Background: Our aim was to determine the value of 99mTc-Sestamibi scanning as functional detection method of P-glycoprotein (Pgp) blockade by PSC 833 in solid tumour patients.
Patients and methods: Day 1 and day 4 after 2,200 mg orally administered PSC 833 the tumour area was scanned after intravenous (i.v.) administration of 400 MBq 99mTc-Sestamibi. In tumours with net 99mTc-Sestamibi uptake and in the hepatic region K-efflux was determined. Whole blood was analyzed for 99mTc-Sestamibi, and PSC 833 levels.
Results: Fourteen patients were included. In the only Pgp-positive tumour with positive 99mTc-Sestamibi scanning K-efflux of 99mTc-Sestamibi decreased significantly after PSC 833 intake. A net inhibition of liver efflux of Sestamibi after PSC 833 intake was observed in all evaluable patients. PSC 833 blood levels were all above 2 mg/L during scanning; 99mTc-Sestamibi blood levels post versus pre PSC 833 were unchanged.
Conclusions: PSC 833 induced modulation of K-efflux of 99mTc-Sestamibi in a Pgp positive tumour and in all patients in the liver.