Theranostics Targeting Fibroblast Activation Protein in the Tumor Stroma: 64Cu- and 225Ac-Labeled FAPI-04 in Pancreatic Cancer Xenograft Mouse Models

Evaluating [225Ac]Ac-FAPI-46 for the treatment of soft-tissue sarcoma in mice

PURPOSE

Fibroblast Activation Protein (FAP) is an emerging theranostic target that is highly expressed on cancer-associated fibroblasts and on certain tumor cells including sarcoma. We investigated the anti-tumor efficacy of [225Ac]Ac-FAPI-46 as monotherapy or in combination with immune checkpoint blockade (ICB) in immunocompetent murine models of sarcoma sensitive or resistant to ICB.

METHODS

[68Ga]Ga- and [225Ac]Ac-FAPI-46 were tested in subcutaneous FAP+ FSA fibrosarcoma bearing C3H/Sed/Kam mice. The efficacy of up to three cycles of 60 kBq [225Ac]Ac-FAPI-46 was evaluated as monotherapy and in combination with an anti-PD-1 antibody. Efficacy of [225Ac]Ac-FAPI-46 and/or ICB was further compared in FAP-overexpressing FSA (FSA-F) tumors that were sensitive to ICB or rendered ICB-resistant by tumor-induction in the presence of Abatacept.

RESULTS

[225Ac]Ac-FAPI-46 was well tolerated up to 3 × 60 kBq but had minimal effect on FSA tumor growth. The combination of three cycles [225Ac]Ac-FAPI-46 and ICB resulted in growth delay in 55% of mice (6/11) and partial tumor regression in 18% (2/11) of mice. In FSA-F tumors with FAP overexpression, both [225Ac]Ac-FAPI-46 and ICB were effective without additional benefits from the combination. In locally immunosuppressed and ICB resistant FAP-F tumors, however, [225Ac]Ac-FAPI-46 restored responsiveness to ICB, resulting in significant tumor regression and tumor-free survival of 56% of mice in the combination group up to 60 days post treatment.

CONCLUSION

[225Ac]Ac-FAPI-46 efficacy is correlated with tumoral FAP expression levels and can restore responsiveness to PD-1 ICB. These data illustrate that careful patient selection based on target expression and rationally designed combination therapies are critically important to maximize the therapeutic impact of FAP-targeting radioligands.

Development of a Supermolecular Radionuclide-Drug Conjugate System for Integrated Radiotheranostics for Non-small Cell Lung Cancer

Radionuclide-drug conjugates (RDCs) designed from small molecule or nanoplatform shows complementary characteristics. We constructed a new RDC system with integrated merits of small molecule and nanoplatform-based RDCs. Erlotinib was labeled with 131I to construct the bulk of RDC (131I-ER). Floxuridine was mixed with 131I-ER to develop a hydrogen bond-driving supermolecular RDC system (131I-ER-Fu NPs). The carrier-free 131I-ER-Fu NPs supermolecule not only demonstrated integrated merits of small molecule and nanoplatform-based RDC, including clear structure definition, stable quality control, prolonged circulation lifetime, enhanced tumor specificity and retention, and rapidly nontarget clearance, but also exhibited low biological toxicity and stronger antitumor effects. In vivo imaging also revealed its application for tumor localization of nonsmall cell lung cancer (NSCLC) and screening of patients suitable for epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) therapy. We considered that 131I-ER-Fu NPs showed potentials as an integrated platform for the radiotheranostics of NSCLC.

[68Ga]Ga-labeled FAPI Conjugated with Gly-Pro Sequence for PET Imaging of Malignant Tumors

PURPOSE

To improve tumor uptake and prolong tumor retention, a novel fibroblast activation protein (FAP) ligand based on a quinoline-based FAP inhibitor (FAPI) conjugated with the Gly-Pro sequence and 1,4,7,10-tetraazacyclododecane-N,N',N″,N‴-tetraacetic acid (DOTA) was radiolabeled with [68Ga]GaCl3 ([68Ga]Ga-DOTA-GPFAPI-04). Due to the tumor heterogeneity, this study aimed to further validate the preclinical value of [68Ga]Ga-DOTA-GPFAPI-04 PET imaging in tumor mice models with different FAP expression levels.

METHODS

[68Ga]Ga-DOTA-GPFAPI-04 was synthesized and its partition coefficient was measured. The stability of [68Ga]Ga-DOTA-GPFAPI-04 was tested in phosphate-buffered saline (PBS, pH 7.4) and fetal bovine serum (FBS). Small animal PET and semi-quantitative studies were conducted in Panc-1 and A549 xenograft tumor mice models compared with [68Ga]Ga-DOTA-FAPI-04. Immunofluorescent and immunohistochemical staining and western blot assay were performed to confirm FAP expression in xenograft tumors.

RESULTS

[68Ga]Ga-DOTA-GPFAPI-04 exhibited a radiochemical purity of > 99% and high stability in PBS and FBS. [68Ga]Ga-DOTA-GPFAPI-04 had higher hydrophilic property than [68Ga]Ga-DOTA-FAPI-04 (-4.09 ± 0.05 vs -3.45 ± 0.05). Small animal PET and semi-quantitative analysis revealed Panc-1 xenograft tumor displayed higher tumor uptake of [68Ga]Ga-DOTA-GPFAPI-04 and tumor-to-background ratios compared to A549 xenograft tumor, consistent with the results of immunofluorescence, immunohistochemistry, and western blot. Moreover, [68Ga]Ga-DOTA-GPFAPI-04 demonstrated higher tumor accumulation and longer tumor retention than [68Ga]Ga-DOTA-FAPI-04 in both Panc-1 and A549 xenograft tumors. Furthermore, the FAP-binding specificity of [68Ga]Ga-DOTA-GPFAPI-04 was confirmed in vivo by co-injection of unlabeled GPFAPI-04.

CONCLUSION

[68Ga]Ga-DOTA-GPFAPI-04 showed more favorable in vivo tumor imaging and longer tumor retention compared to [68Ga]Ga-DOTA-FAPI-04, which has high potential to be a promising PET probe for detecting FAP-positive tumors.

Long-Axial Field-of-View PET Imaging in Patients with Lymphoma: Challenges and Opportunities

[18F]fluoro-2-deoxy-d-glucose PET/computed tomography has been implemented in the management of patients with lymphoma, offering real-time metabolic information on lymphoma with the promise of more accurate staging, treatment response assessment, prognostication, and early detection of disease recurrence. The clinical management of lymphoproliferative disease has recently, rapidly evolved from initial chemotherapeutic to the use of immunotherapy, targeted agents, and to the use of chimeric antigen receptor T-cell therapies. The implementation of these new systems and imaging protocols together with new tracer development creates, in the field of lymphoproliferative disease, both opportunities and challenges that will be detailed in this comprehensive literature review.

Clinical translation of a novel FAPI dimer [68Ga]Ga-LNC1013

Fibroblast activation protein (FAP) has emerged as a highly promising target for cancer diagnostic imaging and targeted radionuclide therapy. To exploit the therapeutic potential of suitably radiolabeled FAP inhibitors (FAPIs), this study presents the design and synthesis of a series of FAPI dimers to increase tumor uptake and retention. Preclinical evaluation and a pilot clinical PET imaging study were conducted to screen the lead compound with the potential for radionuclide therapy.

METHODS

Three new FAPI dimers were synthesized by linking two quinoline-based FAPIs with different spacers. The in vitro binding affinity and preclinical small animal PET imaging of the compounds were compared with their monomeric counterparts, FAPI-04 and FAPI-46. The lead compound, [68Ga]Ga -LNC1013, was then evaluated in a pilot clinical PET imaging study involving seven patients with gastrointestinal cancer.

RESULTS

The three newly synthesized FAPI homodimers had high binding affinity and specificity in vitro and in vivo. Small animal PET imaging and biodistribution studies showed that [68Ga]Ga-LNC1013 had persistent tumor retention for at least 4 h, also higher uptake than the other two dimers and the monomer counterparts, making it the lead compound to enter clinical investigation. In the pilot clinical PET imaging study, seven patients were enrolled. The effective dose of [68Ga]Ga-LNC1013 was 8.24E-03 mSv/MBq. The human biodistribution of [68Ga]Ga-LNC1013 demonstrated prominent tumor uptake and good tumor-to-background contrast. [68Ga]Ga-LNC1013 PET imaging showed potential in capturing primary and metastatic lesions and outperforming 18F-FDG PET in detecting pancreatic and esophageal cancers. The SUVmax for lesions with [68Ga]Ga-FAPI-46 decreased over time, whereas [68Ga]Ga-LNC1013 exhibited persistently high tumor uptake from 1 to 4 h post-injection.

CONCLUSION

Dimerization is an effective strategy to produce FAPI derivatives with favorable tumor uptake, long tumor retention, and imaging contrast over its monomeric counterpart. We demonstrated that [68Ga]Ga-LNC1013, the lead compound without any piperazine moiety, had superior diagnostic potential over [68Ga]Ga-FAPI-46 and 18F-FDG, suggesting the future potential of LNC1013 for radioligand therapy of FAP-positive cancers.

Design of a Fibroblast Activation Protein-Targeted Radiopharmaceutical Therapy with High Tumor-to-Healthy-Tissue Ratios

Because of upregulated expression on cancer-associated fibroblasts, fibroblast activation protein (FAP) has emerged as an attractive biomarker for the imaging and therapy of solid tumors. Although many FAP ligands have already been developed for radiopharmaceutical therapies (RPTs), most suffer from inadequate tumor uptake, insufficient tumor residence times, or off-target accumulation in healthy tissues, suggesting a need for further improvements. Methods: A new FAP-targeted RPT with a novel ligand (FAP8-PEG3-IP-DOTA) was designed by combining the desirable features of several previous ligand-targeted RPTs. Uptake and retention of [111In]In or [177Lu]Lu-FAP8-PEG3-IP-DOTA were assessed in KB, HT29, MDA-MB-231, and 4T1 murine tumor models by radioimaging or ex vivo biodistribution analyses. Radiotherapeutic potencies and gross toxicities were also investigated by monitoring tumor growth, body weight, and tissue damage in tumor-bearing mice. Results: FAP8-PEG3-IP-DOTA exhibited high affinity (half-maximal inhibitory concentration, 1.6 nM) and good selectivity for FAP relative to its closest homologs, prolyl oligopeptidase (half-maximal inhibitory concentration, ∼14.0 nM) and dipeptidyl peptidase-IV (half-maximal inhibitory concentration, ∼860 nM). SPECT/CT scans exhibited high retention in 2 different solid tumor models and minimal uptake in healthy tissues. Quantitative biodistribution analyses revealed tumor-to-healthy-tissue ratios of more than 5 times for all major organs, and live animal studies demonstrated 65%-93% suppression of tumor growth in all 4 models tested, with minimal or no evidence of systemic toxicity. Conclusion: We conclude that [177Lu]Lu-FAP8-PEG3-IP-DOTA constitutes a promising and safe RPT candidate for FAPα-targeted radionuclide therapy of solid tumors.

68Ga-Fibroblast Activation Protein Inhibitor PET/CT Improves Detection of Intermediate and Low-Grade Sarcomas and Identifies Candidates for Radiopharmaceutical Therapy

Fibroblast activation protein-α (FAP) is often highly expressed by sarcoma cells and by sarcoma-associated fibroblasts in the tumor microenvironment. This makes it a promising target for imaging and therapy. The level of FAP expression and the diagnostic value of 68Ga-FAP inhibitor (FAPI) PET for sarcoma subtypes are unknown. We assessed the diagnostic performance and accuracy of 68Ga-FAPI PET in various bone and soft-tissue sarcomas. Potential eligibility for FAP-targeted radiopharmaceutical therapy (FAP-RPT) was evaluated. Methods: This prospective observational trial enrolled 200 patients with bone and soft-tissue sarcoma who underwent 68Ga-FAPI PET/CT and 18F-FDG PET/CT (186/200, or 93%) for staging or restaging. The number of lesions detected and the uptake (SUVmax) of the primary tumor, lymph nodes, and visceral and bone metastases were analyzed. The Wilcoxon test was used for semiquantitative assessment. The association of 68Ga-FAPI uptake intensity, histopathologic grade, and FAP expression in sarcoma biopsy samples was analyzed using Spearman r correlation. The impact of 68Ga-FAPI PET on clinical management was investigated using questionnaires before and after PET/CT. Eligibility for FAP-RPT was defined by an SUVmax greater than 10 for all tumor regions. Results: 68Ga-FAPI uptake was heterogeneous among sarcoma subtypes. The 3 sarcoma entities with the highest uptake (mean SUVmax ± SD) were solitary fibrous tumor (24.7 ± 11.9), undifferentiated pleomorphic sarcoma (18.8 ± 13.1), and leiomyosarcoma (15.2 ± 10.2). Uptake of 68Ga-FAPI versus 18F-FDG was significantly higher in low-grade sarcomas (10.4 ± 8.5 vs. 7.0 ± 4.5, P = 0.01) and in potentially malignant intermediate or unpredictable sarcomas without a World Health Organization grade (not applicable [NA]; 22.3 ± 12.5 vs. 8.5 ± 10.0, P = 0.0004), including solitary fibrous tumor. The accuracy, as well as the detection rates, of 68Ga-FAPI was higher than that of 18F-FDG in low-grade sarcomas (accuracy, 92.2 vs. 80.0) and NA sarcomas (accuracy, 96.9 vs. 81.9). 68Ga-FAPI uptake and the histopathologic FAP expression score (n = 89) were moderately correlated (Spearman r = 0.43, P < 0.0002). Of 138 patients, 62 (45%) with metastatic sarcoma were eligible for FAP-RPT. Conclusion: In patients with low-grade and NA sarcomas, 68Ga-FAPI PET demonstrates uptake, detection rates, and accuracy superior to those of 18F-FDG PET. 68Ga-FAPI PET criteria identified eligibility for FAP-RPT in about half of sarcoma patients.

Covalent targeted radioligands potentiate radionuclide therapy

Targeted radionuclide therapy, in which radiopharmaceuticals deliver potent radionuclides to tumours for localized irradiation, has addressed unmet clinical needs and improved outcomes for patients with cancer1-4. A therapeutic radiopharmaceutical must achieve both sustainable tumour targeting and fast clearance from healthy tissue, which remains a major challenge5,6. A targeted ligation strategy that selectively fixes the radiopharmaceutical to the target protein in the tumour would be an ideal solution. Here we installed a sulfur (VI) fluoride exchange (SuFEx) chemistry-based linker on radiopharmaceuticals to prevent excessively fast tumour clearance. When the engineered radiopharmaceutical binds to the tumour-specific protein, the system undergoes a binding-to-ligation transition and readily conjugates to the tyrosine residues through the 'click' SuFEx reaction. The application of this strategy to a fibroblast activation protein (FAP) inhibitor (FAPI) triggered more than 80% covalent binding to the protein and almost no dissociation for six days. In mice, SuFEx-engineered FAPI showed 257% greater tumour uptake than did the original FAPI, and increased tumour retention by 13-fold. The uptake in healthy tissues was rapidly cleared. In a pilot imaging study, this strategy identified more tumour lesions in patients with cancer than did other methods. SuFEx-engineered FAPI also successfully achieved targeted β- and α-radionuclide therapy, causing nearly complete tumour regression in mice. Another SuFEx-engineered radioligand that targets prostate-specific membrane antigen (PSMA) also showed enhanced therapeutic efficacy. Considering the broad scope of proteins that can potentially be ligated to SuFEx warheads, it might be possible to adapt this strategy to other cancer targets.

Magnetic-optical dual-modality imaging monitoring chemotherapy efficacy of pancreatic ductal adenocarcinoma with a low-dose fibronectin-targeting Gd-based contrast agent

PURPOSE

Pancreatic ductal adenocarcinoma (PDAC) is a lethal hypovascular tumor surrounded by dense fibrosis. Albumin-bound paclitaxel and gemcitabine (AG) chemotherapy is the mainstay of PDAC treatment through depleting peritumoral fibrosis and killing tumor cells; however, it remains challenging due to the lack of a noninvasive imaging method evaluating fibrotic changes during AG chemotherapy. In this study, we developed a dual-modality imaging platform that enables noninvasive, dynamic, and quantitative assessment of chemotherapy-induced fibrotic changes through near-infrared fluorescence molecular imaging (FMI) and magnetic resonance imaging (MRI) using an extradomain B fibronectin (EDB-FN)-targeted imaging probe (ZD2-Gd-DOTA-Cy7).

METHODS

The ZD2-Gd-DOTA-Cy7 probe was constructed by conjugating a peptide (Cys-TVRTSAD) to Gd-DOTA and the near-infrared dye Cy7. PDAC murine xenograft models were intravenously injected with ZD2-Gd-DOTA-Cy7 at a Gd concentration of 0.05 mmol/kg or free Cy7 and Gd-DOTA as control. The normalized tumor background ratio (TBR) on FMI and the T1 reduction ratio on MRI were quantitatively analyzed. For models receiving AG chemotherapy or saline, MRI/FMI was performed before and after treatment. Histological analyses were performed for validation.

RESULTS

The ZD2-Gd-DOTA-Cy7 concentration showed a linear correlation with the fluorescence intensity and T1 relaxation time in vitro. The optimal imaging time was 30 min after injection of the ZD2-Gd-DOTA-Cy7 (0.05 mmol/kg), only half of the clinic dosage of gadolinium. Additionally, ZD2-Gd-DOTA-Cy7 generated a 1.44-fold and 1.90-fold robust contrast enhancement compared with Cy7 (P < 0.05) and Gd-DOTA (P < 0.05), respectively. For AG chemotherapy monitoring, the T1 reduction ratio and normalized TBR in the fibrotic tumor areas were significantly increased by 1.99-fold (P < 0.05) and 1.78-fold (P < 0.05), respectively, in the control group compared with those in the AG group.

CONCLUSION

MRI/FMI with a low dose of ZD2-Gd-DOTA-Cy7 enables sensitive imaging of PDAC and the quantitative assessment of fibrotic changes during AG chemotherapy, which shows potential clinical applications for precise diagnosis, post-treatment monitoring, and disease management.

Rational Design and Comparison of Novel 99mTc-Labeled FAPI Dimers for Visualization of Multiple Tumor Types

Recognizing the significance of SPECT in nuclear medicine and the pivotal role of fibroblast activation protein (FAP) in cancer diagnosis and therapy, this study focuses on the development of 99mTc-labeled dimeric HF2 with high tumor uptake and image contrast. The dimeric HF2 was synthesized and radiolabeled with 99mTc in one pot using various coligands (tricine, TPPTS, EDDA, and TPPMS) to yield [99mTc]Tc-TPPTS-HF2, [99mTc]Tc-EDDA-HF2, and [99mTc]Tc-TPPMS-HF2 dimers. SPECT imaging results indicated that [99mTc]Tc-TPPTS-HF2 exhibited higher tumor uptake and tumor-to-normal tissue (T/NT) ratio than [99mTc]Tc-EDDA-HF2 and [99mTc]Tc-TPPMS-HF2. Notably, [99mTc]Tc-TPPTS-HF2 exhibited remarkable tumor accumulation and retention in HT-1080-FAP and U87-MG tumor-bearing mice, thereby surpassing the monomeric [99mTc]Tc-TPPTS-HF. Moreover, [99mTc]Tc-TPPTS-HF2 achieved acceptable T/NT ratios in the hepatocellular carcinoma patient-derived xenograft (HCC-PDX) model, which provided identifiable contrast and imaging quality. In conclusion, this study presents proof-of-concept research on 99mTc-labeled FAP inhibitor dimers for the visualization of multiple tumor types. Among these candidate compounds, [99mTc]Tc-TPPTS-HF2 showed excellent clinical potential, thereby enriching the SPECT tracer toolbox.

Advances in Radioligand Theranostics in Oncology

Theranostics with radioligands (radiotheranostics) has played a pivotal role in oncology. Radiotheranostics explores the molecular targets expressed on tumor cells to target them for imaging and therapy. In this way, radiotheranostics entails non-invasive demonstration of the in vivo expression of a molecular target of interest through imaging followed by the administration of therapeutic radioligand targeting the tumor-expressed molecular target. Therefore, radiotheranostics ensures that only patients with a high likelihood of response are treated with a particular radiotheranostic agent, ensuring the delivery of personalized care to cancer patients. Within the last decades, a couple of radiotheranostics agents, including Lutetium-177 DOTATATE (177Lu-DOTATATE) and Lutetium-177 prostate-specific membrane antigen (177Lu-PSMA), were shown to prolong the survival of cancer patients compared to the current standard of care leading to the regulatory approval of these agents for routine use in oncology care. This recent string of successful approvals has broadened the interest in the development of different radiotheranostic agents and their investigation for clinical translation. In this work, we present an updated appraisal of the literature, reviewing the recent advances in the use of established radiotheranostic agents such as radioiodine for differentiated thyroid carcinoma and Iodine-131-labeled meta-iodobenzylguanidine therapy of tumors of the sympathoadrenal axis as well as the recently approved 177Lu-DOTATATE and 177Lu-PSMA for differentiated neuroendocrine tumors and advanced prostate cancer, respectively. We also discuss the radiotheranostic agents that have been comprehensively characterized in preclinical studies and have shown some clinical evidence supporting their safety and efficacy, especially those targeting fibroblast activation protein (FAP) and chemokine receptor 4 (CXCR4) and those still being investigated in preclinical studies such as those targeting poly (ADP-ribose) polymerase (PARP) and epidermal growth factor receptor 2.

Synthesis and preclinical evaluation of a novel PET/fluorescence dual-modality probe targeting fibroblast activation protein

Early diagnosis and precise surgical intervention are crucial for cancer patients. We aimed to develop a novel positron emission tomography (PET)/fluorescence dual-modality probe for preoperative diagnosis, intraoperative guidance, and postoperative monitoring of fibroblast activation protein (FAP)-positive tumors. FAPI-FAM was synthesized and labeled with gallium-68. [68Ga]Ga-FAPI-FAM showed favorable in vivo and in vitro characteristics, specific binding affinity, and excellent tumor accumulation in FAP-positive cells and mice xenografts. Excellent tumor-to-background contrast was found owing to high tumor uptake, prolonged retention, and rapid renal clearance of [68Ga]Ga-FAPI-FAM. Moreover, a specific fluorescence signal was detected in FAP-positive tumors during ex vivo fluorescence imaging, demonstrating the feasibility of whole-body tumor detection and intraoperative tumor delineation.

Recent advances in the development of 225Ac- and 211At-labeled radioligands for radiotheranostics

Radiotheranostics utilizes a set of radioligands incorporating diagnostic or therapeutic radionuclides to achieve both diagnosis and therapy. Imaging probes using diagnostic radionuclides have been used for systemic cancer imaging. Integration of therapeutic radionuclides into the imaging probes serves as potent agents for radionuclide therapy. Among them, targeted alpha therapy (TAT) is a promising next-generation cancer therapy. The α-particles emitted by the radioligands used in TAT result in a high linear energy transfer over a short range, inducing substantial damage to nearby cells surrounding the binding site. Therefore, the key to successful cancer treatment with minimal side effects by TAT depends on the selective delivery of radioligands to their targets. Recently, TAT agents targeting biomolecules highly expressed in various cancer cells, such as sodium/iodide symporter, norepinephrine transporter, somatostatin receptor, αvβ3 integrin, prostate-specific membrane antigen, fibroblast-activation protein, and human epidermal growth factor receptor 2 have been developed and have made remarkable progress toward clinical application. In this review, we focus on two radionuclides, 225Ac and 211At, which are expected to have a wide range of applications in TAT. We also introduce recent fundamental and clinical studies of radiopharmaceuticals labeled with these radionuclides.

Synthesis and Evaluation of [64Cu]Cu-NOTA-HFn for PET Imaging of Transferrin Receptor 1 Expression in Nasopharyngeal Carcinoma

As recurrent and metastatic nasopharyngeal carcinoma (NPC) is the most common cause of death among patients with NPC, there is an urgent clinical need for the development of precision diagnosis to guide personalized treatment. Recent emerging evidence substantiates the increased expression of transferrin receptor 1 (also known as cluster of differentiation 71, CD71) within tumor tissues and the inherent targeting capability of natural heavy-chain ferritin (HFn) toward CD71. This study aimed to synthesize and assess a radiotracer ([64Cu]Cu-NOTA-HFn) designed to target CD71 for positron emission tomography (PET) imaging in an NPC tumor-bearing mouse model. The entire radiolabeling process of [64Cu]Cu-NOTA-HFn was completed within 15 min with high yield (>98.5%) and high molar activity (72.96 ± 21.33 GBq/μmol). The in vitro solubility and stability experiments indicated that [64Cu]Cu-NOTA-HFn had a high water solubility (log P = -2.42 ± 0.52, n = 6) and good stability in phosphate-buffered saline (PBS) for up to 48 h. The cell saturation binding assay indicated that [64Cu]Cu-NOTA-HFn had a nanomolar affinity (Kd = 10.9 ± 6.1 nM) for CD71-overexpressing C666-1 cells. To test the target engagement in vivo, prolonged-time PET imaging was performed at 1, 6, 12, 24, and 36 h postinjection (p.i.) of [64Cu]Cu-NOTA-HFn to C666-1 NPC tumor-bearing mice. The C666-1 tumors could be visualized by [64Cu]Cu-NOTA-HFn and blocked by nonradiolabeled HFn. PET imaging quantitative analysis demonstrated that the uptake of [64Cu]Cu-NOTA-HFn in C666-1 tumors peaked at 6 h p.i. and the best radioactive tumor-to-muscle ratio was 10.53 ± 3.11 (n = 3). Ex vivo biodistribution assay at 6 h p.i. showed that the tumor uptakes were 1.43 ± 0.23%ID/g in the nonblock group and 0.92 ± 0.2%ID/g in the block group (n = 3, p < 0.05). Immunohistochemistry and immunofluorescence staining confirmed positive expression of CD71 and the uptake of HFn in C666-1 tumor tissues. In conclusion, our experiments demonstrated that [64Cu]Cu-NOTA-HFn possesses a very high target engagement for CD71-positive NPC tumors and provided a fundamental basis for further clinical translation.

Theranostics - a sure cure for cancer after 100 years?

Cancer has remained a formidable challenge in medicine and has claimed an enormous number of lives worldwide. Theranostics, combining diagnostic methods with personalized therapeutic approaches, shows huge potential to advance the battle against cancer. This review aims to provide an overview of theranostics in oncology: exploring its history, current advances, challenges, and prospects. We present the fundamental evolution of theranostics from radiotherapeutics, cellular therapeutics, and nanotherapeutics, showcasing critical milestones in the last decade. From the early concept of targeted drug delivery to the emergence of personalized medicine, theranostics has benefited from advances in imaging technologies, molecular biology, and nanomedicine. Furthermore, we emphasize pertinent illustrations showcasing that revolutionary strategies in cancer management enhance diagnostic accuracy and provide targeted therapies customized for individual patients, thereby facilitating the implementation of personalized medicine. Finally, we describe future perspectives on current challenges, emerging topics, and advances in the field.

A pilot study of [68Ga]Ga-fibroblast activation protein inhibitor-04 PET/CT in renal cell carcinoma

OBJECTIVES

As a promising positron emission tomography (PET) tracer, [68Ga]Ga-fibroblast activation protein inhibitor-04([68Ga]Ga-FAPI-04) performs better than 2-[18F]fluoro-2-deoxy-d-glucose ([18F]FDG) at diagnosing primary and metastatic lesions in patients with various types of cancer. We investigated the utility of [68Ga]Ga-FAPI-04 PET/CT for the detection of primary and metastatic lesions in renal cell carcinoma (RCC). [18F]FDG PET/CT were used for comparison.

METHODS

Twenty-two patients with suspected RCC or recurrent RCC were enrolled in our study. Among these patients, 14 were newly diagnosed with RCC, 3 had recurrent RCC, and 5 were excluded from further analysis due to having benign renal tumours. Seventeen patients with RCC underwent [68Ga]Ga-FAPI-04 PET/CT, and 6 of them also received [18F]FDG PET/CT. The positive detection rates were calculated and compared with those in patients who underwent both scans.

RESULTS

Data from 17 patients with RCC (median age: 60.5 years, interquartile range [IQR]: 54-70 years) were evaluated. The positive detection rate of [68Ga]Ga-FAPI-04 PET/CT for RCC was 64.7% (11/17). Lymph node metastases (n = 44), lung metastasis (n = 1), and bone metastasis (n = 1) were detected. Six patients with RCC underwent [68Ga]Ga-FAPI-04 and [18F]FDG PET/CT. [68Ga]Ga-FAPI-04 PET/CT showed a higher positive detection rate than [18F]FDG PET/CT in detecting RCC (83.3% [5/6] vs. 50% [3/6], P = 0.545). Additionally, [68Ga]Ga-FAPI-04 PET/CT has higher SUVmax (3.20 [IQR: 2.91-5.80 vs. 2.71 [IQR: 2.13-3.10], P = 0.116) and tumour-to-background ratio (TBR) values (1.60 [IQR: 1.33-3.67] vs. 0.86 [0.48-1.21], P = 0.028) than [18F]FDG PET/CT.

CONCLUSIONS

These findings suggest that [68Ga]Ga-FAPI-04 PET/CT has potential value in RCC diagnosis. Further studies are warranted to validate these results.

ADVANCES IN KNOWLEDGE

Clinical utility of [68Ga]Ga-FAPI-04 in RCC remains unclear, and there are not many similar studies in the literature. We evaluated the role of [68Ga]Ga-FAPI-04 in diagnosing RCC.

Ultrasound-targeted microbubble destruction improves the suppression and magnetic resonance imaging of pancreatic cancer with polyethyleneimine nanogels

The chemoresistance of pancreatic cancer tumors urgently needs to be addressed. Pancreatic cancer is characterized by an abundant stroma, with significant fibrous connective tissue formation that encapsulates the tumor parenchyma and forms an interstitial microenvironment. Pancreatic stellate cells (PSCs) play a crucial role in this microenvironment and specially secrete periosteal protein (periostin), which can promote tumor growth, metastasis, and chemoresistance. Therefore, periostin has become a specific target of chemotherapy resistance intervention methods. The proposed polyethyleneimine (PEI) nanogels have multiple modification and efficient drug-loading properties. Additionally, ultrasound-targeted microbubble destruction (UTMD) supports the breakdown of the tough interstitial barrier of pancreatic cancer. A small interfering RNA (siRNA) can be used to downregulated the periostin gene, while sustained release of gemcitabine can promote killing of tumor cells. This method achieves a combination of gene silencing and chemotherapy. The imaging effect can be evaluated using magnetic resonance imaging (MRI). The ultimate goal of this work is to support individualized and effective therapeutic methods and help develop new strategies for pancreatic cancer treatment.

circNOX4 activates an inflammatory fibroblast niche to promote tumor growth and metastasis in NSCLC via FAP/IL-6 axis

BACKGROUND

Cancer-associated fibroblasts (CAFs) orchestrate a supportive niche that fuels cancer metastatic development in non-small cell lung cancer (NSCLC). Due to the heterogeneity and plasticity of CAFs, manipulating the activated phenotype of fibroblasts is a promising strategy for cancer therapy. However, the underlying mechanisms of fibroblast activation and phenotype switching that drive metastasis remain elusive.

METHODS

The clinical implications of fibroblast activation protein (FAP)-positive CAFs (FAP+CAFs) were evaluated based on tumor specimens from NSCLC patients and bioinformatic analysis of online databases. CAF-specific circular RNAs (circRNAs) were screened by circRNA microarrays of primary human CAFs and matched normal fibroblasts (NFs). Survival analyses were performed to assess the prognostic value of circNOX4 in NSCLC clinical samples. The biological effects of circNOX4 were investigated by gain- and loss-of-function experiments in vitro and in vivo. Fluorescence in situ hybridization, luciferase reporter assays, RNA immunoprecipitation, and miRNA rescue experiments were conducted to elucidate the underlying mechanisms of fibroblast activation. Cytokine antibody array, transwell coculture system, and enzyme-linked immunosorbent assay (ELISA) were performed to investigate the downstream effectors that promote cancer metastasis.

RESULTS

FAP+CAFs were significantly enriched in metastatic cancer samples, and their higher abundance was correlated with the worse overall survival in NSCLC patients. A novel CAF-specific circRNA, circNOX4 (hsa_circ_0023988), evoked the phenotypic transition from NFs into CAFs and promoted the migration and invasion of NSCLC in vitro and in vivo. Clinically, circNOX4 correlated with the poor prognosis of advanced NSCLC patients. Mechanistically, circNOX4 upregulated FAP by sponging miR-329-5p, which led to fibroblast activation. Furthermore, the circNOX4/miR-329-5p/FAP axis activated an inflammatory fibroblast niche by preferentially inducing interleukin-6 (IL-6) and eventually promoting NSCLC progression. Disruption of the intercellular circNOX4/IL-6 axis significantly suppressed tumor growth and metastatic colonization in vivo.

CONCLUSIONS

Our study reveals a role of the circRNA-induced fibroblast niche in tumor metastasis and highlights that targeting the circNOX4/FAP/IL-6 axis is a promising strategy for the intervention of NSCLC metastasis.

Autophagy inhibition improves the targeted radionuclide therapy efficacy of 131I-FAP-2286 in pancreatic cancer xenografts

PURPOSES

Radiotherapy can induce tumor cell autophagy, which might impair the antitumoral effect. This study aims to investigate the effect of autophagy inhibition on the targeted radionuclide therapy (TRT) efficacy of 131I-FAP-2286 in pancreatic cancer.

METHODS

Human pancreatic cancer PANC-1 cells were exposed to 131I-FAP-2286 radiotherapy alone or with the autophagy inhibitor 3-MA. The autophagy level and proliferative activity of PANC-1 cells were analyzed. The pancreatic cancer xenograft-bearing nude mice were established by the co-injection of PANC-1 cells and pancreatic cancer-associated fibroblasts (CAFs), and then were randomly divided into four groups and treated with saline (control group), 3-MA, 131I-FAP-2286 and 131I-FAP-2286 + 3-MA, respectively. SPECT/CT imaging was performed to evaluate the bio-distribution of 131I-FAP-2286 in pancreatic cancer-bearing mice. The therapeutic effect of tumor was evaluated by 18F-FDG PET/CT imaging, tumor volume measurements, and the hematoxylin and eosin (H&E) staining, and immunohistochemical staining assay of tumor tissues.

RESULTS

131I-FAP-2286 inhibited proliferation and increased the autophagy level of PANC-1 cells in a dose-dependent manner. 3-MA promoted 131I-FAP-2286-induced apoptosis of PANC-1 cells via suppressing autophagy. SPECT/CT imaging of pancreatic cancer xenograft-bearing nude mice showed that 131I-FAP-2286 can target the tumor effectively. According to 18F-FDG PET/CT imaging, the tumor growth curves and immunohistochemical analysis, 131I-FAP-2286 TRT was capable of suppressing the growth of pancreatic tumor accompanying with autophagy induction, but the addition of 3-MA enabled 131I-FAP-2286 to achieve a better therapeutic effect along with the autophagy inhibition. In addition, 3-MA alone did not inhibit tumor growth.

CONCLUSIONS

131I-FAP-2286 exposure induces the protective autophagy of pancreatic cancer cells, and the application of autophagy inhibitor is capable of enhancing the TRT therapeutic effect.

Preclinical Evaluation and a Pilot Clinical Positron Emission Tomography Imaging Study of [68Ga]Ga-FAPI-FUSCC-II

Fibroblast activation protein (FAP), a type II integral membrane serine protease, is a promising target for tumor diagnosis and therapy. OncoFAP has been recently discovered for PET imaging procedures for various solid malignancies. In this study, we presented the development of manual radiolabeling procedures for the preparation of OncoFAP-based radiopharmaceuticals for cancer imaging. A novel series of [68Ga/177Lu]Ga/Lu-FAPI-FUSCC-I/II were produced with high radiochemical yields. [68Ga]Ga-FAPI-FUSCC-I/II and [177Lu]Lu-FAPI-FUSCC-I/II were stable in phosphate-buffered saline, fetal bovine serum, and human serum for at least 3 h. In vitro cellular uptake and blocking experiments implied that they had specificity to FAP. Additionally, the low nanomolar IC50 values of FAPI-FUSCC-II indicated that it had a high target affinity to FAP. The in vivo biodistribution and blocking study in mice bearing HT-1080-FAP tumors showed that both exhibited specific tumor uptake. [68Ga]Ga-FAPI-FUSCC-II showed a higher tumor uptake and a higher tumor/nontarget ratio than [68Ga]Ga-FAPI-FUSCC-I and [68Ga]Ga-FAPI-04. The results of ex vivo biodistribution were in accordance with the biodistribution results. Clinical [68Ga]Ga-FAPI-FUSCC-II-PET/CT imaging further demonstrated its favorable biodistribution and kinetics with elevated and reliable uptake by primary tumors (maximum standardized uptake value (SUVmax), 12.17 ± 6.67) and distant metastases (SUVmax, 9.24 ± 4.28). In summary, [68Ga]Ga-FAPI-FUSCC-II displayed increased tumor uptake and retention compared to [68Ga]Ga-FAPI-04, giving it potential as a promising tracer for the diagnostic imaging of malignant tumors with positive FAP expression.

Comparison of Nuclear Medicine Therapeutics Targeting PSMA among Alpha-Emitting Nuclides

Currently, targeted alpha therapy (TAT) is a new therapy involving the administration of a therapeutic drug that combines a substance of α-emitting nuclides that kill cancer cells and a drug that selectively accumulates in cancer cells. It is known to be effective against cancers that are difficult to treat with existing methods, such as cancer cells that are widely spread throughout the whole body, and there are high expectations for its early clinical implementation. The nuclides for TAT, including 149Tb, 211At, 212/213Bi, 212Pb (for 212Bi), 223Ra, 225Ac, 226/227Th, and 230U, are known. However, some nuclides encounter problems with labeling methods and lack sufficient preclinical and clinical data. We labeled the compounds targeting prostate specific membrane antigen (PSMA) with 211At and 225Ac. PSMA is a molecule that has attracted attention as a theranostic target for prostate cancer, and several targeted radioligands have already shown therapeutic effects in patients. The results showed that 211At, which has a much shorter half-life, is no less cytotoxic than 225Ac. In 211At labeling, our group has also developed an original method (Shirakami Reaction). We have succeeded in obtaining a highly purified labeled product in a short timeframe using this method.

Imaging Evaluation of Peritoneal Metastasis: Current and Promising Techniques

Early diagnosis, accurate assessment, and localization of peritoneal metastasis (PM) are essential for the selection of appropriate treatments and surgical guidance. However, available imaging modalities (computed tomography [CT], conventional magnetic resonance imaging [MRI], and 18fluorodeoxyglucose positron emission tomography [PET]/CT) have limitations. The advent of new imaging techniques and novel molecular imaging agents have revealed molecular processes in the tumor microenvironment as an application for the early diagnosis and assessment of PM as well as real-time guided surgical resection, which has changed clinical management. In contrast to clinical imaging, which is purely qualitative and subjective for interpreting macroscopic structures, radiomics and artificial intelligence (AI) capitalize on high-dimensional numerical data from images that may reflect tumor pathophysiology. A predictive model can be used to predict the occurrence, recurrence, and prognosis of PM, thereby avoiding unnecessary exploratory surgeries. This review summarizes the role and status of different imaging techniques, especially new imaging strategies such as spectral photon-counting CT, fibroblast activation protein inhibitor (FAPI) PET/CT, near-infrared fluorescence imaging, and PET/MRI, for early diagnosis, assessment of surgical indications, and recurrence monitoring in patients with PM. The clinical applications, limitations, and solutions for fluorescence imaging, radiomics, and AI are also discussed.

Cancer-associated fibroblasts in neoadjuvant setting for solid cancers

Therapeutic approaches for cancer have become increasingly diverse in recent times. A comprehensive understanding of the tumor microenvironment (TME) holds great potential for enhancing the precision of tumor therapies. Neoadjuvant therapy offers the possibility of alleviating patient symptoms and improving overall quality of life. Additionally, it may facilitate the reduction of inoperable tumors and prevent potential preoperative micrometastases. Within the TME, cancer-associated fibroblasts (CAFs) play a prominent role as they generate various elements that contribute to tumor progression. Particularly, extracellular matrix (ECM) produced by CAFs prevents immune cell infiltration into the TME, hampers drug penetration, and diminishes therapeutic efficacy. Therefore, this review provides a summary of the heterogeneity and interactions of CAFs within the TME, with a specific focus on the influence of neoadjuvant therapy on the microenvironment, particularly CAFs. Finally, we propose several potential and promising therapeutic strategies targeting CAFs, which may efficiently eliminate CAFs to decrease stroma density and impair their functions.

Rapid Radiolabeling for Peptide Radiotracers

Peptide-based radiopharmaceuticals (PRPs) have been developed and introduced into research and clinic diagnostic imaging and targeted radionuclide therapy for more than two decades. In order to efficiently prepare PRPs, some rapid radiolabeling methods have been demonstrated. This chapter presents six common approaches for PRPs radiolabeling with metallic radioisotopes and Fluorine-18.

Biocompatible conjugated polymer nanoparticles labeled with 225Ac for tumor endoradiotherapy

Recently, endoradiotherapy based on actinium-225 (225Ac) has attracted increasing attention, which is due to its α particles can generate maximal damage to cancer cells while minimizing unnecessary radiation effects on healthy tissues. Herein, 111In/225Ac-radiolabeled conjugated polymer nanoparticles (CPNs) coated with amphiphilic polymer DSPE-PEG-DOTA have been developed as a new injectable nano-radiopharmaceuticals for cancer endoradiotherapy under the guidance of nuclear imaging. Single photon emission computed tomography/computed tomography (SPECT/CT) using 111In-DOTA-PEG-CPNs as nano probe indicates a prolonged retention of radiolabeled nanocarriers, which was consistent with the in vivo biodistribution examined by direct radiometry analysis. Significant inhibition of tumor growth has been observed in murine 4T1 models treated with 225Ac-DOTA-PEG-CPNs when compared to mice treated with PBS or DOTA-PEG-CPNs. The 225Ac-DOTA-PEG-CPNs group experienced no single death within 24 days with the median survival considerably extended to 35 days, while all the mice treated with PBS or DOTA-PEG-CPNs died at 20 days post injection. Additionally, the histopathology studies demonstrated no obvious side effects on healthy tissues after treatment with 225Ac-DOTA-PEG-CPNs. All these results reveal that the new 225Ac-labeled DOTA-PEG-CPNs is promising as paradigm for endoradiotherapy.

Synthesis and Evaluation of [18F]SiFA-Conjugated Ligands for Fibroblast Activation Protein Imaging

In recent years, fibroblast activation protein (FAP) has emerged as an important target for the diagnosis and therapy of various tumors due to its high expression on the cell surface of cancer-associated fibroblasts, which are the major components of the tumor stroma. In this study, we synthesized and evaluated 18F-labeled FAP inhibitors (FAPIs) for FAP imaging. Two silicon fluoride acceptor (SiFA)-conjugated FAPIs were synthesized: one containing a γ-carboxy-l-glutamic acid (Gla) residue (1) and another containing two Gla residues (2). Both ligands exhibited high binding affinities for FAP. 18F/19F exchange reactions on both ligands were performed in the presence of 2% water. This resulted in the formation of radioligands [18F]1 and [18F]2 in high radiochemical yields. Radioligand [18F]2, with a more favorable partition coefficient, was selected for the U87MG cell binding study, and the results showed FAP-specific binding of the radioligand to the cells. An ex vivo biodistribution study in U87MG tumor-bearing mice 60 min after injection demonstrated a 5.8-fold higher tumor accumulation of [18F]2 than that of [18F]1. Furthermore, PET and ex vivo biodistribution studies of [18F]2 in U87MG tumor-bearing mice showed high and persistent tumor uptake over time, which was significantly blocked by the preinjection of FAPI-04. Our results indicate that [18F]SiFA-(Gla)2-conjugated FAPI ([18F]2) has the potential for FAP imaging.

Fibroblast Activation Protein-Targeted Radioligand Therapy with 177Lu-EB-FAPI for Metastatic Radioiodine-Refractory Thyroid Cancer: First-in-Human, Dose-Escalation Study

PURPOSE

Fibroblast activation protein (FAP) is a promising target for tumor treatment. In this study, we aimed to investigate the safety and efficacy of the albumin binder-conjugated FAP-targeted radiopharmaceutical, 177Lu-EB-FAPI (177Lu-LNC1004), in patients with metastatic radioiodine-refractory thyroid cancer (mRAIR-TC).

PATIENTS AND METHODS

This open-label, non-randomized, first-in-human, dose-escalation, investigator-initiated trial had a 3+3 design and involved a 6-week 177Lu-LNC1004 treatment cycle in patients with mRAIR-TC at 2.22 GBq initially, with subsequent cohorts receiving an incremental 50% dose increase until dose-limiting toxicity (DLT) was observed.

RESULTS

177Lu-LNC1004 administration was well tolerated, with no life-threatening adverse events observed. No patients experienced DLT in Group A (2.22 GBq/cycle). One patient experienced grade 4 thrombocytopenia in Group B (3.33 GBq/cycle); hence, another three patients were enrolled, none of whom experienced DLT. Two patients experienced grade 3 and 4 hematotoxicity in Group C (4.99 GBq/cycle). The mean whole-body effective dose was 0.17 ± 0.04 mSv/MBq. Intense 177Lu-LNC1004 uptake and prolonged tumor retention resulted in high mean absorbed tumor doses (8.50 ± 12.36 Gy/GBq). The mean effective half-lives for the whole-body and tumor lesions were 90.20 ± 7.68 and 92.46 ± 9.66 hours, respectively. According to RECIST, partial response, stable disease, and progressive disease were observed in 3 (25%), 7 (58%), and 2 (17%) patients, respectively. The objective response and disease control rates were 25% and 83%, respectively.

CONCLUSIONS

FAP-targeted radioligand therapy with 177Lu-LNC1004 at 3.33 GBq/cycle was well tolerated in patients with advanced mRAIR-TC, with high radiation dose delivery to the tumor lesions, encouraging therapeutic efficacy, and acceptable side effects.

Alpha Particle-Emitting Radiopharmaceuticals as Cancer Therapy: Biological Basis, Current Status, and Future Outlook for Therapeutics Discovery

Critical advances in radionuclide therapy have led to encouraging new options for cancer treatment through the pairing of clinically useful radiation-emitting radionuclides and innovative pharmaceutical discovery. Of the various subatomic particles used in therapeutic radiopharmaceuticals, alpha (α) particles show great promise owing to their relatively large size, delivered energy, finite pathlength, and resulting ionization density. This review discusses the therapeutic benefits of α-emitting radiopharmaceuticals and their pairing with appropriate diagnostics, resulting in innovative "theranostic" platforms. Herein, the current landscape of α particle-emitting radionuclides is described with an emphasis on their use in theranostic development for cancer treatment. Commonly studied radionuclides are introduced and recent efforts towards their production for research and clinical use are described. The growing popularity of these radionuclides is explained through summarizing the biological effects of α radiation on cancer cells, which include DNA damage, activation of discrete cell death programs, and downstream immune responses. Examples of efficient α-theranostic design are described with an emphasis on strategies that lead to cellular internalization and the targeting of proteins involved in therapeutic resistance. Historical barriers to the clinical deployment of α-theranostic radiopharmaceuticals are also discussed. Recent progress towards addressing these challenges is presented along with examples of incorporating α-particle therapy in pharmaceutical platforms that can be easily converted into diagnostic counterparts.

Development and Characterization of Novel FAP-Targeted Theranostic Pairs: A Bench-to-Bedside Study

Fibroblast activation protein (FAP) is among the most popular targets in nuclear medicine imaging and cancer theranostics. Several small-molecule moieties (FAPI-04, FAPI-46, etc.) are used for developing FAP-targeted theranostic agents. Nonetheless, the circulation time of FAP inhibitors is relatively short, resulting in rapid clearance via kidneys, low tumor uptake, and associated unsatisfactory treatment efficacy. To address the existing drawbacks, we engineered 3 peptides named FD1, FD2, and FD3 with different circulation times through solid-phase peptide synthesis. All the 3 reported peptides bind to human and murine FAP with single-digit nanomolar affinity measured by surface plasmon resonance. The diagnostic and therapeutic potential of the agents labeled with 68Ga and 177Lu was assessed in several tumor models exhibiting different levels of FAP expression. While radiolabeled FD1 was rapidly excreted from kidneys, radiolabeled FD2/FD3 have significantly prolonged circulation, increased tumor uptake, and decreased kidney accumulation. Our findings indicated that [68Ga]Ga-DOTA-FD1 positron emission tomography (PET) effectively detected FAP dynamics, whereas [177Lu]Lu-DOTA-FD2 and [177Lu]Lu-DOTA-FD3 exhibited remarkable therapeutic efficacy in FAP-overexpressing tumor models, including pancreatic cancer cell models characterized by abundant stroma. Moreover, a pilot translational investigation demonstrated that [68Ga]Ga-DOTA-FD1 had the capability to identify both primary and metastatic tumors with precision and distinction. In summary, we developed [68Ga]Ga-DOTA-FD1 for same-day PET imaging of FAP dynamics and [177Lu]Lu-DOTA-FD2 and [177Lu]Lu-DOTA-FD3 for effective radioligand therapy of FAP-overexpressing tumors.

Gallium-68-labeled fibroblast activation protein inhibitor-46 PET in patients with resectable or borderline resectable pancreatic ductal adenocarcinoma: A phase 2, multicenter, single arm, open label non-randomized study protocol

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease prone to widespread metastatic dissemination and characterized by a desmoplastic stroma that contributes to poor outcomes. Fibroblast activation protein (FAP)-expressing Cancer-Associated Fibroblasts (CAFs) are crucial components of the tumor stroma, influencing carcinogenesis, fibrosis, tumor growth, metastases, and treatment resistance. Non-invasive tools to profile CAF identity and function are essential for overcoming CAF-mediated therapy resistance, developing innovative targeted therapies, and improved patient outcomes. We present the design of a multicenter phase 2 study (clinicaltrials.gov identifier NCT05262855) of [68Ga]FAPI-46 PET to image FAP-expressing CAFs in resectable or borderline resectable PDAC.

METHODS

We will enroll up to 60 adult treatment-naïve patients with confirmed PDAC. These patients will be eligible for curative surgical resection, either without prior treatment (Cohort 1) or after neoadjuvant therapy (NAT) (Cohort 2). A baseline PET scan will be conducted from the vertex to mid-thighs approximately 15 minutes after administering 5 mCi (±2) of [68Ga]FAPI-46 intravenously. Cohort 2 patients will undergo an additional PET after completing NAT but before surgery. Histopathology and FAP immunohistochemistry (IHC) of initial diagnostic biopsy and resected tumor samples will serve as the truth standards. Primary objective is to assess the sensitivity, specificity, and accuracy of [68Ga]FAPI-46 PET for detecting FAP-expressing CAFs. Secondary objectives will assess predictive values and safety profile validation. Exploratory objectives are comparison of diagnostic performance of [68Ga]FAPI-46 PET to standard-of-care imaging, and comparison of pre- versus post-NAT [68Ga]FAPI-46 PET in Cohort 2.

CONCLUSION

To facilitate the clinical translation of [68Ga]FAPI-46 in PDAC, the current study seeks to implement a coherent strategy to mitigate risks and increase the probability of meeting FDA requirements and stakeholder expectations. The findings from this study could potentially serve as a foundation for a New Drug Application to the FDA.

TRIAL REGISTRATION

@ClinicalTrials.gov identifier NCT05262855.

Advances in CAR T Cell Therapy for Non-Small Cell Lung Cancer

Since its first approval by the FDA in 2017, tremendous progress has been made in chimeric antigen receptor (CAR) T cell therapy, the adoptive transfer of engineered, CAR-expressing T lymphocyte. CAR T cells are all composed of three main elements: an extracellular antigen-binding domain, an intracellular signaling domain responsible for T cell activation, and a hinge that joins these two domains. Continuous improvement has been made in CARs, now in their fifth generation, particularly in the intracellular signaling domain responsible for T cell activation. CAR T cell therapy has revolutionized the treatment of hematologic malignancies. Nonetheless, the use of CAR T cell therapy for solid tumors has not attained comparable levels of success. Here we review the challenges in achieving effective CAR T cell therapy in solid tumors, and emerging CAR T cells that have shown great promise for non-small cell lung cancer (NSCLC). A growing number of clinical trials have been conducted to study the effect of CAR T cell therapy on NSCLC, targeting different types of surface antigens. They include epidermal growth factor receptor (EGFR), mesothelin (MSLN), prostate stem cell antigen (PSCA), and mucin 1 (MUC1). Potential new targets such as erythropoietin-producing hepatocellular carcinoma A2 (EphA2), tissue factor (TF), and protein tyrosine kinase 7 (PTK7) are currently under investigation in clinical trials. The challenges in developing CAR T for NSCLC therapy and other approaches for enhancing CAR T efficacy are discussed. Finally, we provide our perspective on imaging CAR T cell action by reviewing the two main radionuclide-based CAR T cell imaging techniques, the direct labeling of CAR T cells or indirect labeling via a reporter gene.

Recent Pre-Clinical Advancements in Nuclear Medicine: Pioneering the Path to a Limitless Future

The theranostic approach in oncology holds significant importance in personalized medicine and stands as an exciting field of molecular medicine. Significant achievements have been made in this field in recent decades, particularly in treating neuroendocrine tumors using 177-Lu-radiolabeled somatostatin analogs and, more recently, in addressing prostate cancer through prostate-specific-membrane-antigen targeted radionuclide therapy. The promising clinical results obtained in these indications paved the way for the further development of this approach. With the continuous discovery of new molecular players in tumorigenesis, the development of novel radiopharmaceuticals, and the potential combination of theranostics agents with immunotherapy, nuclear medicine is poised for significant advancements. The strategy of theranostics in oncology can be categorized into (1) repurposing nuclear medicine agents for other indications, (2) improving existing radiopharmaceuticals, and (3) developing new theranostics agents for tumor-specific antigens. In this review, we provide an overview of theranostic development and shed light on its potential integration into combined treatment strategies.

Evaluation of novel anti-CEACAM6 antibody-based conjugates for radioimmunotheranostics of pancreatic ductal adenocarcinoma

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is a highly malignant solid tumor that lacks early diagnostic methods. Recently, targeted immunotherapy and radiotherapy have been integrated with radionuclide-antibody conjugate drugs, which can be used for targeted diagnosis and dynamic imaging of tumors. CEACAM6 is overexpressed in pancreatic tumors and is a potential theranostic target for PDAC. We aimed to develop a novel targeted carrier for theranostics of PDAC and other solid tumors.

METHODS

Based on camelid heavy-chain-only antibodies, we developed a CEACAM6-targeting recombinant antibody NY004, and evaluated it as a novel antibody-carrier for imaging and therapy of cancer in tumor models. We labeled NY004 with theranostic nuclides and applied this self-developed antibody platform in diagnostic imaging and antitumor assessment in PDAC models.

RESULTS

Through microPET, IHC, and biodistribution assays, targeting and biodistribution of [89Zr]-NY004 in solid tumors including PDAC was examined, and the investigated tumors were all CEACAM6-positive malignancies. We found that NY004 was suitable for use as a drug carrier for radioimmunotheranostics. Our study showed that NY004 was characterized by high targeted uptake and a long retention time in PANC-1 tumors (up to 6 days post-injection), with good specificity and high imaging efficiency. Therapeutic evaluation of the radionuclide-labeled antibody drug [177Lu]-NY004 in PDAC tumor-bearing model revealed that NY004 had high and prolonged uptake in tumors, relatively low non-target organ uptake, and good anti-tumor efficacy.

CONCLUSION

As a drug platform for radiotheranostics, CEACAM6-specific antibody NY004 met the requirements of easy-labeling, targeting specificity, and effective persistence in pancreatic adenocarcinoma tissues.

KEY POINTS

• [89Zr]-NY004 has good specificity and high imaging efficiency, and is characterized by high tumor-targeting uptake and a long tumor retention time as a PET molecular imaging tracer. • Therapeutic radionuclide-conjugated antibody drug [177Lu]-NY004 has high uptake and prolonged uptake duration in tumors, low non-target organ uptake, and significant tumor-inhibiting efficacy in PDAC model. • The self-developed antibody structure NY004 is a promising drug platform for radioimmunotheranostics of CEACAM6-positive tumors including pancreatic ductal adenocarcinoma.

Highlighting Fibroblasts Activation in Fibrosis: The State-of-The-Art Fibroblast Activation Protein Inhibitor PET Imaging in Cardiovascular Diseases

Fibrosis is a common healing process that occurs during stress and injury in cardiovascular diseases. The evolution of fibrosis is associated with cardiovascular disease states and causes adverse effects. Fibroblast activation is responsible for the formation and progression of fibrosis. The incipient detection of activated fibroblasts is important for patient management and prognosis. Fibroblast activation protein (FAP), a membrane-bound serine protease, is almost specifically expressed in activated fibroblasts. The development of targeted FAP-inhibitor (FAPI) positron emission tomography (PET) imaging enabled the visualisation of FAP, that is, incipient fibrosis. Recently, research on FAPI PET imaging in cardiovascular diseases increased and is highly sought. Hence, we comprehensively reviewed the application of FAPI PET imaging in cardiovascular diseases based on the state-of-the-art published research. These studies provided some insights into the value of FAPI PET imaging in the early detection of cardiovascular fibrosis, risk stratification, response evaluation, and prediction of the evolution of left ventricular function. Future studies should be conducted with larger populations and multicentre patterns, especially for response evaluation and outcome prediction.

Theranostics in targeting fibroblast activation protein bearing cells: Progress and challenges

Cancer cells are surrounded by a complex and highly dynamic tumor microenvironment (TME). Cancer-associated fibroblasts (CAFs), a critical component of TME, contribute to cancer cell proliferation as well as metastatic spread. CAFs express a variety of biomarkers, which can be targeted for detection and therapy. Most importantly, CAFs express high levels of fibroblast activation protein (FAP) which contributes to progression of cancer, invasion, metastasis, migration, immunosuppression, and drug resistance. As a consequence, FAP is an attractive theranostic target. In this review, we discuss the latest advancement in targeting FAP in oncology using theranostic biomarkers and imaging modalities such as single-photon emission computed tomography (SPECT), positron emission tomography (PET), computed tomography (CT), fluorescence imaging, and magnetic resonance imaging (MRI).

An antibody-radionuclide conjugate targets fibroblast activation protein for cancer therapy

PURPOSE

Fibroblast activation protein is one of the most attractive targets for tumor diagnosis and therapy. There have been many successful clinical translations with small molecules and peptides, yet only a few anti-FAP antibody diagnostic or therapeutic agents have been reported. Antibodies often feature good tumor selectivity and long tumor retention, which may be a better-match with therapeutic radionuclides (e.g.,177Lu, 225Ac) for cancer therapy. Here we report a 177Lu-labeled anti-FAP antibody, PKU525, as a therapeutic radiopharmaceutical for FAP-targeted radiotherapy.

METHODS

The anti-FAP antibody is produced as a derivative of sibrotuzumab. The pharmacokinetics and blocking study are performed with 89Zr-labeled antibody by PET imaging. The conjugation strategies have been screened and tested with SPECT imaging through 177Lu-labeling. The biodistribution and radiotherapy studies are performed on 177Lu-labeled anti-FAP antibody in NU/NU mice-bearing HT-1080-FAP tumors.

RESULTS

A multiple time-point PET imaging study shows that the tumor accumulation of [89Zr]Zr-DFO-PKU525 is intense, selective, and relatively rapid. The time activity curve indicates that the tumor uptake continually increases until reaches the highest uptake (SUVmax = 18.4 ± 2.3, n = 4) at 192 h, then gradually declines. Radioactivity rapidly cleared from the blood, liver, and other major organs, resulting in high tumor-to-background ratios. An in vivo blocking experiment suggests that [89Zr]Zr-DFO-PKU525 is FAP-specific and the uptake in FAP-negative tumors is almost negligible. Ex vivo biodistribution study shows that the tumor uptake of [177Lu]Lu-DOTA-NCS-PKU525 is 23.04 ± 5.11% ID/g, 33.2 ± 6.36% ID/g, 19.87 ± 6.84% ID/g and 19.02 ± 5.90% ID/g at 24 h, 96 h, 168 h, and 240 h after injection (n = 5), which is corroborated with the PET imaging. In therapeutic assays, multiple doses of [177Lu]Lu-DOTA-NCS-PKU525 have been tested in tumor-bearing mice, and the data suggests that 3.7 MBq may be sufficient to completely suppress the tumor growth in mice without showing observable side effects.

CONCLUSION

A FAP-targeted antibody-radionuclide conjugate was developed and evaluated in vitro and in vivo. Its tumor accumulation is rapid and high with a clean background. It remarkably suppresses the tumors in mice while the side effect is almost negligible, showing that it is promising for further clinical translational studies.

Translational assessment of a DATA-functionalized FAP inhibitor with facile 68Ga-labeling at room temperature

PURPOSE

The present study aims at evaluating the preclinical and the clinical performance of [68Ga]Ga-DATA5m.SA.FAPi, which has the advantage to be labeled with gallium-68 at room temperature.

METHODS

[68Ga]Ga-DATA5m.SA.FAPi was assessed in vitro on FAP-expressing stromal cells, followed by biodistribution and in vivo imaging on prostate and glioblastoma xenografts. Moreover, the clinical assessment of [68Ga]Ga-DATA5m.SA.FAPi was conducted on six patients with prostate cancer, aiming on investigating, biodistribution, biokinetics, and determining tumor uptake.

RESULTS

[68Ga]Ga-DATA5m.SA.FAPi is quantitatively prepared in an instant kit-type version at room temperature. It demonstrated high stability in human serum, affinity for FAP in the low nanomolar range, and high internalization rate when associated with CAFs. Biodistribution and PET studies in prostate and glioblastoma xenografts revealed high and specific tumor uptake. Elimination of the radiotracer mainly occurred through the urinary tract. The clinical data are in accordance with the preclinical data concerning the organ receiving the highest absorbed dose (urinary bladder wall, heart wall, spleen, and kidneys). Different to the small-animal data, uptake of [68Ga]Ga-DATA5m.SA.FAPi in tumor lesions is rapid and stable and tumor-to-organ and tumor-to-blood uptake ratios are high.

CONCLUSION

The radiochemical, preclinical, and clinical data obtained in this study strongly support further development of [68Ga]Ga-DATA5m.SA.FAPi as a diagnostic tool for FAP imaging.

Fibroblast activation protein-α expression in fibroblasts is common in the tumor microenvironment of colorectal cancer and may serve as a therapeutic target

Background: Colorectal cancer (CRC) is still one of the leading causes of cancer death worldwide, emphasizing the need for further diagnostic and therapeutic approaches. Cancer invasion and metastasis are affected by the tumor microenvironment (TME), with cancer-associated fibroblasts (CAF) being the predominant cellular component. An important marker for CAF is fibroblast activation protein-α (FAP) which has been evaluated as therapeutic target for, e.g., radioligand therapy. The aim of this study was to examine CRC regarding the FAP expression as a candidate for targeted therapy. Methods: 67 CRC, 24 adenomas, 18 tissue samples of inflammation sites and 28 non-neoplastic, non-inflammatory tissue samples of colonic mucosa were evaluated for immunohistochemical FAP expression of CAF in tissue microarrays. The results were correlated with clinicopathological data, tumor biology and concurrent expression of additional immunohistochemical parameters. Results: 53/67 (79%) CRC and 6/18 (33%) inflammatory tissue specimens showed expression of FAP. However, FAP was only present in 1/24 (4%) adenomas and absent in normal mucosa (0/28). Thus, FAP expression in CRC was significantly higher than in the other investigated groups. Within the CRC cohort, expression of FAP did not correlate with tumor stage, grading or the MSI status. However, it was observed that tumors exhibiting high immunohistochemical expression of Ki-67, CD3, p53, and β-Catenin showed a significantly higher incidence of FAP expression. Conclusion: In the crosstalk between tumor cells and TME, CAF play a key role in carcinogenesis and metastatic spread. Expression of FAP was detectable in the majority of CRC but nearly absent in precursor lesions and non-neoplastic, non-inflammatory tissue. This finding indicates that FAP has the potential to emerge as a target for new diagnostic and therapeutic concepts in CRC. Additionally, the association between FAP expression and other immunohistochemical parameters displays the interaction between different components of the TME and demands further investigation.

Fibroblast Activation Protein-Targeted Photodynamic Therapy of Cancer-Associated Fibroblasts in Murine Models for Pancreatic Ductal Adenocarcinoma

Patients with pancreatic ductal adenocarcinoma (PDAC) have a dismal 5 year survival of 9%. One important limiting factor for treatment efficacy is the dense tumor-supporting stroma. The cancer-associated fibroblasts in this stroma deposit excessive amounts of extracellular matrix components and anti-inflammatory mediators, which hampers the efficacy of chemo- and immunotherapies. Systemic depletion of all activated fibroblasts is, however, not feasible nor desirable and therefore a local approach should be pursued. Here, we provide a proof-of-principle of using fibroblast activation protein (FAP)-targeted photodynamic therapy (tPDT) to treat PDAC. FAP-targeting antibody 28H1 and irrelevant control antibody DP47GS were conjugated to the photosensitizer IRDye700DX (700DX) and the chelator diethylenetriaminepentaacetic acid. In vitro binding and cytotoxicity were evaluated using the fibroblast cell-line NIH-3T3 stably transfected with FAP. Biodistribution of 111In-labeled antibody-700DX constructs was determined in mice carrying syngeneic tumors of the murine PDAC cell line PDAC299, and in a genetically engineered PDAC mouse model (CKP). Then, tPDT was performed by exposing the subcutaneous or the spontaneous PDAC tumors to 690 nm light. Induction of apoptosis after treatment was assessed using automated analyses of immunohistochemistry for cleaved caspase-3. 28H1-700DX effectively bound to 3T3-FAP cells and induced cytotoxicity upon exposure to 690 nm light, whereas no binding or cytotoxic effects were observed for DP47GS-700DX. Although both 28H1-700DX and DP47GS-700DX accumulated in subcutaneous PDAC299 tumors, autoradiography demonstrated that only 28H1-700DX reached the tumor core. On the contrary, control antibody DP47GS-700DX was only present at the tumor rim. In CKP mice, both antibodies accumulated in the tumor, but tumor-to-blood ratios of 28H1-700DX were higher than that of the control. Notably, in vivo FAP-tPDT caused upregulation of cleaved caspase-3 staining in both subcutaneous and in spontaneous tumors. In conclusion, we have shown that tPDT is a feasible approach for local depletion of FAP-expressing stromal cells in murine models for PDAC.

Advances in PET/CT Imaging for Breast Cancer

One out of eight women will be affected by breast cancer during her lifetime. Imaging plays a key role in breast cancer detection and management, providing physicians with information about tumor location, heterogeneity, and dissemination. In this review, we describe the latest advances in PET/CT imaging of breast cancer, including novel applications of 18F-FDG PET/CT and the development and testing of new agents for primary and metastatic breast tumor imaging and therapy. Ultimately, these radiopharmaceuticals may guide personalized approaches to optimize treatment based on the patient's specific tumor profile, and may become a new standard of care. In addition, they may enhance the assessment of treatment efficacy and lead to improved outcomes for patients with a breast cancer diagnosis.

Organotrifluoroborate enhances tumor targeting of fibroblast activation protein inhibitors for targeted radionuclide therapy

PURPOSE

Fibroblast activation protein (FAP) is a pan-cancer target and now the state-of-the-art to develop radiopharmaceuticals. FAP inhibitors have been of great success in developing imaging tracers. Yet, the overly rapid clearance cannot match with the long half-lives of regular therapeutic radionuclides. Though strategies that aim to elongate the circulation of FAPIs are being developed, here we describe an innovation that uses α-emitters of short half-lives (e.g., 213Bi) to pair the rapid pharmacokinetics of FAPIs.

METHODS

An organotrifluoroborate linker is engineered to FAPIs to give two advantages: (1) selectively increases tumor uptake and retention; (2) facile 18F-radiolabeling for positron emission tomography to guide radiotherapy with α-emitters, which can hardly be traced in general.

RESULTS

The organotrifluoroborate linker helps to improve the internalization in cancer cells, resulting in notably higher tumor uptake while the background is clean. In FAP-expressed tumor-bearing mice, this FAPI labeled with 213Bi, a short half-life α-emitter, exhibits almost complete suppression to tumor growth while the side effect is negligible. Additional data shows that this strategy is generally applicable to guide other α-emitters, such as 212Bi, 212Pb, and 149Tb.

CONCLUSION

The organotrifluoroborate linker may be of importance to optimize FAP-targeted radiopharmaceuticals, and the short half-lived α-emitters may be of choice for the rapid-cleared small molecule-based radiopharmaceuticals.

The Prognostic and therapeutic value and clinical implications of fibroblast activation protein-α as a novel biomarker in colorectal cancer

The identification of contributing factors leading to the development of Colorectal Cancer (CRC), as the third fatal malignancy, is crucial. Today, the tumor microenvironment has been shown to play a key role in CRC progression. Fibroblast-Activation Protein-α (FAP) is a type II transmembrane cell surface proteinase expressed on the surface of cancer-associated fibroblasts in tumor stroma. As an enzyme, FAP has di- and endoprolylpeptidase, endoprotease, and gelatinase/collagenase activities in the Tumor Microenvironment (TME). According to recent reports, FAP overexpression in CRC contributes to adverse clinical outcomes such as increased lymph node metastasis, tumor recurrence, and angiogenesis, as well as decreased overall survival. In this review, studies about the expression level of FAP and its associations with CRC patients' prognosis are reviewed. High expression levels of FAP and its association with clinicopathological factors have made as a potential target. In many studies, FAP has been evaluated as a therapeutic target and diagnostic factor into which the current review tries to provide a comprehensive insight. Video Abstract.

FAPI PET/CT Imaging-An Updated Review

Despite revolutionizing the field of oncological imaging, Positron Emission Tomography (PET) with [¹⁸F]Fluorodeoxyglucose (FDG) as its workhorse is limited by a lack of specificity and low sensitivity in certain tumor subtypes. Fibroblast activation protein (FAP), a type II transmembrane glycoprotein, is expressed by cancer-associated fibroblasts (CAFs) that form a major component of the tumor stroma. FAP holds the promise to be a pan-cancer target, owing to its selective over-expression in a vast majority of neoplasms, particularly epithelial cancers. Several radiolabeled FAP inhibitors (FAPI) have been developed for molecular imaging and potential theranostic applications. Preliminary data on FAPI PET/CT remains encouraging, with extensive multi-disciplinary clinical research currently underway. This review summarizes the existing literature on FAPI PET/CT imaging with an emphasis on diagnostic applications, comparison with FDG, pitfalls, and future directions.

Fibroblast Activation Protein Inhibitor-Based Radionuclide Therapies: Current Status and Future Directions

Metastatic malignancies have limited management strategies and variable treatment responses. Cancer cells develop beside and depend on the complex tumor microenvironment. Cancer-associated fibroblasts, with their complex interaction with tumor and immune cells, are involved in various steps of tumorigenesis, such as growth, invasion, metastasis, and treatment resistance. Prooncogenic cancer-associated fibroblasts emerged as attractive therapeutic targets. However, clinical trials have achieved suboptimal success. Fibroblast activation protein (FAP) inhibitor-based molecular imaging has shown encouraging results in cancer diagnosis, making them innovative targets for FAP inhibitor-based radionuclide therapies. This review summarizes the results of preclinical and clinical FAP-based radionuclide therapies. We will describe advances and FAP molecule modification in this novel therapy, as well as its dosimetry, safety profile, and efficacy. This summary may guide future research directions and optimize clinical decision-making in this emerging field.

Fibroblast activation protein-targeted radionuclide therapy: background, opportunities, and challenges of first (pre)clinical studies

INTRODUCTION

Fibroblast activation protein (FAP) is highly overexpressed in stromal tissue of various cancers. While FAP has been recognized as a potential diagnostic or therapeutic cancer target for decades, the surge of radiolabeled FAP-targeting molecules has the potential to revolutionize its perspective. It is presently hypothesized that FAP targeted radioligand therapy (TRT) may become a novel treatment for various types of cancer. To date, several preclinical and case series have been reported on FAP TRT using varying compounds and showing effective and tolerant results in advanced cancer patients. Here, we review the current (pre)clinical data on FAP TRT and discuss its perspective towards broader clinical implementation.  METHODS: A PubMed search was performed to identify all FAP tracers used for TRT. Both preclinical and clinical studies were included if they reported on dosimetry, treatment response or adverse events. The last search was performed on July 22 2022. In addition, a database search was performed on clinical trial registries (date 15th of July 2022) to search for prospective trials on FAP TRT.

RESULTS

In total, 35 papers were identified that were related to FAP TRT. This resulted in the inclusion of the following tracers for review: FAPI-04, FAPI-46, FAP-2286, SA.FAP, ND-bisFAPI, PNT6555, TEFAPI-06/07, FAPI-C12/C16, and FSDD.

CONCLUSION

To date, data was reported on more than 100 patients that were treated with different FAP targeted radionuclide therapies such as [177Lu]Lu-FAPI-04, [90Y]Y-FAPI-46, [177Lu]Lu-FAP-2286, [177Lu]Lu-DOTA.SA.FAPI and [177Lu]Lu-DOTAGA.(SA.FAPi)2. In these studies, FAP targeted radionuclide therapy has resulted in objective responses in difficult to treat end stage cancer patients with manageable adverse events. Although no prospective data is yet available, these early data encourages further research.

Novel Targets, Novel Treatments: The Changing Landscape of Non-Small Cell Lung Cancer

Treatment of non-small cell lung cancer (NSCLC) has undergone a paradigm shift. Once a disease with limited potential therapies, treatment options for patients have exploded with the availability of molecular testing to direct management and targeted therapies to treat tumors with specific driver mutations. New in vitro diagnostics allow for the early and non-invasive detection of disease, and emerging in vivo imaging techniques allow for better detection and monitoring. The development of checkpoint inhibitor immunotherapy has arguably been the biggest advance in lung cancer treatment, given that the vast majority of NSCLC tumors can be treated with these therapies. Specific targeted therapies, including those against KRAS, EGFR, RTK, and others have also improved the outcomes for those individuals bearing an actionable mutation. New and emerging therapies, such as bispecific antibodies, CAR T cell therapy, and molecular targeted radiotherapy, offer promise to patients for whom none of the existing therapies have proved effective. In this review, we provide the most up-to-date survey to our knowledge regarding emerging diagnostic and therapeutic strategies for lung cancer to provide clinicians with a comprehensive reference of the options for treatment available now and those which are soon to come.

Fibroblast Activation Protein-Targeting Minibody-IRDye700DX for Ablation of the Cancer-Associated Fibroblast with Photodynamic Therapy

Fibroblast activation protein (FAP), expressed on cancer-associated fibroblasts, is a target for diagnosis and therapy in multiple tumour types. Strategies to systemically deplete FAP-expressing cells show efficacy; however, these induce toxicities, as FAP-expressing cells are found in normal tissues. FAP-targeted photodynamic therapy offers a solution, as it acts only locally and upon activation. Here, a FAP-binding minibody was conjugated to the chelator diethylenetriaminepentaacetic acid (DTPA) and the photosensitizer IRDye700DX (DTPA-700DX-MB). DTPA-700DX-MB showed efficient binding to FAP-overexpressing 3T3 murine fibroblasts (3T3-FAP) and induced the protein's dose-dependent cytotoxicity upon light exposure. Biodistribution of DTPA-700DX-MB in mice carrying either subcutaneous or orthotopic tumours of murine pancreatic ductal adenocarcinoma cells (PDAC299) showed maximal tumour uptake of ¹¹¹In-labelled DTPA-700DX-MB at 24 h post injection. Co-injection with an excess DTPA-700DX-MB reduced uptake, and autoradiography correlated with FAP expression in the stromal tumour region. Finally, in vivo therapeutic efficacy was determined in two simultaneous subcutaneous PDAC299 tumours; only one was treated with 690 nm light. Upregulation of an apoptosis marker was only observed in the treated tumours. In conclusion, DTPA-700DX-MB binds to FAP-expressing cells and targets PDAC299 tumours in mice with good signal-to-background ratios. Furthermore, the induced apoptosis indicates the feasibility of targeted depletion of FAP-expressing cells with photodynamic therapy.

Evaluation of Astatine-211-Labeled Fibroblast Activation Protein Inhibitor (FAPI): Comparison of Different Linkers with Polyethylene Glycol and Piperazine

Fibroblast activation proteins (FAP) are overexpressed in the tumor stroma and have received attention as target molecules for radionuclide therapy. The FAP inhibitor (FAPI) is used as a probe to deliver nuclides to cancer tissues. In this study, we designed and synthesized four novel ²¹¹At-FAPI(s) possessing polyethylene glycol (PEG) linkers between the FAP-targeting and ²¹¹At-attaching moieties. ²¹¹At-FAPI(s) and piperazine (PIP) linker FAPI exhibited distinct FAP selectivity and uptake in FAPII-overexpressing HEK293 cells and the lung cancer cell line A549. The complexity of the PEG linker did not significantly affect selectivity. The efficiencies of both linkers were almost the same. Comparing the two nuclides, ²¹¹At was superior to ¹³¹I in tumor accumulation. In the mouse model, the antitumor effects of the PEG and PIP linkers were almost the same. Most of the currently synthesized FAPI(s) contain PIP linkers; however, in our study, we found that PEG linkers exhibit equivalent performance. If the PIP linker is inconvenient, a PEG linker is expected to be an alternative.

A Simple Kit Formulation for Preparation and Exploratory Human Studies of a Novel 99mTc-Labeled Fibroblast Activation Protein Inhibitor Tracer for Imaging of the Fibroblast Activation Protein in Cancers

Fibroblast activation protein (FAP) is a potential target for tumor diagnosis and treatment because it is selectively expressed on the cell membrane of cancer-associated fibroblasts in most solid tumor stroma. The aim of this study was to develop a ^99mTc-labeled fibroblast activation protein inhibitor (FAPI) tracer, evaluate its imaging efficacy in nude mice, and further explore its biodistribution in healthy volunteers and uptake in tumor patients. An FAPI-derived ligand (DP-FAPI) containing d-proline was designed and synthesized as a linker, and a stable hydrophilic ^99mTc-labeled complex ([^99mTc]Tc-DP-FAPI) was obtained by kit formulation. In vitro cellular uptake and saturation binding assays were performed in FAP-transfected HT-1080 cells (FAP-HT-1080). The biodistribution was characterized, and micro-single-photon emission computed tomography (SPECT) imaging was performed in BALB/c nude mice bearing U87 MG tumors. Furthermore, a first-in-man application was performed in four healthy volunteers and three patients with gastrointestinal tumors. In vitro, the nanomolar K_d values of [^99mTc]Tc-DP-FAPI indicated that it had significantly high target affinity for FAP. Biodistribution and micro-SPECT imaging studies showed that [^99mTc]Tc-DP-FAPI exhibited high uptake and high tumor-to-nontargeted ratios. The calculated effective dose for [^99mTc]Tc-DP-FAPI was approximately <5 mSv in four healthy volunteers. In three patients with gastrointestinal tumors, [^99mTc]Tc-DP-FAPI quantitative SPECT/CT revealed high and reliable uptake. [^99mTc]Tc-DP-FAPI exhibited high selectivity and affinity for FAP in vitro. The safety and effectiveness of [^99mTc]Tc-DP-FAPI in primary tumor imaging have been confirmed by animal and clinical studies, revealing the potential clinical application value of this tracer.

Clinical Translation of Targeted α-Therapy: An Evolution or a Revolution?

The field of radioligand therapy has advanced greatly in recent years, driven largely by β-emitting therapies targeting somatostatin receptor-expressing tumors and the prostate-specific membrane antigen. Now, more clinical trials are under way to evaluate α-emitting targeted therapies as potential next-generation theranostics with even higher efficacy due to their high linear energy and short range in human tissues. In this review, we summarize the important studies ranging from the first Food and Drug Administration-approved α-therapy, ²²³Ra-dichloride, for treatment of bone metastases in castration-resistant prostate cancer, including concepts in clinical translation such as targeted α-peptide receptor radiotherapy and ²²⁵Ac-PSMA-617 for treatment of prostate cancer, innovative therapeutic models evaluating new targets, and combination therapies. Targeted α-therapy is one of the most promising fields in novel targeted cancer therapy, with several early- and late-stage clinical trials for neuroendocrine tumors and metastatic prostate cancer already in progress, along with significant interest and investment in additional early-phase studies. Together, these studies will help us understand the short- and long-term toxicity of targeted α-therapy and potentially identify suitable therapeutic combination partners.