Sequential induction of mitotic catastrophe followed by apoptosis in human leukemia MOLT4 cells by imidazoacridinone C-1311

FeCl3-Catalyzed Synthesis of 6-Thioxo-hexahydroindeno[1',2':4,5]imidazo[1,5-a]pyridin-12(6H)-ones via an Interesting [1,2] Oxygen Shift Pathway

An iron-catalyst mediated one-pot multicomponent route for the synthesis of novel 6-thioxo-hexahydroindeno[1',2':4,5]imidazo[1,5-a]pyridin-12(6H)-one scaffolds has been developed using ninhydrin, l-proline, and aryl isothiocyanates in ethanol medium. This methodology offers an interesting [1,2] oxygen shift mechanism pathway via a number of ring-opening and ring-closing cascade steps to provide diverse substituted hexahydroindeno-imidazo[1,5-a]pyridinones in excellent to good yields. The stereochemistry of the proline ring is lost during the course of the reaction. This protocol is well acceptable toward both electron-accepting and electron-donating functionalities at the ortho-, meta-, and para-positions of the isothiocyanate moiety. Nonhazardous conditions, step economic, and easy operational process are the advantages of this methodology.

The Effect of Conjugation with Octaarginine, a Cell-Penetrating Peptide on Antifungal Activity of Imidazoacridinone Derivative

Acridine cell-penetrating peptide conjugates are an extremely important family of compounds in antitumor chemotherapy. These conjugates are not so widely analysed in antimicrobial therapy, although bioactive peptides could be used as nanocarriers to smuggle antimicrobial compounds. An octaarginine conjugate of an imidazoacridinone derivative (Compound 1-R8) synthetized by us exhibited high antifungal activity against reference and fluconazole-resistant clinical strains (MICs ≤ 4 μg mL⁻¹). Our results clearly demonstrate the qualitative difference in accumulation of the mother compound and Compound 1-R8 conjugate into fungal cells. Only the latter was transported and accumulated effectively. Microscopic and flow cytometry analysis provide some evidence that the killing activity of Compound 1-R8 may be associated with a change in the permeability of the fungal cell membrane. The conjugate exhibited low cytotoxicity against human embryonic kidney (HEK-293) and human liver (HEPG2) cancer cell lines. Nevertheless, the selectivity index value of the conjugate for human pathogenic strains remained favourable and no hemolytic activity was observed. The inhibitory effect of the analysed compound on yeast topoisomerase II activity suggested its molecular target. In summary, conjugation with R8 effectively increased imidazoacridinone derivative ability to enter the fungal cell and achieve a concentration inside the cell that resulted in a high antifungal effect.

The survival and proliferation of osteosarcoma cells are dependent on the mitochondrial BIG3-PHB2 complex formation

Previous studies reported the critical role of the brefeldin A-inhibited guanine nucleotide exchange protein 3-prohibitin 2 (BIG3-PHB2) complex in modulating estrogen signaling activation in breast cancer cells, yet its pathophysiological roles in osteosarcoma (OS) cells remain elusive. Here, we report a novel function of BIG3-PHB2 in OS malignancy. BIG3-PHB2 complexes were localized mainly in mitochondria in OS cells, unlike in estrogen-dependent breast cancer cells. Depletion of endogenous BIG3 expression by small interfering RNA (siRNA) treatment led to significant inhibition of OS cell growth. Disruption of BIG3-PHB2 complex formation by treatment with specific peptide inhibitor also resulted in significant dose-dependent suppression of OS cell growth, migration, and invasion resulting from G2/M-phase arrest and in PARP cleavage, ultimately leading to PARP-1/apoptosis-inducing factor (AIF) pathway activation-dependent apoptosis in OS cells. Subsequent proteomic and bioinformatic pathway analyses revealed that disruption of the BIG3-PHB2 complex might lead to downregulation of inner mitochondrial membrane protein complex activity. Our findings indicate that the mitochondrial BIG3-PHB2 complex might regulate PARP-1/AIF pathway-dependent apoptosis during OS cell proliferation and progression and that disruption of this complex may be a promising therapeutic strategy for OS.

The dietary flavonoid eupatilin attenuates in vitro lipid peroxidation and targets lipid profile in cancer HeLa cells

Eupatilin is a dietary flavonoid isolated from the alpine wormwoods, used for the genepy liqueur production. This flavone protects cells and tissues against oxidative stress and targets cancer cells, inducing cytotoxicity, cell circle arrest, apoptosis and mitochondrial dysfunction. This study examines the EUP in vitro antioxidant effects on cholesterol and phospholipid membrane oxidation and explores its ability to modulate the cancer cell lipid profile. This flavone remarkably protected fatty acids and cholesterol against oxidative degradation by scavenging lipoperoxyl radicals. EUP (24 h of incubation) significantly reduced viability and modulated the total lipid and fatty acid profiles in cancer HeLa cells. It induced marked changes in the phospholipid/cholesterol ratio, significant decreases in the levels of oleic and palmitic acids and a marked increase of stearic acid, involving an inhibitory effect on de novo lipogenesis and desaturation in cancer cells. Moreover, a noteworthy mitochondrial membrane depolarization, signs of apoptosis, abnormal mitosis with multi-nucleation (mitotic catastrophe) and morphological alterations were observed in cancer EUP-treated cells. Our results validate the EUP role as antioxidant agent for the treatment/prevention of disorders implicating a membrane lipid oxidative damage and substantiate cell lipid metabolism as another possible target of this dietary natural flavonoid in cancer HeLa cells.

Quantum Dots as a Good Carriers of Unsymmetrical Bisacridines for Modulating Cellular Uptake and the Biological Response in Lung and Colon Cancer Cells

Nanotechnology-based drug delivery provides a promising area for improving the efficacy of cancer treatments. Therefore, we investigate the potential of using quantum dots (QDs) as drug carriers for antitumor unsymmetrical bisacridine derivatives (UAs) to cancer cells. We examine the influence of QD-UA hybrids on the cellular uptake, internalization (Confocal Laser Scanning Microscope), and the biological response (flow cytometry and light microscopy) in lung H460 and colon HCT116 cancer cells. We show the time-dependent cellular uptake of QD-UA hybrids, which were more efficiently retained inside the cells compared to UAs alone, especially in H460 cells, which could be due to multiple endocytosis pathways. In contrast, in HCT116 cells, the hybrids were taken up only by one endocytosis mechanism. Both UAs and their hybrids induced apoptosis in H460 and HCT116 cells (to a greater extent in H460). Cells which did not die underwent senescence more efficiently following QDs-UAs treatment, compared to UAs alone. Cellular senescence was not observed in HCT116 cells following treatment with both UAs and their hybrids. Importantly, QDgreen/red themselves did not provoke toxic responses in cancer or normal cells. In conclusion, QDs are good candidates for targeted UA delivery carriers to cancer cells while protecting normal cells from toxic drug activities.

10-(4-Phenylpiperazine-1-carbonyl)acridin-9(10H)-ones and related compounds: Synthesis, antiproliferative activity and inhibition of tubulin polymerization

As part of our continuing search for potent inhibitors of tubulin polymerization, two novel series of 42 10-(4-phenylpiperazine-1-carbonyl)acridin-9(10H)-ones and N-benzoylated acridones were synthesized on the basis of a retrosynthetic approach. All newly synthesized compounds were tested for antiproliferative activity and interaction with tubulin. Several analogs potently inhibited tumor cell growth. Among the compounds tested, 10-(4-(3-methoxyphenyl)piperazine-1-carbonyl)acridin-9(10H)-one (17c) exhibited excellent growth inhibitory effects on 93 tumor cell lines, with an average GI₅₀ value of 5.4 nM. We were able to show that the strong cytotoxic effects are caused by disruption of tubulin polymerization, as supported by the EBI (N,N'-Ethylenebis(iodoacetamide)) assay and the fact that the most potent inhibitors of cancer cell growth turned out to be the most efficacious tubulin polymerization inhibitors. Potencies were nearly comparable or superior to those of the antimitotic reference compounds. Closely related to this, the most active analogs inhibited cell cycling at the G2/M phase at concentrations down to 30 nM and induced apoptosis in K562 leukemia cells. We believe that our work not only proves the excellent suitability of the acridone scaffold for the design of potent tubulin polymerization inhibitors but also enables synthetic access to further potentially interesting N-acylated acridones.

Synthesis of imidazo[1,5-a]pyridines via cyclocondensation of 2-(aminomethyl)pyridines with electrophilically activated nitroalkanes

Imidazo[1,5-a]pyridines were efficiently prepared via the cyclization of 2-picolylamines with nitroalkanes electrophilically activated in the presence of phosphorous acid in polyphosphoric acid (PPA) medium.

Enhanced Activity of P4503A4 and UGT1A10 Induced by Acridinone Derivatives C-1305 and C-1311 in MCF-7 and HCT116 Cancer Cells: Consequences for the Drugs' Cytotoxicity, Metabolism and Cellular Response

Activity modulation of drug metabolism enzymes can change the biotransformation of chemotherapeutics and cellular responses induced by them. As a result, drug-drug interactions can be modified. Acridinone derivatives, represented here by C-1305 and C-1311, are potent anticancer drugs. Previous studies in non-cellular systems showed that they are mechanism-based inhibitors of cytochrome P4503A4 and undergo glucuronidation via UDP-glucuronosyltranspherase 1A10 isoenzyme (UGT1A10). Therefore, we investigated the potency of these compounds to modulate P4503A4 and UGT1A10 activity in breast MCF-7 and colon HCT116 cancer cells and their influence on cytotoxicity and cellular response in cells with different expression levels of studied isoenzymes. We show that C-1305 and C-1311 are inducers of not only P4503A4 but also UGT1A10 activity. MCF-7 and HCT116 cells with high P4503A4 activity are more sensitive to acridinone derivatives and undergo apoptosis/necrosis to a greater extent. UGT1A10 was demonstrated to be responsible for C-1305 and C-1311 glucuronidation in cancer cells and glucuronide products were excreted outside the cell very fast. Finally, we show that glucuronidation of C-1305 antitumor agent enhances its pro-apoptotic properties in HCT116 cells, while the cytotoxicity and cellular response induced by C-1311 did not change after drug glucuronidation in both cell lines.

Position-Selective Synthesis and Biological Evaluation of Four Isomeric A-Ring Amino Derivatives of the Alkaloid Luotonin A

Following two orthogonal synthetic routes, a series of all four possible A-ring amino derivatives of the natural product Luotonin A (a known Topoisomerase I inhibitor) was synthesized. In both strategies, intramolecular cycloaddition reactions are the key step. The target compounds were obtained in good yields by mild catalytic transfer hydrogenation of the corresponding nitro precursors. In-vitro evaluation of the antiproliferative activity towards human tumor cell lines revealed the 4-amino compound (5b) to be the most effective agent, showing an interesting profile of cytotoxic activity. Among other effects, a significant G2/M cell cycle arrest was observed for this compound, suggesting that either Topoisomerase I is not the only biological target, or that some atypical mechanism is responsible for inhibition of this enzyme.

Caffeine Sensitizes U87-MG Human Glioblastoma Cells to Temozolomide through Mitotic Catastrophe by Impeding G2 Arrest

Temozolomide (TMZ) is the first-line chemotherapeutic agent in the treatment of glioblastoma multiforme (GBM). Despite its cytotoxic effect, TMZ also induces cell cycle arrest that may lead to the development of chemoresistance and eventual tumor recurrence. Caffeine, a widely consumed neurostimulant, shows anticancer activities and is reported to work synergistically with cisplatin and camptothecin. The present study aimed to investigate the effects and the mechanisms of action of caffeine used in combination with TMZ in U87-MG GBM cells. As anticipated, TMZ caused DNA damage mediated by the ATM/p53/p21 signaling pathway and induced significant G2 delay. Concurrent treatment with caffeine repressed proliferation and lowered clonogenic capacity on MTT and colony formation assays, respectively. Mechanistic study showed that coadministration of caffeine and TMZ suppressed the phosphorylation of ATM and p53 and downregulated p21 expression, thus releasing DNA-damaged cells from G2 arrest into premature mitosis. Cell cycle analysis demonstrated that the proportion of cells arrested in G2 phase decreased when caffeine was administered together with TMZ; at the same time, the amount of cells with micronucleation and multipolar spindle poles increased, indicative of enhanced mitotic cell death. Pretreatment of cells with caffeine further enhanced mitotic catastrophe development in combined treatment and sensitized cells to apoptosis when followed by TMZ alone. In conclusion, our study demonstrated that caffeine enhanced the efficacy of TMZ through mitotic cell death by impeding ATM/p53/p21-mediated G2 arrest.

Selective induction of DNA damage, G2 abrogation, and mitochondrial apoptosis by leaf extract of traditional medicinal plant Wrightia arborea in K562 cells

Plants have proved to be an important source of anti-cancer drugs. Wrightia arborea, an Indian Ayurvedic medicinal plant, is used traditionally to treat a variety of ailments. This study evaluates the antiproliferative/apoptotic potential of Wrightia arborea leaf extracts, prepared in different organic solvents, on cancer cell lines. MTT assay, light and fluorescence microscopy, flow cytometry, DNA laddering, alkaline comet assay, and western blotting were some of the techniques used for evaluation. Combinations of camptothecin, either with CHK1 inhibitor-PD407824 or with W. arborea leaf extract, were deployed to determine the G2 abrogating potential of the extract. The chloroform extract (WAC) selectively killed K562 cells, without affecting cancerous MCF-7, Hep G2 cells, and normal human peripheral blood lymphocytes. Cell death was characterized by observation of apoptotic bodies, increased Ca2+ and ROS, phosphatidyl serine externalization, mitochondrial membrane depolarization, DNA laddering, increased sub-G1 population, and altered expression of caspase 3, -9, and PARP. WAC also induced DNA damage, alterations in key G2/M phase protein expression, cell cycle perturbation, and potent G2 abrogation. The present study showed that W. arborea leaf extract, WAC, is capable of selectively killing leukemic cancer cells leaving normal lymphocytes unaffected. Our results indicate that this is effectuated through DNA damage and G2 abrogation leading to mitochondrial apoptosis. Taken together, this report contributes toward a better understanding of the anticancer properties of this traditional medicinal plant extract possessing valuable bioactive constituents which can serve as a bioresource for promising complimentary/alternative/chemopreventive therapeutics.

The imidazoacridinone C-1311 induces p53-dependent senescence or p53-independent apoptosis and sensitizes cancer cells to radiation

C-1311 is a small molecule, which has shown promise in a number of pre-clinical and clinical studies. However, the biological response to C-1311 exposure is complicated and has been reported to involve a number of cell fates. Here, we investigated the molecular signaling which determines the response to C-1311 in both cancer and non-cancer cell lines. For the first time we demonstrate that the tumor suppressor, p53 plays a key role in cell fate determination after C-1311 treatment. In the presence of wild-type p53, cells exposed to C-1311 entered senescence. In contrast, cells lines without functional p53 underwent mitotic catastrophe and apoptosis. C-1311 also induced autophagy in a non-p53-dependent manner. Cells in hypoxic conditions also responded to C-1311 in a p53-dependent manner, suggesting that our observations are physiologically relevant. Most importantly, we show that C-1311 can be effectively combined with radiation to improve the radiosensitivity of a panel of cancer cell lines. Together, our data suggest that C-1311 warrants further clinical testing in combination with radiotherapy for the treatment of solid tumors.

Targeting of tubulin polymerization and induction of mitotic blockage by Methyl 2-(5-fluoro-2-hydroxyphenyl)-1H-benzo[d]imidazole-5-carboxylate (MBIC) in human cervical cancer HeLa cell

Background

Microtubule Targeting Agents (MTAs) including paclitaxel, colchicine and vinca alkaloids are widely used in the treatment of various cancers. As with most chemotherapeutic agents, adverse effects and drug resistance are commonly associated with the clinical use of these agents. Methyl 2-(5-fluoro-2-hydroxyphenyl)-1H- benzo[d]imidazole-5-carboxylate (MBIC), a benzimidazole derivative displays greater toxicity against various cancer compared to normal human cell lines. The present study, focused on the cytotoxic effects of MBIC against HeLa cervical cancer cells and possible actions on the microtubule assembly.

Methods

Apoptosis detection and cell-cycle assays were performed to determine the type of cell death and the phase of cell cycle arrest in HeLa cells. Tubulin polymerization assay and live-cell imaging were performed to visualize effects on the microtubule assembly in the presence of MBIC. Mitotic kinases and mitochondrial-dependent apoptotic proteins were evaluated by Western blot analysis. In addition, the synergistic effect of MBIC with low doses of selected chemotherapeutic actions were examined against the cancer cells.

Results

Results from the present study showed that following treatment with MBIC, the HeLa cells went into mitotic arrest comprising of multi-nucleation and unsegregated chromosomes with a prolonged G₂-M phase. In addition, the HeLa cells showed signs of mitochondrial-dependant apoptotic features such as the release of cytochrome c and activation of caspases. MBIC markedly interferes with tubulin polymerization. Western blotting results indicated that MBIC affects mitotic regulatory machinery by up-regulating BubR1, Cyclin B1, CDK1 and down-regulation of Aurora B. In addition, MBIC displayed synergistic effect when given in combination with colchicine, nocodazole, paclitaxel and doxorubicin.

Conclusion

Taken together, our study demonstrated the distinctive microtubule destabilizing effects of MBIC against cervical cancer cells in vitro. Besides that, MBIC exhibited synergistic effects with low doses of selected anticancer drugs and thus, may potentially reduce the toxicity and drug resistance to these agents.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0332-0) contains supplementary material, which is available to authorized users.

Targeting of FLT3-ITD kinase contributes to high selectivity of imidazoacridinone C-1311 against FLT3-activated leukemia cells

Drugs targeting receptor tyrosine kinase FLT3 are of particular interest since activating FLT3-internal tandem duplication (ITD) mutations abundantly occur in fatal acute myeloid leukemias (AMLs). Imidazoacridinone C-1311, a DNA-reactive inhibitor of topoisomerase II, has been previously shown to be a potent and selective inhibitor of recombinant FLT3. Here, we expand those findings by studying its effect on leukemia cells with wild-type FLT3, FLT3-ITD mutant and no FLT3 receptor. While brief C-1311 exposure blocked wild-type and FLT3-ITD activity, profound and sustained inhibition was achieved only for FLT3-ITD mutants. C-1311 inhibited FLT3 downstream pathways (MAPK and AKT) independent of FLT3 status, yet translation to decreased viability was significant in FLT3-ITD cells. RNA interference against FLT3-ITD reduced cytotoxic effect and apoptosis induced by C-1311, indicating selective inhibition of FLT3-ITD crucial for high efficacy of drug against activated leukemia cells. Cellular responses in treated FLT3-ITD mutants included G1 and G2/M phase arrest, moderate inhibition of Bcl-2, caspase-3 activation, PARP cleavage, and depolarization of mitochondria. Consistent with selective decrease in FLT3-ITD activity, C-1311 remarkably reduced antiapoptotic survivin mRNA and protein expression, correlating well with enhanced apoptosis of FLT3-ITD cells. No survivin decrease and respectively lower level of apoptosis was found in wild-type and null-FLT3 cells. Combination of C-1311 with cytarabine or doxorubicin again showed distinct synergistic activity in FLT3-ITD-positive cells. The ability of C-1311 to selectively target constitutively active FLT3, suggests a favorable therapeutic index for AML carrying FLT3-ITD mutations. Thus further preclinical and clinical studies addressing its potency against FLT3-ITD kinase is well justified.

The antitumor compound triazoloacridinone C-1305 inhibits FLT3 kinase activity and potentiates apoptosis in mutant FLT3-ITD leukemia cells

AIM

FMS-like receptor tyrosine kinase (FLT3) is expressed in some normal hematopoietic cell types and plays an important role in the pathogenesis of acute myeloid leukemia (AML). In this study, we examined the effects of triazoloacridinone C-1305, an antitumor compound, on AML cells with different FLT3 status in vitro.

METHODS

A panel of human leukemic cell lines with different FLT3 status was used, including FLT3 internal tandem duplication mutations (FLT3-ITD, MV-4-11), wild-type FLT3 (RS-4-11) and null-FLT3 (U937) cells. Cell proliferation was estimated using MTT assays, and apoptosis was studied with flow cytometry and fluorescence microscopy. FLT3 kinase activity (phosphorylation of FLT3 at Tyr591) was determined with ELISA and Western blotting. FLT3 downstream signaling proteins involving AKT, MAPK and STAT5 were examined by Western blotting. RNA silencing was used to decrease the endogenous FLT3.

RESULTS

The mutant FLT3-ITD cells were more sensitive to C-1305 than the wild-type FLT3 and null-FLT3 cells (the IC50 values measured at 24 h were 1.2±0.17, 2.0±09, 7.6±1.6 μmol/L, respectively). C-1305 (1-10 μmol/L) dose-dependently inhibited the kinase activity of FLT3, which was more pronounced in the mutant FLT3-ITD cells than in the wild-type FLT3 cells. Furthermore, C-1305 dose-dependently decreased the phosphorylation of STAT5 and MAPK and the inhibitory phosphorylation of Bad, and induced time- and dose-dependent apoptosis in the 3 cell lines with the null-FLT3 cells being the least susceptible to C-1305-induced apoptosis. Knockdown of FLT3 with siRNA significantly decreased C-1305-induced cytotoxicity in the mutant FLT3-ITD cells.

CONCLUSION

C-1305 induces apoptosis in FLT3-ITD-expressing human leukemia cells in vitro, suggesting that mutated FLT3 kinase can be a new target for C-1305, and C-1305 may be a drug candidate for the therapeutic intervention in FLT3-associated AML.

CYP3A4 overexpression enhances apoptosis induced by anticancer agent imidazoacridinone C-1311, but does not change the metabolism of C-1311 in CHO cells

AIM

To examine whether CYP3A4 overexpression influences the metabolism of anticancer agent imidazoacridinone C-1311 in CHO cells and the responses of the cells to C-1311.

METHODS

Wild type CHO cells (CHO-WT), CHO cells overexpressing cytochrome P450 reductase (CPR) [CHO-HR] and CHO cells coexpressing CPR and CYP3A4 (CHO-HR-3A4) were used. Metabolic transformation of C-1311 and CYP3A4 activity were measured using RP-HPLC. Flow cytometry analyses were used to examine cell cycle, caspase-3 activity and cell apoptosis. The expression of pH 6.0-dependent β-galactosidase (SA-β-gal) was studied to evaluate accelerated senescence. ROS generation was analyzed with CM-H2 DCFDA staining.

RESULTS

CYP3A4 overexpression did not change the metabolism of C-1311 in CHO cells: the levels of all metabolites of C-1311 increased with the exposure time to a similar extent, and the differences in the peak level of the main metabolite M3 were statistically insignificant among the three CHO cell lines. In CHO-HR-3A4 cells, C-1311 effectively inhibited CYP3A4 activity without affecting CYP3A4 protein level. In the presence of C-1311, CHO-WT cells underwent rather stable G2/M arrest, while the two types of transfected cells only transiently accumulated at this phase. C-1311-induced apoptosis and necrosis in the two types of transfected cells occurred with a significantly faster speed and to a greater extent than in CHO-WT cells. Additionally, C-1311 induced ROS generation in the two types of transfected cells, but not in CHO-WT cells. Moreover, CHO-HR-3A4 cells that did not die underwent accelerated senescence.

CONCLUSION

CYP3A4 overexpression in CHO cells enhances apoptosis induced by C-1311, whereas the metabolism of C-1311 is minimal and does not depend on CYP3A4 expression.

Modulation of CYP3A4 activity and induction of apoptosis, necrosis and senescence by the anti-tumour imidazoacridinone C-1311 in human hepatoma cells

There is increasing evidence that the expression level of drug metabolic enzymes affects the final cellular response following drug treatment. Moreover, anti-tumour agents may modulate enzymatic activity and/or cellular expression of metabolic enzymes in tumour cells. We have investigated the influence of CYP3A4 overexpression on the cellular response induced by the anti-tumour agent C-1311 in hepatoma cells. C-1311-mediated CYP3A4 activity modulation and the effect of CYP3A4 overexpression on C-1311 metabolism have also been examined. With the HepG2 cell line and its CYP3A4-overexpressing variant, Hep3A4, experiments involving DAPI staining, cell cycle analysis, phosphatidylserine externalisation and senescence-associated (SA)-β-galactosidase expression, were used to monitor the effects of C-1311 exposure. C-1311 cellular metabolism and CYP3A4 activity were investigated by high-performance liquid chromatography. C-1311 metabolism was very low in both hepatoma cell lines and slightly influenced by CYP3A4 expression. Interestingly, in HepG2 cells, C-1311 was an effective modulator of CYP3A4 enzymatic activity, being the inhibitor of this isoenzyme in Hep3A4 cells. Cell cycle analysis showed that HepG2 cells underwent a rather stable G(2) /M arrest following C-1311 exposure, whereas CYP3A4-overexpressing cells accumulated only slightly in this compartment. C-1311-treated cells died by apoptosis and necrosis, whereas surviving cells underwent senescence; however, these effects occurred faster and more intensely in Hep3A4 cells. Although CYP3A4 did not influence C-1311 metabolism, changes in CYP3A4 levels affected the C-1311-induced response in hepatoma cells. Therefore, inter-patient differences in CYP3A4 levels should be considered when assessing the potential therapeutic effects of C-1311.

Metabolic transformation of antitumor acridinone C-1305 but not C-1311 via selective cellular expression of UGT1A10 increases cytotoxic response: implications for clinical use

The acridinone derivates 5-dimethylaminopropylamino-8-hydroxytriazoloacridinone (C-1305) and 5-diethylaminoethylamino-8-hydroxyimidazoacridinone (C-1311) are promising antitumor agents with high activity against several experimental cellular and tumor models and are under evaluation in preclinical and early phase clinical trials. Recent evidence from our laboratories has indicated that both compounds were conjugated by several uridine diphosphate-glucuronyltransferase (UGT) isoforms, the most active being extrahepatic UGT1A10. The present studies were designed to test the ability and selectivity of UGT1A10 in the glucuronidation of acridinone antitumor agents in a cellular context. We show that in KB-3 cells, a HeLa subline lacking expression of any UGT isoforms, both C-1305 and C-1311 undergo metabolic transformation to the glucuronidated forms on overexpression of UGT1A10. Furthermore, UGT1A10 overexpression significantly increased the cytotoxicity of C-1305, but not C-1311, suggesting that the glucuronide was more potent than the C-1305 parent compound. These responses were selective for UGT1A10 because documented overexpression of UGT2B4 failed to produce glucuronide products and failed to alter the cytotoxicity for both compounds. These findings contribute to our understanding of the mechanisms of action of these agents and are of particular significance because data for C-1305 contradict the dogma that glucuronidation typically plays a role in detoxification or deactivation. In summary, these studies suggest that extrahepatic UGT1A10 plays an important role in the metabolism and the bioactivation of C-1305 and constitutes the basis for further mechanistic studies on the mode of action of this drug, as well as translational studies on the role of this enzyme in regulation of C-1305 toxicity in cancer.

Role of human UDP-glucuronosyltransferases in the biotransformation of the triazoloacridinone and imidazoacridinone antitumor agents C-1305 and C-1311: highly selective substrates for UGT1A10

5-Diethylaminoethylamino-8-hydroxyimidazoacridinone, C-1311 (NSC-645809), is an antitumor agent shown to be effective against breast cancer in phase II clinical trials. A similar compound, 5-dimethylaminopropylamino-8-hydroxytriazoloacridinone, C-1305, shows high activity against experimental tumors and is expected to have even more beneficial pharmacological properties than C-1311. Previously published studies showed that these compounds are not substrates for cytochrome P450s; however, they do contain functional groups that are common targets for glucuronidation. Therefore, the aim of this work was to identify the human UDP-glucuronosyltransferases (UGTs) able to glucuronidate these two compounds. High-performance liquid chromatography analysis was used to examine the activities of human recombinant UGT1A and UGT2B isoforms and microsomes from human liver [human liver microsomes (HLM)], whole human intestinal mucosa [human intestinal microsomes (HIM)], and seven isolated segments of human gastrointestinal tract. Recombinant extrahepatic UGT1A10 glucuronidated 8-hydroxyl groups with the highest catalytic efficiency compared with other recombinant UGTs, V(max)/K(m) = 27.2 and 8.8 μl · min⁻¹ · mg protein⁻¹, for C-1305 and C-1311, respectively. In human hepatic and intestinal microsomes (HLM and HIM, respectively), high variability in UGT activities was observed among donors and for different regions of intestinal tract. However, both compounds underwent UGT-mediated metabolism to 8-O-glucuronides by microsomes from both sources with comparable efficiency; V(max)/K(m) values were from 4.0 to 5.5 μl · min⁻¹ · mg protein⁻¹. In summary, these studies suggest that imid azoacridinone and triazoloacridinone drugs are glucuronidated in human liver and intestine in vivo and may form the basis for future translational studies of the potential role of UGTs in resistance to these drugs.

Cell fusion and hyperactive osteoclastogenesis in multiple myeloma

Multiple myeloma (MM) is a hematologic malignancy whose progression may account for uncontrolled osteoclastogenesis promoted by the malignant plasma cells within the marrow microenvironment. Osteoclasts are multinucleated cells derived from the fusion of myeloid progenitors such as monocytes/macrophages, in response to specific differentiation factors released within the marrow niche, that are significantly deregulated in MM. In this malignancy DC-STAMP, a major fusogen protein enrolled by pre-osteoclasts, is highly expressed by peripheral macrophages, whereas dendritic cells and myeloma plasma cells show high fusogenic susceptibility and under specific conditions transdifferentiate to osteoclasts. In particular, the malignant plasma cells, besides altered ploidy, expression of cancer stem cell phenotype and high metastasizing capability, are able to express phenotypic markers of osteclasts, namely the proteolytic enzymes for the bone matrix, and to activate the β3 transcriptional pathway leading to ERK1/2 phosphorylation and initiation of the bone resorbing activity. Thus, based on the imbalanced osteoclast formation and activity that involve cells constitutively uncommitted to osteoclast differentiation, both homotypic and heterotypic cell fusions in myeloma marrow microenvironment represent a major pathogenetic event that drives the development and progression of the skeleton devastation typical of the myeloma bone disease.

Physicochemical interaction of antitumor acridinone derivatives with DNA in view of QSAR studies

The acridinone derivatives with antitumor activity and ability with respect to noncovalent DNA binding were investigated for their quantitative structure–activity relationships (QSAR). Multiple regression analysis was used to model relationships between molecular descriptors and antileukemia activity, or between molecular descriptors and DNA-duplexes stabilization. Studies were performed on molecular modeling using HyperChem and Dragon computer programs, and molecular geometry optimization using MM+ molecular mechanics and semi-empirical AM1 method. Two multiple regression equations were derived and characterized as good and with statistically significant correlations, R = 0.9384 and R = 0.8388, for quantitative structure–antitumor activity relationships and quantitative structure–ability to DNA-duplexes stabilization relationships, respectively. Moreover, hydrophobic and total molecular symmetry properties are important for antitumor activity of acridinone derivatives, and electronic and topological properties are important for physicochemical (noncovalent) DNA-duplexes stabilization of these compounds. The obtained equations can be used for prediction of acridinone derivatives’ activity and their ability to noncovalent interaction with DNA which, as it was shown earlier, play important role in the antitumor mechanism of action of these compounds.

Death through a tragedy: mitotic catastrophe

Mitotic catastrophe (MC) has long been considered as a mode of cell death that results from premature or inappropriate entry of cells into mitosis and can be caused by chemical or physical stresses. Whereas it initially was depicted as the main form of cell death induced by ionizing radiation, it is today known to be triggered also by treatment with agents influencing the stability of microtubule, various anticancer drugs and mitotic failure caused by defective cell cycle checkpoints. Although various descriptions explaining MC exist, there is still no general accepted definition of this phenomenon. Here, we present evidences indicating that death-associated MC is not a separate mode of cell death, rather a process ('prestage') preceding cell death, which can occur through necrosis or apoptosis. The final outcome of MC depends on the molecular profile of the cell.