Developing Potential Endocrine Therapy Controlling Estradiol and DHT by Targeting 17β-HSD7 Against ER+ Breast Cancer

Breast cancer (BC) is the most incidental cancer in women. Patients' living conditions and survival rates have significantly improved with the success of two first-line endocrine therapies of selective estrogen-receptor modulators (SERMs from 1977) and aromatase inhibitors (AIs from 1995). Unfortunately, both therapies have produced significant resistance. AI resistance reaches 50% in metastatic estrogen-dependent BC cases, leading oncologists to seek a substitute for current therapies. We target the reductive 17β-hydroxysteroid dehydrogenase type 7 (17β-HSD7), which stimulates the synthesis of the active estrogen estradiol (E2) and reduces the potent androgen dihydrotestosterone (DHT) simultaneously, triggering negative feedback on 17β-HSD7 expression. INH7(464), an improved 17β-HSD7 inhibitor, efficiently blocks estrogen conversion at an IC₅₀ of 92 ± 8 nM. INH7(464) inhibited cell proliferation by decreasing E2 levels and restoring DHT, successively arresting the cell cycle in G0/G1 phase. In vivo, INH7(464) reduced tumor size by 49% on Day 22 in BC xenografts with T47D. INH7(464) reduced E2 levels in mouse blood circulation and xenograft tumor tissue. There is no demonstrated cytotoxicity or cardiotoxicity of INH7(464) on cellular levels and mouse models under the experimental conditions. 17β-HSD7 is a potential target for estrogen-dependent BC therapy, while INH7(464) is promising for a preclinical lead compound (PCT/CA2022/050966).