Analysis of the antibacterial mechanism of Farnesyltransferase inhibitors

Introduction

Farnesylation is a posttranslational modification, involving the attachment of a C15 isoprene unit (farnesyl) to proteins with a specific CAAX motif. Farnesylation enables over 200 proteins to bind to the membrane and fulfil their function in processes like cell growth, differentiation or apoptosis. The inhibition by farnesyltransferase inhibitors (FTI), such as lonafarnib or tipifarnib, came in focus for the treatment of various diseases, e.g. cancer. Furthermore, we demonstrated antibacterial effects of lonafarnib and tipifarnib in gram-positive bacteria such as S. aureus or S. epidermidis and even in the multi-resistant strain MRSA [1]. However, the underlying molecular mechanism remains elusive.

Material & Methods

We determined the minimal inhibitory concentration (MIC) as well as the physiological effective concentration (PEK) of lonafarnib and tipifarnib on B. subtilis. To analyse the effect of FTIs on the proteome, we performed high-resolution liquid chromatography followed by mass spectrometry analysis.

Results

In total, 1060 proteins were detected via mass spectrometric analysis. Treatment with tipifarnib resulted in the upregulation of 38 proteins in B. subtilis, whereas treatment with lonafarnib upregulated 89 proteins. 33 proteins were regulated by both FTI. Among the identified marker proteins, those involved in the biosynthesis and modification of cell wall components, such as DitE, YocH or PbpE, were particularly important. Additionally, marker proteins related to protein biosynthesis, general stress response, oxidative stress and various transport processes were detected.

Discussion

It is known that both lonafarnib as well as tipifarnib show antibacterial effects in different bacterial strains, however, the underlying mechanism remains elusive. Here, we could show that both lonafarnib and tipifarnib treatment resulted in a significant change in several proteins, whereas the treatment with lonafarnib led to a change in twice as many proteins as tipifarnib. Strikingly, many marker proteins were proteins involved in processes affecting the cell envelope. Therefore, we assume that the cell wall and cell membrane are the main targets for the FTI in B. subtilis.

[1] Weber et al. 2019 Front. Microbiol. 12, 628283