Synthesis and Biological Activity of Azido Analogues of 5,6-Dimethylxanthenone-4-acetic Acid for Use in Photoaffinity Labeling

Abstract

5,6-Dimethylxanthenone-4-acetic acid (1) is scheduled for phase III clinical trials as a vascular disrupting agent. However, its biochemical receptor(s) have yet to be identified. In this report, the synthesis of azido analogues of 1 that could be used for photoaffinity labeling of proteins as an approach toward identifying its molecular targets is described. While 5-azidoxanthenone-4-acetic acid (2) and 5-azido-6-methylxantheone-4-acetic acid (3) were found to have biological activities similar to that of 1, 6-azido-5-methylxanthenone-4-acetic acid (4) was unstable and could not be evaluated. Both azido compounds 2 and 3 activated NF-kappaB, induced the production of tumor necrosis factor in cultured mouse splenocytes, and induced hemorrhagic necrosis of colon 38 tumors in mice. Photoreaction of lysates from spleen cells with tritiated 2 resulted in two radiolabeled protein bands at 50 and 14 kDa that could be competitively inhibited with cold 1 and cold 2. The azido compounds 2 and 3 exhibit all the requirements for use in photoaffinity labeling of potential receptor(s) for 1.

Dissection of stromal and cancer cell-derived signals in melanoma xenografts before and after treatment with DMXAA

“…Multiple targets are likely to be involved in order to account for the numerous and distinct effects that DMXAA has on different cell types. Recent efforts from our laboratory using the approach of photoaffinity labelling (Palmer et al , 2007; Brauer et al , 2010) identified more than 30 cellular proteins that were found to interact with the azido-analogue of DMXAA. Essentially, all the labelled proteins were oxidisable proteins, implicating a role for redox signalling in the action of DMXAA (Brauer et al , 2010).…”

Identification of human-selective analogues of the vascular-disrupting agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA)

“…The NF- κ B signalling pathway (Joseph et al , 1999; Woon et al , 2003; Wang et al , 2006), the TBK1-IRF-3 signalling axis (Roberts et al , 2007), the NOD signalling pathway (Cheng et al , 2010), and at least three members of the MAPK superfamily (Sun et al , 2011) are involved in one or more of the pleiotrophic effects of DMXAA in mice. Studies from our own laboratory showed that more than thirty oxidisable proteins were photoaffinity labelled with an azido-analogue of DMXAA in cellular extracts from murine leukocytes, implicating a role for redox signalling (Palmer et al , 2007; Brauer et al , 2010). The yet unidentified cellular enzymes that catalyse the first-step, one-electron oxidation of DMXAA to form the benzyl radical initiating the generation of reactive oxygen species and redox signalling could also be regarded as biochemical target(s) for this class of compounds.…”

Carboxyxanthones: Bioactive Agents and Molecular Scaffold for Synthesis of Analogues and Derivatives

“…All compounds were tested for antiproliferative activity towards human ovarian adenocarcinoma 2008 cell line, and cisplatin-resistant subline C13* [147]. It was found that compounds 119 and 128 presented good ability to inhibit 2008 cell line [148]. Most of the other compounds only presented cytotoxic activity at the highest tested concentration [147].…”

“…In 2007, eight new analogues of DMXAA ( 2 ) and XAA ( 104 ) bearing azido, nitro and amino moieties, compounds 147 – 154 (Figure 11), were reported by Palmer [148]. All compounds were tested for their cytotoxicity on HECPP murine endothelial cells, as well as their ability to induce hemorrhagic necrosis in mice with colon 38 tumors [148]. It was found that compounds 147 and 148 caused profound necrosis on the tested tumors, when compared to the carboxyxanthone derivative 2 [148].…”