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-trifluoro 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 [125I]
MIBG (0.1 microM) for 2 h in the presence of varying concentrations (10(-8)-10(-3) M) of
ligand. For measuring uptake, cells were incubated with [125I]
IPP (0.1 microM) and cell-associated radioactivity was measured at various times. Retention was studied by incubating cells in the presence of [125I]
IPP (0.1 microM) for 2 h, followed by replacement with
drug-free medium and determination of cell-bound radioactivity. Selectivity of [125I]
IPP uptake was studied by inhibition studies with
MIBG, DMI, 5HT and phenylpiperazines. The biodistribution of [125I]
IPP was measured in normal rats at 0.083, 0.5, 1, 2 and 24 h (six animals per group). The IC50S (microM) for inhibition of [125I]
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 [125I]
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 IC50S (microM) for inhibition of [125I]
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, > or = 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.