Hck inhibitors as potential therapeutic agents in cancer and HIV infection.

Hematopoietic cell kinase (Hck) is a member of the Src-family of non-receptor tyrosine kinases, which plays many roles in signalling pathways involved in the regulation of cell processes. Hck is expressed in cells of hematopoietic origin, specifically myelomonocytic cells and B lymphocytes. It participates in phagocytosis, adhesion, migration, regulation of protrusion formation on cell membrane, lysosome exocytosis, podosome formation and actin polymerization. More importantly from a medicinal chemistry point of view, high levels of Hck are involved in chronic myeloid leukemia and other hematologic tumors. Furthermore, Hck activity has been associated with virus infections including HIV-1. In particular, Hck is activated by the HIV-1 accessory protein Nef, a multifunctional HIV-1 protein that accelerates progression to AIDS and enhances the infectivity of progeny viruses. Nef binding to Hck leads to kinase activation which is important in AIDS pathogenesis. For these reasons, Hck represents a potentially good therapeutic target for the treatment of both specific cancers and HIV infection. This article summarizes Hck biological activities connected with malignancies and HIV infection, many of which have been only recently reported, and presents an overview of the compounds endowed with Hck inhibitory activity, especially focusing on the medicinal chemistry aspect.

SRC kinase inhibitors: an update on patented compounds.

The cytoplasmatic tyrosine in kinase c-Src is involved in the regulation of several cell functions including adhesion, invasion, proliferation, survival and angiogenesis. Src activity is strictly regulated in healthy cells, whereas its overexpression or hyperactivation plays a critical role during tumor development. Recently it has been suggested that the oncogenic potential of Src is linked to its role in the activation of key signalling molecules involved in several cell pathways, rather than its direct activity. For all these reasons Src represents a promising therapeutic target for the treatment of tumors. In this article a number of examples of c-Src inhibitors appeared in selected patents from 2006 to early 2011 will be reported, focusing on their chemical features and, whenever possible, on structure- activity relationships and mechanism of action. Examples of type I or II ATP-competitive inhibitors or substrate competitive inhibitors will be presented. The research in this field is very active and will probably lead to the discovery of therapeutically useful compounds, both c-Src selective and multitargeted inhibitors, that acting on different cell pathways could be more effective in blocking cancer development. However, only the results of clinical trials will show in the near future the most promising compounds.

ATP-competitive inhibitors of mTOR: an update.

mTOR (mammalian target of rapamycin) is a serine-threonine kinase belonging to the PI3K/Akt/mTOR signalling pathway that is involved in several cell functions, including growth, proliferation, apoptosis and autophagy. mTOR hyperactivation has been detected in several human cancers, thus representing, together with its upstream effectors, an important target for cancer therapy. mTOR exists in two different complexes in cells, mTORC1 and mTORC2 which could both be targeted by potential anticancer agents. Rapamycin, the selective and allosteric inhibitor of mTOR, inhibits the enzyme in mTORC1, but not in mTORC2. In the last few years a number of mTOR ATP-competitive inhibitors has been reported acting on mTOR in both complexes and possessing a more complete anticancer activity in comparison with that of rapamycin and its derivatives. mTOR shares high sequence homology in the hinge-region with PI3K that is a lipid kinase upstream to mTOR in the same signaling pathway; for this reason some compounds originally developed as PI3K inhibitors later showed to also target mTOR. As indicated by preclinical and clinical studies, compounds acting on more than one target could result in a better biological response and in enhanced therapeutic potential and also dual PI3K/mTOR inhibitors result of great interest as potential antitumor agents. This review mainly reports the recently discovered mTOR ATP-competitive inhibitors in terms of medicinal chemistry, classified by their chemical structures, focusing on SAR and modelling studies that led to the discovery of very potent and selective agents, such as AZD-8055, OSI-027 and INK128, already entered clinical trials, or WYE-132, Torin1 and others in preclinical studies. Also some examples of dual PI3K/mTOR inhibitors, including PI-103, GNE477, WJD008 and GSK2126458 are reported together with their biological and clinical data.

Fyn kinase in brain diseases and cancer: the search for inhibitors.

Fyn is a non-receptor tyrosine kinase belonging to the Src family kinases. It has been shown to play important roles in neuronal functions, including myelination and oligodendrocytes formation, and in inflammatory processes. It has also demonstrated its involvement in signaling pathways that lead to severe brain pathologies, such as Alzheimer's and Parkinson's diseases. Moreover, Fyn is upregulated in some malignancies. Experimental studies demonstrated that Fyn inhibition could be useful in the disruption of metabolic processes involved in cancer neurodegenerative diseases. Unfortunately, no specific Fyn inhibitor has been discovered till today, active compounds on other members of Src family or on different tyrosine kinases have also been reported. However, multitargeted inhibitors might be endowed with therapeutic potential. Indeed, as increasingly reported, also a not completely selective inhibitor of a specific protein could be therapeutically useful, affecting a number of cell pathways involved especially in cancer development. In this review, we report some examples of small molecule tyrosine kinase inhibitors for which data on Fyn inhibition, both in enzymatic and in cell assays, have been reported, with the aim of giving information as starting point for the researchers working in this field.

GEBR-7b, a novel PDE4D selective inhibitor that improves memory in rodents at non-emetic doses.

BACKGROUND AND PURPOSE: Strategies designed to enhance cerebral cAMP have been proposed as symptomatic treatments to counteract cognitive deficits. However, pharmacological therapies aimed at reducing PDE4, the main class of cAMP catabolizing enzymes in the brain, produce severe emetic side effects. We have recently synthesized a 3-cyclopentyloxy-4-methoxybenzaldehyde derivative, structurally related to rolipram, and endowed with selective PDE4D inhibitory activity. The aim of the present study was to investigate the effect of the new drug, namely GEBR-7b, on memory performance, nausea, hippocampal cAMP and amyloid-ß (Aß) levels. EXPERIMENTAL APPROACH: To measure memory performance, we performed object recognition tests on rats and mice treated with GEBR-7b or rolipram. The emetic potential of the drug, again compared with rolipram, was evaluated in rats using the taste reactivity test and in mice using the xylazine/ketamine anaesthesia test. Extracellular hippocampal cAMP was evaluated by intracerebral microdialysis in freely moving rats. Levels of soluble Aß peptides were measured in hippocampal tissues and cultured N2a cells by elisa. KEY RESULTS: GEBR-7b increased hippocampal cAMP, did not influence Aß levels and improved spatial, as well as object memory performance in the object recognition tests. The effect of GEBR-7b on memory was 3 to 10 times more potent than that of rolipram, and its effective doses had no effect on surrogate measures of emesis in rodents. CONCLUSION AND IMPLICATIONS: Our results demonstrate that GEBR-7b enhances memory functions at doses that do not cause emesis-like behaviour in rodents, thus offering a promising pharmacological perspective for the treatment of memory impairment.

A1 receptors ligands: past, present and future trends.

Adenosine is a neuromodulator that interacting with four receptors, A(1), A(2A), A(2B) and A(3), is involved in the regulation of several biological functions in different organs and tissues, including the central nervous system, the cardiovascular system and the airways; many pathophysiological states are associated with changes of adenosine levels. For these reasons pharmaceutical companies and academicians performed intense efforts to obtain agonists, antagonists and allosteric enhancers selective for each adenosine receptor subtypes as potential clinical candidates. In fact, therapeutic modulation of the adenosine system could offer the possibility of a "soft" treatment of different diseases, but, due to the ubiquitous distribution of adenosine and of its receptors, the challenge in therapy development depends from specificity for the different receptor subtypes. Some A(1) agonists and antagonists, very potent and selective, reached clinical trials for the treatment of different diseases. A(1) agonists are clinical candidates for atrial arrhythmias, angina, type 2 diabetes and in pain management, while A(1) antagonists are in study as potassium-sparing diuretics with kidney-protecting properties and in chronic heart diseases. Several reviews, recently published and herein cited reported in detail the biological and clinical aspects of such molecules. This review focuses on the A(1) adenosine receptor (A(1)AR) ligands, both agonists and antagonists, appeared in the literature in the last few years, together with their potential therapeutic application, pointing the attention on their chemical structures and SAR (Structure Activity Relationship) and also reporting new findings on preclinical or clinical trials of some important A(1)AR ligands synthesized in the past.

New opportunities to treat the T315I-Bcr-Abl mutant in chronic myeloid leukaemia: tyrosine kinase inhibitors and molecules that act by alternative mechanisms.

Resistance to the Bcr-Abl inhibitors approved for the treatment of chronic myeloid leukaemia (CML) may arise from different mechanisms, including Bcr-Abl amino acid mutations, gene amplification and mechanisms independent of Bcr-Abl. The T315I mutation at the gatekeeper residue is very frequent in advanced phases of the disease and is one of the main causes of resistance, disrupting important contact points between the inhibitors and the enzyme. Different strategies have been implemented to overcome this resistance, including the synthesis of new Bcr-Abl ATPcompetitive or non-ATP-competitive inhibitors, dual Aurora/Bcr-Abl inhibitors and multi-targeted kinase inhibitors. An alternative approach is the use of other compounds that do not bind directly to the Bcr-Abl protein; instead, these molecules act on several downstream pathways, regulated by or linked in different ways to Bcr-Abl, that lead to the malignant transformation of the cells. For this reason, farnesyl transferase inhibitors, MAPK inhibitors, Rac guanosine triphosphatase inhibitors, PI3K inhibitors, JAK inhibitors, Hsp90 inhibitors, mTOR inhibitors, PP2A activators and apoptosis inducers have been tested, alone or in combination with ATP-competitive inhibitors, against CML cell lines. This review discusses compounds that act on Bcr-Abl or different cell pathways and reports on the molecules active against the T315I mutation, particularly the most recent findings in this field. New molecules that are claimed by recent patents to be active on this mutation are also reported. When possible, the review will focus on medicinal chemistry in terms of chemical structure, mechanism of action and structure-activity relationships.

Small molecules ATP-competitive inhibitors of FLT3: a chemical overview.

FLT3 is a tyrosine kinase (TK), member of the class III TK receptor family, normally expressed in hematopoietic, immune and neural systems, also playing an important role in the pathogenesis of acute leukemias, particularly acute myeloid leukemia (AML), where it is present in constitutively activated mutated forms, correlated with poor prognosis, in a notable percentage of patients. For these reasons FLT3 soon appeared as a promising target for the therapeutic intervention for this severe and aggressive malignancy; the recent determination of the crystal structure of the autoinhibited form of FLT3 gave new trend for the design and the synthesis of potent inhibitors. Small molecules tyrosine kinase inhibitors represent one of the largest drug family currently targeted by pharmaceutical companies for the treatment of cancer. Exciting examples of such molecules have reached advanced clinical trials and have been recently approved by FDA for the treatment of different solid or haematological tumors. Usually TK inhibitors share common features, namely two hydrophobic/aromatic regions bearing one or more hydrogen bonding substituents. These two regions can be connected by different spacers and almost all the molecules contain a component resembling the ATP purine structure. This review will deal with FLT3 synthetic inhibitors, reporting not only the most important molecules that are in clinical trials, but also the new compounds that have appeared in literature in the last few years. Our attention will be focused on chemical structures, mechanisms of action and structure-activity relationships.

Cytotoxic effects of a novel pyrazolopyrimidine derivative entrapped in liposomes in anaplastic thyroid cancer cells in vitro and in xenograft tumors in vivo.

In this study, we evaluated the activity of two novel pyrazolopyrimidine derivatives (Si 34 and Si 35) against ARO cells, a human anaplastic thyroid cancer cell line. ARO cells exposed to different concentrations of the drugs showed a reduced growth rate and an increase of mortality. After 72 h incubation, doses of 5 and 10 microM Si 34 determined a decrease of cell counts by approximately 25% and approximately 75% compared with those of control cells respectively. Similar findings were observed using Si 35. Treatment with both Si 34 and Si 35 at 10 microM increased cell mortality also ( approximately 29% and approximately 18% respectively). At these concentrations, a decrease in cyclin D1 levels was observed. To improve the biopharmaceutical properties, a liposome formulation was prepared. When entrapped in unilamellar liposomes, Si 34 exerted its cytotoxic effects even at lower doses (maximal inhibition at 5 microM) and after shorter incubation time (48 h) either in ARO or other thyroid cancer cell lines. The effects were associated with weak apoptotic death. Inhibition of epidermal growth factor-stimulated src and ERK phosphorylation, as well as reduction of migration properties of ARO cells was also observed. Moreover, the growth of tumor xenografts induced in severe combined immunodeficiency (SCID) mice was inhibited by i.v. administration of 25-50 mg/kg of the drug liposomal formulation. In conclusion, the liposomal preparation of this novel pyrazolopyrimidine derivative appears to be a promising tool for the treatment of anaplasic thyroid cancer.

Growth inhibition of medullary thyroid carcinoma cells by pyrazolo-pyrimidine derivates.

There is no effective treatment for recurrent or metastatic medullary thyroid carcinoma (MTC), a tumor arising from thyroid C-cells commonly presenting an inherited or acquired RET mutation. In this study we examined the sensitivity of two human MTC cell lines to novel pyrazolopyrimidine derivates, able to inhibit src-family tyrosine kinase activity. In TT cells [carrying the multiple endocrine neoplasia (MEN)2A Ret mutation Cys 634Trp] and MZ-CRC-1 cells (carrying the MEN2B RET mutation Met891Thr), one of these compounds, namely Si 34, determined a significant growth inhibitory effect (approximately 90% vs control for TT, 80% vs control for MZ-CRC-1) mainly due to enhanced cell mortality after a 6-day incubation. At concentrations that increased cell mortality, neither biochemical or morphological characteristics of apoptosis were detected in TT and MZCRC- 1 cells treated with Si 34. These results, when confirmed in other in vivo preclinical models, suggest that this novel tyrosine kinase inhibitor may be useful for the treatment of MTC.

2-Amino/azido/hydrazino-5-alkoxy-5H-[1]benzopyrano[4,3-d]pyrimidines: synthesis and pharmacological evaluation.

New series of 5-alkoxy-benzopyranopyrimidine derivatives were developed from the chemical modulation of the substituent in position 2 of the scaffold, with the aim to produce analgesic/antiphlogistic agents more potent than analogues previously reported. The 2-hydrazino derivatives exhibited a good analgesic activity in writhing test; the analgesic doses of the compounds did not affect mice spontaneous locomotor activity thus any confounding sedative effect could be excluded. These derivatives revealed an aspirin-like profile with a strong inhibition of AA-induced platelet aggregation, probably due to a strong, non selective, inhibition of cyclooxygenases. In spite of the inhibition of COX activity displayed in vitro, the compounds did not cause gastric damage in rats after acute oral administration. A different pharmacological profile was observed for the 2-azido derivatives, particularly in vivo.

New pyrazolo[3,4-d]pyrimidines endowed with A431 antiproliferative activity and inhibitory properties of Src phosphorylation.

New 4-aminopyrazolo[3,4-d]pyrimidines bearing various substituents at the position 1 and 6, were synthesized. The new compounds showed antiproliferative activity toward A431 cells, were found to be inhibitors of Src phosphorylation, and induced apoptotic cell death. In particular, 2h was a better inhibitor of Src phosphorylation than the reference compound PP2.

Synthesis and pharmacological evaluation of 2,5-cycloamino-5H-[1]benzopyrano[4,3-d]pyrimidines endowed with in vitro antiplatelet activity.

A series of new 2,5-cycloamino-5H-[1]benzopyrano[4,3-d]pyrimidines 3a-i have been synthesized and tested in vivo for the anti-inflammatory/analgesic/antipyretic effects and in vitro to evaluate the antiplatelet activity on guinea-pig platelet-rich plasma aggregated by collagen, adenosine-5'-diphosphate (ADP) and arachidonic acid (AA). Title compounds were ineffective in vivo; however, the pyrrolidino derivatives 3a and 3c exhibited an antiplatelet activity against all the aggregants differing from that of acetylsalicylic acid (ASA) while the 5-morpholino derivatives 3g-i showed the most potent ASA-like antiplatelet activity.