A first-in-class POLRMT specific inhibitor IMT1 suppresses endometrial carcinoma cell growth

Deregulation of mitochondrial gene expression in cancer: mechanisms and therapeutic opportunities

"Reprogramming of energy metabolism" was first considered an emerging hallmark of cancer in 2011 by Hanahan & Weinberg and is now considered a core hallmark of cancer. Mitochondria are the hubs of metabolism, crucial for energetic functions and cellular homeostasis. The mitochondrion's bacterial origin and preservation of their own genome, which encodes proteins and RNAs essential to their function, make them unique organelles. Successful generation of mitochondrial gene products requires coordinated functioning of the mitochondrial 'central dogma,' encompassing all steps necessary for mtDNA to yield mitochondrial proteins. Each of these processes has several levels of regulation, including mtDNA accessibility and protection through mtDNA packaging and epigenetic modifications, mtDNA copy number through mitochondrial replication, mitochondrial transcription through mitochondrial transcription factors, and mitochondrial translation through mitoribosome formation. Deregulation of these mitochondrial processes in the context of cancers has only recently been appreciated, with most studies being correlative in nature. Nonetheless, numerous significant associations of the mitochondrial central dogma with pro-tumor phenotypes have been documented. Several studies have even provided mechanistic insights and further demonstrated successful pharmacologic targeting strategies. Based on the emergent importance of mitochondria for cancer biology and therapeutics, it is becoming increasingly important that we gain an understanding of the underpinning mechanisms so they can be successfully therapeutically targeted. It is expected that this mechanistic understanding will result in mitochondria-targeting approaches that balance anticancer potency with normal cell toxicity. This review will focus on current evidence for the dysregulation of mitochondrial gene expression in cancers, as well as therapeutic opportunities on the horizon.

Targeting POLRMT by IMT1 inhibits colorectal cancer cell growth

This study investigates the potential anti-colorectal cancer (CRC) activity of IMT1, a novel specific inhibitor of mitochondrial RNA polymerase (POLRMT). Single-cell RNA sequencing data reveal that POLRMT is overexpressed in CRC cells. Additionally, elevated POLRMT expression was observed in local CRC tissues and cells, while its expression remained relatively low in colon epithelial tissues and cells. IMT1 significantly inhibited colony formation, cell viability, proliferation, cell cycle progression, and migration in both primary and immortalized CRC cells. Furthermore, IMT1 induced apoptosis and cell death in CRC cells. The inhibition of POLRMT by IMT1 disrupted mitochondrial functions in CRC cells, leading to mitochondrial depolarization, oxidative damage, and decreased ATP levels. Using targeted shRNA to silence POLRMT closely mirrored the effects of IMT1, showing robust anti-CRC cell activity. Crucially, the efficacy of IMT1 was diminished in CRC cells with silenced POLRMT. Contrarily, boosting POLRMT expression externally by a lentiviral construct promoted the proliferation and migration of CRC cells. Importantly, treatment with IMT1 or silencing POLRMT in primary colon cancer cells decreased the phosphorylation of Akt1-S6K1, whereas overexpression of POLRMT had the opposite effect. In nude mice, orally administering IMT1 potently restrained primary colon cancer xenograft growth. IMT1 suppressed POLRMT activity, disrupted mitochondrial function, hindered Akt-mTOR activation, and prompted apoptosis within the xenograft tissues. In addition, IMT1 administration suppressed lung metastasis of primary colon cancer cells in nude mice. These combined results highlight the robust anti-CRC activity of IMT1 by specifically targeting POLRMT.

Identification of 6-Fluorine-Substituted Coumarin Analogues as POLRMT Inhibitors with High Potency and Safety for Treatment of Pancreatic Cancer

Increasing evidence has demonstrated that oxidative phosphorylation (OXPHOS) is closely associated with the progression of pancreatic cancer (PC). Given its central role in mitochondrial transcription, the human mitochondrial RNA polymerase (POLRMT) is a promising target for developing PC treatments. Herein, structure-activity relationship exploration led to the identification of compound S7, which was the first reported POLRMT inhibitor possessing single-digit nanomolar potency of inhibiting PC cells proliferation. Mechanistic studies showed that compound S7 exerted antiproliferative effects without affecting the cell cycle, apoptosis, mitochondrial membrane potential (MMP), or intracellular reactive oxygen species (ROS) levels specifically in MIA PaCa-2 cells. Notably, compound S7 inhibited tumor growth in MIA PaCa-2 xenograft tumor model with a tumor growth inhibition (TGI) rate of 64.52% demonstrating significant improvement compared to the positive control (44.80%). In conclusion, this work enriched SARs of POLRMT inhibitors, and compound S7 deserved further investigations of drug-likeness as a candidate for PC treatment.

Identification of the central role of RNA polymerase mitochondrial for angiogenesis

Mitochondria are central to endothelial cell activation and angiogenesis, with the RNA polymerase mitochondrial (POLRMT) serving as a key protein in regulating mitochondrial transcription and oxidative phosphorylation. In our study, we examined the impact of POLRMT on angiogenesis and found that its silencing or knockout (KO) in human umbilical vein endothelial cells (HUVECs) and other endothelial cells resulted in robust anti-angiogenic effects, impeding cell proliferation, migration, and capillary tube formation. Depletion of POLRMT led to impaired mitochondrial function, characterized by mitochondrial depolarization, oxidative stress, lipid oxidation, DNA damage, and reduced ATP production, along with significant apoptosis activation. Conversely, overexpressing POLRMT promoted angiogenic activity in the endothelial cells. In vivo experiments demonstrated that endothelial knockdown of POLRMT, by intravitreous injection of endothelial specific POLRMT shRNA adeno-associated virus, inhibited retinal angiogenesis. In addition, inhibiting POLRMT with a first-in-class inhibitor IMT1 exerted significant anti-angiogenic impact in vitro and in vivo. Significantly elevated expression of POLRMT was observed in the retinal tissues of streptozotocin-induced diabetic retinopathy (DR) mice. POLRMT endothelial knockdown inhibited pathological retinal angiogenesis and mitigated retinal ganglion cell (RGC) degeneration in DR mice. At last, POLRMT expression exhibited a substantial increase in the retinal proliferative membrane tissues of human DR patients. These findings collectively establish the indispensable role of POLRMT in angiogenesis, both in vitro and in vivo.

Fumarate hydratase as a metabolic regulator of immunity

Tricarboxylic acid (TCA) cycle metabolites have been implicated in modulating signalling pathways in immune cells. Notable examples include succinate and itaconate, which have pro- and anti-inflammatory roles, respectively. Recently, fumarate has emerged as having specific roles in macrophage activation, regulating the production of such cytokines as interleukin (IL)-10 and type I interferons (IFNs). Fumarate hydratase (FH) has been identified as a control point. Notably, FH loss in different models and cell types has been found to lead to DNA and RNA release from mitochondria which are sensed by cytosolic nucleic acid sensors including retinoic acid-inducible gene (RIG)-I, melanoma differentiation-associated protein (MDA)5, and cyclic GMP-AMP synthase (cGAS) to upregulate IFN-β production. These findings may have relevance in the pathogenesis and treatment of diseases associated with decreased FH levels such as systemic lupus erythematosus (SLE) or FH-deficient kidney cancer.

Mitochondria transcription and cancer

Mitochondria are major organelles involved in several processes related to energy supply, metabolism, and cell proliferation. The mitochondria function is transcriptionally regulated by mitochondria DNA (mtDNA), which encodes the key proteins in the electron transport chain that is indispensable for oxidative phosphorylation (OXPHOS). Mitochondrial transcriptional abnormalities are closely related to a variety of human diseases, such as cardiovascular diseases, and diabetes. The mitochondria transcription is regulated by the mtDNA, mitochondrial RNA polymerase (POLRMT), two transcription factors (TFAM and TF2BM), one transcription elongation (TEFM), and one known transcription termination factor (mTERFs). Dysregulation of these factors directly leads to altered expression of mtDNA in tumor cells, resulting in cellular metabolic reprogramming and mitochondrial dysfunction. This dysregulation plays a role in modulating tumor progression. Therefore, understanding the role of mitochondrial transcription in cancer can have implications for cancer diagnosis, prognosis, and treatment. Targeting mitochondrial transcription or related pathways may provide potential therapeutic strategies for cancer treatment. Additionally, assessing mitochondrial transcriptional profiles or biomarkers in cancer cells or patient samples may offer diagnostic or prognostic information.

Targeting POLRMT by a first-in-class inhibitor IMT1 inhibits osteosarcoma cell growth in vitro and in vivo

Osteosarcoma (OS) is a highly aggressive form of bone cancer that predominantly affects adolescents and young adults. In this study, we have undertaken an investigation into the potential anti-OS cell activity of IMT1 (inhibitor of mitochondrial transcription 1), a first-in-class inhibitor of RNA polymerase mitochondrial (POLRMT). IMT1 exhibited a profound inhibitory effect on cell survival, proliferation, cell cycle progression, and migration in primary and immortalized OS cells. Furthermore, this POLRMT inhibitor elicited apoptosis in the OS cells, without, however, inducing cytotoxicity in human osteoblasts or osteoblastic cells. IMT1 disrupted mitochondrial functions in OS cells, resulting in mitochondrial depolarization, oxidative injury, lipid peroxidation, and ATP reduction in OS cells. Silencing POLRMT using targeted shRNA closely mimicked the actions of IMT1 and exerted potent anti-OS cell activity. Importantly, IMT1's effectiveness was diminished in POLRMT-silenced OS cells. Subsequent investigations revealed that IMT1 suppressed the activation of the Akt-mammalian target of rapamycin (mTOR) cascade in OS cells. IMT1 treatment or POLRMT silencing in primary OS cells led to a significant reduction in Akt1-S6K-S6 phosphorylation. Conversely, it was enhanced upon POLRMT overexpression. The restoration of Akt-mTOR activation through the introduction of a constitutively active S473D mutant Akt1 (caAkt1) mitigated IMT1-induced cytotoxicity in OS cells. In vivo, oral administration of IMT1 robustly curtailed the growth of OS xenografts in nude mice. Furthermore, IMT1 suppressed POLRMT activity, impaired mitochondrial function, repressed Akt-mTOR activation, and induced apoptosis within xenograft tissues. Collectively, these findings underscore the potent growth-inhibitory effects attributed to IMT1 via targeted POLRMT inhibition. The utilization of this POLRMT inhibitor carries substantial therapeutic promise in the context of OS treatment.

Identification of the mitochondrial protein POLRMT as a potential therapeutic target of prostate cancer

RNA polymerase mitochondria (POLRMT) is essential for mitochondrial transcription machinery and other mitochondrial functions. Its expression and potential functions in prostate cancer were explored here. The Cancer Genome Atlas prostate cancer cohort (TCGA PRAD) shows that POLRMT mRNA expression is upregulated in prostate cancer tissues and POLRMT upregulation is correlated with poor patients' survival. POLRMT mRNA and protein levels were upregulated in local prostate cancer tissues and different primary/immortalized prostate cancer cells. Genetic depletion of POLRMT, using viral shRNA or CRISPR/Cas9 gene editing methods, impaired mitochondrial functions in prostate cancer cells, leading to mitochondrial depolarization, oxidative stress, mitochondria complex I inhibition, and ATP depletion. Moreover, POLRMT depletion resulted in robust inhibition of prostate cancer cell viability, proliferation, and migration, and provoked apoptosis. Conversely, prostate cancer cell proliferation, migration, and ATP contents were strengthened following ectopic POLRMT overexpression. In vivo, intratumoral injection of POLRMT shRNA adeno-associated virus impeded prostate cancer xenograft growth in nude mice. POLRMT silencing, oxidative stress, and ATP depletion were detected in POLRMT shRNA-treated prostate cancer xenograft tissues. IMT1 (inhibitor of mitochondrial transcription 1), the first-in-class POLRMT inhibitor, inhibited prostate cancer cell growth in vitro and in vivo. Together, overexpressed POLRMT is an important mitochondrial protein for prostate cancer cell growth, representing a novel and promising diagnostic and therapeutic oncotarget.

Targeting Mitochondrial DNA Transcription by POLRMT Inhibition or Depletion as a Potential Strategy for Cancer Treatment

Transcription of the mitochondrial genome is essential for the maintenance of oxidative phosphorylation (OXPHOS) and other functions directly related to this unique genome. Considerable evidence suggests that mitochondrial transcription is dysregulated in cancer and cancer metastasis and contributes significantly to cancer cell metabolism. Recently, inhibitors of the mitochondrial DNA-dependent RNA polymerase (POLRMT) were identified as potentially attractive new anti-cancer compounds. These molecules (IMT1, IMT1B) inactivate cancer cell metabolism through reduced transcription of mitochondrially-encoded OXPHOS subunits such as ND1-5 (Complex I) and COI-IV (Complex IV). Studies from our lab have discovered small molecule regulators of the mitochondrial matrix caseinolytic protease (ClpP) as probable inhibitors of mitochondrial transcription. These compounds activate ClpP proteolysis and lead to the rapid depletion of POLRMT and other matrix proteins, resulting in inhibition of mitochondrial transcription and growth arrest. Herein we present a comparison of POLRMT inhibition and ClpP activation, both conceptually and experimentally, and evaluate the results of these treatments on mitochondrial transcription, inhibition of OXPHOS, and ultimately cancer cell growth. We discuss the potential for targeting mitochondrial transcription as a cancer cell vulnerability.

SLC5A3 is important for cervical cancer cell growth

Novel molecular targets for cervical cancer must be identified. This study examined the role of SLC5A3, a myo-inositol transporter, in the pathogenesis of cervical cancer. Through boinformatics analysis, we showed that the SLC5A3 mRNA levels were upregulated in cervical cancer tissues. The upregulated SLC5A3 mRNA levels were negatively correlated with survival and progression-free interval. Genes co-expressed with SLC5A3 were enriched in multiple signaling cascades involved in cancer progression. In primary/established cervical cancer cells, SLC5A3 shRNA/knockout (KO) exerted growth-inhibitory effects and promoted cell death/apoptosis. Furthermore, SLC5A3 knockdown or KO downregulated myo-inositol levels, induced oxidative injury, and decreased Akt-mTOR activation in cervical cancer cells. In contrast, supplementation of myo-inositol or n-acetyl-L-cysteine or transduction of a constitutively active Akt1 construct mitigated SLC5A3 KO-induced cytotoxicity in cervical cancer cells. Lentiviral SLC5A3 overexpression construct transduction upregulated the cellular myo-inositol level and promoted Akt-mTOR activation, enhancing cervical cancer cell proliferation and migration. The binding of TonEBP to the SLC5A3 promoter was upregulated in cervical cancer. In vivo studies showed that intratumoral injection of SLC5A3 shRNA-expressing virus arrested cervical cancer xenograft growth in mice. SLC5A3 KO also inhibited pCCa-1 cervical cancer xenograft growth. The SLC5A3-depleted xenograft tissues exhibited myo-inositol downregulation, Akt-mTOR inactivation, and oxidative injury. Transduction of sh-TonEBP AAV construct downregulated SLC5A3 expression and inhibited pCCa-1 cervical cancer xenograft growth. Together, overexpressed SLC5A3 promotes growth of cervical cancer cells, representing as a novel therapeutic oncotarget for the devastating disease.