Ligand-Specific Antibodies to Insulin-Like Growth Factors Suppress Intestinal Polyp Formation in Apc+/− Mice

Immune targeting of autocrine IGF2 hampers rhabdomyosarcoma growth and metastasis

Background

Insulin-like Growth Factor Receptor-1 (IGF1R) system sustains the genesis of rhabdomyosarcoma through IGF2 autocrine overexpression. While several IGF1R-targeted strategies have been investigated to interphere with rhabdomyosarcoma growth, no attempt to neutralize IGF2 has been reported. We therefore studied the possibility to hamper rhabdomyosarcoma growth with passive and active immune approaches targeting IGF2.

Methods

A murine model developing IGF2-overexpressing pelvic rhabdomyosarcoma, along with IGF2-independent salivary carcinoma, was used to investigate the efficacy and specificity of passive anti-IGFs antibody treatment. Active vaccinations with electroporated DNA plasmids encoding murine or human IGF2 were performed to elicit autochthonous anti-IGF2 antibodies. Vaccinated mice received the intravenous injection of rhabdomyosarcoma cells to study the effects of anti-IGF2 antibodies against developing metastases.

Results

Passive administration of antibodies neutralizing IGFs delayed the onset of IGF2-overexpressing rhabdomyosarcoma but not of IGF2-independent salivary carcinoma. A DNA vaccine against murine IGF2 did not elicit antibodies, even when combined with Treg-depletion, while a DNA vaccine encoding the human IGF2 gene elicited antibodies crossreacting with murine IGF2. Mice with anti-IGF2 antibodies were partially protected against the metastatic growth of IGF2-addicted rhabdomyosarcoma cells.

Conclusions

Immune targeting of autocrine IGF2 inhibited rhabdomyosarcoma genesis and metastatic growth.

Antibody-based inhibition of circulating DLK1 protects from estrogen deficiency-induced bone loss in mice

Soluble delta-like 1 homolog (DLK1) is a circulating protein that belongs to the Notch/Serrate/delta family, which regulates many differentiation processes including osteogenesis and adipogenesis. We have previously demonstrated an inhibitory effect of DLK1 on bone mass via stimulation of bone resorption and inhibition of bone formation. Further, serum DLK1 levels are elevated and positively correlated to bone turnover markers in estrogen (E)-deficient rodents and women. In this report, we examined whether inhibition of serum DLK1 activity using a neutralizing monoclonal antibody protects from E deficiency-associated bone loss in mice. Thus, we generated mouse monoclonal anti-mouse DLK1 antibodies (MAb DLK1) that enabled us to reduce and also quantitate the levels of bioavailable serum DLK1 in vivo. Ovariectomized (ovx) mice were injected intraperitoneally twice weekly with MAb DLK1 over a period of one month. DEXA-, microCT scanning, and bone histomorphometric analyses were performed. Compared to controls, MAb DLK1 treated ovx mice were protected against ovx-induced bone loss, as revealed by significantly increased total bone mass (BMD) due to increased trabecular bone volume fraction (BV/TV) and inhibition of bone resorption. No significant changes were observed in total fat mass or in the number of bone marrow adipocytes. These results support the potential use of anti-DLK1 antibody therapy as a novel intervention to protect from E deficiency associated bone loss.

Obesity, type 2 diabetes, and cancer: the insulin and IGF connection

Epidemiological studies suggest a positive association between obesity and type 2 diabetes mellitus (T2D) with the risk of cancer and cancer-related mortality. Insulin resistance, hyperinsulinemia, increased levels of IGF, elevated levels of steroid and peptide hormones, and inflammatory markers appear to play a role in the connection between these different diseases. Medications, such as metformin and exogenous insulin, used to treat T2D may affect the risk of cancer and cancer-related mortality. Newer therapies targeting the insulin and IGF1 systems are being developed for use in cancer therapy.

A candidate targeting molecule of insulin-like growth factor-I receptor for gastrointestinal cancers

Advances in molecular research in cancer have brought new therapeutic strategies into clinical usage. One new group of targets is tyrosine kinase receptors, which can be treated by several strategies, including small molecule tyrosine kinase inhibitors (TKIs) and monoclonal antibodies (mAbs). Aberrant activation of growth factors/receptors and their signal pathways are required for malignant transformation and progression in gastrointestinal (GI) carcinomas. The concept of targeting specific carcinogenic receptors has been validated by successful clinical application of many new drugs. Type I insulin-like growth factor (IGF) receptor (IGF-IR) signaling potently stimulates tumor progression and cellular differentiation, and is a promising new molecular target in human malignancies. In this review, we focus on this promising therapeutic target, IGF-IR. The IGF/IGF-IR axis is an important modifier of tumor cell proliferation, survival, growth, and treatment sensitivity in many malignant diseases, including human GI cancers. Preclinical studies demonstrated that downregulation of IGF-IR signals reversed the neoplastic phenotype and sensitized cells to anticancer treatments. These results were mainly obtained through our strategy of adenoviruses expressing dominant negative IGF-IR (IGF-IR/dn) against gastrointestinal cancers, including esophagus, stomach, colon, and pancreas. We also summarize a variety of strategies to interrupt the IGFs/IGF-IR axis and their preclinical experiences. Several mAbs and TKIs targeting IGF-IR have entered clinical trials, and early results have suggested that these agents have generally acceptable safety profiles as single agents. We summarize the advantages and disadvantages of each strategy and discuss the merits/demerits of dual targeting of IGF-IR and other growth factor receptors, including Her2 and the insulin receptor, as well as other alternatives and possible drug combinations. Thus, IGF-IR might be a candidate for a molecular therapeutic target in human GI carcinomas.