Evaluation of planar bioluminescence imaging and microPET/CT for therapy monitoring in a mouse model of pigmented metastatic melanoma

Bioluminescence imaging (BLI) is widely used for in-vivo monitoring of anti-cancer therapy in mice. [18F]MEL050 is a Positron Emission Tomography (PET) radiotracer which specifically targets melanin. We evaluated planar BLI and [18F]MEL050-PET/CT for therapy (pro-apoptotic peptide LZDP) monitoring in a mouse model of metastatic pigmented melanoma. Twelve B6-albino mice were intravenously injected with B16-F10-luc2 cells on day 0 (D0). The mice received daily from D2 to D17 either an inactive peptide (G1, n=6), or LZDP (G2, n=6). They underwent both BLI and [18F]MEL050-PET/CT imaging on D2, D8 and D17. The number of visible tumors was determined on BLI and PET/CT. [18F]MEL050 uptake in tumor sites was quantified on PET/CT. After sacrifice (D17), the number of black tumors was counted ex-vivo. On D2, BLI and PET/CT images were visually negative. On D8, BLI detected 8 tumor sites in 4/6 mice of G1 vs 5 in 3/6 mice of G2 (NS); PET/CT was visually negative. On D17, BLI detected 17 tumor sites in 5/6 mice of G1 vs 10 in 4/6 mice of G2 (NS). PET/CT detected 18 tumor sites in 4/4 mice of G1 vs 14 in 3/4 mice of G2 (NS). Mean %ID/g of [18F]MEL050 in tumor sites was lower in G2 than in G1 on D17 (P<0.001), whereas bioluminescence intensity was not different between the 2 groups. Ex-vivo examination confirmed lower number of tumors in G2 (P<0.03). In the small number of animals tested in this study, [18F]MEL050-PET/CT and ex-vivo examination could affirm anti-tumoral effect of LZDP, but not BLI