Histopathological analyses of the antitumor activity of anti-glypican-3 antibody (GC33) in human liver cancer xenograft models: The essential role of macrophages

Abstract

Previously, we demonstrated the antitumor efficacy of the antiglypican-3 (GPC3) antibody GC33 in several human liver cancer xenograft models and the important role of antibody-dependent cellular cytotoxicity (ADCC) in the antitumor mechanism of GC33. Involvement of other mechanisms such as modulation of the functions of GPC3 in antitumor activity remains to be elucidated. In this study, we investigated histopathologically time-course changes in xenografts in mice following a single administration of GC33 to clarify the morphological changes contributing to the tumor growth inhibition of GC33, including the changes in GPC3-related factors/components [proliferation, extracelluar matrices (ECMs) and macrophage]. Histopathological changes peaked 3-5 d after GC33 administration and included increased tumor cell death, tumor cells with round morphology, multinucleated tumor cells and small spindle/round-like cells (mostly F4/80-positive macrophages). No direct effects of GC33 on proliferation activity of tumor cells were observed. Meanwhile, alteration of ECM structures and a remarkable increase in macrophages was noted in the GC33-treated group. Increase in macrophages was observed mainly in the outer layer of tumor nodules; the area of the increase approximately included the area where the change in tumor cells and ECMs were observed. Interestingly, depletion of macrophages in the xenograft models resulted in a marked reduction of the antitumor activity of GC33. In the in vitro ADCC assay, ADCC was only slightly induced by mouse peritoneal macrophages. These data suggest that macrophages play an important role in the antitumor activity of GC33, which is not likely to be direct ADCC by macrophages themselves.

Validation of glypican-3-specific scFv isolated from paired display/secretory yeast display library

“…Expression on the cell surface makes GPC3 an attractive target for antibody-directed therapy. Another group has shown that a murine anti-hGPC3 antibody induces antibody-dependent cytotoxicity that manifests an anti-tumor effect in a xenograft animal model of hepatocellular carcinoma [31]; this antibody has subsequently been humanized [18] and is entering human clinical trials. Thus, available evidence suggests that glypican-3 is a rational target for humoral and potentially chimeric immunotherapy for HCC.…”

Therapeutic Potential of Targeting Glypican-3 in Hepatocellular Carcinoma

“…By using human peripheral blood mononuclear cells (PBMCs) depleted of either CD56+ or CD14+ cells, they show that the ADCC is carried out primarily by CD56 + natural killer cells, while additional studies suggest tumor-associated macrophages play a role in the antitumor effect [40]. They show tumor infiltration by macrophages, but also consider mechanisms other than ADCC such as GPC3 modulation.…”

Glypican-3: A new target for cancer immunotherapy

“…Based on these evidences, they observed the involvements of infiltrated TAM in anti-GPC3 immunotherapy model using GC33, showing macrophages may play an important role in the anti-tumor activity of GC33 by non-ADCC mechanisms such as modulation of GPC3 functions 45. In addition, GC33 does not directly inhibit the proliferation of GPC3-positive tumor cells 45. To fully evaluate GPC3-targeted antibody therapy, the mAbs that target different functional domains (including the HS chain) of GPC3 would be useful.…”

“…investigated the relationship between membrane expression of GPC3 and recruitment of tumor-associated macrophage (TAM) 43,44. Based on these evidences, they observed the involvements of infiltrated TAM in anti-GPC3 immunotherapy model using GC33, showing macrophages may play an important role in the anti-tumor activity of GC33 by non-ADCC mechanisms such as modulation of GPC3 functions 45. In addition, GC33 does not directly inhibit the proliferation of GPC3-positive tumor cells 45.…”