Impact of the Smoothened inhibitor, IPI-926, on smoothened ciliary localization and Hedgehog pathway activity

A requisite step for canonical Hedgehog (Hh) pathway activation by Sonic Hedgehog (Shh) ligand is accumulation of Smoothened (Smo) to the primary cilium (PC). Activation of the Hh pathway has been implicated in a broad range of cancers, and several Smo antagonists are being assessed clinically, one of which is approved for the treatment of advanced basal cell carcinoma. Recent reports demonstrate that various Smo antagonists differentially impact Smo localization to the PC while still exerting inhibitory activity. In contrast to other synthetic small molecule Smo antagonists, the natural product cyclopamine binds to and promotes ciliary accumulation of Smo and “primes” cells for Hh pathway hyper-responsiveness after compound withdrawal. We compared the properties of IPI-926, a semi-synthetic cyclopamine analog, to cyclopamine with regard to potency, ciliary Smo accumulation, and Hh pathway activity after compound withdrawal. Like cyclopamine, IPI-926 promoted accumulation of Smo to the PC. However, in contrast to cyclopamine, IPI-926 treatment did not prime cells for hyper-responsiveness to Shh stimulation after compound withdrawal, but instead demonstrated continuous inhibition of signaling. By comparing the levels of drug-induced ciliary Smo accumulation with the degree of Hh pathway activity after compound withdrawal, we propose that a critical threshold of ciliary Smo is necessary for “priming” activity to occur. This “priming” appears achievable with cyclopamine, but not IPI-926, and is cell-line dependent. Additionally, IPI-926 activity was evaluated in a murine tumor xenograft model and a pharmacokinetic/pharmacodynamic relationship was examined to assess for in vivo evidence of Hh pathway hyper-responsiveness. Plasma concentrations of IPI-926 correlated with the degree and duration of Hh pathway suppression, and pathway activity did not exceed baseline levels out to 96 hours post dose. The overall findings suggest that IPI-926 possesses unique biophysical and pharmacological properties that result in Hh pathway inhibition in a manner that differentiates it from cyclopamine.

PI3K-δ and PI3K-γ inhibition by IPI-145 abrogates immune responses and suppresses activity in autoimmune and inflammatory disease models

Phosphoinositide-3 kinase (PI3K)-δ and PI3K-γ are preferentially expressed in immune cells, and inhibitors targeting these isoforms are hypothesized to have anti-inflammatory activity by affecting the adaptive and innate immune response. We report on a potent oral PI3K-δ and PI3K-γ inhibitor (IPI-145) and characterize this compound in biochemical, cellular, and in vivo assays. These studies demonstrate that IPI-145 exerts profound effects on adaptive and innate immunity by inhibiting B and T cell proliferation, blocking neutrophil migration, and inhibiting basophil activation. We explored the therapeutic value of combined PI3K-δ and PI3K-γ blockade, and IPI-145 showed potent activity in collagen-induced arthritis, ovalbumin-induced asthma, and systemic lupus erythematosus rodent models. These findings support the hypothesis that inhibition of immune function can be achieved through PI3K-δ and PI3K-γ blockade, potentially leading to significant therapeutic effects in multiple inflammatory, autoimmune, and hematologic diseases.

Zinc-related metallothionein metabolism in bovine pulmonary artery endothelial cells

Bovine pulmonary artery endothelial cells (BPAEC) were cultured in vitro under a variety of conditions to investigate how metallothionein (MT) might participate in zinc homeostasis. Experimental conditions included 10% serum to ensure that the in vitro environment would be a better reflection of the in vivo situation than with protein-free medium. MT was increased by acutely high zinc concentrations (100-200 micromol/L) in the extracellular environment. MT was relatively insensitive to moderate changes in zinc concentration (2-50 micromol/L), even after prolonged exposure for 7 to 12 days. BPAEC had reduced MT content when grown in medium containing serum that had been dialyzed to remove components with a molecular mass of less than 1,000, including zinc. Because the principal source of the major minerals in the experimental medium was not the serum, their concentrations in the final medium were not significantly influenced by serum dialysis. Restoring the zinc concentration in the medium containing the dialyzed serum did not restore MT content in BPAEC, suggesting that some small molecular weight molecule other than zinc established their basal MT content. This study did not identify these putative factors in serum, but hormones are likely candidates. Forty-eight-hour incubations of BPAEC with interleukin (IL-6) or dexamethasone increased cellular MT; however, 17beta-estradiol decreased MT, and IL-1 and adenosine 3',5'-cyclic phosphate (cAMP) had no discernible effect. We conclude that extracellular zinc concentrations have relatively little impact on the cellular concentrations of MT and zinc of BPAEC in vitro. Zinc homeostasis by BPAEC is not maintained by changing the MT concentration in response to changes in the extracellular zinc environment. (J. Nutr. Biochem. 10:00-00, 1999).

IKKepsilon and TBK1 are essential components of the IRF3 signaling pathway

The transcription factors interferon regulatory factor 3 (IRF3) and NF-kappaB are required for the expression of many genes involved in the innate immune response. Viral infection, or the binding of double-stranded RNA to Toll-like receptor 3, results in the coordinate activation of IRF3 and NF-kappaB. Activation of IRF3 requires signal-dependent phosphorylation, but little is known about the signaling pathway or kinases involved. Here we report that the noncanonical IkappaB kinase homologs, IkappaB kinase-epsilon (IKKepsilon) and TANK-binding kinase-1 (TBK1), which were previously implicated in NF-kappaB activation, are also essential components of the IRF3 signaling pathway. Thus, IKKepsilon and TBK1 have a pivotal role in coordinating the activation of IRF3 and NF-kappaB in the innate immune response.

Matrix metalloproteinases and tissue inhibitors of metalloproteinases in hamster aortic atherosclerosis: correlation with in-situ zymography

Atherogenesis requires extracellular matrix (ECM) alterations, a process possibly mediated by matrix-degrading metalloproteinases (MMPs) and their endogenous tissue inhibitors (TIMPs). The objective of this study was to examine the immunohistochemical expression patterns of MMPs-1, -2, -3 and -9 and their tissue inhibitors, TIMPs-1, -2, -3 and -4 during the three major stages of atherosclerotic lesion development in hypercholesterolemic Syrian Golden hamsters. Aortic atherosclerotic lesions (fatty streak, fibro-fatty and advanced) were histologically characterized in treated hamsters at 12, 24, and 49 weeks. The immunochemistry expression of these MMPs and TIMPs were examined in treated aortic sections with lesions and control aortic sections without lesions. MMP activity in control aortas and atherosclerotic lesions was characterized by in-situ zymography. Positive immunoreactivity for MMPs-2, -3, -9 and TIMPs-1, -2,-3, and -4 was observed in both control and atherosclerotic aortic arch segments, while MMP-1 was only observed in atherosclerotic lesions. Using in-situ zymography, we identified casein and gelatin degradation in fatty streak, fibro-fatty and advanced lesions. The immunohistochemical expression of these MMPs and TIMPs were examined in treated aortic sections with lesions and control aortic sections without lesions. In all lesion stages, substrate degradation was inhibited with 1,10-phenanthroline. Degradation of these substrates was not observed in control aortas. In addition, substrate degradation was inhibited with 1,10-phenanthroline. These findings suggested that in control segments, the net proteolytic balance was shifted in favor of MMP inhibition. Alternatively, despite the colocalization of MMPs and TIMPs in the treated segments, net proteolytic balance favored the catalytic MMPs.

Beneficial effects of targeting CCR5 in allograft recipients

BACKGROUND

The chemokine receptor, CCR5, and its three high-affinity ligands, macrophage inflammatory protein- (MIP) 1alpha, MIP-1beta, and regulated on activation normal T cell expressed and secreted (RANTES), are expressed by infiltrating mononuclear cells during the rejection of clinical and experimental organ allografts, although the significance of these molecules in the pathogenesis of rejection has not been established.

METHODS

We studied intragraft events in four allograft models. First, we studied cardiac transplants in fully MHC-mismatched mice that were deficient in CCR5 or two of its ligands, MIP-1alpha or RANTES. Second we tested the effects of a neutralizing rat anti-mCCR5 monoclonal antibody on allograft survival. Third we assessed whether a subtherapeutic course of cyclosporine would potentiate enhance survival in CCR5-deficient recipients. Finally, we tested the effect of targeting CCR5 in a class II-mismatched model.

RESULTS

Whereas mice deficient in expression of MIP-1alpha or RANTES reject fully MHC-mismatched cardiac allografts normally, CCR5-/- mice, or CCR5+/+ mice treated with a neutralizing mAb to mCCR5, show enhanced allograft survival. MHC class II-disparate mismatched are permanently accepted in CCR5-/- but not CCR5+/+ recipients. Finally, the beneficial effects of targeting of CCR5 are markedly synergistic with the effects of cyclosporine, resulting in permanent engraftment without development of chronic rejection.

CONCLUSIONS

We conclude that CCR5 plays a key role in the mechanisms of host T cell and macrophage recruitment and allograft rejection, such that targeting of CCR5 clinically may be of therapeutic significance.

Donor-derived IP-10 initiates development of acute allograft rejection

An allograft is often considered an immunologically inert playing field on which host leukocytes assemble and wreak havoc. However, we demonstrate that graft-specific physiologic responses to early injury initiate and promulgate destruction of vascularized grafts. Serial analysis of allografts showed that intragraft expression of the three chemokine ligands for the CXC chemo-kine receptor CXCR3 was induced in the order of interferon (IFN)-gamma-inducible protein of 10 kD (IP-10, or CXCL10), IFN-inducible T cell alpha-chemoattractant (I-TAC; CXCL11), and then monokine induced by IFN-gamma (Mig, CXCL9). Initial IP-10 production was localized to endothelial cells, and only IP-10 was induced by isografting. Anti-IP-10 monoclonal antibodies prolonged allograft survival, but surprisingly, IP-10-deficient (IP-10(-/-)) mice acutely rejected allografts. However, though allografts from IP-10(+/+) mice were rejected by day 7, hearts from IP-10(-/-) mice survived long term. Compared with IP-10(+/+) donors, use of IP-10(-/-) donors reduced intragraft expression of cytokines, chemokines and their receptors, and associated leukocyte infiltration and graft injury. Hence, tissue-specific generation of a single chemokine in response to initial ischemia/reperfusion can initiate progressive graft infiltration and amplification of multiple effector pathways, and targeting of this proximal chemokine can prevent acute rejection. These data emphasize the pivotal role of donor-derived IP-10 in initiating alloresponses, with implications for tissue engineering to decrease immunogenicity, and demonstrate that chemokine redundancy may not be operative in vivo.

Chemokines and their receptors in allograft rejection

Despite current recognition of over 40 chemokines and more than 18 chemokine receptors, understanding of their role in transplant immunobiology and transplant rejection is extremely limited and fragmentary. Recent literature has demonstrated the presence of chemokines and their receptors in transplants and some studies demonstrate important functional roles.