Antineoplastic effect of rapamycin is potentiated by inhibition of IRS-1 signaling in prostate cancer cells xenografts

Diarylpentanoid (1,5-bis(4-hydroxy-3-methoxyphenyl)-1,4-pentadiene-3-one) (MS13) Exhibits Anti-proliferative, Apoptosis Induction and Anti-migration Properties on Androgen-independent Human Prostate Cancer by Targeting Cell Cycle-Apoptosis and PI3K Signalling Pathways

Diarylpentanoids exhibit a high degree of anti-cancer activity and stability in vitro over curcumin in prostate cancer cells. Hence, this study aims to investigate the effects of a diarylpentanoid, 1,5-bis(4-hydroxy-3-methoxyphenyl)-1,4-pentadiene-3-one (MS13) on cytotoxicity, anti-proliferative, apoptosis-inducing, anti-migration properties, and the underlying molecular mechanisms on treated androgen-independent prostate cancer cells, DU 145 and PC-3. A cell viability assay has shown greater cytotoxicity effects of MS13-treated DU 145 cells (EC₅₀ 7.57 ± 0.2 µM) and PC-3 cells (EC₅₀ 7.80 ± 0.7 µM) compared to curcumin (EC₅₀: DU 145; 34.25 ± 2.7 µM and PC-3; 27.77 ± 6.4 µM). In addition, MS13 exhibited significant anti-proliferative activity against AIPC cells compared to curcumin in a dose- and time-dependent manner. Morphological observation, increased caspase-3 activity, and reduced Bcl-2 protein levels in these cells indicated that MS13 induces apoptosis in a time- and dose-dependent. Moreover, MS13 effectively inhibited the migration of DU 145 and PC-3 cells. Our results suggest that cell cycle-apoptosis and PI3K pathways were the topmost significant pathways impacted by MS13 activity. Our findings suggest that MS13 may demonstrate the anti-cancer activity by modulating DEGs associated with the cell cycle-apoptosis and PI3K pathways, thus inhibiting cell proliferation and cell migration as well as inducing apoptosis in AIPC cells.

Integrated Molecular Profiling as an Approach to Identify PI3K Inhibitor Resistance Mechanisms

The identification of drug resistance pathways and approaches to target these pathways remains a significant and important challenge in cancer biology. Here, we address this challenge in the context of ongoing efforts to advance phosphatidylinositol 3-kinase (PI3K) inhibitors for the treatment of PI3K-aberrant cancers. While PI3K inhibitors have had tremendous success in some diseases, such as breast cancer, early clinical trials in other malignancies, such as head and neck squamous cell carcinoma (HNSCC), have not had the same level of success. Since HNSCC and other cancers display relatively high PI3K pathway alteration rates (>45%), these underwhelming results suggest that additional or unexpected factors may contribute to the lower response rates. Here, we highlight some of the emerging functional genomic and sequencing approaches being used to identify predictive biomarkers of PI3K inhibitor response using both cancer cell lines and clinical trial specimens. Importantly, these approaches have uncovered both innate genetic and adaptive mechanisms driving PI3K inhibitor resistance. In this chapter, we describe recent technological advances that have revolutionized our understanding of PI3K inhibitor resistance pathways in HNSCC and highlight how these and other approaches lay the groundwork to make significant strides in our understanding of molecular pharmacology in the cancer field.

The Biased G-Protein-Coupled Receptor Agonism Bridges the Gap between the Insulin Receptor and the Metabolic Syndrome

Insulin signaling, as mediated through the insulin receptor (IR), plays a critical role in metabolism. Aberrations in this signaling cascade lead to several pathologies, the majority of which are classified under the umbrella term "metabolic syndrome". Although many of these pathologies are associated with insulin resistance, the exact mechanisms are not well understood. One area of current interest is the possibility of G-protein-coupled receptors (GPCRs) influencing or regulating IR signaling. This concept is particularly significant, because GPCRs have been shown to participate in cross-talk with the IR. More importantly, GPCR signaling has also been shown to preferentially regulate specific downstream signaling targets through GPCR agonist bias. A novel study recently demonstrated that this GPCR-biased agonism influences the activity of the IR without the presence of insulin. Although GPCR-IR cross-talk has previously been established, the notion that GPCRs can regulate the activation of the IR is particularly significant in relation to metabolic syndrome and other pathologies that develop as a result of alterations in IR signaling. As such, we aim to provide an overview of the physiological and pathophysiological roles of the IR within metabolic syndrome and its related pathologies, including cardiovascular health, gut microflora composition, gastrointestinal tract functioning, polycystic ovarian syndrome, pancreatic cancer, and neurodegenerative disorders. Furthermore, we propose that the GPCR-biased agonism may perhaps mediate some of the downstream signaling effects that further exacerbate these diseases for which the mechanisms are currently not well understood.

The Role of Autophagy in Salivary Gland Homeostasis and Stress Responses

Autophagy is a catabolic process that has been shown to have a role in many cellular processes including the removal of excessive or damaged proteins and protein aggregates. The salivary glands play a critical role in oral health, and their secretory capacity may be critically intertwined with the autophagic process. This review describes the role of autophagy activation in normal salivary gland homeostasis and during the glandular stress responses of therapeutic radiation, ductal ligation, autoimmunity, and salivary gland adenoid cystic carcinoma.

MiR200c targets IRS1 and suppresses prostate cancer cell growth

BACKGROUND

The downregulation of the tumor suppressor miR200c plays important roles in many malignant tumors. This study aims to show that miR200c is a posttranscriptional regulator of insulin receptor substrate 1 (IRS1) and over-expression of miR200c suppresses prostate cancer cell growth.

METHODS

Bioinformatics analysis was used to show potential post-translational regulation of IRS1 by miR200c. Dual reporter gene assays were chosen to test the binding of miR200c to the potential seed sequences in IRS1 3'UTR. RT-PCR, Q-PCR and western blot were applied to determine the regulation effect of miR200c on IRS1. CCK8 assay, soft agar assay, trypan blue exclusion assay and flow cytometric analysis were used to measure the biological effects of miR200c on prostate cancer cell proliferation and apoptosis.

RESULTS

The 449-455 nt, 3061-3067 nt, and 3096-3102 nt of the IRS1 3'-UTR were identified as three potential seed sequences for miR200c. MiR200c directly binds to IRS1 through the seed sequences in IRS1 3'-UTR. Artificial overexpression of miR200c significantly downregulated the mRNA and protein levels of IRS1, together with decreased cell proliferation and increased cell death of PC3 and DU145 cells.

CONCLUSIONS

Our results suggest that miR200c plays crucial roles in prostate cancer by post-transcriptional regulation of IRS1. The mir200c/IRS1 pathway may be a potential therapeutic target to prevent prostate cancer cell growth.

The Novel Functions of High-Molecular-Mass Complexes Containing Insulin Receptor Substrates in Mediation and Modulation of Insulin-Like Activities: Emerging Concept of Diverse Functions by IRS-Associated Proteins

Insulin-like peptides, such as insulin-like growth factors (IGFs) and insulin, induce a variety of bioactivities, such as growth, differentiation, survival, increased anabolism, and decreased catabolism in many cell types and in vivo. In general, IGFs or insulin bind to IGF-I receptor (IGF-IR) or insulin receptor (IR), activating the receptor tyrosine kinase. Insulin receptor substrates (IRSs) are known to be major substrates of receptor kinases, mediating IGF/insulin signals to direct bioactivities. Recently, we discovered that IRSs form high-molecular-mass complexes (referred to here as IRSomes) even without IGF/insulin stimulation. These complexes contain proteins (referred to here as IRSAPs; IRS-associated proteins), which modulate tyrosine phosphorylation of IRSs by receptor kinases, control IRS stability, and determine intracellular localization of IRSs. In addition, in these complexes, we found not only proteins that are involved in RNA metabolism but also RNAs themselves. Thus, IRSAPs possibly contribute to modulation of IGF/insulin bioactivities. Since it is established that disorder of modulation of insulin-like activities causes various age-related diseases including cancer, we could propose that the IRSome is an important target for treatment of these diseases.

New strategies to overcome resistance to mammalian target of rapamycin inhibitors in breast cancer

PURPOSE OF REVIEW

To review the studies addressing mammalian target of rapamycin (mTOR) inhibitors in breast cancer and resistance to rapalogs. Preclinical and clinical studies have suggested mTOR inhibitors may help overcome the resistance to endocrine therapy and trastuzumab. Despite much interest, knowledge of the mechanism and molecular response to mTOR inhibitors is incomplete.

RECENT FINDINGS

Resistance to mTOR inhibitors has been explored in preclinical studies and can be defined as primary, associated with amplifications or mutations of different kinases, or secondary, in which rapalog activates the feedback loops involving the insulin-like growth factor I receptor (IGF-IR), platelet-derived growth factor receptor and mitogen-activated protein kinase (MAPK) pathway. Current clinical trials are testing the combinations of rapamycin with other kinase inhibitors including IGF-IR, phosphoinositide 3-kinase and MAPK-extracellular signal-regulated kinase inhibitors.

SUMMARY

Recent findings on the resistance to rapalogs have stimulated the assessment of combinations of inhibitors in clinical trials. This review summarizes the current knowledge of primary and secondary rapalog resistance, and the current efforts to overcome this resistance.

Impact of targeting insulin-like growth factor signaling in head and neck cancers

The IGF system has been shown to have either negative or negligible impact on clinical outcomes of tumor development depending on specific tumor sites or stages. This review focuses on the clinical impact of IGF signaling in head and neck cancer, the effects of IGF targeted therapies, and the multi-dimensional role of IRS 1/2 signaling as a potential mechanism in resistance to targeted therapies. Similar to other tumor sites, both negative and positive correlations between levels of IGF-1/IGF-1-R and clinical outcomes in head and neck cancer have been reported. In addition, utilization of IGF targeted therapies has not demonstrated significant clinical benefit; therefore the prognostic impact of the IGF system on head and neck cancer remains uncertain.

FMNL1 promotes proliferation and migration of leukemia cells

The human FMNL1 is expressed predominantly in hematopoietic cells and has been described previously as overexpressed in hematopoietic malignancies. However, it is not known whether FMNL1 contributes to leukemogenesis. Here, we investigate the FMNL1 function using two different human leukemia models: Namalwa and K562 cell lines. FMNL1 depletion reduced cell proliferation and colony formation in both leukemic cell types, as well as a decrease in the tumor growth of FMNL1-depleted Namalwa cell xenografts. In addition, there was a decrease in migration and in TEM in FMNL1-depleted Namalwa cells. FMNL1 endogenously associates with Rac1, and FMNL1 silencing resulted in an increased Rac1 activity. The reduced migration observed in FMNL1-depleted cells was restored by inhibiting Rac activity. Our results indicate that FMNL1 stimulates leukemia cell proliferation as well as migration. This suggests that FMNL1 contributes to leukemogenesis and could act in part through Rac1 regulation.

Knockdown of insulin receptor substrate 1 reduces proliferation and downregulates Akt/mTOR and MAPK pathways in K562 cells

BCR-ABL kinase activates downstream signaling pathways, including the PI3K-Akt/mTOR and the MAPK pathway. IRS1 has been previously described as constitutively phosphorylated and associated with BCR-ABL in K562 cells, suggesting that IRS1 has role in the BCR-ABL signaling pathways. In this study, we analyzed the effect of IRS1 silencing, by shRNA-lentiviral delivery, in K562 cells, a CML cell line that presents the BCR-ABL. IRS1 silencing decreased cell proliferation and colony formation in K562 cells, which correlates with the delay of these cells at the G0/G1 phase and a decrease in the S phase of the cell cycle. Furthermore, IRS1 silencing in K562 cells resulted in a decrease of Akt, P70S6K and ERK1/2 phosphorylation. Nevertheless, apoptosis was unaffected by IRS1 knockdown and no alterations were found in the phosphorylation of BAD and in the expression of BCL2 and BAX. BCR-ABL and CRKL phosphorylation levels remained unaffected upon IRS1 silencing, and no synergistic effect was observed with imatinib treatment and IRS1 knockdown, indicating that IRS1 is downstream from BCR-ABL. In conclusion, we demonstrated that inhibition of IRS1 is capable of inducing the downregulation of Akt/mTOR and MAPK pathways and further decreasing proliferation, and clonogenicity and induces to cell cycle delay at G0/G1 phase in BCR-ABL cells.

Targeting mTOR in cancer: renal cell is just a beginning

The mammalian target of rapamycin (mTOR) is a key regulator of cell growth and proliferation. The mTOR pathway integrates signals from nutrients, energy status and extracellular growth factors to regulate many processes, including cell cycle progression, angiogenesis, ribosome biogenesis, and metabolism. Growth factors such as insulin-like growth factor, epidermal growth factor and vascular endothelial growth factor bind to and activate their corresponding tyrosine kinase receptors (TKR) located on the cell surface, to induce signal transduction to the nucleus. TKR induces intracellular signaling cascades via the phosphorylation of the phosphatidylinositol 3-kinase, which in turn phosphorylates Akt. Of particular interest among the Akt targets is the downstream effect on mTOR, which is responsible for protein synthesis of molecules necessary for nutrient uptake, angiogenesis, ribosome biogenesis, cell growth, and proliferation. Growing evidence suggests that mTOR deregulation is associated with many types of human cancer. The importance of mTOR signaling in tumor biology is now widely accepted. Consequently, a number of agents that selectively target mTOR are being developed for cancer treatment and currently temsirolimus and everolimus are approved for the treatment of advanced renal cell cancer. However, the therapeutic benefit of mTOR inhibitors in the clinic may vary depending on the activation state of the different components of the mTOR pathway in a given case. Therefore it seems clear that predicting sensitivity to rapamycins in different cancers will likely require assessing multiple molecular markers related to mTOR signaling pathway, such as phosphatase and tensin homolog (PTEN), phospho-Akt, cytoplasmic p27, and phospho-S6 kinase.

Targeted therapy for advanced prostate cancer: inhibition of the PI3K/Akt/mTOR pathway

A large number of novel therapeutics is currently undergoing clinical evaluation for the treatment of prostate cancer, and small molecule signal transduction inhibitors are a promising class of agents. These inhibitors have recently become a standard therapy in renal cell carcinoma and offer significant promise in prostate cancer. Through an understanding of the key pathways involved in prostate cancer progression, a rational drug design can be aimed at the molecules critical to cellular signaling. This may enable administration of selective therapies based on the expression of molecular targets, more appropriately individualizing treatment for prostate cancer patients. One pathway with a prominent role in prostate cancer is the PI3K/Akt/mTOR pathway. Current estimates suggest that PI3K/Akt/mTOR signaling is upregulated in 30-50% of prostate cancers, often through loss of PTEN. Molecular changes in the PI3K/Akt/mTOR signaling pathway have been demonstrated to differentiate benign from malignant prostatic epithelium and are associated with increasing tumor stage, grade, and risk of biochemical recurrence. Multiple inhibitors of this pathway have been developed and are being assessed in the laboratory and in clinical trials, with much attention focusing on mTOR inhibition. Current clinical trials in prostate cancer are assessing efficacy of mTOR inhibitors in combination with multiple targeted or traditional chemotherapies, including bevacizumab, gefitinib, and docetaxel. Completion of these trials will provide substantial information regarding the importance of this pathway in prostate cancer and the clinical implications of its targeted inhibition. In this article we review the data surrounding PI3K/Akt/mTOR inhibition in prostate cancer and their clinical implications.

Inhibition of mTORC1 leads to MAPK pathway activation through a PI3K-dependent feedback loop in human cancer

Numerous studies have established a causal link between aberrant mammalian target of rapamycin (mTOR) activation and tumorigenesis, indicating that mTOR inhibition may have therapeutic potential. In this study, we show that rapamycin and its analogs activate the MAPK pathway in human cancer, in what represents a novel mTORC1-MAPK feedback loop. We found that tumor samples from patients with biopsy-accessible solid tumors of advanced disease treated with RAD001, a rapamycin derivative, showed an administration schedule-dependent increase in activation of the MAPK pathway. RAD001 treatment also led to MAPK activation in a mouse model of prostate cancer. We further show that rapamycin-induced MAPK activation occurs in both normal cells and cancer cells lines and that this feedback loop depends on an S6K-PI3K-Ras pathway. Significantly, pharmacological inhibition of the MAPK pathway enhanced the antitumoral effect of mTORC1 inhibition by rapamycin in cancer cells in vitro and in a xenograft mouse model. Taken together, our findings identify MAPK activation as a consequence of mTORC1 inhibition and underscore the potential of a combined therapeutic approach with mTORC1 and MAPK inhibitors, currently employed as single agents in the clinic, for the treatment of human cancers.

Inhibition of mTORC1 leads to MAPK pathway activation through a PI3K-dependent feedback loop in human cancer

Numerous studies have established a causal link between aberrant mammalian target of rapamycin (mTOR) activation and tumorigenesis, indicating that mTOR inhibition may have therapeutic potential. In this study, we show that rapamycin and its analogs activate the MAPK pathway in human cancer, in what represents a novel mTORC1-MAPK feedback loop. We found that tumor samples from patients with biopsy-accessible solid tumors of advanced disease treated with RAD001, a rapamycin derivative, showed an administration schedule-dependent increase in activation of the MAPK pathway. RAD001 treatment also led to MAPK activation in a mouse model of prostate cancer. We further show that rapamycin-induced MAPK activation occurs in both normal cells and cancer cells lines and that this feedback loop depends on an S6K-PI3K-Ras pathway. Significantly, pharmacological inhibition of the MAPK pathway enhanced the antitumoral effect of mTORC1 inhibition by rapamycin in cancer cells in vitro and in a xenograft mouse model. Taken together, our findings identify MAPK activation as a consequence of mTORC1 inhibition and underscore the potential of a combined therapeutic approach with mTORC1 and MAPK inhibitors, currently employed as single agents in the clinic, for the treatment of human cancers.

Mammalian target of rapamycin inhibition as a therapeutic strategy in the management of urologic malignancies

The mammalian target of rapamycin (mTOR) is a protein kinase that regulates protein translation, cell growth, and apoptosis. Recently, there has been an enormous increase in our understanding on molecular mechanisms underlying the therapeutics of rapamycin in cancer. Alterations in the pathway regulating mTOR occur in many solid malignancies including prostate, bladder, and kidney cancer; in vitro and in vivo models of prostate and bladder cancer have established the importance of the mTOR pathway in control of cancer progression and metastasis. Temsirolimus (Torisel) and everolimus (RAD-001), two ester analogues of rapamycin, as well as rapamycin itself have clear antitumor activity in in vitro and in vivo models and are under clinical trial investigations for prostate and bladder cancer. Phase II and III trials have already established the clinical efficacy of temsirolimus in renal cancer, and current renal trials are evaluating the combined effects of vascular endothelial growth factor and mTOR inhibition. Ongoing studies in prostate and bladder cancer will soon define the activity and safety profiles of everolimus and temsirolimus. Recent molecular advances have uncovered a startling complexity in the macromolecular function of mTOR complexes, with the identification of new mTOR partners (raptor, rictor, FKBP38, PRAS40, and mSIN1), putative cancer therapeutic/prognostic targets for future clinical trials.

Laser capture microdissection and protein microarray analysis of human non-small cell lung cancer: differential epidermal growth factor receptor (EGPR) phosphorylation events associated with mutated EGFR compared with wild type

Little is known about lung carcinoma epidermal growth factor (EGF) kinase pathway signaling within the context of the tissue microenvironment. We quantitatively profiled the phosphorylation and abundance of signal pathway proteins relevant to the EGF receptor within laser capture microdissected untreated, human non-small cell lung cancer (NSCLC) (n = 25) of known epidermal growth factor receptor (EGFR) tyrosine kinase domain mutation status. We measured six phosphorylation sites on EGFR to evaluate whether EGFR mutation status in vivo was associated with the coordinated phosphorylation of specific multiple phosphorylation sites on the EGFR and downstream proteins. Reverse phase protein array quantitation of NSCLC revealed simultaneous increased phosphorylation of EGFR residues Tyr-1148 (p < 0.044) and Tyr-1068 (p < 0.026) and decreased phosphorylation of EGFR Tyr-1045 (p < 0.002), HER2 Tyr-1248 (p < 0.015), IRS-1 Ser-612 (p < 0.001), and SMAD Ser-465/467 (p < 0.011) across all classes of mutated EGFR patient samples compared with wild type. To explore which subset of correlations was influenced by ligand induction versus an intrinsic phenotype of the EGFR mutants, we profiled the time course of 115 cellular signal proteins for EGF ligand-stimulated (three dosages) NSCLC mutant and wild type cultured cell lines. EGFR mutant cell lines (H1975 L858R) displayed a pattern of EGFR Tyr-1045 and HER2 Tyr-1248 phosphorylation similar to that found in tissue. Persistence of phosphorylation for AKT Ser-473 following ligand stimulation was found for the mutant. These data suggest that a higher proportion of the EGFR mutant carcinoma cells may exhibit activation of the phosphatidylinositol 3-kinase/protein kinase B (AKT)/mammalian target of rapamycin (MTOR) pathway through Tyr-1148 and Tyr-1068 and suppression of IRS-1 Ser-612, altered heterodimerization with ERBB2, reduced response to transforming growth factor beta suppression, and reduced ubiquitination/degradation of the EGFR through EGFR Tyr-1045, thus providing a survival advantage. This is the first comparison of multiple, site-specific phosphoproteins with the EGFR tyrosine kinase domain mutation status in vivo.