Abstract 4681: Functional correlation between cancer stem cells and algorithmic effectiveness of targeted drugs of RAS and PI3K pathways in TNBC
Authors: Aske Jennifer C. , De Pradip K. , Leyland-Jones Brian , Dey Nandini 
Published: August 2019

Background: Cancer stem cells (CSCs) are important for the initiation, metastasis, relapse, and chemo/radio-resistance of several tumors including BC (Polyak K et al., 2008, 2010). We reported a method to study a relationship between the characteristic pattern of CSCs (CD24L/CD44H/CD44v6) expression and the mutational status in PTEN-null MDA-MB468, HCC70; RAS/RAF mutated MDA-MB231; BRCA mutated/PTEN-null SUM149 & HCC1937; PIK3CA mutated BT20 TNBC cells. We also tested CD44/CD24 expression in the context of rational combinations of the PI3K-pathway inhibitors in subtype-specific BC (Carlson et al, AACR, 2016; SABCS 2016). Recently, we studied the role of genetic background in determining the effectiveness of the RAS and PI3K pathway(s) targeted drugs in TNBC by testing a combination of the MEK1/2 inhibitor with mTOR kinase inhibitor or AKT inhibitors (Carlson et al SABCS 2018 P2-03-11).

Hypothesis: This study was undertaken to identify the relationship between CSCs and effectiveness of RAS and PI3K pathway(s) targeted drugs in TNBC by testing a combination of the MEK1/2 inhibitor with mTOR kinase inhibitor or AKT inhibitors or PI3K inhibitors.

Methods: TNBC cell lines MDA-MB231, SUM149, MDA-MB468 and BT20 were used for the study. Proliferation (Incucyte) and apoptosis (AnnexinV) were tested following the drug treatment alone or in combination. Clonogenic growth (3D matrigel assay). WB was used to interogate signaling events in the context of proliferation and apoptosis. CSC subpopulations were monitored by flow cytometry following treatment in both 2D and 3D.

Results: The response to treatment with pathway targeted inhibitor is a function of the relative proportion of CSC and the mutational status of TNBC tumor cells. TNBC cells with higher numbers of CSC tend to be more resistant to PI3K inhibition. Rational drug combinations blocked proliferative signals and enhanced apoptosis (cleaved caspase3) as demonstrated by WB. Single agent treatments were mostly cytostatic and temporarily decreased proliferation, while a marked increase in AnnexinV was seen in doublet combinations. Cells with a higher CSC population demonstrated lower sensitivity to treatment in both 2D and 3D models and a smaller change in the CSC population was seen following 3D growth. The mechanistic details of the effect of this combination on the CD44H/CD24L stem cell populations are being worked out to delineate the relationship between CSC and drug response in TNBC models, the results of which will be presented in the meeting.

Significance: As CSCs are considered one of the targets for obtaining a better therapeutic response (Huang R, Rofstad EK, 2017) additionaly normal as well as neoplastic nonstem cells can spontaneously convert to a stem-like state (Chaffer CL et al., 2011), our study reveals the relationship between the effect of targeted therapy and stem cell population.

Citation Format: Jennifer C. Aske, Pradip K. De, Brian Leyland-Jones, Nandini Dey. Functional correlation between cancer stem cells and algorithmic effectiveness of targeted drugs of RAS and PI3K pathways in TNBC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4681.