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The folate metabolism enzyme MTHFD2 (methylenetetrahydrofolate dehydrogenase/cyclohydrolase) is consistently overexpressed in cancer but its roles are not fully characterized, and current candidate inhibitors have limited potency for clinical development. In the present study, we demonstrate a role for MTHFD2 in DNA replication and genomic stability in cancer cells, and perform a drug screen to identify potent and selective nanomolar MTHFD2 inhibitors; protein cocrystal structures demonstrated binding to the active site of MTHFD2 and target engagement. MTHFD2 inhibitors reduced replication fork speed and induced replication stress followed by S-phase arrest and apoptosis of acute myeloid leukemia cells in vitro and in vivo, with a therapeutic window spanning four orders of magnitude compared with nontumorigenic cells. Mechanistically, MTHFD2 inhibitors prevented thymidine production leading to misincorporation of uracil into DNA and replication stress. Overall, these results demonstrate a functional link between MTHFD2-dependent cancer metabolism and replication stress that can be exploited therapeutically with this new class of inhibitors. Helleday and colleagues describe a nanomolar MTHFD2 inhibitor that causes replication stress and DNA damage accumulation in cancer cells via thymidine depletion, demonstrating a potential therapeutic strategy in AML tumors in vivo.

LSD1 has emerged as a potential therapeutic target to increase the effectiveness of cancer immunotherapy. We have developed a series of novel small molecules, exemplified by the lead substance BEA-17, that modulates LSD1 via binding to an allosteric site, without directly inhibiting its enzymatic activity. In cells, BEA-17 induces a reduction of LSD1 levels. In addition, BEA-17 upregulates the expression of endogenous retroviral genes and T cell-attractant chemokines and does so in an LSD1-dependent manner. In a co-culture of HeLa and PBMCs, BEA-17 increases cell kill of cancer cells by immune effector T cells, also in an LSD1-dependent manner. In a CT26 syngeneic animal model of colon cancer, BEA-17 potentiates the activity of anti-PD1 inhibitors. Finally, in a syngeneic GL261 animal model of glioblastoma, BEA-17 increases the effectiveness of standard-of-care temozolomide + radiation. Citation Format: Wei B. Emond, Rajiv Sawant, Matthis Geitmann, Johan Winquist, Peter Brandt, Ulf Bremberg, Per Källblad, Vendela Parrow, Claes Andersson, Kristin Blom, Nasrin Najafi, Tobias Bergström, Fredrik J. Swartling, Mats Hellström, Konrad F. Koehler. Potentiation of immunotherapy by LSD1 modulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 705.

Supplementary methods for the article "Pharmacological targeting of MTHFD2 suppresses acute myeloid leukemia by inducing thymidine depletion and replication stress".

We recently showed that the anti-helminthic compound mebendazole (MBZ) has immunomodulating activity in monocyte/macrophage models and induces ERK signalling. In the present study we investigated whether MBZ induced ERK activation is shared by other tubulin binding agents (TBAs) and if it is observable also in other human cell types. Curated gene signatures for a panel of TBAs in the LINCS Connectivity Map (CMap) database showed a unique strong negative correlation of MBZ with MEK/ERK inhibitors indicating ERK activation also in non-haematological cell lines. L1000 gene expression signatures for MBZ treated THP-1 monocytes also connected negatively to MEK inhibitors. MEK/ERK phosphoprotein activity testing of a number of TBAs showed that only MBZ increased the activity in both THP-1 monocytes and PMA differentiated macrophages. Distal effects on ERK phosphorylation of the substrate P90RSK and release of IL1B followed the same pattern. The effect of MBZ on MEK/ERK phosphorylation was inhibited by RAF/MEK/ERK inhibitors in THP-1 models, CD3/IL2 stimulated PBMCs and a MAPK reporter HEK-293 cell line. MBZ was also shown to increase ERK activity in CD4+ T-cells from lupus patients with known defective ERK signalling. Given these mechanistic features MBZ is suggested suitable for treatment of diseases characterized by defective ERK signalling, notably difficult to treat autoimmune diseases.

Mebendazole (MBZ), a drug commonly used for helminitic infections, has recently gained substantial attention as a repositioning candidate for cancer treatment. However, the mechanism of action behind its anticancer activity remains unclear. To address this problem, we took advantage of the curated MBZ-induced gene expression signatures in the LINCS Connectivity Map (CMap) database. The analysis revealed strong negative correlation with MEK/ERK1/2 inhibitors. Moreover, several of the most upregulated genes in response to MBZ exposure were related to monocyte/macrophage activation. The MBZ-induced gene expression signature in the promyeloblastic HL-60 cell line was strongly enriched in genes involved in monocyte/macrophage pro-inflammatory (M1) activation. This was subsequently validated using MBZ-treated THP-1 monocytoid cells that demonstrated gene expression, surface markers and cytokine release characteristic of the M1 phenotype. At high concentrations MBZ substantially induced the release of IL-1β and this was further potentiated by lipopolysaccharide (LPS). At low MBZ concentrations, cotreatment with LPS was required for MBZ-stimulated IL-1β secretion to occur. Furthermore, we show that the activation of protein kinase C, ERK1/2 and NF-kappaB were required for MBZ-induced IL-1β release. MBZ-induced IL-1β release was found to be dependent on NLRP3 inflammasome activation and to involve TLR8 stimulation. Finally, MBZ induced tumor-suppressive effects in a coculture model with differentiated THP-1 macrophages and HT29 colon cancer cells. In summary, we report that MBZ induced a pro-inflammatory (M1) phenotype of monocytoid cells, which may, at least partly, explain MBZ's anticancer activity observed in animal tumor models and in the clinic.

Picropodophyllin (PPP) is an anticancer drug undergoing clinical development in NSCLC. PPP has been shown to suppress IGF-1R signaling and to induce a G2/M cell cycle phase arrest but the exact mechanisms remain to be elucidated. The present study identified an IGF-1-independent mechanism of PPP leading to pro-metaphase arrest. The mitotic block was induced in human cancer cell lines and in an A549 xenograft mouse but did not occur in normal hepatocytes/mouse tissues. Cell cycle arrest by PPP occurred in vitro and in vivo accompanied by prominent CDK1 activation, and was IGF-1R-independent since it occurred also in IGF-1R-depleted and null cells. The tumor cells were not arrested in G2/M but in mitosis. Centrosome separation was prevented during mitotic entry, resulting in a monopolar mitotic spindle with subsequent prometaphase-arrest, independent of Plk1/Aurora A or Eg5, and leading to cell features of mitotic catastrophe. PPP also increased soluble tubulin and decreased spindle-associated tubulin within minutes, indicating that it interfered with microtubule dynamics. These results provide a novel IGF-1R-independent mechanism of antitumor effects of PPP.

AKN-028 is a novel tyrosine kinase inhibitor with preclinical activity in acute myeloid leukemia (AML), presently undergoing investigation in a phase I/II study. It is a potent inhibitor of the FMS-like kinase 3 (FLT3) but shows in vitro activity in a wide range of AML samples. In the present study, we have characterized the effects of AKN-028 on AML cells in more detail. AKN-028 induced a dose-dependent G0/1 arrest in AML cell line MV4-11. Treatment with AKN-028 caused significantly altered gene expression in all AML cell types tested (430 downregulated, 280 upregulated transcripts). Subsequent gene set enrichment analysis revealed enrichment of genes associated with the proto-oncogene and cell cycle regulator c-Myc among the downregulated genes in both AKN-028 and midostaurin treated cells. Kinase activity profiling in AML cell lines and primary AML samples showed that tyrosine kinase activity, but not serine/threonine kinase activity, was inhibited by AKN-028 in a dose dependent manner in all samples tested, reaching approximately the same level of kinase activity. Cells sensitive to AKN-028 showed a higher overall tyrosine kinase activity than more resistant ones, whereas serine/threonine kinase activity was similar for all primary AML samples.In summary, AKN-028 induces cell cycle arrest in AML cells, downregulates Myc-associated genes and affect several signaling pathways. AML cells with high global tyrosine kinase activity seem to be more sensitive to the cytotoxic effect of AKN-028 in vitro.

LSD1 has emerged as a potential therapeutic target for a number of cancer types (e.g. AML, SCLC, colorectal, breast, liver, prostate, glioblastoma, Ewing sarcoma), as well as sickle cell anaemia and Alzheimer’s disease. Irreversible LSD1 catalytic inhibitors have shown limited clinical efficacy in AML and SCLC, while solid tumours are largely unaddressed. This is in contrast to LSD1 knockdown with impact on a wide range of cancers, indicating that LSD1 functions other than enzymatic should be targeted. We have developed novel small molecules that modulate LSD1 via an allosteric site - without inhibiting its enzymatic function - inducing a 60% reduction of nuclear LSD1 levels. The sensitivity profile in a cancer cell line panel is unique and dissimilar to >300 diverse reference compounds. In vitro efficacy is observed in glioma-initiating clones that are highly resistant to standard-of-care temozolimide as well as catalytic LSD1 inhibitors. Efficacy in the sub-µM range is observed with other solid tumour models, e.g. prostate cancer. The compounds exhibit synergy (Bliss independence >40%) with HDAC inhibitors as evaluated by viability in cellular cancer models, including lung, liver and glioblastoma. Pharmacokinetic studies show good blood-brain-barrier penetration and oral availability of the allosteric LSD1 modulator BEA-17. A repeat dose of 25 mg/kg was well tolerated by NOD SCID mice, leading to µM level accumulation in the brain. Results from orthotopic glioblastoma PDX models, and in vivo hollow-fiber models of other solid tumours will be presented, as well as mechanistic insights from biophysical assays and gene expression analysis. Citation Format: Wei B. Emond, Matthis Geitmann, Malin Jarvius, Konrad Koehler, Per Källblad, Mia Niklasson, Vendela Parrow, Rajiv Sawant, Maria Sjöberg, Johan Winquist, Anna Segerman, Ulf Bremberg. LSD1 modulation by allosteric ligands [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 3843.

IGF-I is regarded as the most sensitive marker of growth hormone (GH) secretion in both GH deficient individuals and in individuals with excessive GH production. Studies on the effect of inhibitors of GH action in normal experimental animals are difficult to evaluate due to the complex relationship and feed back mechanisms of the GH/IGF-I system and the hypothalamo-pituitary axis. To circumvent the GH/IGF-I feedback mechanisms, we have used hypophysectomized (HX) rats treated with GH to assess the potential of a new low molecular weight compound, BVT-A ((N-[5-(aminosulfonyl)-2-methylphenyl]-5-bromo-2-furamide), to act as a GH receptor antagonist in vivo. GH treatment of HX rats induced serum IGF-I, body weight and hepatic mRNA levels of IGF-I, IGFBP-3, ALS and the IGF-I and GH receptors. Co-treatment with BVT-A suppressed all the GH-induced effects. We conclude that the GH substituted HX rat is a useful model for studies on GH receptor antagonists, and for the first time, a small molecule GH receptor antagonist with in vivo activity has been revealed. This opens up for development of new drugs for diseases in which lowering of GH receptor activity would be beneficial.

The growth-promoting effect of growth hormone (GH) is primarily mediated by insulin-like growth factor-1 (IGF-1). The liver is the main source of circulating IGF-I. The authors have used rodent primary hepatocytes for studies on pharmacological intervention of IGF-I mRNA expression. A 96-well nonradioactive IGF-1 mRNA quantification assay was developed, based on the hybridization of sense and antisense RNA probes, to replicate membranes with crude hepatocyte lysates. The sense hybridization was used as an internal standard. The antagonistic properties of a set of GH-receptor binding compounds were evaluated. Two compounds were found to down-regulate IGF-I mRNA. Effects due to metabolic inhibition or toxicity were excluded using a cell proliferation assay. To investigate potential unspecific transcriptional effects, the mRNA levels of the housekeeping genes, beta-actin and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), were determined. Two other GH-regulated genes, cytochrome P450 2C12 (CYP2C12) and a rat homologue to the human alpha1B-glycoprotein (A1BG), were quantified by RNase protection assays and found to be down-regulated, confirming the antagonistic property of 1 compound. In conclusion, a direct filter hybridization assay of hepatocyte lysates using nonradioactive sense and antisense probes can be used for quantitative mRNA measurements and could constitute a valuable tool in screening for pharmacologically active compounds.

SH-SY5Y cells differentiate into neuronal-like cells and express marker proteins like growth-associated protein (GAP-43) and neuropeptide tyrosine when treated with a low concentration (16 nM) of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) in the presence of growth factors or serum. Both control and differentiated cells expressed protein kinase C-alpha (PKC-alpha), PKC-epsilon, and PKC-zeta as revealed by Western blot analyses, but the subcellular distribution of the three isoforms was not uniform, indicating specific localized functions of the enzymes. In growth cones prepared from differentiating cells PKC-alpha and PKC-epsilon were enriched. In contrast, PKC-zeta was more evenly distributed within the differentiating cell. Cells treated with a high concentration of TPA (1.6 microM) differentiate poorly and continue to proliferate. In those cells, PKC-alpha and PKC-epsilon were found to be down-regulated while PKC-zeta remained present. Thus, down-regulation of PKC-alpha and PKC-epsilon appears to be incompatible with neuronal differentiation of SH-SY5Y cells. These cells also differentiate when treated with a combination of basic fibroblast growth factor and insulin-like growth factor I. Growth cones isolated from such cells are also enriched in PKC-alpha and PKC-epsilon, but not in PKC-zeta. Based on the subcellular distribution of PKC-alpha and epsilon, and that PKC substrates like GAP-43 and pp60c-src are enriched in SH-SY5Y growth cones, a role during neurite growth is suggested.

Phorbolester-triggered differentiation of SH-SY5Y neuroblastoma cells requires serum and a prolonged activation of protein kinase C (PKC). Under serum-free conditions development of a mature phenotype requires phorbolester in combination with a member of either the insulin-like growth factor (IGF) or the platelet-derived growth factor family. Here we report that basic and acidic fibroblast growth factor (FGF) and epidermal growth factor, but not nerve growth factor, synergistically potentiate phorbolester-induced differentiation. Alone these factors induced a mitogenic response which varied in magnitude, with basic FGF and IGF-I being the two most potent mitogens. However, a combination of basic FGF and IGF-I induced differentiation as judged by morphology and the increase in growth associated protein (GAP-43) and neuropeptide tyrosine mRNA levels. In contrast to the phenotype obtained in the presence of phorbolester, bFGF and IGF-I-treated SH-SY5Y cells retained their capacity to proliferate. Finally, in these cells, the phosphorylation of the endogenous PKC substrate, myristoylated alanine-rich C-kinase substrate (MARCKS), was slightly increased during several days, suggesting an involvement of PKC in the bFGF and IGF-I-induced differentiation.

Aberrant signal transduction by mutant or overexpressed protein kinases has emerged as a promising target for treatment of acute myeloid leukemia (AML). We here present a novel low molecular weight kinase inhibitor, AKN-032, targeting the FMS-like tyrosine kinase 3 (FLT3) and discovered in a new type of screening funnel combining the target therapy approach with sequential cellular screens. AKN-032 was identified among 150 selected hits from three different high throughput kinase screens. Further characterization showed inhibitory activity on FLT3 enzyme with an IC(50) of 70 nM. Western blot analysis revealed reduced autophosphorylation of the FLT3-receptor in AML cell line MV4-11 cells after exposure to AKN-032. Flow cytometry disclosed cytotoxic activity against MV4-11, but not against non-malignant 3T3-L1 fibroblast cells. Using a fluorometric microculture cytotoxicity assay, AKN-032 was tested against 15 cell lines and displayed a potent cytotoxic activity in AML cell lines MV4-11 (IC(50)=0.4 μM) and Kasumi-1 (IC(50)=2.3 μM). AKN-032 was also highly cytotoxic in tumor cells from AML patients in vitro. Furthermore, AKN-032 demonstrated significant antileukemic effect in a relatively resistant in vivo hollow fiber mouse model. No major toxicity was observed in the animals. In conclusion, AKN-032 is a promising new kinase inhibitor with significant in vivo and in vitro activity in AML. Results from the hollow fiber mouse assay suggest a favorable toxicity profile. Future studies will focus on pharmacokinetic properties, toxicity as well as further clarifying the mechanisms of action of AKN-032 in AML.

SH-SY5Y human neuroblastoma cells can be induced to differentiate into a neuronal phenotype by treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA). In other cell systems, TPA treatment frequently leads to down-regulation of protein kinase C (PKC). However, we now report that TPA-treated and non-treated SH-SY5Y cells express PKC-alpha, but not PKC-beta and PKC-gamma, mRNA. Furthermore, only a slight down-regulation of the PKC-alpha protein could be seen during prolonged treatment with 16 nM TPA, the concentration giving optimal differentiation. In contrast, a higher concentration of TPA (1.6 microM) results in a poor neuronal differentiation and a complete down-regulation of PKC-alpha. PKC-alpha was rapidly translocated to the particulate fraction and remained membrane bound for at least 4 days during treatment with 16 nM TPA. In such cells a sustained increased level of the phosphorylated form of a 80,000 Dalton PKC-substrate was found. In addition to this sustained augmented phosphorylation, administration of fresh TPA at day 4 caused a small but reproducible further increased level of phosphorylated substrate. When the PKC activity was measured by the histone phosphorylation assay a substantial fraction of the initial enzyme activity could still be detected after 4 days of TPA treatment. Taken together, the data demonstrate that PKC remains functionally active during TPA induced differentiation of SH-SY5Y cells, which may suggest a continuous role for the enzyme during the differentiation process.

Phorbol ester treatment of human SH-SY5Y neuroblastoma cells, which leads to mature neuron-like cells with a sympathetic phenotype, induces outgrowth of neurites which are terminated by growth cones. The neurite extension is parallelled by an increased expression of the growth-associated protein, GAP-43. At the mRNA level, two GAP-43 mRNA species of 1.4 and 1.6 kb, respectively, were detected in SH-SY5Y cells. Both the low- and high-molecular-weight GAP-43 transcripts cosedimented with a polysomal fraction, indicating translation of both types of transcripts. To structurally characterize these GAP-43 mRNAs, several cDNA clones were isolated. The only difference identified corresponded to various size extensions in the 5'-untranslated region. A human genomic DNA fragment extending 1145 bp 5' of the GAP-43 translation start site, including a putative promoter region of the GAP-43 gene, was also characterized. Comparison of human and rat GAP-43 genomic sequences revealed an 85% identity between the first 900 bp 5' of translation start site. By RNase protection analysis, two clusters of putative transcription start sites, located approximately 200 bp apart, were identified. DNaseI footprinting analyses, using nuclear extracts prepared from untreated and TPA-treated SH-SY5Y cells, revealed specific footprints primarily detected in extracts prepared from differentiating cells. These clustered at positions immediately 5' of the two putative transcription start site regions. GAP-43 mRNA expression was finally studied using a probe which specifically recognizes the high-molecular-weight GAP-43 transcripts. Five tested human neuroblastoma cell lines and human fetal brain tissue expressed these transcripts. Furthermore, during differentiation of SH-SY5Y and LA-N-5 cells, both sizes of GAP-43 transcripts were transiently induced with the larger slightly preceeding the smaller mRNA species.

Aberrantly expressed tyrosine kinases have emerged as promising targets for drug development in acute myeloid leukemia (AML). We report that AKN-028, a novel tyrosine kinase inhibitor (TKI), is a potent FMS-like receptor tyrosine kinase 3 (FLT3) inhibitor (IC(50)=6 nM), causing dose-dependent inhibition of FLT3 autophosphorylation. Inhibition of KIT autophosphorylation was shown in a human megakaryoblastic leukemia cell line overexpressing KIT. In a panel of 17 cell lines, AKN-028 showed cytotoxic activity in all five AML cell lines included. AKN-028 triggered apoptosis in MV4-11 by activation of caspase 3. In primary AML samples (n=15), AKN-028 induced a clear dose-dependent cytotoxic response (mean IC(50) 1 μM). However, no correlation between antileukemic activity and FLT3 mutation status, or to the quantitative expression of FLT3, was observed. Combination studies showed synergistic activity when cytarabine or daunorubicin was added simultaneously or 24 h before AKN-028. In mice, AKN-028 demonstrated high oral bioavailability and antileukemic effect in primary AML and MV4-11 cells, with no major toxicity observed in the experiment. In conclusion, AKN-028 is a novel TKI with significant preclinical antileukemic activity in AML. Possible sequence-dependent synergy with standard AML drugs and good oral bioavailability has made it a candidate drug for clinical trials (ongoing).

Abstract 1837 AKN-028 (formerly BVT-II, abstract presented at EHA 2008, Eriksson A et al) is a tyrosine kinase inhibitor originally identified in a screen targeting FLT-3. In vitro testing by fluorometric microculture cytotoxicity assay (FMCA, Lindhagen E. et al, Nat Protoc 2008; 3:1364-9) on primary tumor cells from 29 patients with different haematological malignancies showed that the cytotoxic activity was most pronounced in acute myeloic leukaemia (AML). In vivo, efficacy was demonstrated in a hollow fiber mouse model using MV4-11 cells and primary tumor cells from AML patients. Kinase inhibitors interacting with the ATP-binding pocket usually targets more than one kinase. PKC-412, presently in phase III trials in AML, is a staurosporine analogue targeting many kinases. In this study we show the kinase inhibition profile of AKN-028 when characterised on a broad panel of 320 different kinases. AKN-028 is relatively specific compared to the staurosporine analogues. To further analyse the difference in mechanism of action between the multi-targeting inhibitor PKC-412 and the more selective AKN-028, we have performed global gene expression analysis by Affymetrix arrays using two different leukaemia cell-lines, HL-60 and MV4-11 (expressing FLT3-ITD), and tumour cells from a patient with FLT3-ITDpos AML. The cells were treated with 10 μM of either compound or vehicle control for 6 h. Principal component (PC) analysis was used to visualise the global gene expression pattern, see fig 1. Searching for differential expression of mRNA levels showed that treatment with AKN-028 resulted in significantly altered gene expression in all three cell types tested, compared to vehicle control treated cells. 430 mRNAs were down-regulated, and 280 were up-regulated. By contrast, treatment with PKC-412 caused very few significant alterations of mRNA levels when compared to vehicle treated cells. Further analysis of gene expression patterns to elucidate the mechanism of action of AKN-028 is ongoing. In conclusion, even though AKN-028 is a relatively selective kinase inhibitor targeting FLT-3, it has more profound effects altering gene expression both in cultured AML cell-lines and a primary AML tumor sample than the multikinase inhibitor PKC-412. Disclosures: Parrow: Akinion Pharmaceuticals: Employment, Equity Ownership. Lehmann:Akinion Pharmaceuticals: Consultancy. Larsson:Akinion Pharmaceuticals: Consultancy.