Selective anticancer effects and protection from chemotherapy by the botanical compound LCS101: Implications for cancer treatment.

There is a need for new options for reducing the side effects of cancer treatment, without compromising efficacy, enabling patients to complete treatment regimens. The botanical compound LCS101 exhibits inhibitory effects on cancer cell growth, and reduces chemotherapy-induced hematological toxicities. The aim of the present study is to examine the selectivity of the effects of the compound, alone and in conjunction with conventional chemotherapy agents, on cancer cell proliferation. The effects of LCS101 were tested on a number of cancer cell lines (breast, MCF7, MDA-MB­231; colorectal, HCT116; prostate, PC-3, DU-145) and on non-tumorigenic normal human epithelial cells (breast, MCF10A; prostate, EP#2). Cell viability was analyzed using an XTT assay and observed by light microscopy. Necrosis and apoptosis were examined using FACS analysis and immunoblotting. LCS101 selectively induced cell death in breast, colon and prostate cancer cell lines, as measured by XTT assay. Light microscopy and FACS analysis showed changes indicative of a necrotic process. LCS101 was also found to induce PARP-1 reduction in breast cancer cells, with no effect on non-tumorigenic breast epithelial cells. While LCS101 increased cell death in cancer cells exposed to doxorubicin and 5-FU, it showed a protective effect on non-tumorigenic human epithelial cells from chemotherapy-induced cell death. A similar selective effect was observed with apoptosis-associated PARP-1 cleavage. The findings demonstrate that the anti-proliferative effects exhibited by the botanical compound LCS101 are selective to cancer cells, and offer protection to non-tumorigenic normal epithelial cells from chemotherapy agents.

Akt/protein kinase b and glycogen synthase kinase-3beta signaling pathway regulates cell migration through the NFAT1 transcription factor.

The phosphoinositide 3-kinase (PI3K) pathway regulates a multitude of cellular processes. Deregulation of PI3K signaling is often observed in human cancers. A major effector of PI3K is Akt/protein kinase B (PKB). Recent studies have pointed to distinct roles of Akt/PKB isoforms in cancer cell signaling. Studies have shown that Akt1 (PKBalpha) can attenuate breast cancer cell motility, whereas Akt2 (PKBbeta) enhances this phenotype. Here, we have evaluated the mechanism by which Akt1 blocks the migration of breast cancer cells through the transcription factor NFAT. A major effector of Akt/PKB is glycogen synthase kinase-3beta (GSK-3beta), also a NFAT kinase. Inhibition of GSK-3beta using short hairpin RNA or a selective inhibitor potently blocks breast cancer cell migration concomitant with a reduction in NFAT activity. GSK-3beta-mediated inhibition of NFAT activity is due to proteasomal degradation. Experiments using GSK-3beta mutants, which are unresponsive to Akt/PKB, reveal that inhibition of cell migration by Akt/PKB is mediated by GSK-3beta. These effects are recapitulated at the levels of NFAT degradation by the proteasome. Our studies show that activation of Akt/PKB leads to inactivation of the effector GSK-3beta and the outcome of this signaling event is degradation of NFAT by the proteasome and subsequent inhibition of cell migration.

Akt signaling and cancer: surviving but not moving on.

The frequent deregulation of the phosphoinositide 3-kinase/Akt survival signaling pathway in cancer has prompted significant interest in blocking this pathway to treat cancer. Recently, however, two studies have shown that the Akt isoform Akt1 limits the invasive migration of breast cancer cells. These studies suggest that Akt1 may have a dual role in tumorigenesis, acting not only pro-oncogenically by suppressing apoptosis but also anti-oncogenically by suppressing invasion and metastasis. We discuss the possible implications of these findings for therapeutic development of Akt inhibitors to treat cancer.

Akt/PKB signaling in cancer: a function in cell motility and invasion.

The PI 3-K signaling pathway has been the subject of intense investigation for over a decade because it regulates a multitude of cellular processes. Deregulation of this pathway often results in human diseases such as cancer. The serine/threonine kinase Akt, a major PI 3-K target in all cells, has received considerable attention because it provides tumor cells with enhanced survival capacity. Many tumors and tumor cells display elevated Akt protein expression and activity, and many of the proteins which regulate Akt itself are also often mutated in cancer. For this reason, Akt has become a viable drug target for cancer therapy. However, recent studies have shown that Akt can also function as a suppressor of tumor cell migration and invasion, phenotypes which are directly linked to metastatic tumor progression. Here we review these findings and consider the unexpected notion that Akt may function as a metastasis suppressor.

Akt blocks breast cancer cell motility and invasion through the transcription factor NFAT.

The phosphoinositide 3-kinase (PI 3-K) signaling axis is intimately associated with deregulated cancer cell growth, primarily by promoting increased survival through Akt/PKB (protein kinase B). However, there is relatively little information on the role of Akt in cancer cell motility, a key phenotype of invasive carcinomas. Here we report that activation of Akt inhibits carcinoma migration and invasion of breast cancer cells. Conversely, downregulation of Akt using RNA interference increased migration and invasion. Akt blunts invasion by inhibiting the transcriptional activity of NFAT (nuclear factor of activated T cells). Specifically, signaling through Akt reduces NFAT expression levels due to ubiquitination and proteasomal degradation, mediated by the E3 ubiquitin ligase HDM2. These results indicate that while Akt can promote tumor progression through increased cell survival mechanisms, it can block breast cancer cell motility and invasion by a mechanism that depends, at least in part, on the NFAT transcription factor.

A novel protein derived from the MUC1 gene by alternative splicing and frameshifting.

Genes that have been designated the name "MUC" code for proteins comprising mucin domains. These proteins may be involved in barrier and protective functions. The first such gene to be characterized and sequenced is the MUC1 gene. Here we report a novel small protein derived from the MUC1 gene by alternative splicing that does not contain the hallmark of mucin proteins, the mucin domain. This protein termed MUC1/ZD retains the same N-terminal MUC1 sequences as all of the other known MUC1 protein isoforms. The common N-terminal sequences comprise the signal peptide and a subsequent stretch of 30 amino acids. In contrast, the MUC1/ZD C-terminal 43 amino acids are novel and result from a reading frameshift engendered by a splicing event that forms MUC1/ZD. The expression of MUC1/ZD at the protein level in human tissues is demonstrated by Western blotting, immunohistochemistry, immunoprecipitation, and an ELISA. Utilization was made of affinity-purified MUC1/ZD-specific polyclonal antibodies as well as two different monoclonal antibodies that are monospecific for the MUC1/ZD protein. The MUC1/ZD protein is expressed in tissues as an oligomeric complex composed of monomers linked by disulfide bonds contributed by MUC1/ZD cysteine residues. MUC1/ZD protein expression did not parallel that of the tandem-repeat array-containing MUC1 protein. Results presented here demonstrate for the first time the expression of a novel MUC1 protein isoform MUC1/ZD, which is generated by an alternative splicing event that both deletes the tandem-repeat array and leads to a C-terminal reading frameshift.