Conclusion
Compound 6 displayed high binding affinity to p97, great p97 ATPase inhibition, selective cytotoxicity, remarkable anti-tumor effect, and upregulated safety, which improved the clinical potential of p97 inhibitors.
Results
In the p97 ATPase inhibition assay, compounds 6 and 7 showed higher potency than the known p97 inhibitors, DBeQ and CB-5083. Compounds 4-6 dramatically induced G0/G1 phase arrest in the HCT116 cells, and compound 7 arrested the cells in both G0/G1 and S phases. Western blots showed elevated levels of SQSTM/p62, ATF-4, and NF-κB in HCT116 cells with the treatment of compounds 4-7, confirming their role in inhibiting the p97 signaling pathway in cells. In addition, the IC50 of compounds 4-6 against HCT116, RPMI-8226, and s180 proliferation were 0.24-6.9 µM with comparable potency as DBeQ. However, compounds 4-6 displayed low toxicity against the normal human colon cell line. Thus, compounds 6 and 7 were proved to be potential p97 inhibitors with less cytotoxicity. In vivo studies using the s180 xenograft model have demonstrated that compound 6 inhibited tumor growth, led to a significant reduction of p97 concentration in the serum and tumor, and indicated non-toxicity on the body weight and organ-to-brain weight ratios except for the spleen at the dose of 90 μmol/kg/day for 10 days. Furthermore, the present study indicated that compound 6 may not induce s180 mice myelosuppression often observed in the p97 inhibitors.