Design and applications of bispecific heterodimers: molecular imaging and beyond

Abstract

Ligand-based molecular imaging probes have been designed with high affinity and specificity for monitoring biological process and responses. Single-target recognition by traditional probes can limit their applicability for disease detection and therapy because synergistic action between disease mediators and different receptors is often involved in disease progression. Consequently, probes that can recognize multiple targets should demonstrate higher targeting efficacy and specificity than their monospecific peers. This concept has been validated by multiple bispecific heterodimer-based imaging probes that have demonstrated promising results in several animal models. This review summarizes the design strategies for bispecific peptide- and antibody-based heterodimers and their applications in molecular targeting and imaging. The design and application of bispecific heterodimer-conjugated nanomaterials are also discussed.

Figure 1

Schematic illustration of the synthesis strategies and receptor interaction of bispecific heterodimers. (A) Synthesis strategies of bispecific heterodimer based on chemical coupling, mutation/screening, and gene fusion. (B) The interactions between bispecific heterodimer/monospecific ligand and cellular receptors during the molecular imaging process. Stars stand for the imaging labels for the ligands.

Figure 2

Representative peptide heterodimers used for molecular imaging. (A) Molecular structure of Cy5-labeled heterobivalent ligand 1 (htBVL1) and representative in vivo fluorescence images showing its specific uptake in target tumor (right flank: target tumor with MC1R and CCK2R expression, left flank: control tumor with only MC1R expression). Adapted from reference with permission. (B) Structure and SPECT/CT images of ¹²⁵I-cMBP-click-c(RGDyK) heterodimer in U87MG tumor (c-MET and integrin α_νβ₃ positive) at 1 h p.i. (upper panel) and 4 h p.i. (lower left image). Blocking with cRGDyk (lower middle image) or cMBP (lower right image) was carried out at 4 h p.i. T: tumor; B: bladder; Thy: thyroid; K: kidney. Adapted from reference with permission. (C) PET images of ⁶⁸Ga-NOTA-RGD-BBN, ⁶⁸Ga-NOTA-BBN and ⁶⁸Ga-NOTA-RGD at 1 h p.i. in PC-3 tumor-bearing mice. Adapted from reference with permission.

Figure 3

Representative antibody heterodimers used for molecular imaging. (A) Whole-body SPECT/CT images of ¹¹¹In-Fab-PEG₂₄-HRG in CD1 athymic mice bearing BT-474 (HER2⁺/HER3⁺), SKOV-3 (HER2⁺/HER3⁻) or MDA-MB-468 (HER2⁻/HER3⁺) tumors (arrows) at 48 h. Adapted from reference with permission. (B) Structure of diphtheria toxin (DT₃₉₀)/anti-CD19 and anti-CD22 scFv conjugates (DT2219ARL) and serial bioluminescence images of mice bearing Raji-luc Burkitt’s lymphomas and treated with or without DT2219ARL. Adapted from reference with permission.

Figure 4

Bispecific nanomaterials for molecular targeting and imaging. (A) SPECT/CT images of U87MG tumor bearing mice 4 h p.i. of ¹¹¹In-labeled RGD-liposome, RGD/substance P-liposome (bispecific), and nontargeted liposome. Adapted from reference with permission. (B) Diagram depicting the bottom-up assembly of binding ZnO-binding E32 VHH dimer and surface plasmon resonance (SPR) images of A431 cells treated with gold-binding E32 VHH fragment. Adapted from reference with permission. (C) Schematic illustration of nanoparticle-mediated coupling between a malignant B cell and a DC and fluorescence image of BJAB cells (green cytoplasm) attached to DCs (blue nuclei). Scale bar represents 10 μm. Adapted from reference with permission.