Evaluation of phenylpiperazines as targeting agents for neuroblastoma

The potential of radiolabelled phenylpiperazines as agents for the detection 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-carboxamidino-4-phenyl-piperazine (CAPP), [4-(3-chlorophenyl)-piperazine (mCPP), 4-(3-tritluoro methyl phenyl)-piperazine (TFMPP), and (1,1-dimethyl-4-phenyl)-piperazinium hydrochloride (DMPP) and chlorophenyl hydroxypiperidine [CP(OH)P], to inhibit MIBG uptake by neuroblastoma cells was 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 measuring uptake, cells were incubated with [I-125]IPP (0.1 mu M) and cell-associated radioactivity was measured at various times. Retention was 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 determination of cell-bound radioactivity. Selectivity of [I-125]Ipp uptake was studied by inhibition studies with MIBG, DMI, 5HT and phenylpiperazines. 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) for 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 distribution similar to MIBG. The results demonstrate that phenylpiperazines display significant affinity for neuroblastoma with uptake and retention characteristics similar to MIBG.