Biparatopic anti-HER2 drug radioconjugates as breast cancer theranostics.

Background: HER2 is overexpressed in 25-30% of breast cancer. Multiple domains targeting of a receptor can have synergistic/additive therapeutic effects.

Methods: Two domain-specific ADCs trastuzumab-PEG-DM1 (domain IV) and pertuzumab-PEG-DM1 (domain II) were developed, characterised and radiolabeled to obtain [Zr]Zr-trastuzumab-PEG-DM1 and [Cu]Cu-pertuzumab-PEG-DM1 to study their in vitro (binding assay, internalisation and cytotoxicity) and in vivo (pharmacokinetics, biodistribution and immunoPET/SPECT imaging) characteristics.

Results: The ADCs had an average drug-to-antibody ratio of 3. Trastuzumab did not compete with [Cu]Cu-pertuzumab-PEG-DM1 for binding to HER2. The highest antibody internalisation was observed with the combination of ADCs in BT-474 cells compared with single antibodies or ADCs. The combination of the two ADCs had the lowest IC compared with treatment using the single ADCs or controls. Pharmacokinetics showed biphasic half-lives with fast distribution and slow elimination, and an AUC that was five-fold higher for [Zr]Zr-trastuzumab-PEG-DM1 compared with [Cu]Cu-pertuzumab-PEG-DM1. Tumour uptake of [Zr]Zr-trastuzumab-PEG-DM1 was 51.3 ± 17.3% IA/g (BT-474), and 12.9 ± 2.1% IA/g (JIMT-1) which was similarly to [Cu]Cu-pertuzumab-PEG-DM1. Mice pre-blocked with pertuzumab had [Zr]Zr-trastuzumab-PEG-DM1 tumour uptakes of 66.3 ± 33.9% IA/g (BT-474) and 25.3 ± 4.9% IA/g (JIMT-1) at 120 h p.i.

Conclusion: Using these biologics simultaneously as biparatopic theranostic agents has additive benefits.