Extended Rate Analysis (ExtRA™)

- Kinetic analysis of slowly dissociating compounds

Beactica has developed a proprietary method for determination of slow dissociation rates. The method extends the range for which reliable koff values can be determined, and has a lower limit of ~10-7 s-1. This corresponds to a residence time of >100 days.

In the late stages of lead optimization, it is common that compounds dissociate very slowly from their target. For such interactions, steady-state approaches are not useful and standard kinetic methods can only reliably quantify dissociation rates faster than ~10-4 s-1 [1].

The ExtRA™ method is based on a novel experimental design and analysis procedure and has been successfully applied in several partner projects.

ExtRA range

ExtRA™ range for quantification of dissociation rate constants (koff) or residence times (τ), compared to standard SPR-based assays.

Case study

Eleven high affinity compounds in a late stage project were to be ranked and differentiated on the basis of dissociation rate constants (koff). The ExtRA™ method enabled reliable determination of koff for all compounds (figure below). The ranking correlated perfectly with results from an orthogonal cell-based assay, and the results allowed a SAR analysis and further optimization of the compounds.

11 cmpds ExtRA

All 11 compounds showed koff values below the limit for steady-state and standard SPR assays, and could only be determined using the ExtRA™ method.

ExtRA™ deliverables

• Dissociation rate constants (koff)
• Residence times (t)
• Interaction kinetic profiles
• Mechanistic interpretation



Reference: [1] Önell & Andersson, J. Mol. Recogn. 2005;18:307-317