Molecular imaging of bcl-2 expression in small lymphocytic lymphoma using 111In-labeled PNA-peptide conjugates.
The bcl-2 gene is overexpressed in non-Hodgkin's lymphoma (NHL), such as small lymphocytic lymphoma (SLL), and many other cancers. Noninvasive imaging of bcl-2 expression has the potential to identify patients at risk for relapse or treatment failure. The purpose of this study was to synthesize and evaluate radiolabeled peptide nucleic acid (PNA)-peptide conjugates targeting bcl-2 gene expression. An (111)In-labeled PNA complementary to the translational start site of bcl-2 messenger RNA was attached to Tyr(3)-octreotate for somatostatin receptor-mediated intracellular delivery.


METHODS
DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate (1) and 3 control conjugates (DOTA-nonsense-PNA-Tyr(3)-octreotate (2), DOTA-anti-bcl-2-PNA-Ala[3,4,5,6]-substituted congener (3), and DOTA-Tyr(3)-octreotate (4) [DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid]) were synthesized by standard solid-phase 9-fluorenylmethoxycarbonyl (Fmoc) chemistry. In vitro studies were performed in Mec-1 SLL cells, which express both bcl-2 messenger RNA and somatostatin receptors. Biodistributions and microSPECT/CT studies were performed in Mec-1-bearing SCID (severe combined immunodeficiency) mice, a new animal model of human SLL.


RESULTS
(111)In-Labeled conjugate 1 was taken up by Mec-1 cells through a somatostatin receptor-mediated mechanism. Biodistribution studies showed specific tumor uptake of conjugate 1, the somatostatin analog 4, and the PNA nonsense conjugate 2, but not of the mutant peptide conjugate 3. Mec-1 tumors could be detected by microSPECT/CT using (111)In-labeled DOTA-Tyr(3)-octreotate (4) and the targeted anti-bcl-2 conjugate (1), but not using the 2 negative control conjugates 2 and 3.


CONCLUSIONS
A new (111)In-labeled antisense PNA-peptide conjugate demonstrated proof of principle for molecular imaging of bcl-2 expression in a new mouse model of human SLL. This imaging agent may be useful for identifying NHL patients at risk for relapse and conventional treatment failure.
Jia
Fang
F
Department of Veterinary Medicine and Surgery, University of Missouri-Columbia, Columbia, Missouri 65211, USA.
Figueroa
Said Daibes
SD
Gallazzi
Fabio
F
Balaji
Baghavathy S
BS
Hannink
Mark
M
Lever
Susan Z
SZ
Hoffman
Timothy J
TJ
Lewis
Michael R
MR
D000818:Animals; D045744:Cell Line, Tumor; D007205:Indium Radioisotopes / Q000737:chemistry / Q000493:pharmacokinetics*; D007553:Isotope Labeling; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000000981:diagnostic imaging* / Q000378:metabolism*; D008657:Metabolic Clearance Rate; D051379:Mice; D016513:Mice, SCID; D015336:Molecular Probe Techniques; D009928:Organ Specificity; D020135:Peptide Nucleic Acids / Q000737:chemistry / Q000493:pharmacokinetics*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D014018:Tissue Distribution
D007205:Indium Radioisotopes; D020135:Peptide Nucleic Acids; D019253:Proto-Oncogene Proteins c-bcl-2; D019275:Radiopharmaceuticals