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Differential effects of the oncogenic BRAF inhibitor PLX4032 (vemurafenib) and its progenitor PLX4720 on ABCB1
Purpose:
The clinically approved oncogenic BRAF inhibitor PLX4032 (vemurafenib) was shown to be a substrate of the ATP-binding cassette (ABC) transporter ABCB1. Here, we compared PLX4032 and its structurally closely related precursor compound PLX4720 for their interference with ABCB1 and the ABCB1-mediated compound transport using docking and cell culture experiments.
Methods:
For the docking study of PLX4032 and PLX4720 with ABCB1, we analysed binding of both compounds to mouse Abcb1a and to human ABCB1 using a homology model of human ABCB1 based on the 3D structure of Abcb1a. Naturally ABCB1 expressing cells including V600E BRAF-mutated and BRAF wild-type melanoma cells and cells transduced with a lentiviral vector encoding for ABCB1 were used as cell culture models. ABCB1 expression and function were studied by the use of fluorescent and cytotoxic ABCB1 substrates in combination with ABCB1 inhibitors.
Results:
Docking experiments predicted PLX4032 to interact stronger with ABCB1 than PLX4720. Experimental studies using different cellular models and structurally different ABCB1 substrates confirmed that PLX4032 interfered stronger with ABCB1 function than PLX4720. For example, PLX4032 (20 µM) induced a 4-fold enhanced rhodamine 123 accumulation compared to PLX4720 (20 µM) in ABCB1-transduced UKF-NB-3 cells and reduced the IC₅₀ for the cytotoxic ABCB1 substrate vincristine in this model by 21-fold in contrast to a 9-fold decrease induced by PLX4720.
Conclusions:
PLX4032 exerted stronger effects on ABCB1-mediated drug transport than PLX4720. This indicates that small changes in a molecule can substantially modify its interaction with ABCB1, a promiscuous transporter that transports structurally different compounds.
Insights
The BRAF inhibitor PLX4032 (vemurafenib) interacts more strongly with the ABCB1 transporter than its precursor PLX4720. This difference impacts drug transport, highlighting how molecular changes affect ABCB1 interactions.
Area of Science:
- Pharmacology
- Molecular Biology
- Biochemistry
Background:
- The ATP-binding cassette (ABC) transporter ABCB1 plays a crucial role in drug efflux, influencing the efficacy of various therapeutics.
- PLX4032 (vemurafenib), a clinically approved BRAF inhibitor, is known to be a substrate of ABCB1.
- Understanding the interaction between drug candidates and ABCB1 is vital for predicting drug response and overcoming resistance.
Purpose of the Study:
- To compare the interference of PLX4032 and its precursor PLX4720 with ABCB1.
- To investigate the impact of these compounds on ABCB1-mediated drug transport.
- To elucidate how structural modifications influence the interaction with the promiscuous ABCB1 transporter.
Main Methods:
- Docking studies were performed using homology models of human ABCB1 and mouse Abcb1a to predict binding interactions.
- Cell culture experiments utilized naturally ABCB1-expressing melanoma cells (BRAF-mutated and wild-type) and engineered cell lines overexpressing ABCB1.
- ABCB1 expression and function were assessed using fluorescent and cytotoxic substrates in conjunction with ABCB1 inhibitors.
Main Results:
- Docking simulations indicated stronger predicted binding of PLX4032 to ABCB1 compared to PLX4720.
- Experimental data confirmed that PLX4032 interfered more significantly with ABCB1 function across various cellular models.
- PLX4032 demonstrated a greater enhancement of rhodamine 123 accumulation and a more pronounced reduction in vincristine IC₅₀ in ABCB1-overexpressing cells compared to PLX4720.
Conclusions:
- PLX4032 exhibits a stronger inhibitory effect on ABCB1-mediated drug transport than PLX4720.
- Subtle molecular alterations can substantially alter a compound's interaction with the broadly specific ABCB1 transporter.
- These findings have implications for drug design and the management of therapies involving ABCB1 substrates.
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