# A Reporter Gene Assay for Measuring the Biological Activity of PEGylated Recombinant Human Growth Hormone

## TL;DR

This study introduces a reliable lab-based test to measure the effectiveness of a long-lasting growth hormone treatment, which can improve quality control and drug development.

## Contribution

A novel in vitro reporter gene assay and ion exchange chromatography method for evaluating PEGylated recombinant human growth hormone.

## Key findings

- The reporter gene assay showed high sensitivity, precision, and reproducibility for PEG-rhGH bioactivity.
- The assay correlated well with in vivo studies and the Nb2-11 cell proliferation assay.
- PEG modification sites significantly affect bioactivity, revealed by ion exchange chromatography.

## Abstract

PEGylated recombinant human growth hormone (PEG-rhGH) has garnered significant interest in growth hormone research due to its prolonged half-life and improved patient compliance. An accurate evaluation of its biological activity is critical for ensuring the quality of PEG-rhGH-based therapeutics. In this study, we established an in vitro bioactivity assay using a reporter gene method based on the HepG2/IGF-1 cell line. Key assay parameters, including the initial concentration of PEG-rhGH, serial dilution ratios, cell density, and incubation time, were systematically optimized to generate robust dose–response curves. The assay demonstrated high sensitivity, precision, and reproducibility across multiple batches of PEG-rhGH. The validation results showed an excellent correlation with traditional in vivo animal studies and the Nb2-11 cell proliferation assay, highlighting its suitability for quality control. Furthermore, we developed an ion exchange chromatography (IEC) method to separate five positional isomers of PEG-rhGH, revealing significant differences in bioactivity depending on the PEG modification site. This study demonstrates that the optimized reporter gene assay is not only effective for quality control of PEG-rhGH but also serves as a valuable tool for evaluating and optimizing PEGylated long-acting growth hormone therapeutics.