Apomine

HMG-CoA reductase (HMGCR) is the rate-limiting enzyme in the cholesterol biosynthetic pathway, and is the target of cholesterol-lowering drugs, statins. Previous studies have demonstrated that the enzyme activity is regulated by sterol-induced degradation in addition to transcriptional regulation through sterol-regulatory-element-binding proteins (SREBPs). While 25-hydroxycholesterol induces both HMGCR degradation and SREBP inhibition in a nonselective manner, lanosterol selectively induces HMGCR degradation. Here, to clarify the structural determinants of selectivity for the two activities, we established a luciferase-based assay monitoring HMGCR degradation and used it to profile the structure-activity/selectivity relationships of oxysterols and (oxy)lanosterols. We identified several sterols that selectively induce HMGCR degradation and one sterol, 25-hydroxycholest-4-en-3-one, that selectively inhibits the SREBP pathway. These results should be helpful in designing more potent and selective HMGCR degraders.

Apomine is a novel compound that inhibits the mevalonate/isoprenoid pathway of cholesterol synthesis and may prove effective as a skin cancer chemoprevention therapy. This research was focused on the development of a new delivery approach for chemoprevention of melanoma using topically delivered apomine. This included evaluating the effect of several factors on the stability of apomine in solution, utilizing these to develop a topical formulation, and conducting efficacy studies with the developed topical formulation in the TPras mouse model. Preformulation included the influence of pH, buffer species, ionic strength, and organic solvents on the stability of apomine at four different temperatures. Apomine was determined to undergo apparent first-order degradation kinetics for all conditions evaluated. Apomine undergoes base-catalyzed degradation. Less than 15% degradation is observed after >200 days under acidic conditions. Long-term stability studies were performed on two different topical cream formulations and indicate that both formulations are chemically stable for over 1 year at both 4 and 23 degrees C. The efficacy of topically applied apomine, from ethanol and developed 1% cream, was evaluated in vivo against the incidence of melanoma. Regardless of delivery vehicle apomine treatment caused a significant reduction in tumor incidence. Ethyl alcohol application of apomine resulted in a greater tumor incidence reduction when compared to the development cream formulation; however, this difference was not significant.