Inhibition of the BMP pathway suppresses tumor growth via downregulation of EGFR in MEK/ERK-dependent colorectal cancer

The bone morphogenetic protein (BMP) pathway promotes differentiation and induces apoptosis in normal colorectal epithelial cells. However, the effect of the BMP pathway in colorectal cancer (CRC) is controversial; it can either be tumor promoting or tumor suppressing, depending on the study. In this study, we found that CRC cells reside in a BMP-rich environment based on RNA-sequencing database analysis. Suppression of BMP using a specific BMP inhibitor, LDN193189, suppresses the growth of organoids in some CRC cases. CRC organoids treated with LDN193189 exhibited a decrease in epidermal growth factor receptor, which was, at least in part, mediated by protein degradation induced by leucine-rich repeats and immunoglobulin-like domains protein 1 (LRIG1). Among CRC organoid panels from 18 different patients, suppression of organoid growth by BMP inhibition correlated with the induction of LRIG1 gene expression. Notably, knockdown of LRIG1 in organoids diminished the growth-suppressive effect of LDN193189. Furthermore, simultaneous treatment with LDN192189 and trametinib, an FDA-approved MEK inhibitor, resulted in a combination effect in both in vivo and in vitro xenograft tumor treatment in CRC organoids, which are susceptible to growth suppression by LDN193189. Taken together, the simultaneous inhibition of BMP and MEK can be a novel treatment option in CRC cases, and evaluating in vitro growth suppression and LRIG1 induction by BMP inhibition using patient-derived organoids could offer functional biomarkers for predicting potential responders.