The long-term objective of the proposed study is to develop a monoclonal antibody that inhibits the progression of diabetic retinopathy. Insulin-like growth factor-I (IGF-I) has been implicated in both endothelial dysfunction as well as the proliferative phase of the disease. However directly inhibiting the IGF-I receptor may be lead to neurotoxicity. Following exposure to hyperglycemia, endothelial cells utilize both the PI-3 and MAP kinase pathways to activate changes in endothelial cell permeability and angiogenesis. However unlike cells exposed to normal glucose these pathways are activated in response to IGF-I by an alternative mechanism that requires tyrosine phosphorylation of the transmembrane protein, SHPS-1. SHPS-1 is phosphorylated directly by the IGF-I receptor leading to recruitment of a complex of signaling proteins. For this complex to be activated in response to hyperglycemia plus IGF-I, it must associate with a membrane protein termed integrin associated protein (IAP). Our preliminary studies have shown that in early retinopathy, capillary leakage and leukostasis can be inhibited by disrupting IAP/SHPS-1 association. Additionally IAP knockout mice do not develop increased capillary permeability in spite of longstanding diabetes therefore it appears that IAP/SHPS-1 association is required in vivo for retinopathy progression. The purpose of these studies will be to determine if disrupting IAP/SHPS-1 results in failure of the SHPS-1 complex to assemble normally on endothelial cells and activate the appropriate downstream signaling molecules that mediate endothelial dysfunction. We will determine if a polyclonal antibody direct against amino acids 71-80 in rat IAP has efficacy in vivo. The purified antibody will be injected into diabetic rats and its effects on capillary leakage, leukostasis and endothelial cell apoptosis determined. Subsequently a monoclonal antibody directed against amino acids 71-80 in human IAP will be developed and tested to determine if it inhibits IGF-I stimulated signaling as well as changes in endothelial tube formation and cell permeability. To obtain a monoclonal antibody that can be administered to humans safely it will be necessary to humanize the murine form. A clone secreting the murine antibody will be isolated and cDNAs corresponding to heavy and light chains will be amplified using rtPCR then the cDNAs will be sequenced. These studies should definitively test the hypothesis that inhibiting IGF-I actions by inhibiting SHPS-1/IAP association in endothelial cells in culture and in capillaries in rats inhibis pathophysiologic changes that occur in diabetic retinopathy. If the results of these studies show that the antibody is effective, during phase II studies a humanized form of the monoclonal antibody will be prepared, purified and its effects determined. The long term objective would be to administer this antibody to diabetic patients with early signs of retinopathy to determine if it has efficacy in inhibiting both the early events and preventing late stage manifestations of this disease. Since diabetic retinopathy is the leading cause of blindness in working age adults, there is a need for new therapies that are directed toward treatment of this complication.
This proposal is directed toward the development of a monoclonal antibody as a drug to be administered to patients with diabetic retinopathy. Diabetic retinopathy is the leading cause of blindness in working age adults (25-74 years). As such it represents a significant public health problem. Drugs that are currently available that inhibit thi problem are effective in approximately 1/3 of patients. The drug to be developed functions by a mechanism that is different than those drugs and therefore has the potential to improve the prognosis of this disease in 2/3 of the affected patients. The work in this proposal will determine if this approach is feasible using animal models of this disease state.