Using 99mTc-MIBI to Evaluate the Effects of Chemosensitizer on P-glycoprotein in Multidrug-resistant Carcinoma Cells

Objective: To establish a method to evaluate the effects of chemosensitizer on P-glycoprotein using 99mTc-MIBI, and observe the changes of 99mTc-MIBI uptake kinetics and P-glycoprotein levels after using verapamil in MDR human breast cells MCF-7/Adr. Methods: MDR breast carcinoma cells, MCF-7/Adr, were incubated and different protocols were performed. Protocol I: a chemosensitizer, verapamil (10 µmol/L), was added into cell culture medium, while in control group, the same volume of DMEM was given. Cells were harvested after 2 h incubation with 99mTc-MIBI. Protocol II: Verapamil (10 µmol/L) was added into cell culture medium and incubated for 20 min, 40 min, 60 min, 80 min, 8 h, 24 h, 48 h and 72 h respectively. Cells were harvested after 2 h incubation with 99mTc-MIBI. The radioactivity of the cells was measured and P-glycoprotein expression levels were determined with immunohistochemical stain. Results: Protocol I: After 2h incubation with verapamil the cellular uptake of 99mTc-MIBI was remarkably higher than control group (t=2.33, P<0.05), but there was no difference in P-glycoprotein expression levels between two groups (P<0.05). Protocol II: In verapamil group, 99mTc-MIBI uptake was increased with incubation time prolonging (F=58.2, P<0.05). When verapamil incubation time surpassed 8 h the 99mTc-MIBI uptake negatively correlated to the P-glycoprotein expression levels (r=-0.73, P<0.01). However, when incubation time was less than 80 min, there was no correlation between 99mTc-MIBI accumulation and P-glycoprotein levels (r=0.16, P>0.05). Conclusion: 99mTc-MIBI may be used to evaluate the qualitative as well as quantitative change of P-glycoprotein expression levels induced by the chemosensitizer, verapamil.