# BCL-xL as a therapeutic target in cetuximab-refractory colorectal cancer

## TL;DR

This study explores BCL-xL as a new treatment target for colorectal cancer that has become resistant to cetuximab, showing promising results in triggering cancer cell death.

## Contribution

The study identifies BCL-xL inhibition as a novel therapeutic strategy for cetuximab-refractory colorectal cancer.

## Key findings

- Resistant CRC cells showed increased susceptibility to BH3-mimetics targeting MCL-1 and BCL-xL.
- BCL-xL inhibition triggered apoptosis in heterogeneous PDX tumor models, including those with BRAF mutations.
- Findings were validated in organotypic CRC slice cultures from cetuximab-resistant patient-derived xenografts.

## Abstract

Despite recent medical advances, colorectal cancer (CRC) remains the second-leading cause of cancer-related death worldwide. For patients with KRAS wild-type metastatic CRC, the monoclonal antibody cetuximab, which targets the epidermal growth factor receptor (EGFR), is an approved treatment option. However, therapeutic success is often limited by the emergence of drug-resistant cancer cell populations within a few months. Therefore, alternative strategies to effectively target cetuximab-refractory CRC are urgently needed. Here, we sought to identify second-line therapeutic strategies using a CRC cell line with acquired cetuximab resistance as a model. Transcriptomic profiling of the resistant cells identified the apoptosis pathway as a potential therapeutic target, which was supported by their increased susceptibility to BH3-mimetics targeting the anti-apoptotic proteins MCL-1 and BCL-xL under both 2D and 3D culture conditions. These findings were validated in organotypic CRC slice cultures generated from cetuximab-resistant patient-derived xenografts (PDXs). Multiplex immunofluorescence staining demonstrated that BCL-xL inhibition effectively triggered apoptosis in heterogeneous PDX tumor slice models, including models harboring oncogenic BRAF mutations. Our findings suggest that cetuximab-resistant CRC retains apoptotic competence, and that BCL-xL inhibition serves as a robust alternative therapeutic strategy that is largely independent of the tumor mutational profile.