Preclinical efficacy of the bioreductive alkylating agent RH1 against paediatric tumours

Abstract

BACKGROUND: Despite substantial improvements in childhood cancer survival, drug resistance remains problematic for several paediatric tumour types. The urgent need to access novel agents to treat drug-resistant disease should be expedited by pre-clinical evaluation of paediatric tumour models during the early stages of drug development in adult cancer patients. METHODS/RESULTS: The novel cytotoxic RH1 (2,5-diaziridinyl-3-[hydroxymethyl]-6-methyl-1,4-benzoquinone) is activated by the obligate two-electron reductase DT-diaphorase (DTD, widely expressed in adult tumour cells) to a potent DNA interstrand cross-linker. In acute viability assays against neuroblastoma, osteosarcoma, and Ewing 0 s sarcoma cell lines RH1 IC 50 values ranged from 1-200 nM and drug potency correlated both with DTD levels and drug-induced apoptosis. However, synergy between RH1 and cisplatin or doxorubicin was only seen in low DTD expressing cell lines. In clonogenic assays RH1 IC 50 values ranged from 1.5-7.5 nM and drug potency did not correlate with DTD level. In A673 Ewing's sarcoma and 791T osteosarcoma tumour xenografts in mice RH1 induced apoptosis 24 h after a single bolus injection (0.4 mg/kg) and daily dosing for 5 days delayed tumour growth relative to control. CONCLUSION: The demonstration of RH1 efficacy against paediatric tumour cell lines, which was performed concurrently with the adult Phase 1 Trial, suggests that this agent may have clinical usefulness in childhood cancer.

The anti‐tumour compound, RH1, causes mitochondria‐mediated apoptosis by activating c‐Jun N‐terminal kinase

“…Reduction of RH1 activates aziridine residues, which subsequently induce DNA damage (Cummings et al, 2003;Kim et al, 2004a;Kim et al, 2004b;Ward et al, 2005;Hussein et al, 2009). Because NQO1 is abundantly expressed in a variety of cancer tissues, it has been suggested that such tissues can be selectively damaged by RH1.…”

“…Because NQO1 is abundantly expressed in a variety of cancer tissues, it has been suggested that such tissues can be selectively damaged by RH1. This enzymedirected cancer-targeting agent is currently being tested in clinical trials (Cummings et al, 2003;Kim et al, 2004a;Kim et al, 2004b;Ward et al, 2005;Hussein et al, 2009). However, the molecular mechanisms underlying the therapeutic effects of the agent on solid tumours have not yet been clearly elucidated.…”

“…The anti-cancer activity of RH1 has been attributed to two-electron reduction by NAD(P)H quinone oxidoreductase 1 (NQO1, DTdiaphorase), an enzyme abundantly expressed in a variety of human solid tumours, including those of the breast, pancreas, lung and colon (Cummings et al, 2003;Kim et al, 2004a). NQO1-mediated reduction of RH1 results in activation of the aziridine rings, in turn inducing DNA alkylation and crosslinking (Cummings et al, 2003;Kim et al, 2004a;Kim et al, 2004b;Ward et al, 2005;Hussein et al, 2009). Several lines of evidence indicate that NQO1 positively regulates p53 stability by inhibiting p53 degradation (Asher et al, 2001;Nioi and Hayes, 2004).…”

“…Among these compounds, 2,5-diaziridinyl-3-(hydroxymethyl)-6-methyl-1,4-benzoquinone (RH1) is an especially potent bioreductive agent that has been shown to exert a profound anti-cancer activity in vivo and in vitro (Danson et al, 2007;Hussein et al, 2009). The anti-cancer activity of RH1 has been attributed to two-electron reduction by NAD(P)H quinone oxidoreductase 1 (NQO1, DTdiaphorase), an enzyme abundantly expressed in a variety of human solid tumours, including those of the breast, pancreas, lung and colon (Cummings et al, 2003;Kim et al, 2004a).…”

Cytotoxicity of anticancer aziridinyl-substituted benzoquinones in primary mice splenocytes.

“…Our studies involved the new representative of aziridinyl-benzoquinones, RH1 (2,5-diaziridinyl-3-(hydroxymethyl)-6-methyl-1,4-benzoquinone; Fig. 1), which recently underwent preclinical and Phase-I clinical trials (Ward et al, 2005;Hussein et al, 2009;Danson et al, 2011).…”