Betulin binds to melanocortin receptors and antagonizes α‐melanocyte stimulating hormone induced cAMP generation in mouse melanoma cells

Abstract

Betulin is a principal component of birch bark and is known to possess a broad range of biological activities, including antiinflammatory, antiviral and anticancer actions. The present study was carried out in vitro to clarify the influence of betulin on melanocortin (MC) receptor-ergic signalling by using COS-7 cells transfected with corresponding human MC receptor DNA. The results showed that betulin binds to the human melanocortin MC1, three to five receptors with selectivity to the MC1 subtype (K(i) value 1.022 +/- 0.115 microM). Betulin binds to the MC receptors with the following potency order-MC > MC3 > MC5 > MC4. Betulin itself does not stimulate cAMP generation, however, it slightly antagonizes alpha-melanocyte-stimulating hormone (alpha-MSH)-induced cAMP accumulation in the mouse melanoma cell line B16-F1. As a water-insoluble substance, betulin was dissolved in DMSO therefore DMSO competition with the labelled ligand NDP-MSH for the binding to the MC receptors was tested in the identical experimental set-up. We found that DMSO competes for binding to all the MC receptor subtypes, at 20% concentration and above. Selectivity for one or another receptor subtype was not observed. We have demonstrated for the first time, the ability of the plant compound betulin to bind to the MC receptors. One may suggest MC receptor MC1 subtype as the essential target for the antimelanoma action of betulin and its structurally close molecules such as betulinic acid. Moreover, we have found a new non-peptide small molecule MC mimetic, that is betulin. Thus, we report a new chemical motif for the binding to the MC receptors that could be used as a template for the search of more selective MC mimetics.

Betulin Elicits Anti‐Cancer Effects in Tumour Primary Cultures and Cell Lines In Vitro

“…Moreover, in our experiments, betulin does not change the expression of p21 and p53 genes involved in the cell cycle progression, which is in agreement with other studies [21]. It is also possible that betulin competes with growth factor for binding to its receptors, as reported for melanocortin receptor 1 [22]. Thus, we investigated the pathways essential for cancer cell proliferation, which are stimulated by a variety of growth factors [23].…”

Betulin Complex in γ-Cyclodextrin Derivatives: Properties and Antineoplasic Activities in In Vitro and In Vivo Tumor Models

“…Bet binds to the melanocortin receptors and promotes cell death in mouse melanoma cells [29]. Bet is still being investigated as an antitumor agent.…”

Unifying Mechanisms of Action of the Anticancer Activities of Triterpenoids and Synthetic Analogs

“…Binding studies show that betulin binds the melanocortin receptors with variable K i values and potencies (MC1 > MC3 > MC5 > MC4), and the K i value for MC1 is 1.022 μM [88]. Although betulin does not induce cAMP expression in mouse melanoma cells, betulin inhibits induction of this second messenger by β-melanocyte-stimulating hormone.…”