Abstract 824: Comparative pharmacokinetics (PK) of targeted tissue factor tTF-NGR when intravenously applied alone or in combination with preceding trabectedin

Abstract Trabectedin is a treatment option for relapsed/refractory soft tissue sarcomas (STS). CD13 is a neutral aminopeptidase expressed on invasive endothelial cells (EC) such as in the tumor vasculature. CD13-targeted tissue factor (tTF-NGR) is a recombinant pro-coagulatory fusion protein with a molecular weight of 30381.98 g/mol which accumulates in the tumor vasculature leading to tumor vascular occlusion and tumor infarction. Giving both compounds in sequence could trap trabectedin inside tumors and increase its efficacy. Vice versa trabectedin optimizes activity of tTF-NGR by externalizing phosphatidylserine (PS) on the surface of EC. PK of safety patients treated at our hospital within a multicenter trial of a combination of trabectedin and tTF-NGR in advanced STS patients refractory to 1st line systemic therapy (TRABTRAP, EudraCT 2020-005858-21) were compared with PK from our phase I monotherapy study with tTF-NGR (EudraCT 2016-003042-85). We compared standard PK parameters for tTF-NGR at identical dose levels (1.0 to 3.0 mg/m2) from TRABTRAP and phase I within the same laboratory with identical methods and calculations. Although some PK differences between phase I and TRABTRAP were more pronounced at lower dose levels, global values such as Cmax, AUC, t1/2alpha, t1/2term, and Kel indicated an increased AUC with a delayed elimination of tTF-NGR when given after trabectedin. As tTF-NGR was always given daily, we measured the remaining tTF-NGR concentrations before subsequent applications and found significantly increased values in the combination protocol (1 mg/m2: p<0.0001; 3 mg/m2: p<0.0002) when compared with the phase I values, suggesting a possible accumulation of tTF-NGR which we did not observe with monotherapy. A specific way of tTF-NGR elimination in the vascular system is the internalization of the tTF-NGR:CD13 complex into EC. Using flow cytometry and fluorescence labeling with tTF-NGR and EC in vitro, expression of CD13 on EC was slightly diminished by trabectedin exposure. Also, tTF-NGR binding to CD13 (p<0.01) and internalization (p=0.01) decreased when tested on control and trabectedin-exposed EC. Both lead to more tTF-NGR molecules remaining in the circulation, explaining part of the delayed elimination. Further, we compared functionality of tTF-NGR in the plasma of patients from phase I and TRABTRAP. On the basis of equal protein amounts and without influence of confounders such as storage, the ability of factor VIIa:tTF-NGR:CD13 to activate factor X to Xa was higher when trabectedin was given to the patients before. Among possible explanations are the decreased liver protease levels after trabectedin, which could influence the functionality of tTF-NGR. In summary, these results explain why the Maximum Tolerated Dose level for tTF-NGR established in the TRABTRAP safety cohort is lower than the 3 mg/m2 in the phase I study. Citation Format: Christian Schwöppe, Caroline Brand, Kathrin Hessling, Heike Hintelmann, Andrew F. Berdel, Georg Lenz, Torsten Kessler, Manfred Fobker, Christoph Schliemann, Wolfgang E. Berdel. Comparative pharmacokinetics (PK) of targeted tissue factor tTF-NGR when intravenously applied alone or in combination with preceding trabectedin [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 824.