In vivo activation of the hypoxia-targeted cytotoxin AQ4N in human tumor xenografts

Abstract

AQ4N (banoxantrone) is a prodrug that, under hypoxic conditions, is enzymatically converted to a cytotoxic DNA-binding agent, AQ4. Incorporation of AQ4N into conventional chemoradiation protocols therefore targets both oxygenated and hypoxic regions of tumors, and potentially will increase the effectiveness of therapy. This current pharmacodynamic and efficacy study was designed to quantify tumor exposure to AQ4 following treatment with AQ4N, and to relate exposure to outcome of treatment. A single dose of 60 mg/kg AQ4N enhanced the response of RT112 (bladder) and Calu-6 (lung) xenografts to treatment with cisplatin and radiation therapy. AQ4N was also given to separate cohorts of tumor-bearing mice 24 hours before tumor excision for subsequent analysis of metabolite levels. AQ4 was detected by high performance liquid chromatography/mass spectrometry in all treated samples of RT112 and Calu-6 tumors at mean concentrations of 0.23 and 1.07 μg/g, respectively. These concentrations are comparable with those shown to be cytotoxic in vitro. AQ4-related nuclear fluorescence was observed in all treated tumors by confocal microscopy, which correlated with the high performance liquid chromatography/mass spectrometry data. The presence of the hypoxic marker Glut-1 was shown by immunohistochemistry in both Calu-6 tumors and RT112 tumors, and colocalization of AQ4 fluorescence and Glut-1 staining strongly suggested that AQ4N was activated in these putatively hypoxic areas. This is the first demonstration that AQ4N will increase the efficacy of chemoradiotherapy in preclinical models; the intratumoral levels of AQ4 found in this study are comparable with tumor AQ4 levels found in a recent phase I clinical study, which suggests that these levels could be potentially therapeutic. [Mol Cancer Ther 2009;8 (12):3266-75]

Selective Tumor Hypoxia Targeting by Hypoxia-Activated Prodrug TH-302 Inhibits Tumor Growth in Preclinical Models of Cancer

“…CI-1010 did not proceed to clinical trials because of the irreversible retinal toxicity observed in preclinical testing (21). HAPs that have advanced to clinical trials include tirapazamine (22,23), PR104 (24,25), AQ4N (26,27), and TH-302 (28)(29)(30)(31). TH-302 (1-methyl-2-nitro-1H-imidazole-5-yl) N, N 0 -bis (2-bromoethyl) diamidophosphate is a 2-nitroimidazole-linked prodrug of a brominated version of isophosphoramide mustard (Br-IPM; ref.…”

Dissemination via the lymphatic or angiogenic route impacts the pathology, microenvironment and hypoxia-related drug response of lung metastases

“…radiotherapy that target the proliferating cells, to destroy the cancer cells in hypoxic niches that are protected from cellular damage caused by free oxygen radicals [24]. AQ4N is a prodrug activated under hypoxic conditions to AQ4 which interferes with DNA replication by inhibiting topoisomerase II activity [25][26][27][28][29]. As a single-agent, administration of AQ4N is effective in the treatment of multiple types of pancreatic cancers in mice, controlling the primary tumour growth and spontaneous liver metastasis formation [26].…”

Impact of Tumor Blood Flow Modulation on Tumor Sensitivity to the Bioreductive Drug Banoxantrone

“…Conceivably, the combination of AQ4N with antiangiogenesis that we propose might be more effective when applied to other bioreductive drugs, or in the case of AQ4N by treatment at a lower dose but at a greater frequency of administration or in combination with radiation (Lalani et al, 2007;Williams et al, 2009). We did not directly assay AQ4N penetration to the flank tumors, but we used pimonidazole staining to verify that hydralazine treatment increases tumor hypoxia significantly; this, in turn, is expected to increase tumor accumulation of AQ4, as has been shown in several tumor models (Atkinson et al, 2007;Albertella et al, 2008;Williams et al, 2009). In contrast to AQ4N, mitoxantrone has poor tumor penetration, but the combination of AQ4N with mitoxantrone can result in more effective antitumor activity due to AQ4N targeting hypoxic regions and mitoxantrone targeting less hypoxic regions (Tredan et al, 2009).…”

“…AQ4N is considered an ideal bioreductive drug in that it penetrates deep into tumor tissue (Tredan et al, 2009). Its active metabolite, AQ4, is stable, localizes to hypoxic tumor regions in both preclinical and clinical studies (Albertella et al, 2008;Williams et al, 2009), and binds to DNA even under normoxic conditions, yet can passively diffuse into neighboring tumor cells (Smith et al, 1997). In contrast, poor tumor penetration is achieved with the related drug mitoxantrone.…”

“…Axitinib initially causes tumor growth stasis in the case of 9L gliosarcoma xenografts, but when combined with cyclophosphamide (CPA), it decreases the entry of the liver-activated CPA metabolite 4-OH-CPA into the tumor cells, as well as antitumor innate immune cells, and compromises overall antitumor activity (Ma and Waxman, 2008;Doloff and Waxman, 2012). This limitation of antiangiogenesis may potentially be circumvented by using a bioreductive drug such as AQ4N, which can penetrate into hypoxic tumor regions (Williams et al, 2009).…”