Carfilzomib-induced reticulocytosis in patients with multiple myeloma is caused by impaired terminal erythroid maturation

Proteasome inhibition constitutes a cornerstone of multiple myeloma (MM) treatment, with bortezomib, carfilzomib and ixazomib approved for clinical use. We observed a consistent and highly significant increase in the reticulocyte count during treatment with carfilzomib-based regimens in patients with relapsed MM, an observation not made in a matched cohort of bortezomib-treated patients. As this increased reticulocytosis was neither associated with elevated hemoglobin levels nor with hemolysis, we subsequently performed in vitro experiments to unravel the underlying mechanisms of this clinical observation. While carfilzomib did not affect erythroid differentiation of CD34+ hematopoietic progenitor cells, both continuous and pulse exposure to carfilzomib significantly impaired terminal maturation of purified primary reticulocytes towards erythrocytes. These results indicate that carfilzomib significantly impairs terminal erythroid maturation, independent of erythroid commitment, expansion or differentiation. Our results report the first pharmacologically induced delay in erythroid maturation as a mechanism for carfilzomib-induced reticulocytosis in MM patients. Quantitative proteomics using LC-MS/MS were performed to assess whether carfilzomib treatment alters the protein composition of reticulocytes

蛋白酶体抑制（proteasome inhibition）是多发性骨髓瘤（multiple myeloma, MM）治疗的核心策略，硼替佐米（bortezomib）、卡非佐米（carfilzomib）与伊沙佐米（ixazomib）均已获批用于临床。我们观察到，在接受基于卡非佐米治疗方案的复发型多发性骨髓瘤（relapsed MM）患者中，网织红细胞计数（reticulocyte count）呈现持续且极具统计学意义的升高；而在接受硼替佐米治疗的匹配队列（matched cohort）患者中，并未观察到该现象。由于该网织红细胞增多现象既未伴随血红蛋白水平升高，也未出现溶血（hemolysis），我们后续开展了体外实验（in vitro experiments）以阐明这一临床观察结果的潜在机制。研究发现，卡非佐米并不会影响CD34+造血祖细胞（CD34+ hematopoietic progenitor cells）的红系分化（erythroid differentiation），但无论是持续暴露还是脉冲暴露于卡非佐米，均会显著损伤纯化原代网织红细胞（purified primary reticulocytes）向成熟红细胞的终末成熟（terminal maturation）过程。上述结果表明，卡非佐米可显著损害红系终末成熟，且该过程不依赖于红系定向、扩增或分化环节。本研究首次报道了药物诱导的红系成熟延迟可作为多发性骨髓瘤患者中卡非佐米诱导网织红细胞增多的潜在机制。我们采用液相色谱-串联质谱（LC-MS/MS）开展定量蛋白质组学（quantitative proteomics）分析，以评估卡非佐米处理是否会改变网织红细胞的蛋白质组成。