Radiolabeled peptides - Radiopharmacology

Transcription

1 Radiolabeled peptides - Radiopharmacology Frank Wuest, PhD Department of ncology, University of Alberta, Canada

2 Peptides: Advantages & Challenges Simple synthetic accessibility with very high degree of structural diversity umerous molecular targets for peptides Favorable pharmacokinetics - Automated SPPS - Peptide libraries - Phage display, biopanning - Low molecular weight - Rapid clearance from blood and non-target tissues - Good tumor penetration - igh tumor-background ratios - Fast elimination from the body on-immunogenic Metabolic stability - Peptidases, rapid proteolysis in vivo

3 Radiolabeled peptides: A brief history Reubi (1984): igh density of somatostatin receptors in pituitary tumors Krenning (1989): First human study using a radiolabeled peptide (somatostatin derivative [ 123 I] ) Wester (2003): First human study using a 18 F-labeled peptide ([ 18 F]FP-Gluc-TCA) [ 18 F]FP-Gluc-TCA [ 111 In]ctreoScan

4 Radiolabeled peptides: A brief history Reubi 2003: Most human tumors express receptors for different peptides in high density Molecular Imaging Radiotherapy Somatostatin receptor (SSTR) (neuroendocrine tumors) 111 In-labelled ctreoscan 90 Y-labeled ctreother 90 Y-DTA-TC Gastrin-releasing peptide receptor (GPCR) (prostate, breast cancer) 64 Cu-, 18 F-bombesin analogs (PET) 177 Lu-, 188 Re-bombesin analogs 99m Tc-bombesin analogs (SPECT) Integrin transmembrane glycoprotein (tyrosine kinase receptor) (tumor angiogenesis, melanoma, ovarian and breast cancer) 18 F-Galacto-RGD, 68 Ga-, 64 Cu-TA-RGD analogs 177 Lu-monomeric, multimeric RGD Cholecystokinin (CCK) receptor (medullary thyroid carcinoma, colorectal and pancreatic cancer) 99m Tc-minigastrin analogs 68 Ga-, 111 In-DTA-minigastrin analogs 90 Y-labeled minigastrin

5 18 F-labeled peptides: Radiopharmacology Frequent problems with peptides as molecular probes: Stability in vivo Binding affinities (steric impairment) Internalization Pharmacological activity (agonistic / antagonistic activity) Immunogenicity Ligand-independent biodistribution

6 Multivalent receptor-ligand interactions and MAPs MAPs = Multiple Antigen Peptides Branched multivalent peptides Enhanced stability and affinity Tam JP. Proc atl Acad Sci U S A 1988, 85, MAP receptor receptor Tumor cell receptor receptor Kiessling et al. Curr pin Chem Biol 2000, 4, Multiple-ligand tumor targeting

7 Multivalent peptides: -terminus-branched T(8-13) eurotensin(8-13) monomer Branching unit Classical stabilization tools: Cyclization Pseudo-peptide bonds, on-proteinogenic amino acids Multimeric peptides eurotensin(8-13) dimer eurotensin(8-13) tetramer

8 Multivalent peptides: -terminus-branched T(8-13) a = ultsch et al. Bioorg. Med. Chem. 2006, 14, 5913.

9 Multivalent peptides: -terminus-branched T(8-13) Bound % 3 -T(8-13) Dimer Dimer with Ahx-spacer Dimer with PEG-spacer T(8-13) IC 50 -values (TR1-expressing T29-cells, 3 -T) Peptide concentration (logm) Bound % 3 -T(8-13) Tetramer Tetramer with Ahx-spacer. Tetramer with PEG-spacer. T(8-13) Peptide concentration (logm) Peptide IC 50 value Peptide IC 50 value T(8-13) 0,4 nm ± 0,3 nm T(8-13) 0,4 nm ± 0,3 nm Dimer 5 nm ± 2 nm Tetramer 2 nm ± 2 nm Dimer with Ahx-Spacer 40 nm ± 17 nm Tetramer with Ahx-Spacer 3 nm ± 10 nm Dimer with PEG-Spacer 21 nm ± 7 nm Tetramer with PEG-Spacer 0,4 nm ± 0,2 nm ultsch et al. Bioorg. Med. Chem. 2006, 14, 5913.

10 Stability and internalization Polo-like kinase 1 (PLK1) and the Polo-box domain (PBD) ATP-binding LS T-loop D-box PB1 PB2 site PBD posphopeptide-binding motif Core sequence: Kinase domain Polo-box domain (PBD) Ser-[pSer/pThr]-Pro/Xxx ptimal binding sequence known (K D = 200 nm): -Pro-Met-Gln-Ser-pThr-Pro-Leu- Elia et al., Cell 2003, 115,

11 Radiolabeled phosphopeptides as ligands for the PBD pthr 18 F-labeling at the -terminus (methionine) (prosthetic group chemistry or click-chemistry) Polo-box domain (PBD)

12 Radiolabeled phosphopeptides: Stability 2 - Met - Gln - Ser - XXX - Pro - Leu - XXX = pthr = Thr 18 F 25-28% 18 F Met - Gln - Ser - XXX - Pro - Leu - XXX = pthr = Thr intact 18 F-labeled peptide (%) 100,0 80,0 60,0 40,0 20,0 0,0 in vitro stability time (min) [18F]FB-MQSpTPL, blood [18F]FB-MQSpTPL, plasma [18F]FB-MQSTPL, blood [18F]FB-MQSTPL, plasma intact 18 F-labeled peptide (%) 100,0 80,0 60,0 40,0 20,0 0,0 in vivo stability [18F]FB-MQSpTPL [18F]FB-MQSTPL time (min) Richter et al. Biopolymers, 2009, 92, 479.

13 Radiolabeled phosphopeptides: Internalization uptake (% ID/mg protein) 1,0 0,8 0,6 0,4 0,2 0,0 T-29 [18F]FB-MQSpTPL, 37 C [18F]FB-MQSpTPL, 4 C [18F]FB-MQSTPL, 37 C [18F]FB-MQSTPL, 4 C uptake (% ID/mg protein) 2,0 1,8 1,6 1,4 1,2 1,0 0,8 0,6 0,4 0,2 0,0 [18F]FB-MQSpTPL, 37 C [18F]FB-MQSpTPL, 4 C [18F]FB-MQSTPL, 37 C [18F]FB-MQSTPL, 4 C FaDu time (min) time (min) Improvement of cellular uptake through molecular shuttles (cell-penetrating peptides (CPPs))? Richter et al. Biopolymers, 2009, 92, 479.

14 Molecular shuttles: CPPs Peptide Penetratin Tat Polyarginin Sequence RQIKIWFQRRMKWKK YGRKKRRQRRR RRRRRRRR (R8) uman calcitonin-derived branched peptide hct(18-32)-k7 KFTFPQTAIGVGAP- 2 KKRKAPKKKRKFA

15 Cell-penetrating peptides (CPPs) R S 2 P R 18 F CF-Phosphopeptide-CPP dimer still binds to Plk-1 PBD!!! CF-Phosphopeptide: CF-Dimer: K D = 120 nm K D = 260 nm Richter et al. Bioorg. Med. Chem. Lett. 2011, 21, 4686.

16 Shuttle function Cell penetrating peptides (CPPs) Phosphopeptide-CPP Dimer S 2 P X A B A X = B X = hct(18-32) - k7 Confocal fluorescence microscopy MCF-7 cells (c peptide = 20 µm) 18 F S C X = 2 P X D X = hct(18-32) - k7 % ID/mg Protein C % ID/mg Protein Zeit in min D Cell uptake (37 C, MCF-7 cells) Zeit in min Richter et al. Bioorg. Med. Chem. Lett. 2011, 21, 4686.