A highly selective and potent CXCR4 antagonist for hepatocellular carcinoma treatment.

The CXC chemokine receptor type 4 (CXCR4) receptor and its ligand, CXCL12, are overexpressed in various cancers and mediate tumor progression and hypoxia-mediated resistance to cancer therapy. While CXCR4 antagonists have potential anticancer effects when combined with conventional anticancer drugs, their poor potency against CXCL12/CXCR4 downstream signaling pathways and systemic toxicity had precluded clinical application. Herein, BPRCX807, known as a safe, selective, and potent CXCR4 antagonist, has been designed and experimentally realized. In in vitro and in vivo hepatocellular carcinoma mouse models it can significantly suppress primary tumor growth, prevent distant metastasis/cell migration, reduce angiogenesis, and normalize the immunosuppressive tumor microenvironment by reducing tumor-associated macrophages (TAMs) infiltration, reprogramming TAMs toward an immunostimulatory phenotype and promoting cytotoxic T cell infiltration into tumor. Although BPRCX807 treatment alone prolongs overall survival as effectively as both marketed sorafenib and anti-PD-1, it could synergize with either of them in combination therapy to further extend life expectancy and suppress distant metastasis more significantly.

Hesperetin promotes longevity and delays aging via activation of Cisd2 in naturally aged mice.

BACKGROUND: The human CISD2 gene is located within a longevity region mapped on chromosome 4q. In mice, Cisd2 levels decrease during natural aging and genetic studies have shown that a high level of Cisd2 prolongs mouse lifespan and healthspan. Here, we evaluate the feasibility of using a Cisd2 activator as an effective way of delaying aging. METHODS: Hesperetin was identified as a promising Cisd2 activator by herb compound library screening. Hesperetin has no detectable toxicity based on in vitro and in vivo models. Naturally aged mice fed dietary hesperetin were used to investigate the effect of this Cisd2 activator on lifespan prolongation and the amelioration of age-related structural defects and functional decline. Tissue-specific Cisd2 knockout mice were used to study the Cisd2-dependent anti-aging effects of hesperetin. RNA sequencing was used to explore the biological effects of hesperetin on aging. RESULTS: Three discoveries are pinpointed. Firstly, hesperetin, a promising Cisd2 activator, when orally administered late in life, enhances Cisd2 expression and prolongs healthspan in old mice. Secondly, hesperetin functions mainly in a Cisd2-dependent manner to ameliorate age-related metabolic decline, body composition changes, glucose dysregulation, and organ senescence. Finally, a youthful transcriptome pattern is regained after hesperetin treatment during old age. CONCLUSIONS: Our findings indicate that a Cisd2 activator, hesperetin, represents a promising and broadly effective translational approach to slowing down aging and promoting longevity via the activation of Cisd2.

Protective Effect of CXCR4 Antagonist DBPR807 against Ischemia-Reperfusion Injury in a Rat and Porcine Model of Myocardial Infarction: Potential Adjunctive Therapy for Percutaneous Coronary Intervention.

CXCR4 antagonists have been claimed to reduce mortality after myocardial infarction in myocardial infarction (MI) animals, presumably due to suppressing inflammatory responses caused by myocardial ischemia-reperfusion injury, thus, subsequently facilitating tissue repair and cardiac function recovery. This study aims to determine whether a newly designed CXCR4 antagonist DBPR807 could exert better vascular-protective effects than other clinical counterparts (e.g., AMD3100) to alleviate cardiac damage further exacerbated by reperfusion. Consequently, we find that instead of traditional continuous treatment or multiple-dose treatment at different intervals of time, a single-dose treatment of DBPR807 before reperfusion in MI animals could attenuate inflammation via protecting oxidative stress damage and preserve vascular/capillary density and integrity via mobilizing endothelial progenitor cells, leading to a desirable fibrosis reduction and recovery of cardiac function, as evaluated with the LVEF (left ventricular ejection fraction) in infarcted hearts in rats and mini-pigs, respectively. Thus, it is highly suggested that CXCR4 antagonists should be given at a single high dose prior to reperfusion to provide the maximal cardiac functional improvement. Based on its favorable efficacy and safety profiles indicated in tested animals, DBPR807 has a great potential to serve as an adjunctive medicine for percutaneous coronary intervention (PCI) therapies in acute MI patients.

Drug-like property optimization: Discovery of orally bioavailable quinazoline-based multi-targeted kinase inhibitors.

In an effort to develop new cancer therapeutics, we have reported clinical candidate BPR1K871 (1) as a potentanticancercompound in MOLM-13 and MV4-11 leukemia models, as well as in colorectal and pancreatic animal models. As BPR1K871 lacks oral bioavailability, we continued searching for orally bioavailable analogs through drug-like property optimization. We optimized both the physicochemical properties (PCP) as well as in vitro rat liver microsomal stability of 1, with concomitant monitoring of aurora kinase enzyme inhibition as well as cellular anti-proliferative activity in HCT-116 cell line. Structural modification at the 6- and 7-position of quinazoline core of 1 led to the identification of 34 as an orally bioavailable (F% = 54) multi-kinase inhibitor, which exhibits potent anti-proliferative activity against various cancer cell lines. Quinazoline 34 is selected as a promising oral lead candidate for further preclinical evaluation.

Synthesis and biological evaluation of N-glucosyl indole derivatives as sodium-dependent glucose co-transporter 2 inhibitors.

Sodium-dependent glucose co-transporter 2 (SGLT2) inhibition has been demonstrated to efficiently control hyperglycemia via an insulin secretion-independent pathway. The unique mode of action eliminates the risk of hypoglycemia and makes SGLT2 inhibitors an attractive option for the treatment of type 2 diabetes. In a continuation of our previous studies on SGLT2 inhibitors bearing different sugar moieties, sixteen new N-glucosyl indole derivatives were designed, synthesized, and evaluated for their inhibitory activity against hSGLT2. Of these sixteen, acethydrazide-containing N-glucosyl indole 9d was found to be the most potent SGLT2 inhibitor, and caused a significant elevation in urine glucose excretion in rats at 50 mg/kg, relative to the vehicle control.

Correction: 2-Aroylquinoline-5,8-diones as potent anticancer agents displaying tubulin and heat shock protein 90 (HSP90) inhibition.

Correction for '2-Aroylquinoline-5,8-diones as potent anticancer agents displaying tubulin and heat shock protein 90 (HSP90) inhibition' by Kunal Nepali et al., Org. Biomol. Chem., 2016, 14, 716-723.

4-Bromophenylhydrazinyl benzenesulfonylphenylureas as indoleamine 2,3-dioxygenase inhibitors with in vivo target inhibition and anti-tumor efficacy.

Indoleamine 2,3-dioxygenase is a heme-containing enzyme implicated in the down regulation of the anti-tumor immune response, and considered a promising anti-cancer drug target. Several pharmaceutical companies, including Pfizer, Merck, and Bristol-Myers Squibb, are known to be in pursuit of IDO inhibitors, and Incyte recently reported good results in the phase II clinical trial of the IDO inhibitor Epacadostat. In previous work, we developed a series of IDO inhibitors based on a sulfonylhydrazide core structure, and explored how they could serve as potent IDO inhibitors with good drug profiles. Herein, we disclose the development of the 4-bromophenylhydrazinyl benzenesulfonylphenylurea 5k, a potent IDO inhibitor which demonstrated 25% tumor growth inhibition in a murine CT26 syngeneic model on day 18 with 100 mg/kg oral administration twice daily, and a 30% reduction in tumor weight. Pharmacodynamic testing of 5k found it to cause a 25% and 21% reduction in kyn/trp ratio at the plasma and tumor, respectively. In the CT26 tumor model, 5k was found to slightly increase the percentage of CD3+ T cells and lymphocyte responsiveness, indicating that 5k may have potential in modulating anti-tumor immunity. These data suggest 5k to be worthy of further investigation in the development of anti-tumor drugs.

Targeting Tumor Associated Phosphatidylserine with New Zinc Dipicolylamine-Based Drug Conjugates.

A series of zinc(II) dipicolylamine (ZnDPA)-based drug conjugates have been synthesized to probe the potential of phosphatidylserine (PS) as a new antigen for small molecule drug conjugate (SMDC) development. Using in vitro cytotoxicity and plasma stability studies, PS-binding assay, in vivo pharmacokinetic studies, and maximum tolerated dose profiles, we provided a roadmap and the key parameters required for the development of the ZnDPA based drug conjugate. In particular, conjugate 24 induced tumor regression in the COLO 205 xenograft model and exhibited a more potent antitumor effect with a 70% reduction of cytotoxic payload compared to that of the marketed irinotecan when dosed at the same regimen. In addition to the validation of PS as an effective pharmacodelivery target for SMDC, our work also provided the foundation that, if applicable, a variety of therapeutic agents could be conjugated in the same manner to treat other PS-associated diseases.

1-(2,4-Dibromophenyl)-3,6,6-trimethyl-1,5,6,7-tetrahydro-4H-indazol-4-one: A Novel Opioid Receptor Agonist with Less Accompanying Gastrointestinal Dysfunction than Morphine.

BACKGROUND: The authors investigated the pharmacology and signaling pathways of the opioid receptors modulated by compound 1, 1-(2,4-dibromophenyl)-3,6,6-trimethyl-1,5,6,7-tetrahydro-4H-indazol-4-one. METHODS: In vitro studies of compound 1 were assessed by using a radioligand-binding assay (n = 3), a cyclic adenosine monophosphate assay (n = 3), a ß-arrestin assay (n = 3), an internalization assay (n = 3), and an immunohistochemistry (n = 8). In vivo studies of compound 1 were characterized using a tail-flick test (n = 5 to 6), tail-clip test (n = 7), von Frey hair test (n = 5), and charcoal meal test (n = 5). RESULTS: Compound 1 elicited robust effects in µ-opioid (mean ± SD; binding affinity: 15 ± 2 nM; cyclic adenosine monophosphate assay: 24 ± 6 nM), δ-opioid (82 ± 7 nM; 1.9 ± 0.1 µM), and κ-opioid (76 ± 9 nM; 1.4 ± 0.5 µM) receptor-expressing cells. Compound 1 acts as a full agonist of ß-arrestin-2 recruitment in µ-opioid (1.1 ± 0.3 µM) and δ-opioid (9.7 ± 1.9 µM) receptor-expressing cells. Compound 1 caused less gastrointestinal dysfunction (charcoal meal test: morphine: 82 ± 5%; compound 1: 42 ± 5%) as well as better antinociception in mechanical pain hypersensitivity (tail-clip test: morphine: 10 ± 3 s; compound 1: 19 ± 1 s) and in cancer-induced pain (von Frey hair test: morphine: 0.1 ± 0.1 g; compound 1: 0.3 ± 0.1 g) than morphine at equi-antinociceptive doses. CONCLUSIONS: Compound 1 produced antinociception with less gastrointestinal dysfunction than morphine.

In vitro and in vivo studies of a potent capsid-binding inhibitor of enterovirus 71.

OBJECTIVES: Enterovirus 71 (EV-A71) is an important pathogen that can cause severe neurological symptoms and even death. Our aim was to identify potent anti-EV-A71 compounds and study their underlying mechanisms and in vivo activity. METHODS: We identified a potent imidazolidinone derivative (abbreviated to PR66) as an inhibitor of EV-A71 infection from the screening of compounds and subsequent structure-based modification. Time-course treatments and resistant virus selection of PR66 were employed to study the mode of mechanism of PR66. In vivo activity of PR66 was tested in the ICR strain of new-born mice challenged with EV-A71/4643/MP4. RESULTS: PR66 could impede the uncoating process during viral infection via interaction with capsid protein VP1, as shown by a resistant virus selection assay. Using site-directed mutagenesis, we confirmed that a change from valine to phenylalanine in the 179th amino acid residue of the cDNA-derived resistant virus resulted in resistance to PR66. PR66 increased the virion stability of WT viruses, but not the PR66-resistant mutant, in a particle stability thermal release assay. We further showed that PR66 had excellent anti-EV-A71 activity in an in vivo mouse model of disease, with a dose-dependent increase in survival rate and in protection against virus-induced hind-limb paralysis following oral or intraperitoneal administration. This was associated with reductions of viral titres in brain and muscle tissues. CONCLUSIONS: We demonstrated here for the first time that an imidazolidinone derivative (PR66) could protect against EV-A71-induced neurological symptoms in vivo by suppressing EV-A71 replication. This involved binding to and restricting viral uncoating.

Activation of delta-opioid receptor contributes to the antinociceptive effect of oxycodone in mice.

Oxycodone has been used clinically for over 90 years. While it is known that it exhibits low affinity for the multiple opioid receptors, whether its pharmacological activities are due to oxycodone activation of the opioid receptor type or due to its active metabolite (oxymorphone) that exhibits high affinity for the mu-opioid receptors remains unresolved. Ross and Smith (1997) reported the antinociceptive effects of oxycodone (171nmol, i.c.v.) are induced by putative kappa-opioid receptors in SD rat while others have reported oxycodone activities are due to activation of mu- and/or delta-opioid receptors. In this study, using male mu-opioid receptor knock-out (MOR-KO) mice, we examined whether delta-opioid receptor was involved in oxycodone antinociception. Systemic subcutaneous (s.c.) administration of oxycodone (above 40mg/kg) could induce a small but significant antinociceptive effect in MOR-KO mice by the tail flick test. Delta-opioid receptor antagonist (naltrindole, 10mg/kg or 20mg/kg, i.p.) could block this effect. When oxycodone was injected directly into the brain of MOR-KO mice by intracerebroventricular (i.c.v.) route, oxycodone at doses of 50nmol or higher could induce similar level of antinociceptive responses to those observed in wild type mice at the same doses by i.c.v. Delta-opioid receptor antagonists (naltrindole at 10nmol or ICI 154,129 at 20µg) completely blocked the supraspinal antinociceptive effect of oxycodone in MOR-KO mice. Such oxycodone antinociceptive responses were probably not due to its active metabolites oxymorphone because (a) the relative low level of oxymorphone was found in the brain after systemically or centrally oxycodone injection using LC/MS/MS analysis; (b) oxymorphone at a dose that mimics the level detected in the mice brain did not show any significant antinocieption effect; (c) oxycodone exhibits equal potency as oxymorphone albeit being a partial agonist in regulating [Ca(2+)]I transients in a clonal cell line expressing high level of mu-opioid receptor. These data suggest that oxycodone by itself can activate both the mu- and delta-opioid receptors and that delta-opioid receptors may contribute to the central antinociceptive effect of oxycodone in mice.

2-Aroylquinoline-5,8-diones as potent anticancer agents displaying tubulin and heat shock protein 90 (HSP90) inhibition.

This study reports the synthesis of a series of 2-aroylquinoline-5,8-diones (11-23) on the basis of scaffold hopping. The presence of a methoxy group at C6 assists the highly regioselective incorporation with various amines, and simplifies the structural identification process. Among the synthetic compounds, 6-dimethylamino-2-(3,4,5-trimethoxybenzoyl)-quinoline-5,8-dione (12) and 7-pyrrolidin-1-yl-2-(3,4,5-trimethoxybenzoyl)-quinoline-5,8-dione (23) exhibit remarkable anti-proliferative activity against the cancer cell lines tested with mean IC50 values of 0.14 and 0.27 µM, respectively. Compound 23 showed moderate inhibitory activity against tubulin polymerization with an IC50 value of 5.9 µM. In a western blot analysis, 23 caused induction of HSP70 and degradation of Akt, revealing that it possesses HSP90 inhibitory activity.

N-Indolylglycosides bearing modifications at the glucose C6-position as sodium-dependent glucose co-transporter 2 inhibitors.

Suppression of glucose reabsorption through the inhibition of sodium-dependent glucose co-transporter 2 (SGLT2) is a promising therapeutic approach for the treatment of type 2 diabetes. To investigate the effect of C6-substitution on inhibition of SGLT2 by N-indolylglucosides, a small library of 6-triazole, 6-amide, 6-urea, and 6-thiourea N-indolylglycosides were synthesized and tested. A detailed structure-activity relationship (SAR) study culminated in the identification of 6-amide derivatives 6a and 6o as potent SGLT2 inhibitors, which were further tested for inhibitory activity against SGLT1. The data obtained indicated that 6a and 6o are mildly to moderately selective for SGLT2 over SGLT1. Both compounds were also evaluated in a urinary glucose excretion test and pharmacokinetic study; 6a was found capable of inducing urinary glucose excretion in normal SD rats.

Novel Nrf2/ARE activator, trans-Coniferylaldehyde, induces a HO-1-mediated defense mechanism through a dual p38α/MAPKAPK-2 and PK-N3 signaling pathway.

The induction of detoxifying enzymes and antioxidant proteins by chemopreventive agents protects cells from oxidizing substances capable of damaging DNA integrity and initiating carcinogenesis. Coniferyl aldehyde, a naturally occurring substance, has been found in many foods and edible plants. We and others previously demonstrated that trans-coniferylaldehyde (t-CA) has potential antimutagenic and antioxidant properties. However, the mechanism underlying its Nrf2-mediated antioxidant effect remains largely unknown. In the present study, we demonstrated that t-CA significantly stimulated antioxidant-responsive element (ARE)-driven luciferase activity in a cell model and increased the expression of ARE-dependent detoxifying/antioxidant genes and their protein products in vitro and in vivo. The detoxifying/antioxidant genes activated by t-CA, especially heme oxygenase-1 (HO-1), were found to be involved in its cytoprotective effects against oxidative stress and cell injuries elicited by carcinogens tert-butylhydroperoxide and arecoline. Furthermore, the t-CA-induced phosphorylation and nuclear translocation of nuclear factor erythroid-2-related factor 2 (Nrf2) played a crucial role in this ARE-mediated cellular defense. Moreover, we found that p38 MAPK and protein kinase C (PKC) signaling pathways participated in the t-CA-induced, Nrf2-mediated cytoprotective effect. Among them, p38α/MAPKAPK-2 and an atypical PKC, PK-N3, were critical for the activation of the Nrf2/HO-1 axis by t-CA. In conclusion, we demonstrated for the first time that t-CA attenuates carcinogen-induced oxidative stress by activating Nrf2 via p38α/MAPKAPK-2- and PK-N3-dependent signaling pathways. In addition, t-CA increased the level of Nrf2-mediated detoxifying/antioxidant proteins in vivo, suggesting that t-CA may have potential for use in the management of carcinogenesis and meriting further investigation.

Discovery of a Long Half-Life AURKA Inhibitor to Treat MYC-Amplified Solid Tumors as a Monotherapy and in Combination with Everolimus.

Aurora kinase inhibitors, such as alisertib, can destabilize MYC-family oncoproteins and have demonstrated compelling antitumor efficacy. In this study, we report 6K465, a novel pyrimidine-based Aurora A inhibitor, that reduces levels of c-MYC and N-MYC oncoproteins more potently than alisertib. In an analysis of the antiproliferative effect of 6K465, the sensitivities of small cell lung cancer (SCLC) and breast cancer cell lines to 6K465 were strongly associated with the protein levels of c-MYC and/or N-MYC. We also report DBPR728, an acyl-based prodrug of 6K465 bearing fewer hydrogen-bond donors, that exhibited 10-fold improved oral bioavailability. DBPR728 induced durable tumor regression of c-MYC- and/or N-MYC-overexpressing xenografts including SCLC, triple-negative breast cancer, hepatocellular carcinoma, and medulloblastoma using a 5-on-2-off or once-a-week dosing regimen on a 21-day cycle. A single oral dose of DBPR728 at 300 mg/kg induced c-MYC reduction and cell apoptosis in the tumor xenografts for more than 7 days. The inhibitory effect of DBPR728 at a reduced dosing frequency was attributed to its uniquely high tumor/plasma ratio (3.6-fold within 7 days) and the long tumor half-life of active moiety 6K465. Furthermore, DBPR728 was found to synergize with the mTOR inhibitor everolimus to suppress c-MYC- or N-MYC-driven SCLC. Collectively, these results suggest DBPR728 has the potential to treat cancers overexpressing c-MYC and/or N-MYC.

Discovery of Dual MER/AXL Kinase Inhibitors as Bifunctional Small Molecules for Inhibiting Tumor Growth and Enhancing Tumor Immune Microenvironment.

A series of bifunctional compounds have been discovered for their dual functionality as MER/AXL inhibitors and immune modulators. The furanopyrimidine scaffold, renowned for its suitability in kinase inhibitor discovery, offers at least three distinct pharmacophore access points. Insights from molecular modeling studies guided hit-to-lead optimization, which revealed that the 1,3-diketone side chain hybridized with furanopyrimidine scaffold that respectively combined amino-type substituent and 1H-pyrazol-4-yl substituent on the top and bottom of the aryl regions to produce 22 and 33, exhibiting potent antitumor activities in various syngeneic and xenograft models. More importantly, 33 demonstrated remarkable immune-modulating activity by upregulating the expression of total T-cells, cytotoxic CD8+ T-cells, and helper CD4+ T-cells in the spleen. These findings underscored the bifunctional capabilities of 33 (BPR5K230) with excellent oral bioavailability (F = 54.6%), inhibiting both MER and AXL while modulating the tumor microenvironment and highlighting its diverse applicability for further studies to advance its therapeutic potential.

Resistance studies of a dithiazol analogue, DBPR110, as a potential hepatitis C virus NS5A inhibitor in replicon systems.

Hepatitis C virus (HCV), a member of the Flaviviridae family, affects approximately 3% of the world's population and is becoming the leading cause of liver disease in the world. Therefore, the development of novel or more effective treatment strategies to treat chronic HCV infection is urgently needed. In our previous study, we identified a potential HCV NS5A inhibitor, BP008. After further systemic optimization, we discovered a more potent HCV inhibitor, DBPR110. DBPR110 reduced the reporter expression of the HCV1b replicon with a 50% effective concentration (EC(50)) and a selective index value of 3.9 ± 0.9 pM and >12,800,000, respectively. DBPR110 reduced HCV2a replicon activity with an EC(50) and a selective index value of 228.8 ± 98.4 pM and >173,130, respectively. Sequencing analyses of several individual clones derived from the DBPR110-resistant RNAs purified from cells harboring genotype 1b and 2a HCV replicons revealed that amino acid substitutions mainly within the N-terminal region (domain I) of NS5A were associated with decreased inhibitor susceptibility. P58L/T and Y93H/N in genotype 1b and T24A, P58L, and Y93H in the genotype 2a replicon were the key substitutions for resistance selection. In the 1b replicon, V153M, M202L, and M265V play a compensatory role in replication and drug resistance. Moreover, DBPR110 displayed synergistic effects with alpha interferon (IFN-α), an NS3 protease inhibitor, and an NS5B polymerase inhibitor. In summary, our results present an effective small-molecule inhibitor, DBPR110, that potentially targets HCV NS5A. DBPR110 could be part of a more effective therapeutic strategy for HCV in the future.

1-arylsulfonyl-5-(N-hydroxyacrylamide)indolines histone deacetylase inhibitors are potent cytokine release suppressors.

A series of 1-arylsulfonyl-5-(N-hydroxyacrylamide)indolines (7-15) has been developed; the compounds exhibited potent histone deacetylase (HDAC) inhibitory activities. Notably, almost all of this series exhibited better HDAC-inhibitory and antiproliferative activities than 3-(1-benzenesulfonyl-1H-indol-5-yl)-N-hydroxyacrylamide (6), as reported in a previous study. Among these compounds, 3-[1-(4-methoxybenzenesulfonyl)-2,3-dihydro-1H-indol-5-yl]-N-hydroxyacrylamide (9) showed a two- to tenfold increase in activity compared to SAHA (1) in the suppression of lipopolysaccharide-induced cytokine production. Compound 9 also caused a marked reduction in carrageenan-induced acute inflammation in a rat model. Taken together, these data indicated that 1-arylsulfonyl-5-(N-hydroxyacrylamide)indolines HDAC inhibitors exhibit potent anti-inflammatory activity.

BPR0C305, an orally active microtubule-disrupting anticancer agent.

BPR0C305 is a novel N-substituted indolyl glyoxylamide previously reported with in-vitro cytotoxic activity against a panel of human cancer cells including P-gp-expressing multiple drug-resistant cell sublines. The present study further examined the underlying molecular mechanism of anticancer action and evaluated the in-vivo antitumor activities of BPR0C305. BPR0C305 is a novel synthetic small indole derivative that demonstrates in-vitro activities against human cancer cell growth by inhibiting tubulin polymerization, disrupting cellular microtubule assembly, and causing cell cycle arrest at the G2/M phase. It is also orally active against leukemia and solid tumor growths in mouse models. Findings of these pharmacological and pharmacokinetic studies suggest that BPR0C305 is a promising lead compound for further preclinical developments.

Discovery of 3-phenyl-1H-5-pyrazolylamine derivatives containing a urea pharmacophore as potent and efficacious inhibitors of FMS-like tyrosine kinase-3 (FLT3).

Preclinical investigations and early clinical trials suggest that FLT3 inhibitors are a viable therapy for acute myeloid leukemia. However, early clinical data have been underwhelming due to incomplete inhibition of FLT3. We have developed 3-phenyl-1H-5-pyrazolylamine as an efficient template for kinase inhibitors. Structure-activity relationships led to the discovery of sulfonamide, carbamate and urea series of FLT3 inhibitors. Previous studies showed that the sulfonamide 4 and carbamate 5 series were potent and selective FLT3 inhibitors with good in vivo efficacy. Herein, we describe the urea series, which we found to be potent inhibitors of FLT3 and VEGFR2. Some inhibited growth of FLT3-mutated MOLM-13 cells more strongly than the FLT3 inhibitors sorafenib (2) and ABT-869 (3). In preliminary in vivo toxicity studies of the four most active compounds, 10f was found to be the least toxic. A further in vivo efficacy study demonstrated that 10f achieved complete tumor regression in a higher proportion of MOLM-13 xenograft mice than 4 and 5 (70% vs 10% and 40%). These results show that compound 10f possesses improved pharmacologic and selectivity profiles and could be more effective than previously disclosed FLT3 inhibitors in the treatment of acute myeloid leukemia.