Identification of a Dual Autophagy and REV-ERB Inhibitor with in Vivo Anticancer Efficacy.

The autophagy process appears as a promising target for anticancer interventions. Chloroquine (CQ) and its derivative hydroxychloroquine (HCQ) are the only FDA-approved autophagy flux inhibitors. Although diverse anticancer clinical trials are providing encouraging results, several limitations associated with the need of high dosage and long-term administration of these autophagy inhibitors are also emerging. We showed that the inhibition of REV-ERB, a nuclear receptor regulating circadian rhythm and metabolism, enhances CQ-mediated cancer cell death and identified a class of dual inhibitors of autophagy and REV-ERB displaying an in vitro anticancer activity against diverse tumor cells greatly higher than CQ. Herein, we describe our lead optimization strategy that led to the identification of compound 24 as a dual autophagy and REV-ERB inhibitor, showing improved potency in blocking autophagy, enhanced toxicity against cancer cells, optimal drug-like properties, and efficacy in a mouse xenograft model of melanoma as a single anticancer agent.

MYC-Associated Factor MAX is a Regulator of the Circadian Clock.

The circadian transcriptional network is based on a competition between transcriptional activator and repressor complexes regulating the rhythmic expression of clock-controlled genes. We show here that the MYC-associated factor X, MAX, plays a repressive role in this network and operates through a MYC-independent binding to E-box-containing regulatory regions within the promoters of circadian BMAL1 targets. We further show that this "clock" function of MAX is required for maintaining a proper circadian rhythm and that MAX and BMAL1 contribute to two temporally alternating transcriptional complexes on clock-regulated promoters. We also identified MAX network transcriptional repressor, MNT, as a fundamental partner of MAX-mediated circadian regulation. Collectively, our data indicate that MAX regulates clock gene expression and contributes to keeping the balance between positive and negative elements of the molecular clock machinery.

The efficacy and toxicity of ATM inhibition in glioblastoma initiating cells-driven tumor models.

The Ataxia Telangiectasia Mutated (ATM)-mediated DNA damage response (DDR) is a major mechanism of resistance of glioblastoma (GB) - initiating cells (GICs) to radiotherapy. The closely related Ataxia Telangiectasia and Rad3-related protein (ATR) is also involved in tumor resistance to radio- and chemotherapy. It has been shown that pharmacological inhibition of ATM protein may overcome the DDR-mediated resistance in GICs and significantly radiosensitize GIC-driven GB. Albeit not essential for life as shown by the decade-long lifespan of AT patients, the ATM protein may be involved in a number of important functions other than the response to DNA damage. We discuss our current knowledge about the toxicity of pharmacologic inhibition of ATM and ATR proteins.

Author Correction: Faithful animal modelling of human glioma by using primary initiating cells and its implications for radiosensitization therapy.

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Faithful animal modelling of human glioma by using primary initiating cells and its implications for radiosensitization therapy [ARRIVE 1].

It has been reported that the ATM kinase inhibitor KU60019 preferentially radiosensitizes orthotopic high grade gliomas (HGG) driven by established U87 and U1242 cell lines bearing specific TP53 mutations. We wished to determine whether those results could be extended to tumors driven by primary glioma initiating cells (GIC) that closely mimic clinical tumors. Orthotopic HGG were developed in immunodeficient non-obese diabetic-severe combined immunodeficient (NOD-SCID) mice by intracranial injection of primary GIC isolated from the adult glioblastoma COMI (acronym of patient's name) and the pediatric anaplastic astrocytoma 239/12. Similar to the clinical tumors of origin, the orthotopic tumors COMI and 239/12 displayed different growth properties with a voluminous expansive lesion that exerted considerable mass effect on the adjacent structures and an infiltrating, gliomatosis-like growth pattern with limited compressive attitude, respectively. Significant elongations of median animal survival bearing the adult COMI tumor was observed after one KU60019 convection enhanced delivery followed by total 7.5 Gy of ionizing radiation delivered in fifteen 0.5 Gy fractions, as compared to animals treated with vehicle + ionizing radiation (105 vs 89 days; ratio: 0.847; 95% CI of ratio 0.4969 to 1.198; P:0.0417) [ARRIVE 16]. Similarly, a trend to increased median survival was observed with the radiosensitized pediatric tumor 239/12 (186 vs 167 days; ratio: 0.8978; 95% CI of ratio: 0.5352 to 1.260; P: 0.0891) [ARRIVE 16]. Our results indicate that radiosensitization by KU60019 is effective towards different orthotopic gliomas that faithfully mimic the clinical tumors and that multiple GIC-based animal models may be essential to develop novel therapeutic protocols for HGG transferable to the clinics.

Targeting the Ataxia Telangiectasia Mutated Protein in Cancer Therapy.

Genotoxic anticancer drugs explicate their effects damaging DNA, thus triggering a coordinated signal-transduction network called DNA Damage Response (DDR). Ataxia Telangiectasia Mutated (ATM) protein plays a central role in this response: activated by DNA damage, ATM phosphorylates itself and downstream effectors that arrest cell cycle allowing for DNA repair or, should DNA damage be too severe and not retrievable, inducing apoptosis. ATM is a worth-investigating target for tumor radio- and chemosensitization. During last years, pharmaceutical industries and research laboratories have developed a series of small molecules, capable to inhibit ATM with increasing specificity. Several preclinical studies have demonstrated that these inhibitors alone or in association with other treatments may improve therapeutic outcomes. In this review we discuss ATM inhibitors so far developed, focussing on recent acquisitions on their potential antineoplastic usefulness.

Pharmacokinetics, pharmacodynamics and efficacy on pediatric tumors of the glioma radiosensitizer KU60019.

We have recently reported that glioblastoma (GB)-initiating cells (GIC) with low expression and/or mutation of TP53 and high expression of PI3K ("responder" genetic profile) can be effectively and safely radiosensitized by the ATM inhibitor KU60019. We report here on drug's diffusion and elimination from the animal body and brain, its effects on orthotopic GB and efficacy toward pediatric GIC. Healthy mice were infused by convection enhanced delivery (CED) with KU60019 and the drug kinetics followed by high performance liquid chromatography-mass spectrometry. Already at the end of CED, KU60019 had diffused from the injection site to the ipsilateral and, to a lower extent, controlateral hemisphere. After 24 hr, no drug could be detected all over the brain or in other organs, indicating rapid draining and excretion. After intraperitoneal injection, traces only of KU60019 could be detected in the brain, indicating inability to cross the brain-blood barrier. Consistent with the induction of cell cycle progression previously observed in vitro, KU60019 stimulated proliferation of orthotopic GB cells with the highest effect observed 96 hr after drug delivery. Adult GIC with high expression of TP53 and low expression of PI3K could be radiosensitized by KU60019, although less promptly than GIC bearing the "responder" profile. Consistent with the kinetics of proliferation induction, the highest radiosensitizing effect was observed 96 hr after delivery of KU60019 to GIC. Pediatric GIC could be similarly radiosensitized after exposure to KU60019. The results indicate that ATM inhibition may allow to radiosensitize a wide range of adult and pediatric high-grade gliomas.

Accelerated repair and reduced mutagenicity of DNA damage induced by cigarette smoke in human bronchial cells transfected with E.coli formamidopyrimidine DNA glycosylase.

Cigarette smoke (CS) is associated to a number of pathologies including lung cancer. Its mutagenic and carcinogenic effects are partially linked to the presence of reactive oxygen species and polycyclic aromatic hydrocarbons (PAH) inducing DNA damage. The bacterial DNA repair enzyme formamidopyrimidine DNA glycosylase (FPG) repairs both oxidized bases and different types of bulky DNA adducts. We investigated in vitro whether FPG expression may enhance DNA repair of CS-damaged DNA and counteract the mutagenic effects of CS in human lung cells. NCI-H727 non small cell lung carcinoma cells were transfected with a plasmid vector expressing FPG fused to the Enhanced Green Fluorescent Protein (EGFP). Cells expressing the fusion protein EGFP-FPG displayed accelerated repair of adducts and DNA breaks induced by CS condensate. The mutant frequencies induced by low concentrations of CS condensate to the Na(+)K(+)-ATPase locus (oua(r)) were significantly reduced in cells expressing EGFP-FPG. Hence, expression of the bacterial DNA repair protein FPG stably protects human lung cells from the mutagenic effects of CS by improving cells' capacity to repair damaged DNA.

Predictability, efficacy and safety of radiosensitization of glioblastoma-initiating cells by the ATM inhibitor KU-60019.

We have previously shown that pharmacological inhibition of ataxia telangiectasia mutated (ATM) protein sensitizes glioblastoma-initiating cells (GICs) to ionizing radiation (IR). Herein, we report the experimental conditions to overcome GIC radioresistance in vitro using the specific ATM inhibitor KU-60019, two major determinants of the tumor response to this drug and the absence of toxicity of this treatment in vitro and in vivo. Repeated treatments with KU-60019 followed by IR substantially delayed GIC proliferation in vitro and even eradicated radioresistant cells, whereas GIC treated with vehicle plus radiation recovered early and expanded. The tumor response to the drug occurred under a cutoff level of expression of TP53 and over a cutoff level of expression of phosphatidylinositol 3-kinase (PI3K). No increased clastogenicity or point mutagenicity was induced by KU-60019 plus radiation when compared to vehicle plus radiation. No significant histological changes to the brain or other organs were observed after prolonged infusion into the brain of KU-60019 at millimolar concentrations. Taken together, these findings suggest that GIC-driven tumors with low expression of TP53 and high expression of PI3K might be effectively and safely radiosensitized by KU-60019.

Delayed formation of FancD2 foci in glioma stem cells treated with ionizing radiation.

BACKGROUND: Glioblastoma multiforme (WHO grade IV) is a highly lethal brain tumor. Its malignancy is in part due to cell populations refractory to radiotherapy and chemotherapy, which in some patients display stem properties (glioma stem cells-GSC). We and others have recently shown that a major mechanism of resistance of GSC to therapies resides in their slow proliferation that in turn is linked to constitutive activation of the DNA damage response. FancD2, a central player of the Fanconi anemia pathway, is induced when replication forks stall at DNA damage sites. METHODS: We have analyzed the kinetics of FancD2 induction in two glioma cell lines with pronounced (Borru) and poor (DR177) stem phenotypes, by fluorescence analysis of nuclear foci. RESULTS: FancD2 activation was significantly delayed in Borru, consistent with the slow replication fork progression in these cells. On the contrary, no significant difference between Borru and DR177 was observed for pH2AX nuclear foci formation that hallmarks a number of DNA structure variations including double-strand breaks. CONCLUSION: GSC display reduced FancD2 activation following radiation damage, most probably due to their elongated cell cycle.

Characterization of glioma stem cells through multiple stem cell markers and their specific sensitization to double-strand break-inducing agents by pharmacological inhibition of ataxia telangiectasia mutated protein.

Previous studies have shown that tumor-driving glioma stem cells (GSC) may promote radio-resistance by constitutive activation of the DNA damage response started by the ataxia telangiectasia mutated (ATM) protein. We have investigated whether GSC may be specifically sensitized to ionizing radiation by inhibiting the DNA damage response. Two grade IV glioma cell lines (BORRU and DR177) were characterized for a number of immunocytochemical, karyotypic, proliferative and differentiative parameters. In particular, the expression of a panel of nine stem cell markers was quantified by reverse transcription-polymerase chain reaction (RT-PCR) and flow cytometry. Overall, BORRU and DR177 displayed pronounced and poor stem phenotypes, respectively. In order to improve the therapeutic efficacy of radiation on GSC, the cells were preincubated with a nontoxic concentration of the ATM inhibitors KU-55933 and KU-60019 and then irradiated. BORRU cells were sensitized to radiation and radio-mimetic chemicals by ATM inhibitors whereas DR177 were protected under the same conditions. No sensitization was observed after cell differentiation or to drugs unable to induce double-strand breaks (DSB), indicating that ATM inhibitors specifically sensitize glioma cells possessing stem phenotype to DSB-inducing agents. In conclusion, pharmacological inhibition of ATM may specifically sensitize GSC to DSB-inducing agents while sparing nonstem cells.

The silencing of adenine nucleotide translocase isoform 1 induces oxidative stress and programmed cell death in ADF human glioblastoma cells.

Adenine nucleotide translocases (ANTs) are multitask proteins involved in several aspects of cell metabolism, as well as in the regulation of cell death/survival processes. We investigated the role played by ANT isoforms 1 and 2 in the growth of a human glioblastoma cell line (ADF cells). The silencing of ANT2 isoform, by small interfering RNA, did not produce significant changes in ADF cell viability. By contrast, the silencing of ANT1 isoform strongly reduced ADF cell viability by inducing a non-apoptotic cell death process resembling paraptosis. We demonstrated that cell death induced by ANT1 depletion cannot be ascribed to the loss of the ATP/ADP exchange function of this protein. By contrast, our findings indicate that ANT1-silenced cells experience oxidative stress, thus allowing us to hypothesize that the effect of ANT1-silencing on ADF is mediated by the loss of the ANT1 uncoupling function. Several studies ascribe a pro-apoptotic role to ANT1 as a result of the observation that ANT1 overexpression sensitizes cells to mitochondrial depolarization or to apoptotic stimuli. In the present study, we demonstrate that, despite its pro-apoptotic function at a high expression level, the reduction of ANT1 density below a physiological baseline impairs fundamental functions of this protein in ADF cells, leading them to undertake a cell death process.

Drugs targeting the mitochondrial pore act as cytotoxic and cytostatic agents in temozolomide-resistant glioma cells.

BACKGROUND: High grade gliomas are one of the most difficult cancers to treat and despite surgery, radiotherapy and temozolomide-based chemotherapy, the prognosis of glioma patients is poor. Resistance to temozolomide is the major barrier to effective therapy. Alternative therapeutic approaches have been shown to be ineffective for the treatment of genetically unselected glioma patients. Thus, novel therapies are needed. Mitochondria-directed chemotherapy is an emerging tool to combat cancer, and inner mitochondrial permeability transition (MPT) represents a target for the development of cytotoxic drugs. A number of agents are able to induce MPT and some of them target MPT-pore (MPTP) components that are selectively up-regulated in cancer, making these agents putative cancer cell-specific drugs. OBJECTIVE: The aim of this paper is to report a comprehensive analysis of the effects produced by selected MPT-inducing drugs (Betulinic Acid, Lonidamine, CD437) in a temozolomide-resistant glioblastoma cell line (ADF cells). METHODS: EGFRvIII expression has been assayed by RT-PCR. EGFR amplification and PTEN deletion have been assayed by differential-PCR. Drugs effect on cell viability has been tested by crystal violet assay. MPT has been tested by JC1 staining. Drug cytostatic effect has been tested by mitotic index analysis. Drug cytotoxic effect has been tested by calcein AM staining. Apoptosis has been assayed by Hoechst incorporation and Annexine V binding assay. Authophagy has been tested by acridine orange staining. RESULTS: We performed a molecular and genetic characterization of ADF cells and demonstrated that this line does not express the EGFRvIII and does not show EGFR amplification. ADF cells do not show PTEN mutation but differential PCR data indicate a hemizygous deletion of PTEN gene. We analyzed the response of ADF cells to Betulinic Acid, Lonidamine, and CD437. Our data demonstrate that MPT-inducing agents produce concentration-dependent cytostatic and cytotoxic effects in parallel with MPT induction triggered through MPTP. CD437, Lonidamine and Betulinic acid trigger apoptosis as principal death modality. CONCLUSION: The obtained data suggest that these pharmacological agents could be selected as adjuvant drugs for the treatment of high grade astrocytomas that resist conventional therapies or that do not show any peculiar genetic alteration that can be targeted by specific drugs.