PARG is essential for Polθ-mediated DNA end-joining by removing repressive poly-ADP-ribose marks.

DNA polymerase theta (Polθ)-mediated end-joining (TMEJ) repairs DNA double-strand breaks and confers resistance to genotoxic agents. How Polθ is regulated at the molecular level to exert TMEJ remains poorly characterized. We find that Polθ interacts with and is PARylated by PARP1 in a HPF1-independent manner. PARP1 recruits Polθ to the vicinity of DNA damage via PARylation dependent liquid demixing, however, PARylated Polθ cannot perform TMEJ due to its inability to bind DNA. PARG-mediated de-PARylation of Polθ reactivates its DNA binding and end-joining activities. Consistent with this, PARG is essential for TMEJ and the temporal recruitment of PARG to DNA damage corresponds with TMEJ activation and dissipation of PARP1 and PAR. In conclusion, we show a two-step spatiotemporal mechanism of TMEJ regulation. First, PARP1 PARylates Polθ and facilitates its recruitment to DNA damage sites in an inactivated state. PARG subsequently activates TMEJ by removing repressive PAR marks on Polθ.

Discovery of a small-molecule inhibitor that traps Polθ on DNA and synergizes with PARP inhibitors.

The DNA damage response (DDR) protein DNA Polymerase θ (Polθ) is synthetic lethal with homologous recombination (HR) factors and is therefore a promising drug target in BRCA1/2 mutant cancers. We discover an allosteric Polθ inhibitor (Polθi) class with 4-6 nM IC50 that selectively kills HR-deficient cells and acts synergistically with PARP inhibitors (PARPi) in multiple genetic backgrounds. X-ray crystallography and biochemistry reveal that Polθi selectively inhibits Polθ polymerase (Polθ-pol) in the closed conformation on B-form DNA/DNA via an induced fit mechanism. In contrast, Polθi fails to inhibit Polθ-pol catalytic activity on A-form DNA/RNA in which the enzyme binds in the open configuration. Remarkably, Polθi binding to the Polθ-pol:DNA/DNA closed complex traps the polymerase on DNA for more than forty minutes which elucidates the inhibitory mechanism of action. These data reveal a unique small-molecule DNA polymerase:DNA trapping mechanism that induces synthetic lethality in HR-deficient cells and potentiates the activity of PARPi.

4'-Ethynyl-2'-Deoxycytidine (EdC) Preferentially Targets Lymphoma and Leukemia Subtypes by Inducing Replicative Stress.

Anticancer nucleosides are effective against solid tumors and hematological malignancies, but typically are prone to nucleoside metabolism resistance mechanisms. Using a nucleoside-specific multiplexed high-throughput screening approach, we discovered 4'-ethynyl-2'-deoxycytidine (EdC) as a third-generation anticancer nucleoside prodrug with preferential activity against diffuse large B-cell lymphoma (DLBCL) and acute lymphoblastic leukemia (ALL). EdC requires deoxycytidine kinase (DCK) phosphorylation for its activity and induced replication fork arrest and accumulation of cells in S-phase, indicating it acts as a chain terminator. A 2.1Å co-crystal structure of DCK bound to EdC and UDP reveals how the rigid 4'-alkyne of EdC fits within the active site of DCK. Remarkably, EdC was resistant to cytidine deamination and SAMHD1 metabolism mechanisms and exhibited higher potency against ALL compared to FDA approved nelarabine. Finally, EdC was highly effective against DLBCL tumors and B-ALL in vivo. These data characterize EdC as a pre-clinical nucleoside prodrug candidate for DLBCL and ALL.

Polλ promotes microhomology-mediated end-joining.

The double-strand break (DSB) repair pathway called microhomology-mediated end-joining (MMEJ) is thought to be dependent on DNA polymerase theta (Polθ) and occur independently of nonhomologous end-joining (NHEJ) factors. An unresolved question is whether MMEJ is facilitated by a single Polθ-mediated end-joining pathway or consists of additional undiscovered pathways. We find that human X-family Polλ, which functions in NHEJ, additionally exhibits robust MMEJ activity like Polθ. Polλ promotes MMEJ in mammalian cells independently of essential NHEJ factors LIG4/XRCC4 and Polθ, which reveals a distinct Polλ-dependent MMEJ mechanism. X-ray crystallography employing in situ photo-induced DSB formation captured Polλ in the act of stabilizing a microhomology-mediated DNA synapse with incoming nucleotide at 2.0 Å resolution and reveals how Polλ performs replication across a DNA synapse joined by minimal base-pairing. Last, we find that Polλ is semisynthetic lethal with BRCA1 and BRCA2. Together, these studies indicate Polλ MMEJ as a distinct DSB repair mechanism.

Carbon nano-dot for cancer studies as dual nano-sensor for imaging intracellular temperature or pH variation.

Cellular temperature and pH govern many cellular physiologies, especially of cancer cells. Besides, attaining higher cellular temperature plays key role in therapeutic efficacy of hyperthermia treatment of cancer. This requires bio-compatible, non-toxic and sensitive probe with dual sensing ability to detect temperature and pH variations. In this regard, fluorescence based nano-sensors for cancer studies play an important role. Therefore, a facile green synthesis of orange carbon nano-dots (CND) with high quantum yield of 90% was achieved and its application as dual nano-sensor for imaging intracellular temperature and pH was explored. CND was synthesized from readily available, bio-compatible citric acid and rhodamine 6G hydrazide using solvent-free and simple heating technique requiring purification by dialysis. Although the particle size of 19 nm (which is quite large for CND) was observed yet CND exhibits no surface defects leading to decrease in photoluminescence (PL). On the contrary, very high fluorescence was observed along with good photo-stability. Temperature and pH dependent fluorescence studies show linearity in fluorescence intensity which was replicated in breast cancer cells. In addition, molecular nature of PL of CND was established using pH dependent fluorescence study. Together, the current investigation showed synthesis of highly fluorescent orange CND, which acts as a sensitive bio-imaging probe: an optical nano-thermal or nano-pH sensor for cancer-related studies.

Synthesis of Bioactive Diarylheptanoids from Alpinia officinarum and Their Mechanism of Action for Anticancer Properties in Breast Cancer Cells.

An efficient synthesis of the Alpinia officinarum-derived diarylheptanoids, viz., enantiomers of a ß-hydroxyketone (1) and an α,ß-unsaturated ketone (2) was developed starting from commercially available eugenol. Among these, compound 2 showed a superior antiproliferative effect against human breast adenocarcinoma MCF-7 cells. Besides reducing clonogenic cell survival, compound 2 dose-dependently increased the sub G1 cell population and arrested the G2-phase of the cell cycle, as revealed by flow cytometry. Mechanistically, compound 2 acts as an intracellular pro-oxidant by generating copious amounts of reactive oxygen species. Compound 2 also induced both loss of mitochondrial membrane potential (MMP) as well as lysosomal membrane permeabilization (LMP) in the MCF-7 cells. The impaired mitochondrial and lysosomal functions due to reactive oxygen species (ROS)-generation by compound 2 may contribute to its apoptotic property.

Thiol antioxidants sensitize malabaricone C induced cancer cell death via reprogramming redox sensitive p53 and NF-κB proteins in vitro and in vivo.

Specific focus on "redox cancer therapy" by targeting drugs to redox homeostasis of the cancer cells is growing rapidly. Recent clinical studies showed that N-acetyl cysteine (NAC) treatment significantly decreased the metabolic heterogeneity and reduced Ki67 (a proliferation marker) with simultaneous enhancement in apoptosis of tumor cells in patients. However, it is not yet precisely known how thiol antioxidants enhance killing of cancer cells in a context dependent manner. To this end, we showed that a dietary compound, malabaricone C (mal C) generated copious amounts of reactive oxygen species (ROS) and also reduced GSH level in lung cancer cells. Paradoxically, although antioxidants supplementation reduced mal C-induced ROS, thiol-antioxidants (NAC/GSH) restored intracellular GSH level but enhanced DNA DSBs and apoptotic cell death induced by mal C. Our results unraveled two tightly coupled biochemical mechanisms attributing this sensitization process by thiol antioxidants. Firstly, thiol antioxidants enable the "catechol-quinone redox cycle" of mal C and ameliorate ROS generation and bio-molecular damage (DNA and protein). Secondly, thiol antioxidants cause rapid glutathionylation of transcription factors [p53, p65 (NF-κB) etc.], oxidized by mal C, and abrogates their nuclear sequestration and transcription of the anti-apoptotic genes. Furthermore, analyses of the mitochondrial fractions of p53 expressing and silenced cells revealed that cytoplasmic accumulation of glutathionylated p53 (p53-SSG) triggers a robust mitochondrial death process. Interestingly, mutation of redox sensitive cysteine residues at 124, 141 and 182 position in p53 significantly reduces mal C plus NAC mediated sensitization of cancer cells. The preclinical results, in two different tumor models in mice, provides further support our conclusion that NAC is able to sensitize mal C induced suppression of tumor growth in vivo.

A bis-resorcinol resveratrol congener prevents indomethacin-induced gastric ulceration by inhibiting TNF-α as well as NF-κB and JNK pathways.

The cytoprotective action of the synthetic resveratrol (Resv) congener, E-3,3',5,5'-tetrahydroxystilbene (designated as HST-1) against indomethacin (IND)-induced stomach ulceration has been established using a mice model. HST-1 reversed the adverse effects of IND on several inflammatory (myeloperoxidase, cytokines, adhesion molecules etc.) and ulcer-healing (cyclooxygenases, prostaglandin, growth factors and their receptors etc.) parameters in mice. More importantly, HST-1 down-regulated TNF-α and the TNF-α-mediated activation of NF-κB and JNK/MAPK pathways that are the key determinants in the IND-gastropathy. The effect of HST-1 on all these factors was significantly better than that of Resv, misoprostol, and omeprazole. HST-1 also did not induce small intestinal mucosal injury, unlike some of the proton pump inhibitors. On the other hand, Resv reduced activation of the prosurvival ERK1/2 pathway that may explain its contraindicative property in the gastrointestinal tract.

Salinomycin reduces growth, proliferation and metastasis of cisplatin resistant breast cancer cells via NF-kB deregulation.

Cisplatin (cis-diamminedichloro-platinum, CDDP), is a widely used platinum compound for various solid tumors including breast cancer as first line of therapy. However, its positive effects are limited due to acquired drug resistance and severe side effects in non-malignant tissue, especially due to dose-dependent nephro- and/or neuro-toxicity. Salinomycin is an antibiotic with coccidiostat effect and has shown anticancer efficacy against various cancer cells with selectivity in targeting cancer stem cells. In the present study, anticancer efficacy and mechanism of action of salinomycin in CDDP-resistant human breast cancer (MCF7DDP) cells has been examined. Initially, we generated CDDP-resistant cells by a new protocol followed by checking the anticancer efficacy of salinomycin through MTT, clonogenic, annexin-V/PI and sub-G1 assay. Our results demonstrated that salinomycin diminished both cell proliferation and metastatic migration of MCF7DDP cells. Salinomycin also induced mitochondrial dysfunction in CDDP-resistant breast cancer cells. The analysis of nuclear translocation of pro-survival transcription factors by western blotting showed a distinct role of p65 (NF-κB) in CDDP-mediated resistance in breast cancer. Salinomycin abrogated nuclear translocation of NF-κB proteins and also caused a concurrent reduction in NF-κB regulated expression of pro-survival proteins e.g., survivin, XIAP and BCL-2 in CDDP-resistant cells. These results suggest that a follow up treatment of salinomycin may be promising strategy against CDDP resistant breast cancer cells and metastasis and help in reducing CDDP-induced side effects.

Spice-derived phenolic, malabaricone B induces mitochondrial damage in lung cancer cells via a p53-independent pathway.

The spice-derived phenolic, malabaricone B (mal B) showed selective toxicity to human lung cancer (A549), malignant melanoma (A375) and T cell leukemia (Jurkat) cell lines, without showing toxicity to human normal intestinal (INT407), human kidney (HEK293) and lung fibroblast (WI-38) cells. Among the chosen cancer cell lines, mal B showed maximum cytotoxicity to the A549 cells (IC50 = 8.1 ± 1.0 µM), which was significantly better than that of curcumin (IC50 = 26.7 ± 3.1 µM). Further morphological studies by phase contrast microscopy and a clonogenic assay of the A549 cells revealed that mal B treatment increased the number of shrinking cells and also abolished the clonal proliferation of the cells. Mal B induced apoptotic cell death was confirmed by DNA laddering and quantified by cytoplasmic oligonucleosome formation and annexin V/PI assays. The mal B-induced apoptosis was mediated by an increase in the intracellular reactive oxygen species (ROS), because the cell-permeable antioxidants, N-acetylcysteine (NAC) and PEG-SOD, strongly inhibited its cytotoxicity to the A549 cells. Mal B increased the BAX level while simultaneously decreasing the BCL-2 and BCL-XL levels in the A549 cells, triggering the mitochondrial apoptotic pathway as revealed from the release of cytochrome c, and the activation of caspase-9 and caspase-3. Pre-treatment of cells with caspase-9, caspase-3 and pan-caspase inhibitors made them more resistant to mal B treatment. This effect of mal B was strongly associated with the concomitant decrease in anti-apoptotic (IAP1, IAP2 and survivin), angiogenic (growth factors) and cancer invasiveness (matrix metalloproteinase-9, COX-2) modulating proteins. Mal B induced cytotoxicity was unaffected by the shRNA-mediated depletion of p53 in A549 cells. Most importantly, mal B sensitized a wide range of human carcinoma cells regardless of their p53 status. Finally, mal B (100 mg kg-1) also inhibited lung tumor (xenograft) growth in SCID mice.

Resveratrol analogue, trans-4,4'-dihydroxystilbene (DHS), inhibits melanoma tumor growth and suppresses its metastatic colonization in lungs.

The prevalence of melanoma and the lack of effective therapy for metastatic melanoma warrant extensive and systematic evaluations of small molecules in cellular and pre-clinical models. We investigated, herein, the antitumor and anti-metastatic effects of trans-4,4'-dihydroxystilbene (DHS), a natural product present in bark of Yucca periculosa, using in vitro and in vivo melanoma murine models. DHS showed potent melanoma cytotoxicity, as determined by MTT and clonogenic assay. Further, DHS induced cytotoxicity was mediated through apoptosis, which was assessed by annexin V-FITC/PI, sub-G1 and caspase activation assays. In addition, DHS inhibited cell proliferation by inducing robust cell cycle arrest in G1-phase. Imperatively, these inhibitory effects led to a significant reduction of melanoma tumor in pre-clinical murine model. DHS also inhibited cell migration and invasion of melanoma cells, which were examined using wound healing and Transwell migration/invasion assays. Mechanistically, DHS modulated the expressions of several key metastasis regulating proteins e.g., MMP-2/9, N-cadherin, E-cadherin and survivin. We also showed the anti-metastatic effect of DHS in a melanoma mediated lung metastasis model in vivo. DHS significantly reduced large melanoma nodule formation in the parenchyma of lungs. Therefore, DHS may represent a promising natural drug in the repertoire of treatment against melanoma tumor growth and metastasis.

Syntheses and photodynamic activity of some glucose-conjugated BODIPY dyes.

The syntheses of three water-soluble glucose-conjugated BODIPY dyes with different wavelength emissions and studies of their photodynamic therapeutic (PDT) action on human lung cancer A549 cell line are disclosed. Amongst the chosen compounds, the BODIPY dye 4 possessing a glycosylated styryl moiety at the C-3 position showed best PDT property against the A549 cell line. In particular, it induced reactive oxygen species-mediated caspase-8/caspase-3-dependent apoptosis as revealed from the increased sub G1 cell population and changes in cell morphology. These results along with its localization in the endoplasmic reticulum, as revealed by confocal microscopy suggested that mitochondria may not be directly involved in the photo-cytotoxicity of 4. Compound 4 did not induce any dark toxicity to the A549 cells, and was non-toxic to normal lung cells.

DNA damage dependent activation of checkpoint kinase-1 and mitogen-activated protein kinase-p38 are required in malabaricone C-induced mitochondrial cell death.

BACKGROUND: Given that lung cancer is the second leading cause of cancer-related deaths with low survival rates, the project was aimed to formulate an efficient drug with minimum side effects, and rationalize its action mechanistically. METHODS: Mitochondria deficient cells, shRNA-mediated BCL2 and ATM depleted cells and pharmacological inhibition of DNA-damage response proteins were employed to explore the signaling mechanism governed between nucleus and mitochondria in response to mal C. RESULTS: Mal C decreased cell viability in three lung carcinoma cells, associated with DNA damage, p38-MAPK activation, imbalance in BAX/BCL2 expression, mitochondrial dysfunction and cytochrome-c release. Mitochondria depletion and p38-MAPK inhibition made A549 cells extremely resistant, but BCL2 knock-down partially sensitized the cells to mal C treatment. The mal C-induced apoptosis in A549 cells was initiated by DNA single strand breaks that led to double strand breaks (DSBs). DSB generation paralleled the induction of ATM- and ATR-mediated CHK1 phosphorylation. ATM silencing and ATR inhibition partially attenuated the mal C-induced p38-MAPK activation, CHK1 phosphorylation and apoptosis, which were completely suppressed by CHK1 inhibition. CONCLUSIONS: Mal C activates the ATM-CHK1-p38 MAPK cascade to cause mitochondrial cell death in lung carcinoma cells. GENERAL SIGNIFICANCE: Given that mal C has appreciable natural abundance and is non-toxic to mice, further in vivo evaluation would help in establishing its anti-cancer property.

Rational design of boradiazaindacene (BODIPY)-based functional molecules.

Three boradiazaindacene (BODIPY) dyes with different-coloured (greenish-yellow, orange and red) fluorescence and good Stokes shifts were synthesised starting from the greenish-yellow BODIPY dye PM546. The high Stokes shifts of the dyes are due to the release of the steric strain in their excited states relative to that in the highly twisted ground states. One of these compounds might be a useful water-soluble fluorophore, whereas the other two are promising H(+) sensors.

Molecular mechanism of the anti-inflammatory activity of a natural diarylnonanoid, malabaricone C.

The spice-derived phenolic, malabaricone C (mal C), has recently been shown to accelerate healing of the indomethacin-induced gastric ulceration in mice. In this study, we explored its anti-inflammatory activity and investigated the underlying mechanism of the action. Mal C suppressed the microvascular permeability and the levels of tumor necrosis factor-α, interleukin-1ß, and nitric oxide in the lipopolysaccharide (LPS)-administered mice. At a dose of 10 mg/kg, it showed anti-inflammatory activity comparable to that of omeprazole (5 mg/kg) and dexamethasone (50 mg/kg). It also reduced the expression and activities of inducible nitric oxide synthase, cyclooxygenase-2, as well as the pro- vs anti-inflammatory cytokine ratio in the LPS-treated RAW macrophages. Mal C was found to inhibit LPS-induced NF-kB activation in RAW 264.7 cells by blocking the MyD88-dependent pathway. Mal C suppressed NF-κB activation and iNOS promoter activity, which correlated with its inhibitory effect on IκB phosphorylation and degradation, and NF-κB nuclear translocation, in the LPS-stimulated macrophages. It also inhibited LPS-induced phosphorylation of p38 and JNK, which are also upstream activators of NF-κB, without affecting Akt phosphorylation. Mal C also effectively blocked the PKR-mediated activation of NF-κB. These findings indicate that mal C exerts an anti-inflammatory effect through NF-κB-responsive inflammatory gene expressions by inhibiting the p38 and JNK-dependent canonical NF-κB pathway as well as the PKR pathway, and is a potential therapeutic agent against acute inflammation.

Comparative nuclease and anti-cancer properties of the naturally occurring malabaricones.

The nuclease activities of the malabaricones have been studied so as to establish a structure-activity correlation and deduce the mechanistic pathway of the process. The inactivity of malabaricone A and malabaricone D revealed that the resorcinol moiety, present in the malabaricones did not contribute to the nuclease activity. Amongst the test compounds, malabaricone C (mal C) containing a B-ring catechol moiety showed significantly better Cu(II)-dependent nuclease activity than the partially methylated catechol derivative, mal B and curcumin. Mal C was found to bind efficiently with Cu(II) and DNA to facilitate the DNA nicking via a site-specifically generated Cu(I)-peroxo complex. Consistent with its Cu(II)-dependent nuclease property, mal C showed better cytotoxicity (IC(50)=5.26±1.20 µM) than curcumin (IC(50)=24.46±3.32 µM) against the MCF-7 human breast cancer cell line. The mal C-induced killing of the MCF-7 cells followed an apoptotic pathway involving oxidative damage to the cellular DNA.