Cell‐penetrating peptides, also known as protein transduction domain (PTD), have attracted interest as carriers for intracellular drug delivery. We report the first drug conjugate with a negatively charged amphipathic cell‐penetrating peptide. Furthermore, we compare two different doxorubicin cell‐penetrating peptide conjugates, which are both unique in their properties, due to their net charge at physiological pH, namely the positively charged octaarginine and the negatively charged proline‐rich amphipathic peptide. These conjugates were prepared exploiting a novel heterobifunctional crosslinker to join the N‐terminal cysteine residue of the peptides with the aliphatic ketone of doxorubicin. This small linker contains an activated thiol as well as aminooxy functionality, capable of generating a stable oxime bond with the C‐13 carbonyl group of doxorubicin. The disulfide bond formed between the peptide and doxorubicin enables the release of the drug in the cytosol, as confirmed by drug‐release studies performed in the presence of glutathione. Additionally, the cytotoxicity as well as the cellular uptake and distribution of this tripartite drug delivery system was investigated in MCF‐7 and HT‐29 cell lines.
Heterobifunctional crosslinkers are extensively applied in drug modifications, and their utilization has proven to be very important for the attachment of diverse carriers, such as monoclonal antibodies, proteins, polymers, and peptides, to doxorubicin. Established conjugation technique is applied at the C‐13 keto group by hydrazones, due to their fast hydrolysis in acidic environment existing in biological compartments like endosomes and lysosomes. However, the insufficient stability of the doxorubicin hydrazone conjugates has been reported even at physiological pH (7.4), leading to the release of the free drug in the bloodstream. In order to overcome these difficulties, we have chosen a crosslinker capable of creating an oxime bond on doxorubicin’s ketone, due to the higher hydrolytic stability of the oxime group. Additionally, thiol‐containing carriers, like albumin proteins, have also been conjugated to anthracyclines utilizing functional groups that are highly specific for sulfhydryl groups, e.g. maleimides and pyridyl disulfides. The application of pyridyl disulfides is advantageous, because a disulfide bond between the linker and the cargo is formed, which can be reduced in the cytoplasm by glutathione to deliver the freight. Furthermore, pyridyl disulfides can serve as a protective group during synthesis to avoid undesired dimerization as well as an activating group for the thiol to facilitate disulfide formation. In contrast, maleimides react with a thiol via Michael addition; thus, a covalent bond is created that cannot be cleaved under physiological conditions. Therefore, we have selected a heterobifunctional crosslinker that contains a protected aminooxy group and pyridyl disulfide.
Resveratrol and curcumin are natural products with important therapeutic properties useful to treat several human diseases, including cancer. In the last years, the number of studies describing the effect of both polyphenols against cancer has increased; however, the mechanism of action in all of those cases is not completely comprehended. The unspecific effect and the ability to interfere in assays by both polyphenols make this challenge even more difficult. Herein, we analyzed the anticancer activity of resveratrol and curcumin reported in the literature in the last 11 years, in order to unravel the molecular mechanism of action of both compounds. Molecular targets and cellular pathways will be described. Furthermore, we also discussed the ability of these natural products act as chemopreventive and its use in association with other anticancer drugs.
Papers describing curcumin and/or resveratrol are present in almost fifteen thousand of publications in the last ten years. Both polyphenols have been described as promising anticancer compounds; however, the mode of action for them are still unclear and not fully comprehended.
Curcumin (diferuloylmethane) is an active ingredient of the perennial herb Curcuma longa, also known as turmeric. The yellow color of this polyphenol is chemically related to its major fraction, which contains curcuminoids. Curcumin has been used for a long time in countries such as China and India as traditional medicines. This ancient remedy has brought the attention of scientific community for a wide range of beneficial properties including anti-inflammatory, antioxidant and chemopreventive.
By the other hand, resveratrol (trans-3,5,4′-trihydroxystilbene) is a stilbene phytoalexin synthetized by a variety of plants, specially vine in response to fungi infections and ultraviolet radiation. This compound is found at high concentration in grapes and red wine, which antioxidant effect is well established in several different assays. Resveratrol has been investigated as potential compound for the treatment of several diseases, regulation of immune system and chemoprevention. (Nutrients. 2016 Nov; 8(11): 628. )
Honeybees produce honey, royal jelly, propolis, bee venom, bee pollen, and beeswax, which potentially benefit to humans due to the bioactives in them. Clinical standardization of these products is hindered by chemical variability depending on honeybee and botanical sources, but different molecules have been isolated and pharmacologically characterized. Major honey bioactives include phenolics, methylglyoxal, royal jelly proteins (MRJPs), and oligosaccharides. In royal jelly there are antimicrobial jelleins and royalisin peptides, MRJPs, and hydroxy-decenoic acid derivatives, notably 10-hydroxy-2-decenoic acid (10-HDA), with antimicrobial, anti-inflammatory, immunomodulatory, neuromodulatory, metabolic syndrome preventing, and anti-aging activities. Propolis contains caffeic acid phenethyl ester and artepillin C, specific of Brazilian propolis, with antiviral, immunomodulatory, anti-inflammatory and anticancer effects. Bee venom consists of toxic peptides like pain-inducing melittin, SK channel blocking apamin, and allergenic phospholipase A2. Bee pollen is vitaminic, contains antioxidant and anti-inflammatory plant phenolics, as well as antiatherosclerotic, antidiabetic, and hypoglycemic flavonoids, unsaturated fatty acids, and sterols. Beeswax is widely used in cosmetics and makeup. Given the importance of drug discovery from natural sources, this review is aimed at providing an exhaustive screening of the bioactive compounds detected in honeybee products and of their curative or adverse biological effects.(Front Pharmacol. 2017 Jun 28;8:412.)