A Novel Small-Molecule Inhibitor of Protein Kinase Cι Blocks Transformed Growth of Non–Small-Cell Lung Cancer Cells

Abstract

We recently showed that atypical protein kinase CI (PKCI) is required for transformed growth of human non-small-cell lung cancer (NSCLC) cells by activating Rac1. Genetic disruption of PKCI signaling blocks Rac1 activity and transformed growth, indicating that PKCI is a viable target for development of novel therapeutics for NSCLC. Here, we designed and implemented a novel fluorescence resonance energy transfer-based assay to identify inhibitors of oncogenic PKCI signaling. This assay was used to identify compounds that disrupt the interaction between PKCI and its downstream effector Par6, which links PKCI to Rac1. We identified aurothioglucose (ATG), a gold compound used clinically to treat rheumatoid arthritis, and the related compound, aurothiomalate (ATM), as potent inhibitors of PKCI-Par6 interactions in vitro (IC 50 f1 Mmol/L). ATG blocks PKCIdependent signaling to Rac1 and inhibits transformed growth of NSCLC cells. ATG-mediated inhibition of transformation is relieved by expression of constitutively active Rac1, consistent with a mechanism at the level of the interaction between PKCI and Par6. ATG inhibits A549 cell tumor growth in nude mice, showing efficacy against NSCLC in a relevant preclinical model. Our data show the utility of targeting protein-protein interactions involving PKCI for antitumor drug development and provide proof of concept that chemical disruption of PKCI signaling can be an effective treatment for NSCLC. ATG and ATM will be useful reagents for studying PKCI function in transformation and represent promising new agents for the clinical treatment of NSCLC. (Cancer Res 2006; 66(3): 1767-74)

Identification of small molecule inhibitors of Zcchc11 TUTase activity

“…Aurothioglucose hydrate has been used clinically to treat rheumatoid arthritis and has been reported to inhibit PKCiotaPar6 interaction and suppress the growth of non-small-cell lung cancer in vitro and in vivo. 48 Our data reveal a novel function of Aurothioglucose hydrate in inhibiting Zcchc11 activity. Although the motivation for this study was to find small molecules that can inhibit the TUTase to elevate let-7 level in Lin28-expresisng cells, the treatment of mouse P19 (embryonal carcinoma) cells, mouse embryonic stem cells (ESCs), and a small panel of human cancer cell lines did not lead to elevated let-7 expression (data not shown).…”

Matrix metalloproteinase-10 is a critical effector of protein kinase Cι-Par6α-mediated lung cancer

“…Our published data demonstrate that Rac1 is a critical downstream effector of PKCi in NSCLC cells (Regala et al, 2005a;Stallings-Mann et al, 2006). Figure 1 demonstrates that Par6a plays a requisite role in transformation that involves both the PB1 domain and the CRIB domain of Par6a.…”

“…Likewise ATM, which specifically binds the PB1 domain of PKCi, inhibits anchorage-independent growth of NSCLC cells (Erdogan et al, 2006;Stallings-Mann et al, 2006). Therefore, we assessed the ability of wild-type PKCi and two PB1 domain mutants of PKCi (PKCi-K20A and PKCi-D63A) to support anchorage-independent growth in PKCi-RNAi cells (Figure 1a).…”

“…The gold salt aurothiomalate (ATM) selectively inhibits the PB1-PB1 domain interaction between PKCi and Par6 in vitro by binding to cysteine 69 within the PB1 domain of PKCi (Erdogan et al, 2006;Stallings-Mann et al, 2006). ATM blocks Rac1 activity and inhibits anchorage-independent growth of NSCLC cells, suggesting a role for PB1-PB1 domain interactions between PKCi and Par6 in Rac1 activation and transformation (Erdogan et al, 2006;Stallings-Mann et al, 2006).…”

Atypical Protein Kinase Cι Is Required for Wnt3a-dependent Neurite Outgrowth and Binds to Phosphorylated Dishevelled 2

“…Wnt3a induced the phosphorylation of PKC, and siRNA knockdown of PKC-blocked neurite extension. Furthermore, neuritogenesis was suppressed by aurothiomalate (ATM), a specific inhibitor of PKC binding to Par6 (32). Wnt3a stimulated an association of both endogenous and FLAG-tagged WT Dvl2 with PKC.…”