Direct inhibition of choline kinase by a near-infrared fluorescent carbocyanine

Inhibition of glioblastoma cell proliferation and invasion by the choline-kinase inhibitor JAS239 varies with cell type and hypoxia

Background

Elevated choline kinase alpha (ChoK) is observed in most solid tumours including glioblastomas (GBM), yet until recently, inhibitors of ChoK have demonstrated limited efficacy in GBM models. Given that hypoxia is associated with GBM therapy resistance, we hypothesised that tumour hypoxia could be responsible for such limitations. We therefore evaluated in GBM cells, the effect of hypoxia on the function of JAS239, a potent ChoK inhibitor.

Methods

Rodent (F98 and 9L) and human (U-87 MG and U-251 MG) GBM cell lines were subjected to 72 hours of hypoxia conditioning and treated with JAS239 for 24 hours. NMR metabolomic measurements and analyses were performed to evaluate the signalling pathways involved. In addition, cell proliferation, cell cycle progression and cell invasion were measured in cell monolayers and 3D spheroids, with or without JAS239 treatment in normoxic or hypoxic cells to assess how hypoxia affects JAS239 function.

Results

Hypoxia and JAS239 treatment led to significant changes in the cellular metabolic pathways, specifically the phospholipid and glycolytic pathways associated with a reduction in cell proliferation via induced cell cycle arrest. Interestingly, JAS239 also impaired GBM invasion. However, JAS239 effects were variable depending on the cell line, reflecting the inherent heterogeneity observed in GBMs.

Conclusion

Our findings indicate that JAS239 and hypoxia can deregulate cellular metabolism, inhibit proliferation and alter cell invasion. These results may be useful for the design of new therapeutic strategies based on ChoK inhibition that can act on multiple pro-tumorigenic features.

Choline metabolism and its implications in cancer

Choline, a quintessential quaternary ammonium compound, plays a cardinal role in several pivotal biological mechanisms, chiefly in safeguarding cell membrane integrity, orchestrating methylation reactions, and synthesizing vital neurotransmitters. This systematic review meticulously dissects the complex interplay between choline metabolism and its profound implications in oncology. The exposition is stratified into three salient dimensions: Initially, we delve into the intricacies of choline metabolism, accentuating its indispensability in cellular physiology, the enzymatic labyrinth governing its flux, and the pivotal cellular import mechanisms. Subsequently, we elucidate the contemporary comprehension of choline metabolism in the cancer paradigm, traversing its influence from inception to the intricate metamorphosis during oncogenic progression, further compounded by dysregulated enzyme activities and aberrant signaling cascades. Conclusively, we illuminate the burgeoning potential of choline-centric metabolic imaging modalities, notably magnetic resonance spectroscopy (MRS) and positron emission tomography (PET), as avant-garde tools for cancer diagnostics and therapeutic trajectory monitoring. Synoptically, the nuanced perturbations in choline metabolism in neoplastic entities unfurl critical insights, potentially heralding paradigm shifts in diagnostic and therapeutic oncological stratagems. A deeper foray into this realm is anticipated to fortify our molecular understanding and refine intervention modalities in cancer theranostics.

Emerging biomedical imaging-based companion diagnostics for precision medicine

The tumor heterogeneity, which leads to individual variations in tumor microenvironments, causes poor prognoses and limits therapeutic response. Emerging technology such as companion diagnostics (CDx) detects biomarkers and monitors therapeutic responses, allowing identification of patients who would benefit most from treatment. However, currently, most US Food and Drug Administration-approved CDx tests are designed to detect biomarkers in vitro and ex vivo, making it difficult to dynamically report variations of targets in vivo. Various medical imaging techniques offer dynamic measurement of tumor heterogeneity and treatment response, complementing CDx tests. Imaging-based companion diagnostics allow for patient stratification for targeted medicines and identification of patient populations benefiting from alternative therapeutic methods. This review summarizes recent developments in molecular imaging for predicting and assessing responses to cancer therapies, as well as the various biomarkers used in imaging-based CDx tests. We hope this review provides informative insights into imaging-based companion diagnostics and advances precision medicine.

New bioisosteric sulphur-containing choline kinase inhibitors with a tracked mode of action

Since the identification of human choline kinase as a protein target against cancer progression, many compounds have been designed to inhibit its function and reduce the biosynthesis of phosphatidylcholine. Herein, we propose a series of bioisosteric inhibitors that are based on the introduction of sulphur and feature improved activity and lipophilic/hydrophilic balance. The evaluation of the inhibitory and of the antiproliferative properties of the PL (dithioethane) and FP (disulphide) libraries led to the identification of PL 48, PL 55 and PL 69 as the most active compounds of the series. Docking analysis using FLAP suggests that for hits to leads, binding mostly involves an interaction with the Mg²⁺ cofactor, or its destabilization. The most active compounds of the two series are capable of inducing apoptosis following the mitochondrial pathway and to significantly reduce the expression of anti-apoptotic proteins such as the Mcl-1. The fluorescence properties of the compounds of the PL library allowed the tracking of their mode of action, while PAINS (Pan Assays Interference Structures) filtration databases suggest the lack of any unspecific biological response.

Biological Evaluation of New Thienopyridinium and Thienopyrimidinium Derivatives as Human Choline Kinase Inhibitors

Due to its role in lipid biosynthesis, choline kinase α1 (CKα1) is an interesting target for the development of new antitumor agents. In this work, we present a series of 41 compounds designed based on the well-known and successful strategy of introducing thienopyridine and pyrimidine as bioisosteres of other heterocycles in active antitumor compounds. Notwithstanding the fact that some of these compounds do not show significant enzymatic inhibition, others, in contrast, feature substantially improved enzymatic and antiproliferative inhibition values. This is also confirmed by docking analysis, whereby compounds with longer linkers and thienopyrimidine cationic head have been identified as the most compelling. Among the best compounds is Ff-35, which inhibits the growth of different tumor cells at submicromolar concentrations. Moreover, Ff-35 is more potent in inhibiting CKα1 than other previous biscationic derivatives. Treatment of A549, Hela, and MDA-MB-231 cells with Ff-35 results in their arrest at the G1 phase of the cell cycle. Furthermore, the compound induces cellular apoptosis in a concentration-dependent manner. Altogether, these findings indicate that Ff-35 is a promising new chemotherapeutic agent with encouraging preclinical potential.

Assessing Tumour Haemodynamic Heterogeneity and Response to Choline Kinase Inhibition Using Clustered Dynamic Contrast Enhanced MRI Parameters in Rodent Models of Glioblastoma

To investigate the utility of DCE-MRI derived pharmacokinetic parameters in evaluating tumour haemodynamic heterogeneity and treatment response in rodent models of glioblastoma, imaging was performed on intracranial F98 and GL261 glioblastoma bearing rodents. Clustering of the DCE-MRI-based parametric maps (using Tofts, extended Tofts, shutter speed, two-compartment, and the second generation shutter speed models) was performed using a hierarchical clustering algorithm, resulting in areas with poor fit (reflecting necrosis), low, medium, and high valued pixels representing parameters Ktrans, ve, Kep, vp, τi and Fp. There was a significant increase in the number of necrotic pixels with increasing tumour volume and a significant correlation between ve and tumour volume suggesting increased extracellular volume in larger tumours. In terms of therapeutic response in F98 rat GBMs, a sustained decrease in permeability and perfusion and a reduced cell density was observed during treatment with JAS239 based on Ktrans, Fp and ve as compared to control animals. No significant differences in these parameters were found for the GL261 tumour, indicating that this model may be less sensitive to JAS239 treatment regarding changes in vascular parameters. This study demonstrates that region-based clustered pharmacokinetic parameters derived from DCE-MRI may be useful in assessing tumour haemodynamic heterogeneity with the potential for assessing therapeutic response.

NIR Fluorescent Imaging and Photodynamic Therapy with a Novel Theranostic Phospholipid Probe for Triple-Negative Breast Cancer Cells

New exogenous probes are needed for both imaging diagnostics and therapeutics. Here, we introduce a novel nanocomposite near-infrared (NIR) fluorescent imaging probe and test its potency as a photosensitizing agent for photodynamic therapy (PDT) against triple-negative breast cancer cells. The active component in the nanocomposite is a small molecule, pyropheophorbide a-phosphatidylethanolamine-QSY21 (Pyro-PtdEtn-QSY), which is imbedded into lipid nanoparticles for transport in the body. The probe targets abnormal choline metabolism in cancer cells; specifically, the overexpression of phosphatidylcholine-specific phospholipase C (PC-PLC) in breast, prostate, and ovarian cancers. Pyro-PtdEtn-QSY consists of a NIR fluorophore and a quencher, attached to a PtdEtn moiety. It is selectively activated by PC-PLC resulting in enhanced fluorescence in cancer cells compared to normal cells. In our in vitro investigation, four breast cancer cell lines showed higher probe activation levels than noncancerous control cells, immortalized human mammary gland cells, and normal human T cells. Moreover, the ability of this nanocomposite to function as a sensitizer in PDT experiments on MDA-MB-231 cells suggests that the probe is promising as a theranostic agent.

Recent advances in the design of choline kinase α inhibitors and the molecular basis of their inhibition

Upregulated choline metabolism, characterized by an increase in phosphocholine (PCho), is a hallmark of oncogenesis and tumor progression. Choline kinase (ChoK), the enzyme responsible for PCho synthesis, has consequently become a promising drug target for cancer therapy and as such a significant number of ChoK inhibitors have been developed over the last few decades. More recently, due to the role of this enzyme in other pathologies, ChoK inhibitors have also been used in new therapeutic approaches against malaria and rheumatoid arthritis. Here, we review research results in the field of ChoKα inhibitors from their synthesis to the molecular basis of their binding mode. Strategies for the development of inhibitors and their selectivity on ChoKα over ChoKβ, the plasticity of the choline-binding site, the discovery of new exploitable binding sites, and the allosteric properties of this enzyme are highlighted. The outcomes summarized in this review will be a useful guide to develop new multifunctional potent drugs for the treatment of various human diseases.

Imaging of cancer lipid metabolism in response to therapy

Lipids represent a diverse array of molecules essential to the cell's structure, defense, energy, and communication. Lipid metabolism can often become dysregulated during tumor development. During cancer therapy, targeted inhibition of cell proliferation can likewise cause widespread and drastic changes in lipid composition. Molecular imaging techniques have been developed to monitor altered lipid profiles as a biomarker for cancer diagnosis and treatment response. For decades, MRS has been the dominant non-invasive technique for studying lipid metabolite levels. Recent insights into the oncogenic transformations driving changes in lipid metabolism have revealed new mechanisms and signaling molecules that can be exploited using optical imaging, mass spectrometry imaging, and positron emission tomography. These novel imaging modalities have provided researchers with a diverse toolbox to examine changes in lipids in response to a wide array of anticancer strategies including chemotherapy, radiation therapy, signal transduction inhibitors, gene therapy, immunotherapy, or a combination of these strategies. The understanding of lipid metabolism in response to cancer therapy continues to evolve as each therapeutic method emerges, and this review seeks to summarize the current field and areas of unmet needs.

Detection and Differentiation of Breast Cancer Sub-Types using a cPLA2α Activatable Fluorophore

Cytosolic phospholipase A2α (cPLA2α) has been shown to be elevated in breast cancer and is a potential biomarker in the differentiation of molecular sub-types. Using a cPLA2α activatable fluorophore, DDAO arachidonate, we explore its ability to function as a contrast agent in fluorescence-guided surgery. In cell lines ranging in cPLA2α expression and representing varying breast cancer sub-types, we show DDAO arachidonate activates with a high correlation to cPLA2α expression level. Using a control probe, DDAO palmitate, in addition to cPLA2α inhibition and genetic knockdown, we show that this activation is a result of cPLA2α activity. In mouse models, using an ex vivo tumor painting technique, we show that DDAO arachidonate activates to a high degree in basal-like versus luminal-like breast tumors and healthy mammary tissue. Finally, we show that using an in vivo model, orthotopic basal-like tumors give significantly high probe activation compared to healthy mammary fat pads and surrounding tissue. Together we conclude that cPLA2α activatable fluorophores such as DDAO arachidonate may serve as a useful contrast agent for the visualization of tumor margins in the fluorescence-guided surgery of basal-like breast cancer.

Nonprotecting Group Synthesis of a Phospholipase C Activatable Probe with an Azo-Free Quencher

The near-infrared fluorescent activatable smart probe Pyro-phosphatidylethanolamine (PtdEtn)-QSY was synthesized and observed to selectively fluoresce in the presence of phosphatidylcholine-specific phospholipase C (PC-PLC). PC-PLC is an important biological target as it is known to be upregulated in a variety of cancers, including triple negative breast cancer. Pyro-PtdEtn-QSY features a QSY21 quenching moiety instead of the Black Hole Quencher-3 (BHQ-3) used previously because the latter contains an azo bond, which could lead to biological instability.

Spectroscopic methods to analyze drug metabolites

Drug metabolites have been monitored with various types of newly developed techniques and/or combination of common analytical methods, which could provide a great deal of information on metabolite profiling. Because it is not easy to analyze whole drug metabolites qualitatively and quantitatively, a single solution of analytical techniques is combined in a multilateral manner to cover the widest range of drug metabolites. Mass-based spectroscopic analysis of drug metabolites has been expanded with the help of other parameter-based methods. The current development of metabolism studies through contemporary pharmaceutical research are reviewed with an overview on conventionally used spectroscopic methods. Several technical approaches for conducting drug metabolic profiling through spectroscopic methods are discussed in depth.

Near infrared fluorescent imaging of choline kinase alpha expression and inhibition in breast tumors

Choline kinase alpha (ChoKα) overexpression is associated with an aggressive tumor phenotype. ChoKα inhibitors induce apoptosis in tumors, however validation of their specificity is difficult in vivo. We report the use of optical imaging to assess ChoKα status in cells and in vivo using JAS239, a carbocyanine-based ChoKα inhibitor with inherent near infrared fluorescence. JAS239 attenuated choline phosphorylation and viability in a panel of human breast cancer cell lines. Antibody blockade prevented cellular retention of JAS239 indicating direct interaction with ChoKα independent of the choline transporters and catabolic choline pathways. In mice bearing orthotopic MCF7 breast xenografts, optical imaging with JAS239 distinguished tumors overexpressing ChoKα from their empty vector counterparts and delineated tumor margins. Pharmacological inhibition of ChoK by the established inhibitor MN58b led to a growth inhibition in 4175-Luc+ tumors that was accompanied by concomitant reduction in JAS239 uptake and decreased total choline metabolite levels as measured using magnetic resonance spectroscopy. At higher therapeutic doses, JAS239 was as effective as MN58b at arresting tumor growth and inducing apoptosis in MDA-MB-231 tumors, significantly reducing tumor choline below baseline levels without observable systemic toxicity. These data introduce a new method to monitor therapeutically effective inhibitors of choline metabolism in breast cancer using a small molecule companion diagnostic.

Molecular Effects of Doxorubicin on Choline Metabolism in Breast Cancer

Abnormal choline phospholipid metabolism is a hallmark of cancer. The magnetic resonance spectroscopy (MRS) detected total choline (tCho) signal can serve as an early noninvasive imaging biomarker of chemotherapy response in breast cancer. We have quantified the individual components of the tCho signal, glycerophosphocholine (GPC), phosphocholine (PC) and free choline (Cho), before and after treatment with the commonly used chemotherapeutic drug doxorubicin in weakly metastatic human MCF7 and triple-negative human MDA-MB-231 breast cancer cells. While the tCho concentration did not change following doxorubicin treatment, GPC significantly increased and PC decreased. Of the two phosphatidylcholine-specific PLD enzymes, only PLD1, but not PLD2, mRNA was down-regulated by doxorubicin treatment. For the two reported genes encoding GPC phosphodiesterase, the mRNA of GDPD6, but not GDPD5, decreased following doxorubicin treatment. mRNA levels of choline kinase α (ChKα), which converts Cho to PC, were reduced following doxorubicin treatment. PLD1 and ChKα protein levels decreased following doxorubicin treatment in a concentration dependent manner. Treatment with the PLD1 specific inhibitor VU0155069 sensitized MCF7 and MDA-MB-231 breast cancer cells to doxorubicin-induced cytotoxicity. Low concentrations of 100 nM of doxorubicin increased MDA-MB-231 cell migration. GDPD6, but not PLD1 or ChKα, silencing by siRNA abolished doxorubicin-induced breast cancer cell migration. Doxorubicin induced GPC increase and PC decrease are caused by reductions in PLD1, GDPD6, and ChKα mRNA and protein expression. We have shown that silencing or inhibiting these genes/proteins can promote drug effectiveness and reduce adverse drug effects. Our findings emphasize the importance of detecting PC and GPC individually.

pH-Responsive near-infrared fluorescent cyanine dyes for molecular imaging based on pH sensing

pH-Responsive near-infrared cyanine dyes were synthesized and applied as imaging probes of acidic intracellular compartments of living cells.

Choline kinase alpha-Putting the ChoK-hold on tumor metabolism

It is well established that lipid metabolism is drastically altered during tumor development and response to therapy. Choline kinase alpha (ChoKα) is a key mediator of these changes, as it represents the first committed step in the Kennedy pathway of phosphatidylcholine biosynthesis and ChoKα expression is upregulated in many human cancers. ChoKα activity is associated with drug resistant, metastatic, and malignant phenotypes, and represents a robust biomarker and therapeutic target in cancer. Effective ChoKα inhibitors have been developed and have recently entered clinical trials. ChoKα's clinical relevance was, until recently, attributed solely to its production of second messenger intermediates of phospholipid synthesis. The recent discovery of a non-catalytic scaffolding function of ChoKα may link growth receptor signaling to lipid biogenesis and requires a reinterpretation of the design and validation of ChoKα inhibitors. Advances in positron emission tomography, magnetic resonance spectroscopy, and optical imaging methods now allow for a comprehensive understanding of ChoKα expression and activity in vivo. We will review the current understanding of ChoKα metabolism, its role in tumor biology and the development and validation of targeted therapies and companion diagnostics for this important regulatory enzyme. This comes at a critical time as ChoKα-targeting programs receive more clinical interest.

The novel choline kinase inhibitor ICL-CCIC-0019 reprograms cellular metabolism and inhibits cancer cell growth

The glycerophospholipid phosphatidylcholine is the most abundant phospholipid species of eukaryotic membranes and essential for structural integrity and signaling function of cell membranes required for cancer cell growth. Inhibition of choline kinase alpha (CHKA), the first committed step to phosphatidylcholine synthesis, by the selective small-molecule ICL-CCIC-0019, potently suppressed growth of a panel of 60 cancer cell lines with median GI50 of 1.12 μM and inhibited tumor xenograft growth in mice. ICL-CCIC-0019 decreased phosphocholine levels and the fraction of labeled choline in lipids, and induced G1 arrest, endoplasmic reticulum stress and apoptosis. Changes in phosphocholine cellular levels following treatment could be detected non-invasively in tumor xenografts by [18F]-fluoromethyl-[1,2-2H4]-choline positron emission tomography. Herein, we reveal a previously unappreciated effect of choline metabolism on mitochondria function. Comparative metabolomics demonstrated that phosphatidylcholine pathway inhibition leads to a metabolically stressed phenotype analogous to mitochondria toxin treatment but without reactive oxygen species activation. Drug treatment decreased mitochondria function with associated reduction of citrate synthase expression and AMPK activation. Glucose and acetate uptake were increased in an attempt to overcome the metabolic stress. This study indicates that choline pathway pharmacological inhibition critically affects the metabolic function of the cell beyond reduced synthesis of phospholipids.

Metformin Decouples Phospholipid Metabolism in Breast Cancer Cells

INTRODUCTION

The antidiabetic drug metformin, currently undergoing trials for cancer treatment, modulates lipid and glucose metabolism both crucial in phospholipid synthesis. Here the effect of treatment of breast tumour cells with metformin on phosphatidylcholine (PtdCho) metabolism which plays a key role in membrane synthesis and intracellular signalling has been examined.

METHODS

MDA-MB-468, BT474 and SKBr3 breast cancer cell lines were treated with metformin and [3H-methyl]choline and [14C(U)]glucose incorporation and lipid accumulation determined in the presence and absence of lipase inhibitors. Activities of choline kinase (CK), CTP:phosphocholine cytidylyl transferase (CCT) and PtdCho-phospholipase C (PLC) were also measured. [3H] Radiolabelled metabolites were determined using thin layer chromatography.

RESULTS

Metformin-treated cells exhibited decreased formation of [3H]phosphocholine but increased accumulation of [3H]choline by PtdCho. CK and PLC activities were decreased and CCT activity increased by metformin-treatment. [14C] incorporation into fatty acids was decreased and into glycerol was increased in breast cancer cells treated with metformin incubated with [14C(U)]glucose.

CONCLUSION

This is the first study to show that treatment of breast cancer cells with metformin induces profound changes in phospholipid metabolism.

Synthesis and Evaluation of Cytosolic Phospholipase A(2) Activatable Fluorophores for Cancer Imaging

Activatable fluorophores selective to cytosolic phospholipase A2 (cPLA2) were synthesized and evaluated for their ability to image triple negative breast cancer cells. The activatable constructs were synthesized by esterification of a small molecule fluorophore with a fatty acid resulting in ablated fluorescence. Selectivity for cPLA2 was generated through the choice of fluorophore and fatty acid. Esterification with arachidonic acid was sufficient to impart specificity to cPLA2 when compared to esterification with palmitic acid. In vitro analysis of probes incorporated into phosphatidylcholine liposomes demonstrated that a nonselective phospholipase (sPLA2 group IB) was able to hydrolyze both arachidonate and palmitate coupled fluorophores resulting in the generation of fluorescence. Of the four fluorophores tested, DDAO (7-hydroxy-9H-(1,3-dichloro-9,9-dimethylacridin-2-one)) was observed to perform optimally in vitro and was analyzed further in 4175-Luc+ cells, a metastatic triple negative human breast cancer cell line expressing high levels of cPLA2. In contrast to the in vitro analysis, DDAO arachidonate was shown to activate selectively in 4175-Luc+ cells compared to the control DDAO palmitate as measured by fluorescence microscopy and quantitated with fluorescence spectroscopy. The addition of two agents known to activate cPLA2 enhanced DDAO arachidonate fluorescence without inducing any change to DDAO palmitate. Inhibition of cPLA2 resulted in reduced fluorescence of DDAO arachidonate but not DDAO palmitate. Together, we report the synthesis of a cPLA2 selective activatable fluorophore capable of detecting cPLA2 in triple negative breast cancer cells.

Magnetic resonance spectroscopy for detection of choline kinase inhibition in the treatment of brain tumors

Abnormal choline metabolism is a hallmark of cancer and is associated with oncogenesis and tumor progression. Increased choline is consistently observed in both preclinical tumor models and in human brain tumors by proton magnetic resonance spectroscopy (MRS). Thus, inhibition of choline metabolism using specific choline kinase inhibitors such as MN58b may be a promising new strategy for treatment of brain tumors. We demonstrate the efficacy of MN58b in suppressing phosphocholine production in three brain tumor cell lines. In vivo MRS studies of rats with intracranial F98-derived brain tumors showed a significant decrease in tumor total choline concentration after treatment with MN58b. High-resolution MRS of tissue extracts confirmed that this decrease was due to a significant reduction in phosphocholine. Concomitantly, a significant increase in poly-unsaturated lipid resonances was also observed in treated tumors, indicating apoptotic cell death. MRI-based volume measurements demonstrated a significant growth arrest in the MN58b-treated tumors in comparison with saline-treated controls. Histologically, MN58b-treated tumors showed decreased cell density, as well as increased apoptotic cells. These results suggest that inhibition of choline kinase can be used as an adjuvant to chemotherapy in the treatment of brain tumors and that decreases in total choline observed by MRS can be used as an effective pharmacodynamic biomarker of treatment response.

Effects of deranged metabolism on epigenetic changes in cancer

The concept of epigenetics is now providing the mechanisms by which cells transfer their new environmental-change-induced phenotypes to their daughter cells. However, how extracellular or cytoplasmic environmental cues are connected to the nuclear epigenome remains incompletely understood. Recently emerging evidence suggests that epigenetic changes are correlated with metabolic changes via chromatin remodeling. As many human complex diseases including cancer harbor both epigenetic changes and metabolic dysregulation, understanding the molecular processes linking them has huge implications for disease pathogenesis and therapeutic intervention. In this review, the impacts of metabolic changes on cancer epigenetics are discussed, along with the current knowledge on cancer metabolism and epigenetics.