The anti-anginal drug fendiline increases intracellular Ca(2+) levels in MG63 human osteosarcoma cells

Repurposing of drugs: An attractive pharmacological strategy for cancer therapeutics

Human malignancies are one of the major health-related issues though out the world and anticipated to rise in the future. The development of novel drugs/agents requires a huge amount of cost and time that represents a major challenge for drug discovery. In the last three decades, the number of FDA approved drugs has dropped down and this led to increasing interest in drug reposition or repurposing. The present review focuses on recent concepts and therapeutic opportunities for the utilization of antidiabetics, antibiotics, antifungal, anti-inflammatory, antipsychotic, PDE inhibitors and estrogen receptor antagonist, Antabuse, antiparasitic and cardiovascular agents/drugs as an alternative approach against human malignancies. The repurposing of approved non-cancerous drugs is an effective strategy to develop new therapeutic options for the treatment of cancer patients at an affordable cost in clinics. In the current scenario, most of the countries throughout the globe are unable to meet the medical needs of cancer patients because of the high cost of the available cancerous drugs. Some of these drugs displayed potential anti-cancer activity in preclinic and clinical studies by regulating several key molecular mechanisms and oncogenic pathways in human malignancies. The emerging pieces of evidence indicate that repurposing of drugs is crucial to the faster and cheaper discovery of anti-cancerous drugs.

Inhibitors of K-Ras plasma membrane localization

Oncogenic mutant K-Ras is highly prevalent in multiple human tumors. Despite significant efforts to directly target Ras activity, no K-Ras-specific inhibitors have been developed and taken into the clinic. Since Ras proteins must be anchored to the inner leaflet of the plasma membrane (PM) for full biological activity, we devised a high-content screen to identify molecules with ability to displace K-Ras from the PM. Here we summarize the biochemistry and biology of three classes of compound identified by this screening method that inhibit K-Ras PM targeting: staurosporine and analogs, fendiline, and metformin. All three classes of compound significantly abrogate cell proliferation and Ras signaling in K-Ras-transformed cancer cells. Taken together, these studies provide an important proof of concept that blocking PM localization of K-Ras is a tractable therapeutic target.

Clinically applicable antianginal agents suppress osteoblastic transformation of myogenic cells and heterotopic ossifications in mice

Fibrodysplasia ossificans progressiva (FOP) is a rare autosomal dominant disorder characterized by progressive heterotopic ossification. FOP is caused by a gain-of-function mutation in ACVR1 encoding the bone morphogenetic protein type II receptor, ACVR1/ALK2. The mutant receptor causes upregulation of a transcriptional factor, Id1. No therapy is available to prevent the progressive heterotopic ossification in FOP. In an effort to search for clinically applicable drugs for FOP, we screened 1,040 FDA-approved drugs for suppression of the Id1 promoter activated by the mutant ACVR1/ALK2 in C2C12 cells. We found that that two antianginal agents, fendiline hydrochloride and perhexiline maleate, suppressed the Id1 promoter in a dose-dependent manner. The drugs also suppressed the expression of native Id1 mRNA and alkaline phosphatase in a dose-dependent manner. Perhexiline but not fendiline downregulated phosphorylation of Smad 1/5/8 driven by bone morphogenetic protein (BMP)-2. We implanted crude BMPs in muscles of ddY mice and fed them fendiline or perhexiline for 30 days. Mice taking perhexiline showed a 38.0 % reduction in the volume of heterotopic ossification compared to controls, whereas mice taking fendiline showed a slight reduction of heterotopic ossification. Fendiline, perhexiline, and their possible derivatives are potentially applicable to clinical practice to prevent devastating heterotopic ossification in FOP.

Fendiline inhibits K-Ras plasma membrane localization and blocks K-Ras signal transmission

Ras proteins regulate signaling pathways important for cell growth, differentiation, and survival. Oncogenic mutant Ras proteins are commonly expressed in human tumors, with mutations of the K-Ras isoform being most prevalent. To be active, K-Ras must undergo posttranslational processing and associate with the plasma membrane. We therefore devised a high-content screening assay to search for inhibitors of K-Ras plasma membrane association. Using this assay, we identified fendiline, an L-type calcium channel blocker, as a specific inhibitor of K-Ras plasma membrane targeting with no detectable effect on the localization of H- and N-Ras. Other classes of L-type calcium channel blockers did not mislocalize K-Ras, suggesting a mechanism that is unrelated to calcium channel blockade. Fendiline did not inhibit K-Ras posttranslational processing but significantly reduced nanoclustering of K-Ras and redistributed K-Ras from the plasma membrane to the endoplasmic reticulum (ER), Golgi apparatus, endosomes, and cytosol. Fendiline significantly inhibited signaling downstream of constitutively active K-Ras and endogenous K-Ras signaling in cells transformed by oncogenic H-Ras. Consistent with these effects, fendiline blocked the proliferation of pancreatic, colon, lung, and endometrial cancer cell lines expressing oncogenic mutant K-Ras. Taken together, these results suggest that inhibitors of K-Ras plasma membrane localization may have utility as novel K-Ras-specific anticancer therapeutics.

Bone biology and physiology: implications for novel osteoblastic osteosarcoma treatments?

Healthy bone undergoes a continuous cycle of bone resorption by osteoclasts and formation by osteoblasts. These processes are in turn regulated by developmental sequences involved in differentiation of bone marrow puripotent mesenchymal cells into osteoblasts and mononuclear hemaotpoitic stem cells into osteoclasts. A variety of growth factors and receptors are involved in these maturation sequences. Osteoblast proliferation and inhibition, for example, are highly dependent not only on such factors as bone morphogenic protein and core binding factor a1 (CBFa1), but on intracellular levels of calcium and cAMP. Therefore, agents that affect concentrations of these two compounds may hypothetically play a role in osteoblastic osteosarcoma treatment. Osteoblast proliferation is also under neural control; in particular, the activity of the N-methyl-d-aspartate (NMDA) and alpha adrenergic 1 receptors. Antagonists to these receptors may also hypothetically play a role in osteoblastic osteosarcoma therapy. This article reviews the basic science supporting the putative roles of common, relatively safe but disparate agents-ranging from caffeine and theophylline to dextromethorphan and econazole-in the potential treatment of osteoblastic osteosarcoma.

Clinical potential of GABAB receptor modulators

Metabotropic gamma-aminobutyric acid(B) (GABAB) receptors for the major inhibitory transmitter GABA, together with metabotropic glutamate (mGLuRs) receptors, the extracellular calcium-sensing receptors (CaSRs), some V2R pheromone receptors and T1R taste receptors, belong to the family of 3 G-protein-coupled receptors (GPCRs). GABAB receptors are known to control neuronal excitability and modulate synaptic neurotransmission, playing a very important role in many physiological activities. These receptors are widely expressed and distributed in the nervous system and have been implicated in a variety of neurodegenerative and pathophysiological disorders including epilepsy, spasticity, chronic pain, depression, schizophrenia and drug addiction. To form a functional receptor entity, GABAB receptors must exist as a heterodimer consisting of GABAB1 and GABAB2 receptor subtypes with two 7-transmembrane proteins, and these subunits arise from distinct genes. The GABAB1 subunit binds the endogenous ligand within its extracellular N-terminus, whilst the GABAB2 subunit is not only essential for the correct trafficking of the GABAB1 subunit to the cell surface, but is also responsible for the interaction of the receptor with its cognate G-protein. Allosteric modulation has recently been recognized as an alternative pharmacological approach to gain selectivity in drug action. It is now generally accepted that modulators acting at the allosteric sites provide a novel perspective for the development of subtype-selective agents acting at GPCRs. These agents interact with allosteric binding sites quite separate from the highly conserved agonist binding region. In this review, we present a new class of phenylalkylamines, based on the lead compound fendiline, that are potent positive potentiators of GABAB receptor-mediated function and discuss their putative clinical applications. It is proposed that these new modulators may have therapeutic value in GABAB receptor pharmacology and are capable of selectively modifying GABAB receptor function. The allosteric modulators are offering an attractive and novel means to identify new leads, that are devoid of side effects associated with GABAB receptor agonists, and may, therefore, represent a major advance in the drug discovery process.

The anti-anginal drug fendiline elevates cytosolic Ca(2+) in rabbit corneal epithelial cells

The effect of the anti-anginal drug fendiline on intracellular free Ca(2+) levels ([Ca(2+)](i)) in a rabbit corneal epithelial cell line (SIRC) was explored using fura-2 as a fluorescent Ca(2+) indicator. At a concentration above 1 microM, fendiline increased [Ca(2+)](i) in a concentration-dependent manner with an EC(50) value of 7 microM. The [Ca(2+)](i) response consisted of an immediate rise and an elevated phase. Extracellular Ca(2+) removal decreased half of the [Ca(2+)](i )signal. Fendiline induced quench of fura-2 fluorescence by Mn(2+) (50 microM), suggesting the presence of Ca(2+) influx across the plasma membrane. This Ca(2+) influx was abolished by La(3+) (50 microM), but was insensitive to dihydropyridines, verapamil and diltiazem. Fendiline (10 microM)-induced store Ca(2+) release was largely reduced by pretreatment with thapsigargin (1 microM) (an endoplasmic reticulum Ca(2+) pump inhibitor) to deplete the endoplasmic reticulum Ca(2+). Conversely, pretreatment with 10 microM fendiline abolished thapsigargin-induced Ca(2+) release. Fendiline (10 microM)-induced Ca(2+) release was not altered by inhibiting phospholipase C with 2 microM 1-(6-((17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione (U73122). Cumulatively, this study shows that fendiline induced concentration-dependent [Ca(2+)](i )increases in corneal epithelial cells by releasing the endoplasmic reticulum Ca(2+) in a phospholipase C-independent manner, and by causing Ca(2+) influx.

Effect of the anti-breast cancer drug tamoxifen on Ca(2+) movement in human osteosarcoma cells

The anti-breast cancer drug tamoxifen has recently been shown to cause an increase in [Ca(2+)]i in renal tubular cells, breast cells and bladder cells. Because tamoxifen is known to interact with oestrogens leading to modulation of bone metabolism, the present study was aimed at exploring whether tamoxifen could alter Ca(2+) signaling in human osteoblast-like MG63 cells. Cytosolic free Ca(2+) levels were recorded by using the Ca(2+)-sensitive dye fura-2. Tamoxifen induced a sustained [Ca(2+)]i increase at concentrations above 1 microM with an EC(50) of 8 microM. Removal of extracellular Ca(2+) reduced the response by 40%, suggesting that tamoxifen induced both Ca(2+) influx and store Ca(2+) release. Tamoxifen-induced Ca(2+) influx was confirmed as tamoxifen caused Mn(2+) influx-induced quench of fura-2 fluorescence. In Ca(2+)-free medium, pretreatment with 10 microM tamoxifen abolished the [Ca(2+)]i increase induced by 1 microM thapsigargin (an endoplasmic reticulum Ca(2+) pump inhibitor), and by 2 microM carbonylcyanide m-chlorophenylhydrazone (a mitochondrial uncoupler). Conversely, pretreatment with thapsigargin and carbonylcyanide m-chlorophenylhydrazone only reduced 64% of tamoxifen-induced [Ca(2+)]i increases. Addition of 2 microM U73122 to inhibit phospholipase C activity abolished the [Ca(2+)]i increase induced by 1 microM histamine, a phospholipase C-dependent Ca(2+) mobilizer, without affecting 10 microM tamoxifen-induced Ca(2+) release. The [Ca(2+)]i increase induced by 10 microM tamoxifen was not altered by 10 microM of nifedipine, verapamil and diltiazem. Together, the data show that tamoxifen induced a lasting increase in [Ca(2+)]i in human osteoblast-like cells by causing Ca(2+) influx and releasing Ca(2+) from multiple stores in a phospholipase C-independent manner.