BBI-355 + erlotinib

BBI-355 + erlotinib is an experimental combination of two small molecule drugs: **BBI-355**, an orally available, selective checkpoint kinase 1 (CHK1) inhibitor developed as the first extrachromosomal DNA (ecDNA)-directed therapy (ecDTx) for cancers with oncogene amplifications, and **erlotinib**, a well-established epidermal growth factor receptor (EGFR) inhibitor. The combination targets solid tumors—particularly those with high copy number amplification of oncogenes such as EGFR—by exploiting the synthetic lethal vulnerability these tumors have to CHK1 inhibition due to increased DNA replication stress from ecDNA-mediated oncogene amplification. BBI-355 disrupts CHK1, a master regulator of DNA replication stress, while erlotinib blocks EGFR signaling; together, they are hypothesized to overcome rapid resistance associated with ecDNA-driven adaptation to single-agent targeted therapy. The combination is in phase 1/2 clinical development in the United States (NCT05827614)[1][2][3][7]. Recent company disclosures indicate that clinical development of this combination in its current trial arm has been discontinued due to tolerability issues at effective dose levels[4].