来那度胺抑制RP-MDM2-p53通路的分子机制及其在MDS新型靶向治疗中的研究

Recent investigations have yielded critical insight into the molecular pathobiology underlying the hypoplastic anemia in myelodysplastic syndrome (MDS) with chromosome 5q deletion (del5q). Hemizygous deletion of the ribosomal protein (RP)-S14 gene encoded within the 5q32-33 commonly deleted region (CDR) disrupts ribosome assembly causing nucleolus stress with liberation of free RPs that bind to and accelerate degradation of the human MDM2 analogue, resulting in p53 activation and arrest of erythroid precursors. Lenalidomide as emerged as the only targeted therapeutic approved for the treatment of patients with MDS, yielding high rates of transfusion independence through selective suppression of del5q clones. Our investigations have shown that lenalidomide acts through synthetic lethality, inhibiting activity of remaining alleles of two haplodeficient phosphatases encoded within the proximal CDR to account for its karyotype selective disease specificity. These dual specificity phosphatases, PP2Acα (protein phosphatase type 2A catalytic domain alpha) and Cdc25C (cell division cycle 25C), are key co-regulators of the G2/M checkpoint, inhibition of which results in sustained G2 arrest of del5q progenitors. Our recent work has shown that lenalidomide first stabilizes MDM2 to release p53 arrested del5q progenitors to permit cell cycle re-entry and transition to G2/M. Our preliminary data suggests that lenalidomide accomplishes this by binding to the RING finger of MDM2 to disrupt RP interaction with the acidic domain. These findings are consistent with recent reports that lenalidomide and thalidomide bind to and inhibit an alternate member of the RING finger E3-ubiquitin ligase family complex, cereblon, which accounts for the drug specific myeloma cytotoxicity and teratogenicity, respectively. The investigations in this proposal will build upon our prior work to develop innovative disease specific MDS therapeutics. The first Aim will delineate the precise sites and mechanism of lenalidomide interaction with MDM2 to provide a framework from which to develop novel therapeutics that selectively interfere with RP/MDM2 binding and activation of the RP-MDM2-p53 axis in del5q MDS. In the second Aim we introduce a new concept of 'applied synthetic lethality', intended to render non-del5q progenitors sensitive to clonal suppression by lenalidomide through Toll-like receptor 9 (TLR9) targeted delivery of CpG oligonucleotide-siRNA conjugates. These novel approaches will be validated in vivo in murine models in the final Aim. The strategies proposed are innovative with strong translational potential for development of novel disease-targeted treatments for patients with MDS, and with broad applicability to other malignancies and constitutional ribosomopathies.

骨髓增生异常综合征（MDS）是造血干细胞恶性肿瘤，其发病逐年上升，但由于对MDS病理机制认识有限，目前仍缺乏有效治疗。来那度胺是唯一获得FDA批准用于MDS治疗的靶向药物，但仅对del5q MDS 有效，而对大部分非del5q MDS无效。 本课题将在前期工作基础上研究靶向MDS治疗的新策略。首先，研究来那度胺与MDM2相互作用的机制和确切位点，确认由del5q段单倍缺失基因编码的PP2A/Cdc25c是来那度胺有效作用靶点；其次，根据"合成致死"原理，设计特异性靶向TLR9的CpG oligonucleotide-siRNA新型转运系统，以此诱导非del5q细胞模拟del5q以增加非del5q祖细胞对来那度胺诱导的克隆抑制的敏感性；最后，在小鼠非del5q MDS移植瘤和自发性MDS模型中评价以上治疗策略的有效性。本课题将为来那度胺拓展于非del5q MDS的治疗提供实验和理论依据。