RF07 | PSUN355 Downstream Targets of the Steroidogenic Factor-1 (SF-1) Antagonist OR-449 in PDX Models of ACC

BACKGROUND: Adrenocortical cancer (ACC) is a rare endocrine malignancy frequently diagnosed at an advanced stage when prognosis is dismal. Mitotane, the only approved therapy for locally advanced or metastatic disease, is minimally effective, and recent clinical trials with multi-kinase inhibitors or immunotherapies have been disappointing. OR-449 is a potent, selective, and orally bioavailable small molecule antagonist to steroidogenic factor-1 (SF-1 or NR5A1), a nuclear receptor and a transcription factor essential for the growth and development of the adrenal gland. SF-1 was recently described as a candidate "master transcription factor" in adult ACC (1). We previously reported that OR-449, dosed orally at 30 mg/kg for 28 days, completely blocked the growth of SJ-ACC3, a pediatric ACC patient-derived tumor xenograft (PDX), in immunocompromised mice. To help identify biomarkers for following the action of OR-449 in patient tumors, we evaluated a second pediatric ACC PDX, SW1939, which has high SF-1 expression and responded to OR-449 (10, 30 or 100 mg/kg) with inhibition of tumor growth and improved event-free survival over 24 days of dosing (an event is a 4-fold increase in tumor volume). METHODS: We first measured circulating steroids, steroid precursors and steroid sulfates in SW1939 tumor-bearing mice with or without OR-449 treatment using liquid chromatography/tandem mass spectrometry. Second, we investigated common pathways of gene regulation by OR-449 in SW1939 and SJ-ACC3 tumors by RNAseq after seven days of dosing (100 mg/kg or 30 mg/kg, respectively). RESULTS: Cortisol, DHEAS, steroid precursors (11-deoxycortisol, 17OH-progesterone, 17OH-pregnenolone) and sulfated Δ5 steroid precursors (pregnenolone sulfate, 17OH-pregnenolone sulfate, androstenediol-sulfate) were elevated in serum from SW1939 tumor-bearing mice compared to CD-1 non tumor-bearing mice, consistent with tumor-derived origin. Moreover, DHEAS, pregnenolone sulfate, 17OH-pregnenolone sulfate and androstenediol-sulfate were significantly suppressed (12-fold, 7.6-fold, 10.6-fold and 4.4-fold, respectively) following administration of OR-449 (100 mg/kg/day for 24 days) in SW1939 tumor-bearing mice. Final tumor weights were ∼2-fold lower than controls, indicating that circulating steroid reduction was disproportionately greater than the change in tumor volume. Global gene expression was significantly altered following 7-day exposure to OR-449 in both tumors. Significantly, PAPSS2 and SULT2A1 within the sulfation pathway were down-regulated in both SW1939 (2.3-fold and 1.2-fold, respectively) and SJ-ACC3 (1.6-fold and 5-fold, respectively). CONCLUSIONS: OR-449 reduces steroid production, alters gene expression, and suppresses growth of two PDX models of ACC in mice. Tumor gene expression and steroid regulation by OR-449 are currently under investigation in other pediatric and adult ACC PDX models to evaluate these endpoints as potential biomarkers of SF-1 receptor engagement for initial clinical trials of OR-449 in ACC. Reference: (1) Corces et al., Science. 2018 Oct 26;362(6413): eaav1898; Reddy et al., Sci Adv. 2021 Nov 26;7(48): eabf6123. Presentation: Saturday, June 11, 2022 1:06 p.m. - 1:11 p.m., Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.