Nur77-derived Peptides as a Novel Breast Cancer Therapy

Institution: The Burnham Institute for Medical Research
Investigator(s): Xiao-Kun Zhang, Ph.D. -
Award Cycle: 2006 (Cycle 12) Grant #: 12IB-0168 Award: $286,108
Award Type: IDEA
Research Priorities
Detection, Prognosis and Treatment>Innovative Treatment Modalities: search for a cure

Initial Award Abstract (2006)
A sizeable fraction of cellular machinery is devoted to cell growth or death and its tight control. Drug resistance, which is often responsible for death from breast cancer, results as these controls break down and breast cancer cells proliferate. Bcl-2, a protein gatekeeper of cell death pathways (apoptosis), protects cells from death signals including cancer drugs and gamma-irradiation. Since Bcl-2 is abnormally elevated in the majority of breast cancers, it has come under intensive study and methods have been developed to inhibit its role as gatekeeper. Our laboratory recently discovered a new approach to Bcl-2, based on a protein called Nur77 that moves from the nucleus to mitochondria where it binds Bcl-2. The binding not only inhibits the cancer protective effect of Bcl-2 but also amazingly converts Bcl-2 to a killer of cancer cells. Our discovery thus raised the exciting possibility that the elevated levels of Bcl-2 in breast cancer cells could be turned to advantage by converting Bcl-2 from a protector to a killer of breast cancer cells. To pursue this, we cut back Nur77 to identify a tiny fragment of 9 amino acids, called a peptide, which binds Bcl-2 and induces Bcl-2-dependent death of breast cancer cells in an animal model. This peptide, called Nur77-derived Bcl-2 converting peptide (NuBCP), is the first of a new class of therapeutic lead compounds that can kill breast cancers that are protected from treatment by Bcl-2.

We propose to modify the Nur77 peptide to improve its stability, specificity and efficacy. To improve the therapeutic profile of Nur77 peptide, we plan to link it to various cell penetrating peptides and evaluate their tolerability, toxicity, and pharmacokinetic properties in mice. We will also determine in cell-based and in vitro assays whether NuBCP can work in synergy with taxanes. Finally we will use a mouse breast cancer tumor model to determine the anti-tumor efficacy of the improved Nur77 peptides alone and in combination with taxanes where synergy is anticipated.

Our discovery that the Nur77-Bcl-2 pathway kills cancer cells by converting Bcl-2 protein from a protector to a killer is novel. Our identification of a short Nur77 peptide (NuBCP), which mimics the death effect of Nur77 protein, is the first of an important new class of therapeutics designed to kill drug resistant cancer cells. Our proposed studies have a significant potential for rapid translation to the clinic.

Final Report (2009)
It is well know that cancer cells become dangerous when they grow out of control, start spreading and develop resistance to cancer drugs and y-irradiation. This is often associated with their resistance to cell death. Not surprisingly, the cell death machinery is kept under tight control but kicks in when cells become cancerous or no longer needed. At the center of the cell death machinery is a protein call BcI-2 that acts as a powerful brake. However, Bcl-2 is often elevated in breast cancer cells, keeping these dysfunctional cells alive as well as protecting them from cancer drugs and y-irradiation. Thus pharmaceutical companies have been working to develop small molecule drugs to inhibit this anti-death protein. However, recent discoveries in our laboratory have identified another process that is capable of converting Bcl-2 from a protector to a killer of cancer cells. Thus we identified another protein, Nur77, which can be stimulated to convert Bcl-2 to a killer. Proteins, however, are large and unsuitable for use as drugs since they can not generally get past cell membranes. Thus we proposed to identify the active region of this protein for mimicry with small corresponding protein fragments or peptides, which are often forerunners of small molecule drugs. It was our hope that by identifying a peptide Bcl-2 converter it would initiate a new strategy for designing breast cancer drug. Since Bcl-2 is elevated in breast cancer cells compared with normal cells, we also hoped that breast cancer cells would be more sensitive to killing by a Bcl-2 converter than normal cells with far lower Bcl-2 levels.

With the support of the California Breast Cancer Research Program (CBCRP), we have successfully identified a 9 amino acid Nur77-based Bcl-2 converting peptide (NuBCP-9) that converts Bcl-2 from a protector to a killer of breast cancer cells, in a similar manner as the parent protein, Nur77. NuBCP-9 killing also proved to be Bc1-2-dependent and normal cells were unaffected. In addition, we showed that NuBCP-9 was active against breast cancer tumors grown in animals. Our effort in improving the pharmacological profile of NuBCP-9 led to our identification of NuBCP-9 enantiomer (a structural mirror image), which is more stable and active than NuBCP-9. Our discovery thus raises the possibility that small molecule Bcl-2 converters can eventually be identified for treating resistant breast cancer characterized by high Bcl-2 levels. Our mechanistic studies demonstrated that NuBCP-9 and its enantiomer bind to the unstructured loop domain of Bcl-2, revealing a new protein-protein interaction site in Bcl-2. This finding provides new approaches to regulate Bcl-2 function and NuBCP-9 activity. Thus, our results provide new mechanistic insights into the function of Bcl-2 and its regulation and new therapeutic strategies for developing Bcl-2-based agents for breast cancer therapy.

Our CBCRP supported discovery was published as a featured article in Cancer Cell. The potential significance of the discovery for the development of a new class of breast cancer drugs was immediately recognized and highlighted in several high profile scientific journals including Nature Biotechnology, Nature Reviews Drug Discovery, Nature Chemical Biology and SciBX, a new Nature associated journal targeted to the pharmaceutical industry. We are currently pursuing efforts to improve the efficacy of NuBCP-9 and to identify small molecule Bcl-2 converters.

Targeting Nur77 translocation
Periodical:Expert Opinion on Therapeutic Targets
Index Medicus: Expert Opin Ther Targets
Authors: Zhang XK
Yr: 2007 Vol: 11 Nbr: 1 Abs: Pg:69-79

p53 and Nur77/TR3 - transcription factors that directly target mitochondria for cell death induction.
Index Medicus: Oncogene
Authors: Moll UM, Marchenko N, Zhang XK
Yr: 2006 Vol: 25 Nbr: 34 Abs: Pg:4725-43

RXR agonists inhibit high-glucose-induced oxidative stress by repressing PKC activity in human endothelial cells.
Periodical:Free Radical Biology and Medicine
Index Medicus: Free Radic Biol Med
Authors: Chai D, Wang B, Shen L, Pu J, Zhang XK, He B
Yr: 2008 Vol: 44 Nbr: 7 Abs: Pg:1334-47

A short Nur77-derived peptide converts Bcl-2 from a protector to a killer
Periodical:Cancer Cell
Index Medicus:
Authors: Kolluri SK, et al, and Zhang XK
Yr: 2008 Vol: 14 Nbr: 4 Abs: Pg:285-98

Modulation of orphan nuclear receptor Nur77-mediated apoptotic pathway by acetylshikonin and analogues.
Periodical:Cancer Research
Index Medicus: Cancer Res
Authors: Liu J, et al, and Zhang XK, Zeng JZ
Yr: 2008 Vol: 68 Nbr: 21 Abs: Pg:8871-80