Expanding therapeutic targets in bladder cancer: the PI3K/Akt/mTOR pathway

Absence of signaling into CD4⁺ cells via C3aR and C5aR enables autoinductive TGF-β1 signaling and induction of Foxp3⁺ regulatory T cells

C3a and C5a receptor (C3aR and C5aR) signaling by dendritic cells and CD4⁺ cells provides costimulatory and survival signals to T effector cells. Here, we demonstrate that when C3aR and C5aR signals are not transduced into CD4⁺ cells, PI-3Kγ-AKT-mTOR signaling ceases, PKA activation increases, auto-inductive transforming growth factor- β1 (TGF-β1) signaling initiates, and CD4⁺ cells become Foxp3⁺ T regulatory cells (iT_regs). Endogenous TGF-β1 suppresses C3aR and C5aR signaling by preventing C3a and C5a production and upregulating C5L2, an alternate C5a receptor. Absent C3aR and C5aR signaling decreases costimulatory molecule and interleukin-6 production and augments interleukin-10 production. The resulting iT_regs exert robust suppression, possess enhanced stability, and suppress ongoing autoimmune disease. Human iT_regs with potent suppressor activity can be induced exploiting this insight.

Up-regulation of amino acid transporter SLC6A19 activity and surface protein abundance by PKB/Akt and PIKfyve

BACKGROUND

The amino acid transporter B0AT1 (SLC6A19) accomplishes concentrative cellular uptake of neutral amino acids. SLC6A19 is stimulated by serum- & glucocorticoid-inducible kinase (SGK) isoforms. SGKs are related to PKB/Akt isoforms, which also stimulate several amino acid transporters. PKB/Akt modulates glucose transport in part by phosphorylating and thus activating phosphatidylinositol-3-phosphate-5-kinase (PIKfyve), which fosters carrier protein insertion into the cell membrane. The present study explored whether PKB/Akt and/or PIKfyve stimulate SLC6A19.

METHODS

SLC6A19 was expressed in Xenopus oocytes with or without wild-type PKB/Akt or inactive (T308A/S473A)PKB/Akt without or with additional expression of wild-type PIKfyve or PKB/Akt-resistant (S318A)PIKfyve. Electrogenic amino acid transport was determined by dual electrode voltage clamping.

RESULTS

In SLC6A19-expressing oocytes but not in water-injected oocytes, the addition of the neutral amino acid L-leucine (2 mM) to the bath generated a current (I(le)), which was significantly increased following coexpression of PKB/Akt, but not by coexpression of (T308A/S473A)PKB/Akt. The effect of PKB/Akt was augmented by additional coexpression of PIKfyve but not of (S318A)PIKfyve. Coexpression of PKB/Akt enhanced the maximal transport rate without significantly modifying the affinity of the carrier. The decline of I(le) following inhibition of carrier insertion by brefeldin A (5 µM) was similar in the absence and presence of PKB/Akt indicating that PKB/Akt stimulated carrier insertion into rather than inhibiting carrier retrieval from the cell membrane.

CONCLUSION

PKB/Akt up-regulates SLC6A19 activity, which may foster amino acid uptake into PKB/Akt-expressing epithelial and tumor cells.

Molecular Pathology of Bladder Cancer

This article focuses on several promising candidate biomarkers that may soon make their transition to the realm of clinical management of bladder cancer. Presented are superficial and muscle-invasive urothelial carcinoma of the bladder and the genetic tests currently available in testing for diagnosis and prognosis of these diseases.

Dysregulation of mammalian target of rapamycin pathway in plasmacytoid variant of urothelial carcinoma of the urinary bladder

Plasmacytoid urothelial carcinoma is a rare but aggressive variant of bladder cancer with no clear therapeutic guidelines. Dysregulation of the mammalian target of rapamycin (mTOR) pathway has been linked to oncogenesis in conventional bladder cancer. Several antineoplastic agents targeting mTOR pathway are currently available. This study assesses mTOR pathway status as well as c-myc and p27 expression. We retrieved 19 archival cases of plasmacytoid urothelial carcinoma from two institutions. Whole tissue sections were evaluated for immunoexpression of phosphatase and tensin homolog (PTEN), phosphorylated mTOR, phosphorylated protein kinase B (AKT), phosphorylated S6, c-myc, and p27. We evaluated intensity (0 to 3+) and extent (0%-100%) of expression for all markers. An H score was calculated as the sum of products of intensity and extent for each marker and used during analysis. In addition, PTEN loss was defined as absence of expression in >10% of tumor cells. We encountered PTEN loss in 28%. Higher H score for nuclear phosphorylated AKT and a lower H score for phosphorylated S6 was encountered in muscle invasive tumors compared to non-muscle invasive tumors (P = .007 and P = .009, respectively). Although a trend for negative prognostic impact on overall survival for higher phosphorylated mTOR expression was noted (P = .051), markers expression levels failed to predict survival in our cohort. We found dysregulation of mTOR pathway members in urinary bladder plasmacytoid urothelial carcinoma, suggesting that the use of mTOR pathway inhibitors might be beneficial for patients with this aggressive tumor.

Immunohistochemical expression of mTOR negatively correlates with PTEN expression in gastric carcinoma

The phosphoinositide-3 kinase (PI3K)-AKT-mammalian target of rapamycin (mTOR) pathway is a cellular pathway involved in cell growth, tumorigenesis and cell invasion which is frequently activated in various types of cancer. The downstream effector of the pathway is mTOR which is important in cellular growth and homeostasis and aberrant activation of mTOR has been reported in several types of cancer. The tumor suppressor gene phosphatase and tensin homolog (PTEN) is essential in this pathway for inhibiting tumor invasion and metastasis. However, the involvement of mTOR and PTEN in the progression of human gastric cancer remains to be identified. Immunohistochemical staining was performed to detect the expression of mTOR and PTEN in paraffin-embedded gastric tissue sections obtained from 33 patients with gastric cancer and 30 normal controls. The expressed mTOR was mainly distributed in the cytoplasm, while PTEN was mainly localized to the nucleus. By considering negative mTOR expression with positive PTEN expression as one group and negative PTEN expression with positive mTOR expression as the other, significant statistical differences were observed in various categories, including histological types and metastatic and clinical pathology stages, between the 2 groups (P<0.01 or 0.05). The results indicated that the expression levels of mTOR and PTEN were negatively correlated in the PI3K-AKT-mTOR signaling pathway. Combined detection of mTOR and PTEN expression may be used to evaluate the degree of malignancy in gastric cancer and may be a useful marker for the early diagnosis of gastric cancer.

Emerging critical role of molecular testing in diagnostic genitourinary pathology

CONTEXT

The unprecedented advances in cancer genetics and genomics are rapidly affecting clinical management and diagnostics in solid tumor oncology. Molecular diagnostics is now an integral part of routine clinical management in patients with lung, colon, and breast cancer. In sharp contrast, molecular biomarkers have been largely excluded from current management algorithms of urologic malignancies.

OBJECTIVE

To discuss promising candidate biomarkers that may soon make their transition to the realm of clinical management of genitourologic malignancies. The need for new treatment alternatives that can improve upon the modest outcome so far in patients with several types of urologic cancer is evident. Well-validated prognostic molecular biomarkers that can help clinicians identify patients in need of early aggressive management are lacking. Identifying robust predictive biomarkers that will stratify response to emerging targeted therapeutics is another crucially needed development. A compiled review of salient studies addressing the topic could be helpful in focusing future efforts.

DATA SOURCES

A PubMed (US National Library of Medicine) search for published studies with the following search terms was conducted: molecular , prognostic , targeted therapy , genomics , theranostics and urinary bladder cancer , prostate adenocarcinoma , and renal cell carcinoma . Articles with large cohorts and multivariate analyses were given preference.

CONCLUSIONS

Our recent understanding of the complex molecular alterations involved in the development and progression of urologic malignancies is yielding novel diagnostic and prognostic molecular tools and opening the doors for experimental targeted therapies for these prevalent, frequently lethal solid tumors.

New directions for biologic targets in urothelial carcinoma

Urothelial carcinoma remains an important oncologic problem with significant morbidity and mortality. This article provides an overview of the current status of treatment of urothelial carcinoma, with an update on current trials and recent American Society of Clinical Oncology abstracts. As an alternative to focusing on the metastatic setting, we take a broad look at drug development to date, as it spans from early disease to advanced disease in the context of emerging molecular data. This approach allows us to show that each stage involves key considerations based on emerging evidence regarding molecular biology, stage-specific novel endpoints, and rational patient selection that may help further trial designs in the future. Key issues, such as neoadjuvant versus adjuvant perioperative chemotherapy, approaches to salvage second-line therapy in the metastatic setting, and treatment of elderly and cisplatin-ineligible patients, are discussed. New paradigms in clinical research, including novel endpoints, upfront rational patient selection, biomarkers, and trial design, are also addressed.

Urothelial tumor initiation requires deregulation of multiple signaling pathways: implications in target-based therapies

Although formation of urothelial carcinoma of the bladder (UCB) requires multiple steps and proceeds along divergent pathways, the underlying genetic and molecular determinants for each step and pathway remain undefined. By developing transgenic mice expressing single or combinatorial genetic alterations in urothelium, we demonstrated here that overcoming oncogene-induced compensatory tumor barriers was critical for urothelial tumor initiation. Constitutively active Ha-ras (Ras*) elicited urothelial hyperplasia that was persistent and did not progress to tumors over a 10 months period. This resistance to tumorigenesis coincided with increased expression of p53 and all pRb family proteins. Expression of a Simian virus 40 T antigen (SV40T), which disables p53 and pRb family proteins, in urothelial cells expressing Ras* triggered early-onset, rapidly-growing and high-grade papillary UCB that strongly resembled the human counterpart (pTaG3). Urothelial cells expressing both Ras* and SV40T had defective G(1)/S checkpoint, elevated Ras-GTPase and hyperactivated AKT-mTOR signaling. Inhibition of the AKT-mTOR pathway with rapamycin significantly reduced the size of high-grade papillary UCB but hyperactivated mitogen-activated protein kinase (MAPK). Inhibition of AKT-mTOR, MAPK and STAT3 altogether resulted in much greater tumor reduction and longer survival than did inhibition of AKT-mTOR pathway alone. Our studies provide the first experimental evidence delineating the combinatorial genetic events required for initiating high-grade papillary UCB, a poorly defined and highly challenging clinical entity. Furthermore, they suggest that targeted therapy using a single agent such as rapamycin may not be highly effective in controlling high-grade UCB and that combination therapy employing inhibitors against multiple targets are more likely to achieve desirable therapeutic outcomes.

Antiproliferative factor signaling and interstitial cystitis/painful bladder syndrome

A unique glycopeptide, antiproliferative factor (APF), has been suggested as a urinary biomarker and potential mediator of long-term bladder disorder Interstitial Cystitis/Painful Bladder Syndrome. There is no known cause for this disease. Several mechanistic approaches have been employed to address the underlying mechanism whereby APF regulates cellular responses in the bladder epithelium. A summary of recent literature is provided, and is focused on signal transduction pathways and networks that are responsive to APF.

Molecular biomarkers in urothelial carcinoma of the bladder: are we there yet?

The unprecedented advances in cancer genetics and genomics are rapidly affecting the clinical management of solid tumors. Molecular diagnostics are now an integral part of routine clinical management for patients with lung, colon, and breast cancer. In sharp contrast, molecular biomarkers have been largely excluded from current management algorithms for urologic malignancies. The need for new treatment options that can improve upon the modest outcomes currently associated with muscle-invasive bladder cancer is evident, and validated prognostic molecular biomarkers that can help clinicians to identify patients in need of early, aggressive management are lacking. Robust predictive biomarkers that are able to forecast and stratify responses to emerging targeted therapies are also needed.

Emerging therapies for urothelial cancer

Urothelial carcinoma is one of the leading causes of death in Europe and the United States. Despite its chemosensitivity, median overall survival for advanced disease is still nearly 1 year. Most second-line chemotherapeutic agents tested have been disappointing. Thus, new treatment strategies are clearly needed. This review focuses on emerging therapies in urothelial carcinoma. Results from recent clinical trials, investigating the activity of new generation cytostatic agents, as well as results from studies assessing the toxicity and efficacy of novel targeted therapies, are discussed. In this setting, anti-epidermal growth factor receptor, angiogenesis, and phosphatidylinositol 3-kinase/mammalian target of rapamycin inhibitors account for the majority of phase I and II trials.

Activation of the PI3K/Akt/mTOR pathway correlates with tumour progression and reduced survival in patients with urothelial carcinoma of the urinary bladder

AIMS

Phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway dysregulation has been implicated in the development of urothelial carcinoma. However, its clinical relevance has not been substantially validated in human samples. The aim of this study was to assess the expression of the pathway in a large cohort of bladder cancers using the tissue microarray technique.

METHODS AND RESULTS

Immunohistochemical stains for phosphatase and tensin homologue (PTEN), phosphorylated Akt, mTOR, S6 and 4E-BP1 were performed for 887 cases, and the results were correlated with clinicopathological characteristics. The high expression of p-S6 and p-Akt corresponded significantly with high-grade and advanced-stage, while losses of PTEN and p-4E-BP1 were observed more often in high-grade and high-stage tumours. High expression of p-Akt and p-S6 predicted progression and cancer-specific mortality for non-muscle-invasive cancers treated by transurethral resection, and p-Akt was an independent factor in multivariate analysis. High expression of p-mTOR and p-Akt correlated with higher cumulative incidence of cancer-specific mortality for muscle-invasive cancer, and p-mTOR was an independent prognostic factor.

CONCLUSIONS

We have demonstrated the impact of PI3K/Akt/mTOR alteration on the biological behaviour of bladder tumours. Proper immunohistochemical examination of the PI3K/Akt/mTOR pathway can provide useful prognostic information, and the findings may represent an additional therapeutic avenue in the treatment of bladder cancers.

The effect of a novel frizzled 8-related antiproliferative factor on in vitro carcinoma and melanoma cell proliferation and invasion

Antiproliferative factor (APF) is a potent frizzled protein 8-related sialoglycopeptide inhibitor of bladder epithelial cell proliferation that mediates its activity by binding to cytoskeletal associated protein 4 in the cell membrane. Synthetic asialylated APF (as-APF) (Galβ1-3GalNAcα-O-TVPAAVVVA) was previously shown to inhibit both normal bladder epithelial as well as T24 bladder carcinoma cell proliferation and heparin-binding epidermal growth factor-like growth factor (HB-EGF) production at low nanomolar concentrations, and an L: -pipecolic acid derivative (Galβ1-3GalNAcα-O-TV-pipecolic acid-AAVVVA) was also shown to inhibit normal bladder epithelial cell proliferation. To better determine their spectrum of activity, we measured the effects of these APF derivatives on the proliferation of cells derived from additional urologic carcinomas (bladder and kidney), non-urologic carcinomas (ovary, lung, colon, pancreas, and breast), and melanomas using a (3)H-thymidine incorporation assay. We also measured the effects of as-APF on cell HB-EGF and matrix metalloproteinase (MMP2) secretion plus cell invasion, using qRT-PCR, Western blot and an in vitro invasion assay. L: -pipecolic acid as-APF and/or as-APF significantly inhibited proliferation of each cell line in a dose-dependent manner with IC(50)'s in the nanomolar range, regardless of tissue origin, cell type (carcinoma vs. melanoma), or p53 or ras mutation status. as-APF also inhibited HB-EGF and MMP2 production plus in vitro invasion of tested bladder, kidney, breast, lung, and melanoma tumor cell lines, in a dose-dependent manner (IC(50) = 1-100 nM). Synthetic APF derivatives are potent inhibitors of urologic and non-urologic carcinoma plus melanoma cell proliferation, MMP2 production, and invasion, and may be useful for development as adjunctive antitumor therapy(ies).

Recent advances in anti-angiogenic therapy of cancer

Since angiogenesis is critical for tumor growth and metastasis, anti-angiogenic treatment is a highly promising therapeutic approach. Thus, for over last couple of decades, there has been a robust activity aimed towards the discovery of angiogenesis inhibitors. More than forty anti-angiogenic drugs are being tested in clinical trials all over the world. This review discusses agents that have approved by the FDA and are currently in use for treating patients either as single-agents or in combination with other chemotherapeutic agents.