PD-L1 has a heterogeneous and dynamic expression in gastric cancer with implications for immunoPET.

Introduction: This study aimed to investigate the dynamics of programmed death-ligand 1 (PD-L1) expression, spatial heterogeneity, and binding affinity of FDA-approved anti-PD-L1 antibodies (avelumab and atezolizumab) in gastric cancer. Additionally, we determined how PD-L1 glycosylation impacts antibody accumulation in gastric cancer cells. Methods: Dynamic PD-L1 expression was examined in NCIN87 gastric cancer cells. Comparative binding studies of avelumab and atezolizumab were conducted in gastric cancer models, both in vitro and in vivo. Antibody uptake in tumors was visualized through positron emission tomography (PET) imaging. PD-L1 glycosylation status was determined via Western blot analyses before and after PNGase F treatment. Results: Consistent findings revealed time-dependent PD-L1 induction in NCIN87 gastric cancer cells and spatial heterogeneity in tumors, as shown by PET imaging and immunofluorescence. Avelumab displayed superior binding affinity to NCIN87 cells compared to atezolizumab, confirmed by in vivo PET imaging and ex vivo biodistribution analyses. Notably, PD-L1 glycosylation at approximately 50 kDa was observed, with PNGase F treatment inducing a shift to 35 kDa in molecular weight. Tissue samples from patient-derived xenografts (PDXs) validated the presence of both glycosylated and deglycosylated PD-L1 (degPD-L1) forms in gastric cancer. Immunofluorescence microscopy and binding assays demonstrated enhanced avelumab binding post-deglycosylation. Discussion: This study provides an understanding of dynamic and spatially heterogeneous PD-L1 expression in gastric cancer. Anti-PD-L1 immunoPET was able to visualize gastric tumors, and PD-L1 glycosylation has significant implications for antibody recognition. These insights contribute to demonstrating the complexities of PD-L1 in gastric cancer, holding relevance for refining PD-L1 imaging-based approaches.

Phase 1b study to assess the safety, tolerability, and clinical activity of pamiparib in combination with temozolomide in patients with locally advanced or metastatic solid tumors.

BACKGROUND: Pamiparib is a potent, selective, poly (ADP-ribose) polymerase 1/2 inhibitor that demonstrates synthetic lethality in cells with breast cancer susceptibility gene mutations or other homologous recombination deficiency. This two-stage phase 1b study (NCT03150810) assessed pamiparib in combination with temozolomide (TMZ) in adult patients with histologically confirmed locally advanced and metastatic solid tumors. METHODS: Oral pamiparib 60 mg was administered twice daily. During the dose-escalation stage, increasing doses of TMZ (40-120 mg once daily pulsed or 20-40 mg once daily continuous) were administered to determine the recommended dose to be administered in the dose-expansion stage. The primary objectives were to determine safety and tolerability, maximum tolerated/administered dose, recommended phase 2 dose and schedule, and antitumor activity of pamiparib in combination with TMZ. Pharmacokinetics of pamiparib and TMZ and biomarkers were also assessed. RESULTS: Across stages, 139 patients were treated (dose escalation, n = 66; dose expansion, n = 73). The maximum tolerated dose of TMZ, which was administered during dose expansion, was 7-day pulsed 60 mg once daily. The most common treatment-emergent adverse events (TEAEs) were anemia (dose escalation, 56.1%; dose expansion, 63.0%), nausea (dose escalation, 54.5%; dose expansion, 49.3%), and fatigue (dose escalation, 48.5%; dose expansion, 47.9%). In the dose-escalation stage, four patients experienced dose-limiting toxicities (three neutropenia and one neutrophil count decreased). No TEAEs considered to be related to study drug treatment resulted in death. Antitumor activity was modest, indicated by confirmed overall response rate (dose escalation, 13.8%; dose expansion, 11.6%), median progression-free survival (3.7 and 2.8 months), and median overall survival (10.5 and 9.2 months). Administration of combination therapy did not notably impact pamiparib or TMZ pharmacokinetics. CONCLUSIONS: Pamiparib in combination with TMZ had a manageable safety profile. Further investigation of the efficacy of this combination in tumor types with specific DNA damage repair deficiencies is warranted.

Transferrin receptor in primary and metastatic breast cancer: Evaluation of expression and experimental modulation to improve molecular targeting.

BACKGROUND: Conjugation of transferrin (Tf) to imaging or nanotherapeutic agents is a promising strategy to target breast cancer. Since the efficacy of these biomaterials often depends on the overexpression of the targeted receptor, we set out to survey expression of transferrin receptor (TfR) in primary and metastatic breast cancer samples, including metastases and relapse, and investigate its modulation in experimental models. METHODS: Gene expression was investigated by datamining in twelve publicly-available datasets. Dedicated Tissue microarrays (TMAs) were generated to evaluate matched primary and bone metastases as well as and pre and post chemotherapy tumors from the same patient. TMA were stained with the FDA-approved MRQ-48 antibody against TfR and graded by staining intensity (H-score). Patient-derived xenografts (PDX) and isogenic metastatic mouse models were used to study in vivo TfR expression and uptake of transferrin. RESULTS: TFRC gene and protein expression were high in breast cancer of all subtypes and stages, and in 60-85% of bone metastases. TfR was detectable after neoadjuvant chemotherapy, albeit with some variability. Fluorophore-conjugated transferrin iron chelator deferoxamine (DFO) enhanced TfR uptake in human breast cancer cells in vitro and proved transferrin localization at metastatic sites and correlation of tumor burden relative to untreated tumor mice. CONCLUSIONS: TfR is expressed in breast cancer, primary, metastatic, and after neoadjuvant chemotherapy. Variability in expression of TfR suggests that evaluation of the expression of TfR in individual patients could identify the best candidates for targeting. Further, systemic iron chelation with DFO may upregulate receptor expression and improve uptake of therapeutics or tracers that use transferrin as a homing ligand.