Pharmacokinetics (PK) and pharmacodynamics (PD) of a novel carcinoembryonic antigen (CEA) T-cell bispecific antibody (CEA CD3 TCB) for the treatment of CEA-expressing solid tumors.
Melero I., Segal NH., Saro Suarez JM., Ros W., Martinez Garcia M., Calvo E., Moreno V., Ponce Aix S., Marabelle A., Cleary JM., Hurwitz H., Eder JP., Jamois C., Belousov A., Bouseida S., Sandoval F., Bacac M., Nayak TK., Karanikas V., Argiles G.
2549 Background: CEA CD3 TCB (RO6958688) targets CEA on tumor cells and is agonistic for CD3e on T cells. In mouse models, CEA CD3 TCB displays potent anti-tumor activity, leads to increased intra-tumoral T cell infiltration and activation and up-regulates the PD-1/PD-L1 pathway. Methods: Biodistribution was assessed in mice using SPECT/CT. Patient (pts) samples correspond to 2 dose-escalation studies in CEA+ solid tumors. Study 1 (S1): single agent weekly (qW) (0.052 to 600 mg, iv, n = 80), and Study 2 (S2): combination of RO6958688 qW (5 to 160 mg, iv) with 1200mg atezolizumab q3W (n = 38). Analytical methods: PK - population modeling approach; anti-drug antibodies (ADA) - ELISA; immunophenotyping in peripheral blood (PB) by flow cytometry (FCM), in pre- (BSL) and on-treatment (OT) biopsies by immunohistochemistry (IHC) and FCM; plasma cytokines - multiplex assays; PD-L1 - SP142 assay. Results: In mice, RO6958688 preferentially accumulated in CEA+ tumors. In pts with no ADAs tested thus far in both studies (S1 29; S2 21), RO6958688 showed near linear PK and exposure. In S1, OT biopsies demonstrated a statistically significant increase in density and activation profile of T cells (CD3: 2.6-fold, n = 21; CD3/CD8: 3.7 fold, n = 17; CD3/Ki67: 4-fold, n = 20; CD8/PD1: 1.7-fold, n = 15) without dose-dependence. In S2, preliminary data of T cell density (5-80mg) were similar to S1 (2-fold). In S1, a significant correlation was observed between treatment-induced tumor lesion reduction and increases of OT CD8/CD25 fluorescence intensity from BSL (p = 0.028). PD-L1 expression increased in OT biopsies in both studies. In S1, from week 4, a moderate expansion of activated CD8 T cells (HLA-DR/Ki67) but not of CD4, was detected in PB at doses > 60mg ( > 3.3 fold). Transient increases of several cytokines were seen in both studies with levels peaking within 24hrs. Conclusions: PK and PD results consistent with tumor inflammation and mechanism of action support that RO6958688 is the first tumor-targeted T cell bispecific to show intra-tumoral biological activity in pts with CEA+ solid tumors. Updated data will be presented. Clinical data are reported separately.