Development and pre-clinical testing of a novel hypoxia-activated KDAC inhibitor

Abstract

Summary Tumor hypoxia is associated with therapy resistance and poor patient prognosis. Hypoxia-activated prodrugs, designed to selectively target hypoxic cells while sparing normal tissue, represent a promising treatment strategy. We report the pre-clinical efficacy of 1-methyl-2-nitroimidazole panobinostat (NI-Pano, CH-03), a novel bioreductive version of the clinically used lysine deacetylase inhibitor, panobinostat. NI-Pano was stable in normoxic (21% O 2 ) conditions and underwent NADPH-CYP-mediated enzymatic bioreduction to release panobinostat in hypoxia (<0.1% O 2 ). Treatment of cells grown in both 2D and 3D with NI-Pano increased acetylation of histone H3 at lysine 9, induced apoptosis, and decreased clonogenic survival. Importantly, NI-Pano exhibited growth delay effects as a single agent in tumor xenografts. Pharmacokinetic analysis confirmed the presence of sub-micromolar concentrations of panobinostat in hypoxic mouse xenografts, but not in circulating plasma or kidneys. Together, our pre-clinical results provide a strong mechanistic rationale for the clinical development of NI-Pano for selective targeting of hypoxic tumors.

Comprehension of the Relationship between Autophagy and Reactive Oxygen Species for Superior Cancer Therapy with Histone Deacetylase Inhibitors

“…In response to hypoxia, cancer cells may activate numerous hypoxia-inducible genes and thus promote angiogenesis to enhance proliferation. Hence, tumor hypoxia is usually associated with poor patient prognosis [48]. For example, previous studies have shown a link between hypoxia and CA19-9 that is a poor prognostic marker in cancers [49].…”

Zap‐Pano: a Photocaged Prodrug of the KDAC Inhibitor Panobinostat

“…This modification can prevent the interaction between the compound and the active site Zn 2 + ion, leading to an inactive compound. [12,30] Therefore, we adopted this approach to develop light-activated derivatives of Pano and selected the 4,5-dimethoxy-2-nitrobenzyl group as the photo-labile component (Scheme 1). [31][32][33]36,37] In addition, we also employed two negative control compounds a 4nitrobenzyl analogue (NB, 13) and an unsubstituted benzyl analogue (Bn, 14), which should not photorelease Pano.…”

“…The synthesis of Pano was carried out as has been previously published. [12,38] The photolabile DMNB derivative of Pano (Zap-Pano, 1) and both control compounds were synthesised from the substituted hydroxylamines using a route previously developed within the group (Scheme 1). [12,30] Briefly, the nitrobenzyl halides (3 and 6) were reacted with Nhydroxyphthalimide, before deprotection with hydrazine, to give the substituted hydroxylamines (5 and 8).…”

“…[15][16][17][18] Prodrugs of KDAC inhibitors have been developed that are activated by hydrolysis, [19] thiols, [13] reactive oxygen species, [20] hydrogen peroxide or peroxynitrite, [21] esterases, [22,23] transition metals, [24] and light. [25][26][27][28][29] We have recently reported prodrugs of the KDAC inhibitors vorinostat (SAHA) [30] and Pano [12] that are selectively released in hypoxia.…”

“…[34] This technique provides temporal and spatial control over the release of the active component. Building on our work developing a hypoxia-activate prodrug of Pano, [12] here we report the design, synthesis, and initial validation of a lightactivated prodrug of Pano, Zap-Pano (1, Figure 1). This compound releases Pano with temporal control in the oesophageal cancer cell line, OE21; it will be a useful research tool for those studying lysine acetylation and has the potential to allow the release of Pano while minimising off-target effects.…”