Synthesis and activity of new aryl- and heteroaryl-substituted 5,6-dihydro-4H-pyrrolo[1,2-b]pyrazole inhibitors of the transforming growth factor-beta type I receptor kinase domain

Clinical development of galunisertib (LY2157299 monohydrate), a small molecule inhibitor of transforming growth factor-beta signaling pathway

Transforming growth factor-beta (TGF-β) signaling regulates a wide range of biological processes. TGF-β plays an important role in tumorigenesis and contributes to the hallmarks of cancer, including tumor proliferation, invasion and metastasis, inflammation, angiogenesis, and escape of immune surveillance. There are several pharmacological approaches to block TGF-β signaling, such as monoclonal antibodies, vaccines, antisense oligonucleotides, and small molecule inhibitors. Galunisertib (LY2157299 monohydrate) is an oral small molecule inhibitor of the TGF-β receptor I kinase that specifically downregulates the phosphorylation of SMAD2, abrogating activation of the canonical pathway. Furthermore, galunisertib has antitumor activity in tumor-bearing animal models such as breast, colon, lung cancers, and hepatocellular carcinoma. Continuous long-term exposure to galunisertib caused cardiac toxicities in animals requiring adoption of a pharmacokinetic/pharmacodynamic-based dosing strategy to allow further development. The use of such a pharmacokinetic/pharmacodynamic model defined a therapeutic window with an appropriate safety profile that enabled the clinical investigation of galunisertib. These efforts resulted in an intermittent dosing regimen (14 days on/14 days off, on a 28-day cycle) of galunisertib for all ongoing trials. Galunisertib is being investigated either as monotherapy or in combination with standard antitumor regimens (including nivolumab) in patients with cancer with high unmet medical needs such as glioblastoma, pancreatic cancer, and hepatocellular carcinoma. The present review summarizes the past and current experiences with different pharmacological treatments that enabled galunisertib to be investigated in patients.

Brain perfusion and permeability in patients with advanced, refractory glioblastoma treated with lomustine and the transforming growth factor-β receptor I kinase inhibitor LY2157299 monohydrate

Transforming growth factor-β (TGF-β) signaling is associated with tumor progression and vascularization in malignant glioma. In the present study, magnetic resonance imaging was used to evaluate changes in the size and vascularity of glioblastomas in 12 patients who were treated with lomustine and the novel inhibitor of TGF-β signaling, LY2157299 monohydrate. A response in tumor size was observed in 2 of the 12 patients; in 1 of these 2 patients, a reduction in vascular permeability and perfusion was also detected. The effect was observed following 4 cycles of treatment (~3 months). Changes in vascularity have not previously been attributed to treatment with lomustine; therefore, the effect may be associated with LY2157299 treatment. LY2157299 does not appear to have an anti-angiogenic effect when combined with lomustine, and hence may have a different mechanism of action profile compared with anti-angiogenic drugs.

Anti-tumor activity of the TGF-β receptor kinase inhibitor galunisertib (LY2157299 monohydrate) in patient-derived tumor xenografts

Purpose

The transforming growth factor-beta (TGF-β) signaling pathway is known to play a critical role in promoting tumor growth. Consequently, blocking this pathway has been found to inhibit tumor growth. In order to achieve an optimal anti-tumor effect, however, it remains to be established whether blocking the TGF-β signaling pathway alone is sufficient, or whether the tumor microenvironment plays an additional, possibly synergistic, role.

Methods

To investigate the relevance of blocking TGF-β signaling in tumor cells within the context of their respective tissue microenvironments, we treated a panel of patient-derived xenografts (PDX) with the selective TGF-β receptor kinase inhibitor LY2157299 monohydrate (galunisertib) and assessed both the in vitro and in vivo effects.

Results

Galunisertib was found to inhibit the growth in an in vitro clonogenic assay in 6.3 % (5/79) of the examined PDX. Evaluation of the expression profiles of a number of genes, representing both canonical and non-canonical TGF-β signaling pathways, revealed that most PDX exhibited expression changes affecting TGF-β downstream signaling. Next, we subjected 13 of the PDX to an in vivo assessment and, by doing so, observed distinct response patterns. These results suggest that, next to intrinsic, also extrinsic or microenvironmental factors can affect galunisertib response. pSMAD2 protein expression and TGF-βRI mRNA expression levels were found to correlate with the in vivo galunisertib effects.

Conclusions

From our data we conclude that intrinsic, tumor-dependent TGF-β signaling does not fully explain the anti-tumor effect of galunisertib. Hence, in vivo xenograft models may be more appropriate than in vitro clonogenic assays to assess the anti-tumor activity of TGF-β inhibitors such as galunisertib.

Electronic supplementary material

The online version of this article (doi:10.1007/s13402-014-0210-8) contains supplementary material, which is available to authorized users.

First-in-human dose study of the novel transforming growth factor-β receptor I kinase inhibitor LY2157299 monohydrate in patients with advanced cancer and glioma

PURPOSE

TGFβ signaling plays a key role in tumor progression, including malignant glioma. Small-molecule inhibitors such as LY2157299 monohydrate (LY2157299) block TGFβ signaling and reduce tumor progression in preclinical models. To use LY2157299 in the treatment of malignancies, we investigated its properties in a first-in-human dose (FHD) study in patients with cancer.

EXPERIMENTAL DESIGN

Sixty-five patients (58 with glioma) with measurable and progressive malignancies were enrolled. Oral LY2157299 was given as a split dose morning and evening on an intermittent schedule of 14 days on and 14 days off (28-day cycle). LY2157299 monotherapy was studied in dose escalation (part A) first and then evaluated in combination with standard doses of lomustine (part B). Safety was assessed using Common Terminology Criteria for Adverse Events version 3.0, echocardiography/Doppler imaging, serum troponin I, and brain natriuretic peptide (BNP) levels. Antitumor activity was assessed by RECIST and Macdonald criteria.

RESULTS

In part A, 16.6% (5/30) and in part B, 7.7% (2/26) of evaluable patients with glioma had either a complete (CR) or a partial response (PR). In both parts, 15 patients with glioma had stable disease (SD), 5 of whom had SD ≥ 6 cycles of treatment. Therefore, clinical benefit (CR+PR+SD ≥ 6 cycles) was observed in 12 of 56 patients with glioma (21.4%). LY2157299 was safe, with no cardiac adverse events.

CONCLUSIONS

On the basis of the safety, pharmacokinetics, and antitumor activity in patients with glioma, the intermittent administration of LY2157299 at 300 mg/day is safe for future clinical investigation.

A review on anticancer potential of bioactive heterocycle quinoline

The advent of Camptothecin added a new dimension in the field anticancer drug development containing quinoline motif. Quinoline scaffold plays an important role in anticancer drug development as their derivatives have shown excellent results through different mechanism of action such as growth inhibitors by cell cycle arrest, apoptosis, inhibition of angiogenesis, disruption of cell migration, and modulation of nuclear receptor responsiveness. The anti-cancer potential of several of these derivatives have been demonstrated on various cancer cell lines. In this review we have compiled and discussed specifically the anticancer potential of quinoline derivatives, which could provide a low-height flying bird's eye view of the quinoline derived compounds to a medicinal chemist for a comprehensive and target oriented information for development of clinically viable anticancer drugs.

TGF-β signaling pathway as a pharmacological target in liver diseases

Transforming growth factor β (TGF-β) belongs to a class of pleiotropic cytokines that are involved in the processes of embryonic development, wound healing, cell proliferation, and differentiation. Moreover, TGF-β is also regarded as a central regulator in the pathogenesis and development of various liver diseases because it contributes to almost all of the stages of disease progression. A range of liver cells are considered to secrete TGF-β ligands and express related receptors and, consequently, play a crucial role in the progression of liver disease via different signal pathways. In this manuscript, we review the role of the TGF-β signaling pathway in liver disease and the potential of targeting the TGF-β signaling in the pharmacological treatment of liver diseases.

Discovery of N-((4-([1,2,4]triazolo[1,5-a]pyridin-6-yl)-5-(6-methylpyridin-2-yl)-1H-imidazol-2-yl)methyl)-2-fluoroaniline (EW-7197): a highly potent, selective, and orally bioavailable inhibitor of TGF-β type I receptor kinase as cancer immunotherapeutic/antifibrotic agent

A series of 2-substituted-4-([1,2,4]triazolo[1,5-a]pyridin-6-yl)-5-(6-methylpyridin-2-yl)imidazoles was synthesized and evaluated to optimize a prototype inhibitor of TGF-β type I receptor kinase (ALK5), 6. Combination of replacement of a quinoxalin-6-yl moiety of 6 with a [1,2,4]triazolo[1,5-a]pyridin-6-yl moiety, insertion of a methyleneamino linker, and a o-F substituent in the phenyl ring markedly increased ALK5 inhibitory activity, kinase selectivity, and oral bioavailability. The 12b (EW-7197) inhibited ALK5 with IC50 value of 0.013 μM in a kinase assay and with IC50 values of 0.0165 and 0.0121 μM in HaCaT (3TP-luc) stable cells and 4T1 (3TP-luc) stable cells, respectively, in a luciferase assay. Selectivity profiling of 12b using a panel of 320 protein kinases revealed that it is a highly selective ALK5/ALK4 inhibitor. Pharmacokinetic study with 12b·HCl in rats showed an oral bioavailability of 51% with high systemic exposure (AUC) of 1426 ng × h/mL and maximum plasma concentration (Cmax) of 1620 ng/mL. Rational optimization of 6 has led to the identification of a highly potent, selective, and orally bioavailable ALK5 inhibitor 12b.

Identification of protein binding partners of ALK-5 kinase inhibitors

We have investigated the binding characteristics of a potent member of the bis-ortho-substituted five-membered nitrogen heterocycle class of ALK-5 kinase inhibitors with lysates of cultured HEK-293 cells to identify protein binding partners of potential biological significance. An affinity chromatographic resin containing an immobilized ALK-5 kinase inhibitor, 2-phenyl-4-[3-(pyridin-2-yl)-1H-pyrazol-4-yl]pyridine, was used to capture specific proteins from the cell lysate. The soluble inhibitor was then used to specifically elute the proteins which selectively bound to the pharmacophore ligand structure. Application of 2-D SDS-PAGE analysis with positive and negative controls demonstrated the inhibitor bound several different proteins via selective molecular recognition processes. The structural features of the specifically eluted proteins were identified by peptide mass fingerprinting (PMF) methods and included proteins with structural, metabolic and chaperone functions. Furthermore, these PMF results identified the therapeutic target in various cancer treatment studies, HSP-70, as a potential high-affinity binding partner. These observations warrant examination of bis-ortho-substituted five-membered nitrogen heterocycles as dual ALK-5/HSP-70 inhibitors for anti-cancer drug development.

Computational studies of TGF-βRI (ALK-5) inhibitors: analysis of the binding interactions between ligand-receptor using 2D and 3D techniques

ALK-5 (Activin-Like Kinase 5) is a biological receptor involved in a variety of pathological processes such as cancer and fibrosis. ALK-5 receptor propagates an intracellular signaling that forms a protein complex capable of reaching the nucleus and modulating the gene transcription. In the present study, comparative molecular field analysis (CoMFA) and hologram quantitative structure-activity relationship (HQSAR) studies were conducted on a series of potent ALK-5 inhibitors. Significant correlation coefficients (CoMFA, r(2)=0.99 and q(2)=0.85; HQSAR, r(2)=0.92 and q(2)=0.72) were obtained, indicating the predictive potential of the 2D and 3D models for untested compounds. The models were then used to predict the potency of a test set, and the predicted values from the HQSAR and CoMFA models were in good agreement with the experimental results. The final QSAR models, along with the information obtained from 3D (steric and electrostatic) contour maps and 2D contribution maps, can be useful for the design of novel bioactive ligands.

Directing differentiation of human embryonic stem cells toward anterior neural ectoderm using small molecules

Based on knowledge of early embryo development, where anterior neural ectoderm (ANE) development is regulated by native inhibitors of bone morphogenic protein (BMP) and Nodal/Activin signaling, most published protocols of human embryonic stem cell differentiation to ANE have demonstrated a crucial role for Smad signaling in neural induction. The drawbacks of such protocols include the use of an embryoid body culture step and use of polypeptide secreted factors that are both expensive and, when considering clinical applications, have significant challenges in terms of good manufacturing practices compliancy. The use of small molecules to direct differentiation of pluripotent stem cells toward a specified lineage represents a powerful approach to generate specific cell types for further understanding of biological function, for understanding disease processes, for use in drug discovery, and finally for use in regenerative medicine. We therefore aimed to find controlled and reproducible animal-component-free differentiation conditions that would use only small molecules. Here, we demonstrate that pluripotent stem cells can be reproducibly and efficiently differentiated to PAX6(+) (a marker of neuroectoderm) and OCT4(-) (a marker of pluripotent stem cells) cells with the use of potent small inhibitors of the BMP and Activin/Nodal pathways, and in animal-component-free conditions, replacing the frequently used Noggin and SB431542. We also show by transcript analysis, both at the population level and for the first time at the single-cell level, that differentiated cells express genes characteristic for the development of ANE, in particular for the development of the future forebrain.

TGF-β in the Bone Microenvironment: Role in Breast Cancer Metastases

Breast cancer is the most prevalent cancer among females worldwide. It has long been known that cancers preferentially metastasize to particular organs, and bone metastases occur in ∼70% of patients with advanced breast cancer. Breast cancer bone metastases are predominantly osteolytic and accompanied by bone destruction, bone fractures, pain, and hypercalcemia, causing severe morbidity and hospitalization. In the bone matrix, transforming growth factor-β (TGF-β) is one of the most abundant growth factors, which is released in active form upon tumor-induced osteoclastic bone resorption. TGF-β, in turn, stimulates bone metastatic cells to secrete factors that further drive osteolytic destruction of the bone adjacent to the tumor, categorizing TGF-β as a crucial factor responsible for driving the feed-forward vicious cycle of cancer growth in bone. Moreover, TGF-β activates epithelial-to-mesenchymal transition, increases tumor cell invasiveness and angiogenesis and induces immunosuppression. Blocking the TGF-β signaling pathway to interrupt this vicious cycle between breast cancer and bone offers a promising target for therapeutic intervention to decrease skeletal metastasis. This review will describe the role of TGF-β in breast cancer and bone metastasis, and pre-clinical and clinical data will be evaluated for the potential use of TGF-β inhibitors in clinical practice to treat breast cancer bone metastases.

Screening and identification of a novel class of TGF-β type 1 receptor kinase inhibitor

Transforming growth factor β (TGF-β) type I receptor (activin receptor-like kinase 5, ALK5) has been identified as a promising target for fibrotic diseases. To find a novel inhibitor of ALK5, the authors performed a high-throughput screen of a library of 420,000 compounds using dephosphorylated ALK5. From primary hits of 1521 compounds, 555 compounds were confirmed. In total, 124 compounds were then selected for follow-up based on their unique structures and other properties. Repeated concentration-response testing and final interference assays of the above compounds resulted in the discovery of a structurally novel ALK5 inhibitor (compound 8) (N-(thiophen 2-ylmethyl)-3-(3,4,5 trimethoxyphenyl)imidazo[1,2β]pyridazin 6-amine) with a low IC(50) value of 0.7 µM. Compound 8 also inhibited the TGF-β-induced nuclear translocation of SMAD with an EC(50) value of 0.8 µM. Kinetic analysis revealed that compound 8 inhibited ALK5 via mixed-type inhibition, suggesting that it may bind to ALK5 differently than other published adenosine triphosphate site inhibitors.

Proteins mediating collagen biosynthesis and accumulation in arterial repair: novel targets for anti-restenosis therapy

Events contributing to restenosis after coronary interventions include platelet aggregation, inflammatory cell infiltration, growth factor release, and accumulation of smooth muscle cells (SMCs) and extracellular matrix (ECM). The ECM is composed of various collagen subtypes and proteoglycans and over time constitutes the major component of the mature restenotic plaque. The pathophysiology of collagen accumulation in the ECM during arterial restenosis is reviewed. Factors regulating collagen synthesis and degradation, including various cytokines and growth factors involved in the process, may be targets for therapies aimed at prevention of in-stent restenosis.

The polarization of immune cells in the tumour environment by TGFbeta

Transforming growth factor-beta (TGFbeta) is an immunosuppressive cytokine produced by tumour cells and immune cells that can polarize many components of the immune system. This Review covers the effects of TGFbeta on natural killer (NK) cells, dendritic cells, macrophages, neutrophils, CD8(+) and CD4(+) effector and regulatory T cells, and NKT cells in animal tumour models and in patients with cancer. Collectively, many recent studies favour the hypothesis that blocking TGFbeta-induced signalling in the tumour microenvironment enhances antitumour immunity and may be beneficial for cancer therapy. An overview of the current drugs and reagents available for inhibiting TGFbeta-induced signalling and their phase in clinical development is also provided.

Transforming growth factor-beta: a target for cancer therapy

Transforming growth factor-beta (TGF-beta) is a pleiotropic growth factor that regulates cell growth and differentiation, apoptosis, cell motility, extracellular matrix production, angiogenesis, and cellular immune responses. TGF-beta demonstrates paradoxical action whereby it can function to suppress early tumorigenesis; however, it can also facilitate malignant transformation and stimulate tumor growth by manipulating a more hospitable environment for tumor invasion and the development of metastases. Given the integral role of TGF-beta in transformation and cancer progression, various components of the TGF-beta signaling pathway offer potentially attractive therapeutic targets for cancer treatment. This review focuses on the role of TGF-beta in cancer and discusses both small and large molecule drugs currently in development that target TGF-beta, its receptor and important down stream steps along its signaling pathway.

Identification of host-dependent survival factors for intracellular Mycobacterium tuberculosis through an siRNA screen

The stable infection of host macrophages by Mycobacterium tuberculosis (Mtb) involves, and depends on, the attenuation of the diverse microbicidal responses mounted by the host cell. This is primarily achieved through targeted perturbations of the host cellular signaling machinery. Therefore, in view of the dependency of the pathogen on host molecules for its intracellular survival, we wanted to test whether targeting such factors could provide an alternate route for the therapeutic management of tuberculosis. To first identify components of the host signaling machinery that regulate intracellular survival of Mtb, we performed an siRNA screen against all known kinases and phosphatases in murine macrophages infected with the virulent strain, H37Rv. Several validated targets could be identified by this method where silencing led either to a significant decrease, or enhancement in the intracellular mycobacterial load. To further resolve the functional relevance of these targets, we also screened against these identified targets in cells infected with different strains of multiple drug-resistant mycobacteria which differed in terms of their intracellular growth properties. The results obtained subsequently allowed us to filter the core set of host regulatory molecules that functioned independently of the phenotypic variations exhibited by the pathogen. Then, using a combination of both in vitro and in vivo experimentation, we could demonstrate that at least some of these host factors provide attractive targets for anti-TB drug development. These results provide a “proof-of-concept” demonstration that targeting host factors subverted by intracellular Mtb provides an attractive and feasible strategy for the development of anti-tuberculosis drugs. Importantly, our findings also emphasize the advantage of such an approach by establishing its equal applicability to infections with Mtb strains exhibiting a range of phenotypic diversifications, including multiple drug-resistance. Thus the host factors identified here may potentially be exploited for the development of anti-tuberculosis drugs.

The adaptation of Mycobacterium tuberculosis (Mtb) involves dynamic interactions with the molecular components of the host cellular machinery. Therefore, targeting relevant host factors may provide an alternate approach for the chemotherapy of tuberculosis (TB). To test this, we first performed an siRNA screen targeting all known kinases and phosphatases in murine macrophages infected with a virulent strain of Mtb. A subsequent validation of this screen then identified several host molecules whose depletion severely affected the intracellular survival of mycobacteria. We also then screened against the identified host targets in cells infected with independent isolates of MDR-Mtb. This exercise identified those host molecules that were indispensable for supporting infection, independent of the phenotypic variations exhibited by the pathogen. Then, by using a pharmacological inhibitor that simultaneously targeted two of these molecules, we were able to demonstrate clearance of both drug-sensitive and drug-resistant strains of Mtb from infected cells. Importantly, this inhibitor was also effective in mice infected with the virulent strain of Mtb. Thus, in addition to demonstrating the feasibility of targeting host molecules involved in supporting intracellular persistence of pathogen for TB therapy, our studies also identify several such molecules that may be exploited for the purposes of drug development.

Oncogenic mutations regulate tumor microenvironment through induction of growth factors and angiogenic mediators

Activating mutations in the tyrosine kinase domain of HER2 (ErbB2) have been identified in human cancers. Compared to wild-type HER2, mutant HER2 shows constitutively activate kinase activity and increased oncogenicity. Cells transformed by mutant HER2 are resistant to EGFR tyrosine kinase inhibitors and exhibit an attenuated response to the HER2 antibody trastuzumab. We investigated herein pathways through which mutant HER2 alters the extracellular environment, potentially leading to drug resistance and the effect of simultaneously targeting HER2 and the tumor cell microenvironment with a therapeutic intent. Expression of mutant HER2 in mammary epithelial cells activated autocrine transforming growth factor (TGF) β1 signaling through a mechanism involving Rac1 and JNK-AP1-dependent transcription. Cells transformed by an activating mutant of H-Ras (G12V) also expressed higher TGF-β1 level through Rac1 activation. In addition, mutant HER2 induced the EGFR ligands TGF-α and amphiregulin at the mRNA and protein levels. Vascular endothelial growth factor (VEGF), a target of the TGF-β-Smad transcriptional regulation, was also induced as a result of expression of mutant HER2. Inhibition of TGF-β signaling with the Alk5 small molecule inhibitor LY2109761 reduced growth and invasiveness of cells expressing mutant HER2. Combined inhibition of intracellular and paracrine effects of mutant HER2 by trastuzumab and the EGFR antibody cetuximab was more efficient than single-agent therapies. These data suggest that mutations in oncogenes such as HER2 and Ras not only alter intracellular signaling and also influence on other components of the tumor microenvironment by inducing several pro-invasive growth factors. In turn, these serve as extracellular targets of novel therapeutic strategies directed at both cancer-driving oncogenes and the modified tumor microenvironment.

Strategies for TGF-beta modulation: a review of recent patents

BACKGROUND

TGF-beta has been identified as a key factor in the progression of various diseases, in particular cancer and fibrosis. The signaling of TGF-beta can be modulated through three distinct strategies: using antisense nucleotides that block TGF-beta mRNA (trabedersen (AP 12009)), using monoclonal antibodies to block TGF-beta isoforms (lerdelimumab, metelimumab) or using small molecule inhibitors of the TGF-beta receptor 1 (TGF-betaR1 or ALK-5).

OBJECTIVE

This review focuses on small molecules and summarizes the most recent TGF-betaR1 inhibitors reported in the patent literature.

METHODS

We searched and analyzed the patent literature claiming chemical matter for TGF-betaR1 inhibition from the 1(st) of January 2005 to the 1(st) of January 2009.

RESULTS/CONCLUSIONS

The inhibition of TGF-beta has recently been clinically validated with antisense nucleotide trabedersen. Small molecules inhibitors of TGF-betaR1 that are now in Phase I clinical trials and in preclinical stage are, therefore, of high interest and could provide a more versatile route to TGF-beta modulation through oral dosing while maintaining the same therapeutic benefits.

Rapamycin induces the TGFbeta1/Smad signaling cascade in renal mesangial cells upstream of mTOR

The mTOR kinase inhibitor rapamycin (sirolimus) is a drug with potent immunosuppressive and antiproliferative properties. We found that rapamycin induces the TGFbeta/Smad signaling cascade in rat mesangial cells (MC) as depicted by the nuclear translocation of phospho-Smads 2, -3 and Smad-4, respectively. Concomitantly, rapamycin increases the nuclear DNA binding of receptor (R)- and co-Smad proteins to a cognate Smad-binding element (SBE) which in turn causes an increase in profibrotic gene expression as exemplified by the connective tissue growth factor (CTGF) and plasminogen activator inhibitor 1 (PAI-1). Using small interfering (si)RNA we demonstrate that Smad 2/3 activation by rapamycin depends on its endogenous receptor FK binding protein 12 (FKBP12). Mechanistically, Smad induction by rapamycin is initiated by an increase in active TGFbeta(1) as shown by ELISA and by the inhibitory effects of a neutralizing TGFbeta antibody. Using an activin receptor-like kinase (ALK)-5 inhibitor and by siRNA against the TGFbeta type II receptor (TGFbeta-RII) we furthermore demonstrate a functional involvement of both types of TGFbeta receptors. However, rapamycin did not compete with TGFbeta for TGFbeta-receptor binding as found in radioligand-binding assay. Besides SB203580, a specific inhibitor of the p38 MAPK, the reactive oxygen species (ROS) scavenger N-acetyl-cysteine (NAC) and a cell-permeable superoxide dismutase (SOD) mimetic strongly abrogated the stimulatory effects of rapamycin on Smad 2 and 3 phosphorylation. Furthermore, the rapid increase in dichlorofluorescein (DCF) formation implies that rapamycin mainly acts through ROS. In conclusion, activation of the profibrotic TGFbeta/Smad signaling cascade accompanies the immunosuppressive and antiproliferative actions of rapamycin.

Synthesis and biological evaluation of benzenesulfonamide-substituted 4-(6-alkylpyridin-2-yl)-5-(quinoxalin-6-yl)imidazoles as transforming growth factor-beta type 1 receptor kinase inhibitors

A series of benzenesulfonamide-substituted 4-(6-alkylpyridin-2-yl)-5-(quinoxalin-6-yl)imidazoles have been synthesized and evaluated for their ALK5 inhibitory activity in cell-based luciferase reporter assays. Among them, 4-[5-(6-methylpyridin-2-yl)-4-(quinoxalin-6-yl)-1H-imidazol-2-ylmethyl]benzenesulfonamide and 4-[5-(6-ethylpyridin-2-yl)-4-(quinoxalin-6-yl)-1H-imidazol-2-ylmethyl]benzenesulfonamide showed more than 90% inhibition at 0.5 microM in a luciferase reporter assay using HaCaT cells transiently transfected with p3TP-luc reporter construct, but inhibited p38alpha MAP kinase activity only 11 and 8% at a concentration of 10 microM, respectively.

Transforming growth factor-beta signaling: emerging stem cell target in metastatic breast cancer?

In most human breast cancers, lowering of TGFbeta receptor- or Smad gene expression combined with increased levels of TGFbetas in the tumor microenvironment is sufficient to abrogate TGFbetas tumor suppressive effects and to induce a mesenchymal, motile and invasive phenotype. In genetic mouse models, TGFbeta signaling suppresses de novo mammary cancer formation but promotes metastasis of tumors that have broken through TGFbeta tumor suppression. In mouse models of "triple-negative" or basal-like breast cancer, treatment with TGFbeta neutralizing antibodies or receptor kinase inhibitors strongly inhibits development of lung- and bone metastases. These TGFbeta antagonists do not significantly affect tumor cell proliferation or apoptosis. Rather, they de-repress anti-tumor immunity, inhibit angiogenesis and reverse the mesenchymal, motile, invasive phenotype characteristic of basal-like and HER2-positive breast cancer cells. Patterns of TGFbeta target genes upregulation in human breast cancers suggest that TGFbeta may drive tumor progression in estrogen-independent cancer, while it mediates a suppressive host cell response in estrogen-dependent luminal cancers. In addition, TGFbeta appears to play a key role in maintaining the mammary epithelial (cancer) stem cell pool, in part by inducing a mesenchymal phenotype, while differentiated, estrogen receptor-positive, luminal cells are unresponsive to TGFbeta because the TGFBR2 receptor gene is transcriptionally silent. These same cells respond to estrogen by downregulating TGFbeta, while antiestrogens act by upregulating TGFbeta. This model predicts that inhibiting TGFbeta signaling should drive the differentiation of mammary stem cells into ductal cells. Consequently, TGFbeta antagonists may convert basal-like or HER2-positive cancers to a more epithelioid, non-proliferating (and, perhaps, non-metastatic) phenotype. Conversely, these agents might antagonize the therapeutic effects of anti-estrogens in estrogen-dependent luminal cancers. These predictions need to be addressed prospectively in clinical trials and should inform the selection of patient populations most likely to benefit from this novel anti-metastatic therapeutic approach.

Structure-activity relationship study of bone morphogenetic protein (BMP) signaling inhibitors

A structure-activity relationship study of dorsomorphin, a previously identified inhibitor of SMAD 1/5/8 phosphorylation by bone morphogenetic protein (BMP) type 1 receptors ALK2, 3, and 6, revealed that increased inhibitory activity could be accomplished by replacing the pendent 4-pyridine ring with 4-quinoline. The activity contributions of various nitrogen atoms in the core pyrazolo[1,5-a]pyrimidine ring were also examined by preparing and evaluating pyrrolo[1,2-a]pyrimidine and pyrazolo[1,5-a]pyridine derivatives. In addition, increased mouse liver microsome stability was achieved by replacing the ether substituent on the pendent phenyl ring with piperazine. Finally, an optimized compound 13 (LDN-193189 or DM-3189) demonstrated moderate pharmacokinetic characteristics (e.g., plasma t(1/2)=1.6h) following intraperitoneal administration in mice. These studies provide useful molecular probes for examining the in vivo pharmacology of BMP signaling inhibition.

Transforming growth factor beta engages TACE and ErbB3 to activate phosphatidylinositol-3 kinase/Akt in ErbB2-overexpressing breast cancer and desensitizes cells to trastuzumab

In HER2-overexpressing mammary epithelial cells, transforming growth factor beta (TGF-beta) activated phosphatidylinositol-3 kinase (PI3K)/Akt and enhanced survival and migration. Treatment with TGF-beta or expression of an activated TGF-beta type I receptor (Alk5 with the mutation T204D [Alk5(T204D)]) induced phosphorylation of TACE/ADAM17 and its translocation to the cell surface, resulting in increased secretion of TGF-alpha, amphiregulin, and heregulin. In turn, these ligands enhanced the association of p85 with ErbB3 and activated PI3K/Akt. RNA interference of TACE or ErbB3 prevented TGF-beta-induced activation of Akt and cell invasiveness. Treatment with TGF-beta or expression of Alk5(T204D) in HER2-overexpressing cells reduced their sensitivity to the HER2 antibody trastuzumab. Inhibition of Alk5, PI3K, TACE, or ErbB3 restored sensitivity to trastuzumab. A gene signature induced by Alk5(T204D) expression correlated with poor clinical outcomes in patients with invasive breast cancer. These results suggest that by acting on ErbB ligand shedding, an excess of TGF-beta may result in (i) conditioning of the tumor microenvironment with growth factors that can engage adjacent stromal and endothelial cells; (ii) potentiation of signaling downstream ErbB receptors, thus contributing to tumor progression and resistance to anti-HER2 therapies; and (iii) poor clinical outcomes in women with breast cancer.

Optimization of a dihydropyrrolopyrazole series of transforming growth factor-beta type I receptor kinase domain inhibitors: discovery of an orally bioavailable transforming growth factor-beta receptor type I inhibitor as antitumor agent

In our continuing effort to expand the SAR of the quinoline domain of dihydropyrrolopyrazole series, we have discovered compound 15d, which demonstrated the antitumor efficacy with oral bioavailability. This effort also demonstrated that the PK/PD in vivo target inhibition paradigm is an effective approach to assess potential for antitumor efficacy. The dihydropyrrolopyrazole inhibitor 15d (LY2109761) is representative of a novel series of antitumor agents.