Biological Sex Influences the Pharmacokinetics and Organ Dosimetry of 177Lu-DOTATATE: A Systematic Preclinical Evaluation

Background/Objectives: While 177Lu-DOTATATE has demonstrated clinical efficacy in peptide receptor radionuclide therapy (PRRT) for neuroendocrine tumors (NETs), current dosing regimens do not account for potential sex-based pharmacokinetic differences. Our study systematically characterizes sex-dependent pharmacokinetic variations of 177Lu-DOTATATE in preclinical models to provide the first preclinical evidence base informing future sex-stratified clinical investigations. Methods: Sex-stratified pharmacokinetic and biodistribution studies were conducted in male and female SD rats following intravenous administration of 177Lu-DOTATATE at multiple dose levels: 2.86, 5.71, and 11.43 mCi/kg. Metabolic stability and renal excretion patterns were characterized. Safety assessments included acute toxicity, vascular irritation, hemolysis, and allergenicity testing. Therapeutic efficacy was evaluated exclusively in female AR42J xenograft-bearing CB-17 SCID mice. Results: Significant sex-dependent pharmacokinetic differences were observed at high (11.43 mCi/kg) and low (2.86 mCi/kg) dose levels, with females exhibiting 30–40% higher AUC and Cmax values compared to males (p < 0.05). Both sexes demonstrated preferential accumulation in SSTR-expressing tissues, particularly the pancreas (females: 10.87 ± 2.51% ID/g; males: 9.10 ± 0.76% ID/g) and adrenal glands, with rapid clearance from non-target organs. Radio-HPLC analysis confirmed high metabolic stability with no detectable radiolabeled metabolites, and over 90% of radioactivity was recovered through renal excretion. Safety assessments demonstrated excellent tolerability across dose levels. In female xenograft models, treatment achieved tumor growth inhibition of 92.35–96.44% and 100% survival rate versus 10% in controls, though mid/high doses caused weight loss. Conclusions: Our study provides systematic preclinical evidence of sex-dependent pharmacokinetic differences in 177Lu-DOTATATE, with females demonstrating significantly higher systemic exposure than males at specific dose levels. These findings establish the systematic preclinical evidence base for sex-dependent pharmacokinetic differences in 177Lu-DOTATATE, providing a scientific rationale for incorporating sex as a stratification variable in future dosimetry-guided clinical studies.