Synergistic effects of concurrent blockade of PI3K and MEK pathways in pancreatic cancer preclinical models.

Patients with pancreatic cancer have dismal prognoses, and novel therapies are urgently needed. Mutations of the KRAS oncogene occur frequently in pancreatic cancer and represent an attractive target. Direct targeting of the predominant KRAS pathways have been challenging and research into therapeutic strategies have been now refocused on pathways downstream of KRAS, phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK [MEK]). We hypothesized that concurrent inhibition of the PI3K and MEK pathways would result in synergistic antitumor activity, as it would circumvent the compensatory feedback loop between the two pathways. We investigated the combined effect of the PI3K inhibitor, GDC0941, and the MEK inhibitor, AZD6244, on cell viability, apoptosis and cell signaling in a panel of pancreatic cancer cell lines. An in vivo analysis was conducted on pancreatic cancer xenografts. While BxPC-3 (KRAS wild type) and MIA PaCa-2 (KRAS mutated) cell lines were sensitive to GDC0941 and AZD6244 as single agents, synergistic inhibition of tumor cell growth and induction of apoptosis were observed in both cell lines when the two drugs were combined. Interestingly, phosphorylation of the cap-dependent translational components, 4E-binding protein (p-4E-BP1) and S6 was found to be closely associated with sensitivity to GDC0941 and AZD6244. In BxPC-3 cell xenografts, survival differences were observed between the control and the AZD6244, GDC0941, and combination groups. Our study provides the rationale for concurrent targeting of the PI3K and MEK pathways, regardless of KRAS status, and suggests that phosphorylation of 4E-BP1and S6 can serve as a predictive biomarker for response to treatment.

Pharmacology of PF-4191834, a novel, selective non-redox 5-lipoxygenase inhibitor effective in inflammation and pain.

5-Lipoxygenase (LOX) is an important arachidonic acid-metabolizing enzyme producing leukotrienes and other proinflammatory lipid mediators with potent pathophysiological functions in asthma and other inflammatory diseases. 4-(3-(4-(1-Methyl-1H-pyrazol-5-yl)phenylthio)phenyl)-tetrahydro-2H-pyran-4-carboxamide (PF-4191834) is a novel, selective non-redox 5-lipoxygenase inhibitor effective in inflammation and pain. In vitro and in vivo assays were developed for the evaluation of a novel 5-LOX inhibitor using conditions of maximal enzyme activity. PF-4191834 exhibits good potency in enzyme- and cell-based assays, as well as in a rat model of acute inflammation. Enzyme assay results indicate that PF-4191834 is a potent 5-LOX inhibitor, with an IC(50) = 229 +/- 20 nM. Furthermore, it demonstrated approximately 300-fold selectivity for 5-LOX over 12-LOX and 15-LOX and shows no activity toward the cyclooxygenase enzymes. In addition, PF-4191834 inhibits 5-LOX in human blood cells, with an IC(80) = 370 +/- 20 nM. This inhibitory concentration correlates well with plasma exposures needed for in vivo efficacy in inflammation in models of inflammatory pain. The combination of potency in cells and in vivo, together with a sustained in vivo effect, provides PF-4191834 with an overall pharmacodynamic improvement consistent with once a day dosing.

CJ-13610, an orally active inhibitor of 5-lipoxygenase is efficacious in preclinical models of pain.

Zileuton, a redox and iron chelator 5-lipoxygenase (5-LOX) inhibitor and, leukotriene receptor antagonists are presently used clinically in the long term treatment of asthma. Recent data implicate 5-LOX pathway in pain signaling. We report 5-LOX expression in the central nervous system (CNS) and analyze the pain efficacy of a new class of non redox, non iron chelating 5-LOX inhibitor. CJ-13610, 4-(3-(4-(2-methyl-1H-imidazol-1-yl) phenylthio) phenyl)-tetrahydro-2H-pyran-4-carboxamide, demonstrated antihyperalgesic activity in inflammatory pain models including the acute carrageenan model and the chronic inflammatory model using complete Freund's adjuvant. Following complete Freund's adjuvant stimulus leukotrieneB(4) concentration in the brain was elevated (9+/-1 ng/g, mean+/-S.E.M.) by about 3 times that of the control group (3+/-0.11, mean+/-S.E.M.). Hyperalgesia and leukotrieneB(4) concentration were both reversed following CJ-13610 treatment. Furthermore, we demonstrate CJ-13610 efficacy against osteoarthritis like pain using the rat medial meniscal transection model. CJ-13610 at oral doses of 0.6, 2 and 6 mg/kg/day reversed two modalities of pain in this model; tactile allodynia and weight bearing differential. Taken together, these data suggest that 5-LOX pathway and the leukotriene products are important mediators of pain.

A rat air pouch model for evaluating the efficacy and selectivity of 5-lipoxygenase inhibitors.

The 5-lipoxygenase (5-LOX) pathway has been associated with a variety of inflammatory diseases including asthma, atherosclerosis, rheumatoid arthritis, pain, cancer and liver fibrosis. Several classes of 5-LOX inhibitors have been identified, but only one drug, zileuton, a redox inhibitor of 5-LOX, has been approved for clinical use. To better evaluate the efficacy of 5-LOX inhibitors for pharmacological intervention, a rat model was modified to test the in vivo efficacy of 5-LOX inhibitors. Inflammation was produced by adding carrageenan into a newly formed air pouch and prostaglandins produced. While macrophages and neutrophils are present in the inflamed pouch, little 5-LOX products are formed. Cellular 5-LOX activation was obtained by adding calcium ionophore (A23187) into the pouch thus providing a novel model to evaluate the efficacy and selectivity of 5-LOX inhibitors. Also, we described modifications to the in vitro 5-LOX enzyme and cell assays. These assays included a newly developed fluorescence-based enzyme assay, a 5-LOX redox assay, an ex vivo human whole blood assay and an IgE-stimulated rat mast cell assay, all designed for maximal production of leukotrienes. Zileuton and CJ-13,610, a competitive, non-redox inhibitor of 5-LOX, were evaluated for their pharmacological properties using these assays. Although both compounds achieved dose-dependent inhibition of 5-LOX enzyme activity, CJ-13,610 was 3-4 fold more potent than zileuton in all-assays. Evaluation of 5-LOX metabolites-by LC/MS/MS and ELISA confirmed that both compounds selectively inhibited all products downstream of 5-hydroperoxy eicosatetraenoic acid (5-HPETE), including 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxoETE), without inhibition of 12-lipoxygenase (12-LOX), 15-lipoxygenase (15-LOX), or cyclooxygenase (COX) products. In the rat air pouch model, oral dosing of CJ-13,610 and zileuton resulted in selective inhibition 5-LOX activity from pouch exudate and ex vivo rat whole blood with similar potency to in vitro assay. These data show that the rat air pouch model is a reliable and useful tool for evaluating in vivo efficacy of 5-LOX inhibitors and may aid in the development of the next generation of 5-LOX inhibitors, such as the non-redox inhibitors similar to CJ-13,610.

Development of a fluorescence-based enzyme assay of human 5-lipoxygenase.

Leukotrienes are important mediators in a number of inflammatory diseases and therefore are a target of several therapeutic approaches. The first committed step in the synthesis of leukotrienes is the conversion of arachidonic acid to leukotriene A(4) (LTA(4)) in two successive reactions catalyzed by 5-lipoxygenase (5-LOX). Assays to measure 5-LOX activity typically have been low throughput and time consuming. In this article, we describe a fluorescence assay that is amenable to high-throughput screening in a 384-well microplate format. The fluorescent signal is measured during oxidation of 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA) by human 5-LOX. The assay has been found to reliably identify small molecule inhibitors of human 5-LOX. The IC(50) values of several 5-LOX inhibitors in this new assay are comparable to those determined in a standard spectrophotometric assay that measures the formation of the 5(S)-hydroperoxyeicosatetraenoic acid (5-HpETE) product. In addition, we demonstrate the use of the assay in a high-throughput screen of the Pfizer compound collection to identify inhibitors of 5-LOX.