Remarkable Stability and Cytostatic Effect of a Quercetin Conjugate, 3,7-Bis-O-Pivaloxymethyl (POM) Quercetin

Senolysis-Based Elimination of Chemotherapy-Induced Senescent Breast Cancer Cells by Quercetin Derivative with Blocked Hydroxy Groups

Simple Summary

Cellular senescence may contribute to aging and age-related diseases, and the elimination of senescent cells is considered a promising anti-aging strategy. Drug-induced senescence in cancer cells during chemotherapy may also promote a number of adverse effects. Thus, in the present study, the usefulness of three quercetin derivatives as senolytic agents was studied upon stimulation of senescence program in breast cancer cells. We have shown that quercetin derivative with blocked hydroxy groups (QD3) sensitized etoposide-induced senescent breast cancer cells to apoptotic cell death that was accompanied by a decrease in proinflammatory and HSP70-based responses. We suggest that these prosenescent and senolytic activities can be combined to design a novel anti-cancer strategy, at least, against breast cancer cells.

Abstract

Drug-induced senescence program may be activated both in normal and cancer cells as a consequence of chemotherapeutic treatment, leading to some adverse side effects such as senescence-associated secretory phenotype (SASP), secondary senescence, and cancer promotion. Targeted elimination of senescent cells can be achieved by drugs with senolytic activity (senolytics), for example, the plant-derived natural compound quercetin, especially when co-treated with kinase inhibitor dasatinib. In the present study, three quercetin derivatives were synthesized and tested for improved senolytic action against etoposide-induced senescent human normal mammary epithelial cells and triple-negative breast cancer cells in vitro. Transformation of catechol moiety into diphenylmethylene ketal and addition of three acetyl groups to the quercetin molecule (QD3 derivative) promoted the clearance of senescent cancer cells as judged by increased apoptosis compared to etoposide-treated cells. A QD3-mediated senolytic effect was accompanied by decreased SA-beta galactosidase activity and the levels of p27, IL-1β, IL-8, and HSP70 in cancer cells. Similar effects were not observed in senescent normal cells. In conclusion, a novel senolytic agent QD3 was described as acting against etoposide-induced senescent breast cancer cells in vitro. Thus, a new one-two punch anti-cancer strategy based on combined action of a pro-senescence anti-cancer drug and a senolytic agent is proposed.

New insights for the use of quercetin analogs in cancer treatment

AIM

Quercetin (Q1) is a flavonoid widely present in plants and endowed with several pharmacological properties mostly due to its antioxidant potential. Q1 shows anticancer activity and could be useful in cancer prevention. On the other hand, Q1 is poorly soluble in water and unstable in physiological systems, and its bioavailability is very low.

METHODS

A small set of Q1 derivatives (Q2-Q9) has been synthesized following opportunely modified chemical procedures previously reported. Anticancer activity has been evaluated by MTT assay. Human Topoisomerases inhibition has been performed by direct enzymatic assays. Apoptosis has been evaluated by TUNEL assay. ROS production and scavenging activity have been determined by immunofluorescence.

RESULTS

The anticancer profile of a small library of Q1 analogues, in which the OH groups were all or partially replaced with hydrophobic functional groups, has been evaluated. Two of the studied compounds demonstrated an interesting cytotoxic profile in two breast cancer models showing the capability to inhibit human Topoisomerases.

CONCLUSION

The studied compounds represent suitable leads for the development of innovative anticancer drugs. [Formula: see text].

Research Progress in the Modification of Quercetin Leading to Anticancer Agents

The flavonoid quercetin (3,3′,4′,5,7-pentahydroxyflavone) is widely distributed in plants, foods, and beverages. This polyphenol compound exhibits varied biological actions such as antioxidant, radical-scavenging, anti-inflammatory, antibacterial, antiviral, gastroprotective, immune-modulator, and finds also application in the treatment of obesity, cardiovascular diseases and diabetes. Besides, quercetin can prevent neurological disorders and exerts protection against mitochondrial damages. Various in vitro studies have assessed the anticancer effects of quercetin, although there are no conclusive data regarding its mode of action. However, low bioavailability, poor aqueous solubility as well as rapid body clearance, fast metabolism and enzymatic degradation hamper the use of quercetin as therapeutic agent, so intense research efforts have been focused on the modification of the quercetin scaffold to obtain analogs with potentially improved properties for clinical applications. This review gives an overview of the developments in the synthesis and anticancer-related activities of quercetin derivatives reported from 2012 to 2016.

Water-soluble and cleavable quercetin-amino acid conjugates as safe modulators for P-glycoprotein-based multidrug resistance

Quercetin-amino acid conjugates with alanine or glutamic acid moiety attached at 7-O and/or 3-O position of quercetin were prepared, and their multidrug resistance (MDR)-modulatory effects were evaluated. A quercetin-glutamic acid conjugate, 7-O-Glu-Q (3a), was as potent as verapamil in reversing MDR and sensitized MDR MES-SA/Dx5 cells to various anticancer drugs with EC50 values of 0.8-0.9 μM. Analysis on Rh-123 accumulation confirmed that 3a inhibits drug efflux by Pgp, and Pgp ATPase assay showed that 3a interacts with the drug-binding site of Pgp to stimulate its ATPase activity. Physicochemical analysis of 3a revealed that solubility, stability, and cellular uptake of quercetin were significantly improved by the glutamic acid promoiety, which eventually dissociates from 3a to produce quercetin and quercetin metabolites in intracellular milieu. Taken together, potent MDR-modulating activity along with intracellular conversion into the natural flavonoid quercetin warrants development of the quercetin-amino acid conjugates as safe MDR modulators.

Site-specific anticancer effects of dietary flavonoid quercetin

Food-derived flavonoid quercetin, widely distributed in onions, apples, and tea, is able to inhibit growth of various cancer cells indicating that this compound can be considered as a good candidate for anticancer therapy. Although the exact mechanism of this action is not thoroughly understood, behaving as antioxidant and/or prooxidant as well as modulating different intracellular signalling cascades may all play a certain role. Such inhibitory activity of quercetin has been shown to depend first of all on cell lines and cancer types; however, no comprehensive site-specific analysis of this effect has been published. In this review article, cytotoxicity constants of quercetin measured in various human malignant cell lines of different origin were compiled from literature and a clear cancer selective action was demonstrated. The most sensitive malignant sites for quercetin revealed to be cancers of blood, brain, lung, uterine, and salivary gland as well as melanoma whereas cytotoxic activity was higher in more aggressive cells compared to the slowly growing cells showing that the most harmful cells for the organism are probably targeted. More research is needed to overcome the issues of poor water solubility and relatively low bioavailability of quercetin as the major obstacles limiting its clinical use.

Acetal derivatives as prodrugs of resveratrol

The pharmacological exploitation of resveratrol is hindered by rapid phase-II conjugative metabolism in enterocytes and hepatocytes. One approach to the solution of this problem relies on prodrugs. We report the synthesis and characterization as well as the assessment of in vivo absorption and metabolism of a set of prodrugs of resveratrol in which the OH groups are engaged in the formal (-OCH2OR) or the more labile acetal (-OCH(CH3)OR) linkages. As carrier group (R) of the prodrug, we have used short ethyleneglycol oligomers (OEG) capped by a terminal methoxy group: -O-(CH2CH2O)n-CH3 (n = 0, 1, 2, 3, 4, 6). These moieties are expected to exhibit, to a degree, the favorable properties of longer polyethyleneglycol (PEG) chains, while their relatively small size makes for a more favorable drug loading capacity. After administration of formal-based prodrugs to rats by oral gavage, significant concentrations of derivatives were measured in blood samples over several hours, in all cases except for n = 0. Absorption was maximal for n = 4. Complete deprotection to give resveratrol and its metabolites was however too slow to be of practical use. Administration of the acetal prodrug carrying tetrameric OEG chains resulted instead in the protracted presence of resveratrol metabolites in blood, consistent with a progressive regeneration of the parent molecule from the prodrug after its absorption. The results suggest that prodrugs of polyphenols based on the acetal bond and short ethyleneglycol oligomers of homogeneous size may be a convenient tool for the systemic delivery of the unconjugated parent compound.