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Prostate cancer theranostics using GRPR antagonist RM26
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Medicinal Chemistry. Uppsala University. (Theranostics)ORCID iD: 0000-0001-7921-3268
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The malignant transformation of cells is often associated with an alteration of their molecular phenotype, resulting in overexpression of several cell surface proteins. Gastrin-releasing peptide receptor (GRPR) and prostate-specific membrane antigen (PSMA) are examples of such pro-teins that are expressed at a high density in prostate cancer. GRPR is primarily expressed in earlier stages of prostate cancer and tends to decrease with disease progression. This expression pattern indicates that GRPR could be a promising target for imaging and treatment of oligometa-static prostate cancer, an early step in prostate cancer progression characterized by limited meta-static spread. In contrast, the expression of PSMA increases with cancer progression and is significantly upregulated as tumors dedifferentiate into higher grade, in androgen-insensitive and metastatic lesions.

This thesis is based on five original articles (papers I-V) and focuses on the preclinical de-velopment of radiotracers for imaging and treatment of prostate cancer. The work can be divided into three distinct parts: (1) the development and optimization of GRPR-antagonist RM26 for high contrast PET and SPECT imaging of oligometastatic prostate cancer (papers I-III), (2) the preclinical evaluation of 177Lu-labeled RM26 as a potential candidate for peptide receptor radionuclide therapy (PRRT) in GRPR-expressing tumors, alone or in combination with anti-HER2 antibody trastuzumab (paper IV), and (3) the development of a bispecific heterodimer targeting both PSMA and GRPR in prostate cancer (paper V).

We have demonstrated that the in vitro and in vivo properties of GRPR antagonist RM26 are strongly influenced by the choice of chelator-radionuclide complex and that long-lived radionuclides are desirable for high-contrast imaging. Furthermore, our data indicate that 55Co-NOTA-PEG2-RM26 has remarkable potential for next-day high-contrast PET imaging of GRPR-expressing tumors. Experimental PRRT using 177Lu-DOTAGA-PEG2-RM26 resulted in a pronounced inhibition of tumor growth and a significantly longer median survival. Interestingly, survival was further improved when trastuzumab was co-injected with 177Lu-DOTAGA-PEG2-RM26. These data indicate that blocking HER2 with trastuzumab decreased the repairing ability of irradiated cells. Finally, we developed a heterodimer (NOTA-DUPA-RM26) for imaging GRPR and PSMA expression in prostate cancer shortly after administration.

In conclusion, we have successfully developed and preclinically evaluated radioconjugates for GRPR-directed theranostics in oligometastatic prostate cancer using the bombesin antagonistic analog RM26.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 80
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy, ISSN 1651-6192 ; 274
Keywords [en]
Gastrin-releasing peptide receptor (GRPR), Bombesin, Prostate-specific membrane antigen (PSMA), Antagonist, Radionuclide molecular imaging, Theranostics, Peptide receptor radionuclide therapy (PRRT).
National Category
Medicinal Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-389563ISBN: 978-91-513-0695-7 (print)OAI: oai:DiVA.org:uu-389563DiVA, id: diva2:1337866
Public defence
2019-09-14, Rudbecksalen, Rudbecklaboratoriet, Dag Hammarskjölds väg 20, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2019-08-23 Created: 2019-07-17 Last updated: 2019-09-17
List of papers
1. The effect of macrocyclic chelators on the targeting properties of the 68Ga-labeled gastrin releasing peptide receptor antagonist PEG2-RM26
Open this publication in new window or tab >>The effect of macrocyclic chelators on the targeting properties of the 68Ga-labeled gastrin releasing peptide receptor antagonist PEG2-RM26
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2015 (English)In: Nuclear Medicine and Biology, ISSN 0969-8051, E-ISSN 1872-9614, Vol. 42, no 5, p. 446-454Article in journal (Refereed) Published
Abstract [en]

Introduction

Overexpression of gastrin-releasing peptide receptors (GRPR) has been reported in several cancers. Bombesin (BN) analogs are short peptides with a high affinity for GRPR. Different BN analogs were evaluated for radionuclide imaging and therapy of GRPR-expressing tumors. We have previously investigated an antagonistic analog of BN (D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2, RM26) conjugated to NOTA via a PEG2 spacer (NOTA-PEG2-RM26) labeled with 68Ga, 111In and Al18F. 68Ga-labeled NOTA-PEG2-RM26 showed high tumor-to-organ ratios.

Methods

The influence of different macrocyclic chelators (NOTA, NODAGA, DOTA and DOTAGA) on the targeting properties of 68Ga-labeled PEG2-RM26 was studied in vitro and in vivo.

Results

All conjugates were labeled with generator-produced 68Ga with high yields and demonstrated high stability and specific binding to GRPR. The IC50 values of natGa-X-PEG2-RM26 (X = NOTA, DOTA, NODAGA, DOTAGA) were 2.3 ± 0.2, 3.0 ± 0.3, 2.9 ± 0.3 and 10.0 ± 0.6 nM, respectively. The internalization of the conjugates by PC-3 cells was low. However, the DOTA-conjugated analog demonstrated a higher internalization rate compared to other analogs. GRPR-specific uptake was found in receptor-positive normal tissues and PC-3 xenografts for all conjugates. The biodistribution of the conjugates was influenced by the choice of the chelator moiety. Although all radiotracers cleared rapidly from the blood, [68Ga]Ga-NOTA-PEG2-RM26 showed significantly lower uptake in lung, muscle and bone compared to the other analogs. The uptake in tumors (5.40 ± 1.04 %ID/g at 2 h p.i.) and the tumor-to-organ ratios (25 ± 3, 157 ± 23 and 39 ± 4 for blood, muscle and bone, respectively) were significantly higher for the NOTA-conjugate than the other analogs.

Conclusions

Chelators had a clear influence on the biodistribution and targeting properties of 68Ga-labeled antagonistic BN analogs. Positively charged [68Ga]Ga-NOTA-PEG2-RM26 provided a low kidney radioactivity uptake, high affinity, high tumor uptake and high image contrast.

National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:uu:diva-232120 (URN)10.1016/j.nucmedbio.2014.12.009 (DOI)000353369000005 ()25684649 (PubMedID)
Funder
Swedish Cancer SocietySwedish Research Council
Available from: 2014-09-12 Created: 2014-09-12 Last updated: 2019-07-17Bibliographically approved
2. Selection of optimal chelator improves the contrast of GRPR imaging using bombesin analogue RM26.
Open this publication in new window or tab >>Selection of optimal chelator improves the contrast of GRPR imaging using bombesin analogue RM26.
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2016 (English)In: International journal of oncology, ISSN 1791-2423, Vol. 48, no 5, p. 2124-2134Article in journal (Refereed) Published
Abstract [en]

Bombesin (BN) analogs bind with high affinity to gastrin-releasing peptide receptors (GRPRs) that are up-regulated in prostate cancer and can be used for the visualization of prostate cancer. The aim of this study was to investigate the influence of radionuclide-chelator complexes on the biodistribution pattern of the 111In-labeled bombesin antagonist PEG2-D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2 (PEG2-RM26) and to identify an optimal construct for SPECT imaging. A series of RM26 analogs N-terminally conjugated with NOTA, NODAGA, DOTA and DOTAGA via a PEG2 spacer were radiolabeled with 111In and evaluated both in vitro and in vivo. The conjugates were successfully labeled with 111In with 100% purity and retained binding specificity to GRPR and high stability. The cellular processing of all compounds was characterized by slow internalization. The IC50 values were in the low nanomolar range, with lower IC50 values for positively charged natIn-NOTA-PEG2-RM26 (2.6±0.1 nM) and higher values for negatively charged natIn-DOTAGA-PEG2-RM26 (4.8±0.5 nM). The kinetic binding studies showed KD values in the picomolar range that followed the same pattern as the IC50 data. The biodistribution of all compounds was studied in BALB/c nu/nu mice bearing PC-3 prostate cancer xenografts. Tumor targeting and biodistribution studies displayed rapid clearance of radioactivity from the blood and normal organs via kidney excretion. All conjugates showed similar uptake in tumors at 4 h p.i. The radioactivity accumulation in GRPR-expressing organs was significantly lower for DOTA- and DOTAGA-containing constructs compared to those containing NOTA and NODAGA. 111In-NOTA-PEG2-RM26 with a positively charged complex showed the highest initial uptake and the slowest clearance of radioactivity from the liver. At 4 h p.i., DOTA- and DOTAGA-coupled analogs showed significantly higher tumor-to-organ ratios compared to NOTA- and NODAGA-containing variants. The NODAGA conjugate demonstrated the best retention of radioactivity in tumors, and, at 24 h p.i., had the highest contrast to blood, muscle and bones.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:uu:diva-281358 (URN)10.3892/ijo.2016.3429 (DOI)000372568600037 ()26983776 (PubMedID)
Funder
Swedish Cancer SocietySwedish Research Council
Available from: 2016-03-23 Created: 2016-03-23 Last updated: 2019-07-17Bibliographically approved
3. High Contrast PET Imaging of GRPR Expression in Prostate Cancer Using Cobalt-Labeled Bombesin Antagonist RM26
Open this publication in new window or tab >>High Contrast PET Imaging of GRPR Expression in Prostate Cancer Using Cobalt-Labeled Bombesin Antagonist RM26
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2017 (English)In: Contrast Media & Molecular Imaging, ISSN 1555-4309, E-ISSN 1555-4317, article id UNSP 6873684Article in journal (Refereed) Published
Abstract [en]

High gastrin releasing peptide receptor (GRPR) expression is associated with numerous cancers including prostate and breast cancer. The aim of the current study was to develop a Co-55-labeled PET agent based on GRPR antagonist RM26 for visualization of GRPR-expressing tumors. Labeling with Co-57 and Co-55, stability, binding specificity, and in vitro and in vivo characteristics of Co-57-NOTA-PEG(2)-RM26 were studied. NOTA-PEG(2)-RM26 was successfully radiolabeled with Co-57 and Co-55 with high yields and demonstrated high stability. The radiopeptide showed retained binding specificity to GRPR in vitro and in vivo. Co-57-NOTA-PEG(2)-RM26 biodistribution in mice was characterized by rapid clearance of radioactivity from blood and normal non-GRPR-expressing organs and low hepatic uptake. The clearance was predominantly renal with a low degree of radioactivity reabsorption. Tumor-to-blood ratios were approximately 200 (3 h pi) and 1000 (24 h pi). The favorable biodistribution of cobalt-labeled NOTA-PEG(2)-RM26 translated into high contrast preclinical PET/CT (using Co-55) and SPECT/CT (using Co-57) images of PC-3 xenografts. The initial biological results suggest that Co-55-NOTA-PEG(2)-RM26 is a promising tracer for PET visualization of GRPR-expressing tumors.

Keywords
Positron-Emission-Tomography, Receptor-Positive Tumors, In-Vivo Evaluation, Radiolabeled Peptides, Analog; Agonists, Visualization, Proteins, Affinity, Therapy.
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:uu:diva-334114 (URN)10.1155/2017/6873684 (DOI)000408099300001 ()
Funder
Swedish Cancer Society, CAN2014/474; CAN2015/350Swedish Research Council, 2015-02509; 2015-02353Knut and Alice Wallenberg FoundationScience for Life Laboratory - a national resource center for high-throughput molecular bioscience
Available from: 2017-11-24 Created: 2017-11-24 Last updated: 2019-07-17Bibliographically approved
4. Trastuzumab cotreatment improves survival of mice with PC-3 prostate cancer xenografts treated with the GRPR antagonist 177Lu-DOTAGA-PEG2-RM26
Open this publication in new window or tab >>Trastuzumab cotreatment improves survival of mice with PC-3 prostate cancer xenografts treated with the GRPR antagonist 177Lu-DOTAGA-PEG2-RM26
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2019 (English)In: International Journal of Cancer, ISSN 0020-7136, E-ISSN 1097-0215Article in journal (Refereed) Published
Abstract [en]

Gastrin-releasing peptide receptors (GRPRs) are overexpressed in prostate cancer and are suitable for targeted radionuclidetherapy (TRT). We optimized the bombesin-derived GRPR-antagonist PEG2-RM26 for labeling with 177Lu and further determinedthe effect of treatment with 177Lu-labeled peptide alone or in combination with the anti-HER2 antibody trastuzumab in amurine model. The PEG2-RM26 analog was coupled to NOTA, NODAGA, DOTA and DOTAGA chelators. The peptide-chelatorconjugates were labeled with 177Lu and characterized in vitro and in vivo. A preclinical therapeutic study was performed in PC-3xenografted mice. Mice were treated with intravenous injections (6 cycles) of (A) PBS, (B) DOTAGA-PEG2-RM26, (C) 177LuDOTAGA-PEG2-RM26, (D) trastuzumab or (E) 177Lu-DOTAGA-PEG2-RM26 in combination with trastuzumab. 177Lu-DOTAGA-PEG2-RM26 demonstrated quantitative labeling yield at high molar activity (450 GBq/μmol), high in vivo stability (5 min pi >98% ofradioligand remained when coinjected with phosphoramidon), high affinity to GRPR (KD = 0.4 0.2 nM), and favorablebiodistribution (1 hr pi tumor uptake was higher than in healthy tissues, including the kidneys). Therapy with 177Lu-DOTAGAPEG2-RM26 induced a significant inhibition of tumor growth. The median survival for control groups was significantly shorterthan for treated groups (Group C 66 days, Group E 74 days). Trastuzumab together with radionuclide therapy significantlyimproved survival. No treatment-related toxicity was observed. In conclusion, based on in vitro and in vivo characterization ofthe four 177Lu-labeled PEG2-RM26 analogs, we concluded that 177Lu-DOTAGA-PEG2-RM26 was the most promising analog forTRT. Radiotherapy using 177Lu-DOTAGA-PEG2-RM26 effectively inhibited tumor growth in vivo in a murine prostate cancermodel. Anti-HER2 therapy additionally improved survival.

Keywords
radionuclide therapy, GRPR, HER2, prostate cancer, lutetium-177
National Category
Cancer and Oncology
Identifiers
urn:nbn:se:uu:diva-389561 (URN)10.1002/ijc.32401 (DOI)
Available from: 2019-07-17 Created: 2019-07-17 Last updated: 2019-08-16Bibliographically approved
5. Bispecific GRPR-antagonistic anti-PSMA/GRPR heterodimer for PET and SPECT diagnostic imaging of prostate cancer
Open this publication in new window or tab >>Bispecific GRPR-antagonistic anti-PSMA/GRPR heterodimer for PET and SPECT diagnostic imaging of prostate cancer
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Prostate specific membrane antigen (PSMA) and gastrin-releasing peptide receptor (GRPR) are wellvalidated molecular targets that are overexpressed in most prostate cancers (PCa). Given thecomplexity and heterogeneity of PCa, targeting both receptors using bispecific radiotracers couldimprove the diagnostic accuracy and therapeutic outcome. The aim of this study was to develop aPSMA/GRPR-targeting bispecific heterodimer for SPECT and PET diagnostic imaging of PCa.Bispecific anti-GRPR/PSMA dimer NOTA-DUPA-RM26 was produced using a combination of solidphase and manual peptide synthesis. The heterodimer was successfully labeled with111In for SPECTand 68Ga for PET with radiochemical yields exceeding 99% for 111In and 98% for 68Ga. Theradiolabeled heterodimers demonstrated high label stability and retained binding specificity to PSMAand GRPR when tested using PC3-PIP cell line expressing both PSMA and GRPR. IC50 values fornatIn-NOTA-DUPA-RM26 were 4±1 nM towards GRPR and 350±240 nM towards PSMA. Cellularprocessing assay revealed a low degree of internalization for 111In-NOTA-DUPA-RM26. In vivobinding specificity tests in PC3-PIP xenografted mice 1 h pi of 111In-NOTA-DUPA-RM26demonstrated partially blockable tumor uptake when co-injected with excess of either PSMA- orGRPR-targeting agents. A pronounced blocking effect was observed for 111In and 68Ga-labeledheterodimer when co-injected simultaneously with excess of PSMA- and GRPR-targeting agents 1 hpi. Biodistribution was studied 1, 3 and 24 h pi for 111In-NOTA-DUPA-RM26, and 1 and 3 h pi for68Ga-NOTA-DUPA-RM26 and revealed a fast clearance of radioprobes from blood and normal organsvia renal excretion. Tumor uptake exceeded the uptake in all normal organs including excretory organsfor both 111In and 68Ga-labeled heterodimers 1 h pi. 68Ga-NOTA-DUPA-RM26 had a significantlylower tumor uptake (8±2%ID/g) compared to 111In-NOTA-DUPA-RM26 (12±2%ID/g), but a two-foldhigher uptake in liver 1h pi. The faster clearance of radioactivity from normal tissues compared totumor lead to an overall increase in tumor-to-organ ratios for both 111In and 68Ga-labeled heterodimers3 h pi. At 24 h pi, tumor-to-organ ratios decreased for 111In-NOTA-DUPA-RM26. MicroPET/CT andmicroSPECT/CT scans confirmed the ex vivo data and suggested that anti-GRPR/PSMA heterodimerNOTA-DUPA-RM26 labeled with galium-68 (for PET) and indium-111 (for SPECT) is a suitablecandidate for imaging of GRPR and PSMA expression in PCa shortly after administration.

Keywords
PSMA, GRPR, molecular imaging, prostate cancer
National Category
Cancer and Oncology
Identifiers
urn:nbn:se:uu:diva-389562 (URN)
Available from: 2019-07-17 Created: 2019-07-17 Last updated: 2019-08-15Bibliographically approved

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