Pre-clinical evaluation of eight DOTA coupled gastrin-releasing peptide receptor (GRP-R) ligands for in vivo targeting of receptor-expressing tumors

In vitro and in vivo evaluation of Bombesin-MMAE conjugates for targeted tumour therapy

Targeted tumour therapy has proved to be an efficient alternative to overcome the limitations of conventional chemotherapy. The upregulation of the bombesin receptor 2 (BB2) in several malignancies and the advantages offered by peptide drug conjugates over antibody drug conjugates in terms of production and tumour targeting motivated us to synthesise and test bombesin conjugates armed with the tubulin binder monomethyl auristatin E. The widely used Val-Cit-PABC was initially included as cathepsin cleavable self-immolative linker for the release of the free drug. However, the poor stability of the Val-Cit-conjugates in mouse plasma encouraged us to consider the optimised alternatives Glu-Val-Cit-PABC and Glu-Gly-Cit-PABC. Conjugate BN-EVcM1, featuring Glu-Val-Cit-PABC, combined suitable stability (t(½) in mouse and human plasma: 8.4 h and 4.6 h, respectively), antiproliferative activity in vitro (IC50 = 29.6 nM on the human prostate cancer cell line PC-3) and the full release of the free payload within 24 h. Three conjugates, namely BN-EGcM1, BN-EVcM1 and BN-EVcM2, improved the accumulation of MMAE in PC-3 human prostate cancer xenograft mice models, compared to the administration of the free drug. Among them, BN-EVcM1 also stood out for the significantly extended survival of mice in in vivo acute efficacy studies and for the significant inhibition of the growth of a PC-3 tumour in mice in both acute and chronic efficacy studies.

Radiopharmaceuticals Targeting Gastrin-Releasing Peptide Receptor for Diagnosis and Therapy of Prostate Cancer

The high incidence and heavy disease burden of prostate cancer (PC) require accurate and comprehensive assessment for appropriate disease management. Prostate-specific membrane antigen (PSMA) positron emission tomography (PET) cannot detect PSMA-negative lesions, despite its key role in PC disease management. The overexpression of gastrin-releasing peptide receptor (GRPR) in PC lesions reportedly performs as a complementary target for the diagnosis and therapy of PC. Radiopharmaceuticals derived from the natural ligands of GRPR have been developed. These radiopharmaceuticals enable the visualization and quantification of GRPR within the body, which can be used for disease assessment and therapeutic guidance. Recently developed radiopharmaceuticals exhibit improved pharmacokinetic parameters without deterioration in affinity. Several heterodimers targeting GRPR have been constructed as alternatives because of their potential to detect tumor lesions with a low diagnostic efficiency of single target detection. Moreover, some GRPR-targeted radiopharmaceuticals have entered clinical trials for the initial staging or biochemical recurrence detection of PC to guide disease stratification and therapy, indicating considerable potential in PC disease management. Herein, we comprehensively summarize the progress of radiopharmaceuticals targeting GRPR. In particular, we discuss the impact of ligands, chelators, and linkers on the distribution of radiopharmaceuticals. Furthermore, we summarize a potential design scheme to facilitate the advancement of radiopharmaceuticals and, thus, prompt clinical translation.

Gastrin Releasing Peptide Receptors-targeted PET Diagnostics and Radionuclide Therapy for Prostate Cancer Management: Preclinical and Clinical Developments of the Past 5 Years

Each tumor has its own distinctive molecular identity. Treatment, therefore, should be tailored to this unique cancer phenotype. Theragnostics uses the same compound for targeted imaging and treatment, radiolabeled to an appropriate radionuclide, respectively. Gastrin-releasing peptide receptors (GRPRs) are overexpressed in prostate cancer, and radiolabeled GRPR antagonists have shown high diagnostic performance at staging and biochemical recurrence. Several GRPR-targeting theragnostic compounds have been developed preclinically. Their translation into clinics is underway with 4 clinical trials recruiting participants with GRPR-expressing tumors.

Oxime-Linked Peptide-Daunomycin Conjugates as Good Tools for Selection of Suitable Homing Devices in Targeted Tumor Therapy: An Overview

Chemotherapy is still one of the main therapeutic approaches in cancer therapy. Nevertheless, its poor selectivity causes severe toxic side effects that, together with the development of drug resistance in tumor cells, results in a limitation for its application. Tumor-targeted drug delivery is a possible choice to overcome these drawbacks. As well as monoclonal antibodies, peptides are promising targeting moieties for drug delivery. However, the development of peptide-drug conjugates (PDCs) is still a big challenge. The main reason is that the conjugates have to be stable in circulation, but the drug or its active metabolite should be released efficiently in the tumor cells. For this purpose, suitable linker systems are needed that connect the drug molecule with the homing peptide. The applied linker systems are commonly categorized as cleavable and non-cleavable linkers. Both the groups possess advantages and disadvantages that are summarized briefly in this manuscript. Moreover, in this review paper, we highlight the benefit of oxime-linked anthracycline-peptide conjugates in the development of PDCs. For instance, straightforward synthesis as well as a conjugation reaction proceed in excellent yields, and the autofluorescence of anthracyclines provides a good tool to select the appropriate homing peptides. Furthermore, we demonstrate that these conjugates can be used properly in in vivo studies. The results indicate that the oxime-linked PDCs are potential candidates for targeted tumor therapy.

A Pilot Study of 68Ga-PSMA11 and 68Ga-RM2 PET/MRI for Biopsy Guidance in Patients with Suspected Prostate Cancer

Targeting of lesions seen on multiparametric MRI (mpMRI) improves prostate cancer (PC) detection at biopsy. However, 20%-65% of highly suspicious lesions on mpMRI (PI-RADS [Prostate Imaging-Reporting and Data System] 4 or 5) are false-positives (FPs), while 5%-10% of clinically significant PC (csPC) are missed. Prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptors (GRPRs) are both overexpressed in PC. We therefore aimed to evaluate the potential of 68Ga-PSMA11 and 68Ga-RM2 PET/MRI for biopsy guidance in patients with suspected PC. Methods: A highly selective cohort of 13 men, aged 58.0 ± 7.1 y, with suspected PC (persistently high prostate-specific antigen [PSA] and PSA density) but negative or equivocal mpMRI results or negative biopsy were prospectively enrolled to undergo 68Ga-PSMA11 and 68Ga-RM2 PET/MRI. PET/MRI included whole-body and dedicated pelvic imaging after a delay of 20 min. All patients had targeted biopsy of any lesions seen on PET followed by standard 12-core biopsy. The SUVmax of suspected PC lesions was collected and compared with gold standard biopsy. Results: PSA and PSA density at enrollment were 9.8 ± 6.0 (range, 1.5-25.5) ng/mL and 0.20 ± 0.18 (range, 0.06-0.68) ng/mL2, respectively. Standardized systematic biopsy revealed a total of 14 PCs in 8 participants: 7 were csPC and 7 were nonclinically significant PC (ncsPC). 68Ga-PSMA11 identified 25 lesions, of which 11 (44%) were true-positive (TP) (5 csPC). 68Ga-RM2 showed 27 lesions, of which 14 (52%) were TP, identifying all 7 csPC and also 7 ncsPC. There were 17 concordant lesions in 11 patients versus 14 discordant lesions in 7 patients between 68Ga-PSMA11 and 68Ga-RM2 PET. Incongruent lesions had the highest rate of FP (12 FP vs. 2 TP). SUVmax was significantly higher for TP than FP lesions in delayed pelvic imaging for 68Ga-PSMA11 (6.49 ± 4.14 vs. 4.05 ± 1.55, P = 0.023) but not for whole-body images, nor for 68Ga-RM2. Conclusion: Our results show that 68Ga-PSMA11 and 68Ga-RM2 PET/MRI are feasible for biopsy guidance in suspected PC. Both radiopharmaceuticals detected additional clinically significant cancers not seen on mpMRI in this selective cohort. 68Ga-RM2 PET/MRI identified all csPC confirmed at biopsy.

Nanostrategies for Therapeutic and Diagnostic Targeting of Gastrin-Releasing Peptide Receptor

Advances in nanomedicine bring the attention of researchers to the molecular targets that can play a major role in the development of novel therapeutic and diagnostic modalities for cancer management. The choice of a proper molecular target can decide the efficacy of the treatment and endorse the personalized medicine approach. Gastrin-releasing peptide receptor (GRPR) is a G-protein-coupled membrane receptor, well known to be overexpressed in numerous malignancies including pancreatic, prostate, breast, lung, colon, cervical, and gastrointestinal cancers. Therefore, many research groups express a deep interest in targeting GRPR with their nanoformulations. A broad spectrum of the GRPR ligands has been described in the literature, which allows tuning of the properties of the final formulation, particularly in the field of the ligand affinity to the receptor and internalization possibilities. Hereby, the recent advances in the field of applications of various nanoplatforms that are able to reach the GRPR-expressing cells are reviewed.

Targeting the Gastrin-Releasing Peptide Receptor (GRP-R) in Cancer Therapy: Development of Bombesin-Based Peptide-Drug Conjugates

Targeted tumour therapy has proved to be an efficient alternative to overcome the limitations of conventional chemotherapy. Among several receptors upregulated in cancer cells, the gastrin-releasing peptide receptor (GRP-R) has recently emerged as a promising target for cancer imaging, diagnosing and treatment due to its overexpression on cancerous tissues such as breast, prostate, pancreatic and small-cell lung cancer. Herein, we report on the in vitro and in vivo selective delivery of the cytotoxic drug daunorubicin to prostate and breast cancer, by targeting GRP-R. Exploiting many bombesin analogues as homing peptides, including a newly developed peptide, we produced eleven daunorubicin-containing peptide-drug conjugates (PDCs), acting as drug delivery systems to safely reach the tumour environment. Two of our bioconjugates revealed remarkable anti-proliferative activity, an efficient uptake by all three tested human breast and prostate cancer cell lines, high stability in plasma and a prompt release of the drug-containing metabolite by lysosomal enzymes. Moreover, they revealed a safe profile and a consistent reduction of the tumour volume in vivo. In conclusion, we highlight the importance of GRP-R binding PDCs in targeted cancer therapy, with the possibility of further tailoring and optimisation.

Bioorthogonal Chemistry Approach for the Theranostics of GRPR-Expressing Cancers

Several gastrin-releasing peptide receptor (GRPR) antagonists with improved in vivo behavior have been recently developed and tested in the clinic. However, despite the generally mild side effects of peptide receptor radionuclide therapy (PRRT), toxicity has been observed due to high doses delivered to nontarget tissues, especially in the kidneys and pancreas. Previous experiences with radiolabeled peptides opened a unique opportunity to explore GRPR pretargeting using clickable bombesin antagonists. Toward this goal, we used clickable DOTA-like radiocomplexes which have been previously evaluated by our group. We functionalized a potent GRPR antagonist with a clickable TCO moiety using two different linkers. These precursors were then studied to select the compound with the highest GRPR binding affinity and the best pharmacokinetics to finally explore the advantages of the devised pretargeting approach. Our results provided an important proof of concept toward the development of bioorthogonal approaches to GRPR-expressing cancers, which are worth investigating further to improve the in vivo results. Moreover, the use of clickable GRPR antagonists and DOTA/DOTAGA derivatives allows for fine-tuning of their pharmacokinetics and metabolic stability, leading to a versatile synthesis of new libraries of (radio)conjugates useful for the development of theranostic tools toward GRPR-expressing tumors.

Engineering nanosystems to overcome barriers to cancer diagnosis and treatment

Over the past two decades, multidisciplinary investigations into the development of nanoparticles for medical applications have continually increased. However, nanoparticles are still subject to biological barriers and biodistribution challenges, which limit their overall clinical potential. This has motivated the implementation of innovational modifications to a range of nanoparticle formulations designed for cancer imaging and/or cancer treatment to overcome specific barriers and shift the accumulation of payloads toward the diseased tissues. In recent years, novel technological and chemical approaches have been employed to modify or functionalize the surface of nanoparticles or manipulate the characteristics of nanoparticles. Combining these approaches with the identification of critical biomarkers provides new strategies for enhancing nanoparticle specificity for both cancer diagnostic and therapeutic applications. This review discusses the most recent advances in the design and engineering of nanoparticles as well as future directions for developing the next generation of nanomedicines.

PET Imaging Using Gallium-68 (68Ga) RM2

Molecular imaging is advancing rapidly with promising new molecular targets emerging for theragnostic, ie, imaging and treatment with the same compound, to provide targeted, personalized medicine. Gastrin-releasing peptide receptors (GRPR) are overexpressed in prostate cancer. Gallium-68 (68Ga) RM2 is a GRPR antagonist and shows high sensitivity and specificity for the detection of primary prostate cancer and recurrent disease. However, compared with the widely used 68Ga-PSMA11 and 18F-DCFPyL, a discordance in uptake pattern is seen reflecting the heterogeneity in tumor biology of prostate cancer. In this review, we present the background, current status, and future perspectives of PET imaging using 68Ga-RM2.

New Frontiers in Molecular Imaging Using Peptide-Based Radiopharmaceuticals for Prostate Cancer

The high incidence of prostate cancer (PCa) increases the need for progress in its diagnosis, staging, and precise treatment. The overexpression of tumor-specific receptors for peptides in human cancer cells, such as gastrin-releasing peptide receptor, natriuretic peptide receptor, and somatostatin receptor, has indicated the ideal molecular basis for targeted imaging and therapy. Targeting these receptors using radiolabeled peptides and analogs have been an essential topic on the current forefront of PCa studies. Radiolabeled peptides have been used to target receptors for molecular imaging in human PCa with high affinity and specificity. The radiolabeled peptides enable optimal quick elimination from blood and normal tissues, producing high contrast for positron emission computed tomography and single-photon emission computed tomography imaging with high tumor-to-normal tissue uptake ratios. Owing to their successful application in visualization, peptide derivatives with therapeutic radionuclides for peptide receptor radionuclide therapy in PCa have been explored in recent years. These developments offer the promise of personalized, molecular medicine for individual patients. Hence, we review the preclinical and clinical literature in the past 20 years and focus on the newer developments of peptide-based radiopharmaceuticals for the imaging and therapy of PCa.

Strategies for improving stability and pharmacokinetic characteristics of radiolabeled peptides for imaging and therapy

Tumor cells overexpress a variety of receptors that are emerging targets in cancer chemotherapy. Radiolabeled peptides with high affinity and selectivity for these overexpressed receptors have been designed for both imaging and therapy purposes. Such peptides display advantages such as high selectivity for tumor cells, rapid tumor tissue penetration, and rapid clearance from non-target tissues and the circulation. However, the very short in vivo half-life of radiolabeled peptides, arising from enzymatic degradation and/or efficient clearance by the kidney, limits their accumulation in tumors. This review presents various strategies that have been applied to extend the half-life extension and improve the pharmacokinetic characteristics of radiolabeled peptides. These include amino acid substitution, modification of the peptide termini, dimerization and multimerization of the peptide, cyclization, conjugation with polymers, sugars and albumin and use of peptidase inhibitors.

In Vitro Evaluation and Biodistribution Studies of HPMA Copolymers Targeting the Gastrin Releasing Peptide Receptor in Prostate Cancer

PURPOSE

The development of diagnostic and therapeutic agents utilizing small peptides (e.g., bombesin (BBN)) to target the overexpression of the gastrin-releasing peptide receptor (GRPR) in cancers has been widely investigated. Herein, we examine the capabilities of BBN-modified HPMA copolymers to target the GRPR.

METHODS

Four positive, four negative, and two zwitterionic BBN HPMA copolymer conjugates of varying peptide content and charge were synthesized. In vitro and in vivo studies were conducted in a GRPR-overexpressing prostate cancer cell line (PC-3) and a normal CF-1 mouse model, respectively.

RESULTS

Cellular uptake of the conjugates were found to be charge and BBN density dependent. The positively-charged conjugates illustrated a direct relationship between the extent of cellular internalization, ranging from 0.7 to 20%, and BBN-incorporation density. The negative and zwitterionic conjugates showed low PC-3 uptake values. Blocking studies confirmed the GRPR-targeting effect of the positively-charged constructs. In vivo studies of the positively-charged copolymers resulted in rapid blood clearance by the mononuclear phagocyte system (MPS)-associated tissues (e.g., liver and spleen).

CONCLUSION

Positively-charged BBN-HPMA copolymer conjugates demonstrated good GRPR-targeting and internalization in vitro. However, the impact of peptide density and charge on in vivo MPS recognition are parameters that must be optimized in future agent development.

From Animal Poisons and Venoms to Medicines: Achievements, Challenges and Perspectives in Drug Discovery

Animal poisons and venoms are comprised of different classes of molecules displaying wide-ranging pharmacological activities. This review aims to provide an in-depth view of toxin-based compounds from terrestrial and marine organisms used as diagnostic tools, experimental molecules to validate postulated therapeutic targets, drug libraries, prototypes for the design of drugs, cosmeceuticals, and therapeutic agents. However, making these molecules applicable requires extensive preclinical trials, with some applications also demanding clinical trials, in order to validate their molecular target, mechanism of action, effective dose, potential adverse effects, as well as other fundamental parameters. Here we go through the pitfalls for a toxin-based potential therapeutic drug to become eligible for clinical trials and marketing. The manuscript also presents an overview of the current picture for several molecules from different animal venoms and poisons (such as those from amphibians, cone snails, hymenopterans, scorpions, sea anemones, snakes, spiders, tetraodontiformes, bats, and shrews) that have been used in clinical trials. Advances and perspectives on the therapeutic potential of molecules from other underexploited animals, such as caterpillars and ticks, are also reported. The challenges faced during the lengthy and costly preclinical and clinical studies and how to overcome these hindrances are also discussed for that drug candidates going to the bedside. It covers most of the drugs developed using toxins, the molecules that have failed and those that are currently in clinical trials. The article presents a detailed overview of toxins that have been used as therapeutic agents, including their discovery, formulation, dosage, indications, main adverse effects, and pregnancy and breastfeeding prescription warnings. Toxins in diagnosis, as well as cosmeceuticals and atypical therapies (bee venom and leech therapies) are also reported. The level of cumulative and detailed information provided in this review may help pharmacists, physicians, biotechnologists, pharmacologists, and scientists interested in toxinology, drug discovery, and development of toxin-based products.

Methods to Enhance the Metabolic Stability of Peptide-Based PET Radiopharmaceuticals

The high affinity and specificity of peptides towards biological targets, in addition to their favorable pharmacological properties, has encouraged the development of many peptide-based pharmaceuticals, including peptide-based positron emission tomography (PET) radiopharmaceuticals. However, the poor in vivo stability of unmodified peptides against proteolysis is a major challenge that must be overcome, as it can result in an impractically short in vivo biological half-life and a subsequently poor bioavailability when used in imaging and therapeutic applications. Consequently, many biologically and pharmacologically interesting peptide-based drugs may never see application. A potential way to overcome this is using peptide analogues designed to mimic the pharmacophore of a native peptide while also containing unnatural modifications that act to maintain or improve the pharmacological properties. This review explores strategies that have been developed to increase the metabolic stability of peptide-based pharmaceuticals. It includes modifications of the C- and/or N-termini, introduction of d- or other unnatural amino acids, backbone modification, PEGylation and alkyl chain incorporation, cyclization and peptide bond substitution, and where those strategies have been, or could be, applied to PET peptide-based radiopharmaceuticals.

A convenient and efficient total solid-phase synthesis of DOTA-functionalized tumor-targeting peptides for PET imaging of cancer

Introduction

An efficient and cost-effective synthesis of the metal chelating agents that couple to tumor-targeting peptides is required to enhance the process of preclinical research toward the clinical translation of molecular imaging agents. DOTA is one of the most widely used macrocyclic ligands for the development of new metal-based imaging and therapeutic agents owing to its ability to form stable and inert complexes under physiological conditions. Although solid-phase synthesis compatible DOTA-tris-(t-Bu ester) is a commercial product, it is expensive and contain chemical impurities. There is a need to explore new and cost-effective methods for the preparation of metal chelating agents, i.e., DOTA, directly on solid support to facilitate rapid, cost-effective, and high purity preparation of DOTA-linked peptides for imaging and therapy. In the present study, we describe a facile synthetic strategy of DOTA preparation and its linkage to peptides directly on solid-phase support.

Methods

Bombesin (BN) peptides were functionalized with DOTA chelator prepared from cyclen precursor on solid-phase and from commercial DOTA-tris and radiolabeled with ⁶⁸Ga. In vitro BN/GRP receptor binding affinities of the corresponding radiolabeled peptides were determined by saturation binding assays on human breast MDA-MB-231, MCF7, T47D, and PC3 prostate cancer cells. Pharmacokinetics were studied in Balb/c mice and in vivo tumor targeting in MDA-MB-231 tumor-bearing nude mice.

Results

DOTA was prepared successfully from cyclen on solid-phase support, linked specifically to BN peptides and resultant DOTA-coupled peptides were radiolabeled efficiently with ⁶⁸Ga. The binding affinities of all the six BN peptides were comparable and in the low nanomolar range. All ⁶⁸Ga-labeled peptides showed high metabolic stability in plasma. These radiopeptides exhibited rapid pharmacokinetics in Balb/c mice with excretion mainly through the urinary system. In nude mice, MDA-MB-231 tumor uptake profiles were slightly different; the BN peptide with Ahx spacer and linked to DOTA through cyclen exhibited higher tumor uptake (2.32% ID/g at 1 h post-injection) than other radiolabeled BN peptides investigated in this study. The same leading BN peptide also displayed favorable pharmacokinetic profile in Balb/c mice. The PET images clearly visualized the MDA-MB-231 tumor.

Conclusions

DOTA prepared from cyclen on solid-phase support showed comparable potency and efficiency to DOTA-tris in both in vitro and in vivo evaluation. The synthetic methodology described here allows versatile, site-specific introduction of DOTA into peptides to facilitate the development of DOTA-linked molecular imaging and therapy agents for clinical translation.

Comparison of fusion protein and DC vaccine in inhibition of mouse B16F10 melanoma tumor

Dendritic cell (DC) vaccine and fusion protein vaccine have been put into clinical use in cancer immunotherapy. This study compared DC vaccine and fusion protein vaccine directly in their capability of inducing specific immune response. We used mouse Granulocyte Macrophage-Colony Stimulating Factor (mGM-CSF) fused with gastrin-releasing peptide (GRP) and Gonadotrophin Releasing Hormone (GnRH) respectively to obtain mGM-CSF/GRP6 (mG6) and mGM-CSF/mGGn (mGGn) fusion proteins. We prepared fusion protein vaccine and DC vaccine including mG6 protein vaccine (6P), mGGn protein vaccine (nP), mG6 DC vaccine (6D) and mGGn DC vaccine (nD), then the two proteins were mixed to prepare combination proteins vaccine (6nP) and DC vaccine (6nD). After that, C57BL/6 mice were injected with B16F10 cell line to build melanoma tumor model, and were immunized with vaccines to produce antibodies to inhibit and destruct melanoma tumor cells. The discoveries showed that anti- mGM-CSF-GRP6 and anti- mGM-CSF-mGGn antibody vaccines were successfully created as expected; this was deduced from significant inhibition of melanoma tumor in vivo and significant reduction of tumor weight and volume. The effects of DC groups were better than that of the protein groups and the combination of vaccines were more effective than vaccine given separately. Our results indicate that using combination vaccine provides a new strategy to inhibit melanoma tumor growth but a complete cure of melanoma needs further investigations.

Preparation and Evaluation of 177Lu-Labeled Gemcitabine: An Effort Toward Developing Radiolabeled Chemotherapeutics for Targeted Therapy Applications

OBJECTIVE

Gemcitabine, a nucleoside analogue, is used as a chemotherapeutic drug for the treatment of a wide variety of cancers. Therefore, radiolabeled gemcitabine may have potential as a radiotherapeutic agent for the treatment of various types of cancers. In the present work, an attempt has been made to radiolabel gemcitabine with ¹⁷⁷Lu and study the preliminary biological behavior of ¹⁷⁷Lu-labeled gemcitabine in tumor-bearing animal model.

EXPERIMENTAL

Gemcitabine was coupled with p-NCS-benzyl-DOTA, a bifunctional chelating agent, to facilitate radiolabeling with ¹⁷⁷Lu. The p-NCS-benzyl-DOTA-gemcitabine conjugate was radiolabeled with ¹⁷⁷Lu, produced in-house and characterized by high-performance liquid chromatography. Tumor targeting potential of the radiolabeled agent was determined by biodistribution studies in Swiss mice bearing fibrosarcoma tumors.

RESULTS

¹⁷⁷Lu-gemcitabine was prepared with a radiochemical purity of 95.7% ± 0.3% under the optimized reaction conditions. The radiolabeled agent showed adequate in vitro stability in normal saline as well as in human blood serum. Preliminary biological studies revealed rapid and significant accumulation of the radiotracer in the tumorous lesions along with fast clearance of activity from blood and other vital organs/tissue. Although tumor uptake gradually reduced with time, tumor to blood and tumor to muscle ratios were improved due to the comparatively faster clearance of activity from the nontarget organs/tissue.

CONCLUSION

The present study demonstrates the preliminary potential of ¹⁷⁷Lu-gemcitabine for targeted radiotherapy. However, further studies are warranted to assess its potential for radiotherapeutic applications.

New Insights in the Design of Bioactive Peptides and Chelating Agents for Imaging and Therapy in Oncology

Many synthetic peptides have been developed for diagnosis and therapy of human cancers based on their ability to target specific receptors on cancer cell surface or to penetrate the cell membrane. Chemical modifications of amino acid chains have significantly improved the biological activity, the stability and efficacy of peptide analogues currently employed as anticancer drugs or as molecular imaging tracers. The stability of somatostatin, integrins and bombesin analogues in the human body have been significantly increased by cyclization and/or insertion of non-natural amino acids in the peptide sequences. Moreover, the overall pharmacokinetic properties of such analogues and others (including cholecystokinin, vasoactive intestinal peptide and neurotensin analogues) have been improved by PEGylation and glycosylation. Furthermore, conjugation of those peptide analogues to new linkers and bifunctional chelators (such as AAZTA, TETA, TRAP, NOPO etc.), produced radiolabeled moieties with increased half life and higher binding affinity to the cognate receptors. This review describes the most important and recent chemical modifications introduced in the amino acid sequences as well as linkers and new bifunctional chelators which have significantly improved the specificity and sensitivity of peptides used in oncologic diagnosis and therapy.

PET/MR in invasive ductal breast cancer: correlation between imaging markers and histological phenotype

BACKGROUND

Differences in genetics and receptor expression (phenotypes) of invasive ductal breast cancer (IDC) impact on prognosis and treatment response. Immunohistochemistry (IHC), the most used technique for IDC phenotyping, has some limitations including its invasiveness. We explored the possibility of contrast-enhanced positron emission tomography magnetic resonance (CE-FDG PET/MR) to discriminate IDC phenotypes.

METHODS

21 IDC patients with IHC assessment of oestrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor-2 (HER2), and antigen Ki-67 (Ki67) underwent CE-FDG PET/MR. Magnetic resonance-perfusion biomarkers, apparent diffusion coefficient (ADC), and standard uptake value (SUV) were compared with IHC markers and phenotypes, using a Student's t-test and one-way ANOVA.

RESULTS

ER/PR- tumours demonstrated higher Kepmean and SUVmax than ER or PR+ tumours. HER2- tumours displayed higher ADCmean, Kepmean, and SUVmax than HER2+tumours. Only ADCmean discriminated Ki67⩽14% tumours (lower ADCmean) from Ki67>14% tumours. PET/MR biomarkers correlated with IHC phenotype in 13 out of 21 patients (62%; P=0.001).

CONCLUSIONS

Positron emission tomography magnetic resonance might non-invasively help discriminate IDC phenotypes, helping to optimise individual therapy options.