Poster Presentation 37th Lorne Cancer Conference 2025

Low DUSP4 expression promotes resistance to encorafenib plus cetuximab in BRAF-mutant colorectal cancer (#219)

Kristen A Needham 1 , Fiona Chionh 1 2 , Stan Kaczmarczyk 1 , Conor Kearney 1 , Laura J Jenkins 1 , Ian Y Luk 1 , John M Mariadason 1
  1. Olivia Newton-John Cancer Research Institute, Heidelberg, VICTORIA, Australia
  2. Austin Hospital, Heidelberg, Melbourne, Victoria, Australia

The 5-year survival rate for metastatic colorectal cancer (CRC) is ~14%.  Approximately 5-10% of metastatic CRCs harbour BRAFV600E mutations, which carry an extremely poor prognosis.  BRAFV600E mutations hyperactivate the ERK pathway, which in turn drives tumour growth, survival and de-differentiation.  Use of the BRAF-inhibitor encorafenib in combination with the EGFR-inhibitor cetuximab is now approved for treatment of BRAFV600E CRC, however, the objective response rate is only 20%. Therefore, there is an urgent need to identify predictive biomarkers of response to encorafenib+cetuximab (E+C) treatment.

 

To investigate this, we interrogated RNAseq data from BRAFV600E CRC cell lines sensitive and resistant to E+C.  This analysis revealed significantly lower expression of Dual-specificity phosphatase 4 (DUSP4) in resistant lines.  DUSP4 acts as a critical negative regulator of ERK pathway signaling output by directly de-phosphorylating ERK.  Immunohistochemical staining of 639 CRC patient tumours revealed a wide range of DUSP4 expression, including in BRAF-mutant tumours.  However, whether DUSP4 expression status impacts response to E+C is unknown.  The aim of this study was to determine the role of DUSP4 in sensitivity of BRAF-mutant CRC cells to E+C treatment in vitro. 

 

We examined this using knock-down, knock-out and re-expression approaches.  As expected, siRNA-mediated knock-down of DUSP4 in sensitive BRAFV600E cells increased pERK and pFRA1 levels, indicative of ERK/MAPK signalling activation. DUSP4 knock-down in sensitive BRAFV600E cells also significantly reduced sensitivity to E+C. These findings were validated by deleting DUSP4 in sensitive BRAFV600E cells using CRISPR-Cas9.  Conversely, stable DUSP4 re-expression in a resistant BRAFV600E CRC cell line decreased pERK signaling, and increased sensitivity to E+C.

 

These results confirm that DUSP4 regulates ERK/MAPK signalling in BRAFV600E CRC cell lines, and that cell lines with low basal DUSP4 are inherently resistant to E+C. These findings warrant investigation of DUSP4 expression status as a predictive biomarker of E+C response in BRAFV600E CRC patients.