The NEDD8 pathway as a therapeutic target in HER2-amplified colorectal cancer

Background: Colorectal cancer (CRC) is a heterogeneous disease with a wide spectrum of clinical outcomes, from indolent resectable disease to aggressive-metastatic cases. Primary and acquired resistance limits the efficacy of available treatments, and the identification of effective drug combinations is needed to further improve patients’ outcomes. We previously found that the NEDD8-activating enzyme inhibitor pevonedistat induced tumor stabilization in preclinical models of poorly differentiated, clinically aggressive CRC resistant to available therapies. To identify drugs that can be effectively combined with pevonedistat, we performed a “drop-out” loss-of-function synthetic lethality screening with an shRNA library covering 200 drug-target genes in four different CRC cell lines. Screening hits were then validated. Multiple screening hits were found to be involved in the EGFR signaling pathway, suggesting that, rather than inhibition of a specific gene, interference with the EGFR pathway at any level could be effectively leveraged for combination therapies based on pevonedistat. Exploiting both BRAF-mutant and RAS/RAF wild-type CRC models, we validated the therapeutic relevance of our findings by showing that combined blockade of NEDD8 and EGFR pathways led to increased growth arrest and apoptosis both in vitro and in vivo. Pathway modulation analysis showed that compensatory feedback loops induced by single treatments were blunted by the combinations. Our results suggested possible therapeutic opportunities in specific CRC clinical settings. Materials and methods: We focused on HER-2 amplified CRC cells, testing combinations of HER2/EGFR treatment with NEDD8 blockade by pevonedistat in both short-term and long-term in vitro assays. Results: We observed significant cooperation between pevonedistat and HER-2/EGFR blockade by the trastuzumab+lapatinib combination -the current standard treatment for HER2-amplified CRC. In addition to confirming cooperation in reducing colony formation in vitro, we explored the effect of pevonedistat on long-term persisters, i.e., cell surviving to several weeks of HER2/EGFR blockade. Interestingly, we observed a marked decrease of cell colonies when pevonedistat was added to persisters survived to three weeks of trastuzumab+lapatinib treatment. Conclusions: These results unveil the possibility of testing in vivo the addition of pevonedistat subsequently to tumor stabilization or reduction by HER2/EGFR blockade, to promote further tumor regression. No conflict of interest.