Sarvajit Chakravarty

Targeting Endogenous Transforming Growth Factor β Receptor Signaling in SMAD4-Deficient Human Pancreatic Carcinoma Cells Inhibits Their Invasive Phenotype 1

Transforming growth factor-β (TGF-β) suppresses tumor formation by blocking cell cycle progression and maintaining tissue homeostasis. In pancreatic carcinomas, this tumor suppressive activity is often lost by inactivation of the TGF-β-signaling mediator, Smad4. We found that human pancreatic carcinoma cell lines that have undergone deletion of MADH4 constitutively expressed high endogenous levels of phosphorylated receptor-associated Smad proteins (pR-Smad2 and pR-Smad3), whereas Smad4-positive lines did not. These elevated pR-Smad levels could not be attributed to a decreased dephosphorylation rate nor to increased expression of TGF-β type I (TβR-I) or type II (TβR-II) receptors. Although minimal amounts of free bioactive TGF-β1 and TGF-β2 were detected in conditioned medium, treatment with a pan-specific (but not a TGF-β3 specific) TGF-β-neutralizing antibody and with anti-αVβ6 integrin antibody decreased steady-state pSmad2 levels and activation of a TGF-β-inducible reporter gene in neighboring cells, respectively. Thus, activation of TGF-β at the cell surface was responsible for the increased autocrine endogenous and paracrine signaling. Blocking TβR-I activity using a selective kinase inhibitor (SD-093) strongly decreased the in vitro motility and invasiveness of the pancreatic carcinoma cells without affecting their growth characteristics, morphology, or the subcellular distribution of E-cadherin and F-actin. Moreover, exogenous TGF-β strongly stimulated in vitro invasiveness of BxPC-3 cells, an effect that could also be blocked by SD-093. Thus, the motile and invasive properties of Smad4-deficient pancreatic cancer cells are at least partly driven by activation of endogenous TGF-β signaling. Therefore, targeting the TβR-I kinase represents a potentially powerful novel therapeutic approach for the treatment of this disease.

p38α-Selective Mitogen-Activated Protein Kinase Inhibitor SD-282 Reduces Inflammation in a Subchronic Model of Tobacco Smoke-Induced Airway Inflammation

Chronic obstructive pulmonary disease (COPD) is characterized by pulmonary inflammation, which is relatively insensitive to inhaled corticosteroids. The extent of the pulmonary inflammation in COPD correlates with disease severity, and it is thought to play a significant role in disease progression. We have evaluated a selective p38α-selective mitogen-activated protein kinase (MAPK) inhibitor, indole-5-carboxamide (ATP-competitive inhibitor of p38 kinase) (SD-282), in an 11-day model of tobacco smoke (TS)-induced pulmonary inflammation in A/J mice, by using dexamethasone as a reference steroid. Two oral treatment paradigms were evaluated in this TS model: prophylactic with daily pretreatment before each daily exposure, and therapeutic with daily treatment for 6 days commencing after 5 days of smoke exposure. Bronchoalveolar lavage and histological evaluation of lung sections taken after exposure to TS revealed an inflammatory response composed of increased numbers of macrophages and neutrophils and enhanced mucin staining. Phospho-p38 staining in macrophages and type II epithelial cells after TS exposure was also observed. Given prophylactically or therapeutically, dexamethasone failed to inhibit any of the TS-induced inflammatory changes. By contrast, SD-282 inhibited TS-induced increases in macrophages and neutrophils. Furthermore, SD 282 reduced TS-induced increases in cyclooxygenase-2 and interleukin-6 levels, and phospho-p38 expression in the lungs. In conclusion, SD-282 markedly reduced TS-induced inflammatory responses when given prophylactically or therapeutically whereas dexamethasone was ineffective. This is the first evidence that a p38α-selective MAPK inhibitor can exert pulmonary anti-inflammatory activity in a TS exposure model when given in a therapeutic mode, establishing the potential of p38 MAPK inhibitors as a therapy for COPD.

Inhibition of Transforming Growth Factor β Signaling Reduces Pancreatic Adenocarcinoma Growth and Invasiveness

Transforming growth factor β (TGFβ) is a pleiotropic factor that regulates cell proliferation, angiogenesis, metastasis, and immune suppression. Dysregulation of the TGFβ pathway in tumor cells often leads to resistance to the antiproliferative effects of TGFβ while supporting other cellular processes that promote tumor invasiveness and growth. In the present study, SD-208, a 2,4-disubstituted pteridine, ATP-competitive inhibitor of the TGFβ receptor I kinase (TGFβRI), was used to inhibit cellular activities and tumor progression of PANC-1, a human pancreatic tumor line. SD-208 blocked TGFβ-dependent Smad2 phosphorylation and expression of TGFβ-inducible proteins in cell culture. cDNA microarray analysis and functional gene clustering identified groups of TGFβ-regulated genes involved in metastasis, angiogenesis, cell proliferation, survival, and apoptosis. These gene responses were inhibited by SD-208. Using a Boyden chamber motility assay, we demonstrated that SD-208 inhibited TGFβ-stimulated invasion in vitro. An orthotopic xenograft mouse model revealed that SD-208 reduced primary tumor growth and decreased the incidence of metastasis in vivo. Our findings suggest mechanisms through which TGFβ signaling may promote tumor progression in pancreatic adenocarcinoma. Moreover, they suggest that inhibition of TGFβRI with a small-molecule inhibitor may be effective as a therapeutic approach to treat human pancreatic cancer.

Transforming Growth Factor β Receptor I Kinase Inhibitor Down-Regulates Cytokine Secretion and Multiple Myeloma Cell Growth in the Bone Marrow Microenvironment

Purpose: Transforming growth factors (TGFs) have pleiotropic biological effects on tumor cells and their environment. In multiple myeloma (MM), we have reported that bone marrow stromal cells (BMSCs) from MM patients produce more TGF-β1 than BMSCs from healthy donors, which in turn induces interleukin (IL)-6 secretion. We show here that the TGF-β receptor I kinase inhibitor SD-208 significantly decreases secretion of both IL-6 and vascular endothelial growth factor (VEGF) from BMSCs, as well as tumor cell growth triggered by MM cell adhesion to BMSCs. Experimental Design: Cytokine production and MM cell proliferation triggered by TGF-β1 or adhesion to BMSCs were examined in the presence or absence of SD-208. Effects of SD-208 on TGF-β1–induced signaling pathways triggering IL-6 and VEGF transcription in BMSCs were also delineated. Results: SD-208 significantly inhibits not only transcription but also secretion of both IL-6 and VEGF from BMSCs triggered by either TGF-β1 or adhesion of MM cells to BMSCs. Moreover, SD-208 decreased tumor cell growth triggered by MM cell adhesion to BMSCs. SD-208 works, at least in part, by blocking TGF-β1–triggered nuclear accumulation of Smad2/3 and hypoxia-inducible factor 1α, as well as related production of IL-6 and VEGF, respectively. Conclusions: These studies indicate that SD-208 inhibits production of cytokines mediating MM cell growth, survival, drug resistance, and migration in the BM milieu, thereby providing the preclinical rationale for clinical evaluation of SD-208 to improve patient outcome in MM.

Role of the TGF-β/Alk5 Signaling Pathway in Monocrotaline-induced Pulmonary Hypertension

RATIONALE Pulmonary arterial hypertension is a progressive disease characterized by an elevation in the mean pulmonary artery pressure leading to right heart failure and a significant risk of death. Alterations in two transforming growth factor (TGF) signaling pathways, bone morphogenetic protein receptor II and the TGF-beta receptor I, Alk1, have been implicated in the pathogenesis of pulmonary hypertension (PH). However, the role of TGF-beta family signaling in PH and pulmonary vascular remodeling remains unclear. OBJECTIVES To determine whether inhibition of TGF-beta signaling will attenuate and reverse monocrotaline-induced PH (MCT-PH). METHODS We have used an orally active small-molecule TGF-beta receptor I inhibitor, SD-208, to determine the functional role of this pathway in MCT-PH. MEASUREMENTS AND MAIN RESULTS The development of MCT-PH was associated with increased vascular cell apoptosis, which paralleled TGF-beta signaling as documented by psmad2 expression. Inhibition of TGF-beta signaling with SD-208 significantly attenuated the development of the PH and reduced pulmonary vascular remodeling. These effects were associated with decreased early vascular cell apoptosis, adventitial cell proliferation, and matrix metalloproteinase expression. Inhibition of TGF-beta signaling with SD-208 in established MCT-PH resulted in a small but significant improvement in hemodynamic parameters and medial remodeling. CONCLUSIONS These findings provide evidence that increased TGF-beta signaling participates in the pathogenesis of experimental severe PH.

A Selective p38α Mitogen-Activated Protein Kinase Inhibitor Reverses Cartilage and Bone Destruction in Mice with Collagen-Induced Arthritis

Destruction of cartilage and bone is a poorly managed hallmark of human rheumatoid arthritis (RA). p38 Mitogen-activated protein kinase (MAPK) has been shown to regulate key proinflammatory pathways in RA, including tumor necrosis factor α, interleukin (IL)-1β, and cyclooxygenase-2, as well as the process of osteoclast differentiation. Therefore, we evaluated whether a p38α MAPK inhibitor, indole-5-carboxamide (SD-282), could modulate cartilage and bone destruction in a mouse model of RA induced with bovine type II collagen [collagen-induced arthritis (CIA)]. In mice with early disease, SD-282 treatment significantly improved clinical severity scores, reduced bone and cartilage loss, and reduced mRNA levels of proinflammatory genes in paw tissue, including IL-1β, IL-6, and cyclooxygenase-2. Notably, SD-282 treatment of mice with advanced disease resulted in significant improvement in clinical severity scoring and paw swelling, a reversal in bone and cartilage destruction as assessed by histology, bone volume fraction and thickness, and three-dimensional image analysis. These changes were accompanied by reduced osteoclast number and lowered levels of serum cartilage oligomeric matrix protein, a marker of cartilage breakdown. Thus, in a model of experimental arthritis associated with significant osteolysis, p38α MAPK inhibition not only attenuates disease progression but also reverses cartilage and bone destruction in mice with advanced CIA disease.

Transforming growth factor-β receptor type 1 (TGFβRI) kinase activity but not p38 activation is required for TGFβRI-induced myofibroblast differentiation and profibrotic gene expression

Transforming growth factor-β (TGFβ) is a major mediator of normal wound healing and of pathological conditions involving fibrosis, such as idiopathic pulmonary fibrosis. TGFβ also stimulates the differentiation of myofibroblasts, a hallmark of fibrotic diseases. In this study, we examined the underlying processes of TGFβRI kinase activity in myofibroblast conversion of human lung fibroblasts using specific inhibitors of TGFβRI (SD-208) and p38 mitogen-activated kinase (SD-282). We demonstrated that SD-208, but not SD-282, inhibited TGFβ-induced SMAD signaling, myofibroblast transformation, and collagen gel contraction. Furthermore, we extended our findings to a rat bleomycin-induced lung fibrosis model, demonstrating a significant decrease in the number of myofibroblasts at fibroblastic foci in animals treated with SD-208 but not those treated with SD-282. SD-208 also reduced collagen deposition in this in vivo model. Microarray analysis of human lung fibroblasts identified molecular fingerprints of these processes and showed that SD-208 had global effects on reversing TGFβ-induced genes involved in fibrosis, inflammation, cell proliferation, cytoskeletal organization, and apoptosis. These studies also revealed that although the p38 pathway may not be needed for appearance or disappearance of the myofibroblast, it can mediate a subset of inflammatory and fibrogenic events of the myofibroblast during the process of tissue repair and fibrosis. Our findings suggest that inhibitors such as SD-208 may be therapeutically useful in human interstitial lung diseases and pulmonary fibrosis.

Inhibiting TGF-β signaling restores immune surveillance in the SMA-560 glioma model

Transforming growth factor-beta (TGF-beta) is a proinvasive and immunosuppressive cytokine that plays a major role in the malignant phenotype of gliomas. One novel strategy of disabling TGF-beta activity in gliomas is to disrupt the signaling cascade at the level of the TGF-beta receptor I (TGF-betaRI) kinase, thus abrogating TGF-beta-mediated invasiveness and immune suppression. SX-007, an orally active, small-molecule TGF-betaRI kinase inhibitor, was evaluated for its therapeutic potential in cell culture and in an in vivo glioma model. The syngeneic, orthotopic glioma model SMA-560 was used to evaluate the efficacy of SX-007. Cells were implanted into the striatum of VM/Dk mice. Dosing began three days after implantation and continued until the end of the study. Efficacy was established by assessing survival benefit. SX-007 dosed at 20 mg/kg p.o. once daily (q.d.) modulated TGF-beta signaling in the tumor and improved the median survival. Strikingly, approximately 25% of the treated animals were disease-free at the end of the study. Increasing the dose to 40 mg/kg q.d. or 20 mg/kg twice daily did not further improve efficacy. The data suggest that SX-007 can exert a therapeutic effect by reducing TGF-beta-mediated invasion and reversing immune suppression. SX-007 modulates the TGF-beta signaling pathway and is associated with improved survival in this glioma model. Survival benefit is due to reduced tumor invasion and reversal of TGF-beta-mediated immune suppression, allowing for rejection of the tumor. Together, these results suggest that treatment with a TGF-betaRI inhibitor may be useful in the treatment of glioblastoma.

Antinociceptive action of a p38α MAPK inhibitor, SD-282, in a diabetic neuropathy model

&NA; Diabetes can induce a bewildering list of sensory changes, including alteration in pain sensitivity. Painful diabetic neuropathy is refractory to most common analgesics. This study examined the effect of a p38&agr; MAPK inhibitor, SD‐282, on mechanical allodynia, thermal hyperalgesia, and formalin‐evoked nociception in streptozotocin‐induced diabetic rats. Four‐week diabetic rats exhibited mechanical allodynia, decreased mechanical thresholds, and C‐ and A&dgr;‐fiber mediated thermal hyperalgesia. Mechanical and thermal responses were measured in diabetic rats following acute and repeated intraperitoneal administration of vehicle, 15 or 45 mg/kg SD‐282. Mechanical allodynia was reversed by acute and repeated administration of 15 and 45 mg/kg SD‐282. Repeated administration of 15 or 45 mg/kg SD‐282 prevented the exacerbation of C‐, but not A&dgr;‐fiber, mediated thermal hyperalgesia. Repeated administration of 45 mg/kg SD‐282 attenuated flinching behaviors during the quiescent period and the second phase of the formalin response in diabetic rats. Acute and repeated administration of 15 or 45 mg/kg SD‐282 had no effect on mechanical, thermal or formalin responses in age‐matched control rats. These results indicate a potential therapeutic value of p38&agr; MAPK inhibitors in the treatment of aberrant pain sensitivity produced by diabetes.

A p38α Selective Mitogen-Activated Protein Kinase Inhibitor Prevents Periodontal Bone Loss

In the oral microbial environment, Gram-negative bacterial derived lipopolysaccharide (LPS) can initiate inflammatory bone loss as seen in periodontal diseases. p38 Mitogen-activated protein kinase (MAPK) signaling is critical to inflammatory cytokine and LPS-induced cytokine expression, which may contribute toward periodontal bone loss. The purpose of this proof-of-principle study was to evaluate the ability of an orally active p38α MAPK inhibitor (SD-282) to reduce periopathogenic LPS-induced alveolar bone loss in an experimental rat model. Five groups of Sprague-Dawley rats received one of the following treatments: LPS injected to the palatal gingiva adjacent to the maxillary molars three times per week for 8 weeks, LPS plus two doses of SD-282 (15 or 45 mg/kg) twice daily by oral gavage, or control groups given drug vehicle (1% polyethylene glycol) or SD-282 (45 mg/kg) only. Baseline and 8-week alveolar bone loss was assessed by microcomputed tomography (μCT) and histological examination. LPS induced severe bone loss over this time period, whereas control groups were unchanged from baseline measurements. Both doses of SD-282 showed significant protection from LPS-induced bone loss. Bone area and volumetric analysis of maxillas by μCT indicated significant loss of bone volume with LPS treatment, which was blocked with the p38 inhibitor. Histological examination indicated significantly fewer tartate-resistant acid phosphatase-positive osteoclasts and a significant decrease in interleukin (IL)-6, IL-1β, and tumor necrosis factor α expression in p38 inhibitor-treated groups compared with LPS groups by immunostaining. Results from this in vivo study suggest that orally active p38 MAPK inhibitors can reduce LPS-induced inflammatory cytokine production and osteoclast formation and protect against LPS-stimulated alveolar bone loss.