# Noninvasive Evaluation of Angiogenesis and Therapeutic Response after Hindlimb Ischemia with an Integrin-Targeted Tracer by PET

## TL;DR

This study uses a special PET tracer to noninvasively track blood vessel growth and treatment response in a mouse model of limb ischemia.

## Contribution

The study introduces a one-step labeled RGD tracer for PET imaging to monitor angiogenesis and therapeutic response in hindlimb ischemia.

## Key findings

- 18F-PRGD2 tracer showed specific binding to αvβ3 integrin and detected angiogenesis as early as 3 days after surgery.
- VEGF treatment increased tracer uptake and angiogenesis, confirming the tracer's ability to monitor therapeutic response.
- The tracer's simple synthesis and in vivo performance suggest potential for future clinical use in ischemic diseases.

## Abstract

Peripheral arterial disease (PAD) can severely compromise
limb vitality and function. Angiogenesis plays an important role in healing of
ischemic lesions. Radiolabeled RGD (Arg-Gly-Asp) peptides specifically targeting
αvβ3 integrin are promising tracers for imaging
angiogenesis. In this study, we investigated the application of a one-step
labeled RGD in evaluation of angiogenesis and therapy response in a mouse model
of hindlimb ischemia (HI) by positron emission tomography (PET).

HI was induced by ablation of
the femoral artery in mice. PET imaging using 18F-AlF-NOTA-PRGD2 (18F-PRGD2) tracer was performed at day 0 (pre-surgery) and days 3, 7, 14,
and 21 after surgery to evaluate hindlimb angiogenesis longitudinally and
noninvasively. The control peptide RAD (Arg-Ala-Asp) labeled with a similar
procedure and a block agent were used to confirm the specific binding
of 18F-PRGD2 to αvβ3 integrin. Ex vivo CD31
staining was performed to detect angiogenesis. In addition, the angiogenic
therapy response was monitored with 18F-PRGD2 tracer and immunofluorescence
staining to confirm the imaging data.

The successful
establishment of HI model was confirmed by ultrasound imaging and laser doppler
perfusion imaging (LDPI). Specific binding of 18F-PRGD2 to
αvβ3 integrin was validated by minimal tracer uptake
of the control peptide RAD and significant decrease of tracer accumulation when a
block agent was added. Local accumulation of 18F-RRGD2 in ischemic hindlimb
was detected as early as 3 days and reached a peak at 7 days after surgery. The
temporal change of focal tracer uptake was positively correlated with the pattern
of vascular density. Moreover, vascular endothelial growth factor (VEGF) treatment increased the tracer uptake and
enhanced angiogenesis, which is consistent with integrin β3 expression.

PET imaging of a one-step labeled tracer 18F-PRGD2
targeted to αvβ3 integrin allows longitudinal
monitoring of ischemia-induced angiogenesis and noninvasive assessment of
VEGF treatment response in a mouse model of
hindlimb ischemia. The simple synthesis procedure and in vivo
performance of this PET tracer enables the feasibility of future clinical
translation in ischemic cardiovascular diseases.