Current Protein and Peptide Science - Volume 19, Issue 3, 2018

Cancer, characterized by uncontrolled growth and proliferation of cells, is affecting millions of people every year and estimated as the second leading cause of death. Its successful treatment yet remains a challenge due to the lack of selectivity, toxicity and the development of multidrug resistant cells to the currently available drugs. Plant derived natural products hold great promise for discovery and development of new pharmaceuticals against cancer as evident by the fact that out of 121 drugs prescribed for cancer treatment till date, 90 are derived from plant sources. Furthermore, the plant derived therapeutic molecules are also considered as safer substitutes to those of synthetic ones. In this review, the therapeutic potentials of plant derived natural products belonging to secondary metabolites, namely alkaloids, flavonoids and terpenoids as anticancer molecules, involving various strategies of treatment, have been discussed with special reference to topoisomerases (Topo), cyclooxygenases (COX), lipoxygenase (LOX) and aromatase as enzymatic targets for various types of cancers. Furthermore, in view of the recent advances made in the field of computer aided drug design, the present review also discusses the use of computational approaches such as ADMET, molecular docking, molecular dynamics simulation and QSAR to assess and predict the safety, efficacy, potency and identification of such potent anticancerous therapeutic molecules.

Since ancient times, natural products have been used in treating various diseases effectively and safely. Nowadays, these natural compounds are submitted to sophisticated methodologies from isolation, computing, analytical, and even serving as pharmacophore suggestions for synthesis. The substances extracted from marine species, plants, and microorganisms present activities beneficial to our health, including protection against malignant tumors. The topoisomerase enzymes play an important role in DNA metabolism, and searching for enzyme inhibitors is an important target in the search for new anticancer drugs. This review discusses this problem, reporting research involving alkaloids, terpenes, flavonoids, xanthones, coumarins, acetogenins, and in addition, includes a docking study with our Brazilian diterpenes to topoisomerases I and II. The better compound, the trachylobane 1, forms one hydrogen bond when submitted to docking with Topo I (with the ASP533 residue) and two with residues in Topo II (THR213 and TYR188). The difference observed in the energy of formation can be attributed to hydrogen-bond interactions. The difference observed in the energy of formation can be attributed to hydrogen-bond interactions.

Cancer is the leading cause of death worldwide and anticancer drug discovery is a very hot area of research at present. There are various factors which control and affect cancer, out of which enzymes like cyclooxygenase-2 (COX-2) play a vital role in the growth of tumor cells. Inhibition of this enzyme is a very useful target for the prevention of various types of cancers. Alkaloids are a diverse group of naturally occurring compounds which have shown great COX-2 inhibitory activity both in vitro and in vivo. In this mini-review, we have discussed different alkaloids with COX-2 inhibitory activities and anticancer potential which may act as leads in modern anticancer drug discovery. Different classes of alkaloids including isoquinoline alkaloids, indole alkaloids, piperidine alkaloids, quinazoline alkaloids, and various miscellaneous alkaloids obtained from natural sources have been discussed in detail in this review.

Isosteroidal alkaloids are a category of promising bioactive compounds which mostly exist in plants of genus Veratrum and Fritillaria. The pharmacological activities of isosteroidal alkaloids include antihypertensive, antitussive, anti-inflammatory, antithrombosis, among others. Recently, some studies show that this kind of alkaloids exhibited significant antitumor activity. To the best of our knowledge, there is no review focusing on their antitumor activity and mechanism of their antitumor activity. To fill the gap, in this review, we summarized antitumor effects of the isosteroidal alkaloids from genus Veratrum and Fritillaria on different tumors and the mechanisms of their antitumor activity. In conclusion, this kind of alkaloids has extensive antitumor activity, and there are several main mechanisms of their antitumor activity, including the Hedgehog signaling pathway, caspase-3 dependent apoptosis, cell cycle, and autophagy.

It is an acknowledged fact that health benefits are derived from fruit- and vegetables-enriched diets. In particular, polyphenols, compounds bearing one or more hydroxyl groups attached to an aromatic ring, are ascribed for most of such beneficial effects. Among them, resveratrol, a phytoalexin found in numerous plant species, and more notably in grapes, has widely piqued the interest of the scientific community by virtue of its anti-aging, anti-inflammatory and anti-oxidant properties. Moreover, evidence claiming resveratrol ability to hinder processes underlying all the three steps of carcinogenesis (tumor initiation, progression and metastasization) has propelled an incredibly massive number of studies aimed at enquiring its eventual clinical potential in the fight against cancer. However, despite a large body of data pointing to the advantages of dietary resveratrol intake in respect of certain disease conditions, and cancer inter alia, its real position still remains quite ambiguous. In this uncertain scenario, the present review focuses its attention on the highly entangled relationship between resveratrol and breast cancer, attempting to shape the plethora of controversial results stemming from studies carried out on several in vitro and in vivo breast cancer models. Coping with such a tricky matter, there are so many variabilities concerning both resveratrol itself (dosage, administration, bioavailabilty, among others) and the unique molecular traits of each specific breast cancer subtype that must be taken into account when facing the dilemma: “might resveratrol be protective against breast cancer or does it rather fuel it?”.

Phytoestrogens derived from plants exert estrogenic as well as antiestrogenic effects and multiple actions within breast cancer cells. Chemopreventive properties of phytoestrogens have emerged from epidemiological observations. In recent clinical research studies, phytoestrogens are safe and may even protect against breast cancer. In this brief review, the molecular mechanisms of phytoestrogens on regulation of cell cycle, apoptosis, estrogen receptors, cell signaling pathways, and epigenetic modulations in relation to breast cancer are discussed. Phytoestrogens have a preferential affinity for estrogen receptor (ER)-β, which appears to be associated with antiproliferative and anticarcinogenic effects. Moreover, while phytoestrogens not only inhibit ER-positive but also ER-negative breast cancer cells, the possibility of epigenetic modulation playing an important role is also discussed. In conclusion, as there are multiple targets and actions of phytoestrogens, extensive research is still necessary. However, due to low toxicity, low cost, and easy availability, their potent chemoprevention effects deserve further study.

Acetylation and deactylation of histones are important determinants of gene expression. Histone deacetylases (HDACs) remove acetyl groups from histones leading to suppression and regulation of epigenetic gene expression. Current studies have demonstrated that HDAC-inhibitors (HDACIs) inducing histone hyperacetylation are promising novel agents in cancer treatment. HDACIs have been shown to have significant anticancer effects with negligible toxicity in the preclinical studies. Ongoing clinial trials are being performed to investigate the efficiency of HDACIs in human cancers. We have reviewed the current knowledge about the molecular mechanisms of action of HDACIs and the outcome of clinical studies using HDACIs in the therapy of several cancers.