Src kinase inhibitors: an emerging therapeutic treatment option for prostate cancer

Integrative Analysis of Bulk RNA-Seq and Single-Cell RNA-Seq Unveils the Characteristics of the Immune Microenvironment and Prognosis Signature in Prostate Cancer

The immune microenvironment is a culmination of the collaborative effort of immune cells and is important in cancer development. The underlying mechanisms of the tumor immune microenvironment in regulating prostate cancer (PRAD) are unclear. In the current study, 144 natural killer cell-related genes were identified using differential expression, single-sample gene set enrichment analysis, and weighted gene coexpression network analysis. Furthermore, VCL, ACTA2, MYL9, MYLK, MYH11, TPM1, ACTG2, TAGLN, and FLNC were selected as hub genes via the protein-protein interaction network. Based on the expression patterns of the hub genes, endothelial, epithelial, and tissue stem cells were identified as key cell subpopulations, which could regulate PRAD via immune response, extracellular signaling, and protein formation. Moreover, 27 genes were identified as prognostic signatures and used to construct the risk score model. Receiver operating characteristic curves revealed the good performance of the risk score model in both the training and testing datasets. Different chemotherapeutic responses were observed between the low- and high-risk groups. Additionally, a nomogram based on the risk score and other clinical features was established to predict the 1-, 3-, and 5-year progression-free interval of patients with PRAD. This study provides novel insights into the molecular mechanisms of the immune microenvironment and its role in the pathogenesis of PARD. The identification of key cell subpopulations has a potential therapeutic and prognostic use in PRAD.

Progression-related loss of stromal Caveolin 1 levels fosters the growth of human PC3 xenografts and mediates radiation resistance

Despite good treatment results in localized prostate tumors, advanced disease stages usually have a pronounced resistance to chemotherapy and radiotherapy. The membrane protein caveolin-1 (Cav1) functions here as an important oncogene. Therefore we examined the impact of stromal Cav1 expression for tumor growth and sensitivity to ionizing radiation (IR). Silencing of Cav1 expression in PC3 cells resulted in increased tumor growth and a reduced growth delay after IR when compared to tumors generated by Cav1-expressing PC3 cells. The increased radiation resistance was associated with increasing amounts of reactive tumor stroma and a Cav1 re-expression in the malignant epithelial cells. Mimicking the human situation these results were confirmed using co-implantation of Cav1-silenced PC3 cells with Cav1-silenced or Cav1-expressing fibroblasts. Immunohistochemically analysis of irradiated tumors as well as human prostate tissue specimen confirmed that alterations in stromal-epithelial Cav1 expressions were accompanied by a more reactive Cav1-reduced tumor stroma after radiation and within advanced prostate cancer tissues which potentially mediates the resistance to radiation treatment. Conclusively, the radiation response of human prostate tumors is critically regulated by Cav1 expression in stromal fibroblasts. Loss of stromal Cav1 expression in advanced tumor stages may thus contribute to resistance of these tumors to radiotherapy.

Effect of saracatinib on pulmonary metastases from hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related death worldwide. Src is involved in multiple processes of cancer metastasis; however, its significance in HCC is not well defined. In the present study, overexpression of Src phosphorylation (Y416) was observed in the highly metastatic MHCC97H cell line; additionally, through inhibition of Src kinase activation, HCC cell proliferation, migration, invasion and colony formation were significantly reduced in vitro. Tumour growth was not affected in the orthotopic xenograft HCC model, but the metastasic potential was inhibited as revealed by reduced lung metastasic foci after administration of saracatinib. Phosphorylation level of Src pathway signalling molecules, such as Src, FAK and Stat3, were also reduced in vitro and in vivo, as a result of the anti-metastasic effects caused by saracatinib treatment. In conclusion, we demonstrated the pro-metastasic role of Src in HCC, and further experiments suggest the use of the Src inhibitor in combination with cytotoxic agents and other anticancer treatments to improve HCC prognosis.

Transcriptional signature induced by a metastasis-promoting c-Src mutant in a human breast cell line

Deletions at the C-terminus of the proto-oncogene protein c-Src kinase are found in the viral oncogene protein v-Src as well as in some advanced human colon cancers. They are associated with increased kinase activity and cellular invasiveness. Here, we analyzed the mRNA expression signature of a constitutively active C-terminal mutant of c-Src, c-Src(mt), in comparison with its wild-type protein, c-Src(wt), in the human non-transformed breast epithelial cell line MCF-10A. We demonstrated previously that the mutant altered migratory and metastatic properties. Genome-wide transcriptome analysis revealed that c-Src(mt) de-regulated the expression levels of approximately 430 mRNAs whose gene products are mainly involved in the cellular processes of migration and adhesion, apoptosis and protein synthesis. 82.9% of these genes have previously been linked to cellular migration, while the others play roles in RNA transport and splicing processes, for instance. Consistent with the transcriptome data, cells expressing c-Src(mt), but not those expressing c-Src(wt), showed the capacity to metastasize into the lungs of mice in vivo. The mRNA expression profile of c-Src(mt)-expressing cells shows significant overlap with that of various primary human tumor samples, possibly reflecting elevated Src activity in some cancerous cells. Expression of c-Src(mt) led to elevated migratory potential. We used this model system to analyze the transcriptional changes associated with an invasive cellular phenotype. These genes and pathways de-regulated by c-Src(mt) may provide suitable biomarkers or targets of therapeutic approaches for metastatic cells.

DATABASE

This project was submitted to the National Center for Biotechnology Information BioProject under ID PRJNA288540. The Illumina RNA-Seq reads are available in the National Center for Biotechnology Information Sequence Read Archive under study ID SRP060008 with accession numbers SRS977414 for MCF-10A cells, SRS977717 for mock cells, SRS978053 for c-Src(wt) cells and SRS978046 for c-Src(mt) cells.

miR-203 downregulates Yes-1 and suppresses oncogenic activity in human oral cancer cells

The purpose of this study was to elucidate the molecular mechanisms of microRNA-203 (miR-203) as a tumor suppressor in KB human oral cancer cells. MicroRNA microarray results showed that the expression of miR-203 was significantly down-regulated in KB cells compared with normal human oral keratinocytes. The viability of KB cells was decreased by miR-203 in the time- and dose-dependent manners. In addition, over-expressed miR-203 not only increased the nuclear condensation but also significantly increased the apoptotic population of KB cells. These results indicated that the over-expression of miR-203 induced apoptosis of KB cells. Furthermore, the target gene array analyses revealed that the expression of Yes-1, a member of the Src family kinases (SFKs), was significantly down-regulated by miR-203 in KB cells. Moreover, both the mRNA and protein levels of Yes-1 were strongly reduced in KB cells transfected with miR-203. Therefore, these results indicated that Yes-1 is predicted to be a potential target gene of miR-203. Through a luciferase activity assay, miR-203 was confirmed to directly targets the Yes-1 3' untranslated region (UTR) to suppress gene expression. Therefore, our findings indicate that miR-203 induces the apoptosis of KB cells by directly targeting Yes-1, suggesting its application in anti-cancer therapeutics.

MicroRNAs as the fine-tuners of Src oncogenic signalling

The cellular Src (c-Src) tyrosine kinase is upregulated and believed to play a pivotal role in various human cancers. However, the molecular mechanism underlying c-Src-mediated tumour progression remains elusive. Recent studies have revealed that several microRNAs (miRNAs) function as tumour suppressors by regulating the malignant expression of signalling molecules. Aberrant expression of miRNAs is frequently observed in human cancers and should be exploited to seek related molecular targets. In this review, we focus on miRNAs found to be involved in Src signalling in various cancers. We summarize recent findings on Src-related miRNAs, their target genes, mechanisms behind their interplay and their implications for cancer therapeutics.

Metastatic hormone refractory prostate cancer: recent advances in standard treatment paradigm, and future directions

Until recently, docetaxel-based chemotherapy was the only established treatment for patients with metastatic hormone refractory prostate cancer (mHRPC). In 2010 to 2011, 3 more agents were shown to be associated with a survival benefit in mHRPC, including the dendritic cell vaccine sipuleucel-T, the 17,20 lyase inhibitor abiraterone, and the taxane cabazitaxel. The improved understanding of prostate cancer biology in recent years led to the development of drugs directed against precise tumorigenesis-associated molecular pathways. Molecular pathways involved in the progression of mHRPC include the androgen receptor, angiogenesis, endothelin receptor, tyrosine kinases (SRC, MET, vascular endothelial growth factor receptor, RET), and the receptor activator of nuclear factor-kB-ligand. This review will focus on recent advances in the standard treatments paradigm, and promising new targeted agents that are being investigated, in mHRPC.

Bone-targeting agents in prostate cancer

Bone metastases are present in the vast majority of men with advanced prostate cancer, representing the main cause for morbidity and mortality. Recurrent or metastatic disease is managed initially with androgen deprivation but the majority of the patients eventually will progress to castration-resistant prostate cancer, with patients developing bone metastases in most of the cases. Survival and growth of the metastatic prostate cancer cells is dependent on a complex microenvironment (onco-niche) that includes the osteoblasts, the osteoclasts, the endothelium, and the stroma. This review summarizes agents that target the pathways involved in this complex interaction between prostate cancer and bone microenvironment and aim to transform lethal metastatic prostate cancer into a chronic disease.

SRC: marker or actor in prostate cancer aggressiveness

A key question for urologic practitioners is whether an apparently organ-confined prostate cancer (PCa) is actually aggressive or not. The dilemma is to specifically identify among all prostate tumors the very aggressive high-grade cancers that will become life-threatening by developing extra-prostatic invasion and metastatic potential and the indolent cancers that will never modify a patient's life expectancy. A choice must be made between several therapeutic options to achieve the optimal personalized management of the disease that causes as little harm as possible to patients. Reliable clinical, biological, or pathological markers that would enable distinctions to be made between aggressive and indolent PCas in routine practice at the time of initial diagnosis are still lacking. The molecular mechanisms that explain why a PCa is aggressive or not are also poorly understood. Among the potential markers and/or actors in PCa aggressiveness, Src and other members of the Src kinase family, are valuable candidates. Activation of Src-dependent intracellular pathways is frequently observed in PCa. Indeed, Src is at the cross-roads of several pathways [including androgen receptor (AR), TGFbeta, Bcl-2, Akt/PTEN or MAPK, and ERK …], and is now known to influence some of the cellular and tissular events that accompany tumor progression: cell proliferation, cell motility, invasion, epithelial-to-mesenchymal transition, resistance to apoptosis, angiogenesis, neuroendocrine differentiation, and metastatic spread. Recent work even suggests that Src could also play a part in PCa initiation in coordination with the AR. The aim of this review is to gather data that explore the links between the Src kinase family and PCa progression and aggressiveness.

Androgen receptor activation in castration-recurrent prostate cancer: the role of Src-family and Ack1 tyrosine kinases

There is growing appreciation that castration-recurrent prostate cancer (CR-CaP) is driven by the continued expression of androgen receptor (AR). AR activation in CR-CaP through various mechanisms, including AR overexpression, expression of AR splice variants or mutants, increased expression of co-regulator proteins, and by post-translational modification, allows for the induction of AR-regulated genes in response to very low levels of tissue-expressed, so-called intracrine androgens, resulting in pathways that mediate CaP proliferation, anti-apoptosis and oncogenic aggressiveness. The current review focuses on the role played by Src-family (SFK) and Ack1 non-receptor tyrosine kinases in activating AR through direct phosphorylation, respectively, on tyrosines 534 or 267, and how these modifications facilitate progression to CR-CaP. The fact that SFK and Ack1 are central mediators for multiple growth factor receptor signaling pathways that become activated in CR-CaP, especially in the context of metastatic growth in the bone, has contributed to recent therapeutic trials using SFK/Ack1 inhibitors in monotherapy or in combination with antagonists of the AR activation axis.

Recent advances in bone-targeted therapies of metastatic prostate cancer

Prostate cancer is one of the most common malignancies affecting men worldwide, with bone being the most common site of metastasis in patients that progress beyond organ confinement. Bone metastases are virtually incurable and result in significant disease morbidity and mortality. Bone provides a unique microenvironment whose local interactions with tumor cells offer novel targets for therapeutic interventions. Several attractive molecules or pathways have been identified as new potential therapeutic targets for bone metastases caused by metastatic castration-resistant prostate cancer. In this review, we present the recent advances in molecular targeted therapies for prostate cancer bone metastasis focusing on therapies that target the bone cells and the bone microenvironment. The therapies covered in this review include agents that inhibit bone resorption, agents that stimulate bone formation, and agents that target the bone matrix. Suggestions to devise more effective molecular targeted therapies are proposed. Hopefully, with better understanding of the biology of the disease and the development of more robust targeted therapies, the survival and quality of life of the affected individuals could be significantly improved.

Biochemical and functional analyses of gp130 mutants unveil JAK1 as a novel therapeutic target in human inflammatory hepatocellular adenoma

Inflammatory hepatocellular adenomas (IHCAs) are benign liver lesions that can be characterized histologically by the presence of an inflammatory infiltrate and at the molecular level by the overexpression of acute phase inflammatory response genes. Recurrent somatic mutations of the interleukin-6 (IL-6) signal transducer (IL6ST) locus, encoding the critical component of the IL-6 signal transduction machinery gp130, are present in 60% of IHCAs and in a subset (2%) of hepatocellular carcinoma (HCCs). By screening of 256 human hepatic adenoma specimens (the largest genetic analysis of IL6ST performed to date in this setting), we identified 24 distinct somatic IL6ST mutations among 66 mutant adenomas. The functional analysis of nine different gp130 mutants expressed in hepatic cancer cell lines consistently revealed the constitutive and IL-6-independent activation of the JAK/STAT signaling pathway. We further demonstrated that the signaling activity of mutant gp130 in IHCA remains responsive to suppressor of cytokine signaling 3 (SOCS3), a physiological gp130 inhibitor. Specifically, cells expressing a double mutant variant of gp130 with a disrupted SOCS3-binding site at residue 759 (Y186/Y759F) displayed a hyperactivation of signal transducer and activator of transcription 3 (STAT3) as compared with cells expressing the endogenous IHCA-associated Y186 gp130 mutant. Notably, we identified that constitutive signaling via gp130 in IHCA requires the Janus kinase family member JAK1, but not JAK2 or tyrosine kinase 2. In support of this notion, AG490, a tyrosine kinase inhibitor that selectively blocks JAK2, had no effect on gp130 activity. In stark contrast, we showed that ruxolitinib, a JAK1/JAK2-selective tyrosine kinase inhibitor used to treat patients with myelofibrosis, dramatically impaired JAK1-STAT signaling downstream of all IHCA-associated gp130 mutants. In conclusion, our findings provide a rationale for the use of JAK1 inhibitors for the treatment of HCAs expressing mutant gp130 as well as a subset of HCCs that bear similar mutations.

microRNA-125a-3p reduces cell proliferation and migration by targeting Fyn

Fyn, a member of the Src family kinases (SFKs), has a pivotal role in cell adhesion, proliferation, migration and survival, and its overexpression is associated with several types of cancer. MicroRNAs (miRNAs) play a major role in post-transcriptional repression of protein expression. In light of the significant functions of Fyn, together with studies demonstrating miR-125a as a tumor-suppressing miRNA that is downregulated in several cancer cell types and on our bioinformatics studies presented here, we chose to examine the post-transcription regulation of Fyn by miR-125a-3p in the HEK 293T cell line. We show that Fyn expression can be dramatically reduced by elevated levels of miR-125a-3p. Following this reduction, the activity of proteins downstream of Fyn, such as FAK, paxillin and Akt (proteins known to be overexpressed in various tumors), is also reduced. On a broader level, we show that miR-125a-3p causes an arrest of the cell cycle at the G2/M stage and decreases cell viability and migration, probably in a Fyn-directed manner. The results are reinforced by control experiments conducted using Fyn siRNA and anti-miR-125a-3p, as well as by the fact that numerous cancer cell lines show a significant downregulation of Fyn after mir-125a-3p overexpression. Collectively, we conclude that miR-125a-3p has an important role in the regulation of Fyn expression and of its signaling pathway, which implies that it has a therapeutic potential in overexpressed Fyn-related diseases.

Context-specific protein tyrosine kinase 6 (PTK6) signalling in prostate cancer

BACKGROUND

Protein tyrosine kinase 6 (PTK6) is an intracellular tyrosine kinase that is distantly related to SRC family kinases. PTK6 is nuclear in normal prostate epithelia, but nuclear localization is lost in prostate tumours. Increased expression of PTK6 is detected in human prostate cancer, especially at metastatic stages, and in other types of cancers, including breast, colon, head and neck cancers, and serous carcinoma of the ovary.

MATERIALS AND METHODS

Potential novel substrates of PTK6 identified by mass spectrometry were validated in vitro. The significance of PTK6-induced phosphorylation of these substrates was addressed using human prostate cell lines by knockdown of endogenous PTK6 or overexpression of targeted PTK6 to different intracellular compartments.

RESULTS

We identified AKT, p130CAS and focal adhesion kinase (FAK) as novel PTK6 substrates and demonstrated their roles in promoting cell proliferation, migration and resistance to anoikis. In prostate cancer cells, active PTK6 is primarily associated with membrane compartments, although the majority of total PTK6 is localized within the cytoplasm. Ectopic expression of membrane-targeted PTK6 transforms immortalized fibroblasts. Knockdown of endogenous cytoplasmic PTK6 in PC3 prostate cancer cells impairs proliferation, migration and anoikis resistance. However, re-introduction of PTK6 into the nucleus significantly decreases cell proliferation, suggesting context-specific functions for nuclear PTK6.

CONCLUSIONS

In human prostate cancer, elevated PTK6 expression, translocation of PTK6 from the nucleus to the cytoplasm and its activation at the plasma membrane contribute to increased phosphorylation and activation of its substrates such as AKT, p130CAS and FAK, thereby promoting prostate cancer progression.

Large scale phosphoproteome analysis of LNCaP human prostate cancer cells

Prostate cancer is the most frequently diagnosed cancer among men in the western world. The androgen receptor, a phosphoprotein, is suspected to be involved in all stages of the prostate cancer. Androgen receptor activity can be modulated by various kinases such as PKA, MAPK, AKT, and Src. Phosphorylation is an important post-translational modification and serves as a molecular on-off switch to regulate signaling. Disruptions of cellular phosphorylation are associated with various diseases such as cancer and kinases provide important drug targets. Here we present an analysis of the phosphoproteome in LNCaP human prostate cancer cells. The analytical strategy employed here used proteomics based methodologies with a combination of detergents and chaotropic reagents during trypsin digestion followed by titanium dioxide enrichment of phosphopeptides. Over the course of multiple analyses by mass spectrometry we identified a total of 746 phosphorylation sites in 540 phosphopeptides corresponding to 116 phosphoproteins, of which 56 had not been previously reported. Phosphoproteins identified included transcription factors, co-regulators of the androgen receptor, and cancer-related proteins that include β-catenin, USP10, and histone deacetylase-2. The information of signaling pathways, motifs of phosphorylated peptides, biological processes, molecular functions, cellular components, and protein interactions from the identified phosphoproteins established a map of phosphoproteome and signaling pathways in LNCaP cells.

Recent developments in treatments targeting castration-resistant prostate cancer bone metastases

BACKGROUND

Prostate cancer is the most common male cancer and one of the top causes of male cancer-related death. Most patients with prostate cancer respond to initial androgen deprivation therapy before progressing to castration-resistant prostate cancer (CRPC) and eventually developing bone metastases. Growth of prostate cancer metastases in the bone microenvironment produces numerous factors that disrupt the dynamic equilibrium of osteogenesis and osteolysis existing in healthy bone, leading to progressive morbidity, poor quality of life, and increased treatment costs.

MATERIALS AND METHODS

Relevant studies of CRPC and targeted therapies were identified from literature and clinical trial databases, websites, and conference abstracts.

RESULTS

Available data on agents potentially targeting bone metastatic CRPC or the bone microenvironment in patients with CRPC are discussed, including inhibitors of tumor growth/survival and bone turnover (SRC family kinase inhibitors, endothelin-1 inhibitors, MET inhibitors, and thalidomide and its derivatives), inhibitors of bone turnover (bisphosphonates and receptor activator of nuclear factor-kB ligand inhibitors), antiangiogenic agents (vascular endothelial growth factor receptor and platelet-derived growth factor blockers), prostate cancer vaccines, and bone-directed radiopharmaceuticals.

CONCLUSIONS

With increasing data availability demonstrating tumor-bone microenvironment interactions and routine incorporation of bone-related end points into CRPC trials, bone microenvironment-targeted agents are likely to become an increasingly important component of CRPC treatment.

KAI1 suppresses HIF-1α and VEGF expression by blocking CDCP1-enhanced Src activation in prostate cancer

Background

KAI1 was initially identified as a metastasis-suppressor gene in prostate cancer. It is a member of the tetraspan transmembrane superfamily (TM4SF) of membrane glycoproteins. As part of a tetraspanin-enriched microdomain (TEM), KAI1 inhibits tumor metastasis by negative regulation of Src. However, the underlying regulatory mechanism has not yet been fully elucidated. CUB-domain-containing protein 1 (CDCP1), which was previously known as tetraspanin-interacting protein in TEM, promoted metastasis via enhancement of Src activity. To better understand how KAI1 is involved in the negative regulation of Src, we here examined the function of KAI1 in CDCP1-mediated Src kinase activation and the consequences of this process, focusing on HIF-1 α and VEGF expression.

Methods

We used the human prostate cancer cell line PC3 which was devoid of KAI1 expression. Vector-transfected cells (PC3-GFP clone #8) and KAI1-expressing PC3 clones (PC3-KAI1 clone #5 and #6) were picked after stable transfection with KAI1 cDNA and selection in 800 μg/ml G418. Protein levels were assessed by immunoblotting and VEGF reporter gene activity was measured by assaying luciferase activitiy. We followed tumor growth in vivo and immunohistochemistry was performed for detection of HIF-1, CDCP1, and VHL protein level.

Results

We demonstrated that Hypoxia-inducible factor 1α (HIF-1α) and VEGF expression were significantly inhibited by restoration of KAI1 in PC3 cells. In response to KAI1 expression, CDCP1-enhanced Src activation was down-regulated and the level of von Hippel-Lindau (VHL) protein was significantly increased. In an in vivo xenograft model, KAI1 inhibited the expression of CDCP1 and HIF-1α.

Conclusions

These novel observations may indicate that KAI1 exerts profound metastasis-suppressor activity in the tumor malignancy process via inhibition of CDCP1-mediated Src activation, followed by VHL-induced HIF-1α degradation and, ultimately, decreased VEGF expression.

Reusable amperometric biosensor for measuring protein tyrosine kinase activity

This work presents a simple, low-cost and reusable label-free method for detecting protein tyrosine kinase activity using a tyrosinase-based amperometric biosensor (tyrosine kinase biosensor). This method is based on the observation that phosphorylation can block the tyrosinase-catalyzed oxidation of tyrosine or tyrosyl residue in peptides. Therefore, the activity of p60c-src protein tyrosine kinase (Src) on the developed tyrosine kinase biosensor could be quickly determined when its specific peptide substrate, p60c-src substrate I, was used. The tyrosine kinase biosensor was highly sensitive to the activity of Src with a linear dynamic range of 1.9-237.6 U/mL and the lowest detection limit of 0.23 U/mL. Interestingly, the tyrosine kinase activity can be measured using the developed tyrosine kinase biosensor repetitively without regeneration. The inhibitory effect of various kinase inhibitors on the Src activity could be determined on the tyrosine kinase biosensor. Src-specific inhibitors, PP2 and Src inhibitor I, effectively suppressed Src activity, whereas PD153035, an inhibitor of the epidermal growth factor receptor, was ineffective. Staurosporine, a universal kinase inhibitor, inhibited Src activity in an ATP concentration-dependent manner. These results suggests that the activities of tyrosine kinases and their behaviors toward various reagents can be effectively measured using the developed tyrosine kinase biosensor.

Role of Src in breast cancer cell migration and invasion in a breast cell/bone-derived cell microenvironment

The preferential metastasis of breast cancer cells to bone comprises a complex set of events including homing and preferential growth, which may require unique factors produced by bone or other cells in the immediate microenvironment. In this study, an in vitro co-culture system composed of bone mesenchymal stem cells and breast cancer cell lines is used to examine the role of Src kinase on breast cancer cell migration and invasion in the presence of bone-derived cells. This research shows that Src kinase activity in breast cancer cell lines with either high or low levels of endogenous Src activity is increased by bone-derived cell-conditioned medium but not HS68 fibroblast-conditioned medium. Breast cancer cells exhibit enhanced migration in co-culture with bone-derived cells but not HS68 fibroblasts or no co-cultured cells. Inhibition of Src kinase activity using the inhibitors PP2 or saracatinib or using siRNA abrogates the preferential migration of the breast cancer cell lines in response to bone-derived cells. Inhibition of Src activity with saracatinib does not have any significant effect on breast cancer cell invasion in the presence of bone-derived cells. Factors are identified that are produced preferentially by bone-derived cells over HS68 cells that may impact breast cancer cell behavior. This research implicates Src kinase as an important effector of bone-derived cell signals on breast cancer cell migration.

Management of castration-resistant prostate cancer: bisphosphonates and emerging therapies

Approximately 70% of patients with prostate cancer will develop bone metastases that often lead to bone pain and skeletal-related events. Several bisphosphonates have shown promising activity for palliating pain. Only zoledronic acid has significantly delayed the onset and reduced the incidence of skeletal-related events in men with castration-resistant prostate cancer. In addition, studies suggest that bisphosphonates have anticancer activity that may prevent disease progression and improve survival. Clodronate was shown to improve survival in a study of men with metastatic androgen-sensitive prostate cancer. Emerging therapies are being investigated for their ability to maintain bone health. The findings presented herein highlight the importance of bone-targeted therapies for patients with bone metastases from prostate cancer.

Invasive prostate carcinoma driven by c-Src and androgen receptor synergy

Cellular Src (c-Src) integrates a large number of signal transduction pathways regulating cell division, migration, and other aspects of cell physiology. Mutations of Src kinase have not been described in human prostate cancer, but evidence for increased levels of expression accompanying cancer progression has been reported. We analyzed overexpression of c-Src in naïve mouse prostate epithelium and observed no change in tubule formation frequency or histologic structure. However, when enhanced c-Src expression is coupled with enhanced expression of androgen receptor (AR), it results in a strong activation of Src kinase activity accompanied by activation of the MAPK pathway, and enhanced AR activity. Similar to the pathology induced by constitutively active c-Src(Y529F), the tubules progress to frank carcinoma with invasion and display markers of epithelial-to-mesenchymal transition. These combined results suggest that nonmutated Src kinase may play a more important role in the genesis and progression of prostate cancer than previously appreciated and that epigenetic changes that enhance the level of AR may select for enhanced expression of c-Src with accompanying activation and a strong drive to malignant progression.

Multiple implications of 3-phosphoinositide-dependent protein kinase 1 in human cancer

3-phosphoinositide-dependent protein kinase-1 (PDK1) is a central mediator of cellular signaling between phosphoinositide-3 kinase and various intracellular serine/threonine kinases, including protein kinase B, p70 ribosomal S6 kinase, serum and glucocorticoid-inducible kinase, and protein kinase C. PDK1 activates members of the AGC family of protein kinases by phosphorylating serine/threonine residues in the activation loop. Here, we review the regulatory mechanisms of PDK1 and its roles in cancer. PDK1 is activated by autophosphorylation in the activation loop and other serine residues, as well as by phosphorylation of Tyr-9 and Tyr-373/376. Src appears to recognize PDK1 following tyrosine phosphorylation. The role of heat shock protein 90 in regulating PDK1 stability and PDK1-Src complex formation are also discussed. Furthermore, we summarize the subcellular distribution of PDK1. Finally, an important role for PDK1 in cancer chemotherapy is proposed. In conclusion, a better understanding of its molecular regulatory mechanisms in various signaling pathways will help to explain how PDK1 acts as an oncogenic kinase in various cancers, and will contribute to the development of novel cancer chemotherapies.