5,6-Dimethylxanthenone-4-acetic acid, synthesised in this laboratory, reduces tumour blood flow, both in mice and in patients on Phase I trial. We used TUNEL (TdT-mediated dUTP nick end labelling) assays to investigate whether apoptosis induction was involved in its antivascular effect. 5,6-Dimethylxanthenone-4-acetic acid induced dose-dependent apoptosis in vitro in HECPP murine endothelial cells in the absence of up-regulation of mRNA for tumour necrosis factor. Selective apoptosis of endothelial cells was detected in vivo in sections of Colon 38 tumours in mice within 30 min of administration of 5,6-Dimethylxanthenone-4-acetic acid (25 mg kg −1 ). TUNEL staining intensified with time and after 3 h, necrosis of adjacent tumour tissue was observed. Apoptosis of central vessels in splenic white pulp was also detected in tumour-bearing mice but not in mice without tumours. Apoptosis was not observed in liver tissue. No apoptosis was observed with the inactive analogue 8-methylxanthenone-4-acetic acid. Positive TUNEL staining of tumour vascular endothelium was evident in one patient in a Phase I clinical trial, from a breast tumour biopsy taken 3 and 24 h after infusion of 5,6-Dimethylxanthenone-4-acetic acid (3.1 mg m −2 ). Tumour necrosis and the production of tumour tumour necrosis factor were not observed. No apoptotic staining was seen in tumour biopsies taken from two other patients (doses of 3.7 and 4.9 mg m −2 ). We conclude that 5,6-Dimethylxanthenone-4-acetic acid can induce vascular endothelial cell apoptosis in some murine and human tumours. The action is rapid and appears to be independent of tumour necrosis factor induction. British Journal of Cancer (2002) 86 , 1937–1942. doi: 10.1038/sj.bjc.6600368 www.bjcancer.com © 2002 Cancer Research UK

5,6-Dimethylxanthenone-4-acetic acid (DMXAA) is currently undergoing clinical evaluation as an antivascular agent for the treatment of cancer. We have previously demonstrated that DMXAA induces apoptosis of vascular endothelial cells in murine tumour sections and in a breast carcinoma biopsy from one patient in a Phase I trial. We wished to determine the tissue selectivity of this effect and its relationship to induced blood flow changes. Mice with Colon 38 tumours were treated with DMXAA and tissues were examined for apoptosis by TdT-mediated dUTP nick-end labelling (TUNEL). Hoechst 33342 was used to stain functional vessels, with the loss of stained vessels used as a measure of tumour vascular collapse. Treatment with DMXAA at 25 mg kg À1 , its maximum tolerated dose (MTD), showed, after 3 h, a 12-fold increase in TUNEL staining of tumour vascular endothelial cells. In contrast, tissue from the heart, brain, liver and spleen showed no increase. Induction of apoptosis in tumour tissue was both dose-dependent, observable at doses as low as 5 mg kg À1 , and time-dependent. Apoptosis was significantly lower in Colon 38 tumours of mice, with a targeted disruption in the TNF gene (TNF À/À ), or in the TNF receptor 1 gene (TNFR À/À ), as compared with that in wild-type mice. Increasing the DMXAA dose to 50 mg kg À1 in these knockout mice raised tumour apoptosis to a level comparable to that induced in wild-type mice given DMXAA at the MTD. For all the data, a significant correlation (r ¼ 0.94; Po0.001) was found between logarithmic percentage apoptosis induction and the logarithmic density of Hoechst-stained vessels. These results suggest that blood flow inhibition caused by DMXAA is tumour tissue-specific and is a consequence of induction of apoptosis in tumour vascular endothelial cells.

A series of nitrogen mustard analogues of the DNA minor groove binding fluorophore pibenzimol (Hoechst 33258) have been synthesized and evaluated for antitumor activity. Conventional construction of the bisbenzimidazole ring system from the piperazinyl terminus, via two consecutive Pinner-type reactions, gave low yields of products contaminated with the 2-methyl analogue which proved difficult to separate. An alternative synthesis was developed, involving construction of the bisbenzimidazole from the mustard terminus, via Cu(2+)-promoted oxidative coupling of the mustard aldehydes with 3,4-diaminobenzonitrile to form the monobenzimidazoles, followed by a Pinner-type reaction and condensation with 4-(1-methyl-4-piperazinyl)-o-phenylenediamine. This process gives higher yields and pure products. The mustard analogues showed high hypersensitivity factors (IC50AA8/IC50 UV4), typical of DNA alkylating agents. There was a large increase in cytotoxicity (85-fold) across the homologous series which cannot be explained entirely by changes in mustard reactivity and may be related to altering orientation of the mustard with respect to the DNA resulting in different patterns of alkylation. Pibenzimol itself (which has been evaluated clinically as an anticancer drug) was inactive against P388 in vivo using a single-dose protocol, but the short-chain mustard homologues were highly effective, eliciting a proportion of long-term survivors.

5,6-dimethylxanthenone-4-acetic acid, a novel antivascular anticancer drug, has completed Phase I clinical trial. Its actions in mice include tumour necrosis factor induction, serotonin release, tumour blood flow inhibition, and the induction of tumour haemorrhagic necrosis and regression. We have used mice with a targeted disruption of the tumour necrosis factor receptor-1 gene as recipients for the colon 38 carcinoma to determine the role of tumour necrosis factor signalling in the action of 5,6-dimethylxanthenone-4-acetic acid. The pharmacokinetics of 5,6-dimethylxanthenone-4-acetic acid, as well as the degree of induced plasma and tissue tumour necrosis factor, were similar in tumour necrosis factor receptor-1 7/7 and wild-type mice. However, the maximum tolerated dose of 5,6-dimethylxanthenone-4-acetic acid was considerably higher in tumour necrosis factor receptor-1 7/7 mice (4100 mg kg 71 ) than in wild-type mice (27.5 mg kg 71 ). The antitumour activity of 5,6-dimethylxanthenone-4-acetic acid (25 mg kg 71 ) was strongly attenuated in tumour necrosis factor receptor-1 7/7 mice. However, the reduced toxicity in tumour necrosis factor receptor-1 7/7 mice allowed the demonstration that at a higher dose (50 mg kg 71 ), 5,6-dimethylxanthenone-4-acetic acid was curative and comparable in effect to that of a lower dose (25 mg kg 71 ) in wild-type mice. The 5,6-dimethylxanthenone-4-acetic acid -induced rise in plasma 5-hydroxyindoleacetic acid, used to reflect serotonin production in a vascular response, was larger in colon 38 tumour bearing than in non-tumour bearing tumour necrosis factor receptor-1 7/7 mice, but in each case the response was smaller than the corresponding response in wild-type mice. The results suggest an important role for tumour necrosis factor in mediating both the host toxicity and antitumour activity of 5,6-dimethylxanthenone-4-acetic acid, but also suggest that tumour necrosis factor can be replaced by other vasoactive factors in its antitumour action, an observation of relevance to current clinical studies.

Summary 5,6-Dimethylxanthenone-4-acetic acid (DMXAA), synthesized in this laboratory and currently in phase I clinical trial, is a low molecular weight inducer of tumour necrosis factor-α (TNF-α). Administration of DMXAA to mice with established transplantable tumours elicits rapid vascular collapse selectively in the tumour, followed by extensive haemorrhagic necrosis mediated primarily through the production of TNF-α. In this report we have investigated the synthesis of TNF-α mRNA in hepatic, splenic and tumour tissue. Coadministration of thalidomide with DMXAA increased anti-tumour activity and increased intra-tumoural TNF-α production approximately tenfold over that obtained with DMXAA alone. Thalidomide increased splenic TNF-α production slightly but significantly decreased serum and hepatic levels of TNF-α induced with DMXAA. Lipopolysaccharide (LPS) induced 300-fold higher serum TNF-α than did DMXAA at the maximum tolerated dose, but induced similar amounts of TNF-α in spleen, liver and tumour. Splenic TNF-α activity induced with LPS was slightly increased with thalidomide, but serum and liver TNF-α levels were suppressed. Thalidomide did not increase intra-tumoural TNF-α production induced with LPS, in sharp contrast to that obtained with DMXAA. While thalidomide improved the anti-tumour response to DMXAA, it had no effect on the anti-tumour action of LPS that did not induce a significant growth delay or cures against the Colon 38 tumour. The increase in the anti-tumour action by thalidomide in combination with DMXAA corresponded to an increase in intra-tumoural TNF-α production. Co-administration of thalidomide may represent a novel approach to improving selective intra-tumoural TNF-α production and anti-tumour efficacy of DMXAA.Keywords: DMXAA; thalidomide; Colon 38; endotoxin; tumour necrosis factor 716British Journal of Cancer (1999) 80(5/6), 716-723 © 1999 Cancer Research Campaign Article no. bjoc.1998 Received 30 Silva et al, 1994), but was withdrawn from use as a sedative and anti-emetic in the 1960s because of its teratogenicity (Fabro et al, 1967). Recent studies indicate that its immunosuppressive and anti-inflammatory effects would be beneficial to the treatment of graft-versus-host disease (Vogelsang et al, 1992;Uthoff et al, 1995), rheumatoid arthritis (Gutierrez-Rodriguez et al, 1989), prevention of graft rejection (Vogelsang et al, 1988;Uthoff et al, 1995), HIV/AIDS (Makonkawkeyoon et al, 1993;Moreira et al, 1997), sarcoidosis (Carlesimo et al, 1995) and various other inflammatory diseases (Burroughs et al, 1995). In experiments to determine whether suppression of serum TNF-α production by thalidomide affected the antitumour response to DMXAA, we found that, while serum TNF-α levels decreased, anti-tumour activity was unexpectedly improved . Reduction of tumour blood flow induced by DMXAA, which is thought to be mediated by TNF-α, was not reversed by thalidomide . Thalidomide analogues that were more potent than thalidomide in inhibiting DMXAA-induced serum TNF-α were also more potent in...

Murine P388 (P) leukemia cell lines resistant to amsacrine (P/AMSA), dactinomycin (P/DACT), and doxorubicin (P/DOX) were compared with the parental strain in their sensitivity to a number of derivatives of amsacrine. The P/DACT cell line, which shows the characteristics of a transport-mediated multidrug-resistant cell line, was cross-resistant to vincristine, doxorubicin, etoposide, and a number of acridine-substituted amsacrine derivatives, but was sensitive in vitro and in vivo to amsacrine and its analog CI-921. The P/DOX cell line was cross-resistant to amsacrine but showed a similar pattern of cross-resistance to that of P/DACT in its in vitro response to amsacrine derivatives. In contrast, the P/AMSA line was substantially cross-resistant (from 27- to 146-fold) to all acridine-substituted amsacrine derivatives. However, when the substituents on the anilino side chain of amsacrine were changed, the in vitro cross-resistance of the P/AMSA line could be substantially reduced and even overcome. Derivatives with low cross-resistance ratios were tested in vivo against the P/AMSA leukemia and, in contrast to amsacrine and CI-921, were found to be active. Since the target enzyme for amsacrine action, topoisomerase II, is thought to be structurally modified in the P/AMSA line as well as in some other multidrug-resistant lines, these results suggest the feasibility of tailoring topoisomerase II-directed drugs specifically for the altered enzymes in resistant cells. New drug design approaches are therefore available for overcoming two major types of multidrug resistance.

Summary EMT6 multicellular spheroids were introduced into the peritoneal cavities of mice and allowed to become vascularised, resulting in solid spherical tumours. The necrotic cores of the initially avascular spheroids were replaced by vascularised tumour tissue but the outer zones of the spheroids failed to become vascularised. The presence of both vascular and avascular components in each spheroid allowed the role of the vasculature in the antitumour action of flavone acetic acid (FAA) to be determined. Eighteen hours after treatment with FAA 0.8 mmol kg-', the vascularised core became necrotic and haemorrhagic, while the outer avascular zone remained viable. Tumour Materials and methodsHistological studies EMT6 multicellular tumour spheroids were grown in spinner flask culture in a-MEM + 10% fetal calf serum, and between 15 and 25 spheroids, varying in size from 0.5 to 1.2 mm in diameter, were injected into the peritoneal cavities of anaesthetised Balb/C mice through a 161 gauge needle, as described previously (Zwi et al., 1989). Seven days later the mice in the treatment group (n = 7) were injected with FAA 0.8 mmol kg-' (kindly supplied by Dr K.D. Paull, National Cancer Institute) in 5% w/v sodium bicarbonate by the intravenous (i.v.) or intraperitoneal (i.p.) route, and were killed after a further 18 h. Untreated spheroid-bearing mice (n = 2) were killed after the same interval. The peritoneal cavities of the mice were opened, the free spheroids were collected, and those spheroids which had become attached to host structures were excised with a cuff of adjacent tissue. The spheroids were fixed in either 4% neutral formaldehyde or 2.5% phosphate buffered glutaraldehyde (pH 7.4). The formalin-fixed tissue was embedded in paraffin, and 5 gm sections were stained with haematoxylin and eosin (H&E). The glutaraldehyde-fixed spheroids were embedded in epoxy resin and 2 gim sections stained with toluidine blue. Multiple sections were examined from each spheroid.

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