Table 7.
Effect of Fusion to a Cell-targeting Moiety on Affinity of Ribonucleases for RI
| Ribonuclease | Design | Affinity for RI | Cytotoxicity | Comments | Ref. |
|---|---|---|---|---|---|
| Tf–G89C RNase 1 5E9–G89C RNase 1 Tf–T87C EDN |
Site-specific attachment of either transferin (Tf) or anti-human TfR via a thioether bond | 103-fold lower than bismaleimidohexane–G89C RNase 1; 104-fold lower than RNase 1 | IC50 = 1–2 nM (human glioma cells); 5,000-fold more cytotoxic than wild-type RNase 1 | 200-fold increase in cytotoxicity attributed to RI-evasion and 25-fold to cellular targeting moiety | 152 |
| hERB–RNase 1 | C-Terminus of human anti- ErbB-2 receptor scFv fused to N-terminus of RNase 1 with a His6 tag | Very high, but shown to overwhelm cytosolic RI | IC50 = 12.5–60 nM (four cell lines displaying ErbB-2) | 86% tumor growth inhibition in mice bearing TUBO tumors | 197 |
| Ber-H2-scFv–RNase 1 | C-Terminus of Ber-H2- scFv fused to N-terminus of RNase 1; Ber-H2-scFv binds to CD30 | Evasive | Cytotoxic to CD30+ cell lines | Dramatically reduced tumor growth in mice bearing CD30+ TS/A cells | 198 |
| des.1–7 RNase 1–hEGF | C-Terminus of Δ1–7 RNase 1 fused to N-terminus of human EGF | des.1–7 RNase 1 required 3-fold more RI to acheieve equivalent inhibition of RNase 1 [158] | IC50 = 0.35 μM (A431cells) versus 0.55 μM for RNase 1–hEFG (which has 250-fold higher catalytic activity) | Protein was unstable; 0.34% of RNase 1 catalytic activity | 49 |
| des.1–7 RNase 1–hFGF | C-Terminus of Δ1–7 RNase 1 fused to N-terminus of human FGF | Not determined | IC50 ~2 μM (mouse melanoma B16/BL6 cells) | Comparable cytotoxicity to RNase 1–human FGF, which has 20-fold higher catalytic activity | 157 |
| RNase 1–human bFGF | C-Terminus of human bFGF fused to N-terminus of RNase 1 | Sensitive Ki = 2.1 |
IC50 = 1.6 (mouse melanoma B16/BL6 cells) | 157, 161 | |
| CL-RNase 1 | Disulfide bond added at residues 4 and 118 | Ki = 1.8 nM | None detected | Additional disulfide bond reduces affinity for RI by 13-fold [44] | 161 |
| CL-RNF19 | β-trefoil core region (residues 19–146) of bFGF inserted into RNase 1 between Pro19 and Ser20 | Ki = 2.1 | >3 μM | Negative control, as Pro19 and Ser20 are distal from RI-binding site [199] | 161 |
| CL-RFN89 | β-trefoil core region (residues 19–146) of bFGF inserted to RNase 1 between Gly89 and Ser90 | Ki = 110 | 0.32 μM | Tumor growth inhibition in mice bearing human A431 SCC tumors (anti-angiogenic effect) [50] | 161 |
| CL-RFN89-2 | β-trefoil core region (residues 21–144) of bFGF inserted to RNase 1 between Gly89 and Ser90 | Ki = 193 nM | 0.23 μM | Removal of linker residues enabled more constrained attachment of FGF moiety | 161 |