In vivo antitumor activity of F 11782, a non-intercalating dual catalytic inhibitor of topoisomerases I and II, against a panel of human tumor xenografts

Dual Inhibitors as a New Challenge for Cancer Multidrug Resistance Treatment

BACKGROUND

Dual-targeting in cancer treatment by a single drug is an unconventional approach in relation to drug combinations. The rationale for the development of dualtargeting agents is to overcome incomplete efficacy and drug resistance frequently present when applying individual targeting agents. Consequently, -a more favorable outcome of cancer treatment is expected with dual-targeting strategies.

METHODS

We reviewed the literature, concentrating on the association between clinically relevant and/or novel dual inhibitors with the potential to modulate multidrug resistant phenotype of cancer cells, particularly the activity of P-glycoprotein. A balanced analysis of content was performed to emphasize the most important findings and optimize the structure of this review.

RESULTS

Two-hundred and forty-five papers were included in the review. The introductory part was interpreted by 9 papers. Tyrosine kinase inhibitors' role in the inhibition of Pglycoprotein and chemosensitization was illustrated by 87 papers. The contribution of naturalbased compounds in overcoming multidrug resistance was reviewed using 92 papers, while specific dual inhibitors acting against microtubule assembling and/or topoisomerases were described with 55 papers. Eleven papers gave an insight into a novel and less explored approach with hybrid drugs. Their influence on P-glycoprotein and multidrug resistance was also evaluated.

CONCLUSION

These findings bring into focus rational anticancer strategies with dual-targeting agents. Most evaluated synthetic and natural drugs showed a great potential in chemosensitization. Further steps in this direction are needed for the optimization of anticancer treatment.

HU-331: a cannabinoid quinone, with uncommon cytotoxic properties and low toxicity

The oxidation of cannabis constituents has given rise to their corresponding quinones, which have been identified as cytotoxic agents. Out of these molecules the quinone of cannabidiol--the most abundant non-psychoactive cannabinoid in Cannabis sativa--has shown the highest cytotoxicity. This compound was named HU-331 and it exerts antiangiogenic properties, induces apoptosis to endothelial cells and inhibits topoisomerase II in nanomolar concentrations. Unlike other quinones, it is not cardiotoxic and does not induce the formation of free radicals. A comparative in vivo study in mice has shown HU-331 to be less toxic and more effective than the commonly used doxorubicin. This review summarises the properties of HU-331 and compares it with doxorubicin and other topoisomerase II inhibitors.

Relationships between DNA strand breakage and apoptotic progression upon treatment of HL-60 leukemia cells with tafluposide or etoposide

Tafluposide (F11782), an epipodophyllotoxin derivative currently undergoing phase I clinical trials, is structurally close to the established anti-cancer drug etoposide, but mechanistically distinct. It is a dual inhibitor of topoisomerases I and II which impairs the binding of the enzyme to DNA, but does not stabilize the cleavage complex. Nevertheless, both etoposide and tafluposide induce DNA strand breaks and are potent pro-apoptotic agents. In this study, we have compared the cellular response of HL-60 human promyelocytic leukemia cells treated with etoposide and tafluposide. We show that tafluposide induces delayed, but extensive, DNA strand breaks, whereas etoposide provokes rapid and massive DNA damage. The two drugs trigger similar types of alterations at the mitochondrial and cell cycle levels, and lead to the generation of comparable levels of reactive oxygen species, but with different kinetics. Our data suggest that modification of the mitochondrial mass plays an important role in apoptosis induced by DNA-damaging anti-cancer agents, at least in the epipodophyllotoxin series. We suggest that drug-induced mitochondrial alterations can be divided into three successive steps: (i) hyperpolarization, (ii) depolarization and (iii) increase of the mitochondrial mass.

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.

Novel antitumor indenoindole derivatives targeting DNA and topoisomerase II

We have identified a novel series of indenoindole derivatives endowed with potent cytotoxic activities toward cancer cells. Five compounds containing a 8-[2-(dialkylamino)ethoxy]-2,3-dimethoxy-5H-10H-indeno[1,2-b]indol-10-one-O-propynyl-oxime core substituted with a phenyl, furanyl, or a methyl substituent on the propynyl side chain have been synthesized and their mechanism of action was investigated using a panel of complementary biophysical and biochemical techniques. The compounds were shown to intercalate into DNA with a preference for AT-rich sequences. They have no effect on topoisomerase I but they strongly stimulate DNA cleavage by topoisomerase II. Their capacity to stabilize topoisomerase II-DNA covalent complexes is comparable to that of the reference drug etoposide. The nature and orientation of the substituent on the propynyl chain modulate the DNA binding and topoisomerase II inhibitory properties of the compounds and, apparently, there is a correlation between the cytotoxic potential and the molecular action at the DNA-topoisomerase II level. The growth of human K562 leukemia cells is strongly reduced in the presence of the indenoindoles (IC(50) in the 50nM range) which maintain a high cytotoxic activity toward the adriamycin-resistant K562adr cells line in vitro. The low resistance indexes measured with the indenoindoles (RRI = 10-30) compared to adriamycin (RRI = 1000) suggest that our new compounds are weakly or not sensitive to drug efflux mediated by glycoprotein-P and/or multidrug resistance (MDR) protein pumps. Finally, we also show that these indenoindoles arrest K562 cells in the G2/M phase of the cell cycle and promote apoptosis, as indicated by the appearance of internucleosomal DNA cleavage. One compound in the series was tested for in vivo antitumor activity against the colon 38 model and at 25mg/kg it showed 100% complete tumor regression in the treated mice, without significant body weight loss. Altogether, the results reported here establish that our indenoindole derivatives represent a novel interesting series of DNA-targeted cytotoxic agents.

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.