PERK Inhibition by HC-5404 Sensitizes Renal Cell Carcinoma Tumor Models to Antiangiogenic Tyrosine Kinase Inhibitors

PURPOSE

Tumors activate protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK, also called EIF2AK3) in response to hypoxia and nutrient deprivation as a stress-mitigation strategy. Here, we tested the hypothesis that inhibiting PERK with HC-5404 enhances the antitumor efficacy of standard-of-care VEGF receptor tyrosine kinase inhibitors (VEGFR-TKI).

EXPERIMENTAL DESIGN

HC-5404 was characterized as a potent and selective PERK inhibitor, with favorable in vivo properties. Multiple renal cell carcinoma (RCC) tumor models were then cotreated with both HC-5404 and VEGFR-TKI in vivo, measuring tumor volume across time and evaluating tumor response by protein analysis and IHC.

RESULTS

VEGFR-TKI including axitinib, cabozantinib, lenvatinib, and sunitinib induce PERK activation in 786-O RCC xenografts. Cotreatment with HC-5404 inhibited PERK in tumors and significantly increased antitumor effects of VEGFR-TKI across multiple RCC models, resulting in tumor stasis or regression. Analysis of tumor sections revealed that HC-5404 enhanced the antiangiogenic effects of axitinib and lenvatinib by inhibiting both new vasculature and mature tumor blood vessels. Xenografts that progress on axitinib monotherapy remain sensitive to the combination treatment, resulting in ∼20% tumor regression in the combination group. When tested across a panel of 18 RCC patient-derived xenograft (PDX) models, the combination induced greater antitumor effects relative to monotherapies. In this single animal study, nine out of 18 models responded with ≥50% tumor regression from baseline in the combination group.

CONCLUSIONS

By disrupting an adaptive stress response evoked by VEGFR-TKI, HC-5404 presents a clinical opportunity to improve the antitumor effects of well-established standard-of-care therapies in RCC.

Abstract 4010: Inhibition of PERK by HC-5404 sensitizes clear cell renal cell carcinoma tumor models to anti-angiogenic tyrosine kinase inhibitors

Anti-angiogenic agents form the backbone of standard of care for advanced clear cell renal cell carcinoma (ccRCC), but their clinical impact is limited by primary and secondary resistance mechanisms that remain a critical problem. Furthermore, the approvals for VEGFR-targeting receptor tyrosine kinase inhibitors (VEGFR-TKIs), cabozantinib in second-line, and tivozanib in third-line RCC patients were based on modest objective response rates and median progression-free survival. There is an urgent need for novel mechanisms that target adaptive tumor responses that drive resistance to these agents, as well as combination drug partners that improve outcomes for patients.

As part of their mechanism, VEGFR-TKIs induce oxygen- and nutrient-deprivation that drives ER stress. Tumors can evade deleterious ER stress by activating PERK branch of the integrated stress response, which arrests global translation and restores homeostasis. We hypothesized that inhibiting PERK would enhance the anti-tumor activity of VEGFR-TKIs in vivo and tested this using HC-5404, a potent and selective PERK inhibitor currently in Ph1 clinical testing (NCT04834778). Here, we present preclinical evidence that supports combining HC-5404 with VEGFR-TKIs in ccRCC. We demonstrate that axitinib, cabozantinib, lenvatinib, and sunitinib all activate PERK in 786-O ccRCC xenografts in a dose-responsive manner. The addition of HC-5404 significantly enhanced the tumor growth inhibition (TGI) of VEGFR-TKIs across multiple ccRCC tumor models, resulting in tumor stasis or regression in combination groups. Expression profiling and IHC analysis of tumor sections revealed that HC-5404 enhanced the anti-angiogenic effects of axitinib and lenvatinib in 786-O tumors, highlighting the protective role of PERK in response to anti-angiogenics.

To evaluate whether the combination treatments could benefit a diverse patient population, sensitivity to HC-5404 and axitinib was evaluated across a panel of patient-derived xenograft (PDX) models. This experiment confirmed widespread responsiveness to the combination treatment that in some cases achieved >50% tumor regression. As tumor progression on VEGFR-TKIs limits the success of these agents in the clinic, we evaluated the effect of adding HC-5404 to tumors that have previously progressed on axitinib. In this study, 786-O xenografts were treated with axitinib for 2-weeks and non-responders were rerandomized into groups of either single agent or combination of HC-5404 and axitinib. The combination treatment significantly improved TGI relative to either monotherapy, resulting in tumor regression of ~20%. Taken together, these findings highlight that by disrupting an adaptive stress response evoked by VEGFR-TKIs, HC-5404 presents a clinical opportunity to enhance the anti-tumor effects of well-established standard of care therapies in ccRCC.

Citation Format: Michael E. Stokes, Veronica Calvo, Crissy Dudgeon, Sho Fujisawa, Sharon Huang, Leyi Shen, Nupur Ballal, Joe McGinley, David Liu, Mark J. Mulvihill, Alan C. Rigby, Nandita Bose, Eric S. Lightcap, David Surguladze. Inhibition of PERK by HC-5404 sensitizes clear cell renal cell carcinoma tumor models to anti-angiogenic tyrosine kinase inhibitors. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4010.

Optimization of a Novel Mandelamide-Derived Pyrrolopyrimidine Series of PERK Inhibitors

The protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) is one of three endoplasmic reticulum (ER) transmembrane sensors of the unfolded protein response (UPR) responsible for regulating protein synthesis and alleviating ER stress. PERK has been implicated in tumorigenesis, cancer cell survival as well metabolic diseases such as diabetes. The structure-based design and optimization of a novel mandelamide-derived pyrrolopyrimidine series of PERK inhibitors as described herein, resulted in the identification of compound 26, a potent, selective, and orally bioavailable compound suitable for interrogating PERK pathway biology in vitro and in vivo, with pharmacokinetics suitable for once-a-day oral dosing in mice.

Discovery of 2-amino-3-amido-5-aryl-pyridines as highly potent, orally bioavailable, and efficacious PERK kinase inhibitors

The protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) is one of the three endoplasmic reticulum (ER) transmembrane sensors of the unfolded protein response (UPR) that regulates protein synthesis, alleviates cellular ER stress and has been implicated in tumorigenesis and prolonged cancer cell survival. In this study, we report a series of 2-amino-3-amido-5-aryl-pyridines that we have identified as potent, selective, and orally bioavailable PERK inhibitors. Amongst the series studied herein, compound (28) a (R)-2-Amino-5-(4-(2-(3,5-difluorophenyl)-2-hydroxyacetamido)-2-ethylphenyl)-N-isopropylnicotinamide has demonstrated potent biochemical and cellular activity, robust pharmacokinetics and 70% oral bioavailability in mice. Given these data, this compound (28) was studied in the 786-O renal cell carcinoma xenograft model. We observed dose-dependent, statistically significant tumor growth inhibition, supporting the use of this tool compound in additional mechanistic studies.

Discovery of 2,4-1H-Imidazole Carboxamides as Potent and Selective TAK1 Inhibitors

Herein we report the discovery of 2,4-1H-imidazole carboxamides as novel, biochemically potent, and kinome selective inhibitors of transforming growth factor β-activated kinase 1 (TAK1). The target was subjected to a DNA-encoded chemical library (DECL) screen. After hit analysis a cluster of compounds was identified, which was based on a central pyrrole-2,4-1H-dicarboxamide scaffold, showing remarkable kinome selectivity. A scaffold-hop to the corresponding imidazole resulted in increased biochemical potency. Next, X-ray crystallography revealed a distinct binding mode compared to other TAK1 inhibitors. A benzylamide was found in a perpendicular orientation with respect to the core hinge-binding imidazole. Additionally, an unusual amide flip was observed in the kinase hinge region. Using structure-based drug design (SBDD), key substitutions at the pyrrolidine amide and the glycine resulted in a significant increase in biochemical potency.

Abstract B37: Development of inhibitors of the activated form of KRAS G12C

Activating mutations in RAS proteins occur in ~1/3 of human cancers. These mutations impair the ability of the protein to hydrolyze GTP to GDP. As a result, mutant RAS proteins exist predominantly in the GTP-bound state, which directly activates aberrant downstream signaling via interaction with effectors such as RAF. Most RAS mutations occur at glycine 12 of the KRAS isoform. One such mutation, KRAS G12C, is particularly common in non-small cell lung cancer where it is found in ~15% of lung adenocarcinomas. Recent efforts have targeted KRAS G12C in the GDP-bound state; however, direct pharmacologic inhibition of active, GTP-bound KRAS G12C has proved challenging. Here, we deployed a novel SMARTTM (Small Molecule Assisted Receptor Targeting) platform to advance covalent compounds that selectively inhibit GTP-bound KRAS G12C. Using a mechanism reminiscent of the natural products rapamycin and cyclosporine, these compounds promote formation of a novel inhibitory ternary complex consisting of cyclophilin A (CypA, an abundant immunophilin present in all human cells), the SMART inhibitor, and GTP-KRAS G12C. Structure-based design of the SMART inhibitor yielded potent covalent inhibitors of GTP-KRAS G12C that exhibit >100-fold selectivity for mutant KRAS G12C over WT KRAS. Structural analysis of the ternary complex revealed that the covalent linkage between the SMART inhibitor and the mutant cysteine of KRAS occurred in the context of extensive interactions between CypA, the SMART inhibitor, and GTP-KRAS G12C that provide significant binding affinity (KI = 2.5 μM). The GTP-KRAS G12C|Inhibitor|CypA complex directly occluded effector binding, and as such, the compounds disrupted the KRAS-RAF interaction in biochemical assays. This activity was dependent on CypA, underlining the importance of the KRAS G12C| CypA protein-protein interaction in driving target engagement. In cell-based studies, SMART inhibitors crosslinked KRAS G12C and potently inhibited ERK phosphorylation and cell growth in G12C mutant tumor cell lines but had no effect on non-G12C bearing tumor cells. CRISPR knockout of cellular CypA confirmed that these activities were dependent on the presence of endogenous CypA. Importantly, SMART inhibitors bind directly to active, GTP-KRAS G12C and thus, their activity does not rely on trapping KRAS G12C in the inactive GDP-bound state. As a result, the cellular potency of SMART inhibitors with respect to crosslinking, pERK inhibition, and growth inhibition was maintained in the presence of growth factor treatments that reduce the cellular GDP-KRAS G12C pool. In contrast, we found that the activity of a previously described GDP-KRAS G12C targeting inhibitor was attenuated by growth factor treatment. To our knowledge, these are the first examples of mutant-selective KRAS inhibitors that target the active, GTP-bound state of KRAS G12C. We are currently optimizing the drug-like properties of these SMART inhibitors and evaluating their activity in in vivo models.

Citation Format: Michelle L. Stewart, Nicholas R. Perl, Seung-Joo Lee, Linlong Xue, Minyun Zhou, Jonah Simon, Kathryn M. Luly, Siminia Grigoriu, Alex Yuzhakov, Alec Silver, Jason T. Lowe, Cindy C. Benod, Alan S. Mann, Gregory L. Verdine, Alan C. Rigby, Mark J. Mulvihill, Earl W. May, Anna Kohlmann, Sharon A. Townson, Roy M. Pollock, Meizhong Jin. Development of inhibitors of the activated form of KRAS G12C [abstract]. In: Proceedings of the AACR Special Conference on Targeting RAS-Driven Cancers; 2018 Dec 9-12; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(5_Suppl):Abstract nr B37.

Abstract LB-234: Suppression of Bruton tyrosine kinase with X-022, a highly selective next-generation irreversible inhibitor

BTK is a member of the TEC family of kinases and is a critical component of B cell receptor (BCR) signaling, promoting B cell maturation, survival and proliferation. BCR signaling is requisite in all B cell-mediated malignancies where clinical trials with BTK inhibitors have proven efficacious. X-Rx utilized its drug discovery platform and knowhow to advance multiple novel series of BTK inhibitors. X-022 was then identified as a next generation, oral small molecule BTK inhibitor. X-022 irreversibly inhibits BTK with an IC50 of 2.3 nM. In primary human B cell and HWB assays, X-022 inhibited B cell activity with IC50 values of 49 and 93 nM, respectively. X-022 showed superior selectivity against a panel of 456 kinases, only inhibiting at >90% BTK at a concentration of 1000 nM. Oral bioavailability of >20% is observed in mice, rats and dogs. In a mouse PK/PD model, X-022 showed a dose dependent decrease in B cell activation measured over an 8 hour time interval with >98% inhibition observed at 10 mg/kg po. In an established model of collagen induced arthritis in mice, X-022 caused a dose dependent decrease in disease severity consistent with mechanism of action. No safety issues were identified in a pilot study in rodents at doses up to 300 mg/kg po. X-022 is a promising next generation irreversible oral BTK inhibitor for the treatment of B cell malignancies and chronic autoimmune diseases. In addition, the high degree of selectivity combined with favorable molecular properties make X-022 an excellent candidate for co-formulation with other targeted therapeutics.

Citation Format: Mark J. Mulvihill, Xiangyang Chen, JP Shaw, Richard Liu, Haihong Ni, Lee Babiss, Louis Renzetti. Suppression of Bruton tyrosine kinase with X-022, a highly selective next-generation irreversible inhibitor. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-234. doi:10.1158/1538-7445.AM2014-LB-234

Discovery of novel insulin-like growth factor-1 receptor inhibitors with unique time-dependent binding kinetics

This letter describes a series of small molecule inhibitors of IGF-1R with unique time-dependent binding kinetics and slow off-rates. Structure-activity and structure-kinetic relationships were elucidated and guided further optimizations within the series, culminating in compound 2. With an IGF-1R dissociative half-life (t 1/2) of >100 h, compound 2 demonstrated significant and extended PD effects in conjunction with tumor growth inhibition in xenograft models at a remarkably low and intermittent dose, which correlated with the observed in vitro slow off-rate properties.

Discovery of 7-aminofuro[2,3-c]pyridine inhibitors of TAK1: optimization of kinase selectivity and pharmacokinetics

The kinase selectivity and pharmacokinetic optimization of a series of 7-aminofuro[2,3-c]pyridine inhibitors of TAK1 is described. The intersection of insights from molecular modeling, computational prediction of metabolic sites, and in vitro metabolite identification studies resulted in a simple and unique solution to both of these problems. These efforts culminated in the discovery of compound 13a, a potent, relatively selective inhibitor of TAK1 with good pharmacokinetic properties in mice, which was active in an in vivo model of ovarian cancer.

Modulation of insulin-like growth factor-1 receptor and its signaling network for the treatment of cancer: current status and future perspectives

Based on over three decades of pre-clinical data, insulin-like growth factor-1 receptor (IGF-1R) signaling has gained recognition as a promoter of tumorogenesis, driving cell survival and proliferation in multiple human cancers. As a result, IGF-1R has been pursued as a target for cancer treatment. Early pioneering efforts targeting IGF-1R focused on highly selective monoclonal antibodies, with multiple agents advancing to clinical trials. However, despite some initial promising results, recent clinical disclosures have been less encouraging. Moreover, recent studies have revealed that IGF-1R participates in a dynamic and complex signaling network, interacting with additional targets and pathways thereof through various crosstalk and compensatory signaling mechanisms. Such mechanisms of bypass signaling help to shed some light on the decreased effectiveness of selective IGF- 1R targeted therapies (e.g. monoclonal antibodies) and suggest that targeting multiple nodes within this signaling network might be necessary to produce a more effective therapeutic response. Additionally, such findings have led to the development of small molecule IGF-1R inhibitors which also co-inhibit additional targets such as insulin receptor and epidermal growth factor receptor. Such findings have helped to guide the design rationale of numerous drug combinations that are currently being evaluated in clinical trials.

Modulation of insulin-like growth factor-1 receptor and its signaling network for the treatment of cancer: current status and future perspectives

Based on over three decades of pre-clinical data, insulin-like growth factor-1 receptor (IGF-1R) signaling has gained recognition as a promoter of tumorogenesis, driving cell survival and proliferation in multiple human cancers. As a result, IGF-1R has been pursued as a target for cancer treatment. Early pioneering efforts targeting IGF-1R focused on highly selective monoclonal antibodies, with multiple agents advancing to clinical trials. However, despite some initial promising results, recent clinical disclosures have been less encouraging. Moreover, recent studies have revealed that IGF-1R participates in a dynamic and complex signaling network, interacting with additional targets and pathways thereof through various crosstalk and compensatory signaling mechanisms. Such mechanisms of bypass signaling help to shed some light on the decreased effectiveness of selective IGF-1R targeted therapies (e.g. monoclonal antibodies) and suggest that targeting multiple nodes within this signaling network might be necessary to produce a more effective therapeutic response. Additionally, such findings have led to the development of small molecule IGF-1R inhibitors which also co-inhibit additional targets such as insulin receptor and epidermal growth factor receptor. Such findings have helped to guide the design rationale of numerous drug combinations that are currently being evaluated in clinical trials.

Abstract 2463: Discovery of imidazo[1,5-a]pyrazine derived potent, selective and orally bioavailable ACK1 inhibitors

Activated Cdc42-associated kinase (ACK1) is a non-receptor tyrosine kinase originally identified by virtue of its binding to GTP-bound small GTPase Cdc42. Considerable attention has been paid to ACK1’s involvement in cancer in recent years. For example, gene amplification and over-expression of ACK1 were found in multiple cancers including lung, ovarian and prostate cancers and were associated with poor prognosis and metastatic phenotypes. Activated ACK1 has been shown to phosphorylate and activate androgen receptor function and to promote the progression of prostate cancer. More recently, activated ACK1 was found to phosphorylate and promote the activation of Akt, a protein kinase that plays a central role in growth, proliferation and cell survival in various cancers. Taken together, these literature data suggest that ACK1 is a potential target for cancer treatment. Several series of ACK1 inhibitors have been previously disclosed in literature. Unfortunately, compounds from these series suffer from poor oral pharmacokinetic (PK) properties which have prevented them from being utilized further for in vivo studies. Therefore, there is a clear need for potent, selective and orally bioavailable small molecule ACK1 inhibitors to further probe its role in cancer, both in the in vitro and in vivo setting. This report describes the medicinal chemistry effort towards a series of novel imidazo[1,5-a]pyrazine derived inhibitors of ACK1. Virtual screening led to the discovery of the initial hit, and subsequent exploration of structure-activity relationships and optimization of drug metabolism and pharmacokinetic properties led to the identification of potent, selective and orally bioavailable ACK1 inhibitors.

Citation Format: Meizhong Jin, Jing Wang, Andrew Kleinberg, Mridula Kadalbajoo, Kam W. Siu, Andrew Cooke, Mark Bittner, Yan Yao, April Thelemann, Qunsheng Ji, Shripad Bhagwat, Kristen M. Mulvihill, Josef A. Rechka, Jonathan A. Pachter, Andrew P. Crew, David Epstein, Mark J. Mulvihill. Discovery of imidazo[1,5-a]pyrazine derived potent, selective and orally bioavailable ACK1 inhibitors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2463. doi:10.1158/1538-7445.AM2013-2463

Discovery of potent, selective and orally bioavailable imidazo[1,5-a]pyrazine derived ACK1 inhibitors

This Letter describes the medicinal chemistry effort towards a series of novel imidazo[1,5-a]pyrazine derived inhibitors of ACK1. Virtual screening led to the discovery of the initial hit, and subsequent exploration of structure-activity relationships and optimization of drug metabolism and pharmacokinetic properties led to the identification of potent, selective and orally bioavailable ACK1 inhibitors.

Abstract 2915: Discovery and characterization of OSI-296, a dual inhibitor of cMET and RON kinases

cMET and RON are receptor tyrosine kinases of the MET proto-oncogene family that are activated by their respective ligands HGF and MSP. Signaling through the cMET/HGF system can be deregulated in cancer by HGF-dependent autocrine activation, gene amplification, and/or the presence of activating mutations, among others, while for RON, constitutively active variants generated by alternative splicing or methylation-dependent promoter usage [short-form RON (sfRON)] have been identified. Approaches to abrogate aberrant cMET and RON signaling that have led to agents in clinical trials include inhibiting their kinase function with small molecules. We report here the discovery and characterization of OSI-296, a dual inhibitor of cMET and RON. The compound exhibited selectivity in a panel of 96 kinases with potent activity against cMET, including common Y1230 mutants, and RON. OSI-296 blocked cMET autophosphorylation in MKN45 cells, resulting in dose-dependent inhibition of downstream ERK, AKT, and STAT3 phosphorylation. It also showed potent cellular activity in ELISA-format sfRON and caRON cell mechanistic assays that we developed, resulting in dose-dependent inhibition of downstream ERK and AKT phosphorylation. OSI-296 showed a PK profile in rodents suitable for oral dosing with >70% bioavailability. In multiple xenografts models (cMET: MKN45, SNU-5, U87MG; RON: caRON), significant tumor growth inhibition was observed upon oral dosing with regression at higher doses. OSI-296 was very well tolerated with little body weight loss and no adverse effects even at the highest tested dose of 300 mg/kg p.o. qdx14. Solid PK/PD/TGI correlations have been established wherein >90% inhibition of cMET or RON phosphorylation sustained over 24 h by OSI-296 translated to 100% TGI. In summary, OSI-296 was shown to be a well tolerated, dual inhibitor of cMET and RON with in vivo activity in mouse xenografts models for both targets upon oral dosing.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2915. doi:1538-7445.AM2012-2915

Discovery of an Orally Efficacious Imidazo[5,1-f][1,2,4]triazine Dual Inhibitor of IGF-1R and IR

This report describes the investigation of a series of 5,7-disubstituted imidazo[5,1-f][1,2,4]triazine inhibitors of insulin-like growth factor-1 receptor (IGF-1R) and insulin receptor (IR). Structure-activity relationship exploration and optimization leading to the identification, characterization, and pharmacological activity of compound 9b, a potent, selective, well-tolerated, and orally bioavailable dual inhibitor of IGF-1R and IR with in vivo efficacy in tumor xenograft models, is discussed.

The crystal structure of a constitutively active mutant RON kinase suggests an intramolecular autophosphorylation hypothesis

A complex of RON(M1254T) with AMP-PNP and Mg(2+) reveals a substratelike positioning of Tyr1238 as well as likely catalysis-competent placement of the AMP-PNP and Mg(2+) components and indicates a tendency for cis phosphorylation. The structure shows how the oncogenic mutation may cause the constitutive activation and suggests a mechanistic hypothesis for the autophosphorylation of receptor tyrosine kinases.

Synthesis of substituted imidazo[1,5-a]pyrazines via mono-, di-, and directed remote metalation strategies

Imidazo[1,5-a]pyrazines 1 undergo regioselective C3-metalation and C5/C3-dimetalation to afford a range of functionalized derivatives 2a-2g (Table 1 ), and 4a-4d (Table 2 ). Under similar conditions, the C3-methyl derivatives 2a and 5 undergo surprising regioselective C5-deprotonation to afford, after electrophile quench, products 4b and 6a-6p (Table 3 ), results that are rationalized by quantum mechanical calculations. Benzamide 7b, obtained from such metalation chemistry followed by Suzuki cross coupling, undergoes directed remote metalation-cyclization to afford 8, representing the hitherto unknown triazadibenzo[cd,f]azulen-7(6H)-one tricyclic ring system.

Small-molecule inhibition and activation-loop trans-phosphorylation of the IGF1 receptor

The insulin-like growth factor-1 receptor (IGF1R) is a receptor tyrosine kinase (RTK) that has a critical role in mitogenic signalling during embryogenesis and an antiapoptotic role in the survival and progression of many human tumours. Here, we present the crystal structure of the tyrosine kinase domain of IGF1R (IGF1RK), in its unphosphorylated state, in complex with a novel compound, cis-3-[3-(4-methyl-piperazin-l-yl)-cyclobutyl]-1-(2-phenyl-quinolin-7-yl)-imidazo[1,5-a]pyrazin-8-ylamine (PQIP), which we show is a potent inhibitor of both the unphosphorylated (basal) and phosphorylated (activated) states of the kinase. PQIP interacts with residues in the ATP-binding pocket and in the activation loop, which confers specificity for IGF1RK and the highly related insulin receptor (IR) kinase. In this crystal structure, the IGF1RK active site is occupied by Tyr1135 from the activation loop of an symmetry (two-fold)-related molecule. This dimeric arrangement affords, for the first time, a visualization of the initial trans-phosphorylation event in the activation loop of an RTK, and provides a molecular rationale for a naturally occurring mutation in the activation loop of the IR that causes type II diabetes mellitus.

A novel, potent, and selective insulin-like growth factor-I receptor kinase inhibitor blocks insulin-like growth factor-I receptor signaling in vitro and inhibits insulin-like growth factor-I receptor dependent tumor growth in vivo

Insulin-like growth factor-I receptor (IGF-IR) and its ligands, IGF-I and IGF-II, are up-regulated in a variety of human cancers. In tumors, such as colorectal, non-small cell lung, ovarian, and pediatric cancers, which may drive their own growth and survival through autocrine IGF-II expression, the role of IGF-IR is especially critical. Here, we present a novel small-molecule IGF-IR kinase inhibitor, cis-3-[3-(4-methyl-piperazin-l-yl)-cyclobutyl]-1-(2-phenyl-quinolin-7-yl)-imidazo[1,5-a]pyrazin-8-ylamine (PQIP), which displayed a cellular IC(50) of 19 nmol/L for inhibition of ligand-dependent autophosphorylation of human IGF-IR with 14-fold cellular selectivity relative to the human insulin receptor. PQIP showed minimal activity against a panel of 32 other protein kinases. It also abolished the ligand-induced activation of downstream phosphorylated AKT and phosphorylated extracellular signal-regulated kinase 1/2 in both IGF-IR transfectant cells and a GEO human colorectal cancer cell line. Analysis of GEO cells revealed a significant level of both phosphorylated IGF-IR and IGF-II expression. Furthermore, inactivation of IGF-II in conditioned GEO culture medium by a neutralizing antibody diminished IGF-IR activation, indicating the presence of a functional IGF-II/IGF-IR autocrine loop in GEO cells. Once daily oral dosing of PQIP induced robust antitumor efficacy in GEO xenografts. The antitumor efficacy correlated with the degree and duration of inhibition of tumor IGF-IR phosphorylation in vivo by this compound. Moreover, when mice were treated for 3 days with a dose of PQIP that maximally inhibited tumor growth, only minor changes in blood glucose were observed. Thus, PQIP represents a potent and selective IGF-IR kinase inhibitor that is especially efficacious in an IGF-II-driven human tumor model.

A highly effective one-pot synthesis of quinolines from o-nitroarylcarbaldehydes

A highly effective one-pot Friedländer quinoline synthesis using inexpensive reagents has been developed. o-Nitroarylcarbaldehydes were reduced to o-aminoarylcarbaldehydes with iron in the presence of catalytic HCl (aq.) and subsequently condensed in situ with aldehydes or ketones to form mono- or di-substituted quinolines in high yields (66-100%).

1,3-Disubstituted-imidazo[1,5-a]pyrazines as insulin-like growth-factor-I receptor (IGF-IR) inhibitors

A series of novel 8-amino-1,3-disubstituted-imidazo[1,5-a]pyrazines was designed and synthesized as IGF-IR inhibitors.

3-[6-(2-Dimethylamino-1-imidazol-1-yl-butyl)-naphthalen-2-yloxy]-2,2-dimethyl-propionic acid as a highly potent and selective retinoic acid metabolic blocking agent

3-[6-(2-Dimethylamino-1-imidazol-1-yl-butyl)-naphthalen-2-yloxy]-2,2-dimethyl-propionic acid and analogs were designed and synthesized as highly potent and selective CYP26 inhibitors, serving as retinoic acid metabolic blocking agents (RAMBAs), with demonstrated in vivo efficacy to increase the half-life of exogenous atRA.

Potent and selective [2-imidazol-1-yl-2-(6-alkoxy-naphthalen-2-yl)-1-methyl-ethyl]-dimethyl-amines as retinoic acid metabolic blocking agents (RAMBAs)

A series of [2-imidazol-1-yl-2-(6-alkoxy-naphthalen-2-yl)-1-methyl-ethyl]-dimethyl-amines were designed and synthesized as CYP26 inhibitors, serving as retinoic acid metabolic blocking agents (RAMBA's).

Regio- and Stereospecific Syntheses of syn- and anti-1,2-Imidazolylpropylamines from the Reaction of 1,1‘-Carbonyldiimidazole with syn- and anti-1,2-Amino Alcohols

The regio- and stereospecific conversion of syn- and anti-1,2-amino alcohols to their respective syn- and anti-1,2-imidazolylpropylamines via treatment with 1,1'-carbonyldiimidazole is described. The rationale behind the regio- and stereospecific nature as well as the generality of the reaction is discussed.

Regio- and stereoselective ring openings of 3-Aza-2-oxabicyclo[2.2.1]hept-5-ene systems with copper catalyst-modified grignard reagents: application to the synthesis of an inhibitor of 5-lipoxygenase

Treatment of acylnitroso hetero Diels-Alder cycloadducts 2 with organomagnesium reagents in the presence of a catalytic amount of copper induces ring opening to afford predominantly monocyclic anti-1,2-hydroxamic acids 12. Alkylmagnesium reagents were found to give superior regio- and stereoselectivities compared with vinyl and arylmagnesium reagents. This cycloadduct ring opening methodology was applied to the synthesis of a unique cyclopentenyl hydroxamic acid-based inhibitor of 5-lipoxygenase.

Novel 1,4-benzodiazepines from acylnitroso-derived hetero-Diels-Alder cycloadducts

[reaction: see text] N(4)-Hydroxy-1,4-benzodiazepines were synthesized in a single step from synthetically versatile acylnitroso-derived hetero-Diels-Alder cycloadducts. The efficiency of this transformation was found to be dependent on the NH pK(a) of the cycloadduct sulfonamide.

The synthesis of enantiomerically pure, highly functionalized heterocycles: the products of amino acid based acylnitroso hetero Diels-Alder reactions

The diastereoselectivities of several chiral acylnitroso dienophiles (9a-h, 12 and 15) derived from optically pure, N-protected alpha-amino hydroxamic acids (2a-h, 4 and 7) were determined in an intermolecular hetero Diels-Alder reaction with cyclopentadiene. The diastereomeric excesses ranged from 0 to 72%. Hydroxamic acids with polar functionality were examined extensively to determine the effect of hydrogen bonding on the cycloaddition. The largest increase in diastereoselectivity was observed with increasing the steric bulk at the alpha-position of the hydroxamic acids and not with potential hydrogen bonding interactions. The cycloadditions afforded synthetically useful quantities of functionally rich, enantiomerically pure heterocycles (10a-h, 11a-h, 13, 14, 16 and 17), which have been elaborated into a variety of biologically interesting products.