Immune profiling in patients with glioblastoma treated with VT1021 in a phase I/II expansion study.

Abstract

2021 Background: The cyclic peptide VT1021 is a first-in-class therapeutic agent that has been shown to inhibit tumor growth via stimulation of thrombospondin-1 (TSP-1) and reprogramming the immune tumor microenvironment (TME) in preclinical models. Subsequently, VT1021 has been tested in a phase I/II clinical study in solid tumors (NCT03364400) and has advanced to a phase II/III clinical study in glioblastoma (NCT03970447). VT1021 has demonstrated promising single-agent clinical activity against recurrent glioblastoma (rGBM) in a phase I/II expansion study. Among 22 evaluable subjects with rGBM, 3 had complete response (CR), 1 had partial response (PR), and 6 had stable disease (SD) with an average study duration of over 120 days. One subject has been on VT1021 treatment for > 900 days with no measurable lesion left. The overall disease control rate (DCR) was 45%. Here, we sought to examine the peripheral immune cell profile(s) in response to VT1021 and explore the association between these profiles and clinical responses in rGBM subjects. Methods: In the phase I/II expansion study, 22 evaluable rGBM subjects received VT1021 at a dose of 11.8 mg/kg (twice per week intravenously) until disease progression. Peripheral blood samples were collected from all evaluable subjects; immune cell profiles were analyzed by flow cytometry. Results: The immune profiles following VT1021 treatment on day 1 did not vary significantly among rGBM subjects, regardless of response. Intriguingly, after long-term VT1021 treatment (day 53), our analysis of the immune profiles revealed beneficial and sustained changes in three cytotoxic T Cell (CTL) parameters and PD-L1+ MDSCs that correlated with response. Specifically, CR/PR subjects showed a 20% increase in total CTLs (Pre 33.79% vs. 6hr 40.42%), a 66% increase in proliferating CTLs (Pre 1.37% vs. 6hr 2.28%) and a 63% increase in CTL/Treg ratio (Pre 7.85 vs. 6hr 12.81) on day 53 of VT1021 treatment. In contrast, SD and PD subjects exhibited no change or decrease in these three CTL parameters, respectively. We also observed that CR/PR subjects experienced a sustained decrease in PD-L1+ MDSCs after VT1021 treatment (day 1 Pre 95.96% vs. day 53 Pre 92.66% and day 53 6hr 88.06%). Conversely, the sustained decrease of PD-L1+ MDSCs after VT1021 treatment was not observed in SD and PD subjects. Conclusions: Here we report that the durable responses of peripheral immune cells to VT1021 may be associated with better clinical outcomes in rGBM subjects. These findings are consistent with the MOA of TSP-1 to reprogram the TME by stimulating immune and inflammatory cell functions. While the interpretation of our data is limited by the lack of a control arm and the small sample size, the results provide a signal and warrant continued analysis of these parameters in the ongoing phase II/III trial.