Current Medicinal Chemistry - Volume 20, Issue 19, 2013

Acute myeloid leukemia (AML) is a highly lethal disease, especially in old patients. Chemoresistance and the absence of host immune responses against autochthonous malignancy play a major role in the poor prognosis of AML. The triazene compounds Dacarbazine and Temozolomide are monofunctional alkylators that donate methyl groups to many sites in DNA, including the O6-position of guanine producing O6-methylguanine (O6-MeG). If not repaired, O6- MeG frequently mispairs with thymine during DNA duplication. O6-MeG:T mismatches can be recognized by the mismatch repair (MMR) system which activates a cascade of molecular events leading to cell cycle arrest and cell death. If MMR is defective, cells continue to divide and GC → AT transition mutations occur. In preclinical models, such mutations can lead to the appearance of abnormal proteins containing non-self peptides (“chemical xenogenization” CX) that can be recognized by host cell-mediated immunity. Repair of O6-MeG is achieved by the DNA repair protein, O6- methylguanine-DNA methyltransferase (MGMT), which removes the methyl adduct in an autoinactivating stoichiometric reaction. High MGMT levels attenuate the pharmacodynamic effects of triazenes. In the last few years, triazenes, alone or with MGMT inhibitors, have been tested in AML. In view of their potential activity as CX inducers, triazenes could offer the additional advantage of host anti-leukemia immune responses. The present paper describes several studies of leukemia treatment with triazenes and a case of acute refractory leukemia with massive skin infiltration by malignant cells. Treatment with Temozolomide and Lomeguatrib, a potent MGMT inhibitor, produced a huge, although transient, blastolysis and complete disappearance of all skin lesions.

Acridones are a class of compounds that have attracted attention in recent years for their wide range of biological properties, including selective inhibition of diverse human pathogenic viruses. The wide spectrum of antiviral activity includes DNA and RNA viruses, such as herpes simplex virus, cytomegalovirus, adenovirus, hepatitis C virus, dengue virus, and Junin virus, among others, indicative of the involvement of cellular factors as potential targets of acridone derivatives. At the present, their precise mode of action is not clearly determined, although the predominant action seems to be centered on the synthesis of nucleic acids. Regarding this point, inhibitory activity against cellular and viral enzymes and the ability to intercalate into nucleic acid molecules was demonstrated for some acridone compounds. Then, the possibility of a multiple effect on different targets renewed interest in these agents for virus chemotherapy allowing a potent inhibitory effectiveness associated to less feasibility of generating antiviral resistance. This review summarizes the current knowledge regarding the methods of synthesis, the antiviral properties of acridone derivatives, their mechanism of action, and structural characteristics related to antiviral activity as well as the perspectives of this class of compounds for clinical application against human viral infections.

Although NSAIDs are very effective drugs, their use is associated with a broad spectrum of adverse reactions in the liver, kidney, cardiovascular (CV) system, skin and gut. Gastrointestinal (GI) side effects are the most common and constitute a wide clinical spectrum ranging from dyspepsia, heartburn and abdominal discomfort to more serious events such as peptic ulcer with life-threatening complications of bleeding and perforation. The appreciation that CV risk is also increased further complicates the choices of physicians prescribing anti-inflammatory therapy. Despite prevention strategies should be implemented in patients at risk, gastroprotection is often underused and adherence to treatment is generally poor. A more appealing approach would be therefore to develop drugs that are devoid of or have reduced GI toxicity. Gastro- duodenal mucosa possesses many defensive mechanisms and NSAIDs have a deleterious effect on most of them. This results in a mucosa less able to cope with even a reduced acid load. NSAIDs cause gastro-duodenal damage, by two main mechanisms: a physiochemical disruption of the gastric mucosal barrier and systemic inhibition of gastric mucosal protection, through inhibition of cyclooxygenase (COX, PG endoperoxide G/H synthase) activity of the GI mucosa. However, against a background of COX inhibition by anti-inflammatory doses of NSAIDs, their physicochemical properties, in particular their acidity, underlie the topical effect leading to short-term damage. It has been shown that esterification of acidic NSAIDs suppresses their gastrotoxicity without adversely affecting anti-inflammatory activity. Another way to develop NSAIDs with better GI tolerability is to complex these molecules with cyclodextrins (CDs), giving rise to so-called “inclusion complexes” that can have physical, chemical and biological properties very different from either those of the drug or the cyclodextrin. Complexation of NSAIDs with β-cyclodextrin potentially leads to a more rapid onset of action after oral administration and improved GI tolerability because of minimization of the drug gastric effects. One such drug, piroxicam-β -cyclodextrin (PBC), has been used in Europe for 25 years. Preclinical and clinical pharmacology of PBC do show that the β-cyclodextrin inclusion complex of piroxicam is better tolerated from the upper GI tract than free piroxicam, while retaining all the analgesic and anti-inflammatory properties of the parent compound. In addition, the drug is endowed with a quick absorption rate, which translates into a faster onset of analgesic activity, an effect confirmed in several clinical studies. An analysis of the available trials show that PBC has a GI safety profile, which is better than that displayed by uncomplexed piroxicam. Being an inclusion complex of piroxicam, whose CV safety has been pointed out by several observational studies, PBC should be viewed as a CV safe anti-inflmmatory compound and a GI safer alternative to piroxicam. As a consequence, it should be considered as a useful addition to our therapeutic armamentarium.

The interest in the synthesis and applications of thioxanthones, dibenzo-gamma-thiopyrones, started in the beginning of the 20th century. Thioxanthones are traditionally synthesized via benzophenone, diarylthioether or diarylthioester intermediates. In recent years, more efficient and cleaner synthetic methodologies are being applied to obtain thioxanthone derivatives, especially for photochemical applications. Considering biological activities, the first thioxanthone introduced in therapy in 1945 was Miracil D, as an antischistosomal agent. Since then, the variety of studies of biological/ pharmacological activities of thioxanthones led to the discovery of new agents and to the disclosure of their mechanisms of action. Moreover, the ability to sensitize cancer cells suggested new and promising applications in chemotherapy. New antitumor derivatives are being developed by molecular modifications such as isosterism (aza-thioxanthones and aminoethylthioxanthones) or hybridation (psorospermine and acronycin analogues). The last generation of antitumor thioxanthones rendered a derivative, SR271425, with an excellent preclinical antitumor efficacy. The last decade has been excited in the research of thioxanthones with important achievements in both synthesis and biochemical applications, especially in order to dissociate the antitumor activity from the toxicity of drug candidates. Recently, thioxanthones emerged as dual inhibitors of P-glycoprotein and tumor cell growth. It is expected that in the following years new analogues with the thioxanthone scaffold emerge in the field of anticancer therapy, with enhanced antitumor activity and without serious side effects.

The traditional drug discovery pipeline for the identification and development of compounds that selectively target specific molecules to ameliorate disease remains a major focus for medical research. However, the zebrafish is increasingly providing alternative strategies for various components of this pipeline. Zebrafish and their embryos are small, easily accessible and relatively low cost, making them applicable to high-throughput, small molecule screening. Zebrafish can also be manipulated by a range of forward and reverse genetics techniques to facilitate gene discovery and functional studies. Moreover, their physiological and developmental complexity provides accurate models of human disease to underpin mechanism of action and in vivo validation studies. Finally, several of these biological characteristics make zebrafish eminently suitable for toxicity testing, including eco-toxicology. Here we review the application of zebrafish to preclinical drug development and toxicity testing, including recent advances in mutant generation, drug screening and toxicology that serve to further enhance the capabilities of this valuable model organism in drug discovery.

Multiple myeloma (MM) is a plasma cell malignancy that causes devastating bone destruction by activating osteoclasts in the bone marrow milieu. MM is the second of all hematological malignancies. Thus, the search for new pharmacological weapons is under intensive investigation being MM a critically important public health goal. Recently, it has been demonstrated that macrophage inflammatory protein 1- alpha (MIP-1α) is crucially involved in the development of osteolytic bone lesions in MM. Phenolic components of extra virgin olive oil are reported to have anti tumor activity. However, the underlying mechanisms and specific targets of extra virgin olive oil remain to be elucidated. In the present study, we investigated the effects of a recently isolated novel extra virgin olive oil polyphenol, oleocanthal, on the human multiple myeloma cell line ARH-77. Here we report that this natural compound has a remarkable in vitro activity by inhibiting MIP-1α expression and secretion in MM cells. In addition, we also demonstrated that oleocanthal inhibits MM cells proliferation by inducing the activation of apoptosis mechanisms and by down-regulating ERK1/2 and AKT signal transduction pathways. This in vitro study suggests a therapeutic potential of oleocanthal in treating multiple myeloma.

PHA-E is a natural product extracted from red kidney beans, and it has been reported to induce cell apoptosis by blocking EGFR in lung cancer cells. Because EGF is the major in vivo competitor to PHA-E in clinical application, PHA-E must be proved that has better affinity to EGFR than EGF. This study would focus on how PHA-E tightly bind to EGFR and the results would compare with EGF. The adhesion force, measured by AFM, between EGFR and PHA-E was 207.14±74.42 pN that was higher than EGF (183.65±86.93 pN). The equilibrium dissociation constant of PHA-E and EGF to EGFR was 2.4x 10-9±1.4x10-9 and 7.3x10-8±2.7x-8, respectively, that could evaluate binding affinity. The result showed that binding affinity of PHA-E to EGFR was one order higher than EGF to EGFR. In the results of flow cytometer and confocal microscope, we found binding efficiency of EGF to EGFR was decrease as the concentration of PHA-E increased. In the analysis of Western blot, treatment of A-549 cells with PHA-E resulted in a dose-dependent decrease in EGFR phosphorylation. In conclusion, we found that PHA-E had better adhesion force and binding affinity to EGFR than that of the EGF. The interaction between PHA-E and EGFR could block EGF binding and then inhibit EGFR phosphorylation. PHA-E could be developed into a new target molecule for lung cancer treatment that could be immobilized on the drug carrier to guide therapeutic particles to the tumor site.

The standard targeted therapy for HER2-overexpressing breast cancer is the HER2 monoclonal antibody, trastuzumab. Although effective, many patients eventually develop trastuzumab resistance. The dual EGFR/HER2 small molecule tyrosine kinase inhibitor lapatinib is approved for use in trastuzumab-refractory metastatic HER2-positive breast cancer. However, lapatinib resistance is a problem as most patients with trastuzumab-refractory disease do not benefit from lapatinib. Understanding the mechanisms underlying lapatinib resistance may ultimately facilitate development of new therapeutic strategies for HER2-overexpressing breast cancer. Our current results indicate that MEK inhibition increases lapatinib-mediated cytotoxicity in resistant HER2-overexpressing breast cancer cells. We genetically and pharmacologically blocked MEK/ERK signaling and evaluated lapatinib response by trypan blue exclusion, anchorageindependent growth assays, flow cytometric cell cycle and apoptosis analysis, and in tumor xenografts. Combined MEK inhibition and lapatinib treatment reduced phosphorylated ERK more than single agent treatment. In addition, Western blots, immunofluorescence, and immunohistochemistry demonstrated that the combination of MEK inhibitor plus lapatinib reduced nuclear expression of the MEK/ERK downstream proto-oncogene FOXM1. Genetic knockdown of MEK was tested for the ability to increase lapatinib-mediated cell cycle arrest or apoptosis in JIMT-1 and MDA361 cells. Finally, xenograft studies demonstrated that combined pharmacological inhibition of MEK plus lapatinib suppressed tumor growth and reduced expression of FOXM1 in HER2-overexpressing breast cancers that are resistant to trastuzumab and lapatinib. Our results suggest that FoxM1 contributes to lapatinib resistance downstream of MEK signaling, and supports further study of pharmacological MEK inhibition to improve response to lapatinib in HER2-overexpressing trastuzumabresistant breast cancer.