A Phase II Study Evaluating PD-L1 Expression in Non-Small Cell Lung Cancer Using [99mTc]NM-01 SPECT/CT, a Technetium-99m Radiolabeled Anti-PD-L1 Single Domain Antibody

Introduction: Programmed death-ligand 1 (PD-L1) is a transmembrane protein expressed on the surface of cancer and immune cells. Its pivotal role lies in modulating immune responses by engaging with the programmed cell death protein 1 (PD-1) receptor, leading to the suppression of immune activity. PD-1/PD-L1 checkpoint inhibitor therapy is a standard treatment for advanced non-small cell lung cancer (NSCLC). However, assessment of tumoral PD-L1 by immunohistochemistry (IHC) is invasive and unpredictive of response to PD-1/PD-L1 inhibitor underscoring the need for a predictive tool to evaluate PD-L1 expression which is non-invasive and capable of capturing multiple lesions at multiple time points during treatment. The primary objective of this study was to quantify PD-L1 expression in primary and metastatic lesions in NSCLC using [99mTc]NM-01 SPECT/CT, and compare imaging to PD-L1 expression determined by IHC. We hypothesized that imaging-derived PD-L1 metrics correlates with IHC and that heterogeneity of PD-L1 expression exists between lesions in individual subjects.

Methods: This study was a Phase 2, single-site, non-randomized diagnostic imaging trial (NCT04992715). Subjects provided informed consent and underwent physical and vital signs examinations, electrocardiogram, blood and urine tests prior to receiving [99mTc]NM-01. PD-L1 expression by IHC was obtained from histopathology results dated within past 3 months. Subjects were administered a single intravenous dose of [99mTc]NM-01, approximately 370 MBq (± 10%) and underwent thoracic SPECT/CT scan on a Siemens Intevo scanner two hours post-injection(p.i). A low-dose CT scan was performed for anatomical localization and attenuation correction and image reconstruction using xSPECT Broad Quantification workflow allowed semiquantitative uptake measurements. The primary parameter used for image analysis was T:BP, the ratio between [99mTc]NM-01 uptake in tumor (T) and the blood pool (BP) on the attenuation corrected images, calculated as the ratio of SUVmax(T) and SUVmax(BP). Subjects underwent physical and vital signs examination prior to [99mTc]NM-01 injection and at 30, 60, and 180 minutes p.i. Between Days 5-7 post-injection, subjects visited the clinic for AE safety follow-up and blood tests. An end-of-study safety telephone interview was conducted between Days 10-12 p.i. Blood serum samples collected prior to injection and 10-16 weeks p.i. were tested for anti-drug antibodies against NM-01 using an electrochemiluminescence assay.

Results: Eight subjects (median age 61.5y, 4M, 4F) with metastatic NSCLC were included and completed this study. Tumor uptake against background tissue was observed two hours after [99mTc]NM-01 injection in all subjects. A significant correlation was noted between the primary SPECT/CT parameter, T:BP and PD-L1 expression by IHC (mean (SD) T:BP = 2.62 (0.96); r=0.768, p=0.013) when the T:BP was matched to the lesion from which biopsy tissue sample was obtained. Most subjects with thoracic metastases (n=5/7) exhibited over 25% heterogeneity in PD-L1 expression between primary tumors and metastases, with 13/23 (57%) metastatic lesions showing >25% difference between primary and metastatic tumor T:BPs and 8/23 (35%) exhibiting >50% difference (Figure 1). Three subjects reported AEs ranging Grade 1-3 and one subject experienced an SAE, none were attributed to the tracer. No changes from baseline were noted in laboratory assessments and no anti-drug antibodies were formed post [99mTc]NM-01 administration, highlighting a favorable safety profile.

Conclusions: This study demonstrated the efficacy of [99mTc]NM-01 SPECT/CT in assessing PD-L1 expression, revealing a significant correlation with PD-L1 IHC, and highlighting heterogeneity in PD-L1 expression. [99mTc]NM-01 SPECT/CT has the potential to be used as a non-invasive baseline assessment and monitoring of changes in PD-L1 expression levels during PD-1/PD-L1 checkpoint inhibitor therapy with detailed assessment of inter-lesional heterogeneity.