Our laboratory has a longstanding interest in understanding the relationship between the processes that control normal development and those that go awry in cancer (Abate-Shen, C., et al., 2002). Over the years, our laboratory has taken a multidisciplinary approach to investigating mechanisms of cancer initiation and progression using in vivo mouse models. We have generated unique genetically engineered mouse (GEM) models that have provided novel insights into mechanisms of tumorigenesis as well as valuable preclinical models for analysis of new approaches for treatment (Kobayashi, T., et al., 2014) and prevention (Le Magnen, C., et al., 2015) .
Our major research focus has been on prostate and bladder cancer, which are highly complementary genitourinary malignancies. (See our prostate cancer review and bladder cancer review.) In particular, the prostate and bladder have similar embryological origins from the primitive urogenital sinus and both have a high propensity to develop cancer. Notably, the vast majority of prostate and bladder cancers are relatively indolent, and either require no intervention or can be effectively treated; however, prostate and bladder cancers that progress to advanced disease are highly heterogeneous, complicating their treatment. Moreover, most prostate and bladder cancer deaths occur from metastasis, which has eluded effective therapies. Our research interests are therefore focused on elucidating essential “drivers” (i.e., the master regulators) of specific cancer phenotypes, particularly drivers that distinguish pre-malignant and malignant disease, affect drug response and drug resistance, promote metastasis, and define distinct cancer subtypes.
Modeling indolent prostate cancer in mice
Nowadays, many newly diagnosed cases of prostate cancer are low-grade and unlikely to become lethal. Some, however, will eventually grow and spread through the body with deadly consequences. Currently it is difficult to distinguish the few aggressive tumors from the many indolent ones, particularly at early clinical stages of disease when they might be treated effectively. For these reasons we have been using genetically engineered mouse models to decipher mechanisms of cancer initiation and to identify biomarkers that distinguish cancer subtypes at early stages, based on whether they will or will not progress to cancer.
Nearly two decades ago, in collaboration with Michael Shen, we identified the Nkx3.1 homeobox gene as the earliest known marker of prostate epithelial differentiation. We also showed that its loss of function in mutant mice leads to defects in prostate development and predisposes to prostate cancer (Bhatia-Guar, R., et al., 1999). Over the years, our analyses of these Nkx3.1 mutant mice have provided key insights regarding the relationship between differentiation and cancer initiation.
In particular, we have found that Nkx3.1 is sufficient for prostate epithelial differentiation, while its inactivation leads to increased susceptibility to oxidative damage and promotion of cellular senescence (Ouyang, X., et al., 2005). Michael Shen’s group, in collaboration with us, found that Nkx3.1 marks a rare population of luminal prostate stem cells, which can serve as a cell of origin for prostate cancer (Wang, X., et al., 2009). In our current studies, we are investigating mechanisms of cancer initiation resulting from Nkx3.1 loss-of-function, as well as the role of the tumor microenvironment in mediating these effects. In particular, our recent publication has shown that forced expression of Nkx3.1 causes semical vesicle epithelium to differentiate into prostate. Nkx3.1 regulates the expression of a gene program associated with prostate differentiation by interacting with the G9a histone methyltransferase. (Dutta, A et al., 2016)
Recently, our analysis of Nkx3.1 mutant mice as a model of indolent prostate cancer provided the foundation for a cross-species computational analysis in which we identified a three-gene biomarker panel that distinguishes indolent from aggressive prostate cancer (Irshad, S., et al., 2013). We are currently developing this three-gene panel as prognostic biomarkers for clinical applications in early stage prostate cancer.
Modeling advanced stages of prostate cancer in mice
While most men diagnosed with early stage prostate cancers are now essentially curable, the prognosis for men with advanced prostate cancer is much more tenuous. Advanced prostate cancer is often associated with a transition to a castration-resistant form of the disease that is highly aggressive, usually metastatic, and often fatal (Shen, M. M., and Abate-Shen, C., 2010).
In collaboration with Michael Shen’s group, we have generated a new series of GEM models based on inducible deletion of key tumor suppressors or inducible activation of key oncogenes specifically in the prostate epithelium (Wang, J., et al., 2012; Floc'h, N. and Abate-Shen, C., 2012; Aytes, A., et al., 2013). These models recapitulate the various stages of advanced prostate cancer, including castration resistance and lethal metastasis.
Most of our GEM models of advanced prostate cancer incorporate loss of function of Pten, which we have shown to be essential for castration resistance (Goa, H., et al., 2006). We have also shown that combinatorial activation of the PI3-kinase/Akt/mTOR and Raf/MEK/Erk MAP kinase signaling pathways is prevalent in advanced prostate cancer progression (Goa, H., et al., 2006) (Aytes, A., et al., 2013). Subsequent preclinical analyses of these GEM models demonstrated the efficacy of combinatorial targeting of these signaling pathways for treatment of advanced prostate cancer (Kinkade, C. W., et al., 2008) (Floc’h, N., et al., 2012). In our current studies, we are evaluating the efficacy of targeting these pathways in combination with agents that target androgen receptor signaling for treatment of castration-resistant prostate cancer. These efforts should also help us to better understand mechanisms of resistance.
We have also been developing GEM models of metastatic prostate cancer, including a mouse model that combines inactivation of Pten with activation of Kras. The model displays a fully penetrant metastatic prostate cancer phenotype and shares molecular features in common with lethal prostate cancer in humans (Aytes, A., et al., 2013). Lineage-tracing analyses of metastases in this GEM model in vivo, combined with molecular investigations, led to the identification of the ETS gene, ETV4, as an essential gene for metastasis in the mice that is also conserved in human prostate cancer. In our current studies we have been elucidating drivers of prostate cancer metastasis, particularly those that are potential targets for therapeutic intervention and those that direct metastasis to bone.
Another major focus of our current research has been on applying systems biology approaches to effectively integrate molecular insights from our GEM models into the study of human cancer. In collaboration with the laboratories of Andrea Califano and Michael Shen, we have generated “interactomes” (or regulatory networks) for both mouse and human prostate cancer, using them to pursue cross-species analyses. These studies have led to the identification of synergistic regulators of advanced prostate cancer that are robust biomarkers of its most aggressive subtype (Aytes, A., et al., 2014). Additionally, we are using these interactomes to integrate analyses of drug response in GEM models into the study of human cancer, with the ultimate goal of “personalizing” treatment for more effective therapeutic management of the disease (Mitrofanova, A., et al., 2015).
Modeling invasive bladder cancer in mice
Bladder cancer is a critical problem for human health, as it is the fifth most common cancer occurring worldwide and a major cause of morbidity and mortality. While superficial bladder tumors, which account for ~80% of bladder neoplasms, have good clinical outcome, the remaining ~20% develop into invasive disease with high mortality rates. Few effective treatment options exist for invasive bladder cancer, and currently available strategies have only modestly improved survival over the past 20 years. Nevertheless, despite its significant clinical relevance, the molecular biology of bladder cancer has been relatively understudied. This is due in part to challenges in creating mouse models of the disease (Kobayashi, T., et al., 2015).
To address this problem, our laboratory developed a method for achieving gene recombination specifically in the mouse bladder urothelium that involves introducing an adenovirus-expressing Cre recombinase into the bladder lumen. Using this approach, we showed that the combined loss of function of p53 and Pten leads to invasive bladder tumors that share histological and molecular features of human bladder cancer. This is because pathways associated with loss/mutation of p53 and Pten are often deregulated in human bladder cancer (Puzio-Kuter, A. M., et al., 2009).
Our laboratory also found that the mTOR signaling pathway is activated in muscle invasive bladder cancer, and consequently that intravesical delivery of Rapamycin directly into the bladder lumen is an effective treatment for invasive bladder cancer (Seager, C. M., et al., 2009). These findings demonstrate the potential therapeutic benefit of inhibiting mTOR signaling for treatment of patients at high risk for developing invasive bladder cancer and support a more widespread use of intravesical delivery of therapeutic agents for treatment of high-risk bladder cancer patients (Delto, J. C., et al., 2013).
In our current work, we are developing new approaches for generating more refined mouse models of muscle invasive bladder cancer and investigating treatment responses in our existing models. These efforts have led to new insights into drug response and resistance.