Discovery and optimization of a pH-responsive ultra-long-acting VHH-based growth hormone mimetic.
This study presents a promising ultra-long-acting growth hormone mimetic with extended efficacy in rats, but human trials are needed to determine clinical relevance.
Where it sits
this study against the rest of the hgh (somatropin) corpusSummary and findings
The study developed a pH-responsive ultra-long-acting growth hormone receptor agonist, pH.VHH03, with GH-mimetic activity. In rats, this molecule extended in vivo efficacy from 6 days to over 15 days and promoted body weight gain, IGF-1 secretion, and tibial growth. The optimized molecule showed a 227-fold difference in dissociation rates between neutral and acidic conditions.
Abstract
Weekly formulations of long-acting growth hormone (LAGH) effectively treat growth hormone (GH) deficiency in both children and adults while offering improved convenience compared to daily GH. To further enhance patient convenience and compliance, longer-acting GH preparations have become a key research focus. However, due to the inherent short half-life of protein-based drugs, no ultra-long-acting growth hormone or analog products (with dosing intervals longer than once weekly) are currently available worldwide. In this study, we developed a potentially ultra-long-acting growth hormone receptor (GHR) agonist pH.VHH03 with GH-mimetic activity by engineering hinge region and variable region of a VHH antibody. Through optimization of the hinge region, the <i>in vitro</i> cell proliferation activity of this molecule was significantly enhanced. As a result, it demonstrated LAGH-like effects in promoting body weight gain and stimulating IGF-1 secretion in rats. Furthermore, pH-dependent binding was introduced into the variable region. The optimized molecule exhibited a 227-fold difference in dissociation rates between neutral and acidic conditions. This modification prolonged its <i>in vivo</i> efficacy in rats from 6 days to over 15 days, far exceeding the 3-day duration observed with PEGylated GH. Subsequent <i>in vivo</i> experiments in rats confirmed that the final optimized molecule dose-dependently promoted body weight gain, insulin-like growth factor 1 (IGF-1) secretion, tibial growth, and significantly increased growth plate thickness. The <i>in vivo</i> profile fully replicated the physiological activities of GH. Moreover, at medium to high doses, it induced a notably flatter and sustained IGF-1 response compared to PEGylated GH, suggesting a potentially longer duration of pharmacological activities in humans.
Background
The study addresses the challenge of developing ultra-long-acting growth hormone formulations to improve patient compliance and convenience. Current long-acting growth hormone treatments require weekly dosing, and there is a need for formulations with longer dosing intervals. This research is significant as it explores the potential for a growth hormone mimetic with extended duration of action.
Methods
The study involved engineering the hinge and variable regions of a VHH antibody to create a growth hormone receptor agonist, pH.VHH03, with GH-mimetic activity. The in vitro cell proliferation activity was enhanced through optimization, and the molecule's pH-dependent binding was introduced. In vivo experiments were conducted in rats to assess the molecule's effects on body weight gain, IGF-1 secretion, tibial growth, and growth plate thickness.
Results
The primary finding was a 227-fold difference in dissociation rates between neutral and acidic conditions, which extended the molecule's in vivo efficacy in rats from 6 days to over 15 days. The optimized molecule dose-dependently promoted body weight gain, IGF-1 secretion, tibial growth, and increased growth plate thickness. At medium to high doses, it induced a flatter and sustained IGF-1 response compared to PEGylated GH.
Interpretation
The study suggests that pH.VHH03 could offer a longer duration of action than current PEGylated GH formulations. However, the clinical significance of these findings remains uncertain due to the study's reliance on rat models and surrogate endpoints. Further research in humans is needed to confirm the potential benefits and safety of this approach.
Key findings
- 227-fold difference in dissociation rates between neutral and acidic conditions.
- In vivo efficacy in rats extended from 6 days to over 15 days.
- Significant enhancement in in vitro cell proliferation activity.
- Dose-dependent promotion of body weight gain and IGF-1 secretion in rats.
- Notably flatter and sustained IGF-1 response at medium to high doses compared to PEGylated GH.
Limitations
- rat model, not human data
- surrogate endpoints like IGF-1 secretion
- potential species-specific effects
- unknown long-term safety