Lutetium (177Lu) edotreotide

177Lu-DOTATATE/DOTATOC peptide receptor radionuclide therapy (PRRT) has demonstrated potential for treating pediatric neuroblastoma (NB), and in clinical practice can be measured dosimetry by multi–time point (MTP) dosimetry. However, the high workload and limited patient compliance associated with MTP restrict its application. Consequently, single time point (STP) dosimetry approaches have emerged as a promising alternative, though their effectiveness in pediatric populations has not been thoroughly investigated. This study aimed to assess the dosimetric determination of 177Lu-DOTATATE/DOTATOC in pediatric neuroblastoma patients to determine whether STP could serve as a viable replacement for MTP.

A total of 24 pediatric NB patients who received 1 to 2 cycles of 177Lu-DOTATATE or 177Lu-DOTATOC underwent dosimetric measurement of lesions and critical organs using the 96 hours single time point (STPH) dosimetry method proposed by Hänscheid and colleagues. The results were compared with those obtained from standard MTP.

In patients treated with 177Lu-DOTATATE, the mean relative deviation absolute values of the STPH-calculated absorbed dose from MTP were <10% for lesions, kidneys, bone marrow, liver, and spleen, with Pearson correlation coefficients of 0.99, 0.93, 0.97, 0.84, and 0.84, respectively. In patients treated with 177Lu-DOTATOC, the mean relative deviation absolute values for kidneys, spleen, and bone marrow were <10%, with Pearson correlation coefficients of 0.97, 0.77, 0.35, 0.48, and 0.93 for lesions, kidneys, bone marrow, liver, and spleen, respectively.

The findings confirm that the 96 hours STPH method can reliably replace MTP for dosimetric assessment in pediatric NB patients treated with 177Lu-DOTATATE and performed well in renal dosimetry for 177Lu-DOTATOC therapy.

The coinfusion of amino acids with targeted radiopharmaceutical therapy aims to reduce renal toxicity. Unfortunately, this requires a prolonged, large-volume infusion and often results in side effects such as nausea, vomiting, and hyperkalemia. Sodium paraaminohippurate is a nontoxic compound that has historically been used to measure renal plasma flow. It is excreted by the kidneys via glomerular filtration and tubular secretion using organic anion transporters. Paraaminohippurate has a favorable safety profile at plasma concentrations that saturate the maximum transport capacity of tubular cells. Therefore, paraaminohippurate may potentially reduce the renal accumulation of small-molecule radiopharmaceuticals. Methods: Preclinical studies, including ex vivo biodistribution, SPECT/CT, and PET analyses, were performed in Wistar rats to evaluate how coinjection of a paraaminohippurate solution affects the renal uptake of various radiopharmaceuticals compared with coinjection of a NaCl or arginine-lysine solution. Results: Paraaminohippurate was well tolerated, with no toxicity observed. Accumulated activity measured in the renal cortex was significantly lower for the small-peptide radiopharmaceuticals (0.9-2.5 kDa)-[¹⁷⁷Lu]Lu-DOTATOC, [¹⁷⁷Lu]Lu-DOTATATE, [¹⁷⁷Lu]Lu-DOTA-JR11, [¹⁷⁷Lu]Lu-DOTA-sargastrin, and [¹⁷⁷Lu]Lu-DOTARGD-when paraaminohippurate was coinjected instead of NaCl. The renal uptake of [¹⁷⁷Lu]Lu-DOTATOC, [¹⁷⁷Lu]Lu-DOTATATE, and [¹⁷⁷Lu]Lu-DOTA-JR11 was reduced by 46%, 83%, and 63%, respectively, at 1 h after injection with paraaminohippurate coinjection from the uptake after injection with NaCl. Kidney area-under-the-curve values were reduced by up to 60%, depending on the compound used. To a lesser extent, paraaminohippurate-mediated nephroprotection was observed with the prostate-specific membrane antigen (PSMA)-targeting molecules [¹⁷⁷Lu]Lu-PSMA-I&T and [⁶⁸Ga]Ga-PSMA-11. The renal uptake of the larger recombinant protein [¹⁷⁷Lu]Lu-DOTA-Affiline-22 (18 kDa) and the folate derivative [^99mTc]Tc-etarfolatide was not affected. These in vivo imaging data were confirmed by ex vivo biodistribution studies. Conclusion: Coinjection of paraaminohippurate at a high concentration was found to significantly reduce the renal uptake of a select number of small-molecule radiopharmaceuticals. This indicates the importance of tubular secretion, as well as the potential role of anion transporters that may be saturated by a high paraaminohippurate plasma concentration. Therefore, paraaminohippurate comedication could serve as a fast, safe, and convenient alternative to amino acid infusion as a nephroprotective agent during targeted radiopharmaceutical therapy.