Interrogating the Theranostic Capacity of a MUC16-Targeted Antibody for Ovarian Cancer.

Aberrantly expressed glycans on mucins such as mucin-16 (MUC16) are implicated in the biology that promotes ovarian cancer (OC) malignancy. Here, we investigated the theranostic potential of a humanized antibody, huAR9.6, targeting fully glycosylated and hypoglycosylated MUC16 isoforms. Methods: In vitro and in vivo targeting of the diagnostic radiotracer [89Zr]Zr-DFO-huAR9.6 was investigated via binding experiments, immuno-PET imaging, and biodistribution studies on OC mouse models. Ovarian xenografts were used to determine the safety and efficacy of the therapeutic version, [177Lu]Lu-CHX-A″-DTPA-huAR9.6. Results: In vivo uptake of [89Zr]Zr-DFO-huAR9.6 supported in vitro-determined expression levels: high uptake in OVCAR3 and OVCAR4 tumors, low uptake in OVCAR5 tumors, and no uptake in OVCAR8 tumors. Accordingly, [177Lu]Lu-CHX-A″-DTPA-huAR9.6 displayed strong antitumor effects in the OVCAR3 model and improved overall survival in the OVCAR3 and OVCAR5 models in comparison to the saline control. Hematologic toxicity was transient in both models. Conclusion: PET imaging of OC xenografts showed that [89Zr]Zr-DFO-huAR9.6 delineated MUC16 expression levels, which correlated with in vitro results. Additionally, we showed that [177Lu]Lu-CHX-A″-DTPA-huAR9.6 displayed strong antitumor effects in highly MUC16-expressing tumors. These findings demonstrate great potential for 89Zr- and 177Lu-labeled huAR9.6 as theranostic tools for the diagnosis and treatment of OC.

Development and Validation of Nerve-Targeted Bacteriochlorin Sensors.

We report an innovative approach to producing bacteriochlorins (bacs) via formal cycloaddition by subjecting a porphyrin to a trimolecular reaction. Bacs are near-infrared probes with the intrinsic ability to serve in multimodal imaging. However, despite their ability to fluoresce and chelate metal ions, existing bacs have thus offered limited ability to label biomolecules for target specificity or have lacked chemical purity, limiting their use in bio-imaging. In this work, bacs allowed a precise and controlled appending of clickable linkers, lending the porphyrinoids substantially more chemical stability, clickability, and solubility, rendering them more suitable for preclinical investigation. Our bac probes enable the targeted use of biomolecules in fluorescence imaging and Cerenkov luminescence for guided intraoperative imaging. Bacs' capacity for chelation provides opportunities for use in non-invasive positron emission tomography/computed tomography. Herein, we report the labeling of bacs with Hs1a, a (NaV1.7)-sodium-channel-binding peptide derived from the Chinese tarantula Cyriopagopus schmidti to yield Bac-Hs1a and radiolabeled Hs1a, which shuttles our bac sensor(s) to mouse nerves. In vivo, the bac sensor allowed us to observe high signal-to-background ratios in the nerves of animals injected with fluorescent Bac-Hs1a and radiolabeled Hs1a in all imaging modes. This study demonstrates that Bac-Hs1a and [64Cu]Cu-Bac-Hs1a accumulate in peripheral nerves, providing contrast and utility in the preclinical space. For the chemistry and bio-imaging fields, this study represents an exciting starting point for the modular manipulation of bacs, their development and use as probes for diagnosis, and their deployment as formidable multiplex nerve-imaging agents for use in routine imaging experiments.

Delta-like ligand 3-targeted radioimmunotherapy for neuroendocrine prostate cancer.

Neuroendocrine prostate cancer (NEPC) is a lethal subtype of prostate cancer with limited meaningful treatment options. NEPC lesions uniquely express delta-like ligand 3 (DLL3) on their cell surface. Taking advantage of DLL3 overexpression, we developed and evaluated lutetium-177 (177Lu)-labeled DLL3-targeting antibody SC16 (177Lu-DTPA-SC16) as a treatment for NEPC. SC16 was functionalized with DTPA-CHX-A" chelator and radiolabeled with 177Lu to produce 177Lu-DTPA-SC16. Specificity and selectivity of 177Lu-DTPA-SC16 were evaluated in vitro and in vivo using NCI-H660 (NEPC, DLL3-positive) and DU145 (adenocarcinoma, DLL3-negative) cells and xenografts. Dose-dependent treatment efficacy and specificity of 177Lu-DTPA-SC16 radionuclide therapy were evaluated in H660 and DU145 xenograft-bearing mice. Safety of the agent was assessed by monitoring hematologic parameters. 177Lu-DTPA-SC16 showed high tumor uptake and specificity in H660 xenografts, with minimal uptake in DU145 xenografts. At all three tested doses of 177Lu-DTPA-SC16 (4.63, 9.25, and 27.75 MBq/mouse), complete responses were observed in H660-bearing mice; 9.25 and 27.75 MBq/mouse doses were curative. Even the lowest tested dose proved curative in five (63%) of eight mice, and recurring tumors could be successfully re-treated at the same dose to achieve complete responses. In DU145 xenografts, 177Lu-DTPA-SC16 therapy did not inhibit tumor growth. Platelets and hematocrit transiently dropped, reaching nadir at 2 to 3 wk. This was out of range only in the highest-dose cohort and quickly recovered to normal range by week 4. Weight loss was observed only in the highest-dose cohort. Therefore, our data demonstrate that 177Lu-DTPA-SC16 is a potent and safe radioimmunotherapeutic agent for testing in humans with NEPC.

Radioimmunotherapy Targeting Delta-like Ligand 3 in Small Cell Lung Cancer Exhibits Antitumor Efficacy with Low Toxicity.

PURPOSE: Small cell lung cancer (SCLC) is an exceptionally lethal form of lung cancer with limited treatment options. Delta-like ligand 3 (DLL3) is an attractive therapeutic target as surface expression is almost exclusive to tumor cells. EXPERIMENTAL DESIGN: We radiolabeled the anti-DLL3 mAb SC16 with the therapeutic radioisotope, Lutetium-177. [177Lu]Lu-DTPA-CHX-A"-SC16 binds to DLL3 on SCLC cells and delivers targeted radiotherapy while minimizing radiation to healthy tissue. RESULTS: [177Lu]Lu-DTPA-CHX-A"-SC16 demonstrated high tumor uptake with DLL3-target specificity in tumor xenografts. Dosimetry analyses of biodistribution studies suggested that the blood and liver were most at risk for toxicity from treatment with high doses of [177Lu]Lu-DTPA-CHX-A"-SC16. In the radioresistant NCI-H82 model, survival studies showed that 500 µCi and 750 µCi doses of [177Lu]Lu-DTPA-CHX-A"-SC16 led to prolonged survival over controls, and 3 of the 8 mice that received high doses of [177Lu]Lu-DTPA-CHX-A"-SC16 had pathologically confirmed complete responses (CR). In the patient-derived xenograft model Lu149, all doses of [177Lu]Lu-DTPA-CHX-A"-SC16 markedly prolonged survival. At the 250 µCi and 500 µCi doses, 5 of 10 and 7 of 9 mice demonstrated pathologically confirmed CRs, respectively. Four of 10 mice that received 750 µCi of [177Lu]Lu-DTPA-CHX-A"-SC16 demonstrated petechiae severe enough to warrant euthanasia, but the remaining 6 mice demonstrated pathologically confirmed CRs. IHC on residual tissues from partial responses confirmed retained DLL3 expression. Hematologic toxicity was dose-dependent and transient, with full recovery within 4 weeks. Hepatotoxicity was not observed. CONCLUSIONS: Together, the compelling antitumor efficacy, pathologic CRs, and mild and transient toxicity profile demonstrate strong potential for clinical translation of [177Lu]Lu-DTPA-CHX-A"-SC16.

Molecular Imaging of Neuroendocrine Prostate Cancer by Targeting Delta-Like Ligand 3.

Treatment-induced neuroendocrine prostate cancer (NEPC) is a lethal subtype of castration-resistant prostate cancer. Using the 89Zr-labeled delta-like ligand 3 (DLL3) targeting antibody SC16 (89Zr-desferrioxamine [DFO]-SC16), we have developed a PET agent to noninvasively identify the presence of DLL3-positive NEPC lesions. Methods: Quantitative polymerase chain reaction and immunohistochemistry were used to compare relative levels of androgen receptor (AR)-regulated markers and the NEPC marker DLL3 in a panel of prostate cancer cell lines. PET imaging with 89Zr-DFO-SC16, 68Ga-PSMA-11, and 68Ga-DOTATATE was performed on H660 NEPC-xenografted male nude mice. 89Zr-DFO-SC16 uptake was corroborated by biodistribution studies. Results: In vitro studies demonstrated that H660 NEPC cells are positive for DLL3 and negative for AR, prostate-specific antigen, and prostate-specific membrane antigen (PSMA) at both the transcriptional and the translational levels. PET imaging and biodistribution studies confirmed that 89Zr-DFO-SC16 uptake is restricted to H660 xenografts, with background uptake in non-NEPC lesions (both AR-dependent and AR-independent). Conversely, H660 xenografts cannot be detected with imaging agents targeting PSMA (68Ga-PSMA-11) or somatostatin receptor subtype 2 (68Ga-DOTATATE). Conclusion: These studies demonstrated that H660 NEPC cells selectively express DLL3 on their cell surface and can be noninvasively identified with 89Zr-DFO-SC16.