p53 oligomerization status as an indicator of sensitivity of p53-wildtype neuroblastomas to the combination of DNA damaging agent and Chk1 inhibitor.

Neuroblastomas are one of the most common types of solid tumors in infants and children and are responsible for approximately 15% of childhood cancer deaths. Neuroblastomas rarely have mutations in p53, with less than 2% of NB containing mutations in p53, compared to up to 60% for other tumor classes. Previous studies on the therapeutic combination of a DNA damaging agent and checkpoint kinase 1 (Chk1) inhibitor have shown that DNA damage-induced cell cycle arrest can be specifically abrogated in p53-defective tumors. However, some p53-wildtype tumors have also been shown to be sensitive to this therapeutic combination, suggesting that these cells have other defects in the p53 response that can be exploited for therapeutic purposes. In the current study, we investigated the response to the combination of a DNA damaging agent (SN38) and a Chk1 inhibitor (UCN-01) of four p53-wildtype neuroblastoma cell lines: SK-N-SH, SH-SY5Y, SK-N-AS, and Lan-5. When the cells were treated with concentrations of SN38 ranging from 0-30 ng/ml, all four cell lines accumulated p53 which was phosphorylated on serines 15 and 20. However, only the SK-N-SH were found to activate p21waf1 and repress cyclin B. In order to assess sensitivity to UCN-01-mediated abrogation of cell cycle arrest, cell were treated with 10 ng/ml SN38 for 24 h, followed by 25 nM UCN-01 for 6 and 24 h. The SK-N-SH showed no sensitivity to UCN-01 treatment whereas the SH-SY5Y, SK-N-AS, and Lan-5 abrogated G2 arrest within 24 h. Our recent studies revealed that cells that are sensitive to checkpoint abrogation lack p53 dimers and tetramers, so we analyzed the oligomerization status of p53 in all four cell lines using glutaraldehyde crosslinking. The SK-N-SH cells possessed levels of p53 dimers and tetramers similar to what has previously been reported in p53-wildtype MCF10A cells. The SH-SY5Y, SK-N-AS, and Lan-5 however, had extremely low to undetectable levels of dimers and tetramers. Our study also showed no cytoplasmic accumulation of p53 in these cells contrary to some previous reports. The results of this study suggest that oligomerization status may serve as an indicator of sensitivity of p53-wildtype tumors to the therapeutic combination of DNA damaging agent and Chk1 inhibitor.

Recent Advances in Therapeutic Application of DNA Damage Response Inhibitors against Cancer.

DNA's integrity is continuously challenged by intrinsic cellular processes and environmental agents. To overcome this genomic damage, cells have developed multiple signalling pathways collectively named as DNA Damage Response (DDR) and composed of three components: (i) sensor proteins, which detect DNA damage, (ii) mediators that relay the signal downstream and recruit the repair machinery and (iii) the repair proteins, which restore the damaged DNA. A flawed DDR and failure to repair the damage lead to the accumulation of genetic lesions and increased genomic instability, which is recognized as a hallmark of cancer. Cancer cells tend to harbor increased mutations in DDR genes and often have fewer DDR pathways than normal cells. This makes cancer cells more dependent on particular DDR pathways and thus become more susceptible to compounds inhibiting those pathways compared to normal cells, which have all the DDR pathways intact. Understanding the roles of different DDR proteins in the DNA damage response and repair pathways and the identification of their structures have paved the way for development of their inhibitors as targeted cancer therapy. In this review, we describe the major participants of various DDR pathways, their significance in carcinogenesis and focus on the inhibitors developed against several key DDR proteins.

DNA-Unresponsive Platinum(II) Complex Induces ERS-Mediated Mitophagy in Cancer Cells.

Mitophagy is a selective autophagic process that degrades dysfunctional mitochondria. Monofunctional platinum(II) complexes are candidates for anticancer drugs with the potential to circumvent the drug resistance and side effects of cisplatin and its analogues, but their mechanism of action is elusive. Complex Mono-Pt kills cancer cells through a mitophagic pathway. The mechanism involves the stimulation of endoplasmic reticulum stress (ERS) and activation of the unfolded protein response. Mono-Pt severely impairs the structure and function of mitochondria, including disruption of morphological integrity, dissipation of membrane potential, elevation of reactive oxygen species, inhibition of mtDNA transcription, and reduction of adenosine triphosphate (ATP), which ultimately leads to mitophagy. Mono-Pt does not react with nuclear DNA but exhibits potent antiproliferative activity against cancer cells, thus breaking the DNA-binding paradigm and classical structure-activity rules for platinum drugs. The ERS-mediated mitophagy provides an alternative mechanism for platinum complexes, which broadens the way for developing new platinum anticancer drugs.

X-ray repair cross-complementing protein 1 (XRCC1) loss promotes ß-lapachone -induced apoptosis in pancreatic cancer cells.

BACKGROUND: ß-lapachone (ß-lap), the NQO1 bioactivatable drug, is thought to be a promising anticancer agent. However, the toxic side effects of ß-lap limit the drug use, highlighting the need for a thorough understanding of ß-lap's mechanism of action. ß-lap undergoes NQO1-dependent futile redox cycling, generating massive ROS and oxidative DNA lesions, leading to cell death. Thus, base excision repair (BER) pathway is an important resistance factor. XRCC1, a scaffolding component, plays a critical role in BER. METHODS: We knocked down XRCC1 expression by using pLVX-shXRCC1 in the MiaPaCa2 cells and BxPC3 cells and evaluated ß-lap-induced DNA lesions by γH2AX foci formation and alkaline comet assay. The cell death induced by XRCC1 knockdown + ß-lap treatment was analysed by relative survival, flow cytometry and Western blotting analysis. RESULTS: We found that knockdown of XRCC1 significantly increased ß-lap-induced DNA double-strand breaks, comet tail lengths and cell death in PDA cells. Furthermore, we observed combining XRCC1 knockdown with ß-lap treatment switched programmed necrosis with ß-lap monotherapy to caspase-dependent apoptosis. CONCLUSIONS: These results indicate that XRCC1 is involved in the repair of ß-lap-induced DNA damage, and XRCC1 loss amplifies sensitivity to ß-lap, suggesting targeting key components in BER pathways may have the potential to expand use and efficacy of ß-lap for gene-based therapy.

Targeted methylation facilitates DNA double strand breaks and enhances cancer suppression: A DNA intercalating/methylating dual-action chimera Amonafidazene.

A DNA intercalating agent Amonafide interferes with topoisomerase 2 (Topo II) activity and prevents re-ligation of DNA strands, leading to double strand breaks (DSB). If DSB repair fails, cells stop dividing and eventually die. In a search of approaches to enhance anti-cancer activities of Topo II inhibitors, we hypothesized that introduction of additional damage in proximity to the DSB may suppress DNA repair and enhance cancer cell killing. Accordingly, chimeric molecules were created that target a DNA alkylating component to the proximity of Topo II-induced DSBs. These chimeras consist of Amonafide or its 4-amino isomer, and DNA methylating methyl triazene moiety Azene protected with a carbamate group, connected via linker. Treatment of cancer cells with the chimeric molecules leads to significantly higher number of DSBs, which were repaired slower compared to Amonafide or monomethyl triazene-treated cells. On the other hand, methyl triazene linked to non-intercalating Amonafide analogs was ineffective. Together, these data strongly support our hypothesis. In line with increased DSBs, the chimeric molecules exhibited significantly higher antiproliferative activity in cancer cell lines compared to Amonafide or monomethyl triazene constituent Azene. We utilized the fluorescent properties of chimera Amonafidazene to develop ''photo-switchable'' reporting system to monitor the prodrug activation. Using this approach, we found that the chimera accumulated and was activated at the tumor sites specifically and demonstrated significantly stronger tumor suppressing activities compared to Amonafide in a xenograft model. Therefore, targeting alkylating groups to the proximity of DSB sites may become an effective approach towards enhancing anti-cancer activities of inhibitors of topoisomerases.

Anticancer effect evaluation in vitro and in vivo of iridium(III) polypyridyl complexes targeting DNA and mitochondria.

To investigate the antitumor effect of iridium complexes, three iridium (III) complexes [Ir(ppy)2(dcdppz)]PF6 (ppy = 2-phenylpyridine, dcdppz = 11,12-dichlorodipyrido[3,2-a:2',3'-c]phenazine) (Ir1), [Ir(bzq)2(dcdppz)]PF6 (bzq = benzo[h]quinoline) (Ir2) and [Ir(piq)2(dcdppz)]PF6 (piq = 1-phenylisoquinoline) (Ir3) were synthesized and characterized. Geometry optimization, molecular dynamics simulation and docking studies have been performed to further explore the antitumor mechanism. The cytotoxicity of Ir1-3 toward cancer cells was studied by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. The localization of complexes Ir1-3 in the mitochondria, intracellular accumulation of reactive oxygen species (ROS) levels, the changes of mitochondrial membrane potential and morphological changes in apoptosis were investigated. Flow cytometry was applied to quantify fluorescence intensity and determine cell cycle distribution. Western blotting was used to detect the expression of apoptosis-related proteins. The anti-tumor effect of Ir1 in vivo was evaluated. The results showed that Ir1-3 had high cytotoxicity to most tumor cells, especially to SGC-7901 cells with a low IC50 value. Ir1-3 can increase the intracellular ROS levels, reduce the mitochondrial membrane potential. Additionally, the complexes induce an increase of apoptosis-related protein expression, enhance the percentage of apoptosis. The complexes inhibit the cell proliferation at G0/G1 phase. The results obtained from antitumor in vivo indicate that Ir1 can significantly inhibit the growth of tumors with an inhibitory rate of 54.08%. The docking studies show that complexes Ir1-3 interact with DNA through minor-groove intercalation, which increases the distance of DNA base pairs, leading to a change of DNA helix structure. These experimental and theoretical findings indicate that complexes Ir1-3 can induce apoptosis in SGC-7901 cells through the mitochondrial dysfunction and DNA damage pathways, and then exerting anti-tumor activity in vitro and vivo.

Effects of N-terminus modified Hx-amides on DNA binding affinity, sequence specificity, cellular uptake, and gene expression.

Five X-HxIP (Hx-amides) 6a-e, in which the N-terminus p-anisyl moiety is modified, were designed and synthesised with the purpose of optimising DNA binding, improving cellular uptake/nuclear penetration, and enhancing the modulation of the topoisomerase IIα (TOP2A) gene expression. The modifications include a fluorophenyl group and other heterocycles bearing different molecular shapes, size, and polarity. Like their parent compound HxIP 3, all five X-HxIP analogues bind preferentially to their cognate sequence 5'-TACGAT-3', which is found embedded on the 5' flank of the inverted CCAAT box-2 (ICB2) site in the TOP2A gene promoter, and inhibit protein complex binding. Interestingly, the 4-pyridyl analog 6a exhibits greater binding affinity for the target DNA sequence and abolishes the protein:ICB2 interaction in vitro, at a lower concentration, compared to the prototypical compound HxIP 3. Analogues 6b-e, display improved DNA sequence specificity, but reduced binding affinity for the cognate sequence, relative to the unmodified HxIP 3, with polyamides 6b and 6e being the most sequence selective. However, unlike 3 and 6b, 6a was unable to enter cells, access the nucleus and thereby affect TOP2A gene expression in confluent human lung cancer cells. These results show that while DNA binding affinity and sequence selectivity are important, consideration of cellular uptake and concentration in the nucleus are critical when exerting biological activity is the desired outcome. By characterising the DNA binding, cellular uptake and gene regulatory properties of these small molecules, we can elucidate the determinants of the elicited biological activity, which can be impacted by even small structural modifications in the polyamide molecular design.

Quinoline anticancer agents active on DNA and DNA-interacting proteins: From classical to emerging therapeutic targets.

Quinoline is one of the most important and versatile nitrogen heterocycles embodied in several biologically active molecules. Within the numerous quinolines developed as antiproliferative agents, this review is focused on compounds interfering with DNA structure or with proteins/enzymes involved in the regulation of double helix functional processes. In this light, a special focus is given to the quinoline compounds, acting with classical/well-known mechanisms of action (DNA intercalators or Topoisomerase inhibitors). In particular, the quinoline drugs amsacrine and camptothecin (CPT) have been studied as key lead compounds for the development of new agents with improved PK and tolerability properties. Moreover, notable attention has been paid to the quinoline molecules, which are able to interfere with emerging targets involved in cancer progression, as G-quadruplexes or the epigenetic ones (e.g.: histone deacetylase, DNA and histones methyltransferase). The antiproliferative and the enzymatic inhibition data of the reviewed compounds have been analyzed. Furthermore, concerning the SAR (structure-activity relationship) aspects, the most recurrent ligand-protein interactions are summarized, underling the structural requirements for each kind of mechanism of action.

An oxo(corrolato)chromium(V) complex selectively kills cancer cells by inducing DNA damage.

An oxo(corrolato)chromium(v) complex selectively kills leukemia cells. However, this complex did not induce cell death in primary non-cancer cells. It has been observed that oxo(corrolato)chromium(v) complex induced cell death is associated with DNA damage. Interestingly, the DNA in primary cells largely remained unaffected. DNA isolated from normal and cancerous cell lines also follows similar trends. A chemical reductant, DTT, was used to probe the mechanism of DNA damage. However, it does not show any additive effect on DNA damage.

Novel amino substituted tetracyclic imidazo[4,5-b]pyridine derivatives: Design, synthesis, antiproliferative activity and DNA/RNA binding study.

A novel series of tetracyclic imidazo[4,5-b]pyridine derivatives was designed and synthesized as potential antiproliferative agents. Their antiproliferative activity against human cancer cells was influenced by the introduction of chosen amino side chains on the different positions on the tetracyclic skeleton and particularly, by the position of N atom in the pyridine nuclei. Thus, the majority of compounds showed improved activity in comparison to standard drug etoposide. Several compounds showed pronounced cytostatic effect in the submicromolar range, especially on HCT116 and MCF-7 cancer cells. The obtained results have confirmed the significant impact of the position of N nitrogen in the pyridine ring on the enhancement of antiproliferative activity, especially for derivatives bearing amino side chains on position 2. Thus, regioisomers 6, 7 and 9 showed noticeable enhancement of activity in comparison to their counterparts 10, 11 and 13 with IC50 values in a nanomolar range of concentration (0.3-0.9 µM). Interactions with DNA (including G-quadruplex structure) and RNA were influenced by the position of amino side chains on the tetracyclic core of imidazo[4,5-b]pyridine derivatives and the ligand charge. Moderate to high binding affinities (logKs = 5-7) obtained for selected imidazo[4,5-b]pyridine derivatives suggest that DNA/RNA are potential cell targets.

The role of DNA damage response in chemo- and radio-resistance of cancer cells: Can DDR inhibitors sole the problem?

Up to now, many improvements have been made in providing more therapeutic strategies for cancer patients. The lack of susceptibility to common therapies like chemo- and radio-therapy is one of the reasons why we need more methods in the field of cancer therapy. DNA damage response (DDR) is a set of mechanisms which identifies DNA lesions and triggers the repair process for restoring DNA after causing an arrest in the cell cycle. The ability of DDR in maintaining the genome stability and integrity can be favorable to cancerous cells which are exposed to radiation therapy or are treated with chemotherapeutic agents. When DDR mechanisms are error-free in cancer cells, they can escape the expected cellular death and display resistance to treatment. In this regard, targeting different components of DDR can help to increase the susceptibility of advanced tumors to chemo- and radio-therapy.

G-quadruplexes: a promising target for cancer therapy.

DNA and RNA can fold into a variety of alternative conformations. In recent years, a particular nucleic acid structure was discussed to play a role in malignant transformation and cancer development. This structure is called a G-quadruplex (G4). G4 structure formation can drive genome instability by creating mutations, deletions and stimulating recombination events. The importance of G4 structures in the characterization of malignant cells was currently demonstrated in breast cancer samples. In this analysis a correlation between G4 structure formation and an increased intratumor heterogeneity was identified. This suggests that G4 structures might allow breast cancer stratification and supports the identification of new personalized treatment options. Because of the stability of G4 structures and their presence within most human oncogenic promoters and at telomeres, G4 structures are currently tested as a therapeutic target to downregulate transcription or to block telomere elongation in cancer cells. To date, different chemical molecules (G4 ligands) have been developed that aim to target G4 structures. In this review we discuss and compare G4 function and relevance for therapeutic approaches and their impact on cancer development for three cancer entities, which differ significantly in their amount and type of mutations: pancreatic cancer, leukemia and malignant melanoma. G4 structures might present a promising new strategy to individually target tumor cells and could support personalized treatment approaches in the future.

Salicylates enhance CRM1 inhibitor antitumor activity by induction of S-phase arrest and impairment of DNA-damage repair.

Chromosome region maintenance protein 1 (CRM1) mediates protein export from the nucleus and is a new target for anticancer therapeutics. Broader application of KPT-330 (selinexor), a first-in-class CRM1 inhibitor recently approved for relapsed multiple myeloma and diffuse large B-cell lymphoma, have been limited by substantial toxicity. We discovered that salicylates markedly enhance the antitumor activity of CRM1 inhibitors by extending the mechanisms of action beyond CRM1 inhibition. Using salicylates in combination enables targeting of a range of blood cancers with a much lower dose of selinexor, thereby potentially mitigating prohibitive clinical adverse effects. Choline salicylate (CS) with low-dose KPT-330 (K+CS) had potent, broad activity across high-risk hematological malignancies and solid-organ cancers ex vivo and in vivo. The K+CS combination was not toxic to nonmalignant cells as compared with malignant cells and was safe without inducing toxicity to normal organs in mice. Mechanistically, compared with KPT-330 alone, K+CS suppresses the expression of CRM1, Rad51, and thymidylate synthase proteins, leading to more efficient inhibition of CRM1-mediated nuclear export, impairment of DNA-damage repair, reduced pyrimidine synthesis, cell-cycle arrest in S-phase, and cell apoptosis. Moreover, the addition of poly (ADP-ribose) polymerase inhibitors further potentiates the K+CS antitumor effect. K+CS represents a new class of therapy for multiple types of blood cancers and will stimulate future investigations to exploit DNA-damage repair and nucleocytoplasmic transport for cancer therapy in general.

Venetoclax and dexamethasone synergize with inotuzumab ozogamicin-induced DNA damage signaling in B-lineage ALL.

Adult patients with relapsed B-cell precursor acute lymphoblastic leukemia (BCP-ALL) have a dismal prognosis. To improve pharmacotherapy, we analyzed induction of apoptosis by venetoclax and inotuzumab ozogamicin in terms of cytotoxicity and mode of action. Flow cytometry-based analyses of mitochondrial outer membrane permeabilization (MOMP) and ataxia telangiectasia mutated activation demonstrate rapid induction of MOMP by venetoclax and DNA damage signaling by inotuzumab ozogamicin, respectively. In primary ALL samples and patient-derived xenograft (PDX) models, venetoclax and inotuzumab ozogamicin cooperated and synergized in combination with dexamethasone in vitro in all tested samples of ALL. In murine PDX models, inotuzumab ozogamicin, but not venetoclax, induced complete remission in a dose-dependent manner but constantly failed to achieve relapse-free survival. In contrast, combination therapy with venetoclax, dexamethasone, and inotuzumab ozogamicin induced long-term leukemia-free survival and treatment-free survival in all 3 ALL-PDX models tested. These data demonstrate synergistic and highly efficient pharmacotherapy in preclinical models that qualify for evaluation in clinical trials.

Genome Repair Takes a Spotlight during the ACS TOXI Meeting.

DNA damage and mutations are a major primary cause of cancer. Chemical bombardment of DNA is a major contributor to DNA damage. The Division of Chemical Toxicology recently hosted a panel of researchers who provided updates on the field of chemical toxicology at the nexus of DNA damage and repair.

Temporal modulation of the NF-κB RelA network in response to different types of DNA damage.

Different types of DNA damage can initiate phosphorylation-mediated signalling cascades that result in stimulus specific pro- or anti-apoptotic cellular responses. Amongst its many roles, the NF-κB transcription factor RelA is central to these DNA damage response pathways. However, we still lack understanding of the co-ordinated signalling mechanisms that permit different DNA damaging agents to induce distinct cellular outcomes through RelA. Here, we use label-free quantitative phosphoproteomics to examine the temporal effects of exposure of U2OS cells to either etoposide (ETO) or hydroxyurea (HU) by monitoring the phosphorylation status of RelA and its protein binding partners. Although few stimulus-specific differences were identified in the constituents of phosphorylated RelA interactome after exposure to these DNA damaging agents, we observed subtle, but significant, changes in their phosphorylation states, as a function of both type and duration of treatment. The DNA double strand break (DSB)-inducing ETO invoked more rapid, sustained responses than HU, with regulated targets primarily involved in transcription, cell division and canonical DSB repair. Kinase substrate prediction of ETO-regulated phosphosites suggest abrogation of CDK and ERK1 signalling, in addition to the known induction of ATM/ATR. In contrast, HU-induced replicative stress mediated temporally dynamic regulation, with phosphorylated RelA binding partners having roles in rRNA/mRNA processing and translational initiation, many of which contained a 14-3-3ε binding motif, and were putative substrates of the dual specificity kinase CLK1. Our data thus point to differential regulation of key cellular processes and the involvement of distinct signalling pathways in modulating DNA damage-specific functions of RelA.

Beyond DNA-targeting in Cancer Chemotherapy. Emerging Frontiers - A Review.

Modern anti-cancer drugs target DNA specifically for rapid division of malignant cells. One downside of this approach is that they also target other rapidly dividing healthy cells, such as those involved in hair growth leading to serious toxic side effects and hair loss. Therefore, it would be better to develop novel agents that address cellular signaling mechanisms unique to cancerous cells, and new research is now focussing on such approaches. Although the classical chemotherapy area involving DNA as the set target continues to produce important findings, nevertheless, a distinctly discernible emerging trend is the divergence from the cisplatin operation model that uses the metal as the primary active center of the drug. Many successful anti-cancer drugs present are associated with elevated toxicity levels. Cancers also develop immunity against most therapies and the area of cancer research can, therefore, be seen as an area with a high unaddressed need. Hence, ongoing work into cancer pathogenesis is important to create accurate preclinical tests that can contribute to the development of innovative drugs to manage and treat cancer. Some of the emergent frontiers utilizing different approaches include nanoparticles delivery, use of quantum dots, metal complexes, tumor ablation, magnetic hypothermia and hyperthermia by use of Superparamagnetic Iron oxide Nanostructures, pathomics and radiomics, laser surgery and exosomes. This review summarizes these new approaches in good detail, giving critical views with necessary comparisons. It also delves into what they carry for the future, including their advantages and disadvantages.

Anti-Cancer Stem Cells Potentiality of an Anti-Malarial Agent Quinacrine: An Old Wine in a New Bottle.

Quinacrine (QC) is a tricyclic compound and a derivative of 9-aminoacridine. It has been widely used to treat malaria and other parasitic diseases since the last century. Interestingly, studies have revealed that it also displays anti-cancer activities. Here, we have discussed the anti-cancer mechanism of QC along with its potentiality to specifically target cancer stem cells. The anti-cancer action of this drug includes DNA intercalation, inhibition of DNA repair mechanism, prevention of cellular growth, cell cycle arrest, inhibition of DNA and RNA polymerase activity, induction of autophagy, promotion of apoptosis, deregulation of cell signaling in cancer cells and cancer stem cells, inhibition of metastasis and angiogenesis. In addition, we have also emphasized on the synergistic effect of this drug with other potent chemotherapeutic agents and mentioned its different applications in anti-cancer therapy.