A physiologically based pharmacokinetic model for [68Ga]Ga-(HA-)DOTATATE to predict whole-body distribution and tumor sink effects in GEP-NET patients

EJNMMI Research

Table 3 Fixed and fitted input parameters for the PBPK model, showing compound-specific parameter differences between [⁶⁸Ga]Ga-DOTATATE and [⁶⁸Ga]Ga-HA-DOTATATE, and system-specific parameter differences between the tumor compartments

Parameter	Fixed or fitted (*) value [range used in predictions]
Compound-specific	[⁶⁸Ga]Ga-DOTATATE	[⁶⁸Ga]Ga-HA-DOTATATE
Molecular weight	1502.3 g/mol	1628.5 g/mol
Lipophilicity	− 3.69	− 3.12
K_D	0.20 nmol/L	0.23 nmol/L *
k_off	0.012 min⁻¹	0.0071 min⁻¹ *
k_int	0.161 min⁻¹	0.268 min⁻¹
k_deg	0.00012 min⁻¹	0.00012 min⁻¹
Fraction unbound	0.69	0.69

System-specific	Primary tumor	Liver metastases	Other metastases
Fraction vascular	0.21 [0.09–0.34]	0.17 [0.1–0.23]	0.075 [0.025–0.125]
Fraction interstitial	0.3	0.3	0.3
Blood flow	152 mL/min/100 g [53–252]	203 mL/min/100 g [139–363]	152 mL/min/100 g [53–252]
SSTR concentration (interstitial)	168 nmol/L	224 nmol/L	224 nmol/L

K_D Equilibrium dissociation constant; k_off Dissociation rate constant; k_int Internalization rate; k_deg Degradation rate; SSTR Somatostatin receptor