Cusatuzumab plus azacitidine in Japanese patients with newly diagnosed acute myeloid leukemia ineligible for intensive treatment.

We present the results of a phase 1 study that evaluated the safety, pharmacokinetics, pharmacodynamics, immunogenicity, and preliminary disease response to cusatuzumab, a novel anti-CD70 monoclonal antibody, in combination with azacitidine, in newly diagnosed acute myeloid leukemia Japanese participants who were not candidates for intensive treatment. In this multicenter, single-arm study, six participants were enrolled and treated. Only in cycle 1, participants received cusatuzumab monotherapy on day 14. Subsequently, cusatuzumab was administered intravenously on days 3 and 17 at 20 mg/kg in combination with azacitidine (75 mg/m2 ) on days 1-7 of each 28-day cycle. All six participants had at least one treatment-emergent adverse event, and the most common treatment-emergent adverse events (all grades) were leukopenia (four participants [66.7%]) and constipation (three participants [50.0%]). No dose-limiting toxicity was observed during the study period. The combination of cusatuzumab and azacitidine is generally well tolerated in Japanese participants, and further exploration of this combination is warranted.

Ciltacabtagene autoleucel in patients with relapsed/refractory multiple myeloma: CARTITUDE-1 (phase 2) Japanese cohort.

Chimeric antigen receptor (CAR) T cells targeting B-cell maturation antigen have shown positive responses in patients with multiple myeloma (MM). The phase 2 portion of the CARTITUDE-1 study of ciltacabtagene autoleucel (cilta-cel) included a cohort of Japanese patients with relapsed/refractory MM. Following a conditioning regimen of cyclophosphamide (300 mg/m2 ) and fludarabine (30 mg/m2 ), patients received a single cilta-cel infusion at a target dose of 0.75 × 106 (range, 0.5-1.0 × 106 CAR-positive viable T cells/kg). The primary endpoint was overall response rate (ORR; defined as partial response or better) by International Myeloma Working Group criteria. A key secondary endpoint was the rate of very good partial response (VGPR) or better (defined as VGPR, complete response, stringent complete response). This first analysis was performed at 6 months after the last patient received cilta-cel. Thirteen patients underwent apheresis, nine of whom received cilta-cel infusion. Eight patients who received cilta-cel at the target dose responded, yielding an ORR of 100%. Seven of eight (87.5%) patients achieved a VGPR or better. One additional patient who received a below-target dose of cilta-cel also achieved a best response of VGPR. MRD negativity (10-5 threshold) was achieved in all six evaluable patients. Eight of nine (88.9%) patients who received cilta-cel infusion experienced a grade 3 or 4 adverse event, and eight (88.9%) patients experienced cytokine release syndrome (all grade 1 or 2). No CAR-T cell neurotoxicity was reported. A positive benefit/risk profile for cilta-cel was established for heavily pretreated Japanese patients with relapsed or refractory MM.

Differential roles of ubiquitination in the degradation mechanism of cell surface-resident bile salt export pump and multidrug resistance-associated protein 2.

We previously showed that ubiquitination, a reversible post-translational modification, facilitates degradation of cell surface-resident bile salt export pump (BSEP) and multidrug resistance-associated protein 2 (MRP2), ABC transporters that are expressed at the canalicular membrane (CM) of hepatocytes. In the current study, its underlying mechanism was investigated by evaluating the role of ubiquitination in the processes of internalization and subsequent degradation of cell surface-resident BSEP and MRP2. Cell surface biotinylation analysis using Flp-In T-REx 293 cells showed that ectopic expression of Ub(Δ)(GG), which is ubiquitin (Ub) lacking the two C-terminal glycines essential for the Ub conjugation reaction, inhibited the internalization of 3× FLAG-BSEP, but not of MRP2, and the degradation of the internalized MRP2, but not of the internalized 3× FLAG-BSEP. Its inhibitory effect on BSEP internalization was also indicated by a time-lapse imaging analysis using the rat hepatoma cell line McA-RH7777 in which Ub(Δ)(GG) delayed the loss of fluorescence from photoactivated Dronpa-BSEP on the CM. The effect of Ub(Δ)(GG) on BSEP internalization in these experiments was abrogated by treatment with chlorpromazine, an inhibitor of clathrin-mediated endocytosis, and the introduction of a Y1311A mutation into BSEP. This mutation eliminates the ability of BSEP to interact with the AP2 adaptor complex, an adaptor protein required for cargo selection in clathrin-mediated endocytosis. In conclusion, our data suggest that ubiquitination facilitates clathrin-mediated endocytosis of BSEP and the degradation of internalized MRP2, leading to the degradation of the cell surface-resident form of both transporters.

AP2 adaptor complex mediates bile salt export pump internalization and modulates its hepatocanalicular expression and transport function.

UNLABELLED: The bile salt export pump (BSEP) mediates the biliary excretion of bile salts and its dysfunction induces intrahepatic cholestasis. Reduced canalicular expression of BSEP resulting from the promotion of its internalization is one of the causes of this disease state. However, the molecular mechanism underlying BSEP internalization from the canalicular membrane (CM) remains unknown. We have shown previously that 4-phenylbutyrate (4PBA), a drug used for ornithine transcarbamylase deficiency (OTCD), inhibited internalization and subsequent degradation of cell-surface-resident BSEP. The current study found that 4PBA treatment decreased significantly the expression of α- and µ2-adaptin, both of which are subunits of the AP2 adaptor complex (AP2) that mediates clathrin-dependent endocytosis, in liver specimens from rats and patients with OTCD, and that BSEP has potential AP2 recognition motifs in its cytosolic region. Based on this, the role of AP2 in BSEP internalization was explored further. In vitro analysis with 3×FLAG-human BSEP-expressing HeLa cells and human sandwich-culture hepatocytes indicates that the impairment of AP2 function by RNA interference targeting of α-adaptin inhibits BSEP internalization from the plasma membrane and increases its cell-surface expression and transport function. Studies using immunostaining, coimmunoprecipitation, glutathione S-transferase pulldown assay, and time-lapse imaging show that AP2 interacts with BSEP at the CM through a tyrosine motif at the carboxyl terminus of BSEP and mediates BSEP internalization from the CM of hepatocytes. CONCLUSION: AP2 mediates the internalization and subsequent degradation of CM-resident BSEP through direct interaction with BSEP and thereby modulates the canalicular expression and transport function of BSEP. This information should be useful for understanding the pathogenesis of severe liver diseases associated with intrahepatic cholestasis.