Pharmacological evaluation of the role of cytochrome P450 in intracellular calcium signalling in rat pancreatic acinar cells

New frontiers in the design and discovery of therapeutics that target calcium ion signaling: a novel approach in the fight against cancer

INTRODUCTION

The Ca2+ signaling toolkit is currently under investigation as a potential target for addressing the threat of cancer. A growing body of evidence suggests that calcium signaling plays a crucial role in promoting various aspects of cancer, including cell proliferation, progression, drug resistance, and migration-related activities. Consequently, focusing on these altered Ca2+ transporting proteins has emerged as a promising area of research for cancer treatment.

AREAS COVERED

This review highlights the existing research on the role of Ca2+-transporting proteins in cancer progression. It discusses the current studies evaluating Ca2+ channel/transporter/pump blockers, inhibitors, or regulators as potential anticancer drugs. Additionally, the review addresses specific gaps in our understanding of the field that may require further investigation.

EXPERT OPINION

Targeting specific Ca2+ signaling cascades could disrupt normal cellular activities, making cancer therapy complex and elusive. Therefore, there is a need for improvements in current Ca2+ signaling pathway focused medicines. While synthetic molecules and plant compounds show promise, they also come with certain limitations. Hence, exploring the framework of targeted drug delivery, structure-rationale-based designing, and repurposing potential drugs to target Ca2+ transporting proteins could potentially lead to a significant breakthrough in cancer treatment.

Short-term toxicity study of 1-aminobenzotraizole, a CYP inhibitor, in Wistar rats

1-Aminobenzotriazole (ABT) is a pan-specific, mechanism-based inhibitor of CYP P450 enzymes, often used as co-treatment to investigate the metabolism-dependent toxicity of drugs or chemicals. To assess the confounding effects of ABT in such kind of mechanistic studies, a repeated dose toxicity study with ABT following 7 days oral administration at 0, 25, 50 and 100 mg/kg/day was performed in Wistar rats (5 rats/sex/group). Wistar rat is selected as a model being one of the well characterized rodent species, widely used for toxicity and toxicokinetics studies. The standard parameters of general toxicity study viz. clinical signs, body weight, feed consumption, clinical, gross and histopathology were evaluated. The ABT was tolerated up to the highest tested dose of 100 mg/kg/day. No clinical signs, mortality or effect on feed consumption at any dose. Slight increase in body weight gain was noted in ABT treated females. Increased reticulocyte, and decreased triglycerides, BUN, A/G ratio and plasma potassium; increased weight of liver, kidneys, adrenals and thyroid was noted in ABT treated animals. Microscopically, hypertrophic findings were noted in liver, thyroid, adrenal glands, pituitary and uterus. Some of these changes were observed at as low as 25 mg/kg/day, therefore, NOEL could not be established. Based on this study, it is concluded that ABT is tolerable up to 100 mg/kg/day with some variations in clinical pathology, organ weight and histopathology; these changes should be considered during the assessment of any mechanistic study with ABT. Findings of this manuscript were presented at 58th meeting of the Society of Toxicology, Baltimore, 11 March 2019.

1-Aminobenzotriazole: A Mechanism-Based Cytochrome P450 Inhibitor and Probe of Cytochrome P450 Biology

1-Aminobenzotriazole (1-ABT) is a pan-specific, mechanism-based inactivator of the xenobiotic metabolizing forms of cytochrome P450 in animals, plants, insects, and microorganisms. It has been widely used to investigate the biological roles of cytochrome P450 enzymes, their participation in the metabolism of both endobiotics and xenobiotics, and their contributions to the metabolism-dependent toxicity of drugs and chemicals. This review is a comprehensive evaluation of the chemistry, discovery, and use of 1-aminobenzotriazole in these contexts from its introduction in 1981 to the present.

Targeting calcium signaling in cancer therapy

The intracellular calcium ions (Ca2+) act as second messenger to regulate gene transcription, cell proliferation, migration and death. Accumulating evidences have demonstrated that intracellular Ca2+ homeostasis is altered in cancer cells and the alteration is involved in tumor initiation, angiogenesis, progression and metastasis. Targeting derailed Ca2+ signaling for cancer therapy has become an emerging research area. This review summarizes some important Ca2+ channels, transporters and Ca2+-ATPases, which have been reported to be altered in human cancer patients. It discusses the current research effort toward evaluation of the blockers, inhibitors or regulators for Ca2+ channels/transporters or Ca2+-ATPase pumps as anti-cancer drugs. This review is also aimed to stimulate interest in, and support for research into the understanding of cellular mechanisms underlying the regulation of Ca2+ signaling in different cancer cells, and to search for novel therapies to cure these malignancies by targeting Ca2+ channels or transporters.

A novel role for carbon monoxide as a potent regulator of intracellular Ca2+and nitric oxide in rat pancreatic acinar cells

Carbon monoxide (CO) is known as an essential gaseous messenger that regulates a wide array of physiological and pathological processes, similar to nitric oxide (NO) and hydrogen sulfide. The aim of the present study was to elucidate the potential role of CO in Ca2+homeostasis and to explore the underlying mechanisms in pancreatic acinar cells. The exogenous application of a CO-releasing molecule dose-dependently increased intracellular Ca2+concentration ([Ca2+]i). A heme oxygenase (HO) inducer increased [Ca2+]iin a concentration-dependent manner, and the increase was diminished by an HO inhibitor. The CO-induced [Ca2+]iincrease persisted in the absence of extracellular Ca2+, indicating that Ca2+release is the initial source for the increase. The inhibition of G protein, phospholipase C (PLC), and inositol 1,4,5-trisphosphate (IP3) receptor diminished the CO-induced [Ca2+]iincrease. CO upregulated endothelial nitric oxide synthase (eNOS) expression and stimulated NO production, and NOS inhibitor, calmodulin inhibitor, or the absence of extracellular Ca2+eliminated the latter response. Blocking the phosphatidylinositol 3-kinase (PI3K)-Akt/protein kinase B (PKB) pathway abolished CO-induced NO production. Pretreatment with an NOS inhibitor, NO scavenger, or soluble guanylate cyclase inhibitor, did not affect the CO-induced [Ca2+]iincrease, indicating that NO, soluble guanylate cyclase, and cyclic guanosine 5′-monophosphate are not involved in the CO-induced [Ca2+]iincrease. CO inhibited the secretory responses to CCK-octapeptide or carbachol. We conclude that CO acts as a regulator not only for [Ca2+]ihomeostasis via a PLC-IP3-IP3receptor cascade but also for NO production via the calmodulin and PI3K-Akt/PKB pathway, and both CO and NO interact. Moreover, CO may provide potential therapy to ameliorate acute pancreatitis by inhibiting amylase secretion.

Reappraisal of xenobiotic-induced, oxidative stress-mediated cellular injury in chronic pancreatitis: A systematic review

AIM: To reappraise the hypothesis of xenobiotic induced, cytochrome P450-mediated, micronutrient-deficient oxidative injury in chronic pancreatitis.

METHODS: Individual searches of the Medline and Embase databases were conducted for each component of the theory of oxidative-stress mediated cellular injury for the period from 1^st January 1990 to 31^st December 2012 using appropriate medical subject headings. Boolean operators were used. The individual components were drawn from a recent update on theory of oxidative stress-mediated cellular injury in chronic pancreatitis.

RESULTS: In relation to the association between exposure to volatile hydrocarbons and chronic pancreatitis the studies fail to adequately control for alcohol intake. Cytochrome P450 (CYP) induction occurs as a diffuse hepatic and extra-hepatic response to xenobiotic exposure rather than an acinar cell-specific process. GSH depletion is not consistently confirmed. There is good evidence of superoxide dismutase depletion in acute phases of injury but less to support a chronic intra-acinar depletion. Although the liver is the principal site of CYP induction there is no evidence to suggest that oxidative by-products are carried in bile and reflux into the pancreatic duct to cause injury.

CONCLUSION: Pancreatic acinar cell injury due to short-lived oxygen free radicals (generated by injury mediated by prematurely activated intra-acinar trypsin) is an important mechanism of cell damage in chronic pancreatitis. However, in contemporary paradigms of chronic pancreatitis this should be seen as one of a series of cell-injury mechanisms rather than a sole mediator.

25-Hydroxyvitamin D(3) suppresses PTH synthesis and secretion by bovine parathyroid cells

Active vitamin D compounds repress parathyroid hormone (PTH) gene transcription and block chief cell hyperplasia, making them integral tools in the treatment of secondary hyperparathyroidism in patients with chronic kidney disease. Recently, human parathyroid glands have been shown to express 25-hydroxyvitamin D 1alpha-hydroxylase (1alphaOHase), but documentation of the 1alphaOHase activity in parathyroid cells and its potential role in activating 25-hydroxyvitamin D(3) (25(OH)D(3)) to 1,25-dihydroxyvitamin D(3) (1,25(OH)2D3) have not been reported. The relative potencies of 25(OH)D(3) and 1,25(OH)(2)D(3) in reducing PTH secretion and mRNA were determined in primary cultures of bovine parathyroid cells (bPTC). The effects of blocking 1alphaOHase activity on suppression of PTH mRNA and induction of 24-hydroxylase mRNA were examined. Vitamin D receptor (VDR) affinities were estimated by intact cell competitive binding assay. Metabolism of 25(OH)D(3) by bPTC was assessed using a radioimmunoassay that measures all 1-hydroxylated metabolites of vitamin D. 25(OH)D(3) suppressed PTH secretion and mRNA (ED(50)=2 nM), but was several hundred times less potent than 1,25(OH)(2)D(3). The lower potency of 25(OH)D(3) correlated with its lower VDR affinity. bPTCs converted 25(OH)D(3) to 1-hydroxylated metabolites, but the rate of conversion was low. Inhibition of 1alphaOHase with the cytochrome P450 inhibitor clotrimazole did not block 25(OH)D(3)-mediated suppression of PTH. Clotrimazole enhanced 24-hydroxylase mRNA induction, presumably by inhibiting catabolism of 25(OH)D(3). In conclusion, 25(OH)D(3) suppresses PTH synthesis by parathyroid cells, possibly by direct activation of the VDR.

Altered arachidonic acid-mediated responses in the perfused kidney of the streptozotocin-induced diabetic rat

Using perfused kidneys isolated from age-matched controls and streptozotocin (STZ)-induced diabetic rats, we investigated the effects of arachidonic acid (AA) on perfusion pressure in the presence of methoxamine. AA elicited a transient contraction followed by a sustained relaxation in each group. The amplitude of contraction was smaller in the diabetic group than in the control group, whereas the amplitude of the sustained relaxation was greater in the former than in the latter group. In the diabetic group, the AA-induced sustained relaxation was completely inhibited by indomethacin [cyclooxygenase (COX) inhibitor], SKF525A [cytochrome P450 (CYP450) inhibitor], or clotrimazole (epoxygenase inhibitor), but not by furegrelate [thromboxane A(2) (TXA(2))-synthase inhibitor], SQ29548 (TXA(2)-receptor antagonist), or baicalein [lipoxygenase (LOX) inhibitor]. In the diabetic kidney, more-or-less additive inhibitions of the AA-induced relaxation were seen when indomethacin was given with either SKF525A or clotrimazole. These results suggest that in the STZ-induced diabetic perfused kidney, vasorelaxant metabolites derived from AA (probably COX and/or CYP450 metabolites) are increased, and may serve to regulate vascular tone.

Export of a heterologous cytochrome P450 (CYP105D1) in Escherichia coli is associated with periplasmic accumulation of uroporphyrin

This report suggests an important physiological role of a CYP in the accumulation of uroporphyrin I arising from catalytic oxidative conversion of uroporphyrinogen I to uroporphyrin I in the periplasm of Escherichia coli cultured in the presence of 5-aminolevulinic acid. A structurally competent Streptomyces griseus CYP105D1 was expressed as an engineered, exportable form in aerobically grown E. coli. Its progressive induction in the presence of 5-aminolevulinic acid-supplemented medium was accompanied by an accumulation of a greater than 100-fold higher amount of uroporphyrin I in the periplasm relative to cells lacking CYP105D1. Expression of a cytoplasm-resident engineered CYP105D1 at a comparative level to the secreted form was far less effective in promoting porphyrin accumulation in the periplasm. Expression at a 10-fold molar excess over the exported CYP105D1 of another periplasmically exported hemoprotein, the globular core of cytochrome b5, did not substitute the role of the periplasmically localized CYP105D1 in promoting porphyrin production. This, therefore, eliminated the possibility that uroporphyrin accumulation is merely a result of increased hemoprotein synthesis. Moreover, in the strain that secreted CYP105D1, uroporphyrin production was considerably reduced by azole-based P450 inhibitors. Production of both holo-CYP105D1 and uroporphyrin was dependent upon 5-aminolevulinic acid, except that at higher concentrations this resulted in a decrease in uroporphyrin. This study suggests that the exported CYP105D1 oxidatively catalyzes periplasmic conversion of uroporphyrinogen I to uroporphyrin I in E. coli. The findings have significant implications in the ontogenesis of human uroporphyria-related diseases.

Calcium influx factor from cytochrome P-450 metabolism and secretion-like coupling mechanisms for capacitative calcium entry in corneal endothelial cells

Notwithstanding extensive efforts, the mechanism of capacitative calcium entry (CCE) remains unclear. Two seemingly opposed theories have been proposed: secretion-like coupling (Patterson, R. L., van Rossum, D. B., and Gill, D. L. (1999) Cell 98, 487-499) and the calcium influx factor (CIF) (Randriamampita, C., and Tsien, R. Y. (1993) Nature 364, 809-814). In the current study, a combinatorial approach was taken to investigate the mechanism of CCE in corneal endothelial cells. Induction of cytochrome P-450s by beta-naphthoflavone (BN) enhanced CCE measured by Sr(2+) entry after store depletion. 5,6-Epoxyeicosatrienoic acid (5,6-EET), a proposed CIF generated by cytochrome P-450s (Rzigalinski, B. A., Willoughby, K. A., Hoffman, S. W., Falck, J. R., and Ellis, E. F. (1999) J. Biol. Chem. 274, 175-182), induced Ca(2+) entry. Both BN-enhanced CCE and the 5,6-EET-induced Ca(2+) entry were inhibited by the CCE blocker 2-aminoethoxydiphenyl borate, indicating a role for cytochrome P-450s in CCE. Treatment with calyculin A (CalyA), which causes condensation of cortical cytoskeleton, inhibited CCE. The actin polymerization inhibitor cytochalasin D partially reversed the inhibition of CCE by CalyA, suggesting a secretion-like coupling mechanism for CCE. However, CalyA could not inhibit CCE in BN-treated cells, and 5,6-EET caused a partial activation of CCE in CalyA-treated cells. These results further support the notion that cytochrome P-450 metabolites may be CIFs. The vesicular transport inhibitor brefeldin A inhibited CCE in both vehicle- and BN-treated cells. Surprisingly, Sr(2+) entry in the absence of store depletion was enhanced in BN-treated cells, which was also inhibited by 2-aminoethoxydiphenyl borate. An integrative model suggests that both CIF from cytochrome P-450 metabolism and secretion-like coupling mechanisms play roles in CCE in corneal endothelial cells.

Recent developments in non-excitable cell calcium entry

Influx of calcium into cells following stimulation of cell surface receptors is a key process controlling cellular activity. However, despite intensive research, there is still no consensus on precisely how calcium entry is controlled in electrically no n-excitable cells. In particular, the regulation of depletion-activated or 'capacitative' calcium entry continues to be a focus of debate. Work published in the last 2 years has lent new impetus to the so-called 'conformational coupling' theory, although evidence for the existence of soluble messengers between the ER and the plasma membrane also continues to appear. In addition, there remains disagreement on whether intra-store [Ca(2+)] has to fall below a threshold before Ca(2+)entry is activated. A further major question is the identity of the putative depletion-operated Ca(2+)channel or channels. Here discussion has largely focussed on whether homologue(s) of the Drosophila TRP ('Transient Receptor Potential') protein is/are the elusive channel, or at least a part of it. Finally, it remains possible that Ca(2+)entry mechanisms other than depletion-activated channels may be important in agonist-evoked Ca(2+)influx. This commentary summarizes recent developments in the field, and highlights both current debates and critical unsolved questions.