Ryanodine Receptors as Therapeutic Targets to Prevent Doxorubicin-Induced Lymphatic Dysfunction - PROJECT SUMMARY/ABSTRACT Lymphedema is a major complication after radiation and/or surgery for breast and gynecological cancers. Advancements in surgical techniques mitigate the risk, but the incidence of lymphedema is still high, and there are no approved medications to prevent or treat it. Doxorubicin (DOX) is a central chemotherapy drug for treating breast and gynecological cancers, but it increases the risk of lymphedema by 3-fold. The mechanism by which DOX contributes to chronic lymphedema is unknown, but we found that clinically relevant concentrations of DOX acutely inhibit lymph vessel (LV) contractions and reduce lymph flow by activating ryanodine receptors (RYRs, intracellular calcium channels) in lymph muscle cells (LMCs), resulting in tonic Ca2+ leak from the sarcoplasmic reticulum (SR) and lymphostasis. Sustained high levels of cytosolic Ca2+ [Ca2+i] can promote lipid peroxidation and cell death pathways, and the increase in intraluminal pressure produced by lymphostasis can damage LV walls and valve leaflets, synergistically causing chronic lymphatic injury. It is unclear whether DOX activates RYRs through a direct interaction or indirectly by mediating the oxidation of RYRs. Indeed, DOX elevates both cytosolic and mitochondrial superoxide (O2•-), which could contribute to RYR oxidation (receptor opening) and subsequent Ca2+ leak. It is also unknown which RYR subtype (RYR1, RYR2, RYR3) is activated by DOX in LMCs; if known, it could serve as a potential therapeutic target to prevent DOX-induced lymphatic dysfunction. We propose RYRs are novel therapeutic targets in LMCs to prevent DOX-induced lymphatic dysfunction and the development of chronic lymphedema. We hypothesize that DOX generates O2•- to acutely oxidize and open RYRs to increase [Ca2+i] in LMCs, inhibiting LV contractions and inducing lymphostasis and lymphatic injury, and added surgical insult potentiates this effect. Accordingly, we will use our well-established rat model to evaluate RYRs as therapeutic targets to prevent DOX-induced lymphatic dysfunction. Three aims will integrate techniques in preclinical studies to explore this hypothesis and will rely on protein and functional analysis of isolated LVs, use optical imaging to assess volumetric lymph flow in vivo in response to DOX and RYR blockade, and investigate the utility of RYR blockers, as a potential therapeutics in a preclinical model of lymphatic insufficiency. Aim 1 will determine whether DOX-induced RYR activation is mediated by O2•- in LMCs. Aim 2 will define the role of RYR subtypes in DOX-induced Ca2+ leak in isolated LVs and in lymph flow in vivo. Aim 3 will investigate the combined impact of DOX ± RYR blocker on lymphatic function, lipid peroxidation, and lymphatic morphology in a preclinical rat model of lymphatic insufficiency. Thus, we plan to explore RYRs as novel therapeutic targets to prevent DOX-related lymphedema and evaluate whether RYR blockers can be utilized as anti-lymphedema agents.
