Rusalatide Acetate (TP508) Mitigation of Genotoxic Radiation Damage in Human Lens Epithelial Cells

Cancer patients benefit from radiation therapy but can incur side effects to normal tissues including the ocular lens, leading to cataracts. Although not directly life threatening, cataract disease has major medical, economic, and social impacts on individuals, families, and society as a whole. Radiation-induced lens opacification is a complex event and has been attributed to DNA double strand breaks (DSB) in the germinative epithelium, leading to defective differentiation of lens fiber cells and subsequent abnormal folding of lens proteins. Rusalatide acetate (TP508) is a radio-modulating peptide that has been shown to increase survival of irradiated animals via activation of signal transduction pathways in endothelial cells, initiating repair of DSB, increasing NO levels and reversing of endothelial cell dysfunction. This investigation will determine if TP508 will have a similar effect on human lens epithelial cells (HLEC) and mitigate radiation-induced pathophysiological pathways that are associated with abnormal differentiation of fiber cells, abnormal protein folding and opacification. The hypothesis is that through the direct activation of molecular pathways in irradiated HLEC, TP508 treatment will mitigate or repair DSB and restore normal cell differentiation. In contrast to other investigative approaches that focus on a single downstream mechanism, this investigation will examine molecular activity of TP508 across multiple pathophysiological pathways associated with normal differentiation of HLEC. Study aims are to establish the molecular activity and optimum dosage thresholds, and timing of treatments of TP508 in mitigating X-ray or proton damage with single fraction exposures of 0.5, 1.0, 2.0, or 4 Gy in HLEC (CRL-11421 [B3], SRA01/04 and HLEpiC cells. Aim (1) is to determine drug toxicity levels using clonogenic survival assays and cell doubling times to identify the optimum TP508 concentration and administration schedule (before or after radiation) for producing protective effects on radiation induced HLEC viability. Aim (2) will determine if TP508 can maintain or restore normal cell differentiation required for normal protein folding, using the most optimized dosage and administration schedule established in Aim 1. Investigations will include the effects of TP508 on molecular markers and proteins associated with abnormal differentiation of lens fiber cells (CRYAB [αB-crystallin], CRYBB2 [βB2-crystallin]) and proteins involved in signaling pathways for apoptosis, necrosis, senescence, and mitotic catastrophe. Studies are expected to provide the following: (i) determine limits of toxicity with increasing doses of TP508 and the survival effect on irradiated HLEC at different doses applied before and after radiation; and (ii) identify if the molecular mechanisms and protein markers associated with the progression of lens opacification are mitigated by the optimum doses of TP508 (from Aim 1) in HLEC at different levels of radiation. Successfully developed, future investigations of TP508 could expand its application to mitigate additional ocular radiation therapy side effects including dry eye and retinopathy.Cataracts are the leading cause of preventable blindness worldwide and a frequent adverse effect of radiation therapy used to treat cancer patients. This study will investigate the regenerative activity and optimum dosage of an investigational peptide drug, rusalatide acetate (TP508), to mitigate radiation induced DNA damage to lens epithelial cells which has been suggested as the initiating event in cataract formation. Successfully developed, a drug to mitigate cataract progression could mean improved outcomes and health related quality of life for a significant population of people who are at risk of therapeutic and occupational exposures of radiation.