Surface activity profiling: a novel physicochemical tool for the prediction of blood-brain-barrier permeation Paavo K.J. Kinnunen Helsinki Biophysics & Biomembrane Group Institute of Biomedicine University of Helsinki Finland

Pharmocokinetics Challenge: Design good physicochemistry into the molecules as early as possible. What we know: Physicochemistry correlates with ADME/tox.

Outline 1.Existing assays logP, TPSA, CACO2, PAMPA,... 2.Amphiphilicity through surface activity Model justification Physicochemical parameters obtained 3. Overview on Delta-8 technology Features and specifications

Lipid bilayers: barrier for the entry of drugs into cells by passive diffusion

Ambiguous amphiphiles In order to be useful as a drug a compound has to dissolve in water  hydrophilicity required has to permeate lipid bilayers  lipophilicity required Hydrophilic part e.g. carboxylic acid derivatives Lipophilic part e.g. hydrocarbon chain

Air-water interface – a good model for lipid membranes Amphiphiles are strongly oriented in lipid membranes and in the air-water interface. Partitioning into both interfaces is mainly driven by the hydrophobic effect Air/water interface:Phospholipid bilayer:

Air-water interface: presence of multiple equilibria Partitioning Micellization Air Aqueous phase

Amphiphilicity is monitored through surface tension Maximum pull technique:

Looking at the hydrophobic effect in action... ~1/K aw CMC Slope= 1/A s =d  /RTdlnc

Compound structure must be optimized for optimum performance. Can surface activity profiling help?

Importance of the interfacial area ”common” phys-chem K aw > CMC 14678AsAs Amphiphilicity profiling 4136TPSA LogP MW -+CNS Phenyl butazone Hydroxyzine

Prerequisites for passive permeation... NalbuphineDisopyramide CNS+- common physchem MW LogP TPSA surface activity profiling K AW A S (Å 2 )65129

Spatial arrangement does matter PropranololMetoprolol CNS+CNS-

Solubility/hydrophobicity - antidepressants

Solubility/hydrophobicity – antidepressants CompoundAmitriptylineProtriptylineDoxepin K AW

Fraction absorbed: surface excess vs logP Kiehm et al., AAPS, 2005

Correlation between surface activity and PAMPA

Literature for BBB-permeability P. Suomalainen et al., Surface Activity Profiling of Drugs Applied to the Prediction of Blood-Brain Barrier Permeability. J. Med.Chem., 47: ,2004. H. Fischer et al., Blood-Brain Barrier Permeation; Molecular Parameters Governing Passive Diffusion. J.Membr.Biol., 165: , 1998 A.Seelig et al. A Method to Determine the Ability of Drugs to Diffuse Through the Blood-Brain Barrier. Proc. Natl.Acad.Sci., 91:68-72, 1994

Delta-8 Multichannel microtensiometer 96-well compatible Software controlled Fully automated

Use of standard footprint 96-well plate 50  l per well Optimized for surface tension measurements

The core: 8 high sensitivity microbalances Fixed to meet the positions of the wells in the 96-well plate Maximum pull force/du Nouy technique Probes instead of ring(s)

Automated cleaning Electric owen heating up to 1000°C