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The protocadherin proteins are cell adhesion molecules at the crossroad of signaling pathways playing a major role in neuronal development. It is now understood that their role as signaling hubs is not only important for the normal physiology of cells but also for the regulation of hallmarks of cancerogenesis. Importantly, protocadherins form a cluster of genes that are regulated by DNA methylation. We have identified for the first time that PCDHB15 gene is DNA-hypermethylated on its unique exon in the metastatic melanoma-derived cell lines and patients’ metastases compared to primary tumors. This DNA hypermethylation silences the gene, and treatment with the DNA demethylating agent 5-aza-2′-deoxycytidine reinduces its expression. We explored the role of PCDHB15 in melanoma aggressiveness and showed that overexpression impairs invasiveness and aggregation of metastatic melanoma cells in vitro and formation of lung metastasis in vivo. These findings highlight important modifications of the methylation of the PCDHβ genes in melanoma and support a functional role of PCDHB15 silencing in melanoma aggressiveness.

Background Efficient treatments against metastatic melanoma dissemination are still lacking. Here, we report that low-cytotoxic concentrations of 5-aza-2′-deoxycytidine, a DNA demethylating agent, prevent in vitro 3D invasiveness of metastatic melanoma cells and reduce lung metastasis formation in vivo. Results We unravelled that this beneficial effect is in part due to MIR-199A2 re-expression by promoter demethylation. Alone, this miR showed an anti-invasive and anti-metastatic effect. Throughout integration of micro-RNA target prediction databases with transcriptomic analysis after 5-aza-2′-deoxycytidine treatments, we found that miR-199a-3p downregulates set of genes significantly involved in invasion/migration processes. In addition, analysis of data from melanoma patients showed a stage- and tissue type-dependent modulation of MIR-199A2 expression by DNA methylation. Conclusions Thus, our data suggest that epigenetic- and/or miR-based therapeutic strategies can be relevant to limit metastatic dissemination of melanoma. Electronic supplementary material The online version of this article (10.1186/s13148-018-0600-2) contains supplementary material, which is available to authorized users.

International audience; DNA methylation is a mammalian epigenetic mark that participates to define where and when genes are expressed, both in normal cells and in the context of diseases. Like other epigenetic marks, it is reversible and can be modulated by chemical agents. Because it plays an important role in cancer by silencing certain genes, such as tumour suppressor genes, it is a promising therapeutic target. Two compounds are already approved to treat haematological cancers, and many efforts have been carried out to discover new molecules that inhibit DNA methyltransferases, the enzymes responsible for DNA methylation. Here, we analyse the molecular mechanisms and cellular pharmacology of these inhibitors, pointing out the necessity for new pharmacological models and paradigms. The parameters of pharmacological responses need to be redefined: the aim is cellular reprogramming rather than general cytotoxicity. Thus, ''epigenetic" rather than cytotoxic dosages are defined. Another issue is the delay of the response: cellular reprogramming can take several generations to produce observable phenotypes. Is this compatible with laboratory scale experiments? Finally, it is important to consider the specificity for cancer cells compared to normal cells and the appearance of resistance. We also discuss different techniques that are used and the selection of pharmacological models.

Antitumor activities of substances from natural sources apart from vascular plants and micro-organisms have been poorly investigated. Here we report on a pharmacological screening of a bryophyte extract library using a phenotypic cell-based assay revealing microtubules, centrosomes and DNA. Among the 219 moss extracts tested, we identified 41 extracts acting on cell division with various combinations of significant effects on interphasic and mitotic cells. Seven extracts were further studied using a cell viability assay, cell cycle analysis and the phenotypic assay. Three distinct pharmacological patterns were identified including two unusual phenotypes.

Rad51 protein plays an essential role in recombination repair of DNA double-strand breaks and DNA crosslinking adducts. It is part of complexes which can vary with the stage of the cell cycle and the nature of the DNA lesions. During a search for Rad51-associated proteins in CHO nuclear extracts of S-phase cells by mass spectrometry of proteins immunoprecipitated with Rad51 antibodies, we identified a centrosomal protein, gamma-tubulin. This association was confirmed by the reverse immunoprecipitation with gamma-tubulin antibodies. Both proteins copurified from HeLa cells nuclear extracts following a tandem affinity purification of double-tagged Rad51. Immunofluorescence analysis showed colocalization of both Rad51 and gamma-tubulin in discrete foci in mammalian cell nuclei. The number of colocalized foci and their overlapping area increased in the presence of DNA damage produced by genotoxic treatments either during S phase or in exponentially growing cells. These variations did not result from an overall stress because microtubule cytoskeleton poisons devoid of direct interactions with DNA, such as taxol or colcemid, did not lead to an increase of this association. The recruitment of Rad51 and gamma-tubulin in the same nuclear complex suggests a link between DNA recombination repair and the centrosome function during the cell cycle.

Starting from a FPP analogue with nanomolar inhibitory activity against isolated FPTase, yet lacking activity in cellular assays, structural modifications were performed to enhance cellular activity by removing all acidic functionalities. Overall, these changes resulted in the transformation of a pure FPP to a mixed FPP and CAAX competitive inhibitor with nanomolar activity on isolated FPTase and micromolar inhibitory activity in the farnesylation of H-Ras in cultured DLD-1 cells.

A novel series of compounds, derived from 4-amino-phenyl piperazine, has been designed to selectively inhibit farnesyl protein transferase (FPTase) as CAAX tetrapeptide analogues. Certain of these compounds were shown to possess low nanomolar inhibitory activity both against the isolated enzyme and in cultured cells.

F 11782 (2",3"-bis-pentafluorophenoxyacetyl-4",6"ethylidene-beta-D-glucoside of 4'-phosphate-4'-dimethylepipodophyllotoxin-2N-methyl glucamine salt), is a novel dual catalytic inhibitor of topoisomerases I and II characterised by marked in vivo antitumour activity, which also proved cytotoxic and exhibited DNA damaging properties in vitro. Mechanisms associated with this cell killing by F 11782 have been examined in P388 leukaemia cells. Treatment with F 11782 resulted in a dose-dependent DNA fragmentation coupled with the characteristic morphological features of apoptosis. Apoptosis-inducing concentrations of F 11782 induced caspases-3/7 activation accompanied by proteolytic cleavage of poly(ADP-ribose)-polymerase, which could be inhibited by the caspase inhibitor acetyl-Asp-Glu-Val-Asp-aldehyde. In addition, F 11782-induced apoptosis in P388 cells was associated with an increased expression of the pro-apototic Bax protein, without significant changes in the level of the anti-apoptotic Bcl-2 protein, and with modification at the mitochondrial membrane function. These results indicate that F 11782 leads to apoptosis through a caspase-3/7 dependent mechanism and suggest that the so-called "mitochondrial pathway" is implicated in F 11782-induced apoptosis in P388 cells.

Purpose: Vinflunine (VFL) is a novel Vinca alkaloid with markedly superior experimental in vivo antitumour activity to its parent molecule, vinorelbine (Navelbine, NVB), against a panel of murine and human tumours. The aim of this study was to establish whether there are differences in the rate and extent of development of resistance, both in vivo and in vitro, to these two newer Vinca alkaloids under identical selection conditions. Methods: Using P388 leukaemia cells in vivo, it was evident that VFL induced drug resistance far less readily than NVB, as shown by the number of passages required to select for total resistance. Under in vitro conditions, using A549 human lung carcinoma cells, it was also clearly shown by drug sensitivity determinations that VFL was a less-potent inducer of drug resistance than NVB. Resistance resulting from either in vivo or in vitro selection was associated with a classic multidrug resistance profile. Further characterization of the drug-resistance phenotype of the most highly resistant A549 sublines showed that the level of total β-tubulin expression appeared to be modified exclusively in the NVB-resistant cells. Conclusion: The clear demonstration that resistance to VFL developed far less readily than resistance to NVB both in vivo and in vitro may have potential clinical implications.

F 11782 is a newly identified catalytic inhibitor of topoisomerases I and II, without any detectable interaction with DNA. This study aimed to establish whether its catalytic inhibition of topoisomerase II was mediated by mechanisms similar to those identified for the bisdioxopiperazines. In vitro combinations of F 11782 with etoposide resulted in greater than additive cytotoxicity in L1210 cells, contrasting with marked antagonism for combinations of etoposide with either ICRF-187 or ICRF-193. All three compounds caused a G2/M blockade of P388 cells after an 18-h incubation, but by 40 h polyploidization was evident only with the bisdioxopiperazines. Gel retardation data revealed that only F 11782, and not the bisdioxopiperazines, was capable of completely inhibiting the DNA-binding activity of topoisomerase II, confirming its novel mechanism of action. Furthermore, unlike ICRF-187 and ICRF-193, the cytotoxicity of F 11782 appeared mediated, at least partially, by DNA damage induction in cultured GCT27 human teratoma cells, as judged by a fluorescence-enhancement assay and monitoring p53 activation. Finally, the major in vivo antitumor activity of F 11782 against the murine P388 leukemia (i.v. implanted) and the B16 melanoma (s.c. grafted) contrasted with the bisdioxopiperazines' general lack of activity. Overall, F 11782 and the bisdioxopiperazines appear to function as quite distinctive catalytic topoisomerase II inhibitors.

Failure of chemotherapy is frequently observed in patients previously treated with radiotherapy. To establish a cellular model for examining this resistance phenotype a series of mammalian tumor cell lines were exposed in vitro to fractionated X-irradiation and were then shown to express resistance to multiple antitumor drugs, including vincristine, etoposide and cisplatin. In these experiments the radiation was delivered as 10 fractions of 5 Gy (dose resulting in 1 log cell kill) given intermittently over several months. We now report that a comparable multidrug-resistance profile is expressed by human SK-OV-3 human ovarian tumor cells exposed in vitro to low dose (2 Gy) twice-daily fractions of X-rays given for 5 days on two consecutive weeks, essentially mimicking clinical practice, involving an overexpression of two MDR-associated proteins, P-glycoprotein and the multidrug resistance protein 1 (MRP1), with the latter being readily detectable by immunocytochemistry.

This study aimed to define the mechanism of action of vinflunine, a novel Vinca alkaloid synthesised from vinorelbine using superacidic chemistry and characterised by superior in vivo activity to vinorelbine in preclinical tumour models. In vitro vinflunine cytotoxicity proved dependent on concentration and exposure duration, with IC50 values (72-hr exposures) generally ranging from 60-300 nM. Vinflunine induced G2 + M arrest, associated with mitotic accumulation and a concentration-dependent reduction of the microtubular network of interphase cells, accompanied by paracrystal formation. These effects, while comparable to those of vincristine, vinblastine or vinorelbine, were achieved with 3- to 17-fold higher vinflunine concentrations. However, vinflunine and the other Vincas all inhibited microtubule assembly at micromolar concentrations. Vinflunine, like vinblastine, vincristine and vinorelbine, appeared to interact at the Vinca binding domain, as judged by proteolytic cleavage patterns, and induced tubulin structural changes favouring an inhibition of GTP hydrolysis. However, vinflunine did not prevent [3H]vincristine binding to unassembled tubulin at concentrationsor = 100 microM, and only weakly inhibited binding of [3H]vinblastine or [3H]vinorelbine. Indeed, specific binding of [3H]vinflunine to tubulin was undetectable by centrifugal gel filtration. Thus, the comparative capacities of these Vincas to bind to or to interfere with their binding to tubulin could be classified as: vincristinevinblastinevinorelbinevinflunine. By monitoring alkylation of sulfhydryl groups, differential effects on tubulin conformation were identified with vinflunine and vinorelbine acting similarly, yet distinctively from vinblastine and vincristine. Overall, vinflunine appears to function as a definite inhibitor of tubulin assembly, while exhibiting quantitatively different tubulin binding properties to the classic Vinca alkaloids.

This paper describes differentiation in terms of population dynamics through the medium of Voronoi paving which enables (via digital cell image analysis) the structure of human LOVO and HCT-15 colorectal neoplastic cell colonies growing on histological slides to be characterized. Two other tests were also used, i.e., the colorimetric MTT assay that enables the cell growth level to be determined, and a test allowing the assessment of the proliferation index, i.e., the percentage of cells in the S phase of the cell cycle. The results show that these colorectal neoplastic cells exhibited a comparatively high level of organisation in terms of the topographical distribution of nuclei within the clones when the cells were cultivated in media containing even small amounts of fetal calf serum. On the other hand, certain chemically defined media completely overturned this “pseudo-tissular” architecture. Furthermore, the colorectal cells growing in media including fetal calf serum exhibited relatively large and dense clones, undergoing an increase in the density of these clones when hormones were added to the culture medium and, concomitantly, a decrease in their proliferation. In contrast, the cells growing in chemically defined media generally exhibited smaller clones whose cell proliferation was paradoxically greater than that of the cells referred to above. This seems to bring out the importance of the part played by the cell loss factor in this cell population dynamic. © 1993 Wiley-Liss, Inc.

Six protoflavonoids, including two new compounds, were isolated during a large scale screening of fern extracts for original interaction with mitosis. The new compounds isolated from PHEGOPTERIS DECURSIVE-PINNATA and EQUISETUM FLUVIATILE were 2′,3′-dihydroprotogenkwanone ( 1) and 2′,3′-dihydro-2′-hydroxyprotoapigenone ( 2). Known compounds were: protoapigenone, protogenkwanone, protoapigenin, and 4′- O- β-D-glucopyranosyl protoapigenin. They showed a cytotoxic activity against HeLa cells at a micromolar level. IC 50 values were 2 µM for compound 1, > 10 µM for compound 2, and respectively 2.4, 0.6, > 10 µM for the known compounds. Their cytotoxic effects were associated with phenotypic changes never observed before and characterized by the loss of centrosomal γ-tubulin labelling in both mitotic and interphasic cells.

A series of 3-amino- and 3-alkylamino-2-deoxy-β-d-ribo- and β-d-arabino-glycosides of 4‘-demethylepipodophyllotoxin have been synthesized by means of an improved trimethylsilyliodide procedure for the podophyllotoxin-4‘-demethylepipodophyllotoxin conversion, an efficient and high yielding synthesis of silyl glycoside donors of 3-azido-2,3-dideoxy-β-d-ribo- and β-d-arabino-hexopyranosides and stereoselective glycosylations. In vitro evaluation of cytotoxic effects against murine L1210 leukemia critically demonstrates the essential role played by a 4,6-acetal for biological activity. Among the most cytotoxic compounds, 3-amino-2,3-dideoxy- and 3-N,N-(dimethylamino)-2,3-dideoxy etoposide analogues, 17 and 27−29 are at least as potent as etoposide on the in vivo P388 (iv/ip) murine leukemia models. However, surprisingly enough, none of these compounds inhibits the human DNA topoisomerases I or II or binds to tubulin to prevent its polymerization and microtubule assembly. Therefore, their mechanism of action r...

We set up in vitro several human colorectal neoplastic cell lines that we labelled "hormone-sensitive" (HS) in comparison to the original cell lines which appeared to be rather "hormone-insensitive" (HI). We used LoVo and HCT-15 human colorectal neoplastic cell lines and studied the influence of 17 beta-oestradiol (E2), gastrin and two gonadotropin-releasing hormone (GnRH) analogues, HRF and buserelin, on the proliferation of the HS and HI variants of the LoVo and HCT-15 cell lines. Cell proliferation was evaluated by a colorimetric assay, the MTT test. Our results show that E2, gastrin, HRF and buserelin did not induce a significant stimulatory influence on the HI variants of the LoVo and HCT-15 cells, i.e. the cells that were cultured in a hormone-free 10% FCS-supplemented medium. In sharp contrast, the colorectal cells cultured for 30 passages in an E2 and/or gastrin + 1% FCS-supplemented medium showed a marked tropic response to E2, gastrin, HRF and buserelin. However, the HS variants of the HCT-15 cells appeared less sensitive to the two GnRH analogues than did the HS variants of the LoVo cells.

Metastatic melanomas are the deadliest form of skin cancer and are very aggressive tumors showing highly invasive properties and a rapid chemoresistance to standard treatment (Dacarbazine) and to specific BRAF-V600E kinase inhibitors (Vemurafenib). Thus, targeting these tumors remains a major concern for novel therapeutic proposals. Abnormal patterns of DNA methylation, an epigenetic modification that cells use to control gene expression, have been described in these tumors. These epigenetic modifications participate in melanoma formation and maintenance. The aim of our project is to characterize the DNA methylation changes that occur in the most aggressive form of melanoma and to reverse these changes by using clinically active DNA methyltransferase inhibitors (5-aza-2′-deoxycytidine, 5-aza-dC). To date a limited number of datasets have been published depicting the effects of inhibitors of DNA methylation on invasive capacities of metastatic melanoma cells. The work presented here, focuses on the study of the effects of DNA methylation inhibition on metastatic melanoma invasiveness. We have set up an original method to quantify DNA methylation by FACS and shown that non cytotoxic nanomolar 5-aza-dC concentrations were able to demethylate DNA of WM-266-4 metastatic melanoma cells. Then using an in vitro 3D spheroids cell invasion assay and fluorescent microscopy to measure invasion capacities of metastatic cell lines, we showed that 5-aza-dC was able to inhibit invasion of WM-266-4 cells at these non-cytotoxic demethylating concentrations. Citation Format: Chantal Etiévant, Cécile Desjobert, Arnaud Carrier, Audrey Delmas, Jorg Tost, Gilles Favre, Joelle Riond, Paola Arimondo. 5-aza-2′-deoxycytidine, a DNA demethylating agent, inhibits metastatic melanoma invasiveness. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5524. doi:10.1158/1538-7445.AM2014-5524

Purpose. F 11782, or 2′,3′-bis-pentafluorophenoxyacetyl-4′,6′-ethylidine-β-D-glucoside of 4′-phosphate-4′-dimethylepipodophyllotoxin 2N-methyl glucamine salt, a novel dual catalytic inhibitor of topoisomerases I and II, characterized by marked antitumour activity in vivo in a series of experimental murine and human tumours, has been selected for further development. This preclinical study was undertaken to investigate its potential for inclusion in combination chemotherapy regimens. The in vitro cytotoxicity of F 11782 incubated simultaneously with the following drugs was investigated: aclarubicin, cisplatin, doxorubicin, etoposide, 5-fluorouracil, mitomycin C, paclitaxel, topotecan or vinorelbine. Methods. The combinations were first evaluated in vitro against the GCT27 human testicular teratoma cell line and then against the A549 human non-small cell lung cancer cell line using median effect analysis. Results. F 11782 in combination with cisplatin, mitomycin C, etoposide or doxorubicin showed synergistic cytotoxicity against both cell lines. Moreover, F 11782 combined with cisplatin or mitomycin C showed antitumour activity in vivo against P388 murine leukaemia grafted intravenously. Such synergy might have resulted from the identified nucleotide excision repair inhibitory activity of F 11782. Conclusions. F 11782 appears to be a promising candidate for combination chemotherapy, especially with DNA-damaging agents.

The ability of a class of C-20' modified vinca alkaloid congeners to induce tubulin spiral formation was investigated relative to their ability to inhibit microtubule assembly, their cytotoxicity against a leukemic cell line, L1210, and their measured and calculated partition coefficients. These studies were prompted by the observation that the energetics of vinca alkaloid-induced tubulin spiral polymers, or spiraling potential, is inversely related to their clinical dosage and are aimed at the long-term goal of developing the ability to predict the cytotoxic and antineoplastic properties of antimitotic drugs. We demonstrate here that vinca-induced tubulin-spiraling potential is significantly correlated with cytotoxicity against L1210 cells. This is consistent with the size of spirals formed being proportional to the relaxation time for polymer redistribution, the lifetime of cell retention, and effects on microtubule ends and dynamics. Spiraling potential also correlates with calculated but not measured partition coefficients. Surprisingly, spiraling potential does not correlate with the ability to inhibit microtubule formation with purified tubulin or microtubule protein. For the set of C-20' modified compounds studied, the largest inhibitory effects on spiraling potential and cytotoxicity are caused by multiple sites of halogen (-F, -Cl) substitution with the introduction of increased rigidity in the ring. This suggests the C-20 ' position interacts with a hydrogen bond acceptor or an electrophilic region on the protein that electrostatically disfavors halogen substitutions. These studies are discussed in terms of the cellular mode of action of antimitotic drugs, particularly the importance of microtubule dynamics during mitosis and the factors that regulate those dynamics.

Purpose: F 11782 (2′′,3′′-bis pentafluorophenoxyacetyl-4′′,6′′-ethylidene-β-d-glucoside of 4′-phosphate-4′-dimethylepipodophyllotoxin, di-N-methyl glucamine salt) is a newly synthesized dual catalytic inhibitor of topoisomerases I and II with major in vivo antitumour activity. In this study, we compared and contrasted F 11782 with three other known inhibitors of both these nuclear enzymes, namely aclarubicin, intoplicin and TAS-103, and established its novel mechanism of action. Methods: In vitro growth-inhibitory effects against a panel of murine and tumour cell lines were measured by cell counting, clonogenicity or tetrazolium metabolic dye (MTT) assays. In vivo antitumour activities were evaluated against two murine tumour models (i.v. P388 leukaemia and s.c. B16 melanoma). Finally, interactions with either DNA or DNA-topoisomerases were determined using various methodologies: DNA-intercalator displacement, pBR322 DNA relaxation, kDNA decatenation, topoisomerase II extractability measurements, stabilization of topoisomerase-induced cleavable complexes (CC) in vitro and in cells, and gel retardation assays. Results: F 11782 had a different profile of sensitivities and proved generally less cytotoxic than the other dual inhibitors tested in vitro, while showing significantly superior antitumour activity in vivo. F 11782, which did not stabilize CC either in vitro or in cells, was the only compound of this series capable of inhibiting the catalytic activity of both DNA-topoisomerases without interacting with DNA, and of completely impairing the binding of these nuclear proteins to DNA. Moreover, only cotreatment of cells in vitro with F 11782 enhanced the cytotoxic activity of etoposide. Conclusion: These results emphasize the novel mechanism of action of F 11782 vis-a-vis the other dual inhibitors of topoisomerases I and II and so augur well for its future clinical development.

Purpose: Vinflunine (20′-20′-difluoro-3′,4′-dihydrovinorelbine), a novel derivative of vinorelbine characterized by marked antitumour activity in vivo in a series of experimental murine and human tumours is currently undergoing phase I evaluation. To investigate its potential for inclusion in combination chemotherapy regimens, this preclinical study was undertaken. The in vitro cytotoxicity of vinflunine incubated simultaneously with one of the following drugs was investigated: camptothecin, cisplatin, doxorubicin, etoposide, 5-fluorouracil, gemcitabine, mitomycin C, paclitaxel or vinorelbine. Methods: The combinations were first evaluated in vitro against the A549 human non-small-cell lung cancer cell line using median-effect analyses. Results: The results revealed synergistic cytotoxicity when vinflunine was combined with cisplatin, mitomycin C, doxorubicin or 5-fluorouracil. Synergy was also observed when testing similar combinations against CCRF-CEM human leukaemia cells. Finally, these findings were comparable with those resulting from such combinations involving vinorelbine instead of vinflunine. Conclusion: Vinflunine appears a promising candidate for combining with other anticancer drugs.

F 11782, a novel epipodophylloid, proved a potent inhibitor of the catalytic activities of both topoisomerases I and II. Unlike classical inhibitors such as camptothecin or etoposide, F 11782 did not stabilise cleavable complexes induced by either topoisomerases I or II nor did it preferentially inhibit the religation step of the catalytic cycle of either enzyme. F 11782 neither intercalated DNA nor bound in its minor groove, and showed only weak inhibition of the ATPase activity associated with topoisomerase II. F 11782 appeared to act by inhibiting the binding of topoisomerases I and II to DNA in a manner dependent both on drug and enzyme concentrations, via a mechanism not previously described or shared by other known topoisomerase ‘poisons’ or inhibitors. In contrast, F 11782 had only a weak effect or none at all on various other DNA-interacting enzymes. In conclusion, F 11782, as a non-intercalating, specific catalytic inhibitor of both topoisomerases I and II with an original mechanism of action, may be considered to represent the first of a new class of topoisomerase-interacting agents.

A series of 3-amino- and 3-alkylamino-2-deoxy-beta-D-ribo- and beta-D-arabino-glycosides of 4'-demethylepipodophyllotoxin have been synthesized by means of an improved trimethylsilyliodide procedure for the podophyllotoxin-4'-demethylepipodophyllotoxin conversion, an efficient and high yielding synthesis of silyl glycoside donors of 3-azido-2,3-dideoxy-beta-D-ribo- and beta-D-arabino-hexopyranosides and stereoselective glycosylations. In vitro evaluation of cytotoxic effects against murine L1210 leukemia critically demonstrates the essential role played by a 4,6-acetal for biological activity. Among the most cytotoxic compounds, 3-amino-2,3-dideoxy- and 3-N, N-(dimethylamino)-2,3-dideoxy etoposide analogues, 17 and 27-29 are at least as potent as etoposide on the in vivo P388 (iv/ip) murine leukemia models. However, surprisingly enough, none of these compounds inhibits the human DNA topoisomerases I or II or binds to tubulin to prevent its polymerization and microtubule assembly. Therefore, their mechanism of action remains to be cleared up.

Vinflunine (VFL) is a novel derivative of vinorelbine (NVB, Navelbine®), which has shown markedly superior antitumor activity to NVB, in various experimental animal models. To establish whether this new Vinca alkaloid participates in P-glycoprotein (Pgp)-mediated multidrug resistance (MDR), VFL-resistant murine P388 cells (P388/VFL) were established in vivo and used in conjunction with the well established MDR P388/ADR subline, to define the in vivo resistance profile for VFL. P388/VFL cells proved cross-resistant to drugs implicated in MDR (other Vinca alkaloids, doxorubicin, etoposide), but not to campothecin or cisplatin and showed an increased expression of Pgp, without any detectable alterations in topoisomerase II or in glutathione metabolism. The P388/ADR cells proved cross-resistant to VFL both in vivo and in vitro, and this VFL resistance was efficiently modulated by verapamil in vitro. Cellular transport experiments with tritiated-VFL revealed differential uptake by P388 sensitive and P388/ADR resistant cells, comparable with data obtained using tritiated-NVB. In various in vitro models of human MDR tumor cells, whilst full sensitivity was retained in cells expressing alternative non-Pgp-mediated MDR mechanisms, cross resistance was identified in Pgp-overexpressing cells. Differences were, however, noted in terms of the drug resistance profiles relative to the other Vincas, with tumor cell lines proving generally least cross-resistant to VFL. Overall, these results suggest that VFL, like other Vinca alkaloids, participates in Pgp-mediated MDR, with tumor cells selected for resistance to VFL overexpressing Pgp, yet MDR tumor cell lines proved generally less cross resistant to VFL relative to the other Vinca alkaloids.

The Ubiquitin-Proteasome System (UPS) is the main non-lysosomial proteolytic machinery in the eukaryotic cells. Prior to their degradation proteins are adressed to the catalytic 26S proteasome complex composed of a 20S “core” that contains proteolytic activities, assembled with one or two 19S regulatory particles that bind proteins to be degraded. Due to its central role of in regulating cell cycle progression and signal transduction the UPS has been proposed as a suitable target for antineoplastic strategies. To date only catalytic inhibitors of proteasome, targeting proteolytic activities of the 20S core particle, have been characterized and/or have emerged as potent anticancer drugs (1). However, the capacity of the UPS to degrade proteins not only depends of the catalytic activities of the 20S core, but also of the 26S proteasome assembly, a dynamic and tightly controlled cellular process. Thus, compounds impairing 26S proteasome assembly could represent a novel class of proteasome inhibitors. With the aim of identifying such molecules we first set up a robust biochemical screening assay allowing us to follow 26S proteasome assembly in vitro. First, 26S proteasome was purified from Hela cells using affinity chromatography followed by gel filtration. Then, experimental conditions were determined for in vitro 26S disassembly into its constitutive sub-complexes (19S+20S) ands its re-assembly as an active and functional 26S entity. The differential CTL-activity between 26S and 20S proteasomes (2) was then used as the readout to follow the reassembly of 26S in vitro, prior to be confirmed using in gel overlay experiments and western-blotting. Using this biochemical assay: 1) we screened naturals compounds endowed with antiproliferative properties and described as inhibitors of the ubiquitine-proteasome pathway (3). 2) we identified structurally-related natural molecules, epidithiodioxopiperazine and diketodithiopiperazine derivatives, as the first class of molecules inhibiting proteasome assembly without significantly affecting neither 26S nor 20S catalytic activity in vitro. Our research efforts now concentrate in showing that: 1) these molecules inhibit proteasome assembly in cells, and that 2) this inhibition can be correlated with their antiproliferative effects. References Sterz J. et al. Extert Opin. Invest. Drugs, 2008, 17 Rivett AJ et al., Experimental Gerontology, 2002, 37 Vandenberghe I. et al., Biochem. Pharmacol., 2008, 76 Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-295.

Background NEDD1 is a protein that binds to the gamma-tubulin ring complex, a multiprotein complex at the centrosome and at the mitotic spindle that mediates the nucleation of microtubules. Results We show that NEDD1 is expressed at comparable levels in a variety of tumor-derived cell lines and untransformed cells. We demonstrate that silencing of NEDD1 expression by treatment with siRNA has differential effects on cells, depending on their status of p53 expression: p53-positive cells arrest in G1, whereas p53-negative cells arrest in mitosis with predominantly aberrant monopolar spindles. However, both p53-positive and -negative cells arrest in mitosis if treated with low doses of siRNA against NEDD1 combined with low doses of the inhibitor BI2536 against the mitotic kinase Plk1. Simultaneous reduction of NEDD1 levels and inhibition of Plk1 act in a synergistic manner, by potentiating the anti-mitotic activity of each treatment. Conclusion We propose that NEDD1 may be a promising target for controlling cell proliferation, in particular if targeted in combination with Plk1 inhibitors.

// Stephane Vispe 1 , Arthur Deroide 1 , Emeline Davoine 1 , Cecile Desjobert 1 , Fabrice Lestienne 2 , Lucie Fournier 1 , Natacha Novosad 1 , Sophie Breand 3 , Jerome Besse 3 , Florence Busato 4 , Jorg Tost 4 , Luc De Vries 2 , Didier Cussac 2 , Joelle Riond 1 , Paola B. Arimondo 1 1 Unite de Service et de Recherche n°3388 CNRS-Pierre Fabre, ETaC Epigenetic Targeting of Cancer, CRDPF, Toulouse, France 2 Molecular and Cellular Biology Department, Centre de Recherche Pierre Fabre, Castres, France 3 Informatique de Recherche (Bioinformatics and Statistics), Centre de Recherche Pierre Fabre, Castres, France 4 Laboratory for Epigenetics and Environment, Centre National de Genotypage, CEA-Institut de Genomique, Evry, France Correspondence to: Stephane Vispe, e-mail: stephane.vispe@pierre-fabre.com Paola B. Arimondo, e-mail: paola.arimondo@etac.cnrs.fr Keywords: leukemia, DNA methylation, DNMT, 5-aza-2’-deoxycytidine, DNA damage Received: December 28, 2014 Accepted: February 08, 2015 Published: March 20, 2015 ABSTRACT 5-azacytidine and 5-aza-2′-deoxycytidine are clinically used to treat patients with blood neoplasia. Their antileukemic property is mediated by the trapping and the subsequent degradation of a family of proteins, the DNA methyltransferases (DNMT1, DNMT3A, and DNMT3B) leading to DNA demethylation, tumor suppressor gene re-expression and DNA damage. Here we studied the respective role of each DNMT in the human leukemia KG1 cell line using a RNA interference approach. In addition we addressed the role of DNA damage formation in DNA demethylation by 5-aza-2′-deoxycytidine. Our data show that DNMT1 is the main DNMT involved in DNA methylation maintenance in KG1 cells and in mediating DNA damage formation upon exposure to 5-aza-2′-deoxycytidine. Moreover, KG1 cells express the DNMT1 protein at a level above the one required to ensure DNA methylation maintenance, and we identified a threshold for DNMT1 depletion that needs to be exceeded to achieve DNA demethylation. Most interestingly, by combining DNMT1 siRNA and treatment with low dose of 5-aza-2′-deoxycytidine, it is possible to uncouple DNA damage formation from DNA demethylation. This work strongly suggests that a direct pharmacological inhibition of DNMT1, unlike the use of 5-aza-2′-deoxycytidine, should lead to tumor suppressor gene hypomethylation and re-expression without inducing major DNA damage in leukemia.