MPN-inducing mutations as biomarkers of synthetic lethality

骨髓增生性肿瘤（MPN），如真性红细胞增多症（PV）、原发性血小板增多症 (ET)原发性骨髓纤维化（PMF）通常携带JAK 2（V617 F），MPL（W515 L）和突变， 钙网蛋白（CALR mut）。这些畸变可能伴随TET 2，ASXL 1， DNMT 3A、EZH 2和其他基因使MPN的遗传/表观遗传利用进一步复杂化 标记作为治疗决策的潜在生物标志物。 目前MPN的治疗选择包括骨髓抑制治疗，其形式为 i）ruxolitinib。MPN可具有延长的慢性期， 但最终可能加速并转化为继发性急性髓细胞白血病， 最终致命。因此，迫切需要产生单独或组合的新疗法， 已经批准的药物可能会延长完全缓解时间和/或用于 在进展到恶性阶段的患者中。由于所有3种“主要”突变[JAK 2（V617 F）， CALR（del 52）和MPL（W515 L）]在MPN干细胞（MPNSC）中被发现，这些细胞必须是 以改善治疗效果。不幸的是，潜在的治疗方法 针对MPNSC的方法有限。 包括MPNSC在内的MPN细胞积累潜在致死的DNA双链断裂（DSB）， 其通过两种主要机制修复，BRCA介导的同源重组（HR）和 DNA-PK介导的非同源末端连接（D-NHEJ）。HR和D-NHEJ修复DSB D-NHEJ在增殖细胞中起主要作用，而D-NHEJ在静止细胞中起主要作用。PARP 1依赖性备份NHEJ （B-NHEJ）在增殖和静止细胞中充当备份。 DSB修复中的癌症特异性缺陷创造了使用合成致死性的机会，例如， 通过PARP 1抑制剂（PARP 1 i）消除BRCA 1/2突变的癌细胞。BRCA1/2 突变在MPN中是罕见的。我们假设MPN诱导突变是预后性的， 由DNA修复抑制剂引发的治疗性合成致死性的生物标志物。 我们将确定特定的MPN诱导突变（生物标志物）是否易使静止期 和/或增殖来自个体患者的MPN干细胞和祖细胞以使PARP 1 i诱导的 与HR和D-NHEJ的抑制剂（目标#1）或与JAK 2 i（目标#2）组合的合成致死性。 我们还将采用MPN和原发性MPN异种移植物的鼠敲入/敲除模型， 人源化免疫缺陷小鼠，以确定DNA修复抑制剂和/或JAK 2 i是否发挥抗MPN 临床前环境中的合成致死效应（目标3）。

Myeloproliferative neoplasms (MPNs) such as polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) often carry JAK2(V617F), MPL(W515L) and mutations in calreticulin (CALRmut). These aberrations may be accompanied by mutations in TET2, ASXL1, DNMT3A, EZH2, and other genes further complicating utilization of MPNs genetic/epigenetic signatures as potential biomarkers for therapeutic decisions. Current treatment options for MPNs include myelosuppressive therapy in the form of hydroxyurea and JAK1/2 inhibitor QAK1/2i) ruxolitinib. MPNs can have prolonged chronic phases, but may eventually accelerate and transform into a secondary acute myeloid leukemia that is ultimately fatal. Therefore, it is imperative to generate new therapies that alone or in combination with already approved drugs could potentially extend the complete remission time and/or be used in patients which progressed to the malignant stage. Since all 3 "main" mutations [JAK2 (V617F), CALR(del52), and MPL(W515L)] were found in MPN stem cells (MPNSCs) these cells must be eliminated in order to improve therapeutic outcome. Unfortunately, the potential therapeutic approaches against MPNSCs are limited. MPN cells, including MPNSCs accumulate potentially lethal DNA double-strand breaks (DSBs), which are repaired by two major mechanisms, BRCA-mediated homologous recombination (HR) and DNA-PK -mediated non-homologous end-joining (D-NHEJ). HR and D-NHEJ repair DSBs in proliferating cells and D-NHEJ plays a major role in quiescent cells. PARP1 -dependent back-up NHEJ (B-NHEJ) serves as back-up in both proliferating and quiescent cells. Cancer-specific defects in DSB repair create the opportunity to employ synthetic lethality, e.g. elimination of BRCA1/2-mutated cancer cells by PARP1 inhibitor (PARP1i). However, BRCA1/2 mutations are rare in MPNs. We hypothesize that MPN-inducing mutations are prognostic biomarkers of therapeutic synthetic lethality triggered by DNA repair inhibitors. We will determine if specific MPN-inducing mutation(s) (biomarkers) predispose quiescent and/or proliferating MPN stem and progenitor cells from individual patients to PARP1i-induced synthetic lethality combined with the inhibitors of HR and D-NHEJ (Aim #1) or with JAK2i (Aim #2). We will also employ murine knockin/knockout models of MPNs and primary MPN xenografts in humanized immunodeficient mice to determine if DNA repair inhibitors and/or JAK2i exert anti-MPN synthetic lethal effect in pre-clinical settings (Aim #3).