MYC upstream region orchestrates resistance to PI3K inhibitors in cancer cells through FOXO3a-mediated autophagic adaptation.

The MYC oncogene is frequently overexpressed in tumors and inhibition of its translation is considered an attractive therapeutic opportunity. Despite numerous reports proposing an internal ribosome entry site (IRES) within the MYC Upstream Region (MYC UR) to sustain MYC translation during cellular stress or chemotherapy, conflicting evidence remains regarding the validity of such a mechanism. Through comprehensive investigations in MYC-driven Colorectal Cancer (CRC) and Burkitt Lymphoma (BL) cells, we demonstrate that MYC UR does not facilitate cap-independent translation, but instead orchestrates resistance to PI3K inhibitors. Genomic deletion of MYC UR neither impacts MYC protein levels nor viability in CRC cells, either untreated or exposed to cellular stress. However, in response to PI3K inhibitors, MYC UR drives a FOXO3a-dependent transcriptional upregulation of MYC, conferring drug resistance. This resistance is mediated by enhanced autophagic flux, governed by MYC, and blockade of autophagy sensitizes CRC cells to PI3K inhibition in vitro and in vivo. Remarkably, BL cells lacking the translocation of MYC UR exhibit sensitivity to PI3K inhibitors, whereas MYC UR-translocated cells respond to these drugs only when autophagy is inhibited. These findings challenge previous notions regarding IRES-mediated translation and highlight a promising strategy to overcome resistance to PI3K inhibitors in MYC-driven malignancies, offering potential clinical implications for CRC and BL treatment.

Partial Truncation of the C-Terminal Domain of PTCH1 in Cancer Enhances Autophagy and Metabolic Adaptability.

The Hedgehog receptor, Patched1 (PTCH1), is a well-known tumour suppressor. While the tumour suppressor's activity is mostly ascribed to its function as a repressor of the canonical Smoothened/Gli pathway, its C-terminal domain (CTD) was reported to have additional non-canonical functions. One of them is the reduction of autophagic flux through direct interaction with the Unc-51, like the autophagy activating kinase (ULK) complex subunit autophagy-related protein-101 (ATG101). With the aim of investigating whether this function of PTCH1 is important in cancer cell fitness, we first identified frameshift mutations in the CTD of PTCH1 in cancer databases. We demonstrated that those mutations disrupt PTCH1 interaction with ATG101 and increase autophagic flux. Using deletion mutants of the PTCH1 CTD in co-immunoprecipitation studies, we established that the 1309-1447 region is necessary and sufficient for interaction with ATG101. We next showed that the three most common PTCH1 CTD mutations in endometrial, stomach and colon adenocarcinomas that cause frameshifts at S1203, R1308 and Y1316 lack the ability to interact with ATG101 and limit autophagic flux, determined by bafilomycin A1-sensitive accumulation of the autophagy markers LC3BII and p62. We next engineered PTCH1 indel mutations at S1223 by CRISPR/Cas9 in SW620 colon cancer cells. Comparison of two independent clones harbouring PTCH1 S1223fs mutations to their isogenic parental cell lines expressing wild-type PTCH1 showed a significant increase in basal and rapamycin-stimulated autophagic flux, as predicted by loss of ATG101 interaction. Furthermore, the PTCH1 CTD mutant cells displayed increased proliferation in the presence of rapamycin and reduced sensitivity to glycolysis inhibitors. Our findings suggest that loss of the PTCH1-ATG101 interaction by mutations in the CTD of PTCH1 in cancer might confer a selective advantage by stimulating autophagy and facilitating adaptation to nutrient deprivation conditions.

Combined inhibition of polyamine metabolism and eIF5A hypusination suppresses colorectal cancer growth through a converging effect on MYC translation.

A key mechanism driving colorectal cancer (CRC) development is the upregulation of MYC and its targets, including ornithine decarboxylase (ODC), a master regulator of polyamine metabolism. Elevated polyamines promote tumorigenesis in part by activating DHPS-mediated hypusination of the translation factor eIF5A, thereby inducing MYC biosynthesis. Thus, MYC, ODC and eIF5A orchestrate a positive feedback loop that represents an attractive therapeutic target for CRC therapy. Here we show that combined inhibition of ODC and eIF5A induces a synergistic antitumor response in CRC cells, leading to MYC suppression. We found that genes of the polyamine biosynthesis and hypusination pathways are significantly upregulated in colorectal cancer patients and that inhibition of ODC or DHPS alone limits CRC cell proliferation through a cytostatic mechanism, while combined ODC and DHPS/eIF5A blockade induces a synergistic inhibition, accompanied to apoptotic cell death in vitro and in mouse models of CRC and FAP. Mechanistically, we found that this dual treatment causes complete inhibition of MYC biosynthesis in a bimodal fashion, by preventing translational elongation and initiation. Together, these data illustrate a novel strategy for CRC treatment, based on the combined suppression of ODC and eIF5A, which holds promise for the treatment of CRC.

4-(3-Phenyl-4-(3,4,5-trimethoxybenzoyl)-1H-pyrrol-1-yl)benzenesulfonamide, a Novel Carbonic Anhydrase and Wnt/ß-Catenin Signaling Pathway Dual-Targeting Inhibitor with Potent Activity against Multidrug Resistant Cancer Cells.

We synthesized new pyrrole and indole derivatives as human carbonic anhydrase (hCA) inhibitors with the potential to inhibit the Wnt/ß-catenin signaling pathway. The presence of both N1-(4-sulfonamidophenyl) and 3-(3,4,5-trimethoxyphenyl) substituents was essential for strong hCA inhibitors. The most potent hCA XII inhibitor 15 (Ki = 6.8 nM) suppressed the Wnt/ß-catenin signaling pathway and its target genes MYC, Fgf20, and Sall4 and exhibited the typical markers of apoptosis, cleaved poly(ADP-ribose)polymerase, and cleaved caspase-3. Compound 15 showed strong inhibition of viability in a panel of cancer cells, including colorectal cancer and triple-negative breast cancer cells, was effective against the NCI/ADR-RES DOX-resistant cell line, and restored the sensitivity to doxorubicin (DOX) in HT29/DX and MDCK/P-gp cells. Compound 15 is a novel dual-targeting compound with activity against hCA and Wnt/ß-catenin. It thus has a broad targeting spectrum and is an anticancer agent with specific potential in P-glycoprotein overexpressing cell lines.

The Mechanism of Action of Biguanides: New Answers to a Complex Question.

Biguanides are a family of antidiabetic drugs with documented anticancer properties in preclinical and clinical settings. Despite intensive investigation, how they exert their therapeutic effects is still debated. Many studies support the hypothesis that biguanides inhibit mitochondrial complex I, inducing energy stress and activating compensatory responses mediated by energy sensors. However, a major concern related to this "complex" model is that the therapeutic concentrations of biguanides found in the blood and tissues are much lower than the doses required to inhibit complex I, suggesting the involvement of additional mechanisms. This comprehensive review illustrates the current knowledge of pharmacokinetics, receptors, sensors, intracellular alterations, and the mechanism of action of biguanides in diabetes and cancer. The conditions of usage and variables affecting the response to these drugs, the effect on the immune system and microbiota, as well as the results from the most relevant clinical trials in cancer are also discussed.

Induction of Ferroptosis in Glioblastoma and Ovarian Cancers by a New Pyrrole Tubulin Assembly Inhibitor.

We synthesized new aroyl diheterocyclic pyrrole (ARDHEP) 15 that exhibited the hallmarks of ferroptosis. Compound 15 strongly inhibited U-87 MG, OVCAR-3, and MCF-7 cancer cells, induced an increase of cleaved PARP, but was not toxic for normal human primary T lymphocytes at 0.1 µM. Analysis of the levels of lactoperoxidase, malondialdehyde, lactic acid, total glutathione, and ATP suggested that the in vivo inhibition of cancer cell proliferation by 15 went through stimulation of oxidative stress injury and Fe2+ accumulation. Quantitative polymerase chain reaction analysis of the mRNA expression in U-87 MG and SKOV-3 tumor tissues from 15-treated mice showed the presence of Ptgs2/Nfe2l2/Sat1/Akr1c1/Gpx4 genes correlated with ferroptosis in both groups. Immunofluorescence staining revealed significantly lower expressions of proteins Ki67, CD31, and ferroptosis negative regulation proteins glutathione peroxidase 4 (GPX4) and FTH1. Compound 15 was found to be metabolically stable when incubated with human liver microsomes.

Translational control of polyamine metabolism by CNBP is required for Drosophila locomotor function.

Microsatellite expansions of CCTG repeats in the cellular nucleic acid-binding protein (CNBP) gene leads to accumulation of toxic RNA and have been associated with myotonic dystrophy type 2 (DM2). However, it is still unclear whether the dystrophic phenotype is also linked to CNBP decrease, a conserved CCHC-type zinc finger RNA-binding protein that regulates translation and is required for mammalian development. Here, we show that depletion of Drosophila CNBP in muscles causes ageing-dependent locomotor defects that are correlated with impaired polyamine metabolism. We demonstrate that the levels of ornithine decarboxylase (ODC) and polyamines are significantly reduced upon dCNBP depletion. Of note, we show a reduction of the CNBP-polyamine axis in muscles from DM2 patients. Mechanistically, we provide evidence that dCNBP controls polyamine metabolism through binding dOdc mRNA and regulating its translation. Remarkably, the locomotor defect of dCNBP-deficient flies is rescued by either polyamine supplementation or dOdc1 overexpression. We suggest that this dCNBP function is evolutionarily conserved in vertebrates with relevant implications for CNBP-related pathophysiological conditions.

Blockade of EIF5A hypusination limits colorectal cancer growth by inhibiting MYC elongation.

Eukaryotic Translation Initiation Factor 5A (EIF5A) is a translation factor regulated by hypusination, a unique posttranslational modification catalyzed by deoxyhypusine synthetase (DHPS) and deoxyhypusine hydroxylase (DOHH) starting from the polyamine spermidine. Emerging data are showing that hypusinated EIF5A regulates key cellular processes such as autophagy, senescence, polyamine homeostasis, energy metabolism, and plays a role in cancer. However, the effects of EIF5A inhibition in preclinical cancer models, the mechanism of action, and specific translational targets are still poorly understood. We show here that hypusinated EIF5A promotes growth of colorectal cancer (CRC) cells by directly regulating MYC biosynthesis at specific pausing motifs. Inhibition of EIF5A hypusination with the DHPS inhibitor GC7 or through lentiviral-mediated knockdown of DHPS or EIF5A reduces the growth of various CRC cells. Multiplex gene expression analysis reveals that inhibition of hypusination impairs the expression of transcripts regulated by MYC, suggesting the involvement of this oncogene in the observed effect. Indeed, we demonstrate that EIF5A regulates MYC elongation without affecting its mRNA content or protein stability, by alleviating ribosome stalling at five distinct pausing motifs in MYC CDS. Of note, we show that blockade of the hypusination axis elicits a remarkable growth inhibitory effect in preclinical models of CRC and significantly reduces the size of polyps in APCMin/+ mice, a model of human familial adenomatous polyposis (FAP). Together, these data illustrate an unprecedented mechanism, whereby the tumor-promoting properties of hypusinated EIF5A are linked to its ability to regulate MYC elongation and provide a rationale for the use of DHPS/EIF5A inhibitors in CRC therapy.

Mitogen-activated kinase kinase kinase 1 inhibits hedgehog signaling and medulloblastoma growth through GLI1 phosphorylation.

The aberrant activation of hedgehog (HH) signaling is a leading cause of the development of medulloblastoma, a pediatric tumor of the cerebellum. The FDA­approved HH inhibitor, Vismodegib, which targets the transmembrane transducer SMO, has shown limited efficacy in patients with medulloblastoma, due to compensatory mechanisms that maintain an active HH­GLI signaling status. Thus, the identification of novel actionable mechanisms, directly affecting the activity of the HH­regulated GLI transcription factors is an important goal for these malignancies. In this study, using gene expression and reporter assays, combined with biochemical and cellular analyses, we demonstrate that mitogen­activated kinase kinase kinase 1 (MEKK1), the most upstream kinase of the mitogen­activated protein kinase (MAPK) phosphorylation modules, suppresses HH signaling by associating and phosphorylating GLI1, the most potent HH­regulated transcription factor. Phosphorylation occurred at multiple residues in the C­terminal region of GLI1 and was followed by an increased association with the cytoplasmic proteins 14­3­3. Of note, the enforced expression of MEKK1 or the exposure of medulloblastoma cells to the MEKK1 activator, Nocodazole, resulted in a marked inhibitory effect on GLI1 activity and tumor cell proliferation and viability. Taken together, the results of this study shed light on a novel regulatory mechanism of HH signaling, with potentially relevant implications in cancer therapy.