審視cabozantinib對同時具t(8;21)轉位及KIT N822K突變之急性骨髓性白血病細胞的抗癌效果 ─ 從轉錄體分析重新定位cabozantinib

Abstract

急性骨髓性白血病中，約有10%~15%的病人有t(8;21)染色體轉位的現象，形成異常的AML1-ETO融合蛋白。值得注意的是，具t(8;21)染色體轉位的病人，常伴有KIT基因突變，使得預後較差。到目前為止，對於這類病人，仍是以7+3化學治療為主；然而，高劑量的化學治療並不適合年紀較大的患者。因此，針對此基因分型，找到更好的用藥策略仍是非常重要的。 Cabozantinib為一種口服的多激酶小分子抑制劑，目前已經被FDA同意用於多種固態腫瘤的病患。在本篇論文研究中，我們利用cabozantinib在KIT激酶的抑制潛力來重新定位其在白血病治療的發展性，並審視其潛在的分子機制。Cabozantinib對於帶有t(8;21)以及KIT基因突變的Kasumi-1細胞株有顯著的細胞毒殺效果，其72小時後在88.06 nM左右可抑制一半細胞生長，且這個濃度遠低於臨床cabozantinib在人體血漿可達到的濃度 (1 μM)。另外，cabozantinib的確能抑制KIT以及其下游AKT/mTOR、STAT3以及ERK1/2的磷酸化，可能伴隨著影響調節細胞週期以及細胞凋亡相關的分子。在小鼠皮下異種移植模式，則可以看到給予小鼠低劑量 (10 mg/kg) cabzozantinib即可以看到顯著的抑制腫瘤生長效果，並延長小鼠的存活時間。我們也發現cabozantinib可以顯著地下調Kasumi-1細胞AML1-ETO的蛋白質表達，進一步的研究則發現藉由干擾致癌融合蛋白的合成是cabozantinib來下調AML1-ETO蛋白質表達量的原因之一。 最後，我們利用RNA定序實驗發現cabozantinib處理Kasumi-1細胞可以藉由下調mTOR調節的訊息傳遞路徑來進一步影響癌細胞核糖體合成及糖解作用。瞭解這些分子機制更支持著我們重新定位藥物的想法，未來相關的臨床試驗，則可能可以將cabozantinib應用在這類特定基因異常的族群。

The chromosome translocation t(8;21), generating aberrant fusion protein AML1-ETO, is found in approximately 10%~15% AML cases. Of note, KIT mutations are highly prevalent in AML1-ETO patients, associated with adverse prognosis. As yet, the main treatment for this kind of patients is 7+3 regimen; nonetheless, high-dose administration is inappropriate for elder patients. Hence, to uncover a better therapeutic strategy for this AML cohort is of sheer significance. Cabozantinib is an orally available multiple tyrosine kinase inhibitor which has been approved by US FDA to treat several solid tumors. Herein, our current study leverages the potent inhibitory effect of KIT to reprofile cabozantinib in leukemia treatments, scrutinizing the implicit molecular mechanisms. Cabozantinib displayed profound cytotoxicity in Kasumi-1 cells, bearing t(8;21) as well as KIT mutation, with IC50 values of 88.06 nM for 72 h, a substantially lower dose than clinically achievable plasma level (1 μM). The bona fide suppression of KIT phosphorylation and downstream signals such as AKT/mTOR, STAT3 and ERK1/2 were elicited by cabozantinib treatment, associated with alterations of cell cycle- and apoptosis-related molecules. In mouse xenograft model, cabozantinib conspicuously suppressed tumorigenesis at a lower dosage of 10 mg/kg and prolonged survival. We also found that cabozantinib perturbed AML1-ETO fusion protein synthesis in a dose- and time-dependent manner. Further investigation revealed that cabozantinib-treatment could dysregulate AML1-ETO protein expression, at least partly, through interfering with oncofusion protein synthesis. Ultimately, RNA-sequencing analysis unleashed that mTOR-mediated signaling pathways were markedly inactivated upon cabozantinib treatment, thereby downregulating ribosome biogenesis and glycolysis, underpinning us to repurpose cabozantinib in this specific patient cohort; relevant clinical trials are warranted in the near future.