Targeted radionuclide therapy with RAFT-RGD radiolabelled with (90)Y or (177)Lu in a mouse model of αvβ3-expressing tumours

Integrin-αvβ3 is a Therapeutically Targetable Fundamental Factor in Medulloblastoma Tumorigenicity and Radioresistance

Medulloblastoma is one of the most prevalent solid tumors found in children, occurring in the brain's posterior fossa. The standard treatment protocol involves maximal resection surgery followed by craniospinal irradiation and chemotherapy. Despite a long-term survival rate of 70%, wide disparities among patients have been observed. The identification of pertinent targets for both initial and recurrent medulloblastoma cases is imperative. Both primary and recurrent medulloblastoma are marked by their aggressive infiltration into surrounding brain tissue, robust angiogenesis, and resistance to radiotherapy. While the significant role of integrin-αvβ3 in driving these characteristics has been extensively documented in glioblastoma, its impact in the context of medulloblastoma remains largely unexplored. Integrin-αvβ3 was found to be expressed in a subset of patients with medulloblastoma. We investigated the role of integrin-αvβ3 using medulloblastoma-derived cell lines with β3-subunit depletion or overexpression both in vitro and in vivo settings. By generating radioresistant medulloblastoma cell lines, we uncovered an increased integrin-αvβ3 expression, which correlated with increased susceptibility to pharmacologic integrin-αvβ3 inhibition with cilengitide, a competitive ligand mimetic. Finally, we conducted single-photon emission computed tomography (SPECT)/MRI studies on orthotopic models using a radiolabeled integrin-αvβ3 ligand (99mTc-RAFT-RGD). This innovative approach presents the potential for a novel predictive imaging technique in the realm of medulloblastoma. Altogether, our findings lay the foundation for employing SPECT/MRI to identify a specific subset of patients with medulloblastoma eligible for integrin-αvβ3-directed therapies. This breakthrough offers a pathway toward more targeted and effective interventions in the treatment of medulloblastoma.

SIGNIFICANCE

This study demonstrates integrin-αvβ3's fundamental role in medulloblastoma tumorigenicity and radioresistance and the effect of its expression on cilengitide functional activity.

Multimeric RGD-Based Strategies for Selective Drug Delivery to Tumor Tissues

RGD peptides have received a lot of attention over the two last decades, in particular to improve tumor therapy through the targeting of the αVβ3 integrin receptor. This review focuses on the molecular design of multimeric RGD compounds, as well as the design of suitable linkers for drug delivery. Many examples of RGD-drug conjugates have been developed, and we show the importance of RGD constructs to enhance binding affinity to tumor cells, as well as their drug uptake. Further, we also highlight the use of RGD peptides as theranostic systems, promising tools offering dual modality, such as tumor diagnosis and therapy. In conclusion, we address the challenging issues, as well as ongoing and future development, in comparison with large molecules, such as monoclonal antibodies.

Comparison of integrin αvβ3 expression with 68Ga-NODAGA-RGD PET/CT and glucose metabolism with 18F-FDG PET/CT in esophageal or gastroesophageal junction cancers

BACKGROUND

The primary aims of this study were to compare in patients with esophageal or esophagogastric junction cancers the potential of ⁶⁸Ga-NODAGA-RGD PET/CT with that of ¹⁸F-FDG PET/CT regarding tumoral uptake and distribution, as well as histopathologic examination.

METHODS

Ten ⁶⁸Ga-NODAGA-RGD and ten ¹⁸F-FDG PET/CT were performed in nine prospectively included participants (1 woman; aged 58 ± 8.4 y, range 40-69 y). Maximum SUV (SUV_max) and metabolic tumor volumes (MTV) were calculated. The Mann-Whitney U test and Spearman correlation analysis (ρ) were used.

RESULTS

⁶⁸Ga-NODAGA-RGD PET/CT detected positive uptake in 10 primary sites (8 for primary tumors and 2 for local relapse suspicion), 6 lymph nodes and 3 skeletal sites. ¹⁸F-FDG PET/CT detected positive uptake in the same sites but also in 16 additional lymph nodes and 1 adrenal gland. On a lesion-based analysis, SUV_max of ¹⁸F-FDG was significantly higher than those of ⁶⁸Ga-NODAGA-RGD (4.9 [3.7-11.3] vs. 3.2 [2.6-4.2] g/mL, p = 0.014). Only one participant showed a higher SUV_max in an osseous metastasis with ⁶⁸Ga-NODAGA-RGD as compared to ¹⁸F-FDG (6.6 vs. 3.9 g/mL). Correlation analysis showed positive correlation between ¹⁸F-FDG and ⁶⁸Ga-NODAGA-RGD PET parameters (ρ = 0.56, p = 0.012 for SUV_max, ρ = 0.78, p < 0.001 for lesion-to-background ratios and ρ = 0.58, p = 0.024 for MTV). We observed that ¹⁸F-FDG uptake was homogenous inside all the confirmed primary sites (n = 9). In contrast, ⁶⁸Ga-NODAGA-RGD PET showed more heterogenous uptake in 6 out of the 9 confirmed primary sites (67%), seen mostly in the periphery of the tumor in 5 out of the 9 confirmed primary sites (56%), and showed slight extensions into perilesional structures in 5 out of the 9 confirmed primary sites (56%).

CONCLUSIONS

In conclusion, ⁶⁸Ga-NODAGA-RGD has lower potential in the detection of esophageal or esophagogastric junction malignancies compared to ¹⁸F-FDG. However, the results suggest that PET imaging of integrin α_vβ₃ expression may provide complementary information and could aid in tumor diversity and delineation.

TRIAL REGISTRATION

Trial registration: NCT02666547. Registered January 28, 2016-Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT02666547 .

Multiplexed Imaging Reveals the Spatial Relationship of the Extracellular Acidity-Targeting pHLIP with Necrosis, Hypoxia, and the Integrin-Targeting cRGD Peptide

pH (low) insertion peptides (pHLIPs) have been developed for cancer imaging and therapy targeting the acidic extracellular microenvironment. However, the characteristics of intratumoral distribution (ITD) of pHLIPs are not yet fully understood. This study aimed to reveal the details of the ITD of pHLIPs and their spatial relationship with other tumor features of concern. The fluorescent dye-labeled pHLIPs were intravenously administered to subcutaneous xenograft mouse models of U87MG and IGR-OV1 expressing αVβ3 integrins (using large necrotic tumors). The αVβ3 integrin-targeting Cy5.5-RAFT-c(-RGDfK-)4 was used as a reference. In vivo and ex vivo fluorescence imaging, whole-tumor section imaging, fluorescence microscopy, and multiplexed fluorescence colocalization analysis were performed. The ITD of fluorescent dye-labeled pHLIPs was heterogeneous, having a high degree of colocalization with necrosis. A direct one-to-one comparison of highly magnified images revealed the cellular localization of pHLIP in pyknotic, karyorrhexis, and karyolytic necrotic cells. pHLIP and hypoxia were spatially contiguous but not overlapping cellularly. The hypoxic region was found between the ITDs of pHLIP and the cRGD peptide and the Ki-67 proliferative activity remained detectable in the pHLIP-accumulated regions. The results provide a better understanding of the characteristics of ITD of pHLIPs, leading to new insights into the theranostic applications of pHLIPs.

Synergism of 64Cu-Labeled RGD with Anti-PD-L1 Immunotherapy for the Long-Acting Antitumor Effect

We put forward a novel targeting-triggering-therapy (TTT) scheme that combines ⁶⁴Cu-based targeted radionuclide therapy (TRT) with programmed death-ligand 1 (PD-L1)-based immunotherapy for enhancing therapeutic efficacy. The α_vβ₃ integrin-targeted ⁶⁴Cu-DOTA-EB-cRGDfK (⁶⁴Cu-DER) was synthesized. Flow cytometry, immunofluorescence staining, and RT-qPCR were performed to verify PD-L1 upregulation after irradiation with ⁶⁴Cu-DER. Positron emission tomography imaging was performed to investigate the prominent tumor retention property of ⁶⁴Cu-DER. In the MC38 tumor model, anti-PD-L1 antibody (αPD-L1 mAb) was delivered in a concurrent or sequential manner after ⁶⁴Cu-DER was injected, followed by the testing of changes in tumor microenvironment (TME). PD-L1 was upregulated in a time- and dose-dependent manner after being induced by ⁶⁴Cu-DER. The combination of ⁶⁴Cu-DER TRT (925 MBq/kg) and αPD-L1 mAb (10 mg/kg) resulted in significant delay in tumor growth and protected against tumor rechallenge. Blockade of PD-L1 at 4 h after ⁶⁴Cu-DER TRT (⁶⁴Cu-DER + αPD-L1 mAb @ 4 h combination group) was able to achieve 100% survival rate, prevent tumor relapse, and evidently prolong the survival of mice. In summary, the combination of ⁶⁴Cu-DER and αPD-L1 mAb in a time-dependent manner could be a promising approach to improve therapeutic efficacy. Understandably, this strategy has the potential to extend the scope of ⁶⁴Cu-based TTT and merits translation into clinical practice for the better management of immune checkpoint blockade immunotherapy.

Radiotheranostic Agent 64Cu-cyclam-RAFT-c(-RGDfK-)4 for Management of Peritoneal Metastasis in Ovarian Cancer

PURPOSE

Ovarian cancer peritoneal metastases (OCPMs) are a pathophysiologically heterogeneous group of tumors that are rarely curable. α_Vβ₃ integrin (α_Vβ₃) is overexpressed on tumoral neovessels and frequently on ovarian cancer cells. Here, using two clinically relevant α_Vβ₃-positive OCPM mouse models, we studied the theranostic potential of an α_Vβ₃-specific radiopeptide, ⁶⁴Cu-cyclam-RAFT-c(-RGDfK-)₄ (⁶⁴Cu-RaftRGD), and its intra- and intertumoral distribution in relation to the tumor microenvironment.

EXPERIMENTAL DESIGN

α_Vβ₃-expressing peritoneal and subcutaneous models of ovarian carcinoma (IGR-OV1 and NIH:OVCAR-3) were established in nude mice. ⁶⁴Cu-RaftRGD was administered either intravenously or intraperitoneally. We performed intratumoral distribution (ITD) studies, PET/CT imaging and quantification, biodistribution assay and radiation dosimetry, and therapeutic efficacy and toxicity studies.

RESULTS

Intraperitoneal administration was an efficient route for targeting ⁶⁴Cu-RaftRGD to OCPMs with excellent tumor penetration. Using the fluorescence surrogate, Cy5.5-RaftRGD, in our unique high-resolution multifluorescence analysis, we found that the ITD of ⁶⁴Cu-RaftRGD was spatially distinct from, but complementary to, that of hypoxia. ⁶⁴Cu-RaftRGD-based PET enabled clear visualization of multiple OCPM deposits and ascites and biodistribution analysis demonstrated an inverse correlation between tumor uptake and tumor size (1.2-17.2 mm). ⁶⁴Cu-RaftRGD at a radiotherapeutic dose (148 MBq/0.357 nmol) showed antitumor activities by inhibiting tumor cell proliferation and inducing apoptosis, with negligible toxicity.

CONCLUSIONS

Collectively, these results demonstrate the all-in-one potential of ⁶⁴Cu-RaftRGD for imaging guided radiotherapy of OCPM by targeting both tumoral neovessels and cancerous cells. On the basis of the ITD finding, we propose that pairing α_Vβ₃- and hypoxia-targeted radiotherapies could improve therapeutic efficacy by overcoming the heterogeneity of ITD encountered with single-agent treatments.

Non-oncological applications of RGD-based single-photon emission tomography and positron emission tomography agents

INTRODUCTION

Non-invasive imaging techniques (especially single-photon emission tomography and positron emission tomography) apply several RGD-based imaging ligands developed during a vast number of preclinical and clinical investigations. The RGD (Arg-Gly-Asp) sequence is a binding moiety for a large selection of adhesive extracellular matrix and cell surface proteins. Since the first identification of this sequence as the shortest sequence required for recognition in fibronectin during the 1980s, fundamental research regarding the molecular mechanisms of integrin action have paved the way for development of several pharmaceuticals and radiopharmaceuticals with clinical applications. Ligands recognizing RGD may be developed for use in the monitoring of these interactions (benign or pathological). Although RGD-based molecular imaging has been actively investigated for oncological purposes, their utilization towards non-oncology applications remains relatively under-exploited.

METHODS AND SCOPE

This review highlights the new non-oncologic applications of RGD-based tracers (with the focus on single-photon emission tomography and positron emission tomography). The focus is on the last 10 years of scientific literature (2009-2020). It is proposed that these imaging agents will be used for off-label indications that may provide options for disease monitoring where there are no approved tracers available, for instance Crohn's disease or osteoporosis. Fundamental science investigations have made progress in elucidating the involvement of integrin in various diseases not pertaining to oncology. Furthermore, RGD-based radiopharmaceuticals have been evaluated extensively for safety during clinical evaluations of various natures.

CONCLUSION

Clinical translation of non-oncological applications for RGD-based radiopharmaceuticals and other imaging tracers without going through time-consuming extensive development is therefore highly plausible. Graphical abstract.

A 64 Cu-porphyrin-based dual-modal molecular probe with integrin αv β3 targeting function for tumour imaging

Pyropheophorbide-a (Pyro) is a promising multifunctional molecule for multimodal tumour imaging and photodynamic therapy, but its clinical applications are seriously restricted by the limited tumour accumulation capability. Here, we designed and synthesized a small-molecule probe that achieved specific dual-modal tumour imaging based on Pyro. Briefly, a novel molecule combining Pyro, an RGD dimer peptide (3PRGD₂ ) and ⁶⁴ Cu, was designed and synthesized, and the obtained molecule, ⁶⁴ Cu-Pyro-3PRGD₂ , exhibited high tumour specificity in both positron emission tomography and optical imaging in vivo. c (RGDfk) peptide blocking significantly reduced the efficacy of the probe, which confirmed the integrin α_V β₃ targeting of this molecular probe. ⁶⁴ Cu-Pyro-3PRGD₂ had very low accumulation in normal organs and could be rapidly cleared through kidney metabolism, which prevented the potential damage to adjacent normal tissues. Overall, combining tumour targeting, dual-modal imaging, and biosafety, ⁶⁴ Cu-Pyro-3PRGD₂ has the potential for clinical use as a molecular imaging probe for tumour diagnosis.

[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.

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.