Safety and Tolerability of Suprachoroidal Axitinib Injectable Suspension, for Neovascular Age-related Macular Degeneration; Phase I/IIa Open-Label, Dose-Escalation Trial.

Purpose: To evaluate the safety and tolerability of a single dose of axitinib injectable suspension (CLS-AX), a pan-anti-VEGF tyrosine kinase inhibitor (TKI), administered via suprachoroidal injection in patients with neovascular age-related macular degeneration (nAMD). Design: Phase I/IIa, open-label, sequential dose escalation. Participants: Anti-VEGF treatment-experienced patients with active subfoveal choroidal neovascularization secondary to nAMD. Methods: The study included 4 cohorts (0.03, 0.10, 0.50, and 1.0 mg) of approximately 5 patients each enrolled in a dose-escalating fashion. Enrolled patients received intravitreal aflibercept (2 mg) followed by a single unilateral dose of CLS-AX 1 month later. All patients were followed monthly for 3 months with the option of an additional 3 months of extended follow-up for cohorts 2 to 4. End points included systemic and ocular safety and tolerability, visual acuity, retinal thickness, and need for aflibercept therapy. Main Outcome Measures: The number of patients reporting treatment-emergent adverse events (TEAEs) and serious adverse events (SAEs), changes in ophthalmic examinations, and the number of patients qualifying for additional therapy for nAMD based on protocol-defined criteria. Results: OASIS enrolled 27 patients with nAMD with mean age of 81 years, mean duration of nAMD diagnosis of 54 months, and between 5 and 90 prior anti-VEGF treatments. Twenty-six patients completed through 3 months, with 14 entering and completing the 3-month extension. No SAEs, drug-related TEAEs, or TEAEs leading to discontinuation were observed after CLS-AX administration; there were no adverse events related to ocular inflammation, vasculitis, intraocular pressure, or dispersion of drug into the vitreous or anterior chamber. Through 6 months, stable mean best-corrected visual acuity and stable mean central subfield thickness (CST) were observed, suggestive of TKI biologic effect. No aflibercept therapy was administered up to 3 months in 58% (15/26) of patients who completed 3 months of follow-up in OASIS. In the Extension, 57% (8/14) of patients went up to 6 months without receiving aflibercept therapy. Conclusions: Up to 1.0 mg CLS-AX, a highly potent TKI targeted to the suprachoroidal space (SCS) via the SCS Microinjector, was well tolerated, with stable mean visual acuity and mean CST. A majority of patients followed for 6 months did not require aflibercept therapy. Financial Disclosures: Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

A validated UPLC-MS/MS method for quantification of pyrotinib and population pharmacokinetic study of pyrotinib in HER2-positive breast cancer patients.

Objective: Pyrotinb has been approved for the treatment of HER2-positive advanced or metastatic breast cancer in China. However, the plasma concentration of pyrotinb in different patients varies greatly, and in the course of treatment, if patients have intolerable adverse reactions, the drug dosage will be reduced or even stopped. This study set out to establish an ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) for the determination of pyrotinb in human plasma, analyze the population pharmacokinetics (PPK) of pyrotinib and assess the influence of patient variables on PK of pyrotinib in patients with HER2 positive breast cancer. Method: An UPLC-MS/MS method was developed to measure pyrotinib in human plasma. Utilizing a gradient elution procedure and a Kinetex C18 column (2.1 mm × 100 mm, 1.7 µm), sample separation was accomplished in 5.5 min. Pyrotinb extraction via protein precipitation was used as a sample pre-treatment technique. In total, 50 patients provided 158 plasma samples, which were identified and used in the PPK investigation. The non-linear mixed-effects modeling (NONMEM) approach was used to assess the plasma concentrations and covariates information. For the final PPK model evaluation, external evaluation, non-parametric bootstrap, visual predictive check (VPC), and goodness-of-fit (GOF) were used. Results: The UPLC-MS/MS method for determining plasma concentration of pyrotinib in patients had good selectivity and linearity in the range of 1-1,000 ng/mL. Pyrotinib concentration profile in HER2-positive breast cancer patients was well described by a single-compartment PPK model with first-order absorption and elimination. The formulas for the final estimated values of overall parameters of CL/F and Vd/F and Ka are respectively: C L / F L / h = 88.8 × e TP / 67.2 × 0.376 , V / F L = 3940 , K A h - 1 = 0.357 F I X E D . No dosage adjustment was advised, despite the possibility that the total protein levels could have a substantial impact on the apparent distribution volume of pyrotinib with limited magnitude. Conclusion: In this study, an UPLC-MS/MS method was established to determine the concentration of pyrotinib in human plasma. A population pharmacokinetic model of pyrotinib in HER2 positive breast cancer patients suggested that low serum total protein reduced the clearance rate of pyrotinib in patients. Clinical medical staff should pay attention to the liver function of patients with abnormal serum total protein and be alert to the occurrence of adverse drug reactions.

An analysis of the clinical significance of the TKI-resistant gene ZNF687 for hepatocellular carcinoma patients.

BACKGROUND: Novel treatments such as monotherapy and combined immunotherapy significantly extend overall survival (OS) for hepatocellular carcinoma (HCC) patients, but HCC is susceptible to treatment resistance during long-term therapy. The resistance mechanism to targeted drugs in HCC remains ambiguous, making research on HCC drug resistance targets crucial for the development of precision medicine. OBJECTIVES: To investigate the transcriptional features, biological functions and potential clinical value of the tyrosine kinase inhibitor (TKI)-resistant gene ZNF687 in HCC. MATERIAL AND METHODS: The TKI-resistant genes of HCC were identified using clustered regularly interspaced short palindromic repeats (CRISPR) in vitro screening. Then, the dependence of HCC cell lines on ZNF687 was investigated in silico. We collected global mRNA datasets of HCC tissue, integrated the mRNA expression characteristics of ZNF687 in HCC and explored the impact of ZNF687 on HCC patient prognoses using the Kaplan-Meier method (in silico). The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analyses were then conducted, and a connectivity map and molecular docking technology were applied to find the underlying agent opposing ZNF687. RESULTS: In vitro, the guide RNA corresponding to ZNF687 was weakly detected in HCC cells, and ZNF687 deficiency was found to inhibit growth in HCC cell lines. ZNF687 mRNA was overexpressed and had a high discriminatory ability for HCC in 2,975 HCC samples, contrasting with 2,340 non-HCC samples. Moreover, an excessive ZNF687 transcript level was related to a worse overall survival (OS) prognosis. Histone modification, spliceosome, transcription coregulator activity, and nucleocytoplasmic transport were the most significant pathways for ZNF687 differential-related gene enrichment. Chaetocin was found to be a candidate compound and presented a strong affinity to ZNF687. CONCLUSIONS: ZNF687 represents a TKI-resistant and growth-dependent gene for HCC, the overexpression of which indicates poor OS for HCC patients. Additionally, ZNF687 is expected to be a druggable target for overcoming TKI resistance, and chaetocin may be a candidate therapeutic compound for ZNF687.

Design, synthesis and biological evaluation of thienopyridine derivatives as c-Met kinase inhibitors.

With cabozantinib as the precursor, a novel small molecule inhibitors of c-Met kinase with thieno [2,3-b] pyridine as the scaffold were designed, synthesized and evaluated for their biological activity against A549, Hela and MCF-7 cell lines. The in vitro activities of 16 compounds were tested by MTT method with cabozantinib as control drug. Most compounds had moderate to strong inhibitory activities on cells. Among them, compound 10 had the strongest inhibitory activity, which was superior to the lead compound cabozantinib. Its IC50 values for A549, Hela and MCF-7 cells were 0.005, 2.833 and 13.581 µM, respectively. The colony formation assay demonstrated that compound 10 significantly inhibited the colony formation of A549 cells and suppressed their growth in a concentration-dependent manner. The wound healing assay showed that compound 10 could effectively inhibit the migration of cancer cells compared to a blank control group. The AO/EB assay demonstrated that compound 10 possesses the capability to effectively trigger apoptosis in a concentration-dependent manner. The elementary structure-activity relationship, molecular docking and pharmacokinetics studies revealed the significance of thieno [2,3-b] pyridine derivatives in anti-tumor activity.

Comprehensive combined analysis of physician-initiated phase II and III clinical trials on a cultured human corneal endothelial cell product for treating bullous keratopathy.

To evaluate the efficacy and safety of a cultured human corneal endothelial cell (cHCEC) product in eyes with bullous keratopathy (BK). Combined analysis of multicenter phase II and III clinical trials. This analysis involved 15 BK eyes in the phase II trial and 12 BK eyes in the phase III trial that underwent cHCEC transplant therapy. Safety was assessed in all the cases. Efficacy was assessed in 17 cases with exclusion of the low- and medium-dose groups in the phase II trial. The primary endpoint was a corneal endothelial cell density of 1000 cells/mm2 or more at 24 weeks post-transplant, which was attained in 94.1% of the eyes (16 of 17), with a 95% CI of 71.3-99.9%. Additionally, 82.4% of the eyes (14 of 17) met the secondary endpoint of reduction in corneal thickness to less than 630 µm without corneal epithelial edema within the same time frame, with a 95% CI of 56.6-96.2%. The mean decrease in corneal thickness from baseline to 24 weeks post-transplant was -187.4 µm (95% CI, -240.2 µm to -134.5 µm). Furthermore, all the eyes exhibited improvement in best-corrected visual acuity from baseline to 24 weeks post-transplant (95% CI, 80.5-100.0%). By 24 weeks post-transplant, 88.9% of the patients (24 of 27) had experienced adverse events, which were mostly local, mild, and transient. The cHCEC product of this study reconstitutes the corneal endothelial layer with high cellular density and restores corneal thickness and improves visual acuity.

Tailored management of advanced thyroid cancer patients treated with lenvatinib or vandetanib: the role of a multimodal approach.

BACKGROUND: In differentiated/poorly differentiated (DTC/PDTC) or medullary thyroid cancer (MTC) treated with kinase inhibitors (KIs), additional treatments (ATs) can be performed in selected cases. METHODS: We retrospectively analysed all the ATs performed in our center in KI-treated TC patients, evaluating the subsequent KI modulation, the local PD in case of loco-regional procedure (LRP) and the AT-related complications. DTC/PDTC patients with or without progressive disease before the first AT (PD and NO PD GROUP, respectively) were analysed separately. RESULTS: In our center, 32 ATs (30 LRPs and 2 radioactive iodine treatments) were performed in 14 DTC/PDTC patients and 4 MTC subjects after the start of systemic therapy with lenvatinib or vandetanib (27 and 5 ATs, respectively). Brain was the most treated site (11/30 LRPs) and external beam radiation was the most employed LRP (18/30 LRPs). KIs dose reduction or discontinuation of KI therapy (at least transient) was performed after 50% of ATs in DTC/PDTC NO PD GROUP. The KI was maintained at the same dosage after 75% and 50% of the ATs performed in DTC/PDTC PD GROUP and MTC, respectively. During the follow-up, local PD was detected after 14 LRPs. Local progression-free survival (LPFS) was significantly shorter in DTC/PDTC PD GROUP in comparison to NO PD GROUP (12 month-LPFS 91.7% versus 15.2%); in patients with MTC, 12 month-LPFS was 50%. AT-related AEs were mostly G1-G2. CONCLUSIONS: In selected DTC/PDTC without previous PD and treated with a multimodal strategy, local disease control is generally maintained regardless the KI dose modulation. In DTC/PDTC patients with previous limited PD and in MTC subjects, the choice of performing a LRP and continue the ongoing KI therapy must consider the risk of early local progression. AT-related AEs in KI treated patients were mild in most cases.

Protein kinase C (PKC) inhibitor calphostin C activates PKC in a light-dependent manner at high concentrations via the production of singlet oxygen.

Calphostin C (Cal-C) is a protein kinase C (PKC) inhibitor that binds to its C1 domain. The aim of the present study was to elucidate the action of Cal-C in addition to PKC inhibition. First, we confirmed that Cal-C at low concentrations (< 200 nM) inhibit phorbol ester-induced PKC translocation and G-protein-coupled receptor (GPCR)-mediated PKC activation. Cal-C at higher concentrations (> 2 µM) increased intracellular calcium ion concentrations ([Ca2+]i) in a concentration-dependent manner. The origin of this increase is the mobilization of the endoplasmic reticulum (ER), which does not involve GPCR or ryanodine receptors. Cal-C at high concentrations also cause structural changes in the ER, such as the formation of vacuoles and aggregates, and calcium leakage from the ER. At 2 µM, Cal-C translocated a calcium-sensitive PKCα. Studies using a C-kinase activity reporter and a myristoylated alanine-rich protein kinase C substrate fused with green fluorescent protein (GFP) have also revealed that Cal-C at high concentrations activate PKC in living cells. Additionally, the PKC-activating effects of Cal-C were light-dependent. Finally, studies using Si-DMA, an indicator of singlet oxygen, showed that Cal-C at high concentrations generated singlet oxygen, causing structural changes in the ER and leakage of calcium into the cytosol, which triggered PKC activation. This study confirms the novel action of Cal-C, solely considered a PKC inhibitor. Cal-C acted as a PKC inhibitor at low concentrations and a PKC activator at high concentrations by generating singlet oxygen in a light-dependent manner, suggesting that Cal-C can be used in photodynamic therapy.

Clinical research progress of fruquintinib in the treatment of malignant tumors.

Malignant tumors represent an important cause of mortality within the global population. Tumor angiogenesis, recognized as one of the key hallmarks of malignant tumors, is crucial for supplying essential nutrients and oxygen for tumor growth. Vascular endothelial growth factor (VEGF) and its receptor (VEGFR) are key drivers of tumor angiogenesis. Targeted therapeutic interventions not only effectively inhibit tumor growth by specifically blocking tumor angiogenesis but have also made breakthroughs in the treatment of malignant tumors. Fruquintinib, an anti-angiogenic small molecule drug developed independently in China, functions as a potent tyrosine kinase inhibitor with high selectivity. It effectively curtails tumor growth by binding to and inhibiting VEGFR-1, VEGFR-2, and VEGFR-3. Additionally, fruquintinib offers several advantages including minimal off-target toxicity, robust resistance profiles, and commendable efficacy. This agent can be used alone or in combination with other treatments. It has shown high effectiveness and survival benefits across various malignant tumors such as colorectal cancer, gastric cancer, non-small cell lung cancer, breast cancer, and other malignant tumors. Therefore, this article conducts a systematic review encompassing the mechanism of action, pharmacokinetics, clinical efficacy, and safety profile of fruquintinib. Through this review, we aimed to offer a reference for the clinical application and subsequent development of fruquintinib.

Real-world clinical efficacy of tofacitinib in moderate-to-severe ulcerative colitis.

Tofacitinib is an oral small-molecule Janus kinase (JAK) inhibitor that preferentially inhibits JAK1 and JAK3. Its efficacy in inducing and maintaining remission in ulcerative colitis (UC) as well as its safety profile has been demonstrated in multicenter, randomized, double-blind, placebo-controlled trials. Additionally, real-world studies evaluating the effectiveness and adverse effects of tofacitinib have been conducted, affirming its clinical efficacy in moderate-to-severe UC.

Opportunities and challenges for targeting HPK1 in cancer immunotherapy.

Hematopoietic Progenitor Kinase 1 (HPK1, also known as MAP4K1) is a hematopoiesis-specific serine/threonine kinase that belongs to the MAP4K family of Ste20-related protein kinases. HPK1 has been identified as a negative regulator of T-cell receptor signaling. Recent studies have indicated that the inhibition or knockout of HPK1 kinase function can effectively alleviate T cell exhaustion, enhance T cell functionality, and improve the therapeutic efficacy of tumor immunotherapy. In recent years, small molecule chemical drugs targeting HPK1 have made significant progress and have become a hot topic in the research and development of tumor immunotherapy drugs. However, the advancement of small molecule drugs that target HPK1 is hindered by various challenges, including the limited selectivity, insufficient immune stimulation, and the ambiguity surrounding role of non-kinase scaffold functions of HPK1 in tumor immune responses. This review briefly describes the biological structure of HPK1 and its related signaling pathways in tumor immunity, systematically discusses the latest research progress in small molecule chemical drugs targeting HPK1. Finally, we summarize and prospect the opportunities and challenges in the drug development of small molecule chemical drugs targeting HPK1 in tumor immunity.

The Prospective Role of Lapatinib as an Adjuvant Therapy in Prevalent Cancers: Insights from In Silico Analysis Targeting EGFR and HER2.

INTRODUCTION: Various pieces of evidence suggest an elevation in the levels of EGFR and HER2 in different cancers leading to the proliferation, invasion, and metastasis of cancer cells. In this study, we conducted a comprehensive investigation into the expression alterations of these two receptors in various cancers using in silico data. In addition, we investigated the therapeutic potential of lapatinib as an inhibitor of these receptors in various cancer types. METHODS: RNAseq data for prevalent cancers were downloaded from The Cancer Genome Atlas (TCGA). After initial preprocessing, expression changes of HER2, EGFR, and candidate genes-identified based on their association with EGFR and HER2 signaling pathways-were examined. Human protein atlas data were utilized to assess the protein expression of HER2 and EGFR. GSE129254 was employed to identify molecular pathways and candidate genes associated with lapatinib. The protein-protein interaction network was used to identify lapatinib-influenced hub genes. Clinical data for common cancers were used to investigate the correlation between the expression of candidate genes and patients' mortality rates by Cox regression test. RESULTS: The findings clearly indicated a significant increase in the expression levels of HER2 and EGFR in cancers such as kidney, lung, breast, bladder, pancreas, head and neck, stomach, and endometrial, both at the mRNA and protein levels (p-value < 0.01). Additionally, more than 30% of samples in some cancers showed a twofold increase in HER2 or EGFR expression. The analysis of GSE129254 data revealed that lapatinib reduces the expression of numerous genes associated with cell proliferation. METTL1, LYAR, LTV1, CCND1, NOP2, and DDX21 were identified as hub genes related to the effect of lapatinib. Our results demonstrated that many hub genes exhibited elevated expression in candidate cancers, and the upregulation of some of them was correlated with poor prognosis. CONCLUSION: Our results indicate an upregulation in the expression levels of HER2 and EGFR in certain common cancers, suggesting that lapatinib, in addition to breast cancer, could be considered for the treatment of these cancers. Furthermore, we demonstrated that some genes with increased expression in prevalent cancers and associated with poor prognosis have the potential to be modulated by lapatinib.

Successful Treatment of Monoclonal Immunotactoid Glomerulopathy Associated with Chronic Lymphocytic Leukemia Using Ibrutinib.

A 71-year-old woman developed nephrotic syndrome during 10-year follow-up for chronic lymphocytic leukemia. A renal biopsy sample analysis revealed IgG1-lambda-positive monoclonal immunotactoid glomerulopathy (mITG). The patient was treated with ibrutinib, a Bruton tyrosine kinase inhibitor, and complete renal remission was achieved after 24 months. ITG is a rare disease that is characterized by glomerular deposition. In particular, mITG, which presents immune deposits that exhibit light-chain restriction, is often associated with hematologic disorders. Most patients with mITG receive immunosuppressive therapy and/or chemotherapy; however, to our knowledge, there have been no reports of treatment with ibrutinib.

[Chronic myeloid leukemia: 2024 update on novel therapeutic strategies].

Many patients with chronic myeloid leukemia (CML) can now maintain response thanks to the advent of tyrosine kinase inhibitors (TKIs) and STAMP inhibitors, but adverse events associated with prolonged TKI therapy have become a problem. Adequate management of adverse events is key to successful treatment, as some can significantly impact the patient's prognosis. The goal of CML treatment was once to prevent acute transformation, but now that many patients achieve deep remission and long-term survival, the goal has shifted to achieving long-term treatment free remission (TFR). It is essential to carefully consider disease risk, patient background, and adverse events of each therapeutic agent in order to make the appropriate choice. This article reviews the treatment of chronic phase CML (CML-CP) as described in the 2023 edition of the Guidelines for Hematopoietic Tumors, focusing on treatment options for first-line CML-CP, dose optimization of ponatinib, outcomes with the new CML drug asciminib, and TFR.

The tyrosine kinase inhibitor lenvatinib is oxidized by rat cytochromes P450 and affects their expression in rat liver.

Lenvatinib is an orally effective tyrosine kinase inhibitor used to treat several types of tumors, including progressive, radioiodine-refractory differentiated thyroid cancer and advanced renal cell carcinoma. Although this drug is increasingly used in therapy, its metabolism and effects on the organism are still not described in detail. Using the rat as an experimental animal model, this study aimed to investigate the metabolism of lenvatinib by rat microsomal enzymes and cytochrome P450 (CYPs) enzymes recombinantly expressed in SupersomesTM in vitro and to assess the effect of lenvatinib on rat CYP expression in vivo. Two metabolites, O-desmethyl lenvatinib, and lenvatinib N-oxide, were produced by rat CYPs in vitro. CYP2A1 and 2C12 were found to be the most effective in forming O-desmethyl lenvatinib, while CYP3A2 was found to primarily form lenvatinib N-oxide. The administration of lenvatinib to rats caused changes in the expression of mRNA and protein, as well as the activity of various CYPs, particularly in an increase in CYP1A1. Thus, the administration of lenvatinib to rats has an impact on the level of CYPs.

Are 19del and L858R really different disease entities?

Clinicians have recognized the similarities and differences between the two subtypes of common epidermal growth factor receptor (EGFR) mutations, but actual treatment strategies have not yet changed. The L858R mutation can be understood by considering the pharmacological conformational plasticity of the receptor protein and the presence of other co-occurring mutations, whether subtypes of EGFR or non-EGFR mutations and differences in downstream signaling pathways. As long as we know that molecular differences lead to biological differences, it is a challenge for all of us that our treatment strategies must change.

[Box: see text].

The combination of a tyrosine kinase inhibitor and blinatumomab in patients with Philadelphia chromosome-positive acute lymphoblastic leukemia or Philadelphia chromosome-like acute lymphoblastic leukemia.

Tyrosine kinase inhibitors (TKIs) have revolutionized Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) treatment. The combination of blinatumomab and a TKI in the frontline setting has shown the safety and efficacy of the chemotherapy-free treatment approach in patients with Ph + ALL. This retrospective analysis included 19 patients with Ph + ALL and Ph-like ALL treated with the combination of blinatumomab and a TKI. Of the 14 newly diagnosed patients, the overall response, complete remission (CR), and molecular response (CMR) rates after one cycle of blinatumomab were 100% (10/10), 90% (9/10), and 57% (8/14), respectively. Of the five relapsed patients, the CR and CMR rates were 50% (2/4) and 40% (2/5). Blinatumomab in combination with TKIs is safe and effective and hence this combination therapy could be a viable therapeutic option in front-line treatment of patients with Ph + ALL.

Imatinib­ and ponatinib­mediated cardiotoxicity in zebrafish embryos and H9c2 cardiomyoblasts.

Tyrosine kinase inhibitors (TKIs) offer targeted therapy for cancers but can cause severe cardiotoxicities. Determining their dose­dependent impact on cardiac function is required to optimize therapy and minimize adverse effects. The dose­dependent cardiotoxic effects of two TKIs, imatinib and ponatinib, were assessed in vitro using H9c2 cardiomyoblasts and in vivo using zebrafish embryos. In vitro, H9c2 cardiomyocyte viability, apoptosis, size, and surface area were evaluated to assess the impact on cellular health. In vivo, zebrafish embryos were analyzed for heart rate, blood flow velocity, and morphological malformations to determine functional and structural changes. Additionally, reverse transcription­quantitative PCR (RT­qPCR) was employed to measure the gene expression of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), established markers of cardiac injury. This comprehensive approach, utilizing both in vitro and in vivo models alongside functional and molecular analyses, provides a robust assessment of the potential cardiotoxic effects. TKI exposure decreased viability and surface area in H9c2 cells in a dose­dependent manner. Similarly, zebrafish embryos exposed to TKIs exhibited dose­dependent heart malformation. Both TKIs upregulated ANP and BNP expression, indicating heart injury. The present study demonstrated dose­dependent cardiotoxic effects of imatinib and ponatinib in H9c2 cells and zebrafish models. These findings emphasize the importance of tailoring TKI dosage to minimize cardiac risks while maintaining therapeutic efficacy. Future research should explore the underlying mechanisms and potential mitigation strategies of TKI­induced cardiotoxicities.

Phase II trial of multi-kinase inhibitor ESK981 in patients with metastatic castration-resistant prostate cancer.

ESK981 is a potent tyrosine kinase and PIKfyve lipid kinase inhibitor. This phase II trial evaluated the efficacy of ESK981 as a single agent in patients with androgen receptor-positive (AR +) metastatic castration-resistant prostate cancer (mCRPC). Eligible patients had mCRPC with progression on AR-targeted agents and without prior chemotherapy treatment. Each patient received 160 mg ESK981 once daily for 5 days per week for 4 weeks per cycle (except for an adverse event (AE) occurrence). The primary endpoints were a 50% reduction in prostate-specific antigen (PSA50), and safety. Secondary endpoints included the time and the duration of PSA response, PSA progression rates, PSA progression free survival (PFS) and overall survival (OS). Exploratory investigations included whole exome sequencing in patients before treatment, and morphological evaluation of biopsy samples pre- and post-treatment. PSA was evaluated in 13 patients. Only one patient (7.7% two-sided 95% Wilson CI (0.4%, 33.3%)) experienced a reduction in their PSA levels by 50% or more. The most common grade 3 treatment-related AEs were cardiac disorders, diarrhea, hypertension, alanine transaminase and aspartate transaminase elevations. No grade 4-5 events occurred. Median PFS was 1.8 months, and median OS was 12.1 months. Peripheral immune cells showed increased T cell activation and cytokine production in two patients who received 12-weeks of ESK981. Although relatively well tolerated, ESK981 alone showed no anti-tumor activity in patients with AR + mCRPC and its further evaluation as a single agent in AR + mCRPC is not warranted. (Trial registration: ClinicalTrials.gov, NCT03456804. Registration date: March 7, 2018).