Inhibition of insulin-like growth factor-I receptor (IGF-IR) signaling and tumor cell growth by a fully human neutralizing anti-IGF-IR antibody.

Insulin-like growth factor-I receptor (IGF-IR) plays an important role in tumor cell growth and survival. On ligand stimulation, IGF-IR, a receptor tyrosine kinase, phosphorylates tyrosine residues on two major substrates, IRS-1 and Shc, which subsequently signal through the Ras/mitogen-activated protein kinase and phosphatidylinositol 3-kinase/AKT pathways. Here, we describe the characterization of a fully human anti-IGF-IR monoclonal antibody 19D12 that inhibits IGF binding and autophosphorylation of both IGF-IR/IGF-IR homodimers and IGF-IR/insulin receptor heterodimers. 19D12 does not recognize insulin receptor homodimers. In addition to inhibiting IGF-IR autophosphorylation, 19D12 also inhibits IRS-1 phosphorylation and activation of the major downstream signaling molecules AKT and extracellular signal-regulated kinase 1/2. Furthermore, the antibody down-regulates the total IGF-IR protein level and can exhibit antibody-dependent cellular cytotoxicity activity against a non-small cell adenocarcinoma cell line in vitro in the presence of isolated human natural killer cells. 19D12 binds tightly to the receptor, with an affinity of 3.8 pmol/L as measured by KinExA. In cell culture, 19D12 inhibits proliferation and soft agar growth of various tumor cell lines. In vivo, 19D12 inhibits the tumor growth of a very aggressive human ovarian tumor xenograft model A2780. These data support the development of this anti-IGF-IR monoclonal antibody as a promising anticancer agent.

Neutralizing anti-insulin-like growth factor receptor 1 antibodies inhibit receptor function and induce receptor degradation in tumor cells.

Insulin-like growth factor receptor 1 (IGFR1) plays a crucial role in oncogenic transformation [C. Sell et al., Mol. Cell. Biol., 14: 3604-3612,1994]. Compared with the normal human mammary epithelial cell line MCF12A, MCF7 human mammary carcinoma cells overexpress IGFR1 on the cell surface. To measure the effects of IGFR1 inhibition on tumor cells, we tested two mouse neutralizing antibodies against human IGFR1 in cell-based assays. Both MAB391 and anti-IR3 antibodies inhibit IGFR1 autophosphorylation upon IGF-I ligand stimulation with IC50s of 0.58 and 0.80 nM, respectively. When cells were treated with neutralizing anti-IGFR1 antibodies for > or = 4 h, the total receptor level was dramatically decreased. IGF-I-stimulated activation of AKT was also inhibited by anti-IGFR1 antibodies. Furthermore, MAB391 and anti-IR3 inhibited the growth of MCF7 cells in soft agar. In addition to MCF7 cells, MAB391 also inhibited IGFR1 autophosphorylation and induced IGFR1 down-modulation in HT29 colorectal and Du145 prostate cancer cells. Therefore, neutralizing antibodies against IGFR1 represent a valid approach to inhibit growth of tumor cells.

Screening for small molecule inhibitors of insulin-like growth factor receptor (IGF-1R) kinase: comparison of homogeneous time-resolved fluorescence and 33P-ATP plate assay formats.

Insulin-like growth factor receptor 1 (IGF-1R) plays a critical role in oncogenic transformation (1). IGF-1R is overexpressed in some tumors including breast, lung, cervical, and Wilms' tumors (2-6). Upon binding of IGF-I or IGF-II, IGF-1R, a tyrosine kinase, phosphorylates tyrosine residues on two major substrates, IRS-1 and Shc, which subsequently signal through the Ras/Raf and PI 3-kinase/AKT pathways (7). Extensive literature has shown that when the IGF-1R signaling pathway is blocked by antisense, dominant negative truncation or neutralizing antibodies, cellular transformation and tumor formation in mice is inhibited (8-18). Small molecule kinase inhibitors represent a valid approach to inhibit activity and downstream signalling of IGF-1R. To date, few potent and selective small molecule inhibitors of IGF-1R kinase activity have been reported. We expressed the tyrosine kinase domain of IGF-1R (IGF-1R/TK) in insect cells and subsequently purified the partially activated IGF-1R/TK. A compound library has been screened using a homogeneous time-resolved fluorescence (HTRF) assay. The hits generated by HTRF were then evaluated in a 33P ATP streptavidin-Flashplate assay (Flashplate). There was approximately 78% hit congruence between the two assay formats. One compound, C100, inhibited the IGF-1R kinase activity with an IC50 of 1 microM. C100 also inhibited IGF-1R autophosphorylation, AKT and MAPK activations in cells. This inhibitor provides a useful tool for studying IGF-1R in cells.

A fully human insulin-like growth factor-I receptor antibody SCH 717454 (Robatumumab) has antitumor activity as a single agent and in combination with cytotoxics in pediatric tumor xenografts.

The insulin-like growth factor-I receptor (IGF-IR) and its ligands (IGF-I and IGF-II) have been implicated in the growth, survival, and metastasis of a broad range of malignancies including pediatric tumors. Blocking the IGF-IR action is a potential cancer treatment. A fully human neutralizing monoclonal antibody, SCH 717454 (19D12, robatumumab), specific to IGF-IR, has shown potent antitumor effects in ovarian cancer in vitro and in vivo. In this study, SCH 717454 was evaluated in several pediatric solid tumors including neuroblastoma, osteosarcoma, and rhabdomyosarcoma. SCH 717454 is shown here to downregulate IGF-IR as well as inhibit IGF-IR and insulin receptor substrate-1 phosphorylation in pediatric tumor cells. IGF-IR and insulin receptor substrate-1 phosphorylation in the tumor cells. In vivo, SCH 717454 exhibits activity as a single agent and significantly inhibited growth of neuroblastoma, osteosarcoma, and rhabdomyosarcoma tumor xenografts. Combination of SCH 717454 with cisplatin or cyclophosphamide enhanced both the degree and the duration of the in vivo antitumor activity compared with single-agent treatments. Furthermore, SCH 717454 treatment markedly reduced Ki-67 expression and blood vessel formation in tumor xenografts, showing that the in vivo activity is derived from its inhibition of tumor cell proliferation and angiogenesis activity.