Backgroundβ1- and β2–adrenergic receptors (ARs) play distinct roles in the heart, e.g. β1AR is pro-contractile and pro-apoptotic but β2AR anti-apoptotic and only weakly pro-contractile. G protein coupled receptor kinase (GRK)-2 desensitizes and opposes βAR pro-contractile signaling by phosphorylating the receptor and inducing beta-arrestin (βarr) binding. We posited herein that GRK2 blockade might enhance the pro-contractile signaling of the β2AR subtype in the heart. We tested the effects of cardiac-targeted GRK2 inhibition in vivo exclusively on β2AR signaling under normal conditions and in heart failure (HF).ResultsWe crossed β1AR knockout (B1KO) mice with cardiac-specific transgenic mice expressing the βARKct, a known GRK2 inhibitor, and studied the offspring under normal conditions and in post-myocardial infarction (MI). βARKct expression in vivo proved essential for β2AR-dependent contractile function, as β2AR stimulation with isoproterenol fails to increase contractility in either healthy or post-MI B1KO mice and it only does so in the presence of βARKct. The main underlying mechanism for this is blockade of the interaction of phosphodiesterase (PDE) type 4D with the cardiac β2AR, which is normally mediated by the actions of GRK2 and βarrs on the receptor. The molecular “brake” that PDE4D poses on β2AR signaling to contractility stimulation is thus “released”. Regarding the other beneficial functions of cardiac β2AR, βARKct increased overall survival of the post-MI B1KO mice progressing to HF, via a decrease in cardiac apoptosis and an increase in wound healing-associated inflammation early (at 24 hrs) post-MI. However, these effects disappear by 4 weeks post-MI, and, in their place, upregulation of the other major GRK in the heart, GRK5, is observed.ConclusionsGRK2 inhibition in vivo with βARKct is absolutely essential for cardiac β2AR pro-contractile signaling and function. In addition, β2AR anti-apoptotic signaling in post-MI HF is augmented by βARKct, although this effect is short-lived.

Background: Epidemiologic studies in pediatric oncology have demonstrated disparities in Acute Lymphoblastic Leukemia (ALL) outcomes and survival for various ethnic minorities including Hispanic patients. While differences between outcomes and survival of different racial/ethnic groups in pediatric ALL is well documented, the impact of race/ethnicity on the incidence of methotrexate related toxicities in this population has not been fully described. Methotrexate, a mainstay of pediatric ALL regimens, has the potential to cause a variety of toxicities including myelosuppression, hepatic injury, acute kidney injury (AKI), mucositis, and central nervous system (CNS) injury. Recent literature suggests that Hispanic ethnicity may be associated with an increased risk of methotrexate toxicity, specifically neurotoxicity (Giordano (2017)). This project evaluated ethnicity associated with the incidence of methotrexate toxicities that could lead to dose reduction or delays in therapy such as grade 3 or 4 myelosuppression, hepatic injury, nephrotoxicity, and mucositis in patients receiving dose escalating methotrexate. Methods: A single-center, retrospective chart review was conducted at a 224 bed pediatric hospital. Patients were eligible for inclusion if they had a diagnosis of ALL and received intravenous (IV) dose escalating methotrexate between August 1, 2011 and March 31, 2019. Electronic medical records were used to identify eligible patients using medication identification numbers cross referenced with diagnosis codes. Toxicity data was collected to evaluate interruption in dose escalation of IV methotrexate due to grade 3 or 4 liver dysfunction, nephrotoxicity, mucositis, neutropenia, or thrombocytopenia. The primary outcome was percentage of doses which resulted in a dose-limiting toxicity. A two-sample t-test was performed for the primary outcome between Hispanic white and non-Hispanic white patients. Results: Of the 64 patients initially identified, 60 patients were included for final analysis. Two patients were excluded due to a diagnosis of Acute Biphenotypic Leukemia, one patient did not receive IV methotrexate per protocol due to delay in therapy and was subsequently ineligible, and one patient did not receive dose escalating methotrexate per protocol for unspecified reasons. A total of 460 doses were given to 60 patients. The sample size consisted of 22 non-Hispanic white, 21 Hispanic white, 9 Black, 3 Hispanic black, 1 Asian, 1 multi-racial, and 3 patients with unspecified ethnicity. The percentage of patients who experienced at least one toxicity was 58.3% (35 patients). The most common grade 3 or 4 toxicity experienced per dose was thrombocytopenia (6.5%), followed by neutropenia (6.3%), mucositis (1.3%), liver dysfunction (0.22%), and no patient experienced nephrotoxicity. When comparing the rate of toxicity between Hispanic and non-Hispanic patients, Hispanic patients experienced toxicity at a rate of 17.4% per dose compared to non-Hispanic patients at 12.2% per dose, although this was not a statistical significant difference (p = 0.61). Hispanic white and non-Hispanic white patients received the same amount of doses at 165 doses of IV methotrexate. Hispanic white patients experienced a toxicity rate of 19.4% per dose compared to 12.1% per dose in the non-Hispanic white patients. Hispanic white patients experience more thrombocytopenia, where as non-Hispanic white patients experienced more neutropenia. Although not statistically significant possibly due to small sample size, Hispanic ethnicity was associated with higher rates of methotrexate toxicities. Understanding the impact of methotrexate toxicity in respect to ethnicity is important to improving treatment outcomes for pediatric patients with ALL. More robust studies with a larger sample size are warranted to explore the potential impact of ethnicity on tolerability of this regimen. Disclosures No relevant conflicts of interest to declare.

Introduction Hypersensitivity reactions (HSRs) can be induced by many medications, including chemotherapy agents and monoclonal antibodies (mAbs). Virtually all chemotherapeutics have the potential to initiate infusion reactions. Allergies to chemotherapeutics and biologic agents usually manifest with skin symptoms (rash, itching, and swelling), angioedema, or even potentially fatal anaphylactic reactions. Medication allergies may lead to discontinuation of life-prolonging therapies and therefore worsen prognosis. For clinical situations where hypersensitivity reactions prevent administration of a critical medication, desensitization can be an extremely useful addition to the clinical toolkit. In the early 2000s, multiple clinical trials showed that Rapid Drug Desensitization (RDD) for chemotherapy and mAbs was safe and effective in improving clinical outcomes and allowing patients to remain on preferred first-line therapy. Desensitization is challenging however, and this is reflected in variable success rates reported in the literature. One recent review noted successful desensitization in anywhere from 20 to 75% of cases (Ruggiero et al. 2017). This wide range is likely due to different methods of desensitization used in various studies. There are multiple variables influencing the success of desensitization, including the starting dose, the infusion rate, and the number of increments. Desensitization protocols are often complex requiring multiple changes in the rate and volume of medication administered between steps--making it difficult to complete them correctly. We have developed a new, simpler desensitization method that does not require multiple changes in the infusion rate and volume, thus reducing clinical confusion and leading to improved patient outcomes. Methods We developed a standardized protocol for rapid desensitization in patients who had hypersensitivity reactions to carboplatin or rituximab. This new desensitization method utilizes the same rate, administration time, and volume for each dose, only changing the drug concentration gradually between steps. This method helps minimize the chance of errors that occur due to repeatedly reprogramming the rate and volume of the infusion. A total of 10 patients were treated under this desensitization protocol between November 2017 and June 2020 for a total of 76 desensitization episodes. Initial desensitization occurred in the medical intensive care unit and subsequent infusions of carboplatin took place in an outpatient hematology-oncology setting. We retrospectively analyzed safety and efficacy of this novel desensitization protocol through review of treatment records. Results Of the 76 desensitizations performed, no adverse reactions occurred during desensitization and patients received their full target dose in all cases. No breakthrough reactions were noted during subsequent infusions of carboplatin or rituximab in desensitized patients. To prevent breakthrough reactions, antihistamines, corticosteroids and a leukotriene modifier were administered as pre-medications. Patients undergoing carboplatin desensitization were able to be switched from a 12-step protocol to a 10-step protocol with the same 100 % success rate in completing the entire planned cycle of chemotherapy. Discussion This retrospective analysis demonstrated a statistically and clinically significant reduced rate of breakthrough reactions in comparison to previous reports (Brennan et al. 2009). The other benefits of this novel method include improvement in safety of administration and cost savings. Disclosures No relevant conflicts of interest to declare.

Introduction: The scaffolding protein βarrestin1 (βarr1) by the angiotensin II (AngII) type 1 receptor (AT 1 R) mediates AngII-induced aldosterone production in vitro and physiologically in vivo, thereby exacerbating heart failure (HF) progression post-myocardial infarction (MI). Herein, we sought to investigate the relative potency of various AT 1 R antagonist drugs (sartans) at inhibiting βarr vs. G protein activation and hence aldosterone production in vitro and in vivo. We also investigated the alterations in plasma aldosterone levels conferred by these agents and their impact on cardiac function of post-MI rats. Methods: For the in vitro tests, transfected CHO and adrenocortical H295R cells were used. For in vivo studies, post-MI rats overexpressing βarr1 in their adrenals received 7-day-long treatments with the drugs of interest. Results: Among the sartans tested, candesartan and valsartan were the most potent βarr activation and βarr-mediated aldosterone production inhibitors in vitro, as well as the most “biased” antagonists towards βarr vs. G-protein inhibition. Conversely, losartan and irbesartan were the least potent βarr inhibitors and the least “biased” antagonists towards βarr inhibition. These in vitro findings were corroborated in vivo, since candesartan and valsartan, contrary to irbesartan, caused significant plasma aldosterone reductions in post-MI rats. Accordingly, cardiac ejection fraction (EF) and contractility were significantly augmented in candesartan- and valsartan-treated rats (EF: 41.1±1% and 40±1% respectively, vs. 35±0.3% for saline-treated), but further deteriorated in irbesartan-treated post-MI rats (EF: 32±1%, n=7 rats/group). Conclusions: These findings provide important insights that might aid pharmacotherapeutic decisions (i.e. individual agent selections) involving this commonly prescribed cardiovascular drug class (sartans).

Introduction: Chronic heart failure (HF) is characterized by enhanced circulating cardiotoxic hormones, among the most prominent of which is aldosterone, which contributes to the increased morbidity and mortality of the disease by promoting cardiac adverse remodeling post-myocardial infarction (MI). Cardiac β-adrenergic receptor (ΑR) desensitization and downregulation are a hallmark abnormality in HF at the molecular level and are due to the concerted action of cardiac G protein-coupled receptor kinase-2 (GRK2), together with its co-factors in receptor desensitization, the βarrestins (βarrs). We have also recently established that βarr1 promotes angiotensin II-dependent aldosterone production in the adrenal cortex, and this leads to elevated circulating aldosterone levels in vivo, both under normal conditions and during post-MI HF progression. Hypothesis: Herein, we sought to investigate the effects of genetically deleting βarr1 on post-MI cardiac function and hyperaldosteronic status in mice progressing to HF. Methods: We uitilized the βarr1KO mouse model and studied these mice at 4 weeks after surgically induced MI, in parallel with C57/B6 wild type (WT) controls. Cardiac function was assessed by echocardiography and in vivo catheterization. Plasma aldosterone was measured by ELISA. Results: Cardiac function is markedly improved in βarr1KO`s at 4 weeks post-MI, as evidenced by increased ejection fraction compared to WT mice (41.5 + 2.8 % vs. 21.8 + 2.4 %, respectively, n=9, p<0.0001) and increased isoproterenol-induced contractility. Additionally, cardiac dimensions are significantly reduced compared to WT`s, indicating attenuation of adverse cardiac remodeling. Importantly, plasma circulating aldosterone levels are significantly lowered and cardiac βAR signaling and function appear elevated in post-MI βarr1KO`s compared to control WT`s. Conclusions: Genetic deletion of βarr1 substantially improves cardiac function, adverse remodeling, hyperaldosteronism, and cardiac βAR function during post-MI HF progression. The underlying mechanism is attenuation of both cardiac βAR desensitization/downregulation and adrenal aldosterone production, which is βarr1-dependent.