Background Upregulation of immune checkpoints, such as LAG-3, plays an important role in promoting resistance to anti-PD-(L)1 therapy. Targeting PD-L1 and LAG-3 using a bispecific antibody may overcome resistance to PD-(L)1 blockade.¹ We report initial data from a first-in-human study evaluating FS118 in patients with advanced cancer and resistance to PD-(L)1 therapy.

Methods The ongoing Phase I FIH study (NCT03440437) is being conducted to evaluate safety, tolerability, immunogenicity, PK/PD and clinical activity of FS118 administered IV weekly to heavily pre-treated patients who had previously received anti-PD-(L)1 therapy for a minimum of 12 weeks. Adverse events were assessed using CTCAEv4.03 and tumor responses assessed using RECISTv1.1 and iRECIST. Single subject dose escalation cohorts were followed by a 3+3 ascending dose design. Three cohorts (3, 10, 20 mg/kg) were expanded to evaluate PK, PD and clinical activity. Pharmacodynamic studies examined soluble LAG-3 production and peripheral T-cell expansion.

Results Forty-three patients (median 6 lines of prior therapy, including ICB) with solid tumors received FS118 at doses from 0.8 mg up to 20 mg/kg across 8 dose levels. Weekly administration of FS118 was well tolerated and did not result in dose- or treatment-limiting toxicities. An MTD was not reached. No safety signals unexpected for the drug class of immune-checkpoint inhibitors were identified in the early study population. The majority (95%) of treatment-emergent adverse events (TEAE) considered by the Safety Review Committee (SRC) to be treatment-related were Grade 1 and 2. Grade 3 TEAEs toxicities (elevated liver enzymes) were observed in 2 patients (5%). No SAEs or deaths were attributed to FS118 treatment. Anti-drug antibodies, observed in half of patients, were typically transient in nature. The pharmacokinetic profile confirmed preclinical predictions and PD parameters included a dose-dependent increase in serum soluble LAG-3 and expansion of peripheral T cells. Long-lasting disease stabilisation (>6 months) was observed in a subset of patients with acquired resistance (defined as a CR, PR or SD ≥3 months on previous PD-(L)1 treatment), but not in patients with primary resistance. Two patients remain on FS118 treatment as of 2 Jul 2020 (duration 10 and 16 months). Retrospective IHC analysis of PD-L1 and LAG-3 co-expression in the tumor was assessed as a potential biomarker associated with clinical outcome.

Conclusions Weekly treatment with FS118 was well tolerated up to 20 mg/kg and was associated with pharmacodynamic markers of FS118 activity. Encouraging signs of clinical activity were observed in highly pre-treated patients who had acquired resistance to prior PD-(L)1 therapy.

Trial Registration Registered at www.clinicaltrials.gov, NCT03440437

Reference

1. Kraman M, Faroudi M, Allen N, Kmiecik K, Gliddon D, Seal C, Koers A, Wydro M, Winnewisser J, Young L, Tuna M, Doody J, Morrow M, Brewis N. FS118, a bispecific antibody targeting LAG-3 and PD-L1, Enhances T-Cell activation resulting in potent antitumor activity. Clin Cancer Res 2020; 26:3333–3344.