Development of 2-Morpholino-N-hydroxybenzamides as anti-proliferative PC-PLC inhibitors

Phosphatidylcholine-Specific Phospholipase C as a Promising Drug Target

Phosphatidylcholine-specific phospholipase C (PC-PLC) is an enzyme that catalyzes the formation of the important secondary messengers phosphocholine and diacylglycerol (DAG) from phosphatidylcholine. Although PC-PLC has been linked to the progression of many pathological conditions, including cancer, atherosclerosis, inflammation and neuronal cell death, studies of PC-PLC on the protein level have been somewhat neglected with relatively scarce data. To date, the human gene expressing PC-PLC has not yet been found, and the only protein structure of PC-PLC that has been solved was from Bacillus cereus (PC-PLCBc). Nonetheless, there is evidence for PC-PLC activity as a human functional equivalent of its prokaryotic counterpart. Additionally, inhibitors of PC-PLCBc have been developed as potential therapeutic agents. The most notable classes include 2-aminohydroxamic acids, xanthates, N,N'-hydroxyureas, phospholipid analogues, 1,4-oxazepines, pyrido[3,4-b]indoles, morpholinobenzoic acids and univalent ions. However, many medicinal chemistry studies lack evidence for their cellular and in vivo effects, which hampers the progression of the inhibitors towards the clinic. This review outlines the pathological implications of PC-PLC and highlights current progress and future challenges in the development of PC-PLC inhibitors from the literature.

Synthesis and Anti-Proliferative Activity of 5-Benzoyl and 5-Benzylhydroxy Derivatives of 3-Amino-2-Arylcarboxamido-Thieno[2-3-b]Pyridines

3-Amino-2-arylcarboxamido-thieno[2-3-b]pyridines have been previously described as having potent anti-proliferative activity against MDA-MB-231 and HCT116 cancer cell lines. The mechanism by which these molecules prevent cancer cell growth is proposed to be through interfering with phospholipid metabolism via inhibition of PI-PLC, along with other cellular processes. Previously, 5-cinnamyl derivatives of these thieno[2-3-b]pyridines have been shown to have enhanced anti-proliferative activity compared to compounds lacking this moiety, indicating a tethered aromatic ring is important for this western region of the pharmacophore. Herein, we report the synthesis and biological evaluation of a library of 40 novel thieno[2-3-b]pyridine analogues containing shorter benzoyl or secondary benzyl alcohol tethers at the 5-position, in addition to various substituents on the two phenyl rings present on the molecule. Compounds bearing alcohol functionality had improved efficacy compared to their benzoyl counterparts, in addition to a 2-methyl-3-halogen substitution on the 2-arylcarboxamide ring being important for maximising anti-proliferative activity. The most potent molecules 7h and 7i demonstrated IC₅₀ concentrations of 25-50 nM against HCT116 and MDA-MB-231 cells, a similar level of activity as previous thienopyridine compounds bearing cinnamyl moieties, suggesting that these novel derivatives with shorter tethers were able to maintain potent anti-proliferative activity, while allowing for a more concise synthesis.

Investigation of 2-phenylimidazo[1,2-a]quinolines as potential antiproliferative agents

Background: It has been demonstrated that the lead compound 2-phenylimidazo[1,2-a]quinoline 1a selectively inhibits CYP1 enzymes. Additionally, CYP1 inhibition has been linked to inducing antiproliferative effects in various breast cancer cell lines as well as relieving drug resistance caused by CYP1 upregulation. Materials & methods: Herein, 54 novel analogs of 2-phenylimidazo[1,2-a]quinoline 1a have been synthesized with varied substitution on the phenyl and imidazole rings. Antiproliferative testing was conducted using ³H thymidine uptake assays. Results: 2-Phenylimidazo[1,2-a]quinoline 1a and phenyl-substituted analogs 1c (3-OMe), 1n (2,3-napthalene) displayed excellent anti-proliferative activities, demonstrating their potency against cancer cell lines for the first time. Molecular modeling suggested that 1c and 1n bind similarly to 1a in the CYP1 binding site.

Synthesis and Anti-Proliferative Evaluation of Arctigenin Analogues with C-9' Derivatisation

Dibenzylbutyrolactone lignans (DBLs) are a class of natural products with a wide variety of biological activities. Due to their potential for the development of human therapeutic agents, DBLs have been subjected to various SAR studies in order to optimise activity. Previous reports have mainly considered changes on the aromatic rings and at the benzylic carbons of the compounds, whilst the effects of substituents in the lactone, at the C-9' position, have been relatively unexplored. This position has an unexploited potential for the development of novel dibenzyl butyrolactone derivatives, with previous preliminary findings revealing C-9'-hydroxymethyl analogues inducing programmed cell cycle death. Using the core structure of the bioactive natural product arctigenin, C-9' derivatives were synthesised using various synthetic pathways and with prepared derivatives providing more potent anti-proliferative activity than the C-9'-hydroxymethyl lead compound.

PLCβ2 Promotes VEGF-Induced Vascular Permeability

BACKGROUND

Regulation of vascular permeability is critical to maintaining tissue metabolic homeostasis. VEGF (vascular endothelial growth factor) is a key stimulus of vascular permeability in acute and chronic diseases including ischemia reperfusion injury, sepsis, and cancer. Identification of novel regulators of vascular permeability would allow for the development of effective targeted therapeutics for patients with unmet medical need.

METHODS

In vitro and in vivo models of VEGFA-induced vascular permeability, pathological permeability, quantitation of intracellular calcium release and cell entry, and phosphatidylinositol 4,5-bisphosphate levels were evaluated with and without modulation of PLC (phospholipase C) β2.

RESULTS

Global knock-out of PLCβ2 in mice resulted in blockade of VEGFA-induced vascular permeability in vivo and transendothelial permeability in primary lung endothelial cells. Further work in an immortalized human microvascular cell line modulated with stable knockdown of PLCβ2 recapitulated the observations in the mouse model and primary cell assays. Additionally, loss of PLCβ2 limited both intracellular release and extracellular entry of calcium following VEGF stimulation as well as reduced basal and VEGFA-stimulated levels of phosphatidylinositol 4,5-bisphosphate compared to control cells. Finally, loss of PLCβ2 in both a hyperoxia-induced lung permeability model and a cardiac ischemia:reperfusion model resulted in improved animal outcomes when compared with wild-type controls.

CONCLUSIONS

The results implicate PLCβ2 as a key positive regulator of VEGF-induced vascular permeability through regulation of both calcium flux and phosphatidylinositol 4,5-bisphosphate levels at the cellular level. Targeting of PLCβ2 in a therapeutic setting may provide a novel approach to regulating vascular permeability in patients.

Synthesis and HDAC inhibitory activity of pyrimidine-based hydroxamic acids

Histone deacetylases (HDACs) play an essential role in the transcriptional regulation of cells through the deacetylation of nuclear histone and non-histone proteins and are promising therapeutic targets for the treatment of various diseases. Here, the synthesis of new compounds in which a hydroxamic acid residue is attached to differently substituted pyrimidine rings via a methylene group bridge of varying length as potential HDAC inhibitors is described. The target compounds were obtained by alkylation of 2-(alkylthio)pyrimidin-4(3H)-ones with ethyl 2-bromoethanoate, ethyl 4-bromobutanoate, or methyl 6-bromohexanoate followed by aminolysis of the obtained esters with hydroxylamine. Oxidation of the 2-methylthio group to the methylsulfonyl group and following treatment with amines resulted in the formation of the corresponding 2-amino-substituted derivatives, the ester group of which reacted with hydroxylamine to give the corresponding hydroxamic acids. The synthesized hydroxamic acids were tested as inhibitors of the HDAC4 and HDAC8 isoforms. Among the synthesized pyrimidine-based hydroxamic acids N-hydroxy-6-[6-methyl-2-(methylthio)-5-propylpyrimidin-4-yloxy]hexanamide was found to be the most potent inhibitor of both the HDAC4 and HDAC8 isoforms, with an IC50 of 16.6 µM and 1.2 µM, respectively.

Incorporation of a Nitric Oxide Donating Motif into Novel PC-PLC Inhibitors Provides Enhanced Anti-Proliferative Activity

Inhibition of phosphatidylcholine-specific phospholipase C (PC-PLC) has previously been shown to be a potential target for novel cancer therapeutics. One downstream consequence of PC-PLC activity is the activation of NF-κB, a nuclear transcription factor responsible for transcribing genes related to oncogenic traits, such as proliferation, angiogenesis, metastasis, and cancer cell survival. Another biological pathway linked to NF-κB is the exogenous delivery of nitric oxide (NO), which decreases NF-κB activity through an apparent negative-feedback loop. In this study, we designed and synthesised 13 novel NO-releasing derivatives of our previously reported class of PC-PLC inhibitors, 2-morpholinobenzoic acids. These molecules contained a secondary benzylamine group, which was readily nitrosylated and subsequently confirmed to release NO in vitro using a DAF-FM fluorescence-based assay. It was then discovered that these NO-releasing derivatives possessed significantly improved anti-proliferative activity in both MDA-MB-231 and HCT116 cancer cell lines compared to their non-nitrosylated parent compounds. These results confirmed that the inclusion of an exogenous NO-releasing functional group onto a known PC-PLC inhibitor enhances anti-proliferative activity and that this relationship can be exploited in order to further improve the anti-proliferative activity of current/future PC-PLC inhibitors.