Model-Informed Drug Development of the Masked Anti-PD-L1 Antibody CX-072.

CX-072 is an anti-PD-L1 (programmed death ligand 1) Probody therapeutic (Pb-Tx) designed to be preferentially activated by proteases in the tumor microenvironment and not in healthy tissue. Here, we report the model-informed drug development of CX-072. A quantitative systems pharmacology (QSP) model that captured known mechanisms of Pb-Tx activation, biodistribution, elimination, and target engagement was used to inform clinical translation. The QSP model predicted that a trough level of masked CX-072 (intact CX-072) of 13-99 nM would correspond to a targeted, 95% receptor occupancy in the tumor. The QSP model predictions appeared consistent with preliminary human single-dose pharmacokinetic (PK) data following CX-072 0.03-30.0 mg/kg as monotherapy: CX-072 circulated predominantly as intact CX-072 with minimal evidence of target-mediated drug disposition. A preliminary population PK (POPPK) analysis based upon 130 subjects receiving 0.03-30.0 mg/kg as monotherapy included a provision for a putative time-dependent and dose-dependent antidrug antibody (ADA) effect on clearance (CL) with a mixture model. Preliminary POPPK estimates for intact CX-072 time-invariant CL and volume of distribution were 0.306 L/day and 4.84 L, respectively. Exposure-response analyses did not identify statistically significant relationships with best change from baseline sum of measurements and either adverse events of grade ≥ 3 or of special interest. Simulations suggested that > 95% of patients receiving CX-072 10 mg/kg every two weeks would exceed the targeted trough level regardless of ADA, and that dose adjustment by body weight was not necessary, supporting a fixed 800 mg dose for evaluation in phase II.

Tumor-specific activation of an EGFR-targeting probody enhances therapeutic index.

Target-mediated toxicity constitutes a major limitation for the development of therapeutic antibodies. To redirect the activity of antibodies recognizing widely distributed targets to the site of disease, we have applied a prodrug strategy to create an epidermal growth factor receptor (EGFR)-directed Probody therapeutic-an antibody that remains masked against antigen binding until activated locally by proteases commonly active in the tumor microenvironment. In vitro, the masked Probody showed diminished antigen binding and cell-based activities, but when activated by appropriate proteases, it regained full activity compared to the parental anti-EGFR antibody cetuximab. In vivo, the Probody was largely inert in the systemic circulation of mice, but was activated within tumor tissue and showed antitumor efficacy that was similar to that of cetuximab. The Probody demonstrated markedly improved safety and increased half-life in nonhuman primates, enabling it to be dosed safely at much higher levels than cetuximab. In addition, we found that both Probody-responsive xenograft tumors and primary tumor samples from patients were capable of activating the Probody ex vivo. Probodies may therefore improve the safety profile of therapeutic antibodies without compromising efficacy of the parental antibody and may enable the wider use of empowered antibody formats such as antibody-drug conjugates and bispecifics.

Targeting FGFR4 inhibits hepatocellular carcinoma in preclinical mouse models.

The fibroblast growth factor (FGF)-FGF receptor (FGFR) signaling system plays critical roles in a variety of normal developmental and physiological processes. It is also well documented that dysregulation of FGF-FGFR signaling may have important roles in tumor development and progression. The FGFR4-FGF19 signaling axis has been implicated in the development of hepatocellular carcinomas (HCCs) in mice, and potentially in humans. In this study, we demonstrate that FGFR4 is required for hepatocarcinogenesis; the progeny of FGF19 transgenic mice, which have previously been shown to develop HCCs, bred with FGFR4 knockout mice fail to develop liver tumors. To further test the importance of FGFR4 in HCC, we developed a blocking anti-FGFR4 monoclonal antibody (LD1). LD1 inhibited: 1) FGF1 and FGF19 binding to FGFR4, 2) FGFR4-mediated signaling, colony formation, and proliferation in vitro, and 3) tumor growth in a preclinical model of liver cancer in vivo. Finally, we show that FGFR4 expression is elevated in several types of cancer, including liver cancer, as compared to normal tissues. These findings suggest a modulatory role for FGFR4 in the development and progression of hepatocellular carcinoma and that FGFR4 may be an important and novel therapeutic target in treating this disease.

FGF19 and cancer.

Fibroblast growth factors (FGFs) and their cognate receptors, FGF receptors (FGFRs), play critical roles in a variety of normal developmental and physiological processes. Numerous reports support a role for deregulation of FGF-FGFR signaling, whether it is at the ligand and/or receptor level, in tumor development and progression. The FGF19-FGFR4 signaling axis has been implicated in the pathogenesis of several cancers, including hepatocellular carcinomas in mice and potentially in humans. This chapter focuses on recent progress in the understanding of the molecular mechanisms of FGF19 action and its potential involvement in cancer.

Liver-specific activities of FGF19 require Klotho beta.

Hepatocyte function is regulated by members of the fibroblast growth factor (FGF) family of proteins, but little is known about the specific molecular mechanisms of this endocrine pathway. FGF19 regulates bile acid homeostasis and gall bladder filling; FGF19 binds only to FGF receptor 4 (FGFR4), but its liver-specific activity cannot be explained solely by the distribution of this receptor. Although it has been suggested that Klotho beta (KLB) may have a role in mediating FGF19 activity, we have provided for the first time definitive evidence that KLB is required for FGF19 binding to FGFR4, intracellular signaling, and downstream modulation of gene expression. We have shown that FGFR4 is widely distributed in mouse, whereas KLB distribution is more restricted. Liver was the only organ in which both genes were abundantly expressed. We show that in mice, FGF19 injection triggers liver-specific induction of c-Fos and repression of CYP7A1. The tissue-specific activity of FGF19 supports the unique intersection of KLB and FGFR4 distribution in liver. These studies define KLB as a novel FGFR4 coreceptor required for FGF19 liver specific functions.