Background AMG 160 is an HLE BiTE^® (half-life extended bispecific T-cell engager) that binds PSMA on prostate cancer cells and CD3 on T-cells and induces redirected T-cell lysis of PSMA-expressing cells. This mechanism may allow the BiTE molecule to be active in settings where other targeted or immune therapies have failed. Here, we evaluated the activity of AMG 160 in mouse models of advanced prostate cancer that are resistant to ¹⁷⁷Lu-PSMA-617, a PSMA-targeted radioligand therapy that has emerged as a promising treatment modality for metastatic castration-resistant prostate cancer (mCRPC).

Methods Two prostate cancer models were tested in 6–8-week-old male NCG mice: one cohort had established subcutaneous C4-2 TP53^-/- tumors (C4-2 cells with TP53 knockout), and the other cohort had established systemic C4-2 TP53^wt/wttumors that mimic metastatic lesions (intracardiac injection). PSMA levels in both models (~255,000 PSMA/cell) are sufficient for tumor growth inhibition with ¹⁷⁷Lu-PSMA-617. Mice were administered a single intravenous (IV) infusion of human T-cells. Three days later, mice were treated with 1 cycle of ¹⁷⁷Lu-PSMA-617 (30 MBq, IV), or 3 weekly doses of AMG 160 (1 mg/kg, IV) or of a control HLE BiTE molecule (1 mg/kg, IV; target not expressed on C4-2 cells). Therapeutic efficacy was assessed by tumor burden measurements, time to progression (TTP), and survival.

Results In both prostate cancer models, AMG 160 treatment significantly improved disease control (figure 1). Median TTP was not reached in the AMG 160 group (p<0.0001), whereas it was 31d (¹⁷⁷Lu-PSMA-617) and 23.5d (control) in the subcutaneous model, and 68d (¹⁷⁷Lu-PSMA-617) and 50.5d (control) in the systemic model. Median survival was not reached in the AMG 160 group (p<0.0001); it was 39d (¹⁷⁷Lu-PSMA-617) and 26.5d (control) in the subcutaneous model, and 77d (¹⁷⁷Lu-PSMA-617) and 61d (control) in the systemic model. Following treatment with AMG 160, 2/10 mice with subcutaneous and 7/9 mice with systemic tumors had not progressed at the end of the observation period (>100 days). In contrast, all mice in the ¹⁷⁷Lu-PSMA-617 and control groups succumbed to progressive disease.

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Abstract 717 Figure 1

AMG 160 treatment extended survival in mouse models of advanced prostate cancer

Conclusions Our study demonstrates potent antitumor activity of AMG 160 monotherapy in models of metastatic CRPC that are resistant to PSMA-targeted radioligand therapy with ¹⁷⁷Lu-PSMA-617. These data provide a rationale for evaluating AMG 160 in patients with mCRPC who have progressed on ¹⁷⁷Lu-PSMA-617. AMG 160 is currently being evaluated in a phase 1 study in patients with mCRPC (NCT03792841).

Acknowledgements The authors would like to acknowledge Micah Robinson, PhD of Amgen Inc. for medical writing support and Hosein Kouros-Mehr, MD, PhD of Amgen Inc. for facilitating the collaboration and helpful discussions.

Trial Registration ClinicalTrials. gov Identifier: NCT03792841

Ethics Approval All animal experimental protocols were approved by the UCLA Animal Research Committee (# 2005-090).