Clinical Study on Noninvasive Evaluation of Ivonescimab Antibody Distribution and Expression in Esophageal Cancer Patients by 89Zr-AK112 PET Imaging

1.1. Epidemiological Characteristics of Esophageal Cancer Esophageal cancer (EC) is one of the most common malignant tumors worldwide. In 2022, there were 511,054 new EC cases globally, with a crude incidence rate of 6.5 per 100,000 cases and an ASIR of 5.0 per 100,000. China reported 224,012 new EC cases, accounting for 43.8% of the global total, ranking first worldwide; the crude incidence rate was 15.9 per 100,000, and the ASMR was 8.3 per 100,000. Globally, there were 445,391 deaths from esophageal cancer, with a crude mortality rate of 5.7 per 100,000 and an ASMR of 4.3 per 100,000. China recorded 187,467 deaths from esophageal cancer, accounting for 42.1% of the global total, ranking first worldwide; the crude mortality rate was 13.3 per 100,000, and the ASMR was 6.7 per 100,000. Although the incidence and mortality rates of esophageal cancer in China showed a downward trend between 2000 and 2018, the country remains one of the high-incidence regions. In 2022, esophageal cancer ranked 7th among newly diagnosed cancers in China and 5th among cancer-related deaths, indicating a severe disease burden. Esophageal squamous cell carcinoma (ESCC) and esophageal adenocarcinoma (EAC) are the two main histological subtypes of EC. In China, ESCC predominates, accounting for approximately 90%.

1.2. Current Status of Neoadjuvant Therapy for Esophageal Cancer Approximately 70% of esophageal squamous cell carcinoma (ESCC) patients are diagnosed at locally advanced stages, where direct surgical intervention yields suboptimal outcomes and carries high recurrence risks. Currently, surgery, chemotherapy, and radiotherapy constitute the three primary treatment modalities for esophageal cancer. For locally advanced ESCC, either surgical resection alone or surgical resection combined with adjuvant chemoradiotherapy demonstrates limited efficacy, with a high propensity for local recurrence and distant metastasis postoperatively, adversely affecting overall prognosis and survival. Over the past three decades, researchers have explored various neoadjuvant regimens (neoadjuvant chemotherapy, neoadjuvant radiotherapy, neoadjuvant chemoradiotherapy) aimed at reducing tumor volume and eliminating potential metastatic cancer cells at an early stage, thereby facilitating subsequent surgical treatment and improving patient survival outcomes.

Neoadjuvant chemotherapy (nCT) has increasingly been employed in recent years as an adjuvant therapy for malignant tumors. The theoretical advantages of neoadjuvant chemotherapy include: ① reducing tumor stage and shrinking tumor volume, thereby increasing the rate of surgical resection; ② controlling and treating micro-metastases in the body to reduce recurrence rates; ③ chemotherapeutic agents can reach tumor tissues in sufficient quantities through the intact blood supply system; ④ evaluating the sensitivity of chemotherapeutic agents in vivo to guide postoperative treatment.

Currently, the majority of neoadjuvant chemotherapy regimens are platinum-based combination regimens, with cisplatin (DDP) combined with fluorouracil (5-FU) being the most commonly used. In the randomized study JCOG9907 conducted in Japan, a total of 330 subjects were enrolled, with 164 assigned to the nCT group and 166 to the control group (surgical group alone). The nCT group received two cycles of FP regimen induction chemotherapy preoperatively, and the results demonstrated a 9% increase in 5-year survival rate compared to the control group (P=0.01). This study confirmed the efficacy of the FP regimen, establishing it as a standard neoadjuvant chemotherapy regimen for stage II and III esophageal cancer in Japan. The study by Leone AG et al. also validated the effectiveness of the FP regimen, showing that the nCT group (n=55) receiving FP regimen preoperatively had significantly improved disease-free survival (P=0.003) and overall survival (P=0.016) compared to the control group (n=57). In recent years, the emergence of new chemotherapeutic agents such as paclitaxel, oxaliplatin, docetaxel, and nedaplatin, along with immunotherapy drugs, has provided more options for neoadjuvant chemotherapy regimens, opening new avenues for neoadjuvant treatment of esophageal cancer.

1.3 In preclinical studies, it was found that anti-vascular endothelial growth factor (VEGF) and anti-PD-(L)1 antibodies exhibit synergistic antitumor activity. Anti-VEGF not only inhibits angiogenesis but also enhances the transport and infiltration of immune effector cells into the tumor microenvironment, modulates T regulatory cells and myeloid-derived suppressor cells, thereby creating an immunoregulatory environment that amplifies the efficacy of anti-PD-(L)1 inhibitors. Studies have demonstrated that the combination of anti-PD-(L)1 antibodies with anti-angiogenic agents demonstrates antitumor activity and tolerable safety in advanced solid tumors.

Ivonesimab (also known as AK112 or SMT112) is a first-in-class humanized bispecific antibody targeting PD-1 and VEGF-A, with its anti-PD-1 ScFv attached to the C-terminus of each anti-VEGF heavy chain. Ivonesimab has an iso-tetrameric structure composed of two heavy chains from the IgG1 subclass and two light chains from the kappa subclass, covalently linked via disulfide bonds. It is modified at the Fc region to eliminate antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity. Studies have demonstrated that ivonesimab exhibits enhanced binding affinity to PD-1 in the presence of VEGF. Consequently, concurrent blockade of PD-1 and VEGF may yield enhanced antitumor activity and improved safety compared to the sole combination of anti-PD-L1 and anti-VEGF therapies. Recent literature has reported a phase 1b study of ivonesimab (a bispecific antibody targeting programmed cell death protein-1 and vascular endothelial growth factor) as a first-or second-line therapy for advanced or metastatic immunotherapy-naïve non-small cell lung cancer (NSCLC). According to this phase 1b study, ivonesimab monotherapy demonstrated tolerable safety in patients with locally advanced or metastatic NSCLC, regardless of histological or PD-L1 status. Ivonesimab also exhibited dose-dependent antitumor activity, particularly in PD-L1-positive patients receiving ivonesimab at doses ≥20 mg/kg as first-line therapy.

1.4 Effective Biomarker of Imotacitinib As a humanized bispecific antibody targeting PD-1 and VEGF-A, imotacitinib exhibits high specificity for binding PD-1 and VEGF-A in vivo. This critical property was systematically validated in a recent molecular imaging study using positron emission tomography (PET). The study employed radionuclide-labeled imotacitinib to construct an imotacitinib PET probe, enabling non-invasive and dynamic monitoring of drug distribution and targeting behavior in living organisms. The PET probe demonstrated superior target tissue enrichment in the HCT-116 colorectal cancer xenograft model. In vivo PET imaging revealed sustained time-dependent uptake in the tumor region, peaking at 48 hours post-administration at 13.73 ± 0.95% ID/g, indicating strong tumor retention. Blocking experiments (pre-injection of excess imotacitinib) significantly reduced tumor uptake to 5.20 ± 0.10% ID/g (P=0.00011), strongly supporting that its in vivo targeting is mediated by PD-1/VEGF-A-specific interactions rather than nonspecific accumulation. At 48 hours, the tumor-to-muscle signal-to-noise ratio (T/M ratio) reached 15.62, with an excellent target-to-background ratio explaining the superior efficacy and safety of imotacitinib. Furthermore, in vitro distribution studies confirmed that the retention levels of this antibody in non-target organs such as the liver and blood were significantly lower than those in tumor tissues, suggesting favorable pharmacokinetic properties that may reduce associated potential toxicity risks. Histopathological analysis (H\&E staining) demonstrated the absence of inflammatory, necrotic, or other pathological injury signs in major organs (including the heart, liver, spleen, and kidneys), indicating that evolocimab exhibits good biocompatibility and tolerable safety characteristics.