Current Medicinal Chemistry (v.19, #23)

Synthetic Lethality to Overcome Cancer Drug Resistance by L. Porcelli, A. E. Quatrale, P. Mantuano, N. Silvestris, A. E. Brunetti, H. Calvert, A. Paradiso, A. Azzariti (3858-3873).
A large body of evidence point out that the onset of synthetic lethality may provide a useful tool for amplifying the efficacy of drugs in anticancer regimens, to uncover interdependence between genes and to identify predictive factors that would be extremely useful to guide in the selection of more effective targeted drugs and drug combinations for each patient. Here, we provide an overview on the exploitation of synthetic lethality to overcome drug resistance to conventional chemotherapy in several types of solid tumors. We report recent findings on cellular markers and gene mutations which are specifically essential for the viability of cancer cells and for resistance to chemotherapeutics. In addition, new molecularly targeted strategies to overcome drug resistance are suggested.

DNA Repair and Resistance to Topoisomerase I Inhibitors: Mechanisms, Biomarkers and Therapeutic Targets by M. Alagoz, D. C. Gilbert, S. El-Khamisy, A. J. Chalmers (3874-3885).
Irinotecan and topotecan are derivatives of the naturally occurring cytotoxic compound camptothecin that are used in the treatment of patients with colorectal cancer, either as single agents or in combination with radiotherapy and/or other chemotherapy drugs. They are inhibitors of DNA topoisomerase I (Top I) and exert their cytotoxic effects in replicating cells by inducing DNA strand breaks. A wide range of DNA repair proteins is involved in the recognition and repair of these breaks, and depletion or inhibition of some of these proteins increases the cytotoxic effects of Top I inhibitors. Building on these laboratory observations, ongoing translational research is aiming to establish whether this mechanistic information can be used to improve the treatment of patients with certain types of cancer. Two potential strategies are under investigation: (1) individualising treatment by evaluating levels and/or patterns of expression of DNA repair proteins that predict clinical response to Top I inhibitors, and (2) developing small molecule inhibitors of these repair enzymes to overcome tumour resistance and improve outcomes. This review summarises the current status of these research endeavours, focusing on the key roles of tyrosyl DNA phosphodiesterase 1 (Tdp1) and poly(ADP-ribose) polymerase (PARP), and examines the pre-clinical and clinical data that support the potential value of these and other DNA repair proteins as predictive markers and therapeutic targets. Since irinotecan is increasingly being combined with radiotherapy, the potential for these proteins to act as predictive biomarkers for both Top I inhibitors and radiation is proposed, and the possibility of synergistic potentiation of chemoradiation regimes by Tdp1 and/or PARP inhibitors is considered.

Strategies to Improve the Killing of Tumors Using Temozolomide: Targeting the DNA Repair Protein MGMT by G. Jiang, L. -T. Li, Y. Xin, L. Zhang, Y. -Q. Liu, J. -N. Zheng (3886-3892).
Alkylating agents such as temozolomide (TMZ) are effective anticancer drugs for treating a variety of solid tumors including melanoma, glioma, and astrocytoma. TMZ exerts its effects mainly via the mutagenic product O6-methylguanine, a cytotoxic DNA lesion. This damage may be repaired by the DNA repair enzyme O6-methylguanine DNA methyltransferase (MGMT), a key player in the resistance of cancers to TMZ. Several strategies are presently being pursued to improve the killing of tumor cells by TMZ, with inhibition of MGMT being the most promising. In this review, we provide an overview of recent advances in this field.

Circumventing Melanoma Chemoresistance by Targeting DNA Repair by S. Mocellin, L Bertazza, C. Benna, P. Pilati (3893-3899).
Available evidence demonstrates that the DNA repair machinery is involved in melanoma resistance to chemotherapeutics. Furhtermore, preclinical findings suggest that interfering with DNA repair could increase chemosensitivity of melanoma cells. However, the clinical implementation of these principles is still in its infancy and no such strategy is currently proven to be effective in patients with advanced melanoma. Since the molecular mechanisms governing the relationship between chemoresistance and DNA repair are not fully elucidated, more basic and translational research is needed to understand the reasons for the failures and to identify novel targets. In this review we summarize the experimental and clinical findings that are fostering the research in this promising field of oncology.

Cancer Resistance to Type II Topoisomerase Inhibitors by P. Pilati, D. Nitti, S. Mocellin (3900-3906).
Type II topoisomerases (TOPO2) are ubiquitously expressed enzymes that overcome topological problems in genomic DNA, which can result from DNA replication, transcription and repair. The class of compounds targeting TOPO2 includes some of the most active chemotherapy agents currently available for the treatment of patients with different cancer types. Therefore, understanding of the molecular mechanisms underlying resistance to these drugs is of pivotal importance to improve their efficacy and ultimately increase the life expectancy of cancer patients. The first aim of this review is to summarize the molecular biology of TOPO2 inhibitors, which is the key to understand cancer resistance to them; the second part of this work is dedicated to overview and discuss the available evidence on the mechanisms of resistance to these drugs, with special attention to the strategies that might be useful to circumvent this phenomenon on the clinical ground.

Role of PARP Inhibitors in Cancer Biology and Therapy by D. Davar, J. H. Beumer, L. Hamieh, H. Tawbi (3907-3921).
Deeper understanding of DNA repair mechanisms and their potential value as therapeutic targets in oncology heralded the clinical development of poly(ADP-ribose) polymerase (PARP) inhibitors. Although initially developed to exploit synthetic lethality in models of cancer associated with defective DNA repair, our burgeoning knowledge of PARP biology has resulted in these agents being exploited both in cancer with select chemotherapeutic agents and in non-malignant diseases. In this review article, we briefly review the mechanisms of DNA repair and pre-clinical development of PARP inhibitors before discussing the clinical development of the various PARP inhibitors in depth.

Cancer treatments often lose their effectiveness due to the development of multiple drug resistance. Thus, identification of key proteins involved in the tumorigenic process and the survival mechanism(s), coupled with the design of novel therapeutic compounds (such as small molecule inhibitors), are essential steps towards the establishment of improved anticancer treatment strategies. DNA repair pathways and their proteins have been exposed as potential targets for combinatorial anticancer therapies that involve DNA-interactive cytotoxins, such as alkylating agents, because of their central role in providing resistance against DNA damage. In addition, an understanding of the tumor-specific genetics and associated DNA repair capacity has allowed research scientists and clinicians to begin to devise more targeted treatment strategies based on the concept of synthetic lethality. In this review, the repair mechanisms, as well as the links to cancer progression and treatment, of three key proteins that function in the base excision repair pathway, i.e. APE1, POLβ, and FEN1, are discussed.

Polo-Like Kinases Inhibitors by L. Garuti, M. Roberti, G. Bottegoni (3937-3948).
Polo-like kinases (PLKs) are a family of serine/threonine kinases that play crucial roles in multiple stages of mitosis. PLK1 is the most studied member of the family. It is overexpressed in a wide spectrum of cancer types and is a promising target in oncology. Most of PLK1 inhibitors are ATP-competitive. Despite the structural similarities among various kinases, several inhibitors are selective. Some areas of the PLK1 active site are important for selectivity against other kinases. These include a small pocket formed by Leu 132 in the hinge region, a bulky phenylalanine and a small cysteine at the bottom and in the roof of the ATP pocket, respectively, and an unusual concentration of positively charged residues in the solvent-exposed region. Many ATP-competitive inhibitors are heterocyclic systems able to interact with the unique features of the PLK1 binding site. Other inhibitors target regions outside the ATP pocket, such as the substrate binding domain or a hydrophobic pocket, formed when the kinase is in the inactive conformation. An alternative approach to obtain specificity and to overcome drug resistance often associated with kinase inhibitors is the inhibition of the polo-box domain (PBD) of PLK1. The PBD is unique for the family of PLKs and is essential for PLK functions; so it is a useful target for the development of selective and potent inhibitors for clinical uses. In this review some PLK inhibitors are reported, focusing on chemical structures, structure-activity-relationships (SAR) and biological activities. The great potential of these compounds could open promising perspectives. Moreover, a combination of polo-like kinases inhibitors with other anticancer drugs might offer new opportunities for cancer therapy.

Coinage Metal Complexes Against Breast Cancer by B. Biersack, A. Ahmad, F. H. Sarkar, R. Schobert (3949-3956).
Breast cancer is still the leading cause of cancer deaths among women worldwide, and new therapies to treat this dangerous disease are desperately needed. The serendipitously found anticancer drug cisplatin and its second-generation congener carboplatin appear to be promising drug systems for the treatment of breast tumors, in particular of multidrug resistant and highly aggressive triplenegative subtypes. In the wake of these platinum drugs, complexes of the coinage metals copper, silver, and gold were developed that showed enhanced selectivity for breast cancer while causing fewer and weaker side-effects. This review takes stock of the latest developments in the field of coinage metal anticancer drugs with an emphasis on their biological and mechanistic aspects. Pertinent literature is covered up to 2012.

This review presents a general overview of the subtype-selective dopamine receptor radioligands for in vivo imaging of dopamine receptor expression by positron emission tomography (PET). Besides the 11C- and 18F-labeled radioligands which are already in clinical use, a summary of subtype-selective radioligands which had been studied in vitro and in vivo is provided, which shines light onto the current status and recent developments in this field of radiopharmaceutical research.

Palladacycles as Antimicrobial Agents by A. -S.S.H. Elgazwy, N. S.M. Ismail, S. R. Atta-Allah, M. T. Sarg, D. H.S. Soliman, M. Y. Zaki, M. A. Elgamas (3967-3981).
This review article deals with the structure activity relationship (SAR) for a variety of palladacycles in biomedical applications. Moreover, the types of antibacterial, antifungal, antimycobacterial and antiprotozoal (antiamoebic and antitrypanosomal) activities will vary considerably from one country to another. Therefore, all efforts will be required to face such a vast diversity of problems. This study gives an up to date overview of the antibacterial, antifungal, antimycobacterial and antiprotozoal chemistry of the palladium group elements with an emphasis on the new strategies used in the development of new antibacterial agents. Methodologies for application of bulky aromatic or aliphatic nitrogen ligands, chiral organic moieties, chelates containing other donor atoms than nitrogen, and biologically active ligands in the design of agents analogous to palladacycles are presented. Therefore, the use of palladacycles in medicinal chemistry is interesting as potential application in the biological properties with less toxic drugs compounds..

Dipeptidyl peptidase 4 (DPP-4), a substrate-specific serine protease, has been validated as a promising drug target for the treatment of type 2 diabetes. DPP-4 inhibitors significantly lowered blood glucose levels in patients with type 2 diabetes without common body weight gain, hypoglycemia and gastrointestinal disturbance side effects. Therefore, DPP-4 inhibitors attracted more and more attention. In particular, non-peptidomimetic DPP-4 inhibitors have been a focus of research and development and made great progress in recent years, which resulted in the discovery of a wide variety of potent non-peptidomimetic DPP-4 inhibitors. Some of them, such as sitagliptin, alogliptin and linagliptin have already been used as marketed drugs, while others have been into clinical trials. Based on the core structural features of non-peptidomimetic DPP-4 inhibitors, seven types were classified in the article. For each type, we focused on the description of strategies for design and optimization, together with a discussion on concluded structure-activity relationships (SAR). In addition, the contribution of specific substituents to the inhibition of DPP-4 was summarized. Selectivity towards the inhibition of DPP-4 over dipeptidyl peptidase 8 (DPP-8) and dipeptidyl peptidase 9 (DPP-9) was also presented.

Glutathione-Related Factors and Oxidative Stress in Autism, A Review by A. Ghanizadeh, S. Akhondzadeh, M. Hormozi, A. Makarem, M. Abotorabi-Zarchi, A. Firoozabadi (4000-4005).
Autism spectrum disorders are complex neuro-developmental disorders whose neurobiology is proposed to be associated with oxidative stress which is induced by reactive oxygen species. The process of oxidative stress can be a target for therapeutic interventions. In this study, we aimed to review the role of oxidative stress, plasma glutathione (GSH), and related factors as the potential sources of damage to the brain as well as the possible related factors which reduce the oxidative stress. Methylation capacity, sulfates level, and the total glutathione level are decreased in autism. On the other hand, both oxidized glutathione and the ratio of oxidized to reduced glutathione are increased in autism. In addition, the activity of glutathione peroxidase, superoxide dismutase, and catalase, as a part of the antioxidative stress system are decreased. The current literature suggests an imbalance of oxidative and anti-oxidative stress systems in autism. Glutathione is involved in neuro-protection against oxidative stress and neuro-inflammation in autism by improving the anti-oxidative stress system. Decreasing the oxidative stress might be a potential treatment for autism.

Anti-Inflammatory Effect of 3,4-DHPEA-EDA [2-(3,4 -Hydroxyphenyl) ethyl (3S, 4E)- 4-Formyl-3-(2-Oxoethyl)Hex-4-Enoate] on Primary Human Vascular Endothelial Cells by G. Sindona, A. Caruso, A. Cozza, S. Fiorentini, B. Lorusso, E. Marini, M. Nardi, A. Procopio, S. Zicari (4006-4013).
Diets in which fat is significantly provided by olive oil and are relatively rich in vegetables, have been associated with a low incidence of cardiovascular diseases, mostly due to the presence of several phenolic compounds which have anti-oxidant and antiinflammatory properties. [1]. In this work, we describe the anti-inflammatory effect of 3,4-DHPEA-EDA in a cell model that we developed to mimic inflammatory injury of endothelium. This was based on the production of the proinflammatory chemokine CCL2, following in vitro stimulation of primary human endothelial cells. Pre-treatment of cells with 3,4-DHPEA-EDA resulted in a dosedependent inhibition of CCL2 secretion. The effect of 3,4-DHPEA-EDA on CCL2 expression was observed at the transcriptional level. Functional data have shown that 3,4-DHPEA-EDA diminished monocyte adhesion to HUVECs. These results point on the use of 3,4- DHPEA-EDA as a novel drug aimed to prevent or reduce inflammation of endothelium.

AG490 Promotes HIF-1α Accumulation by Inhibiting Its Hydroxylation by R. Fernandez-Sanchez, S. Berzal, Maria-Dolores Sanchez-Nino, F. Neria, S. Goncalves, O. Calabia, A. Tejedor, M. J. Calzada, C. Caramelo, J. J.P. Deudero, A. Ortiz (4014-4023).
AG490 is a tyrphostin originally described as a Janus Activated Kinase (JAK) 2 inhibitor. AG490 also inhibits epidermal growth factor receptor (EGFR) and guanylyl cyclases (GC). More recently, AG490 was associated with oxidative stress protection in experimental acute kidney injury models. We now show that AG490 is also a strong activator of the Hypoxia Inducible Factor (HIF)-1. Under normoxic conditions HIF-1α is degraded through hydroxylation, von Hippel Lindau protein (VHL)-mediated ubiquitin tagging and proteasomal degradation. AG490 increased HIF-1α protein, but not HIF-1α mRNA levels, dose- and time-dependently in cultured endothelial, vascular smooth muscle and kidney proximal tubular epithelial cells. AG490 increased HIF-1α protein half-life, suggesting that HIF-1α protein accumulation resulted from a decreased degradation. In this regard, AG490 prevented HIF-1α hydroxylation and increased HIF-1α protein levels in human renal carcinoma cells expressing VHL, but did not further increase HIF-1α in VHL negative cells. AG490 did not prevent the proteasomal degradation of other proteins. HIF-1α was not upregulated by dominant negative JAK2constructs, tyrphostin AG9, the EGFR inhibitors erbstatin and genistein, the GC inhibitor Ly83583 or cGMP analogues. Finally, AG490 also increased HIF-1α transcriptional activity evidenced by the increased HIF-1α-dependent VEGF expression. In conclusion, AG490 is a novel HIF-1α activator that increases HIF-1α half-life and protein levels through interference with HIF-1α hydroxylation and VHL-mediated degradation. This action may contribute to the cell and tissue protective effects of AG490.

P38 kinase plays a vital role in the inflammation mediated by tumor necrosis factor-α and interleukin-1β pathways, and thus the inhibitors of p38 kinase provide effective approach for the treatment of inflammatory diseases. Presently, a combined study of threedimensional quantitative structure-activity relationship, molecular docking and molecular dynamics (MD) was undertaken to explore the structural insights of 174 2-thioimidazole compounds influencing the p38α inhibitory activities. Both the ligand-based resultant comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA) models exhibited satisfactory predictability (with Q2=0.475, R2 ncv=0.774, R2 pre=0.668 and Q2=0.504, R2 ncv=0.745, R2 pre=0.709, respectively). Furthermore, good consistency was observed between the 3D-QSAR models, docking and MD results. Our findings are: i) hydrogen bonding and steric size of the molecules play crucial roles in the mechanisms of action that a medium-sized bulky substituent on the 2-position, an electropositive H-bond donor substituent on the 6-position of the pyridine ring are favorable for increasing the inhibition activity; ii) 2- Thioimidazole derivatives may bind to the p38α kinase with a “lobster” active conformation, which is fixed by four hydrogen bonds they formed with the adjacent residues (Lys53, Gly110, Met109 and Ala157) and two hydrophobic interactions (in hydrophobic pockets I and II respectively) in p38α binding site. These models and the derived information may afford valuable clues for design of new potent p38α inhibitors.