Tankyrase-selective inhibitor STP1002 shows preclinical antitumour efficacy without on-target toxicity in the gastrointestinal tract

Basroparib overcomes acquired resistance to MEK inhibitors by inhibiting Wnt-mediated cancer stemness in KRAS-mutated colorectal cancer

Mitogen-activated protein kinase (MEK) inhibitors show promise in treating KRAS-mutated cancers, including colorectal cancer (CRC). However, acquired resistance to MEK inhibitors often results in failure of effective treatment in patients with KRAS-mutated CRC. Here, we demonstrated that basroparib overcomes MEK inhibitor resistance in KRAS-G12V- or -G12D-mutated CRC. This basroparib-mediated sensitization was dependent on the KRAS mutation status and was enhanced specifically in KRAS-G12V- or -G12D-mutated cells. Additionally, when combined with MEK inhibitors, basroparib significantly reduced tumor growth in KRAS-G12V-mutated CRC xenograft models, but not in KRAS-G13D-mutated and -wild-type models. Furthermore, basroparib sensitized KRAS-G12V-mutated CRC cells with acquired resistance to MEK inhibitors. Notably, when combined with MEK inhibitors, basroparib not only suppressed tumor regrowth but also prolonged the survival of tumor models with acquired resistance to MEK inhibitors. Mechanistically, basroparib suppressed Wnt-mediated cancer stemness, a bypass mechanism for acquired resistance to MEK inhibitors in KRAS-mutated CRC. This study provides the first preclinical evidence of the relevance of basroparib in treating CRC with acquired resistance to MEK inhibitors due to APC and KRAS mutations, possibly by reducing the Wnt-mediated cancer stemness.

AXIN2 promotes degradation of AXIN1 through tankyrase in colorectal cancer cells

AXIN1 and AXIN2 are homologous proteins that inhibit the Wnt/β-catenin signaling pathway, which is frequently hyperactive in colorectal cancer. Stabilization of AXIN1 and AXIN2 by inhibiting their degradation through tankyrase (TNKS) allows the attenuation of Wnt signaling in cancer, attracting interest for potential targeted therapy. Here, we found that knockout or knockdown of AXIN2 in colorectal cancer cells increased the protein stability of AXIN1. The increase in AXIN1 overcompensated for the loss of AXIN2 with respect to protein levels; however, functionally it did not because loss of AXIN2 activated the pathway. Moreover, AXIN2 was highly essential in the context of TNKS inhibition because TNKS-targeting small-molecule inhibitors completely failed to inhibit Wnt signaling and to stabilize AXIN1 in AXIN2 knockout cells. The increased AXIN1 protein stability and the impaired stabilization by TNKS inhibitors indicated disrupted TNKS-AXIN1 regulation in AXIN2 knockout cells. Concordantly, mechanistic studies revealed that co-expression of AXIN2 recruited TNKS to AXIN1 and stimulated TNKS-mediated degradation of transiently expressed AXIN1 wild-type and AXIN1 mutants with impaired TNKS binding. Taken together, our data suggest that AXIN2 promotes degradation of AXIN1 through TNKS in colorectal cancer cells by directly linking the two proteins, and these findings may be relevant for TNKS inhibition-based colorectal cancer therapies.

Emerging regulatory mechanisms and functions of biomolecular condensates: implications for therapeutic targets

Cells orchestrate their processes through complex interactions, precisely organizing biomolecules in space and time. Recent discoveries have highlighted the crucial role of biomolecular condensates-membrane-less assemblies formed through the condensation of proteins, nucleic acids, and other molecules-in driving efficient and dynamic cellular processes. These condensates are integral to various physiological functions, such as gene expression and intracellular signal transduction, enabling rapid and finely tuned cellular responses. Their ability to regulate cellular signaling pathways is particularly significant, as it requires a careful balance between flexibility and precision. Disruption of this balance can lead to pathological conditions, including neurodegenerative diseases, cancer, and viral infections. Consequently, biomolecular condensates have emerged as promising therapeutic targets, with the potential to offer novel approaches to disease treatment. In this review, we present the recent insights into the regulatory mechanisms by which biomolecular condensates influence intracellular signaling pathways, their roles in health and disease, and potential strategies for modulating condensate dynamics as a therapeutic approach. Understanding these emerging principles may provide valuable directions for developing effective treatments targeting the aberrant behavior of biomolecular condensates in various diseases.

Origin, development and therapy of colorectal cancer from the perspective of a biologist and an oncologist

The intestinal epithelium, a rapidly renewing tissue, is characterized by a continuous cell turnover that occurs through a well-coordinated process of cell proliferation and differentiation. This dynamic is crucial for the long-term function of the gastrointestinal tract. Disruption of this process can lead to colorectal carcinoma, a common malignancy worldwide. The first part of the review focuses on the cellular composition of the epithelium and the molecular mechanisms that control its functions, and describes the pathways that lead to epithelial transformation and tumor progression. This forms the basis for understanding the development and progression of advanced colorectal cancer. The second part deals with current therapeutic approaches and presents the latest treatment options, ongoing clinical trials and new drugs. In addition, the biological and medical perspectives of the adverse effects of therapies and models of regeneration of the intestinal epithelium are highlighted and, finally, future treatment options are discussed.

Targeting ErbB and tankyrase1/2 prevent the emergence of drug-tolerant persister cells in ALK-positive lung cancer

Targeting the drug tolerant persister (DTP) state in cancer cells should prevent further development of resistance mechanisms. This study explored combination therapies to inhibit alectinib-induced DTP cell formation from anaplastic lymphoma kinase-positive non-small cell lung cancer (ALK + NSCLC) patient-derived cells. After drug-screening 3114 compounds, pan-HER inhibitors (ErbB pathway) and tankyrase1/2 inhibitors (Wnt/β-catenin signaling) emerged as top candidates to inhibit alectinib-induced DTP cells growth. We confirmed knockdown of both TNKS1/2 in DTP cells recovered the sensitivity to alectinib. Further, our study suggested knockdown of TNKS1/2 increased stability of Axin1/2, which induced β-catenin degradation and decreased its nuclear translocation, thereby suppressing transcription of antiapoptotic and proliferation-related genes (survivin, c-MYC). Targeting both pathways with alectinib+pan-HER inhibitor and alectinib+TNKS1/2 inhibitor suppressed alectinib-induced DTP cells, and the triple combination almost completely prevented the appearance of DTP cells. In conclusion, combination with ALK-TKI, pan-HER and TNKS1/2 inhibitors has the potential to prevent the emergence of DTP in ALK + NSCLC.

Regulation of PARP1/2 and the tankyrases: emerging parallels

ADP-ribosylation is a prominent and versatile post-translational modification, which regulates a diverse set of cellular processes. Poly-ADP-ribose (PAR) is synthesised by the poly-ADP-ribosyltransferases PARP1, PARP2, tankyrase (TNKS), and tankyrase 2 (TNKS2), all of which are linked to human disease. PARP1/2 inhibitors have entered the clinic to target cancers with deficiencies in DNA damage repair. Conversely, tankyrase inhibitors have continued to face obstacles on their way to clinical use, largely owing to our limited knowledge of their molecular impacts on tankyrase and effector pathways, and linked concerns around their tolerability. Whilst detailed structure-function studies have revealed a comprehensive picture of PARP1/2 regulation, our mechanistic understanding of the tankyrases lags behind, and thereby our appreciation of the molecular consequences of tankyrase inhibition. Despite large differences in their architecture and cellular contexts, recent structure-function work has revealed striking parallels in the regulatory principles that govern these enzymes. This includes low basal activity, activation by intra- or inter-molecular assembly, negative feedback regulation by auto-PARylation, and allosteric communication. Here we compare these poly-ADP-ribosyltransferases and point towards emerging parallels and open questions, whose pursuit will inform future drug development efforts.

Tankyrase inhibition interferes with junction remodeling, induces leakiness, and disturbs YAP1/TAZ signaling in the endothelium

Tankyrase inhibitors are increasingly considered for therapeutic use in malignancies that are characterized by high intrinsic β-catenin activity. However, how tankyrase inhibition affects the endothelium after systemic application remains poorly understood. In this study, we aimed to investigate how the tankyrase inhibitor XAV939 affects endothelial cell function and the underlying mechanism involved. Endothelial cell function was analyzed using sprouting angiogenesis, endothelial cell migration, junctional dynamics, and permeability using human umbilical vein endothelial cells (HUVEC) and explanted mouse retina. Underlying signaling was studied using western blot, immunofluorescence, and qPCR in HUVEC in addition to luciferase reporter gene assays in human embryonic kidney cells. XAV939 treatment leads to altered junctional dynamics and permeability as well as impaired endothelial migration. Mechanistically, XAV939 increased stability of the angiomotin-like proteins 1 and 2, which impedes the nuclear translocation of YAP1/TAZ and consequently suppresses TEAD-mediated transcription. Intriguingly, XAV939 disrupts adherens junctions by inducing RhoA-Rho dependent kinase (ROCK)-mediated F-actin bundling, whereas disruption of F-actin bundling through the ROCK inhibitor H1152 restores endothelial cell function. Unexpectedly, this was accompanied by an increase in nuclear TAZ and TEAD-mediated transcription, suggesting differential regulation of YAP1 and TAZ by the actin cytoskeleton in endothelial cells. In conclusion, our findings elucidate the complex relationship between the actin cytoskeleton, YAP1/TAZ signaling, and endothelial cell function and how tankyrase inhibition disturbs this well-balanced signaling.

BET protein-dependent E2F pathway activity confers bell-shaped type resistance to tankyrase inhibitors in APC-mutated colorectal cancer

WNT/β-catenin signaling is aberrantly activated in colorectal cancer (CRC) mainly by loss-of-function mutations in adenomatous polyposis coli (APC) and is involved in tumor progression. Tankyrase inhibitors, which suppress WNT/β-catenin signaling, are currently in pre-clinical and clinical trials. However, the mechanisms of resistance to tankyrase inhibitors remain unclear. In this study, we established tankyrase inhibitor-resistant CRC cells, JC73-RK100, from APC-mutated patient-derived CRC cells. JC73-RK100 cells and several CRC cell lines were sensitive to tankyrase inhibitors at low concentrations but were resistant at high concentrations, showing an intrinsic/acquired bell-shaped dose response. Mechanistically, tankyrase inhibitors at high concentrations promoted BRD3/4-dependent E2F target gene transcription and over-activated cell cycle progression in these cells. BET inhibitors canceled the bell-shaped dose response to tankyrase inhibitors. Combination of tankyrase and BET inhibitors significantly suppressed tumor growth in a mouse xenograft model. These observations suggest that the combination of tankyrase and BET inhibitors may be a useful therapeutic approach to overcome the resistance of a subset of CRCs to tankyrase inhibitors.

APC/PIK3CA mutations and β-catenin status predict tankyrase inhibitor sensitivity of patient-derived colorectal cancer cells

BACKGROUND

Aberrant WNT/β-catenin signaling drives carcinogenesis. Tankyrases poly(ADP-ribosyl)ate and destabilize AXINs, β-catenin repressors. Tankyrase inhibitors block WNT/β-catenin signaling and colorectal cancer (CRC) growth. We previously reported that 'short' APC mutations, lacking all seven β-catenin-binding 20-amino acid repeats (20-AARs), are potential predictive biomarkers for CRC cell sensitivity to tankyrase inhibitors. Meanwhile, 'Long' APC mutations, which possess more than one 20-AAR, do not predict inhibitor-resistant cells. Thus, additional biomarkers are needed to precisely predict the inhibitor sensitivity.

METHODS

Using 47 CRC patient-derived cells (PDCs), we examined correlations between the sensitivity to tankyrase inhibitors (G007-LK and RK-582), driver mutations, and the expressions of signaling factors. NOD.CB17-Prkdcscid/J and BALB/c-nu/nu xenograft mice were treated with RK-582.

RESULTS

Short APC mutant CRC cells exhibited high/intermediate sensitivities to tankyrase inhibitors in vitro and in vivo. Active β-catenin levels correlated with inhibitor sensitivity in both short and long APC mutant PDCs. PIK3CA mutations, but not KRAS/BRAF mutations, were more frequent in inhibitor-resistant PDCs. Some wild-type APC PDCs showed inhibitor sensitivity in a β-catenin-independent manner.

CONCLUSIONS

APC/PIK3CA mutations and β-catenin predict the sensitivity of APC-mutated CRC PDCs to tankyrase inhibitors. These observations may help inform the strategy of patient selection in future clinical trials of tankyrase inhibitors.

Nonsense mutation suppression is enhanced by targeting different stages of the protein synthesis process

The introduction of premature termination codons (PTCs), as a result of splicing defects, insertions, deletions, or point mutations (also termed nonsense mutations), lead to numerous genetic diseases, ranging from rare neuro-metabolic disorders to relatively common inheritable cancer syndromes and muscular dystrophies. Over the years, a large number of studies have demonstrated that certain antibiotics and other synthetic molecules can act as PTC suppressors by inducing readthrough of nonsense mutations, thereby restoring the expression of full-length proteins. Unfortunately, most PTC readthrough-inducing agents are toxic, have limited effects, and cannot be used for therapeutic purposes. Thus, further efforts are required to improve the clinical outcome of nonsense mutation suppressors. Here, by focusing on enhancing readthrough of pathogenic nonsense mutations in the adenomatous polyposis coli (APC) tumor suppressor gene, we show that disturbing the protein translation initiation complex, as well as targeting other stages of the protein translation machinery, enhances both antibiotic and non-antibiotic-mediated readthrough of nonsense mutations. These findings strongly increase our understanding of the mechanisms involved in nonsense mutation readthrough and facilitate the development of novel therapeutic targets for nonsense suppression to restore protein expression from a large variety of disease-causing mutated transcripts.

Phosphorylation of axin within biomolecular condensates counteracts its tankyrase-mediated degradation

Axin (also known as AXIN1) is a central negative regulator of the proto-oncogenic Wnt/β-catenin signaling pathway, as axin condensates provide a scaffold for the assembly of a multiprotein complex degrading β-catenin. Axin, in turn, is degraded through tankyrase. Consequently, tankyrase small-molecule inhibitors block Wnt signaling by stabilizing axin, revealing potential for cancer therapy. Here, we discovered that axin is phosphorylated by casein kinase 1 alpha 1 (CSNK1A1, also known as CK1α) at an N-terminal casein kinase 1 consensus motif, and that this phosphorylation is antagonized by the catalytic subunit alpha of protein phosphatase 1 (PPP1CA, hereafter referred to as PP1). Axin condensates promoted phosphorylation by enriching CK1α over PP1. Importantly, the phosphorylation took place within the tankyrase-binding site, electrostatically and/or sterically hindering axin-tankyrase interaction, and counteracting tankyrase-mediated degradation of axin. Thus, the presented data propose a novel mechanism regulating axin stability, with implications for Wnt signaling, cancer therapy and self-organization of biomolecular condensates.

Unravelling the Role of PARP1 in Homeostasis and Tumorigenesis: Implications for Anti-Cancer Therapies and Overcoming Resistance

Detailing the connection between homeostatic functions of enzymatic families and eventual progression into tumorigenesis is crucial to our understanding of anti-cancer therapies. One key enzyme group involved in this process is the Poly (ADP-ribose) polymerase (PARP) family, responsible for an expansive number of cellular functions, featuring members well established as regulators of DNA repair, genomic stability and beyond. Several PARP inhibitors (PARPi) have been approved for clinical use in a range of cancers, with many more still in trials. Unfortunately, the occurrence of resistance to PARPi therapy is growing in prevalence and requires the introduction of novel counter-resistance mechanisms to maintain efficacy. In this review, we summarize the updated understanding of the vast homeostatic functions the PARP family mediates and pin the importance of PARPi therapies as anti-cancer agents while discussing resistance mechanisms and current up-and-coming counter-strategies for countering such resistance.