Refining Liver Safety Risk Assessment: Application of Mechanistic Modeling and Serum Biomarkers to Cimaglermin Alfa (GGF2) Clinical Trials

Abstract

Cimaglermin alfa (GGF2) is a recombinant human protein growth factor in development for heart failure. Phase I trials were suspended when two cimaglermin alfa-treated subjects experienced concomitant elevations in serum aminotransferases and total bilirubin, meeting current US Food and Drug Administration criteria for a serious liver safety signal (i.e., "Hy's Law"). We assayed mechanistic biomarkers in archived clinical trial serum samples which confirmed the hepatic origin of the aminotransferase elevations in these two subjects and identified apoptosis as the major mode of hepatocyte death. Using a mathematical model of drug-induced liver injury (DILIsym) and a simulated population, we estimated that the maximum hepatocyte loss in these two subjects was <13%, which would not result in liver dysfunction sufficient to significantly increase serum bilirubin levels. We conclude that the two subjects should not be considered Hy's Law cases and that mechanistic biomarkers and modeling can aid in refining liver safety risk assessment in clinical trials.

Figure 1

Serum levels of liver safety biomarkers (a) microRNA‐122 (miR‐122), (b) glutamate dehydrogenase (GLDH), (c) caspase‐cleaved fragment of K18 (cc‐K18), (d) full length keratin‐18 (FL‐K18), and (e) macrophage colony stimulating factor (CSF‐1). Serum samples were collected at four different timepoints relative to cimaglermin alfa (or placebo) administration from 12 patients who participated in phase I clinical trials including two patients which met FDA drug‐induced liver injury (DILI) guidance stopping criteria (Subjects 8 and 12), as well as others with elevated serum aminotransferases that fell short of meeting FDA DILI guidance stopping criteria (Subjects 1, 2, 3, 4, 7, 9, 10, 11), and two placebo‐dosed individuals (Subjects 5 and 6).

Figure 2

Diagrams of serum alanine transaminase (ALT) (a), serum aspartate transaminase (AST) (b), and bilirubin (c) submodels within DILIsym version 4B.

Figure 3

Observed and simulated plasma levels of (a) alanine transaminase (ALT), (b) aspartate transaminase (AST), and (c) bilirubin for the four cimaglermin alfa‐treated subjects and the placebo‐treated subject included in the DILIsym analyses. Subjects included in the DILIsym analyses consist of two subjects who met FDA DILI guidance stopping criteria (Subjects 8 and 12), as well as two subjects with elevated serum aminotransferases who fell short of meeting FDA DILI guidance stopping criteria (Subjects 7 and 11), and one placebo‐treated subject (Subject 6). Subjects 6, 7, 8, 11, and 12 were also included in the set of 12 subjects included in the serum biomarker analysis (Figure 1). Simulations on the baseline human in DILIsym were performed assuming 100% apoptosis as the cell death modality. (Analogous simulation results with 100% necrosis as the cell death modality are shown in Supplementary Figure S1.) The ALT model was optimized to the cimaglermin alfa ALT clinical data. AST and bilirubin data were not used for the optimization; plasma AST and bilirubin levels were simulated based on the amount of hepatocyte injury optimized to ALT dynamics. Closed black circles represent clinical data. Solid red lines represent simulated results due to 100% apoptosis.

Figure 4

Range of estimated hepatocyte loss as a function of observed plasma peak alanine transaminase (ALT) range in cimaglermin alfa subjects for two different cell death modalities (100% apoptosis (a), 100% necrosis (b)). Dashed lines show the corresponding peak ALT bins for each of the four specific cimaglermin alfa phase I subjects. The five subjects included in the DILIsym analyses consist of two subjects whom met FDA DILI guidance stopping criteria (Subjects 8 and 12), as well as two subjects with elevated serum aminotransferases who fell short of meeting FDA DILI guidance stopping criteria (Subjects 7 and 11), and one placebo‐treated subject (Subject 6). Subjects 6, 7, 8, 11, and 12 were also included in the set of 12 subjects included in the serum biomarker analysis (Figure 2).