LAUSR

4519 Background: INDUCE-1 is a first-in-human trial evaluating fela, an IgG4 ICOS agonist non-T-cell depleting mAb, as monotherapy (mono) and in combo with P. ECs include tumor types, such as UC, with high ICOS expression and immunotherapy-favorable features. Fela induced IFNγ, increased PD-1/L1 expression, and enhanced antitumor activity in combo with PD-1 blockade nonclinically. We report preliminary efficacy, safety, and biomarker data of fela ± P in INDUCE-1 UC ECs. Methods: Eligible patients (pts) had recurrent/metastatic (R/M) UC of the upper or lower urinary tract, ≤6 prior systemic therapy lines in the advanced setting, measurable disease, and no active autoimmune disease. Pts received 0.3 or 1 mg/kg fela (mono EC; anti-PD-1/L1–experienced [exp] pts) or 0.3 mg/kg fela + 200 mg P (combo EC; anti-PD-1/L1–naïve pts) every 3 wks, up to 35 cycles until disease progression or unacceptable toxicity. Disease was assessed every 9 wks through wk 54, then every 12 wks. Archival and/or fresh biopsy tumor tissue was collected for biomarker analyses and safety assessed. Results: By Nov 6 2020, 13 anti-PD-1/L1–exp and 32 anti-PD-1/L1–naïve pts were evaluable in the mono and combo ECs, respectively. In the mono EC, median age was 69 yrs (range: 47–82), 92% of pts were male, and 85% received ≥2 prior therapy lines in the metastatic setting. In the combo EC, median age was 70 yrs (range: 42–84), 75% of pts were male, and 72% received ≥1 prior therapy line in the metastatic setting. In the mono EC, median duration of follow-up (mDoF) was 10.6 mo (range: 1.1–22.8); overall response rate (ORR) was 8% (1 partial response [PR]; 95% CI: 0.2, 36.0) with a duration of response (DoR) of 6.1 mo; disease control rate (DCR [response or stable disease for ≥9 wks]) was 23% (95% CI: 5.0, 53.8), and median overall survival (mOS) was 14.5 mo (95% CI: 2.8, NR), with 74% of pts alive at 6 mo. In the combo EC, mDoF was 9.6 mo (range: 0.9–28.3); ORR was 22% (7 PRs; 95% CI: 9.3, 40.0) with a median DoR of 8.3 months (range: 3.5–23.3+); DCR was 63% (95% CI: 43.7, 78.9), and mOS was 10.7 mo (95% CI: 5.2, 18.1), with 64% of pts alive at 6 mo. Grade ≥3 treatment-related AEs were reported for 0% and 9% of pts in the mono (N = 16) and combo (N = 44) safety populations, respectively. PD-L1 expression and ICOS-specific biomarkers are being evaluated, with promising trends observed in enrichment of clinical activity in preliminary analyses. Conclusions: Fela is the first ICOS agonist with reported single-agent activity in anti-PD-1/L1–exp relapsed/refractory UC. Fela + P in combo shows promising clinical activity and manageable safety in PD-1/L1–naïve R/M UC. Further study is warranted. Updated data to be presented. Funding: Study 204691 (NCT02723955) funded by GlaxoSmithKline in collaboration with Merck Sharp & Dohme Corp, a subsidiary of Merck & Co, Inc, Kenilworth, NJ, USA. Clinical trial information: NCT02723955.