Autophagy inhibition switches low-dose camptothecin-induced premature senescence to apoptosis in human colorectal cancer cells.

Recently, several studies indicated that senescent tumor cells are resistant to apoptosis in chemotherapy. They may return to cell cycle, thus act as stumbling blocks in anticancer treatments. In the present study, we found that, in human colorectal cancer cells, low-dose camptothecin (CPT) simultaneously induced autophagy and premature senescence through AMPK-TSC2-mTOR pathway and ATM-Chk2-p53-p21 pathway respectively. What's important is the suppression of autophagy substantially increased apoptosis and greatly attenuated senescence possibly by blocking p53/p21 pathway, which suggests that autophagy plays an indispensable role in sustaining cell senescence caused by low-dose CPT. The combination of low-dose CPT and autophagy inhibitor, a way to lead senescent cells to die, would be potentially valuable in cancer therapy.

Bortezomib induces protective autophagy through AMP-activated protein kinase activation in cultured pancreatic and colorectal cancer cells.

BACKGROUND: Bortezomib, a selective and potent inhibitor of the proteasome, has demonstrated broad anti-tumor activities in many malignancies. In the current study, we aimed to understand the potential resistance factor of bortezomib in cultured pancreatic and colorectal cancer cells. RESULTS: We observed that bortezomib-induced protective autophagy in cultured PANC-1 pancreatic cancer cells and HT-29 colorectal cancer cells. Inhibition of autophagy by 3-methyladenine (3-MA) and chloroquine enhanced bortezomib-induced apoptosis and cytotoxicity in both PANC-1 and HT-29 cells. Activation of AMP-activated protein kinase (AMPK) was required for bortezomib-induced autophagy induction in PANC-1 and HT-29 cells, and AMPK inhibition by its inhibitor compound C (CC) or RNAi-depletion suppressed bortezomib-induced autophagy, while dramatically enhancing cancer cell apoptosis/cytotoxicity. Meanwhile, significant AMPK activation and autophagy induction were observed after bortezomib stimulation in primary cultured pancreatic cancer cells derived from a patient's tumor tissue. Both CC and 3-MA facilitated bortezomib-induced cytotoxicity in primary cultured pancreatic cancer cells. CONCLUSIONS: In conclusion, our data here suggest that bortezomib induces protective autophagy in pancreatic and colorectal cancer cells through activating AMPK-Ulk1 signalings. AMPK or autophagy inhibitors could be developed as an adjunct or chemo-sensitizer for bortezomib.

Alpha-lipoic acid protects against cisplatin-induced ototoxicity via the regulation of MAPKs and proinflammatory cytokines.

Cisplatin is an effective antineoplastic drug that is widely used to treat various cancers; however, it causes side effects such as ototoxicity via the induction of apoptosis of hair cells in the cochlea. Alpha-lipoic acid (ALA) has been reported to exert a protective effect against both antibiotic-induced and cisplatin-induced hearing loss. Therefore, this study was conducted to (1) elucidate the mechanism of the protective effects of ALA against cisplatin-induced ototoxicity using in vitro and ex vivo culture systems of HEI-OC1 auditory cells and rat cochlear explants and (2) to gain additional insight into the apoptotic mechanism of cisplatin-induced ototoxicity. ALA pretreatment significantly reduced apoptotic cell death of the inner and outer hair cells in cisplatin-treated organ of Corti explants and attenuated ototoxicity via marked inhibition of the increase in the expression of IL-1ß and IL-6, the phosphorylation of ERK and p38, the degradation of IκBα, the increase in intracellular levels of ROS, and the activation of caspase-3 in cisplatin-treated HEI-OC1 cells. This study represents the first histological evaluation of the organ of Corti following treatment with ALA, and these results indicate that the protective effects of ALA against cisplatin-induced ototoxicity are mediated via the regulation of MAPKs and proinflammatory cytokines.

Anti-neoplastic activity of low-dose endothelial-monocyte activating polypeptide-II results from defective autophagy and G2/M arrest mediated by PI3K/Akt/FoxO1 axis in human glioblastoma stem cells.

Glioblastoma multiforme (GBM) is a life-threatening brain tumor with fatal recurrence, for which glioblastoma stem cells (GSCs) are held responsible. Though endothelial-monocyte activating polypeptide-II (EMAP-II) has been confirmed as a possible antitumor agent that can induce apoptosis of endothelial cells and inhibit tumor angiogenesis, the direct cytotoxicity by EMAP-II on tumor cells and its underlying mechanism are largely unknown. In the present study, it was demonstrated that low-dose (0.05 nM) EMAP-II reduces cell viability and mitochondrial membrane potential in vitro. Likewise, EMAP-II suppressed tumor growth in GSC-xenografted mice. Though no apoptosis was detected, all these antitumor effects were attenuated when GSCs were pretreated with 3-methyladenine (3-MA). Analysis of EMAP-II-treated GSCs exhibited the morphological and biochemical changes typical of autophagy, which was further shown to be defective. Moreover, EMAP-II was found to suppress tumor growth by inducing G2/M arrest in GSCs. Our data further showed that EMAP-II inhibited PI3K/Akt activation with concomitant induction of FoxO1 activation. FoxO1 knockdown significantly attenuated the induction of autophagy and G2/M arrest. Excessive accumulation of lipid droplets was intriguingly detected by transmission electron microscope, which was accompanied by autophagosomes. Further investigation indicated that the transcriptional regulation of Atg2B by FoxO1 was responsible for the induction of autophagy and formation of lipid droplets. These results suggest that EMAP-II is an effective anticancer agent for glioblastoma therapy, which can induce direct growth suppression in GSCs through defective autophagy and G2/M arrest mediated by the PI3K/Akt/FoxO1 axis.

Assessing cisplatin-induced ototoxicity and otoprotection in whole organ culture of the mouse inner ear in simulated microgravity.

Cisplatin is a widely used anti-cancer drug. Ototoxicity is a major dose-limiting side-effect. A reproducible mammalian in-vitro model of cisplatin ototoxicity is required to screen and validate otoprotective drug candidates. We utilized a whole organ culture system of the postnatal mouse inner ear in a rotating wall vessel bioreactor under "simulated microgravity" culture conditions. As previously described this system allows whole organ culture of the inner ear and quantitative assessment of ototoxic effects of aminoglycoside induced hair cell loss. Here we demonstrate that this model is also applicable to the assessment of cisplatin induced ototoxicity. In this model cisplatin induced hair cell loss was dose and time dependent. Increasing exposure time of cisplatin led to decreasing EC50 concentrations. Outer hair cells were more susceptible than inner hair cells, and hair cells in the cochlear base were more susceptible than hair cells in the cochlear apex. Initial cisplatin dose determined the final extent of hair cell loss irrespective if the drug was withdrawn or continued. Dose dependant otoprotection was demonstrated by co-administration of the antioxidant agent N-acetyl l-cysteine. The results support the use of this inner ear organ culture system as an in vitro assay and validation platform for inner ear toxicology and the search for otoprotective compounds.

Topical amphotericin B in combination with standard therapy for severe necrotizing skin and soft-tissue mucormycosis in an infant with bilineal leukemia: case report and review.

During chemotherapy for bilineal leukemia, a 6-month-old infant presented with a necrotizing skin and soft-tissue infection of the chest wall due to Rhizopus sp. Successful outcome was achieved by systemically administered liposomal amphotericin B and local wound control with the novel administration of topical deoxycholate amphotericin B and surgical resection.

Structural determinants of the catalytic inhibition of human topoisomerase IIα by salicylate analogs and salicylate-based drugs.

We previously identified salicylate as a novel catalytic inhibitor of human DNA topoisomerase II (topo II; EC 5.99.1.3) that preferentially targets the alpha isoform by interfering with topo II-mediated DNA cleavage. Many pharmaceuticals and compounds found in foods are salicylate-based. We have now investigated whether these are also catalytic inhibitors of topo II and the structural determinants modulating these effects. We have determined that a number of hydroxylated benzoic acids attenuate doxorubicin-induced DNA damage signaling mediated by the ATM protein kinase and inhibit topo II decatenation activity in vitro with varying potencies. Based on the chemical structures of these and other derivatives, we identified unique properties influencing topo II inhibition, including the importance of substitutions at the 2'- and 5'-positions. We extended our findings to a number of salicylate-based pharmaceuticals including sulfasalazine and diflunisal and found that both were effective at attenuating doxorubicin-induced DNA damage signaling, topo II DNA decatenation and they blocked stabilization of doxorubicin-induced topo II cleavable complexes in cells. In a manner similar to salicylate, we determined that these agents inhibit topo II-mediated DNA cleavage. This was accompanied by a concomitant decrease in topo II-mediated ATP-hydrolysis. Taken together, these findings reveal a novel function for the broader class of salicylate-related compounds and highlight the need for additional studies into whether they may impact the efficacy of chemotherapy regimens that include topo II poisons.

Gabapentin inhibits bortezomib-induced mechanical allodynia through supraspinal action in mice.

Bortezomib, an inhibitor of proteasome holoenzyme, is used to treat relapsed and refractory multiple myeloma. Peripheral neuropathy is a treatment-limiting adverse effect of bortezomib and is very difficult to control. In this study, we examined the efficacy of gabapentin in inhibiting bortezomib-induced peripheral neuropathy. Single intravenous injections of bortezomib (0.03 - 0.3 mg/kg) dose-dependently induced mechanical allodynia with a peak effect 12 days after injection. Bortezomib (0.3 mg/kg) also caused mechanical hyperalgesia, but neither affected thermal nociception nor induced cold allodynia. Bortezomib increased the response of the saphenous nerve to weak punctate stimulation but not response to cool stimulation of the skin. When administered 12 days after bortezomib injection, oral and intracisternal gabapentin markedly inhibited mechanical allodynia. Intrathecal, but not intraplantar, gabapentin had a tendency to reduce mechanical allodynia. The antiallodynic activity of orally administered gabapentin was suppressed by noradrenaline, but not serotonin, depletion in the spinal cord. Bortezomib did not affect the expression levels of the calcium channel α2δ-1 subunit, a high-affinity binding site of gabapentin, in the plantar skin, spinal cord, medulla oblongata, and pons. These results suggest that gabapentin inhibits bortezomib-induced mechanical allodynia, most likely through the activation of the descending noradrenergic system.

The reduction of anti-cancer drug antagonism by the spatial protection of drugs with PLA-TPGS nanoparticles.

Docetaxel (DCL) and tamoxifen (TAM) individually are potent drugs in the fight against breast cancer. However when used in combination, they become antagonistic because of differential metabolism of both drugs. We reasoned that by spatially protecting them from metabolizing enzymes with poly (lactide)-D-α-tocopheryl polyethylene glycol succinate (PLA-TPGS) nanoparticles (NPs), we might reduce this drug antagonism. We now report that the drug antagonism between DCL and TAM in MCF7 cell line, was significantly reduced when co-delivered in PLA-TPGS NPs. In addition, this effect of NPs attenuated at high drug concentrations. To investigate the role of NPs in the reduction of drug antagonism, we quantified cellular uptake of the fluorescent model drug coumarin 6 (C6) encapsulated in a rigorous permutation of drugs-nanoparticles ratios. NPs carrying C6 exhibited enhanced cellular uptake over their free C6 counterparts at correspondingly low drug concentrations. This led us to conclude that the reduction of drug antagonism by NPs is correlated to cellular uptake and being in NPs therefore protects both drugs until they are released intracellular for therapeutic anti-cancer effect.

An investigation of the effect of thiamine pyrophosphate on cisplatin-induced oxidative stress and DNA damage in rat brain tissue compared with thiamine: thiamine and thiamine pyrophosphate effects on cisplatin neurotoxicity.

This study investigated the effects of thiamine pyrophosphate (TPP) at dosages of 10 and 20 mg/kg on oxidative stress induced in rat brain tissue with cisplatin and compared this with thiamine. Cisplatin neurotoxicity represents one of the main restrictions on the drug being given in effective doses. Oxidative stress is considered responsible for cisplatin toxicity. Our results showed that cisplatin increased the levels of oxidant parameters such as lipid peroxidation (thio barbituric acid reactive substance (TBARS)) and myeloperoxidase (MPO) in brain tissue and suppressed the effects of antioxidants such as total glutathione (GSH) and superoxide dismutase (SOD). TPP, especially at a dosage of 20 mg/kg, significantly reduced TBARS and MPO levels that increase with cisplatin administration compared with the thiamine group, while TPP significantly increases GSH and SOD levels. In addition, the level of 8-Gua (guanine), a product of DNA damage, was 1.7 ± 0.12 8-hydroxyl guanine (8-OH Gua)/105 Gua in brain tissue in the control group receiving cisplatin, compared with 0.97 ± 0.03 8-OH Gua/105 Gua in the thiamine pyrophosphate (20 mg/kg) group and 1.55 ± 0.11 8-OH Gua/105 Gua in the thiamine (20 mg/kg) group. These results show that thiamine pyrophosphate significantly prevents oxidative damage induced by cisplatin in brain tissue, while the protective effect of thiamine is insignificant.

The eukaryotic initiation factor 2 kinase GCN2 protects against hepatotoxicity during asparaginase treatment.

Asparaginase is an important drug in the treatment regimen for acute lymphoblastic leukemia. Asparaginase depletes circulating asparagine and glutamine, activating an amino acid stress response (AAR) involving phosphorylation of eukaryotic initiation factor 2 (eIF2) by general control nonderepressible kinase 2 (GCN2). We hypothesized that GCN2 functions to mitigate hepatic stress during asparaginase therapy by activating the AAR. To test this idea, C57BL/6J wild-type mice (Gcn2(+/+)) and those deleted for Gcn2 (Gcn2(-/-)) were injected with asparaginase or saline excipient one time daily for 1 or 6 days. In liver, increased phosphorylation of eIF2 and mRNA expression of AAR target genes activating transcription factor 4, asparagine synthetase, eIF4E-binding protein 1, and CAAT enhancer-binding protein homologous protein were significantly blunted or blocked in the liver of Gcn2(-/-) mice. Loss of AAR during asparaginase coincided with increases in mammalian target of rapamycin signaling, hepatic triglyceride accumulation, and DNA damage in association with genetic markers of oxidative stress (glutathione peroxidase) and inflammation (tumor necrosis factor alpha-α). Although asparaginase depleted circulating asparagine in both Gcn2(+/+) and Gcn2(-/-) mice, all other amino acids, including plasma glutamine, were elevated in the plasma of Gcn2(-/-) mice. This study shows that loss of GCN2 promotes oxidative stress and inflammatory-mediated DNA damage during asparaginase therapy, suggesting that patients with reduced or dysfunctional AAR may be at risk of developing hepatic complications during asparaginase treatment.

Disparity in actions of rosiglitazone against cisplatin-induced nephrotoxicity in female Sprague-Dawley rats.

Cisplatin is one of the most common chemotherapeutic drugs used against various solid, tumours. Despite of its therapeutic benefits, its use in clinical practice is often limited because of dose, related toxicity. The nephrotoxic potential of cisplatin has been ascribed to its accumulation in the, renal tubular cells generating reactive oxygen species (ROS), activation of Bax, increased secretion of, TNFα and activation of certain inflammatory mediators like cytokines. The present investigation was, undertaken with an objective to study the effect of rosiglitazone against cisplatin induced, nephrotoxicity. Pretreatment of rosiglitazone prevents cisplatin induced nephrotoxicity which was, clearly evident from the renal biochemical parameters like reduced BUN, creatinine and TNFα levels, and increased albumin levels, which was also supported by histopathological studies of the kidneys. In contrast, posttreatment of rosiglitazone was not able to protect the renal damage in cisplatin induced, renal toxicity. These results showed the variation of pre & posttreatment effects of rosiglitazone, against the cisplatin induced nephrotoxicity.

Comparative study of the possible protective effects of cinnamic acid and cinnamaldehyde on cisplatin-induced nephrotoxicity in rats.

This study aimed to assess the protective effect of cinnamic acid (CA) and cinnamaldehyde (CD) against cisplatin-induced nephrotoxicity. A single dose of cisplatin (5 mg/kg), injected intraperitoneally to male rats, caused significant increases in serum urea, creatinine levels, and lipid peroxides measured as the malondialdehyde content of kidney, with significant decreases in serum albumin, reduced glutathione, and the activity of antioxidant enzymes (catalase, superoxide dismutase, and glutathione peroxidase) of kidney as compared with the control group. On the other hand, administration of CA (50 mg/kg, p.o.) or CD (40 mg/kg, p.o.) for 7 days before cisplatin ameliorated the cisplatin-induced nephrotoxicity as indicated by the restoration of kidney function and oxidative stress parameters. Furthermore, they reduced the histopathological changes induced by cisplatin. In conclusion, CA and CD showed protective effects against cisplatin-induced nephrotoxicity where CD was more effective than CA; affects that might be attributed to their antioxidant activities.

Novel o-naphthoquinones induce apoptosis of EL-4 T lymphoma cells through the increase of reactive oxygen species.

Novel ß-lapachone analogs 2-phenyl-3,4-dihydro-2H-benzo[h]chromene-5,6-dione (NQ1), 2-p-tolyl-3,4-dihydro-2H-benzo[h]chromene-5,6-dione (NQ3) and 2-methyl-2-phenyl-3,4-dihydro-2H-benzo[h]chromene-5,6-dione (NQ7), which have trypanocidal activity, were assayed for cytotoxic effects on murine EL-4 T lymphoma cells. The NQs inhibited the proliferation of EL-4 cells at concentrations above 1µM. Nuclear staining of the EL-4 cells revealed chromatin condensation and a nuclear morphology compatible with the induction of apoptosis. Flow cytometry assays with annexin V-FITC and propidium iodide confirmed the cell death by apoptosis. Using electron paramagnetic resonance (EPR), a semiquinone radical was detected in EL-4 cells treated with NQs. In addition, a decrease in the GSH level in parallel with reactive oxygen species (ROS) production was observed. Preincubation with n-acetyl-l-cysteine (NAC) was able to reverse the inhibitory effects of the NQs on cell proliferation, indicating that ROS generation is involved in NQ-induced apoptosis. In addition, the NQs induced a decrease in the mitochondrial membrane potential and increased the proteolytic activation of caspases 9 and 3 and the cleavage of Poly (ADP-Ribose) Polymerase (PARP). In conclusion, these results indicate that redox cycling is induced by the NQs in the EL-4 cell line, with the generation of ROS and other free radicals that could inhibit cellular proliferation as a result of the induction of the intrinsic apoptosis pathway.

Identification of the ZAK-MKK4-JNK-TGFß signaling pathway as a molecular target for novel synthetic iminoquinone anticancer compound BA-TPQ.

Identification and validation of molecular targets are considered as key elements in new drug discovery and development. We have recently demonstrated that a novel synthetic iminoquinone analog, termed [7-(benzylamino)- 1,3,4,8-tetrahydropyrrolo [4,3, 2-de]quinolin-8(1H)-one] (BA-TPQ), has significant anti-breast cancer activity both in vitro and in vivo, but the underlying molecular mechanisms are not fully understood. Herein, we report the molecular studies for BA-TPQ's effects on JNK and its upstream and downstream signaling pathways. The compound up-regulates the JNK protein levels by increasing its phosphorylation and decreasing its polyubiquitination-mediated degradation. It activates ZAK at the MAPKKK level and MKK4 at the MAPKK level. It also up-regulates the TGFß2 mRNA level, which can be abolished by the JNK-specific inhibitor SP600125, but not TGFß pathway-specific inhibitor SD-208, indicating that both JNK and TGFß signaling pathways are activated by BA-TPQ and that the JNK pathway activation precedes TGFß activation. The pro-apoptotic and anti-growth effects of BA-TPQ are significantly blocked by both the JNK and TGFß pathway inhibitors. In addition, BA-TPQ activates the ZAK-MKK4-JNK pathway in MCF7 cells, but not normal MCF10A cells, demonstrating its cancer-specific activities. In conclusion, our results demonstrate that BA-TPQ activates the ZAK-MKK4-JNK-TGFß signaling cascade as a molecular target for its anticancer activity.

The impact of escitalopram on IL-2-induced neuroendocrine, immune, and behavioral changes in patients with malignant melanoma: preliminary findings.

Interleukin (IL)-2, a T-cell cytokine used to treat malignant melanoma, can induce profound depression. To determine whether pretreatment with the antidepressant escitalopram could reduce IL-2-induced neuroendocrine, immune, and neurobehavioral changes, 20 patients with Stage IV melanoma were randomized to either placebo or the serotonin reuptake inhibitor, escitalopram (ESC) 10-20 mg/day, 2 weeks before, and during IL-2 treatment (720 000 units/kg Q8 h × 5 days (1 cycle) every 3 weeks × 4 cycles). Generalized estimation equations were used to examine HPA axis activity (plasma ACTH and cortisol), immune activation (plasma IL-6), and depressive symptoms (Hamilton Depression Rating Scale (HDRS) score). Tolerance of IL-2 treatment (concomitant medications required) and adherence (number of IL-2 doses received) were also assessed. Both the groups (ESC (n=9), placebo (n=11)) exhibited significant IL-2-induced increases in plasma cortisol, IL-6, and depressive symptoms (p<0.05), as well as a temporal trend for increases in plasma ACTH (p=0.054); the effects of age and treatment were not significant. Higher plasma ACTH concentrations were associated with higher depressive symptoms during cycles 1-3 of IL-2 therapy (p<0.01). Although ESC had no significant effects on ACTH, cortisol, IL-6, tolerance of, or adherence to IL-2, ESC treatment was associated with lower depressive symptoms, ie, a maximal difference of ∼3 points on the HDRS, which, though not statistically significant (in part, due to small sample size), represents a clinically significant difference according to the National Institute for Health and Clinical Excellence guidelines. A larger sample size will establish whether antidepressant pretreatment can prevent IL-2-induced neurobehavioral changes.

N-acetylcysteine for the prevention of non-contrast media agent-induced kidney injury: from preclinical data to clinical evidence.

PURPOSE: To review available evidence on the effectiveness of N-acetylcysteine (NAC) as a prophylactic agent in the prevention of non-contrast media agent-induced kidney injury. METHOD: Data were collected by searching Scopus, PubMed, Medline, Science direct and Cochrane database systematic reviews. A total of 26 relevant experimental studies up to the date of publication were included in the review. RESULTS: Available evidence shows that NAC has the potential to exert significant protective or ameliorative effects against drug-induced kidney injury in experimental models. The possible suggested renoprotective mechanisms of NAC in different experimental settings were acting as an antioxidant by restoring the pool of intracellular reduced glutathione, scavenging of free radicals, and/or interacting with reactive oxygen species. CONCLUSION: Whether the administration of NAC could be an effective protective clinical strategy to prevent drug-induced kidney injury or not is a question that remains to be answered in future clinical trials.

Zinc coproporphyrin I derived from meconium has an antitumor effect associated with singlet oxygen generation.

INTRODUCTION: Zinc coproporphyrin I (ZnCP-I) is a photosensitive molecule and a major component of meconium. Here, we examined the effects of ZnCP-I as a potential photosensitizer in photodynamic therapy for tumors. MATERIALS AND METHODS: (1) Aqueous ZnCP-I was irradiated with a pulsed YAG-SHG laser (wavelength: 532 nm)/YAG-SHG dye laser (wavelength: 566 nm). (2) HeLa cells were incubated in 200 mM ZnCP-I, and accumulation of ZnCP-I in HeLa cells was evaluated with ZnCP-I-specific fluorescence over 500 nm. (3) Aqueous ZnCP-I was administered intravenously to HeLa tumor-bearing mice at a dose of 10.2 mg/kg body weight. The tumors were irradiated with a filtered halogen lamp (wavelength: 580 nm) at 100 J/cm(2) 20 min after administration. RESULTS: (1) An intense near-infrared emission spectrum was observed at around 1,270 nm after irradiation. The emission intensity was proportional to the laser power between 10 and 80 mW and was completely inhibited by addition of NaN3, a singlet oxygen scavenger. (2) ZnCP-I-specific fluorescence was detected in the HeLa cell cytoplasm. (3) Irradiated tumors treated with ZnCP-I were mostly necrotized. CONCLUSION: ZnCP-I accumulated in tumor cells, produced singlet oxygen upon irradiation, and necrotized the tumor cells. These results suggest that ZnCP-I may be an effective photosensitizer.

The sphingosine kinase inhibitor 2-(p-hyroxyanilino)-4-(p-chlorophenyl)thiazole reduces androgen receptor expression via an oxidative stress-dependent mechanism.

BACKGROUND AND PURPOSE: Sphingosine kinase catalyses the formation of sphingosine 1-phosphate and is linked with androgen receptor signalling in prostate cancer cells. Therefore, we investigated the effect of sphingosine kinase inhibitors on androgen receptor expression. EXPERIMENTAL APPROACH: Androgen-sensitive LNCaP cells were treated with SKi (2-(p-hydroxyanilino)-4-(p-chlorophenyl)thiazole), which inhibits sphingosine kinases 1 and 2 activity, and the effect on androgen receptor expression was measured. KEY RESULTS: Treatment of cells with SK1 inhibitors reduced the expression of the androgen receptor and prostate-specific antigen, while (R)-FTY720 methyl ether (a sphingosine-kinase-2-selective inhibitor), at a concentration that eliminates sphingosine kinase 2 from cells, had no significant effect on androgen receptor expression. The effect of SKi on androgen receptor expression was independent of the SKi-induced proteasomal degradation of SK1 and was post translational, although androgen receptor mRNA transcript was reduced. Fumonisin B1 (a ceramide synthase inhibitor) also failed to reverse the effect of SKi on androgen receptor expression, thereby excluding a role for ceramide derived from the salvage pathway. The effect of SKi on androgen receptor expression was reversed by N-acetylcysteine, which was used to scavenge reactive oxygen species. CONCLUSION AND IMPLICATIONS: Inhibition of sphingosine kinase 1 activity abrogates androgen receptor signalling via an oxidative stress-induced, p53-independent mechanism in prostate cancer cells. Therefore, SK1 inhibitors may offer therapeutic potential in promoting the removal of AR receptors from prostate cancer cells, resulting in an increased efficacy, which is likely to be superior to inhibitors that simply reversibly inhibit AR signalling.