Systemic effects of 177Lu-DOTATATE therapy to patients with metastatic neuroendocrine tumors: mechanistic insights and role of exosome.

PURPOSE: The present study aimed to evaluate the systemic redox status in metastatic neuroendocrine tumor (NET) patients following 177Lu-DOTATATE therapy and to explore the role of exosomes in communicating the redox signals in-vitro.

METHODS

Levels of reactive oxygen species (ROS), enzymes associated with oxidative stress and lipid peroxidation, gene expression of oxidative stress markers (COX2, iNOS, NF-κB and SOD) were determined in peripheral blood mononuclear cells (PBMCs) and serum isolated from a total of 30 NET subjects at three time points viz.: before, 4 weeks after first and fourth cycle of 177Lu-DOTATATE therapy. Serum cytokine levels (IL-2, IL-6, IFN-γ, TNF-α, IL-4, IL-10 and TGF-β) were measured by ELISA. DNA damage was assessed by checking the expression of γH2AX and DNA repair genes (ATM: Ataxia-Telangiectasia Mutated and ATR: Ataxia-Telangiectasia and Rad3-related). Plasma-derived exosomes were characterized, their uptake by PBMCs was visualized and consequent ROS generation was assessed in in-vitro co-culture.

RESULTS

The study exhibits a significant increase in ROS level and relatively higher expression of COX2 and iNOS in PBMCs of NET patients post therapy. Serum inflammatory cytokines including IL-2, IL-6 and TNF-α were found elevated. The study did not find any change in the expression of genes associated with DNA damage. In-vitro co-culture of PBMCs (isolated before therapy) with exosomes derived after therapy exhibited significant increase in ROS as compared to control cells.

CONCLUSION

The study concludes that 177Lu-DOTATATE therapy alters redox status, however it does not cause DNA damage, suggestive of its safety. Further, the study demonstrates the role of exosomes in spreading of oxidative stress systemically.