Abstract 53P
Background
Mutations of the KRAS and BRAF are the most frequent genetic alterations in colorectal cancer (CRC) and lead to the activation of the mitogen-activated protein kinase (MAPK) signaling pathway. CRC patients harboring KRAS or BRAF mutations have poor prognoses and show limited therapeutic effects to the drugs targeting those mutations. PHI-501 is a potent and highly selective dual inhibitor for pan-RAF and DDRs. In this study, we investigated the anti-tumor effect of PHI-501 as monotherapy and addressed the molecular mechanism underlying overcoming BRAF inhibitor resistance.
Methods
The growth inhibitory activity of PHI-501 was measured using the CCK-8 assay. The biochemical responses of cells were analyzed by western blot. BRAF inhibitor-resistant COLO205ER cells were established by long-term treatment of cells with encorafenib. In vivo anti-tumor activities of PHI-501 were evaluated in the HCT116, RKO, and COLO205ER mouse xenograft models.
Results
PHI-501 demonstrated potent anti-proliferation activity in drug-resistant COLO205ER cells as well as CRC cell lines harboring BRAF V600E or KRAS mutations. Western blot revealed that PHI-501 inhibited the phosphorylation of MEK, ERK, AKT, and SHP2 proteins in the downstream signaling of RAF/DDRs. PHI-501 monotherapy resulted in tumor regression superior to control groups in mice models with KRAS G13D HCT116, BRAF V600E RKO, and BRAF inhibitor-resistant COLO205ER cells (Tumor growth inhibition(%): 71.3, 91.6, and 74.1, respectively, P<0.01). Consistently, analysis of in vivo tumor samples reveals that PHI-501 considerably suppressed the reactivation of pERK and pAKT. In BRAF- or KRAS-mutated patient-derived 3D ex vivo experiments, the antitumor efficacy of PHI-501 was shown to be about 13-fold higher compared to that of other BRAF inhibitors.
Conclusions
The treatment of PHI-501 alone showed robust growth inhibition in CRC cells harboring BRAF V600E or KRAS mutations and BRAF-targeted therapy-resistant CRC cells. Our results suggest that PHI-501 as the pan-RAF/DDRs dual inhibitor is beneficial for the treatment of colorectal cancer and even helps overcome the resistance of previous BRAF inhibitor treatments.
S.M. Kim and G-J. Sung have contributed equally to the study.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Pharos iBio.
Disclosure
J.H. Han, K. Nam: Financial Interests, Personal, Full or part-time Employment: Pharos iBio; Financial Interests, Personal, Stocks/Shares: Pharos iBio. G. Sung, K. Kim: Financial Interests, Personal, Full or part-time Employment: Pharos iBio. J.H. Yoon: Financial Interests, Personal, Ownership Interest: Pharos iBio; Financial Interests, Personal, Stocks/Shares: Pharos iBio. S.J. Shin: Financial Interests, Personal and Institutional, Research Grant: Pharos iBio. All other authors have declared no conflicts of interest.