Presentations

Abstract

Introduction: There is increasing evidence demonstrating that breast cancer tumorigenesis is initiated in breast-cancer stem cells (CSC). These early progenitor cells demonstrate both a self-renewal capability as well as Epithelial to Mesenchymal transition (EMT), which is a large contributor to metastasis and poor prognosis. The stem cell marker Doublecortin-like kinase 1 (DCLK-1) is a microtubule associated protein-kinase functioning in EMT that is upregulated in breast CSC and contains an extracellular domain that provides a target for highly specific homing sequences to directly target therapeutics to the breast CSC. Our lab created a homing peptide complementary to DCLK-1 that can act as a carrier for therapeutic agent to directly target breast cancer CSC. As DCLK-1 is expressed in other cell types, most notably neuronal cells, the carrier also has a highly specific cyclic nine-amino-acid breast homing peptide with the sequence CPGPEGAGC, referred to as PEGA homing peptide, known to home to breast cancer cells. The linear structures of DCLK-1 and PEGA will be combined into a single circular structure to act as the carrier that will be able carry therapeutics to target breast CSC and provide a more selective therapeutic option and maximal therapeutic potential. We propose that DCLK-1 homing sequence can act as a carrier to selectively deliver therapeutic agents directly to breast CSC.

Methods: i. To explore the potential use of DCLK-1 carrier peptide, we performed a binding assay on MCF-7, a tamoxifen sensitive line of breast cancer cells that is documented to have high expression of DCLK-1. Decreasing concentrations of DCLK-1 homing peptide tagged with the fluorophore tetramethyl rhodamine (TAMRA) will be added and fluorescence will be measured via the Synergy HT microplate reader. In addition, we will be using fluorescence microscopy to visualize the homing ability of DCLK-1 carrier to breast CSC. Breast cancer stem cells can be isolated and grown from their unique ability to proliferate while not adhered to the bottom of the plate. Thus, breast cancer stem cells will be grown on Polyhydroxyethylmethacrylate (pHEMA) coated plates to prevent adherence and allow the isolation of stem cells. To verify the stemness of the cell line, we used the fluorophore ALEXA (emission 488 nm) indirect antibody labeling using cancer stem cell marker CD 133 that will be visualized through fluorescence microscopy. Once stemness has been verified, DCLK-1 homing peptide linked to TAMRA (emission of 578 nm) will be allowed to bind with MCF-7 breast tissue cells to investigate DCLK-1 peptide homing potential and visualization will be done with fluorescence microscopy.

Results: The binding study indicates there is decreasing fluorescence as the concentration of the DCLK-1 homing peptide decreases. This result is in line with what we expected, as this indicates a directly proportional relationship in the concentration of DCLK-1 and fluorescence, demonstrating that DCLK-1 carrier peptide can bind with the extracellular DCLK-1 binding domain. Graphical analysis demonstrates two plateaus, corresponding to two binding sites due to the PEGA and DCLK-1 both binding to the target cells, providing increased selectivity of the drug to the breast cancer cells. The dissociation constant (Kd) values for the each of the plateaus are Kd 1 of 0.5x10-7 mM and Kd2 of 0.5x10-2 mM, and the small Kd values at each plateau indicating a high binding affinity of the DCLK-1 carrier peptide and PEGA carrier peptide directly to breast CSC. The antibody labeling of the MCF-7 breast cancer stem cells demonstrated bright green fluorescence on fluorescence microscopy, verifying the stemness of the MCF-7 stem cell culture. The fluorescence microscopy results of the DCLK-1 homing peptide linked to TAMRA demonstrated bright red fluorescence, indicating the successful binding of DCLK-1 homing peptide to the extracellular DCLK-1 binding domain upon MCF-7 stem cells. The verified the binding ability of DCLK-1 homing peptide to MCF-7 stem cells.

Conclusion: In this study, we were able to demonstrate the binding capability and selectiveness of the DCLK-1 homing peptide to the DCLK-1 extracellular domain present on breast cancer tissue and breast (CSC). Through the binding assay, we were able to demonstrate the binding ability and the high affinity of DCLK-1 and PEGA carriers to directly target breast CSC. Through the indirect antibody labeling and fluorescence microscopy, we were able to isolate breast CSC and demonstrate the binding ability of the DCLK-1 homing peptide specifically to breast CSC, indicating that DCLK-1 offers the opportunity to target early progenitor tumor cells and allow direct targeting of therapeutics to the cells that pose the greatest risk for tumorigenesis. This study demonstrated a great potential for the therapeutic use of these carrier proteins for the administration of therapeutics to directly target malignant cells and increase treatment options for breast cancer patients.