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2553 Background: ORIC-101 is a potent and selective, orally bioavailable, small molecule antagonist of the glucocorticoid receptor (GR). Preclinical studies have demonstrated that activation of GR signaling leads to decreased responsiveness to chemotherapeutics (eg, taxanes) and antiandrogens across multiple tumor types. Mechanistically, ORIC-101 inhibits GR transcriptional activity and blocks the prosurvival signals mediated by the activated nuclear hormone receptor. Methods: A 3+3 dose escalation design was used to assess safety, pharmacokinetics (PK), pharmacodynamics (PD), and select the Recommended Phase 2 Dose (RP2D) of ORIC-101 in combination with nab-paclitaxel (nab-pac; NCT03928314). ORIC-101 doses ranging from 80 to 240 mg once daily, given either intermittently or in a continuous dosing regimen, were evaluated in combination with weekly nab-pac at 75 or 100 mg/m2. Plasma PK and PD biomarkers were assessed on day 1 and after repeat dosing. PD modulation in blood-derived peripheral blood mononuclear cells (PBMCs) was assessed by RT-qPCR for GR target genes. Antitumor activity was assessed by RECIST v1.1. Results: 21 patients with 10 different solid tumors, with and without a prior taxane, were treated in 5 cohorts. ORIC-101 exposure increased with dose, with no evidence for drug-drug interaction with nab-pac. In the initial cohort at 240 mg ORIC-101 and 100 mg/m2 nab-pac, 2 patients experienced dose limiting toxicities (DLTs) of Grade 3 fatigue and Grade 4 neutropenia/thrombocytopenia, respectively. No further DLTs were observed in subsequent cohorts and the RP2D was established as 160 mg ORIC-101 dosed once daily continuously for 21 days with nab-pac 75 mg/m2 given on days 1, 8, and 15 of each 28-day cycle, without requirement for prophylactic granulocyte colony-stimulating factor (G-CSF). The most common (> 15%), all grade treatment-related adverse events (AEs) were nausea (38%), diarrhea (33%), fatigue (29%), leukopenia (29%), neutropenia (29%), anemia (24%), and 19% of patients had increased liver function tests and alopecia. Biomarker data demonstrated ORIC-101-induced reduction in GR target gene expression in PBMCs, indicating PD modulation at all dose levels of ORIC-101. Preliminary antitumor activity was observed in 3 taxane-refractory patients with breast, endometrial, and pancreatic cancers. Conclusions: The combination of ORIC-101 and nab-paclitaxel demonstrated an acceptable tolerability profile and does not require prophylactic G-CSF. PK and PD showed no evidence of drug-drug-interaction and demonstrated GR target inhibition. Preliminary antitumor activity was observed in patients with solid tumors that previously progressed on a taxane-containing regimen. Dose expansion is ongoing at the RP2D in dedicated pancreatic, ovarian, triple negative breast cancers, and tissue-agnostic cohorts. Clinical trial information: NCT03928314.