A non-internalised CD38-binding radiolabelled single-domain antibody fragment to monitor and treat multiple myeloma

Table 1 Summary of in vitro and in vivo characterisation of the different anti-CD38 sdAbs. The affinities and competition behaviour towards the human monoclonal antibody daratumumab were obtained by the biolayer interferometry method

Parameters sdAbs	#375	#1053	#551	#2F8
Affinity (K_D)	1.49 nm	1.7 nM	1.50 nM	1.48 nM
Competition Vs daratumumab	Competitor	Competitor	Partial competitor	Non-competitor
Biodistribution
Location	ND	1.78 ± 0.37	3.37 ± 0.38	2.22 ± 0.47
Tumour	ND	258.00 ± 19.08	402.20 ± 22.46	169.32 ± 4.56
Blood	ND	0.61 ± 0.26	1.33 ± 0.08	0.53 ± 0.12
Liver	ND	1.28 ± 0.28	1.33 ± 0.08	0.53 ± 0.12
Thermal stability (Tm*)	69.1 ± 0.1 °C	73.1 ± 0.1 °C	72.2 ± 0.2 °C	88.7 ± 0.3 °C

All the sdAbs have an affinity in the nanomolar range. #375 and #1053 are in competition with daratumumab, while a partial and no competition are observed for #551 and #2F8, respectively. The data included in the biodistribution section correspond to the results obtained after radiolabelling of sdAbs with the ^99mTc radioisotope (Fig. 3); #551 and #2F8 show the best tumour uptake. The thermal stability (Tm*) of the sdAbs was evaluated by far UV circular dichroism. The most stable is #2F8. Based on these characteristics, sdAb 2F8 was chosen for further work. (ND: not-determined, protein not studied in vivo because its in vitro behaviour is similar to that of sdAb 1053)

ISSN: 1756-8722