Anti-angiogenic, vascular-disrupting and anti-metastatic activities of vinflunine, the latest vinca alkaloid in clinical development.

The aim of this study was to investigate the anti-angiogenic, vascular-disrupting and anti-metastatic properties of vinflunine, the latest vinca alkaloid in phase III clinical development. The effects of vinflunine on in vitro endothelial cell functions relevant to the performance of an already formed vasculature and to the angiogenic process were evaluated. The in vivo anti-angiogenic properties of vinflunine were also investigated, as were its activity against a model of experimental metastasis. In vitro vinflunine induced a rapid change in the morphology of endothelial cells and disrupted the network of capillary-like structures, indicating potential vascular-disrupting activity. Furthermore, vinflunine showed anti-angiogenic properties, since it inhibited endothelial cell migration and the capacity of these cells to organise into a network of capillary-like structures. All these effects were observed under conditions that only marginally affect endothelial cell proliferation. In vivo, vinflunine inhibited bFGF-induced angiogenesis in Matrigel implants at doses 40-20-fold lower than its maximal therapeutic dose (MTD). Treatment of mice with vinflunine reduced the number of liver metastases induced by intrasplenic injection of LS174T cells, with significant effects also observed at low doses; i.e. 16-fold lower than the MTD. This study demonstrates that vinflunine expresses both vascular-disrupting and anti-angiogenic activities and induced marked effects against experimental metastases, all properties that support its ongoing clinical development.

Synthesis of 9-acridinyl sulfur derivatives: sulfides, sulfoxides and sulfones. Comparison of their activity on tumour cells.

The synthesis of several acridine thioethers is described. These compounds were oxidized to give new sulfoxides and sulfones. Among 23 compounds prepared, 19 were tested in vitro against the human cancer cell lines panel of NCI screening. Activity is increased 5-10 times from sulfides to sulfoxides. Among substituted groups in the side chain, sulfur mustard, epoxy sulfide and sulfoxide displayed the most interesting activity.

Decreased nucleotide excision repair activity and alterations of topoisomerase IIalpha are associated with the in vivo resistance of a P388 leukemia subline to F11782, a novel catalytic inhibitor of topoisomerases I and II.

PURPOSE: The purpose of the study was to investigate the mechanisms associated with antitumor activity and resistance to F11782, a novel dual catalytic inhibitor of topoisomerases with DNA repair-inhibitory properties. EXPERIMENTAL DESIGN: For that purpose, an F11782-resistant P388 leukemia subline (P388/F11782) has been developed in vivo and characterized. RESULTS: Weekly subtherapeutic doses of F11782 (10 mg/kg) induced complete resistance to F11782 after 8 weekly passages. This resistant P388/F11782 subline retained some in vivo sensitivity to several DNA-topoisomerase II and/or I complex-stabilizing poisons and showed marked collateral sensitivity to cisplatin, topotecan, colchicine, and Vinca alkaloids, while proving completely cross-resistant only to merbarone and doxorubicin. Therefore, resistance to F11782 did not appear to be associated with a classic multidrug resistance profile, as further reflected by unaltered drug uptake and no overexpression of resistance-related proteins or modification of the glutathione-mediated detoxification process. In vivo resistance to F11782 was, however, associated with a marked reduction in topoisomerase IIalpha protein (87%) and mRNA (50%) levels, as well as a diminution of the catalytic activity of topoisomerase IIalpha. In contrast, only minor reductions in topoisomerases IIbeta and I levels were recorded. However, of major interest, nucleotide excision repair activity was decreased 3-fold in these P388/F11782 cells and was more specifically associated with a decreased (67%) level of XPG (human xeroderma pigmentosum group G complementing protein), an endonuclease involved in this DNA repair system. CONCLUSIONS: These findings suggest that both topoisomerase IIalpha and XPG are major targets of F11782 in vivo and further demonstrate the original mechanism of action of this novel compound.

A dual mechanism of action of the anticancer agent F 11782 on human topoisomerase II alpha.

F 11782 is a novel epipodophyllotoxin that targets eukaryotic topoisomerases and inhibits enzyme binding to DNA. While F 11782 has not been found to stabilize either topoisomerase I or topoisomerase II covalent complexes, drug treatment appears to result in DNA damage. F 11782 has also been shown to inhibit the DNA nucleotide excision repair (NER) pathway. Bisdioxopiperazine-resistant small cell lung cancer (SCLC) OC-NYH/Y165S and Chinese hamster ovary (CHO) CHO/159-1 cells having functional Y49F and Y165S mutations in the topoisomerase II alpha isoform were both resistant to F 11782. The catalytic activity of purified human Y50F and Y165S mutant topoisomerase II alpha (Y50F in the human protein corresponds to Y49F in the CHO protein) was likewise resistant to the inhibitory action of F 11782. F 11782 was also found to induce a non-covalent salt-stable complex of human topoisomerase II with DNA that was ATP-independent. F 11782 thus displays a dual mechanism of action on human topoisomerase II alpha, reducing its affinity for DNA while also stabilizing the protein bound in the form of a salt-stable complex. Our results suggest that topoisomerase II alpha is a target of F 11782 in vivo, and that F 11782 may act as a novel topoisomerase II poison.

Ex vivo effects of the dual topoisomerase inhibitor tafluposide (F 11782) on cells isolated from fresh tumor samples taken from patients with cancer.

Tafluposide (F 11782), a novel epipodophylloid with a unique mechanism of interaction with both topoisomerase I and II, has shown outstanding antitumor activity in vivo against a panel of experimental human tumor xenografts. The aim of this study was to evaluate its cytotoxicity against fresh tumor cells taken from patients. Cells derived from bone marrow, peripheral blood, malignant effusions or solid biopsies from 84 patients with either hematological or solid tumors were exposed continuously to 0.8-100 nuM tafluposide for 48 h, 96 h or 7 days. Cell survival was measured using an MTT assay or the ATP assay and LC(50) values (drug concentration required for 50% cell kill) were calculated. Tafluposide showed significant cytotoxicity against cells derived from either hematological or solid tumors, with a marked inter-patient variation. There was no significant difference between the effect of tafluposide in samples from untreated or previously treated patients (p>0.05 for all cancer types). Whilst tafluposide appeared to show weak (p<0.05) cross-resistance with the topoisomerase II inhibitor etoposide in acute myeloid leukemia (AML), there did not appear to be any correlation with the effect of the topoisomerase I inhibitor topotecan (p>0.05) in either hematological or solid malignancies. True synergism was identified when combining tafluposide with cisplatin in ovarian cancer [combination index (CI)=0.14, 0.79] and with etoposide in AML (CI=0.49, 0.63 and 0.78). Our results suggest that tafluposide is a strong candidate for inclusion in clinical trials, particularly in hematological malignancies.

The effects of vinflunine, vinorelbine, and vinblastine on centromere dynamics.

Vinflunine is a novel fluorinated Vinca alkaloid currently in Phase II clinical trials, which in preclinical studies exhibited superior antitumor activity to that of two clinically useful Vinca alkaloids, vinorelbine and vinblastine. All three of the drugs block mitosis at the metaphase/anaphase transition, leading to apoptosis. The mechanism of the mitotic block is not known. On the basis of results with purified microtubules and in living interphase cells, we hypothesized that it involves suppression of spindle microtubule dynamics. Here we measured the effects of the three Vinca alkaloids on dynamics of centromeres and spindle kinetochore-microtubules by a novel approach involving quantitative time-lapse confocal microscopy in living mitotic human U2OS cells. Green fluorescent protein-labeled centromere-binding protein B was used to mark centromeres and kinetochore-microtubule plus ends. In controls, pairs of centromeres on sister chromatids alternated under tension between increasing and decreasing separation (stretching and relaxing). All three of the Vinca alkaloids suppressed centromere dynamics similarly at concentrations that block mitosis. At concentrations approximating the IC(50)s for mitotic accumulation (18.8 nM vinflunine, 7.3 nM vinorelbine, and 6.1 nM vinblastine), centromere dynamicity decreased by 44%, 25%, and 26%, respectively, and the time centromeres spent in a paused state increased by 63%, 52%, and 36%, respectively. Centromere relaxation rates, stretching durations, and transition frequencies all decreased. Thus all three of the drugs decreased the normal microtubule-dependent spindle tension at the centromeres/kinetochores, thereby preventing the signal for mitotic checkpoint passage. The strong correlation between suppression of kinetochore-microtubule dynamics and mitotic block indicates that the primary mechanism by which the Vinca alkaloids block mitosis is suppression of spindle microtubule dynamics.

Apoptotic cell death induction by F 11782 a novel dual catalytic inhibitor of topoisomerases I and II.

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.

Synergistic effects of F 11782, a novel dual inhibitor of topoisomerases I and II, in combination with other anticancer agents.

PURPOSE: F 11782, or 2',3'-bis-pentafluorophenoxyacetyl-4',6'-ethylidine-beta- D-glucoside of 4'-phosphate-4'-dimethylepipodophyllotoxin 2 N-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.

F 11782, a novel catalytic inhibitor of topoisomerases I and II, induces atypical, yet cytotoxic DNA double-strand breaks in CHO-K1 cells.

F 11782, or 2'', 3''-bispentafluorophenoxyacetyl-4, 6'-ethylidene-beta-D glucoside of 4'-phosphate-4'-dimethylepipodopliyllotoxin 2N-methyl glucamine salt, is a novel fluorinated lipophylic epipodophylloid which has shown marked antitumour activity in vivo. In vitro studies have demonstrated a dual catalytic inhibitory activity of F 11782 against topoisomerases and I and II by an original mechanism involving interference with the DNA binding activity of these enzymes, without DNA intercalating properties. Nevertheless, the precise mechanism(s) of cytotoxicity of F 11782 remains unclear and recent studies have suggested that this cytotoxicity might result, at least in part, from an induction of DNA-strand breaks without stabilisation of cleavable complex. In this study, DNA damage induced by F 11782 and its repair by non-homologous recombination was investigated in CHO-K1 cells. The results suggest that the nature of such damage differs from that induced by etoposide, a structurally-related topoisomerase II poison and identify a high level of stability of the damage induced which may account, at least in part, for the superior preclinical anti-tumour activity of F 11782.

Inhibition of nucleotide excision repair and sensitisation of cells to DNA cross-linking anticancer drugs by F 11782, a novel fluorinated epipodophylloid.

F 11782, or 2',3'-bis-pentafluorophenoxyacetyl-4',6'-ethylidene-beta-D-glucoside of 4'-phosphate-4'-dimethylepipodophyllotoxin 2-N-methyl glucamine salt, a novel dual catalytic inhibitor of topoisomerases I and II, was identified as a potent inhibitor of nucleotide excision repair (NER) by screening procedures using the in vitro 3D (DNA damage detection) assay. F 11782 was then shown predominantly to inhibit the incision rather than the repair synthesis step, using two new methodologies derived from this 3D assay, effectively ruling out any inhibition of polymerases delta/var epsilon. Moreover, data from two other in vitro assays showed an absence of any effect of F 11782 on: (i) the DNA damage binding of the XPA-RPA complex, and (ii) on SV40 large T-antigen helicase activity. Therefore, the inhibitory activity of F 11782 on NER may involve an inhibition of the ERCC1-XPF or XPG endonuclease activity. Moreover, inhibition of DNA repair by F 11782 was confirmed in human A549 cells by monitoring unscheduled DNA synthesis following mechlorethamine treatment. Such an inhibition provides an explanation for the highly synergistic cytotoxicity observed against cultured A549 lung tumour cells, when F 11782 was combined with cross-linking agents, such as cisplatin or mitomycin C. These results emphasise the unique mode of action of this novel molecule in inhibiting NER and provide a basis for its evaluation in clinical trials in combination with DNA cross-linking agents.

Classic in vivo cancer models: three examples of mouse models used in experimental therapeutics.

Transplantable animal tumors have been associated with the discovery of most clinically active anticancer agents. They are still useful today in conducting detailed evaluations of new candidate anticancer drugs. Three protocols relating to transplantable experimental tumors are described in this unit. Included are the intravenously-implanted murine P388 leukemia, the subcutaneously-implanted murine B16 melanoma and two examples of subcutaneously-implanted human tumor xenografts, the LX-1 (lung) and MX-1 (breast) tumors.