However , the tracer uptake (%ID/g) derived from static images at 1-h time point did not show significant difference between the treated and control tumors until day a few. (p <0. 05), and the difference was more significant at day a few (p <0. 01), compared with the control group. However PLX8394 , the tracer uptake (%ID/g) derived from static images at 1-h time point did not show significant difference between the PLX8394 treated and control tumors until day a few. Little difference in tracer uptake (%ID/g) or BPNDwas found between treated and control A549 tumors. Considering the tracer retention in tumor and the slower clearance due to damaged tumor vasculature after treatment, BPNDrepresenting the actual specific binding portion appears to be more sensitive and accurate than the semiquantitative parameters (such as %ID/g) derived from static images to assess the early response of tumor to VDA treatment. == Conclusions == Quantitative analysis based on dynamic PET with [18F]FPPRGD2 shows advantages in distinguishing effective from ineffective treatment during the course of VEGF121/rGel therapy at early stage and is therefore more sensitive in assessing therapy response than static PET. Keywords: Dynamic PET, Vascular-disrupting agent, Integrin v3, [18F]FPPRGD2 == Introduction == The battle against cancer using conventional therapies, such as chemotherapy and radiotherapy, has been challenged by the lack of specific targets, which results in mild tumor damage but serious side effects [1]. The failure to detect lesions at early stage, the insufficient damage to cancer targets, and the inability to quantify therapy response are all challenges TSHR to achieve curative effects. Instead of attacking the tumor cells directly, which has been proven difficult, an alternative way is to firmly hit the intratumoral targets that are closely associated with tumor cells both functionally and locally. It has been well established that not only the rapid growth of primary tumor but also the maintenance of metastases places tremendous strains on the neovasculature, which shows abnormalities such as rapidly dividing endothelial population, blind ends, leaky vessels, and a reduction in pericytes [25]. As a result, angiogenesis has been a major focus of recent cancer research in tumor growth, invasion, and metastasis, prompting the development of numerous vasculature targeted therapies [6]. In recent years, a novel class of vascular-disrupting agents (VDAs) that causes a rapid and selective shutdown of the tumor vessels has been under active investigation [2]. PLX8394 VDAs perturb the tumor vascular endothelial cells, causing loss of morphology, cohesion, and cytotoxicity, leading to selective collapse of the tumor vasculature and subsequent tumor necrosis [7]. The vascular endothelial growth factor (VEGF)/vascular endothelial growth factor receptor (VEGFR) signaling pathway plays a pivotal role in both normal vasculature development and many disease PLX8394 processes [811]. The importance of VEGF/VEGFR signaling pathway in cancer is underscored by the approval of the humanized anti-VEGF monoclonal antibody bevacizumab for the first-line treatment of cancer patients [12]. The proangiogenic actions of VEGF/VEGFR pathway are mainly mediated by the cytokine vascular endothelial growth factor-A (VEGF-A) and two endothelium-specific receptor tyrosine kinases, VEGFR-1 (Flt-1/FLT-1) and VEGFR-2 (Flk-1/KDR) [13]. Upregulation/overexpression of the KDR or the VEGF-A ligand itself has been implicated as poor prognostic markers in clinical studies [4]. Thus, many therapeutic agents and approaches targeting the VEGF-A pathway have been developed [14]. We previously characterized a vasculature-targeting fusion protein (VEGF121/recombinant plant toxin gelonin (rGel)), a VDA composed of the VEGF-A isoform VEGF121and rGel, in several tumor models [6, 15, 16]. The VEGF121/rGel fusion toxin has been shown to be highly specific and cytotoxic for both quiescent and dividing porcine aortic endothelial (PAE) cells expressing VEGFR-2 (KDR), but not cytotoxic for those cells expressing VEGFR-1 (Flt) and normal organs [6]. Conventional assessment of therapy PLX8394 response is usually assessed.