The small molecule TGF-ß signaling inhibitor SM16 synergizes with agonistic OX40 antibody to suppress established mammary tumors and reduce spontaneous metastasis.

Effective tumor immunotherapy may require not only activation of anti-tumor effector cells, but also abrogation of tumor-mediated immunosuppression. The cytokine TGF-ß, is frequently elevated in the tumor microenvironment and is a potent immunosuppressive agent and promoter of tumor metastasis. OX40 (CD134) is a member of the TNF-α receptor superfamily and ligation by agonistic antibody (anti-OX40) enhances effector function, expansion, and survival of activated T cells. In this study, we examined the therapeutic efficacy and anti-tumor immune response induced by the combination of a small molecule TGF-ß signaling inhibitor, SM16, plus anti-OX40 in the poorly immunogenic, highly metastatic, TGF-ß-secreting 4T1 mammary tumor model. Our data show that SM16 and anti-OX40 mutually enhanced each other to elicit a potent anti-tumor effect against established primary tumors, with a 79% reduction in tumor size, a 95% reduction in the number of metastatic lung nodules, and a cure rate of 38%. This positive treatment outcome was associated with a 3.2-fold increase of tumor-infiltrating, activated CD8+ T cells, an overall accumulation of CD4+ and CD8+ T cells, and an increased tumor-specific effector T cell response. Complete abrogation of the therapeutic effect in vivo following depletion of CD4+ and CD8+ T cells suggests that the anti-tumor efficacy of SM16+ anti-OX40 therapy is T cell dependent. Mice that were cured of their tumors were able to reject tumor re-challenge and manifested a significant tumor-specific peripheral memory IFN-γ response. Taken together, these data suggest that combining a TGF-ß signaling inhibitor with anti-OX40 is a viable approach for treating metastatic breast cancer.

Discovery of a potent and highly selective PDK1 inhibitor via fragment-based drug discovery.

We report the use of a fragment-based lead discovery method, Tethering with extenders, to discover a pyridinone fragment that binds in an adaptive site of the protein PDK1. With subsequent medicinal chemistry, this led to the discovery of a potent and highly selective inhibitor of PDK1, which binds in the 'DFG-out' conformation.

Design, synthesis, and biological evaluation of pyrazolopyrimidine-sulfonamides as potent multiple-mitotic kinase (MMK) inhibitors (part I).

A novel class of pyrazolopyrimidine-sulfonamides was discovered as selective dual inhibitors of aurora kinase A (AKA) and cyclin-dependent kinase 1 (CDK1). These inhibitors were originally designed based on an early lead (compound I). SAR development has led to the discovery of potent inhibitors with single digit nM IC(50)s towards both AKA and CDK1. An exemplary compound 1a has demonstrated good efficacy in an HCT116 colon cancer xenograft model.

Pyrazolone based TGFbetaR1 kinase inhibitors.

Interruption of TGFbeta signaling through inhibition of the TGFbetaR1 kinase domain may prove to have beneficial effect in both fibrotic and oncological diseases. Herein we describe the SAR of a novel series of TGFbetaR1 kinase inhibitors containing a pyrazolone core. Most TGFbetaR1 kinase inhibitors described to date contain a core five-membered ring bearing N as H-bond acceptor. Described herein is a novel strategy to replace the core structure with pyrazolone ring, in which the carbonyl group is designed as an H-bond acceptor to interact with catalytic Lys 232.

Stereochemistry-activity relationship of orally active tetralin S1P agonist prodrugs.

Modifying FTY720, an immunosuppressant modulator, led to a new series of well phosphorylated tetralin analogs as potent S1P1 receptor agonists. The stereochemistry effect of tetralin ring was probed, and (-)-(R)-2-amino-2-((S)-6-octyl-1,2,3,4-tetrahydronaphthalen-2-yl)propan-1-ol was identified as a good SphK2 substrate and potent S1P1 agonist with good oral bioavailability.

SM16, an orally active TGF-beta type I receptor inhibitor prevents myofibroblast induction and vascular fibrosis in the rat carotid injury model.

OBJECTIVE: TGF-beta plays a significant role in vascular injury-induced stenosis. This study evaluates the efficacy of a novel, small molecule inhibitor of ALK5/ALK4 kinase, in the rat carotid injury model of vascular fibrosis. METHODS AND RESULTS: The small molecule, SM16, was shown to bind with high affinity to ALK5 kinase ATP binding site using a competitive binding assay and biacore analysis. SM16 blocked TGF-beta and activin-induced Smad2/3 phosphorylation and TGF-beta-induced plasminogen activator inhibitor (PAI)-luciferase activity in cells. Good overall selectivity was demonstrated in a large panel of kinase assays, but SM16 also showed nanomolar inhibition of ALK4 and weak (micromolar) inhibition of Raf and p38. In the rat carotid injury model, SM16 dosed once daily orally at 15 or 30 mg/kg SM16 for 14 days caused significant inhibition of neointimal thickening and lumenal narrowing. SM16 also prevented induction of adventitial smooth muscle alpha-actin-positive myofibroblasts and the production of intimal collagen, but did not decrease the percentage of proliferative cells. CONCLUSIONS: These results are the first to demonstrate the efficacy of an orally active, small-molecule ALK5/ALK4 inhibitor in a vascular fibrosis model and suggest the potential therapeutic application of these inhibitors in vascular fibrosis.

2-Aminoimidazoles inhibitors of TGF-beta receptor 1.

The 4-(5-fluoro-6-methyl-pyridin-2-yl)-5-quinoxalin-6-yl-1H-imidazol-2-ylamine 3 is a potent and selective inhibitor of TGF-betaR1. Substitution of the amino group of 3 typically led to a slight decrease in the affinity for the receptor and in TGF-beta-inducted PAI-luciferase reporter activity. However, 2-acetamidoimidazoles were identified as attractive candidates for further optimization as a result of their significant activity combined to their superior pharmacokinetic profile.

An orally active small molecule TGF-beta receptor I antagonist inhibits the growth of metastatic murine breast cancer.

BACKGROUND: Transforming growth factor beta (TGF-beta) plays a complex role in breast carcinogenesis. Initially functioning as a tumor suppressor, this cytokine later contributes to the progression of malignant cells by enhancing their invasive and metastatic potential as well as suppressing antitumor immunity. The purpose of this study was to investigate the efficacy of SM16, a novel small molecule ALK5 kinase inhibitor, to treat a highly metastatic, TGF-beta-producing murine mammary carcinoma (4T1). MATERIALS AND METHODS: Mice bearing established 4T1 tumors were treated with SM16 intraperitoneally (i.p.) or orally, and primary and metastatic tumor growth was assessed. RESULTS: SM16 inhibited Smad2 phosphorylation in cultured 4T1 tumor cells as well as primary and metastatic 4T1 tumor tissue. Blockade of TGF-beta signal transduction in 4T1 tumor cells by SM16 prevented TGF-beta-induced morphological changes and inhibited TGF-beta-induced invasion in vitro. When delivered via daily i.p. injection or orally through mouse chow, SM16 inhibited the growth of primary and metastatic 4T1 tumors. Splenocytes isolated from mice on the SM16 diet displayed enhanced IFN-gamma production and antitumor CTL activity. Furthermore, SM16 failed to inhibit the growth and metastasis of established 4T1 tumors in immunodeficient SCID mice. CONCLUSION: Taken together, the data indicate that the antitumor efficacy of SM16 is dependent on an immune-mediated mechanism and that SM16 may represent a safe and effective treatment for metastatic breast cancer.

A novel small-molecule inhibitor of transforming growth factor beta type I receptor kinase (SM16) inhibits murine mesothelioma tumor growth in vivo and prevents tumor recurrence after surgical resection.

Malignant mesothelioma is an aggressive and lethal pleural cancer that overexpresses transforming growth factor beta (TGFbeta). We investigated the efficacy of a novel small-molecule TGFbeta type I receptor (ALK5) kinase inhibitor, SM16, in the AB12 syngeneic model of malignant mesothelioma. SM16 inhibited TGFbeta signaling seen as decreased phosphorylated Smad2/3 levels in cultured AB12 cells (IC(50), approximately 200 nmol/L). SM16 penetrated tumor cells in vivo, suppressing tumor phosphorylated Smad2/3 levels for at least 3 h following treatment of tumor-bearing mice with a single i.p. bolus of 20 mg/kg SM16. The growth of established AB12 tumors was significantly inhibited by 5 mg/kg/d SM16 (P < 0.001) delivered via s.c. miniosmotic pumps over 28 days. The efficacy of SM16 was a result of a CD8+ antitumor response because (a) the antitumor effects were markedly diminished in severe combined immunodeficient mice and (b) CD8+ T cells isolated from spleens of mice treated with SM16 showed strong antitumor cytolytic effects whereas CD8+ T cells isolated from spleens of tumor-bearing mice treated with control vehicle showed minimal activity. Treatment of mice bearing large tumors with 5 mg/kg/d SM16 after debulking surgery reduced the extent of tumor recurrence from 80% to <20% (P < 0.05). SM16 was also highly effective in blocking and regressing tumors when given p.o. at doses of 0.45 or 0.65 g/kg in mouse chow. Thus, SM16 shows potent activity against established AB12 malignant mesothelioma tumors using an immune-mediated mechanism and can significantly prevent tumor recurrence after resection of bulky AB12 malignant mesothelioma tumors. These data suggest that ALK5 inhibitors, such as SM16, offer significant potential for the treatment of malignant mesothelioma and possibly other cancers.

Small molecular inhibitor of transforming growth factor-beta protects against development of radiation-induced lung injury.

PURPOSE: To determine whether an anti-transforming growth factor-beta (TGF-beta) type 1 receptor inhibitor (SM16) can prevent radiation-induced lung injury. METHODS AND MATERIALS: One fraction of 28 Gy or sham radiotherapy (RT) was administered to the right hemithorax of Sprague-Dawley rats. SM16 was administered in the rat chow (0.07 g/kg or 0.15 g/kg) beginning 7 days before RT. The rats were divided into eight groups: group 1, control chow; group 2, SM16, 0.07 g/kg; group 3, SM16, 0.15 g/kg; group 4, RT plus control chow; group 5, RT plus SM16, 0.07 g/kg; group 6, RT plus SM16, 0.15 g/kg; group 7, RT plus 3 weeks of SM16 0.07 g/kg followed by control chow; and group 8, RT plus 3 weeks of SM16 0.15 g/kg followed by control chow. The breathing frequencies, presence of inflammation/fibrosis, activation of macrophages, and expression/activation of TGF-beta were assessed. RESULTS: The breathing frequencies in the RT plus SM16 0.15 g/kg were significantly lower than the RT plus control chow from Weeks 10-22 (p <0.05). The breathing frequencies in the RT plus SM16 0.07 g/kg group were significantly lower only at Weeks 10, 14, and 20. At 26 weeks after RT, the RT plus SM16 0.15 g/kg group experienced a significant decrease in lung fibrosis (p = 0.016), inflammatory response (p = 0.006), and TGF-beta1 activity (p = 0.011). No significant reduction was found in these measures of lung injury in the group that received SM16 0.7 g/kg nor for the short-course (3 weeks) SM16 at either dose level. CONCLUSION: SM16 at a dose of 0.15 g/kg reduced functional lung damage, morphologic changes, inflammatory response, and activation of TGF-beta at 26 weeks after RT. The data suggest a dose response and also suggest the superiority of long-term vs. short-term dosing.

Intracellular TGF-beta receptor blockade abrogates Smad-dependent fibroblast activation in vitro and in vivo.

Fibrosis, the hallmark of scleroderma, is characterized by excessive synthesis of collagen and extracellular matrix proteins and accumulation of myofibroblasts. Transforming growth factor-beta (TGF-beta), a potent inducer of collagen synthesis, cytokine production, and myofibroblast transdifferentiation, is implicated in fibrosis. Profibrotic TGF-beta responses are induced primarily via the type I activin-like receptor kinase 5 (ALK5) TGF-beta receptor coupled to Smad signal transducers. Here, we investigated the effect of blocking ALK5 function with SM305, a novel small-molecule kinase inhibitor, on fibrotic TGF-beta responses. In normal dermal fibroblasts, SM305 abrogated the ligand-induced phosphorylation, nuclear import, and DNA-binding activity of Smad2/3 and Smad4, and inhibited Smad2/3-dependent transcriptional responses. Furthermore, SM305 blocked TGF-beta-induced extracellular matrix gene expression, cytokine production, and myofibroblast transdifferentiation. In unstimulated scleroderma fibroblasts, SM305 caused a variable and modest reduction in type I collagen levels, and failed to abrogate constitutive nuclear accumulation of Smad2/3, or alter the proportion of smooth muscle actin stress fiber-positive fibroblasts. In vivo, SM305 prevented TGF-beta-induced Smad2/3 phosphorylation type I collagen (COL1)A2 promoter activation in dermal fibroblasts. Taken together, these results indicate that SM305 inhibits intracellular TGF-beta signaling through selective interference with ALK5-mediated Smad activation, resulting in marked suppression of profibrotic responses induced by TGF-beta in vivo and in vitro.

Transforming the TGFbeta pathway: convergence of distinct lead generation strategies on a novel kinase pharmacophore for TbetaRI (ALK5).

The pathological activation of the transforming growth factor beta (TGFbeta) pathway plays a critical role in the progression of fibrotic diseases and also enhances tumor invasiveness and metastasis. Due to its central role in TGFbeta signaling, the TGFbeta type I receptor (TbetaRI) is emerging as an exciting target for blockade of the TGFbeta pathway. In this review we will discuss how three independent drug discovery strategies, ie, target-hopping, high-throughput screening and virtual screening, have converged in the identification of inhibitors of TalphaRI kinase. Structural studies have provided insight into the potency and selectivity of these inhibitors and form the basis for structure-based design optimization strategies. These efforts have enabled the production of potent, selective inhibitors for dissecting the TGFalpha pathway and assessing the usefulness of TalphaRI blockade in the treatment of fibrotic diseases and cancer.

Rational design of potent and selective VLA-4 inhibitors and their utility in the treatment of asthma.

Asthma, a chronic inflammatory disease of the airways, is a significant burden on our healthcare system. There is high unmet need for treatments directed towards the underlying causes of the disease. The cell surface integrin VLA-4 (very late antigen-4; alpha4beta1; CD49d/CD29) plays an important role in the trafficking of white blood cells to sites of inflammation and represents an exciting target for the development of novel anti-inflammatory drugs for the treatment of asthma. Here, we review our efforts to use rational design to identify potent, selective inhibitors of VLA-4. We describe the discovery of a series of potent VLA-4 inhibitors through the addition of a novel N-terminal organic cap to a tetrapeptide VLA-4 binding motif 4-((N'-2-methylphenyl)uriedo)phenylacetyl-Leu-Asp-Val-Pro ; Kd = 70 pM), and rationalize their structure-activity relationships using 3D-QSAR. Also, we show our rational peptidomimetic design strategy using "template hopping" from the gpIIb/IIIa integrin antagonist field, and also a novel virtual screening strategy. Two series have been developed, one that has high selectivity for the activated over the non-activated state of the receptor, and the other which is non-selective inhibiting both activated and non-activated VLA-4. Both series are highly selective for VLA-4 versus against other integrin family members. These inhibitors show promise in the treatment of asthma, based upon efficacy in a sheep model of asthma, where they inhibit both the early and late-phase responses to asthma and also block hypersensitivity.

Identification of potent and novel alpha4beta1 antagonists using in silico screening.

The antigen alpha4beta1 (very late antigen-4, VLA-4) plays an important role in the migration of white blood cells to sites of inflammation. It has been implicated in the pathology of a variety of diseases including asthma, multiple sclerosis, and rheumatoid arthritis. We describe a series of potent inhibitors of alpha4beta1 that were discovered using computational screening for replacements of the peptide region of an existing tetrapeptide-based alpha4beta1 inhibitor (1; 4-[N'-(2-methylphenyl)ureido]phenylacetyl-Leu-Asp-Val) derived from fibronectin. The search query was constructed using a model of 1 that was based upon the X-ray conformation of the related integrin-binding region of vascular cell adhesion molecule-1 (VCAM-1). The 3D search query consisted of the N-terminal cap and the carboxyl side chain of 1 because, upon the basis of existing structure-activity data on this series, these were known to be critical for high-affinity binding to alpha4beta1. The computational screen identified 12 reagents from a virtual library of 8624 molecules as satisfying the model and our synthetic filters. All of the synthesized compounds tested inhibit alpha4beta1 association with VCAM-1, with the most potent compound having an IC(50) of 1 nM, comparable to the starting compound. Using CATALYST, a 3D QSAR was generated that rationalizes the variation in activities of these alpha4beta1 antagonists. The most potent compound was evaluated in a sheep model of asthma, and a 30 mg nebulized dose was able to inhibit early and late airway responses in allergic sheep following antigen challenge and prevented the development of nonspecific airway hyperresponsiveness to carbachol. Our results demonstrate that it is possible to rapidly identify nonpeptidic replacements of integrin peptide antagonists. This approach should be useful in identification of nonpeptidic alpha4beta1 inhibitors with improved pharmacokinetic properties relative to their peptidic counterparts.

Tgf-beta type I receptor (Alk5) kinase inhibitors in oncology.

The TGFß type I receptor kinase (ALK5) is an attractive target for intervention in TGFß signaling due to its druggability as well as its centrality and specificity in the pathway. A number of potent, selective ALK5 inhibitors have been discovered which interact with the ATP-binding site of ALK5. Crystallographic studies of these molecules bound to ALK5 have provided an understanding of potency and selectivity achieved by these inhibitors. ALK5 kinase inhibitors are potently active in models of cancer due to mechanisms of action similar to those for other TGFß inhibitory agents. Recent insights into the function of TGFß in human tumors as well as in preclinical models of cancer are helping to identify potential target patient populations and drug combinations for the development of ALK5 kinase inhibitors and other TGFß- targeted therapeutics. Differences in the toxicological effects, pharmacokinetics and clinical side effects of ALK5 kinase inhibitors and other TGFß-targeted agents provide a useful and differentiated set of TGFß signaling inhibitory agents to investigate in clinical studies.

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.

Duplexed, bead-based competitive assay for inhibitors of protein kinases.

BACKGROUND: Many cellular signal transduction cascades have protein kinases as critical components. Small molecule protein kinase inhibitors can be effective as laboratory probes and drugs. Methods that allow two or more kinases to be evaluated simultaneously for inhibition by a small molecule would allow unequivocal tests of specificity and selectivity of action of the small molecule. METHODS: Two hexahistidine-tagged activin receptor-like kinases were expressed in E. coli, purified, and bound to nickel beads. A fluorescent kinase ligand (F-KL) that binds to the ATP-binding site of these kinases with nanomolar affinity was developed. Binding of F-KL with kinase on the bead made the beads bright, and inhibitors decreased the brightness. RESULTS: A test panel of 17 nonfluorescent kinase inhibitors, spanning two orders of magnitude affinity for the kinases, gave K(d) values for the kinases that correlated well with a fluorescence polarization assay. Results were obtained for the kinases in duplex, using an autosampler to send beads from a 96-well plate to a flow cytometer in a format suitable for high throughput screening. CONCLUSIONS: Inhibitors of kinases can be measured in duplex in a high throughput format by flow cytometry, if a suitable fluorescent ligand is available.

A kinase-focused compound collection: compilation and screening strategy.

Lead identification by high-throughput screening of large compound libraries has been supplemented with virtual screening and focused compound libraries. To complement existing approaches for lead identification at Biogen Idec, a kinase-focused compound collection was designed, developed and validated. Two strategies were adopted to populate the compound collection: a ligand shape-based virtual screening and a receptor-based approach (structural interaction fingerprint). Compounds selected with the two approaches were cherry-picked from an existing high-throughput screening compound library, ordered from suppliers and supplemented with specific medicinal compounds from internal programs. Promising hits and leads have been generated from the kinase-focused compound collection against multiple kinase targets. The principle of the collection design and screening strategy was validated and the use of the kinase-focused compound collection for lead identification has been added to existing strategies.