In vitro and in vivo targeting of different folate receptor-positive cancer cell lines with a novel 99mTc-radiofolate tracer.
OBJECTIVE
For the assessment of folate-based radiopharmaceuticals, human nasopharyngeal KB carcinoma cells are traditionally used although nasopharyngeal cancer is rare. On the other hand, the folate receptor (FR) is frequently overexpressed on diverse cancer types, the highest frequency (>90%) being on ovarian carcinomas. The goal of our study was the in vitro and in vivo assessment of different FR-positive human carcinoma cells. In addition, a murine sarcoma cell line was assessed as a pre-clinical alternative to human xenograft models.


METHODS
FR-positive human nasopharyngeal, cervical, ovarian and colorectal cancer cell lines and the transgenic mouse sarcoma (24JK-FBP) cell line were targeted with a novel 99mTc-tricarbonyl folate derivative 2. Comparative in vitro cell binding studies were carried out under standardised folate-deficient conditions. In vivo studies were performed in nude mice and C6 black mice.


RESULTS
The in vitro cell experiments revealed only FR-specific binding (unspecific <0.02%), ranging from 3.5% to 52% of complex 2 owing to variable levels of FR expression of the cell lines. In vivo tumour uptake of radiotracer 2 varied less than in vitro. It ranged from 0.66+/-0.17% ID/g (LoVo) through 1.16+/-0.64% ID/g (IGROV-1) and 1.55+/-0.43% ID/g (24JK-FBP) to 2.33+/-0.36% ID/g (KB) 4 h p.i.


CONCLUSIONS
These pre-clinical studies indicate that in vitro data obtained in FR-positive cancer cells do not necessarily correspond with or predict in vivo radiofolate uptake in corresponding (xeno)grafts. In addition, the murine 24JK-FBP cell line proved to be a valuable pre-clinical alternative to human tumour models.
Müller
Cristina
C
Center for Radiopharmaceutical Science ETH-PSI-USZ, Paul Scherrer Institute, 5232, Villigen-PSI, Switzerland.
Schubiger
P August
PA
Schibli
Roger
R
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D016503:Drug Delivery Systems / Q000379:methods; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000493:pharmacokinetics*; D006801:Humans; D008657:Metabolic Clearance Rate; D051379:Mice; D015336:Molecular Probe Techniques; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism*; D009928:Organ Specificity; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D011956:Receptors, Cell Surface / Q000378:metabolism*; D013667:Technetium / Q000493:pharmacokinetics*; D014018:Tissue Distribution
D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D019275:Radiopharmaceuticals; D011956:Receptors, Cell Surface; D013667:Technetium; D005492:Folic Acid