HJURP is recruited to double-strand break sites and facilitates DNA repair by promoting chromatin reorganization.

HJURP is overexpressed in several cancer types and strongly correlates with patient survival. However, the mechanistic basis underlying the association of HJURP with cancer aggressiveness is not well understood. HJURP promotes the loading of the histone H3 variant, CENP-A, at the centromeric chromatin, epigenetically defining the centromeres and supporting proper chromosome segregation. In addition, HJURP is associated with DNA repair but its function in this process is still scarcely explored. Here, we demonstrate that HJURP is recruited to DSBs through a mechanism requiring chromatin PARylation and promotes epigenetic alterations that favor the execution of DNA repair. Incorporation of HJURP at DSBs promotes turnover of H3K9me3 and HP1, facilitating DNA damage signaling and DSB repair. Moreover, HJURP overexpression in glioma cell lines also affected global structure of heterochromatin independently of DNA damage induction, promoting genome-wide reorganization and assisting DNA damage response. HJURP overexpression therefore extensively alters DNA damage signaling and DSB repair, and also increases radioresistance of glioma cells. Importantly, HJURP expression levels in tumors are also associated with poor response of patients to radiation. Thus, our results enlarge the understanding of HJURP involvement in DNA repair and highlight it as a promising target for the development of adjuvant therapies that sensitize tumor cells to irradiation.

The MicroRNA miR-696 is regulated by SNARK and reduces mitochondrial activity in mouse skeletal muscle through Pgc1α inhibition.

OBJECTIVE: MicroRNAs (miRNA) are known to regulate the expression of genes involved in several physiological processes including metabolism, mitochondrial biogenesis, proliferation, differentiation, and cell death. METHODS: Using "in silico" analyses, we identified 219 unique miRNAs that potentially bind to the 3'UTR region of a critical mitochondrial regulator, the peroxisome proliferator-activated receptor gamma coactivator (PGC) 1 alpha (Pgc1α). Of the 219 candidate miRNAs, miR-696 had one of the highest interactions at the 3'UTR of Pgc1α, suggesting that miR-696 may be involved in the regulation of Pgc1α. RESULTS: Consistent with this hypothesis, we found that miR-696 was highly expressed in the skeletal muscle of STZ-induced diabetic mice and chronic high-fat-fed mice. C2C12 muscle cells exposed to palmitic acid also exhibited a higher expression of miR-696. This increased expression corresponded with a reduced expression of oxidative metabolism genes and reduced mitochondrial respiration. Importantly, reducing miR-696 reversed decreases in mitochondrial activity in response to palmitic acid. Using C2C12 cells treated with the AMP-activated protein kinase (AMPK) activator AICAR and skeletal muscle from AMPKα2 dominant-negative (DN) mice, we found that the signaling mechanism regulating miR-696 did not involve AMPK. In contrast, overexpression of SNF1-AMPK-related kinase (SNARK) in C2C12 cells increased miR-696 transcription while knockdown of SNARK significantly decreased miR-696. Moreover, muscle-specific transgenic mice overexpressing SNARK exhibited a lower expression of Pgc1α, elevated levels of miR-696, and reduced amounts of spontaneous activity. CONCLUSIONS: Our findings demonstrate that metabolic stress increases miR-696 expression in skeletal muscle cells, which in turn inhibits Pgc1α, reducing mitochondrial function. SNARK plays a role in this process as a metabolic stress signaling molecule inducing the expression of miR-696.

HJURP knockdown disrupts clonogenic capacity and increases radiation-induced cell death of glioblastoma cells.

The Holliday Junction-Recognition Protein (HJURP) was reported as overexpressed in several cancers and also strongly correlated with poor prognosis of patients, especially in glioblastoma (GBM), the most common and deadly type of primary brain tumor. HJURP is responsible for loading the histone H3 variant-the Centromeric Protein A (CENP-A)-at the centromeres in a cell cycle-regulated manner, being required for proper chromosome segregation. Here we investigated HJURP association with survival and radioresistance of different GBM cell lines. HJURP knockdown compromised the clonogenic capacity and severely impaired survival of five distinct GBM cells, while nontumor astrocytes were not affected. U251MG cells showed a robust cell cycle arrest in G2/M phases followed by a drastic increment in cell death after HJURP silencing, while U138MG and U343MG cell lines presented augmented senescence with a comparable increase in cell death. Importantly, we verified that the impact on cell cycle dynamics and clonogenic survival were associated with loss CENP-A at the centromeres. Moreover, radiation resistance was also impacted by HJURP modulation in several GBM cell lines. U87MG, T98G, U138MG, and U343MG cells were all sensitized to ionizing radiation after HJURP reduction. These data reinforce the requirement of HJURP for proliferative capacity and radioresistance of tumor cells, underlining its potential as a promising therapeutic target for GBM.

Myosin Va interacts with the exosomal protein spermine synthase.

Myosin Va (MyoVa) is an actin-based molecular motor that plays key roles in the final stages of secretory pathways, including neurotransmitter release. Several studies have addressed how MyoVa coordinates the trafficking of secretory vesicles, but why this molecular motor is found in exosomes is still unclear. In this work, using a yeast two-hybrid screening system, we identified the direct interaction between the globular tail domain (GTD) of MyoVa and four protein components of exosomes: the WD repeat-containing protein 48 (WDR48), the cold shock domain-containing protein E1 (CSDE1), the tandem C2 domain-containing protein 1 (TC2N), and the enzyme spermine synthase (SMS). The interaction between the GTD of MyoVa and SMS was further validated in vitro and displayed a Kd in the low micromolar range (3.5 ± 0.5 µM). SMS localized together with MyoVa in cytoplasmic vesicles of breast cancer MCF-7 and neuroblastoma SH-SY5Y cell lines, known to produce exosomes. Moreover, MYO5A knockdown decreased the expression of SMS gene and rendered the distribution of SMS protein diffuse, supporting a role for MyoVa in SMS expression and targeting.

The lncRNA RMEL3 protects immortalized cells from serum withdrawal-induced growth arrest and promotes melanoma cell proliferation and tumor growth.

RMEL3 is a recently identified lncRNA associated with BRAFV600E mutation and melanoma cell survival. Here, we demonstrate strong and moderate RMEL3 upregulation in BRAF and NRAS mutant melanoma cells, respectively, compared to melanocytes. High expression is also more frequent in cutaneous than in acral/mucosal melanomas, and analysis of an ICGC melanoma dataset showed that mutations in RMEL3 locus are preponderantly C > T substitutions at dipyrimidine sites including CC > TT, typical of UV signature. RMEL3 mutation does not correlate with RMEL3 levels, but does with poor patient survival, in TCGA melanoma dataset. Accordingly, RMEL3 lncRNA levels were significantly reduced in BRAFV600E melanoma cells upon treatment with BRAF or MEK inhibitors, supporting the notion that BRAF-MEK-ERK pathway plays a role to activate RMEL3 gene transcription. RMEL3 overexpression, in immortalized fibroblasts and melanoma cells, increased proliferation and survival under serum starvation, clonogenic ability, and xenografted melanoma tumor growth. Although future studies will be needed to elucidate the mechanistic activities of RMEL3, our data demonstrate that its overexpression bypasses the need of mitogen activation to sustain proliferation/survival of non-transformed cells and suggest an oncogenic role for RMEL3.

RMEL3, a novel BRAFV600E-associated long noncoding RNA, is required for MAPK and PI3K signaling in melanoma.

Previous work identified RMEL3 as a lncRNA with enriched expression in melanoma. Analysis of The Cancer Genome Atlas (TCGA) data confirmed RMEL3 enriched expression in melanoma and demonstrated its association with the presence of BRAFV600E. RMEL3 siRNA-mediated silencing markedly reduced (95%) colony formation in different BRAFV600E melanoma cell lines. Multiple genes of the MAPK and PI3K pathways found to be correlated with RMEL3 in TCGA samples were experimentally confirmed. RMEL3 knockdown led to downregulation of activators or effectors of these pathways, including FGF2, FGF3, DUSP6, ITGB3 and GNG2. RMEL3 knockdown induces gain of protein levels of tumor suppressor PTEN and the G1/S cyclin-Cdk inhibitors p21 and p27, as well as a decrease of pAKT (T308), BRAF, pRB (S807, S811) and cyclin B1. Consistently, knockdown resulted in an accumulation of cells in G1 phase and subG0/G1 in an asynchronously growing population. Thus, TCGA data and functional experiments demonstrate that RMEL3 is required for MAPK and PI3K signaling, and its knockdown decrease BRAFV600E melanoma cell survival and proliferation.

Role of myosin Va in neuritogenesis of chick dorsal root ganglia nociceptive neurons.

Myosin-Va, widely distributed throughout the developing nervous system, is involved in the transport of vesicles and other intracellular components with its globular tail domain (GTD) implicated in cargo recognition/interaction. Inactivation of myosin-Va in dorsal root ganglia (DRG) neurons of chick embryos, in vitro, decreases the rate of filopodial extension. MYO5A mutant mice have severe neurological defects. We have found that the overexpression of GTD in DRG cultures reduces the number of neurons with long neurites (above fourfold cell body length) and increased the number of neurons with short or no neurites. However, if transfection occurred after the onset of neuritogenesis, this was not seen. In embryo, we characterized the expression pattern of myosin-Va during neuritogenesis of TrkA-positive cells at different stages of chick DRG development. Myosin-Va expression was detected starting from HH25. At this stage, it was present in cells both with and without neurites. The presence of myosin-Va in DRG neurites persisted throughout the last stage analysed (HH34). The data suggest that Myosin Va can participate in embryonic DRG neuritogenesis.

trans-[Ru(NO)Cl(cyclam)](PF6)2 and [Ru(NO)(Hedta)] incorporated in PLGA nanoparticles for the delivery of nitric oxide to B16-F10 cells: cytotoxicity and phototoxicity.

The immobilization and characterization of trans-[Ru(NO)Cl(cyclam)](PF6)2 (cyclam=1,4,8,11-tetraazacyclotetradecane), and [Ru(NO)(Hedta)] (Hedta=ethylenediaminetetraacetic acid) entrapped in poly(d,l-lactic-co-glycolic) acid (PLGA) nanoparticles (NP) using the double emulsification process is described. Scanning electron microscopy and dynamic light scattering revealed that the particles are spherical in shape, have a size distribution between 220 and 840 nm of diameter, and have a tendency to aggregate confirmed by a zeta potential between -3.2 and +3.5 mV. Using this method the loading efficiency was 26% for trans-[Ru(NO)Cl(cyclam)](PF6)2 and 32% for [Ru(NO)(Hedta)]. The release of the complexes from the NPs shows that cyclam-NP and Hedta-NP exhibited a two-phase exponential association release pattern, which was characterized by an initial complex burst during the first 24 h, followed by a slower release phase complex profile, due to a few pores observed in surface of nanoparticles using atomic force microscopy. The in vitro cytotoxic activity of the nitrosyl complexes in solution and incorporated in PLGA nanoparticles on melanoma cancer cells (cell line B16-F10) was investigated. The lower cytotoxicity of trans-[RuCl(cyclam)(NO)]2+ (12.4±2.6%) and [Ru(NO)(Hedta)] (4.0±2.7%) in solution compared to that of trans-[Ru(NO)(NH3)4py]3+ (46.1±6.4%) is consistent with the rate constant release of NO of these complexes (k-NO=6.2×10(-4) s(-1), 2.0×10(-3) s(-1), and 6.0×10(-2) s(-1), respectively); the cytotoxicities are also inhibited in the presence of the NO scavenger carboxy-PTIO. The phototoxicity of these complexes is due to NO release, which lead to 53.8±6.2% of cell death in the presence of trans-[Ru(NO)Cl(cyclam)](PF6)2 and 22.3±5.1% in the presence of [Ru(NO)(Hedta)]. The PLGA nanoparticles loaded with trans-[Ru(NO)Cl(cyclam)](PF6)2 and [Ru(NO)(Hedta)] exerted in vitro a reduced activity against melanoma cells when compared to the activity of complex in solution (nonentrapped in nanoparticles). Blank PLGA nanoparticles did not exhibit cytotoxicity. In the presence of light and of ruthenium nitrosyl complexes or cyclam-NP and Hedta-NP, B16-F10 cells displayed a considerable damage of the surface with rupture of the plasma membrane. This behavior is an indicative of the efficiency of the DDS to deliver the NO from the entrapped complex when photoinduced.

Development, characterization, and photocytotoxicity assessment on human melanoma of chloroaluminum phthalocyanine nanocapsules.

In this work we have developed nanocapsules containing chloroaluminum phthalocyanine (ClAlPc) and assessed their phototoxic action on WM1552C, WM278, and WM1617 human melanoma cell lines. The ClAlPc-loaded nanocapsules were prepared by the nanoprecipitation method and optimized by means of a 2(3) full factorial design. The ClAlPc nanocapsules were characterized by particle size and distribution, zeta potential, morphology, encapsulation efficiency, singlet oxygen production, stability, and phototoxic action on melanoma cells. Both the development and optimization studies revealed that stable colloidal formulations could be obtained by using 1.75% (w/v) soybean lecithin, 1.25% (w/v) Poloxamer 188, 2.5% (v/v) soybean oil, and 0.75% (w/v) poly(D,L-lactide-co-glycolide). The nanocapsules had a mean diameter of 230 nm, homogeneous size distribution (polydispersity index<0.3), and negative zeta potential (about -30 mV). Their morphology was spherical, with evident polymer membrane coating droplet. The encapsulation efficiency was 70%, as expected for hydrophobic drugs, and the nanoencapsulated ClAlPc was able to produce high singlet oxygen quantum yield. ClAlPc nanocapsules exhibited good physical stability over a 12-month period. WM1552C primary melanoma cells were more sensitive (p<0.05) to the phototoxic effect elicited by ClAlPc nanocapsules (0.3 µg ml(-1)) under light irradiation at 20 mJ cm(-2). On the other hand, the cell survival percentage for all the melanoma cell lines treated with the highest light dose (150 mJ cm(-2)) was lower than 10%. In summary, ClAlPc nanoencapsulation could enable application of this hydrophobic photosensitizer in the treatment of malignant melanoma with the use of both low sensitizer drug concentration and light dose.

Expression of soluble and functional full-length human matrix metalloproteinase-2 in Escherichia coli.

Characterization of the matrix metalloproteinase-2 (MMP-2) substrates and understanding of its function remain difficult because up to date preparations containing minor amounts of other eukaryotic proteins that are co-purified with MMP-2 are still used. In this work, the expression of a soluble and functional full-length recombinant human MMP-2 (rhMMP-2) in the cytoplasm of Escherichia coli is reported, and the purification of this metalloproteinase is described. Culture of this bacterium at 18°C culminated in maintenance of the soluble and functional rhMMP-2 in the soluble fraction of the E. coli lysate and its purification by affinity with gelatin-sepharose yielded approximately 0.12mg/L of medium. Western Blotting and zymographic analysis revealed that the most abundant form was the 72-kDa MMP-2, but some gelatinolytic bands corresponding to proteins with lower molecular weight were also detected. The obtained rhMMP-2 was demonstrated to be functional in a gelatinolytic fluorimetric assay, suggesting that the purified rhMMP-2 was correctly folded. The method described here involves fewer steps, is less expensive, and is less prone to contamination with other proteinases and MMP inhibitors as compared to expression of rhMMP-2 in eukaryotic tissue culture. This protocol will facilitate the use of the full-length rhMMP-2 expressed in bacteria and will certainly help researchers to acquire new knowledge about the substrates and biological activities of this important proteinase.

The myosin Va head domain binds to the neurofilament-L rod and modulates endoplasmic reticulum (ER) content and distribution within axons.

The neurofilament light subunit (NF-L) binds to myosin Va (Myo Va) in neurons but the sites of interaction and functional significance are not clear. We show by deletion analysis that motor domain of Myo Va binds to the NF-L rod domain that forms the NF backbone. Loss of NF-L and Myo Va binding from axons significantly reduces the axonal content of ER, and redistributes ER to the periphery of axon. Our data are consistent with a novel function for NFs as a scaffold in axons for maintaining the content and proper distribution of vesicular organelles, mediated in part by Myo Va. Based on observations that the Myo Va motor domain binds to intermediate filament (IF) proteins of several classes, Myo Va interactions with IFs may serve similar roles in organizing organelle topography in different cell types.

Novel primate-specific genes, RMEL 1, 2 and 3, with highly restricted expression in melanoma, assessed by new data mining tool.

Melanoma is a highly aggressive and therapy resistant tumor for which the identification of specific markers and therapeutic targets is highly desirable. We describe here the development and use of a bioinformatic pipeline tool, made publicly available under the name of EST2TSE, for the in silico detection of candidate genes with tissue-specific expression. Using this tool we mined the human EST (Expressed Sequence Tag) database for sequences derived exclusively from melanoma. We found 29 UniGene clusters of multiple ESTs with the potential to predict novel genes with melanoma-specific expression. Using a diverse panel of human tissues and cell lines, we validated the expression of a subset of three previously uncharacterized genes (clusters Hs.295012, Hs.518391, and Hs.559350) to be highly restricted to melanoma/melanocytes and named them RMEL1, 2 and 3, respectively. Expression analysis in nevi, primary melanomas, and metastatic melanomas revealed RMEL1 as a novel melanocytic lineage-specific gene up-regulated during melanoma development. RMEL2 expression was restricted to melanoma tissues and glioblastoma. RMEL3 showed strong up-regulation in nevi and was lost in metastatic tumors. Interestingly, we found correlations of RMEL2 and RMEL3 expression with improved patient outcome, suggesting tumor and/or metastasis suppressor functions for these genes. The three genes are composed of multiple exons and map to 2q12.2, 1q25.3, and 5q11.2, respectively. They are well conserved throughout primates, but not other genomes, and were predicted as having no coding potential, although primate-conserved and human-specific short ORFs could be found. Hairpin RNA secondary structures were also predicted. Concluding, this work offers new melanoma-specific genes for future validation as prognostic markers or as targets for the development of therapeutic strategies to treat melanoma.

In vitro phototoxicity of liposomes and nanocapsules containing chloroaluminum phthalocyanine on human melanoma cell line.

In this study, the photodynamic action of liposomes (LP) and nanocapsules (NC) containing Chloroaluminum phthalocyanine (CIAIPc), on the human melanoma cell (WM 1552C), was assessed. The light source was setup at 672 nm, which corresponds to the maximum absorption wavelength of the CIAIPc. Both colloidal carriers presented size in nanometric scale as well as negative zeta potential. The cellular damage was light dose dependent ranging from 30% of cell death at 70 mJ x cm-2 to 90% of death at 700 mJ x cm(-2). However, the photocytotoxic effect of LP at 70 mJ x cm(-2) was slightly more efficient to induce cellular death than NC formulation. At 140 mJ x cm(-2), and 700 mJ x cm(-2) both nanocarriers were equally efficient to induce cellular damage. Therefore, in the present work, the maximum phototoxic effect was obtained with 700 mJ x cm(-2) of light dose, in combination with 0.29 microg x mL(-1) of CIAIPc encapsulated into LP and NC. The cells were also positive to annexin V, after the PDT treatment with LP and NC, showing that one of the mechanisms of cellular death involved is apoptosis. In summary, the potential of LP and NC as a drug delivery system, in Photodynamic Therapy (PDT) against melanoma, has been confirmed using a lower concentration of the photosensitizer and lower light doses than that applied in current protocols. This is an innovative proposal to treat melanoma cell lines that until now have not received the benefit of the PDT protocol for treatment.

Localization of myosin-Va in subpopulations of cells in rat endocrine organs.

Myosin-Va is a Ca(2+)/calmodulin-regulated unconventional myosin involved in the transport of vesicles, membranous organelles, and macromolecular complexes composed of proteins and mRNA. The cellular localization of myosin-Va has been described in great detail in several vertebrate cell types, including neurons, melanocytes, lymphocytes, auditory tissues, and a number of cultured cells. Here, we provide an immunohistochemical view of the tissue distribution of myosin-Va in the major endocrine organs. Myosin-Va is highly expressed in the pineal and pituitary glands and in specific cell populations of other endocrine glands, especially the parafollicular cells of the thyroid, the principal cells of the parathyroid, the islets of Langerhans of the pancreas, the chromaffin cells of the adrenal medulla, and a subpopulation of interstitial testicular cells. Weak to moderate staining has been detected in steroidogenic cells of the adrenal cortex, ovary, and Leydig cells. Myosin-Va has also been localized to non-endocrine cells, such as the germ cells of the seminiferous epithelium and maturing oocytes and in the intercalated ducts of the exocrine pancreas. These data provide the first systematic description of myosin-Va localization in the major endocrine organs of rat.

Myosin Va phosphorylated on Ser1650 is found in nuclear speckles and redistributes to nucleoli upon inhibition of transcription.

Nuclear actin and nuclear myosins have been implicated in the regulation of gene expression in vertebrate cells. Myosin V is a class of actin-based motor proteins involved in cytoplasmic vesicle transport and anchorage, spindle-pole alignment and mRNA translocation. In this study, myosin-Va, phosphorylated on a conserved serine in the tail domain (phospho-ser(1650) MVa), was localized to subnuclear compartments. A monoclonal antibody, 9E6, raised against a peptide corresponding to phosphoserine(1650) and flanking regions of the murine myosin Va sequence, was immunoreactive to myosin Va heavy chain in cellular and nuclear extracts of HeLa cells, PC12 cells and B16-F10 melanocytes. Immunofluorescence microscopy with this antibody revealed discrete irregular spots within the nucleoplasm that colocalized with SC35, a splicing factor that earmarks nuclear speckles. Phospho-ser(1650) MVa was not detected in other nuclear compartments, such as condensed chromatin, Cajal bodies, gems and perinucleolar caps. Although nucleoli also were not labeled by 9E6 under normal conditions, inhibition of transcription in HeLa cells by actinomycin D caused the redistribution of phospho-ser(1650) MVa to nucleoli, as well as separating a fraction of phospho-ser(1650) MVa from SC35 into near-neighboring particles. These observations indicate a novel role for myosin Va in nuclear compartmentalization and offer a new lead towards the understanding of actomyosin-based gene regulation.

Suppression subtractive hybridization profiles of radial growth phase and metastatic melanoma cell lines reveal novel potential targets.

BACKGROUND: Melanoma progression occurs through three major stages: radial growth phase (RGP), confined to the epidermis; vertical growth phase (VGP), when the tumor has invaded into the dermis; and metastasis. In this work, we used suppression subtractive hybridization (SSH) to investigate the molecular signature of melanoma progression, by comparing a group of metastatic cell lines with an RGP-like cell line showing characteristics of early neoplastic lesions including expression of the metastasis suppressor KISS1, lack of alphavbeta3-integrin and low levels of RHOC. METHODS: Two subtracted cDNA collections were obtained, one (RGP library) by subtracting the RGP cell line (WM1552C) cDNA from a cDNA pool from four metastatic cell lines (WM9, WM852, 1205Lu and WM1617), and the other (Met library) by the reverse subtraction. Clones were sequenced and annotated, and expression validation was done by Northern blot and RT-PCR. Gene Ontology annotation and searches in large-scale melanoma expression studies were done for the genes identified. RESULTS: We identified 367 clones from the RGP library and 386 from the Met library, of which 351 and 368, respectively, match human mRNA sequences, representing 288 and 217 annotated genes. We confirmed the differential expression of all genes selected for validation. In the Met library, we found an enrichment of genes in the growth factors/receptor, adhesion and motility categories whereas in the RGP library, enriched categories were nucleotide biosynthesis, DNA packing/repair, and macromolecular/vesicular trafficking. Interestingly, 19% of the genes from the RGP library map to chromosome 1 against 4% of the ones from Met library. CONCLUSION: This study identifies two populations of genes differentially expressed between melanoma cell lines from two tumor stages and suggests that these sets of genes represent profiles of less aggressive versus metastatic melanomas. A search for expression profiles of melanoma in available expression study databases allowed us to point to a great potential of involvement in tumor progression for several of the genes identified here. A few sequences obtained here may also contribute to extend annotated mRNAs or to the identification of novel transcripts.

trans-[Ru(NO)(NH3)4(py)](BF4)3.H2O encapsulated in PLGA microparticles for delivery of nitric oxide to B16-F10 cells: Cytotoxicity and phototoxicity.

The NO donor trans-[Ru(NO)(NH(3))(4)(py)](BF(4))(3).H(2)O (py=pyridine) was loaded into poly-lactic-co-glycolic acid (PLGA) microparticles using the double emulsification technique. Scanning electron microscopy (SEM) and dynamic light scattering revealed that the particles are spherical in shape, have a diameter of 1600nm, and have low tendency to aggregate. The entrapment efficiency was 25%. SEM analysis of the melanoma cell B16-F10 in the presence of the microparticles containing the complex trans-[Ru(NO)(NH(3))(4)(py)](BF(4))(3).H(2)O (pyMP) showed that the microparticles were adhered to the cell surface after 2h of incubation. The complex with concentrations lower than 1x10(-4)M did not show toxicity in B16-F10 murine cells. The complex in solution is toxic at higher concentrations (>1x10(-3)M), with cell death attributed to NO release following the reduction of the complex. pyMP is not cytotoxic due to the lower bioavailability and availability of the entrapped complex to the medium and its reducing agents. However, pyMP is phototoxic upon light irradiation. The phototoxicity strongly suggests that cell death is due to NO release from trans-[Ru(NO)(NH(3))(4)(py)](3+). This work shows that pyMP can serve as a model for a drug delivery system carrying the NO donor trans-[Ru(NO)(NH(3))(4)(py)](BF(4))(3).H(2)O, which can release NO locally at the tumor cell by irradiation with light only.