Model Organisms in Drug Discovery

174 MECHANISM OF ACTION IN MODEL ORGANISMS
Figure 6.7 Antimicrobial gene expression is altered by the RNAi to NF-kB pathway and
parthenolide in S2 cells. The hatch-shaded columns represent CecropinA1 gene expression
in samples treated with Relish dsRNA relative to no dsRNA treatment control. Relish
RNAi treatment shows a dose-dependent inhibition of CecropinA gene expression. The
black-shaded columns represent Drosomycin gene expression in samples treated with
Cactus dsRNA relative to no dsRNA treatment control. Cactus RNAi treatment causes
upregulation of Drosomycin gene expression. The no-treatment controls are represented by
a ‘one-fold’ change in the zero dsRNA Relish and Cactus columns. All samples shown have
been treated with LPS (20 mg/ml) for 1 h. The gray column represents S2 cell treatment with
parthenolide (50 mm) for 30 min prior to LPS treatment.
probable MOA is that parthenolide binds IkK, a kinase that when activated
inhibits IkB (Kwok et al., 2001). We have found that pretreating S2 cells with
parthenolide inhibits LPS-induced gene activation (Figure 6.7). This result
indicates that compounds can target similar NF-kB pathways in Drosophila
and mammals, and S2 cell-based experiments can model a high-content assay
for the activity of the mammalian NF-kB pathway. For example, candidate
novel components that function in NF-kB signaling could be determined in an
RNAi-based or compound-based screen that tests for the disruption of LPSinducible
gene activation. In a related experiment, researchers using pools of
random library generated dsRNAs identified 34 gene products as being
involved in the phagocytosis of Gram-negative bacteria (Ramet et al., 2002).
One of these gene products was identified as PGRP-LC. Work by Ramet and
others found PGRP-LC to be the elusive receptor for Gram-negative bacteria
(Choe et al., 2002; Gottar et al., 2002; Ramet et al., 2002).