Cell experiment:

HT29 cells are washed with Phosphate buffer saline (PBS) and harvested with a 0.5% trypsin solution at 50-60% confluency. Cells are then added to wells at a density of 104 cells/well in a 96-well plate to a final volume of 100 μL/well. After 24 hours of incubation at 37℃ in a 5% CO2 atmosphere, the culture medium is replaced with 200 μL fresh culture medium containing 5HT hydrochloride, Phenylbiguanide hydrochloride at concentrations of: 3.125, 6.25, 12.5, 25, 50, and 100 μM . Cells cultured solely in media served as negative controls. After 48 hours of incubation at 37℃ in a 5% CO2 atmosphere, the culture medium is removed and 8 μL MTT reagent (diluted in PBS at a concentration of 4 mg/mL) is added to 50 μL of fresh culture medium at a final concentration of 0.55 mg/mL. The optimum incubation period time is determined in a pilot study[2].

Animal experiment:

Mice[3] Adult male specified pathogen free (SPF) BALB/c mice (28-33 g; n=10) are used throughout this study. All mice have free access to water and food in a light (12: 12 h light/ dark cycle, lights on at 0700 h) and temperature-controlled (21-23℃) environment. Mice are randomly assigned to two treatment groups, 1) intra-atrial injection of 0.9% saline (controls, n=5) or 2) intra-atrial injection of vehicle containing Phenylbiguanide (n=5). For the PBGinjected group, mice are injected with an effective dose of Phenylbiguanide (1-1.5 μg in 10-15 μL saline) . This is repeated five times in total with each injection separated by 8-10 min. For control mice, each mouse receives five saline injections (10-15 μL each), also at 8-10 min intervals[3].

Phenylbiguanide is a 5-HT3 receptor selective agonist with an EC50 of 3.0±0.1 μM.

Phenylbiguanide (1-Phenylbiguanide) is a 5-HT3 receptor selective agonist with pEC50s of 5.57, 4.07, and 4.47 for r5-HT3A(b), h5-HT3A, m5-HT3A(b) , respectively[1]. The effect of Phenylbiguanide (1-Phenylbiguanide hydrochloride) in promoting the growth of the HT29 cell line is investigated. Phenylbiguanide causes a dose dependent proliferation of HT29 cells after 48 hours incubation. The maximum proliferation is at a 5HT concentration of 12.5 μM (P≤0.01). Phenylbiguanide significantly stimulates the growth of cells at concentrations of 3.125 μM (P≤0.05) and 6.25 μM (P≤0.01)[2].

In anaesthetised mice, Phenylbiguanide (PBG), a drug that is known to stimulate cardiopulmonary afferent C-fibres,is injected into the right atrium of the heart and mapped c-Fos expression within specific regions of the central nervous system. Intraatrial injection of PBG produces a reflex cardiorespiratory response including a pronounced bradycardia and a respiratory depression[3].

[1]. Mair ID, et al. Pharmacological characterization of a rat 5-hydroxytryptamine type3 receptor subunit (r5-HT3A(b)) expressed in Xenopus laevis oocytes. Br J Pharmacol. 1998 Aug;124(8):1667-74. [2]. Ataee R, et al. Study of 5HT3 and HT4 receptor expression in HT29 cell line and human colon adenocarcinoma tissues. Arch Iran Med. 2010 Mar;13(2):120-5. [3]. de Vries A, et al. Characterisation of c-Fos expression in the central nervous system of mice following right atrialinjections of the 5-HT3 receptor agonist Phenylbiguanide. Auton Neurosci. 2005 Dec 30;123(1-2):62-75.