Carcinogenicity Evaluation of Baclofen in TgrasH2 Mice

Baclofen is a γ-aminobutyric acid-B receptor agonist used for control of spastic muscle activity and as a treatment for alcohol abuse. The review of the nonclinical database suggested a data gap for potential carcinogenicity following long-term use. Regulatory requirements for pharmaceutical safety testing of cancer-causing potential have historically included 2-year rodent studies in rats and mice. The availability of transgenic models with greater specificity and sensitivity to carcinogens provides safety testing alternatives that align with the 3Rs. The carcinogenicity of baclofen was evaluated in CB6F1-TgrasH2 transgenic mice following daily oral administration at 45, 90, and 180 mg/kg/d for 26 weeks, preceded by a 2-week drug-conditioning period. There were no treatment-related palpable masses or neoplastic findings, and survival rates were not affected by the baclofen treatment. In conclusion, baclofen was considered as noncarcinogenic in CB6F1-TgrasH2 mice, which is consistent with results previously obtained in a 2-year rat study.

Effect of Nonionizing Radiation on Progesterone Treatment in Endometrial Hyperplasia: An Experimental Rat Study

<b><i>Objectives:</i></b> The aim of the study was to evaluate the negative effect of nonionizing radiation on the treatment of endometrial hyperplasia (EH) with oral progesterone. <b><i>Design:</i></b> Forty oophorectomized Wistar Albino female rats were included in this experimental rat study. <b><i>Materials and Methods:</i></b> The 4 groups were planned as follows: Group A; sham group; Group B; group receiving oral estradiol hemihydrate 4 mg/kg/day; Group C; 4 mg/kg/day oral estradiol hemihydrate followed with 1 mg/day medroxy progesterone acetate (MPA) and Group D; 4 mg/kg/day oral estradiol hemihydrate followed with 1 mg/day MPA with exposure to nonionizing radiation at 1800 mHz/3 h/day. After the experimental model, uterine horns were sampled and the preparations were evaluated for pathological parameters (glandular density, epithelial cell length, and luminal epithelial cell length) via light microscopy. Nonionizing radiation was created by a signal generator and a compatible mobile phone. <b><i>Results:</i></b> Estrogen was found to increase all parameters related to EH (<i>p</i> &#x3c; 0.05). Progesterone treatment was found to decrease parameters related to EH (Group B vs. C; luminal epithelial cell length, glandular density, and epithelial length; 11.2 vs. 13.2 μm <i>p</i> = 0.007; 32.5 vs. 35.5, <i>p</i> = 0.068; and 219.9 μm vs. 285 µm, <i>p</i> &#x3c; 0.001, respectively). Final analyses revealed reduced effectiveness of progesterone treatment in the rats exposed to nonionizing radiation (Group C vs. D); luminal epithelial cell length, glandular density, and epithelial length (11.2 μm vs. 13.5 μm, <i>p</i> = 0.179; 32.5 vs. 52, <i>p</i> &#x3c; 0.001; and 219.9 μm vs. 374.1 μm, <i>p</i> = 0.001, respectively). <b><i>Limitations:</i></b> The limitations of our study are that the results of animal experiments may not be appropriate for direct adaptation to humans and the relatively low number of rats included in the study. <b><i>Conclusion:</i></b> Nonionizing radiation reduces the effect of progesterone in patients receiving treatment for EH.

Preclinical Safety Assessment and Toxicokinetics of Apitegromab, an Antibody Targeting Proforms of Myostatin for the Treatment of Muscle-Atrophying Disease

Myostatin is a negative regulator of skeletal muscle and has become a therapeutic target for muscle atrophying disorders. Although previous inhibitors of myostatin offered promising preclinical data, these therapies demonstrated a lack of specificity toward myostatin signaling and have shown limited success in the clinic. Apitegromab is a fully human, monoclonal antibody that binds to human promyostatin and latent myostatin with a high degree of specificity, without binding mature myostatin and other closely related growth factors. To support the clinical development of apitegromab, we present data from a comprehensive preclinical assessment of its pharmacology, pharmacokinetics, and safety across multiple species. In vitro studies confirmed the ability of apitegromab to inhibit the activation of promyostatin. Toxicology studies in monkeys for 4 weeks and in adult rats for up to 26 weeks showed that weekly intravenous administration of apitegromab achieved sustained serum exposure and target engagement and was well-tolerated, with no treatment-related adverse findings at the highest doses tested of up to 100 mg/kg and 300 mg/kg in monkeys and rats, respectively. Additionally, results from an 8-week juvenile rat study showed no adverse effects on any endpoint, including neurodevelopmental, motor, and reproductive outcomes at 300 mg/kg administered weekly IV. In summary, the nonclinical pharmacology, pharmacokinetic, and toxicology data demonstrate that apitegromab is a selective inhibitor of proforms of myostatin that does not exhibit toxicities observed with other myostatin pathway inhibitors. These data support the conduct of ongoing clinical studies of apitegromab in adult and pediatric patients with spinal muscular atrophy (SMA).

MO323MEDICATION INDUCED RELAPSE OF FGSG

Background and Aims 31-year-old female with past medical history of Multiple Sclerosis diagnosed with Minimal Change Disease (MCD) in 2011. At diagnosis she had proteinuria that exceeded 7 g per day. She was treated with steroids and went into complete remission. In 2017 presented again with nephrotic syndrome and on repeat biopsy she was diagnosed with Focal Segmental Glomerulosclerosis (FSGS). She was restarted on steroids and had some improvement but despite 20 weeks of high dose steroids did not achieve remission. After every attempt of tapering, she would relapse. Method Other treatments tried without success were tacrolimus, cyclophosphamide and rituximab. Mild improvement with tacrolimus but stopped after a grand mal seizure. The lowest achievable steroid dose was 20mg daily. She was started on combination therapy tacrolimus and mycophenolate mofetil and was able to come off steroids and went into remission. Results After a few months of remission, she began to relapse. It was noted after extensive investigation that she had been placed on cabergolin for hyperprolactinemia by her endocrinologist at the time she began to relapse. Cabergolin was stopped and she went into remission again. We present the first case of FSGS relapse due to cabergolin. Conclusion Cabergoline is metabolized by hydrolysis and has limited cytochrome P450 (CYP) metabolism. Despite limited CYP metabolism, cabergoline does have an interaction with clarithromycin, a known inhibitor of CYP and p-glycoprotein. One rat study suggest that mycophenolate is a substrate for p-glycoprotein, so it is possible that there is some competitive inhibition. This would explain why the patient relapsed while on cabergoline and in remission after stopping it.

Optogenetic current in myofibroblasts acutely alters electrophysiology and conduction of co-cultured cardiomyocytes

Interactions between cardiac myofibroblasts and myocytes may slow conduction and generate spontaneous beating in fibrosis, increasing the chance of life-threatening arrhythmia. While co-culture studies have shown that myofibroblasts can affect cardiomyocyte electrophysiology in vitro, the extent of myofibroblast-myocyte electrical conductance in a syncytium is unknown. In this neonatal rat study, cardiac myofibroblasts were transduced with Channelrhodopsin-2, which allowed acute and selective increase of myofibroblast current, and plated on top of cardiomyocytes. Optical mapping revealed significantly decreased conduction velocity (− 27 ± 6%, p < 10–3), upstroke rate (− 13 ± 4%, p = 0.002), and action potential duration (− 14 ± 7%, p = 0.004) in co-cultures when 0.017 mW/mm2 light was applied, as well as focal spontaneous beating in 6/7 samples and a decreased cycle length (− 36 ± 18%, p = 0.002) at 0.057 mW/mm2 light. In silico modeling of the experiments reproduced the experimental findings and suggested the light levels used in experiments produced excess current similar in magnitude to endogenous myofibroblast current. Fitting the model to experimental data predicted a tissue-level electrical conductance across the 3-D interface between myofibroblasts and cardiomyocytes of ~ 5 nS/cardiomyocyte, and showed how increased myofibroblast-myocyte conductance, increased myofibroblast/myocyte capacitance ratio, and increased myofibroblast current, which occur in fibrosis, can work in tandem to produce pro-arrhythmic increases in conduction and spontaneous beating.