Enhanced anti-proliferative action of busulphan by quercetin on the human leukaemia cell line K562

Advances in heterocycles as DNA intercalating cancer drugs

The insertion of a molecule between the bases of DNA is known as intercalation. A molecule is able to interact with DNA in different ways. DNA intercalators are generally aromatic, planar, and polycyclic. In chemotherapeutic treatment, to suppress DNA replication in cancer cells, intercalators are used. In this article, we discuss the anticancer activity of 10 intensively studied DNA intercalators as drugs. The list includes proflavine, ethidium bromide, doxorubicin, dactinomycin, bleomycin, epirubicin, mitoxantrone, ellipticine, elinafide, and echinomycin. Considerable structural diversities are seen in these molecules. Besides, some examples of the metallo-intercalators are presented at the end of the chapter. These molecules have other crucial properties that are also useful in the treatment of cancers. The successes and limitations of these molecules are also presented.

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].

Anti-Proliferative Effects of Dendrophthoe pentandra Methanol Extract on BCR/ABL-Positive and Imatinib-Resistant Leukemia Cell Lines

Background:

Imatinib mesylate, a tyrosine kinase inhibitor specifically targeting the BCR/ABL fusion protein, induces hematological remission in patients with chronic myeloid leukemia (CML). However, the majority of CML patients treated with imatinib develop resistance with prolonged therapy. Dendrophthoe pentandra (L.) Miq. is a Malaysian mistletoe species that has been used as a traditional treatment for several ailments such as smallpox, ulcers, and cancers.

Methods:

We developed a resistant cell line (designated as K562R) by long-term co-culture of a BCR/ABL positive CML cell line, K562, with imatinib mesylate. We then investigated the anti-proliferative effects of D. pentandra methanol extract on parental K562 and resistant K562R cells. Trypan blue exclusion assays were performed to determine the IC50 concentration; apoptosis and cell cycle analysis were conducted by flow cytometry.

Results:

D. pentandra extract had greater anti-proliferative effects towards K562R (IC50= 192 μg/mL) compared to K562 (500 μg/mL) cells. Upon treatment with D. pentandra extract at the IC50 concentration: K562 but not K562R demonstrated increase in apoptosis and cell cycle arrest in the G2/M phase.

Conclusion:

D. pentandra methanol extract exerts potent anti-proliferative effect on BCR/ABL positive K562 cells.

Synergistic anticancer activity of dietary tea polyphenols and bleomycin hydrochloride in human cervical cancer cell: Caspase-dependent and independent apoptotic pathways

Bleomycin is a chemotherapeutic agent that is frequently used in the treatment of various cancers. Bleomycin causes serious adverse effects via antioxidant defense abnormalities against reactive oxygen species (ROS). However, the current cervical cancer monodrug therapy strategy has failed to produce the expected outcomes; hence, combinational therapies are gaining great interest. Tea polyphenols are also effective antioxidative and chemo-preventive agents. However, the combined effect of tea polyphenol (TPP) and bleomycin (BLM) against cervical cancer remains unknown. In this study, we focused on the potential of TPP on BLM anticancer activity against cervical cancer cells. Cervical cancer cells (SiHa) were treated with various concentrations of TPP, BLM and TPP combined with BLM (TPP-BLM), and their effects on cell growth, intracellular reactive oxygen species, poly-caspase activity, early apoptosis and the expression of caspase-3, caspase-8 and caspase-9, Bcl-2 and p53 were assessed. The MTT assay revealed that the SiHa cells were less sensitive to growth inhibition by TPP treatment compared with both BLM and the combination therapy. Nuclear staining indicated that exposure to TPP-BLM increased the percentage of apoptotic nuclei compared with a mono-agent treatment. Caspase activation assay demonstrated that proportion of early and late apoptotic/secondary necrotic cells was higher in the cells treated with the combination therapy than in those treated with either TPP or BLM alone. The TPP-BLM treatment synergistically induced apoptosis through caspase-3, caspase-8 and caspase-9 activation, Bcl-2 upregulation and p53 overexpression. This study suggests that TPP-BLM may be used as an efficient antioxidant-based combination therapy for cervical cancer.

Chemotherapy and dietary phytochemical agents

Chemotherapy has been used for cancer treatment already for almost 70 years by targeting the proliferation potential and metastasising ability of tumour cells. Despite the progress made in the development of potent chemotherapy drugs, their toxicity to normal tissues and adverse side effects in multiple organ systems as well as drug resistance have remained the major obstacles for the successful clinical use. Cytotoxic agents decrease considerably the quality of life of cancer patients manifesting as acute complaints and impacting the life of survivors also for years after the treatment. Toxicity often limits the usefulness of anticancer agents being also the reason why many patients discontinue the treatment. The nutritional approach may be the means of helping to raise cancer therapy to a new level of success as supplementing or supporting the body with natural phytochemicals cannot only reduce adverse side effects but improve also the effectiveness of chemotherapeutics. Various plant-derived compounds improve the efficiency of cytotoxic agents, decrease their resistance, lower and alleviate toxic side effects, reduce the risk of tumour lysis syndrome, and detoxify the body of chemotherapeutics. The personalised approach using various phytochemicals provides thus a new dimension to the standard cancer therapy for improving its outcome in a complex and complementary way.

PLGA nanoparticles loaded with etoposide and quercetin dihydrate individually: in vitro cell line study to ensure advantage of combination therapy

PLGA nanoparticles, separately loaded with etoposide (ETN) and quercetin dihydrate (QDN), were prepared by adapting the solvent diffusion (nanoprecipitation) technique. The effect of formulation variables such as amount of polymer, theoretical drug loading, surfactant concentration, and aqueous and organic phase volumes on particle size and entrapment efficiency, were systematically studied. The optimal formulations obtained were of submicron size (153.4 ± 4.2 nm for ETN and 148.6 ± 1.6 nm for QDN) and with low polydispersity indices (0.058 ± 0.02 for ETN and 0.088 ± 0.03 for QDN). The entrapment efficiencies were found as 63.88 ± 1.5 % and 41.36 ± 3.4 % for ETN and QDN, respectively. The characterization of ETN and QDN was done by measuring the zeta potential, TEM, and DSC analysis. The comparison was made in respect of in vitro cytotoxicity assay using cancer cell line A549 (human lung adenocarcinoma epithelial cell line). The results revealed significant increase in cytotoxicity in nanoparticle formulations than their respective free drug. The comparison was also made with respect to cytotoxic activity of individual drug and combination of drugs in the form of free drugs as well as nanoparticles. The combination treatment in the form of nanoparticles is found to produce best results among the treatments used in cytotoxicity studies.

The biochemistry and medical significance of the flavonoids

Flavonoids are plant pigments that are synthesised from phenylalanine, generally display marvelous colors known from flower petals, mostly emit brilliant fluorescence when they are excited by UV light, and are ubiquitous to green plant cells. The flavonoids are used by botanists for taxonomical classification. They regulate plant growth by inhibition of the exocytosis of the auxin indolyl acetic acid, as well as by induction of gene expression, and they influence other biological cells in numerous ways. Flavonoids inhibit or kill many bacterial strains, inhibit important viral enzymes, such as reverse transcriptase and protease, and destroy some pathogenic protozoans. Yet, their toxicity to animal cells is low. Flavonoids are major functional components of many herbal and insect preparations for medical use, e.g., propolis (bee's glue) and honey, which have been used since ancient times. The daily intake of flavonoids with normal food, especially fruit and vegetables, is 1-2 g. Modern authorised physicians are increasing their use of pure flavonoids to treat many important common diseases, due to their proven ability to inhibit specific enzymes, to simulate some hormones and neurotransmitters, and to scavenge free radicals.

Dietary antioxidants during cancer chemotherapy: impact on chemotherapeutic effectiveness and development of side effects

Several studies suggest that dietary supplementation with antioxidants can influence the response to chemotherapy as well as the development of adverse side effects that results from treatment with antineoplastic agents. Administration of antineoplastic agents results in oxidative stress, i.e., the production of free radicals and other reactive oxygen species (ROS). Oxidative stress reduces the rate of cell proliferation, and that occurring during chemotherapy may interfere with the cytotoxic effects of antineoplastic drugs, which depend on rapid proliferation of cancer cells for optimal activity. Antioxidants detoxify ROS and may enhance the anticancer effects of chemotherapy. For some supplements, activities beyond their antioxidant properties, such as inhibition of topoisomerase II or protein tyrosine kinases, may also contribute. ROS cause or contribute to certain side effects that are common to many anticancer drugs, such as gastrointestinal toxicity and mutagenesis. ROS also contribute to side effects that occur only with individual agents, such as doxorubicin-induced cardiotoxicity, cisplatin-induced nephrotoxicity, and bleomycin-induced pulmonary fibrosis. Antioxidants can reduce or prevent many of these side effects, and for some supplements the protective effect results from activities other than their antioxidant properties. Certain side effects, however, such as alopecia and myelosuppression, are not prevented by antioxidants, and agents that interfere with these side effects may also interfere with the anticancer effects of chemotherapy.

Quercetin and the growth of leukemic progenitors

The bioflavonoid quercetin (3, 3', 4', 5-7-pentahydroxyflavone) inhibits in a dose-dependent manner the in vitro growth of acute leukemias and enhances the anti-proliferative activity of cytosine arabinoside. Quercetin exerts a blocking action of cell transition from the G0/G1 to the S phase of the cell cycle. Acute myeloid leukemias (AML)-M3,-M4 and -M5, and acute lymphoid leukemias (ALL) were more sensitive to quercetin than AML-M1 and -M2 subtypes. The sensitivity of leukemic progenitors to the growth inhibitory effect of quercetin significantly correlated with their clonogenic efficiency. We postulate that quercetin exerts its growth inhibitory action by interaction with type II estrogen binding sites and subsequent induction of Transforming Growth Factor-beta 1 expression and secretion. Finally quercetin is synergistic with hyperthermia in inducing apoptosis of leukemic cells sparing normal stem cell progenitors. Taken together these results stress the potential role of quercetin in the treatment of acute leukemias and its in vitro use in purging procedures for autologous bone marrow transplantation.

Modulation of adriamycin accumulation and efflux by flavonoids in HCT-15 colon cells. Activation of P-glycoprotein as a putative mechanism

Since P-glycoprotein (P-gp) in normal tissues may serve as a cellular defense mechanism against naturally occurring xenobiotics, we considered whether physiologically active components of commonly ingested plant foods could influence P-gp function. To examine this possibility, a series of flavonoids commonly found in plant foods was tested for their ability to modulate [14C]Adriamycin ([14C]ADR) accumulation and efflux in P-gp-expressing HCT-15 colon cells. Many flavonoids, in the micromolar range, inhibited the accumulation of [14C]ADR. Detailed experiments utilizing flavonoids with the greatest activity in reducing [14C]ADR accumulation, i.e. galangin, kaempferol, and quercetin, revealed that the efflux of [14C]ADR is increased markedly in the presence of these compounds. Flavonoid-induced stimulation of efflux was rapid and was blocked by the multidrug-resistant (MDR) reversal agents verapamil, vinblastine, and quinidine. The magnitude of flavonoid-stimulated efflux in sodium butyrate-treated cells with a 4-fold induction of P-gp protein was similar to that in uninduced cells. [3H]Azidopine photoaffinity labeling of P-gp in crude membrane preparations revealed mild to no competition for binding by flavonoids possessing either activity or inactivity in reducing ADR accumulation. Although flavonoid hydrophobicity was found to be unrelated to flavonoid activity in altering [14C]ADR accumulation, certain structural features were associated with enhancement or diminution of activity. Finally, the significance of flavonoid-related reduction of [14C]ADR accumulation was underscored in cell growth studies, showing partial protection by quercetin against ADR-induced growth inhibition. It is concluded that certain naturally occurring plant flavonoids may acutely upregulate the apparent activity of P-gp.

The combination of quercetin and cytosine arabinoside synergistically inhibits leukemic cell growth

It has been demonstrated that quercetin (3,3',4',5,7-pentahydroxyflavone) inhibits the growth of several cancer cell lines and that the antiproliferative activity of this substance is probably mediated through a binding interaction with type II estrogen binding sites (type II EBS). The effect of quercetin and cytosine arabinoside (Ara-C) alone or in combination, was tested on HL-60 cell growth. Quercetin significantly synergized the inhibitory activity of Ara-C on HL-60 cell growth while rutin, the 3-rhamnosylglucoside of quercetin, neither competed with [3H]estradiol for type II EBS nor was effective alone or in combination with Ara-C. Based on these results, we studied by a clonogenic assay the effect of quercetin and Ara-C alone and in combination on colony formation by human leukemic cells (CFU-L). In all cases both drugs exhibited a dose-related inhibition of CFU-L in a range of concentrations between 10 nM and 10 microM and 0.01 nM and 10 microM for quercetin and Ara-C, respectively. The combination of the two drugs resulted in a synergistic inhibitory activity on CFU-L. Considering that plasma concentrations of quercetin effective in vitro were obtained in vivo without any apparent side effects, we conclude that this report represents further experimental evidence that quercetin could be used in the treatment of acute leukemias.

Antiproliferative activity of quercetin on normal bone marrow and leukaemic progenitors

We used an in vitro clonogenic assay in semi-solid medium to test the sensitivity of normal bone marrow and acute myeloid and lymphoid leukaemia progenitors to the flavonol quercetin. We have studied 14 acute myeloid (AML) and four acute lymphoid (ALL) leukaemias. All ALL and the vast majority of AML (12/14) had a high sensitivity to quercetin with more than 50% growth inhibition at 2 x 10(-6) M quercetin. One M3-AML was partially quercetin-sensitive displaying 60% surviving AML-colony forming units (CFU-AML) at a quercetin concentration of 10(-5) M. One M1-AML was resistant to the growth inhibitory effect of quercetin at a concentration of 2 x 10(-5) M. The clonogenic efficiency of both AML and ALL positively correlated with leukaemic colony-forming unit (CFU-L) sensitivity to quercetin suggesting that this parameter can be useful in predicting quercetin responsiveness of leukaemic cells. We have also studied the effect of various quercetin concentrations on colony formation by normal bone marrow cells. At a quercetin concentration of 10(-5) M, we observed (in five different experiments) a mean recovery of 53% and 65% of erythroid blast-forming units (BFU-E) and granulocyte-macrophage colony-forming units (CFU-GM), respectively. Thus, normal bone marrow appeared partially resistant to quercetin, being inhibited less than 50% by quercetin concentration higher than 2 x 10(-5). When normal bone marrow were deprived in CD34+ haematopoietic progenitors the resultant population became highly sensitive to quercetin, with a mean recovery of BFU-E and CFU-GM of 5% and 12% of controls respectively in the presence of 2 x 10(-5) M quercetin. Furthermore, CD34 progenitors, positively selected, appeared fully resistant to quercetin concentrations as high as 2 x 10(-5) M. Thus, CD34+ progenitors are a quercetin-resistant component in normal bone marrow. In conclusion, our results further provide a biological basis for the therapeutic use of quercetin, considering that this compound could inhibit leukaemic cell growth without suppressing normal haematopoiesis.

Quercetin induces recombinational mutations in cultured cells as detected by DNA fingerprinting

Quercetin, a flavonoid, is found in many fruits and vegetables. This drug was previously shown to affect the metastatic potential of mouse tumor cells. Mutagenicity of quercetin was examined by means of DNA fingerprint analysis using the Pc-1 probe that efficiently detects mutations due to recombination. Treatment of BMT-11 and FM3A tumor cells with 55 microM quercetin resulted in gain and loss of bands in the fingerprints in both cell lines. The frequencies of the clones having undergone mutation were 3/11 and 6/26, respectively. This suggests that quercetin is mutagenic and induces recombination. This result seems to provide a molecular basis for the phenotypic variations of BMT-11 tumor cells induced by quercetin.

Quercetin inhibits the growth of a multidrug-resistant estrogen-receptor-negative MCF-7 human breast-cancer cell line expressing type II estrogen-binding sites

It has been demonstrated that the flavonoid quercetin (3,3',4',5,7-pentahydroxyflavone; Q) inhibits the growth of several cancer cell lines. There is evidence suggesting that the antiproliferative activity of this substance is mediated by the so-called type II estrogen-binding site (type II EBS). We looked for the presence of type II EBS and the effect of Q on the proliferation of an Adriamycin-resistant estrogen-receptor-negative human breast-cancer cell line (MCF-7 ADRr). By whole-cell assay using estradiol labelled with 6,7-tritium [( 3H]-E2) as a tracer, we demonstrated that MCF-7 ADRr cells contain type II EBSs. Competition analysis revealed that diethylstilbestrol (DES) and Q competed with similar potency for [3H]-Es binding to type II EBSs. The antiestrogen tamoxifen (TAM) competed for type II EBSs, albeit to a lesser extent than either DES or Q. Growth experiments demonstrated that Q and DES exerted a dose-dependent inhibition of cell proliferation in the range of concentrations between 10 nM and 10 microM, whereas TAM was less effective. Q could also inhibit colony formation in a clonogenic assay. Our results indicate that multidrug-resistant estrogen-receptor-negative MCF-7 cells express type II EBSs and are sensitive to the inhibitory effect of Q. This substance could be the parent compound of a novel class of anticancer agents.

Role of protein kinase C in adriamycin-induced erythroid differentiation of K562 cells

Modulators of protein kinase C (PKC) were used to investigate the role of this enzyme during Adriamycin-induced erythroid differentiation of K562 cells. Adriamycin (0.1 microM) induced erythroid differentiation in 60% +/- 10% of K562 cells. Phorbol myristate-12-acetate, an activator of protein kinase C, was strongly anti-proliferative to K562 cells (IC50, 8 nM) but did not induce erythroid differentiation. Staurosporine inhibited PKC from K562 cells (IC50, 8 nM) and blocked Adriamycin-induced erythroid differentiation, but only at concentrations marginally below those that inhibited proliferation (IC50, 81 nM), 1-(5-Isoquinolinylsulphonyl)-2-methylpiperazine (H-7) inhibited K562 PKC (IC50, 26 microM) but reduced Adriamycin-induced differentiation by less than 50% at concentrations of up to 600 microM. These data argue against a major role for PKC during Adriamycin-induced erythroid differentiation in K562 cells.

Type-II estrogen binding sites in a lymphoblastoid cell line and growth-inhibitory effect of estrogen, anti-estrogen and bioflavonoids

Type-II estrogen-binding sites (type-II EBS) have been demonstrated in the human lymphoblastoid cell line IM-9 using a whole-cell assay with (6,7-3H) estradiol (3H-E2) as tracer. Competition analysis showed that the anti-estrogen tamoxifen and the flavonoids quercetin and rutin competed for (3H)-E2 binding to type-II EBS. Growth experiments demonstrated that diethylstilbestrol (DES) tamoxifen (TAM), quercetin and rutin exerted a reversible dose-dependent inhibition of cell proliferation in the range of concentrations between 10 nM and 10 microM. The relative binding affinity of quercetin, rutin, DES and TAM for type-II EBS correlated well with their potency as cell growth inhibitors. Moreover, hesperidin, a flavonoid which does not bind to type-II EBS, was ineffective in inhibiting cell growth. Cell-cycle analysis showed that the growth-inhibitory effect of DES, TAM or quercetin was due to a blocking effect in the G0-G1 phases. Our results suggest that high estrogen and anti-estrogen concentrations and flavonoids may regulate IM-9 cell growth through a common mechanism involving a binding interaction with type-II EBS.

Inhibitory effect of quercetin on OVCA 433 cells and presence of type II oestrogen binding sites in primary ovarian tumours and cultured cells

We investigated the effect of the flavonoid quercetin (Q) on the proliferation of the ovarian cancer cell line OVCA 433. Growth experiments demonstrated that Q exerted a reversible dose-dependent inhibition of cell proliferation in the range of concentrations between 10 nM and 10 microM. Two other flavonoids tested, rutin and hesperidin, were ineffective in inhibiting cell growth. Cell cycle analysis showed that the growth inhibitory effect of Q was due to a blocking effect in the GO/G1 phase. Using a whole cell assay with (6.7-3H) oestradiol (3H-E2) as tracer we demonstrated that OVCA 433 cells contain type II oestrogen binding sites (type II EBS). Competition analysis showed that Q competed for 3H-E2 binding to type II EBS while both rutin and hesperidin did not. Appreciable amounts of type II EBS were also detected in seven primary ovarian tumours. Our results suggest that Q may regulate ovarian cancer cell growth through a mechanism involving a binding interaction with type II EBS. This mechanism could also be active in vivo since primary ovarian tumours contain type II EBS.

Type II oestrogen binding sites in acute lymphoid and myeloid leukaemias: growth inhibitory effect of oestrogen and flavonoids

The presence of oestrogen receptors (ER) and type II oestrogen binding sites (type II EBS) have been investigated by a whole cell assay in seven cases of acute lymphoid leukaemia (ALL) and 16 cases of acute myeloid leukaemia (AML). ER were detected in 6/7 ALL patients with values ranging between 133 and 2268 sites/cell and in 12/16 AML patients with values ranging between 274 and 4197 sites/cell. The apparent dissociation constant (KD) for ER was 0.6 +/- 0.3 nM (mean + SD of 20 cases). All blasts from ALL and AML patients expressed type II EBS at variable levels ranging between 3109 and 239450 sites/cell. The mean KD value for these sites was 18.3 +/- 5.6 nM (mean +/- SD of 23 cases). Specificity experiments demonstrated that type II EBS are oestrogen specific relative to the class of steroid hormones. In addition, the flavonol quercetin was able to compete for [3H]17 beta-oestradiol (E2) binding to type II EBS, the relative binding affinity (RBA) of quercetin being greater than that of diethylstillboestrol (DES). DES and quercetin exerted a dose-dependent inhibition of ALL and AML blast proliferation in the range of concentrations between 10(-8) and 10(-5) M. The RBA of DES and quercetin for type II EBS correlated well with their potency as cell growth inhibitors. Moreover, the flavonols rutin and hesperidin which compete slightly for [3H]E2 binding to type II EBS, were scarcely effective in inhibiting leukaemic cell proliferation. The inhibitory effect of DES and quercetin was not due to a non-specific cytotoxic action since after a 1 d culture period, cell viability did not vary between control and treated cells, being greater than 80%. Our results suggest that high oestrogen concentrations and the flavonol quercetin may inhibit leukaemic blast proliferation through a common mechanism involving a binding interaction with type II EBS.