AQ4N: an alkylaminoanthraquinone N-oxide showing bioreductive potential and positive interaction with radiation in vivo

Abstract

S-y AQ4N (l,4-bLs-q25ddimthyai oo y}amin5dydroxy-anthrane-9,10-dione) is a novel alkylaminoanthraquinone N-oxide which, on reducin, forms a stable DNA affinic cytotoxi compound AQ4. The The failure to cure tumours with radiotherapy and chemotherapy has been attributed in part to the presence of treatment-resistant subpopulations of hypoxic tumour cells (Bush et at., 1978). Bioreductive agents provide a novel approach to this problem: reduction of the prodrug within a hypoxic cell to produce a cytotoxic metabolite should selectively target this sub population within tumours. Since normal tissus contain few, if any, poorly oxygenated cells, systemic reductive activation and its attendant toxicity should be minimal. Several classe of bioreductive agents have been described, icluding the nitroimidazoles, benzotriazene di-N-oXides and mitosenes (Workman, 1992). Using a different class of compounds, i.e. the anthraquinones, we have developed a novel alkylamnoanthraquinone N-oxide, AQ4N (1,4-bis-{[2-(di-methylamino-N-oxide)ethylarmino}5,8-dihydroxyanthracene-9,10-ione), which is susceptible to reduction under hypoxic conditions (Patterson, 1993). AQ4N is a weak DNA-binding agent and weak topoisomerase H inhibitor, critically, the electrically neutral N-oxide function prevents stable binding to the DNA helix (Patterson, 1993). In contrast, the reduction product of AQ4N, i.e. AQ4 (1,4-bis-{[2-(dimethylamino) ethylnamino}5,8-dihydroxyanthracene-9,10-dione) (Figure 1), is a cationic compound with high affinity for DNA. Interaction of AQ4 with DNA is facilitated by the planar, eletrondeficient antraquinone chromophore intercalating between adjcent DNA bases. Tlis complex is further stabiised by electrostatic interactions and hydrogen bonding with the deoxyribose phosphate backbone, as has been observed for similar anthraquinones (Denny and Wakelin, 1990 al., 1992). This will allow metabolism of the drug in cells which will contribute, when the hypoxic stimulus is removed, to the main growth frction within the tumour. Secondly, the drug can be combined with an agent which is selectively toxic to well-oxygenated cells to evahuate the effect of targeting the two subpopulations of cells (Brown and Lemmon, 1991;Grau and Overgaard, 1991). We have used both these approaches to study the effect of AQ4N on tumour growth in vivo. Firstly, we tested the anti-tumour effect of AQ4N when combined with hypobaric hypoxia. Following this we combined AQ4N with radiation as both single and fractionated doses. Materiak an mth Tumour systemThe T50/80 tumour is a poorly differentiated mammary carcinoma which arose in a B6D2FI mouse. Tumour and breeding colonies for mice were obtained from Dr JV Moore, Paterson Laboratory, Christie Hospital, Manchster, UK.Male B6D2FI mice aged 8-12 weeks were used for all studies, which were carried out in accordance with the UK. Animals (Scientific Procedures) Act 1986. The tumour has been maintained by intadermal passage for up to ten passages and then re-establshed from frozm stock. Tumour brei (0.05 ml) w...

AQ4N: a new approach to hypoxia-activated cancer chemotherapy

“…It was observed that normoxic mice tolerated single doses up to 320 mg kg -1 in the hypobaric chamber experiments (McKeown et al, 1995). In two studies over 400 mg kg -1 was tolerated (Wilson et al, 1996, Bibby, personal communication); this has since been confirmed by preclinical toxicity trials carried out by BIBRA (personal communication).…”

“…When combined with radiation in vivo a substantial enhancement of antitumour efficacy is observed with a dose modification factor of about two. This enhancement is found irrespective of whether AQ4N is administered before or after the radiation exposure providing strong evidence that this agent does act as a bioreductive cytotoxin (Figure 2; McKeown et al, 1995McKeown et al, , 1996 Tumour growth delay when AQ4N was administered before or after a single dose of radiation (12 Gy). AQ4N (200 mg kg -1 ) was administered at a range of times up to 120 h before and 48 h after a single dose of X-irradiation (12 Gy).…”

“…The first demonstration that AQ4N had potential in vivo as a hypoxic cell cytotoxin was shown using a hypobaric chamber (McKeown et al, 1995). Previously this model system was used to show that the anti-tumour efficacy of Tirapazamine was significantly enhanced when mice were placed in a chamber at 0.5 atm (i.e.…”

“…Bars show the tumour growth delay obtained for AQ4N and radiation administered alone. The results are the pooled data from three experiments (McKeown et al, 1995) 2000). Further evidence of the bioreductive nature of AQ4N was shown using the MDAH-Mca-4 tumour in vivo; the anti-tumour effect was enhanced with AQ4N when administered before or after radiation (Wilson et al, 1996).…”

Modification of vascular tone using iNOS under the control of a radiation-inducible promoter

“…iNOS is found in elevated levels in mammalian tumours [8][9][10] and employing an antisense gene therapy approach could lead to a constriction in tumour vessels and subsequent decrease in oxygenation levels. This artificially hypoxic tumour environment could then be targeted with any novel bioreductive drugs (eg AQ4N 27 ) subsequently shown to be effective in the clinic.…”