Targeting radioimmunotherapy of hepatocellular carcinoma with iodine (¹³¹I) metuximab injection: Clinical Phase I/II trials

Purpose: HAb18G/CD147 is a hepatocellular carcinoma (HCC)-associated antigen. We developed iodine (¹³¹I) metuximab injection (Licartin), a novel ¹³¹I-labeled HAb18G/CD147-specific monoclonal antibody F(ab’)₂ fragment, and evaluated its safety, pharmacokinetics, and clinical efficacy on HCC in Phase I/II trials.

Methods and Materials: In a Phase I trial, 28 patients were randomly assigned to receive the injection in 9.25-, 18.5-, 27.75-, or 37-MBq/kg doses by hepatic artery infusion. In a multicenter Phase II trial, 106 patients received the injection (27.75 MBq/kg) on Day 1 of a 28-day cycle. Response rate and survival rate were the endpoints.

Results: No life-threatening toxic effects were found. The safe dosage was 27.75 MBq/kg. The blood clearance fitted a biphasic model, and its half-life was 90.56–63.93 h. In the Phase II trial, the injection was found to be targeted and concentrated to tumor tissues. Of the 73 patients completing two cycles, 6 (8.22%) had a partial response, 14 (19.18%) minor response, and 43 (58.90%) stable disease. The 21-month survival rate was 44.54%. The survival rate of progression-free patients was significantly higher than that of patients with progressive disease after either one or two cycles (p < 0.0001 or p = 0.0019).

Conclusion: Iodine (¹³¹I) metuximab injection is safe and active for HCC patients.

Introduction

Primary liver cancer ranks second among cancers as a cause of death, owing to its high incidence rate, rapid progression, poor prognosis, and tumor recurrence (1). The mean natural survival time of patients with hepatocellular carcinoma (HCC), the most common type of primary liver cancer, is only 3.2 months, and the 5-year survival rate is 5% (1). Less than 20% of HCC patients are fit for traditional therapies, such as surgery or chemotherapy (1, 2). In addition, at least 85% of HCC patients in China also have liver cirrhosis, which makes therapy more difficult (1). Since the 1980s, radioimmunotherapy (RIT) has become a promising therapy for tumors, because the specificity of the antibodies and the killing power of the radionuclides tend to bring about better clinical efficacy with fewer side effects.

Iodine (¹³¹I) metuximab injection (brand name, Licartin; Chengdu Hoist Hitech Co., Ltd., Chengdu, China) is an iodine ¹³¹I-labeled murine monoclonal antibody (mAb) HAb18 F(ab’)₂ fragment against the HCC-associated antigen HAb18G/CD147. The mAb HAb18 (immunoglobulin G1) was obtained by using a cell suspension extracted from fresh human HCC tissues to immunize BALB/c mice and to prepare hybridoma (3, 4, 5). Its antigen, HAb18G/CD147, a member of the CD147 family, was highly expressed on HCC cells (6, 7). The binding rate of HAb18 to human 7721 hepatoma cells, determined by flow cytometry, was 99.55%, and the mean fluorescent intensity was 171.31. Immunohistochemistry performed with HAb18 showed that the positive rate of HCC staining was 75% (39 of 52) without cross-reaction to normal tissues (5). Metuximab was prepared by pepsin digestion of HAb18 to remove the Fc fragment. Its molecular weight ranged from 94 kd to 98 kd by analysis of nonreductive sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and the molecular weight of the heavy chain and light chain ranged 26–28 kd and 21–23 kd, respectively, by reductive SDS-PAGE analysis. Its titer was >1:8000 by immunofluorescence staining analysis on HCC cells, and its affinity constant to the recombined HAb18G/CD147 molecule was determined to be 6.32 × 10⁻¹⁰ mol/L by surface plasmon resonance analysis. A pharmacokinetics study conducted in BALB/c mice showed that the blood clearance of the iodine (¹³¹I) metuximab injection fitted a biphasic model, and the half life (t_1/2) in blood was 34.61 h (8). Biologic distribution analysis of metuximab in a human HCC xenografts model in BALB/c nude mice showed that the tumor/nontumor radiation absorbed dose ratio ranged from 2.51 ± 0.69 to 18.60 ± 2.05 (4, 9). The 30% and 50% effective doses of the iodine (¹³¹I) metuximab injection were, respectively, 133.2 and 370 MBq/kg for mice, equal to 15.54 and 43.29 MBq/kg for humans. The nontoxic dose in the long-term toxicity test was 277.5 MBq/kg for rats, equal to 45.88 MBq/kg for humans. The results of safety pharmacology studies showed that iodine (¹³¹I) metuximab injection caused no impairment to cardiovascular, respiratory, or nervous systems. The above results have all been sanctioned by the China State Food and Drug Administration (SFDA).

In the preliminary clinical study (approved by the Health Bureau of Shaanxi Province, China, 1999), the evidence of anti-HCC effects in 7 of 9 assessable HCC patients (77.78%) was observed, of whom 1 had complete response (CR), 1 partial response (PR), 1 minor response (MR), and 4 stable disease (SD). After the preliminary clinical study, we conducted Phase I and Phase II clinical trials to assess the safety, pharmacokinetics, and efficacy of iodine (¹³¹I) metuximab injection in HCC patients.