miRNA Therapeutic Promise
Curator: Larry H. Bernstein, MD, FCAP
MicroRNA Expression Could Be Key to Leukemia Treatment
http://www.genengnews.com/gen-news-highlights/microrna-expression-could-be-key-to-leukemia-treatment/81252662/
Generalized gene regulation mechanisms of miRNAs. [NIH]
Increasingly, cancer researchers are discovering novel biological pathways that regulate the expression of various genes that are often strongly associated with tumorigenesis. These new molecular mechanisms represent important potential therapeutic targets for aggressive and difficult-to-treat cancers. In particular, microRNAs (miRNAs)—small, noncoding genetic material that regulates gene expression—have steadily become implicated in the progression of some cancers.
Now, researchers at the University of Cincinnati (UC) have found a particular signaling route for a microRNA, miR-22, that they believe leads to targets for acute myeloid leukemia (AML), the most common type of fast-growing cancer of the blood and bone marrow.
The findings from this study were published recently in Nature Communications in an article entitled “miR-22 Has a Potent Anti-Tumour Role with Therapeutic Potential in Acute Myeloid Leukaemia.”
Structure of mi-22 miccroRNA. [Ppgardne at el., via Wikimedia Commons]
Increasingly, cancer researchers are discovering novel biological pathways that regulate the expression of various genes that are often strongly associated with tumorigenesis. These new molecular mechanisms represent important potential therapeutic targets for aggressive and difficult-to-treat cancers. In particular, microRNAs (miRNAs)—small, noncoding genetic material that regulates gene expression—have steadily become implicated in the progression of some cancers.
Now, researchers at the University of Cincinnati (UC) have found a particular signaling route for a microRNA, miR-22, that they believe leads to targets for acute myeloid leukemia (AML), the most common type of fast-growing cancer of the blood and bone marrow.
The findings from this study were published recently in Nature Communications in an article entitled “miR-22 Has a Potent Anti-Tumour Role with Therapeutic Potential in Acute Myeloid Leukaemia.”
“MicroRNAs make up a class of small, noncoding internal RNAs that control a gene’s job, or expression, by directing their target messaging RNAs, or mRNAs, to inhibit or stop. Cellular organisms use mRNA to convey genetic information,” explained senior study author Jianjun Chen, Ph.D., associate professor in the department of cancer biology at the UC College of Medicine. “Previous research has shown that microRNA miR-22 is linked to breast cancer and other blood disorders which sometimes turn into AML, but we found in this study that it could be an essential anti-tumor gatekeeper in AML when it is down-regulated, meaning its function is minimized.”
AML—most common type of acute leukemia—arises when the bone marrow begins to make blasts, cells that have not yet completely matured. These blast cells typically develop into white blood cells; however, in AML the cells do not develop and are unable to aid in warding off infections. In the current study, the UC team describes how altering the expression of miR-22 affected AML pathogenesis.
“When we forced miR-22 expression, we saw difficulty in leukemia cells developing, growing, and thriving. miR-22 targets multiple cancer-causing genes (CRTC1, FLT3, and MYCBP) and blocks certain pathways (CREB and MYC),” Dr. Chen noted. “The downregulation, or decreased output, of miR-22 in AML, is caused by the loss of the number of DNA being copied and/or stopping their expression through a pathway called TET1/GFI1/EZH2/SIN3A. Also, nanoparticles carrying miR-22 DNA oligonucleotides (short nucleic acid molecules) prevented leukemia advancement.”
The investigators conducted the study using bone marrow transplant samples and animal models. The researchers showed that the ten-eleven translocation proteins (TET1/2/3) in mammals helped to control genetic expression in normal developmental processes. This was in sharp contrast to mutations that cause function loss and tumor-slowing with TET2, which has been observed previously in blood and stem cell cancers.
“We recently reported that TET1 plays an essential cancer generating role in certain AML where it activates expression of homeobox genes, which are a large family of similar genes that direct the formation of many body structures during early embryonic development,” remarked Dr. Chen. “However, it is unknown whether TET1 can also function as a repressor for cellular function in cancer, and its role in microRNA expression has rarely been studied.”
Dr. Chen added that these findings are important in targeting a cancer that is both common and fatal, stating that “the majority of patients with ALM usually don’t survive longer than 5 years, even with chemotherapy, which is why the development of new effective therapies based on the underlying mechanisms of the disease is so important.”
“Our study uncovers a previously unappreciated signaling pathway (TET1/GFI1/EZH2/SIN3A/miR-22/CREB-MYC) and provides new insights into genetic mechanisms causing and progressing AML and also highlights the clinical potential of miR-22-based AML therapy. More research on this pathway and ways to target it are necessary,” Dr. Chen concluded.
miR-22 has a potent anti-tumour role with therapeutic potential in acute myeloid leukaemia
Xi Jiang, Chao Hu, Stephen Arnovitz, Jason Bugno, Miao Yu, Zhixiang Zuo, Ping Chen, et al.
Nature Communications 26 Apr 2016; 7(11452). http://dx.doi.org:/doi:10.1038/ncomms11452
MicroRNAs are subject to precise regulation and have key roles in tumorigenesis. In contrast to the oncogenic role of miR-22 reported in myelodysplastic syndrome (MDS) and breast cancer, here we show that miR-22 is an essential anti-tumour gatekeeper in de novo acute myeloid leukaemia (AML) where it is significantly downregulated. Forced expression of miR-22 significantly suppresses leukaemic cell viability and growth in vitro, and substantially inhibits leukaemia development and maintenance in vivo. Mechanistically, miR-22 targets multiple oncogenes, including CRTC1, FLT3 and MYCBP, and thus represses the CREB and MYC pathways. The downregulation of miR-22 in AML is caused by TET1/GFI1/EZH2/SIN3A-mediated epigenetic repression and/or DNA copy-number loss. Furthermore, nanoparticles carrying miR-22 oligos significantly inhibit leukaemia progression in vivo. Together, our study uncovers a TET1/GFI1/EZH2/SIN3A/miR-22/CREB-MYC signalling circuit and thereby provides insights into epigenetic/genetic mechanisms underlying the pathogenesis of AML, and also highlights the clinical potential of miR-22-based AML therapy.
As one of the most common and fatal forms of hematopoietic malignancies, acute myeloid leukaemia (AML) is frequently associated with diverse chromosome translocations (for example t(11q23)/MLL-rearrangements, t(15;17)/PML-RARA and t(8;21)/AML1-ETO) and molecular abnormalities (for example, internal tandem duplications of FLT3 (FLT3-ITD) and mutations in nucleophosmin (NPM1c+))1. Despite intensive chemotherapies, the majority of patients with AML fail to survive longer than 5 years2, 3. Thus, development of effective therapeutic strategies based on a better understanding of the molecular mechanisms underlying the pathogenesis of AML is urgently needed.
MicroRNAs (miRNAs) are a class of small, non-coding RNAs that post-transcriptionally regulate gene expression4. Individual miRNAs may play distinct roles in cancers originating from different tissues or even from different lineages of hematopoietic cells4. It is unclear whether a single miRNA can play distinct roles between malignancies originating from the same hematopoietic lineage, such as de novo AML and myelodysplastic syndrome (MDS). Although around 30% of MDS cases transform to AML, the genetic and epigenetic landscapes of MDS or MDS-derived AML are largely different from those of de novo AML5, 6. MDS and MDS-derived AML are more responsive to hypomethylating agents than de novo AML7. The molecular mechanisms underlying the distinct pathogenesis and drug response between MDS (or MDS-derived AML) and de novo AML remain unclear.
The ten-eleven translocation (Tet1/2/3) proteins play critical transcriptional regulatory roles in normal developmental processes as activators or repressors8, 9, 10. In contrast to the frequent loss-of-function mutations and tumour-suppressor role of TET2 observed in hematopoietic malignancies11, 12, 13, we recently reported that TET1 plays an essential oncogenic role in MLL-rearranged AML where it activates expression of homeobox genes14. However, it is unknown whether TET1 can also function as a transcriptional repressor in cancer. Moreover, Tet1-mediated regulation of miRNA expression has rarely been studied10.
In the present study, we demonstrate that miR-22, an oncogenic miRNA reported in breast cancer and MDS15, 16, is significantly downregulated in most cases of de novo AML due to TET1/GFI1/EZH2/SIN3A-mediated epigenetic repression and/or DNA copy-number loss. miR-22 functions as an essential anti-tumour gatekeeper in various AML and holds great therapeutic potential to treat AML.
The downregulation of miR-22 in de novo AML
Through Exiqon miRNA array profiling, we previously identified a set of miRNAs, such as miR-150, miR-148a, miR-29a, miR-29b, miR-184, miR-342, miR-423 and miR-22, which are significantly downregulated in AML compared with normal controls17. Here we showed that among all the above miRNAs, miR-150 and especially miR-22 exhibited the most significant and consistent inhibitory effect on MLL-AF9-induced cell immortalization in colony-forming/replating assays (CFA) (Supplementary Fig. 1a). In contrast to the reported upregulation of miR-22 in MDS16, our original microarray data17 (Fig. 1a,b) and new quantitative PCR-independent validation data (Supplementary Fig. 1b) demonstrated a significant and global downregulation of miR-22 in de novo AML relative to normal controls. Notably, miR-22 is significantly downregulated in AML samples (P<0.05) compared with all three sub-populations of normal control cells, that is, normal CD34+ hematopoietic stem/progenitor cells (HSPCs), CD33+ myeloid progenitor cells, or mononuclear cells (MNCs) (Fig. 1a). Expression of miR-22 is significantly downregulated in all or the majority of individual subsets of AML samples than in the normal CD33+ or CD34+ cell samples (Fig. 1b).
To rule out the possibility that the inhibitory effect of miR-22 shown in Supplementary Fig. 1a was due to a non-specific effect of our miR-22 construct, we included the MSCV-PIG-miR-22 construct from Song et al.16 in a repeated CFA. Both miR-22 constructs dramatically inhibited MLL-AF9-induced colony formation (Fig. 1c). As the ‘seed’ sequences at the 5′ end of individual miRNAs are essential for the miRNA-target binding18, we also mutated the 6-bases ‘seed’ sequence of miR-22 and found that the miR-22 mutant did not inhibit colony formation anymore (Fig. 1c). In human AML cells, forced expression of miR-22, but not miR-22 mutant, significantly inhibited cell viability and growth/proliferation, while promoting apoptosis (Supplementary Fig. 1c,d).
Furthermore, as miR-22 is globally downregulated in all major types of AML (Fig. 1b), we also investigated the role of miR-22 in colony formation induced by other oncogenic fusion genes, including MLL-AF10/t(10;11), PML-RARA/t(15;17) and AML1-ETO9a/t(8;21) (ref. 19). As expected, forced expression of miR-22 significantly inhibited colony formation induced by all individual oncogenic fusions; conversely, miR-22 knockout20 significantly enhanced colony forming (Fig. 1d). These results suggest that miR-22 likely plays a broad anti-tumour role in AML.
In accordance with the potential anti-tumour function of miR-22 in AML, miR-22 was expressed at a significantly higher level (P<0.05) in human normal CD33+ myeloid progenitor cells than in more immature CD34+ HSPCs or MNC cells (a mixed population containing both primitive progenitors and committed cells) (Fig. 1a,b), implying that miR-22 is upregulated during normal myelopoiesis. Similarly, we showed that miR-22 was also expressed at a significantly higher level in mouse normal bone marrow (BM) myeloid (Gr-1+/Mac-1+) cells, relative to lineage negative (Lin−) progenitor cells, long-term hematopoietic stem cells (LT-HSCs), short-term HSCs (ST-HSCs), and committed progenitors (CPs) (Supplementary Fig. 1e), further suggesting that miR-22 is upregulated in normal myelopoiesis.
The anti-tumour effect of miR-22 in the pathogenesis of AML
Through bone marrow transplantation (BMT) assays, we showed that forced expression of miR-22 (but not miR-22 mutant) dramatically blocked MLL-AF9 (MA9)-mediated leukemogenesis in primary BMT recipient mice, with a more potent inhibitory effect than miR-150 (Fig. 1e;Supplementary Fig. 2a). All MA9+miR-22 mice exhibited normal morphologies in peripheral blood (PB), BM, spleen and liver tissues (Fig. 1f), with a substantially reduced c-Kit+ blast cell population in BM (Supplementary Fig. 2b). Forced expression of miR-22 also almost completely inhibited leukemogenesis induced by MLL-AF10 (Fig. 1g; Supplementary Fig. 2a). Conversely, miR-22 knockout significantly promoted AML1-ETO9a (AE9a)-induced AML (Fig. 1h). Thus, the repression of miR-22 is critical for the development of primary AML. Notably, forced expression of miR-22 inMLL-AF9 and MLL-AF10 leukaemia mouse models caused only a 2–3-fold increase in miR-22 expression level (Supplementary Fig. 2a), in a degree comparable to the difference in miR-22 expression levels between human AML samples and normal controls (Fig. 1a), suggesting that a 2–3-fold change in miR-22 expression level appears to be able to exert significant physiological or pathological effects.
To examine whether the maintenance of AML is also dependent on the repression of miR-22, we performed secondary BMT assays. Forced expression of miR-22 remarkably inhibited progression of MLL-AF9-, AE9a– or FLT3-ITD/NPM1c+-induced AML in secondary recipient mice (Fig. 2a–d), resulting in largely normal morphologies in PB, BM, spleen and liver tissues (Fig. 2b;Supplementary Fig. 2c). Collectively, our findings demonstrate that miR-22 is a pivotal anti-tumour gatekeeper in both development and maintenance of various AML.
To identify potential targets of miR-22 in AML, we performed a series of data analysis. Analysis of In-house_81S (ref. 21) and TCGA_177S (ref. 22) data sets revealed a total of 999 genes exhibiting significant inverse correlations with miR-22 in expression. Of them, 137 genes, including 21 potential targets of miR-22 as predicted by TargetScan18 (Supplementary Table 1), were significantly upregulated in both human and mouse AML compared with normal controls as detected in two additional in-house data sets14, 23. Among the 21 potential targets, CRTC1, ETV6and FLT3 are known oncogenes24, 25, 26, 27, 28, 29. We then focused on these three genes, along with MYCBP that encodes the MYC-binding protein and is an experimentally validated target of miR-22 (ref. 30) although due to a technical issue it was not shown in the 21-gene list (Supplementary Table 1), for further studies.
As expected, all four genes were significantly downregulated in expression by ectopic expression of miR-22 in human MONOMAC-6/t(9;11) cells (Fig. 3a). The coincidence of downregulation of those genes and upregulation of miR-22 was also observed in mouse MLL-ENL-ERtm cells, a leukaemic cell line with an inducible MLL-ENL derivative31, when MLL-ENL was depleted by 4-hydroxy-tamoxifen (4-OHT) withdrawal (Fig. 3b; Supplementary Fig. 3a). While MLL-AF9 remarkably promoted expression of those four genes in mouse BM progenitor cells, co-expressed miR-22 reversed the upregulation (Fig. 3c). In leukaemia BM blast cells of mice with MLL-AF9-induced AML, the expression of Crtc1, Flt3 and Mycbp, but not Etv6, was significantly downregulated by co-expressed miR-22 (but not by miR-22 mutant) (Fig. 3d). Because miR-22-mediated downregulation of Etv6 could be observed only in the in vitro models (Fig. 3a–c), but not in the in vivo model (Fig. 3d), which was probably due to the difference between in vitro and in vivo microenvironments, we decided to focus on the three target genes (that is, Crtc1, Flt3 and Mycbp) that showed consistent patterns between in vitro and in vivo for further studies. The repression of Crtc1, Flt3 and Mycbpwas also found in leukaemia BM cells of mice with AE9a or FLT3-ITD/NPM1c+-induced AML (Fig. 3e,f). As Mycbp is already a known target of miR-22 (ref. 30), here we further confirmed that FLT3and CRTC1 are also direct targets of miR-22 (Fig. 3g,h). The downregulation of CRTC1, FLT3 and MYCBP by miR-22 at the protein level was confirmed in both human and mouse leukaemic cells (Supplementary Fig. 3b,c). Overexpression of miR-22 had no significant influence on the level of leukaemia fusion genes (Supplementary Fig. 3d).
Figure 5: Transcriptional correlation between miR-22 and TET1.
http://www.nature.com/ncomms/2016/160426/ncomms11452/images_article/ncomms11452-f5.jpg
Restoration of miR-22 expression and function to treat AML
Figure 7: Therapeutic effect of miR-22-nanoparticles in treating AML.
http://www.nature.com/ncomms/2016/160426/ncomms11452/images_article/ncomms11452-f7.jpg
(a,b) Primary leukaemia BM cells bearing MLL-AF9 (a) or AE9a (b) were transplanted into sublethally irradiated secondary recipient mice. After the onset of secondary AML (usually 10 days post transplantation), the recipient mice were treated with PBS control, or 0.5 mg kg−1 miR-22 or miR-22 mutant RNA oligos formulated with G7 PAMAM dendrimer nanoparticles, i.v., every other day, until the PBS-treated control group all died of leukaemia. (c) NSGS mice49 were transplanted with MV4;11/t(4;11) AML cells. Five days post transplantation, these mice started to be treated with PBS control, miR-22 or miR-22 mutant nanoparticles at the same dose as described above. Kaplan–Meier curves are shown; the drug administration period and frequency were indicated with yellow arrows. The P values were detected by log-rank test. (d) Wright–Giemsa stained PB and BM, and H&E stained spleen and liver of the MLL-AF9-secondary leukaemic mice treated with PBS control, miR-22 or miR-22 mutant nanoparticles.
We then tested the miR-22 nanoparticles in a xeno-transplantation model49. Similarly, the nanoparticles carrying miR-22 oligos, but not miR-22 mutant, significantly delayed AML progression induced by human MV4;11/t(4;11) cells (Fig. 7c). The miR-22-nanoparticle administration also resulted in less aggressive leukaemic pathological phenotypes in the recipient mice (Supplementary Fig. 6e). Thus, our studies demonstrated the therapeutic potential of using miR-22-based nanoparticles to treat AML.
It remains poorly understood how TET proteins mediate gene regulation in cancer. Here we show that in de novo AML, it is TET1, but not TET2 (a reported direct target of miR-22 in MDS and breast cancer15, 16), that inversely correlates with miR-22 in expression and negatively regulates miR-22 at the transcriptional level. Likely together with GFI1, TET1 recruits polycomb cofactors (for example, EZH2/SIN3A) to the miR-22 promoter, leading to a significant increase in H3K27me3 occupancy and decrease in RNA pol II occupancy at that region, and thereby resulting in miR-22 repression in AML cells; such a repression can be abrogated by ATRA treatment. Thus, our study uncovers a novel epigenetic regulation mechanism in leukaemia involving the cooperation between TET1/GFI1 and polycomb factors.
Besides GFI1, it was reported that LSD1 is also a binding partner of TET1 (ref. 50). Interestingly, LSD1 is known as a common binding partner shared by TET1 and GFI1, and mediates the effect of GFI1 on hematopoietic differentiation51, 52. Thus, it is possible that LSD1 might also participate in the transcriptional repression of miR-22 as a component of the GFI1/TET1 repression complex.
We previously reported that TET1 cooperates with MLL fusions in positively regulating their oncogenic co-targets in MLL-rearranged AML14. Here we show that TET1 can also function as a transcriptional repressor (of a miRNA) in cancer. The requirement of TET1-mediated regulation on expression of its positive (for example, HOXA/MEIS1/PBX3)14 or negative (for example, miR-22) downstream effectors in leukemogenesis likely explains the rareness of TET1 mutations in AML53, and highlights its potent oncogenic role in leukaemia.
The aberrant activation of both CREB and MYC signalling pathways has been shown in AML24, 25,26, 54, 55, but the underlying molecular mechanisms remain elusive. Our data suggest that the activation of these two signalling pathways in AML can be attributed, at least in part, to the repression of miR-22, which in turn, results in the de-repression of CRTC1 (CREB pathway), FLT3and MYCBP (MYC pathway), and leads to the upregulation of oncogenic downstream targets (for example, CDK6, HOXA7, BMI1, FASN and HMGA1) and downregulation of tumour-suppressor downstream targets (for example, RGS2).
In summary, we uncover a TET1/GFI1/EZH2/SIN3A⊣miR-22⊣CREB-MYC signalling circuit in de novo AML, in which miR-22 functions as a pivotal anti-tumour gate-keeper, distinct from its oncogenic role reported in MDS or MDS-derived AML16. Thus, our study together with the study of Song et al.16 highlight the complexity and functional importance of miR-22-associated gene regulation and signalling pathways in hematopoietic malignancies, and may provide novel insights into the genetic/epigenetic differences between de novo AML and MDS.
Our findings also highlight the possibility of using miR-22-based therapy to treat AML patients. Our proof-of-concept studies demonstrate that the nanoparticles carrying miR-22 oligos significantly inhibit AML progression and prolong survival of leukaemic mice in both BMT and xeno-transplantation models. Notably, miRNA-based nanoparticles have already entered clinical trials56. It would be important, in the future, to further test the combination of miR-22-carrying nanoparticles (or small-molecule compounds that can induce endogenous expression of miR-22) with standard chemotherapy agents (cytosine arabinoside and anthracycline), or with the emerging small molecule inhibitors against MYC and/or CREB pathway effectors, to achieve optimal anti-leukaemia effect with minimal side effects. Overall, our results suggest that restoration of miR-22 expression/function (for example, using miR-22-carrying nanoparticles or small-molecule compounds) holds great therapeutic potential to treat AML, especially those resistant to current therapies.
MicroRNAs: A Gene Silencing Mechanism with Therapeutic Implications
Wed, July 13, 2016 The New York Academy of Sciences Presented by the Biochemical Pharmacology Discussion Group
http://www.nyas.org/Events/Detail.aspx?cid=787a5d77-8354-4df7-92d5-91db18b2ce49
MicroRNAs (miRNAs) are single-stranded RNAs about 22 nucleotides in length that repress the expression of specific proteins by annealing to complementary sequences in the 3′ untranslated regions (UTRs) of target mRNAs. Apart from their posttranscriptional expression, or silencing, miRNAs may also direct mRNA destabilization and cleavage. Moreover, rather than targeting a single disease-associated protein target as many small molecule drugs and antibodies do, each miRNA may serve to repress the expression of numerous proteins involved in the pathogenesis and progression of various diseases and could therefore potentially interfere with multiple disease-promoting signal transduction pathways. Because aberrant expression of miRNAs has been implicated in numerous disease states, miRNA-based therapies have sparked much interest for the treatment of a variety of diseases. The objective of this symposium is to bring together investigators who have led the field in describing what miRNAs do and their potential in treating diseases, as well as those who are translating these findings into promising drug candidates, some of which have already advanced into early stage clinical trials.
Call for Poster Abstracts
Abstract submissions are invited for a poster session. For complete submission instructions, please send an email to miRNA@nyas.org with the words “Abstract Information” in the subject line. The deadline for abstract submission is May 13, 2016.
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