Design, synthesis, and biological evaluation of radioiodinated benzo[d]imidazole-quinoline derivatives for platelet-derived growth factor receptor β (PDGFRβ) imaging

Several malignant tumors and fibrotic diseases are associated with PDGFRβ overexpression and excessive signaling, making this receptor attractive for molecular targeting and imaging approaches. A series of benzo[d]imidazole-quinoline derivatives were designed and synthesized to develop radioiodinated compounds as PDGFRβ-specific imaging probes. The structure activity relationship (SAR) evaluation of the designed compounds was performed. Among them, 2-[5-(2-methoxyethoxy)-1H-benzo[d]imidazol-1-yl]-8-(piperazin-1-yl)quinoline (5a) and 4-{2-[5-(2-methoxyethoxy)-1H-benzo[d]imidazol-1-yl]quinolin-8-yl}morpholine (5d) exhibited a relatively high PDGFRβ-TK inhibitory potency, whereas iodinated 5a derivative 5-iodo-2-[5-(2-methoxyethoxy)-1H-benzo[d]imidazol-1-yl]-8-(piperazin-1-yl)quinoline (8) exhibited a superior inhibitory potency as PDGFRβ inhibitor than iodinated 5d derivative 4-{5-iodo-2-[5-(2-methoxyethoxy)-1H-benzo[d]imidazol-1-yl]quinolin-8-yl}morpholine (11). Furthermore, [ ¹²⁵ I]8 and [ ¹²⁵ I]11 were synthesized and evaluated for PDGFRβ radioligand ability, both in vitro and in vivo. Cellular uptake experiments showed that [ ¹²⁵ I]8 had a higher uptake in BxPC3-luc cells as PDGFRβ-positive cells than [ ¹²⁵ I]11. Incubation of [ ¹²⁵ I]8 after pretreatment of PDGFRβ ligands significantly reduced the uptake of [ ¹²⁵ I]8. In biodistribution experiments using tumor-bearing mice, [ ¹²⁵ I]8 accumulation in the tumor 1 h postinjection was higher than that of the benzo[d]imidazol-quinoline derivative [ ¹²⁵ I]IIQP, used in our previous research. These results indicate that [ ¹²⁵ I]8 could be a promising PDGFRβ imaging agent. Although its clinical application requires further structural modifications, the results obtained in this research may be useful for the development of PDGFRβ-specific radioligands.