Development and evaluation of a single domain antibody targeting folate receptor alpha for radioligand therapy.

BACKGROUND

Folate receptor alpha (FRα) overexpression is seen in many cancers. Radioligand therapy (RLT) has emerged as a promising tool to target FRα and has been investigated previously, but further progression was limited due to high kidney retention and, subsequently, toxicity. To circumvent this, we present here the development of a [I]I-GMIB-conjugated anti-human FRα (hFRα) single-domain antibody (sdAb), with intrinsically fast renal clearance and concomitant low kidney retention. We report the hit-to-lead development of an anti-hFRα sdAb. We evaluated its potential in vitro and assessed its targeting ability using SPECT imaging in hFRα-knockin and tumour-bearing mice. The toxicity and therapeutic efficacy of the [I]I-GMIB-sdAb were investigated in mouse models.

RESULTS

The lead anti-hFRα sdAb 2BD42 was developed with picomolar affinities, low k, and radiolabelled using [I]I with yields of > 41% and purity > 99%. [I]I-GMIB-2BD42 retained tumour uptake (> 5%IA/g at 1 h p.i. and > 1.5%IA/g at 24 h p.i.) and fast kidney clearance (< 1%IA/g at 24 h p.i.) in athymic and hFRα-knock-in mice. Athymic mice bearing hFRα-positive xenografts treated with [I]I-GMIB-2BD42 showed prolonged survival without toxicity compared to animals that received the vehicle solution or radioactive control.

CONCLUSION

The therapeutic lead radiopharmaceutical [I]I-GMIB-2BD42 showed fast pharmacokinetics with specific retention in hFRα + tumours. In addition, we report therapeutic efficacy with no signs of toxicity. In this study, we successfully designed a new drug for RLT, overcoming previous limitations, such as high kidney retention, which could aid in revitalising FRα-targeted radiotherapy.