Annotating CD38 Expression in Multiple Myeloma with [18F]F-Nb1053

Theranostics in Hematological Malignancies: Cutting-Edge Advances in Diagnosis and Targeted Therapy

Hematologic malignancies, including leukemia, lymphoma, and multiple myeloma, continue to challenge clinicians with complex treatment regimens that often involve significant side effects and limited success, especially in advanced stages. Recent advancements in nuclear medicine have introduced theranostic strategies that merge diagnostic imaging with targeted therapeutic approaches, offering the potential for more precise and personalized treatment. A key area of progress lies in the development of alpha-emitting radiopharmaceuticals, such as 225Ac, 211At, or 212Pb, which can deliver potent radiation directly to tumor cells, sparing healthy tissue and minimizing collateral damage. In parallel with these therapeutic advancements, molecular imaging using radiolabeled agents enables better disease monitoring, assessment of treatment efficacy, and personalized management of patients with hematologic malignancies. The integration of diagnostic imaging with radiotherapy allows for a more tailored approach, where treatment can be adjusted based on real-time information about tumor progression and response. This review examines the recent strides made in both the development of radiopharmaceuticals and their applications in molecular imaging, with a focus on the potential to improve precision, reduce toxicity, and optimize patient outcomes. The synergy between targeted therapy and molecular imaging represents a transformative shift in the management of hematologic malignancies. As these technologies evolve, they are poised to redefine treatment paradigms, offering new hope for patients and potentially improving survival rates with more effective and less toxic treatment options.

Dual-Functional Nanobody Optical Probes for In Vivo Fluorescence Imaging and Photodynamic Therapy

Nanobodies have gained significant attention as promising tools for cancer diagnostics and treatment due to their unique ability to precisely target specific cancer cells. However, a major challenge lies in the site-specific incorporation of multifunctional molecules into nanobodies, as it is essential to link these molecules in a manner that preserves the nanobody's function and stability while retaining the desired therapeutic or diagnostic properties. This study outlines the development of dual-functional nanobody optical probes for enhanced cancer diagnostics and therapeutic interventions. We designed a dual-functional clickable linker that enables site-specific functionalization of the nanobody, facilitating the simultaneous conjugation of two dyes: indocyanine green for imaging and chlorin e6 for photodynamic therapy. In vitro cellular assays confirmed the successful labeling of the dual-functional dyes, with the nanobody probe exhibiting high cellular binding specificity. In vivo imaging of mice bearing Hep3B tumors revealed clear visualization with a high signal-to-noise ratio. Furthermore, PEGylated probes significantly improved tumor retention, enhancing both imaging contrast and photodynamic therapy efficacy as compared to free chlorin e6. These dual-functional nanobody probes show great promise for the precise diagnosis and treatment of malignant tumors.

Immuno-PET/CT Imaging of Trop2 with [18F]AlF-RESCA-T4 Differentiates Lung Cancer from Inflammation

Immuno-PET/CT imaging, a branch of molecular imaging, can noninvasively and specifically visualize biomarker expression across the body. Trophoblast cell surface antigen 2 (Trop2) is a pan-cancer biomarker and plays a crucial role in tumorigenesis through multiple signaling pathways. The study aims to develop and translate novel Trop2 single-domain antibody (sdAb) tracers for clinical use. Methods: Two sdAbs (i.e., His-tagged T4 and His-tag-free RT4) are recombinantly expressed in Chinese hamster ovary cells. The purities and binding kinetics are determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis, high-performance liquid chromatography, and surface plasmon resonance assays. The AlF restrained complexing agent (RESCA) method is applied to develop 18F-labeled sdAb tracers ([18F]AlF-RESCA-T4 and [18F]AlF-RESCA-RT4), followed by thorough preclinical imaging and blocking studies on tumor-bearing mice and a pilot clinical trial evaluating the clinical imaging safety and feasibility of [18F]AlF-RESCA-T4 immuno-PET/CT. Results: [18F]AlF-RESCA-T4 and [18F]AlF-RESCA-RT4 possess high radiochemical purities. Preclinical imaging in the T3M-4 tumor model revealed prominent uptake (percentage injected dose/g) of [18F]AlF-RESCA-T4 (11.13 ± 1.53, n = 4) and [18F]AlF-RESCA-RT4 (8.83 ± 1.22, n = 4), which were significantly reduced by coinjection of unlabeled T4 and RT4 in blocking studies. The His-tag removal strategy further optimized the probe's in vivo pharmacokinetics and reduced renal radioactivity accumulation without significantly decreasing tumor uptake. In a pilot clinical trial, [18F]AlF-RESCA-T4 immuno-PET/CT showed promising potency in annotating Trop2 expression and differentiating tumors from inflammatory diseases such as tuberculosis. Conclusion: [18F]AlF-RESCA-T4 and [18F]AlF-RESCA-RT4 can specifically annotate Trop2 expression. Clinical [18F]AlF-RESCA-T4 immuno-PET/CT imaging can screen patients for Trop2-targeted therapies and differentiate lung inflammation from cancer.

CD38 as theranostic target in oncology

CD38 is a multifunctional transmembrane glycoprotein found in multiple tissues and overexpressed in many cancer cells, notably in hematological malignancies such as leukemia and multiple myeloma (MM). Therefore, targeting CD38 remains an attractive strategy for cancer treatment in hematological malignancies as well as in solid tumors. It plays a critical role in the progression of these diseases through its ADP-ribosyl cyclase and cADPR-hydrolase activities. Its importance has led to the development of various anti-CD38 monoclonal antibodies (mAbs), including daratumumab and isatuximab, approved for MM treatment. These mAbs exert their anti-tumor effects through Fc-dependent immune mechanisms and immunomodulation, enhancing T-cell and NK-cell-mediated responses. However, resistance mechanisms arise during the treatment with daratumumab, creating the necessity for new therapies. This review explains current knowledge about the role of CD38 as a target in oncology and aims to delineate the use of single domain antibodies (sdAbs) as innovative theranostic tools in nuclear medicine. For diagnostic purposes, PET radionuclides like 68 Ga, 64Cu, and SPECT radionuclides like 99mTc and 111In, are commonly used. Significant progress has been made in anti-CD38 radioligand therapy (RLT), with anti-CD38 antibodies providing insights into tumor biology and treatment efficacy. In terms of therapy, RLT is a promising approach that offers precise targeting of malignant cells while minimizing exposure to healthy tissue. This involves the use of radionuclides emitting α particles, like 225Ac, 212Pb or 211At, and β--particles like 90Y, 131I, or 177Lu, to exert cytotoxic effects. Derived from Camelidae heavy chain antibodies, sdAbs offer advantages over conventional mAbs such as small size, high stability, specificity, and ability to recognize hidden epitopes. CD38-specific sdAbs, such as sdAb 2F8, characterized by our laboratory, showing excellent tumor targeting and their engineered constructs, such as biparatopic antibodies and chimeric antibodies, represent a new generation of theranostic agents for diagnosis and treatment CD38-expressing malignancies.

Development of a Novel Peptide-Based PET Tracer [68Ga]Ga-DOTA-BP1 for BCMA Detection in Multiple Myeloma

B-cell maturation antigen (BCMA) has emerged as a promising tumor marker for the diagnosis and treatment of multiple myeloma. The noninvasive and rapid detection of BCMA expression in vivo provides significant value in screening and evaluating multiple myeloma patients receiving BCMA-targeted therapy. We identified the BCMA-targeting peptide BP1 from a one-bead-one-compound (OBOC) peptide library using a high-throughput microarray strategy. The BCMA-targeting specificity and affinity of BP1 were assessed by surface plasmon resonance imaging (SPRi), flow cytometry, and confocal imaging. BCMA-positive (H929) and BCMA-negative (K562) subcutaneous tumor models were established and labeled with 68Ga for BP1, followed by PET imaging and biodistribution studies. PET imaging demonstrated that 68Ga-labeled BP1 has significant specific uptake in multiple myeloma, enabling rapid identification of BCMA expression and precise delineation of the disease. Thus, BP1 represents an ideal candidate for multiple myeloma imaging.

The discovery and evaluation of [18F]BMS-986229, a novel macrocyclic peptide PET radioligand for the measurement of PD-L1 expression and in-vivo PD-L1 target engagement

PURPOSE

A same-day PET imaging agent capable of measuring PD-L1 status in tumors is an important tool for optimizing PD-1 and PD-L1 treatments. Herein we describe the discovery and evaluation of a novel, fluorine-18 labeled macrocyclic peptide-based PET ligand for imaging PD-L1.

METHODS

[18F]BMS-986229 was synthesized via copper mediated click-chemistry to yield a PD-L1 PET ligand with picomolar affinity and was tested as an in-vivo tool for assessing PD-L1 expression.

RESULTS

Autoradiography showed an 8:1 binding ratio in L2987 (PD-L1 (+)) vs. HT-29 (PD-L1 (-)) tumor tissues, with >90% specific binding. Specific radioligand binding (>90%) was observed in human non-small-cell lung cancer (NSCLC) and cynomolgus monkey spleen tissues. Images of PD-L1 (+) tissues in primates were characterized by high signal-to-noise, with low background signal in non-expressing tissues. PET imaging enabled clear visualization of PD-L1 expression in a murine model in vivo, with 5-fold higher uptake in L2987 (PD-L1 (+)) than in control HT-29 (PD-L1 (-)) tumors. Moreover, this imaging agent was used to measure target engagement of PD-L1 inhibitors (peptide or mAb), in PD-L1 (+) tumors as high as 97%.

CONCLUSION

A novel 18F-labeled macrocyclic peptide radioligand was developed for PET imaging of PD-L1 expressing tissues that demonstrated several advantages within a nonhuman primate model when compared directly to adnectin- or mAb-based ligands. Clinical studies are currently evaluating [18F]BMS-986229 to measure PD-L1 expression in tumors.

Site-Specific Modification of Single Domain Antibodies by Enzyme-Immobilized Magnetic Beads

Nanobodies as imaging agents and drug conjugates have shown great potential for cancer diagnostics and therapeutics. However, site-specific modification of a nanobody with microbial transglutaminase (mTGase) encounters problems in protein separation and purification. Here, we describe a facile yet reliable strategy of immobilizing mTGase onto magnetic beads for site-specific nanobody modification. The mTGase immobilized on magnetic beads (MB-mTGase) exhibits catalytic activity nearly equivalent to that of the free mTGase, with good reusability and universality. Magnetic separation simplifies the protein purification step and reduces the loss of nanobody bioconjugates more effectively than size exclusion chromatography. Using MB-mTGase, we demonstrate site-specific conjugation of nanobodies with fluorescent dyes and polyethylene glycol molecules, enabling targeted immunofluorescence imaging and improved circulation dynamics and tumor accumulation in vivo. The combined advantages of MB-mTGase method, including high conjugation efficiency, quick purification, less protein loss, and recycling use, are promising for site-specific nanobody functionalization and biomedical applications.

Development and Characterization of Nanobody-Derived CD47 Theranostic Pairs in Solid Tumors

Overexpression of CD47 is frequently observed in various types of human malignancies, inhibiting myeloid-mediated elimination of tumor cells and affecting the prognosis of cancer patients. By mapping biomarker expression, immuno-positron emission tomography has been increasingly used for patient screening and response monitoring. By immunization alpacas with recombinant human CD47, we prepared a CD47-targeting nanobody C2 and developed [⁶⁸Ga]Ga-NOTA-C2, followed by an exploration of the diagnostic value in CD47-expressing tumor models including gastric-cancer patient-derived xenograft models. By fusing C2 to an albumin binding domain (ABD), we synthesized ABDC2, which had increased in vivo half-life and improved targeting properties. We further labeled ABDC2 with ⁶⁸Ga/⁸⁹Zr/¹⁷⁷Lu to develop radionuclide theranostic pairs and evaluated the pharmacokinetics and theranostic efficacies of the agents in cell- and patient-derived models. Both C2 and ABDC2 specifically reacted with human CD47 with a high K _D value of 23.50 and 84.57 pM, respectively. [⁶⁸Ga]Ga-NOTA-C2 was developed with high radiochemical purity (99 >%, n = 4) and visualized CD47 expression in the tumors. In comparison to the rapid renal clearance and short half-life of [⁶⁸Ga]Ga-NOTA-C2, both [⁶⁸Ga]Ga-NOTA-ABDC2 and [⁸⁹Zr]Zr-DFO-ABDC2 showed prolonged circulation and increased tumor uptake, with the highest uptake of [⁸⁹Zr]Zr-DFO-ABDC2 occurring at 72 h post-injection. Moreover, [¹⁷⁷Lu]Lu-DOTA-ABDC2 radioimmunotherapy suppressed the tumor growth but was associated with toxicity, warranting further optimization of the treatment schedules. Taken together, we reported a series of nanobody-derived CD47-targeted agents, of which [⁶⁸Ga]Ga-NOTA-C2 and [⁸⁹Zr]Zr-DFO-ABDC2 are readily translatable. Optimization and translation of CD47-targeted theranostic pair may provide new prospects for CD47-targeted management of solid tumors.

Development and comparison of 68Ga/18F/64Cu-labeled nanobody tracers probing Claudin18.2

Claudin 18.2 (CLDN18.2) is an emerging target for the treatment of gastric cancers. We aim to develop tracers to image the expression of CLDN18.2. A humanized nanobody targeting CLDN18.2 (clone hu19V3) was produced and labeled with ⁶⁸Ga, ⁶⁴Cu, and ¹⁸F. The tracers were investigated in subcutaneous and metastatic models established using two different mouse types (nude and Balb/c mice) and two different cell lines (CHO-CLDN18.2 and CT26-CLDN18.2). Gastric cancer patient-derived xenograft (PDX) models were further established for validation experiments. Three novel CLDN18.2-targeted tracers (i.e., [⁶⁸Ga]Ga-NOTA-hu19V3, [⁶⁴Cu]Cu-NOTA-hu19V3, and [¹⁸F]F-hu19V3) were developed with good radiochemical yields and excellent radiochemical purities. [⁶⁸Ga]Ga-NOTA-hu19V3 immuno-positron emission tomography (immunoPET) rapidly delineated subcutaneous CHO-CLDN18.2 lesions and CT26-CLDN18.2 tumors, as well as showing excellent diagnostic value in PDX models naturally expressing CLDN18.2. While [⁶⁸Ga]Ga-NOTA-hu19V3 had high kidney accumulation, [⁶⁴Cu]Cu-NOTA-hu19V3 showed reduced kidney accumulation and improved image contrast at late time points. Moreover, [¹⁸F]F-hu19V3 was developed via click chemistry reaction under mild conditions and precisely disseminated CHO-CLDN18.2 lesions in the lungs. Furthermore, region of interest analysis, biodistribution study, and histopathological staining results correlated well with the in vivo imaging results. Taken together, immunoPET imaging with the three tracers can reliably visualize CLDN18.2 expression.

Recent developments on the application of molecular probes in multiple myeloma: Beyond [18F]FDG

Multiple myeloma (MM) is a neoplastic plasma cell proliferative disorder characterized by various osteolytic bone destruction as a radiological morphological marker. Functional imaging, particularly nuclear medicine imaging, is a promising method to visualize disease processes before the appearance of structural changes by targeting specific biomarkers related to metabolism ability, tumor microenvironment as well as neoplastic receptors. In addition, by targeting particular antigens with therapeutic antibodies, immuno-PET imaging can support the development of personalized theranostics. At present, various imaging agents have been prepared and evaluated in MM at preclinical and clinical levels. A summary overview of molecular functional imaging in MM is provided, and commonly used radiotracers are characterized.

99mTc-CD3813: A Nanobody-Based Single Photon Emission Computed Tomography Radiotracer with Clinical Potential for Myeloma Imaging and Evaluation of CD38 Expression

Daratumumab (DARA) is an anti-CD38 monoclonal antibody for the treatment of multiple myeloma (MM). The tumor CD38 expression level is one of the important factors in determining the efficacy of DARA treatment. Therefore, there is an urgent clinical need for a noninvasive tool to evaluate the CD38 levels in cancer patients before, during, and after DARA treatment. In this study, we prepared a new molecular imaging probe ^99mTc-CD3813, the ^99mTc-labeled nanobody CD3813, for noninvasive imaging of CD38 expression by single photon emission computed tomography (SPECT). We evaluated ^99mTc-CD3813 for its CD38 affinity and specificity and its capacity to image the CD38 expression in the MM and lymphoma xenografts models. ^99mTc-CD3813 SPECT/CT is able to visualize subcutaneous/orthotopic myeloma lesions in animal models and has advantages over ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography. Excess DARA has less impact on its tumor uptake (3.14 ± 0.83 vs 2.29 ± 0.91 %ID/g, n.s.), strongly suggesting that there is no competition between ^99mTc-CD3813 and DARA in binding to CD38. ^99mTc-CD3813 SPECT/CT revealed significant reduction in CD38 expression in the Ramos-bearing mice under DARA treatment, as evidenced by their reduced tumor uptake (3.04 ± 0.70 vs 1.07 ± 0.28 %ID/cc, P < 0.001). ^99mTc-CD3813 SPECT/CT was also able to detect the increased tumor uptake (0.79 ± 0.29 vs 2.12 ± 0.12 %ID/cc, P < 0.001) due to the upregulation of CD38 levels caused by all-trans retinoic acid infection. ^99mTc-CD3813 is a promising SPECT radiotracer for imaging the CD38-positive tumors and has clinical potential as a molecular imaging tool for evaluation of the CD38 expression level in patients before, during, and after DARA treatment.

GPC3-targeted immunoPET imaging of hepatocellular carcinomas

PURPOSE

Early detection of hepatocellular carcinoma (HCC) remains a clinical challenge. Glypican 3 (GPC3) is a proteoglycan highly specific for HCC and is a potential diagnostic and therapeutic target for HCC. This work aims to develop GPC3-targeted immuno-positron emission tomography (immunoPET) imaging strategies and to assess the diagnostic values in preclinical HCC models.

METHODS

Flow cytometry was used to screen GPC3-positive HCC cell lines. The expression of GPC3 in HCCs was detected by immunohistochemistry on tissue microarray. A novel GPC3-specific single domain antibody (sdAb) was produced and labeled with gallium-68 (⁶⁸Ga, T_1/2 = 1.1 h) and fluorine-18 (¹⁸F, T_1/2 = 1.8 h) to develop radiotracers with different half-lives. The diagnostic efficacies of the developed probes (i.e., [⁶⁸Ga]Ga-NOTA-G2, [¹⁸F]F-G2, and [⁶⁸Ga]Ga-NOTA-ABDG2) were interrogated in preclinical HCC models bearing varying GPC3 levels.

RESULTS

GPC3 was strongly expressed on HCC cell lines and patients with poorly differentiated HCC. [⁶⁸Ga]Ga-NOTA-G2 immunoPET imaging specifically delineated the subcutaneous HCC lesions, outperforming the traditional ¹⁸F-fluorodeoxyglucose PET and the nonspecific [⁶⁸Ga]Ga-NOTA-NbGFP immunoPET. ImmunoPET imaging with [¹⁸F]F-G2 also efficiently diagnosed the tumors with clarity. Moreover, the fusion of G2 to an albumin-binding domain (ABD) significantly increased the tumor uptake and decreased kidney accumulation of the radiotracer when compared to [⁶⁸Ga]Ga-NOTA-G2.

CONCLUSIONS

In the work, we successfully developed sdAb-derived GPC3-targeted immunoPET imaging strategies and characterized the superior diagnostic accuracies in preclinical HCC models. Furthermore, we synthesized a fusion protein ABDG2 with improved targeting and pharmacokinetic properties, serving as a promising candidate for developing radioimmunotherapy agents.