Pathway In Human Tumors Research Articles

Exosomal microRNA as a key regulator of PI3K/AKT pathways in human tumors.

MicroRNAs (miRNAs) are conserved non-protein-coding RNAs that are naturally present in organisms and can control gene expression by suppressing the translation of mRNA or causing the degradation of mRNA. MicroRNAs are highly concentrated in the PI3K/AKT pathway, and abnormal activation of the PI3K/AKT pathway plays a role in cancer progression. The AKT/PI3K pathway is critical for cellular functions and can be stimulated by cytokines and in normal situations. It is involved in regulating various intracellular signal transduction, including development, differentiation, transcriptional regulation, protein, and synthesis. There is a growing body of evidence indicating that miRNAs, which are abundant in exosomes released by different cells, can control cellular biological activities via modulating the PI3K/AKT pathway, hence influencing cancer progression and drug resistance. This article provides an overview of the latest research progress regarding the function and medical use of the PI3K/AKT pathway and exosomal miRNA/AKT/PI3K axis in the behaviors of cancer cells.

Abstract 4859: Bi-steric mTORC1 inhibitors are superior to rapamycin and induce apoptotic cell death in tumor models with hyperactivated mTORC1

Abstract The PI3K-mTOR pathway is one of the most commonly dysregulated pathways in human tumors. Rapalogs have been used extensively in human clinical trials but exhibit modest clinical benefit for the most part, possibly due to their lack of effect on 4E-BP1, a key target downstream of mTORC1. ATP-competitive mTOR inhibitors can fully inhibit mTORC1 but are poorly tolerated possibly due to their inhibition of mTORC2. A new class of selective mTORC1 inhibitors has been developed and termed ‘bi-steric’, which comprise a rapamycin-like core moiety covalently linked to an mTOR active-site inhibitor. We report that bi-steric mTORC1-selective inhibitors (RMC-4627 and RMC-6272) have greater activity than rapalogs for tumors with mTORC1 hyperactivation. RMC-4627 and RMC-6272 showed more effective growth inhibition in multiple tumor cell lines with mTORC1 dysfunction compared to rapamycin. Both RMC-4627 and RMC-6272 at ~1 nM showed near complete inhibition of p4E-BP1T37/46, which was not seen with rapamycin treatment. Rapamycin and both bi-steric compounds markedly reduced kidney tumor burden and human bladder cancer PDX tumor size after four weeks of treatment. Tumor regrowth assessed after two-month treatment cessation was significantly reduced in the RMC-6272 group as compared to the rapamycin group. Finally, TUNEL staining showed RMC-6272 treatment led to a greater induction of apoptosis in kidney tumor cells and human bladder cancer PDX tumors relative to rapamycin after a single dose of each compound. This is the first time that clear evidence for cell death after mTORC1 inhibition has been seen. Integrative multi-omic analysis reveals differential global rewiring induced by RMC-6272 in comparison to rapamycin. Genes involved in cell cycle transition were downregulated by RMC-6272 vs. rapamycin. Proteins downregulated by RMC-6272 treatment relative to rapamycin were enriched for translation and ribosome-related proteins, consistent with effects of non-phosphorylated 4E-BP1 on synthesis of those proteins. Multiple purine metabolites were decreased to a greater extent in RMC-6272 treated cells as compared to rapamycin treatment, including deoxyadenosine, AICAR, AMP, IMP, and GMP. Notably, there was no significant change in R5P, suggesting that downregulation of the purine de novo synthesis pathway was the cause of these changes. Strong tumor cell apoptosis was induced by the suppression of de novo purine synthesis through mTORC1-PRPS1 axis. PRPS1, the rate-limit enzyme involving in purine synthesis was regulated by mTORC1 activity. In summary, RMC-4627 and RMC-6272 demonstrate improved in vitro and in vivo inhibition of mTORC1 in comparison to rapamycin, and induced more cell death in preclinical models, indicating the potential of bi-steric mTORC1-selective inhibitors as a novel therapeutic strategy to treat tumors with mTORC1 dysregulation. Citation Format: Heng Du, Yu Chi Yang, Heng-Jia Liu, Min Yuan, John Asara, Kwok-Kin Wong, Mallika Singh, David Kwiatkowski. Bi-steric mTORC1 inhibitors are superior to rapamycin and induce apoptotic cell death in tumor models with hyperactivated mTORC1. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4859.

Protein Kinase Signaling by Shiga Toxin Subunits.

Background:Escherichia coli produces Shiga toxin (Stx), a pentamer composed of one A subunit and four B subunits. The B subunit of Stx (StxB) mediated the attachment of the holotoxin to the cell surface while the A subunit (StxA) has N-glycosidase activity, resulting in protein synthesis and cell death inhibition. Stx-induced cytotoxicity and apoptosis have been observed in various cell lines, although the signaling effectors are not precisely defined. Activated by protein kinases (PK), the signaling pathway in human tumors plays an oncogenic role. Tumor proliferation, survival, and metastasis are promoted by kinase receptors. In this regard, PK regulatory effects on the cellular constituents of the tumor microenvironment can affect immunosuppressive purposes.Methods:In this study, kinase inhibitors were used to evaluate the influence of Stx and its subunits on HeLa and Vero cells. Selective inhibitors of protein kinase C (PKC), CaM kinase (calmodulin kinase), protein kinase A (PKA), and protein kinase G (PKG) were used to compare the signaling activity of each subunit.Results:The ribotoxic activity in the target cells will lead to rapid protein synthesis inhibition and cell death in the mammalian host. The expression of Bcl2 family members was also assessed. Protein kinase signaling by Stx and its A and B subunits was induced by PKA, PKG, and PKC in HeLa cells. CaM kinase induction was significant in Vero cells. StxB significantly induced the pro-apoptotic Bax signaling factor in HeLa cells.Conclusion:The assessment of different signaling pathways utilized by Stx and its subunits could help in a better understanding of various cell death responses. The use of inhibitors can block cell damage and disease progression and create therapeutic compounds for targeted cancer therapy. Inhibition of these pathways is the primary clinical goal.

Abstract 1026: Bi-steric mTORC1-selective inhibitors demonstrate improved potency and efficacy in tumors with mTORC1 hyperactivation

Abstract The PI3K-mTOR pathway is one of the most commonly dysregulated pathways in human tumors. Rapalogs have been used extensively in human clinical trials but exhibit modest clinical benefit for the most part, possibly due to their lack of effect on 4E-BP1, a key target downstream of mTORC1. ATP-competitive mTOR inhibitors can fully inhibit mTORC1 but are poorly tolerated possibly due to their inhibition of mTORC2. A new class of selective mTORC1 inhibitors has been developed and termed ‘bi-steric', which comprise a rapamycin-like core moiety covalently linked to an mTOR active-site inhibitor. RMC-5552 is the first clinical candidate of this class and clinical testing is planned in 2021. RM-001 and RM-006 (also known as RMC-6272) are representative bi-steric tool compounds that exhibit potent and selective (> 10-fold) inhibition of mTORC1 over mTORC2. We report that bi-steric mTORC1-selective inhibitors have greater activity than rapalogs for tumors with mTORC1 hyperactivation secondary to TSC1/2 loss. RM-001 and RM-006 showed more effective growth inhibition in multiple TSC1 or TSC2 mutant tumor cell lines compared to rapamycin. RM-001 and RM-006 caused a more profound growth inhibition in the TSC1 or TSC2 mutant cells than the wild type cells. Two-week low dilution clonogenic assays in TSC1 or TSC2 mutant cells showed clone numbers were significantly reduced by rapamycin, RM-001, and RM-006, whereas in the wild type cells, Rapamycin and RM compounds had less reduction in clone numbers, indicating a differential sensitivity in TSC-null cells. Both RM-001 and RM-006 at ~1 nM showed near complete inhibition of p4E-BP1T37/46, which was not seen with rapamycin treatment, while inhibition of pS6S240/244 levels was similar for rapamycin and RM compounds. Further, the RM compounds had prolonged anti-proliferative activity in TSC-null cells, as shown by washout studies. Rapamycin, MLN0128 and both RM compounds markedly reduced kidney tumor burden in Tsc2+/- A/J mice after four weeks of treatment. Tumor regrowth was assessed two months after treatment cessation, tumor burden was significantly reduced in the RM-006 group as compared to the rapamycin and MLN0128 groups. Finally, TUNEL staining showed RM-006 treatment led to a greater induction of apoptosis in kidney tumor cells relative to rapamycin and MLN0128 after a single dose of each compound in Tsc2+/- A/J mice. This is the first time that clear evidence for cell death after mTORC1 inhibition has been seen in TSC rodent models. In summary, RM-001 and RM-006 demonstrate improved in vitro and in vivo inhibition of mTORC1 in comparison to rapamycin, and induced more cell death in TSC2 null tumors in vivo, indicating the potential of bi-steric mTORC1-selective inhibitors as a novel therapeutic strategy to treat tumors with mTORC1 dysregulation. Citation Format: Heng Du, Yu Chi Yang, Mallika Singh, Heng-jia Liu, David Kwiatkowski. Bi-steric mTORC1-selective inhibitors demonstrate improved potency and efficacy in tumors with mTORC1 hyperactivation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1026.

NRF2-Dependent Bioactivation of Mitomycin C as a Novel Strategy To Target KEAP1-NRF2 Pathway Activation in Human Cancer.

Activating mutations in the KEAP1-NRF2 pathway are found in approximately 25% of lung tumors, where the hijacking of NRF2's cytoprotective functions results in aggressive tumor growth, chemoresistance, and a poor prognosis for patients. There are currently no approved drugs which target aberrant NRF2 activation, which means that there is an urgent clinical need to target this orphan oncogenic pathway in human tumors. In this study, we used an isogenic pair of wild-type and Keap1 knockout cells to screen a range of chemotherapeutic and pathway-targeted anticancer drugs in order to identify compounds which display enhanced toxicity toward cells with high levels of Nrf2 activity. Through this approach, complemented by validation across a panel of eight human cancer cell lines from a range of different tissues, we identified the DNA-damaging agent mitomycin C to be significantly more toxic in cells with aberrant Nrf2 activation. Mechanistically, we found that the NRF2 target genes for cytochrome P450 reductase, NQO1, and enzymes in the pentose phosphate pathway are all responsible for the NRF2-dependent enhanced bioactivation of mitomycin C. As mitomycin C is already approved for clinical use, it represents as excellent drug repositioning candidate to target the currently untreatable NRF2 activation in human tumors.

Curcumin: a potent agent to reverse epithelial-to-mesenchymal transition.

Epithelial-to-mesenchymal transition (EMT) is involved in tumor progression, invasion, migration and metastasis. EMT is a process by which polarized epithelial cells acquire motile mesothelial phenotypic features. This process is initiated by disassembly of cell-cell contacts through the loss of epithelial markers and replacement of these markers by mesenchymal markers. Reconstruction of the cytoskeleton and degradation of the tumor basement membrane ensures the spread of invasive malignant tumor cells to distant locations. Accumulating evidence indicates that curcumin, as a well-known phytochemical, can inhibit EMT/metastasis through various mechanisms and pathways in human tumors. In this review, we summarize the mechanisms by which curcumin may affect EMT in cells under pathological conditions to understand its potential as a novel anti-tumor agent. Curcumin can exert chemo-preventive effects by inhibition and reversal of the EMT process through both TGF-β-dependent (e.g. in hepatoma and retinal pigment epithelial cancer) and -independent (e.g. in oral cancer, colorectal cancer, pancreatic cancer, hepatocellular carcinoma, breast cancer, melanoma, prostate cancer, bladder cancer, thyroid cancer and lung cancer) pathways. Curcumin can also mitigate chemoresistance through EMT suppression and promotion of the antiproliferative effects of conventional chemotherapeutics. Therefore, curcumin has the potential to be used as a novel adjunctive agent to prevent tumor metastasis, which may at least partly be attributed to its hampering of the EMT process.

Abstract 5262: The inhibitory effect of combinations of curcumin, ursolic acid, and metformin on skin tumor promotion by TPA

Abstract The purpose of this study was to examine the effects of combinations of ursolic acid (UA), curcumin (Curc), and metformin (Met) for potential synergistic chemopreventive activity to inhibit tumor promotion using the mouse two-stage skin carcinogenesis model. UA and Curc have been shown to inhibit tumorigenesis in several mouse models, and both have been shown to inhibit mouse skin tumor promotion by 12-O-tetradecanoylphorbol-13-acetate (TPA). The anti-cancer activity of these phytochemicals is due to their anti-inflammatory, anti-oxidant, and anti-proliferative effects. These effects are accomplished by acting on a broad spectrum of signaling pathways. Met has also been shown to have anti-cancer activity. In retrospective studies, type II diabetes patients taking Met have been shown to have a decreased cancer incidence. Met has also been shown to inhibit mouse skin tumor promotion by TPA. Met activates AMP-activated protein kinase (AMPK), which in turn inhibits mammalian target of rapamycin complex 1 (mTORC1) signaling. mTORC1 is a key kinase involved in the phosphatidylinositol-3 kinase (PI3K)/Akt pathway, one of the most commonly altered pathways in human tumors. In initial short-term experiments (mice treated twice weekly for two weeks with TPA), combinations of UA and Curc pretreated topically inhibited TPA-induced activation of epidermal NF-κB, Cox-2, epidermal growth factor receptor (EGFR) and JNK to a greater extent than either compound alone. Additionally, these compounds increased levels of AMPK and programmed cell death protein 4 (Pdcd4). The alterations in these signaling pathways by the combination of UA and Curc were associated with decreased epidermal proliferation and skin inflammation as assessed by measuring BrdU incorporation and inflammatory gene expression, respectively. Further studies using dietary administration of a combination of UA and Curc, as well as combinations of UA or Curc (in diet) with Met administered in the drinking water were conducted. These combinations produced greater inhibition of TPA-induced activation of epidermal NFκB, Cox-2, and EGFR than the compounds given alone. These combinations also decreased epidermal proliferation, again shown by an inhibition of BrdU incorporation. In addition to these data, the results from ongoing skin tumor experiments (mice initiated with DMBA and promoted twice weekly with TPA) using both topical administration and dietary administration of the various combinations will be presented. The current results indicate that certain combinations of UA, Curc and Met may inhibit mouse skin tumor promotion by TPA to a greater extent than the compounds alone. The ability of the combinations to work when given both topically as well as in the diet suggests the potential for broad applications for chemopreventive strategies. Citation Format: Lisa Tremmel, Okkyung Rho, John DiGiovanni. The inhibitory effect of combinations of curcumin, ursolic acid, and metformin on skin tumor promotion by TPA [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5262. doi:10.1158/1538-7445.AM2017-5262

Genistein suppresses the proliferation of telomerase-negative cells.

In both tumor and yeast cells that lack telomerase, telomeres are maintained via an alternative recombination mechanism. In this study, we tested genistein, a potential TOP2 inhibitor required for telomere–telomere recombination, on the repression of telomere–telomere recombination. Genistein on the repression of type II recombination on a tlc1 yeast strain was examined by the telomeric DNA structures using Southern blot analysis. Telomere patterns of freshly dissected tlc1 spores containing an empty plasmid (pYES2) or a yeast TOP2 (yTOP2) plasmid were analyzed. The results indicated that the reintroduction of TOP2 recovered the type II pattern, implying genistein in the blockage of type II survivors in the tlc1 strain. The effects of genistein on both tlc1 and tlc1 rad 51 strains in liquid and solid mediums were also examined. Finally, treatment of 10 μmol/L of genistein showed inhibitory effect on the growth of telomerase‐negative U2OS alternative lengthening of telomere (ALT) cells, but not in telomerase‐positive HCT116 cells. These results provide evidences that the inhibitory effects of genistein on telomerase‐negative cells depend on type II recombination pathway in yeast and the ALT pathway in human tumors.

MicroRNA-147 suppresses proliferation, invasion and migration through the AKT/mTOR signaling pathway in breast cancer.

The Akt/mTOR pathway is considered to be the most frequently aberrantly activated pathway in human tumors. It is activated in a variety of types of tumor, and is therefore an attractive target for study, including it's potential regulation by microRNAs. A number of microRNAs (miRs) have been demonstrated to target the Akt/mTOR pathway. A previous study reported that miR-147 targets the EGFR-driven cell-cycle protein network in breast cancer. EGFR serves a crucial role upstream to Akt/mTOR. To define the function and mechanism of miR-147 in breast cancer, the present study assessed miR-147 expression in a normal mammary epithelial cell line and three breast cancer cell lines, and observed that miR-147 expression was markedly low in the highly invasive cell line, MDA-MB-231. Ectopic expression of miR-147 in MDA-MB-231 resulted in a reduction of the phosphorylation of crucial molecules in the Akt/mTOR pathway and the proliferation, invasion and migration of the cell line was also reduced. The effects of miR-147 expression are similar to that of shRNA which is specifically designed to silence the expression of Akt. The findings of the present study indicate that miR-147 suppressed the proliferation, invasion and migration of breast cancer cells through targeting the Akt/mTOR signaling pathway. As a new microRNA targeting Akt/mTOR pathway. Using miR-147 may therefore provide an effective therapeutic approach to suppress tumorigenicity in breast cancer.

Elevated Src expression associated with hepatocellular carcinoma metastasis in northern Chinese patients.

Src, a non-receptor type of tyrosine, was recently reported to modulate multiple signaling pathways in human tumors. Therefore, the present study aimed to determine the expression and distribution of Src on hepatocellular carcinoma (HCC). The expressions of total Src (t-Src) and an active form of Src [phosphorylated (p-) Y416Src] were analyzed in 52 northern Chinese patients with HCC using immunohistochemistry. The positive expression rates of t-Src and p-Y416Src in HCC tissue were 65.38 and 42.30%, respectively, which is significantly higher than that in adjacent non-tumor tissue (30.76 and 13.46%; P<0.001 and P=0.010, respectively). The staining intensity of t-Src and p-Y416Src were also significantly higher in HCC tissues compared with adjacent normal tissues (P<0.001 and P=0.023, respectively). t-Src expression was positively and significantly correlated with tumor stage (P=0.002), cellular differentiation (P=0.007), metastasis (P=0.030) and the expression level of CA19-9 (P=0.016), while p-Y416Src expression was only significantly correlated with tumor stage (P=0.010). The expression of t-Src and p-Y416Src were also investigated using immunocytochemistry in two HCC cell lines with different metastatic potentials (MHCC97-L and HCCLM3) that are derived from a single HCC patient. Consistently, the expression of t-Src and p-Y416Src were stronger in the cells with higher metastatic potential compared with those exhibiting lower metastatic potential. Taken together, the current data indicate that Src expression is elevated and active in Chinese patients with HCC and that t-Src may have a key role in promoting HCC metastasis.

Notch signaling regulates proliferation and differentiation in the adult mouse intestine (899.4)

Human gastrointestinal tumors can exhibit increased Notch signaling; accordingly, intestinal Notch over‐activation was examined in genetic mouse models ubiquitously expressing the Notch intracellular domain (NICD) in the intestinal epithelium. Based on previous studies, we hypothesized that Notch over‐activation would induce increased proliferation, decreased secretory cells, and increased absorptive cell numbers. NICD expression was activated in bitransgenic mice (Villin‐CreERT2 ; Rosa‐FSF‐NICD‐nGFP) by 5 daily doses of tamoxifen with intestine collected on day 6. We found that epithelial proliferation was increased and the goblet cell population was decreased in the NICD intestine. However, contrary to our hypothesis, the alkaline phosphatase‐positive enterocyte population appeared decreased, which was confirmed by reduced mRNA levels of the enterocyte marker sucrase‐isomaltase. Based on these data, we concluded that Notch over‐activation increases proliferation and decreases all differentiated cell types, not just secretory cells. This finding suggests that constitutive Notch activation in the intestine leads to a hyperproliferative state, consistent with activation of this pathway in human tumors.Grant Funding Source: Supported by APS Fellowship (NEZ) and NIH grants R01‐DK078927 (LCS) and F30‐DK095517 (AJC).

Abstract 3065: The role of miR-18b in MDM2-p53 pathway signaling and melanoma progression.

Abstract MicroRNAs regulate gene expression and are differentially expressed in various tumors. While p53 is inactivated by point mutations in many tumors, melanomas rarely harbor mutations in the p53 gene. Here we report the biological role of miR-18b in melanoma via targeting the MDM2-p53 pathway. Expression of miR-18b was significantly suppressed in melanoma specimens and cell lines by virtue of hypermethylation, and was re-induced in melanoma cell lines following 5-AZA-deoxycytidine treatment. Lower levels of miR-18b expression in primary melanoma were associated with significantly reduced overall survival. MDM2 was identified as a target of miR-18b action, as miR-18b significantly suppressed the luciferase activity of a reporter plasmid containing the 3’UTR sequence of MDM2 complementary to the miR-18b seed sequence. Induction of miR-18b expression in melanoma cells resulted in reduced MDM2 expression, upregulation of p53 as well as PUMA and p21, and suppression of the anti-apoptotic BCL2 and BCL-XL genes, resulting in significant suppression of melanoma cell proliferation. The effects of miR-18b overexpression on the p53 pathway and on melanoma cell growth were reversed by MDM2 overexpression. Stable overexpression of miR-18b produced potent tumor suppressor activity, as evidenced by suppressed melanoma cell proliferation, induction of apoptosis, and reduced tumor cell growth in vivo. In addition, miR-18b overexpression suppressed melanoma cell migration and invasiveness, and reversed epithelial-to-mesenchymal transition in melanoma cell lines. Our results demonstrate a novel role for miR-18b as a tumor suppressor in melanoma, identify the MDM2-p53 pathway as a target of miR-18b action, and suggest miR-18b overexpression as a novel strategy to reactivate the p53 pathway in human tumors. Citation Format: Altaf A. Dar, Shahana Majid, David de Semir, Vladimir Bezrookove, Mehdi Nosrati, Mohammed Kashani-Sabet. The role of miR-18b in MDM2-p53 pathway signaling and melanoma progression. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3065. doi:10.1158/1538-7445.AM2013-3065

Molecular Pathways: Blockade of the PRLR Signaling Pathway as a Novel Antihormonal Approach for the Treatment of Breast and Prostate Cancer

The prolactin (PRL)-prolactin receptor (PRLR) signaling complex has been implicated in the pathology of breast and prostate carcinoma. A multitude of pro-oncogenic intracellular signaling pathways are activated by PRL in breast and prostate epithelial cells, leading to enhanced cellular proliferation, survival, and tumorigenesis in numerous model systems. Emerging evidence suggests that targeting the PRL-PRLR axis in human cancer may represent an unexploited avenue for therapeutic intervention and, given the extensive cross-talk between PRLR and other signal transduction pathways, a potential means through which other anticancer agents could be rendered more efficacious in the clinic. LFA102 is a potent anti-PRLR neutralizing antibody that efficiently abrogates the function of this receptor in vivo, mediating significant antitumor effects in preclinical models. The clean safety profile of this antibody in animals and in the clinical experiences to date suggests that blocking the PRLR signaling pathway in human tumors may have few significant toxicologic consequences and may be a promising approach to treating cancer. A phase I trial in patients with breast and prostate cancer is underway to better understand the clinical utility of LFA102 and the contribution of PRL to the maintenance and progression of human cancer.

The Role of miR-18b in MDM2-p53 Pathway Signaling and Melanoma Progression

BackgroundAlthough p53 is inactivated by point mutations in many tumors, melanomas infrequently harbor mutations in the p53 gene. Here we investigate the biological role of microRNA-18b (miR-18b) in melanoma by targeting the MDM2-p53 pathway.MethodsExpression of miR-18b was examined in nevi (n = 48) and melanoma (n = 92) samples and in melanoma cell lines and normal melanocytes. Immunoblotting was performed to determine the expression of various proteins regulated by miR-18b. The effects of miR-18b overexpression in melanoma cell lines were investigated using assays of colony formation, cell viability, migration, invasion, and cell cycle and in a xenograft model (n = 10 mice per group). Chromatin immunoprecipitation and methylation assays were performed to determine the mechanism of microRNA silencing.ResultsExpression of miR-18b was substantially reduced in melanoma specimens and cell lines by virtue of hypermethylation and was reinduced (by 1.5- to 5.3-fold) in melanoma cell lines after 5-AZA-deoxycytidine treatment. MDM2 was identified as a target of miR-18b action, and overexpression of miR-18b in melanoma cells was accompanied by 75% reduced MDM2 expression and 2.5-fold upregulation of p53, resulting in 70% suppression of melanoma cell colony formation. The effects of miR-18b overexpression on the p53 pathway and on melanoma cell growth were reversed by MDM2 overexpression. Stable overexpression of miR-18b produced potent tumor suppressor activity, as evidenced by suppressed melanoma cell viability, induction of apoptosis, and reduced tumor growth in vivo. miR-18b overexpression suppressed melanoma cell migration and invasiveness and reversed epithelial-to-mesenchymal transition.ConclusionsOur results demonstrate a novel role for miR-18b as a tumor suppressor in melanoma, identify the MDM2-p53 pathway as a target of miR-18b action, and suggest miR-18b overexpression as a novel strategy to reactivate the p53 pathway in human tumors.

Targeting PI3K in Cancer: Any Good News?

The phosphatidylinositol 3-kinase (PI3K) signaling pathway regulates several cellular processes and it’s one of the most frequently deregulated pathway in human tumors. Given its prominent role in cancer, there is great interest in the development of inhibitors able to target several members of PI3K signaling pathway in clinical trials. These drug candidates include PI3K inhibitors, both pan- and isoform-specific inhibitors, AKT, mTOR, and dual PI3K/mTOR inhibitors. As novel compounds progress into clinical trials, it’s becoming urgent to identify and select patient population that most likely benefit from PI3K inhibition. In this review we will discuss individual PIK3CA mutations as predictors of sensitivity and resistance to targeted therapies, leading to use of novel PI3K/mTOR/AKT inhibitors to a more “personalized” treatment.

Targeting mTOR Pathways in Human Malignancies

The mammalian target of rapamycin (mTOR) is a protein kinase involved in the phosphatidylinositol 3-Kinase (PI3K)/AKT signalling pathway with a central role in the control of cell growth, survival and angiogenesis. Multiple and frequent dysregulations of this pathway in human tumors make it a central target in the development of new anticancer treatments. To review the most significant data on mTOR pathway, role of mTOR inhibitors in cancer treatment, preclinical and clinical data of the three first generation mTOR inhibitors (temsirolimus, everolimus and deferolimus), rationales, preclinical and clinical data of second generation mTOR inhibitors. Review of published literature on mTOR and related pathways, rapalogs and novel mTOR inhibitors. Temsirolimus and everolimus have been approved for the treatment of metastatic Renal Cell Carcinoma (RCC), temsirolimus also for Mantle Cell Lymphoma (MCL) and everolimus will be approved for pancreatic neuroendocrine tumors; all three rapalogs are currently evaluated in phase III studies in several tumors. Only limited published data are available on new mTOR inhibitors; however, in vitro and in vivo in preclinical studies they have shown a significant antiproliferative activity against a broad panel of tumors and a favourable safety profile, with disease stabilization or even tumor regression, either as single agent or in combination.

DNA damage induces the IL-6/STAT3 signaling pathway, which has anti-senescence and growth-promoting functions in human tumors

IL-6 is a multifunctional cytokine that is important for immune responses, cell survival, apoptosis, and proliferation. However, little is known about the correlation between the IL-6 signaling pathway and DNA damage in human tumors. The present study demonstrates the role of the IL-6/STAT3 signaling pathway in human tumor cells exposed to DNA damage. Tumor cells exposed to DNA damage increase the expression and secretion of IL-6 and the phosphorylation of JAK1 and STAT3. The activation of the JAK1–STAT3 signaling pathway is inhibited by knockdown of gp130 or neutralization of soluble IL-6, implying that DNA damage induces the phosphorylation of JAK1 and STAT3 by autocrine IL-6. Interestingly, inhibition of the IL-6/STAT3 signaling pathway impairs the growth of tumor cells exposed to DNA damage and results in the induction of senescence. Therefore, the present study suggests that IL-6 inhibits senescence but promotes the survival and proliferation of tumor cells exposed to DNA damage through the activation of the JAK1–STAT3 signaling pathway.

Abstract SY11-01: Targeting the Fanconi anemia/BRCA pathway in cancer therapy

Abstract SY11-01: Targeting the Fanconi anemia/BRCA pathway in cancer therapy

Targeting Nonclassical Oncogenes for Therapy in T-ALL

Constitutive phosphoinositide 3-kinase (PI3K)/Akt activation is common in Tcell acute lymphoblastic leukemia (T-ALL). Although four distinct class I PI3K isoforms (α, β, γ, δ) could participate in T-ALL pathogenesis, none has been implicated in this process. We report that in the absence of PTEN phosphatase tumor suppressor function, PI3Kγ or PI3Kδ alone can support leukemogenesis, whereas inactivation of both isoforms suppressed tumor formation. The reliance of PTEN null T-ALL on the combined activities of PI3Kγ/δ was further demonstrated by the ability of a dual inhibitor to reduce disease burden and prolong survival in mice as well as prevent proliferation and promote activation of proapoptotic pathways in human tumors. These results support combined inhibition of PI3Kγ/δ as therapy for T-ALL.

Abstract CN05-02: Targeting the Fanconi anemia/BRCA pathway in cancer therapy.

Abstract CN05-02: Targeting the Fanconi anemia/BRCA pathway in cancer therapy.