The Selectivity of CK2 Inhibitor Quinalizarin: A Reevaluation

Insights into the computer-aided drug design and discovery based on anthraquinone scaffold for cancer treatment: A systematic review

BACKGROUND

In the search for better anticancer drugs, computer-aided drug design (CADD) techniques play an indispensable role in facilitating the lengthy and costly drug discovery process especially when natural products are involved. Anthraquinone is one of the most widely-recognized natural products with anticancer properties. This review aimed to systematically assess and synthesize evidence on the utilization of CADD techniques centered on the anthraquinone scaffold for cancer treatment.

METHODS

The conduct and reporting of this review were done in accordance to the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) 2020 guideline. The protocol was registered in the "International prospective register of systematic reviews" database (PROSPERO: CRD42023432904) and also published recently. The search strategy was designed based on the combination of concept 1 "CADD or virtual screening", concept 2 "anthraquinone" and concept 3 "cancer". The search was executed in PubMed, Scopus, Web of Science and MedRxiv on 30 June 2023.

RESULTS

Databases searching retrieved a total of 317 records. After deduplication and applying the eligibility criteria, the final review ended up with 32 articles in which 3 articles were found by citation searching. The CADD methods used in the studies were either structure-based alone (69%) or combined with ligand-based methods via parallel (9%) or sequential (22%) approaches. Molecular docking was performed in all studies, with Glide and AutoDock being the most popular commercial and public software used respectively. Protein data bank was used in most studies to retrieve the crystal structure of the targets of interest while the main ligand databases were PubChem and Zinc. The utilization of in-silico techniques has enabled a deeper dive into the structural, biological and pharmacological properties of anthraquinone derivatives, revealing their remarkable anticancer properties in an all-rounded fashion.

CONCLUSION

By harnessing the power of computational tools and leveraging the natural diversity of anthraquinone compounds, researchers can expedite the development of better drugs to address the unmet medical needs in cancer treatment by improving the treatment outcome for cancer patients.

Recent Advances in the Discovery of CK2 Inhibitors

CK2 is a vital enzyme that phosphorylates a large number of substrates and thereby controls many processes in the body. Its upregulation was reported in many cancer types. Inhibitors of CK2 might have anticancer activity, and two compounds are currently under clinical trials. However, both compounds are ATP-competitive inhibitors that may have off-target side effects. The development of allosteric and dual inhibitors can overcome this drawback. These inhibitors showed higher selectivity and specificity for the CK2 enzyme compared to the ATP-competitive inhibitors. The present review summarizes the efforts exerted in the last five years in the design of CK2 inhibitors.

Quinalizarin as a potential antifungal drug for the treatment of Candida albicans fungal infection in cancer patients

This study aims to analyze the antifungal properties of quinalizarin, a plant-derived compound with proven anticancer effects. Quinalizarin exhibited antifungal activity against opportunistic pathogenic Candida species and Geotrichum capitatum. The treatment with this anthraquinone reduced hyphal growth, inhibited biofilm formation, and damaged mature Candida albicans biofilms. Real-time RT-PCR revealed that quinalizarin downregulated the expression of hyphae-related and biofilm-specific genes. The flow cytometry method used in the study showed that both apoptosis and necrosis were the physiological mechanisms of quinalizarin-induced C. albicans cell death, depending on the dose of the antifungal agent. A further study revealed an increase in the levels of intracellular reactive oxygen species and alterations in mitochondrial membrane potential after treatment with quinalizarin. Finally, quinalizarin was found to have low toxicity in a hemolytic test using human erythrocytes. In conclusion, we have identified quinalizarin as a potential antifungal compound.IMPORTANCEThis article is a study to determine the antifungal activity of quinalizarin (1,2,5,8-tetrahydroxyanthraquinone). Quinalizarin has potential antitumor properties and is effective in different types of tumor cells. The aim of the present study was to prove that quinalizarin can be used simultaneously in the treatment of cancer and in the treatment of intercurrent fungal infections. Quinalizarin was identified as a novel antifungal compound with low toxicity. These results may contribute to the development of a new drug with dual activity in the treatment of cancer-associated candidiasis.

Strategies of Targeting CK2 in Drug Discovery: Challenges, Opportunities, and Emerging Prospects

CK2 (casein kinase 2) is a serine/threonine protein kinase that is ubiquitous in eukaryotic cells and plays important roles in a variety of cellular functions, including cell growth, apoptosis, circadian rhythms, DNA damage repair, transcription, and translation. CK2 is involved in cancer pathogenesis and the occurrence of many diseases. Therefore, targeting CK2 is a promising therapeutic strategy. Although many CK2-specific small-molecule inhibitors have been developed, only CX-4945 has progressed to clinical trials. In recent years, novel CK2 inhibitors have gradually become a research hotspot, which is expected to overcome the limitations of traditional inhibitors. Herein, we summarize the structure, biological functions, and disease relevance of CK2 and emphatically analyze the structure-activity relationship (SAR) and binding modes of small-molecule CK2 inhibitors. We also discuss the latest progress of novel strategies, providing insights into new drugs targeting CK2 for clinical practice.

CK2 and protein kinases of the CK1 superfamily as targets for neurodegenerative disorders

Casein kinases are involved in a variety of signaling pathways, and also in inflammation, cancer, and neurological diseases. Therefore, they are regarded as potential therapeutic targets for drug design. Recent studies have highlighted the importance of the casein kinase 1 superfamily as well as protein kinase CK2 in the development of several neurodegenerative pathologies, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. CK1 kinases and their closely related tau tubulin kinases as well as CK2 are found to be overexpressed in the mammalian brain. Numerous substrates have been detected which play crucial roles in neuronal and synaptic network functions and activities. The development of new substances for the treatment of these pathologies is in high demand. The impact of these kinases in the progress of neurodegenerative disorders, their bona fide substrates, and numerous natural and synthetic compounds which are able to inhibit CK1, TTBK, and CK2 are discussed in this review.

E2 + norethisterone promotes the PI3K-AKT pathway via PGRMC1 to induce breast cancer cell proliferation

OBJECTIVE

This study aimed to find evidence that progesterone receptor membrane component 1 (PGRMC1) promotes estradiol (E2) + norethisterone (NET)-induced breast cancer proliferation through activation of the phosphatidylinositol-3-kinase (PI3K)-AKT pathway.

METHODS

PGRMC1-mediated breast cancer cellular proliferation and phosphorylation of PGRMC1 were studied using wild-type (hemagglutinin [HA]-tagged) MCF-7 cells, which were stably transfected with expression vector containing HA (MCF-7-HA cells), PGRMC1 (MCF-7-PGRMC1 cells) and Ser181 point mutated PGRMC1 (MCF-7-PGRMC1-S181A cells). Bioinformatics, cell proliferation, western blot, isobaric tags for relative and absolute quantitation (iTRAQ)-based RNA sequencing, real-time quantitative polymerase chain reaction (RT-qPCR) and cell cycle in vitro assays were performed to indicate the function of PGRMC1 and its possible mechanisms in breast cancer.

RESULTS

NET + E2 elicited a significant proliferation in MCF-7-Vec at 10^-6 M and 10^-10 M, respectively. MCF-7-PGRMC1 did increase the phosphorylation of AKT or ERK, which can be blocked by treatment with casein kinase 2 (CK2) inhibitor quinalizarin or in MCF-7-PGRMC1-S181A cells. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that the PI3K-AKT pathway is upregulated in MCF-7-PGRMC1 cells. Importantly, upregulation of the PI3K-AKT pathway mainly through promotion of cell cycle regulation strongly promoted cell proliferation in MCF-7-PGRMC1 cells.

CONCLUSIONS

CK2 is involved in phosphorylation of PGRMC1 at S181. The mechanism for the action of PGRMC1 for mediating proliferative progestogen effects obviously starts with promotion cell cycle regulation, and then activation of the PI3K-AKT pathway.

SGC-CK2-1 Is an Efficient Inducer of Insulin Production and Secretion in Pancreatic β-Cells

The pyrazolopyrimidine based compound SGC-CK2-1 is a potent and highly specific CK2 inhibitor and a new tool to study the biological functions of protein kinase CK2 irrespective from off-target effects. We used this compound in comparison with the well-established CK2 inhibitor CX-4945 to analyze the importance of CK2 for insulin production and secretion from pancreatic β-cells. Both inhibitors affected the proliferation and viability of MIN6 cells only marginally and downregulated the endogenous CK2 activity to a similar level. Furthermore, both inhibitors increased the message for insulin and boosted the secretion of insulin from storage vesicles. Thus, regarding the high specificity of SGC-CK2-1, we can clearly attribute the observed effects to biological functions of protein kinase CK2.

ROCK2-Specific Inhibitor KD025 Suppresses Adipocyte Differentiation by Inhibiting Casein Kinase 2

KD025, a ROCK2 isoform-specific inhibitor, has an anti-adipogenic activity which is not mediated by ROCK2 inhibition. To identify the target, we searched binding targets of KD025 by using the KINOMEscanTM screening platform, and we identified casein kinase 2 (CK2) as a novel target. KD025 showed comparable binding affinity to CK2α (Kd = 128 nM). By contrast, CK2 inhibitor CX-4945 and ROCK inhibitor fasudil did not show such cross-reactivity. In addition, KD025 effectively inhibited CK2 at a nanomolar concentration (IC50 = 50 nM). We examined if the inhibitory effect of KD025 on adipocyte differentiation is through the inhibition of CK2. Both CX-4945 and KD025 suppressed the generation of lipid droplets and the expression of proadipogenic genes Pparg and Cebpa in 3T3-L1 cells during adipocyte differentiation. Fasudil exerted no significant effect on the quantity of lipid droplets, but another ROCK inhibitor Y-27632 increased the expression of Pparg and Cebpa. Both CX-4945 and KD025 acted specifically in the middle stage (days 1-3) but were ineffective when treated at days 0-1 or the late stages, indicating that CX-4945 and KD025 may regulate the same target, CK2. The mRNA and protein levels of CK2α and CK2β generally decreased in 3T3-L1 cells at day 2 but recovered thereafter. Other well-known CK2 inhibitors DMAT and quinalizarin inhibited effectively the differentiation of 3T3-L1 cells. Taken together, the results of this study confirmed that KD025 inhibits ROCK2 and CK2, and that the inhibitory effect on adipocyte differentiation is through the inhibition of CK2.

Protein kinase CK2: a potential therapeutic target for diverse human diseases

CK2 is a constitutively active Ser/Thr protein kinase, which phosphorylates hundreds of substrates, controls several signaling pathways, and is implicated in a plethora of human diseases. Its best documented role is in cancer, where it regulates practically all malignant hallmarks. Other well-known functions of CK2 are in human infections; in particular, several viruses exploit host cell CK2 for their life cycle. Very recently, also SARS-CoV-2, the virus responsible for the COVID-19 pandemic, has been found to enhance CK2 activity and to induce the phosphorylation of several CK2 substrates (either viral and host proteins). CK2 is also considered an emerging target for neurological diseases, inflammation and autoimmune disorders, diverse ophthalmic pathologies, diabetes, and obesity. In addition, CK2 activity has been associated with cardiovascular diseases, as cardiac ischemia-reperfusion injury, atherosclerosis, and cardiac hypertrophy. The hypothesis of considering CK2 inhibition for cystic fibrosis therapies has been also entertained for many years. Moreover, psychiatric disorders and syndromes due to CK2 mutations have been recently identified. On these bases, CK2 is emerging as an increasingly attractive target in various fields of human medicine, with the advantage that several very specific and effective inhibitors are already available. Here, we review the literature on CK2 implication in different human pathologies and evaluate its potential as a pharmacological target in the light of the most recent findings.

Protein kinase CK2 inhibition as a pharmacological strategy

CK2 is a constitutively active Ser/Thr protein kinase which phosphorylates hundreds of substrates. Since they are primarily related to survival and proliferation pathways, the best-known pathological roles of CK2 are in cancer, where its targeting is currently being considered as a possible therapy. However, CK2 activity has been found instrumental in many other human pathologies, and its inhibition will expectably be extended to different purposes in the near future. Here, after a description of CK2 features and implications in diseases, we analyze the different inhibitors and strategies available to target CK2, and update the results so far obtained by their in vivo application.

Structural and thermodynamic analyses of interactions between death-associated protein kinase 1 and anthraquinones

Death-associated protein kinase 1 (DAPK1) is a serine/threonine protein kinase that regulates apoptosis and autophagy. DAPK1 is considered to be a therapeutic target for amyloid-β deposition, endometrial adenocarcinomas and acute ischemic stroke. Here, the potent inhibitory activity of the natural anthraquinone purpurin against DAPK1 phosphorylation is shown. Thermodynamic analysis revealed that while the binding affinity of purpurin is similar to that of CPR005231, which is a DAPK1 inhibitor with an imidazopyridazine moiety, the binding of purpurin was more enthalpically favorable. In addition, the inhibition potencies were correlated with the enthalpic changes but not with the binding affinities. Crystallographic analysis of the DAPK1-purpurin complex revealed that the formation of a hydrogen-bond network is likely to contribute to the favorable enthalpic changes and that stabilization of the glycine-rich loop may cause less favorable entropic changes. The present findings indicate that purpurin may be a good lead compound for the discovery of inhibitors of DAPK1, and the observation of enthalpic changes could provide important clues for drug development.

Quinalizarin induces ROS‑mediated apoptosis via the MAPK, STAT3 and NF‑κB signaling pathways in human breast cancer cells

Quinalizarin has been demonstrated to exhibit potent antitumor activities in lung cancer and gastric cancer cells, but currently, little is known regarding its anticancer mechanisms in human breast cancer cells. The aim of the present study was to investigate the apoptotic effects of quinalizarin in MCF-7 cells and to analyze its molecular mechanisms. The MTT assay was used to evaluate the viability of human breast cancer cells that had been treated with quinalizarin and 5-fluorouracil. Flow cytometric analyses and western blotting were used to investigate the effects of quinalizarin on apoptosis and cycle arrest in MCF-7 cells with focus on reactive oxygen species (ROS) production. The results demonstrated that quinalizarin exhibited significant cytotoxic effects on human breast cancer cells in a dose-dependent manner. Accompanying ROS, quinalizarin induced MCF-7 cell mitochondrial-associated apoptosis by regulating mitochondrial-associated apoptosis, and caused cell cycle arrest at the G₂/M phase in a time-dependent manner. Furthermore, quinalizarin can activate p38 kinase and JNK, and inhibit the extracellular signal-regulated kinase, signal transducer and activator of transcription 3 (STAT3) and NF-κB signaling pathways. These effects were blocked by mitogen-activated protein kinase (MAPK) inhibitor and N-acetyl-L-cysteine. The results from the present study suggested that quinalizarin induced G₂/M phase cell cycle arrest and apoptosis in MCF-7 cells through ROS-mediated MAPK, STAT3 and NF-κB signaling pathways. Thus, quinalizarin may be useful for human breast cancer treatment, as well as the treatment of other cancer types.

Involvement of endothelial CK2 in the radiation induced perivascular resistant niche (PVRN) and the induction of radioresistance for non-small cell lung cancer (NSCLC) cells

BACKGROUND

Tumor microenvironment (TME) plays a vital role in determining the outcomes of radiotherapy. As an important component of TME, vascular endothelial cells are involved in the perivascular resistance niche (PVRN), which is formed by inflammation or cytokine production induced by ionizing radiation (IR). Protein kinase CK2 is a constitutively active serine/threonine kinase which plays a vital role in cell proliferation and inflammation. In this study, we investigated the potential role of CK2 in PVRN after IR exposure.

RESULT

Specific CK2 inhibitors, Quinalizarin and CX-4945, were employed to effectively suppressed the kinase activity of CK2 in human umbilical vein endothelial cells (HUVECs) without affecting their viability. Results showing that conditioned medium from IR-exposed HUVECs increased cell viability of A549 and H460 cells, and the pretreatment of CK2 inhibitors slowed down such increment. The secretion of IL-8 and IL-6 in HUVECs was induced after exposure with IR, but significantly inhibited by the addition of CK2 inhibitors. Furthermore, IR exposure elevated the nuclear phosphorylated factor-κB (NF-κB) p65 expression in HUVECs, which was a master factor regulating cytokine production. But when pretreated with CK2 inhibitors, such elevation was significantly suppressed.

CONCLUSION

This study indicated that protein kinase CK2 is involved in the key process of the IR induced perivascular resistant niche, namely cytokine production, by endothelial cells, which finally led to radioresistance of non-small cell lung cancer cells. Thus, the inhibition of CK2 may be a promising way to improve the outcomes of radiation in non-small cell lung cancer cells.

Association of protein kinase CK2 inhibition with cellular radiosensitivity of non-small cell lung cancer

Protein kinase CK2 is a highly conserved protein Ser/Thr protein kinase and plays important roles in cell proliferation, protein translation and cell survival. This study investigated the possibility of using CK2 inhibition as a new approach for increasing the efficacy of radiotherapy in non-small cell lung cancer (NSCLC) and its underlying mechanisms. Kinase inhibition of CK2 was attempted either by using the specific CK2 inhibitor, Quinalizarin or by applying siRNA interference technology to silence the expression of the catalytic subunit of CK2 in A549 and H460 cells. The results showed that CK2α knockdown or Quinalizarin significantly enhanced the radiosensitivity of various NSCLC cells. The notable findings we observed after exposure to both CK2 inhibition and ionizing radiation (IR) were a prolonged delay in radiation-induced DNA double-strand breaks (DSB) repair, robust G2/M checkpoint arrest and increased apoptosis. In vivo studies further demonstrated that compared with each treatment alone, CK2 inhibition combined with IR reduced tumor growth in the H460 cell xenograft model. In conclusion, CK2 is a promising target for the enhancement of radiosensitivity in NSCLC.

Progesterone receptor membrane component 1 is phosphorylated upon progestin treatment in breast cancer cells

Menopausal hormone therapy, using estrogen and synthetic progestins, is associated with an increased risk of developing breast cancer. The effect of progestins on breast cells is complex and not yet fully understood. In previous in vitro and in vivo studies, we found different progestins to increase the proliferation of Progesterone Receptor Membrane Component-1 (PGRMC1)-overexpressing MCF7 cells (MCF7/PGRMC1), suggesting a possible role of PGRMC1 in transducing membrane-initiated progestin signals.

Understanding the activation mechanism of PGRMC1 by progestins will provide deeper insights into the mode of action of progestins on breast cells and the often-reported phenomenon of elevated breast cancer rates upon progestin-based hormone therapy. In the present study, we aimed to further investigate the effect of progestins on receptor activation in MCF7 and T47D breast cancer cell lines. We report that treatment of both breast cancer cell lines with the progestin norethisterone (NET) induces phosphorylation of PGRMC1 at the Casein Kinase 2 (CK2) phosphorylation site Ser181, which can be decreased by treatment with CK2 inhibitor quinalizarin. Point mutation of the Ser181 phosphorylation site in MCF7/PGRMC1 cells impaired proliferation upon NET treatment. This study gives further insights into the mechanism of differential phosphorylation of the receptor and confirms our earlier hypothesis that phosphorylation of the CK2-binding site is essential for activation of PGRMC1. It further suggests an important role of PGRMC1 in the tumorigenesis and progression of breast cancer in progestin-based hormone replacement therapy.

Impact of protein kinase CK2 inhibitors on proliferation and differentiation of neural stem cells

BACKGROUND

Protein kinases play central roles in cell and tissue development. Protein kinase CK2, an ubiquitously expressed serine/threonine kinase has severe impacts on embryo- and spermatogenesis. Since its role in neurogenesis has so far only been investigated in very few studies, we analysed the role of CK2 in neural stem cells by using two specific inhibitors.

METHODS

Neural stem cells were isolated from the subventricular zone of neonatal mice, using a neurosphere approach. Proliferation of the neurospheres, as well as their differentiation was investigated with and without inhibition of CK2. Changes in proliferation were assessed by counting the number and measuring the diameter of the neurospheres. Furthermore, the absolute cell numbers within the neurospheres were estimated. Differentiation was induced by retinoic acid in single cells after dissociation of the neurospheres. CK2 was inhibited at consecutive time points after induction of the differentiation process.

RESULTS

CK2 inhibition reduced the amount and size of proliferating neurospheres dose dependently. Adding the CK2 inhibitor CX-4945 at the start of differentiation we observed a dose-dependent effect of CX-4945 on cell viability and glia cell differentiation. Adding quinalizarin, a second CK2 inhibitor, at the start of differentiation led to an elevated level of apoptosis, which was accompanied by a reduced neural differentiation. Adding the CK2 inhibitors at 72 h after the start of differentiation had no effect on stem cell differentiation. Conclusion: Inhibition of CK2 influences early gliogenesis in a time point and concentration dependent manner.

GENERAL SIGNIFICANCE

The use of a CK2 inhibitor significantly affects the neural stem cell niche.

The Development of CK2 Inhibitors: From Traditional Pharmacology to in Silico Rational Drug Design

Casein kinase II (CK2) is an ubiquitous and pleiotropic serine/threonine protein kinase able to phosphorylate hundreds of substrates. Being implicated in several human diseases, from neurodegeneration to cancer, the biological roles of CK2 have been intensively studied. Upregulation of CK2 has been shown to be critical to tumor progression, making this kinase an attractive target for cancer therapy. Several CK2 inhibitors have been developed so far, the first being discovered by "trial and error testing". In the last decade, the development of in silico rational drug design has prompted the discovery, de novo design and optimization of several CK2 inhibitors, active in the low nanomolar range. The screening of big chemical libraries and the optimization of hit compounds by Structure Based Drug Design (SBDD) provide telling examples of a fruitful application of rational drug design to the development of CK2 inhibitors. Ligand Based Drug Design (LBDD) models have been also applied to CK2 drug discovery, however they were mainly focused on methodology improvements rather than being critical for de novo design and optimization. This manuscript provides detailed description of in silico methodologies whose applications to the design and development of CK2 inhibitors proved successful and promising.

CK2 in Cancer: Cellular and Biochemical Mechanisms and Potential Therapeutic Target

CK2 genes are overexpressed in many human cancers, and most often overexpression is associated with worse prognosis. Site-specific expression in mice leads to cancer development (e.g., breast, lymphoma) indicating the oncogenic nature of CK2. CK2 is involved in many key aspects of cancer including inhibition of apoptosis, modulation of signaling pathways, DNA damage response, and cell cycle regulation. A number of CK2 inhibitors are now available and have been shown to have activity against various cancers in vitro and in pre-clinical models. Some of these inhibitors are now undergoing exploration in clinical trials as well. In this review, we will examine some of the major cancers in which CK2 inhibition has promise based on in vitro and pre-clinical studies, the proposed cellular and signaling mechanisms of anti-cancer activity by CK2 inhibitors, and the current or recent clinical trials using CK2 inhibitors.

Protein Kinase CK2: A Targetable BCR-ABL Partner in Philadelphia Positive Leukemias

BCR-ABL-mediated leukemias, either Chronic Myeloid Leukemia (CML) or Philadelphia positive Acute Lymphoblastic Leukemia (ALL), are the paradigm of targeted molecular therapy of cancer due to the impressive clinical responses obtained with BCR-ABL specific tyrosine kinase inhibitors (TKIs). However, BCR-ABL TKIs do not allow completely eradicating both CML and ALL. Furthermore, ALL therapy is associated with much worse responses to TKIs than those observed in CML. The identification of additional pathways that mediate BCR-ABL leukemogenesis is indeed mandatory to achieve synthetic lethality together with TKI. Here, we review the role of BCR-ABL/protein kinase CK2 interaction in BCR-ABL leukemias, with potentially relevant implications for therapy.

Casein kinases as potential therapeutic targets

INTRODUCTION

The conventional term 'casein kinase' (CK) denotes three classes of kinases - CK1, CK2 and Golgi-CK (G-CK)/Fam20C (family with sequence similarity 20, member C) - sharing the ability to phoshorylate casein in vitro, but otherwise unrelated to each other. All CKs have been reported to be implicated in human diseases, and reviews individually dealing with the druggability of CK1 and CK2 are available. Our aim is to provide a comparative analysis of the three classes of CKs as therapeutic targets.

AREAS COVERED

CK2 is the CK for which implication in neoplasia is best documented, with the survival of cancer cells often relying on its overexpression. An ample variety of cell-permeable CK2 inhibitors have been developed, with a couple of these now in clinical trials. Isoform-specific CK1 inhibitors that are expected to play a beneficial role in oncology and neurodegeneration have been also developed. In contrast, the pathogenic potential of G-CK/Fam20C is caused by its loss of function. Activators of Fam20C, notably sphingolipids and their analogs, may prove beneficial in this respect.

EXPERT OPINION

Optimization of CK2 and CK1 inhibitors will prove useful to develop new therapeutic strategies for treating cancer and neurodegenerative disorders, while the design of potent activators of G-CK/Fam20C will provide a new tool in the fields of bio-mineralization and hypophosphatemic diseases.