A role for caspase-2 in sphingosine kinase 1 proteolysis in response to doxorubicin in breast cancer cells - implications for the CHK1-suppressed pathway

Molecular dynamics investigation on synthesis of a pH- and temperature-sensitive carbon nanotube loaded with doxorubicin

The many exotic properties of carbon nanotubes (CNTs) make them a powerful attraction in the field of drug delivery systems (DDS). In this work, based on quantum chemical calculation and molecular simulation techniques, polyacrylic acid (PAA) and N-isopropyl acrylamide (NIP) are selected and acted simultaneously on the CNT to form a stable system (FCNT). As a potential DDS, FCNT captures the dispersed doxorubicin (DOX) molecules around it and maintains a stable configuration. In these processes, electrostatic and van der Waals forces act synergistically, with van der Waals forces dominating. Compared to NIP, PAA molecules exhibit stronger adhesion and encapsulation efficiency to CNT and stronger adsorption capacity to DOX. This study reveals the mechanism of action among PAA, NIP, CNT, and DOX, providing feasibility verification and prospective guidance for the experimental synthesis of PAA-NIP-CNT-type multifunctional DDS, and also broadening the idea for exploring more efficient DDS suitable for DOX.

Targeting sphingosine kinase 1 in p53KO thymic lymphoma

Sphingosine kinase 1 (SK1) is a key sphingolipid enzyme that is upregulated in several types of cancer, including lymphoma which is a heterogenous group of malignancies. Treatment for lymphoma has improved significantly by the introduction of new therapies; however, subtypes with tumor protein P53 (p53) mutations or deletion have poor prognosis, making it critical to explore new therapeutic strategies in this context. SK1 has been proposed as a therapeutic target in different types of cancer; however, the effect of targeting SK1 in cancers with p53 deletion has not been evaluated yet. Previous work from our group suggests that loss of SK1 is a key event in mediating the tumor suppressive effect of p53. Employing both genetic and pharmacological approaches to inhibit SK1 function in Trp53KO mice, we show that targeting SK1 decreases tumor growth of established p53KO thymic lymphoma. Inducible deletion of Sphk1 or its pharmacological inhibition drive increased cell death in tumors which is accompanied by selective accumulation of sphingosine levels. These results demonstrate the relevance of SK1 in the growth and maintenance of lymphoma in the absence of p53 function, positioning this enzyme as a potential therapeutic target for the treatment of tumors that lack functional p53.

Upregulation of sphingosine kinase 1 in response to doxorubicin generates an angiogenic response via stabilization of Snail

Sphingosine kinase 1 (SK1) converts the pro-death lipid sphingosine to the pro-survival sphingosine-1-phosphate (S1P) and is upregulated in several cancers. DNA damaging agents, such as the chemotherapeutic doxorubicin (Dox), have been shown to degrade SK1 protein in cancer cells, a process dependent on wild-type p53. As mutations in p53 are very common across several types of cancer, we evaluated the effects of Dox on SK1 in p53 mutant cancer cells. In the p53 mutant breast cancer cell line MDA-MB-231, we show that Dox treatment significantly increases SK1 protein and S1P. Using MDA-MB-231 cells with CRISPR-mediated knockout of SK1 or the selective SK1 inhibitor PF-543, we implicated SK1 in both Dox-induced migration and in a newly uncovered proangiogenic program induced by Dox. Mechanistically, inhibition of SK1 suppressed the induction of the cytokine BMP4 and of the EMT transcription factor Snail in response to Dox. Interestingly, induction of BMP4 by SK1 increased Snail levels following Dox treatment by stabilizing Snail protein. Furthermore, we found that SK1 was required for Dox-induced p38 MAP kinase phosphorylation and that active p38 MAPK in turn upregulated BMP4 and Snail, positioning p38 downstream of SK1 and upstream of BMP4/Snail. Modulating production of S1P by inhibition of de novo sphingolipid synthesis or knockdown of the S1P-degrading enzyme S1P lyase identified S1P as the sphingolipid activator of p38 in this model. This work establishes a novel angiogenic pathway in response to a commonly utilized chemotherapeutic and highlights the potential of SK1 as a secondary drug target for patients with p53 mutant cancer.

Cytotoxic mechanisms of doxorubicin at clinically relevant concentrations in breast cancer cells

Doxorubicin (DOX) is a chemotherapeutic agent frequently used for the treatment of a variety of tumor types, such as breast cancer. Despite the long history of DOX, the mechanistic details of its cytotoxic action remain controversial. Rather than one key mechanism of cytotoxic action, DOX is characterized by multiple mechanisms, such as (1) DNA intercalation and adduct formation, (2) topoisomerase II (TopII) poisoning, (3) the generation of free radicals and oxidative stress, and (4) membrane damage through altered sphingolipid metabolism. Many past reviews of DOX cytotoxicity are based on supraclinical concentrations, and several have addressed the concentration dependence of these mechanisms. In addition, most reviews lack a focus on the time dependence of these processes. We aim to update the concentration and time-dependent trends of DOX mechanisms at representative clinical concentrations. Furthermore, attention is placed on DOX behavior in breast cancer cells due to the frequent use of DOX to treat this disease. This review provides insight into the mechanistic pathway(s) of DOX at levels found within patients and establishes the magnitude of effect for each mechanism.

Sphingosine kinase 1 downregulation is required for adaptation to serine deprivation

It has been well-established that cancer cells often display altered metabolic profiles, and recent work has concentrated on how cancer cells adapt to serine removal. Serine can be either taken exogenously or synthesized from glucose, and its regulation forms an important mechanism for nutrient integration. One of the several important metabolic roles for serine is in the generation of bioactive sphingolipids since it is the main substrate for serine palmitoyltransferase, the initial and rate-limiting enzyme in the synthesis of sphingolipids. Previously, serine deprivation has been connected to the action of the tumor suppressor p53, and we have previously published on a role for p53 regulating sphingosine kinase 1 (SK1), an enzyme that phosphorylates sphingosine to form sphingosine-1-phosphate (S1P). SK1 is a key enzyme in sphingolipid synthesis that functions in pro-survival and tumor-promoting pathways and whose expression is also often elevated in cancers. Here we show that SK1 was degraded during serine starvation in a time and dose-dependent manner, which led to sphingosine accumulation. This was independent of effects on p53 but required the action of the proteasome. Furthermore, we show that overexpression of SK1, to compensate for SK1 loss, was detrimental to cell growth under conditions of serine starvation, demonstrating that the suppression of SK1 under these conditions is adaptive. Mitochondrial oxygen consumption decreased in response to SK1 degradation, and this was accompanied by an increase in intracellular reactive oxygen species (ROS). Suppression of ROS with N-acteylcysteine resulted in suppression of the metabolic adaptations and in decreased cell growth under serine deprivation. The effects of SK1 suppression on ROS were mimicked by D-erythro-sphingosine, whereas S1P was ineffective, suggesting that the effects of loss of SK1 were due to the accumulation of its substrate sphingosine. This study reveals a new mechanism for regulating SK1 levels and a link of SK1 to serine starvation as well as mitochondrial function.

The Tumorigenic Effect of Sphingosine Kinase 1 and Its Potential Therapeutic Target

Sphingosine kinase 1 (SPHK1) regulates cell proliferation and survival by converting sphingosine to the signaling mediator sphingosine 1-phosphate (S1P). SPHK1 is widely overexpressed in most cancers, promoting tumor progression and is associated with clinical prognosis. Numerous studies have explored SPHK1 as a promising target for cancer therapy. However, due to insufficient knowledge of SPHK1 oncogenic mechanisms, its inhibitors’ therapeutic potential in preventing and treating cancer still needs further investigation. In this review, we summarized the metabolic balance regulated by the SPHK1/S1P signaling pathway and highlighted the oncogenic mechanisms of SPHK1 via the upregulation of autophagy, proliferation, and survival, migration, angiogenesis and inflammation, and inhibition of apoptosis. Drug candidates targeting SPHK1 were also discussed at the end. This review provides new insights into the oncogenic effect of SPHK1 and sheds light on the future direction for targeting SPHK1 as cancer therapy.

Bioactive sphingolipids: Advancements and contributions from the laboratory of Dr. Lina M. Obeid

Sphingolipids and their synthetic enzymes have emerged as critical mediators in numerous diseases including inflammation, aging, and cancer. One enzyme in particular, sphingosine kinase (SK) and its product sphingosine-1-phosphate (S1P), has been extensively implicated in these processes. SK catalyzes the phosphorylation of sphingosine to S1P and exists as two isoforms, SK1 and SK2. In this review, we will discuss the contributions from the laboratory of Dr. Lina M. Obeid that have defined the roles for several bioactive sphingolipids in signaling and disease with an emphasis on her work defining SK1 in cellular fates and pathobiologies including proliferation, senescence, apoptosis, and inflammation.

Dysregulation of lysophospholipid signaling by p53 in malignant cells and the tumor microenvironment

The TP53 gene has been widely studied for its roles in cell cycle control, maintaining genome stability, activating repair mechanisms upon DNA damage, and initiating apoptosis should repair mechanisms fail. Thus, it is not surprising that mutations of p53 are the most common genetic alterations found in human cancer. Emerging evidence indicates that dysregulation of lipid metabolism by p53 can have a profound impact not only on cancer cells but also cells of the tumor microenvironment (TME). In particular, intermediates of the sphingolipid and lysophospholipid pathways regulate many cellular responses common to p53 such as cell survival, migration, DNA damage repair and apoptosis. The majority of these cellular events become dysregulated in cancer as well as cell senescence. In this review, we will provide an account on the seminal contributions of Prof. Lina Obeid, who deciphered the crosstalk between p53 and the sphingolipid pathway particularly in modulating DNA damage repair and apoptosis in non-transformed as well as transformed cells. We will also provide insights on the integrative role of p53 with the lysophosphatidic acid (LPA) signaling pathway in cancer progression and TME regulation.

Molecular engineering of the last-generation CNTs in smart cancer therapy by grafting PEG-PLGA-riboflavin

In this work, the effect of environment and additives on the self-assembly and delivery of doxorubicin (DOX) have been studied. A microfluidic system with better control over molecular interactions and high surface to volume ratio has superior performance in comparison to the bulk system. Moreover, carbon nanotube (CNT) and CNT-doped structures have a high surface area to incorporate the DOX molecules into a polymer and the presence of functional groups can influence the polymer-drug interactions. In this work, the interactions of DOX with both the polymeric complex and the nanotube structure have been investigated. For quantification of the interactions, H-bonding, gyration radius, root-mean-square deviation (RMSD), Gibbs free energy, radial distribution function (RDF), energy, and Solvent Accessible Surface Area (SASA) analyses have been performed. The most stable micelle-DOX interaction is attributed to the presence of BCN in the microfluidic system according to the gyration radius and RMSD. Meanwhile, for DOX-doped CNT interaction the phosphorus-doped CNT in the microfluidic system is more stable. The highest electrostatic interaction can be seen between polymeric micelles and DOX in the presence of BCN. For nanotube-drug interaction, phosphorus-doped carbon nanotubes in the microfluidic system have the largest electrostatic interaction with the DOX. RDF results show that in the microfluidic system, nanotube-DOX affinity is larger than that of nanotube-micelle.

pH-sensitive loading/releasing of doxorubicin using single-walled carbon nanotube and multi-walled carbon nanotube: A molecular dynamics study

BACKGROUND AND OBJECTIVE

Doxorubicin is one of the drugs used to treat cancer, and many studies have been conducted to control its release. In this study, carbon nanotubes have been proposed as a doxorubicin carrier, and the effect of carboxyl functional group on the controlled release of doxorubicin has been studied.

METHODS

This study has been done by molecular dynamics simulation and was based on changing the pH as a mechanism controller.

RESULTS

This work is intended to test the efficacy of this drug carrier for the release of doxorubicin. A comparison was also made between single-walled and double-walled carbon nanotubes to answer the question of which one can be a better carrier for doxorubicin. The study of DOXORUBICIN adsorption and release showed that the DOXORUBICIN adsorption on single-walled carbon nanotube and multi-walled carbon nanotube in neutral pH was stronger than it was in acidic pH, which could be due to the electrostatic interactions between the carboxyl group of nanotubes and DOXORUBICIN. Based on this and according to the investigation of hydrogen bonds, diffusion coefficients, and other results it was clear that the drug release in acidic pH was appropriate for body conditions. Since cancer tissues pH is acidic, this shows the suitability of carbon nanotube in drug delivery and DOXORUBICIN release in cancer tissues. In addition, it was shown that the blood pH (pH = 7) is suitable for DOXORUBICIN loading on the carbon nanotube and carbon nanotube-DOXORUBICIN linkage remained stable at this pH; accordingly, the carbon nanotube could deliver DOXORUBICIN in blood quite well and release it in cancerous tissues. This suggests the carbon nanotubes as a promising drug carrier in the cancer therapy which can be also investigated in experiments.

CONCLUSION

It was revealed that the bonds between multi-walled carbon nanotube and DOXORUBICIN was stronger and this complex had a slower release in the cancer tissues compared to the single-walled carbon nanotube; this can be regarded as an advantage over the single-walled carbon nanotube in the DOXORUBICIN delivery and release.

Targeting PI3K/Akt/mTOR signaling pathway by polyphenols: Implication for cancer therapy

Cancer is one of the biggest challenges facing medicine and its cure is regarded to be the Holy Grail of medicine. Therapy in cancer is consisted as various artificial cytotoxic agents and radiotherapy, and recently immunotherapy. Recently much attention has been directed to the use of natural occurring agents in cancer therapy. One of the main group of agents utilized in this regard is polyphenols which are found abundantly in berries, fruits and vegetables. Polyphenols show to exert direct and indirect effects in progression of cancer, angiogenesis, proliferation and enhancing resistance to treatment. One of the cellular pathways commonly affected by polyphenols is PI3K/Akt/mTOR pathway, which has far ranging effects on multiple key aspects of cellular growth, metabolism and death. In this review article, evidence regarding the biology of polyphenols in cancer via PI3K/Akt/mTOR pathway is discussed and their application on cancer pathophysiology in various types of human malignancies is shown.

Molecular dynamics simulation of Doxorubicin loading with N-isopropyl acrylamide carbon nanotube in a drug delivery system

BACKGROUND AND OBJECTIVE

Doxorubicin is one of the common drugs used for cancer therapy. Molecular dynamics were applied to investigate the loading of Doxorubicin with thermosensitive N-isopropyl acrylamide Carbon nanotube carrier.

METHODS

The results showed that the smaller polymer chain length has more decrease of gyration radius. A decrease of gyration radius resulted in more concentrated aggregation with stronger bonds. Therefore, the shorter the polymer chain lengths, the more stable polymer interaction and better Doxorubicin delivery. Smaller polymers also form more hydrogen bonds with the drug leading to stronger and more stable carriers.

RESULTS

A lower amount of wall shear stress was found near the inner wall of the artery, distal to the plaque region (stenosis), and in both percentages of stenosis the maximum wall shear stress will accrue in the middle of the stenosis; however it is much more in the higher rate of stenosis.

CONCLUSIONS

The results indicated that N-isopropyl acrylamide - Carbon nanotube is suitable for the delivery of Doxorubicin, and five mer N-isopropyl acrylamide is the optimum carrier for Doxorubicin loading.

The regulation of p53, p38 MAPK, JNK and XBP-1s by sphingosine kinases in human embryonic kidney cells

Since inhibitors of sphingosine kinases (SK1, SK2) have been shown to induce p53-mediated cell death, we have further investigated their role in regulating p53, stress activated protein kinases and XBP-1s in HEK293T cells. Treatment of these cells with the sphingosine kinase inhibitor, SKi, which fails to induce apoptosis, promoted the conversion of p53 into two proteins with molecular masses of 63 and 90 kDa, and which was enhanced by over-expression of ubiquitin. The SKi induced conversion of p53 to p63/p90 was also enhanced by siRNA knockdown of SK1, but not SK2 or dihydroceramide desaturase (Degs1), suggesting that SK1 is a negative regulator of this process. In contrast, another sphingosine kinase inhibitor, ABC294640 only very weakly stimulated formation of p63/p90 and induced apoptosis of HEK293T cells. We have previously shown that SKi promotes the polyubiquitination of Degs1, and these forms positively regulate p38 MAPK/JNK pathways to promote HEK293T cell survival/growth. siRNA knockdown of SK1 enhanced the activation of p38 MAPK/JNK pathways in response to SKi, suggesting that SK1 functions to oppose these pro-survival pathways in HEK293T cells. SKi also enhanced the stimulatory effect of the proteasome inhibitor, MG132 on the expression of the pro-survival protein XBP-1s and this was reduced by siRNA knockdown of SK2 and increased by knockdown of p53. These findings suggest that SK1 and SK2 have opposing roles in regulating p53-dependent function in HEK293T cells.

Kelch-like protein 5-mediated ubiquitination of lysine 183 promotes proteasomal degradation of sphingosine kinase 1

Sphingosine kinase 1 (SK1) is a signalling enzyme that catalyses the phosphorylation of sphingosine to generate the bioactive lipid sphingosine 1-phosphate (S1P). A number of SK1 inhibitors and chemotherapeutics can induce the degradation of SK1, with the loss of this pro-survival enzyme shown to significantly contribute to the anti-cancer properties of these agents. Here we define the mechanistic basis for this degradation of SK1 in response to SK1 inhibitors, chemotherapeutics, and in natural protein turnover. Using an inducible SK1 expression system that enables the degradation of pre-formed SK1 to be assessed independent of transcriptional or translational effects, we found that SK1 was degraded primarily by the proteasome since several proteasome inhibitors blocked SK1 degradation, while lysosome, cathepsin B or pan caspase inhibitors had no effect. Importantly, we demonstrate that this proteasomal degradation of SK1 was enabled by its ubiquitination at Lys183 that appears facilitated by SK1 inhibitor-induced conformational changes in the structure of SK1 around this residue. Furthermore, using yeast two-hybrid screening, we identified Kelch-like protein 5 (KLHL5) as an important protein adaptor linking SK1 to the cullin 3 (Cul3) ubiquitin ligase complex. Notably, knockdown of KLHL5 or Cul3, use of a cullin inhibitor or a dominant-negative Cul3 all attenuated SK1 degradation. Collectively this data demonstrates the KLHL5/Cul3-based E3 ubiquitin ligase complex is important for regulation of SK1 protein stability via Lys183 ubiquitination, in response to SK1 inhibitors, chemotherapy and for normal SK1 protein turnover.

Nuclear Lipid Microdomains Regulate Daunorubicin Resistance in Hepatoma Cells

Daunorubicin is an anticancer drug, and cholesterol is involved in cancer progression, but their relationship has not been defined. In this study, we developed a novel experimental model that utilizes daunorubicin, cholesterol, and daunorubicin plus cholesterol in the same cells (H35) to search for the role of nuclear lipid microdomains, rich in cholesterol and sphingomyelin, in drug resistance. We find that the daunorubicin induces perturbation of nuclear lipid microdomains, localized in the inner nuclear membrane, where active chromatin is anchored. As changes of sphingomyelin species in nuclear lipid microdomains depend on neutral sphingomyelinase activity, we extended our studies to investigate whether the enzyme is modulated by daunorubicin. Indeed the drug stimulated the sphingomyelinase activity that induced reduction of saturated long chain fatty acid sphingomyelin species in nuclear lipid microdomains. Incubation of untreated-drug cells with high levels of cholesterol resulted in the inhibition of sphingomyelinase activity with increased saturated fatty acid sphingomyelin species. In daunodubicin-treated cells, incubation with cholesterol reversed the action of the drug by acting via neutral sphingomyelinase. In conclusion, we suggest that cholesterol and sphingomyelin-forming nuclear lipid microdomains are involved in the drug resistance.

Ceramide Signaling and p53 Pathways

Ceramides, important players in signal transduction, interact with multiple cellular pathways, including p53 pathways. However, the relationship between ceramide and p53 is very complex, and mechanisms underlying their coregulation are diverse and not fully characterized. The role of p53, an important cellular regulator and a transcription factor, is linked to its tumor suppressor function. Ceramides are involved in the regulation of fundamental processes in cancer cells including cell death, proliferation, autophagy, and drug resistance. This regulation, however, can be pro-death or pro-survival depending on cancer type, the balance between ceramide species, the rate of their synthesis and utilization, and the availability of a specific array of downstream targets. This chapter highlights the central role of ceramide in sphingolipid metabolism, its role in cancer, specific effectors in ceramide pathways controlled by p53, and coregulation of ceramide and p53 signaling. We discuss the recent studies, which underscore the function of p53 in the regulation of ceramide pathways and the reciprocal regulation of p53 by ceramide. This complex relationship is based on several molecular mechanisms including the p53-dependent transcriptional regulation of enzymes in sphingolipid pathways, the activation of mutant p53 through ceramide-mediated alternative splicing, as well as modulation of the p53 function through direct and indirect effects on p53 coregulators and downstream targets. Further insight into the connections between ceramide and p53 will allow simultaneous targeting of the two pathways with a potential to yield more efficient anticancer therapeutics.