p97 as a Therapeutic Target in Breast Cancer Metastasis

Institution: Proteomics Research Institute for Systems Medicine
Investigator(s): Martin Latterich, Ph.D. -
Award Cycle: 2010 (Cycle 16) Grant #: 16IB-0104 Award: $292,500
Award Type: IDEA
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease

Initial Award Abstract (2010)

The AAA protein family ("Triple A", ATPases Associated with various cellular Activities) is widespread through evolution, but a fairly recent discovery in terms of cancer biology. One member of this family, called p97 (also called VCP for valosin-containing protein), is key in many cellular protein degradation and protein remodeling pathways. When mutated, p97 causes hereditary diseases that lead to muscle, bone and brain wasting. The mechanism for this pathological process is unknown, although preliminary data from our work and that of others suggest an apoptotic (programmed cell death) mechanism. When expressed in abundance, p97 can prevent apoptosis. Recent clinical studies have demonstrated that p97 over expression is a hallmark for the most aggressive metastatic breast cancers with poor prognosis.

In this project we will generate a mouse tumor model of metastatic breast cancer that allows us to test if p97 over expression is sufficient and necessary to “drive” breast cancer cells towards metastasis, and if ablation of p97 function alone can prevent breast cancer from metastasizing. Specifically, we will generate a breast cancer mouse model with fluorescently-tagged tumor spheroids that enable us to readily detect secondary tumors in other tissues. Additionally, we will use constitutive and inducible inhibitory RNA (shRNA) approaches to ablate p97 function in tumor cells and subsequently analyze the tumor cells’ potential to form secondary tumors.

If our hypothesis connecting p97 as supportive of tumor metastasis, then we expect that genetic or chemical ablation of p97 function will prevent metastatic cells from leaving the primary tumor, or from implanting into target organs. This will lay the groundwork for identifying a novel mechanism whose interference by general or targeted drugs could prevent breast cancer from metastasizing and reduce morbidity.

Final Report (2012)

One of the prominent biomarkers for metastatic breast cancer is an enzyme called p97 or VCP for Valosin Containing Protein. The protein is expressed over one hundred-fold in breast cancer metastases, irrespective of their location when compared to healthy cells. Since p97/VCP is essential for cell growth and survival, we predicted that having more of the protein would fuel uncontrollable cellular growth. Our laboratory has shown previously that mild perturbation of p97/VCP results in cells dying, while over expression potentiates their rapid growth. We therefore proposed to test if partial inactivation of p97 would prevent tumor growth and metastatic spread to other organs. In an unrelated study we showed that p97 functions in conjunction with different adapters, some which are required for cell growth, others in unrelated functions.

We therefore decided to combine our original hypothesis to test if p97 ablation can abolish metastatic stead of breast cancer in a mouse model, together with our recent findings about the importance of these adapter molecules. In this study, we tested if p97 and its 23 known adapter molecules, when ablated through inducible shRNA vectors, can prevent breast cancer metastasis.

We succeeded in generating a mouse model for breast cancer that allowed us to monitor tumor growth as well as eventual metastatic spread of the tumor. We were also successful in generating constructs to suppress p97 function in tumor cells to analyze their potential to form secondary tumors. When lenti-viral based vector systems were directly injected into tumors in a flank model of breast cancer, we discovered that a single injection of virus was able to rapidly and steadily reduce the tumor size, suggesting that suppression of the p97 and FAF1 gene products is essential for tumor growth. This unexpected finding has major ramifications for anti-cancer treatment, because our data suggests that the simple ablation of a branch at the p97 pathway will stop the otherwise aggressive tumor growth of N202 breast tumors. Our findings will be expanded upon to optimize a therapeutic intervention of breast cancer metastasis.

In vivo proteomic imaging analysis of caveolae reveals pumping system to penetrate solid tumors
Periodical:Nature Medicine
Index Medicus: Nat Med
Authors: Oh P, Testa JE, Borgstrom P, Witkiewicz H, Li Y, Schnitzer JE
Yr: 2014 Vol: 20 Nbr: Abs: Pg:1062-1068