AbstractIntroductionA neurotrophic tropomyosin receptor kinase (NTRK)‐tyrosine kinase inhibitor (TKI) has shown dramatic efficacy against malignant tumors harboring an NTRK fusion gene. However, almost all tumors eventually acquire resistance to NTRK‐TKIs.MethodTo investigate the mechanism of resistance to NTRK‐TKIs, we established cells resistant to three types of NTRK‐TKIs (larotrectinib, entrectinib, and selitrectinib) using KM12 colon cancer cells with a TPM3‐NTRK1 rearrangement.ResultOverexpression of 3‐hydroxy‐3‐methylglutaryl‐CoA synthase 2 (HMGCS2) was observed in three resistant cells (KM12‐LR, KM12‐ER, and KM12‐SR) by microarray analysis. Lower expression of sterol regulatory element‐binding protein 2 (SREBP2) and peroxisome proliferator activated receptor α (PPARα) was found in two cells (KM12‐ER and KM12‐SR) in which HMGCS2 was overexpressed compared to the parental KM12 and KM12‐LR cells. In resistant cells, knockdown of HMGCS2 using small interfering RNA improved the sensitivity to NTRK‐TKI. Further treatment with mevalonolactone after HMGCS2 knockdown reintroduced the NTRK‐TKI resistance. In addition, simvastatin and silibinin had a synergistic effect with NTRK‐TKIs in resistant cells, and delayed tolerance was observed after sustained exposure to clinical concentrations of NTRK‐TKI and simvastatin in KM12 cells. In xenograft mouse models, combination treatment with entrectinib and simvastatin reduced resistant tumor growth compared with entrectinib alone.ConclusionThese results suggest that HMGCS2 overexpression induces resistance to NTRK‐TKIs via the mevalonate pathway in colon cancer cells. Statin inhibition of the mevalonate pathway may be useful for overcoming this mechanistic resistance.