Schiff bases and their metal complexes to target and overcome (multidrug) resistance in cancer

Overcoming multidrug resistance (MDR) is one of the major challenges in cancer therapy. In this respect, Schiff base-related compounds (bearing a R1R2CNR3 bond) gained high interest during the past decades. Schiff bases are considered privileged ligands for various reasons, including the easiness of their preparation and the possibility to form complexes with almost all transition metal ions. Schiff bases and their metal complexes exhibit many types of biological activities and are used for the treatment and diagnosis of various diseases. Until now, 13 Schiff bases have been investigated in clinical trials for cancer treatment and hypoxia imaging. This review represents the first collection of Schiff bases and their complexes which demonstrated MDR-reversal activity. The areas of drug resistance covered in this article involve: 1) Modulation of ABC transporter function, 2) Targeting lysosomal ABCB1 overexpression, 3) Circumvention of ABC transporter-mediated drug efflux by alternative routes of drug uptake, 4) Selective activity against MDR cancer models (collateral sensitivity), 5) Targeting GSH-detoxifying systems, 6) Overcoming apoptosis resistance by inducing necrosis and paraptosis, 7) Reactivation of mutated p53, 8) Restoration of sensitivity to DNA-damaging anticancer therapy, and 9) Overcoming drug resistance through modulation of the immune system. Through this approach, we would like to draw attention to Schiff bases and their metal complexes representing highly interesting anticancer drug candidates with the ability to overcome MDR.

Development and In Vivo Application of a Water-Soluble Anticancer Copper Ionophore System Using a Temperature-Sensitive Liposome Formulation

Liposomes containing copper and the copper ionophore neocuproine were prepared and characterized for in vitro and in vivo anticancer activity. Thermosensitive PEGylated liposomes were prepared with different molar ratios of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and hydrogenated soybean phosphatidylcholine (HSPC) in the presence of copper(II) ions. Optimal, temperature dependent drug release was obtained at 70:30 DPPC to HSPC weight ratio. Neocuproine (applied at 0.2 mol to 1 mol phospholipid) was encapsulated through a pH gradient while using unbuffered solution at pH 4.5 inside the liposomes, and 100 mM HEPES buffer pH 7.8 outside the liposomes. Copper ions were present in excess, yielding 0.5 mM copper-(neocuproine)₂ complex and 0.5 mM free copper. Pre-heating to 45 °C increased the toxicity of the heat-sensitive liposomes in short-term in vitro experiments, whereas at 72 h all investigated liposomes exhibited similar in vitro toxicity to the copper(II)-neocuproine complex (1:1 ratio). Thermosensitive liposomes were found to be more effective in reducing tumor growth in BALB/c mice engrafted with C26 cancer cells, regardless of the mild hyperthermic treatment. Copper uptake of the tumor was verified by PET/CT imaging following treatment with [⁶⁴Cu]Cu-neocuproine liposomes. Taken together, our results demonstrate the feasibility of targeting a copper nanotoxin that was encapsulated in thermosensitive liposomes containing an excess of copper.

Rising horizon in circumventing multidrug resistance in chemotherapy with nanotechnology

Multidrug resistance (MDR) is one of the key barriers in chemotherapy, leading to the generation of insensitive cancer cells towards administered therapy. Genetic and epigenetic alterations of the cells are the consequences of MDR, resulted in drug resistivity, which reflects in impaired delivery of cytotoxic agents to the cancer site. Nanotechnology-based nanocarriers have shown immense shreds of evidence in overcoming these problems, where these promising tools handle desired dosage load of hydrophobic chemotherapeutics to facilitate designing of safe, controlled and effective delivery to specifically at tumor microenvironment. Therefore, encapsulating drugs within the nano-architecture have shown to enhance solubility, bioavailability, drug targeting, where co-administered P-gp inhibitors have additionally combat against developed MDR. Moreover, recent advancement in the stimuli-sensitive delivery of nanocarriers facilitates a tumor-targeted release of the chemotherapeutics to reduce the associated toxicities of chemotherapeutic agents in normal cells. The present article is focused on MDR development strategies in the cancer cell and different nanocarrier-based approaches in circumventing this hurdle to establish an effective therapy against deadliest cancer disease.

Example of two novel thiocyanato bridged copper (II) complexes derived from substituted thiosemicarbazone ligand: structural elucidation, DNA/albumin binding, biological profile analysis, and molecular docking study

Two novel copper (II) substituted thiosemicarbazone Schiff base complexes [Cu(L₁)(µ-SCN)]_n(NO₃)₂ (1) and [Cu₂(µ-SCN)(SCN)(L₂)₂](NO₃) (2) have been synthesized by condensing substituted thiosemicarbazides like 4-methyl-3-thiosemicarbazide or 4-ethyl-3-thiosemicarbazide with 2-acetylpyridine. Both the metal complexes 1 and 2 are characterized using different spectroscopic techniques like IR, UV-Vis, ESR spectroscopy followed by elemental analysis, cyclic voltammetric measurement and single crystal X-ray structure analysis. X-ray crystal structure analysis reveal that complex 1 is polymeric while complex 2 is dimeric in nature. The coordination geometry around Cu(II) are square pyramidal in which thiosemicarbazone Schiff base ligand coordinate to the central Cu(II) atom in tridentate fashion. The prominent interaction patterns of 1 and 2 with CT-DNA were examined by employing electronic absorption and emission spectral titrations, cyclic voltammetry and viscosity measurements. All the results show that CT-DNA binds with both copper (II) complexes 1 and 2. Furthermore, protein binding ability in vitro of complexes 1 and 2 with both BSA and HSA were carried out using multispectroscopic techniques and a static quenching pattern was observed in both cases. Molecular docking study was employed to ascertain the exact mechanism of action of 1 and 2 with DNA and protein molecules (BSA and HSA). In vitro cytotoxicity activity of complexes 1 and 2 toward AGS and A549 was evaluated using MTT assay which demonstrates that both complexes 1 and 2 have superior prospectus to act as anticancer agents. Communicated by Ramaswamy H. Sarma.

Copper(ii) complexes based on quinoline-derived Schiff-base ligands: synthesis, characterization, HSA/DNA binding ability, and anticancer activity

Three copper(ii) complexes, [Cu(L1)(NO₃)₂] (C1), [Cu(L2)Cl₂] (C2) and [Cu(L2)SO₄]₂·H₂O (C3), were designed and synthesized by the reaction of Cu(NO₃)₂·3H₂O, CuCl₂·2H₂O and CuSO₄·5H₂O with a quinoline-derived Schiff base ligand, L1 or L2, prepared by the condensation of quinoline-8-carbaldehyde with 4-aminobenzoic acid methyl ester or 4-aminobenzoic acid ethyl ester (benzocaine). The efficient bindings of the C1-C3 complexes with human serum albumin (HSA) and calf thymus DNA (CT-DNA) were analyzed by spectroscopy and molecular docking. These complexes could significantly quench the fluorescence of HSA through the static quenching process, and hydrophobic interactions with HSA through the sub-domain IIA and IIIA cavities. The complexes bind to DNA via the intercalative mode and they fit well into the curved contour of the DNA target in the minor groove region. Furthermore, the interaction abilities of the Cu(ii) complexes with HSA/DNA were greater as compared to their corresponding ligands. Interestingly, C1-C3, particularly C3, exhibited more cytotoxicity toward HeLa cells compared to normal HL-7702 cells and three other tumor cell lines (Hep-G2, NCI-H460, and MGC80-3). Their cytotoxicity toward the HeLa cell lines was 1.9-3.5-fold more potent than cisplatin. Further studies indicated that these complexes arrested the cell cycle in the G0/G1 phase and promoted tumor cell apoptosis via a reactive oxygen species (ROS)-mediated mitochondrial pathway.

A zinc Schiff base complex inhibits cancer progression both in vivo and in vitro by inducing apoptosis

Cancer chemotherapy suffers from selectivity and undesired toxicity of the drugs. Since zinc is a biocompatible tracer element and cysteine derivatives are used in cancer chemoprevention, we intend to develop a complex of zinc and cysteine-derivatives as potent, non-toxic anticancer agents. Herein, we synthesized and characterized cysteine based ligand, 2-[(2-Hydroxy-3-methoxy-benzylidene)-amino]-3-mercapto-propionic acid and its Zn-complex, which are found to be non-toxic towards normal human PBMC. Data also revealed that only Zn-complex exhibited remarkable apoptosis in drug-sensitive CCRF-CEM and multidrug-resistant CEM/ADR5000 cancer cells as assessed by MTT, Cell cycle and AnnexinV binding assay. Moreover, Zn-complex altered ROS and GSH level of the respective cell lines. Finally, treatment of Zn-complex in Swiss albino mice did not show any systemic toxicity in preliminary trials in normal mice and remarkably increased the life-span of EAC bearing mice. In conclusion, the synthesized Zn-complex may be developed for efficacious, multidrug resistance reversal, non-toxic chemotherapeutic agents in future.

A newly synthesized nickel chelate can selectively target and overcome multidrug resistance in cancer through redox imbalance both in vivo and in vitro

Induction of undesired toxicity and emergence of multidrug resistance (MDR) are the major obstacles for cancer treatment. Moreover, aggressive cancers are less sensitive towards existing chemotherapeutics. Therefore, selective targeting of cancers without inducing undesired side effects and designing proper strategies to overcome MDR has utmost importance in modern chemotherapy. Previously we revealed the anticancer properties of some transition metal chelates of Schiff base, but the effectiveness of nickel complex is still unrevealed. Herein, we synthesized and characterized a Schiff base nickel chelate, nickel-(II) N-(2-hydroxyacetophenone) glycinate (NiNG), through different spectroscopic means. NiNG proves to be a broad spectrum anticancer agent with considerable efficacy to overcome MDR in cancer. Antiproliferative effects of NiNG was evaluated using drug-resistant (CEM/ADR5000; NIH-MDR-G185; EAC/Dox), drug-sensitive aggressive (Hct116; CCRF-CEM; EAC/S) and normal (NIH-3T3) cells that reveal the selective nature of NiNG towards drug resistant and sensitive cancer cells without inducing any significant toxicity in normal cells. Moreover, NiNG involves reactive oxygen species (ROS)-mediated redox imbalance for induction of caspase 3-dependent apoptosis in aggressive drug-sensitive Hct116 and drug-resistant NIH-MDR-G185 cells through disruption of mitochondrial membrane potential. Moreover, intraperitoneal (i.p.) application of NiNG at non-toxic doses caused significant increase in the life-span of Swiss albino mice bearing sensitive and doxorubicin-resistant subline of Ehrlich ascites carcinoma cells. It is noteworthy that, in vitro NiNG can only overcome P-glycoprotein-mediated MDR while in vivo NiNG can overcome MRP1-mediated MDR in cancer. Therefore, NiNG has therapeutic potential to target and overcome MDR in cancer.

Induction of apoptosis in human colorectal cancer cell line, HCT-116 by a vanadium- Schiff base complex

Vanadium compounds are well known for their therapeutic interventions against several diseases. Various biochemical attributes of vanadium complexes inspired us to evaluate the cancer cell killing efficacy of the vanadium complex, viz., vanadyl N-(2-hydroxyacetophenone) glycinate [VO(NG)₂]. Previously we showed that VO(NG)₂ is an effective anticancer agent in in vitro and in vivo cancer models and imposed miniscule side effects. Herein we report that VO(NG)₂ is significantly cytotoxic to various cancer cell lines. Furthermore, this redox active vanadyl complex altered the redox homeostatsis of many human cancer cell lines significantly. VO(NG)₂ actuates programmed cell death in human colorectal carcinoma cells(HCT-116) through mitochondrial outer membrane permeabilization but in caspase independent manner, possibly by altering cellular redox status and by inflicting DNA damage. Thus, the present work is an attempt to provide many evidences regarding the potent and selective chemotherapeutic efficacy of the novel VO(NG)₂.

Modulation of cell death in human colorectal and breast cancer cells through a manganese chelate by involving GSH with intracellular p53 status

Chemotherapy is central to current treatment modality especially for advanced and metastatic colorectal and breast cancers. Targeting the key molecular events of the neoplastic cells may open a possibility to treat cancer. Although some improvements in understanding of colorectal and breast cancer treatment have been recorded, the involvement of glutathione (GSH) and dependency of p53 status on the modulation of GSH-mediated treatment efficacy have been largely overlooked. Herein, we tried to decipher the underlying mechanism of the action of Mn-N-(2-hydroxyacetophenone) glycinate (MnNG) against differential p53 status bearing Hct116, MCF-7, and MDA-MB-468 cells on the backdrop of intracellular GSH level and reveal the role of p53 status in modulating GSH-dependant abrogation of MnNG-induced apoptosis in these cancer cells. Present study discloses that MnNG targets specifically wild-type-p53 expressing Hct116 and MCF-7 cells by significantly depleting both cytosolic, mitochondrial GSH, and modulating nuclear GSH through Glutathione reductase and Glutamate-cysteine ligase depletion that may in turn induce p53-mediated intrinsic apoptosis in them. Thus GSH addition abrogates p53-mediated apoptosis in wild-type-p53 expressing cells. GSH addition also overrides MnNG-induced modulation of phase II detoxifying parameters in them. However, GSH addition partially replenishes the down-regulated or modulated GSH pool in cytosol, mitochondria, and nucleus, and relatively abrogates MnNG-induced intrinsic apoptosis in p53-mutated MDA-MB-468 cells. On the contrary, although MnNG induces significant cell death in p53-null Hct116 cells, GSH addition fails to negate MnNG-induced cell death. Thus p53 status with intracellular GSH is critical for the modulation of MnNG-induced apoptosis.

Induction of intrinsic and extrinsic apoptosis through oxidative stress in drug-resistant cancer by a newly synthesized Schiff base copper chelate

Multidrug resistance (MDR) in cancer represents a variety of strategies employed by tumor cells to evade the beneficial cytotoxic effects of structurally different anticancer drugs and thus confers impediments to the successful treatment of cancers. Efflux of drugs by MDR protein-1, functional P-glycoprotein and elevated level of reduced glutathione confer resistance to cell death or apoptosis and thus provide a possible therapeutic target for overcoming MDR in cancer. Previously, we reported that a Schiff base ligand, potassium-N-(2-hydroxy 3-methoxy-benzaldehyde)-alaninate (PHMBA) overcomes MDR in both in vivo and in vitro by targeting intrinsic apoptotic/necrotic pathway through induction of reactive oxygen species (ROS). The present study describes the synthesis and spectroscopic characterization of a copper chelate of Schiff base, viz., copper (II)-N-(2-hydroxy-3-methoxy-benzaldehyde)-alaninate (CuPHMBA) and the underlying mechanism of cell death induced by CuPHMBA in vitro. CuPHMBA kills both the drug-resistant and sensitive cell types irrespective of their drug resistance phenotype. The cell death induced by CuPHMBA follows apoptotic pathway and moreover, the cell death is associated with intrinsic mitochondrial and extrinsic receptor-mediated pathways. Oxidative stress plays a pivotal role in the process as proved by the fact that antioxidant enzyme; polyethylene glycol conjugated-catalase completely blocked CuPHMBA-induced ROS generation and abrogated cell death. To summarize, the present work provides a compelling rationale for the future clinical use of CuPHMBA, a redox active copper chelate in the treatment of cancer patients, irrespective of their drug-resistance status.

Mixed-ligand copper(ii) Schiff base complexes: the role of the co-ligand in DNA binding, DNA cleavage, protein binding and cytotoxicity

Four novel mixed-ligand copper(ii) Schiff base complexes were synthesized and characterized. The biological features of the complexes and how acetic auxiliary ligands manipulate these features were investigated.

In vitro and in vivo Anticancer Effects of a Novel 9-Phenyldibenzo[a,c]phenazin-9-ium Cation and Its Ligands

BACKGROUND

Multidrug resistance (MDR) is a major problem in cancer treatment. Cu complexes possess the ability to overcome MDR in cancer. Therefore, the search for new Cu complexes is of great clinical significance and we address the anticancer effects of a previously synthesized novel 9-phenyldibenzo[a,c]phenazin-9-ium cation [1(+)] as [1] [CuCl2] and as [1] [I].

METHODS

The existence of the monovalent Cu(I) in [1] [CuCl2] was proven by electron paramagnetic resonance (EPR) studies and in vivo anticancer effects were studied in animals.

RESULTS

The monovalent nature of the Cu ion in [1] [CuCl2] was determined through EPR. The mean survival time of mice bearing doxorubicin-resistant Ehrlich ascites carcinoma cells is longer when [1] [I] is injected intraperitoneally whereas [1] [CuCl2] does not significantly increase the median survival in tumor-bearing mice. Compounds do not follow the immunomodulatory route and only [1] [I] shows cytotoxic activity in both MDR and drug-sensitive leukemia cell lines.

CONCLUSION

An organic iodide complex rather than a cupric complex possesses direct cytotoxic potential.

Effects of P-glycoprotein and its inhibitors on apoptosis in K562 cells

P-glycoprotein (P-gp) is a major factor in multidrug resistance (MDR) which is a serious obstacle in chemotherapy. P-gp has also been implicated in causing apoptosis of tumor cells, which was shown to be another important mechanism of MDR recently. To study the influence of P-gp in tumor cell apoptosis, K562/A cells (P-gp+) and K562/S cells (P-gp−) were subjected to doxorubicin (Dox), serum withdrawal, or independent co-incubation with multiple P-gp inhibitors, including valspodar (PSC833), verapamil (Ver) and H108 to induce apoptosis. Apoptosis was simultaneously detected by apoptotic rate, cell cycle by flow cytometry and cysteine aspartic acid-specific protease 3 (caspase 3) activity by immunoassay. Cytotoxicity and apoptosis induced by PSC833 were evaluated through an MTT method and apoptosis rate, and cell cycle combined with caspase 3 activity, respectively. The results show that K562/A cells are more resistant to apoptosis and cell cycle arrest than K562/S cells after treatment with Dox or serum deprivation. The apoptosis of K562/A cells increased after co-incubation with each of the inhibitors of P-gp. P-gp inhibitors also enhanced cell cycle arrest in K562/A cell. PSC833 most strikingly decreased viability and led to apoptosis and S phase arrest of cell cycle in K562/A cells. Our study demonstrates that P-gp inhibits the apoptosis of tumor cells in addition to participating in the efflux of intracellular chemotherapy drugs. The results of the caspase 3 activity assay also suggest that the role of P-gp in apoptosis avoidance is caspase-related.

A copper chelate selectively triggers apoptosis in myeloid-derived suppressor cells in a drug-resistant tumor model and enhances antitumor immune response

Myeloid-derived suppressor cells (MDSCs), one of the major orchestrators of immunosuppressive network are present in the tumor microenvironment suppress antitumor immunity by subverting Th1 response in tumor site and considered as a great obstacle for advancement of different cancer immunotherapeutic protocols. Till date, various pharmacological approaches have been explored to modulate the suppressive functions of MDSCs in vivo. The present study describes our endeavor to explore a possibility of eradicating MDSCs by the application of a copper chelate, namely copper N-(2-hydroxy acetophenone) glycinate (CuNG), previously found to be a potential immunomodulator that can elicit antitumorogenic Th1 response in doxorubicin-resistant EAC (EAC/Dox) bearing mice. Herein, we demonstrated that CuNG treatment could reduce Gr-1+CD11b+ MDSC accumulation in ascitic fluid and spleen of EAC/Dox tumor model. Furthermore, we found that CuNG mediated reduction in MDSCs is associated with induction of Th1 response and reduction in Treg cells. Moreover, we observed that CuNG could deplete MDSCs by inducing Fas-FasL mediated apoptotic cell death where death receptor Fas expression is enhanced in MDSCs and FasL is provided by activated T cells. However, MDSC expansion from bone marrow cells and their differentiation was not affected by CuNG. Altogether, these findings suggest that the immunomodulatory property of CuNG is attributed to, at least in part, by its selective cytotoxic action on MDSCs. So, this preclinical study unveils a new mechanism of regulating MDSC levels in drug-resistant cancer model and holds promise of translating the findings into clinical settings.

Selective anticancer copper(ii)-mixed ligand complexes: targeting of ROS and proteasomes

The ternary copper(ii) complexes 1–4 exhibited anticancer selectivity, as evidenced by MTT assay, % apoptosis, cell cycle arrest, ROS induction and DNA DSBs. Proteasome of cancer cells are also inhibited.

ROS and RNS induced apoptosis through p53 and iNOS mediated pathway by a dibasic hydroxamic acid molecule in leukemia cells

Anticancer drugs induce apoptosis to cancer cells and also exhibit undesired toxicity to normal cells. Therefore development of novel agents triggering apoptosis and have low toxicity towards normal cells is most important. Hydroxamic acids suppress tumour cell growth through apoptosis but the underlying mechanism is poorly understood. Herein, we describe the apoptotic potential of a dibasic hydroxamic acid derivative, viz., oxayl bis (N-phenyl) hydroxamic acid (OBPHA), which induces apoptosis through generation of both ROS and NO in doxorubicin resistant T-lymphoblastic leukemia, CEM/ADR5000 cells. Present study discloses that OBPHA selectively kills cancerous cells irrespective of their drug resistant phenotype. We also determined the crystal structure of OBPHA to understand the structural requirements for apoptosis; the study reveals that the presence of substituted hydroxamic acid groups (-CO-NH-OH) favours the generation of NO possibly through auto degeneration. Along with the induction of caspase 3 mediated intrinsic apoptosis; OBPHA also activates p53 dependent signalling cascade and downregulates HDAC3 expression in a time dependent manner possibly due to increased ROS and NO production and simultaneous decrease in cellular GSH level. Thus ROS and NO mediated downstream signalling are essential for the anticancer effect of OBPHA. Therefore OBPHA, having a structurally relevant pharmacophore provides important insight into the development of new ROS and RNS generating chemicals inducing p53 dependent apoptosis.

The role of a Schiff base scaffold, N-(2-hydroxy acetophenone) glycinate-in overcoming multidrug resistance in cancer

Drug resistance is a problem that hinders the numerous successes of chemotherapeutic intervention of cancer and continues to be a major obstacle for cures. Till date, several attempts have been made to develop suitable multidrug resistance (MDR) reversing agents. But, throughout the clinical development of MDR reversing agents, patients repeatedly suffer from toxicities. So far, some anticancer activity of Schiff bases which are the condensation products of carbonyl compounds and primary amines and their metal complexes has been described. But, overcoming multidrug resistance, by the use of such small molecules still remain unexplored. Under this backdrop, in search of less toxic and more effective MDR reversing agents our laboratory has developed the different metal chelates of Schiff base N-(2-hydroxy acetophenone)glycinate (NG) which is structurally similar to azatyrosine [L-β-(5-hydroxy-2-pyridyl)-alanine] that inhibits tumor formation by deactivating the c-Raf-1 kinase and c-Ha-ras signalling pathway. A decade-long research proposes possible strategies to overcome MDR by exploiting the chemical nature of such metal chelates. In this review we have catalogued the success of metal chelates of NG to overcome MDR in cancer. The review depict that the problem of MDR can be circumvent by synchronized activation of immunogenic cell death pathways that utilize the components of a host's immune system to kill cancer cells in combination with other conventional strategies. The current wealth of preclinical information promises better understanding of the cellular processes underlying MDR reversing activity of metal derivatives of NG and thus exposes several cellular targets for rational designing of new generation of Schiff base metal chelates as MDR reversing agents.

A novel manganese complex, Mn-(II) N-(2-hydroxy acetophenone) glycinate overcomes multidrug-resistance in cancer

Multidrug resistance (MDR) remains a significant problem for effective cancer chemotherapy. In spite of considerable advances in drug discovery, most of the cancer cases still stay incurable because of resistance to chemotherapy. We synthesized a novel, Mn (II) complex (chelate), viz., manganese N-(2-hydroxy acetophenone) glycinate (MnNG) that exhibits considerable efficacy to overcome drug resistant cancer. The antiproliferative activity of MnNG was studied on doxorubicin resistant and sensitive human T lymphoblastic leukemia cells (CEM/ADR 5000 and CCRF/CEM). MnNG induced apoptosis significantly in CEM/ADR 5000 cells probably through generation of reactive oxygen species. Moreover, intraperitoneal (i.p.) application of MnNG at non-toxic doses caused significant increase in the life-span of Swiss albino mice bearing sensitive and doxorubicin resistant subline of Ehrlich ascites carcinoma cells.

7,3',4'-Trihydroxyisoflavone modulates multidrug resistance transporters and induces apoptosis via production of reactive oxygen species

The development of multidrug resistance (MDR) to conventional chemoradiation therapy usually leads to failure in treating cervical cancer. This study aims to explore the effects and mechanisms of 7,3',4'-trihydroxyisoflavone (7,3',4'-THIF), one of the major metabolites of daidzein, on potentiating cytotoxicity of epirubicin (Epi), an anticancer drug in human cervical cancer HeLa cells. The cytotoxicity of Epi remarkably increased when it was combined with 7,3',4'-THIF. The cotreatment increased the reactive oxygen species (ROS) levels, including hydrogen peroxide and superoxide free radicals. 7,3',4'-THIF was shown to down-regulate the MDR1 promoter region composed of the elements of AP1, GC-box, and Y-box, as demonstrated by a luciferase assay. A negative regulation of hMDR1 gene with multiple transcription factors by this isoflavone may provide a novel molecular mechanism for MDR modulation. The mRNA expressions of MDR1, MDR-associated protein (MRP) 1, and MRP2 for the combined treatment were significantly lower than those of the Epi treatment. This result implies that MDR transporter-mediated Epi resistance is inhibited at various degrees by the addition of 7,3',4'-THIF. This isoflavone significantly enhanced intracellular Epi accumulation in HeLa cells. 7,3',4'-THIF and/or Epi triggered apoptosis through the upregulation of p53, Bax, and caspase-9. Apoptosis induction was also confirmed by the reduced mitochondrial membrane potential, increased sub-G1 and G2/M phases, nuclear DNA fragmentation, and chromatin condensation. Our findings demonstrate for the first time that 7,3',4'-THIF causes cell death in human cervical cancer cells through the ROS-dependent suppression of MDR transporters and p53-mediated activation of the intrinsic mitochondrial pathway of apoptosis. Thus, 7,3',4'-THIF has the potential to enhance the activity of a broad range of cancer chemotherapeutics in the MDR spectrum with the advantage of reducing adverse effects.