Mathematical modelling of [C-11]-(+)-PHNO human competition studies

作者：Searle Graham E^*; Beaver John D; Tziortzi Andri; Comley Robert A; Bani Massimo; Ghibellini Giulia; Merlo Pich Emilio; Rabiner Eugenii A; Laruelle Marc; Gunn Roger N

来源：NeuroImage, 2013, 68: 119-132.

DOI：10.1016/j.neuroimage.2012.11.033

• C-11-(+)-PHNO
• Dopamine
• D-2 receptor
• D-3 receptor
• PET

The D-2/D-3 agonist radioligand [C-11]-(+)-PHNO is currently the most suitable D-3 imaging agent available, despite its limited selectivity for the D-3 over the D-2. Given the collocation of D-2 and D-3 receptors, and generally higher densities of D-2, the separation of D-2 and D-3 information from [C-11]-(+)-PHNO PET data are somewhat complex. This complexity is compounded by recent data suggesting that [C-11]-(+)-PHNO PET scans might be routinely performed in non-tracer conditions (with respect to D-3 receptors), and that the cerebellum (used as a reference region) might manifest some displaceable binding signal.
Here we present the modelling and analysis of data from two human studies which employed an adequate dose range of selective D-3 antagonists (GSK598809 and GSK618334) to interrogate the [C-11]-(+)-PHNO PET signal. Models describing the changes observed in the PET volume of distribution (V-T) and binding potential (BPND) were used to identify and quantify a [C-11]-(+)-PHNO mass dose effect at the D-3, and displaceable signal in the cerebellum, as well as providing refined estimates of regional D-3 fractions of [C-11]-(+)-PHNO BPND. The close of (+)-PHNO required to occupy half of the available D-3 receptors (ED50PHNO,D3) was estimated as 40 ng/kg, and the cerebellum BPND was estimated as 0.40.
These findings confirm that [C-11]-(+)-PHNO human PET studies are in fact routinely performed under non-tracer conditions. This suggests that (+)-PHNO injection masses should be minimised and tightly controlled in order to mitigate the mass dose effect. The specific binding detected in the cerebellum was modest but could have a significant effect, for example on estimates of D-3 potency in drug occupancy studies. A range of methods for the analysis of future [C-11]-(+)-PHNO data, incorporating models for the effects quantified here, were developed and evaluated. The comparisons and conclusions drawn from these can inform the design and analysis of future PET studies with [C-11]-(+)-PHNO.

• 出版日期2013-3