Current Medicinal Chemistry (v.19, #6)

Photodynamic therapy (PDT) is a clinically approved treatment modality for various types of diseases, including cancer, that produces a selective cytotoxic effect on the target cells. It involves the use of a photosensitizing molecule and a source of light with a wavelength that corresponds to the absorption band of the photosensitizer. After photoactivation, the photosensitizer occupies an excited triplet state from which it transfers its energy to neighboring oxygen molecules, thus generating singlet oxygen and reactive oxygen species (“oxidative stress”) which lead to cell death mediated by apoptosis and/or necrosis. PDT is less invasive than conventional chemotherapy, as the photosensitizer is not cytotoxic in the dark and the photoprocess is confined to the diseased tissue irradiated by light. In addition to the treatment of cancer and precancerous conditions, the use of PDT to cure microbial localized infections and inactivate pathogens is rapidly expanding. This special issue will address (i) the application of nanotechnology to PDT for improving the delivery of photosensitizers to the diseased tissue; (ii) the molecular response of cancer cells to the naturally-occurring photosensitizer hypericin; (iii) the photosensitizing properties of pheophorbide, a chlorophyll derivative, as a free or conjugated molecule; (iv) applications of PDT to water- and vector-borne diseases. Most of the clinically used photosensitizers are scarcely soluble in aqueous media, they do not accumulate efficiently in tumor tissues and often show an undesired liver accumulation. In an effort to overcome these shortcomings, research work has recently been directed to the development of nanoparticle-based photosensitizers. The contribution of Frochot and co-workers summarizes the use of nanoparticles (NPs) to enhance the delivery of scarcely soluble photosensitizers. NP technology offers a variety of advantages that are discussed in this review, including the transport of hydrophobic drugs in the blood, the possibility to decorate the NP surface with specific molecules in order to improve both uptake and tumor selectivity, the capacity of NPs to deliver a high “payload” in the diseased tissue and, in certain cases, the possibility to excite directly NPs to generate oxidative stress. The review describes the chemical nature of NPs and the recent advances in the area of non-polymeric nanoparticles. A comprehensive presentation of gold and silica nanoparticles, carbon nanotubes, TiO2/ZnO and magnetic nanoparticles is provided. Krammer and Verwanger focus their review on the molecular response of cancer cells to PDT. The authors provide a thorough analysis of the cellular response to hypericin-induced photodamage and describe how the hypericin-PDT dose can dictate cell growth or cell death. Low doses stimulate cell growth via the p38 or JNK survival pathways, whereas high doses favor apoptosis or autophagic cell death, depending on the availability of Bax/Bak. The different modes of cellular responses correlate with the PDT-protocol, photosensitizer localization, cell damage protection and available intracellular energy. This review provides useful information for the design of new protocols aiming to reduce cell recurrence in PDT....

Photodynamic therapy has emerged as an alternative to chemotherapy and radiotherapy for cancer treatment. Nanoparticles have recently been proposed as effective carriers for photosensitizers. Depending on their chemical composition, these can be used for diagnosis and therapy due to the selective accumulation of the photosensitizer in cancer cells in vitro or in tumors in vivo. Multifunctional nanoplatforms combining several applications within the same nano-object emerge as potential important theranostic tools. This review, based on the chemical nature of the nanoparticles will discuss recent advances in the area of non polymeric nanoparticles for photodynamic therapy applications.

Hypericin (Hyp) is used as a powerful natural photosensitizer in photodynamic therapy (PDT). After selective accumulation in tumor tissue, vessels and matrix, and activated by visible light, it destroys the tumor mainly via generation of reactive oxygen species. After photoactivation, molecular biological mechanisms lead to different cellular endpoints: “biostimulation” (increased proliferation rate), repair of the damage leading to rescue of the cells, autophagy, apoptosis and necrosis. Growth stimulation after low-dose Hyp-PDT seems to be induced via the p38 or JNK survival pathways. Since both pathways are also activated by stress, modification of these pathways may also contribute to rescue mechanisms as well as to damage processing. By increasing PDT doses beyond sublethal damage, stress response pathways are activated such as the ER-stress pathway with disruption of Ca2+ homeostasis and unfolded protein response. This leads either to apoptosis or autophagic cell death, dependent on the availability of Bax/Bak. Apoptosis triggered directly at the mitochondria or by the ER-stress response is executed via the mitochondrial pathway, whereas in some cases, the receptor-mediated pathway is preferred. If the damage is too severe, the cellular energy level low and /or the cytoplasma membrane leaky, cells will die necrotically. The different modes of cellular responses depend mainly on the PDT-protocol, photosensitizer localisation, cellular damage protection and the available intracellular energy.

Pheophorbide a is a clorophyll catabolite that recently has drawn the attention of several investigators for its potential in photodynamic therapy. In this review we summarize its photophysical properties, phototoxicity, cellular localization, biodistribution and PDT activity as a free or conjugated molecule.

Water- and vector-borne diseases are a global burden which is estimated to cause several million deaths and innumerable cases of sickness every year. These infectious illnesses are emerging or resurging as a result of several factors, such as changes in climate, in public health and demography policy, as well as the spread of resistance to insecticide and drug, and genetic changes in pathogens. Integrated prevention strategies must be developed and implemented in endemic disease areas to reverse the trend of emergent/resurgent water- and vector-borne diseases. With this perspective porphyrins and their analogues, that have been shown to act as very efficient photosensitising agents against a broad number of microbial pathogens (bacteria, fungi, protozoa) and parasitic animals, could represent an important tool for the prevention and control of these pathologies. The application of photosensitised processes can be exploited to address environmental problems of high significance, including the decontamination of waste waters, the disinfection of fish-farming tanks and the control of populations of noxious insects. Such diversified applications take advantage of the availability of a truly large number of porphyrin derivatives with chemical structures which can be tailored to comply with the physical and chemical properties, as well as the biological features of several milieus. In addition, the property typical of porphyrins to absorb essentially all the wavelengths in the sun emission spectrum allows the promotion of processes largely based on natural resources with significant energy saving and low impact on the ecosystems.

Starting from the discovery in 1940 of the first zinc metalloenzyme, carbonic anhydrase II, a very large number of enzymes requiring zinc as essential cofactor has been identified in all organisms, showing a variety of important physiological functions. These enzymes have a wide range of specific biological activities residing in the intra- and extracellular environments, and are implicated in several types of pathologies, such as cancer, cardiovascular and neuronal degenerative diseases, atherosclerosis, glaucoma and inflammation. For this reason, they are very attractive targets for drug design, and some of their inhibitors are commonly used for pharmacological treatment during pathology. Even though several drugs have been so far designed and developed against zinc metalloenzyme targets, there is still need of progress and improvement in this research area. The importance and wide variety of zinc-containing enzymes induced me to focus this issue on some members of this family that have been shown to be relevant for biomedical applications. In particular, carbonic anhydrases (CAs), metalloproteases (MPs), angiotensin-1 converting enzyme (ACE) and glutamate carboxypeptidase II (GPII) have been chosen as representative examples. CAs are ubiquitous metallo-enzymes present in prokaryotes and eukaryotes and encoded by five evolutionarily unrelated gene families: α,β,γ,δ,ζ and . Since their discovery, these enzymes have been widely investigated due to their important pathophysiological roles in all kingdoms of life. The first paper of this special issue is focused on carbonic anhydrase IX (CA IX), a human member of this family, which has recently been shown to be a marker of tumor hypoxia and a prognostic factor in several human cancers. The most recent catalytic and structural features uncovered of this enzyme have been comprehensively summarized by the Authors, highlighting how this information has been exploited to develop antibodies and small molecules with therapeutic potential. CAs, this time isolated from bacterial sources, as well as zinc MPs are the topic of the second paper, which overviews in vitro and in vivo biochemical and inhibition studies reported for these enzymes so far. It is highlighted the importance of this research since in some cases bacterial proteins can represent future drug targets for obtaining conceptually novel antibiotics.

Carbonic anhydrase IX (CA IX) is a tumor associated protein, since it is highly expressed in a multitude of carcinomas, while it is present in a limited number of normal tissues. It is a multi-domain protein consisting of an N-terminal proteoglycan-like (PG) domain, a catalytic domain, a trans-membrane portion (TM) and an intracytoplasmatic (IC) segment. These domains have peculiar biochemical and physiological features. Among these, only the PG domain is unique among the CA family. This review focuses on the most recent molecular and catalytic features uncovered of this enzyme, the role of its different domains in tumor physiology, and its three dimensional structure which has recently been solved. In addition, we present recent advances in the development of antibodies and small inhibiting molecules able to target CA IX for diagnostic and therapeutic applications.

Zinc-containing enzymes, such as carbonic anhydrases (CAs) and metalloproteases (MPs) play critical functions in bacteria, being involved in various steps of their life cycle, which are important for survival, colonization, acquisition of nutrients for growth and proliferation, facilitation of dissemination, invasion and pathogenicity. The development of resistance to many classes of clinically used antibiotics emphasizes the need of new antibacterial drug targets to be explored. There is a wealth of data regarding bacterial CAs and zinc MPs present in many pathogenic species, such as Neisseria spp., Helycobacter pylori Escherichia coli, Mycobacterium tuberculosis, Brucella spp., Streptococcus pneumoniae, Salmonella enterica, Haemophilus influenzae, Listeria spp, Vibrio spp., Pseudomonas aeruginosa, Legionella pneumophila, Streptomyces spp., Clostridium spp., Enterococcus spp., etc. Some of these enzymes have been cloned, purified and characterized by crystallographic techniques. However, for the moment, few potent and specific inhibitors for bacterial MPs have been reported except for Clostridium histolyticum collagenase, botulinum and tetanus neurotoxin and anthrax lethal factor, which will be reviewed in this article. Bacteria encode α-,β-, and/or γ-CA families, but up to now only the first two classes have been investigated in some detail in different species. The α-CAs from Neisseria spp. and H. pylori as well as the β-class enzymes from E. coli, H. pylori, M. tuberculosis, Brucella spp., S. pneumoniae, S. enterica and H. influenzae have been cloned and characterized. The catalytic/inhibition mechanisms of these CAs are well understood as X-ray crystal structures are available for some of them, but no adducts of these enzymes with inhibitors have been characterized so far. In vitro and in vivo studies with various classes of inhibitors, such as anions, sulfonamides and sulfamates have been reported. Only for Neisseria spp., H. pylori, B. suis and S. pneumoniae CAs it has been possible to evidence inhibition of bacterial growth in vivo. Thus, bacterial CAs and MPs represent at this moment very promising targets for obtaining antibacterials devoid of the resistance problems of the clinically used such agents but further studies are needed to validate these and other less investigated enzymes as novel drug targets.

Cardiovascular disease (CVD) is responsible for ∼27% of deaths worldwide, with 80% of these occuring in developing countries. Hypertension is one of the most important treatable factors in the prevention of CVD. Angiotensin-I converting enzyme (ACE) is a two-domain dipeptidylcarboxypeptidase that is a key regulator of blood pressure as a result of its critical role in the reninangiotensin- aldosterone and kallikrien-kinin systems. Consequently, ACE is an important drug target in the treatment of CVD. ACE is primarily known for its ability to cleave angiotensin-I to the vasoactive octapeptide angiotensin-II, but is also able to cleave a number of other substrates including the vasodilator bradykinin and N-acetyl-seryl-aspartyl-lysyl-proline (acetyl-SDKP), a physiological modulator of hematopoiesis. Numerous ACE inhibiors are available clinically, and these are generally effective in treating hypertension. However some adverse effects are associated with ACE inhibition, such as the persistent dry cough and the potentially fatal angioedema. The solution of ACE crystal structures over the last decade has facilitated rational drug design which has contributed to the development of domain-selective ACE inhibitors, the most notable of which include RXP407 (N-domain) and RXPA380 (C-domain), which in principle may herald new therapeutic approaches for ACE inhibition. Additionally, dual inhibitors to ACE and other targets such as neprilysin, endothelin converting enzyme and chymase have been developed. The success of ACE inhibitors has also led to the search for novel inhibitors in food and natural products and the structure guided screening of such libraries may well reveal a number of new ACE inhibitors.

Glutamate carboxypeptidase II (GCPII) is a membrane-bound binuclear zinc metallopeptidase with the highest expression levels found in the nervous and prostatic tissue. Throughout the nervous system, glia-bound GCPII is intimately involved in the neuronneuron and neuron-glia signaling via the hydrolysis of N-acetylaspartylglutamate (NAAG), the most abundant mammalian peptidic neurotransmitter. The inhibition of the GCPII-controlled NAAG catabolism has been shown to attenuate neurotoxicity associated with enhanced glutamate transmission and GCPII-specific inhibitors demonstrate efficacy in multiple preclinical models including traumatic brain injury, stroke, neuropathic and inflammatory pain, amyotrophic lateral sclerosis, and schizophrenia. The second major area of pharmacological interventions targeting GCPII focuses on prostate carcinoma; GCPII expression levels are highly increased in androgenindependent and metastatic disease. Consequently, the enzyme serves as a potential target for imaging and therapy. This review offers a summary of GCPII structure, physiological functions in healthy tissues, and its association with various pathologies. The review also outlines the development of GCPII-specific small-molecule compounds and their use in preclinical and clinical settings.

Chemical space is defined as all possible small organic molecules, including those present in biological systems, which is so vast that so far only a tiny fraction of it has been explored. Indeed, a thorough examination of all “chemical space” is practically impossible. The success of three EGFR inhibitors (Gefitnib, Erlotinib, Lapatinib) suggests that 4-anilinoquinazoline scaffold is still worth developing in the future. To date hundreds of this sort of derivatives have been synthesized and show potent anticancer activities. Most of the compounds have been proved to be EGFR/HER2 kinase inhibitors, binding at the hinge region of the ATP site and some lead compounds have been optimized against a number of different kinases, including VEGFR-2, Src, Aurora A/B, Tpl, Clk and PDE10A. Now there is now a rich pipeline of novel anticancer agents based on 4-anilinoquinazoline in early phase clinical trials. This review will highlight the exploration of chemical space of 4-anilinoquinazoline in the past ten years and we hope that increasing knowledge of the SAR and cellular processes underlying the antitumor-activity of anilinoquinazoline derivatives will be beneficial to the rational design of new generation of small molecule anticancer drugs.

Abnormal and exaggerated deposition of extracellular matrix proteins is the common feature of fibrotic diseases. The resulting fibrosis disrupts the normal architecture of the affected organs and finally leads to their dysfunction and failure. At present, there are no effective therapies for fibrotic diseases. Protein degradation via the ubiquitin-proteasome system is the major pathway for non-lysosomal proteolysis and controls many critical cellular functions including cell-cycle progression, deoxyribonucleic acid repair, growth and differentiation. Therefore, aberration of the system leads to dysregulation of cellular homeostasis and development of many diseases such as cancers, degenerative diseases and fibrotic diseases. Although the ubiquitin-proteasome system has mainly been investigated in the field of cancers so far and several anti-cancer drugs that modulate the activity of the system have been used clinically, the recent findings regarding the system and fibrosis can provide a rational basis for the discovery of novel therapy for fibrotic diseases. In this article, we discuss (i) the basic mechanism of the ubiquitin-proteasome system and (ii) the recent findings regarding the association between the system and pathological organ fibrosis. These examples indicate that the ubiquitin-proteasome system plays diverse roles in the progression of fibrotic diseases, and further studies of the system are expected to reveal new strategies for overcoming pathological fibrosis.

Coronary atherosclerosis is the pathophysiologic background of coronary artery disease. Vascular calcification is an actively regulated form of calcified tissue metabolism and a common feature of coronary atherosclerotic plaques. Interestingly, systematic research has revealed that vascular mineralization, is also a strong and independent predictor of cardiovascular morbidity and mortality. Recently, several biomarkers, including osteopontin, fetuin-A, matrix-carboxyglutamic acid protein, pyrophosphates, bone morphogenetic proteins, leptin, osteoprotegerin have emerged as surrogate markers of coronary calcification. Furthermore, biomarkers of vascular calcification can be used as prognostic markers of coronary artery disease and can predict future cardiovascular events and mortality. Nevertheless, there is little knowledge on the usefulness of these biomarkers in evaluating the results of treatments targeting coronary artery disease. Within this context, the present review sets out to discuss the role of new biomarkers assessing calcium deposition in coronary arteries and their role in the prognosis, progression, and treatment of cardiovascular disease.

Manipulation of DNA presents a great interest in biotechnology and therapeutics. The molecules that damage DNA selectively offer new prospects for controlled manipulation of DNA. The conjugations of DNA-code reading molecules such as polyamides to reagents that induce DNA damages provide an approach to reach this goal. In this work, a new compound which contained polyamide and ascorbic acid conjugated by flexible linker (polyamide-Vc), was successfully synthesized, characterized, and evaluated as DNA cleavage agent, compared with that by using ascorbic acid molecule. The kinetics data showed that polyamide-Vc successfully promoted the cleavage of plasmid DNA, with kmax of 0.314 h-1 and Kd of 0.105 mM. The evaluation of DNA linearization elicited that the activity of cleaving double-strand in the supercoiled pUC18 plasmid DNA by polyamide-Vc was enhanced remarkably, achieving n1/n2 ratio of 13.9 at 1.2 mM for 1 h. The introduction of polyamide to Vc could also partially weaken the inhibition of hydrogen radical to double-strand cleavage process because of its good binding activity to DNA. We anticipate that this work could provide a method for improving the efficiency of double-strand cleavage, especially to oxidative cleavage agents.

According to the structure-function relationship of podophyllotoxin (PTOX) and its analogue of 4'- demethylepipodophyllotoxin (DMEP), the 4 β-substitution of sulfur-containing heterocyclic compounds with a carbon-sulfur bond at 4 position of PTOX or DMEP is an essential modification direction for improving the anti-tumor activity. So, four novel 4 β-sulfursubstituted podophyllum derivatives (i.e., 4β -(1,2,4-triazole-3-yl)sulfanyl-4-deoxy-podophyllotoxin (4-MT-PTOX), 4β-(1,3,4- thiadiazole-2-yl)sulfanyl-4-deoxy-podophyllotoxin (4-MTD-PTOX), 4β-(1,2,4-triazole-3-yl)sulfanyl-4-deoxy-4' -demethylepipodophyllotoxin (4-MT-DMEP), and 4β-(1,3,4-thiadiazole-2-yl)sulfanyl-4-deoxy-4'-demethylepipodophyllotoxin (4-MTD-DMEP)) were designed and then successfully biosynthesized in this work. In the novel sulfur-substituted biotransformation processes, PTOX and DMEP was linked with sulfur-containing compounds (i.e., 3-mercapto-1,2,4-triazole (MT) and 2-mercapto-1,3,4-thiadiazole (MTD)) at 4 position of cycloparaffin to produce 4-MT-PTOX (1), 4-MTD-PTOX (2), 4-MT-DMEP (3), and 4-MTD-DMEP (4) by Penicillium purpurogenum Y.J. Tang, respectively, which was screened out from Diphylleia sinensis Li (Hubei, China). All the novel compounds exhibited promising in vitro bioactivity, especially 4-MT-PTOX (1). Compared with etoposide (i.e., a 50 % effective concentration [EC50] of 25.72, 167.97, and 1.15 M), the EC50 values of 4-MT-PTOX (1) against tumor cell line BGC-823, A549 and HepG2 (i.e., 0.28, 0.76, and 0.42 M) were significantly improved by 91, 221 and 2.73 times, respectively. Moreover, the EC50 value of 4-MT-PTOX (1) against the normal human cell line HK-2 (i.e., 182.4μM) was 19 times higher than that of etoposide (i.e., 9.17 μM). Based on the rational design, four novel 4 β-sulfur-substituted podophyllum derivatives with superior in vitro anti-tumor activity were obtained for the first time. The correctness of structure-function relationship and rational drug design was strictly demonstrated by the in vitro biological activity tests.