Methylene blue reverts multidrug resistance: sensitivity of multidrug resistant cells to this dye and its photodynamic action

Progress of Phototherapy Applications in the Treatment of Bone Cancer

Bone cancer including primary bone cancer and metastatic bone cancer, remains a challenge claiming millions of lives and affecting the life quality of survivors. Conventional treatments of bone cancer include wide surgical resection, radiotherapy, and chemotherapy. However, some bone cancer cells may remain or recur in the local area after resection, some are highly resistant to chemotherapy, and some are insensitive to radiotherapy. Phototherapy (PT) including photodynamic therapy (PDT) and photothermal therapy (PTT), is a clinically approved, minimally invasive, and highly selective treatment, and has been widely reported for cancer therapy. Under the irradiation of light of a specific wavelength, the photosensitizer (PS) in PDT can cause the increase of intracellular ROS and the photothermal agent (PTA) in PTT can induce photothermal conversion, leading to the tumoricidal effects. In this review, the progress of PT applications in the treatment of bone cancer has been outlined and summarized, and some envisioned challenges and future perspectives have been mentioned. This review provides the current state of the art regarding PDT and PTT in bone cancer and inspiration for future studies on PT.

Recent progress of graphene oxide-based multifunctional nanomaterials for cancer treatment

Background

In the last decade, graphene oxide-based nanomaterials, such as graphene oxide (GO) and reduced graphene oxide (rGO), have attracted more and more attention in the field of biomedicine. Due to the versatile surface functionalization, ultra-high surface area, and excellent biocompatibility of graphene oxide-based nanomaterials, which hold better promise for potential applications than among other nanomaterials in biomedical fields including drug/gene delivery, biomolecules detection, tissue engineering, especially in cancer treatment.

Results

Here, we review the recent progress of graphene oxide-based multifunctional nanomaterials for cancer treatment. A comprehensive and in-depth depiction of unique property of graphene oxide-based multifunctional nanomaterials is first interpreted, with particular descriptions about the suitability for applying in cancer therapy. Afterward, recently emerging representative applications of graphene oxide-based multifunctional nanomaterials in antitumor therapy, including as an ideal carrier for drugs/genes, phototherapy, and bioimaging, are systematically summarized. Then, the biosafety of the graphene oxide-based multifunctional nanomaterials is reviewed.

Conclusions

Finally, the conclusions and perspectives on further advancing the graphene oxide-based multifunctional nanomaterials toward potential and versatile development for fundamental researches and nanomedicine are proposed.

Graphic abstract

Global priority multidrug-resistant pathogens do not resist photodynamic therapy

Microbial drug-resistance demands immediate implementation of novel therapeutic strategies. Antimicrobial photodynamic therapy (aPDT) combines the administration of a photosensitizer (PS) compound with low-irradiance light to induce photochemical reactions that yield reactive oxygen species (ROS). Since ROS react with nearly all biomolecules, aPDT offers a powerful multitarget method to avoid selection of drug-resistant strains. In this study, we assayed photodynamic inactivation under a standardized method, combining methylene blue (MB) as PS and red light, against global priority pathogens. The species tested include Acinetobacter baumannii, Klebsiella aerogenes, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterococcus faecium, Enterococcus faecalis, Staphylococcus aureus, Candida albicans and Cryptococcus neoformans. Our strain collection presents resistance to all tested antimicrobials (>50). All drug-resistant strains were compared to their drug-sensitive counterparts. Regardless of resistance phenotype, MB-aPDT presented species-specific dose-response kinetics. More than 5log₁₀ reduction was observed within less than 75 s of illumination for A. baumannii, E. coli, E. faecium, E. faecalis and S. aureus and within less than 7 min for K. aerogenes, K. pneumoniae, P. aeruginosa, C. albicans and C. neoformans. No signs of correlations in between drug-resistance profiles and aPDT sensitivity were observed. Therefore, MB-aPDT can provide effective therapeutic protocols for a very broad spectrum of pathogens. Hence, we believe that this study represents a very important step to bring aPDT closer to implementation into mainstream medical practices.

Novel anti-HER2 peptide-conjugated theranostic nanoliposomes combining NaYF4:Yb,Er nanoparticles for NIR-activated bioimaging and chemo-photodynamic therapy against breast cancer

Herein, we reported the fabrication of novel peptide-conjugated ligand-targeted nanoliposomes (LTLs) for chemo-photodynamic therapy against HER2-positive breast cancer. The LTL core was utilized for encapsulating doxorubicin (DOX) for chemotherapy, and methylene blue (MB) attached NaYF₄:Yb,Er upconversion nanoparticles (UCNPs) for NIR-activated bioimaging and leveraging its visible emission for photoexciting MB for enhanced photodynamic therapy (PDT). The specificity of our LTLs was achieved by conjugating a newly discovered anti-HER2 peptide screened from a phage display peptide library. The high selectivity of the peptide-conjugated LTLs was confirmed by confocal imaging of SKBR-3 (HER2-positive) and MCF-7 (HER2-negative) breast cancer cell lines, illustrating its target-specific nature. The energy transfer from UCNPs to MB was verified, thus enabling the generation of reactive oxygen species upon activation with a 975 nm laser source (0.60 W cm^-2) under 5 min continuous excitation. A significant decline in the cell viability by 95% was observed using chemo-photodynamic combinational therapy, whereas for chemo-drug alone and PDT alone, the cell proliferation declined by 77% and 84%, respectively. Furthermore, we demonstrated an improved uptake of the LTLs inside a 3D model of SKBR-3 tumor spheroids, where the spheroid cell viability was suppressed by 66% after the use of combinational therapy. Thus, our results suggest great prospective use of theranostic LTLs for breast cancer management.

Chemophototherapy: An Emerging Treatment Option for Solid Tumors

Near infrared (NIR) light penetrates human tissues with limited depth, thereby providing a method to safely deliver non-ionizing radiation to well-defined target tissue volumes. Light-based therapies including photodynamic therapy (PDT) and laser-induced thermal therapy have been validated clinically for curative and palliative treatment of solid tumors. However, these monotherapies can suffer from incomplete tumor killing and have not displaced existing ablative modalities. The combination of phototherapy and chemotherapy (chemophototherapy, CPT), when carefully planned, has been shown to be an effective tumor treatment option preclinically and clinically. Chemotherapy can enhance the efficacy of PDT by targeting surviving cancer cells or by inhibiting regrowth of damaged tumor blood vessels. Alternatively, PDT-mediated vascular permeabilization has been shown to enhance the deposition of nanoparticulate drugs into tumors for enhanced accumulation and efficacy. Integrated nanoparticles have been reported that combine photosensitizers and drugs into a single agent. More recently, light-activated nanoparticles have been developed that release their payload in response to light irradiation to achieve improved drug bioavailability with superior efficacy. CPT can potently eradicate tumors with precise spatial control, and further clinical testing is warranted.

Tumor-Homing and Penetrating Peptide-Functionalized Photosensitizer-Conjugated PEG-PLA Nanoparticles for Chemo-Photodynamic Combination Therapy of Drug-Resistant Cancer

The combination of photodynamic therapy (PDT) and chemotherapy holds great potential in combating drug-resistant cancers. However, the major challenge that lies ahead is how to achieve high coloading capacity for both photosensitizer and chemo-drugs and how to gain efficient delivery of drugs to the drug-resistant tumors. In this study, we prepared a nanovehicle for codelivery of photosensitizer (pyropheophorbide-a, PPa) and chemo-drugs (paclitaxel, PTX) based on the synthesis of PPa-conjugated amphiphilic copolymer PPa-PLA-PEG-PLA-PPa. The obtained nanoparticles (PP NP) exhibited a satisfactory high drug-loading capacity for both drugs. To achieve effective tumor-targeting therapy, the surface of PP NP was decorated with a tumor-homing and penetrating peptide F3. In vitro cellular experiments showed that F3-functionalized PP NP (F3-PP NP) exhibited higher cellular association than PP NP and resulted in the strongest antiproliferation effect. In addition, compared with the unmodified nanoparticles, F3-PP NP exhibited a more preferential enrichment at the tumor site. Pharmacodynamics evaluation in vivo demonstrated that a longer survival time was achieved by the tumor-bearing mice treated with PP NP (+laser) than those treated with chemotherapy only or PDT only. Such antitumor efficacy of combination therapy was further improved following the F3 peptide functionalization. Collectively, these results suggested that targeted combination therapy may pave a promising way for the therapy of drug-resistant tumor.

Resistance of Nonmelanoma Skin Cancer to Nonsurgical Treatments. Part II: Photodynamic Therapy, Vismodegib, Cetuximab, Intralesional Methotrexate, and Radiotherapy

A wide range of treatments is now available for nonmelanoma skin cancer, including 5-fluorouracil, ingenol mebutate, imiquimod, diclofenac, photodynamic therapy, methotrexate, cetuximab, vismodegib, and radiotherapy. All are associated with high clinical and histologic response rates. However, some tumors do not respond due to resistance, which may be primary or acquired. Study of the resistance processes is a broad area of research that aims to increase our understanding of the nature of each tumor and the biologic features that make it resistant, as well as to facilitate the design of new therapies directed against these tumors. In this second article, having covered the topical treatments of nonmelanoma skin cancer, we review resistance to other nonsurgical treatments, such as monoclonal antibodies against basal and squamous cell carcinomas, intralesional chemotherapy, photodynamic therapy, and radiotherapy.

Anthracycline Nano-Delivery Systems to Overcome Multiple Drug Resistance: A Comprehensive Review

Anthracyclines (doxorubicin, daunorubicin, and idarubicin) are very effective chemotherapeutic drugs to treat many cancers; however, the development of multiple drug resistance (MDR) is one of the major limitations for their clinical applications. Nano-delivery systems have emerged as the novel cancer therapeutics to overcome MDR. Up until now, many anthracycline nano-delivery systems have been developed and reported to effectively circumvent MDR both in-vitro and in-vivo, and some of these systems have even advanced to clinical trials, such as the HPMA-doxorubicin (HPMA-DOX) conjugate. Doxil, a DOX PEGylated liposome formulation, was developed and approved by FDA in 1995. Unfortunately, this formulation does not address the MDR problem. In this comprehensive review, more than ten types of developed anthracycline nano-delivery systems to overcome MDR and their proposed mechanisms are covered and discussed, including liposomes; polymeric micelles, conjugate and nanoparticles; peptide/protein conjugates; solid-lipid, magnetic, gold, silica, and cyclodextrin nanoparticles; and carbon nanotubes.

Anti-MDR and antitumoral action of acetylsalicylic acid on leukaemic cells

ASA (acetylsalicylic acid) is an NSAID (non-steroidal anti-inflammatory drug). ASA has gained attention as a potential chemopreventive and chemotherapeutic agent for several neoplasms. The aim of this study was to analyse the possible antitumoural effects of ASA in two erythroleukaemic cell lines, with or without the MDR (multidrug resistance) phenotype. The mechanism of action of different concentrations of ASA were compared in K562 (non-MDR) and Lucena (MDR) cells by analysing cell viability, apoptosis and necrosis, intracellular ROS (reactive oxygen species) formation and bcl-2, p53 and cox-2 gene expression. ASA inhibited the cellular proliferation or induced toxicity in K562 and Lucena cell lines, irrespective of the MDR phenotype. The ASA treatment provoked death by apoptosis and necrosis in K562 cells and only by necrosis in Lucena cells. ASA also showed antioxidant activity in both cell lines. The bcl-2, p53 and cox-2 genes in both cell lines treated with ASA seem to exhibit different patterns of expression. However, normal lymphocytes treated with the same ASA concentrations were more resistant than tumoral cells. The results of this work show that both cell lines responded to treatment with ASA, demonstrating a possible antitumoral and anti-MDR role for this drug.

Methylene blue covalently loaded polyacrylamide nanoparticles for enhanced tumor-targeted photodynamic therapy

The use of targeted nanoparticles (NPs) as a platform for loading photosensitizers enables selective accumulation of the photosensitizers in the tumor area, while maintaining their photodynamic therapy (PDT) effectiveness. Here two novel kinds of methylene blue (MB)-conjugated polyacrylamide (PAA) nanoparticles, MBI-PAA NPs and MBII-PAA NPs, based on two separate MB derivatives, are developed for PDT. This covalent conjugation with the NPs (i) improves the loading of MB, (ii) prevents any leaching of MB from the NPs and (iii) protects the MB from the effects of enzymes in the biological environment. The loading of MB into these two kinds of NPs was controlled by the input amount, resulting in concentrations with optimal singlet oxygen production. For each of the MB-NPs, the highest singlet oxygen production was found for an MB loading of around 11 nmol mg(-1). After attachment of F3 peptide groups, for targeting, each of these NPs was taken up, selectively, by MDA-MB-435 tumor cells, in vitro. PDT tests demonstrated that both kinds of targeted NPs resulted in effective tumor cell kill, following illumination, while not causing dark toxicity.

Apoptosis of ovarian cancer cells induced by methylene blue-mediated sonodynamic action

OBJECTIVE

The present study aims to investigate apoptosis of ovarian cancer cells induced by methylene blue (MB)-mediated sonodynamic therapy (SDT).

METHODS

The MB concentration was kept constant at 100μM and ovarian cancer HO-8910 cells were exposed to ultrasound therapy for 5s with an intensity of 0.46W/cm(2). The cytotoxicity was investigated 24h after MB-mediated sonodynamic action. Apoptosis was analyzed using a flow cytometer with Annexin V-FITC and propidium iodine (PI) staining as well as fluorescence microscopy with Hoechst 33258 staining. Intracellular reactive oxygen species (ROS) level was measured by flow cytometer with 2,7-dichlorodihydrofluorescein diacetate (DCFH-DA) staining.

RESULTS

The cytotoxicity of MB-mediated SDT on HO-8910 cells after MB-mediated SDT was significantly higher than those of other treatments including ultrasound alone, MB alone and sham treatment. Flow cytometric analysis showed a significant increase in the early and late apoptotic cell populations by MB-mediated SDT of HO-8910 cells. Nuclear condensation and increased ROS levels were also found in HO-8910 cells treated by MB-mediated SDT.

CONCLUSIONS

Our findings demonstrated that MB-mediated sonodynamic action significantly induced apoptosis of HO-8910 cells and an increase in intracellular ROS level. This indicates that apoptosis is an important mechanism of cell death induced by MB-mediated SDT. Thus, MB-mediated SDT might be a potential therapeutic strategy for combating ovarian cancer.

Mechanisms of resistance to photodynamic therapy

Photodynamic therapy (PDT) involves the administration of a photosensitizer (PS) followed by illumination with visible light, leading to generation of reactive oxygen species. The mechanisms of resistance to PDT ascribed to the PS may be shared with the general mechanisms of drug resistance, and are related to altered drug uptake and efflux rates or altered intracellular trafficking. As a second step, an increased inactivation of oxygen reactive species is also associated to PDT resistance via antioxidant detoxifying enzymes and activation of heat shock proteins. Induction of stress response genes also occurs after PDT, resulting in modulation of proliferation, cell detachment and inducing survival pathways among other multiple extracellular signalling events. In addition, an increased repair of induced damage to proteins, membranes and occasionally to DNA may happen. PDT-induced tissue hypoxia as a result of vascular damage and photochemical oxygen consumption may also contribute to the appearance of resistant cells. The structure of the PS is believed to be a key point in the development of resistance, being probably related to its particular subcellular localization. Although most of the features have already been described for chemoresistance, in many cases, no cross-resistance between PDT and chemotherapy has been reported. These findings are in line with the enhancement of PDT efficacy by combination with chemotherapy. The study of cross resistance in cells with developed resistance against a particular PS challenged against other PS is also highly complex and comprises different mechanisms. In this review we will classify the different features observed in PDT resistance, leading to a comparison with the mechanisms most commonly found in chemo resistant cells.

Relationships between multidrug resistance (MDR) and stem cell markers in human chronic myeloid leukemia cell lines

The K562 cell line (chronic myeloid leukemia), sensitive to chemotherapy (non-MDR), and the Lucena cell line, resistant to chemotherapy (MDR) were investigated. The results suggest that both cell lines possess CD34+CD38- profiles of hematopoietic stem cell markers. The promoter regions of ABCB1, ABCG2 and ABCC1 genes contain binding sites for the Oct-4 transcripton factor, which is also considered a marker of tumor stem cells. Lucena cells showed an over-expression of the ABCB1 gene and a high expression of the Oct-4, ABCG2 and ABCC1 genes as compared to K562 cells.

Nanoparticle-mediated combination chemotherapy and photodynamic therapy overcomes tumor drug resistance

Tumor drug resistance significantly limits the success of chemotherapy in the clinic. Tumor cells utilize multiple mechanisms to prevent the accumulation of anticancer drugs at their intracellular site of action. In this study, we investigated the anticancer efficacy of doxorubicin in combination with photodynamic therapy using methylene blue in a drug-resistant mouse tumor model. Surfactant-polymer hybrid nanoparticles formulated using an anionic surfactant, Aerosol-OT (AOT), and a naturally occurring polysaccharide polymer, sodium alginate, were used for synchronized delivery of the two drugs. Balb/c mice bearing syngeneic JC tumors (mammary adenocarcinoma) were used as a drug-resistant tumor model. Nanoparticle-mediated combination therapy significantly inhibited tumor growth and improved animal survival. Nanoparticle-mediated combination treatment resulted in enhanced tumor accumulation of both doxorubicin and methylene blue, significant inhibition of tumor cell proliferation, and increased induction of apoptosis. These data suggest that nanoparticle-mediated combination chemotherapy and photodynamic therapy using doxorubicin and methylene blue has significant therapeutic potential against drug-resistant tumors.

Inhibition of human glutathione transferases by multidrug resistance chemomodulatorsin vitro

Reversal of the drug-resistance phenotype in cancer cells usually involves the use of a chemomodulator that inhibits the function of a resistance-related protein. The aim of this study was to investigate the effects of MDR chemomodulators on human recombinant glutathione S-transferase (GSTs) activity. IC50 values for 15 MDR chemomodulators were determined using 1-chloro-dinitrobenzene (CDNB), cumene hydroproxide (CuOOH) and anticancer drugs as substrates. GSTs A1, P1 and M1 were inhibited by O6-benzylguanine (IC50s around 30 microM), GST P1-1 by sulphinpyrazone (IC50 = 66 microM), GST Al-1 by sulphasalazine, and camptothecin (34 and 74 microM respectively), and GST M1-1 by sulphasalazine, camptothecin and indomethacin (0.3, 29 and 30 microM respectively) using CDNB as a substrate. When ethacrynic acid (for GST P1-1), CuOOH (for A1-1) and 1,3-bis (2-chloroethyl)-1-nitrosourea (for GST M1-1) were used as substrates, these compounds did not significantly inhibit the GST isoforms. However, progesterone was a potent inhibitor of GST P1-1 (IC50 = 1.4 microM) with ethacrynic acid as substrate. These results suggest that the target of chemomodulators in vivo could be a specific resistance-related protein.

Methylene blue in photodynamic therapy: From basic mechanisms to clinical applications

Methylene blue (MB) is a molecule that has been playing important roles in microbiology and pharmacology for some time. It has been widely used to stain living organisms, to treat methemoglobinemia, and lately it has been considered as a drug for photodynamic therapy (PDT). In this review, we start from the fundamental photophysical, photochemical and photobiological characteristics of this molecule and evolved to show in vitro and in vivo applications related to PDT. The clinical cases shown include treatments of basal cell carcinoma, Kaposi's Sarcoma, melanoma, virus and fungal infections. We concluded that used together with a recently developed continuous light source (RL50(®)), MB has the potential to treat a variety of cancerous and non-cancerous diseases, with low toxicity and no side effects.

Methylene blue is more toxic to erythroleukemic cells than to normal peripheral blood mononuclear cells: a possible use in chemotherapy

Methylene blue (MB) is a phenothiazine with radio and photosensitizing properties and anti-tumoral activity. Our group has shown that MB was capable of inhibiting the in vitro growth of erythroleukemic cells with multidrug resistance (MDR). However, there are no studies comparing the cytotoxicity of this molecule for normal and tumoral cells. In this work, the cytotoxicity of MB was measured by MTT method in erythroleukemic and melanoma lineages, comparing it with that of normal cells:lymphocytes and melanocytes. MB was more cytotoxic for tumoral cells; however, there was no difference between erytroleukemic cells with or without MDR phenotype. Lymphocytes and erythroleukemic cells were much more sensitive to the effects of MB than melanoma cells and melanocytes. The proliferation of phytohemagglutinin-activated lymphocytes was inhibited when 3H-thymidine incorporation to DNA was measured. We tried to analyze whether the cells were dying, via apoptosis or necrosis, using Anexin-V and propidium iodide. Despite higher levels of Anexin-V, it was not possible to distinguish necrosis from apoptosis, as the fluorescence of MB is in the same channel as propidium iodide. The production of hydrogen peroxide was measured by cytometry using dihydrorhodamine 123 (DHR). Despite the erythroleukemic cells and lymphocytes being capable of producing free radicals, there was no relation between the production and the sensitivity of various cells to MB. Our results suggest that MB should be used as a chemotherapeutic agent, because of its preferential cytotoxic effects over tumor cells, considering the fact that MDR cells are also sensitive, and due to its radio and photosensitizing activities.

Photodynamic toxicity and its prevention by antioxidative agents in Bufo arenarum embryos

In this work we describe an experimental model to evaluate the photodynamic toxicity on amphibian embryos, as well as the protective effect of antioxidants against the lethal oxidative stress induced by photosensitization. Bufo arenarum embryos were treated with 10 mg/l methylene blue (MB) in AMPHITOX solution for 72 h and then irradiated with a red laser or white light for variable times. Both light sources affected the survival of MB-treated animals and lethal effects occurred within the initial 12 h post-irradiation. For white light irradiation, the most effective phototoxic condition in our study, the LD10, 50 and 90 at 6 h post-irradiation corresponded to 13.57, 19.87 and 29.10 J/cm2, respectively. To explore the action of antioxidants against the photogenerated oxidative stress, MB-treated embryos were incubated with 1mM glutathione (GSH) or ascorbic acid (AA) during 48 h before irradiation. For GSH and 21.6 J/cm2 irradiation, the survival increased from 20 to 90%, whereas 100% survival was achieved with AA even after 43.2 J/cm2 irradiation. These results indicate that both the lethal photodynamic effect and its prevention by antioxidants can be evaluated by means of a simple toxicity test employing amphibian embryos.

A light in multidrug resistance: photodynamic treatment of multidrug-resistant tumors

The major drawback of cancer chemotherapy is the development of multidrug-resistant (MDR) tumor cells, which are cross-resistant to a broad range of structurally and functionally unrelated agents, making it difficult to treat these tumors. In the last decade, a number of authors have studied the effects of photodynamic therapy (PDT), a combination of visible light with photosensitizing agents, on MDR cells. The results, although still inconclusive, have raised the possibility of treating MDR tumors by PDT. This review examines the growing literature concerning the responses of MDR cells to PDT, while stressing the need for the development of new photosensitizers that possess the necessary characteristics for the photodynamic treatment of this class of tumor.

The medicinal chemistry of multidrug resistance (MDR) reversing drugs

Multidrug resistance (MDR) is a kind of resistance of cancer cells to multiple classes of chemotherapic drugs that can be structurally and mechanistically unrelated. Classical MDR regards altered membrane transport that results in lower cell concentrations of cytotoxic drug and is related to the over expression of a variety of proteins that act as ATP-dependent extrusion pumps. P-glycoprotein (Pgp) and multidrug resistance protein (MRP1) are the most important and widely studied members of the family that belongs to the ABC superfamily of transporters. It is apparent that, besides their role in cancer cell resistance, these proteins have multiple physiological functions as well, since they are expressed also in many important non-tumoural tissues and are largely present in prokaryotic organisms. A number of drugs have been identified which are able to reverse the effects of Pgp, MRPI and sister proteins, on multidrug resistance. The first MDR modulators discovered and studied in clinical trials were endowed with definite pharmacological actions so that the doses required to overcome MDR were associated with unacceptably high side effects. As a consequence, much attention has been focused on developing more potent and selective modulators with proper potency, selectivity and pharmacokinetics that can be used at lower doses. Several novel MDR reversing agents (also known as chemosensitisers) are currently undergoing clinical evaluation for the treatment of resistant tumours. This review is concerned with the medicinal chemistry of MDR reversers, with particular attention to the drugs that are presently in development.

Multidrug resistance in tumour cells: characterization of the multidrug resistant cell line K562-Lucena 1

Multidrug resistance to chemotherapy is a major obstacle in the treatment of cancer patients. The best characterised mechanism responsible for multidrug resistance involves the expression of the MDR-1 gene product, P-glycoprotein. However, the resistance process is multifactorial. Studies of multidrug resistance mechanisms have relied on the analysis of cancer cell lines that have been selected and present cross-reactivity to a broad range of anticancer agents. This work characterises a multidrug resistant cell line, originally selected for resistance to the Vinca alkaloid vincristine and derived from the human erythroleukaemia cell K562. This cell line, named Lucena 1, overexpresses P-glycoprotein and have its resistance reversed by the chemosensitisers verapamil, trifluoperazine and cyclosporins A, D and G. Furthermore, we demonstrated that methylene blue was capable of partially reversing the resistance in this cell line. On the contrary, the use of 5-fluorouracil increased the resistance of Lucena 1. In addition to chemotherapics, Lucena 1 cells were resistant to ultraviolet A radiation and hydrogen peroxide and failed to mobilise intracellular calcium when thapsigargin was used. Changes in the cytoskeleton of this cell line were also observed.