Acute accumulation of PIM2 and NRF2 and recovery of ß5 subunit activity mitigate multiple myeloma cell susceptibility to proteasome inhibitors.

Resistance to proteasome inhibitors (PIs) has emerged as an important clinical issue. We investigated the mechanisms underlying multiple myeloma (MM) cell resistance to PIs. To mimic their pharmacokinetic/pharmacodynamic (PK/PD) profiles, MM cells were treated with bortezomib and carfilzomib for 1 h at concentrations up to 400 and 1,000 nM, respectively. Susceptibility to these PIs markedly varied among MM cell lines. Pulsatile treatments with PIs suppressed translation, as demonstrated by incorporation of puromycin at 24 h in PI-susceptible MM.1S cells, but not PI-resistant KMS-11 cells. Inhibition of ß5 subunit activity decreased at 24 h in KMS-11 cells, even with the irreversible PI carfilzomib, but not under suppression of protein synthesis with cycloheximide. Furthermore, the proteasome-degradable pro-survival factors PIM2 and NRF2 acutely accumulated in MM cells subjected to pulsatile PI treatments. Accumulated NRF2 was trans-localized into the nucleus to induce the expression of its target gene, HMOX1, in MM cells. PIM and Akt inhibition restored the anti-MM effects of PIs, even against PI-resistant KMS-11 cells. Collectively, these results suggest that increased synthesis of ß5 proteasome subunit and acute accumulation of PIM2 and NRF2 reduce the anti-MM effects of PIs.

Mechanisms of preferential bone formation in myeloma bone lesions by proteasome inhibitors.

Proteasome inhibitors (PIs) can preferentially restore bone in bone-defective lesions of patients with multiple myeloma (MM) who respond favorably to these drugs. Most prior in vitro studies on PIs used continuous exposure to low PI concentrations, although pharmacokinetic analysis in patients has shown that serum concentrations of PIs change in a pulsatile manner. In the present study, we explored the effects of pulsatile treatment with PIs on bone metabolism to simulate in vivo PI pharmacokinetics. Pulsatile treatment with bortezomib, carfilzomib, or ixazomib induced MM cell death but only marginally affected the viability of osteoclasts (OCs) with F-actin ring formation. Pulsatile PI treatment suppressed osteoclastogenesis in OC precursors and bone resorption by mature OCs. OCs robustly enhanced osteoblastogenesis in cocultures with OCs and MC3T3-E1 pre-osteoblastic cells, indicating OC-mediated coupling to osteoblastogenesis. Importantly, pulsatile PI treatment did not impair robust OC-mediated osteoblastogenesis. These results suggest that PIs might sufficiently reduce MM cell-derived osteoblastogenesis inhibitors to permit OC-driven bone formation coupling while suppressing OC differentiation and activity in good responders to PIs. OC-mediated coupling to osteoblastogenesis appears to be a predominant mechanism for preferential occurrence of bone regeneration at sites of osteoclastic bone destruction in good responders.

The Xanthine Oxidase Inhibitor Febuxostat Suppresses Adipogenesis and Activates Nrf2.

Xanthine oxidoreductase (XOR) is a rate-limiting enzyme in purine catabolism that acts as a novel regulator of adipogenesis. In pathological states, xanthine oxidoreductase activity increases to produce excess reactive oxygen species (ROS). The nuclear factor erythroid 2-related factor 2 (Nrf2) is a critical inducer of antioxidants, which is bound and repressed by a kelch-like ECH-associated protein 1 (Keap1) in the cytoplasm. The Keap1-Nrf2 axis appears to be a major mechanism for robust inducible antioxidant defenses. Here, we demonstrate that febuxostat, a xanthine oxidase inhibitor, alleviates the increase in adipose tissue mass in obese mouse models with a high-fat diet or ovariectomy. Febuxostat disrupts in vitro adipocytic differentiation in adipogenic media. Adipocytes appeared at day 7 in absence or presence of febuxostat were 160.8 ± 21.2 vs. 52.5 ± 12.7 (p < 0.01) in 3T3−L1 cells, and 126.0 ± 18.7 vs. 55.3 ± 13.4 (p < 0.01) in 10T1/2 cells, respectively. Adipocyte differentiation was further enhanced by the addition of hydrogen peroxide, which was also suppressed by febuxostat. Interestingly, febuxostat, but not allopurinol (another xanthine oxidase inhibitor), rapidly induced the nuclear translocation of Nrf2 and facilitated the degradation of Keap1, similar to the electrophilic Nrf2 activator omaveloxolone. These results suggest that febuxostat alleviates adipogenesis under oxidative conditions, at least in part by suppressing ROS production and Nrf2 activation. Regulation of adipocytic differentiation by febuxostat is expected to inhibit obesity due to menopause or overeating.

Establishment of a new rehabilitation program using masticatory training food for jaw deformity patients.

Background/purpose: Patients with jaw deformities may show a reduction in masticatory function as a result of postoperative hypofunction. This study aimed to establish a novel rehabilitation program using a commercially available masticatory training food for patients with jaw deformities after orthognathic surgery. Materials and methods: Nine patients with mandibular prognathism (the training group: n = 5, and the non-training group: n = 4) and 6 control participants with normal occlusion were included in this study. For the rehabilitation program with masticatory exercise, patients were instructed to chew the training food once a day for 60 days starting from 10 days after the surgery. The effects of the rehabilitation program were assessed by determining the maximum bite force (MBF) and the masticatory performance (MP). Clinical assessments were performed just before orthognathic surgery (Pre) and at 10 days (T0), 1 month (T1), 2 months (T2), and 3 months (T3) after surgery. Results: Compared with the non-training group, the training group showed a trend toward greater recovery amount of MBF from Pre to T3, and a significantly greater recovery amount in MP (p < 0.05) from Pre to T3. When the time-series change of MP was evaluated in both groups from T0 to T3, a significant difference was observed in the interaction terms (p = 0.03). This result indicates that the effectiveness of the training may be demonstrated by following the postoperative course further. Conclusion: The rehabilitation using this training food may become a useful method for postoperative hypofunction in patients with jaw deformities.