Synthesis, biological evaluation and SAR of 3-benzoates of ingenol for treatment of actinic keratosis and non-melanoma skin cancer

Ingenol Disoxate: A Novel 4-Isoxazolecarboxylate Ester of Ingenol with Improved Properties for Treatment of Actinic Keratosis and Other Non-Melanoma Skin Cancers

“…In our compound screening program, we utilized a simple chemical stability assessment in aqueous buffer (pH 7.4; 16 h, room temperature) as a first tier assay [17, 18]. At these conditions 60% ingenol mebutate and at least 95% ingenol disoxate were recovered.…”

“…We have previously published some of our efforts towards novel analogues of ingenol mebutate having improved physicochemical properties [17, 18], such as chemical stability and preserved favorable in vitro pharmacological properties. Some key findings from the structure-activity studies should be pointed out: (1) methylation of the 5- or 20-hydroxyl groups in the rigid ingenol scaffold eliminated the biological effects, (2) ingenol itself lacks biological activity, (3) the carbonyl moiety of the ester groups is essential for biological effects and the activation of PKC, likely via an interaction with the Gly23 NH in the C1 domain, and (4) the 4-, 5-, and 20-hydroxyl groups form a framework for a pH-dependent acyl migration of the ester moiety leading to degradation of ingenol mebutate resulting in limited shelf life [17].…”

“…A recent study on a series of ingenol scaffold-modified cyclohexyl esters showed that complete removal of the 4- or 5-hydroxyl groups led to a moderate drop in activity, whereas removal of both hydroxyl groups resulted in a significant loss in activity [19]. The chemical stability could be improved by having substituents flanking the ester group, but this often resulted in reduced potency [17, 18]. A series of substituted benzoate esters provided a reasonable compromise of features for enhanced stability and good potency as exemplified with the anthranilate 10 and salicylate 11 —both capable of forming intramolecular hydrogen bonds (Table 1) [18].…”

“…The chemical stability could be improved by having substituents flanking the ester group, but this often resulted in reduced potency [17, 18]. A series of substituted benzoate esters provided a reasonable compromise of features for enhanced stability and good potency as exemplified with the anthranilate 10 and salicylate 11 —both capable of forming intramolecular hydrogen bonds (Table 1) [18]. However, the overall properties were not deemed sufficiently good to continue development.…”

Biphasic Effects of Ingenol 3,20-Dibenzoate on the Erythropoietin Receptor: Synergism at Low Doses and Antagonism at High Doses

“…IGN binds and activates partially purified PKC (Hasler et al, 1992), and IGN mebutate binds conventional PKC and nPKC (Kedei et al, 2004). However, the interactions between IGN derivatives and PKCs were only analyzed by the indirect method of [ 3 H]phorbol 12,13-dibutyrate binding (Hasler et al, 1992;Kedei et al, 2004) or the docking simulation model (Grue-Sørensen et al, 2014). IDB can selectively activate nPKC (Asada et al, 1998), but direct binding kinetics have never been measured.…”