Anti-Cancer Agents in Medicinal Chemistry (Formerly Current Medicinal Chemistry - Anti-Cancer Agents) - Volume 14, Issue 10, 2014

We have studied the anti-cancer activities of antofine N-oxide isolated and purified from the medicinal plant Cynanchum vincetoxicum. Antofine N-oxide displayed a strong inhibitory effect on several solid tumor cell lines (glioblastoma, breast carcinoma and lung carcinoma) and on a T-cell leukemia cell line. Remarkably, its cytotoxic effect was considerably weaker in non-cancer cells. Antofine N-oxide was found to inhibit proliferation of the solid tumor cells whereas it caused apoptotic cell death in the leukemia cells. A microarray analysis after a short treatment revealed that the number of differentially expressed genes was considerably higher in solid tumor than in leukemia cells. Up-regulated genes in the three solid tumor cell lines include genes related to TNFα signaling, of which TNFα was among the most significantly induced. A functional analysis revealed that TNFR1 signaling was most likely activated in the solid tumor cells. The increased mRNA levels of several genes of this pathway (namely TNFα, TNFAIP3 and BIRC3) were confirmed by real-time quantitative PCR after different treatment durations. Finally a slight inhibition of NFΚB-mediated transcription was observed in the same cells. Together our results suggest that inhibition of cell proliferation in solid tumor cells essentially occurs through TNFα signaling whereas this pathway is not activated in leukemia cells. Apoptotic cell death in the latter is induced by a distinct yet unknown pathway.

In animal cells, the anticancer function played by plant saponins involves a complex network of molecular processes that still deserves investigation and apoptosis seems to be the outstanding pathway. An intriguing aspect of the biological activity of saponins is related to their effects on genome integrity. As demonstrated by the studies carried out in white poplar (Populus alba L., cv Villafranca) cell suspension cultures, plant cells can as well be used as a model system to unravel the molecular mechanisms activated by plant saponins. These recent studies have evidenced that animal and plant cells share common features in their response to saponins, paving the way for novel opportunities for both basic and applied research. Indeed, there is a certain interest in replacing the animal models for pharmacological research, at least when preliminary large-scale cytotoxicity tests are performed on wide collections of natural extracts and/or purified compounds. The review provides an up-date of the molecular pathways (signal transduction, antioxidant response, DNA repair) associated with plant saponin bioactivity, with an emphasis on apoptosis induced by alfalfa (Medicago sativa L.) saponins. The comparison between animal and plant cells as tools for the study of saponin bioactivity is also discussed in view of the most recent literature and innovative future applications.

Plant polyphenols exhibit potentially useful effects in a wide variety of pathophysiological settings. They interact with proteins such as signalling kinases, transcription factors and ion channels, and modulate redox processes, such as those taking place in mitochondria. Biomedical applications of these natural compounds are however severely hindered by their low bioavailability, rapid metabolism, and often by unfavourable physico-chemical properties, e.g. a generally low water solubility. Derivatives are under development with the aim of improving their bioavailability and/or bioefficacy. Various strategies can be adopted. An increase in circulating blood levels of non-metabolized natural compound may be attainable through prodrugs. In the ideal prodrug, phenolic hydroxyls are protected by capping groups which a) help or at least do not hinder permeation of epithelia; b) prevent conjugative modifications during absorption and first-pass through the liver; c) are eliminated with opportune kinetics to regenerate the parent compound. Moreover, prodrugs may be designed with the goals of modulating physical properties of the parent compound, and/or changing its distribution in the body. A more specific action may be achieved by concentrating the compounds at specific sites of action. An example of the second approach is represented by mitochondria-targeted redox-active polyphenol derivatives, designed to intervene on radical processes in these organelles and as a tool either to protect cells from oxidative insults or to precipitate their death. Mitochondrial targeting can be achieved through conjugation with a triphenylphosphonium lipophilic cation. Quercetin and resveratrol were chosen as model polyphenols for these proof-of-concept studies. Data available at the moment show that both quercetin and resveratrol mitochondria-targeted derivatives are pro-oxidant and cytotoxic in vitro, selectively killing fast-growing and tumoural cells when supplied in the low μM range; the mechanism of ROS generation appears to differ between the two classes of compounds. These approaches are emerging as promising strategies to obtain new efficient chemopreventive and/or chemotherapeutic drugs based on polyphenols derivatives.

Tea catechins exhibit a broad range of pharmacological activities that impart beneficial effects on human health. Epigallocatechin-3-gallate (EGCG), one of the major tea catechins, has been widely associated with cancer prevention and treatment. In addition, tea catechins in combination with anticancer drugs are being evaluated as a new cancer treatment strategy. However, the interactions of anticancer drugs with tea catechins are largely unknown. Accumulated data indicate significant interactions between anticancer drugs and tea catechins, such as synergistic tumor inhibition or antagonist activity. Therefore, it is critical to understand comprehensively the effects of tea catechins on anticancer drugs. Focusing on evidence from preclinical studies, this paper will review the interactions between anticancer drugs and tea catechins, including pharmacodynamics and pharmacokinetics effects. We hope that by detailing the interactions between anticancer drugs and tea catechins, more attention will be directed to this important therapeutic combination in the future.

Natural products are often used in drug development due to their ability to form unique and diverse chemical structures. Coumestans are polycyclic aromatic plant secondary metabolites containing a coumestan moiety, which consists of a benzoxole fused to a chromen-2-one to form 1-Benzoxolo[3,2-c]chromen-6-one. These natural compounds are known for large number of biological activities. Many of their biological effects can be attributed to their action as phytoestrogens and polyphenols. In the last decade, anticancer effects of these compounds have been described in vitro but there is only limited number of studies based on models in vivo. More information concerning their in vivo bioavailability, stability, metabolism, toxicity, estrogenicity, cellular targets and drug interactions is therefore needed to proceed further to clinical studies. This review focuses on coumestans exhibiting anticancer properties and summarizes mechanisms of their toxicity to cancer cells. Moreover, the possible role of coumestans in cancer prevention is discussed.

Polyphenols, secondary metabolites widely present in plant kingdom, are known for their positive effects on human health, such as treatments of degenerative disease and cancer. Many dietary polyphenols show anti-inflammatory, immunomodulatory and antioxidant properties and they are proposed as chemopreventive agents for many skin disorders and cancer. Exposure to solar UV radiation is widely considered to cause skin cancer and a consistent carcinogenic dose derived from UVA causes several skin disorders as a consequence of free radicals generation and DNA damages. In this study, verbascoside, isoverbascoside and tyrosol were investigated for their effects on HEKa (Human Epidermal Keratinocytes adult) cell cultures challenged from UVA-rays. Non-toxic doses of each polyphenol were assayed on HEKa before, during and after the exposure to a damaging dose of UVA. Treatment with polyphenols before and after the UVA-irradiation exerted a pro-oxidant effect, while the simultaneous treatment caused a weak decrease of ROS production. The increasing of ROS levels was associated with a proapoptotic effect on HEKa, detected by AnnexinV/Propidiun Iodide, mainly evident in surviving cells treated with the polyphenols after the UVA-irradiation. The pro-apoptotic effect was confirmed by the immunodetection of significant changes in the Bax and Bcl-xL protein levels, leading to apoptotic events. The hypothesis that these polyphenols could trigger the apoptosis pathway mainly in UVA-damaged cells, via ROS increase, is here proposed as action mechanism behind their protective effect.

Epidemiological studies have shown that a reduced risk of chronic diseases such as cancer and cardiovascular diseases is correlated with a regular consumption of fruits and vegetable, many of which are rich in polyphenols. The additive and synergistic effect of phytochemicals in fruits and vegetables may reduce chronic diseases related to oxidative stress in human body. Olea europaea L. leaf are rich in phenolic components, which have been proposed to play a role in cancer prevention. The purpose of this study was to identify the main components in the Olea europaea L. leaf (cv. Leccino) preserved during the decoction preparation, in order to delineate the antioxidant activities of the crude extracts and its isolated compounds by using different in vitro assays including DPPH radicalscavenging capacity, total antioxidant capacity (TAC), xanthine oxidase (XO) inhibitory effect and the ability to delay the linoleic acid peroxidation process (ALP). The aqueous decoction was partitioned obtaining four extracts and the n-butanol extract showed the highest antioxidant activity and the highest total phenolic content. Phytochemical investigation leads to the isolation of thirteen secondary metabolites including simple phenolics, flavonoids, secoiridoids whose structures were elucidated by spectroscopic data (1D and 2D NMR) and spectrometric techniques. A significant free radical scavenging effect against DPPH has been evidenced in fraxamoside (1) (EC50 62.6 µM) and taxifolin (5) (EC50 50.0 µM), isolated for the first time from the water decoction. The most active compound in the TAC evaluation, was the 3,4 dihydro-phenyl glycol (8) (0.90 caffeic acid equiv.) while taxifolin and fraxamoside resulted as the most efficient inhibitors of XO activity (IC50 2.7 and 5.2 µM, respectively). Secoxyloganin (4), oleuropein (2) and tyrosol (6) showed the highest ALP activity. This study adds to the growing body of data supporting the bioactivities of phytochemicals and their potential impact on human health.

Prostate function is critical for male fertility and its well-known oncological biomarker, namely Prostate-Specific Antigen (PSA), can be also used to monitor prostate epithelial human cells upon treatment with pharmaceutical drugs or natural bioactive compounds. The LNCaP human prostate cell line was previously set up as a model system to investigate chemicals affecting prostate epithelium functionality by means of a tiered approach integrating two different toxicological endpoints, cell viability (MTS) and PSA secretion assays. Here, the same approach has been used to characterize the biological effects of phytochemicals on prostate epithelium. The antiandrogenic ability of phytochemicals to inhibit DHT-induced PSA secretion has been investigated also characterizing their intracellular distribution, in the presence or absence of sex steroids. Intracellular distribution allows to verify whether and to which extent each phytochemical is able to enter the cell and to reach the nucleus, the latter being the target of the supposed transcriptional modulatory activity upon phytochemicals’ binding to sex steroid receptors. Some phytochemicals, supposed to have a role in the functionality of the prostate epithelium, have been tested in a dose-dependent manner in both MTS and PSA secretion assays. In parallel, to establish the “effective concentration”, in comparison to the “nominal one”, the intracellular amount of each phytochemical has been assessed upon cell fractionation of LNCaP-treated cells and subsequent chromatographic measurements.

Hyperforin is a natural phloroglucinol that has been known for the treatment of depression. Hyperforin displays also antibacterial, antiproliferant and antiangiogenic activity. Synthetic derivatives of hyperforin have also recently been reported to possess increased bioactivity. The clinical applications are limited by the hydrophobic characteristics and the instability of the molecule. In this review we discuss about some of the derivatives of hyperforin (aristoforin, tetrahydrohyperforin and octahydrohyperforin) that demonstrated promising antitumor activity. Among these, octahydrohyperforin also possesses antibacterial activity against both the planktonic and biofilm states of bacteria.

Colorectal cancer (CRC) is a leading cause of cancer mortality in the industrialized world, second to lung cancer. A lot of evidences highlight that a diet rich in fruits and vegetables may reduce the risk of some types of cancer including CRC. In this study we demonstrate that Citrus bergamia juice extracts (BJe) reduces CRC cell growth by multiple mechanisms. Low BJe concentrations inhibit MAPKs pathway and alter apoptosis-related proteins, that in turn induce cell cycle arrest and apoptosis in HT-29 cells. Instead, high concentrations of BJe induce oxidative stress causing DNA damage. Our study highlights the role of BJe as modulator of cell apoptosis in CRC cells and strengthens our previous hypothesis that the flavonoid fraction of bergamot juice may play a role as anti-cancer drug.

Breast cancer (BC) is the leading cause of death among women all over the world. Estrogen receptor (ER) based therapy is one of the major approaches to target BC and is associated with various problems such as primary as well as secondary resistance. ER signaling is a complex pathway as many factors are involved; including several types of ERs and their associated co-regulators. Increasing understanding of ER signals results in new approaches targeting towards BCs. In this context, ER co-regulators have been explored and many modulators of ER co-regulators have been found out. EGFR and mTOR pathways also have significant impact on BC endocrine therapy because of the complex crosstalk mechanism which is responsible for primary and secondary resistance. Triple negative breast cancer (TNBC) is majorly associated with BRCA mutations. Currently there is no approved targeted therapy available in such form of cancer. Although PARP inhibitors seem to be suitable candidates for it. The present review is focused on the current scenario of ER, EGFR, as well as mTOR signaling target therapy. We have also discussed the current status of PARP inhibitors in BC chemotherapy.

3-(Aminoalkylamino)-1,2,4-benzotriazine-1,4-dioxide-extended derivatives were synthesized by the structural modification of 3-amino-1,2,4-benzotriazine-1,4-dioxide (tirapazamine, TPZ) that incorporated homologue-alkyl linkers, without or with an extended 3- amino-1,2,4-benzotriazine-1-oxide moiety at the 3-position of the TPZ. According to sequential evaluation of preferentially normoxic and hypoxic cytotoxicities against MCF-7, NCI-H460 and HCT-116, most of the synthesized compounds exhibited hypoxic cytotoxicity greater than or comparable to that of TPZ. Among them, compounds 9a and 9b more powerfully inhibited the proliferation of MCF-7, NCI-H460 and HCT-116 in hypoxia than did TPZ. The representative of 3-(aminoalkylamino)-1,2,4-benzotriazine-1,4-dioxide-extended derivatives, 9a exhibited greater hypoxic cytotoxicity than TPZ, mediated by cell cycle arrest. The induction of DNA damage, the activation of caspase 3/7 and cleaved poly(ADP-ribose) polymerase-related apoptosis, which were detected in HCT-116 cells in both normoxia and hypoxia. In vitro anti-angiogenic assay of co-cultured HUVECs and fibroblasts that were exposed to the selected 7b, 8g, 9a and 9b exhibited 80-90% inhibition of tube formation at 20 µM, whereas TPZ exhibited approximately 50% inhibition of tube formation at 20 µM. At 2 µM, 9a and 9b significantly reduced the areas, lengths, paths and joints of tube formation by 70-80% and 45-50%, respectively. These results reveal that most of synthesized TPZ derivatives in this study exhibited more potent anti-angiogenesis than TPZ.