Design and evaluation of radiolabeled tracers for tumor imaging

Application of micro/nanorobot in medicine

The development of micro/nanorobots and their application in medical treatment holds the promise of revolutionizing disease diagnosis and treatment. In comparison to conventional diagnostic and treatment methods, micro/nanorobots exhibit immense potential due to their small size and the ability to penetrate deep tissues. However, the transition of this technology from the laboratory to clinical applications presents significant challenges. This paper provides a comprehensive review of the research progress in micro/nanorobotics, encompassing biosensors, diagnostics, targeted drug delivery, and minimally invasive surgery. It also addresses the key issues and challenges facing this technology. The fusion of micro/nanorobots with medical treatments is poised to have a profound impact on the future of medicine.

The preclinical study of 177Lu-DOTA-LTVSPWY as a potential therapeutic agent against HER2 overexpressed cancer

BACKGROUND

Peptide receptor radionuclide therapy (PRRT) has evolved in cancer therapy and diagnosis. LTVSPWY, as a peptide, can target HER2 receptor; on the other hand, ¹⁷⁷Lu emits β^- which is helpful for cancer therapy. The radiolabeling of LTVSPWY with ¹⁷⁷Lu results in a therapeutic agent (¹⁷⁷Lu-DOTA-LTVSPWY) capable of cancer treatment.

METHODS

¹⁷⁷Lu-DOTA-LTVSPWY was prepared with high radiochemical purity (RCP). The stability was investigated in saline and human serum. The radiotracer affinity toward the SKOV-3 cell line with overexpression of the HER2 receptor was evaluated. Then the impact of the radiotracer on the colony formation of the SKOV-3 cell line was investigated with colony assay. Moreover, the biodistribution of this radiotracer in SKOV-3 xenograft tumor-bearing nude mice were also studied to determine the radiotracer accumulation in the tumor site. The mice were treated with ¹⁷⁷Lu-DOTA-LTVSPWY and subjected to histopathological evaluation.

RESULTS

The RCP of ¹⁷⁷Lu-DOTA-LTVSPWY after radiolabeling and stability tests was more than 97.7%. The radiotracer displayed high affinity toward the SKOV-3 cell line (K_D = 6.6 ± 3.2 nM). Treatment of the SKOV-3 cell line with the radiotracer reduces the SKOV-3 colony survival to less than 3% for 5 MBq of the radiotracer. Tumor-to-muscle (T/M) ratio is the highest at 48 h and 1 h post-injection (2.3 and 4.75, respectively). The histopathological study also confirms the cellular damage to the tumor tissue.

CONCLUSIONS

¹⁷⁷Lu-DOTA-LTVSPWY can recognize HER2 receptors in vivo and in vitro; hence, it can serve as a therapeutic agent.

Novel EBV LMP1 C-terminal domain binding affibody molecules as potential agents for in vivo molecular imaging diagnosis of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is consistently associated with Epstein-Barr virus (EBV) latent infection and is common in Southern China and Southeast Asia. The viral latent membrane proteins LMP1 and LMP2 are persistently expressed in NPC tissues; the cytoplasmic domain of LMP1 (LMP1 C-terminal) and LMP2A (LMP2A N-terminal) proteins is essential for maintenance of latency and can alter host cell signaling to facilitate tumor growth and progression. Thus, targeting LMP1 or LMP2 oncoprotein has been an increasing interest for diagnosis and targeted therapy of NPC. Affibody molecules, a new class of small-affinity engineered scaffold proteins, have demonstrated high potential for therapeutics, diagnostics, and biotechnological applications. More recently, radiolabelled HER2-specific affibody molecules have demonstrated to be useful in imaging of HER2 expressing tumor. In this study, we report three novel EBV LMP1 C-terminal (EBV LMP1-C) domain affibody molecules (Z_LMP1-C15, Z_LMP1-C114, and Z_LMP1-C277) were selected by biopanning from a random-peptide displayed phage library and used for molecular imaging in tumor-bearing nude mice. Surface plasmon resonance (SPR), indirect immunofluorescence, and immunohistochemistry (IHC) clearly showed that all three selected affibody molecules have high affinity and specificity in binding to EBV LMP1 protein. Moreover, in vivo tumor imaging revealed that Dylight-755-labeled affibody molecules accumulated rapidly in tumor site after injection (1 h) and then were continuously maintained for 24 h in EBV-positive NPC xenograft mice model. In conclusion, our findings highlight the potential use of Z_LMP1-C affibody molecules as tumor-specific molecular imaging agents of EBV-associated NPC.Key points• We screened three novel affibody molecules (Z_LMP1-C15, Z_LMP1-C114, and Z_LMP1-C277) targeting EBV LMP1-C terminal domain• Z_LMP1-C recognize the recombinant and native LMP1-C with high affinity and specificity• Z_LMP1-C can be used for molecular imaging.

Medical Imaging of Microrobots: Toward In Vivo Applications

Medical microrobots (MRs) have been demonstrated for a variety of non-invasive biomedical applications, such as tissue engineering, drug delivery, and assisted fertilization, among others. However, most of these demonstrations have been carried out in in vitro settings and under optical microscopy, being significantly different from the clinical practice. Thus, medical imaging techniques are required for localizing and tracking such tiny therapeutic machines when used in medical-relevant applications. This review aims at analyzing the state of the art of microrobots imaging by critically discussing the potentialities and limitations of the techniques employed in this field. Moreover, the physics and the working principle behind each analyzed imaging strategy, the spatiotemporal resolution, and the penetration depth are thoroughly discussed. The paper deals with the suitability of each imaging technique for tracking single or swarms of MRs and discusses the scenarios where contrast or imaging agent's inclusion is required, either to absorb, emit, or reflect a determined physical signal detected by an external system. Finally, the review highlights the existing challenges and perspective solutions which could be promising for future in vivo applications.

Imaging of Tumor Spheroids, Dual-Isotope SPECT, and Autoradiographic Analysis to Assess the Tumor Uptake and Distribution of Different Nanobodies

PURPOSE

Recent studies have shown rapid accumulation of nanobodies (NBs) in tumors and fast clearance of the unbound fraction, making NBs exceptional tracers for cancer imaging. In this study, we investigate the combination of in vitro imaging of tumor spheroids, in vivo dual-isotope single-photon emission computed tomography (SPECT), and ex vivo autoradiographic analysis of tumors to efficiently, and with few mice, assess the tumor uptake and distribution of different NBs.

PROCEDURES

The irrelevant NB R2 (16 kDa) and the EGFR-targeted NBs 7D12 (16 kDa) and 7D12-R2 (32 kDa) were investigated. Confocal microscopy was used to study the penetration of the NBs into A431 tumor spheroids over time, using the anti-EGFR monoclonal antibody (mAb) cetuximab (150 kDa) as a reference. Dual-isotope [¹¹¹In]DOTA-NB/[¹⁷⁷Lu]DOTA-NB SPECT was used for longitudinal imaging of multiple tracers in the same animal bearing A431 tumor xenografts. Tumor sections were analyzed using autoradiography.

RESULTS

No binding of the irrelevant NB was observed in spheroids, whereas for the specific tracers an increase in the spheroid's covered area was observed over time. The NB 7D12 saturated the spheroid earlier than the larger, 7D12-R2. Even slower penetration was observed for the large mAb. In vivo, the tumor uptake of 7D12 was 19-fold higher than R2 after co-injection in the same animal, and 2.5-fold higher than 7D12-R2 when co-injected. 7D12-R2 was mainly localized at the rim of tumors, while 7D12 was found to be more evenly distributed.

CONCLUSIONS

This study demonstrates that the combination of imaging of tumor spheroids, dual-isotope SPECT, and autoradiography of tumors is effective in comparing tumor uptake and distribution of different NBs. Results were in agreement with published data, highlighting the value of monomeric NBs for tumor imaging, and re-enforcing the value of these techniques to accurately assess the most optimal format for tumor imaging. This combination of techniques requires a lower number of animals to obtain significant data and can accelerate the design of novel tracers.

Investigation of biodistribution and tissue penetration of PEGylated gold nanostars and their application for photothermal cancer treatment in tumor-bearing mice

PEGylated gold nanostars (pAuNSs) and their radioactive surrogate (¹¹¹In–DTPA–pAuNS), with unique physiochemical properties, are thought to be a promising agent for image-guided photothermal therapy (PTT).

Bispecific affibody molecule targeting HPV16 and HPV18E7 oncoproteins for enhanced molecular imaging of cervical cancer

High-risk human papillomavirus (HPV16 and HPV18) are now widely recognized as responsible for cervical cancer, which remains to be the most common gynecologic malignancy in women worldwide. It is well known that viral oncoproteins E6/E7 play key roles in HPV-associated cervical carcinogenesis. Thus, in vivo detection of the two oncoproteins may provide important diagnostic information influencing patient management. More recently, affibody molecules have been demonstrated to be a promising candidate for development as molecular imaging probes. Based on the two monomeric affibody molecules (Z_HPV16E7 and Z_HPV18E7) generated in our laboratory, here, we used a peptide linker (Gly₄Ser)₃ to link Z_HPV16E7 and Z_HPV18E7 to develop a novel heterodimeric affibody Z_HPV16E7-(Gly₄Ser)₃-Z_HPV18E7. Both biosensor and immunofluorescence assays have proved that the heterodimeric affibody molecule targeted simultaneously HPV16 and HPV18E7 proteins by binding to the viral oncoproteins. In vivo tumor-imaging experiments using the Dylight755-labeled heterodimeric affibody revealed that strongly high-contrast tumor retention of the heterodimers occurred in both HPV16- and HPV18-derived tumors of nude mice 0.5 h post-injection. The accumulation of Dylight755-labeled heterodimers in tumors was achieved over 48 h. Therefore, we believe that this novel heterodimeric affibody molecule has great potential utility in molecular imaging in vivo and diagnosis of HPV-associated cervical cancers.

Early detection of pancreatic cancer in mouse models using a novel antibody, TAB004

Pancreatic ductal adenocarcinoma (PDA) is the fourth-leading cause of cancer death in the United States with a 5-year overall survival rate of 8% for all stages combined. But this decreases to 3% for the majority of patients that present with stage IV PDA at time of diagnosis. The lack of distinct early symptoms for PDA is one of the primary reasons for the late diagnosis. Common symptoms like weight loss, abdominal and back pains, and jaundice are often mistaken for symptoms of other issues and do not appear until the cancer has progressed to a late stage. Thus the development of novel imaging platforms for PDA is crucial for the early detection of the disease. MUC1 is a tumor-associated antigen (tMUC1) expressed on 80% of PDA. The goal of this study was to determine the targeting and detection capabilities of a tMUC1 specific antibody, TAB004. TAB004 antibody conjugated to a near infrared fluorescent probe was injected intraperitoneally into immune competent orthotopic and spontaneous models of PDA. Results show that fluorophore conjugated TAB004 specifically targets a) 1 week old small tumor in the pancreas in an orthotopic PDA model and b) very early pre-neoplastic lesions (PanIN lesions) that develop in the spontaneous PDA model before progression to adenocarcinoma. Thus, TAB004 is a promising antibody to deliver imaging agents directly to the pancreatic tumor microenvironment, significantly affecting early detection of PDA.

Affibody Molecules in Biotechnological and Medical Applications

Affibody molecules are small (6.5-kDa) affinity proteins based on a three-helix bundle domain framework. Since their introduction 20 years ago as an alternative to antibodies for biotechnological applications, the first therapeutic affibody molecules have now entered clinical development and more than 400 studies have been published in which affibody molecules have been developed and used in a variety of contexts. In this review, we focus primarily on efforts over the past 5 years to explore the potential of affibody molecules for medical applications in oncology, neurodegenerative, and inflammation disorders, including molecular imaging, receptor signal blocking, and delivery of toxic payloads. In addition, we describe recent examples of biotechnological applications, in which affibody molecules have been exploited as modular affinity fusion partners.

Radiolabeled 111In-FGF-2 Is Suitable for In Vitro/Ex Vivo Evaluations and In Vivo Imaging

Fibroblast growth factor-2 (FGF-2) is a potent modulator of cell growth and regulation, with improper FGF-2 signaling being involved in impaired responses to injury or even cancer. Therefore, the exploitation of FGF-2 as a therapeutic drives the prerequisite for effective insight into drug disposition kinetics. In this article, we present an ¹¹¹In-radiolabeled FGF-2 derivative for noninvasive imaging in small animals deploying single photon emission tomography (SPECT). ¹¹¹In-FGF-2 is equally well suitable for in vitro and ex vivo investigations as ¹²⁵I-FGF-2. Furthermore, ¹¹¹In-FGF-2 permits the performance of in vivo imaging, for example for the analysis of FGF-2 containing pharmaceutical formulations in developmental or preclinical stages. ¹¹¹In-FGF-2 had affinity for the low-molecular-weight heparin enoxaparin identical to that of unlabeled FGF-2 (K_d: 0.6 ± 0.07 μM and 0.33 ± 0.03 μM, respectively) as assessed by isothermal titration calorimetry. The binding of ¹¹¹In-FGF-2 to heparan sulfate proteoglycans (HPSGs) and the biological activity were comparable to those of unlabeled FGF-2, with EC₅₀ values of 12 ± 2 pM and 25 ± 6 pM, respectively. In vivo biodistribution in healthy nude mice indicated a predominant accumulation of ¹¹¹In-FGF-2 in filtering organs and minor uptake in the retina and the salivary and pituitary glands, which was confirmed by SPECT imaging. Therefore, ¹¹¹In-FGF-2 is a valid tracer for future noninvasive animal imaging of FGF-2 in pharmaceutical development.

ADAPT, a Novel Scaffold Protein-Based Probe for Radionuclide Imaging of Molecular Targets That Are Expressed in Disseminated Cancers

Small engineered scaffold proteins have attracted attention as probes for radionuclide-based molecular imaging. One class of these imaging probes, termed ABD-Derived Affinity Proteins (ADAPT), has been created using the albumin-binding domain (ABD) of streptococcal protein G as a stable protein scaffold. In this study, we report the development of a clinical lead probe termed ADAPT6 that binds HER2, an oncoprotein overexpressed in many breast cancers that serves as a theranostic biomarker for several approved targeting therapies. Surface-exposed amino acids of ABD were randomized to create a combinatorial library enabling selection of high-affinity binders to various proteins. Furthermore, ABD was engineered to enable rapid purification, to eradicate its binding to albumin, and to enable rapid blood clearance. Incorporation of a unique cysteine allowed site-specific conjugation to a maleimido derivative of a DOTA chelator, enabling radionuclide labeling, ¹¹¹In for SPECT imaging and ⁶⁸Ga for PET imaging. Pharmacologic studies in mice demonstrated that the fully engineered molecule (111)In/⁶⁸Ga-DOTA-(HE)3-ADAPT6 was specifically bound and taken up by HER2-expressing tumors, with a high tumor-to-normal tissue ratio in xenograft models of human cancer. Unbound tracer underwent rapid renal clearance followed by high renal reabsorption. HER2-expressing xenografts were visualized by gamma-camera or PET at 1 hour after infusion. PET experiments demonstrated feasibility for discrimination of xenografts with high or low HER2 expression. Our results offer a preclinical proof of concept for the use of ADAPT probes for noninvasive in vivo imaging.