Page 68 - SRPSKO DRUŠTVO ISTRAŽIVAČA RAKA

Serbian Association for Cancer Research SDIRSACR

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Multidrug resistance – poly-specific drug recognition by ABC transporters

Katalin Goda , Kuljeet Singh , Vikas Patel , Nimrah Ghaffar , Rajesh Patil , Tamás Hegedűs 3
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1 Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary
2 Sinhgad Technical Education Society’s Sinhgad College of Pharmacy, Department of Pharmaceutical Chemistry, OffSinhgad Road,
Vadgaon (Bk), Pune 411041, Maharashtra, India
3 Department of Biophysics and Radiation Biology, Semmelweis University, 1085 Budapest, Hungary
Keywords: ATP-Binding Cassette (ABC) transporters; multidrug resistance; P-glycoprotein (Pgp; ABCB1)

ABC transporters such as ABCB1 and ABCG2 are active exporter proteins expressed in the plasma membrane of cells
forming biological barriers. In accordance with their broad substrate spectrum and tissue expression pattern, they
affect the pharmacokinetics of numerous chemotherapeutic drugs and they may be involved in unwanted drug-drug
interactions leading to side effects or toxicities. When expressed in tumor tissues, they contribute to the development
of chemotherapy resistance in malignancies. Therefore, the understanding of the molecular details of the ligand-
ABC transporter interactions is of crucial importance. In our previous studies we identified numerous compounds of
diverse origin and chemical nature as ABCB1 substrates or inhibitors using ATPase activity measurements, transport
assays, and exploiting the UIC2 conformation-selective monoclonal antibody (mAb), that recognizes the inward-facing
(IF) conformer of ABCB1. Our measurements demonstrated that the most potent transport inhibitors strongly inhibit
ATPase activity and stabilize ABCB1 in the UIC2-reactive IF conformation. In a recent study, we analyzed the interaction
of numerous polyphenols with ABCB1. We found that quercetin (QUR) hampers both the transport and ATPase activity
of ABCB1, while cyandin-3O-sophroside (C3S) stimulates the ATPase activity and causes only a weak inhibition of
substrate transport. When QUR and C3S were applied together, both a stronger ATPase inhibition and a robust decrease
in substrate transport were observed, supporting their synergistic ABCB1 inhibitory effect. Similar to cyclosporine A, a
potent ABCB1 inhibitor, co-treatment with QUR and C3S shifted the conformational equilibrium to the IF conformer of
ABCB1. To gain deeper insight into the molecular details of ligand-ABCB1 interactions, molecular docking experiments
and MD simulations were also carried out. Our in silico studies confirmed that QUR and C3S can bind simultaneously
to the substrate-binding pocket of ABCB1. The C3S-QUR combination formed a larger number of hydrogen bonds with
higher occupancy involving the amino acid side chains of the substrate-binding pocket compared to the simultaneous
binding of two QUR molecules, thereby contributing to the conformational stabilization and stronger inhibition of
ABCB1.

Acknowledgments and funding: The authors acknowledge the computational resources made available on the GPU
cluster Komondor (Governmental Information-Technology Development Agency, Hungary)
The work was supported by the University of Debrecen “Program for Scientific Publication” and the Hungarian National
Science and Research Foundation (OTKA) grant K124815 and GINOP-2.2.1-15-2017-00079.

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Eliminating Oral Cancer Stem Cells by Targeting Oncogenic miR-21 and BET-Mediated Transcription

Milos Lazarevic , Milica Jaksic Karisik , Dijana Mitic , Jelena Milasin 1
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1 University of Belgrade, School of Dental Medicine, Department of Human Genetics, Belgrade
Keywords: Cancer stem cells; Epigenetics; Oral cancer; microRNA.

Background: Oral squamous cell carcinoma (OSCC) remains the most widespread and aggressive form of head and
neck cancer, with cancer stem cells (CSCs)—identified by CD44 expression—contributing significantly to its progression,
therapeutic resistance, and recurrence. MicroRNA-21 (miR-21), a well-characterized oncogenic microRNA (miR), is
implicated in promoting chemoresistance and poor patient prognosis across multiple tumor types.
Material and Methods: In this study, we explored the impact of miR-21 suppression on CD44+ CSCs in the context
of treatment with the BET bromodomain inhibitor JQ1. CD44+ subpopulations were isolated from OSCC cell lines,

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