8-Cl-adenosine is an active metabolite of 8-Cl-cAMP responsible for its in vitro antiproliferative effects on CHO mutants hypersensitive to cytostatic drugs.

8-Cl-cAMP has been undergoing clinical trials as a potential chemotherapy agent, but there is much discussion in the literature as to whether the active agent is 8-Cl-cAMP itself, or its major metabolite, 8-Cl-adenosine. 8-Cl-cAMP is susceptible to the action of serum enzymes such as phosphodiesterases, and its metabolism when administered to cancer patients raises questions as to the mechanism of action of 8-Cl-cAMP. The stability of 8-Cl-cAMP when incubated with serum, and the effects of both 8-Cl-cAMP and 8-Cl-adenosine on the proliferation of variant lines of CHO cells hypersensitive to 8-Cl-cAMP were investigated. A solid-phase extraction (SPE) purification protocol and the HPLC method previously developed were used to determine 8-Cl-cAMP and 8-Cl-adenosine. Heat treatment of serum inactivated the enzymes in the culture medium responsible for activating 8-Cl-cAMP. Under these conditions 8-Cl-cAMP remained stable and there were no traces of its metabolite, 8-Cl-adenosine. Cell culture experiments showed that 8-Cl-cAMP only affected cell growth in medium that contained untreated serum. In contrast, 8-Cl-adenosine was shown to be growth inhibitory in medium containing either heat-treated or untreated serum. HPLC analysis of the culture medium from the cell culture experiments supported the hypothesis that 8-Cl-cAMP was only effective in inhibiting cell growth after metabolism to 8-Cl-adenosine. Thus further studies of this drug and its mechanism of action should focus on 8-Cl-adenosine.

Evaluation of toremifene for reversal of multidrug resistance in renal cell cancer patients treated with vinblastine.

PURPOSE: Expression of P-glycoprotein (Pgp), which confers the multidrug resistance (MDR) phenotype, is thought to contribute to the insensitivity of renal cell cancer (RCC) to chemotherapy. The development of Pgp inhibitors for clinical application has been hampered by unacceptable toxicity at doses required to achieve adequate cellular concentration. Toremifene is able to reverse MDR and sensitise RCC to vinblastine in vitro. However, in vivo toremifene is tightly bound to serum proteins, in particular the acute phase protein alpha1-acid glycoprotein (AAG), which may limit tissue availability. In this phase I-II study we assessed the tolerability of short courses of high dose toremifene in combination with vinblastine and evaluated the key determinants of MDR reversal in vivo. METHODS: Twenty-seven patients with metastatic RCC received escalating doses of oral toremifene for 3 days every 2 weeks in combination with vinblastine 6 mg/m2 i.v. on day 3 of each cycle. The serum concentration of toremifene, its metabolites and AAG were measured and the effect of patients' serum on inhibition of Pgp in vitro was determined. RESULTS: Twenty-six patients were evaluable for response. Eight patients (31%) had stable disease and 18 patients (69%) progressive disease. The mean serum concentration of toremifene at 780 mg daily for 3 days was 7.82 microM [standard deviation (SD) 2.48, range 2.50 to 14.70], which exceeds that known to reverse MDR in vitro. The serum concentration of the major metabolite of toremifene, N-demethyltoremifene, which also reverses MDR, was 5.13 microM (SD 1.78, range 1.80 to 9.00). In 60% of patients the pre-treatment AAG concentration was above that known to block the effects of toremifene in vitro. However, addition of serum from patients on toremifene to MCF-7 adr cells in vitro inhibited Pgp-mediated efflux of rhodamine 123. CONCLUSIONS: We have shown that short course, high-dose toremifene in combination with vinblastine is generally well tolerated and that the concentration of toremifene required to reverse MDR in vitro is achievable in vivo.

Induction of thymidine phosphorylase as a pharmacodynamic end-point in patients with advanced carcinoma treated with 5-fluorouracil, folinic acid and interferon alpha.

Thymidine phosphorylase (TP) is an essential enzyme for the biochemical activation of 5-fluorouracil (5-FU). Interferon upregulates TP in vivo, although the dose and schedule of interferon for optimal biomodulation of 5-FU is not known. In this study, TP activity was measured in peripheral blood lymphocytes (PBLs) from patients with advanced carcinoma receiving treatment with 5-FU and folinic acid. Cohorts of patients were treated with interferon alpha (IFNalpha), immediately prior to 5-FU/folinic acid, at doses of 3 MIU m(-2), 9 MIU m(-2) and 18 MIUm(-2). IFNalpha was administered on day 0 cycle two, day-1 and day 0 cycle three and day-2, day-1 and day 0 cycle four. A fourth cohort was treated with IFNalpha 9 MIU m(-2) three times per week from cycle 2 onwards. Twenty-one patients were entered into the study with 19 evaluable for response. Six patients (32%) had stable disease and 13 (68%) progressive disease. There were no grade-IV toxicities. TP activity was detected in PBLs from all patients with wide interpatient variability in constitutive TP activity prior to chemotherapy, and in response to IFNalpha. 5-FU/folinic acid alone did not induce TP activity but a single dose of IFNalpha led to upregulation of TP within 2 h of administration with a further increase by 24 h (signed rank test, P = 0.006). TP activity remained elevated for at least 13 days (signed rank test, P= 0.02). There were no significant differences in TP activity between schedules or with additional doses of IFNalpha. A single dose of IFNalpha as low as 3 MIU m(-2) can cause sustained elevation of PBL TP activity in vivo indicating that biochemical markers are important pharmacodynamic endpoints for developing optimal schedules of IFNalpha for biomodulation of 5-FU.

Evaluation of the alkaline comet assay and urinary 3-methyladenine excretion for monitoring DNA damage in melanoma patients treated with dacarbazine and tamoxifen.

PURPOSE: To develop, using dacarbazine as a model, reliable techniques for measuring DNA damage and repair as pharmacodynamic endpoints for patients receiving chemotherapy. METHODS: A group of 39 patients with malignant melanoma were treated with dacarbazine 1 g/m(2) i.v. every 21 days. Tamoxifen 20 mg daily was commenced 24 h after the first infusion and continued until 3 weeks after the last cycle of chemotherapy. DNA strand breaks formed during dacarbazine-induced DNA damage and repair were measured in individual cells by the alkaline comet assay. DNA methyl adducts were quantified by measuring urinary 3-methyladenine (3-MeA) excretion using immunoaffinity ELISA. Venous blood was taken on cycles 1 and 2 for separation of peripheral blood lymphocytes (PBLs) for measurement of DNA strand breaks. RESULTS: Wide interpatient variation in PBL DNA strand breaks occurred following chemotherapy, with a peak at 4 h (median 26.6 h, interquartile range 14.75-40.5 h) and incomplete repair by 24 h. Similarly, there was a range of 3-MeA excretion with peak levels 4-10 h after chemotherapy (median 33 nmol/h, interquartile range 20.4-48.65 nmol/h). Peak 3-MeA excretion was positively correlated with DNA strand breaks at 4 h (Spearman's correlation coefficient, r=0.39, P=0.036) and 24 h (r=0.46, P=0.01). Drug-induced emesis correlated with PBL DNA strand breaks (Mann Whitney U-test, P=0.03) but not with peak 3-MeA excretion. CONCLUSIONS: DNA damage and repair following cytotoxic chemotherapy can be measured in vivo by the alkaline comet assay and by urinary 3-MeA excretion in patients receiving chemotherapy.

Relationship of hypoxia-inducible factor (HIF)-1alpha and HIF-2alpha expression to vascular endothelial growth factor induction and hypoxia survival in human breast cancer cell lines.

Hypoxia-inducible factors (HIF-1 and HIF-2) are two closely related protein complexes that activate transcription of target genes in response to hypoxia. Expression of HIF-1alpha and HIF-2alpha and their effects on survival under hypoxia were studied in six human breast cancer cell lines. We also evaluated the basal and inducible expression of two hypoxically regulated genes, vascular endothelial growth factor (VEGF) and lactate dehydrogenase-A (LDH-A). All of the cell lines studied expressed HIF-1alpha at various levels, but HIF-2alpha was low or absent from the more aggressive cell lines. There was an inverse correlation between HIF-1alpha and HIF-2alpha induction and clonogenic survival under hypoxia. Thus, cell lines with reduced induction of HIF-1alpha or HIF-2alpha showed high basal levels of VEGF and improved survival under hypoxia. A reduction in HIF expression was also associated with a more aggressive phenotype in vivo. To confirm these results, we carried out stable transfection of the MDA 435 cell line with human HIF-2alpha cDNA. There was no change in the growth rate in monolayer culture. However, in vitro growth as colonies and in vivo tumor growth of the HIF-2alpha overexpressing cells were significantly impaired compared with the control transfectants. Thus, despite the fact that HIF proteins are necessary for optimal tumor growth and angiogenesis in vivo, overexpression of these molecules seems detrimental to tumor growth. A balance between the angiogenic and tumor-inhibiting levels of HIF proteins may, therefore, be necessary for optimal tumor growth.

Human cultured dendritic cells show differential sensitivity to chemotherapy agents as assessed by the MTS assay.

Assessment of the chemosensitivity of dendritic cells (DC) may allow more rational development of combined chemotherapy and immunotherapy protocols. Human monocyte-derived DC generated reproducible results in the MTS (Owen's reagent) assay, which was then used to study DC survival after treatment with four different chemotherapy agents. DC preparations from three different donors were used per drug. DC were sensitive to doxorubicin (concentration range 0.1-50 microM) with variation in sensitivity between donors (IC50 244-1100 nM). The most extreme variation was seen for vinblastine (concentration range 250-0.025 microM with IC50 0.15-17.25 microM). In contrast, there was relative resistance to etoposide (concentration range 0.2-200 microM) and 5-fluorouracil (concentration range 0.7-7700 microM) with no toxicity seen until 50 microM and 770 microM respectively. The function of DC in allogeneic mixed leucocyte reactions closely paralleled results from the MTS assays. The differential sensitivity to chemotherapy agents did not appear to be due to expression of P-glycoprotein. These results suggest that etoposide or 5-fluorouracil is less likely to reduce the immunotherapeutic potential of DC and may be valuable in the design of prodrug activation therapy.

Synthesis and cytotoxic activity of thiazolyl indolequinones.

A number of thiazolyl indolequinones have been prepared and evaluated for their antitumor properties. The compounds were synthesized from the appropriate indole, building up the thiazole ring using the Hantzsch reaction. Cytotoxic activity was determined in the human breast cancer SKBr3 cell line. Selected compounds were also studied in human lung carcinoma A549 and PV9 cell lines. In addition, some compounds were evaluated for their possible bioreductive action by determining their cytotoxicity towards V79 Chinese hamster lung fibroblasts in air and under anaerobic (hypoxic) conditions.

The distribution and expression of the two isoforms of DNA topoisomerase II in normal and neoplastic human tissues.

In mammalian cells, there are two isoforms of DNA topoisomerase II, designated alpha (170-kDa form) and beta (180-kDa form). Previous studies using cell lines have shown that the topoisomerase IIalpha and beta isoforms are differentially regulated during the cell cycle and in response to changes in growth state. Moreover, both isoforms can act as targets for a range of anti-tumour drugs. Here, we have analysed the normal tissue distribution in humans of topoisomerase IIalpha and beta using isoform-specific antibodies. In addition, we have studied expression of these isoforms in 69 primary tumour biopsies, representative either of tumours that are responsive to topoisomerase II-targeting drugs (breast, lung, lymphoma and seminoma) or of those that show de novo drug resistance (colon). Topoisomerase IIalpha was expressed exclusively in the proliferating compartments of all normal tissues, and was detectable in both the cell nucleus and cytoplasm. In biologically aggressive or rapidly proliferating tumours (e.g. high-grade lymphomas and seminomas), there was a high level of topoisomerase IIalpha, although expression was still detectable in colon tumours, indicating that expression of this isoform is not sufficient to explain the intrinsic drug resistance of colon tumours. Topoisomerase IIbeta was expressed ubiquitously in vivo and was localized in both the nucleoli and the nucleoplasm. This isoform was present in quiescent cell populations, but was expressed at a generally higher level in all tumours and proliferating cells than in normal quiescent tissues. We conclude that topoisomerase IIalpha is a strict proliferation marker in normal and neoplastic cells in vivo, but that topoisomerase IIbeta has a much more general cell and tissue distribution than has topoisomerase IIalpha. The apparent up-regulation of topoisomerase IIbeta in neoplastic cells has implications for the response of patients to anti-tumour therapies that include topoisomerase II-targeting drugs.

Relationship between topoisomerase II levels and resistance to topoisomerase II inhibitors in lung cancer cell lines.

Topoisomerase II is a key target of many anticancer drugs used to treat lung cancer. We measured the expression of topoisomerase II alpha and beta mRNA's and also the levels of cellular topoisomerase II alpha and beta protein and concluded that topoisomerase II alpha levels are important in cellular resistance to the topoisomerase II inhibitors examined. This can be clearly seen in pairs of matched cell lines. However, when looking at a panel of cell lines with a range of histological types the importance of the enzyme can be masked by other cellular characteristics such as repair and detoxification mechanisms.

Relationship between expression of topoisomerase II isoforms and intrinsic sensitivity to topoisomerase II inhibitors in breast cancer cell lines.

Topoisomerase II is a key target for many anti-cancer drugs used to treat breast cancer. In human cells there are two closely related, but differentially expressed, topoisomerase II isoforms, designated topoisomerase II alpha and beta. Here, we report the production of a new polyclonal antibody raised against a fragment of the C-terminal domain of the 180 kDa form of topoisomerase II (the beta isoform), which does not cross-react with the 170 kDa form (the alpha isoform). Using this antibody, together with a polyclonal antibody specific for the 170 kDa isoform of topoisomerase II, we have examined the relationship between the sensitivity of a panel of human breast cancer cell lines to different classes of topoisomerase II inhibitors and cellular levels of the topoisomerase II alpha and beta proteins. We found that sensitivity to amsacrine showed a correlation with the level of expression of topoisomerase II alpha protein, and that sensitivity to etoposide showed a similar correlation with the level of expression of topoisomerase II beta protein. There was also a relationship between sensitivity of these cell lines to mitoxantrone and the cellular level of both isoforms of topoisomerase II. No relationship was found between the level of mRNA for topoisomerase II alpha or beta, and either sensitivity of breast cancer cell lines to topoisomerase II inhibitors or the level of topoisomerase II protein expression.

Synthesis and biological activity of thiazolylindolequinones, analogues of the natural product BE 10988.

A number of analogues of the naturally occurring thiazolylindolequinone BE 10988, a reported potent inhibitor of topoisomerase II, have been prepared and evaluated. The compounds were synthesized from 4-(benzyloxy)-5-methoxy-1-methylindole by appropriate substitution at the indole 3-position followed by standard thiazole ring-forming reactions. The toxicity of these potentially bioreductively activated indolequinones was measured in Chinese hamster V79 cells under aerobic and hypoxic conditions. In addition, toxicity was measured in a human breast cancer cell line that shows amplification of the topo II alpha gene and hypersensitivity to known topo II inhibitors such as mAMSA and mitoxantrone. Using a DNA decatenation assay, a comparison was also made of the inhibitory effects of BE 10988 and mitoxantrone on topo II activity.

The role of DT-diaphorase in determining the sensitivity of human tumor cells to tirapazamine (SR 4233).

PURPOSE: To determine the dependency of the aerobic and hypoxic toxicity of tirapazamine on the intracellular activity of DT-diaphorase. METHODS AND MATERIALS: A panel of 18 human cell lines comprising predominantly small cell and nonsmall cell lung cancer and breast cancer lines were used. The activity of DT-diaphorase was determined in cytosolic preparations from cell lysates. The toxicity of tirapazamine was determined using the MTT assay after either 96 or 3 h aerobic exposure or 3 h treatment in hypoxia. RESULTS: The cell lines exhibited a 5000-fold range in DT-diaphorase activity. In toxicity experiments, values of IC50 range from 10.2-120 microM and from 155-1230 for 96 and 3 h aerobic exposures, respectively. In N2, IC50s ranged from 8-55 microM. None of the toxicity values correlate with activity of DT-diaphorase, neither did the ratio of aerobic:hypoxic toxicity (differential toxicity). CONCLUSION: The expression of DT-diaphorase in human tumor cells does not affect the toxicity of tirapazamine.

Differential modulation of doxorubicin toxicity to multidrug and intrinsically drug resistant cell lines by anti-oestrogens and their major metabolites.

The ability of the anti-oestrogens tamoxifen, toremifene and their 4-hydroxy and N-desmethyl metabolites to modify doxorubicin (dox) toxicity to intrinsically resistant and multidrug resistant cell lines was compared, using human breast and lung cancer, and Chinese hamster ovary cell lines. The anti-oestrogens significantly enhanced dox toxicity to multidrug resistant, P-glycoprotein-positive cell lines, but did not affect toxicity to intrinsically resistant, P-glycoprotein-negative cells. Modification was observed at clinically achievable anti-oestrogen concentrations. Toremifene and tamoxifen would therefore appear to be good candidates for in vivo studies as MDR modulating agents in selected patients with P-glycoprotein-positive tumours.

Topoisomerase II alpha co-amplification with erbB2 in human primary breast cancer and breast cancer cell lines: relationship to m-AMSA and mitoxantrone sensitivity.

Topoisomerase II alpha (topo II alpha) is a key enzyme in DNA replication and a target for many anti-cancer drugs. High levels are associated with sensitivity to topoisomerase II inhibitors. Because its chromosome location is similar to erbB2 (17q21-22), which is frequently amplified in breast cancer, co-amplification of these genes was assessed. In 117 primary breast cancers, 25 were amplified for erbB2. Three of these cases showed co-amplification of topo II alpha. Topo II beta was not amplified. Four human breast cancer cell lines were assessed for erbB2 and topo II alpha co-amplification. They were also analysed for sensitivity to the topoisomerase inhibitors m-AMSA and mitoxantrone. The most sensitive cell line was SKBr3, which was the only one with erbB2 amplification. Topo II alpha was co-amplified to a similar extent as in tumours. This suggests that patients whose tumours show topo II alpha amplification should be assessed specifically for therapy with topoisomerase inhibitors.

Selective reversal of vinblastine resistance in multidrug-resistant cell lines by tamoxifen, toremifene and their metabolites.

In this study we describe the effects of tamoxifen, toremifene and their 4-hydroxy and N-desmethyl metabolites on the toxicity of a range of drugs to human breast and lung cancer and to Chinese hamster ovary cell lines, determined using a tetrazolium-based semi-automated colorimetric assay. Vinblastine resistance was completely abolished in an mdr1-transfected lung cancer cell line (S1/1.1), indicating that P-glycoprotein-mediated multidrug resistance can be fully reversed by anti-oestrogens. A substantial (14- to 39-fold) enhancement of vinblastine toxicity to highly multidrug-resistant (MCF-7Adr) cells expressing P-glycoprotein was also observed in the presence of tamoxifen, toremifene and their metabolites, while m-amsacrine, cisplatin and melphalan toxicity was unaffected.

High-dose tamoxifen as an enhancer of etoposide cytotoxicity. Clinical effects and in vitro assessment in p-glycoprotein expressing cell lines.

Twenty-six patients with relapsed or drug-resistant cancer were treated with a combination of oral etoposide (300 mg day-1 for 3 days) and high-dose oral tamoxifen as a potential modulator of drug resistance (480 or 720 mg day-1 for 6 days beginning 3 days before etoposide). One patient with relapsed high-grade lymphoma and one with adenocarcinoma of unknown primary site has a partial response. Toxicity consisting of nausea, vomiting and subjective dizziness, unsteadiness of gait and malaise occurred during tamoxifen treatment. Serum levels of tamoxifen averaged 3-3.5 microM on day 4 of all courses of treatment at both 480 and 720 mg day-1. N-desmethyltamoxifen levels were lower than tamoxifen during the first course (2 microM) but increased to equal tamoxifen levels during the second course. Didesmethyltamoxifen levels remained below 1 microM. In vitro, both tamoxifen and the standard modulator of multidrug resistance, verapamil, produced minor enhancement of etoposide cytotoxicity in the MCF-7 wt cell line but produced no enhancement with any other cell line. High, intermittent doses of tamoxifen can be given with acceptable toxicity and produce serum levels that have been shown to modulate drug resistance in vitro. In vitro, however, such levels have no significant effect on etoposide cytotoxicity towards a range of wild-type and MDR cell lines.

The sensitivity of human tumour cells to quinone bioreductive drugs: what role for DT-diaphorase?

15 human tumour cell lines (lung, breast and colon) have been evaluated for their sensitivity to the quinone based anti-cancer drugs Mitomycin C, Porfiromycin, and EO9 (3-hydroxymethyl-5-aziridinyl-1-methyl-2-(IH-indole-4,7-dione)prop-beta- en-alpha-ol). Sensitivity has been compared with the intra-cellular levels of DT-diaphorase, an enzyme thought to be important in the reductive activation of these quinones. No correlation exists between levels of DT-diaphorase and sensitivity to Mitomycin C or Porfiromycin. However, for EO9 those cell lines showing highest levels of DT-diaphorase activity tend to be the most sensitive.

Tissue plasminogen activators in breast cancer.

Increased levels of tissue fibrinolytic activity have been detected in some malignant tumours and they have been implicated in metastatic spread. We have investigated tissue plasminogen activator (tPA) and urokinase (UK) in 26 breast carcinomas and 13 benign breast biopsies. Tissue extracts were analysed for overall fibrinolytic activity on fibrin plates and by fibrin-overlay zymography after electrophoresis on SDS-PAG. Supernatants of the extracts were analysed by an antigenic immunoassay (ELISA) and a functional bioimmunoassay (BIA) using polyclonal antibodies. Total ELISA and BIA results correlated (P less than 0.001) and all the tissues contained similar tPA levels. Malignant extracts contained significantly increased UK compared with benign extracts (1.60 +/- 0.37 iu, 0.36 +/- 0.16 iu; P less than 0.002). Zymography showed no high molecular weight inhibitor complexes and UK was almost exclusively confined to the malignant tissues (P much less than 0.02). The results suggest that malignant transformation of breast tissue is associated with the significantly increased production of UK. This may be responsible for the characteristics of malignancy or it may be a growth factor.