(D)-PPA 1 TFA, a hydrolysis-resistant D-peptide antagonist, is a potent PD-1/PD-L1 inhibitor with an affinity for PD-1 of 0.51 μM, demonstrating efficacy both in vitro and in vivo [1].

(D)-PPA 1 TFA at concentrations of (0.2 mg/mL, 1.0 mg/mL) inhibits the interaction between PD-1 and PD-L1 at 1.0 mg/mL [1]. (D)-PPA 1 (3.125-100 μM; 24 h, 48 h) does not directly kill tumor cells and has no effect on the growth of CT26 cells [1].

(D)-PPA 1 TFA administered at a dose of 2 mg/kg through subcutaneous or intraperitoneal injection once daily for seven consecutive days inhibited the growth of CT26 tumors in mice [1]. Additionally, a single intravenous dose of 40 μg/mouse in 200 μL demonstrated the capability to target tumor tissue in CT26 tumor-bearing mice [1].