Dual Amylin and Calcitonin Receptor Agonists: A Novel Treatment for Obesity and Related Co-Morbidities

Abstract

Amylin and/or calcitonin receptor agonists such as pramlintide and davalintide have shown promise on weight reduction in preclinical models and clinical settings, albeit with limited efficacy on glucose homeostasis. The overall aim of this Ph.D. project was to investigate the metabolic effect of the dual amylin and calcitonin receptor agonists (DACRA), KBP-042, KBP-088, KBP-089, focusing on the weight reducing and glucoregulatory potential in preclinical animal models of obesity and related morbidities like type 2 diabetes (T2D) and nonalcoholic steatohepatitis (NASH). Both synthetic and naturally occurring DACRAs exert prolonged receptor activation and it is hypothesized that this prolonged receptor activation will improve the in vivo efficacy. Furthermore, it is hypothesized that DACRAs have beneficial metabolic effects beyond caloric intake and simple diet-induced weight loss. In this series of studies, the focus was on metabolic effects of KBPs. Effects on body weight and adipose tissue as well as glucose metabolism were thoroughly explored in experimental rat models resembling the phenotypes of obesity, T2D and NASH, to address whether these beneficial effects were solely due to suppression of food intake and the subsequent weight loss. As amylin agonism induces a well-known anorexic effect at dose initiation, these studies also focused on different dosing regimens including dose escalation and dosing frequency. Finally, we compared KBPs to a second-generation amylinomimetic, davalintide, and combination of KBPs with the GLP-1 analogue, liraglutide. KBPs potently activated both the amylin and calcitonin receptors in vitro, and demonstrated a prolonged receptor activation when compared to second-generation amylinomimetic, davalintide. KBPs transiently suppressed caloric intake, and induced and sustained a dose-dependent weight loss compared to vehicle and pair-fed rats. Concomitantly, overall adiposity was decreased and obesity related adipocyte hypertrophy were improved – findings superior to the effects obtained with davalintide treatment. The inappropriate high fat diet-induced lipid accumulation was eliminated by KBP treatment, and interestingly, KBPs alleviated hyperinsulinemia and improved glucose tolerance even with significantly lower insulin levels. KBP treatment increased the glucose infusion rate during a hyperinsulinemic euglycemic clamp indicating enhanced insulin action. Importantly, KBPs also improved glucose homeostasis and enhanced insulin action in Zucker Diabetic Fatty rats. To investigate beneficial effects beyond weight loss, a weight-matched group was implemented. Of interest, weight matching led to improved glucose homeostasis through lowered plasma insulin; however, these were inferior to the effect of KBPs. KBPs were introduced using various dosing regimens and frequencies. Dosing every day and every second day resulted in an equal weight loss at study end; however, with a later onset of maximal weight loss. To optimize tolerability, KBPs were introduced by dose escalation. In a 4-fold dose escalation, KBPs induced a transient reduction in food intake at every escalation step – with reducing magnitude over time. Two-fold and linear escalations suppressed body weight evenly with no significant reduction in food intake at either escalation step; however, with a delayed onset of maximum efficacy. Interestingly, when KBP and liraglutide were combined, the effect on acute food intake was superior to either of peptides as single-dose. Chronically, KBP-089 (1.25 μg/kg) and liraglutide (50 μg/kg) lowered body weight 8% and 2% in HFD rats, respectively, while the combination resulted in a 12% body weight reduction. Moreover, the combination improved glucose tolerance. In a rat model resembling the phenotype of human NASH, KBP treatment led to a reduction of the high fat, high cholesterol and cholate diet induced increase in liver weight and circulating aspartate transaminase (AST) levels. Finally, at the histological level KBP treatment reduced hepatic steatosis, ballooning and inflammation, hence resulting in a reduced NAS score in combination with a lowered fibrosis stage. In conclusion, KBPs induce and sustain weight loss, leading to improved metabolic parameters including food preference, and these are beyond those observed simply by dietinduced weight loss. Additionally, these peptides are well tolerated when introduced by dose escalation. Finally, KBPs reduce liver steatosis in both obese and NASH rats, and importantly reduced inflammation and fibrosis scores in NASH, hence underscoring the DACRA potential as an anti-obesity agent with benefits on glucose control and NASH.