Development of Cilofexor, an intestinally-biased Farnesoid X Receptor agonist, for the treatment of fatty liver disease.

The farnesoid X receptor (FXR) is a nuclear receptor that controls bile acid, lipid, and cholesterol metabolism. FXR-targeted drugs have shown promise in late-stage clinical trials for non-alcoholic steatohepatitis. Herein, we used clinical results from our first non-steroidal FXR agonist, Px-102 (4-[2-[2-chloro-4-[[5-cyclopropyl-3-(2,6-dichlorophenyl)-4-isoxazolyl]methoxy]phenyl]cyclopropyl] benzoic acid), to develop cilofexor, a potent, non-steroidal FXR agonist with a more manageable safety profile. Px-102 demonstrated the anticipated pharmacodynamic (PD) effects in healthy volunteers but caused a 2-fold increase in alanine aminotransferase (ALT) activity and changes in cholesterol levels. These data guided development of a high fat diet mouse model to screen FXR agonists based on ALT and cholesterol changes. Cilofexor was identified to elicit only minor changes in these parameters. The differing effects of cilofexor and Px-102 on ALT/cholesterol in the model could not be explained by potency or specificity, and we hypothesized that the relative contribution of intestinal and liver FXR activation may be responsible. Gene expression analysis from rodent studies revealed that cilofexor, but not Px-102, had a bias for FXR transcriptional activity in the intestine compared to the liver. Fluorescent imaging in hepatoma cells demonstrated similar subcellular localization for cilofexor and Px-102, but cilofexor was more rapidly washed out, consistent with a lower membrane residence time contributing to reduced hepatic transcriptional effects. Cilofexor demonstrated antisteatotic and antifibrotic efficacy in rodent models and antisteatotic efficacy in a monkey model, with the anticipated PD and a manageable safety profile in human phase I studies. Significance Statement FXR (farnesoid X receptor) agonists have shown promise in treating non-alcoholic steatohepatitis and other liver diseases in the clinic, but balancing efficacy with undesired side effects has been difficult. Here, we examined the preclinical and clinical effects of the first-generation FXR agonist, Px-102 (4-[2-[2-chloro-4-[[5-cyclopropyl-3-(2,6-dichlorophenyl)-4-isoxazolyl]methoxy]phenyl]cyclopropyl] benzoic acid), to enable the selection of an analog, cilofexor, with unique properties that reduced side effects yet maintained efficacy. Cilofexor is one of few remaining FXR agonists in clinical development.

Preclinical evaluation of AMG 925, a FLT3/CDK4 dual kinase inhibitor for treating acute myeloid leukemia.

Acute myeloid leukemia (AML) remains a serious unmet medical need. Despite high remission rates with chemotherapy standard-of-care treatment, the disease eventually relapses in a major proportion of patients. Activating Fms-like tyrosine kinase 3 (FLT3) mutations are found in approximately 30% of patients with AML. Targeting FLT3 receptor tyrosine kinase has shown encouraging results in treating FLT3-mutated AML. Responses, however, are not sustained and acquired resistance has been a clinical challenge. Treatment options to overcome resistance are currently the focus of research. We report here the preclinical evaluation of AMG 925, a potent, selective, and bioavailable FLT3/cyclin-dependent kinase 4 (CDK4) dual kinase inhibitor. AMG 925 inhibited AML xenograft tumor growth by 96% to 99% without significant body weight loss. The antitumor activity of AMG 925 correlated with the inhibition of STAT5 and RB phosphorylation, the pharmacodynamic markers for inhibition of FLT3 and CDK4, respectively. In addition, AMG 925 was also found to inhibit FLT3 mutants (e.g., D835Y) that are resistant to the current FLT3 inhibitors (e.g., AC220 and sorafenib). CDK4 is a cyclin D-dependent kinase that plays an essential central role in regulating cell proliferation in response to external growth signals. A critical role of the CDK4-RB pathway in cancer development has been well established. CDK4-specific inhibitors are being developed for treating RB-positive cancer. AMG 925, which combines inhibition of two kinases essential for proliferation and survival of FLT3-mutated AML cells, may improve and prolong clinical responses.

Energy balance in congenital generalized lipodystrophy type I.

Congenital generalized lipodystrophy type 1 (CGL-1) is characterized by an absence of adipose tissue and decreased serum leptin levels. Low leptin levels in CGL-1 support the claim that subjects are hypermetabolic and hyperphagic. The present study examines this claim. We determined 24-hour energy expenditure (24-h EE) (kilocalories) (n = 2) and resting metabolic rate (RMR) per kilogram of lean body mass (LBM) (n = 3) in CGL-1 and in 18 healthy control subjects. The 24-h EEs of control and subjects with CGL were compared with respect to kilocalories required per day relative to kilograms of LBM and with respect to RMR relative to kilograms of LBM. Fasting leptin, adiponectin, and 24-hour ghrelin levels were also measured in subjects with CGL-1. The 24-h EE per kilogram of LBM for the subjects with CGL-1 falls on the same regression line observed for this relationship in the controls. The RMR per kilogram of LBM in subjects with CGL-1 also was similar to that in controls. Both 24-h EE and RMR were quite increased when reported per kilogram of total body weight. Subjects with CGL-1 also have decreased fasting leptin and adiponectin hormone levels and no premeal ghrelin rise. People with CGL-1 have similar RMR and daily caloric requirements as healthy controls when these parameters are expressed as a function of LBM. Appetite-regulating hormone levels in CGL-1 suggest that multiple factors act to control appetite in these individuals.

Antileukemic activity of lysophosphatidic acid acyltransferase-beta inhibitor CT32228 in chronic myelogenous leukemia sensitive and resistant to imatinib.

PURPOSE: Lysophosphatidic acid acyltransferase (LPAAT)-beta catalyzes the conversion of lysophosphatidic acid to phosphatidic acid, an essential component of several signaling pathways, including the Ras/mitogen-activated protein kinase pathway. Inhibition of LPAAT-beta induces growth arrest and apoptosis in cancer cell lines, implicating LPAAT-beta as a potential drug target in neoplasia. EXPERIMENTAL DESIGN: In this study, we investigated the effects of CT32228, a specific LPAAT-beta inhibitor, on BCR-ABL-transformed cell lines and primary cells from patients with chronic myelogenous leukemia. RESULTS: CT32228 had antiproliferative activity against BCR-ABL-positive cell lines in the nanomolar dose range, evidenced by cell cycle arrest in G2-M and induction of apoptosis. Treatment of K562 cells with CT32228 led to inhibition of extracellular signal-regulated kinase 1/2 phosphorylation, consistent with inhibition of mitogen-activated protein kinase signaling. Importantly, CT32228 was highly active in cell lines resistant to the Bcr-Abl kinase inhibitor imatinib. Combination of CT32228 with imatinib produced additive inhibition of proliferation in cell lines with residual sensitivity toward imatinib. In short-term cultures in the absence of growth factors, CT32228 preferentially inhibited the growth of granulocyte-macrophage colony-forming units from chronic myelogenous leukemia patients compared with healthy controls. CONCLUSION: These data establish LPAAT-beta as a potential drug target for the treatment of BCR-ABL-positive leukemias.

Effect of lysophosphatidic acid acyltransferase-beta inhibition in acute leukemia.

Phosphatidic acid (PA) is an important component of mammalian target of rapamycin (mTOR) signaling and in the recruitment of Raf to the cell membrane. PA can be produced by several mechanisms, including by a series of lysophosphatidic acid acyl transferases (LPAATs). LPAAT-beta is an isoform that is overexpressed in some human cancers and its inhibition has been investigated as a potential targeted cancer therapy. We report that LPAAT-protein and enzyme activity in acute leukemia cell lines and blasts from patient samples are equivalent to levels in normal mononuclear cells. Treatment with the LPAAT-beta inhibitor CT-32228 (Cell Therapeutics, Seattle, WA) uniformly induces apoptosis in multiple leukemia cell lines. In patient samples, however, apoptosis was variably induced by CT-32228 and appeared to be related to the degree of cellular proliferation. The growth inhibitory effect of CT-32228 on normal hematopoietic progenitors was more pronounced in cells induced to proliferate by growth factors. These data suggest that CT-32228 may have potential in the treatment of acute leukemias, but that efficacy is more directly related to the degree of cell proliferation rather than to the level of LPAAT-beta expression or activity.

Substrate specificity of lysophosphatidic acid acyltransferase beta -- evidence from membrane and whole cell assays.

Membranes of mammalian cells contain lysophosphatidic acid acyltransferase (LPAAT) activities that catalyze the acylation of sn-1-acyl lysophosphatidic acid (lysoPA) to form phosphatidic acid. As the biological roles and biochemical properties of the six known LPAAT isoforms have yet to be fully elucidated, we have characterized human LPAAT-beta activity using two different assays. In a membrane-based assay, LPAAT-beta used lysoPA and lysophosphatidylmethanol (lysoPM) but not other lysophosphoglycerides as an acyl acceptor, and it preferentially transferred 18:1, 18:0, and 16:0 acyl groups over 12:0, 14:0, 20:0, and 20:4 acyl groups. The fact that lysoPM could traverse cell membranes permitted additional characterization of LPAAT-beta activity in cells: PC-3 and DU145 cells converted exogenously added lysoPM and (14)C-labeled 18:1 into (14)C-labeled phosphatidylmethanol (PM). The rate of PM formation was higher in cells that overexpressed LPAAT-beta and was inhibited by the LPAAT-beta inhibitor CT-32501. In contrast, if lysoPM and (14)C-labeled 20:4 were added to PC-3 or DU145 cells, (14)C-labeled PM was also formed, but the rate was neither higher in cells that overexpressed LPAAT-beta nor inhibited by CT-32501. We propose that LPAAT-beta catalyzes the intracellular transfer of 18:1, 18:0, and 16:0 acyl groups but not 20:4 groups to lysoPA.

Induction of apoptosis using inhibitors of lysophosphatidic acid acyltransferase-beta and anti-CD20 monoclonal antibodies for treatment of human non-Hodgkin's lymphomas.

PURPOSE: Lysophosphatidic acid acyltransferase-beta (LPAAT-beta) is a transmembrane enzyme critical for the biosynthesis of phosphoglycerides whose product, phosphatidic acid, plays a key role in raf and AKT/mTor-mediated signal transduction. EXPERIMENTAL DESIGN: LPAAT-beta may be a novel target for anticancer therapy, and, thus, we examined the effects of a series of inhibitors of LPAAT-beta on multiple human non-Hodgkin's lymphoma cell lines in vitro and in vivo. RESULTS: We showed that five LPAAT-beta inhibitors at doses of 500 nmol/L routinely inhibited growth in a panel of human lymphoma cell lines in vitro by >90%, as measured by [3H]thymidine incorporation. Apoptotic effects of the LPAAT-beta inhibitors were evaluated either alone or in combination with the anti-CD20 antibody, Rituximab. The LPAAT-beta inhibitors induced caspase-mediated apoptosis at 50 to 100 nmol/L in up to 90% of non-Hodgkin's lymphoma cells. The combination of Rituximab and an LPAAT-beta inhibitor resulted in a 2-fold increase in apoptosis compared with either agent alone. To assess the combination of Rituximab and a LPAAT-beta inhibitor in vivo, groups of athymic mice bearing s.c. human Ramos lymphoma xenografts were treated with the LPAAT-beta inhibitor CT-32228 i.p. (75 mg/kg) daily for 5 d/wk x 4 weeks (total 20 doses), Rituximab i.p. (10 mg/kg) weekly x 4 weeks (4 doses total), or CT-32228 plus Rituximab combined. Treatment with either CT-32228 or Rituximab alone showed an approximate 50% xenograft growth delay; however, complete responses were only observed when the two agents were delivered together. CONCLUSIONS: These data suggest that Rituximab, combined with a LPAAT-beta inhibitor, may provide enhanced therapeutic effects through apoptotic mechanisms.

Inhibition of lysophosphatidic acid acyltransferase beta disrupts proliferative and survival signals in normal cells and induces apoptosis of tumor cells.

Lysophosphatidic acid acyltransferase beta (LPAAT-beta) is an intrinsic membrane protein that catalyzes the synthesis of phosphatidic acid (PA) from lysoPA. Given that PA is a cofactor in a number of signaling cascades that are constitutively active in tumors, we evaluated the role of PA produced by LPAAT-beta in Xenopus oocyte meiotic maturation assays and an isoform-specific inhibitor of LPAAT-beta in mammalian cell assays. We found that ectopic overexpression of LPAAT-beta cooperates in activation of the Ras/Raf/Erk pathway in Xenopus oocytes and that inhibition of LPAAT-beta inhibits signaling in both the Ras/Raf/Erk and PI3K/Akt pathways. When LPAAT-beta activity is suppressed by CT32228 (N-(4-bromo-phenyl)-6-(5-chloro-2-methyl-phenyl)-[1,3,5]triazine-2,4-diamine), an isoform-specific noncompetitive inhibitor, tumor cells undergo mitotic catastrophe while most normal cells simply arrest or become quiescent. The data presented here suggest that PA produced by LPAAT-beta plays an important role in signaling pathways critical to tumor cell survival.

Lysophosphatidic acid acyltransferase-beta: a novel target for induction of tumour cell apoptosis.

Phosphatidic acid (PA) is a component of cellular membranes that is also a mediator of certain cell signalling functions associated with oncogenesis. These include ras/raf/Erk and Akt/mTor [1-3]. The authors have investigated whether it would be possible to interrupt these known oncogenic pathways through the inhibition of lysophosphatidic acid acyltransferase (LPAAT), an enzyme that catalyses the biosynthesis of PA. The expression and activity of the LPAAT-beta isoform are elevated in human tumours, and the respective gene displays transforming capacity when overexpressed in vitro. Inhibition by either genetic means or by isoform-specific small molecules results in a block to cell signalling pathways and apoptosis. Furthermore, the small-molecule inhibitors of LPAAT-beta are not cytotoxic to a number of normal cell types, including primary bone marrow progenitors, indicating a differential dependence of tumour cells on LPAAT-beta function. These discoveries indicate that LPAAT-beta represents a potential novel cancer therapy target.