Achieving selectivity among ATP-competitive kinase inhibitors remains a major challenge due to the high conservation of the ATP-binding pocket across the kinome. Although most kinase inhibitors target the ATP-binding site, ATP-mimicking compounds remain relatively uncommon due to concerns regarding selectivity. Here, we report the structural and biophysical characterization of the atypical serine/threonine kinase haploid germ cell-specific nuclear protein kinase (HASPIN) with two ATP-mimicking inhibitors, LJ-5157 and LJ-5242. Crystal structures of HASPIN in complex with LJ-5157 and with LJ-5242 were determined at resolutions of 1.74 Å and 1.88 Å, respectively, revealing ATP-like binding modes within the catalytic pocket. Structural analysis showed that the regulatory and catalytic spines of HASPIN are preorganized through extensive hydrophobic packing, particularly within the N-lobe, stabilizing the αC helix independently of nucleotide binding. Despite similar binding modes, microscale thermophoresis measurements demonstrated that LJ-5242 binds ~ 10-fold more tightly than LJ-5157. LJ-5157 and LJ-5242 exhibited selective HASPIN inhibition, with LJ-5242 showing ~ 10-fold and ~ 100-fold higher potency and selectivity in kinase inhibition and antiproliferative activity assays, respectively. These findings demonstrate that the distinctive architecture of the HASPIN ATP-binding pocket enables selective recognition of ATP-mimicking inhibitors and provides a framework for designing kinase inhibitors that retain ATP-like scaffolds while achieving selectivity.

Human prostamide/prostaglandin F synthase (PGFS) catalyzes the NADPH-dependent conversion of prostaglandin H2 (PGH2) to prostaglandin F2α that plays a key role in regulating intraocular pressure and labor. Despite its physiological importance, structural and biochemical information of the human PGFS has been limited because of difficulties in obtaining sufficient quality of PGFS wild-type crystal and short half-life of PGH2. Here, we report the crystal structure of human PGFS with two active site mutations, C44S/C47S double mutant (DM), which mimics the reduced active form of the CXXC motif of human PGFS. Structural analysis revealed that PGFS DM adopts a typical thioredoxin (Trx)-like fold. Analysis of B-factors and MD simulations reveals that Tyr108-Asp124 is an intrinsically flexible region, devoid of any stabilizing crystal contacts. Unlike canonical Trx-like proteins, Pro167 in PGFS adopts a trans-conformation, inducing a specific Arg40 side chain localization that creates a positive charge near the CXXC motif. Activation of PGFS by reduction of disulfide bond in the CXXC motif enhanced the thermal stability via core stabilization, yet an unexpected increase in the structural disorder was detected with CD spectroscopy, especially upon ligand binding. These findings collectively establish PGFS as a structurally distinct and redox-regulated enzyme. Our results provide novel molecular insights into PGFS as an underexplored but promising therapeutic target.

Selective inhibition of MEK isoforms remains a central challenge in MAPK-targeted drug discovery, largely due to the structural similarity between MEK1 and MEK2. While MEK1 has been extensively characterized, the structural basis of MEK2-specific ligand recognition is not fully understood. Here, we present crystal structures of human MEK2 in complex with the noncompetitive inhibitor U0126 and the allosteric inhibitor refametinib at resolutions of 3.15 Å and 3.30 Å, respectively. Despite a conserved kinase fold, MEK2 exhibits isoform-specific features within the N-lobe β-sheet. Additional differences are observed in the relative orientation of the helix C and activation segment, and the helix F-supported regulatory spine. Structural differences are reflected in micromolar binding affinities for U0126 (Kd = 9.8 μM) and refametinib (Kd = 7.4 μM). Notably, a single N-lobe substitution (Thr87 in MEK2 versus Phe83 in MEK1) selectively enhanced U0126 binding. The MEK2 T87F mutant exhibited an approximately twofold increase in affinity, while refametinib binding remained largely unchanged. SEC-MALS analysis demonstrated that MEK2 predominantly exists as a monomer in solution, contrasting with the reported homodimeric behavior of MEK1. Molecular dynamics simulations supported these findings by revealing isoform-specific differences in oligomeric state-dependent flexibility and inhibitor-induced dynamics. Collectively, our findings define the structural basis underlying the differential inhibitor recognition of MEK2 and MEK1, providing mechanistic insight into isoform-selective MEK-targeted drug design.

Background/Objectives: Fibroblast growth factor receptors (FGFRs) are frequently dysregulated in diverse cancers and represent important therapeutic targets. Here, we report the design and synthesis of a novel nucleoside-based scaffold which enables irreversible pan-FGFR inhibition as a potential anticancer strategy. Methods: A series of nucleoside analogues was synthesized and assessed through structure–activity relationship studies. Structural analyses, including X-ray co-crystallography and molecular dynamics simulations, were performed to define key determinants of potency and selectivity. Biochemical assays against FGFR1–4 proteins, cellular antiproliferative assays in HCT116 (FGFR1 amplification) and RT4 (FGFR3-TACC3) models, metabolic stability evaluations and covalent bonding confirmation were conducted to characterize representative compounds. Results: SAR studies revealed that fused aromatic substituents and 4′-thio ribose enhanced FGFR potency, whereas enantiomeric inversion of ribose reduced activity. X-ray co-crystallography further demonstrated that two hydroxyl groups form a key water-mediated hydrogen bond network, uniquely stabilizing the ligand and enhancing potency of inhibitors compared to reference compounds. The 7-methoxy-5-methylbenzo[b]thiophene scaffold and ribose moiety emerged as critical features. Compounds 13f, 19e, and 22f demonstrated potent inhibition of FGFR1-4 and dose-dependent suppression of FGFR1-mediated signaling, with strong antiproliferative activity in both FGFR-driven and wild-type cancer models. Compound 22f showed efficient irreversible covalent engagement of FGFRs, confirmed at the protein and cellular levels, and exhibited improved metabolic stability. Conclusions: Nucleoside analogues represent a privileged scaffold for covalent pan-FGFR inhibition. The findings highlight their potential as promising therapeutic candidates for targeting FGFR-driven malignancies. Future efforts will focus on further improving stability and optimizing physicochemical properties to advance these compounds toward translational development.

Chronic myeloid leukemia (CML) remains a therapeutic challenge, particularly in patients who develop resistance to standard tyrosine kinase inhibitors (TKIs) such as imatinib. Here, we present the first demonstration of the potent anti-leukemic activity of the histone deacetylase (HDAC) inhibitor martinostat in both TKI-sensitive and TKI-resistant CML. Structural and biochemical analyses confirmed the efficient and selective binding of martinostat to HDAC isoenzyme ligand-binding pockets, resulting in histone and tubulin hyperacetylation in both imatinib-sensitive and resistant CML cells, outperforming vorinostat, a clinically used HDAC inhibitor (HDACi). It selectively impaired CML cell proliferation and viability and induced apoptosis across various CML models, including resistant cell models and patient blasts, with minimal toxicity to healthy cells and low developmental toxicity in zebrafish. In addition to its single-agent efficacy, martinostat demonstrated enhanced anticancer effects when combined with imatinib, both in vitro and in vivo, significantly reducing tumor growth in resistant CML xenograft models. Mechanistically, mRNA-seq data showed that martinostat disrupted key survival signaling pathways and amplified apoptotic responses, contributing to its anticancer activity. These findings highlight the potential of martinostat as a selective, low-toxicity HDACi that, combined with TKIs, could provide an effective strategy to overcome drug resistance in CML and improve therapeutic outcomes.

Acute myeloid leukemia (AML) is a highly aggressive cancer with a 5-year survival rate of less than 35

Carfilzomib (CFZ) is a tetrapeptide epoxyketone-based proteasome inhibitor (PI) drug approved for multiple myeloma therapy. Despite its improved efficacy and safety profiles over bortezomib (the first-in-class PI drug), CFZ has a short half-life in vivo (< 1 hour), possibly contributing to the lack of efficacy against solid cancers. Previous studies indicated that microsomal epoxide hydrolase (mEH) plays a predominant role in the metabolic degradation of CFZ. With that in mind, we synthesized a novel hydroxylated analog of CFZ (dubbed "CFZ-OH"), which was predicted to have a lower affinity to mEH than CFZ. Here, we assessed the metabolic stability of CFZ-OH under varying conditions in vitro: HEK293 cells expressing human mEH, rat liver homogenates, rat or human liver microsomes, and rat or human primary hepatocytes. In vitro, CFZ-OH showed protection from mEH-mediated metabolism and improved metabolic stability over CFZ. In rats receiving CFZ-OH or CFZ (4 mg/kg, intravenously), CFZ-OH exhibited 2.6-fold higher systemic exposure, consistent with the protection of CFZ-OH from mEH-mediated metabolism. However, CFZ-OH and CFZ displayed comparable terminal half-lives, suggesting that CFZ-OH may be subjected to metabolic degradation in vivo by enzymes other than mEH. CFZ-OH degradation was faster than CFZ in rat blood and lung homogenates but was partially inhibited by bortezomib (a PI) or N-ethylmaleimide (a broad-spectrum cysteine protease inhibitor). Together, our results indicate the need to assess the stability of epoxyketone-based PI drugs through multiple metabolic components, including cysteine proteases, and their relative contribution in developing next-generation PI drugs with prolonged circulation in vivo. SIGNIFICANCE STATEMENT: The hydroxylated analog of Carfilzomib (CFZ-OH) displayed enhanced proteasome target binding and greater in vitro metabolic stability against microsomal epoxide hydrolase, previously considered a main contributor to the in vivo instability of CFZ. In vivo, CFZ-OH exhibited a higher systemic exposure than CFZ, but their terminal half-lives were comparable. These findings suggest that enhancing the in vivo circulation of CFZ requires structural modifications that confer protection against microsomal epoxide hydrolase and other enzymes, such as cysteine proteases.

Triple-negative breast cancer (TNBC) is a subtype of breast cancer associated with a poor prognosis and decreased patient survival. It is intimately linked to AXL overexpression and AXL hyperactivation. Here, we explored the therapeutic potential of AX-0085, a small molecule AXL inhibitor. While AX-0085 was previously characterized in the context of lung adenocarcinoma, this study demonstrates its application in triple-negative breast cancer (TNBC) models. AX-0085 exhibited high binding affinity to the ATP binding site located beneath the conserved glycine-rich loop (P-loop) that links the β1 and β2 strands of the AXL kinase domain. Furthermore, it was demonstrated that the benzamide group of AX-0085 and LyS567's Nζ atom could generate a hydrogen bond. AX-0085 efficiently suppressed the AXL/GAS6 signaling pathway activation in TNBC cells in vitro, which in turn prevented AXL/GAS6 signaling-dependent pro-cancerous behavior like cell proliferation, invasion, migration, and epithelial-mesenchymal transition (EMT). In TNBC, an AX-0085-induced cell cycle arrest that took place during the G1 phase reduced the expression of CYCLIN E and CDK2. Additionally, AX-0085 facilitated apoptotic cell death in TNBC. Treatment of AX-0085 on in vivo mouse xenografts transplanted with 4 T1 cells showed a significant tumor reduction. Thus, our findings demonstrate that AX-0085 has an effective therapeutic role in TNBC by inhibiting AXL activation.

Myelomonocytic and monocytic acute myeloid leukemia (AML) subtypes are intrinsically resistant to venetoclax-based regimens. Identifying targetable vulnerabilities would limit resistance and relapse. We previously documented the synergism of venetoclax and cardiac glycoside (CG) combination in AML. Despite preclinical evidence, the repurposing of cardiac glycosides (CGs) in cancer therapy remained unsuccessful due to a lack of predictive biomarkers. We report that the ex vivo response of AML patient blasts and the in vitro sensitivity of established cell lines to the hemi-synthetic CG UNBS1450 correlates with the ATPase Na + /K + transporting subunit alpha 1 (ATP1A1)/BCL2 like 1 (BCL2L1) expression ratio. Publicly available AML datasets identify myelomonocytic/monocytic differentiation as the most robust prognostic feature, along with core-binding factor subunit beta ( CBFB ), lysine methyltransferase 2A ( KMT2A ) rearrangements, and missense Fms-related receptor tyrosine kinase 3 ( FLT3 ) mutations. Mechanistically, BCL2L1 protects from cell death commitment induced by the CG-mediated stepwise triggering of ionic perturbation, protein synthesis inhibition, and MCL1 downregulation. In vivo, CGs showed an overall tolerable profile while impacting tumor growth with an effect ranging from tumor growth inhibition to regression. These findings suggest a predictive marker for CG repurposing in specific AML subtypes.

Malaria poses an enormous threat to human health. With ever increasing resistance to currently deployed drugs, breakthrough compounds with novel mechanisms of action are urgently needed. Here, we explore pyrimidine-based sulfonamides as a new low molecular weight inhibitor class with drug-like physical parameters and a synthetically accessible scaffold. We show that the exemplar, OSM-S-106, has potent activity against parasite cultures, low mammalian cell toxicity and low propensity for resistance development. In vitro evolution of resistance using a slow ramp-up approach pointed to the Plasmodium falciparum cytoplasmic asparaginyl tRNA synthetase (PfAsnRS) as the target, consistent with our finding that OSM-S-106 inhibits protein translation and activates the amino acid starvation response. Targeted mass spectrometry confirms that OSM-S-106 is a pro-inhibitor and that inhibition of PfAsnRS occurs via enzyme-mediated production of an Asn-OSM-S-106 adduct. Human AsnRS is much less susceptible to this reaction hijacking mechanism. X-ray crystallographic studies of human AsnRS in complex with inhibitor adducts and docking of pro-inhibitors into a model of Asn-tRNA-bound PfAsnRS provide insights into the structure activity relationship and the selectivity mechanism.

The N-degron pathway determines the half-life of proteins by selectively destabilizing the proteins bearing N-degrons. N-terminal glutamine amidohydrolase 1 (NTAQ1) plays an essential role in the arginine N-degron (Arg/N-degron) pathway as an initializing enzyme via the deamidation of the N-terminal (Nt) glutamine (Gln). However, the Nt-serine-bound conformation of hNTAQ1 according to the previously identified crystal structure suggests the possibility of other factors influencing the recognition of Nt residues by hNTAQ1. Hence, in the current study, we aimed to further elucidate the substrate recognition of hNTAQ1; specifically, we explored 12 different substrate-binding conformations of hNTAQ1 depending on the subsequent residue of Nt-Gln. Results revealed that hNTAQ1 primarily interacts with the protein Nt backbone, instead of the side chain, for substrate recognition. Here, we report that the Nt backbone of proteins appears to be a key component of hNTAQ1 function and is the main determinant of substrate recognition. Moreover, not all second residues from Nt-Gln, but rather distinctive and charged residues, appeared to aid in detecting substrate recognition. These new findings define the substrate-recognition process of hNTAQ1 and emphasize the importance of the subsequent Gln residue in the Nt-Gln degradation system. Our extensive structural and biochemical analyses provide insights into the substrate specificity of the N-degron pathway and shed light on the mechanism underlying hNTAQ1 substrate recognition. An improved understanding of the protein degradation machinery could aid in developing therapies to promote overall health through enhanced protein regulation, such as targeted protein therapies.

Abstract HEPN–MNT, a type VII TA module, comprises the HEPN toxin and the MNT antitoxin, which acts as a nucleotidyltransferase that transfers the NMP moiety to the corresponding HEPN toxin, thereby interfering with its toxicity. Here, we report crystal structures of the Legionella pneumophila HEPN–MNT module, including HEPN, AMPylated HEPN, MNT, and the HEPN–MNT complex. Our structural analysis and biochemical assays, suggest that HEPN is a metal-dependent RNase and identify its active site residues. We also elucidate the oligomeric state of HEPN in solution. Interestingly, L. pneumophila MNT, which lacks a long C-terminal α4 helix, controls the toxicity of HEPN toxin via a distinct binding mode with HEPN. Finally, we propose a comprehensive regulatory mechanism of the L. pneumophila HEPN–MNT module based on structural and functional studies. These results provide insight into the type VII HEPN–MNT TA system.

BACKGROUND:Despite advancements in chronic myeloid leukemia (CML) therapy with tyrosine kinase inhibitors (TKIs), resistance and intolerance remain significant challenges. Leukemia stem cells (LSCs) and TKI-resistant cells rely on altered mitochondrial metabolism and oxidative phosphorylation. Targeting rewired energy metabolism and inducing non-apoptotic cell death, along with the release of damage-associated molecular patterns (DAMPs), can enhance therapeutic strategies and immunogenic therapies against CML and prevent the emergence of TKI-resistant cells and LSC persistence.METHODS:Transcriptomic analysis was conducted using datasets of CML patients' stem cells and healthy cells. DNA damage was evaluated by fluorescent microscopy and flow cytometry. Cell death was assessed by trypan blue exclusion test, fluorescent microscopy, flow cytometry, colony formation assay, and in vivo Zebrafish xenografts. Energy metabolism was determined by measuring NAD+ and NADH levels, ATP production rate by Seahorse analyzer, and intracellular ATP content. Mitochondrial fitness was estimated by measurements of mitochondrial membrane potential, ROS, and calcium accumulation by flow cytometry, and morphology was visualized by TEM. Bioinformatic analysis, real-time qPCR, western blotting, chemical reaction prediction, and molecular docking were utilized to identify the drug target. The immunogenic potential was assessed by high mobility group box (HMGB)1 ELISA assay, luciferase-based extracellular ATP assay, ectopic calreticulin expression by flow cytometry, and validated by phagocytosis assay, and in vivo vaccination assay using syngeneic C57BL/6 mice.RESULTS:Transcriptomic analysis identified metabolic alterations and DNA repair deficiency signatures in CML patients. CML patients exhibited enrichment in immune system, DNA repair, and metabolic pathways. The gene signature associated with BRCA mutated tumors was enriched in CML datasets, suggesting a deficiency in double-strand break repair pathways. Additionally, poly(ADP-ribose) polymerase (PARP)1 was significantly upregulated in CML patients' stem cells compared to healthy counterparts. Consistent with the CML patient DNA repair signature, treatment with the methylated indolequinone MAC681 induced DNA damage, mitochondrial dysfunction, calcium homeostasis disruption, metabolic catastrophe, and necroptotic-like cell death. In parallel, MAC681 led to PARP1 degradation that was prevented by 3-aminobenzamide. MAC681-treated myeloid leukemia cells released DAMPs and demonstrated the potential to generate an immunogenic vaccine in C57BL/6 mice. MAC681 and asciminib exhibited synergistic effects in killing both imatinib-sensitive and -resistant CML, opening new therapeutic opportunities.CONCLUSIONS:Overall, increasing the tumor mutational burden by PARP1 degradation and mitochondrial deregulation makes CML suitable for immunotherapy.

SORT1 (sortilin 1), a member of the the Vps10 (vacuolar protein sorting 10) family, is involved in hepatic lipid metabolism by regulating very low-density lipoprotein (VLDL) secretion and facilitating the lysosomal degradation of CES1 (carboxylesterase 1), crucial for triglyceride (TG) breakdown in the liver. This study explores whether SORT1 is targeted for degradation by chaperone-mediated autophagy (CMA), a selective protein degradation pathway that directs proteins containing KFERQ-like motifs to lysosomes via LAMP2A (lysosomal-associated membrane protein 2A). Silencing LAMP2A or HSPA8/Hsc70 with siRNA increased cytosolic SORT1 protein levels. Leupeptin treatment induced lysosomal accumulation of SORT1, unaffected by siLAMP2A co-treatment, indicating CMA-dependent degradation. Human SORT1 contains five KFERQ-like motifs (658VVTKQ662, 730VREVK734, 733VKDLK737, 734KDLKK738, and 735DLKKK739), crucial for HSPA8 recognition; mutating any single amino acid within these motifs decreased HSPA8 binding. Furthermore, compromised CMA activity resulted in elevated SORT1-mediated degradation of CES1, contributing to increased lipid accumulation in hepatocytes. Consistent with in vitro findings, LAMP2A knockdown in mice exacerbated high-fructose diet-induced fatty liver, marked by increased SORT1 and decreased CES1 levels. Conversely, LAMP2A overexpression promoted SORT1 degradation and CES1D accumulation, counteracting fasting-induced CES1D suppression through CMA activation. Our findings reveal that SORT1 is a substrate of CMA, highlighting its crucial role in directing CES1 to lysosomes. Consequently, disrupting CMA-mediated SORT1 degradation significantly affects CES1-dependent TG hydrolysis, thereby affecting hepatic lipid homeostasis.Abbreviations: APOB: apolipoprotein B; CES1: carboxylesterase 1; CMA: chaperone-mediated autophagy; HSPA8/Hsc70: heat shock protein family A (Hsp70) member 8; LAMP2A: lysosomal associated membrane protein 2A; LDL-C: low-density lipoprotein-cholesterol; PLIN: perilipin; SORT1: sortilin 1; TG: triglyceride; VLDL: very low-density lipoprotein; Vps10: vacuolar protein sorting 10.

Despite genetic perturbations resulting in embryo lethality for most mitotic kinases, loss of the histone H3 mitotic kinase HASPIN reveals no adverse effect in mice models, establishing HASPIN as a promising target for anticancer therapy. However, developing a HASPIN inhibitor from conventional pharmacophores poses a technical challenge as this atypical kinase shares slight similarities with eukaryotic protein kinases. Chemically modifying a cytotoxic 4'-thioadenosine analogue through high genotoxicity yielded several novel nongenotoxic kinase inhibitors. In silico apporoaches utilizing transcriptomic and chemical similarities with known compounds and KINOMEscan profiles unveiled the HASPIN inhibitor LJ4827. LJ4827's specificity and potency as a HASPIN inhibitor were verified through in vitro kinase assay and X-ray crystallography. HASPIN inhibition by LJ4827 reduced histone H3 phosphorylation and impeded Aurora B recruitment in cancer cell centromeres but not in noncancer cells. Through transcriptome analysis of lung cancer patients, PLK1 was determined as a druggable synergistic partner to complement HASPIN inhibition. Chemical or genetic PLK1 perturbation with LJ4827 effectuated pronounced lung cancer cytotoxicity in vitro and in vivo. Therefore, LJ4827 is a novel anticancer therapeutic for selectively impeding cancer mitosis through potent HASPIN inhibition, and simultaneous HASPIN and PLK1 interference is a promising therapeutic strategy for lung cancer.

Peroxisome proliferator-activated receptors (PPARs) are ligand-inducible transcription factors that belong to thyroid/retinoid hormone receptor-like nuclear receptors [1,2].In particular, PPARα as one of the subtype of PPARs is known for regulating the metabolism of fatty acids and lipid homeostasis in various organs [1].Since PPARα activation has also been found to reduce inflammation, PPARα has been considered to be a potential therapeutic target for cancer as an agonist and antagonist [2][3][4].Lobeglitazone is one of TZD(Thiazolidinedione) which is known as an anti-diabetic drug and a recent study revealed lobeglitazone is a dual agonist on PPARα and PPARγ [2, 4].In clinical use, PPARα has therapeutic effects on dyslipidemia and insulin resistance [3, 4].As known in previous studies PPARα has a high potency of lobeglitazone as an agonist, however, there was no evidence of a molecular mechanism for lobeglitazone and PPARα complex.Here we report purification steps, PPARα crystals complexed with lobeglitazone, and their X-ray diffraction data.Structural analysis is currently in progress, and it would help elucidate molecular interaction between PPARα and lobeglitazone.

e15120 Background: Triple-negative breast cancer (TNBC) is insensitive to targeted therapies due to the negative expression of human epidermal growth factor receptor-2, estrogen receptor and progesterone receptor. TNBC cells express higher levels of AXL more often than other breast cancer subtypes. The receptor tyrosine kinase AXL plays a role in survival, invasion, migration, epithelial-mesenchymal transition (EMT), metastasis, resistance, and immune suppression in cancer cells including in TNBC. Thus, AXL is a promising therapeutic target for the treatment of TNBC, and we developed a new small-molecule AXL inhibitor, AX-0085. Methods: The interaction mechanism between AX-0085 and AXL was studied by molecular dynamic simulations, cell-based kinase assay, and western blotting in TNBC cells. We investigated the anti-tumor activity of AX-0085 on the AXL-dependent pro-tumorigenic properties such as cell proliferation, invasion, migration, EMT, and immune suppression (PD-L1 expression) in TNBC cell lines and investigated in vivo efficacy of AX-0085 with the 4T1 xenograft model. Results: In the molecular dynamic simulations, estimated binding energy of AX-0085 and cabozantinib to AXL was -10.1Kcal/mol and -8.1Kcal/mol, respectively. AX-0085 was made a hydrogen bond with catalytically important residue Lys567 and blocked the activation of AXL by inhibiting the salt bridge with Lys567-Glu585. AX-0085 (IC 50 : 4.4nM for AXL kinase in cell-based kinase assay) was one of the most potent AXL inhibitors. AX-0085 showed a high antitumor activity against all TNBC subtypes and was a more potent anti-proliferative activity than other kinase inhibitors in MDA-MB-231 cell line. AX-0085 effectively blocked the activation of AXL in TNBC and further inhibited AXL-dependent pro-tumorigenic events such as cell proliferation, invasion, migration, EMT, and PD-L1 expression in TNBC cell. AX-0085 induced cell cycle arrest at G1 phase and suppressed the expression of CDK2 and Cyclin E in TNBC. AX-0085 promoted apoptotic cell death by up-regulating cleaved caspase-9 and down-regulating Bcl-2 in TNBC. Pharmacological investigation showed that the AX-0085 treated tumors displayed a dose-dependent reduction in volume and weight of the tumors in the 4T1 mouse xenograft. Conclusions: Our results demonstrated that AX-0085 selectively blocks AXL activation which confers an effective therapeutic value in the treatment of TNBC. Currently, AX-0085 is undergoing non-clinical trials.