Stratification of 18F-Labeled PET Imaging Agents for the Assessment of Antiangiogenic Therapy Responses in Tumors

Enantioselective photocatalytic synthesis of bicyclo[2.1.1]hexanes as ortho-disubstituted benzene bioisosteres with improved biological activity

1,5-Disubstituted bicyclo[2.1.1]hexanes are bridged scaffolds with well-defined exit vectors that are becoming increasingly popular building blocks in medicinal chemistry because they are saturated bioisosteres of ortho-substituted phenyl rings. Here we have developed a Lewis-acid-catalysed [2 + 2] photocycloaddition to obtain these motifs as enantioenriched scaffolds, providing an efficient approach for their incorporation in a variety of drug analogues. Retention of the biological activity of the bicyclo[2.1.1]hexane-containing analogues in the specific proteins targeted by the original drugs has confirmed the suitability of this moiety to serve as a bioisostere of ortho-substituted phenyl rings. Moreover, we have studied the potential of the different enantiomers of the drug analogues to selectively induce cytotoxicity in a panel of tumour cell lines, observing markedly differential effects for the two enantiomers and a substantial improvement over the corresponding sp2-based drugs. This showcases that the control of the absolute configuration and tridimensionality of the drug analogue has a large impact on its biological properties.

Treatment of malignant pleural effusion in non-small cell lung cancer with VEGF-directed therapy

BACKGROUND

Vascular endothelial growth factor (VEGF) is a critical regulator of malignant pleural effusion (MPE) in non-small-cell lung cancer (NSCLC). Bevacizumab (BEV) and apatinib (APA) are novel VEGF blockers that inhibit lung cancer cell proliferation and the development of pleural effusion.

METHODS

In this study, we established Lewis lung cancer (LLC) xenograft mouse models to compare the therapeutic effect of APA and BEV in combination with cisplatin (CDDP) against MPE. The anti-tumour and anti-angiogenic effects of this combination therapy were evaluated by ¹⁸F-FDG PET/CT imaging, TUNEL assay and Immunohistochemistry.

RESULTS

The triple drug combination significantly prolonged the overall survival of the tumour-bearing mice by reducing MPE and glucose metabolism and was more effective in lowering VEGF/soluble VEGFR-2 levels in the serum and pleural exudates compared to either of the monotherapies. Furthermore, CDDP + APA + BEV promoted in vivo apoptosis and decreased microvessel density.

CONCLUSIONS

Mechanistically, LLC-induced MPE was inhibited by targeting the VEGF-MEK/ERK pathways. Further studies are needed to establish the synergistic therapeutic effect of these drugs in NSCLC patients with MPE.KEY MESSAGESCombined treatment of MPE with apatinib, bevacizumab and cisplatin can prolong the survival time of mice, reduce the content of MPE, decrease the SUV_max of thoracic tumour tissue, down-regulate the content of VEGF and sVEGFR-2 in serum and pleural fluid, and promote the apoptosis of tumour cells. Angiogenesis and MPE formation can be inhibited by down-regulation of HIF-1α, VEGF, VEGFR-2, MEK1 and MMP-2 molecular signalling pathway proteins.

Visualization of Diagnostic and Therapeutic Targets in Glioma With Molecular Imaging

Gliomas, particularly high-grade gliomas including glioblastoma (GBM), represent the most common and malignant types of primary brain cancer in adults, and carry a poor prognosis. GBM has been classified into distinct subgroups over the years based on cellular morphology, clinical characteristics, biomarkers, and neuroimaging findings. Based on these classifications, differences in therapeutic response and patient outcomes have been established. Recently, the identification of complex molecular signatures of GBM has led to the development of diverse targeted therapeutic regimens and translation into multiple clinical trials. Chemical-, peptide-, antibody-, and nanoparticle-based probes have been designed to target specific molecules in gliomas and then be visualized with multimodality molecular imaging (MI) techniques including positron emission tomography (PET), single-photon emission computed tomography (SPECT), near-infrared fluorescence (NIRF), bioluminescence imaging (BLI), and magnetic resonance imaging (MRI). Thus, multiple molecules of interest can now be noninvasively imaged to guide targeted therapies with a potential survival benefit. Here, we review developments in molecular-targeted diagnosis and therapy in glioma, MI of these targets, and MI monitoring of treatment response, with a focus on the biological mechanisms of these advanced molecular probes. MI probes have the potential to noninvasively demonstrate the pathophysiologic features of glioma for diagnostic, treatment, and response assessment considerations for various targeted therapies, including immunotherapy. However, most MI tracers are in preclinical development, with only integrin αVβ3 and isocitrate dehydrogenase (IDH)-mutant MI tracers having been translated to patients. Expanded international collaborations would accelerate translational research in the field of glioma MI.

Bevacizumab combined with apatinib enhances antitumor and anti-angiogenesis effects in a lung cancer model in vitro and in vivo

Angiogenesis is involved in the proliferation and metastasis of solid tumours; hence, it is an attractive therapeutic target. However, most patients who undergo anti-angiogenic drug treatment do not achieve complete tumour regression, resulting in drug resistance. The objective of this research is to explore the therapeutic effect of combining bevacizumab (Bev), an anti-vascular endothelial growth factor (VEGF)-A antibody, with apatinib (Apa), a VEGR receptor (VEGFR)-2-targeting tyrosine kinase inhibitor, in non-small cell lung cancer (NSCLC). In vitro, we assessed the influence which Bev + Apa treatment exerts upon the proliferation as well as apoptosis of Lewis lung carcinoma (LLC) cells in virtue of the 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide as assay as well as Annexin V staining, respectively. For in vivo assessment, we established a tumour-bearing mouse model with LLC cells and investigated the anti-angiogenic and antitumor effects of Bev + Apa by ¹⁸F-FDG PET/CT imaging, immunohistochemistry and TUNEL staining. Bev + Apa treatment significantly inhibited LLC cell growth and proliferation in a larger scale compared to therapy of either of the only agent. Bev + Apa inhibited tumour growth and extended the median survival time of tumour-bearing mice. Mechanistically, Bev + Apa reduced angiogenesis by inhibiting VEGF and VEGFR-2 expression and reducing glucose metabolism in tumour tissues. Thus, Bev and Apa inhibited tumour angiogenesis synergistically, indicating their potential clinical utility for NSCLC treatment.

Preclinical Imaging in Targeted Cancer Therapies

Preclinical imaging with radiolabeled probes can provide noninvasive tools to test the efficacy of targeted agents in tumors harboring specific genetic alterations and to identify imaging parameters that can be used as pharmacodynamics markers in cancer patients. The present review will primarily focus on preclinical imaging studies that can accelerate the clinical approval of targeted agents and promote the development of imaging biomarkers for clinical applications. Since only subgroups of patients may benefit from treatment with targeted anticancer agents, the identification of a patient population expressing the target is of primary importance for the success of clinical trials. Preclinical imaging studies tested the ability of new radiolabeled compounds to recognize mutant, amplified, or overexpressed targets and some of these tracers were transferred to the clinical setting. More common tracers such as ¹⁸F-Fluorothymidine and ¹⁸F-Fluorodeoxyglucose were employed in animal models to test the inhibition of the target and downstream pathways through the evaluation of early changes of proliferation and glucose metabolism allowing the identification of sensitive and resistant tumors. Furthermore, since the majority of patients treated with targeted anticancer agents will invariably develop resistance, preclinical imaging studies were performed to test the efficacy of reversal agents to overcome resistance. These studies provided consistent evidence that imaging with radiolabeled probes can monitor the reversal of drug resistance by newly designed alternative compounds. Finally, despite many difficulties and challenges, preclinical imaging studies targeting the expression of immune checkpoints proved the principle that it is feasible to select patients for immunotherapy based on imaging findings. In conclusion, preclinical imaging can be considered as an integral part of the complex translational process that moves a newly developed targeted agent from laboratory to clinical application intervening in all clinically relevant steps including patient selection, early monitoring of drug effects and reversal of drug resistance.

[68Ga]RGD Versus [18F]FDG PET Imaging in Monitoring Treatment Response of a Mouse Model of Human Glioblastoma Tumor with Bevacizumab and/or Temozolomide

PURPOSE

The aim of this study was to evaluate positron emission tomography (PET) imaging with [⁶⁸Ga]NODAGA-c(RGDfK) ([⁶⁸Ga]RGD), in comparison with 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG), for early monitoring of the efficacy of an antiangiogenic agent associated or not with chemotherapy, in a mouse model of glioblastoma (GB).

PROCEDURES

Mice bearing U87MG human GB cells line were parted into five groups of five mice each. One group was imaged at baseline before the treatment phase; another group was treated with bevacizumab (BVZ), another group with temozolomide (TMZ), another group with both agents, and the last one was the control group. Tumors growth and biological properties were evaluated by caliper measurements and PET imaging at three time points (baseline, during treatment t1 = 4-6 days and t2 = 10-12 days). At the end of the study, tumors were counted and analyzed by immunohistochemistry (CD31 to evaluate microvessel density).

RESULTS

The tumor volume assessed by caliper measurements was significantly greater at t1 in the control group than in the TMZ + BVZ-treated group or in the BVZ-treated group. At t2, tumor volume of all treated groups was significantly smaller than that of the control group. [¹⁸F]FDG PET failed to reflect this efficacy of treatment. In contrast, at t1, the [⁶⁸Ga]RGD tumor uptake was concordant with tumor growth in controls and in treated groups. At t2, a significant increase in tumor uptake of [⁶⁸Ga]RGD vs. t1 was only observed in the TMZ-treated group, reflecting a lack of angiogenesis inhibition, whereas TMZ + BVZ resulted in a dramatic tumor arrest, reduction in microvessel density and stable tumor [⁶⁸Ga]RGD uptake.

CONCLUSIONS

[⁶⁸Ga]RGD is a useful PET agent for in vivo angiogenesis imaging and can be useful for monitoring antiangiogenic treatment associated or not with chemotherapy.

Binding of αvβ3 Integrin-Specific Radiotracers Is Modulated by Both Integrin Expression Level and Activation Status

PURPOSE

Molecular imaging of α_vβ₃ integrin has exhibited real potential to guide the appropriate use of anti-angiogenic therapies. However, an incomplete understanding of the factors that influence binding of α_vβ₃ integrin-specific radiotracers currently limits their use for assessing response to therapy in cancer patients. This study identifies two fundamental factors that modulate uptake of these radiotracers. Procedures Experiments were performed in prostate cancer (PC3) and glioblastoma (U87MG) cells, which differentially express α_vβ₃ integrin. α_vβ₃ integrin-specific radiotracers were used to investigate the effect of manipulating α_vβ₃ integrin expression or activation in cellular binding assays. β₃ integrin and α_vβ₃ integrin expression were measured by western blotting and flow cytometry, respectively. The effect of select pharmacological inhibitors on α_vβ₃ integrin activation and expression was also determined.

RESULTS

Radiotracer binding was proportional to α_vβ₃ integrin expression when it was decreased (β₃ knock-down cells) or increased, either using pharmacological inhibitors of cell signalling or by culturing cells for different times. Studies with both small molecule and arginine-glycine-aspartic acid (RGD)-based radiotracers revealed increased radiotracer binding after activation of α_vβ₃ integrin with Mn²⁺ or talin head domain. Moreover, inhibition of fundamental signalling pathways (mitogen-activated protein kinase kinase (MEK), Src and VEGFR2) decreased radiotracer binding, reflecting reduced α_vβ₃ integrin activity.

CONCLUSION

Binding of small molecule ligands and radiolabelled RGD peptides is modulated by expression and activation status of α_vβ₃ integrin. α_vβ₃ integrin-specific radiotracers can provide otherwise inaccessible information of the effect of signalling pathways on α_vβ₃ integrin. This has significant implications for assessing response to anti-angiogenic therapies in clinical studies.

Comparison and evaluation of two RGD peptides labelled with 68Ga or 18F for PET imaging of angiogenesis in animal models of human glioblastoma or lung carcinoma

The aim of this study was to evaluate two RGD radiotracers radiolabelled with fluorine-18 or gallium-68, in detecting angiogenesis in grafted human tumours and monitoring their treatment with the anti-angiogenic agent bevacizumab.

Sixteen mice bearing an U87MG tumour in one flank and a contralateral A549 tumour were treated with intravenous injections of bevacizumab twice a week for 3 weeks. PET images with ¹⁸F-RGD-K5 and ⁶⁸Ga-RGD were acquired before treatment (baseline), after three bevacizumab injections (t1) and after seven bevacizumab injections (t2).

In A549 tumours, the treatment stopped the tumour growth, with a tumour volume measured by calliper remaining between 0.28 and 0.40 cm³. The decrease in tumour uptake of both RGD tracers was non-significant. Therefore it was not possible to predict this efficacy on tumour growth based on RGD PET results, whereas ex vivo measurements showed a significantly lower tumour uptake of both tracers in mice sacrificed at t2 vs. at baseline.

In U87MG tumours, the uptake measured on PET decreased during treatment, reflecting the partial therapeutic effect observed on tumour volume, consisting in a decrease in the slope of tumour growth. Using ¹⁸F-RGD-K5, this decrease in tumour SUVmax became significant at t1, whereas it was also observed with the ⁶⁸Ga-RGD tracer, but only at t2. ¹⁸F-RGD-K5 appeared more efficient than ⁶⁸Ga-RGD in the visualisation and follow-up of U87MG tumours.

The comparison of those results with those of immunohistochemistry at baseline and at t2 favoured the hypothesis that tumour RGD uptake reflects other cancer properties than just its angiogenic capacity.

Hybrid Manganese Dioxide Nanoparticles Potentiate Radiation Therapy by Modulating Tumor Hypoxia

Hypoxia in the tumor microenvironment (TME) mediates resistance to radiotherapy and contributes to poor prognosis in patients receiving radiotherapy. Here we report the design of clinically suitable formulations of hybrid manganese dioxide (MnO₂) nanoparticles (MDNP) using biocompatible materials to reoxygenate the TME by reacting with endogenous H₂O₂ MDNP containing hydrophilic terpolymer-protein-MnO₂ or hydrophobic polymer-lipid-MnO₂ provided different oxygen generation rates in the TME relevant to different clinical settings. In highly hypoxic murine or human xenograft breast tumor models, we found that administering either MDNP formulation before radiotherapy modulated tumor hypoxia and increased radiotherapy efficacy, acting to reduce tumor growth, VEGF expression, and vascular density. MDNP treatment also increased apoptosis and DNA double strand breaks, increasing median host survival 3- to 5-fold. Notably, in the murine model, approximately 40% of tumor-bearing mice were tumor-free after a single treatment with MDNPs plus radiotherapy at a 2.5-fold lower dose than required to achieve the same curative treatment without MDNPs. Overall, our findings offer a preclinical proof of concept for the use of MDNP formulations as effective radiotherapy adjuvants. Cancer Res; 76(22); 6643-56. ©2016 AACR.

Optimization of Early Response Monitoring and Prediction of Cancer Antiangiogenesis Therapy via Noninvasive PET Molecular Imaging Strategies of Multifactorial Bioparameters

Objective: Antiangiogenesis therapy (AAT) has provided substantial benefits regarding improved outcomes and survival for suitable patients in clinical settings. Therefore, the early definition of therapeutic effects is urgently needed to guide cancer AAT. We aimed to optimize the early response monitoring and prediction of AAT efficacy, as indicated by the multi-targeted anti-angiogenic drug sunitinib in U87MG tumors, using noninvasive positron emission computed tomography (PET) molecular imaging strategies of multifactorial bioparameters.

Methods: U87MG tumor mice were treated via intragastric injections of sunitinib (80 mg/kg) or vehicle for 7 consecutive days. Longitudinal MicroPET/CT scans with ¹⁸F-FDG, ¹⁸F-FMISO, ¹⁸F-ML-10 and ¹⁸F-Alfatide II were acquired to quantitatively measure metabolism, hypoxia, apoptosis and angiogenesis on days 0, 1, 3, 7 and 13 following therapy initiation. Tumor tissues from a dedicated group of mice were collected for immunohistochemical (IHC) analysis of key biomarkers (Glut-1, CA-IX, TUNEL, α_νβ₃ and CD31) at the time points of PET imaging. The tumor sizes and mouse weights were measured throughout the study. The tumor uptake (ID%/g_max), the ratios of the tumor/muscle (T/M) for each probe, and the tumor growth ratios (TGR) were calculated and used for statistical analyses of the differences and correlations.

Results: Sunitinib successfully inhibited U87MG tumor growth with significant differences in the tumor size from day 9 after sunitinib treatment compared with the control group (P < 0.01). The uptakes of ¹⁸F-FMISO (reduced hypoxia), ¹⁸F-ML-10 (increased apoptosis) and ¹⁸F-Alfatide II (decreased angiogenesis) in the tumor lesions significantly changed during the early stage (days 1 to 3) of sunitinib treatment; however, the uptake of ¹⁸F-FDG (increased glucose metabolism) was significantly different during the late stage. The PET imaging data of each probe were all confirmed via ex vivo IHC of the relevant biomarkers. Notably, the PET imaging of ¹⁸F-Alfatide II and ¹⁸F-FMISO was significantly correlated (all P < 0.05) with TGR, whereas the imaging of ¹⁸F-FDG and ¹⁸F-ML-10 was not significantly correlated with TGR.

Conclusion: Based on the tumor uptake of the PET probes and their correlations with MVD and TGR, ¹⁸F-Alfatide II PET may not only monitor the early response but also precisely predict the therapeutic efficacy of the multi-targeted, anti-angiogenic drug sunitinib in U87MG tumors. In conclusion, it is feasible to optimize the early response monitoring and efficacy prediction of cancer AAT using noninvasive PET molecular imaging strategies of multifactorial bioparameters, such as angiogenesis imaging with ¹⁸F-Alfatide II, which represents an RGD-based probe.

Early treatment response to sorafenib for rabbit VX2 orthotic liver tumors: evaluation by quantitative contrast-enhanced ultrasound

The aim of our study was to investigate the application of contrast-enhanced ultrasound (CEUS) and its quantification analysis for the prediction of early treatment response of sorafenib on rabbit VX2 liver tumor model. Rabbits were implanted VX2 tumor mass to establish a liver tumor model. Fourteen days after tumor implantation, rabbits presented with single liver tumor were randomly divided into two groups. Rabbits in treatment group were given by gavage once a day for 14 days with sorafenib suspension at a dose of 30 mg/kg, whereas rabbits in control group were given saline by gavage of the same volume. CEUS was performed before treatment and 3, 7, 14 days after treatment for the analysis of tumor size, enhancement pattern, and necrosis range. The time intensity curve (TIC) was used to obtain quantitative parameters of enhancement patterns. Before sorafenib administration, tumor volumes ranged from 0.24 to 0.75 cm(3) (mean 0.49 ± 0.18 cm(3)) in treatment group and 0.24 to 0.44 cm(3) (mean 0.30 ± 0.12 cm(3)) in control group. The dynamic enhancement patterns of tumors were homogeneous hyper-enhancement (n = 8), heterogeneous hyper-enhancement (n = 4), and peripheral rim-like enhancement (n = 2). All tumors of the treatment group presented with peripheral rim-like enhancement with large necrotic area after sorafenib administration, whereas tumors of the control group showed heterogeneous hyper-enhancement (n = 5) and peripheral rim-like enhancement (n = 2). There was a significant difference in area under the curve (AUC) before and after sorafenib treatment (P = 0.045). CEUS may be of value in the evaluation of early therapeutic response after sorafenib administration.

Imaging of Tumor Angiogenesis for Radiologists--Part 2: Clinical Utility

Angiogenesis is a key cancer hallmark involved in tumor growth and metastasis development. Angiogenesis and tumor microenvironment significantly influence the response of tumors to therapies. Imaging techniques have changed our understanding of the process of angiogenesis, the resulting vascular performance, and the tumor microenvironment. This article reviews the status and potential clinical value of the imaging modalities used to assess the status of tumor vasculature in vivo, before, during, and after treatment.

Can 111In-RGD2 monitor response to therapy in head and neck tumor xenografts?

RGD (arginylglycylaspartic acid)-based imaging tracers allow specific imaging of integrin αvβ3 expression, proteins overexpressed during angiogenesis; however, few studies have investigated the potential of these tracers to monitor responses of antiangiogenic or radiation therapy. In the studies presented here, (111)In-RGD2 was assessed for its potential as an imaging tool to monitor such responses to therapies.

METHODS

DOTA-E-[c(RGDfK)]2 was radiolabeled with (111)In ((111)In-RGD2), and biodistribution studies were performed in mice with subcutaneous FaDu or SK-RC-52 xenografts after treatment with either antiangiogenic therapy (bevacizumab or sorafenib) or tumor irradiation (10 Gy). Micro-SPECT imaging studies and subsequent quantitative analysis were also performed. The effect of bevacizumab, sorafenib, or radiation therapy on tumor growth was determined.

RESULTS

The uptake of (111)In-RGD2 in tumors, as determined from biodistribution studies, correlated well with that quantified from micro-SPECT images, and both showed that 15 d after irradiation (111)In-RGD2 uptake was enhanced. Specific or nonspecific uptake of (111)In-RGD2 in FaDu or SK-RC-52 xenografts was not affected after antiangiogenic therapy, except in head and neck squamous cell carcinoma 19 d after the start of sorafenib therapy (P < 0.05). The uptake of (111)In-RGD2 followed tumor volume in studies featuring antiangiogenic therapy. However, the uptake of (111)In-RGD2 in FaDu xenografts was decreased as early as 4 h after tumor irradiation, despite nonspecific uptake remaining unaltered. Tumor growth was inhibited after antiangiogenic or radiation therapy.

CONCLUSION

Here, it is suggested that (111)In-RGD2 could allow in vivo monitoring of angiogenic responses after radiotherapy and may therefore prove a good clinical tool to monitor angiogenic responses early after the start of radiotherapy in patients with head and neck squamous cell carcinoma. Despite clear antitumor efficacy, antiangiogenic therapy did not alter tumor uptake of (111)In-RGD2, indicating that integrin expression was not altered.

A direct comparison of tumor angiogenesis with ⁶⁸Ga-labeled NGR and RGD peptides in HT-1080 tumor xenografts using microPET imaging

Peptides containing asparagine-glycine-arginine (NGR) and arginine-glycine-aspartic acid (RGD) sequence are being developed for tumor angiogenesis-targeted imaging and therapy. The aim of this study was to compare the efficacy of NGR- and RGD-based probes for imaging tumor angiogenesis in HT-1080 tumor xenografts. Two PET probes, (68)Ga-NOTA-G₃-NGR2 and ⁶⁸Ga-NOTA-G₃-RGD2, were successfully prepared. In vitro stability, partition coefficient, tumor cell binding, as well as in vivo biodistribution properties were also analyzed for both PET probes. The results revealed that the two probes were both hydrophilic and stable in vitro and in vivo, and they were excreted predominately and rapidly through the kidneys. For both probes, the higher tumor uptake and lower accumulation in vital organs were determined. No significant difference between two probes was observed in terms of tumor uptake and the in vivo biodistribution properties. We concluded that these two probes are promising in tumor angiogenesis imaging. ⁶⁸Ga-NOTA-G₃-NGR2 has the potential as an alternative for PET imaging in patients with fibrosarcoma, and it may offer an opportunity to noninvasively monitor CD13-targeted therapy.

Early monitoring antiangiogenesis treatment response of Sunitinib in U87MG Tumor Xenograft by (18)F-FLT MicroPET/CT imaging

AIM

It was aimed to monitor early treatment response of Sunitinib in U87MG models mimicking glioblastoma multiforme by longitudinal (18)F-FLT microPET/CT imaging in this study.

METHODS

U87MG tumor mice were intragastrically injected with Sunitinib at a dose of 80 mg/kg for consecutive 7 days. (18)F-FLT microPET/CT scans were acquired on days 0, 1, 3, 7, and 13 after therapy. Tumor sizes and body weight were measured. Tumor samples were collected for immunohistochemical analysis of proliferation and microvessel density (MVD) with anti-Ki67 and anti-CD31, respectively.

RESULTS

The uptake ratios of tumor to the contralateral muscle (T/M) of (18)F-FLT in the Sunitinib group decreased from baseline to day 3 (T/M0 = 2.98 ± 0.33; T/M3 = 2.23 ± 0.36; P < 0.001), reached the bottom on day 7 (T/M7 = 1.96 ± 0.35; P < 0.001), and then recovered on day 13. The T/M of (18)F-FLT uptake in the control group remained around 3.0. There was no difference for the tumor size between both groups until day 11. (18)F-FLT uptakes of tumor were correlated with Ki67 staining index and MVD.

CONCLUSION

Early therapy response to Sunitinib could be predicted via (18)F-FLT PET, which will contribute to monitoring antiangiogenesis treatment.