Synthesis and photodynamic activity of diaryl-porphyrins characterized by the presence of nitro groups

A panel of nitro substituted 5,15-diaryl-porphyrins, featuring nitro groups either on the phenyl rings or on one of the two free meso-positions, was synthesized. In the former category, compounds 5-(3-nitrophenyl)-15-phenylporphyrin, 5,15-di(3-nitrophenyl)porphyrin and 5-(4-nitrophenyl)-15-phenylporphyrin were obtained following standard procedures by reacting dipyrromethane and aromatic aldehydes. In the latter category, porphyrins 10-nitro-5,15-diphenylporphyrin, 10-nitro-5-(3-methoxyphenyl)-15-phenylporphyrin and 10-nitro-5,15-di(3-methoxyphenyl)porphyrin were generated by nitration of 5,15-diarylporphyrins with trifluoroacetic acid/sodium nitrite under particularly mild conditions. The new molecules bearing one or two nitro-groups were tested as photosensitizers during in vitro experiments on a human colon adenocarcinoma cell line (HCT116), and their effects were compared with those induced by temoporfin, porfimer sodium and by some previously published electron-rich diarylporphyrins. The results, expressed as IC50 values obtained by the MTT test following 24 h incubation with the photosensitizers and 2 h irradiation with a 500 W tungsten-halogen lamp, indicate that the presence of an electron withdrawing substituent, on a meso-position, decreases the photodynamic activity of the compound. Conversely, 5-(3-nitrophenyl)-15-phenylporphyrin, a non symmetrically substituted diarylporphyrin bearing both one electron-deficient and one lipophilic moiety, resulted in high phototoxic activity.

Changes in the two-dimensional electrophoresis pattern of the Parkinson's disease related protein DJ-1 in human SH-SY5Y neuroblastoma cells after dopamine treatment

DJ-1 is a mitochondrial protein linked to Parkinson's disease. DJ-1 has been suggested to have several possible functions, although it has been mainly associated to oxidative stress defence. Changes in the two-dimensional electrophoresis pattern have been thoroughly described as a consequence of oxidative modification of the Cys106 residue. There is accumulating evidence supporting a specific role of DJ-1 in protecting dopaminergic neurons from dopamine itself. By exposing SH-SY5Y human neuroblastoma catecholaminergic cells to dopamine, we observed a specific increase in the most acidic forms in the DJ-1 two-dimensional electrophoresis pattern together with a significant decrease of the most basic spot. Unlike cells exposed to generic oxidative conditions, no additional shift was observed. The results are corroborated by a meta-analysis of the literature showing that in the absence of dopamine treatment the specific acidic form is underrepresented.

The IGFR1 inhibitor NVP-AEW541 disrupts a pro-survival and pro-angiogenic IGF-STAT3-HIF1 pathway in human glioblastoma cells

Inappropriate activation of the IGF (insulin-like growth factor) system has been implicated in the growth and progression of a number of tumor types. Recent evidence indicates a possible role for the IGF system in modulating/mediating tumor cell response to hypoxia, a common occurrence in solid tumors, and particularly in malignant gliomas, causing tumor cells either to die, or to mount a pleiotropic adaptive response that is mainly orchestrated through activation of the hypoxia-inducible transcription factor HIF1. Experimental evidence suggests possible links between IGF- and HIF1-dependent signaling pathways, as well as a role for activated STAT3 in mediating their activities. Interestingly, igf2 is among the target genes transactivated by HIF1, thereby providing the missing link in a hypothetical autocrine self-amplifying circuit. The present study investigates the presence of the IGF-HIF1-VEGF axis in the human glioma cell line U-87 MG, and characterizes its molecular effectors. Our results show that exogenous IGF-I causes IGF1R and STAT3 activation, and increases HIF1alpha protein levels and HIF1 trascriptional activity, inducing VEGF release; a similar response, mediated by IGF-II release, is observed following HIF1alpha stabilization. The existence of an autocrine loop is confirmed by its down-regulation following inactivation of IGF1R (using the IGF1R-specific tyrosine kinase inhibitor NVP-AEW541), STAT3 (transfecting the cells with an expression vector encoding a dominant negative form of STAT3), or HIF1 (using the small molecule inhibitor YC-1). The ability of NVP-AEW541 to block this circuit could be beneficial in suppressing the growth and angiogenic potential of hypoxic glial tumors.

Abstract B253: The IGF1R inhibitor NVP-AEW541 disrupts a pro-survival and pro-angiogenic IGF-Stat3-HIF1 pathway in human glioblastoma cells

Glioblastomas (GBMs) typically develop hypoxic areas within the tumor mass, which for some cells results in necrosis, but for others leads to pleiotropic adaptive changes promoting tumor progression through activation of survival pathways, disruption of apoptosis, increase in invasive potential and neovascularization. The transcription factor HIF1 (hypoxia-inducible factor 1) is known to play a major role in directing this adaptive program, following stabilization of its inducible -subunit under hypoxic conditions; however, HIF1 activity can also be enhanced by oxygen-independent mechanisms upon activation of growth factor receptors and their downstream signal transduction pathways. The present study investigates a) the possible presence of a regulatory loop linking IGF1R and HIF1 in human glioblastoma cells; b) the role played by the signal transducer and activator of transcription 3 (Stat3) in this pathway; and c) the ability of the IGF1R inhibitor NVP-AEW541 (Novartis Pharma, Basel, CH) to disrupt this pathway. We show that activation of IGF1R by its ligand IGF1 causes Stat3 activation, increased levels of HIF1α and increased release of VEGF, the product of one of the major target genes for HIF1 transcriptional activity. Treatment with NVP-AEW541 reverses all these changes, and so does transfection of the cells with a dominant negative form of Stat3. Interestingly, we also observe that IGF-independent activation of HIF1, obtained in the presence of the hypoxia mimic CoCl2, results in IGF1R activation, thereby indicating that a two-way relationship exists between growth factor receptor activation and increase in HIF1 transcriptional activity; NVP-AEW541 treatment significantly reduces both HIF1α protein levels and IGF1R tyrosine-specific phosphorylation in CoCl2-treated cells. Because cells surviving under hypoxic condition often become resistant to radiotherapy and chemotherapy, modulation of the IGF1R-HIF1 pathway could be a viable approach to increase the effectiveness of conventional cytotoxic agents; as GBM typically presents hypoxic areas, this strategy might prove particularly valuable in improving the poor prognosis of patients affected by this tumor type.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B253.

Effect of HIF-1 modulation on the response of two- and three-dimensional cultures of human colon cancer cells to 5-fluorouracil

Tumour hypoxia represents a major obstacle to the success of radiotherapy and chemotherapy. The discovery that the hypoxia-inducible factor 1 (HIF-1) is a master regulator of cellular response to low oxygen led to the concept that inhibiting HIF-1 activity may sensitise hypoxic cancer cells to radiation and cytotoxic drugs. In the present study we investigate the effects of HIF-1 modulation on the response of the human colon adenocarcinoma cell line HCT116 to 5-fluorouracil (5FU). Increasing HIF-1 activity, either by exposing cells to hypoxia or by forced expression of a degradation-resistant form of HIF-1alpha, results in poor cell response to 5FU; conversely, knockdown of HIF-1alpha by RNA interference prevents hypoxia-induced resistance to 5FU. PMX290, a thioredoxin-1 inhibitor, significantly inhibits HIF-1 activity and concomitantly sensitises hypoxic cells to 5FU. These results were confirmed in HCT116 cells grown as three-dimensional spheroids, a model that more closely reproduces the hypoxic environment of solid tumours.

Linalool, a plant-derived monoterpene alcohol, reverses doxorubicin resistance in human breast adenocarcinoma cells

Essential oils from various aromatic plants have been reported to exert chemopreventive and/or antitumor effects. In addition, a number of studies have shown the ability of chemopreventive phytochemicals to increase the sensitivity of cancer cells to conventional anticancer drugs. The success of chemotherapeutic agents is often hindered by the development of drug resistance, with multidrug resistant (MDR) phenotypes reported in a number of tumors, generally involving reduced intracellular drug accumulation due to increased drug efflux by membrane transporters. In the present study, the effects of linalool (LIN), a monoterpene alcohol found in the essential oils from many aromatic plants, on the growth of two human breast adenocarcinoma cell lines, MCF7 WT and multidrug resistant MCF7 AdrR, were investigated, both as a single agent and in combination with doxorubicin (DOX). The results reported here show that LIN only moderately inhibits cell proliferation; interestingly, however, subtoxic concentrations of LIN potentiate DOX-induced cytotoxicity and pro-apoptotic effects in both cell lines. A significant synergism can be observed in MCF7 AdrR cells, which may be due, at least in part, to the ability of LIN to increase DOX accumulation and to induce a decrease in Bcl-xL levels. In summary, the results of the present study suggest that LIN may improve the therapeutic index of anthracyclines in the management of breast cancer, especially in MDR tumors.

The nitroxide Tempol modulates anthracycline resistance in breast cancer cells

The occurrence of multidrug resistance (MDR) is the major obstacle to successful anthracycline-based cancer chemotherapy. In the present study, we assessed the effects of Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, TPL), a piperidine nitroxide with growth-inhibitory properties in tumor cell lines, on a number of molecular mechanisms involved in the resistance of human breast adenocarcinoma cell lines to doxorubicin (DOX). Cytotoxicity studies in MCF-7 wildtype and their MDR variant MCF-7 Adr(R) cells showed a synergistic effect between TPL and DOX when exposure to TPL preceded or was simultaneous with DOX treatment in MCF-7 Adr(R) cells. This effect of TPL seems to be due in part to its ability to increase peroxide levels and to deplete cellular glutathione pools. In addition, TPL increased DOX accumulation in MCF-7 Adr(R) cells by interfering with P-glycoprotein-mediated DOX efflux, as evidenced using a specific antibody that recognizes the active form of the protein. TPL was also found to affect the expression levels of proteins involved in response to drug treatment (e.g., p53, bcl2, bax, p21). Taken together, our results indicate that TPL is a potential new agent that may improve the clinical effect of DOX in tumors exhibiting a MDR phenotype.

Photodynamic effects of porphyrin and chlorin photosensitizers in human colon adenocarcinoma cells

Photodynamic therapy (PDT) is a cancer treatment involving systemic administration of a tumor-localizing photosensitizer; this, when activated by the appropriate wavelength of light, interacts with molecular oxygen to form a toxic, short-lived species known as singlet oxygen, which is thought to mediate cellular death. Photofrin, a complex mixture of porphyrin oligomers has recently received FDA approval for the photodynamic treatment of esophageal and endobronchial carcinoma, but its photodynamic and toxicity profiles are far from ideal. In the present study we evaluated a series of porphyrin-based PSs, some of which newly synthesized by our group, with the aim to identify agents with more favorable characteristics. For the most effective compounds in the porphyrin series, chlorin analogs were also synthesized; for comparison, the screening also included Photofrin. Cytotoxicity studies were performed by the MTT assay on a cultured human colon adenocarcinoma cell line (HCT116); the results indicate that the 3,4,5-trimethoxyphenyl, 3OH- and 4OH-phenyl, and the sulfonamidophenyl derivatives are significantly more potent than Photofrin. Flow cytometric studies and fluorescence microscopy indicate that in PDT-treated HCT116 cells death occurs mainly by apoptosis. In summary, novel PSs described in the present study, belonging both to the porphyrin and chlorin series, have proven more effective than Photofrin in killing colon cancer cells in vitro; extending these observation to in vivo models, particularly regarding the deeper reaching chlorin derivatives, might lead to significant advances in the development of tumor PDT.

The piperidine nitroxide Tempol potentiates the cytotoxic effects of temozolomide in human glioblastoma cells

Temozolomide (TMZ) is a methylating agent with promising antitumor efficacy for the treatment of melanomas and intermediate-grade gliomas. Unfortunately, its use in the management of high-grade gliomas (glioblastomas) is limited by multifaceted resistance mechanisms. The aim of this study was to evaluate the possibility to improve the cytotoxic response of two human glioblastoma cell lines, U87MG and U373MG, to TMZ by the use of Tempol (TPL), a low molecular weight piperidine nitroxide that has been shown to inhibit in vitro and in vivo growth of murine glioma cells. To this purpose, we used two different schedules for the combined exposure to the two agents. Our data indicate that TPL synergizes with TMZ in both U87MG and U373MG cells for both schedules tested. This effect is accompanied by an increase in apoptotic cell death and by changes in the expression of genes involved in control of the apoptotic process. TPL was also observed to induce a cell-type specific decrease in GSH levels and in GSH-related enzyme activities that could contribute to its sensitizing effect.

Molecular determinants of intrinsic resistance to doxorubicin in human cancer cell lines

Intrinsic or acquired drug resistance poses a major challenge to the success of chemotherapy in the clinical management of human cancers. While acquired multidrug resistance (MDR), whereby cells become refractory to multiple drugs, has been extensively investigated, the mechanistic basis for intrinsic resistance remains elusive, so that this condition is largely unmanageable in the clinical setting. To address this issue, we have assessed the effects of the anticancer agent doxorubicin (DX) on a panel of human tumor cell lines originally derived from untreated patients and tried to establish a correlation between cell response and a number of parameters, including drug accumulation and/or drug efflux; differences in expression and/or subcellular distribution of proteins involved in the apoptotic process (e.g., p53, Bcl-2, Bax) and intracellular signal transducers (PKCalpha); changes in key detoxification processes. Based on our results, 'classic' multispecific drug transporters (P-glycoprotein, MDR-related proteins) only seem to play a minor role in the intrinsically resistant phenotype, whereas LRP may contribute to resistance in non-small cell lung carcinoma (NSCLC) cells. No relationship was observed between drug response and expression and/or subcellular localization of apoptosis-related proteins; however, increased PKCalpha levels are associated with poor drug response, suggesting that one or more substrates of this enzyme may be relevant to the resistant phenotype. Finally, overactive glutathione-recycling pathways may contribute to DX resistance.

Study of in vitro and in vivo effects of the piperidine nitroxide Tempol--a potential new therapeutic agent for gliomas

The identification of novel therapeutic agents for the management of malignant gliomas represents an area of active research. Here, we show that Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl; TPL), a stable nitroxide free radical, inhibits the growth of C6 glioma cells both in vitro and in vivo. Morphological features of apoptosis were apparent in C6 cells following in vitro treatment with TPL. Cell death was preceded by dose-dependent increase in p21(WAF1/CIP1) expression, without apparent stabilisation of the TP53 gene product. When C6 cells were grown as xenografts in nude mice, treatment with TPL induced a significant dose-dependent decrease in tumour growth, without signs of general or organ toxicity. Tumours from treated mice showed an increase in the number of apoptotic cells and a decrease in the rate of neo-vascularisation compared with tumours from control mice. Our findings suggest a potential use for TPL as a novel antiproliferative agent for the treatment of malignant gliomas.

Nitroxide TEMPOL impairs mitochondrial function and induces apoptosis in HL60 cells

The piperidine nitroxide TEMPOL induces apoptosis in a number of tumor cell lines through free radical-dependent mechanisms. As mitochondria play a major role in apoptosis as both source and target for free radicals, the present study focuses on mitochondrial effects of TEMPOL in a human promyelocytic leukemic cell line (HL-60). On 24-h exposure to TEMPOL, the following alterations were observed: 1) decrease in both the intracellular and mitochondrial glutathione pools; 2) impairment of oxidative phosphorylation; and 3) decrease in mitochondrial membrane potential. In addition, TEMPOL was found to specifically target complex I of the respiratory chain, with minor effects on complexes II and IV, suggesting that mitochondrial effects might play a role in TEMPOL-induced oxidative stress and apoptosis, and that TEMPOL might sensitize tumor cells to the pro-apoptotic effects of cytotoxic agents.

Resistance of human leukemic cell lines to 1-beta-D-arabinofuranosylcytosine: characterization of an experimental model

1-beta-D-arabinofuranosylcytosine (ara-C) is an antimetabolite used for the treatment of acute myelogenous leukemia. The ability of ara-C to kill neoplastic cells has been correlated to the induction of apoptosis. The clinical use of ara-C is limited by the development of drug resistance. Alterations in drug-induced apoptosis play a critical role in ara-C resistance. In particular, the proto-oncogene bcl-2 has been implicated in this phenomenon. To better understand the molecular basis of the role of bcl-2 in ara-C resistance, we investigated the relationship between the cytotoxic effect of ara-C, the expression levels and the subcellular localization of bcl-2 in three human leukemic cell lines (HL-60, KG1, J111). We have also evaluated the effects of ara-C on the J111 leukemic cell line (showing the lowest levels of Bcl-2 and the highest sensitivity to ara-C) overexpressing the bcl-2 oncogene. The model we developed here will allow further studies on the role of post-translational events involving bcl-2 (such as translocation and/or phosphorylation) in the cellular response to ara-C treatment.

Extrinsic visual and auditory cortical connections in the 4-day-old kitten

The major extrinsic projections to and from the visual and auditory cortical areas were examined in 4-day-old kittens using axonal transport of horseradish peroxidase (HRP) and/or tritiated proline. Six different afferent and seven different efferent systems were studied; all 13 were present by postnatal day 4 as revealed by either HRP, or autoradiography alone, or these two techniques combined. Topographical projections were found for the corticopetal pathways from the thalamus and claustrum and for the corticofugal pathways to the thalamus, claustrum, striatum, and tectum, as well as for the inter- and intrahemispheric pathways. No topographical relations were seen in projections to the cortex from the basal ganglia or the lower brainstem. The results of the present study indicate that most or all of the major extrinsic connections of the kitten's visual and auditory cortical areas are present neonatally, and that both the cells of origin and the axonal targets are arranged topographically much like those of adult cats. However, the origins of callosal projections from visual cortex are more widespread in newborn kittens than in adult cats. In addition, the laminar arrangements of the kitten's corticocortical connections differ from those of adult cats in a number of details. The results suggest that the sparing of some visual and auditory functions after neonatal lesions occurs despite the fact that the cortical areas removed have formed extrinsic connections.

Unilateral ablation of the auditory cortex in the cat impairs complex sound localization

Unilateral ablation of the auditory cortex in the cat results in a profound deficit in attending to stimuli on the side contralateral to the lesion. The deficit is also manifested in an abnormal perception of left-right pulse pairs when the pulse which leads by a few milliseconds is contralateral to the damaged hemisphere.

Unilateral lesions of the auditory cortex and the 'precedence effect'

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