effects on thiamine transport. A pharmacophore model derived from the minimized structure of thiamine suggests that 2,4-diaminopyrimidine-containing compounds can adopt a conformation matching several key features of thiamine. Further studies with drugs containing a 2,4-diaminopyrimidine resulted in the discovery that the antibiotic trimethoprim also potently inhibits thiamine uptake mediated by THTR-1 (IC50 = 6.84 µM) and THTR-2 (IC50 = 5.56 µM). Fedratinib and trimethoprim were also found to be substrates for THTR, a finding with important implications for their disposition in the body. In summary, our results show that not all JAKi have the potential to inhibit thiamine transport and further establish the interaction of these transporters with xenobiotics.

Colony-Stimulating Factor-1 Receptor Is Required for Nurse-like Cell Survival in Chronic Lymphocytic Leukemia

PURPOSE

Monocytes and their progeny are abundant constituents of the tumor microenvironment in lymphoproliferative disorders, including chronic lymphocytic leukemia (CLL). Monocyte-derived cells, including nurse-like cells (NLC) in CLL, promote lymphocyte proliferation and survival, confer resistance to chemotherapy, and are associated with more rapid disease progression. Colony-stimulating factor-1 receptor (CSF-1R) regulates the homeostatic survival of tissue-resident macrophages. Therefore, we sought to determine whether CSF-1R is similarly required for NLC survival.

EXPERIMENTAL DESIGN

CSF-1R expression by NLC was examined by flow cytometry and IHC. CSF-1R blocking studies were performed using an antagonistic mAb to examine its role in NLC generation and in CLL survival. A rational search strategy was performed to identify a novel tyrosine kinase inhibitor (TKI) targeting CSF-1R. The influence of TKI-mediated CSF-1R inhibition on NLC and CLL viability was examined.

RESULTS

We demonstrated that the generation and survival of NLC in CLL is dependent upon CSF-1R signaling. CSF-1R blockade is associated with significant depletion of NLC and consequently inhibits CLL B-cell survival. We found that the JAK2/FLT3 inhibitor pacritinib suppresses CSF-1R signaling, thereby preventing the generation and survival of NLC and impairs CLL B-cell viability.

CONCLUSIONS

CSF-1R is a novel therapeutic target that may be exploited in lymphoproliferative disorders, like CLL, that are dependent upon lymphoma-associated macrophages. Clin Cancer Res; 22(24); 6118-28. ©2016 AACR.

JAK2 inhibitor TG101348 overcomes erlotinib-resistance in non-small cell lung carcinoma cells with mutated EGF receptor

Non-small cell lung cancer (NSCLC) patients with epidermal growth factor receptor (EGFR) mutations are responsive to EGFR-tyrosine kinase inhibitor (EGFR-TKI). However, NSCLC patients with secondary somatic EGFR mutations are resistant to EGFR-TKI treatment. In this study, we investigated the effect of TG101348 (a JAK2 inhibitor) on the tumor growth of erlotinib-resistant NSCLC cells. Cell proliferation, apoptosis, gene expression and tumor growth were evaluated by diphenyltetrazolium bromide (MTT) assay, flow cytometry, terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) staining, Western Blot and a xenograft mouse model, respectively. Results showed that erlotinib had a stronger impact on the induction of apoptosis in erlotinib-sensitive PC-9 cells but had a weaker effect on erlotinib-resistant H1975 and H1650 cells than TG101348. TG101348 significantly enhanced the cytotoxicity of erlotinib to erlotinib-resistant NSCLC cells, stimulated erlotinib-induced apoptosis and downregulated the expressions of EGFR, p-EGFR, p-STAT3, Bcl-xL and survivin in erlotinib-resistant NSCLC cells. Moreover, the combined treatment of TG101348 and erlotinib induced apoptosis, inhibited the activation of p-EGFR and p-STAT3, and inhibited tumor growth of erlotinib-resistant NSCLC cells in vivo. Our results indicate that TG101348 is a potential adjuvant for NSCLC patients during erlotinib treatment.

Effective Concentration of a Multikinase Inhibitor within Bone Marrow Correlates with In Vitro Cell Killing in Therapy-Resistant Chronic Myeloid Leukemia

Leukemia cells escape BCR-ABL-targeted therapy by developing mutations, such as T315I, in the p210(BCR-ABL) fusion protein in Philadelphia chromosome-positive chronic myeloid leukemia (CML). Although most effort has been focused on development of new tyrosine kinase inhibitors, enrichment of these small-molecule inhibitors in the tumor tissue can also have a profound impact on treatment outcomes. Here, we report that a 2-hour exposure of the T315I-mutant CML cells to 10 μmol/L of the multikinase inhibitor TG101209 suppressed BCR-ABL-independent signaling and caused cell-cycle arrest at G2-M. Further increase in drug concentration to 17.5 μmol/L blocked phosphorylation of the mutant BCR-ABL kinase and its downstream JAK2 and STAT5. The effective dosage to overcome therapy resistance identified in an in vitro setting serves as a guidance to develop the proper drug formulation for in vivo efficacy. A targeted formulation was developed to achieve sustained bone marrow TG101209 concentration at or above 17.5 μmol/L for effective killing of CML cells in vivo Potent inhibition of leukemia cell growth and extended survival were observed in two murine models of CML treated with 40 mg/kg intravenously administered targeted TG101209, but not with the untargeted drug at the same dosage. Our finding provides a unique approach to develop treatments for therapy-resistant CML. Mol Cancer Ther; 15(5); 899-910. ©2016 AACR.

Serum-resistant CpG-STAT3 decoy for targeting survival and immune checkpoint signaling in acute myeloid leukemia

Targeting oncogenic transcription factor signal transducer and activator of transcription 3 (STAT3) in acute myeloid leukemia (AML) can reduce blast survival and tumor immune evasion. Decoy oligodeoxynucleotides (dODNs), which comprise STAT3-specific DNA sequences are competitive inhibition of STAT3 transcriptional activity. To deliver STAT3dODN specifically to myeloid cells, we linked STAT3dODN to the Toll-like receptor 9 (TLR9) ligand, cytosine guanine dinucleotide (CpG). The CpG-STAT3dODN conjugates are quickly internalized by human and mouse TLR9(+)immune cells (dendritic cells, B cells) and the majority of patients' derived AML blasts, including leukemia stem/progenitor cells. Following uptake, CpG-STAT3dODNs are released from endosomes, and bind and sequester cytoplasmic STAT3, thereby inhibiting downstream gene expression in target cells. STAT3 inhibition in patients' AML cells limits their immunosuppressive potential by reduced arginase expression, thereby partly restoring T-cell proliferation. Partly chemically modified CpG-STAT3dODNs have >60 hours serum half-life which allows for IV administration to leukemia-bearing mice (50% effective dose ∼ 2.5 mg/kg). Repeated administration of CpG-STAT3dODN resulted in regression of human MV4-11 AML in mice. The antitumor efficacy of this strategy is further enhanced in immunocompetent mice by combining direct leukemia-specific cytotoxicity with immunogenic effects of STAT3 blocking/TLR9 triggering. CpG-STAT3dODN effectively reducedCbfb/MYH11/MplAML burden in various organs and eliminated leukemia stem/progenitor cells, mainly through CD8/CD4 T-cell-mediated immune responses. In contrast, small-molecule Janus kinase 2/STAT3 inhibitor failed to reproduce therapeutic effects of cell-selective CpG-STAT3dODN strategy. These results demonstrate therapeutic potential of CpG-STAT3dODN inhibitors with broad implications for treatment of AML and potentially other hematologic malignancies.

The STAT3 pathway as a therapeutic target in head and neck cancer: Barriers and innovations

Proteins of the signal transducer and activator of transcription (STAT) family mediate cellular responses to cytokines and growth factors. Aberrant regulation of the STAT3 oncogene contributes to tumor formation and progression in many cancers, including head and neck squamous cell carcinoma (HNSCC), where hyperactivation of STAT3 is implicated in both treatment resistance and immune escape. There are no oncogenic gain-of-function mutations in HNSCC. Rather, aberrant STAT3 signaling is primarily driven by upstream growth factor receptors, such as Janus kinase (JAK) and epidermal growth factor receptor (EGFR). Moreover, genomic silencing of select protein tyrosine phosphatase receptors (PTPRs), tumor suppressors that dephosphorylate STAT3, may lead to prolonged phosphorylation and activation of STAT3. This review will summarize current knowledge of the STAT3 pathway and its contribution to HNSCC growth, survival, and resistance to standard therapies, and discuss STAT3-targeting agents in various phases of clinical development.