Antitumor efficacy and potential mechanism of FAP-targeted radioligand therapy combined with immune checkpoint blockade

Radiotherapy combined with immune checkpoint blockade holds great promise for synergistic antitumor efficacy.Targeted radionuclide therapy delivers radiation directly to tumor sites.LNC1004 is a fibroblast activation protein(FAP)-targeting radiopharmaceutical,conjugated with the albumin binder Evans Blue,which has demonstrated enhanced tumor uptake and retention in previous preclinical and clinical studies.Herein,we demonstrate that^(68)Ga/^(177)Lu-labeled LNC1004 exhibits increased uptake and prolonged retention in MC38/NIH3T3-FAP and CT26/NIH3T3-FAP tumor xenografts.Radionuclide therapy with^(177)Lu-LNC1004 induced a transient upregulation of PD-L1 expression in tumor cells.The combination of^(177)Lu-LNC1004 and anti-PD-L1 immunotherapy led to complete eradication of all tumors in MC38/NIH3T3-FAP tumor-bearing mice,with mice showing 100%tumor rejection upon rechallenge.Immunohistochemistry,single-cell RNA sequencing(scRNA-seq),and TCR sequencing revealed that combination therapy reprogrammed the tumor microenvironment in mice to foster antitumor immunity by suppressing malignant progression and increasing cell-to-cell communication,CD8^(+)T-cell activation and expansion,M1 macrophage counts,antitumor activity of neutrophils,and T-cell receptor diversity.A preliminary clinical study demonstrated that^(177)Lu-LNC1004 was well-tolerated and effective in patients with refractory cancers.Further,scRNA-seq of peripheral blood mononuclear cells underscored the importance of addressing immune evasion through immune checkpoint blockade treatment.This was emphasized by the observed increase in antigen processing and presentation juxtaposed with T cell inactivation.In conclusion,our data supported the efficacy of immunotherapy combined with^(177)Lu-LNC1004 for cancer patients with FAP-positive tumors.

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.