K. Ikezaki et al., SELECTIVE AND PROLONGED MRI ENHANCEMENT BY MN-TPPS IN AN EXPERIMENTALRAT-BRAIN TUMOR WITH PERIPHERAL BENZODIAZEPINE RECEPTORS, Neurological research, 16(5), 1994, pp. 393-397
Synthesized Mn-TPPS, a paramagnetic metalloporphyrin, is expected to b
e a tumour specific contrast media for magnetic resonance (MR) imaging
. We investigated the enhancing characteristics of Mn-TPPS using a tra
nsplanted rat C6 glioma model with peripheral type benzodiazepine (PBD
) receptors since porphyrins are thought to possibly be endogenous lig
ands for PBD receptors. An Mn-TPPS enhancement study was then performe
d either with or without pretreatment while using peripheral and centr
al type benzodiazepine receptor specific ligands (PK11195 and clonazep
am, respectively). A signal intensity analysis disclosed the selective
and prolonged enhancement of the brain tumour even at 17 h after the
Mn-TPPS injection. This specific enhancement of the tumour, however, w
as not inhibited nor replaced by benzodiazepines. The tissue concentra
tion of Mn-TPPS was significantly higher in the glioma tissue than the
other tissues, while PK11195 petreatment could not reduce the intratu
moural Mn-TPPS concentration. A subcellular distribution study disclos
ed that Mn-TPPS was readily incorporated into the tumour cells. On the
other hand, Mn-TPPS was not specifically distributed in the mitochond
rial fraction where PBD receptors exist. The present study therefore i
ndicates that Mn-TPPS could be incorporated into tumour cells and supp
orts the potential use of this agent to improve the diagnostic specifi
city of MR imaging for brain tumours.