Targeting Drug Resistant Breast Cancer by microRNAs

Institution: University of California, Los Angeles
Investigator(s): Hailiang Hu, Ph.D. -
Award Cycle: 2010 (Cycle 16) Grant #: 16IB-0016 Award: $100,000
Award Type: IDEA
Research Priorities
Detection, Prognosis and Treatment>Innovative Treatment Modalities: search for a cure

Initial Award Abstract (2010)

Endocrine therapy and radio/chemotherapy for local and metastatic breast cancers has significantly improved the survival rate of breast cancer patients. However, drug resistance developed from the two therapies limits their treatment efficiency and finally leads to patient death. The mechanisms underlying drug resistance (endocrine-resistance and/or radio/chemo-resistance) are remained to be fully defined. At the cellular level, breast cancer stem/initiating cells (BCSCs) are thought to be a major subpopulation that mediates the therapy resistance. At the molecular level, two important proteins, c-MYC and ATM, have been shown to be associated with the development of endocrine resistance and radio/chemo-resistance respectively.

The goal of this project is to establish the role of microRNA (miRNA) in regulating sensitivity of breast cancer cells, including BCSCs, to therapeutic drugs such as antiestrogen, doxorubicin and radiation. MiRNAs are short, regulatory ribonucleic acid (RNA) molecules, on average only 22 nucleotides in size. The human genome may encode >1000 miRNAs, which may target the majority of mammalian genes. This study derives from an exciting finding by the PI that miR-421 can suppress ATM expression (Proc Natl Acad Sci 2010; 107(4):1506-11). Further analysis reveals that another miRNA, miR-374b, is just 85bp upstream of miR-421 and forms a "miRNA cluster" (miR-374b/421). Our specific aim is to show that this miRNA cluster could suppress c-MYC and ATM expression concurrently in breast cancer cells. We will use breast cancer cells, including resistant breast cancer cells and BCSCs, as models to test the effects of miR-374b/421 on cell’s sensitivity to anti-estrogen, irradiation or doxorubicin by survival, cell death (apoptosis) and cell cycle (growth potential) analysis.

A long-term goal of our research is to develop new strategies to augment endocrine therapy or radio/chemotherapy and to modify the drug resistance. A significant proportion of breast cancer patients still develop resistance to these standard treatments, resulting in cancer-related death and treatment failure. In order to develop new strategies against drug resistance, we need to first understand the molecular mechanisms underlying the resistance.

Final Report (2012)

The development of drug resistance of breast cancer to a specific therapy, such as endocrine or radio/chemotherapy, limits their treatment efficiency and also underscores the importance of identifying new therapeutic agents against drug resistance. This undergoing project is to investigate the role of a miRNA cluster (miR-374b/miR-421) in drug resistance for breast cancer and would contribute to better understanding of the underlying molecular and cellular mechanisms. Given that c-MYC and ATM are involved in endocrine resistance and radio/chemo-resistance respectively, our project with the hypothesis that this miRNA cluster could overcome these resistances by suppressing c-MYC and ATM expression provides a unique opportunity to modulate two different therapy resistances at the same time.

To test this hypothesis, we pursued three specific aims:

  1. Examine the role of miR-374b- c-MYC pathway in breast cancer endocrine resistance;
  2. Evaluate the contribution of miR-421-mediated ATM suppression to radio/chemo-resistance of breast cancer cells;
  3. Test the miR-374b/421 cluster’s effects on the radio/chemosensitivity of breast cancer stem/initiation cells.

During the past year, we have made significant progress including:

  1. Demonstrated that miR-374b could suppress c-MYC expression by targeting its 3’UTR. Given that c-MYC is such an important oncogene, we expect this miR-374b-c-MYC pathway will play a critical role in cancer development and would provide a therapeutic target for c-MYC overexpression tumors and drug resistance.
  2. Shown that miR-421 can increase radio-sensitivity of breast cancer cells by downregulating ATM expression. This is an important indicator for miR-421 as a potential radiosensitizer for breast cancer treatment.
  3. Found that miR-421 was downregulated while ATM protein was upregulated in CD24-CD44+ cancer stem/initiation cells, suggestion of the contribution of the miR-421-ATM pathway to the radio/chemoresistance of cancer stem cells.
  4. More interestingly, identified a novel ATM-dependent double strand break (DSB) response mechanism through miRNAs, in which we showed that DSB-activated ATM downregulated miR-335 expression, which further modulated CtIP expression to regulate cell cycle checkpoints and DNA damage repair.

Our future plans include:

  1. Further characterize the miR-374b –c-MYC pathway in breast cancer. We will see whether miR-374b regulates cell cycle progression through c-MYC and miR-374b overexpression leads to the overcome of endocrine resistance for breast cancer cells.
  2. Examine the miR-421’s effect on the resistance of breast cancer stem/initiating cells. We will optimize the lentivirus of miR-421 infection into breast cancer stem cells and examine their effects on sensitivity of breast cancer stem cells to ionizing radiation.
  3. Continue the work of new finding and try to establish a novel ATM-dependent microRNA pathway to regulate DNA repair.

ATM-dependent MiR-335 targets CtIP and modulates the DNA damage response.
Periodical:PLoS Genetics
Index Medicus: PLoS Genet
Authors: Martin NT, Nakamura K, Davies R, Nahas SA, Brown C, Tunuguntla R, Gatti RA, Hu H.
Yr: 2013 Vol: Nbr: 5 Abs: Pg:

MicroRNAs: new players in the DNA damage response.
Periodical:Journal of Molecular Cell Biology
Index Medicus: J Mol Cell Biol
Authors: Hu H, Gatti RA
Yr: 2010 Vol: 3 Nbr: 3 Abs: Pg:151-8