EVALUATION OF PHENYLPIPERAZINES AS TARGETING AGENTS FOR NEUROBLASTOMA

The potential of radiolabelled phenylpiperazines as agents for the det ection and therapy of tumours of neural crest origin was evaluated by in vitro pharmacological studies with human neuroblastoma cell lines [ SK-N-SH and SK-N-BE(2C)], and in vivo by biodistribution measurements. The ability of phenylpiperazines: 4-phenyl-piperazine (PP), 1-carboxa midino-4-phenyl-piperazine (CAPP), [4-(3-chlorophenyl)-piperazine (mCP P), 4-(3-tritluoro methyl phenyl)-piperazine (TFMPP), and (1,1-dimethy l-4-phenyl)-piperazinium hydrochloride (DMPP) and chlorophenyl hydroxy piperidine [CP(OH)P], to inhibit MIBG uptake by neuroblastoma cells wa s determined by incubation with [I-125]MIBG (0.1 mu M) for 2 h in the presence of varying concentrations (10(-8)-10(-3) M) of ligand. For me asuring uptake, cells were incubated with [I-125]IPP (0.1 mu M) and ce ll-associated radioactivity was measured at various times. Retention w as studied by incubating cells in the presence of [I-125]IPP (0.1 mu M ) for 2 h, followed by replacement with drug-free medium and determina tion of cell-bound radioactivity. Selectivity of [I-125]Ipp uptake was studied by inhibition studies with MIBG, DMI, 5HT and phenylpiperazin es. The biodistribution of [I-125]IPP was measured in normal rats at 0 .083, 0.5, 1, 2 and 24 h (six animals per group). The IC(50)s (mu M) f or inhibition of [I-125]MIBG uptake were: PP, 1.5; Cpp, 2.5; CAPP, 2.5 ; DMPP, 5; CP(OH)P, 30 and TFMPP, 65. The rate of cellular uptake of [ I-125]IPP was greatest between 0 and 60 min and decreased after 60 min , similar to MIBG. After an initial rapid washout of approximately 50% of the radioactivity, retention remained constant for 3 h. The IC(50) s (mu M) for inhibition of [I-125]IPP uptake were: MIBG, 18-25; DMI, 0 .6-1.5; 5HT, > 100; IPP, 1.8-2.5; CPP, 7.0-9.0 and TFMPP, greater than or equal to 20. The in vivo studies demonstrated a pattern of distrib ution similar to MIBG. The results demonstrate that phenylpiperazines display significant affinity for neuroblastoma with uptake and retenti on characteristics similar to MIBG.