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Myeloid differentiation factor 88 (MyD88), which is a key regulator of nuclear factor kappa B (NF-κB), plays an important role in tumorigenesis in lymphoid malignancies such as Waldenstrom's macroglobulinemia (WM). However, its biological function in multiple myeloma (MM), which is a malignant plasma cell disorder like WM, remains unexplored. In this article, we first demonstrated that higher expression MyD88 was significantly correlated with poor survival in patients with MM using multiple publicly available datasets. Interestingly, bioinformatic analysis also revealed that MyD88 gene alteration, which is recognized in nearly 80% of patients with WM, was extremely rare in MM. In addition, ST2825 (a specific inhibitor of MyD88) suppressed cell growth followed by apoptosis. Furthermore, ST2825 induced intracellular reactive oxygen species (ROS) in MM cells, and N-acetyl-l-cysteine, which is known as a ROS scavenger, significantly decreased the number of apoptotic MM cells evoked by ST2825 treatment. Taken together, our results indicated that ST2825 leads to ROS-dependent apoptosis in MM cells and could be an attractive therapeutic candidate for patients with MM. By highlighting the pathological mechanism of MyD88 in MM, this study also provides novel treatment strategies to conquer MM.

N-Methyl-D-aspartate receptors (NMDARs) in the brain are influenced by psychoactive drugs such as 2-(2-chlorophenyl)-2-(methylamino)cyclohexan-1-one (ketamine) and its analog 2-(ethylamino)-2-(3-methoxyphenyl)-cyclohexanone (methoxetamine). The recreational methoxetamine use can cause several toxicities and methoxetamine-related deaths have also been reported. Therefore, it has been banned in many countries. Since 2020, methoxetamine derivatives, 2-(ethylamino)-2-(m-tolyl)cyclohexan-1-one (deoxymethoxetamine) and 2-(isopropylamino)-2-(3-methoxyphenyl)cyclohexan-1-one (methoxisopropamine), have been sold online as designer drugs. However, how deoxymethoxetamine and methoxisopropamine act on NMDARs remains unknown. In this study, we first performed in silico docking studies of NMDARs, and deoxymethoxetamine and methoxisopropamine in addition to the major methoxetamine metabolites, 2-amino-2-(3-methoxyphenyl)-cyclohexanone (N-desethyl methoxetamine) and 2-(ethylamino)-2-(3-hydroxyphenyl)-cyclohexanone (O-desmethyl methoxetamine). The docking study suggested each compound interacts with NMDARs. We also determined the half-maximal inhibitory concentration (IC50s) of the methoxetamine-related compounds for NMDARs using NMDAR-expressing cartwheel interneurons of mice and patch-clamp recordings. We found that the IC50s of methoxetamine, deoxymethoxetamine, methoxisopropamine, N-desethyl methoxetamine, and O-desmethyl methoxetamine for NMDARs were 0.524, 0.679, 0.661, 1.649, and 0.227 μM, respectively. These results indicate that the methoxetamine-related compounds act as potent NMDAR blockers. Thus, deoxymethoxetamine and methoxisopropamine, both of which may cause damage by blocking NMDARs, are serious concerns. N-Desethyl methoxetamine and O-desmethyl methoxetamine may cause several adverse effects when methoxetamine is metabolized.

Effects of 4-methyl-2-mercaptobenzimidazole (4-MeMBI) and 5-methyl-2- mercaptobenzimidazole (5-MeMBI) on cytochrome P450 (CYP) activity were examined in primary cultured rat hepatocytes. Hepatocytes from male Wistar rats were cultured in the presence of 4-MeMBI or 5-MeMBI (0−400 μM), and the activity of CYPs 3A2/4 (48 and 96 h) and 1A1/2 (48 h) was determined by measuring the activity of testosterone 6β-hydroxylation and 7-ethoxyresorufin O-deethylation, respectively. As a result, 4-MeMBI and 5-MeMBI (≥12.5 μM) inhibited CYP3A2 activity. On the other hand, 4-MeMBI (≥25 μM) and 5-MeMBI (≥100 μM) induced CYP1A1/2 activity, being consistent with the previous in vivo results. In a comparative metabolism study using primary cultured human hepatocytes from two Caucasian donors, 4-MeMBI and 5-MeMBI induced the activity of CYPs 3A4 and 1A1/2 with individual variability. It was concluded from these results that 4-MeMBI, 5-MeMBI and MBI caused inhibition of CYP3A2 activity in primary cultured rat hepatocytes, suggesting their potential for metabolic drug-drug interactions. Primary cultured rat and human hepatocytes were considered to be useful for the evaluation of effects of the benzimidazole compounds on their inducibility and inhibitory activities of cytochrome P450 forms.