Delia Preti

Oxaliplatin elicits mechanical and cold allodynia in rodents via TRPA1 receptor stimulation

&NA; Platinum‐based anticancer drugs cause neurotoxicity. In particular, oxaliplatin produces early‐developing, painful, and cold‐exacerbated paresthesias. However, the mechanism underlying these bothersome and dose‐limiting adverse effects is unknown. We hypothesized that the transient receptor potential ankyrin 1 (TRPA1), a cation channel activated by oxidative stress and cold temperature, contributes to mechanical and cold hypersensitivity caused by oxaliplatin and cisplatin. Oxaliplatin and cisplatin evoked glutathione‐sensitive relaxation, mediated by TRPA1 stimulation and the release of calcitonin gene‐related peptide from sensory nerve terminals in isolated guinea pig pulmonary arteries. No calcium response was observed in cultured mouse dorsal root ganglion neurons or in naïve Chinese hamster ovary (CHO) cells exposed to oxaliplatin or cisplatin. However, oxaliplatin, and with lower potency, cisplatin, evoked a glutathione‐sensitive calcium response in CHO cells expressing mouse TRPA1. One single administration of oxaliplatin produced mechanical and cold hyperalgesia in rats, an effect selectively abated by the TRPA1 antagonist HC‐030031. Oxaliplatin administration caused mechanical and cold allodynia in mice. Both responses were absent in TRPA1‐deficient mice. Administration of cisplatin evoked mechanical allodynia, an effect that was reduced in TRPA1‐deficient mice. TRPA1 is therefore required for oxaliplatin‐evoked mechanical and cold hypersensitivity, and contributes to cisplatin‐evoked mechanical allodynia. Channel activation is most likely caused by glutathione‐sensitive molecules, including reactive oxygen species and their byproducts, which are generated after tissue exposure to platinum‐based drugs from cells surrounding nociceptive nerve terminals. TRPA1 is necessary and sufficient for mechanical‐ and cold‐hypersensitivity evoked by oxaliplatin/cisplatin. TRPA1 activation occurs through reactive molecules, after tissue exposure to platinum‐based drugs.

Transient receptor potential ankyrin receptor 1 is a novel target for pro‐tussive agents

Background and purpose:  The transient receptor potential ankyrin receptor 1 (TRPA1) is a cation channel, co‐expressed with the pro‐tussive transient receptor potential vanilloid type 1 (TRPV1) channel in primary sensory neurons. TRPA1 is activated by a series of irritant exogenous and endogenous α,β‐unsaturated aldehydes which seem to play a role in airway diseases. We investigated whether TRPA1 agonists provoke cough in guinea pigs and whether TRPA1 antagonists inhibit this response.

Design, synthesis, and biological evaluation of thiophene analogues of chalcones

Chalcones are characterized by possessing an enone moiety between two aromatic rings. A series of chalcone-like agents, in which the double bond of the enone system is embedded within a thiophene ring, were synthesized and evaluated for antiproliferative activity and inhibition of tubulin assembly and colchicine binding to tubulin. The replacement of the double bond with a thiophene maintains antiproliferative activity and therefore must not significantly alter the relative conformation of the two aryl rings. The synthesized compounds were found to inhibit the growth of several cancer cell lines at nanomolar to low micromolar concentrations. In general, all compounds having significant antiproliferative activity inhibited tubulin polymerization with an IC(50)<2microM. Several of these compounds caused K562 cells to arrest in the G2/M phase of the cell cycle.

Acetaminophen, via its reactive metabolite N-acetyl-p-benzo-quinoneimine and transient receptor potential ankyrin-1 stimulation, causes neurogenic inflammation in the airways and other tissues in rodents

Acetaminophen [N-acetyl-p-aminophenol (APAP)] is the most common antipyretic/analgesic medicine worldwide. If APAP is overdosed, its metabolite, N-acetyl-p-benzo-quinoneimine (NAPQI), causes liver damage. However, epidemiological evidence has associated previous use of therapeutic APAP doses with the risk of chronic obstructive pulmonary disease (COPD) and asthma. The transient receptor potential ankyrin-1 (TRPA1) channel is expressed by peptidergic primary sensory neurons. Because NAPQI, like other TRPA1 activators, is an electrophilic molecule, we hypothesized that APAP, via NAPQI, stimulates TRPA1, thus causing airway neurogenic inflammation. NAPQI selectively excites human recombinant and native (neuroblastoma cells) TRPA1. TRPA1 activation by NAPQI releases proinflammatory neuropeptides (substance P and calcitonin gene-related peptide) from sensory nerve terminals in rodent airways, thereby causing neurogenic edema and neutrophilia. Single or repeated administration of therapeutic (15-60 mg/kg) APAP doses to mice produces detectable levels of NAPQI in the lung, and increases neutrophil numbers, myeloperoxidase activity, and cytokine and chemokine levels in the airways or skin. Inflammatory responses evoked by NAPQI and APAP are abated by TRPA1 antagonism or are absent in TRPA1-deficient mice. This novel pathway, distinguished from the tissue-damaging effect of NAPQI, may contribute to the risk of COPD and asthma associated with therapeutic APAP use.

The P2X7 receptor as a therapeutic target

Background: The P2X7 receptor is present in a variety of cell types involved in pain, inflammatory processes and neurodegenerative conditions, thus it may be an appealing target for pharmacological intervention. The extensive use of high-throughput screening (HTS) followed by a hit-to-lead (HtL) program, has prompted a number of firms to identify highly selective and metabolically stable small-molecules possessing activity for both the rat and human P2X7 receptor, which provide a novel therapeutic approach to the treatment of pain as well as neurodegenerative and inflammatory disorders. Objective: To describe the current status of and potential for development of P2X7 receptor-antagonists. Methods: A literature review. Results/conclusions: We describe the recent discoveries of novel P2X7 receptor-selective antagonists, along with their biological activity and therapeutic potential.

Synthesis and evaluation of 1,5-disubstituted tetrazoles as rigid analogues of combretastatin A-4 with potent antiproliferative and antitumor activity.

Tubulin, the major structural component of microtubules, is a target for the development of anticancer agents. Two series of 1,5-diaryl substituted 1,2,3,4-tetrazoles were concisely synthesized, using a palladium-catalyzed cross-coupling reaction, and identified as potent antiproliferative agents and novel tubulin polymerization inhibitors that act at the colchicine site. SAR analysis indicated that compounds with a 4-ethoxyphenyl group at the N-1 or C-5 position of the 1,2,3,4-tetrazole ring exhibited maximal activity. Several of these compounds also had potent activity in inhibiting the growth of multidrug resistant cells overexpressing P-glycoprotein. Active compounds induced apoptosis through the mitochondrial pathway with activation of caspase-9 and caspase-3. Furthermore, compound 4l significantly reduced in vivo the growth of the HT-29 xenograft in a nude mouse model, suggesting that 4l is a promising new antimitotic agent with clinical potential.

Synthesis and biological evaluation of 1-methyl-2-(3 ',4 ',5 '-trimethoxybenzoyl)-3-aminoindoles as a new class of antimitotic agents and tubulin inhibitors

The 2-(3,4,5-trimethoxybenzoyl)-2-aminoindole nucleus was used as the fundamental structure for the synthesis of compounds modified with respect to positions C-4 to C-7 with different moieties (chloro, methyl, or methoxy). Additional structural variations concerned the indole nitrogen, which was alkylated with small alkyl groups such as methyl or ethyl. We have identified 1-methyl-2-(3,4,5-trimethoxybenzoyl)-3-amino-7-methoxyindole as a new highly potent antiproliferative agent that targets tubulin at the colchicine binding site and leads to apoptotic cell death.

ACTIVATION OF TRPA1 ON DURAL AFFERENTS: A POTENTIAL MECHANISM OF HEADACHE PAIN

Summary TRPA1 is expressed on dural afferent neurons and activation of dural TRPA1 produces behavioral responses consistent with headache. Abstract Activation of transient receptor potential ankyrin‐1 (TRPA1) on meningeal nerve endings has been suggested to contribute to environmental irritant–induced headache, but this channel may also contribute to other forms of headache, such as migraine. The preclinical studies described here examined functional expression of TRPA1 on dural afferents and investigated whether activation of TRPA1 contributes to headache‐like behaviors. Whole‐cell patch‐clamp recordings were performed in vitro with 2 TRPA1 agonists, mustard oil (MO), and the environmental irritant umbellulone (UMB) on dural‐projecting trigeminal ganglion neurons. Application of MO and UMB to dural afferents produced TRPA1‐like currents in approximately 42% and 38% of cells, respectively. By means of an established in vivo behavioral model of migraine‐related allodynia, dural application of MO and UMB produced robust time‐related tactile facial and hind paw allodynia that was attenuated by pretreatment with the TRPA1 antagonist HC‐030031. Additionally, MO or UMB were applied to the dura, and exploratory activity was monitored for 30 min with an automated open‐field activity chamber. Dural MO and UMB decreased the number of vertical rearing episodes and the time spent rearing in comparison to vehicle‐treated animals. This change in activity was prevented in rats pretreated with HC‐030031 as well as sumatriptan, a clinically effective antimigraine agent. These data indicate that TRPA1 is expressed on a substantial fraction of dural afferents, and activation of meningeal TRPA1 produces behaviors consistent with those observed in patients during migraine attacks. Further, they suggest that activation of meningeal TRPA1 via endogenous or exogenous mechanisms can lead to afferent signaling and headache.

Adenosine Modulates HIF-1α, VEGF, IL-8, and Foam Cell Formation in a Human Model of Hypoxic Foam Cells

Objective—Foam cell (FC) formation by oxidized low-density lipoprotein (oxLDL) accumulation in macrophages is crucial for development of atherosclerosis. Hypoxia has been demonstrated in atherosclerosis and hypoxia-inducible factor-1 (HIF-1) has been shown to promote intraplaque angiogenesis and FC development. As hypoxia induces HIF-1&agr; stabilization and adenosine (ado) accumulation, we investigated whether this nucleoside regulates HIF-1&agr; in FCs. Methods and Results—Ado, under hypoxia, stimulates HIF-1&agr; accumulation by activating all adenosine receptors (ARs). HIF-1&agr; modulation involved extracellular signal-regulated kinase 1/2 (ERK 1/2), p38 mitogen-activated protein kinase (p38 MAPK), and protein kinase B (Akt) phosphorylation in the case of A1, A2A, A2B, and ERK 1/2 phosphorylation in the case of A3 receptors. Ado, through the activation of A3 and A2B receptors, stimulates vascular endothelial growth factor (VEGF) secretion in a HIF-1&agr;–dependent way. Furthermore, ado, through the A2B subtype, induces an increase of Interleukin-8 (IL-8) secretion in a ERK 1/2, p38, and Akt kinase–dependent but not HIF-1&agr;–mediated way. Finally, ado stimulates FC formation, and this effect is strongly reduced by A3 and A2B blockers and by HIF-1&agr; silencing. Conclusions—This study provides the first evidence that A3, A2B, or mixed A3/A2B antagonists may be useful to block important steps in the atherosclerotic plaque development ado-induced.

TRP channels as therapeutic targets in airway disorders: a patent review

Introduction: Chronic respiratory diseases, such as asthma and chronic obstructive pulmonary disease, affect millions of patients worldwide. New therapeutic approaches to these conditions are urgently needed since current treatment options provide only symptomatic relief. Transient receptor potential (TRP) ion channels are emerging molecular target candidates for the development of novel, disease-modifying drugs addressing airway diseases. Areas covered: The authors review the patent literature on novel molecules targeting TRP channels (in particular TRPA1, TRPV1, TRPM8 and TRPC6) that are currently studied in clinical trials or are candidates for future clinical evaluation in the management of respiratory diseases. Expert opinion: The patent literature highlights TRPA1 and TRPV1 channels as the most advanced therapeutic targets in respiratory disorders. TRPV1 antagonists relieve cough in preclinical studies. TRPA1 antagonists not only are anti-tussive but also show efficacy in allergic asthma models. However, to date, only minimal clinical data are available regarding the effects of selective, small-molecule TRPV1 and TRPA1 blockers in respiratory disorders. Clearly, long-term clinical studies are required to confirm the expectations based on preclinical data. In conclusion, the current status of this rapidly expanding research area raises cautious optimism for TRPA1 (and possibly also TRPV1) antagonists as promising anti-tussive/anti-asthma drug candidates.