ICRF-187 rescue in etoposide treatment in vivo. A model targeting high-dose topoisomerase II poisons to CNS tumors

Protection of mouse bone marrow from etoposide-induced genomic damage by dexrazoxane

PURPOSE

The objective of the current investigation is to determine whether non-toxic doses of the catalytic topoisomerase-II inhibitor, dexrazoxane, have influence on the genomic damage induced by the anticancer topoisomerase-II poison, etoposide, on mice bone marrow cells.

METHOD

The scoring of micronuclei, chromosomal aberrations, and mitotic activity were undertaken as markers of cyto- and genotoxicity. Oxidative damage markers such as reduced glutathione and lipid peroxidation were assessed as a possible mechanism underlying this amelioration.

RESULTS

Dexrazoxane pre-treatment significantly reduced the etoposide-induced micronuclei formation, chromosomal aberrations, and also the suppression of erythroblast proliferation in bone marrow cells of mice. These effects were dose dependent. Etoposide induced marked biochemical alterations characteristic of oxidative stress including enhanced lipid peroxidation and reduction in the reduced glutathione level. Prior administration of dexrazoxane ahead of etoposide challenge ameliorated these biochemical markers.

CONCLUSION

Based on our data presented, strategies can be developed to decrease the etoposide-induced genomic damage in normal cells using dexrazoxane.

The HSP90 and DNA topoisomerase VI inhibitor radicicol also inhibits human type II DNA topoisomerase

Radicicol derivatives are currently investigated as promising antitumoral drugs because they inhibit the activity of the molecular chaperone heat shock protein (HSP90), causing the destabilization and eventual degradation of HSP90 client proteins that are often associated with tumor cells. These drugs interact with the ATP-binding site of HSP90 which is characterized by a structural element known as the Bergerat fold, also present in type II DNA topoisomerases (Topo II). We have previously shown that radicicol inhibits archaeal DNA topoisomerase VI, the prototype of Topo II of the B family (present in archaea, some bacteria and all the plants sequenced so far). We show here that radicicol also inhibits the human Topo II, a member of the A family (comprising the eukaryotic Topo II, bacterial gyrase, Topo IV and viral Topo II), which is a major target for antitumoral drugs. In addition, radicicol prevents in vitro induction of DNA cleavage by human Topo II in the presence of the antitumoral drug etoposide. The finding that radicicol can inhibit at least two different antitumoral drug targets in human, and interferes with drugs currently used in cancer treatment, could have implications in cancer therapy.

Combining Etoposide and Dexrazoxane Synergizes with Radiotherapy and Improves Survival in Mice with Central Nervous System Tumors

PURPOSE

The treatment of patients with brain metastases is presently ineffective, but cerebral chemoradiotherapy using radiosensitizing agents seems promising. Etoposide targets topoisomerase II, resulting in lethal DNA breaks; such lesions may increase the effect of irradiation, which also depends on DNA damage. Coadministration of the topoisomerase II catalytic inhibitor dexrazoxane in mice allows for more than 3-fold higher dosing of etoposide. We hypothesized that dexrazoxane combined with escalated etoposide doses might improve the efficacy of cerebral radiotherapy.

EXPERIMENTAL DESIGN

Mice with cerebrally inoculated Ehrlich ascites tumor (EHR2) cells were treated with combinations of etoposide + dexrazoxane + cerebral radiotherapy. Similar chemotherapy and radiation combinations were investigated by clonogenic assays using EHR2 cells, and by DNA double-strand break assay through quantification of phosphorylated histone H2AX (gammaH2AX).

RESULTS

Escalated etoposide dosing (90 mg/kg) combined with dexrazoxane (125 mg/kg) and cerebral radiotherapy (10 Gy x 1) increased the median survival by 60% (P = 0.001) without increased toxicity, suggesting that escalated etoposide levels may indeed represent a new strategy for improving radiotherapy. Interestingly, 125 mg/kg dexrazoxane combined with normal etoposide doses (34 mg/kg) also increased survival from radiotherapy, but only by 27% (P = 0.002). This indicates a direct dexrazoxane modulation of the combined effects of etoposide and radiation in brain tumors. Further, in vitro, concurrent dexrazoxane, etoposide, and irradiation significantly increased DNA double-strand breaks.

CONCLUSION

Combining etoposide (high or normal doses) and dexrazoxane synergizes with cerebral radiotherapy and significantly improves survival in mice with central nervous system tumors. This regimen may thus improve radiation therapy of central nervous system tumors.

Substituted Purine Analogues Define a Novel Structural Class of Catalytic Topoisomerase II Inhibitors

By screening 1,990 compounds from the National Cancer Institute diversity set library against human topoisomerase IIalpha, we identified a novel catalytic topoisomerase II inhibitor NSC35866, a S6-substituted analogue of thioguanine. In addition to inhibiting the DNA strand passage reaction of human topoisomerase IIalpha, NSC35866 also inhibited its ATPase reaction. NSC35866 primarily inhibited DNA-stimulated ATPase activity, whereas DNA-independent ATPase activity was less sensitive to inhibition. We compared the mode of topoisomerase II ATPase inhibition induced by NSC35866 with that of 12 other substituted purine analogues of different chemical classes. The ability of thiopurines with free SH functionalities to inhibit topoisomerase II ATPase activity was completely abolished by DTT, suggesting that these thiopurines inhibit topoisomerase II ATPase activity by covalently modifying free cysteine residues. In contrast, NSC35866 as well as two O6-substituted guanine analogues, O6-benzylguanine and NU2058, could inhibit topoisomerase II ATPase activity in the presence of DTT, indicating that they have a different mechanism of inhibition. NSC35866 did not increase the level of topoisomerase II covalent cleavable complexes with DNA, indicating that it is a catalytic inhibitor and not a poison. NSC35866 was also capable of inducing a salt-stable complex of topoisomerase II on closed circular DNA. In accordance with these biochemical data, NSC35866 could antagonize etoposide-induced cytotoxicity and DNA breaks in human and murine cancer cells, confirming that NSC35866 also functions as a catalytic topoisomerase II inhibitor in cells.

Dexrazoxane : a review of its use for cardioprotection during anthracycline chemotherapy

Dexrazoxane (Cardioxane, Zinecard, a cyclic derivative of edetic acid, is a site-specific cardioprotective agent that effectively protects against anthracycline-induced cardiac toxicity. Dexrazoxane is approved in the US and some European countries for cardioprotection in women with advanced and/or metastatic breast cancer receiving doxorubicin; in other countries dexrazoxane is approved for use in a wider range of patients with advanced cancer receiving anthracyclines. As shown in clinical trials, intravenous dexrazoxane significantly reduces the incidence of anthracycline-induced congestive heart failure (CHF) and adverse cardiac events in women with advanced breast cancer or adults with soft tissue sarcomas or small-cell lung cancer, regardless of whether the drug is given before the first dose of anthracycline or the administration is delayed until cumulative doxorubicin dose is > or =300 mg/m2. The drug also appears to offer cardioprotection irrespective of pre-existing cardiac risk factors. Importantly, the antitumour efficacy of anthracyclines is unlikely to be altered by dexrazoxane use, although the drug has not been shown to improve progression-free and overall patient survival. At present, the cardioprotective efficacy of dexrazoxane in patients with childhood malignancies is supported by limited data. The drug is generally well tolerated and has a tolerability profile similar to that of placebo in cancer patients undergoing anthracycline-based chemotherapy, with the exception of a higher incidence of severe leukopenia (78% vs 68%; p < 0.01). Dexrazoxane is the only cardioprotective agent with proven efficacy in cancer patients receiving anthracycline chemotherapy and is a valuable option for the prevention of cardiotoxicity in this patient population.

Dexrazoxane Protects against Myelosuppression from the DNA Cleavage–Enhancing Drugs Etoposide and Daunorubicin but not Doxorubicin

PURPOSE

The anthracyclines daunorubicin and doxorubicin and the epipodophyllotoxin etoposide are potent DNA cleavage-enhancing drugs that are widely used in clinical oncology; however, myelosuppression and cardiac toxicity limit their use. Dexrazoxane (ICRF-187) is recommended for protection against anthracycline-induced cardiotoxicity.

EXPERIMENTAL DESIGN

Because of their widespread use, the hematologic toxicity following coadministration of dexrazoxane and these three structurally different DNA cleavage enhancers was investigated: Sensitivity of human and murine blood progenitor cells to etoposide, daunorubicin, and doxorubicin +/- dexrazoxane was determined in granulocyte-macrophage colony forming assays. Likewise, in vivo, B6D2F1 mice were treated with etoposide, daunorubicin, and doxorubicin, with or without dexrazoxane over a wide range of doses: posttreatment, a full hematologic evaluation was done.

RESULTS

Nontoxic doses of dexrazoxane reduced myelosuppression and weight loss from daunorubicin and etoposide in mice and antagonized their antiproliferative effects in the colony assay; however, dexrazoxane neither reduced myelosuppression, weight loss, nor the in vitro cytotoxicity from doxorubicin.

CONCLUSION

Although our findings support the observation that dexrazoxane reduces neither hematologic activity nor antitumor activity from doxorubicin clinically, the potent antagonism of daunorubicin activity raises concern; a possible interference with anticancer efficacy certainly would call for renewed attention. Our data also suggest that significant etoposide dose escalation is perhaps possible by the use of dexrazoxane. Clinical trials in patients with brain metastases combining dexrazoxane and high doses of etoposide is ongoing with the aim of improving efficacy without aggravating hematologic toxicity. If successful, this represents an exciting mechanism for pharmacologic regulation of side effects from cytotoxic chemotherapy.

Characterisation of cytotoxicity and DNA damage induced by the topoisomerase II-directed bisdioxopiperazine anti-cancer agent ICRF-187 (dexrazoxane) in yeast and mammalian cells

Background

Bisdioxopiperazine anti-cancer agents are inhibitors of eukaryotic DNA topoisomerase II, sequestering this protein as a non-covalent protein clamp on DNA. It has been suggested that such complexes on DNA represents a novel form of DNA damage to cells. In this report, we characterise the cytotoxicity and DNA damage induced by the bisdioxopiperazine ICRF-187 by a combination of genetic and molecular approaches. In addition, the well-established topoisomerase II poison m-AMSA is used for comparison.

Results

By utilizing a panel of Saccharomyces cerevisiae single-gene deletion strains, homologous recombination was identified as the most important DNA repair pathway determining the sensitivity towards ICRF-187. However, sensitivity towards m-AMSA depended much more on this pathway. In contrast, disrupting the post replication repair pathway only affected sensitivity towards m-AMSA. Homologous recombination (HR) defective irs1SF chinese hamster ovary (CHO) cells showed increased sensitivity towards ICRF-187, while their sensitivity towards m-AMSA was increased even more. Furthermore, complementation of the XRCC3 deficiency in irs1SF cells fully abrogated hypersensitivity towards both drugs. DNA-PK_cs deficient V3-3 CHO cells having reduced levels of non-homologous end joining (NHEJ) showed slightly increased sensitivity to both drugs. While exposure of human small cell lung cancer (SCLC) OC-NYH cells to m-AMSA strongly induced γH2AX, exposure to ICRF-187 resulted in much less induction, showing that ICRF-187 generates fewer DNA double strand breaks than m-AMSA. Accordingly, when yeast cells were exposed to equitoxic concentrations of ICRF-187 and m-AMSA, the expression of DNA damage-inducible genes showed higher levels of induction after exposure to m-AMSA as compared to ICRF-187. Most importantly, ICRF-187 stimulated homologous recombination in SPD8 hamster lung fibroblast cells to lower levels than m-AMSA at all cytotoxicity levels tested, showing that the mechanism of action of bisdioxopiperazines differs from that of classical topoisomerase II poisons in mammalian cells.

Conclusion

Our results point to important differences in the mechanism of cytotoxicity induced by bisdioxopiperazines and topoisomerase II poisons, and suggest that bisdioxopiperazines kill cells by a combination of DNA break-related and DNA break-unrelated mechanisms.

Pharmacokinetics of etoposide in cancer patients treated with high-dose etoposide and with dexrazoxane (ICRF-187) as a rescue agent

PURPOSE

The pharmacokinetics of etoposide were studied in cancer patients with brain metastases treated with high-dose etoposide in order to determine if the pharmacokinetics were altered by the use of dexrazoxane as a rescue agent to reduce the extracerebral toxicity of etoposide.

METHODS

Etoposide plasma levels were determined by HPLC.

RESULTS

The etoposide pharmacokinetics described by a monophasic first-order elimination model were found to be similar to other reported data in other settings and at similar doses.

CONCLUSIONS

The pharmacokinetics of etoposide were unaffected by dexrazoxane rescue.

Dexrazoxane in combination with anthracyclines lead to a synergistic cytotoxic response in acute myelogenous leukemia cell lines

In an attempt to improve current therapeutic strategies for acute myelogenous leukemia (AML), we studied the effects of a commercially available drug, dexrazoxane (DEX), which protects against anthracycline-induced cardiotoxicity. The rationale was that DEX would permit higher doses of cardiotoxic drugs to be given. The drug itself may have therapeutic potential as well. Finally, there are concerns that the drug may, as a protective agent, diminish the effectiveness of various chemotherapeutics. To help resolve the question about potential drug antagonism, we undertook a series of in vitro analyses of DEX and various combinations with anthracyclines and other agents. Colony-forming assays were used to evaluate stem-cell renewal of myeloid cells in vitro, and median-effect analysis was used to evaluate antagonism, synergism, and additivity. The anthracyclines doxorubicin, daunorubicin, and idarubicin were individually combined with DEX to study in vitro effects in leukemic myeloid cell lines. In the hope, we could extend the findings to non-anthracyclines, etoposide and cytosine arabinoside were also evaluated in combination with DEX using the same in vitro model and method. We found that the effects of DEX in combination with any of the anthracyclines were schedule dependent. The antitumor effect was greater for each combination than for any anthracycline alone except when DEX was administered 24h before doxorubicin or daunorubicin. These data were corroborated through median-effect analysis. Etoposide in combination with DEX was synergistic for all combinations and schedules, and the combination of cytosine arabinoside and DEX was effective depending on the schedule used. DEX appears to be a promising drug in the treatment of AML and warrants further clinical study involving novel drug combinations.

Probing the role of linker substituents in bisdioxopiperazine analogs for activity against wild-type and mutant human topoisomerase II alpha

The bisdioxopiperazines are catalytic inhibitors of eukaryotic type II DNA topoisomerases capable of trapping these enzymes as a salt-stable closed-clamp complex on circular DNA. The various bisdioxopiperazine analogs differ from each other because of structural differences in the linker connecting the two dioxopiperazine rings. Although the composition of this linker region has been found to be important for potency, the structural basis for this is largely unknown. To elucidate the role of the linker region in drug action, we have analyzed the effect of different linker substituents in otherwise identical analogs by studying their interaction with wild-type and mutant human topoisomerase II alpha. Two mutations, L169I and R162Q, displayed differential sensitivity toward closely related analogs, suggesting that the linker region in these compounds plays a highly specific role in protein drug interaction. The finding that the L169I mutation, which probably represents a subtle structural change, was sufficient to confer resistance further emphases the importance of this region of the protein for bisdioxopiperazine inhibition of topoisomerase II. Comparing the sensitivity profiles of different bisdioxopiperazines against wild-type and mutant proteins with that of mitindomide, we observed a spectrum of sensitivity closely resembling that of ICRF-154, a bisdioxopiperazine with no linker substituents. We discuss the implications of these observations for the understanding of the mechanism of bisdioxopiperazine action on topoisomerase II.

Culprit and victim -- DNA topoisomerase II

The phylogenetic antiquity of DNA topoisomerases indicates their vital function. Structure and maintenance of genomic DNA depend on the activity of these enzymes, and without them DNA replication and cell division are impossible. Topoisomerase II alpha has therefore become the main target of many antitumour therapy regimens, even though the exact mechanism of cell killing remains elusive. The success of this approach is limited by the development of spontaneous resistance, and drug-induced DNA damage can increase malignancy. Nevertheless, the combined use of topoisomerase-inhibiting drugs with different mechanisms of action promises to improve particular treatment designs. The degree of topoisomerase II expression in tumours may predict the clinical course and responsiveness to therapy.

Acute dosage with dexrazoxane, but not doxorubicin, is associated with increased rates of hepatic protein synthesis in vivo

An investigation was carried out into the effects of dexrazoxane and doxorubicin on hepatic protein synthesis in vivo. The protocol included 8 groups of rats and involved a pretreatment stage of 30 min followed by a treatment stage of either 2.5 or 24 h. Male Wistar rats (=0.15-0.20 kg) were pretreated with either dexrazoxane (100 mg/kg; 5 ml/kg) or saline (0.15 mol/l NaCl; 5 ml/kg). At 30 min after the pretreatment, rats were again injected with either doxorubicin (5 mg/kg; 10 ml/kg) or saline (0.15 mol/l NaCl; 10 ml/kg) in the treatment phase. Rats were sacrificed at either 2.5 or 24 h after the last doxorubicin or saline injection. Rate of protein synthesis were measured 10 min prior to sacrificing rats, with a flooding dose of L-[4-3H]phenylalanine. Liver was analyzed for the protein synthetic capacity (Cs, mg RNA/g protein), the fractional rate of protein synthesis (k(s), %/d), and the RNA activity (kRNA mg protein/d/mg RNA). Complementary analysis included plasma albumin, total protein and activities of alkaline phosphatase, and aspartate aminotransferase. In the 2.5-h study, doxorubicin alone had no effect on any of the above variables. Dexrazoxane alone increased Cs, k(s) and kRNA at 2.5 h. Combined dexrazoxane + doxorubicin increased hepatic Cs and k(s) with concomitant reductions in total plasma protein. In the 24-h study, doxorubicin alone had no effect on any of the variables. Dexrazoxane alone had no effect on either Cs, k(s), or kRNA but raised plasma activities of alkaline phosphatase and aspartate aminotransferase. Combined dexrazoxane + doxorubicin increased Cs and k(s) and decreased total plasma protein and increased plasma aspartate aminotransferase activities at 24 h. In conclusion, there is no evidence that acutely doxorubicin per se has measurable effects on hepatic protein synthesis in vivo in an acute period. However, acutely dexrazoxane increases hepatic protein synthesis, which may represent its putative cytotoxic effects, as indicated by raised serum activities of liver enzymes. A combination of both dexrazoxane + doxorubicin appears to have a greater effect in increasing liver protein synthesis than dexrazoxane alone.

Effects of Doxorubicin (Adriamycin) and [(+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)]propane (ICRF-187) on skeletal muscle protease activities

Adverse effects of doxorubicin (adriamycin) have been reported to be due to iron-catalyzed free radical formation, which can be prevented with the cytoprotective chelating agent [(+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)]propane (dexrazoxane; ICRF-187). Affected tissues include the heart, gastrointestinal tract, and kidney. However, there is very little information on the effects of adriamycin on skeletal muscle, despite the fact that there is direct and indirect evidence to show that both adriamycin and ICRF-187 are myotoxic. To investigate the mechanisms of cytotoxicity of these agents in skeletal muscle, we have conducted a systematic investigation of the activities of the major lysosomal (dipeptidyl aminopeptidase I and II and cathepsins B, D, H, and L) and cytoplasmic (alanyl-, arginyl-, and leucyl aminopeptidase, dipeptidyl aminopeptidase IV, tripeptidyl aminopeptidase, and proline endopeptidase) muscle proteases. These enzymes play an important role in normal cellular function and represent potential targets for toxic and protective agents. Male Wistar rats (approx. 0.2 kg) were subjected to a pretreatment phase of 30 min followed by a treatment stage of either 2.5 or 24 h. The pretreatment involved injection of a single bolus of either saline (0.15 mol/l NaCl; 5 ml/kg ip) or ICRF-187 (100 mg/kg; 5 ml/kg ip). After 30 min, rats were injected again with a single bolus of either adriamycin (5 mg/kg; 10 ml/kg ip) or saline (0.15 mol/l NaCl; 10 ml/kg ip) in the treatment phase. At either 2.5 or 24 h after the last adriamycin or saline injection, rats were killed for subsequent dissection of the gastrocnemius muscle for analysis. In the 2.5-h study, there were significant reductions in cathepsin D activities of adriamycin-treated rats compared to saline injected control (p = 0.02). In both 2.5- and 24-h studies there were also significant differences (p = 0.05) in cathepsin H activities between rats treated with adriamycin and ICRF-187, although these differences were not significant when data were compared with corresponding saline-injected rats. There were no other overt effects for any of the other proteases at either 2.5 or 24 h. We conclude that both adriamycin and ICRF-187 have very little effect on the activities of muscle proteases and that altered proteolysis is not involved in the reported pathological reactions induced by these agents.

Dexrazoxane is a potent and specific inhibitor of anthracycline induced subcutaneous lesions in mice

BACKGROUND

Recently, we have shown that dexrazoxane (ICRF-187) is an effective antidote against accidental extravasation of anthracyclines. Thus, it inhibits the lesions induced by subcutaneous (s.c.) daunorubicin, idarubicin, and doxorubicin in mice and has proven to be successful clinically as well. Dexrazoxane is a potent metal ion chelator as well as being a catalytic inhibitor of DNA topoisomerase II. However, the mechanism behind the protection against anthracycline extravasation is not known.

MATERIALS AND METHODS

Mice were injected s.c. with daunorubicin or doxorubicin. Systemic N-acetylcysteine, alfa-tocoferol, amifostine, merbarone, aclarubicin, ADR-925, and EDTA were administered i.p. immediately hereafter or as a triple-treatment over six hours. Intralesional (i.l.) adjuvants were injected immediately after and into the same area as the anthracycline. The frequency, duration, and sizes of wounds were observed until complete healing of all wounds.

RESULTS

Triple-treatment with systemic dexrazoxane was superior to single dosage and completely prevented lesions after s.c. daunorubicin and doxorubicin. Low-dose i.l. dexrazoxane was effective in protecting as well. In contrast, none of the other seven adjuvants was effective. Protection was not achieved with local cooling, however, topical ice did not impair the efficacy of dexrazoxane.

CONCLUSIONS

Dexrazoxane is extremely effective and apparently quite specific in protecting against lesions after s.c. doxorubicin and daunorubicin.

Tumor cell resistance to DNA topoisomerase II inhibitors: new developments

DNA topoisomerases are critical enzymes involved in replication, transcription, chromatin assembly and other aspects of DNA metabolism. They are also the targets of important anticancer drugs. The type II topoisomerases are specific targets of drug classes that comprise complex-stabilizing (epipodophyllotoxins, anthracyclines) and catalytic (merbarone, bisdioxopiperazines) inhibitors. In this review, we update our current knowledge of resistance to the antitumor inhibitors of the type II DNA topoisomerases, with special emphasis on the catalytic inhibitors, since novel catalytic inhibitor resistant cell lines have only recently been described. Resistance to topoisomerase II inhibitors can manifest as decreased or increased expression of or mutation in the topoisomerase II genes. However, the tumor cell's response to exposure to these inhibitors involves more than the target enzyme, and these other responses are a major focus of this review. Such cellular changes are associated with and may contribute to the drug resistance phenotype. They involve decreased drug accumulation due to expression of membrane 'pump' proteins, altered cytotoxic signaling through stress-activated protein kinases, and alterations in apoptosis and cell cycle proteins (e.g. Bcl-2, Bax, p53, Rb). While it is evident that mutation in or altered expression of the topoisomerase II genes are sufficient to confer resistance to topoisomerase inhibitors, it is not clear whether the other changes are a consequence of the selection or a response to the cytotoxic insult, nor is it clear how these other cellular changes contribute to the drug resistance phenotype. Copyright 1999 Harcourt Publishers Ltd.

Dexrazoxane (ICRF-187)

1. Dexrazoxane (ICRF-187) is the only clinically approved drug for use in cancer patients to prevent anthracycline mediated cardiotoxicity. 2. The mode of action appears to be mainly due to the potential of the drug to remove iron from iron/anthracycline complexes and thus reduce free radical formation by these complexes. 3. Dexrazoxane also influences cell biology by its ability to inhibit topoisomerase II and its effects on the regulation of cellular iron homeostasis. 4. Although the cardioprotective effect of dexrazoxane in cancer patients undergoing chemotherapy with anthracyclines is well documented, the potential of this drug to modulate topoisomerase II activity and cellular iron metabolism may hold the key for future applications of dexrazoxane in cancer therapy, immunology, or infectious diseases.

Catalytic inhibitors of DNA topoisomerase II

Catalytic inhibitors of mammalian DNA topoisomerase II have been found recently in natural and synthetic compounds. These compounds target the enzyme within the cell and inhibit various genetic processes involving the enzyme, such as DNA replication and chromosome dynamics, and thus proved to be good probes for the functional analyses of the enzyme in a variety of eukaryotes from yeast to mammals. Catalytic inhibitors were shown to be antagonists against topoisomerase II poisons. Thus bis(2,6-dioxopiperazines) have a potential to overcome cardiac toxicity caused by potent antitumor anthracycline antibiotics such as doxorubicin and daunorubicin. ICRF-187, a (+)-enantiomer of racemic ICRF-159, has been used in clinics in European countries as cardioprotector. Furthermore, bis(2,6-dioxopiperazines) enhance the efficacy of topoisomerase II poisons by reducing their side effects in preclinical and clinical settings. Bis(2,6-dioxopiperazines) per se among others have antitumor activity, and one of their derivatives, MST-16 or Sobuzoxane, bis(N1-isobutyloxycarbonyloxymethyl-2, 6-dioxopiperazine), has been developed in Japan as an anticancer drug used for malignant lymphomas and adult T-cell leukemia in clinics.

Meningeosis leukaemica in adult acute lymphoblastic leukaemia

This review addresses diagnosis of CNS involvement, incidence and treatment of CNS disease at time of diagnosis, prophylaxis and treatment of CNS relapse and risk factors for meningeal recurrence in adult acute lymphoblastic leukaemia (ALL). At the time of diagnosis meningeosis leukaemica is present in about 6% (1-10%) of the adult ALL patients with a higher incidence in ALL subgroups T-ALL (8%) and B-ALL (13 %). With the invention of early additional CNS directed therapy it no longer represents an unfavourable prognostic factor. In the absence of prophylaxis meningeal relapses occur in approximately one third of adults with ALL. A literature review including more than 4000 adult ALL patients showed for the different prophylactic treatment approaches the following CNS relapse rates: intrathecal therapy alone 13% (8-19%), intrathecal therapy and CNS irradiation 15% (6-22%), high dose chemotherapy 14% (10-16%), high dose chemotherapy and intrathecal therapy 8% (2-16%) and high dose chemotherapy, intrathecal therapy together with CNS irradiation 5% (1-12%). It became obvious that the early onset of intrathecal therapy and CNS irradiation and the continuation of intrathecal administrations throughout maintenance are essential. The most favourable results where achieved with high dose chemotherapy combined with intrathecal therapy and/or CNS irradiation. The majority of treatment regimens in adult ALL already include high dose chemotherapy in order to reduce the risk of bone marrow relapse. The outcome of patients with CNS relapse is still poor. Although a remission can be induced in the majority of patients (> 60%) it is usually followed by a bone marrow relapse and the survival is poor (< 5-10%). Bone marrow transplantation might be in adults at present the only curative approach.

Bis(2,6-dioxopiperazines), catalytic inhibitors of DNA topoisomerase II, as molecular probes, cardioprotectors and antitumor drugs

Bis(2,6-dioxopiperazines) and other catalytic inhibitors of mammalian DNA topoisomerase II have recently been found in natural and synthetic compounds. These compounds target the enzyme within the cell and inhibit various genetic processes involving the enzyme such as DNA replication and chromosome dynamics and thus proved to be good probes for the functional analyses of the enzyme in a variety of eucaryotes from yeast to mammals. Catalytic inhibitors were shown to be antagonists against topoisomerase II poisons under some conditions, but to be synergistic under others. Bis(2,6-dioxopiperazines) have a potential to overcome cardiac toxicity caused by potent antitumor anthracycline antibiotics such as doxorubicin and daunorubicin. ICRF-187, +enantiomer of racemic ICRF-159, has been used in EU countries as cardioprotector in cancer clinics. Furthermore, bis(2,6-dioxopiperazines) enhance the efficacy of antitumor topoisomerase II poisons, e.g. anthracycline antibiotics such as daunorubicin and doxorubicin, by reducing their side effects and by allowing dose escalation of the antitumor drugs in preclinical and clinical settings. Besides bis(2,6-dioxopiperazines) per se having antitumor activity, and one of their derivatives, MST-16 or sobuzoxane, bis(N1-isobutyloxycarbonyloxymethyl-2,6-dioxopiperazine), has been developed in Japan and used in clinics as anticancer drug for malignant lymphomas and adult T-cell leukemia (ATL). Further developments of bis(2,6-dioxopiperazines) as antimetastatic agents are expected.

DNA topoisomerase II rescue by catalytic inhibitors: a new strategy to improve the antitumor selectivity of etoposide

The nuclear enzyme DNA topoisomerase II (topo II) is the target of important antitumor agents such as etoposide. Recent work has classified topo II targeting drugs into either topo II poisons that act by stabilizing enzyme-DNA cleavable complexes leading to DNA breaks, or topo II catalytic inhibitors that act at stages in the catalytic cycle of the enzyme where both DNA strands are intact and, therefore, do not cause DNA breaks. Accordingly, catalytic inhibitors are known to abrogate DNA damage and cytotoxicity caused by topo II poisons. In this commentary, we have focused on the possibilities of enabling high-dose therapy with the topo II poison etoposide by protection of normal tissue with catalytic inhibitors, analogous to folinic acid rescue in high-dose methotrexate treatment. Thus, we have demonstrated recently that (+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane (ICRF-187) enabled a 3- to 4-fold dose escalation of etoposide in mice. Two high-dose etoposide models are described, namely use of the weak base chloroquine in tumors with acidic extracellular pH and targeting of CNS tumors with protection of normal tissue by the bisdioxopiperazine ICRF-187. In conclusion, high supralethal doses of topo II poisons in combination with catalytic inhibitor protection form a new strategy to improve the antitumor selectivity of etoposide and other topo II poisons. Such an approach may be used to overcome problems with drug resistance and drug penetration.