Gregg F. Keaney

H3B-8800, an orally available small-molecule splicing modulator, induces lethality in spliceosome-mutant cancers

Genomic analyses of cancer have identified recurrent point mutations in the RNA splicing factor–encoding genes SF3B1, U2AF1, and SRSF2 that confer an alteration of function. Cancer cells bearing these mutations are preferentially dependent on wild-type (WT) spliceosome function, but clinically relevant means to therapeutically target the spliceosome do not currently exist. Here we describe an orally available modulator of the SF3b complex, H3B-8800, which potently and preferentially kills spliceosome-mutant epithelial and hematologic tumor cells. These killing effects of H3B-8800 are due to its direct interaction with the SF3b complex, as evidenced by loss of H3B-8800 activity in drug-resistant cells bearing mutations in genes encoding SF3b components. Although H3B-8800 modulates WT and mutant spliceosome activity, the preferential killing of spliceosome-mutant cells is due to retention of short, GC-rich introns, which are enriched for genes encoding spliceosome components. These data demonstrate the therapeutic potential of splicing modulation in spliceosome-mutant cancers.

Total Synthesis of 6-Deoxypladienolide D and Assessment of Splicing Inhibitory Activity in a Mutant SF3B1 Cancer Cell Line

A total synthesis of the natural product 6-deoxypladienolide D (1) has been achieved. Two noteworthy attributes of the synthesis are (1) a late-stage allylic oxidation which proceeds with full chemo-, regio-, and diastereoselectivity and (2) the development of a scalable and cost-effective synthetic route to support drug discovery efforts. 6-Deoxypladienolide D (1) demonstrates potent growth inhibition in a mutant SF3B1 cancer cell line, high binding affinity to the SF3b complex, and inhibition of pre-mRNA splicing.

Abstract 1891: Pharmacological target validation studies of fatty acid synthase in carcinoma using the potent, selective and orally bioavailable inhibitor IPI-9119.

Fatty acid synthase (FASN) is a key enzyme responsible for fatty acids synthesis de novo in mammals. Overexpression of FASN is common in many cancers including prostate, breast and colon cancer and elevated expression of FASN has been linked with poor prognosis and reduced disease-free survival. Experiments with RNAi and small molecule inhibitors suggest that FASN is a metabolic oncogene with an important role in tumor growth and survival and an appealing target for cancer therapy. However, studies utilizing small molecule FASN inhibitors like orlistat and C75 have been confounded by the lack of potency and selectivity, as well as the poor pharmacological properties of these inhibitors. Herein we report pharmacological target validation studies of FASN using a potent, selective and orally bioavailable FASN inhibitor IPI-9119. Building on previous experience with serine hydrolase inhibitors, a series of novel mechanism-based FASN inhibitors were designed based on a tetrazolone carboxamide scaffold. Like orlistat, these analogs are irreversible inhibitors that specifically target the FASN thioesterase domain. Tetrazolone carboxamide analogs were shown to potently inhibit cellular FASN using an occupancy assay and to completely block de novo palmitate synthesis in HCT-116 colon cancer cells using a 13 C-glucose incorporation assay. Lead optimization of the tetrazolone carboxamide series resulted in the identification of IPI-9119 as a tool for in vivo proof-of-concept studies. IPI-9119 is a potent FASN inhibitor in both biochemical (IC 50 ∼1nM) and cellular occupancy assays (IC 50 ∼10nM), and shows more than 400-fold selectivity against several additional serine hydrolases. Importantly, IPI-9119 is orally bioavailable and has pharmacokinetic (PK) properties suitable for in vivo pharmacology studies. IPI-9119 was tested for growth inhibition in cancer cell lines in vitro and tumor xenograft models in vivo. Unexpectedly, in contrast to the knock-down studies and to data reported for orlistat and C75, IPI-9119 failed to elicit anti-proliferative effects in multiple cancer cell lines in vitro. Similarly, PK/PD experiments demonstrated that a single oral dose of IPI-9119 at 200 mg/kg leads to complete and sustained blockade of FASN in HCT-116 tumor xenografts, but IPI-9119 failed to show any anti-tumor activity when dosed as a single agent at 200 mg/kg BID for 10 days. In summary, we identified IPI-9119 as a potent, selective and orally bioavailable FASN inhibitor. Preliminary target validation studies with IPI-9119 in cancer cell lines and an HCT-116 xenograft model suggest that FASN inhibition alone is not sufficient to affect cancer cell proliferation and tumor growth. Further studies exploring combination treatments with IPI-9119 are warranted. Citation Format: Erin Brophy, James Conley, Patrick O9Hearn, Mark Douglas, Culver Cheung, John Coco, Laura D9Anello, Andrew Wylie, Thomas Tibbitts, Gregg Keaney, Lawrence Chan, Adilah Bahadoor, Dan Snyder, Marta Nevalainen, Alfredo Castro, Vito Palombella, Massimo Loda, Stephane Peluso. Pharmacological target validation studies of fatty acid synthase in carcinoma using the potent, selective and orally bioavailable inhibitor IPI-9119. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1891. doi:10.1158/1538-7445.AM2013-1891

Abstract 1185: H3B-8800, a novel orally available SF3b modulator, shows preclinical efficacy across spliceosome mutant cancers

Genomic characterization of hematologic and solid cancers has revealed recurrent somatic mutations affecting genes encoding the RNA splicing factors SF3B1, U2AF1, SRSF2 and ZRSR2. Recent data reveal that these mutations confer an alteration of function inducing aberrant splicing and rendering spliceosome mutant cells preferentially sensitive to splicing modulation compared with wildtype (WT) cells. Here we describe a novel orally bioavailable small molecule SF3B1 modulator identified through a medicinal chemistry effort aimed at optimizing compounds for preferential lethality in spliceosome mutant cells. H3B-8800 potently binds to WT or mutant SF3b complexes and modulates splicing in in vitro biochemical splicing assays and cellular pharmacodynamic assays. The selectivity of H3B-8800 was confirmed by observing lack of activity in cells expressing SF3B1R1074H, the SF3B1 mutation previously shown to confer resistance to other splicing modulators. Although H3B-8800 binds both WT and mutant SF3B1, it results in preferential lethality of cancer cells expressing SF3B1K700E, SRSF2P95H, or U2AF1S34F mutations compared to WT cells. In animals xenografted with SF3B1K700E knock-in leukemia K562 cells or mice transplanted with Srsf2P95H/MLL-AF9 mouse AML cells, oral H3B-8800 treatment demonstrated splicing modulation and inhibited tumor growth, while no therapeutic impact was seen in WT controls. These data were also evident in patient-derived xenografts (PDX) from patients with CMML where H3B-8800 resulted in a substantial reduction of leukemic burden only in SRSF2-mutant but not in WT CMML PDX models. Additionally, due to the high frequency of U2AF1 mutations in non-small cell lung cancer, H3B-8800 was tested in U2AF1S34F-mutant H441 lung cancer cells. Similar to the results from leukemia models, H3B-8800 demonstrated preferential lethality of U2AF1-mutant cells in vitro and in in vivo orthotopic xenografts at well tolerated doses. RNA-seq of isogenic K562 cells treated with H3B-8800 revealed dose-dependent inhibition of splicing. Although global inhibition of RNA splicing was not observed; H3B-8800 treatment led to preferential intron retention of transcripts with shorter and more GC-rich regions compared to those unaffected by drug. Interestingly, H3B-8800-retained introns commonly disrupted the expression of spliceosomal genes, suggesting that the preferential effect of H3B-8800 on spliceosome mutant cells is due to the dependency of these cells on expression of WT spliceosomal genes. These data identify a novel therapeutic approach with selective lethality in leukemias and lung cancers bearing a spliceosome mutation. Despite the essential nature of splicing, cancer cells without a spliceosome mutation were less sensitive to H3B-8800 compared with potent eradication of mutant counterparts. H3B-8800 is currently undergoing clinical evaluation in patients with MDS, AML, and CMML. Citation Format: Silvia Buonamici, Akihide Yoshimi, Michael Thomas, Michael Seiler, Betty Chan, Benjamin Caleb, Fred Csibi, Rachel Darman, Peter Fekkes, Craig Karr, Gregg Keaney, Amy Kim, Virginia Klimek, Pavan Kumar, Kaiko Kunii, Stanley Chun-Wei Lee, Xiang Liu, Crystal MacKenzie, Carol Meeske, Yoshiharu Mizui, Eric Padron, Eunice Park, Ermira Pazolli, Sudeep Prajapati, Nathalie Rioux, Justin Taylor, John Wang, Markus Warmuth, Huilan Yao, Lihua Yu, Ping Zhu, Omar Abdel-Wahab, Peter Smith. H3B-8800, a novel orally available SF3b modulator, shows preclinical efficacy across spliceosome mutant cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1185. doi:10.1158/1538-7445.AM2017-1185

Abstract B125: Mutant SF3B1 downregulates proteins involved in differentiation, including ABCB7

Refractory Anemia with Ringed Sideroblasts (RARS), a subtype of Myelodysplatic Syndrome (MDS), occurs with a high frequency of hotspot mutations in HEAT (Huntingtin, Elongation factor 3, protein phosphatase 2A, Targets of rapamycin 1 domains) domains of SF3B1. This protein component of the U2 snRNP complex of the spliceosome is essential in the proper selection and usage of 39 splice sites. RNAseq analysis of MDS and other tumor types in which SF3B1 hotspot mutations have been found show that alternative 39 splice site usage is the predominant cause of RNA transcript aberration. These modifications can result in mRNAs encoding novel peptides, or they can introduce premature termination codons into the pre-mRNA, most likely directing it to the Nonsense Mediated Decay (NMD) pathway for degradation. Using a predictive tool to determine the likelihood of a given aberrant transcript to be targeted for NMD, we determined that nearly 50% of the SF3B1-mutant-associated aberrant transcripts were candidates for degradation. We confirmed this experimentally by treating isogenic Nalm-6 cells (engineered by AAV homology to express SF3B1 K700E or K700K) with or without cycloheximide, an agent known to inhibit translation and RNA degradation by NMD. Investigation of the resulting RNAseq data showed significant rescue of gene expression only for the transcripts predicted to be NMD targets. Ingenuity Pathway Analysis indicated that many of the downregulated genes in SF3B1 mutant samples were involved in differentiation, which has been shown to be dysregulated in MDS. We tested the idea that such modifications in the transcriptome confer selective advantage or impair differentiation in SF3B1 mutant cells. We began by manipulating the expression of ABCB7, one of the genes identified in our RNAseq analysis to be downregulated by aberrant splicing and subsequent NMD. ABCB7 is a mitochondrial transporter important in cellular iron metabolism and, indirectly, in heme production. Additionally, loss of function of ABCB7 is causal in X-linked sideroblastic anemia and has been implicated in RARS MDS. We discovered in our SILAC proteomic analysis that ABCB7 protein was dramatically decreased in K700E SF3B1 Nalm-6 cells relative to K700K Nalm-6, in agreement with our RNAseq analysis. Using doxycycline-inducible shRNA expression, we knocked down ABCB7 mRNA and protein expression in TF-1 erythroblasts. These cells show significant decreases in erythropoeitin (EPO)-induced differentiation when expressing exogenous K700E SF3B1, but not K700R (a very conservative mutation) or WT SF3B1. With direct knock down of ABCB7, we observed a similar phenotype - impairment of EPO-induced differentiation in ABCB7 shRNA-induced cells by Day 7, with no overall decline in cell viability. Interestingly, knock down of SF3B1 expression with shRNA also reduces ABCB7 mRNA. However, it also promotes cell death. This is consistent with the heterozygous nature of SF3B1 hotspot mutations; severe loss of SF3B1 function is deleterious. We propose that hotspot SF3B1 mutants promote aberrant splicing of multiple genes, inducing a general “spliceosomal sickness” in addition to downregulating key genes (e.g. ABCB7) responsible for erythroid differentiation impairment, such as that observed in RARS. Citation Format: Rachel B. Darman, Samantha A. Perino, Michael Seiler, Shouyong Peng, Jacob Feala, Peter Fekkes, Gregg F. Keaney, Kaiko Kunii, Linda Lee, Kian Huat Lim, Yoshiya Oda, Khin Myint, Esther A. Obeng, Ermira Pazolli, Eun Sun Park, John Yuan Wang, Markus Warmuth, Lihua Yu, Ping Zhu, Yoshiharu Mizui, Benjamin L. Ebert, Peter G. Smith, Silvia Buonamici. Mutant SF3B1 downregulates proteins involved in differentiation, including ABCB7. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B125.

Abstract 2941: Targeting MCL1-dependent cancers through RNA splicing modulation

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA Myeloid cell leukemia 1 (MCL1) is a member of the BCL2-family of proteins governing the apoptosis pathway and is one of the most frequently amplified genes in cancer. MCL1 overexpression often results in dependence on MCL1 for survival and is linked to resistance to anticancer therapies. However, the development of direct MCL1 inhibitors has proven challenging and thus far has been unsuccessful. Alternative splicing of MCL1 converts the anti-apoptotic MCL1 long (MCL1-L) isoform to the BH3-only containing MCL1 short (MCL1-S) isoform. As a potential approach for targeting MCL1-dependent cancers, we explored the use of MCL1 splicing modulators. We screened a unique chemical library of compounds that span a range of splicing activities on various substrates in an in vitro assay. Interestingly, we found a subset of general splicing modulators, as well as a subset of SF3B1 inhibitors, that are capable of driving the distinctive alterations in MCL1 splicing that in turn can trigger preferential killing of MCL1-dependent cell lines. The best modulators induce a prominent down-regulation of MCL1-L, up-regulation of MCL1-S, and accumulation of intron-retained MCL1 transcript. Somewhat surprisingly, several additional avenues of investigation pointed to MCL1-L down-regulation rather than MCL1-S up-regulation as the driver of preferential killing of MCL1-dependent cells. This includes the fact that compound-induced cytotoxicity can be rescued by expression of a MCL1-L cDNA and MCL1-L specific shRNA knockdown is sufficient to kill MCL1-dependent cells. On the other hand, overexpression of MCL1-S cDNA had no significant effect on cells and splicing modulators that induced very high levels of MCL1-S mRNA in the absence potent MCL1-L down-regulation exhibit minimal cytotoxicity. Biochemical characterization and understanding of these MCL1 splicing modulators has enabled further optimization of compounds that can induce potent and preferential killing of MCL1-dependent cancer cell lines in vitro. Preliminary studies in mice bearing MCL1-dependent NSCLC xenografts confirmed current lead compounds can indeed induce rapid down-regulation of MCL1-L, induction of apoptosis, and antitumor activity. Collectively these data yield insight into mechanisms of MCL1 splicing modulation that can trigger acute apoptosis in MCL1-dependent cancers and provides support for the idea of using splicing modulators to target difficult-to-drug oncogenic drivers such as MCL1. Citation Format: Eun Sun Park, Michelle Aicher, Daniel Aird, Silvia Buonamici, Betty Chan, Cheryl Eifert, Peter Fekkes, Craig Furman, Baudouin Gerard, Craig Karr, Gregg Keaney, Kaiko Kunii, Linda Lee, Ermira Pazolli, Sudeep Prajapati, Takashi Satoh, Peter Smith, John Yuan Wang, Karen Wang, Markus Warmuth, Lihua Yu, Ping Zhu, Yoshiharu Mizui, Laura B. Corson. Targeting MCL1-dependent cancers through RNA splicing modulation. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2941. doi:10.1158/1538-7445.AM2015-2941

Abstract 5564: Total synthesis of 6-deoxypladienolide D and assessment of splicing inhibitory activity in a mutant SF3B1 cancer cell line

Hotspot mutations in several components of the spliceosome have been reported in various hematological (CLL, MDS, etc.) and solid tumor (melanoma, pancreatic, etc.) malignancies. SF3B1 is a component of the U2 snRNP complex of the spliceosome and is involved in the recognition of 3′-splice sites during early spliceosomal assembly. We and others have demonstrated that mutations in SF3B1 result in neomorphic activity and trigger the production of aberrantly spliced transcripts. Thus, the discovery of small molecule modulators of SF3B1 splicing activity may have therapeutic potential in cancers harboring SF3B1 mutations. Members of the pladienolide family of natural products have been shown to affect RNA splicing through interaction with SF3B1. We have found that one particular natural product in this family, 6-deoxypladienolide D, demonstrates potent growth inhibition and cellular lethality in Panc 05.04 cells (a hotspot mutant SF3B1 cancer cell line). Due to the limited natural supply of 6-deoxypladienolide D and our interest in identifying chemical matter able to modulate splicing in these newly-identified mutant SF3B1 cancers, a total synthesis of 6-deoxypladienolide D using versatile and modular fragments was initiated. We will describe the first total synthesis of the natural product 6-deoxypladienolide D. Two noteworthy synthetic attributes are: 1) a late-stage allylic oxidation which proceeds with full chemo-, regio-, and diastereoselectivity and 2) the use of cost-effective starting materials and reagents to enable access to 6-deoxypladienolide D and its analogs for biological evaluation. We will show that 6-deoxypladienolide D demonstrates: 1) high binding affinity to the SF3b complex, 2) ability to modulate canonical pre-mRNA splicing, and 3) modulation of aberrant splicing induced by mutant SF3B1. Citation Format: Kenzo Arai, Silvia Buonamici, Betty Chan, Laura Corson, Atsushi Endo, Baudouin Gerard, Ming-Hong Hao, Craig Karr, Kazunobu Kira, Linda Lee, Xiang Liu, Jason T. Lowe, Tuoping Luo, Lisa A. Marcaurelle, Yoshiharu Mizui, Marta Nevalainen, Morgan Welzel O9Shea, Eun Sun Park, Samantha A. Perino, Sudeep Prajapati, Mingde Shan, Peter G. Smith, Parcharee Tivitmahaisoon, John Yuan Wang, Markus Warmuth, Kuo-Ming Wu, Lihua Yu, Huiming Zhang, Guo Zhu Zheng, Gregg F. Keaney. Total synthesis of 6-deoxypladienolide D and assessment of splicing inhibitory activity in a mutant SF3B1 cancer cell line. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5564. doi:10.1158/1538-7445.AM2015-5564

Abstract 2040: Mutations in SF3B1 lead to aberrant splicing through cryptic 3′ splice site selection and impair hematopoietic cell differentiation

Heterozygous mutations in SF3B1, a component of the U2 complex involved in the recognition of 3′ splice sites (ss), have been reported with high frequency in refractory anemia with ring sideroblasts (RARS, a subtype of myelodysplastic syndrome, MDS) and have also been observed in chronic lymphocytic leukemia (CLL) and several solid tumors. To study the impact of SF3B1 mutations on splicing, RNAseq data obtained from breast cancer, melanoma, CLL and MDS samples with mutant (SF3B1MUT) or wild-type SF3B1 (SF3B1WT) were compared. The majority of aberrant junctions identified in the samples with mutant SF3B1 utilized an alternative 3′ss, suggesting its neomorphic function. Motif analysis of the sequences used by SF3B1MUT revealed the usage of a cryptic AG with a shorter and weaker polypyrimidine tract. Minigenes with modifications of these sites revealed the importance of both intronic and exonic sequence features for the recognition of the cryptic AG by SF3B1MUT. Of the aberrant junctions identified, several were common across all hotspot mutations and diseases; however, a unique aberrant splicing profile was found for each disease suggesting lineage and disease specific effects. The majority of splicing defects introduced a premature termination codon downstream of the cryptic AG leading to nonsense mediated decay (NMD) of aberrant transcripts and downregulation of gene expression, such as ABCB7. Gene-set enrichment analysis of aberrantly spliced and differentially expressed genes in SF3B1MUT MDS samples identified genes involved in cell differentiation and epigenetic pathways which are known to be deregulated in MDS. The impact on erythroid differentiation by SF3B1MUT was studied in transduced TF-1 cells following erythropoietin (EPO) stimulation. As expected, TF-1 SF3B1WT cells were able to differentiate normally after EPO treatment; however, expression of SF3B1K700E (the most common hotspot mutation found in RARS and CLL) induced a block in erythoid differentiation. This differentiation block was not observed with the expression of SF3B1G742D, a mutation found in CLL but not RARS, suggesting a context dependent role for SF3B1 mutations. Interestingly, the differentiation block observed in SF3B1K700E was associated with cytokine independent growth. Initial mining of RNAseq data from SF3B1MUT TF-1 cells highlighted several aberrantly spliced and NMD-downregulated genes previously implicated in MDS. Finally, a xenograft model was developed by subcutaneous implantation of transduced TF-1 cells. After several passages, an enrichment of TF-1 SF3B1K700E cells was observed, suggesting a growth advantage for SF3B1MUT cells over SF3B1WT cells. This data suggests that the K700E SF3B1 mutation can lead to a block in differentiation and competitive advantage as observed in human RARS. Citation Format: Silvia Buonamici, Samantha Perino, Kian Huat Lim, Jacob Feala, Rachel Darman, Esther Obeng, Richard R. Furman, Suzanna Bailey, Gregg Keaney, Pavan Kumar, Yoshiharu Mizui, Eunice Park, John Wang, Markus Warmuth, Lihua Yu, Ping Zhu, Benjamin L. Ebert, Peter Smith. Mutations in SF3B1 lead to aberrant splicing through cryptic 3′ splice site selection and impair hematopoietic cell differentiation. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2040. doi:10.1158/1538-7445.AM2015-2040

Abstract 2932: SF3B1 mutations induce aberrant mRNA splicing in cancer and confer sensitivity to spliceosome inhibition

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Recurrent heterozygous mutations of the spliceosome protein SF3B1 have been identified in myelodysplastic syndromes, chronic lymphocytic leukemia (CLL), breast, pancreatic and skin cancers. SF3B1 is a component of the U2 snRNP complex which binds to the pre-mRNA branch point site and is involved in recognition and stabilization of the spliceosome at the 3′ splice site. To understand the impact of SF3B1 mutations, we compared RNAseq profiles from tumor samples with SF3B1 hotspot mutations (SF3B1-MUT) or wild-type SF3B1 (SF3B1-WT) in breast cancer, melanoma and CLL. This analysis revealed significant increases in the usage of novel alternative splice junctions in SF3B1-MUT samples including selection of alternative 3′ splice sites and less frequently exon skipping. These events induce expression of alternative mRNAs that are translated into novel proteins or aberrant mRNAs that are decayed by cells. A common alternative splicing profile was shared across different hotspot mutations and lineages (e.g. ZDHHC16 and COASY); however, unique alternative splicing profiles were also observed suggesting lineage specific effects. RNAseq analysis of several cell lines with endogenous SF3B1 hotspot mutations confirmed the presence of the same spliced isoforms as observed in tumor samples. To prove that SF3B1-MUT were inducing alternative splicing, transient transfection of several SF3B1 hotspot mutations in 293FT cells induced the expression of the common alternatively spliced genes suggesting functional similarity. Selective shRNA depletion of mutant SF3B1 allele in SF3B1-MUT cells resulted in downregulation of the same splice isoforms. Furthermore, isogenic B-cell lines (NALM-6) expressing the most frequent SF3B1 mutation (K700E) were generated and profiled by RNAseq. As expected, similar alternatively spliced genes were observed in NALM-6 SF3B1-K700E cells exclusively. To investigate the role of nonsense-mediated mRNA decay (NMD) in eliminating aberrant mRNAs induced by SF3B1-MUT, we treated NALM-6 SF3B1-K700E cells with cycloheximide, a translation inhibitor known to inhibit NMD. In the treated samples, expression of several aberrant mRNAs was revealed and some of these transcripts were shown to be downregulated in patient samples. Taken together, these results confirm the association between different SF3B1 hotspot mutations and the presence of novel splice isoforms. We demonstrated that E7107, a potent and selective inhibitor of wild-type SF3B1, also binds and inhibits SF3B1-MUT protein. In addition, E7107 represses the expression of several common aberrant splice mRNA products in SF3B1-MUT cells in vitro and in vivo. When tested in a NALM-6 mouse model, E7107 induced tumor regression and increased the overall survival of animals implanted with NALM-6 SF3B1-K700E cells. These data suggest splicing inhibitors as a promising therapeutic approach for cancer patients carrying SF3B1 mutations. Citation Format: Silvia Buonamici, Kian Huat Lim, Jacob Feala, Eunice Park, Laura Corson, Michelle Aicher, Daniel Aird, Betty Chan, Erik Corcoran, Rachel Darman, Peter Fekkes, Gregg Keaney, Pavan Kumar, Kaiko Kunii, Linda Lee, Xiaoling Puyang, Jose Rodrigues, Anand Selvaraj, Michael Thomas, John Wang, Markus Warmuth, Lihua Yu, Ping Zhu, Peter Smith, Yoshiharu Mizui. SF3B1 mutations induce aberrant mRNA splicing in cancer and confer sensitivity to spliceosome inhibition. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2932. doi:10.1158/1538-7445.AM2014-2932