In vivo tumor targeting with dual-labeled mesoporous silica nanoparticles

Objectives To develop novel multifunctional mesoporous silica nanoparticles (MSN) for in vivo tumor targeting, and to track them with PET and near-infrared fluorescence (NIRF) imaging.

Methods Fab fragment of TRC105 (an antibody that binds to CD105, overexpressed on tumor neovasculature) was generated by enzymatic papain digestion. Uniform ~80 nm sized MSNs were synthesized via a soft-template method, and conjugated to 800CW (a NIRF dye), NOTA (a chelator for ⁶⁴Cu labeling), polyethylene glycol (PEG) and TRC105(Fab) to form ⁶⁴Cu-NOTA-MSN-800CW-PEG-TRC105(Fab). Similar conjugate without TRC105(Fab) was also made as non-targeted control. Systematic in vivo PET/NIRF imaging, biodistribution, and blocking studies were performed in 4T1 tumor-bearing mice (CD105+) to evaluate and confirm tumor targeting capability, validated by various in vitro/ex vivo studies.

Results TRC105(Fab) was produced with high purity, confirmed by SDS-PAGE and HPLC. After confirmation of successful surface modifications of MSN to yield NOTA-MSN-800CW-PEG-TRC105(Fab), in vitro CD105 targeting studies in HUVEC (CD105+) and MCF-7 cells (CD105-) showed strong and specific binding of the conjugate to CD105, with negligible non-specific binding. NOTA-MSN-800CW-PEG-TRC105(Fab) was labeled with ⁶⁴Cu with good yield and high purity (>95%). High stability of both 800CW and ⁶⁴Cu in ⁶⁴Cu-NOTA-MSN-800CW-PEG-TRC105(Fab) was confirmed by serum stability studies for 48 h. In vivo PET/NIRF imaging showed specific targeting of ⁶⁴Cu-NOTA-MSN-800CW-PEG-TRC105(Fab) in 4T1 mice, with peak tumor uptake of 5.5±0.4 %ID/g at 0.5 h (n=3), ~ 2 fold higher than the non-targeted control. CD105 specificity of ⁶⁴Cu-NOTA-MSN-800CW-PEG-TRC105(Fab) was confirmed by blocking and ex vivo histology studies.

Conclusions This is the first example of tumor targeted dual-modality PET/NIRF imaging with functionalized MSN, which had ~2 fold higher tumor uptake than that of passive targeting alone. With high drug loading capability and good biocompatibility of MSN, this nanosystem is highly suitable for PET/NIRF image-guided drug delivery and targeted cancer therapy.