Methylthioadenosine Research Articles

Abstract LB-A18: The frequent tumor deletion of MTAP is a newly recognized potent immune checkpoint that is effectively reversed by a human methylthioadenosine degrading drug candidate

Abstract Our lab has obtained strong in vivo evidence from multiple murine tumor models that the production of methylthioadenosine (MTA) by methylthioadenosine phosphorylase (MTAP) deficient tumors potently attenuates anti-tumor immune responses, validating its role as a potent immunosuppressive molecule. We demonstrate that administration of an engineered human MTA degrading enzyme therapeutic reverses the deleterious effects of MTA on lymphocytes in vitro, and in vivo drastically impedes the growth of MTAP deficient tumors including MTAP-/- leukemia (L1210), MTAP low colon carcinoma (CT26) and an engineered MTAP-/- B16-F10 melanoma. As a single agent our therapeutic candidate elicits a large fraction of complete and durable responses in animals with established tumors, correlating with significant increases in the populations of effector T cells in both the tumor and tumor draining lymph node. We also note that enzyme treatment displays synergism in combination with existing immune checkpoint inhibitors. Despite the remarkable success of immune checkpoint inhibitors such as anti-PD1 and anti-CTLA-4 antibodies, a large fraction of tumors do not respond to immunotherapy due to additional suppressive mechanisms such as adenosinergic signaling. Approximately 15% of all cancers exhibit homozygous MTAP deletions resulting in accumulation and secretion of the adenosine (ADO) analog, MTA. Patients with cancer MTAP deletions show reduced tumor infiltrating lymphocytes (TILs) and poor overall survival in multiple tumor types. Recent work has even suggested that MTAP loss may confer resistance to antibody immune checkpoint inhibitors. Although MTA is reported to be an ADO receptor agonist, purinergic signaling alone does not explain the distinct immune suppression associated with increased MTA. In vitro, MTA (but not ADO) strongly inhibits the proliferation and viability of both CD4+ and especially CD8+ murine T cells. Similarly, treatment with ADO receptor antagonists does not restore proliferation or reverse the cytotoxicity of MTA. Only exogenous administration of MTA degrading enzymes was able to reverse these effects, indicating that MTA impacts the viability and proliferation of T cells by a mechanism independent of ADO receptor signaling. Quantitative proteomic data suggests instead that MTA acts, at least in part, via the inhibition of methyltransferases, chromatin remodeling and upregulation of P53/apoptotic pathways in lymphocytes. Collectively our data suggest that enzymatic depletion of MTA represents a unique opportunity for a biomarker driven (namely, tumor MTAP status) immunotherapeutic modality. The evidence that the consequence of MTAP deletion acts to suppress immune effector cells and promote tumor tolerance through the buildup of MTA now suggests a clear mechanism for why this is one of the more common gene deletions observed in cancer. Citation Format: Donjeta Gjuka, George Georgiou, Everett M Stone. The frequent tumor deletion of MTAP is a newly recognized potent immune checkpoint that is effectively reversed by a human methylthioadenosine degrading drug candidate [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr LB-A18. doi:10.1158/1535-7163.TARG-19-LB-A18

Abstract B115: Mitotic defects induced by MAT2A inhibitors guides translational drug combination strategies with AG-270 and taxanes

Abstract Methylthioadenosine phosphorylase (MTAP) is the enzyme in the methionine salvage pathway that metabolizes the byproduct of polyamine biosynthesis, 5′-methylthioadenosine (MTA). The MTAP gene is deleted in approximately 15% of all human cancers and results in accumulation of MTA that partially inhibits protein arginine methyl transferase 5 (PRMT5) function. Recent studies have demonstrated that loss of the MTAP gene sensitizes cancer cells to genetic depletion of PRMT5 and the upstream metabolic enzyme methionine adenosyltransferase 2 alpha (MAT2A). We have developed a first-in-class, highly potent, orally bioavailable MAT2A inhibitor, AG-270, which is currently under investigation in a phase 1 clinical trial (ClinicalTrials.gov NCT03435250). AG-270 selectively inhibits the growth of HCT116 MTAP-/- cells compared to HCT116 MTAP+/+ cells in vitro and in vivo. We utilized RNA sequencing and proteomic approaches to study the underlying mechanism of action for AG-270. The results of these analyses demonstrated that AG-270 treatment induces substantial splicing changes in an MTAP selective manner. The majority of these abnormal splicing events were detained introns, which included genes involved in cell cycle regulation and DNA damage response. Moreover, AG-270 treatment resulted in accumulation of DNA damage and increased mitotic defects in HCT116 MTAP-/- cells. Furthermore, we demonstrated substantially advantageous combination benefits between AG-270 and anti-mitotic taxanes in in vitro cell lines and in in vivo patient-derived xenograft models of non-small cell lung, pancreatic and esophageal cancers. These findings uncover relevant combination strategies targeting MTAP-deleted malignancies, and provide preclinical mechanistic proof-of-concept to explore such combinations in the clinical setting. Citation Format: Peter Kalev, Marc L Hyer, Mark Fletcher, Peili Zhang, Elia Aguado-Fraile, Everton Mandley, Yesim Tuncay, Zenon Konteatis, Jeremy Travins, Kevin M Marks, Katya Marjon. Mitotic defects induced by MAT2A inhibitors guides translational drug combination strategies with AG-270 and taxanes [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr B115. doi:10.1158/1535-7163.TARG-19-B115

Epigenetic modification of H3K4 and oxidative stress are involved in MC-LR-induced apoptosis in testicular cells of SD rats.

Microcystin-leucine arginine (MC-LR) is a cyclic heptapeptide, produced by aquatic cyanobacteria such as microcystis, with strong reproductive toxicity which poses greater threat to the reproductive abilities of humans and animals. By exploring the role of trimethylation of histone H3 at lysine 4 (H3K4me3) and the role of oxidative stress in MC-LR-induced apoptosis in testicular Sertoli cells in Sprague-Dawley (SD) rats, this study indicated that MC-LR increased the expression levels of apoptosis-related genes by raising the levels of H3K4me3. 5'-Deoxy-5'-methylthioadenosine (MTA), the inhibitor of H3K4me3, reduced apoptosis, indicating for the first time that epigenetic modification is closely related to the testicular reproductive toxicity induced by MC-LR. MC-LR also induced oxidative stress by stimulating the generation of reactive oxygen species (ROS), and subsequently triggering mitochondria-mediated apoptotic pathway by decreasing mitochondrial membrane potential and increasing the levels of Bax, Bcl-2, Caspase-3, and so on. MC-LR-induced apoptosis of testicular cells could be decreased after pretreatment with oxidative stress inhibitor N-acetyl-cysteine (NAC). Furthermore, the pathological damage to mitochondria and testes were observed in SD rats. These results show that MC-LR can induce apoptosis by raising the levels of H3K4me3, and pretreatment with MTA can ameliorate the MC-LR-induced apoptosis of cocultured cells by lowering the levels of H3K4me3. Furthermore, NAC has a protective effect on MC-LR-induced apoptosis of testicular cells in SD rats by inhibiting the oxidative stress.

ES03.02 Targeting CDKN2A in Mesothelioma

Interrogation of the genomic landscape in mesothelioma has revealed considerable inter-patient genomic heterogeneity, however development of molecularly targeted stratified therapy is currently in its infancy. Somatic copy number loss involving the chromosome 9p21-3 locus occurs at high frequency (45% deep deletion in the TCGA cohort), and its expression may be further suppressed by DNA methylation. 9p21-3 harbours CDKN2A. Conditional Knockout of CDKN2A is sufficient to initiate mesotheliomas in vivo consistent with a role in tumorigenesis. This is supported by emerging phylogenetic analysis in which 9p21-3 occurs as an early (clonal or truncal) homozygous event during tumour evolution, in around 20% of cases. Late homozygous and heterogzyous losses also occur, with evidence of parallel evolution. Importantly, CDKN2A is a major negative prognostic factor associated with earlier progression following surgical resection. CDKN2A encodes two genes; 1, the inhibitor of cyclin dependent kinases 4 and 6 known as p16ink4A, and 2. MDM2, an inhibitor of the p53-MDM2 interaction. Early preclinical studies showed that re-introducing p16ink4A transgene in a CDKN2A negative mesothelioma exhibited anti-tumour activity. Small molecule inhibition of CDK4/6 essentially phenocopies p16ink4a (in the presence of wild type RB1). Large scale drug-gene interaction studies have revealed CDKN2A dependent sensitivity to CDK4/6 inhibition suggesting a possible strategy in mesothelioma. We have therefore developed the MiST stratified umbrella trial (NCT NCT03654833) is therefore evaluating the CDK4/6 inhibitor abemaciclib in p16ink4a negative relapsed mesothelioma (arm 2) Loss of p14ARF expression promotes MDM2, an E3 ubiquin ligase targeting p53. Given the low mutation rate for p53 in mesothelioma (around 16% in the TCGA), MDM2 inhibitors may, in the context of p14ARF loss, de-repress p53 to mediate tumour suppression. Preclinical data supports this hypothesis which has translational potential. Co-deletion of the gene MTAP with CDKN2A is common, and coincident with around 80% of CDKN2A losses. MTAP (methylthioadenosine phosphorylase) may represent a potential molecular target in 9p21-3 deleted mesothelioma. This tumour suppressor salvages the essential amino acid methionine, as well as adenine, and plays a critical role in the polyamine salvage pathway. Recently it has been shown that loss of MTAP leads to an increase level in its substrate, methylthioadenosine (MTA). This metabolite directly interacts with and inhibits the epigenetic modifier, PRMT5 (protein arginine methyltransferase 5) that mediates symmetrical arginine di-methylation of histone H4 (H4R3me2s). A direct consequence of this is a reduction in the pool of functional PRMT5 enzyme, revealing a vulnerability to 1. Inhibition of PRMT5 expression or 2. Inhibition of PRMT5 substrate (SAM) synthesis via MAT2A (which converts methionine to SAM). 1st generation small molecule PRMT5 inhibitors are currently undergoing phase 1 clinical evaluation, however MTA dependent allosteric antagonism of such inhibitors presents a challenge to achieving efficacy. Small molecule transcriptional suppression may present a solution. Accordingly, using the connectivity map, we have identified quinacine as a PRMT5 transcriptional suppressor capable of suppressing PRMT5 transcription (which is c-jun dependent), mediating MTAP selective loss of viability with commensurate reduction in H4R3me2s, consistent with an on-target effect. In summary, 9p21-3 loss encompassing CDKN2A and MTAP is one of the most common genomic aberrations in mesothelioma. Novel strategies are emerging with significant translational potential to deliver targeted therapies for mesothelioma. CDKN2A MTAP synthetic lethality

Abstract 18: Doubled lifespan in APCMin/+ mice by targeting MTAP

Abstract Humans with Familial Adenomatous Polyposis (FAP) have increased risk of colon cancer. Mice with the APCMin/+ mutation provide an animal model of FAP. Interruption of epigenetic control by preventing salvage of S-adenosylmethionine from 5′-methylthioadenosine (MTA) was tested as a potential FAP therapy. 5′-Methylthioadenosine phosphorylase (MTAP) catalyzes the phosphorolysis of MTA to adenine and methylthioribose-1-phosphate for methionine recycling. The effect of MTDIA, a transition state analogue of MTAP, was tested as an oral agent in APCMin/+ mice. Survival analysis with 10, 20 and 30 mg/kg/day oral doses of MTDIA showed a 2-fold increase in mouse lifespan at the optimal 20 mg/kg/day dose. Metabolomic analysis (mouse liver) showed significant changes in metabolites relevant to methionine metabolism. The >4-fold increase in MTA, confirmed the physiologic target. Histologic analysis of intestinal tissue revealed slowed tumor progression in treated mice. RNAseq and Western blots provide additional information about the consequences of MTAP inhibition. Citation Format: Ross S. Firestone, Mu Feng, Vern L. Schramm. Doubled lifespan in APCMin/+ mice by targeting MTAP [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 18.

Abstract 2714: Targeting MAT2A in CDKN2A/MTAP-deleted cancers

Abstract While deletions of the p16/CDKN2A tumor suppressor were first discovered more than 30 years ago, therapeutics that selectively target such tumors have proven elusive. Recent work utilizing functional genomics has identified a synthetic lethal vulnerability that arises due to co-deletion of the adjacent metabolic gene, methylthioadenosine phosphorylase (MTAP). Loss of MTAP in these tumors leads to an accumulation of MTAP substrate 5'-methylthioadenosine (MTA), which partially inhibits the arginine methyltransferase PRMT5 and sensitizes tumors to shRNA-mediated depletion of PRMT5 and the upstream metabolic enzyme, methionine adenosyltransferase 2 alpha (MAT2A). To investigate the therapeutic potential of this finding, we utilized a biophysical binding screen followed by iterative structure-guided design to make the first highly potent, selective, and orally bioavailable inhibitors of MAT2A. MAT2A inhibitor treatment leads to potent inhibition of the growth of HCT116 MTAP-/- cells while sparing isogenic HCT116 MTAP+/+ cells. Tumor xenograft studies similarly demonstrated MTAP-selective growth inhibition in HCT116 MTAP-/- tumors compared to isogenic HCT116 MTAP+/+ tumors. Further, MTAP-deletion correlated with MAT2A inhibitor efficacy across a panel of >300 cell lines in vitro, and MAT2A inhibitor treatment was efficacious in a variety of MTAP-deleted patient-derived xenografts in vivo. Having demonstrated that potent MAT2A inhibitors selectively block the proliferation of MTAP-deleted cells and tumors, we sought to investigate the mechanism by which these effects arise. Using methylation proteomics we noted that MAT2A inhibitor treatment leads to selective inhibition of PRMT5 methylation activity in MTAP-deleted cancers in vitro and in vivo. RNA-seq analyses revealed that MAT2A inhibition leads to substantial defects in RNA splicing in MTAP-deleted cancers, consistent with published findings that PRMT5-mediated methylation of splicing complex proteins is critical for their function. MAT2A inhibitor treatment led to a substantial increase in detained introns, which were enriched in genes involved in cell cycle regulation and DNA damage response, thus implicating dysregulated splicing in the antiproliferative effects of MAT2A inhibition in MTAP-deleted cancer cells. Furthermore, we demonstrated substantial drug-drug synergy between MAT2A inhibitors and select agents inhibiting cell cycle progression or DNA repair. Importantly we validated key combination findings in vivo, including demonstration of synergy with the MAT2A inhibitor AG-270 and anti-mitotic taxanes. AG-270 is the first MAT2A inhibitor to enter clinical development and is under investigation in a Phase I trial that is currently enrolling patients with MTAP-deleted solid tumors (NCT03435250). Our findings suggest clinically-applicable combination strategies which may further enhance the efficacy of AG-270 in malignancies with this genetic lesion. Citation Format: Katya Marjon, Peter Kalev, Marc Hyer, Mark Fletcher, Peili Zhang, Elia Aguado-Fraile, Everton Mandley, Zenon Konteatis, Jeremy Travins, Kevin Marks. Targeting MAT2A in CDKN2A/MTAP-deleted cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2714.

Abstract 385: MTAP gene deficiency creates vulnerability to anti-folate therapy in urothelial bladder carcinoma

Abstract Background: The methylthioadenosine phosphorylase (MTAP) gene encodes an essential enzyme for the salvage pathway of adenosine synthesis and is frequently lost in different types of cancer including urothelial bladder carcinoma. Therefore, MTAP-deficient tumors are theoretically very sensitive to anti-folate agents such as pemetrexed that can effectively block the de novo pathway of adenosine synthesis and as a result, create a state of synthetic lethality. We thus hypothesize that tumor MTAP gene deficiency is associated with response to pemetrexed therapy in bladder cancer. Methods: In this study, we investigated MTAP gene deficiency rates in the TCGA database and confirmed MTAP protein loss by immunohistochemistry using a tumor tissue microarray containing bladder tumor tissues from 151 patients. We then performed in vitro and in vivo studies using MTAP-proficient and MTAP-deficient human bladder cancer cell lines. Functional loss of MTAP was verified with mass spectrometry, which detects its substrate methylthioadenosine (MTA) levels. We also correlated these pre-clinical studies with clinical response data on patients with metastatic bladder cancer treated with pemetrexed. Results: We identified that 27.8% bladder cancer patients have MTAP protein deficiency, which is consistent with exome sequencing data from the TCGA database. In vitro data showed MTAP-deficient human bladder cancer cell lines were significantly more sensitive to pemetrexed, with IC50 at least 40 times lower than MTAP-proficient cell lines. Subsequent knockdown of the MTAP gene in MTAP-proficient cell lines increased sensitivities to pemetrexed treatment. Consistent with the in vitro data, pemetrexed significantly inhibited the growth of MTAP-deficient or knockdown xenograft tumors but not MTAP-proficient tumors. Furthermore, 4 of 4 (100%) patients with MTAP-deficient metastatic bladder cancer responded to pemetrexed treatment, whereas only 1 of 11 (9%) patients with MTAP-proficient metastatic bladder cancer responded to pemetrexed. Conclusion: Our data demonstrate that MTAP gene loss in urothelial bladder cancer leads to a metabolic state of synthetic lethality with pemetrexed therapy. Therefore, bladder tumor MTAP loss should be further investigated as a potential biomarker for selection of patients for anti-folate therapy. Citation Format: Jianfeng Chen, Omar Alhalabi, Guangchun Han, Wei-Lien Wang, Xin-Qiao Zhang, Jian H. Song, Lidia P. Lopez, Sumankalai Ramachandran, Anh G. Hoang, Tyrone Garnett, Matthew Campbell, Amishi Y. Shah, Jennifer Wang, Arlene O. Siefker-Radtke, Shi-Ming Tu, Mark Titus, Charles C. Guo, Gary E. Gallick, Eleni Efstathiou, William F. Benedict, Christopher J. Logothetis, Thai H. Ho, Linghua Wang, Jianjun Gao. MTAP gene deficiency creates vulnerability to anti-folate therapy in urothelial bladder carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 385.

Deciphering the regulatory and catalytic mechanisms of an unusual SAM-dependent enzyme

S-adenosyl-1-methionine (SAM)-dependent enzymes regulate various disease-related behaviors in all organisms. Recently, the leporin biosynthesis enzyme LepI, a SAM-dependent enzyme, was reported to catalyze pericyclic reactions in leporin biosynthesis; however, the mechanisms underlying LepI activation and catalysis remain unclear. This study aimed to investigate the molecular mechanisms of LepI. Here, we reported crystal structures of LepI bound to SAM/5′-deoxy-5′-(methylthio) adenosine (MTA), S-adenosyl-homocysteine (SAH), and SAM/substrate states. Structural and biochemical analysis revealed that MTA or SAH inhibited the enzyme activities, whereas SAM activated the enzyme. The analysis of the substrate-bound structure of LepI demonstrated that this enzymatic retro-Claisen rearrangement was primarily driven by three critical polar residues His133, Arg197, Arg295 around the active site and assisted by SAM with unclear mechanism. The present studies indicate that the unique mechanisms underlying regulatory and catalysis of the unusual SAM-dependent enzyme LepI, not only strengthening current understanding of the fundamentally biochemical catalysis, but also providing novel insights into the design of SAM-dependent enzyme-specific small molecules.

Metabolites Involved in Immune Evasion by Batrachochytrium dendrobatidis Include the Polyamine Spermidine.

Amphibians have been declining around the world for more than four decades. One recognized driver of these declines is the chytrid fungus Batrachochytrium dendrobatidis, which causes the disease chytridiomycosis. Amphibians have complex and varied immune defenses against B. dendrobatidis, but the fungus also has a number of counterdefenses. Previously, we identified two small molecules produced by the fungus that inhibit frog lymphocyte proliferation, methylthioadenosine (MTA) and kynurenine (KYN). Here, we report on the isolation and identification of the polyamine spermidine (SPD) as another significant immunomodulatory molecule produced by B. dendrobatidis SPD and its precursor, putrescine (PUT), are the major polyamines detected, and SPD is required for growth. The major pathway of biosynthesis is from ornithine through putrescine to spermidine. An alternative pathway from arginine to agmatine to putrescine appears to be absent. SPD is inhibitory at concentrations of ≥10 μM and is found at concentrations between 1 and 10 μM in active fungal supernatants. Although PUT is detected in the fungal supernatants, it is not inhibitory to lymphocytes even at concentrations as high as 100 μM. Two other related polyamines, norspermidine (NSP) and spermine (SPM), also inhibit amphibian lymphocyte proliferation, but a third polyamine, cadaverine (CAD), does not. A suboptimal (noninhibitory) concentration of MTA (10 μM), a by-product of spermidine synthesis, enhances the inhibition of SPD at 1 and 10 μM. We interpret these results to suggest that B. dendrobatidis produces an "armamentarium" of small molecules that, alone or in concert, may help it to evade clearance by the amphibian immune system.

The methionine salvage pathway-involving ADI1 inhibits hepatoma growth by epigenetically altering genes expression via elevating S-adenosylmethionine

The 5′-methylthioadenosine (MTA) cycle-participating human acireductone dioxygenase 1 (ADI1) has been implicated as a tumor suppressor in prostate cancer, yet its role remains unclear in hepatocellular carcinoma (HCC). Here, we demonstrated a significant reduction of ADI1, either in protein or mRNA level, in HCC tissues. Additionally, higher ADI1 levels were associated with favorable postoperative recurrence-free survival in HCC patients. By altering ADI1 expression in HCC cells, a negative correlation between ADI1 and cell proliferation was observed. Cell-based and xenograft experiments were performed by using cells overexpressing ADI1 mutants carrying mutations at the metal-binding sites (E94A and H133A, respectively), which selectively disrupted differential catalytic steps, resulting in staying or leaving the MTA cycle. The results showed that the growth suppression effect was mediated by accelerating the MTA cycle. A cDNA microarray analysis followed by verification experiments identified that caveolin-1 (CAV1), a growth-promoting protein in HCC, was markedly decreased upon ADI1 overexpression. Suppression of CAV1 expression was mediated by an increase of S-adenosylmethionine (SAMe) level. The methylation status of CAV1 promoter was significantly altered upon ADI1 overexpression. Finally, a genome-wide methylation analysis revealed that ADI1 overexpression altered promoter methylation profiles in a set of cancer-related genes, including CAV1 and genes encoding antisense non-coding RNAs, long non-coding RNAs, and microRNAs, resulting in significant changes of their expression levels. In conclusion, ADI1 expression promoted MTA cycle to increase SAMe levels, which altered genome-wide promoter methylation profiles, resulting in altered gene expression and HCC growth suppression.

Targeting the insulin-like growth factor-1 receptor in MTAP-deficient renal cell carcinoma

Renal cell carcinoma (RCC) has emerged as a metabolic disease characterized by dysregulated expression of metabolic enzymes. Patients with metastatic RCC have an unusually poor prognosis and near-universal resistance to all current therapies. To improve RCC treatment and the survival rate of patients with RCC, there is an urgent need to reveal the mechanisms by which metabolic reprogramming regulates aberrant signaling and oncogenic progression. Through an integrated analysis of RCC metabolic pathways, we showed that methylthioadenosine phosphorylase (MTAP) and its substrate methylthioadenosine (MTA) are dysregulated in aggressive RCC. A decrease in MTAP expression was observed in RCC tissues and correlated with higher tumor grade and shorter overall survival. Genetic manipulation of MTAP demonstrated that MTAP expression inhibits the epithelial-mesenchymal transition, invasion and migration of RCC cells. Interestingly, we found a decrease in the protein methylation level with a concomitant increase in tyrosine phosphorylation after MTAP knockout. A phospho-kinase array screen identified the type 1 insulin-like growth factor-1 receptor (IGF1R) as the candidate with the highest upregulation in tyrosine phosphorylation in response to MTAP loss. We further demonstrated that IGF1R phosphorylation acts upstream of Src and STAT3 signaling in MTAP-knockout RCC cells. IGF1R suppression by a selective inhibitor of IGF1R, linsitinib, impaired the cell migration and invasion capability of MTAP-deleted cells. Surprisingly, an increase in linsitinib-mediated cytotoxicity occurred in RCC cells with MTAP deficiency. Our data suggest that IGF1R signaling is a driver pathway that contributes to the aggressive nature of MTAP-deleted RCC.

Mechanisms of Trained Innate Immunity in oxLDL Primed Human Coronary Smooth Muscle Cells.

Objective: Damage and pathogen associated molecular patterns such as oxidized low-density lipoprotein (oxLDL) or bacillus Calmette-Guerin (BCG) vaccine can induce long term pro-inflammatory priming in monocytes and macrophages due to metabolic and epigenetic reprogramming—an emerging new concept called trained innate immunity. Vascular smooth muscle cells express pattern recognition receptors involved in trained innate immunity in monocytes. Here we investigated whether the mechanisms of trained innate immunity also control a proinflammatory phenotype in human coronary smooth muscle cells.Methods: Human coronary smooth muscle cells were primed with oxLDL or BCG for 24 h. After a resting time of 4 to 7 days, the cells were restimulated with either PAM3cys4, LPS or TNFα and cytokine production or mRNA expression were measured. Then, mechanisms of monocyte trained innate immunity were analyzed in smooth muscle cells, including receptors, intracellular pathways as well as metabolic and epigenetic reprogramming.Results: Priming with oxLDL or BCG lead to a significantly increased production of IL6, IL8 and MCP-1 following restimulation. OxLDL priming had little effect on the expression of macrophage or SMC marker genes. Proinflammatory priming of smooth muscle cells induced mTOR-HIF1α-signaling and could be blocked by mTOR-, TLR2-, and TLR4-inhibition. Finally, metabolic and epigenetic mechanisms of trained innate immunity in monocytes could be replicated in smooth muscle cells, including increased glucose consumption, lactate production, responsiveness to 6-fluoromevalonate and mevalonate treatment and inhibition of priming by the histone methyltransferase inhibitor methylthioadenosine (MTA).Conclusion: We demonstrate for the first time that mechanisms of the so called trained innate immunity control a proinflammatory phenotype in non-immune cells of the vascular wall. Our findings warrant further research into the specificity of trained innate immunity as an immune cell response as well as the mechanisms of vascular smooth muscle cells inflammation.

Oral Delivery of Methylthioadenosine to the Brain Employing Solid Lipid Nanoparticles: Pharmacokinetic, Behavioral, and Histopathological Evidences.

The present study aimed to orally deliver methylthioadenosine (MTA) to the brain employing solid lipid nanoparticles (SLNs) for the management of neurological conditions like multiple sclerosis. The stearic acid-based SLNs were below 100nm with almost neutral zeta potential and offered higher drug entrapment and drug loading. Cuprizone-induced demyelination model in mice was employed to mimic the multiple sclerosis-like conditions. It was observed that the MTA-loaded SLNs were able to maintain the normal metabolism, locomotor activity, motor coordination, balancing, and grip strength of the rodents in substantially superior ways vis-à-vis plain MTA. Histopathological studies of the corpus callosum and its subsequent staining with myelin staining dye luxol fast blue proved the potential of MTA-loaded SLNs in the remyelination of neurons. The pharmacokinetic studies provided the evidences for improved bioavailability and enhanced bioresidence supporting the pharmacodynamic findings. The studies proved that SLN-encapsulated MTA can be substantially delivered to the brain and can effectively remyelinate the neurons. It can reverse the multiple sclerosis-like symptoms in a safer and effective manner, that too by oral route.

5'-Methylthioadenosine and Cancer: old molecules, new understanding.

While the metabolic changes in cancer tissues were first observed by Warburg Otto almost a century ago, altered metabolism has recently returned as a focus of cancer research. 5'-Methylthioadenosine (MTA) is a naturally occurring sulfur-containing nucleoside found in numerous species. While MTA was first isolated several decades ago, a lack of sensitive and specific analytical methodologies designed for its direct quantification has hampered the study of its physiological and pathophysiological features. Many studies indicate that MTA suppresses tumors by inhibiting tumor cell proliferation, invasion, and the induction of apoptosis while controlling the inflammatory micro-environments of tumor tissue. In this review, we assessed the effects of MTA and of related materials on the growth and functions of normal and malignant cells.

SET7/9 promotes hepatocellular carcinoma progression through regulation of E2F1.

Hepatocellular carcinoma (HCC) is one of the most prevalent malignancies worldwide. Histone-lysine N-methyltransferase SET7/9 is a protein lysine monomethylase that methylates histone H3K4 as well as various non-histone proteins. Deregulation of SET7/9 is frequently detected in human cancers. However, the role of SET7/9 in HCC development remains unclear. In the present study, upregulation of SET7/9 and E2F transcription factor 1 (E2F1) expression was detected in 68 samples of HCC tissues compared with these levels noted in the paired healthy liver samples. The expression levels of SET7/9 and E2F1 were significantly correlated with pathological stage and tumor size. Subcellular fractionation and co-immunoprecipitation analyses revealed protein-protein interaction between SET7/9 and E2F1 in the cytoplasm of HCC cells. Silencing of SET7/9, as well as treatment with 5′-deoxy-5′-methylthioadenosine (MTA), a protein methylation inhibitor, led to reduced E2F1 protein abundance in HCC cells. Using Cell Counting Kit-8 (CCK-8) assay, Transwell migration assay and wound healing assay, significantly decreased cell proliferation, migration and invasion were observed in cells exhibiting downregulation of SET7/9 and E2F1 expression, as well as in wild-type HCC cells treated with MTA. Furthermore, SET7/9 downregulation and MTA treatment resulted in reduced expression of downstream targets of E2F1, including cyclin A2, cyclin E1 and CDK2. In conclusion, the present study revealed an oncogenic function of SET7/9 in HCC and demonstrated that SET7/9 may be responsible for alterations in the proliferative ability, aggressiveness and invasive/metastatic potential of HCC cells through post-translational regulation of E2F1.

Specific Targeting of MTAP-Deleted Tumors with a Combination of 2'-Fluoroadenine and 5'-Methylthioadenosine.

Homozygous deletion of the methylthioadenosine phosphorylase (MTAP) gene is a frequent event in a wide variety of human cancers and is a possible molecular target for therapy. One potential therapeutic strategy to target MTAP-deleted tumors involves combining toxic purine analogues such as 6'-thioguanine (6TG) or 2'-fluoroadenine (2FA) with the MTAP substrate 5'-deoxy-5'-methylthioadenosine (MTA). The rationale is that excess MTA will protect normal MTAP+ cells from purine analogue toxicity because MTAP catalyzes the conversion of MTA to adenine, which then inhibits the conversion of purine base analogues into nucleotides. However, in MTAP- tumor cells, no protection takes place because adenine is not formed. Here, we examine the effects of 6TG and 2FA in combination with MTA in vitro and in vivoIn vitro, MTA protected against both 6TG and 2FA toxicity in an MTAP-dependent manner, shifting the IC50 concentration by one to three orders of magnitude. However, in mice, MTA protected against toxicity from 2FA but failed to protect against 6TG. Addition of 100 mg/kg MTA to 20 mg/kg 2FA entirely reversed the toxicity of 2FA in a variety of tissues and the treatment was well tolerated by mice. The 2FA+MTA combination inhibited tumor growth of four different MTAP- human tumor cell lines in mouse xenograft models. Our results suggest that 2FA+MTA may be a promising combination for treating MTAP-deleted tumors.Significance: Loss of MTAP occurs in about 15% of all human cancers; the MTAP protection strategy presented in this study could be very effective in treating these cancers. Cancer Res; 78(15); 4386-95. ©2018 AACR.

Abstract 3835: Targeting loss of MTAP expression in glioblastoma multiforme with a combination of 2-fluoroadenine and methylthioadenosine

Abstract Methylthioadenosine Phosphorylase (MTAP) is a key enzyme in the purine and methionine salvage pathways that convert the polyamine byproduct 5′-deoxy-5′-methylthioadenosine (MTA) into adenine and methylthioribose-1-phosphate. Homozygous deletion of the MTAP gene is observed in 55% of all glioblastoma multiforme (GBM) tumors. Since MTAP is a house-keeping enzyme found in all normal tissues, the lack of MTAP in GBM makes MTAP-loss a potential therapeutic target. In this study, we explore a novel strategy to target MTAP-loss in GBM by combining 2-fluoroadenine (2FA), a highly toxic adenine analogue, with MTA. Because MTAP is expressed in all normal tissues, MTA will be converted to adenine, which will protect against 2FA toxicity. However, in tumor cells, the effects of 2FA will not be ameliorated because they lack MTAP. Here we show that there is undetectable expression of MTAP in A172 and U87 GBM cell lines by both western blot and MTAP enzyme activity assays. In vitro toxicity studies in which cells were cultured with either 2FA alone or 2FA plus MTA revealed that both cell lines were sensitive to 2FA with or without MTA. The LD50 of A172 cells was 110 nM (2FA) and 127 nM (2FA + 5 μM MTA), while for U87 cells it was 397 nM (2FA) and 323 nM (2FA + 5 μM MTA). This is in sharp contrast to MTAP+ NIH3T3 cells in which we observed a 44 fold shift in the ratio of the LD50 concentration in the presence and absence of MTA (160 nM versus 7000 nM). Addition of MTA protected normal tissues against 2FA toxicity in SCID mice. SCID mice subcutaneously injected with either A172 or U87 cells and then treated with 2FA(10 mg/kg) + MTA(50 mg/kg) showed significantly reduced tumor growth compared to vehicle treated controls. Our results indicated that 2FA+MTA might be effective in treating GBM. Citation Format: Baiqing Tang. Targeting loss of MTAP expression in glioblastoma multiforme with a combination of 2-fluoroadenine and methylthioadenosine [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3835.

Abstract 4482: MTAP regulates cell malignancy and is novel prognostic factor for kidney cancer

Abstract Renal cell carcinoma (RCC), the 6th most common cancer in the US, is now considered a metabolic disease, which is increasing in incidence and demonstrates resistance usually within 2 years to all available therapies. Given that patients with metastatic RCC have unusually poor prognosis, it is urgent to discover potential molecules for predicting malignant changes that will lead to RCC. Herein, we have identified S-methyl- 5'-thioadenosine phosphorylase (MTAP) and its substrate methylthioadenosine (MTA) as a possible biomarker for early detection of RCC. In a screen of patients with RCC, we found that low MTAP expression is accompanied by high MTA level in RCC specimens, whereas concomitant high level of MTAP and low MTA abundance are detected in adjacent normal kidney tissues. Datasets for RCC (n=538) from The Cancer Genome Atlas (TCGA) showed that the patients with low MTAP levels have a significantly shorter overall survival as compared to the high MTAP group. Immunohistochemistry staining of normal kidney tissues confirmed an increase of MTAP protein expression compared to RCC tissues, and MTAP gene expression is inversely proportional to tumor grade. Accumulation of the metabolite MTA, a major substrate of MTAP, was observed in high-grade tumors showing high malignant potential. MTAP-knockout RCC cells displayed an elongated, spindle-like morphology with extended pseudopodial branches. Genetic manipulation of MTAP studies demonstrated that MTAP expression inhibits epithelial-mesenchymal transition, invasion and migration of RCC cells. Loss of MTAP resulted in an activation of IGF1R signaling in RCC cells. Taken together, our findings indicate a major contribution of MTAP loss to kidney cancer cell malignancy and provide a viable biomarker for tumor detections. Citation Format: Carissa Huang, Jihao Xu, Yichin Wu, Robert H. Weiss, Ching-Hsien Chen. MTAP regulates cell malignancy and is novel prognostic factor for kidney cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4482.

Two Distinct Aerobic Methionine Salvage Pathways Generate Volatile Methanethiol in Rhodopseudomonas palustris.

ABSTRACT5′-Methyl-thioadenosine (MTA) is a dead-end, sulfur-containing metabolite and cellular inhibitor that arises from S-adenosyl-l-methionine-dependent reactions. Recent studies have indicated that there are diverse bacterial methionine salvage pathways (MSPs) for MTA detoxification and sulfur salvage. Here, via a combination of gene deletions and directed metabolite detection studies, we report that under aerobic conditions the facultatively anaerobic bacterium Rhodopseudomonas palustris employs both an MTA-isoprenoid shunt identical to that previously described in Rhodospirillum rubrum and a second novel MSP, both of which generate a methanethiol intermediate. The additional R. palustris aerobic MSP, a dihydroxyacetone phosphate (DHAP)-methanethiol shunt, initially converts MTA to 2-(methylthio)ethanol and DHAP. This is identical to the initial steps of the recently reported anaerobic ethylene-forming MSP, the DHAP-ethylene shunt. The aerobic DHAP-methanethiol shunt then further metabolizes 2-(methylthio)ethanol to methanethiol, which can be directly utilized by O-acetyl-l-homoserine sulfhydrylase to regenerate methionine. This is in contrast to the anaerobic DHAP-ethylene shunt, which metabolizes 2-(methylthio)ethanol to ethylene and an unknown organo-sulfur intermediate, revealing functional diversity in MSPs utilizing a 2-(methylthio)ethanol intermediate. When MTA was fed to aerobically growing cells, the rate of volatile methanethiol release was constant irrespective of the presence of sulfate, suggesting a general housekeeping function for these MSPs up through the methanethiol production step. Methanethiol and dimethyl sulfide (DMS), two of the most important compounds of the global sulfur cycle, appear to arise not only from marine ecosystems but from terrestrial ones as well. These results reveal a possible route by which methanethiol might be biologically produced in soil and freshwater environments.

Microbial pathway for anaerobic 5′-methylthioadenosine metabolism coupled to ethylene formation

Numerous cellular processes involving S-adenosyl-l-methionine result in the formation of the toxic by-product, 5'-methylthioadenosine (MTA). To prevent inhibitory MTA accumulation and retain biologically available sulfur, most organisms possess the "universal" methionine salvage pathway (MSP). However, the universal MSP is inherently aerobic due to a requirement of molecular oxygen for one of the key enzymes. Here, we report the presence of an exclusively anaerobic MSP that couples MTA metabolism to ethylene formation in the phototrophic bacteria Rhodospirillum rubrum and Rhodopseudomonas palustris In vivo metabolite analysis of gene deletion strains demonstrated that this anaerobic MSP functions via sequential action of MTA phosphorylase (MtnP), 5-(methylthio)ribose-1-phosphate isomerase (MtnA), and an annotated class II aldolase-like protein (Ald2) to form 2-(methylthio)acetaldehyde as an intermediate. 2-(Methylthio)acetaldehyde is reduced to 2-(methylthio)ethanol, which is further metabolized as a usable organic sulfur source, generating stoichiometric amounts of ethylene in the process. Ethylene induction experiments using 2-(methylthio)ethanol versus sulfate as sulfur sources further indicate anaerobic ethylene production from 2-(methylthio)ethanol requires protein synthesis and that this process is regulated. Finally, phylogenetic analysis reveals that the genes corresponding to these enzymes, and presumably the pathway, are widespread among anaerobic and facultatively anaerobic bacteria from soil and freshwater environments. These results not only establish the existence of a functional, exclusively anaerobic MSP, but they also suggest a possible route by which ethylene is produced by microbes in anoxic environments.