Venodhar K. Reddy

Antizyme induction mediates feedback limitation of the incorporation of specific polyamine analogues in tissue culture.

Spermidine, spermine and putrescine are essential for mammalian cell growth, and there has been a pervasive effort to synthesize analogues of these polyamines that will disrupt their function and serve as tools to inhibit cell proliferation. Recently, we demonstrated that a number of such polyamine analogues are also capable of inducing the regulatory protein AZ (antizyme). In the present study the incorporation of a few sample analogues [mimics of bis(ethyl)spermine] was shown to be significantly limited by a decrease in the V(max) for the polyamine transport system in response to analogue-induced AZ. This creates an unusual circumstance in which compounds that are being designed for therapeutic use actually inhibit their own incorporation into targeted cells. To explore the impact of this feedback system, cultures of rat hepatoma HTC cells were pre-treated to exhibit either low or high polyamine uptake activity and then exposed to polyamine analogues. As predicted, regardless of initial uptake activity, all cultures eventually achieved the same steady-state levels of the cellular analogue and AZ. Importantly, analogue-induced AZ levels remained elevated with respect to controls even after the native polyamines were reduced by more than 70%. To model the insufficient AZ expression found in certain tumours, GS-CHO (GS Chinese-hamster ovary) cells were transfected to express high levels of exogenic AZI (AZ inhibitor). As anticipated, this clone incorporated significantly higher levels of the polyamine analogues examined. This study reveals a potential limitation in the use of polyamine-based compounds as therapeutics, and strategies are presented to either circumvent or exploit this elegant transport feedback system.

aci-Reductones: Drug design, enantioselective syntheses and biological activities within lipid membranes

Atherosclerosis is a chronic inflammatory disease which correlates with both elevated levels of lipids and depleted levels of endogenous antioxidants, a measure of oxidative stress. Oxidatively modified LDL (LDL-ox), monocytes, macrophages, smooth muscle cells, adhesion cell molecules, cytokines, foam cells and reactive oxygen species (ROS) are intrinsically linked to the inflammatory response element, nuclear factor-κB (NF-κB), in a biochemical cascade that leads to arterial plaque formation and progression.1 Dual lipophilic chain breaking antioxidant/arachidonic acid (AA) metabolic inhibitors are expected to retard atherosclerotic plaque formation through simultaneous blockade of multiple mechanisms of atherogenesis, protect against ROS induced tissue damage and restore natural antioxidant defenses. Several series of racemic and enantiomerically pure 4-substituted 2-hydroxytetronic acids, which represent both substrates and inhibitors of cyclooxygenase have been prepared and screened in a multitude of in vitro biological assays. These aci-reductones inhibit NF-κB activation (50% @ 30nM), protect against Cu++ catalyzed LDL oxidation in vitro and prevent monocyte/HUVEC binding significantly better than the antilipidemic drug probucol, and enantioselectively inhibit AA induced platelet aggregation (AAIPA) of human platelet rich plasma (PRP). This data indicates that some of these experimental antioxidants may be particularly useful for the treatment of atherosclerosis and associated vascular diseases.