Isoform selective PLD inhibition by novel, chiral 2,8-diazaspiro[4.5]decan-1-one derivatives.

This letter describes the on-going SAR efforts to develop PLD1, PLD2 and dual PLD1/2 inhibitors with improved physiochemical and disposition properties as well as securing intellectual property position. Previous PLD inhibitors, based on a triazaspiro[4.5]decanone core proved to be highly selective PLD2 inhibitors, but with low plasma free fraction (rat, human fu < 0.03), high predicted hepatic clearance (rat CLhep > 65 mL/min/kg) and very short half-lives in vivo (t1/2 < 0.15 h). Removal of a nitrogen atom from this core generated a 2,8-diazaspiro[4.5]decanone core, harboring a new chiral center, as well as increased sp3 character. This new core demonstrated enantioselective inhibition of the individual PLD isoforms, enhanced free fraction (rat, human fu < 0.13), engendered moderate predicted hepatic clearance (rat CLhep ∼ 43 mL/min/kg), improved half-lives in vivo (t1/2 > 3 h), and led to the first issued US patent claiming composition of matter for small molecule PLD inhibitors.

Lipidomics: when apocrypha becomes canonical.

Lipidomics is a branch of the field of metabolomics. Although only about a decade since its inception, lipidomics has already had a major influence on the way in which questions about lipid metabolism and signaling are posed. The field is intertwined in the culture and rich history of mass spectrometry. Early work emphasized analytical issues such as limits of detection and numbers of molecular species quantitated in single injections. Increased sophistication in applications of lipidomic analysis and emerging technologies, such as imaging mass spectrometry, are facilitating the study of lipid metabolism and signaling species in cellular functions and human diseases. In the coming years we anticipate a richer understanding of how specific lipid species mediate complex biological processes and interconnections between cellular pathways that were thought to be disparate.

Autoregulation of phospholipase D activity is coupled to selective induction of phospholipase D1 expression to promote invasion of breast cancer cells.

Phospholipase D (PLD) is an important signaling enzyme implicated in the control of many biological processes, including cell proliferation and survival. Despite the importance of the duration and amplitude of PLD signaling in carcinogenesis, mechanisms that regulate PLD expression remain poorly understood. In our study, we define the regulatory components of the machinery that specifies selective PLD1 induction via signals propagated through PLD activity. We demonstrate for the first time that establishment of a positive feedback loop that is dependent on enzymatic activity originating from both PLD1 and PLD2 isozymes enhances selective expression of PLD1, but not PLD2. Phosphatidic acid, the product of PLD activity, leads to an increase in the Ras-ERK/PI3K-NFκB signaling cascade and enhances binding of NFκB to the PLD1 promoter, consequently inducing selective PLD1 expression in SK-BR3 breast cancer cells. Moreover, selective PLD inhibitor suppressed epidermal growth factor-induced matrix metalloproteinase upregulation and invasion by inhibiting PLD1 expression. In conclusion, we propose that autoregulation of PLD activity might be coupled to induction of PLD1 expression, and thereby play a role in carcinogenesis.

Modeling species-specific diacylglycerol dynamics in the RAW 264.7 macrophage.

A mathematical model of the G protein signaling pathway in RAW 264.7 macrophages downstream of P2Y(6) receptors activated by the ubiquitous signaling nucleotide uridine 5'-diphosphate is developed. The model, which is based on time-course measurements of inositol trisphosphate, cytosolic calcium, and diacylglycerol, focuses particularly on differential dynamics of multiple chemical species of diacylglycerol. When using the canonical pathway representation, the model predicted that key interactions were missing from the current network structure. Indeed, the model suggested that accurate depiction of experimental observations required an additional branch to the signaling pathway. An intracellular pool of diacylglycerol is immediately phosphorylated upon stimulation of an extracellular receptor for uridine 5'-diphosphate and subsequently used to aid replenishment of phosphatidylinositol. As a result of sensitivity analysis of the model parameters, key predictions can be made regarding which of these parameters are the most sensitive to perturbations and are therefore most responsible for output uncertainty.

Design and synthesis of isoform-selective phospholipase D (PLD) inhibitors. Part II. Identification of the 1,3,8-triazaspiro[4,5]decan-4-one privileged structure that engenders PLD2 selectivity.

This Letter describes the synthesis and structure-activity relationships (SAR) of isoform-selective PLD inhibitors. By virtue of the installation of a 1,3,8-triazaspiro[4,5]decan-4-one privileged structure, PLD inhibitors with nanomolar potency and an unprecedented 40-fold selectivity for PLD2 over PLD1 were developed. Interestingly, SAR for this diverged from our earlier efforts, and dual PLD1/2 inhibitors were also discovered within this series.

Lipidomics: an analysis of cellular lipids by ESI-MS.

Recognition of the importance of lipid signaling in cellular function has led to rapid progress in the technology of lipid analysis. Measurements of lipid species changes are central to defining the networks of cell signaling (e.g., receptor activation by hormones or drugs) and lipids are involved in many biochemical and pathological processes. During the last several years our laboratory has focused on developing efficient methods for extraction of glycerophospholipids from biological systems and their detection and identification by mass spectrometry. We analyze phospholipid changes in mammalian cells as a result of a defined ligand stimulation strategy that supports the research questions of the consortium. The improvement of mass spectrometry techniques for phospholipid analysis combined with sophisticated computational methods developed in our group has facilitated simultaneous analysis of hundreds of phospholipid species in mammalian cells. This information is presented as Lipid Arrays (or more precisely as virtual arrays) and allows identification of temporal changes in membrane phospholipid species between two contrasting biological conditions (e.g., unstimulated basal vs. stimulated or as a contrast between normal and disease stages). Using the lipidomics approach, we are able to identify approximately 450 phospholipid species from total membrane extracts and qualitatively measure pattern response changes initiated by cell surface receptors. As such, this approach facilitates the elucidation of the metabolic changes induced by a perturbation in the cell and recognition of patterns of signaling.