ARF Confers a Context-Dependent Response to Chemotherapy in Muscle-Invasive Bladder Cancer.

Muscle-invasive bladder cancer (MIBC) generally responds poorly to treatment and tends to exhibit significant mortality. Here we show that expression of the tumor suppressor p14ARF (ARF) is upregulated in aggressive subtypes of MIBC. Accumulation of ARF in the nucleolus is associated with poor outcome and attenuated response to chemotherapy. In both genetically engineered mouse models and murine xenograft models of human MIBC, we demonstrate that tumors expressing ARF failed to respond to treatment with the platinum-based chemotherapy agent cisplatin. Resistance was mediated in part by the integrin-binding protein ITGB3BP (CENPR) and reflected ARF-dependent impairment of protein translation, which was exaggerated by drug treatment. Overall, our results highlight a context-dependent role for ARF in modulating the drug response of bladder cancer. Cancer Res; 77(4); 1035-46. ©2017 AACR.

The Role of the p53 Protein in Stem-Cell Biology and Epigenetic Regulation.

The p53 protein plays a passive and an active role in stem cells. The transcriptional activities of p53 for cell-cycle arrest and DNA repair are largely turned off in stem cells, but there is some indication that long-term stem-cell viability may require other p53-regulated functions. When p53 is activated in stem cells, it stops cell division and promotes the commitment to a differentiation pathway and the formation of progenitor cells. In the absence of any p53 activity, stem-cell replication continues and mistakes in the normal epigenetic pathway occur at a higher probability. In the presence of a functionally active p53 protein, epigenetic stability is enforced and stem-cell replication is regulated by commitment to differentiation. Over a lifetime of an organism, stem-cell clones compete in a tissue niche for Darwinian replicative advantages and in doing so accumulate mutations that permit stem-cell replication. Mutations in the p53 gene give stem cells this advantage, increase the clonal stem-cell population, and lower the age at which cancers can occur. Li-Fraumeni patients that inherit p53 mutations develop tumors in a tissue-type-specific fashion at younger ages. Throughout the life of a Li-Fraumeni patient, the tumor types that arise occur in tissues where stem cells are active and cell division is most rapid. Thus, p53 mutations that are inherited or occur during developmental life act in stem cells of the mesenchymal and epithelial lineages, whereas p53 mutations that occur in progenitor or differentiated (somatic) cells later in life function in tissues of endodermal origins, indicating that p53 may function differently in different developmental lineages.

The Role of p53 in Metabolic Regulation.

The metabolic changes that occur in a cancer cell have been studied for a few decades, but our appreciation of the complexity and importance of those changes is now being realized. The metabolic switch from oxidative phosphorylation to aerobic glycolysis provides intermediates for cell growth and division and is regulated by both oncogenes and tumor suppressor genes. The p53 tumor suppressor gene has long been shown to play key roles in responding to DNA damage, hypoxia, and oncogenic activation. However, now p53 has added the ability to mediate metabolic changes in cells through the regulation of energy metabolism and oxidative stress to its repertoire of activities. It is therefore the focus of this review to discuss the metabolic pathways regulated by p53 and their cooperation in controlling cancer cell metabolism.

The control of the metabolic switch in cancers by oncogenes and tumor suppressor genes.

Cells from some tumors use an altered metabolic pattern compared with that of normal differentiated adult cells in the body. Tumor cells take up much more glucose and mainly process it through aerobic glycolysis, producing large quantities of secreted lactate with a lower use of oxidative phosphorylation that would generate more adenosine triphosphate (ATP), water, and carbon dioxide. This is the Warburg effect, which provides substrates for cell growth and division and free energy (ATP) from enhanced glucose use. This metabolic switch places the emphasis on producing intermediates for cell growth and division, and it is regulated by both oncogenes and tumor suppressor genes in a number of key cancer-producing pathways. Blocking these metabolic pathways or restoring these altered pathways could lead to a new approach in cancer treatments.

Mouse models of human bladder cancer as a tool for drug discovery.

Muscle-invasive bladder cancer is a deadly condition in dire need of effective new treatments. This unit contains a description of mouse models suitable for the evaluation of potential new therapies. Included is a genetically engineered mouse model of bladder cancer generated by the delivery of an adenovirus expressing Cre recombinase into the bladder lumen. Also described is an orthotopic mouse model created by the instillation of human bladder tumor cells into the bladder lumen of immune deficient mice. Protocols are also provided on the use of these models for the preclinical evaluation of new chemical entities, with mTOR inhibitors shown as an example.

Intravesical delivery of rapamycin suppresses tumorigenesis in a mouse model of progressive bladder cancer.

Early-stage bladder cancer occurs as two distinct forms: namely, low-grade superficial disease and high-grade carcinoma in situ (CIS), which is the major precursor of muscle-invasive bladder cancer. Although the low-grade form is readily treatable, few, if any, effective treatments are currently available for preventing progression of nonmuscle-invasive CIS to invasive bladder cancer. Based on our previous findings that the mammalian target of Rapamycin (mTOR) signaling pathway is activated in muscle-invasive bladder cancer, but not superficial disease, we reasoned that suppression of this pathway might block cancer progression. To test this idea, we performed in vivo preclinical studies using a genetically engineered mouse model that we now show recapitulates progression from nonmuscle-invasive CIS to muscle-invasive bladder tumors. We find that delivery of Rapamycin, an mTOR inhibitor, subsequent to the occurrence of CIS effectively prevents progression to invasive bladder cancer. Furthermore, we show that intravesical delivery of Rapamycin directly into the bladder lumen is highly effective for suppressing bladder tumorigenesis. Thus, our findings show the potential therapeutic benefit of inhibiting mTOR signaling for treatment of patients at high risk of developing invasive bladder cancer. More broadly, our findings support a more widespread use of intravesical delivery of therapeutic agents for treatment of high-risk bladder cancer patients, and provide a mouse model for effective preclinical testing of potential novel agents.

Inactivation of p53 and Pten promotes invasive bladder cancer.

Although bladder cancer represents a serious health problem worldwide, relevant mouse models for investigating disease progression or therapeutic targets have been lacking. We show that combined deletion of p53 and Pten in bladder epithelium leads to invasive cancer in a novel mouse model. Inactivation of p53 and PTEN promotes tumorigenesis in human bladder cells and is correlated with poor survival in human tumors. Furthermore, the synergistic effects of p53 and Pten deletion are mediated by deregulation of mammalian target of rapamycin (mTOR) signaling, consistent with the ability of rapamycin to block bladder tumorigenesis in preclinical studies. Our integrated analyses of mouse and human bladder cancer provide a rationale for investigating mTOR inhibition for treatment of patients with invasive disease.