Cancer patients benefit from radiation therapy but can incur side effects to non-targeted tissues includingcataracts. Although not directly life threatening, cataract disease has major medical, economic, and socialimpacts on individuals, families, and society as a whole. Radiation-induced lens opacification is a complexevent and has been attributed to DNA double strand breaks (DSB) in the germinative epithelium, leading todefective differentiation of lens fiber cells and subsequent abnormal folding of lens proteins. Rusalatideacetate (TP508) is a radio-modulating peptide that has been shown to increase survival of irradiatedanimals via activation of signal transduction pathways in endothelial cells, initiating repair of DSB, increasingNO levels and reversing of endothelial cell dysfunction. This investigation will determine if, in the absence ofendothelial cells, TP508 will have a similar effect on human lens epithelial cells (HLEC) and mitigateradiation induced pathophysiological pathways that lead to DSB. The hypothesis is that through the directactivation of molecular pathways in irradiated HLEC, TP508 treatment will mitigate or repair DSB. Incontrast to other investigative approaches that focus on a single downstream mechanism, this investigationwill examine molecular activity of TP508 across multiple pathophysiological pathways associated with thehealth of HLEC. Study aims are to establish the molecular activity and optimum dosage thresholds, andtiming of treatments of TP508 in mitigating X-ray or proton radiation damage with single fraction exposuresof 0.5, 1.0, 2.0, or 4 Gy in HLEC (CRL-11421 [B3] and SRA01/04 lines). Aim (1) is to determine the mostoptimized concentration and administration schedule for TP508 effects on radiation induced HLEC viabilityusing a clonogenic survival assay, MTT assay, and cell doubling time to assess the effects of variousconcentrations of TP508 on the sensitivity of HLECs applied before and after irradiation. Aim (2) is tofurther identify the effects of TP508 on specific HLEC molecular responses, using the most optimizedconcentration and administration schedule of TP508 comparing the single fraction radiation exposuresapplied with or without TP508, and analyzed with assays for apoptosis, necrosis, senescence, mitoticcatastrophe and protein expression; 53BP1 foci staining for dynamics of DSB; and western blot assays forrelated signaling pathways and protein profiles including amyloid beta, an early marker of cataractformation. Studies are expected to provide the following: (i) determine if TP508 provides a survival effect onirradiated HLEC at different doses applied before and after radiation; (ii) identify if the molecularmechanisms and protein profiles underlying the protective effect of TP508 in HLEC at different doses ofradiation are attributed to DSB repair; and (iii) determine the most effective dosage and timing (before orafter radiation) of TP508 application. Successfully developed, future investigations of TP508 could expandits application to mitigate additional radiation side effects including dry eye, retinopathy, and xerostomia..
Public Health Relevance Statement: 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 radiomodulating 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.
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