We have injected a radiolabeled small protein (10 kDa) to an animal model bearing positive and negative tumors. During submission process, reviewers asked for the concentration of accumulated protein in the positive tumor and... I really don't know how to do this.

I've tried with the "binding potential" formula, but we aren't in the good experimental conditions (the concentration of radiolabeled protein is too low and we have only one time point). Help!

What we know :

- Number of receptors of interest per cell : 5 × 10^5 EGFR per cell (5x10^6 cells were injected in each mouse).

- Effective specific activity of the injected proteins (mixture of labeled and unlabeled proteins): 37.0 – 53.6 MBq/nmol

- Total quantity of injected proteins: 10 nmol

- Uptake in the positive tumor 2.5h p.i. : 1.42 ± 0.18 %ID/g 

- Uptake in the negative tumor 2.5h p.i. : 0.56 ± 0.10 %ID/g 

- In vitro affinity of the protein for the receptor : Kd = 27 nM