. 2023 Apr 28;28(9):3798. doi: 10.3390/molecules28093798

Table 2.

Radiolabeling methods, their advantages, and their disadvantages.

Radiolabeling Method	Radioisotope	Chelator/Other Molecules	Advantages	Disadvantages	Ref.
Passive encapsulation	^99mTc	-	Direct incubation during liposome manufacturing	Limited encapsulating capacity, low loading efficiency, low stability, requires freshly prepared liposomes	[42]
Passive encapsulation	¹⁸F-fludeoxyglucose (¹⁸F-FDG)	-	Direct incubation during liposome manufacturing		[49,50]
Membrane labeling	^99mTc	SnCl₂ (reducing agent)	High labeling efficiency	Low in vivo stability	[51,52,53]
Remote labeling—ionophore	¹¹¹In, ⁶⁷Ga, ^99mTc	nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA), tetraxetan, 2,2′,2′′,2′′′-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid (DOTA) Ionophore: A23187, small molecular weight ionophore (oxine)	Labeling efficiency between 60 and 90%	Additional step required for purification procedures	[54,55,56,57,58]
Remote labeling—lipophilic chelator	^99mTc	hexamethylpropyleneamine oxime (HMPAO)	Higher labeling efficiency than passive encapsulation	Additional step required for purification procedures	[59]
	^99mTc, ¹⁸⁸Re, ¹⁸⁶Re	N,N-bis(2-mercapatoethly)-N’,N’-diethylenediamine (BMEDA)	Higher labeling efficiency than passive encapsulation	Additional step required for purification procedures	[60,61]
	⁶⁴Cu, ⁵²Mn	DOTA	-	Poor loading efficiency	[62]
	⁶⁴Cu	Oxine, DOTA	High labeling efficiency and stability; the addition of oxine facilitates the transport of ⁶⁴Cu into liposomes	Synthesis of preformed liposomes that contain oxine	[63,64]
Remote labeling—surface chelator	⁸⁹Zr	Deferoxamine (DFO)	High stability in vitro	Low labeling yield (~44%)	[65]
	^99mTc, ⁶⁷Ga	DTPA conjugated to stearylamine	High labeling efficiency	Low in vitro and in vivo stability	[66,67]
	⁶⁴Cu	4-(N-hydroxyamino)-2R-isobuty-2S-(2-thienylthiomethyl)succinyl-l-phenylalanine-N-methylamide (BAT)	High labeling efficiency	Additional heating step (>70 °C) required for the incorporation of ⁶⁴Cu into BAT	[68]
	^99mTc, ¹¹¹In	N-hydroxy succinimidyl hydrazine nicotinate hydrochloride (HYNIC) conjugated to 1,2-Distearoyl-sn-glycero-3-phosphoethanolamine (DSPE)	High stability and labeling efficiency (>95%), rapid labeling procedure without purification required	Limited radionuclide choices	[67,69]
	^99mTc-tricarbonyl complex	2-iminothiolane	High labeling efficiency (>90%) and stability	Tedious preparation method required for the synthesis of ^99mTc-tricarbonyl (^99mTc-(CO₃⁺))	[54,55,56,57,58,63,64,68,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84]
	⁶⁴Cu, ⁵²Mn, ⁶⁸Ga	DOTA conjugated to DSPEIonophore: oxine	High labeling efficiency (>90%) and stability	Labeling needs to be performed at pH 4 due to the use of ethanol for oxine solubility	[62,63,68]