Comparative analysis of the phototoxicity induced by BRAF inhibitors and alleviation through antioxidants

Markus V Heppt,Bernhard Przybilla,Lars E French,Markus Reinholz,Benjamin M Clanner‐Engelshofen,Carola Berking,Enklajd Marsela,Anja Wessely,Claudia Kammerbauer

doi:10.1111/phpp.12520

Abstract

Small molecules tackling mutated BRAF (BRAFi) are an important mainstay of targeted therapy in a variety of cancers including melanoma. Albeit commonly reported as side effect, the phototoxic potential of many BRAFi is poorly characterized. In this study, we evaluated the phototoxicity of 17 distinct agents and investigated whether BRAFi-induced phototoxicity can be alleviated by antioxidants. The ultraviolet (UV) light absorbance of 17 BRAFi was determined. Their phototoxic potential was investigated independently with a reactive oxygen species (ROS) and the 3T3 neutral red uptake (NRU) assay in vitro. To test for a possible phototoxicity alleviation by antioxidants, vitamin C, vitamin E phosphate, trolox, and glutathione (GSH) were added to the 3T3 assay of selected inhibitors. The highest cumulative absorbance for both UVA and UVB was detected for vemurafenib. The formation of ROS was more pronounced for all compounds after irradiation with UVA than with UVB. In the 3T3 NRU assay, 8 agents were classified as phototoxic, including vemurafenib, dabrafenib, and encorafenib. There was a significant correlation between the formation of singlet oxygen (P=.026) and superoxide anion (P<.001) and the phototoxicity observed in the 3T3 NRU assay. The phototoxicity of vemurafenib was fully rescued in the 3T3 NRU assay after GSH was added at different concentrations. Our study confirms that most of the BRAF inhibitors exhibited a considerable phototoxic potential, predominantly after exposure to UVA. GSH may help treat and prevent the phototoxicity induced by vemurafenib.

Highlights

The identification of somatic mutations of the BRAF gene has paved the way for targeted therapy with small molecules in a variety of cancer entities in recent years.[1]
This cutaneous adverse event is well known for vemurafenib, while the phototoxic potential of dabrafenib and encorafenib is much lower in pivotal trials.[9,10,11,12,13]
In this study we comparatively evaluated the phototoxicity of 17 distinct BRAF inhibitors (BRAFi) or multikinase inhibitors and tested whether phototoxicity can be reduced by antioxidants in vitro

Summary

| INTRODUCTION

The identification of somatic mutations of the BRAF gene has paved the way for targeted therapy with small molecules in a variety of cancer entities in recent years.[1]. Smaller well‐binding structures are joined covalently to form a superiorly target‐binding drug candidate.[4] As a result, the BRAF inhibitors (BRAFi) vemurafenib and dabrafenib were developed and approved by the FDA for the treatment of metastatic or unresect‐ able melanoma in 2011 and 2013, respectively, showing substantial survival benefits compared with chemotherapy.[5,6] In 2018, a third inhibitor, encorafenib, has been approved in combination with the MEK inhibitor binimetinib.[7] All substances selectively bind to and inhibit the active‐state BRAF kinase, with most BRAFi sharing com‐ mon structural motifs: the A ring binding in the nucleobase‐binding pocket, the B ring as a sterically important stiff core, the BC linker (salt bridge linker) for ionic interactions, and the lipophilic C ring.[8] As the A ring resembles the aromatic, bicyclic adenine‐moiety of the native substrate ATP, most inhibitors rely on a mono‐ or bicyclic, heavily substituted aromatic structure for strong binding charac‐ teristics For this reason, most inhibitors exhibit strong UVA absor‐ bance which is a prerequisite for UVA‐induced phototoxicity. In this study we comparatively evaluated the phototoxicity of 17 distinct BRAFi or multikinase inhibitors and tested whether phototoxicity can be reduced by antioxidants in vitro

| MATERIALS AND METHODS

| DISCUSSION

Findings

CONFLICT OF INTEREST