cancer , which is commonly a harbinger of imminent patient death , is a group of diseases characterized by uncontrolled growth and spread of abnormal cells and aberrant cell behavior , which leads to expansive masses that destroy surrounding normal tissue and is able to attack vital organs resulting in disseminated disease . it is an inevitable matter of concern in the medicinal chemistry era and an increasing burden to the population . according to estimates from the international agency for research on cancer ( iarc ) , the global burden is expected to grow to 21.4 million new cancer cases and 13.2 million cancer deaths by 2030 . there were 12.7 million new cancer cases in 2008 worldwide , of which 5.6 million were in the economically developed countries and 7.1 million were in the economically developing countries . the corresponding estimates for total cancer deaths in 2008 were 7.6 million ( about 21,000 cancer deaths a day ) , 2.8 million in the economically developed countries and 4.8 million in the economically developing countries [ 1 , 2 ] . pathophysiology of all cancers involves the malfunction of genes that control cell growth , division , and death . cancers evolve through multiple changes resulting from a combination of hereditary and environmental factors , which mutate genes encoding critical cell - regulatory proteins . the new generations of anticancer drugs affect the signals that promote or regulate the cell cycle , growth factors and their receptors , signal transduction pathways , and pathways affecting dna repair and apoptosis rather than targeting the direct synthesis of dna . chalcone derivatives of diverse chemical architectures are quite significant in anticancer drug discovery and hence are in the center of attention of drug hunters . anticancer activity of chalcone might be due to molecular alteration such as induction of apoptosis , dna and mitochondrial damage , inhibition of angiogenesis , tubulin inhibition , kinases inhibition , and also drug efflux protein activities . chalcone is chemically 1,3-diaryl-2-propen-1-one ( figure 1 ) in which the two aromatic rings are joined by a three - carbon ,-unsaturated carbonyl system , representing a class of flavonoids that occur naturally in fruits and vegetables . chalcones are also metabolic precursors of some flavonoids and isoflavonoids . the plants containing chalcone are traditionally employed for therapeutical purposes [ 37 ] . chalcones were exploited well for their wide application in pharmacological area . it is reported that chalcones have several advantages such as poor interaction with dna and low risk of mutagenicity . hence , some clinically useful anticancer drugs have reported genotoxicity due to their interaction with amino groups in nucleic acids ; chalcones may be devoid of these side effects due to their structural flexibility . literature reveals that natural and synthetic chalcones are desirable to elicit cytotoxic and apoptotic activity ( figure 2 ) . they have been reviewed not only in the articles mentioned in the text but also in more recent articles , which have eluded the authors [ 911 ] . this review ( surveyed database , 20132015 ) is complementary to the researchers for optimizing the lead chalcone as potential anticancer scaffold with increased potency . cell death in tumors is a passive degradative reaction known as necrosis , most likely due to inadequate angiogenesis within the tumor cell . on the other hand , apoptotic cell death includes a number of gene families , and altering proapoptotic pathways specifically in tumors is something of a holy grail for oncology and medicinal chemistry . when cell production rate exceeds the cell loss rate through mitosis , it results in net tumor . apoptosis is often referred to as an altruistic cell suicide process , where damaged dna in the cell produces signals , resulting in both repair and apoptotic pathways , and if repair can not be done then the cell undergoes apoptosis in a manner like  better dead than wrong . the cells which harbour mutant p53 will have a survival advantage over normal cells . in response to dna damage , normal cells upregulate p53 which acts as a transcription factor for cell cycle arrest and apoptosis ; thereafter , p53-mutant cells become unable to carry out this protective arrest or apoptosis and might survive with what otherwise would turn to lethal genetic damage , perhaps explaining why p53 mutations are so common in human cancers . the decision of apoptosis is largely played out on the mitochondrial surface between three major families : the so - called three horsemen of apoptosis . the final executioner proteases called caspases play pivotal role by cleaving critical substrates such as dna repair enzymes and cytoskeletal proteins , but they are stored as zymogens bound to an apoptotic adenosine triphosphate , apoptosis - activating factor-1 ( apaf-1 ) , which is the mammalian homologue of the nematode caenorhabditis elegans cell death protein , ced-4 . once cytochrome c is released , it binds to the cytosolic protein apaf-1 to facilitate the formation of apoptosome , which in turn activates apoptotic caspases . however , proapoptotic bcl-2 family proteins such as bax which is upregulated by p53 can activate apoptosis by releasing cytochrome c ( cyt - c ) from mitochondria , where apaf-1 activation takes place [ 2 , 6 , 12 , 13 ] . literature on anticancer chalcones highlights the employment of three pronged strategies , namely , structural manipulation of both aryl rings , replacement of aryl rings with heteroaryl scaffolds , and molecular hybridization through conjugation with other pharmacologically interesting scaffolds for enhancement of anticancer properties . various substitutions on both aryl rings ( a and b ) of the chalcones , depending upon their positions in the aryl rings , appear to influence anticancer activity by interfering with various biological targets . similarly , heterocyclic rings , either as ring a or as ring b in chalcones , also influence the anticancer activity shown by this class of compounds . hybrid chalcones formulated by chemically linking chalcones to other prominent anticancer scaffolds such as benzodiazepines , benzothiazoles , and imidazolones have demonstrated synergistic or additive pharmacological activities too . anticancer activity of three naphthyl chalcones , 1 , 2 , and 3 , shown in figure 3 was investigated by winter et al . , these chalcones were found to possess concentration- and time - dependent cytotoxicity on murine lymphoblastic leukemia cell line ( l1210 ) . chalcones 1 , 2 , and 3 induced apoptosis via an activated caspases - dependent pathway . the activities of caspase-8 , caspase-9 , and caspase-12 were found to increase after the treatment of l1210 cells with the cc50 of 30  m of chalcone 1 and 40  m of chalcones 2 and 3 . it was found that chalcones 1 and 2 induced an increase of proapoptotic proteins bax , bid , and bak ( only chalcone 2 ) , as well as a decrease in antiapoptotic bcl-2 expression . these chalcones also induced an increase in death receptor fas and a decrease in p21 and p53 expression . chalcones 1 and 2 exert a statistically significant increase in cytochrome c release from mitochondria to cytoplasm . cytochrome c release mediates caspase-9 activation , while the apoptosis inhibitors from bcl-2 family prevent the efflux of cytochrome c from mitochondria . chalcone 3 seems to act by a different mechanism to promote cell death , as it did not change the mitochondrion - related proteins nor did it induce the cytochrome c release . chalcones 1 , 2 , and 3 induced an increase in cell calcium concentration and an increase in chop ( c / ebp homologous protein ) expression which is the transcription factor involved in endoplasmic reticulum stress , together with an increase in caspase-12 activity , suggesting that chalcones could induce an endoplasmic reticulum ( er ) stress . they did not result in the arrest of g0/g1 , s , or g2/m phases of the cell cycle in contrast to paclitaxel , which was used as a positive control in this study and induced a statistically significant enrichment of g2/m fraction . they presented a selectivity index ( si ) higher than one , indicating that chalcones show higher selectivity to leukemic cells when compared to nontumoral cells ( vero = monkey kidney cells and nih/3t3 = murine fibroblast ) . the only exception was chalcone 3 which presented the same toxicity in l1210 and vero cells . the selectivity index ( si ) corresponds to cc50 ( concentration of the compounds , which results in 50% of cell viability ) of chalcones on nontumoral cell lines ( vero and nih/3t3 ) divided by cc50 determined for cancer cells ( l1210 ) . 2,4,5-trimethoxychalcones 4 , 5 ( figure 3 ) were found to reduce the viability of human k562 acute myeloid leukemia cell and human jurkat acute lymphoid leukemia cell significantly and caused a cytotoxic effect in both cell lines in a concentration- and time - dependent manner . they were found to have low ic50 values ( 4 to 8  m ) against both cell lines and did not have a cytotoxic effect on normal human lymphocytes . the mechanism of action involves the reduction of cell proliferation which has been shown by a reduction in the expression of cell proliferation marker ki67 . cell death induced by 2,4,5-trimethoxychalcones was due to induction of apoptosis through the reduction of the mitochondrial membrane potential , reduction in bcl-2 expression , increase in bax expression , increase in active caspase-3 , and activating the intrinsic pathway and execution phase of apoptosis . histone deacetylases ( hdacs ) are enzymes which catalyze removal of acetyl groups from lysine residues . hdacs play a critical role in epigenetic gene regulation and hence control multiple cellular events . hence , hdacs expressions and/or activity are deregulated in various cancer subtypes , leading to a target for anticancer therapy . coumarin - containing compounds 6a , 6b , and 6c ( figure 3 ) were found to inhibit total hdac activity by 2050% at 100  m in chronic myeloid leukemia k562 and histiocytic lymphoma u937 cell lines . the activity of the compounds was compared to peripheral blood mononuclear cells ( pbmcs ) of healthy donors , which showed no effect on pbmc viability . in comparison to 6a , compound 6b , with a methoxy group at r3 , presented increased levels of inhibition . compound 6b was tested against seven hdac isoenzymes ( 1 , 2 , 3 , 6 , 8 , 10 , and 11 ) and acted as a pan - hdaci with ic50s between 12 and 85  m . 6b inhibited hdac3 with an ic50 at 12  m and may serve as a lead for targeting this nuclear isoenzyme . chalcone 7 ( figure 3 ) with monomethoxy group at the ortho position showed a significant effect on downregulation of cancer cell proliferation and viability in three different leukemia cell lines ( k562 , jurkat , and u937 ) . the executioner caspase cleavage analyses indicated that the cytotoxic effect mediated by chalcone 6 is due to induction of apoptotic cell death by caspase-3 and caspase-7 activation . the cytotoxic effect was cell type - specific and targeted preferentially cancer cells as peripheral blood mononuclear cells ( pbmcs ) from healthy donors were less affected by the treatment compared to k562 , jurkat , and u937 leukemia cells . it was observed that compound 6 obeyed lipinski 's rule of five which indicates drug - likeness property of that molecule . 2-hydroxy-2,4,6-trimethoxy-5,6-naphthochalcone , 8 ( figure 4 ) , had most effectively inhibited the clonogenicity of sw620 colon cancer cells . the ic50 value for compound 8 was 14.5  1.1  m against sw620 cells . mechanistically , compound 8 triggered cell cycle arrest at g2/m phase , followed by an increase in apoptotic cell death , which involves the disruption of microtubular networks . the mitotic spindle network is essential for appropriate segregation of chromosomes between the two daughter cells at cell division , where disruption leads to apoptosis . compound 8 was found to destabilize microtubule assembly during mitosis , associated with failure of mitotic spindle formation , in turn blocking mitosis at the prometaphase or metaphase - anaphase transition . however , the study did not distinguish between the dna damage checkpoint and mitotic checkpoint pathways of apoptosis . trail ( tumor necrosis factor- ( tnf- ) related apoptosis - inducing ligand ) is a member of the tnf superfamily of cytokines . tnf family members contain highly conserved carboxyl - terminal domains and induce receptor trimerization for the transduction of intracellular signal . trail binds to four different receptors , two of which are death receptors 4 and 5 ( dr4 and dr5 , resp . ) , induces apoptosis , and decoys receptors , dcr1 and dcr2 , which lack the cytoplasmic death domain for transducing apoptotic death signals and protect cells from trail induced cell death by interfering with signaling through dr4 and dr5 . it is generally believed that transformed tumor cells are more susceptible to trail - mediated cell death owing to the selective loss of decoy receptors . chalcone 9 ( figure 4 ) ( ic50 = 4.39  m ) containing an amino ( -nh2 ) group was the most potent and selective against trail - resistant human colon cancer ( ht-29 ) and nontoxic against normal human embryonic kidney ( hek-293 ) cells . it was observed that a large portion of ht-29 cells had undergone late apoptosis and/or necrosis after treatment with 5-fluorouracil ( 5  m ) . these findings were consistent to show that chalcone 33 induces apoptosis rather than necrosis in ht-29 cells . it increases the death receptors expression ( trail - r1 and trail - r2 ) and proapoptotic markers ( p21 , bad , bim , bid , bax , smac , caspase-3 , and caspase-8 ) as well as reducing the antiapoptotic markers ( livin , xiap , and hsp27 ) . anthraquinone based chalcone compounds were synthesized and evaluated for their anticancer potential , where compounds 10a , 10b , and 10c ( figure 5 ) showed promising activity in inhibition of cervix adenocarcinoma ( hela ) cells with ic50 values ranging from 2.36 to 2.73  m and low cytotoxicity against healthy human fetal lung fibroblast cell lines ( mrc-5 ) . all the compounds cause the accumulation of cells in s and g2/m phases in a dose - dependent manner and induce caspase-3-dependent apoptosis and noncovalent interaction with the minor groove of the double - helical ct - dna and the damage of dna double helix structure . significant increase of p18 bax in treated hela cell line yielded consistency with the higher cytotoxic efficacy of compounds which implies the involvement of mitochondria in apoptotic process . synthesis and antiproliferative activity of a series of novel coumarin - chalcone hybrids were done by singh et al . . the most potent molecule of the series was compound 11 ( figure 5 ) . regression of tumors induced by hela cell xenografts in nod scid mice was found after oral administration of this molecule . it inhibited proliferation of cervical cancer cells ( hela and c33a ) by inducing apoptosis and arresting cell cycle at g2/m phase . apoptosis was due to induction of caspase - dependent intrinsic pathway and alterations in the cellular levels of bcl-2 family proteins . the mitochondrial transmembrane potential also got highly depleted in compound 11 treated cells due to an increase in bax / bcl-2 ratio and intracellular ros . compound 11 induced release of cytochrome c into the cytosol and activation of initiator caspase-9 and executioner caspase-3 and caspase-7 . tumor suppressor protein p53 and its transcriptional target puma ( p53 upregulated modulator of apoptosis ) were upregulated , suggesting their role in mediating the cell death . based on dose response curves , the calculated ic50 ( after 48  h treatment ) was 4.7  1.0  m for c33a cells and 7.6  2.0  m for hela cells . similar results were found in colony formation assay , where significant decrease in cellular colonies was observed in compound treated groups . chalcone 11 was apparently nontoxic to the animals as they did not show any loss of weight during experiment . cell population with fragmented nuclei increased in a time - dependent manner with the addition of chalcone 11 . significant increase in apoptotic cells with fragmented nuclei , which is consistent with the changes in nuclear morphology and flow cytometry analysis , indicated induction of apoptosis by chalcone 11 . novel isoxazolyl chalcones were synthesized and evaluated for their activities in vitro against human non - small lung cancer cells ( h1792 , h157 , a549 , and calu-1 ) . compounds 12a and 12b ( figure 6 ) were identified as the most potent anticancer agents with ic50 values ranging from 1.35 to 2.07  m and from 7.27 to 11.07  m against h175 , a549 , and calu-1 cell lines , respectively . the structure - activity relationship study showed that compounds bearing electron withdrawing groups ( ewg ) at the 2-position of the phenyl ring in aryl group were more effective . compounds 12a and 12b increased the percentage of cell in sub - g0 phase and decreased the percentage of cell in g0/g1 phase . these results suggested that 12a and 12b induced apoptosis in a549 cells in a dose - dependent manner . they have upregulated the dr5 in a dose - dependent manner which suggests the extrinsic pathways of apoptosis . cleaved bands of caspase-8 , caspase-9 , caspase-3 , and poly ( adp - ribose ) polymerase ( parp ) also indicated the induction of apoptosis . imine derivatives of hybrid chalcone analogues 13a , 13b , 13c , and 13d ( figure 6 ) containing anthraquinone scaffold were synthesized and evaluated for their in vitro cytotoxic activity against hela , ls174 , and a549 cancer cells . compound 13c with furan ring linked to imino group showed potent activity against all target cells with ic50 values ranging from 1.76 to 6.11  m , which are comparable to cisplatin . generally , introduction of electron withdrawing substituents such as -cl and -cf3 in metaposition of the phenyl ring was found to exert good cytotoxicity . compounds did not have tendency to significantly accumulate the cells in sub - g1 phase , except compound 13a , which led to an increase in sub - g1 ( observed only in cells undergoing apoptosis ) phase in a549 cells as well as changes in g2/m arrest of a549 and ls174 cells . compounds induced the activities of caspase-3 and caspase-8 in treated hela cells and exhibited strong antiangiogenic activity by showing potent inhibitory potential against matrix metalloproteinases ( mmp-2 ) secretion . strong implication of mmp-2 is found in angiogenesis and promotes tumor metastatic potential playing crucial role not only in invasion but also in determination of cancer cell transformation , growth , apoptosis , and signal transduction pathways . 3-phenylquinolinylchalcone derivatives , 14 and 15 ( figure 6 ) , were synthesized and evaluated for their antiproliferative activities . compound 14 was active against the growth of non - small cell lung cancer cells h1299 and skbr-3 breast cancer cells with ic50 values of 1.41 and 0.70  m , respectively , which was more active than the positive topotecan ( ic50 values of 6.02 and 8.91  m , resp . ) . compound 15 exhibited an ic50 value of less than 0.10  m against the growth of mda - mb231 in a dose- and time - dependent manner and was noncytotoxic to the normal mammary epithelial cell ( h184b5f5/m10 ) . the proportion of cells was decreased in g1 and accumulated in g2/m phase after 24  h treatment of compound 15 , while the hypodiploid ( sub - g0/g1 phase ) cells increased . compound 15 caused activation of caspase-3 , cleavage of parp , and consequently the cell death . caspase-3 is an executioner caspase whose activation leads to the cleavage of key cellular proteins including dna repair enzyme poly ( adp - ribose ) polymerase which is involved in dna repair predominantly in response to environmental stress and is important for the maintenance of cell viability . -cyano bis(indolyl)chalcone 16 ( figure 6 ) was found to be the most potent and selective against a549 lung cancer cell line ( ic50 = 0.8  m ) in vitro which is time - dependent . the activity is due to the presence of methoxy and fluoro substituents on indole rings . it was found to enhance tubulin polymerization suggesting the activity as microtubule stabilizing agents , though it was a preliminary study . nf-b pathway has been shown to be critical to survival of lung cancer cells , and many natural products obtained from plants were found to inhibit the activation of this pathway . two cardamonin analogs , 4,4-dihydroxylchalcone , 17 , and 4,4-dihydroxy-2-methoxychalcone , 18 ( figure 6 ) , were found to suppress the activation of nf-b pathway in lung cancer cells . compound 17 inhibited the survival of primary lung cancer cells with ic50 values of 0.44  0.05 and 0.16  0.03  m , respectively , against two lung cancer cells tested . compound 18 inhibited their survival with similar ic50 values ( 0.56  0.12  m and 0.65  1.36  m ) . immunoblot analysis displayed that caspase-3 and parp were both cleaved in the two lung cancer cell lines treated with compounds 17 and 18 , indicating the activation of apoptotic pathway . subsequent estimation of the phosphorylation level of ikk , nf-b pathway stimulating kinase , by immunoblotting assay demonstrated that both decreased ikk phosphorylation in lung cancer cell lines including a549 , nci - h460 , and nci - h1668 and lead to the accumulation of ib and ib and the export of nuclear p65 transcription factor . from the immunofluorescent staining , it was shown that transcription factor p65 , which is a downstream effect of nf-b pathway , was sequestered in the cytoplasm of a549 cells treated by compound 17 or compound 18 . incorporation of luciferase reporter system also results in transcription activity of nf-b in lung cancer cells treated with compound 17 or compound 18 and demonstrated that relative luciferase expression was significantly reduced in compound 17 or compound 18 treated lung cancer cells . in addition , the transcription of target genes of nf-b pathway , bcl-2 , and survivin was found to be suppressed in lung cancer cells treated with the two compounds . . higher concentration of the two compounds greatly inhibited the growth of tumors by 71.0 and 79.1% , respectively , although inhibitory effect was not significant at lower concentration . compared with compound 17 , compound 18 appeared to be slightly more potent to retard the growth of established tumors . -carboline based chalcones were synthesized and evaluated for their cytotoxic activity against a panel of human cancer cell lines . compounds 19a and 19b ( figure 6 ) showed very good antiproliferative activity against breast cancer cell line ( mcf-7 ) , where ic50 values were recorded at 2.25  m and 3.29  m , respectively . furthermore , compound 19a markedly induced dna fragmentation and apoptosis in breast cancer cells , which is an essential step in the cells undergoing apoptosis . the molecular mechanism to induce apoptosis in human hepatoma smmc-7721 cells was investigated by using 2,4-dihydroxy-6-methoxy-3,5-dimethylchalcone , 20 ( figure 7 ) , isolated from the buds of cleistocalyx operculatus . compound 20 induced apoptosis via a mitochondria dependent pathway involving inhibition of bcl-2 expression leading to disintegration of the outer mitochondrial membrane . further downstream of the apoptosis cascade , compound 20 , increases caspase-3 and caspase-9 activities . angiogenesis and invasion are two highly interconnected events in cancerous cells where involvement of multiple molecules and pathways takes place . hypoxia inducible factor-1 ( hif-1 ) has been identified as an important protein involved in those events . activated hif-1 controls the expression of genes involved in tumor cell immortalization , stem cell maintenance , metabolic reprogramming , autocrine growth , and treatment failure , thereby making it an important target for the development of new antitumor therapy . a novel series of chalcone derivatives were synthesized and their biological activities against hif-1 were evaluated by wang et al . it has been found that compound 21 ( figure 7 ) exhibited inhibitory effects on hif-1 at 10  m concentration by downregulating the expression of hif-1 and hif-1 under hypoxic conditions . the hif inhibition rate has been found to be 83.0  16.9% , while topotecan , hif-1 inhibitor , was used as control and for comparison it has the inhibition rate of 82.8  2.9% . in addition , compound 21 displayed inhibitive effect against the migration and the invasion of hep3b ( human liver cancer cell line ) and human umbilical vein endothelial cells ( huvec ) and tube formation of huvecs and significant antiangiogenic and anti - invasive activities . from the in vivo study it has been found that 21 could retard tumor growth of hep3b xenograft models and reduced cd31 and mmp-2 expression in tumor tissues . cd31 ( cluster of differentiation 31 ) is platelet endothelial cell adhesion molecule ( pecam-1 ) , which is a protein found to be expressed in certain tumors . compound 27 was well tolerated and was found to be nontoxic up to 200  mg / kg in swiss mice in acute intravenous toxicity . the molecular mechanisms of growth inhibition in human bladder cancer cell lines t24 and ht-1376 by chalcone 22 ( figure 8) are due to the induction of apoptosis , cell cycle progression inhibition by regulating cell cycle related factor like significant reduction in the expression of cyclin a and cyclin b1 , decreases in the expression of cdc2 , and also increases in the expression of p21 and p27 . so , chalcone may cause cell cycle arrest by reducing the complex of cdc2/cyclin b due to downregulation of multiple g2/m regulating proteins . it triggers the mitochondrial apoptotic pathway by releasing cytochrome c from the cytoplasm with an increase in caspase-9 and activating caspase-3 . it is also increases the expression of proapoptotic proteins bax and bak , which are responsible for the initiation of mitochondrial apoptotic pathway , and decreases the expression of antiapoptotic proteins bcl-2 and bcl - xl , while overexpression of bcl-2 and bcl - xl is associated with enhanced oncogenic potential . chalcone inhibits the nf-b activation by increasing the expression of ib in cytoplasm , leading to apoptosis . the copper chelate complex 23 ( figure 8) showed promising activity with ic50 value of 5.95  m against pc3 cancer cell line in vitro . the estimated ic50 value for doxorubicin was 8.7  m , which was used as positive control . it was found that cancer cells have high affinity to copper ions ; thus , upon chelation of chalcones with copper they are thought to be more liable to target cancer cells in microdendron architecture . it was assumed that copper ions might act as penetration enhancers of chalcones into cancer cells . even if copper ions are noncytotoxic to cancer cells , they might act as inhibitors of drug efflux proteins characteristic to cancer cells . drug efflux proteins , such as p - glycoproteins ( pgp ) , breast cancer resistance protein ( bcrp ) , and multidrug resistance - associated protein 1 ( mrp1 ) , are responsible for drug resistance of cancer cells . the high cytotoxic activity is attributed to the presence of the p - methylphenyl moiety of ring b and the copper ion . hybrids of n-4-piperazinyl - ciprofloxacin - chalcone were prepared by abdel - aziz et al . national cancer institute ( nci ) selected 5 compounds , namely , 24a , 24b , 24c , 24d , and 24e ( figure 9 ) , to carry out in vitro one - dose anticancer assay against full nci 60 cell lines derived from leukemia , lungs , colon , renal , melanoma , cns , prostate , ovarian , and breast cancer cell lines . of the selected compounds , 24a and 24d exhibited the highest ability to inhibit the proliferation of different cancer cell lines while undergoing one - dose anticancer test . among the nine tumor subpanels tested for , compound 24a was found to have broad - spectrum antitumor activity with selectivity ratios ranging between 0.42 and 1.87 at the gi50 level without producing selectivity , while compound 24d showed high selectivity towards the leukemia subpanel with selectivity ratio of 6.71 at gi50 level . moreover compound 24d showed remarkable anticancer activity against most of the tested cell lines with gi50 ranging from 0.21 to 57.6  m . furthermore , compounds 24c and 24e have shown remarkable topo - ii inhibitory activity compared to etoposide at 100  m and 20  m concentrations . compounds 24c and 24e were found to be potent topo - i inhibitors at 20  m concentration when compared to camptothecin . the results that were obtained indicated that introduction of n-4-piperazinyl moiety of ciprofloxacin into the chalcones derivatives dramatically increases the anticancer activity of the tested compounds severalfold higher than that of the activity shown by weak anticancer ciprofloxacin . increase in antiproliferative activity of the tested compounds might be the result of either synergistic effect of the chalcone derivatives and/or alteration of the physicochemical properties of ciprofloxacin . to determine the dna unwinding properties of 24c and 24e , amsacrine ( m - amsa ) , a well - known dna intercalator , was chosen as a standard where a supercoiled phot1 dna was used as a substrate since unwinding of the double strand of dna helix is a practical characteristic of intercalating drugs . amsacrine blocked unwinding of phot1 dna in the presence of excess topo - i in dose - dependent manner , while compounds 24c and 24e did not block dna unwinding at high concentration up to 1000  m treatment . the assay indicated that 24c and 24e do not interact with dna but interact with topoisomerases for their inhibitory activity . compound 25 ( figure 9 ) with a propionyloxy group at the 4-position of the left phenyl ring showed the most potent inhibition activity which inhibited the growth of hepg2 , a549 , a375 , smmc-7221 , and k562 cancer cell lines with ic50 values of 0.15 , 0.36 , 0.62 , 0.61 , and 0.52  m , respectively . compound 25 was also shown to arrest cells in the g2/m phase of the cell cycle and inhibit the polymerization of tubulin . molecular docking study suggested that compound 25 binds into the colchicine binding site of tubulin . in summary , these findings suggest that compound 23 is a promising new antimitotic compound for the potential treatment of cancer . a new series of pyrano chalcone derivatives containing indole moiety synthesized by wang et al . ( 2014 ) were evaluated for antiproliferative activities . among those , compound 26 ( figure 9 ) , with a propionyloxy group at the 4-position of the phenyl ring a and n - methyl-5-indolyl on the b ring displayed the most potent cytotoxic activity against all tested cancer cell lines including multidrug resistant phenotype , which inhibits cancer cell growth with ic50 values ranging from 0.22 to 1.80  m . the tested cell lines were smmc-7221 , hepg2 ( liver ) , pc-3 ( prostate ) , a549 ( lung ) , k562 ( leukemia ) , hct116 ( colon ) , skov3 ( ovarian ) , mcf-7 ( breast ) , vincristine resistant hct-8 ( hct-8/v ) , and taxol resistant hct-8 ( hct-8/t ) . compound 26 was the most potent towards hepg2 cells with ic50 value of 0.22  m . colchicine ( 2.5  m ) and paclitaxel ( 2.5  m ) were used as a reference . compound 26 produced cytotoxic activity in normal human liver cell line ( lo2 ) above the concentration of 10  m . it significantly induced cell cycle arrest in g2/m phase and inhibited the polymerization of tubulin . it was also shown from molecular docking analysis that compound 26 binds at the colchicine binding site of tubulin . chalcone 26 also exerted potent anticancer activity in hepg2 xenografts in balb / c nude mice , where the growth of tumors in mice treated with chalcone 26 ( 30  mg / kg ) was reduced by 56.58% compared with that in control mice treated with vehicle only at day 35 . positive control reduced the growth of tumors by 25.93% . cell division cycle 25 ( cdc25 ) , which includes cdc25a , b , and c homologues , a subfamily of dual - specificity protein tyrosine phosphatases , plays a role in the regulation of the cell cycle . the cdc25a and cdc25b isoforms are overexpressed in primary tissue samples from various human cancers , which is strongly associated with tumor aggressiveness and poor prognosis . cdc25b controls cell cycle progression by catalyzing removal of covalently attached contiguous phosphates and the subsequent activation of cyclin - dependent kinase 1 ( cdk1 ) . cdc25b overexpression has been documented in a variety of human cancers , including head and neck and colon , and non - small cell lung cancer validates its oncogenic potential . a series of 2-hydroxy-4-isoprenyloxychalcone derivatives were evaluated for the inhibition of cdc25b activity by zhang et al . ( 2014 ) . among those , two compounds , 27 and 28 ( figure 9 ) , have been found to have the potent inhibition activity and significantly inhibited cdc25b with inhibition rates of 99.95% and 99.75% , respectively , at a dose of 20  g / ml , which is similar to the known tyrosine phosphatase inhibitor sodium orthovanadate . in vitro cytotoxic activity assays showed that compounds 27 and 28 were potent against hct116 , hela , and a549 cells . they were particularly cytotoxic against colon hct116 cancer cell line with ic50 values of 0.89 and 1.76 irinotecan ( ic50 = 2.14  mol / l ) , a clinically relevant camptothecin , was chosen as a reference drug . in colo205 xenograft balb / c nude male mice , compound 27 produced a tumor volume inhibition of about 50% . a new series of pyrazole chalcones were screened for the in vitro anticancer activities against mcf-7 ( human breast adenocarcinoma ) and hela ( human cervical tumor cells ) cell lines . compound 29 ( figure 9 ) showed the highest inhibition in human mcf-7 and hela cell lines with an ic50 value of 0.018  g / ml and 0.047  g / ml , respectively . the ic50 for standard doxorubicin in hela and mcf-7 cells was 1.15  g / ml and 1.84  g / ml , respectively . new prenylated chalcone , 30 ( figure 9 ) , named as renifolin c , was isolated from whole desmodium renifolium plants and cytotoxicity was evaluated against five human tumor cell lines ( nb4 , a549 , shsy5y , pc3 , and mcf7 ) using the mtt method , using paclitaxel as a positive control . the ic50 values were 6.4  m and 8.5  m against nb4 and pc3 cell lines and above 10  m for the other cell line tested . various benzylidene pregnenolones were synthesized and in vitro cytotoxicity studies were performed by banday et al . compounds 31a and 31b ( figure 9 ) were found to be active against the hct-15 ( colon ) and mcf-7 ( breast ) cell lines . chalcone 31a has ic50 value of 1.02  m and 0.79  m , respectively , against hct-15 and mcf-7 , while 31b has 0.81  m and 1  m , respectively . chalcone - coumarin hybrid 33 ( figure 10 ) ( ic50 = 0.53  m ) displayed cytotoxicity against human lymphoblastic leukemia cell line ( molt-3 ) , where etoposide ( ic50 = 0.05  m ) was taken as a standard . compounds 32 and 33 shown in figure 10 displayed higher cytotoxic potency against hepg2 cells than the control drug , etoposide . the hybrid 33 ( ic50 = 4.26  m ) was potent but was found to be toxic toward noncancerous african green monkey kidney cell line ( vero ) . though analog 32 displayed cytotoxic activity against hepg2 with ic50 value of 8.18  m , it was found to be nontoxic against vero cells . it has been shown from molecular docking study that compounds could snugly occupy the colchicine binding site of -tubulin . ( 2013 ) . among them , potent chalcone 34 ( figure 10 ) induced apoptotic cell death of a wide variety of tumor cell lines including multidrug resistant human tumor cell lines in the nanomolar range by attacking microtubules . flow cytometric study showed that chalcone 34 significantly induced cell cycle arrest in g2/m phase at 0.2  m concentration . in vitro immunofluorescence staining and tubulin polymerization assay displayed that chalcone 34 promoted tubulin polymerization into microtubules and caused microtubule stabilization similar to paclitaxel , which is suggesting that chalcone 34 is a microtubule stabilizer via enhancing the rate of tubulin polymerization . then , in in vivo study , 34 exhibited potent inhibitory activities in human hepg2 xenograft tumor models . chalcone derivatives , named parasiticins c , 35 and 36 ( figure 10 ) , were isolated from the leaves of cyclosorus parasiticus . the in vitro cytotoxic activities were evaluated against lung cancer a549 , hepatocellular carcinoma hepg2 , breast cancer mcf-7 and mda - mb-231 , leukemia all - sil , and pancreatic cancer sw1990 . compounds 35 and 36 exhibited substantial cytotoxicity against all six cell lines , especially toward hepg2 with the ic50 values of 1.60 and 2.82  m , respectively , which is comparable to the doxorubicin positive control ( 1.19  m ) . they induced apoptosis in the hepg2 cell line . in the clonogenicity assay on hepg2 cell line , capacity of single cancer cells to generate colonies compound 35 showed more potent cytotoxicity than 36 , suggesting that the presence of an additional lactone ring fused enhances the cytotoxic activity . a fission yeast , schizosaccharomyces pombe , was utilized in bioassay guided screening on several plant extracts to search for anticancer agents by snchez - pic et al . it was found that an extract from leaves of corema album belonging to family ericaceae had antiproliferative activity . 2,4-dihydroxychalcone , 37 ( figure 11 ) , the promising cytotoxic compound , was found in this extract and cytotoxic activity is likely due to its ability to induce dna damage which blocks cell cycle progression at the g2/m transition in a concentration of 8  m to 20  m . compound 37 could induce dna damage or interfere with dna replication , which would eventually result in the activation of the cell cycle checkpoints , thus blocking cell cycle in g2 . in subsequent study , deletions of rad3 , chk1 , and cds1 , three key kinases required for dna checkpoints operating at g2/m , were done . rad3 is required in order to signal downstream of either dna replication problems or dna damage , whereas chk1 transmits dna damage - induced signals and cds1 signals in response to defective dna replication . it was found that both rad3 and chk1 deletions suppressed the cell cycle block produced by compound 37 , while cds1 deletion showed partial suppression , suggesting that the g2/m block observed in compound 37 is mostly caused by the activation of dna damage checkpoint response . methyl methanesulfonate ( mms ) , an alkylating compound that induces dna damage , was used as control . thus , compound 37 ( 820  m ) directly or indirectly causes damage to the dna which results in a rad3-dependent and chk1-dependent cell cycle block at the g2/m transition . cathepsins have emerged as a potential target for chemoprevention and anticancer therapy . increased levels of cathepsin b and cathepsin h in a variety of tumors have shown their contribution towards invasion and metastasis . molecule 38 ( figure 12 ) has been found to be potent among the synthesized inhibitors , which inhibits cathepsin b and h. the ki ( inhibition constant ) value against cathepsin b was 6.18  10  m and 2.8  10  m for cathepsin h. the inhibition was of competitive type . 2-hydroxychalcones have been evaluated as potential inhibitors to these cysteine proteases probably due to presence of ,-unsaturated carbonyl moiety in the molecule . -ch2sh moiety present at the active site of enzymes can interact with the electron deficient center present in the chalcones inhibiting the enzymes activity . nitrosubstitution is useful for an effective interaction with cathepsins b and h. its inhibition to cathepsin b as compared with cathepsin h indicates that cathepsin b 's active site is more susceptible to these compounds as compared to cathepsin h. the results were also found to be consistent when compared with in silico docking studies . cotreatment with a chemosensitizer such as compounds 39a and 39b ( figure 13 ) and trail was found to be more efficient to treat gbm ( glioblastoma multiforme ) than treatment with trail alone . gbm is one of the most aggressive forms of human malignant brain tumors , characterized by rapid growth , extensive invasiveness , and robust neoangiogenesis . against human crt - mg astroglioma cells by using the lactate dehydrogenase ( ldh ) release assay , it was found that compounds 39a and 39b with trail ( 25  ng / ml ) showed good cytotoxicity . 2-ethylamino and substituted triazole groups are promising templates in the backbone of chalcone to develop trail sensitizers as anticancer agents . mdr ( multidrug resistance ) can be defined as the ability of cancer cells to survive exposure to different chemotherapeutic agents and is a major cause of treatment failure in human cancers . 4-hydroxy-2,6-dimethoxychalcone , 40 ( figure 14 ) , was isolated from polygonum limbatum with ic50 values of 2.54  m against multidrug resistant cem / adr5000 leukemia cells . p - glycoprotein - expressing and multidrug resistant cem / adr5000 cells were much more sensitive toward compound 40 than doxorubicin ( ic50 = 195.12  m ) , which is a reference drug . compound 40 ( figure 14 ) has been found to arrest the cell cycle between g0/g1 phases , which is via the strong induction of apoptosis by disrupting mitochondrial membrane potential ( mmp ) and an increased production of reactive oxygen species ( ros ) in the studied leukemia cell line . it was found that caspases were not involved in the apoptotic pathway induced by compound 40 . the presence of hydroxyl ( -oh ) and methoxy ( -och3 ) substituents influences the activity of compound 40 . the membrane transporter p - glycoprotein ( p - gp ) , encoded by mdr1 gene , is the main mechanism responsible for resulting in decreased intracellular drug accumulation in human mdr cancers . mitogen activated protein ( map ) kinase pathway is involved in p - gp - mediated mdr . dimer of chalcone named as tomoroside b , 41 ( figure 14 ) , was isolated from the aerial parts of helichrysum zivojinii . the combined effects of chalcone dimer 41 and tipifarnib ( the inhibitor of map kinase signaling cascade , a farnesyltransferase inhibitor ) in mdr cancer cell line , nci - h460/r , were found . these results point to the ability of compound 41 to enhance tipifarnib efficacy in mdr cancer cells as it reduced the ic50 for tipifarnib from 9.0  m ( applied alone ) to 3.8  m . activity was compared to tipifarnib employing human sensitive non - small cell carcinoma cell line nci - h460 ( ic50 = 198  m for compound 41 alone ) , its multidrug resistant ( mdr ) counterpart nci - h460/r ( ic50 = 172  m for compound 41 alone ) , and spontaneously immortalized normal human keratinocyte cell line hacat . the concentration around 100  m of compound 41 significantly inhibited the growth of normal hacat cells , considering that hacat are normal , but transformed cells with immortalized phenotype ; these results point to the potential of compound 41 to exert the cancer preventive effects . compound 41 increased the expression of hif-1 , probably by exerting antioxidant and redox status modulator effect . compound 41 increased the expression of hif-1 and acted synergistically with tipifarnib probably by inhibiting the map kinase prosurvival signaling . to identify potent anticancer agents against the cisplatin - resistant human ovarian cancer cell line the two most active compounds were 42 ( gi50 = 3.87  m ) and 43 ( gi50 = 3.95  m ) ( figure 14 ) . it was found that compounds 42 and 43 trigger cell cycle arrest at the g2/m phase and apoptotic cell death in a2780/cis cancer cells . aurora a kinase is known to be involved in cell cycle arrest at the g2/m phase . in vitro aurora a kinase assay of compound 42 showed the half - maximal inhibitory concentration ( ic50 ) of 66.4  m . because aurora a kinase may not be a real molecular target of compound 42 , gi50 value of compound 42 is higher than the ic50 value of 42 . chalcone architecture linked with various substitutions , such as methoxy , amino , and hydroxyl , and alteration of both rings has been found to be effective in making it a potential candidate in the anticancer armamentarium . the related studies showed excellent cytotoxic activities of chalcones in the different cell death pathways , not just acting in blocking the process of cell division . inhibitory concentrations in nanomolar range were impressive to show its ability to arrest cell division . furthermore , besides preclinical study , clinical study of chalcone may yield the development of research in this field . it is expected that this review may give the medicinal chemists a basis to get in touch with the recent updates and will be helpful for enrichment in this field .
cancer is an inevitable matter of concern in the medicinal chemistry era . 
 chalcone is the well exploited scaffold in the anticancer domain . 
 the molecular mechanism of chalcone at cellular level was explored in past decades . 
 this mini review provides the most recent updates on anticancer potential of chalcones .