Investigations on the Relationship between Ovarian, Endocrine, and Renal Findings in Nonclinical Safety Studies of the γ-secretase Inhibitor Avagacestat

Onset and resolution of ovarian toxicity with nirogacestat treatment in females with desmoid tumors: Updated safety analyses from the DeFi phase 3 study

INTRODUCTION

Nirogacestat is a targeted gamma secretase inhibitor approved in the United States for adults with progressing desmoid tumors. In the phase 3 DeFi study (NCT03785964) of nirogacestat, ovarian toxicity (OT) was identified as a safety signal among females of reproductive potential (FORP). This analysis further describes the incidence, presentation, and resolution of OT.

METHODS

Patients were randomized to twice-daily oral nirogacestat (150 mg) or placebo, taken in continuous 28-day cycles. Investigator-identified OT in FORP was based on abnormal reproductive hormone values or perimenopausal symptoms (or both). Adverse event follow-up was conducted to assess OT resolution. Post hoc analyses included return of menstruation and return of follicle-stimulating hormone (FSH) to within normal limits (WNL) (≤20.4 mIU/mL).

RESULTS

Of 92 randomized females, 73 in the safety population were FORP (n = 36 nirogacestat, n = 37 placebo). OT was identified in 75% (27 of 36) receiving nirogacestat and 0% (0 of 37) receiving placebo. As of October 24, 2022, investigators reported OT resolution in 78% (21 of 27) of patients, with median OT duration of 19.1 weeks. Off-treatment resolution was reported in all 11 patients (100%) who stopped nirogacestat treatment; of these, all nine with available menstruation information experienced return of menstruation and eight had FSH WNL at last reported assessment. Resolution was reported in 10 of 14 (71%) while on nirogacestat; of these, all 10 experienced return of menstruation and seven had FSH WNL. Two patients were lost to follow-up.

CONCLUSION

Most FORP treated with nirogacestat experienced OT, with the majority resolving, including all who stopped treatment, suggesting that OT is transient.

Gamma secretase inhibition: Effects on fertility and embryo-fetal development in rats

Avagacestat inhibits γ-secretase, a protease that cleaves the amyloid precursor protein (APP) to produce amyloid beta (Aβ). Aβ plaques, a predominant lesion in Alzheimer's patient's brain, is considered a mechanism driving neurodegeneration. As part of the nonclinical reproductive safety assessment, avagacestat effects on fertility and early embryonic development and embryo-fetal development were evaluated in rats. In the embryo-fetal development study, avagacestat was a selective developmental toxicant with dose-related increased fetal mortality, decreased fetal growth, and increased fetal malformations and variations (primarily affecting the axial and appendicular skeletal system) at ≥3 mg/kg/day. In the female fertility and early embryonic development study, avagacestat-related reductions in female fecundity at ≥5 mg/kg/day were attributed to impaired ovarian follicular development that was reflected in dose-dependent reductions in implantation sites, litter size, and gravid uterine weights. In the male fertility and early embryonic development study, avagacestat-related effects on reproduction could not be fully assessed because of low systemic exposures achieved due to extensive metabolism and clearance of the drug. The results obtained in these studies were consistent with pharmacologically mediated inhibition of γ-secretase and resulting inhibition of Notch processing and signaling that are key for embryonic development and ovary folliculogenesis. These findings are not considered a risk for late-onset AD where the patient population is ≥65 years old most with women who are post-menopausal. However, for treatment of early onset AD with a younger patient population, there are risks for reproductive or developmental toxicities with treatment with gamma secretase inhibitors like avagacestat.