The Effect of Bromo-domain Inhibitors on the Development of Resistance to Dasatinib by Cancer Cells

Undergraduate #22
Discipline: Biological Sciences
Subcategory: Cancer Research

De'Ajree Branch - North Carolina Central University
Co-Author(s): John Scott and Syed Ahmed, North Carolina Central University

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Triple negative breast cancer (TNBC) cell is an aggressive type of breast cancer which has a lower five-year survival rate compared to other breast cancers. TNBC cells are generally sensitive to traditional anti-cancer drugs, but they quickly gain resistance. In vitro, TNBC cell lines are sensitive to the kinase inhibitor drug dasatinib, but this drug does not kill cells, it just inhibits cell proliferation. However, dasatinib has failed to show efficacy in a human clinical trial. We have observed that TNBC cell lines rapidly acquire resistance to dasatinib, in vitro. Our hypothesis is that rapidly acquired resistance to dasatinib by TNBC cell lines can be prevented by co-treatment with bromodomain inhibitors. Bromo-domains are small protein domains that bind monoacetylated lysine residues and regulate gene transcription. Small molecule inhibitors have been developed to bind to this domain and inhibit transcription of genes, including those that promote cancer. Recently, it was reported that bromo-domain inhibitors could inhibit the ability of breast cancer cell lines to adapt and grow in the presence of the kinase inhibitor drug lapatinib. Thus, we will determine whether the bromo-domain inhibitor I-BET151 can prevent acquired resistance to dasatinib using the TNBC cell line HCC-1806. We will use resazurin-based cell viability/proliferation assays to establish cytotoxicity of bromo-domain inhibitors on the TNBC cell line HCC-1806. In order to validate this assay, we plated a dilution series of cells into a 96-well plate and the next day measured the fluorescence after addition of resazurin. We have validated that this resazurin assay yields a fluorescence signal that is proportional to the number of viable cells plated. Using this assay, I-BET151 had no cytotoxicity up to the highest concentration tested (10 µM). Thus, we use 10 µM I-BET151 for the combination studies. For measuring outgrowth of dasatinib resistance, we grow cells in petri dishes in the presence of 300 nM dasatinib or the bromo-domain inhibitor I-BET151 or the combination of both of them. We follow cell proliferation for 14 days by counting viable cells with an automated cell counter. In the future, we will use other bromo-domain inhibitors and other cell lines to verify our results.

Funder Acknowledgement(s): This study was supported, in part, by a grant from the NSF awarded to De’Ajree Branch undergraduate, performing research in the Biomanufacturing Research Institute and Technology Enterprise (BRITE) building; North Carolina Central University, Durham, NCCU 27707.

Faculty Advisor: John Scott,