Citations

Abstract The antirheumatoid agent aurothiomalate (ATM) is a potent inhibitor of oncogenic PKCι. ATM inhibits non–small lung cancer (NSCLC) growth by binding PKCι and blocking activation of a PKCι-Par6-Rac1-Pak-Mek 1,2-Erk 1,2 signaling pathway. Here, we assessed the growth inhibitory activity of ATM in a panel of human cell lines representing major lung cancer subtypes. ATM inhibited anchorage-independent growth in all lines tested with IC50s ranging from ∼300 nmol/L to >100 μmol/L. ATM sensitivity correlates positively with expression of PKCι and Par6, but not with the PKCι binding protein p62, or the proposed targets of ATM in rheumatoid arthritis (RA), thioredoxin reductase 1 or 2. PKCι expression profiling revealed that a significant subset of primary NSCLC tumors express PKCι at or above the level associated with ATM sensitivity. ATM sensitivity is not associated with general sensitivity to the cytotoxic agents cis-platin, placitaxel, and gemcitabine. ATM inhibits tumorigenicity of both sensitive and insensitive lung cell tumors in vivo at plasma drug concentrations achieved in RA patients undergoing ATM therapy. ATM inhibits Mek/Erk signaling and decreases proliferative index without effecting tumor apoptosis or vascularization in vivo. We conclude that ATM exhibits potent antitumor activity against major lung cancer subtypes, particularly tumor cells that express high levels of the ATM target PKCι and Par6. Our results indicate that PKCι expression profiling will be useful in identifying lung cancer patients most likely to respond to ATM therapy in an ongoing clinical trial. [Cancer Res 2008;68(14):5888–95]

PKC (protein kinase C) isoenzymes are key signalling components involved in the regulation of normal cell proliferation, differentiation, polarity and survival. The aberrant regulation of PKC isoenzymes has been implicated in the development of many human diseases including cancer [Fields and Gustafson (2003) Methods Mol. Biol. 233, 519–537]. To date, however, only one PKC isoenzyme, the aPKC [atypical PKCι (protein kinase Cι)], has been identified as a human oncogene [Regala, Weems, Jamieson, Khoor, Edell, Lohse and Fields (2005) Cancer Res. 65, 8905–8911]. PKCι has also proven to be a useful prognostic marker and legitimate target for the development of novel pharmacological agents for the treatment of cancer. The PKCι gene resides at chromosome 3q26 and is a frequent target of tumour-specific gene amplification in multiple forms of human cancer. PKCι gene amplification in turn drives PKCι overexpression in these cancers. Genetic disruption of PKCι expression blocks multiple aspects of the transformed phenotype of human cancer cells including transformed growth in soft agar, invasion through Matrigel and growth of subcutaneous tumours in nude mice. Genetic dissection of oncogenic PKCι signalling mechanisms demonstrates that PKCι drives transformed growth by activating a PKCι → Rac1 → PAK (p21-activated kinase) → MEK [MAPK (mitogen-activated protein kinase) 1,2/ERK (extracellular-signal-regulated kinase) kinase] 1,2 signalling pathway [Regala, Weems, Jamieson, Copland, Thompson and Fields (2005) J. Biol. Chem. 280, 31109–31115]. The transforming activity of PKCι requires the N-terminal PB1 (Phox-Bem1) domain of PKCι, which serves to couple PKCι with downstream effector molecules. Hence, there exists a strong rationale for developing novel cancer therapeutics that target the PB1 domain of PKCι and thereby disrupt its interactions with effector molecules. Using a novel high-throughput drug screen, we identified compounds that can disrupt PB1–PB1 domain interactions between PKCι and the adaptor molecule Par6 [Stallings-Mann, Jamieson, Regala, Weems, Murray and Fields (2006) Cancer Res. 66, 1767–1774]. Our screen identified the gold compounds ATG (aurothioglucose) and ATM (aurothiomalate) as specific inhibitors of the PB1–PB1 domain interaction between PKCι and Par6 that exhibit anti-tumour activity against NSCLC (non-small-cell lung cancer) both in vitro and in vivo. Structural analysis, site-directed mutagenesis and modelling indicate that ATM specifically targets the PB1 domain of PKCι to mediate its anti-tumour activity [Erdogan, Lamark, Stallings-Mann, Lee, Pellechia, Thompson, Johansen and Fields (2006) J. Biol. Chem. 281, 28450–28459]. Taken together, our recent work demonstrates that PKCι signalling is required for transformed growth of human tumours and is an attractive target for development of mechanism-based cancer therapies. ATM is currently in Phase I clinical trials for the treatment of NSCLC.

Suppression of colon carcinogenesis by peroxisome proliferator-activated receptor (PPAR)-γ is likely due to some effect of PPAR-γ on normal colonic epithelial cells. However, our understanding of the effects of PPAR-γ in such cells is limited. We analyzed the abundance, distribution, and function of PPAR-γ in epithelial cells isolated from the murine proximal and distal colon. Marked differences in PPAR-γ abundance and distribution were observed, suggesting tissue-specific responses. Analysis of PPAR-γ effects on DNA synthesis, formation of preneoplastic lesions, and activation of MAPK signaling in proximal and distal colonic epithelial cells in vivo indicates that PPAR-γ regulates both tissue-specific and common responses within the proximal and distal colon. Three major functional cohorts of PPAR-γ target genes were identified by genomic profiling of isolated colonic epithelial cells: genes that are involved in metabolism, in signaling, and in cellular adhesion and motility. Two subsets of PPAR-γ target genes were differentially expressed in the proximal and distal epithelium. Proximal target genes were primarily involved in metabolic activities, whereas signal transduction, adhesion, and motility targets were more pronounced in the distal colon. Remarkably, those target genes that are differentially expressed in the proximal colon were all induced on activation of PPAR-γ, whereas all target genes that are preferentially expressed in the distal colon were repressed. Our data indicate that PPAR-γ exerts both common and tissue-specific effects in the colon and challenge the general conclusions that PPAR-γ is induced on differentiation of colonic epithelial cells and that this receptor stimulates differentiated function in epithelial cells throughout the colon.

Abstract We recently showed that atypical protein kinase Cι (PKCι) is required for transformed growth of human non–small-cell lung cancer (NSCLC) cells by activating Rac1. Genetic disruption of PKCι signaling blocks Rac1 activity and transformed growth, indicating that PKCι 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 PKCι signaling. This assay was used to identify compounds that disrupt the interaction between PKCι and its downstream effector Par6, which links PKCι 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 PKCι-Par6 interactions in vitro (IC50 ∼1 μmol/L). ATG blocks PKCι-dependent 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 PKCι 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 PKCι for antitumor drug development and provide proof of concept that chemical disruption of PKCι signaling can be an effective treatment for NSCLC. ATG and ATM will be useful reagents for studying PKCι function in transformation and represent promising new agents for the clinical treatment of NSCLC. (Cancer Res 2006; 66(3): 1767-74)

Canine blood was diluted with isotonic Rous-Turner solution at pH 5.8 or at 7.0. The suspended erythrocytes were exposed to ultrasonic energy at 495 kc/sec with cavitation either occurring or being suppressed by excess pressure. The same power was applied to the transducer whether or not cavitation was occurring. The rupture of the cells was measured spectrophotometrically. In addition, the osmotic fragility of the exposed cells was compared with that of control cells. The results were analyzed and graphed, using an IBM-1620 computer. These studies indicated that (1) canine erythrocytes can be ruptured in the absence of cavitation, albeit more slowly; (2) mechanical strength as determined ultrasonically is not simply related to osmotic fragility; (3) the changes of osmotic fragility after ultrasonic treatment were different from those after heating; (4) the destruction not due to cavitation occurred at intensities between those used for surgery and those used for physical therapy. [This work, performed with the technical assistance of N. Nolder, A. Hildestad, and L. C. Gatewood, was aided by National Institutes of Health grants GM 08299-02 and FR-00007.]

Abstract Protein kinase C (PKC) isozymes have long been implicated in carcinogenesis. However, little is known about the functional significance of these enzymes in human cancer. We recently showed that the atypical PKC (aPKC) isozyme PKCι is overexpressed in human non–small cell lung cancer (NSCLC) cells and that PKCι plays a critical role in the transformed growth of the human lung adenocarcinoma A549 cell line in vitro and tumorigenicity in vivo. Here we provide compelling evidence that PKCι is an oncogene in NSCLC based on the following criteria: (a) aPKCι is overexpressed in the vast majority of primary NSCLC tumors; (b) tumor PKCι expression levels predict poor survival in patients with NSCLC; (c) the PKCι gene is frequently amplified in established NSCLC cell lines and primary NSCLC tumors; (d) gene amplification drives PKCι expression in NSCLC cell lines and primary NSCLC tumors; and (e) disruption of PKCι signaling with a dominant negative PKCι allele blocks the transformed growth of human NSCLC cells harboring PKCι gene amplification. Taken together, our data provide conclusive evidence that PKCι is required for the transformed growth of NSCLC cells and that the PKCι gene is a target for tumor-specific genetic alteration by amplification. Interestingly, PKCι expression predicts poor survival in NSCLC patients independent of tumor stage. Therefore, PKCι expression profiling may be useful in identifying early-stage NSCLC patients at elevated risk of relapse. Our functional data indicate that PKCι is an attractive target for development of novel, mechanism-based therapeutics to treat NSCLC.

Protein kinase C ι (PKCι) has been implicated in Ras signaling, however, a role for PKCι in oncogenic Ras-mediated transformation has not been established. Here, we show that PKCι is a critical downstream effector of oncogenic Ras in the colonic epithelium. Transgenic mice expressing constitutively active PKCι in the colon are highly susceptible to carcinogen-induced colon carcinogenesis, whereas mice expressing kinase-deficient PKCι (kdPKCι) are resistant to both carcinogen- and oncogenic Ras-mediated carcinogenesis. Expression of kdPKCι in Ras-transformed rat intestinal epithelial cells blocks oncogenic Ras-mediated activation of Rac1, cellular invasion, and anchorage-independent growth. Constitutively active Rac1 (RacV12) restores invasiveness and anchorage-independent growth in Ras-transformed rat intestinal epithelial cells expressing kdPKCι. Our data demonstrate that PKCι is required for oncogenic Ras- and carcinogen-mediated colon carcinogenesis in vivo and define a procarcinogenic signaling axis consisting of Ras, PKCι, and Rac1.

A technique for measuring instantaneous three-dimensional pressure in a wideband ultrasound pulse is presented. A collimated laser pulse impinges on the ultrasound field, and the optical intensity in a diffraction plane subsequent to this scattering event is imaged onto a CCD camera and stored. Timing is controlled precisely, allowing the acousto-optic interaction to occur at the same point in the temporal evolution of the sound field each time the experiment is performed. After interaction with the ultrasound pulse, the optical phase is approximately proportional to the ray sum of instantaneous pressure in the pulse (taken in the direction of optical propagation). Optical phase immediately subsequent to passage through the ultrasound pulse is computed from recorded optical intensity via a phase retrieval algorithm. The experiment is performed at several angles as the ultrasound transducer is rotated about an axis normal to the optical axis of the imaging system. Tomographic reconstruction algorithms are applied to the retrieved optical phase data, computing pressure at all points in the ultrasound pulse. The resulting pulse may be propagated forward or backward in time under a source-free model. Reconstructions of the field from a 2.5-MHz array transducer compare well with hydrophone measurements.