Investigating intrinsic radiosensitivity biomarkers to peptide receptor radionuclide therapy with [Lu]Lu-DOTATATE in a panel of cancer cell lines.

Introduction: [Lu]Lu-DOTATATE is an effective systemic targeted radionuclide therapy for somatostatin receptor (SSTR) positive metastatic or inoperable neuroendocrine tumours (NET). However, for a given injected activity, tumour responses are variable. Our aim was to investigate whether SSTR expression/functionality and known characteristics of intrinsic radiosensitivity, namely proliferation rate, glucose metabolism, cell cycle phase, DNA repair and antioxidant defences were predictors of sensitivity to [Lu]Lu-DOTATATE in SSTR expressing human cancer cell lines.

Methods: In six human cancer cell lines and under basal condition, SSTR expression was assessed by qRT-PCR and immunocytochemistry. Its functionality was evaluated by binding/uptake assays with [Ga]Ga- and [Lu]Lu-DOTATATE. The radiosensitivity parameters were evaluated as follows: proliferation rate (cell counting), glucose metabolism ([F]FDG uptake), antioxidant defences (qRT-PCR, colorimetric assay, flow cytometry), DNA repair (qRT-PCR) and cell cycle (flow cytometry). Effect of [Lu]Lu-DOTATATE on cell viability was assessed 3, 7 and 10 days after 4 h incubation with [Lu]Lu-DOTATATE using crystal violet.

Results: Based on cell survival at day 10, cell lines were classified into two groups of sensitivity to [Lu]Lu-DOTATATE. One group with <20% of survival decrease (-14 to -1%) and one group with >20% of survival decrease (-22 to -33%) compared to the untreated control cell lines. The latter had significantly lower total antioxidant capacity, glutathione (GSH) levels and glucose metabolism (p < 0.05) compared to the first group. SSTR (p = 0.64), proliferation rate (p = 0.74), cell cycle phase (p = 0.55), DNA repair (p > 0.22), combined catalase and GSH peroxidase expression (p = 0.42) and superoxide dismutase (SOD) activity (p = 0.41) were not significantly different between the two groups.

Conclusion: Antioxidant defences may be major determinants in [Lu]Lu-DOTATATE radiosensitivity.