Discovery of a Novel Small-Molecule Inhibitor that Targets PP2A-β-Catenin Signaling and Restricts Tumor Growth and Metastasis

LASS2 enhances chemosensitivity to cisplatin by inhibiting PP2A-mediated β-catenin dephosphorylation in a subset of stem-like bladder cancer cells

BACKGROUND

The benefits of first-line, cisplatin-based chemotherapy for muscle-invasive bladder cancer are limited due to intrinsic or acquired resistance to cisplatin. Increasing evidence has revealed the implication of cancer stem cells in the development of chemoresistance. However, the underlying molecular mechanisms remain to be elucidated. This study investigates the role of LASS2, a ceramide synthase, in regulating Wnt/β-catenin signaling in a subset of stem-like bladder cancer cells and explores strategies to sensitize bladder cancer to cisplatin treatment.

METHODS

Data from cohorts of our center and published datasets were used to evaluate the clinical characteristics of LASS2. Flow cytometry was used to sort and analyze bladder cancer stem cells (BCSCs). Tumor sphere formation, soft agar colony formation assay, EdU assay, apoptosis analysis, cell viability, and cisplatin sensitivity assay were used to investigate the functional roles of LASS2. Immunofluorescence, immunoblotting, coimmunoprecipitation, LC-MS, PCR array, luciferase reporter assays, pathway reporter array, chromatin immunoprecipitation, gain-of-function, and loss-of-function approaches were used to investigate the underlying mechanisms. Cell- and patient-derived xenograft models were used to investigate the effect of LASS2 overexpression and a combination of XAV939 on cisplatin sensitization and tumor growth.

RESULTS

Patients with low expression of LASS2 have a poorer response to cisplatin-based chemotherapy. Loss of LASS2 confers a stem-like phenotype and contributes to cisplatin resistance. Overexpression of LASS2 results in inhibition of self-renewal ability of BCSCs and increased their sensitivity to cisplatin. Mechanistically, LASS2 inhibits PP2A activity and dissociates PP2A from β-catenin, preventing the dephosphorylation of β-catenin and leading to the accumulation of cytosolic phospho-β-catenin, which decreases the transcription of the downstream genes ABCC2 and CD44 in BCSCs. Overexpression of LASS2 combined with a tankyrase inhibitor (XAV939) synergistically inhibits tumor growth and restores cisplatin sensitivity.

CONCLUSIONS

Targeting the LASS2 and β-catenin pathways may be an effective strategy to overcome cisplatin resistance and inhibit tumor growth in bladder cancer patients.

Loss of PERK function promotes ferroptosis by downregulating SLC7A11 (System Xc⁻) in colorectal cancer

Ferroptosis, a genetically and biochemically distinct form of programmed cell death, is characterised by an iron-dependent accumulation of lipid peroxides. Therapy-resistant tumor cells display vulnerability toward ferroptosis. Endoplasmic Reticulum (ER) stress and Unfolded Protein Response (UPR) play a critical role in cancer cells to become therapy resistant. Tweaking the balance of UPR to make cancer cells susceptible to ferroptotic cell death could be an attractive therapeutic strategy. To decipher the emerging contribution of ER stress in the ferroptotic process, we observe that ferroptosis inducer RSL3 promotes UPR (PERK, ATF6, and IRE1α), along with overexpression of cystine-glutamate transporter SLC7A11 (System Xc-). Exploring the role of a particular UPR arm in modulating SLC7A11 expression and subsequent ferroptosis, we notice that PERK is selectively critical in inducing ferroptosis in colorectal carcinoma. PERK inhibition reduces ATF4 expression and recruitment to the promoter of SLC7A11 and results in its downregulation. Loss of PERK function not only primes cancer cells for increased lipid peroxidation but also limits in vivo colorectal tumor growth, demonstrating active signs of ferroptotic cell death in situ. Further, by performing TCGA data mining and using colorectal cancer patient samples, we demonstrate that the expression of PERK and SLC7A11 is positively correlated. Overall, our experimental data indicate that PERK is a negative regulator of ferroptosis and loss of PERK function sensitizes colorectal cancer cells to ferroptosis. Therefore, small molecule PERK inhibitors hold huge promise as novel therapeutics and their potential can be harnessed against the apoptosis-resistant condition.

Biased holoenzyme assembly of protein phosphatase 2A (PP2A): From cancer to small molecules

Protein phosphatase 2A (PP2A) is a family of serine threonine phosphatases responsible for regulating protein phosphorylation, thus opposing the activity of cellular kinases. PP2A is composed of a catalytic subunit (PP2A Cα/β) and scaffolding subunit (PP2A Aα/β) and various substrate-directing B regulatory subunits. PP2A biogenesis is regulated at multiple levels. For example, the sequestration of the free catalytic subunit during the process of biogenesis avoids promiscuous phosphatase activity. Posttranslational modifications of PP2A C direct PP2A heterotrimeric formation. Additionally, PP2A functions as a haploinsufficient tumor suppressor, where attenuated PP2A enzymatic activity creates a permissive environment for oncogenic transformation. Recent work studying PP2A in cancer showed that its role in tumorigenesis is more nuanced, with some holoenzymes being tumor suppressive, while others are required for oncogenic transformation. In cancer biology, PP2A function is modulated through various mechanisms including the displacement of specific B regulatory subunits by DNA tumor viral antigens, by recurrent mutations, and through loss of carboxymethyl-sensitive heterotrimeric complexes. In aggregate, these alterations bias PP2A activity away from its tumor suppressive functions and toward oncogenic ones. From a therapeutic perspective, molecular glues and disruptors present opportunities for both the selective stabilization of tumor-suppressive holoenzymes and disruption of holoenzymes that are pro-oncogenic. Collectively, these approaches represent an attractive cancer therapy for a wide range of tumor types. This review will discuss the mechanisms by which PP2A holoenzyme formation is dysregulated in cancer and the current therapies that are aimed at biasing heterotrimer formation of PP2A for the treatment of cancer.

EZH2-H3K27me3 mediated KRT14 upregulation promotes TNBC peritoneal metastasis

Triple-Negative Breast Cancer (TNBC) has a poor prognosis and adverse clinical outcomes among all breast cancer subtypes as there is no available targeted therapy. Overexpression of Enhancer of zeste homolog 2 (EZH2) has been shown to correlate with TNBC's poor prognosis, but the contribution of EZH2 catalytic (H3K27me3) versus non-catalytic EZH2 (NC-EZH2) function in TNBC progression remains elusive. We reveal that selective hyper-activation of functional EZH2 (H3K27me3) over NC-EZH2 alters TNBC metastatic landscape and fosters its peritoneal metastasis, particularly splenic. Instead of H3K27me3-mediated repression of gene expression; here, it promotes KRT14 transcription by attenuating binding of repressor SP1 to its promoter. Further, KRT14 loss significantly reduces TNBC migration, invasion, and peritoneal metastasis. Consistently, human TNBC metastasis displays positive correlation between H3K27me3 and KRT14 levels. Finally, EZH2 knockdown or H3K27me3 inhibition by EPZ6438 reduces TNBC peritoneal metastasis. Altogether, our preclinical findings suggest a rationale for targeting TNBC with EZH2 inhibitors.

C-Peptide Promotes Cell Migration by Controlling Matrix Metallopeptidase-9 Activity Through Direct Regulation of β-Catenin in Human Endometrial Stromal Cells

The motility of endometrial stromal cells (ESCs) contributes to the restoration of the endometrial functional layer and subsequently supports the trophoblast invasion during early pregnancy. Following ESCs differentiation through decidualization in response to progesterone during the menstrual cycle and embryo implantation, decidualized ESCs (D-ESCs) have greater motility and invasive activity. The human proinsulin-connecting peptide (C-peptide) is produced in equimolar amounts during the proteolysis of insulin in pancreatic β-cells. However, the function of C-peptide in the cellular motility of the human endometrium remains unexamined. In the present study, C-peptide was identified as a determinant of undecidualized human endometrial stromal cells (UnD-ESCs) migration. C-peptide promoted the migration and invasion of UnD-ESCs and trophoblast-derived Jeg3 cells, but not that of ESCs post decidualization, a functional and biochemical differentiation of UnD-ESCs. Both Akt and protein phosphatase 1 regulated β-catenin phosphorylation in UnD-ESCs, not D-ESCs, thereby promoting β-catenin nuclear translocation in C-peptide-treated UnD-ESCs. C-peptide was also observed to increase matrix metallopeptidase-9 (MMP9) activity by increasing MMP9 expression and decreasing the expression of metallopeptidase inhibitor 1 (TIMP1) and TIMP3. Their expression was modulated by the direct binding of β-catenin in the regulatory region of the promoter of MMP9, TIMP1, and TIMP3. Inhibition of either β-catenin or MMP9 dampened C-peptide-enhanced migration in UnD-ESCs. Together, these findings suggest that C-peptide levels are critical for the regulation of UnD-ESC migration, providing evidence for the association between C-peptide levels and the failure rate of trophoblast invasion by inducing abnormal migration in UnD-ESCs in hyperinsulinemia or PCOS patients.

C644-0303, a small-molecule inhibitor of the Wnt/β-catenin pathway, suppresses colorectal cancer growth

The Wnt/β‐catenin signaling pathway plays an important role in tissue homeostasis, and its malignant activation is closely related to the occurrence and development of many cancers, especially colorectal cancer with adenomatous polyposis coli (APC) and CTNNB1 mutations. By applying a TCF/lymphoid‐enhancing factor (LEF) luciferase reporter system, the high‐throughput screening of 18 840 small‐molecule compounds was performed. A novel scaffold compound, C644‐0303, was identified as a Wnt/β‐catenin signaling inhibitor and exhibited antitumor efficacy. It inhibited both constitutive and ligand activated Wnt signals and its downstream gene expression. Functional studies showed that C644‐0303 causes cell cycle arrest, induces apoptosis, and inhibits cancer cell migration. Moreover, transcription factor array indicated that C644‐0303 could suppress various tumor‐promoting transcription factor activities in addition to Wnt/β‐catenin. Finally, C644‐0303 suppressed tumor spheroidization in a 3‐dimensional cell culture model and inhibited xenograft tumor growth in mice. In conclusion, we report a novel structural small molecular inhibitor targeting the Wnt/β‐catenin signaling pathway that has therapeutic potential for colorectal cancer treatment.

CXCR4 intracellular protein promotes drug resistance and tumorigenic potential by inversely regulating the expression of Death Receptor 5

Chemokine receptor CXCR4 overexpression in solid tumors has been strongly associated with poor prognosis and adverse clinical outcome. However, blockade of CXCL12-CXCR4 signaling axis by inhibitors like Nox-A12, FDA approved CXCR4 inhibitor drug AMD3100 have shown limited clinical success in cancer treatment. Therefore, exclusive contribution of CXCR4-CXCL12 signaling in pro-tumorigenic function is questionable. In our pursuit to understand the impact of chemokine signaling in carcinogenesis, we reveal that instead of CXCR4-CXCL12 signaling, presence of CXCR4 intracellular protein augments paclitaxel resistance and pro-tumorigenic functions. In search of pro-apoptotic mechanisms for CXCR4 mediated drug resistance; we discover that DR5 is a new selective target of CXCR4 in breast and colon cancer. Further, we detect that CXCR4 directs the differential recruitment of transcription factors p53 and YY1 to the promoter of DR5 in course of its transcriptional repression. Remarkably, inhibiting CXCR4-ligand-mediated signals completely fails to block the above phenotype. Overexpression of different mutant versions of CXCR4 lacking signal transduction capabilities also result in marked downregulation of DR5 expression in colon cancer indeed confirms the reverse relationship between DR5 and intracellular CXCR4 protein expression. Irrespective of CXCR4 surface expression, by utilizing stable gain and loss of function approaches, we observe that intracellular CXCR4 protein selectively resists and sensitizes colon cancer cells against paclitaxel therapy in vitro and in vivo. Finally, performing TCGA data mining and using human breast cancer patient samples, we demonstrate that expression of CXCR4 and DR5 are inversely regulated. Together, our data suggest that targeting CXCR4 intracellular protein may be critical to dampen the pro-tumorigenic functions of CXCR4.

Salinomycin inhibits epigenetic modulator EZH2 to enhance death receptors in colon cancer stem cells

Drug resistance is one of the trademark features of Cancer Stem Cells (CSCs). We and others have recently shown that paucity of functional death receptors (DR4/5) on the cell surface of tumour cells is one of the major reasons for drug resistance, but their involvement in the context of in CSCs is poorly understood. By harnessing CSC specific cytotoxic function of salinomycin, we discovered a critical role of epigenetic modulator EZH2 in regulating the expression of DRs in colon CSCs. Our unbiased proteome profiler array approach followed by ChIP analysis of salinomycin treated cells indicated that the expression of DRs, especially DR4 is epigenetically repressed in colon CSCs. Concurrently, EZH2 knockdown demonstrated increased expression of DR4/DR5, significant reduction of CSC phenotypes such as spheroid formation in-vitro and tumorigenic potential in-vivo in colon cancer. TCGA data analysis of human colon cancer clinical samples shows strong inverse correlation between EZH2 and DR4. Taken together, this study provides an insight about epigenetic regulation of DR4 in colon CSCs and advocates that drug-resistant colon cancer can be therapeutically targeted by combining TRAIL and small molecule EZH2 inhibitors.

Computational investigation of phytomolecules as resuscitation-promoting factor B (RpfB) inhibitors for clinical suppression of Mycobacterium tuberculosis dormancy reactivation

Among the various strategies of curbing tuberculosis, suppression of Mycobacterium tuberculosis (Mtb) is a primary goal of the WHO to stop its infection, which is further strengthened by the presence of a massive reservoir of latently infected individuals. Several efforts have been made to explore potential candidates, including drug-repurposing, phytomolecules evaluation, and de novo designs. Compared to other strategies, investigation of phytomolecules with known experimental evidence represents a highly cost-effective and less time-consuming approach. Interestingly, some of the phytomolecules, previously known to show anti-tuberculosis effects, are known. While, these compounds have not yet been tested for their additional abilities to interact with resuscitation-promoting factor B (RpfB), an essential protein involved in revoking of Mtb dormancy. We, therefore, performed an initial computational study to evaluate the binding affinity of 38 phytomolecules to select the most effective ligands against RpfB. The studies were carried out using AutoDock and associated tools for static interaction analysis, while molecular dynamics (MD) simulations were performed to examine the stability of predicted protein-ligand complexes using the Desmond MD package. As an outcome of this study, we have reported four potential compounds, viz. diospyrin, 2'-Nortiliacorinine, 5,4'-dihydroxy-3,7,8,3'-tetramethoxyflavone, and tiliacorine which showed a putative binding affinity with significant intermolecular interactions, docking energy of -8.0 kcal/mol or higher, and vital complex stability (~2.4 Å RMSD) during 100 ns MD simulation. The findings of this study indicated that phytomolecules are capable to efficiently inhibit the RpfB, which is vital for reactivation of dormant Mtb. Characterization of the molecular targets for hits with intriguingly selective activity against dormant Mtb would be helpful to elucidate the essential mechanisms underlying the survival of dormant Mtb during latent infections.

New Spisulosine Derivative promotes robust autophagic response to cancer cells

Therapy resistance by evasion of apoptosis is one of the hallmarks of human cancer. Therefore, restoration of cell death by non-apoptotic mechanisms is critical to successfully overcome therapy resistance in cancer. By rational drug design approach, here we try to provide evidence that subtle changes in the chemical structure of spisulosine completely switched its cytotoxic function from apoptosis to autophagy. Our most potent molecule (26b) in a series of 16 synthesized derivatives showed robust autophagic cell death in diverse cancer cells sparing normal counterpart. Compound 26b mediated lethal autophagy induction was confirmed by formation of characteristic autophagic vacuoles, LC3 puncta formation, upregulation of signature autophagy markers like Beclin and Atg family proteins. Altogether, we have detected novel autophagy inducer small molecule which can be tested further for drug discovery research.