Design, synthesis and validation of integrin α2β1-targeted probe for microPET imaging of prostate cancer

Development and preliminary evaluation of an integrin α2β1-targeted PET probe as a supplement and alternative of PSMA imaging for prostate cancer

An integrin α₂β₁-targeted PET probe (⁶⁸Ga-IABtP) was developed to serve as a supplement and alternative of PSMA imaging for prostate cancer. ⁶⁸Ga-IABtP was synthesized by labeling the precursor peptide with ⁶⁸Ga with 93% labeling yield and 4.14 MBq/μg specific radioactivity. ⁶⁸Ga-IABtP showed no specific uptake in LNCaP prostate cancer cell with low integrin α₂β₁ expression but significantly increased uptake in PC-3 prostate cancer cell with high integrin α₂β₁ expression, which could be specifically blocked by the integrin α₂β₁ monoclonal antibody. The efflux experiments demonstrated that ⁶⁸Ga-IABtP could rapidly penetrate into PC-3 cell after cell binding, thereby prolonging the residence time in the tumor and allow enough time for probe clearance from the circulation and non-specific organs. The biodistribution study indicated that ⁶⁸Ga-IABtP showed no specific accumulation in non-target organs and was quickly cleared from the kidney. The in vivo PET-CT imaging demonstrated that ⁶⁸Ga-IABtP showed no specific uptake in LNCaP tumor but could specifically accumulate in the PC-3 tumor, and was rapidly cleared from spleen, intestine, kidney and liver, resulting in excellent contrast effect with low background signal and high target to non-target ratios.

Imaging assisted evaluation of antitumor efficacy of a new histone deacetylase inhibitor in the castration-resistant prostate cancer

PURPOSE

Castration-resistant prostate cancer (CRPC) is the most common cause of death in men. The effectiveness of HDAC inhibitors has been demonstrated by preclinical models, but not in clinical studies, probably due to the ineffectively accumulation of HDACI in prostate cancer cells. The purpose of this work was to evaluate effects of a novel HDACI (CN133) on CRPC xenograft model and 22Rv1 cells, and develops methods, PET/CT imaging, to detect the therapeutic effects of CN133 on this cancer.

METHODS

We designed and performed study to compare the effects of CN133 with SAHA on the 22Rv1 xenograft model and 22Rv1 cells. Using PET/CT imaging with [¹¹C] Martinostat and [¹⁸F] FDG, we imaged mice bearing 22Rv1 xenografts before and after 21-day treatment with placebo and CN133 (1 mg/kg), and uptake on pre-treatment and post-treatment imaging was measured. The anti-tumor mechanisms of CN133 were investigated by qPCR, western blot, and ChIP-qPCR.

RESULTS

Our data showed that the CN133 treatment led to a 50% reduction of tumor volume compared to the placebo that was more efficacious than SAHA treatment in this preclinical model. [¹¹C] Martinostat PET imaging could identify early lesions of prostate cancer and can also be used to monitor the therapeutic effect of CN133 in CRPC. Using pharmacological approaches, we demonstrated that effects of CN133 showed almost 100-fold efficacy than SAHA treatment in the experiment of cell proliferation, invasion, and migration. The anti-tumor mechanisms of CN133 were due to the inhibition of AR signaling pathway activity by decreased HDAC 2 and 3 protein expressions.

CONCLUSION

Taken together, these studies provide not only a novel epigenetic approach for prostate cancer therapy but also offering a potential tool, [¹¹C] Martinostat PET/CT imaging, to detect the early phase of prostate cancer and monitor therapeutic effect of CN133. These results will likely lead to human trials in the future.

The Use of PET Imaging for Prognostic Integrin α2β1 Phenotyping to Detect Non-Small Cell Lung Cancer and Monitor Drug Resistance Responses

PURPOSE: Growing evidence has demonstrated that aberrant expression of integrin α2β1 might contribute to the invasion, metastasis and drug resistance of non-small cell lung cancer (NSCLC). Thus, the integrin α2β1 targeting ⁶⁸Ga-DOTA-A2B1 tracer was validated in NSCLC in contrast to accumulation of the clinically used ¹⁸F-FDG PET tracer to see if ⁶⁸Ga-DOTA-A2B1-PET imaging can offer a valuable and critical diagnostic imaging criterion for the identification of phenotypes of aggressive lung cancer.

METHODS: To verify the prognostic value of integrin α2β1, several quantitative and functional in vitro assays were validated in different NSCLC cell lines (CL1-0, CL1-5, A549 and selected A549⁺⁺ cells). Positron emission tomography (PET) imaging studies using both standard ¹⁸F-FDG and a newly developed ⁶⁸Ga-labeled integrin α2β1 (⁶⁸Ga-DOTA-A2B1) tracer were sequentially performed on mice with lung tumor xenografts in different anatomic locations (subcutaneous, orthotopic and osseous) to validate the targeting capability of the ⁶⁸Ga-DOTA-A2B1 tracers. Treatment responses were monitored by injecting animals with metastatic bone tumors with 5 mg/kg doxorubicin. All in vivo treatment responses in each treatment subgroup were monitored with a PET imaging system to evaluate the up-regulation of integrin expression at the earliest stage of treatment (6 h).

RESULTS: The PET and computed tomography (CT) images from NSCLC xenograft animals unambiguously demonstrated accumulation of the integrin tracer ⁶⁸Ga-DOTA-A2B1 in the tumor lesions at all locations. The average tumor uptake and tumor-to-normal (T/N) ratio were 2.51 ± 0.56 %ID/g and T/N = 2.82, 3.40 ± 0.42 %ID/g and T/N = 1.52, and 1.58 ± 0.108 %ID/g and T/N = 2.31 in subcutaneous, orthotopic and osseous tumors, respectively (n = 5; p < 0.05). The xenograft tumors were all clearly visible. In contrast, the accumulation of ¹⁸F-FDG reached 3.6 ± 0.76 %ID/g, 1.39 ± 0.075 %ID/g and 3.78 ± 0.73 %ID/g in subcutaneous, orthotopic and osseous tumors, respectively (n = 5; p < 0.05). However, due to the high background uptake by normal tissue, the T/N values were less than or close to 1, making the tumors almost indistinguishable in the PET imaging analysis. Furthermore, ⁶⁸Ga-DOTA-A2B1-PET imaging of the treated osseous tumor model demonstrated more than 19% tracer uptake in A549 lesions (1.72 ± 0.95 %ID/g vs. pretreatment 1.44 ± 0.12 %ID/g,p = 0. 015) 6 h post-treatment with doxorubicin. The elevated intensity of tracer uptake was in accordance with the results of in vitroWestern blot and ex vivo integrin staining, demonstrating elevated integrin α2β1 expression.

CONCLUSION: In this study, integrin α2β1 was identified as a biomarker of aggressive malignant NSCLC. Thus, efforts should be devoted to validating integrin α2β1 as a potential target for non-invasive diagnosis and as a predictive marker for monitoring treatment responses using a preclinical PET imaging system.

Advancement in integrin facilitated drug delivery

The research of integrin-targeted anticancer agents has recorded important advancements in ingenious design of delivery systems, based either on the prodrug approach, or on nanoparticle carriers, but for now, none of these has reached a clinical stage of development. Past work in this area has been extensively reviewed by us and others. Thus, the purpose and scope of the present review is to survey the advancement reported in the last 3years, with focus on innovative delivery systems that appear to afford openings for future developments. These systems exploit the labelling with conventional and novel integrin ligands for targeting the interface of cancer cells and of endothelial cells involved in cancer angiogenesis, with the proteins of the extracellular matrix, in the circulation, in tissues, and in tumour stroma, as the site of progression and metastatic evolution of the disease. Furthermore, these systems implement the expertise in the development of nanomedicines to the purpose of achieving preferential biodistribution and uptake in cancer tissues, internalisation in cancer cells, and release of the transported drugs at intracellular sites. The assessment of the value of controlling these factors, and their combination, for future developments requires support of biological testing in appropriate mechanistic models, but also imperatively demand confirmation in therapeutically relevant in vivo models for biodistribution, efficacy, and lack of off-target effects. Thus, among many studies, we have tried to point out the results supported by relevant in vivo studies, and we have emphasised in specific sections those addressing the medical needs of drug delivery to brain tumours, as well as the delivery of oligonucleotides modulating gene-dependent pathological mechanism. The latter could constitute the basis of a promising third branch in the therapeutic armamentarium against cancer, in addition to antibody-based agents and to cytotoxic agents.

Recent advances in biological applications of cage metal complexes

This review highlights advances in biochemical and medical applications of cage metal complexes (clathrochelates) and related polyhedral compounds.

Nanodiamond-DGEA peptide conjugates for enhanced delivery of doxorubicin to prostate cancer

The field of nanomedicine has emerged as an approach to enhance the specificity and efficacy of cancer treatments as stand-alone therapies and in combination with standard chemotherapeutic treatment regimens. The current standard of care for metastatic cancer, doxorubicin (DOX), is presented with challenges, namely toxicity due to a lack of specificity and targeted delivery. Nano-enabled targeted drug delivery systems can provide an avenue to overcome these issues. Nanodiamonds (ND), in particular, have been researched over the past five years for use in various drug delivery systems but minimal work has been done that incorporates targeting capability. In this study, a novel targeted drug delivery system for bone metastatic prostate cancer was developed, characterized, and evaluated in vitro. NDs were conjugated with the Asp-Gly-Glu-Ala (DGEA) peptide to target α2β1 integrins over-expressed in prostate cancers during metastasis. To facilitate drug delivery, DOX was adsorbed to the surface of the ND-DGEA conjugates. Successful preparation of the ND-DGEA conjugates and the ND-DGEA+DOX system was confirmed with transmission electron microscopy, hydrodynamic size, and zeta potential measurements. Since traditional DOX treatment regimens lack specificity and increased toxicity to normal tissues, the ND-DGEA conjugates were designed to distinguish between cells that overexpress α2β1 integrin, bone metastatic prostate cancers cells (PC3), and cells that do not, human mesenchymal stem cells (hMSC). Utilizing the ND-DGEA+DOX system, the efficacy of 1 µg/mL and 2 µg/mL DOX doses increased from 2.5% to 12% cell death and 11% to 34% cell death, respectively. These studies confirmed that the delivery and efficacy of DOX were enhanced by ND-DGEA conjugates. Thus, the targeted ND-DGEA+DOX system provides a novel approach for decreasing toxicity and drug doses.

(64)Cu labeled sarcophagine exendin-4 for microPET imaging of glucagon like peptide-1 receptor expression

The Glucagon-like peptide 1 receptor (GLP-1R) has become an important target for imaging due to its elevated expression profile in pancreatic islets, insulinoma, and the cardiovascular system. Because native GLP-1 is degraded rapidly by dipeptidyl peptidase-IV (DPP-IV), several studies have conjugated different chelators to a more stable analog of GLP-1 (such as exendin-4) as PET or SPECT imaging agents with various advantages and disadvantages. Based on the recently developed Sarcophagin chelator, here, we describe the construction of GLP-1R targeted PET probes containing monomeric and dimeric exendin-4 subunit. The in vitro binding affinity of BarMalSar-exendin-4 and Mal2Sar-(exendin-4)2 was evaluated in INS-1 cells, which over-express GLP-1R. Mal2Sar-(exendin-4)2 demonstrated around 3 times higher binding affinity compared with BaMalSar-exendin-4. After (64)Cu labeling, microPET imaging of (64)Cu-BaMalSar-exendin-4 and (64)Cu-Mal2Sar-(exendin-4)2 were performed on subcutaneous INS-1 tumors, which were clearly visualized with both probes. The tumor uptake of (64)Cu-Mal2Sar-(exendin-4)2 was significantly higher than that of (64)Cu-BaMaSarl-exendin-4, which could be caused by polyvalency effect. The receptor specificity of these probes was confirmed by effective blocking of the uptake in both tumor and normal positive organs with 20-fold excess of unlabeled exendin-4. In conclusion, sarcophagine cage conjugated exendin-4 demonstrated persistent and specific uptake in INS-1 insulinoma model. Dimerization of exendin-4 could successfully lead to increased tumor uptake in vivo. Both (64)Cu-BaMalSar-exendin-4 and (64)Cu-Mal2Sar-(exendin-4)2 hold a great potential for GLP-1R targeted imaging.

Molecular imaging of prostate cancer: PET radiotracers

OBJECTIVE

Recent advances in the fundamental understanding of the complex biology of prostate cancer have provided an increasing number of potential targets for imaging and treatment. The imaging evaluation of prostate cancer needs to be tailored to the various phases of this remarkably heterogeneous disease.

CONCLUSION

In this article, I review the current state of affairs on a range of PET radiotracers for potential use in the imaging evaluation of men with prostate cancer.

Emerging putative biomarkers: the role of alpha 2 and 6 integrins in susceptibility, treatment, and prognosis

The genetic architecture underpinning prostate cancer is complex, polygenic and despite recent significant advances many questions remain. Advances in genetic technologies have greatly improved our ability to identify genetic variants associated with complex disease including prostate cancer. Genome-wide association studies (GWASs) and microarray gene expression studies have identified genetic associations with prostate cancer susceptibility and tumour development. The integrins feature prominently in both studies examining the underlying genetic susceptibility and mechanisms driving prostate tumour development. Integrins are cell adhesion molecules involved in extracellular and intracellular signalling and are imperative for tumour development, migration, and angiogenesis. Although several integrins have been implicated in tumour development, the roles of integrin α(2) and integrin α(6) are the focus of this paper as evidence is now emerging that these integrins are implicit in prostate cancer susceptibility, cancer stem cell biology, angiogenesis, cell migration, and metastases to bone and represent potential biomarkers and therapeutic targets. There currently exists an urgent need to develop tools that differentiate indolent from aggressive prostate cancers and predict how patients will respond to treatment. This paper outlines the evidence supporting the use of α(2) and α(6) integrins in clinical applications for tailored patient treatment.

In vivo near-infrared fluorescence imaging of integrin α2β1 in prostate cancer with cell-penetrating-peptide-conjugated DGEA probe

The overexpression of integrin α(2)β(1) has been demonstrated to correlate with prostate tumor aggressiveness and metastatic potential. Recently, we reported that the DGEA peptide is a promising targeting ligand for near-infrared fluorescence and microPET imaging of integrin α(2)β(1) expression in prostate cancers. Here, we aimed to further improve the targeting efficacy of this peptide by incorporating a series of cell-penetrating peptides (CPPs) into the DGEA sequence.

METHODS

After the conjugation with appropriate fluorescent dyes, the CPP-DGEA peptides were evaluated in human prostate cell lines (PC-3, CWR-22, and LNCaP) that contain different integrin α(2)β(1) expression levels. In addition, to reduce excess kidney uptake, a carboxypeptidase-specific sequence Gly-Lys was incorporated into the probe design, allowing for cleavage by the kidney brush border enzymes of the CPP before uptake by proximal tubule cells.

RESULTS

Although the CPP motif greatly facilitated the translocation of CPP-DGEA without affecting binding specificity in vitro, fluorescent dye-labeled CPP-DGEA demonstrated extremely high kidney uptake in vivo. Kidney uptake was dramatically decreased after a carboxypeptidase-specific peptide linker (Gly-Lys) had been incorporated into the probe design. The optimized probe demonstrated a prominent accumulation of activity in PC-3 tumor (integrin α(2)β(1)-positive). Receptor specificity was confirmed with blocking experiments and evaluation in a CWR-22 control tumor model with low α(2)β(1) expression.

CONCLUSION

This study demonstrated that the introduction of a CPP sequence can facilitate the internalization of an integrin-targeted peptide probe in vitro. Moreover, a cleavable peptide linker successfully reduced kidney uptake while preserving good tumor uptake in vivo.