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Mitocurcumin is a derivative of curcumin, which has been shown to selectively enter mitochondria. Here we describe the anti-tumor efficacy of mitocurcumin in lung cancer cells and its mechanism of action. Mitocurcumin, showed 25-50 fold higher efficacy in killing lung cancer cells as compared to curcumin as demonstrated by clonogenic assay, flow cytometry and high throughput screening assay. Treatment of lung cancer cells with mitocurcumin significantly decreased the frequency of cancer stem cells. Mitocurcumin increased the mitochondrial reactive oxygen species (ROS), decreased the mitochondrial glutathione levels and induced strand breaks in the mitochondrial DNA. As a result, we observed increased BAX to BCL-2 ratio, cytochrome C release into the cytosol, loss of mitochondrial membrane potential and increased caspase-3 activity suggesting that mitocurcumin activates the intrinsic apoptotic pathway. Docking studies using mitocurcumin revealed that it binds to the active site of the mitochondrial thioredoxin reductase (TrxR2) with high affinity. In corroboration with the above finding, mitocurcumin decreased TrxR activity in cell free as well as the cellular system. The anti-cancer activity of mitocurcumin measured in terms of apoptotic cell death and the decrease in cancer stem cell frequency was accentuated by TrxR2 overexpression. This was due to modulation of TrxR2 activity to NADPH oxidase like activity by mitocurcumin, resulting in higher ROS accumulation and cell death. Thus, our findings reveal mitocurcumin as a potent anticancer agent with better efficacy than curcumin. This study also demonstrates the role of TrxR2 and mitochondrial DNA damage in mitocurcumin mediated killing of cancer cells.

Nrf2 is a redox sensitive transcription factor that is involved in the co-ordinated transcription of genes involved in redox homeostasis. But the role of Nrf2 in DNA repair is not investigated in detail. We have employed A549 and MCF7 cells to study the role of Nrf2 on DNA repair by inhibiting Nrf2 using all-trans retinoic acid (ATRA) or by knock down approach prior to radiation exposure (4 Gy). DNA damage and repair analysis was studied by γH2AX foci formation and comet assay. Results suggested that the inhibition of Nrf2 in A549 or MCF7 cells led to significant slowdown in DNA repair as compared to respective radiation controls. The persistence of residual DNA damage even in the presence of free radical scavenger N-acetyl cysteine, suggested that the influence of Nrf2 on DNA repair was not linked to its antioxidant functions. Further, its influence on non-homologous end joining repair pathway was studied by inhibiting both Nrf2 and DNA-PK together. This led to synergistic reduction of survival fraction, indicating that Nrf2 may not be influencing the NHEJ pathway. To investigate the role of homologous recombination repair (HR) pathway, RAD51 foci formation was monitored. There was a significant reduction in the foci formation in cells treated with ATRA or shRNA against Nrf2 as compared to their respective radiation controls. Further, Nrf2 inhibition led to significant reduction in mRNA levels of RAD51. BLAST analysis was also performed on upstream regions of DNA repair genes to identify antioxidant response element and found that many repair genes that are involved in HR pathway may be regulated by Nrf2. Together, these results suggest the involvement of Nrf2 in DNA repair, a hitherto unknown function of Nrf2, putatively through its influence on HR pathway.

Metal-based photosensitizers of the type [Co(L)Cl2] (1), [Ni(L)Cl2] (2) and [Cu(L)]Cl2 (3), where L = N′1,N′3-bis[(E)-thiophen-2-ylmethylidene]benzene-1,3-dicarbohydrazide have been synthesized and characterized by advanced spectroscopic and analytical techniques. The interactions of the complexes with CT DNA were investigated by viscosity analysis, thermal denaturation and absorption spectroscopic techniques. Absorption spectral (Kb = 5.57 × 104 M−1 (1), 4.45 × 104 M−1 (2), 2.8 × 104 M−1 (3)), thermal denaturation and viscosity measurements reveal that 1, 2 and 3 interact with DNA through intercalation. The complexes are photocleavers of SC pUC19 DNA in UV-A light forming 1O2 as the reactive oxygen species. The in-vitro cytotoxicity of 1, 2 and 3 towards MCF-7 tumor cell lines has been evaluated by MTT method, and show an enhancement of cytotoxicity in UV-A light. The results revealed that complex 1 has superior prospectus to act as cancer chemotherapeutic candidate than that of complex 2 and complex 3.

Background Radioresistance is the major impediment in radiotherapy of many cancers including prostate cancer, necessitating the need to understand the factors contributing to radioresistance in tumor cells. In the present study, the role of cellular redox and redox sensitive transcription factor, Nrf2 in the radiosensitivity of prostate cancer cell lines PC3 and DU145, has been investigated. Materials and methods Differential radiosensitivity of PC3 and DU145 cells was assessed using clonogenic assay, flow cytometry, and comet assay. Their redox status was measured using DCFDA and DHR probes. Expression of Nrf2 and its dependent genes was measured by EMSA and real time PCR. Knockdown studies were done using shRNA transfection. Results PC3 and DU145 cells differed significantly in their radiosensitivity as observed by clonogenic survival, apoptosis and neutral comet assays. Both basal and inducible levels of ROS were higher in PC3 cells than that of DU145 cells. DU145 cells showed higher level of basal GSH content and GSH/GSSG ratio than that of PC3 cells. Further, significant increase in both basal and induced levels of Nrf2 and its dependent genes was observed in DU145 cells. Knock-down experiments and pharmacological intervention studies revealed the involvement of Nrf2 in differential radio-resistance of these cells. Conclusion Cellular redox status and Nrf2 levels play a causal role in radio-resistance of prostate cancer cells. General significance The pivotal role Nrf2 has been shown in the radioresistance of tumor cells and this study will further help in exploiting this factor in radiosensitization of other tumor cell types.

The present study was aimed to evaluate the in vivo radioprotective efficacy of quercetin-3-O-rutinoside (PMC-1), the key bioactive constituent flavonoid glycoside isolated from the whole plant of Pilea microphylla was evaluated. In vivo survival studies established the optimum effective dose of PMC-1 at 25 mg/kg/i.p. At the optimum dose, PMC-1 prevented the depletion of endogenous antioxidants in the liver of irradiated mice. In vivo protection towards gastrointestinal tract and haematopoietic system was confirmed by the restoration of radiation-induced reduction in villi height, number of crypt cells and spleen index. PMC-1 also attenuated the radiation-induced apoptosis in spleenocytes significantly. Single cell gel electrophoresis of peripheral blood leukocytes showed inhibition of radiation-induced DNA damage by PMC-1. PMC-1 pretreatment significantly reversed the changes by increasing pro-survival (ERK) and decreasing pro-apoptotic (BAX) gene expressions compared to radiation control. Thus, PMC-1 exhibits protective effects against γ-radiation and the probable mechanism of action involves maintenance of antioxidant enzymes, prophylactic action and inhibition of apoptosis.