Development and evaluation of albumin binder-conjugated heterodimeric radiopharmaceuticals targeting integrin αβ and CD13 for cancer therapy.

Purpose: The advancement of heterodimeric tracers, renowned for their high sensitivity, marks a significant trend in the development of radiotracers for cancer diagnosis. Our prior work on [Ga]Ga-HX01, a heterodimeric tracer targeting CD13 and integrin αβ, led to its approval for phase I clinical trials by the China National Medical Production Administration (NMPA). However, its fast clearance and limited tumor retention pose challenges for broader clinical application in cancer treatment. This study aims to develop a new radiopharmaceutical with increased tumor uptake and prolonged retention, rendering it a potential therapeutic candidate.

Methods: New albumin binder-conjugated compounds were synthesized based on the structure of HX01. In vitro and in vivo evaluation of these new compounds were performed after labelling with Ga. Small-animal PET/CT imaging were conducted at different time points at 0.5-6 h post injection (p.i.) using BxPC-3 xenograft mice models. The one with the best imaging performance was further radiolabeled with Lu for small-animal SPECT/CT and ex vivo biodistribution investigation.

Results: We have synthesized novel albumin binder-conjugated compounds, building upon the structure of HX01. When radiolabeled with Ga, all compounds demonstrated improved pharmacokinetics (PK). Small-animal PET/CT studies revealed that these new albumin binder-conjugated compounds, particularly [Ga]Ga-L6, exhibited significantly enhanced tumor accumulation and retention compared with [Ga]Ga-L0 without an albumin binder. [Ga]Ga-L6 outperformed [Ga]Ga-L7, a compound developed using a previously reported albumin binder. Furthermore, [Lu]Lu-L6 demonstrated rapid clearance from normal tissues, high tumor uptake, and prolonged retention in small-animal SPECT/CT and biodistribution studies, positioning it as an ideal candidate for radiotherapeutic applications.

Conclusion: A new integrin αβ and CD13 targeting compound was screened out. This compound bears a novel albumin binder and exhibits increased tumor uptake and prolonged tumor retention in BxPC-3 tumors and low background in normal organs, making it a perfect candidate for radiotherapy when radiolabeled with Lu.