Sulforaphane covalently interacts with the transglutaminase 2 cancer maintenance protein to alter its structure and suppress its activity

Reassessing the role of phytochemicals in cancer chemoprevention

In this comprehensive review we tried to reassess the role of phytochemicals in cancer chemoprevention. The exploration of the "synergistic effect" concept, advocating combined chemopreventive agents, faces challenges like low bioavailability. The review incorporates personal, occasionally controversial, viewpoints on natural compounds' cancer preventive capabilities, delving into mechanisms. Prioritizing significant contributions within the vast research domain, we aim stimulating discussion to provide a comprehensive insight into the evolving role of phytochemicals in cancer prevention. While early years downplayed the role of phytochemicals, the late nineties witnessed a shift, with leaders exploring their potential alongside synthetic compounds. Challenges faced by chemoprevention, such as limited pharmaceutical interest and cost-effectiveness issues, persist despite successful drugs. Recent studies, including the EPIC study, provide nuanced insights, indicating a modest risk reduction for increased fruit and vegetable intake. Phytochemicals, once attributed to antioxidant effects, face scrutiny due to low bioavailability and conflicting evidence. The Nrf2-EpRE signaling pathway and microbiota-mediated metabolism emerge as potential mechanisms, highlighting the complexity of understanding phytochemical mechanisms in cancer chemoprevention.

Natural Compounds in Non-Melanoma Skin Cancer: Prevention and Treatment

The elevated occurrence of non-melanoma skin cancer (NMSC) and the adverse effects associated with available treatments adversely impact the quality of life in multiple dimensions. In connection with this, there is a necessity for alternative approaches characterized by increased tolerance and lower side effects. Natural compounds could be employed due to their safety profile and effectiveness for inflammatory and neoplastic skin diseases. These anti-cancer drugs are often derived from natural sources such as marine, zoonotic, and botanical origins. Natural compounds should exhibit anti-carcinogenic actions through various pathways, influencing apoptosis potentiation, cell proliferation inhibition, and metastasis suppression. This review provides an overview of natural compounds used in cancer chemotherapies, chemoprevention, and promotion of skin regeneration, including polyphenolic compounds, flavonoids, vitamins, alkaloids, terpenoids, isothiocyanates, cannabinoids, carotenoids, and ceramides.

Cell-Impermeable Inhibitors Confirm That Intracellular Human Transglutaminase 2 Is Responsible for the Transglutaminase-Associated Cancer Phenotype

Transglutaminase 2 (TG2) is a multifunctional enzyme primarily responsible for crosslinking proteins. Ubiquitously expressed in humans, TG2 can act either as a transamidase by crosslinking two substrates through formation of an Nε(ɣ-glutaminyl)lysine bond or as an intracellular G-protein. These discrete roles are tightly regulated by both allosteric and environmental stimuli and are associated with dramatic changes in the conformation of the enzyme. The pleiotropic nature of TG2 and multi-faceted activities have resulted in TG2 being implicated in numerous disease pathologies including celiac disease, fibrosis, and cancer. Targeted TG2 therapies have not been selective for subcellular localization, such that currently no tools exist to selectively target extracellular over intracellular TG2. Herein, we have designed novel TG2-selective inhibitors that are not only highly potent and irreversible, but also cell impermeable, targeting only extracellular TG2. We have also further derivatized the scaffold to develop probes that are intrinsically fluorescent or bear an alkyne handle, which target both intra- and extracellular TG2, in order to facilitate cellular labelling and pull-down assays. The fluorescent probes were internalized and imaged in cellulo, and provide the first implicit experimental evidence that by comparison with their cell-impermeable analogues, it is specifically intracellular TG2, and presumably its G-protein activity, that contributes to transglutaminase-associated cancer progression.

ΔNp63α in cancer: importance and therapeutic opportunities

Our understanding of cancer and the key pathways that drive cancer survival has expanded rapidly over the past several decades. However, there are still important challenges that continue to impair patient survival, including our inability to target cancer stem cells (CSCs), metastasis, and drug resistance. The transcription factor p63 is a p53 family member with multiple isoforms that carry out a wide array of functions. Here, we discuss the critical importance of the ΔNp63α isoform in cancer and potential therapeutic strategies to target ΔNp63α expression to impair the CSC population, as well as to prevent metastasis and drug resistance to improve patient survival.

The war on hTG2: warhead optimization in small molecule human tissue transglutaminase inhibitors

Human tissue transglutaminase (hTG2) is a multifunctional enzyme with protein cross-linking and G-protein activity, both of which have been implicated in the progression of diseases such as fibrosis and cancer stem cell propagation when dysregulated, prompting the development of small molecule targeted covalent inhibitors (TCIs) possessing a crucial electrophilic 'warhead'. In recent years there have been significant advances in the library of warheads available for the design of TCIs; however, the exploration of warhead functionality in hTG2 inhibitors has remained relatively stagnant. Herein, we describe a structure-activity relationship study entailing rational design and synthesis for systematic variation of the warhead on a previously reported small molecule inhibitor scaffold, and rigorous kinetic evaluation of inhibitory efficiency, selectivity, and pharmacokinetic stability. This study reveals a strong influence on the kinetic parameters k inact and K I with even subtle variation in warhead structure, suggesting that the warhead plays a significant role in not only reactivity, but also binding affinity, which consequently extends to isozyme selectivity. Warhead structure also influences in vivo stability, which we model by measuring intrinsic reactivity with glutathione, as well as stability in hepatocytes and in whole blood, giving insight into degradation pathways and relative therapeutic potential of different functional groups. This work provides fundamental structural and reactivity information highlighting the importance of strategic warhead design for the development of potent hTG2 inhibitors.

Sulforaphane inhibits CD44v6/YAP1/TEAD signaling to suppress the cancer phenotype

Sulforaphane (SFN) is a promising cancer prevention and treatment agent that strongly suppresses the cutaneous squamous cell carcinoma (CSCC) cell cancer phenotype. We previously showed that yes-associated protein 1 (YAP1)/TEAD signaling is a key procancer stimulator of the aggressive CSCC cell cancer phenotype. However, SFN-responsive upstream regulators of YAP1/TEAD signaling are not well characterized and so there is a pressing need to identify these factors. We show that CD44v6 knockdown reduces YAP1/TEAD-dependent transcription and target gene expression, and that this is associated with reduced spheroid formation, invasion and migration. CD44v6 knockout cell lines also display reduced YAP1/TEAD activity and target gene expression and attenuated spheroid formation, invasion, migration and tumor formation. An important finding is that SFN treatment suppresses CD44v6 level leading to a reduction in YAP1/TEAD signaling and marker gene expression. Sox2 level and epithelial-mesenchymal transition (EMT) are also reduced. Forced expression of constitutive active YAP1 in CD44v6 knockdown cells partially restores the aggressive cancer phenotype. These important findings suggest that CD44v6 drives YAP1/TEAD signaling to enhance the CSCC cell cancer phenotype and that SFN treatment reduces CD44v6 level/function which, in turn, reduces YAP1/TEAD signaling leading to reduced stemness, EMT and tumor growth.

The Impact of Nε-Acryloyllysine Piperazides on the Conformational Dynamics of Transglutaminase 2

In addition to the classic functions of proteins, such as acting as a biocatalyst or binding partner, the conformational states of proteins and their remodeling upon stimulation need to be considered. A prominent example of a protein that undergoes comprehensive conformational remodeling is transglutaminase 2 (TGase 2), the distinct conformational states of which are closely related to particular functions. Its involvement in various pathophysiological processes, including fibrosis and cancer, motivates the development of theranostic agents, particularly based on inhibitors that are directed toward the transamidase activity. In this context, the ability of such inhibitors to control the conformational dynamics of TGase 2 emerges as an important parameter, and methods to assess this property are in great demand. Herein, we describe the application of the switchSENSE^® principle to detect conformational changes caused by three irreversibly binding N^ε-acryloyllysine piperazides, which are suitable radiotracer candidates of TGase 2. The switchSENSE^® technique is based on DNA levers actuated by alternating electric fields. These levers are immobilized on gold electrodes with one end, and at the other end of the lever, the TGase 2 is covalently bound. A novel computational method is introduced for describing the resulting lever motion to quantify the extent of stimulated conformational TGase 2 changes. Moreover, as a complementary biophysical method, native polyacrylamide gel electrophoresis was performed under similar conditions to validate the results. Both methods prove the occurrence of an irreversible shift in the conformational equilibrium of TGase 2, caused by the binding of the three studied N^ε-acryloyllysine piperazides.

The transglutaminase 2 cancer cell survival factor maintains mTOR activity to drive an aggressive cancer phenotype

Transglutaminase 2 (TG2) is an important cancer stem-like cell survival protein that is highly expressed in epidermal squamous cell carcinoma and drives an aggressive cancer phenotype. In the present study, we show that TG2 knockdown or inactivation results in a reduction in mammalian target of rapamycin (mTOR) level and activity in epidermal cancer stem-like cells which are associated with reduced spheroid formation, invasion, and migration, and reduced cancer stem cell and epithelial-mesenchymal transition (EMT) marker expression. Similar changes were observed in both cultured cells and tumors. mTOR knockdown or treatment with rapamycin phenocopies the reduction in spheroid formation, invasion, and migration, and cancer stem cell and EMT marker expression. Moreover, mTOR appears to be a necessary mediator of TG2 action, as a forced expression of constitutively active mTOR in TG2 knockdown cells partially restores the aggressive cancer phenotype and cancer stem cell and EMT marker expression. Tumor studies show that rapamycin reduces tumor growth and cancer stem cell marker expression and EMT. These studies suggest that TG2 stimulates mTOR activity to stimulate cancer cell stemness and EMT and drive aggressive tumor growth.

Investigating Cutaneous Squamous Cell Carcinoma in vitro and in vivo: Novel 3D Tools and Animal Models

Cutaneous Squamous Cell Carcinoma (cSCC) represents the second most common type of skin cancer, which incidence is continuously increasing worldwide. Given its high frequency, cSCC represents a major public health problem. Therefore, to provide the best patients’ care, it is necessary having a detailed understanding of the molecular processes underlying cSCC development, progression, and invasion. Extensive efforts have been made in developing new models allowing to study the molecular pathogenesis of solid tumors, including cSCC tumors. Traditionally, in vitro studies were performed with cells grown in a two-dimensional context, which, however, does not represent the complexity of tumor in vivo. In the recent years, new in vitro models have been developed aiming to mimic the three-dimensionality (3D) of the tumor, allowing the evaluation of tumor cell-cell and tumor-microenvironment interaction in an in vivo-like setting. These models include spheroids, organotypic cultures, skin reconstructs and organoids. Although 3D models demonstrate high potential to enhance the overall knowledge in cancer research, they lack systemic components which may be solved only by using animal models. Zebrafish is emerging as an alternative xenotransplant model in cancer research, offering a high-throughput approach for drug screening and real-time in vivo imaging to study cell invasion. Moreover, several categories of mouse models were developed for pre-clinical purpose, including xeno- and syngeneic transplantation models, autochthonous models of chemically or UV-induced skin squamous carcinogenesis, and genetically engineered mouse models (GEMMs) of cSCC. These models have been instrumental in examining the molecular mechanisms of cSCC and drug response in an in vivo setting. The present review proposes an overview of in vitro, particularly 3D, and in vivo models and their application in cutaneous SCC research.

Structure-activity relationships of hydrophobic alkyl acrylamides as tissue transglutaminase inhibitors

Tissue transglutaminase (TG2) is a multifunctional protein that plays biological roles based on its ability to catalyse protein cross-linking and to function as a non-canonical G-protein known as Ghα. The non-regulated activity of TG2 has been implicated in fibrosis, celiac disease and the survival of cancer stem cells, underpinning the therapeutic potential of cell permeable small molecule inhibitors of TG2. In the current study, we designed a small library of inhibitors to explore the importance of a terminal hydrophobic moiety, as well as the length of the tether to the irreversible acrylamide warhead. Subsequent kinetic evaluation using an in vitro activity assay provided values for the k _inact and K _I parameters for each of these irreversible inhibitors. The resulting structure-activity relationship (SAR) clearly indicated the affinity conferred by dansyl and adamantyl moieties, as well as the efficiency provided by the shortest warhead tether. We also provide the first direct evidence of the capability of these inhibitors to suppress the GTP binding ability of TG2, at least partially. However, it is intriguing to note that the SAR trends observed herein are opposite to those predicted by molecular modelling - namely that longer tether groups should improve binding affinity by allowing for deeper insertion of the hydrophobic moiety into a hydrophobic pocket on the enzyme. This discrepancy leads us to question whether the existing crystallographic structures of TG2 are appropriate for docking non-peptidic inhibitors. In the absence of a more relevant crystallographic structure, the data from rigorous kinetic studies, such as those provided herein, are critically important for the development of future small molecule TG2 inhibitors.

Regulation of ZO-1 on β-catenin mediates sulforaphane suppressed colorectal cancer stem cell properties in colorectal cancer

ZO-1 suppresses colorectal CSCs by interacting with β-Catenin and attenuating its nuclear translocation.