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

Abstract

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.

Trial registration: ClinicalTrials.gov NCT02687230 NCT03118349 NCT04199741.

Conflict of interest statement

Potential Conflicts of Interest

CMR has consulted regarding oncology drug development with Amgen, AstraZeneca, Celgene, Epizyme, Genentech/Roche, Ipsen, Jazz, Lilly, Pfizer, PharmaMar, Syros, and Vavotek. He serves on the scientific advisory boards of Bridge Medicines, Earli, and Harpoon Therapeutics. JSL has consulted for InVicro, TPG Capital, Longitude Capital, Curie Therapeutics, Earli and Sharp RTx. He serves on the scientific advisory boards of pHLIP, Clarity Pharmaceuticals, Evergreen Theragnostics and Telix Pharmaceuticals Ltd. He is a co-inventor on licensed technology to pHLIP, Elucida Oncology, Samus Therapeutics, CheMatech, Theragnostics, Daiichi Sankyo, Diaprost AB and Sharp RTx. KMT, JTP, CMR, and JSL are inventors on filed patents involving DLL3 antibodies.

©2022 American Association for Cancer Research.

Figures

Figure 1.

A) Representative structures of the unmodified SC16 antibody, the antibody-drug conjugate SC16LD6.5 (Rovalpituzumab tesirine), and the radioimmunoconjugate [177Lu]Lu-DTPA-CHX-A”-SC16. The cytotoxic moieties of each therapeutic are highlighted in blue. B) A radioligand binding assay of [177Lu]Lu-DTPA-CHX-A”-SC16 in H82 and A549 cells. Error bars represent SD (n=3). An unpaired, two-tailed t-test was performed (p-value = 0.001) C) DLL3 immunohistochemistry on subcutaneous tumor xenografts. Scale bar: 20 μm. See Figure S4 Mouse 108 for the lower magnification image of the H82 tumor DLL3 IHC and corresponding histology. D) The ex vivo biodistribution data of select organs from athymic mice bearing subcutaneous H82 xenografts after the administration of [177Lu]Lu-DTPA-CHX-A”-SC16 (10–30 μCi; 3 μg in 150 uL PBS; n=3 mice per time point) via tail vein. The tumor uptake at 72h was sufficiently blocked using 100-fold excess of unlabeled SC16 (p-value = 0.0212). See Figure S9 for the uptake in all organs collected. E) Representative whole body SPECT/CT images of athymic mice bearing subcutaneous H82 xenografts 120h after the administration of [177Lu]Lu-DTPA-CHX-A”-SC16 (1050–1100 μCi; 60–70 μg in 150 uL PBS) via tail vein. The tumors (indicated by white arrows) can clearly be delineated in the maximum intensity projection (MIP), coronal, and sagittal images.

Figure 2.

A) The average tumor volume of mice bearing H82 xenografts after treatment (error bars indicate SD; n=8–10). The averages were adjusted by including the final tumor volume of each mouse if the mouse reached its endpoint prior to 100 days post-treatment (e.g. if a mouse reached its endpoint on day 20, the volume of the tumor on day 20 was still included in the averages after day 20 despite the mouse being euthanized). B) Percent survival as a function of time for mice bearing H82 xenografts following the administration of treatment or vehicle. Log-rank tests were performed for comparing each treatment to saline cohort (shading indicates 95% CI; n=8–10; *** p-value = 0.0003, **** p-value < 0.0001). C) The median survival of mice bearing H82 xenografts post-treatment. Log-rank tests were performed for comparing each treatment to saline cohort (n=8–10; “und” = undefined; *** p-value = 0.0003, **** p-value < 0.0001). D) The average tumor volume of mice bearing Lu149 xenografts after treatment (error bars indicate SD; n=9–10). The averages were adjusted by including the final tumor volume of each mouse if the mouse reached its endpoint prior to 100 days post-treatment (e.g. if a mouse reached its endpoint on day 20, the volume of the tumor on day 20 was still included in the averages after day 20 despite the mouse being euthanized). E) Percent survival as a function of time for mice bearing Lu149 xenografts following the administration of treatment or vehicle. Log-rank tests were performed for comparing each treatment to saline cohort (shading indicates 95% CI; n=9–10; * p-value = 0.0108 and 0.0193 for 750 μCi [177Lu]Lu-DTPA-CHX-A”-SC16 and [177Lu]Lu-DTPA-CHX-A”-IgG, respectively; **** p-value < 0.0001). F) The median survival of mice bearing Lu149 xenografts post-treatment. Log-rank tests were performed for comparing each treatment to saline cohort (n=9–10; “und” = undefined; * p-value = 0.0108 and 0.0193 for 750 μCi [177Lu]Lu-DTPA-CHX-A”-SC16 and [177Lu]Lu-DTPA-CHX-A”-IgG, respectively; **** p-value < 0.0001).

Figure 3.

A) Representative H&E staining and Ki67 immunohistochemistry of residual tissues from tumor beds of mice that demonstrated complete responses (H82 mouse 114 and Lu149 mouse 428). Scale bar: 500 μm. B) Representative H&E staining, Ki67 immunohistochemistry and DLL3 immunohistochemistry of the tumor from a mouse that demonstrated a sustained partial response (H82 mouse 126). Scale bar: 2000 μm. C) Representative H&E staining, Ki67 immunohistochemistry and DLL3 immunohistochemistry of the tumor from a mouse that demonstrated a transient partial response (H82 mouse 122). Scale bar: 2000 μm.

Figure 4.

A-C) White blood cell (WBC) counts, red blood cell (RBC) counts, and platelet (PLT) counts of mice bearing H82 xenografts who received [177Lu]Lu-DTPA-CHX-A”-SC16. Complete blood count analyses were performed once a week on a subset of the animals used in the survival study (n=3–4). Twenty parameters were recorded, and three are represented. Values are represented as means with error bars indicating SD. Grey boxes indicate the mean ± SD of values collected from the entire cohort of H82-bearing mice two days prior to therapy administration. Grey dotted lines indicate the healthy range for female athymic mice. D-F) White blood cell (WBC) counts, red blood cell (RBC) counts, and platelet (PLT) counts of mice bearing Lu149 xenografts who received [177Lu]Lu-DTPA-CHX-A”-SC16. Complete blood count analyses were performed once a week on a subset of the animals used in the survival study (n=3–4). Twenty parameters were recorded, and three are represented. Values are represented as means with error bars indicating SD. Grey boxes indicate the mean ± SD of values collected from the entire cohort of Lu149-bearing mice two days prior to therapy administration. Grey dotted lines indicate the healthy range for female athymic mice. H-I) Box plots of the terminal alanine transaminase (ALT), aspartate transaminase (AST) and bilirubin serum levels from H82-bearing mice used in the survival study. Multiple t-tests were performed comparing each radiotherapy cohort to saline, and no significant differences were found (n=4–7). J-L) Box plots of the terminal alanine transaminase (ALT), aspartate transaminase (AST) and bilirubin serum levels from Lu149-bearing mice used in the survival study. Multiple t-tests were performed comparing each radiotherapy cohort to saline (n=5–10; ** p-value = 0.0044 and 0.0067 for 250 and 500 μCi [177Lu]Lu-DTPA-CHX-A”-SC16, respectively).