Efficacy and Safety of Brodalumab in Patients with Moderate-to-Severe Plaque Psoriasis and Skin of Color: Results from the Pooled AMAGINE-2/-3 Randomized Trials.

BACKGROUND: Data on treatment outcomes in patients with psoriasis who have skin of color are limited. Brodalumab has shown efficacy in patients with moderate-to-severe plaque psoriasis. OBJECTIVE: Our objective was to evaluate the efficacy, safety, and health-related quality of life associated with brodalumab in patients with skin of color participating in two phase III, multicenter, randomized, double-blind, placebo- and active comparator-controlled studies (AMAGINE-2/-3). METHODS: Patients were self-categorized into racial subgroups (black, Asian, or white) or the non-mutually exclusive ethnic subgroup Hispanic/Latino. Patients were randomized to receive brodalumab 210 mg every 2 weeks (Q2W) or ustekinumab (45 mg in patients weighing ≤ 100 kg and 90 mg in patients weighing > 100 kg) for 52 weeks. Skin clearance was monitored using the Psoriasis Area and Severity Index (PASI) and Static Physician's Global Assessment (sPGA). Treatment-emergent adverse events (TEAEs) were summarized by treatment and racial and ethnic subgroup. Health-related quality of life was assessed using the Dermatology Life Quality Index (DLQI). RESULTS: During the 12-week induction phase, 613 patients received ustekinumab (black, n = 20; Asian, n = 24; white, n = 551; Hispanic/Latino, n = 68) and 1236 patients received brodalumab 210 mg Q2W (black, n = 36; Asian, n = 39; white, n = 1116; Hispanic/Latino, n = 132). At week 52, a total of 590 patients received continuous ustekinumab (black, n = 19; Asian, n = 23; white, n = 532; Hispanic/Latino, n = 64) and 339 patients were re-randomized to continue receiving brodalumab 210 mg Q2W (black, n = 10; Asian, n = 7; white, n = 308; Hispanic/Latino, n = 40). Among patients who received brodalumab 210 mg Q2W, skin clearance response rates were similar across racial and ethnic subgroups at week 12 and week 52; rates of 75%, 90%, and 100% improvement in PASI from baseline were also higher, as was sPGA score ≤ 1, than in patients who received ustekinumab across all racial and ethnic subgroups. Rates of TEAEs and ≥ 5-point improvement in DLQI score were similar across racial and ethnic subgroups. CONCLUSIONS: Brodalumab 210 mg Q2W is well tolerated and efficacious across diverse racial and ethnic subgroups in patients with psoriasis, including black, Asian, white, and Hispanic/Latino patients. TRIAL REGISTRY: ClinicalTrials.gov identifier NCT01708603 (AMAGINE-2); NCT01708629 (AMAGINE-3).

Effect of Prior Biologic Use on Cost-Effectiveness of Brodalumab vs. Ustekinumab for Treatment of Moderate-to-Severe Psoriasis in the United States.

INTRODUCTION: Clinical trials have shown brodalumab to have better efficacy than ustekinumab for the treatment of moderate-to-severe psoriasis. An estimation of the cost-effectiveness of brodalumab vs. ustekinumab is warranted and may be useful for treatment decision-making processes, especially in the context of the cost considerations of the current US healthcare system. Therefore, we compared the cost-effectiveness of brodalumab with ustekinumab for treatment of moderate-to-severe psoriasis in biologic-naïve and biologic-experienced patients in the USA. METHODS: An Excel-based economic model was developed to estimate and compare total annual costs to health plans associated with treatment with brodalumab vs. ustekinumab per achievement of Psorasis Area and Severity Index (PASI) 75, 90, and 100 for patients with moderate-to-severe psoriasis. RESULTS: For treatment with brodalumab vs. ustekinumab, total annual treatment costs per PASI 75, 90, and 100 were $31,106, $57,776, and $163,069, respectively, lower for a patient naïve to prior biologic treatment; they were $40,535, $65,472, and $223,610, respectively, lower for a patient experienced with prior biologic treatment. In an additional analysis among patients with and without prior biologic failure, they were $52,822, $93,309, and $365,606, respectively, lower for a patient with failure and they were $31,660, $57,128, and $164,996, respectively, lower for a patient without failure. CONCLUSION: Compared to ustekinumab, treatment with brodalumab was associated with better cost-effectiveness ratios for biologic-naïve and experienced-patients and also patients with and without prior biologic treatment failure. The greater cost-effectiveness of brodalumab was most prominent for biologic-experienced and prior biologic treatment failure patients. FUNDING: Ortho Dermatologics.

Comparison of the cost-effectiveness of biologic drugs used for moderate-to-severe psoriasis treatment in the United States.

PURPOSE: To compare the cost-effectiveness of the newly approved biologic drug, brodalumab, with other commonly used biologics for the treatment of moderate-to-severe psoriasis in the United States. METHODS: An economic model was constructed in Excel to compare average costs to achieve Psoriasis Area and Severity Index (PASI) 75, 90 and 100 among moderate-to-severe psoriasis patients treated with biologics. Total annual costs to health plans associated with treatment with five different biologics were estimated and cost-effectiveness compared using the estimated average cost per PASI 75, PASI 90 and PASI 100. RESULTS: Total annual costs to a health plan per patient with adalimumab, brodalumab, ixekizumab, secukinumab and ustekinumab were estimated at $51,246, $38,538, $65,484, $57,510 and $57,013. Mean annual treatment costs per PASI 75, 90 and 100 were the lowest for brodalumab, with the annual cost per PASI 75 for brodalumab, adalimumab, ixekizumab, secukinumab and ustekinumab estimated at $48,782, $82,655, $77,957, $75,671 and $87,243, per PASI 90 at $51,383, $119,178, $94,904, $108,509 and $130,615, and per PASI 100 at $87,585, $284,702, $176,983, $205,393, and $366,645. CONCLUSIONS: Brodalumab, which had the lowest drug cost and high drug efficacy, was associated with the lowest cost per PASI 75, 90 and 100 among the biologics evaluated.

The budget impact of brodalumab for the treatment of moderate-to-severe plaque psoriasis on US commercial health plans.

INTRODUCTION: Brodalumab is a new biologic approved by the US Food and Drug Administration in 2017 for the treatment of moderate-severe psoriasis. This study evaluated the impact of the introduction of brodalumab on the pharmacy budget on US commercial health plans. METHODS: An Excel-based health economic decision analytic model with a US health plan perspective was developed. The model incorporated published moderate-to-severe psoriasis prevalence data; market shares of common biologic drugs, including adalimumab, ustekinumab, secukinumab, ixekizumab, and etanercept, used for the treatment of moderate-severe psoriasis; 2017-year Wholesale Acquisition Costs for the biologic drugs; drug dispensing fee; patient co-pay; and drug contracting discount. Total annual health plan costs for the biologic drugs were estimated. Scenarios with different proportions of patients treated with brodalumab were compared to a control scenario when no brodalumab was used. RESULTS: In a hypothetical commercial health plan covering two million members, 7,038 moderate-to-severe psoriasis patients were estimated to be eligible for treatment with brodalumab. Prior to brodalumab approval, the proportions of patients treated by other biologics were estimated at 50.8% for adalimumab, 13.5% for ustekinumab, 14.1% for secukinumab, 4.4% for ixekizumab, and 17.2% for etanercept. With a 20% drug price discount applied to all biologics, the annual health plan costs for brodalumab, adalimumab, ustekinumab, secukinumab, ixekizumab, and etanercept were estimated at $37,224, $49,166, $55,084, $56,061, $64,396, and $57,170, respectively. When no brodalumab is used, the total annual pharmacy budget for the biologics used among these patients was estimated at $414,362,647. Among scenarios where the proportions of brodalumab usage were 3%, 8%, 16%, and 30%, the total annual pharmacy cost was estimated to be reduced by $3,698,129, $9,861,677, $19,723,355, and $36,981,290, respectively. CONCLUSION: Based on the economic model, brodalumab has the potential to substantially reduce pharmacy expenditures for the treatment of patients with moderate-to-severe plaque psoriasis in the US.

Psychiatric adverse events during treatment with brodalumab: Analysis of psoriasis clinical trials.

BACKGROUND: Individuals with psoriasis are at increased risk for psychiatric comorbidities, including suicidal ideation and behavior (SIB). OBJECTIVE: To distinguish between the underlying risk and potential for treatment-induced psychiatric adverse events in patients with psoriasis being treated with brodalumab, a fully human anti-interleukin 17 receptor A monoclonal antibody. METHODS: Data were evaluated from a placebo-controlled, phase 2 clinical trial; the open-label, long-term extension of the phase 2 clinical trial; and three phase 3, randomized, double-blind, controlled clinical trials (AMAGINE-1, AMAGINE-2, and AMAGINE-3) and their open-label, long-term extensions of patients with moderate-to-severe psoriasis. RESULTS: The analysis included 4464 patients with 9161.8 patient-years of brodalumab exposure. The follow-up time-adjusted incidence rates of SIB events were comparable between the brodalumab and ustekinumab groups throughout the 52-week controlled phases (0.20 vs 0.60 per 100 patient-years). In the brodalumab group, 4 completed suicides were reported, 1 of which was later adjudicated as indeterminate; all patients had underlying psychiatric disorders or stressors. LIMITATIONS: There was no comparator arm past week 52. Controlled study periods were not powered to detect differences in rare events such as suicide. CONCLUSIONS: Comparison with controls and the timing of events do not indicate a causal relationship between SIB and brodalumab treatment.

A randomized, placebo-controlled, single-blinded, split-faced clinical trial evaluating the efficacy and safety of KLOX-001 gel formulation with KLOX light-emitting diode light on facial rejuvenation.

PURPOSE: Many treatment modalities exist to counteract the effects of cutaneous aging. Ablative methods have been the mainstay for nonsurgical facial rejuvenation. In recent years, nonablative techniques have been developed with the aim of achieving facial rejuvenation without epidermal damage. Light-emitting diode (LED) photorejuvenation is a novel nonablative technique that induces collagen synthesis through biophotomodulatory pathways. MATERIALS AND METHODS: A single-center, randomized, single-blinded, placebo-controlled, split-faced clinical trial was designed. Thirty-two patients were enrolled for a 12-week study. Patients were randomized into one of four groups: Group A, treatment with KLOX-001 gel formulation and white LED (placebo) light; Group B, treatment with a placebo/base gel (no active chromophore) formulation and KLOX LED light; Group C, treatment with KLOX-001 gel formulation and KLOX LED light; and Group D, treatment with the standard skin rejuvenating treatment (0.1% retinol-based cream). Patients received treatment at weeks 0, 1, 2, and 3, and returned to the clinic at weeks 4, 8, and 12 for clinical assessments performed by an independent, blinded committee of physicians using subjective clinician assessment scales. Tolerability, adverse outcomes, and patient satisfaction were also assessed. RESULTS: Analysis demonstrated that the KLOX LED light with KLOX placebo/base gel and the KLOX LED light + KLOX-001 gel formulation groups were superior to standard of care and KLOX-001 gel formulation with placebo light on subjective clinical assessment and multiple wrinkle scales, with statistically significant results obtained for brow positioning, perioral wrinkling, and total wrinkle score. CONCLUSION: The study results show that KLOX LED light with KLOX-001 gel formulation and KLOX LED light with KLOX placebo/base gel are effective, safe, well-tolerated, and painless treatment modalities for skin rejuvenation.

Nicotine induces cell proliferation, invasion and epithelial-mesenchymal transition in a variety of human cancer cell lines.

Cigarette smoking is strongly correlated with the onset of nonsmall cell lung cancer (NSCLC). Nicotine, an active component of cigarettes, has been found to induce proliferation of lung cancer cell lines. In addition, nicotine can induce angiogenesis and confer resistance to apoptosis. All these events are mediated through the nicotinic acetylcholine receptors (nAChRs) on lung cancer cells. In this study, we demonstrate that nicotine can promote anchorage-independent growth in NSCLCs. In addition, nicotine also induces morphological changes characteristic of a migratory, invasive phenotype in NSCLCs on collagen gel. These morphological changes were similar to those induced by the promigratory growth factor VEGF. The proinvasive effects of nicotine were mediated by alpha7-nAChRs on NSCLCs. RT-PCR analysis showed that the alpha7-nAChRs were also expressed on human breast cancer and pancreatic cancer cell lines. Nicotine was found to promote proliferation and invasion in human breast cancer. The proinvasive effects of nicotine were mediated via a nAChR, Src and calcium-dependent signaling pathway in breast cancer cells. In a similar fashion, nicotine could also induce proliferation and invasion of Aspc1 pancreatic cancer cells. Most importantly, nicotine could induce changes in gene expression consistent with epithelial to mesenchymal transition (EMT), characterized by reduction of epithelial markers like E-cadherin expression, ZO-1 staining and concomitant increase in levels of mesenchymal proteins like vimentin and fibronectin in human breast and lung cancer cells. Therefore, it is probable that the ability of nicotine to induce invasion and EMT may contribute to the progression of breast and lung cancers.

Glut-1 antibodies induce growth arrest and apoptosis in human cancer cell lines.

Glucose transporters (Gluts) facilitate glucose uptake and tumors frequently over express the Gluts, especially Glut-1. Breast cancer and lung cancer (NSCLC) cell lines were incubated with anti-Glut-1 antibodies alone or with cisplatin, paclitaxel or gefitinib. Inhibition of proliferation and apoptosis was assessed. Antibodies to Glut-1 inhibited proliferation by 50% and 75% in the tested NSCLC and breast cancer cell lines, respectively. They also potentiate the anti-proliferative effects of cisplatin, paclitaxel and gefitinib. Our results indicate that anti-Glut-1 antibodies inhibit proliferation and induce apoptosis in the evaluated cell lines and provide preliminary evidence of their anti-tumor activity.

Protective effect of Ocimum sanctum on 3-methylcholanthrene, 7,12-dimethylbenz(a)anthracene and aflatoxin B1 induced skin tumorigenesis in mice.

A study on the protective effect of alcoholic extract of the leaves of Ocimum sanctum on 3-methylcholanthrene (MCA), 7,12-dimethylbenzanthracene (DMBA) and aflatoxin B1 (AFB1) induced skin tumorigenesis in a mouse model has been investigated. The study involved pretreatment of mice with the leaf extract prior to either MCA application or tetradecanoyl phorbol acetate (TPA) treatment in a two-stage tumor protocol viz a viz, DMBA/TPA and AFB1/TPA. The results of the present study indicate that the pretreatment with alcoholic extract of the leaves of O. sanctum decreased the number of tumors in MCA, DMBA/TPA and AFB1/TPA treated mice. The skin tumor induced animals pretreated with alcoholic extract led to a decrease in the expression of cutaneous gamma-glutamyl transpeptidase (GGT) and glutathione-S-transferase-P (GST-P) protein. The histopathological examination of skin tumors treated with leaf extract showed increased infiltration of polymorphonuclear, mononuclear and lymphocytic cells, decreased ornithine decarboxylase activity with concomitant enhancement of interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) in the serum, implying the in vivo antiproliferative and immunomodulatory activity of leaf extract. The decrease in cutaneous phase I enzymes and elevation of phase II enzymes in response to topical application of leaf extract prior to MCA, AFB1, DMBA/TPA and AFB1/TPA treatment indicate the possibility of impairment in reactive metabolite(s) formation and thereby reducing skin carcinogenicity. Furthermore, pretreatment of leaf extract in the carcinogen induced animals resulted in elevation of glutathione levels and decrease in lipid peroxidation along with heat shock protein expression, indicating a scavenging or antioxidant potential of the extract during chemical carcinogenesis. Thus it can be concluded that leaf extract of O. sanctum provides protection against chemical carcinogenesis in one or more of the following mechanisms: (i) by acting as an antioxidant; (ii) by modulating phase I and II enzymes; (iii) by exhibiting antiproliferative activity.

Nicotine induces cell proliferation by beta-arrestin-mediated activation of Src and Rb-Raf-1 pathways.

Recent studies have shown that nicotine, a component of cigarette smoke, can stimulate the proliferation of non-neuronal cells. While nicotine is not carcinogenic by itself, it has been shown to induce cell proliferation and angiogenesis. Here we find that mitogenic effects of nicotine in non-small cell lung cancers (NSCLCs) are analogous to those of growth factors and involve activation of Src, induction of Rb-Raf-1 interaction, and phosphorylation of Rb. Analysis of human NSCLC tumors show enhanced levels of Rb-Raf-1 complexes compared with adjacent normal tissue. The mitogenic effects of nicotine were mediated via the alpha7-nAChR subunit and resulted in enhanced recruitment of E2F1 and Raf-1 on proliferative promoters in NSCLC cell lines and human lung tumors. Nicotine stimulation of NSCLC cells caused dissociation of Rb from these promoters. Proliferative signaling via nicotinic acetylcholine receptors (nAChRs) required the scaffolding protein beta-arrestin; ablation of beta-arrestin or disruption of the Rb-Raf-1 interaction blocked nicotine-induced proliferation of NSCLCs. Additionally, suppression of beta-arrestin also blocked activation of Src, suppressed levels of phosphorylated ERK, and abrogated Rb-Raf-1 binding in response to nicotine. It appears that nicotine induces cell proliferation by beta-arrestin-mediated activation of the Src and Rb-Raf-1 pathways.

Prohibitin facilitates cellular senescence by recruiting specific corepressors to inhibit E2F target genes.

Prohibitin is a growth regulatory gene that has pleiotropic functions in the nucleus, mitochondria, and cytoplasmic compartments. Earlier studies had proposed a role for prohibitin in modulating cellular senescence, but the underlying mechanisms remain unknown. Here we show that senescence induced by DNA-damaging agents causes the localization of prohibitin to specific heterochromatic foci. Prohibitin could bind to heterochromatin protein 1 (HP1) family proteins and colocalized with HP1gamma in senescence-associated heterochromatic foci. Further, HP1gamma could synergize with prohibitin to repress E2F1-mediated transcriptional activity. The depletion of prohibitin by small interfering RNA or antisense techniques led to a reduction in the senescent phenotype, correlating with a reduced expression of senescence-associated beta-galactosidase and fewer numbers of senescence-associated heterochromatic foci. Chromatin immunoprecipitation assays showed that prohibitin is needed for the recruitment of HP1gamma to E2F1-regulated proliferative promoters, leading to their repression. The ablation of prohibitin prevented the recruitment of HPIgamma, but not Suv39H, to the promoters upon senescence. Prohibitin-mediated recruitment of HP1gamma occurred in only senescent cells, not in quiescent cells; thus, there is a dichotomy in the recruitment of different corepressors by prohibitin, depending on the type of growth arrest. These studies show that prohibitin plays a vital role in inducing cellular senescence.

Skin tumorigenic potential of aflatoxin B1 in mice.

Aflatoxin B1 (AFB1) has been classified as a category I human carcinogen, which is responsible for a high incidence of hepatocellular carcinoma. Since exposure to AFB1 can occur through skin contact in addition to ingestion and inhalation, the carcinogenic potential of topically applied AFB1 on mouse skin was investigated. Our results show that single topical application of AFB1 (80 nmol) as a tumor initiator, followed by twice weekly application of 12-tetradecanoyl phorbol myristate acetate (TPA, 4 nmol), resulted in tumor formation after 13 weeks. However, no tumorigenic potential was observed when AFB1 (16 nmol) was used either as a complete carcinogen or as a tumor promoter (4 nmol). Histological analysis of skin showed squamous cell carcinoma in the AFB1/TPA treated group. The application of AFB1 as a complete carcinogen, an initiator or a promoter after 24 weeks demonstrated widespread degenerative and necrotic changes in hepatic tissue as well, suggesting liver to be the target organ following percutaneous absorption. Additionally, twice weekly topical application of AFB1 caused significant induction of cutaneous CYP IA monoxygenases without any effect on hepatic levels while glutathione-S-transferase activity was induced more in the liver than skin. The topical application of AFB1 also resulted in increased hepatic and cutaneous lipid peroxidation with concomitant depletion of glutathione content. It is likely that due to higher induction of hepatic GST activity, products of lipid peroxidation may be detoxified and therefore unable to cause DNA damage making mice resistant to hepatic tumor formation. The overall results indicate a tumor initiating potential of AFB1 in mice and suggest that continued dermal exposure of AFB1, even at low doses, might lead to degenerative changes in hepatocytes.

Camptothecin induces nuclear export of prohibitin preferentially in transformed cells through a CRM-1-dependent mechanism.

Prohibitin is a growth-suppressive protein that has multiple functions in the nucleus and the mitochondria. Our earlier studies had shown that prohibitin represses the activity of E2F transcription factors while enhancing p53-mediated transcription. At the same time, prohibitin has been implicated in mediating the proper folding of mitochondrial proteins. We had found that treatment of cells with camptothecin, a topoisomerase 1 inhibitor, led to the export of prohibitin and p53 from the nucleus to the mitochondria. Here we show that the camptothecin-induced export of prohibitin occurs preferentially in transformed cell lines, but not in untransformed or primary cells. Cells that did not display the translocation of prohibitin were refractive to the apoptotic effects of camptothecin. The translocation was mediated by a putative nuclear export signal at the C-terminal region of prohibitin; fusion of the nuclear export signal (NES) of prohibitin to green fluorescence protein led to its export from the nucleus. Leptomycin B could inhibit the nuclear export of prohibitin showing that it was a CRM-1-dependent event driven by Ran GTPase. Confirming this, prohibitin was found to physically interact with CRM-1, and this interaction was significantly higher in transformed cells. Delivery of a peptide corresponding to the NES of prohibitin prevented the export of prohibitin to cytoplasm and protected cells from apoptosis. These results suggest that the regulated translocation of prohibitin from the nucleus to the mitochondria facilitates its pleiotropic functions and might contribute to its anti-proliferative and tumor suppressive properties.

Activation of a methylated promoter mediated by a sequence-specific DNA-binding protein, RFX.

The roles of eukaryotic DNA methylation in the repression of mRNA transcription and in the formation of heterochromatin have been extensively elucidated over the past several years. However, the role of DNA methylation in transcriptional activation remains a mystery. In particular, it is not known whether the transcriptional activation of methylated DNA is promoter-specific, depends directly on sequence-specific DNA-binding proteins, or is facilitated by the methylation. Here we report that the sequence-specific DNA-binding protein, RFX, previously shown to mediate the transition from an inactive to an active chromatin structure, activates a methylated promoter. RFX is capable of mediating enhanceosome formation on a methylated promoter, thereby mediating a transition from a methylation-dependent repression of the promoter to a methylation-dependent activation of the promoter. These results indicate novel roles for DNA methylation and sequence-specific DNA-binding proteins in transcriptional activation.

Mechanism to study 1:1 stoichiometry of NADPH and alkoxyphenoxazones metabolism spectrophotometrically in subcellular biological preparations.

Our prior studies have shown that pentoxyresorufin-O-dealkylation (PROD) can be measured spectrophotometrically with simultaneous monitoring of stoichiometry of NADPH/substrate and NADP/product as 10:1:10:1 [Rastogi et al. FEBS Letters 512 (2002) 121-124]. In the present investigation, mechanism of action of other enzymes in modulating the stoichiometry of alkoxyphenoxazones metabolism to 1:1 for electron donor/substrate and oxidized electron donor/product in the same incubation mixture was studied. The spectrophotometric analysis reveals 10:1 ratio between NADPH and pentoxyresorufin (PRF)-ethoxyresorufin (ERF) in microsomal system. The high ratio of electron donor to substrate is due to the presence of the other forms of P-450, which may participate in endogenous metabolism of compounds, thereby reducing the ratio to 4:1 and 7:1 for NADPH/PRF-ERF. Incubation of dicumarol in the microsomal PROD or ethoxyresorufin-O-dealkylase (EROD) assay led to significant decrease in the consumption of NADPH with a ratio of 4:1 and 7:1 for NADPH/PRF-ERF which is due to inhibition of NADPH cytochrome c (P-450) reductase. In post mitochondrial fraction (S-9), the ratio of 11:1 and 15:1 is seen for NADPH/PRF-ERF. The addition of dicumarol in S-9 fraction showed enhanced rate of alkoxyphenoxazone utilization, suggesting the possibility of reduced resorufin product as a feedback inhibitor. Equating the ratio of NADPH/substrate(s) derived after endogenous utilization of NADPH with the ratio after accounting for NADPH consumption following dicumarol addition in either S-9 or microsomal fraction, a 1:1 mol of NADPH/substrate(s) and oxidized electron donor/product is obtained. The results further suggest that cytosolic fraction may interfere in monitoring the formation of resorufin during dealkylation of alkoxyphenoxazones making dicumarol a mandatory cofactor.

Direct binding of apoptosis signal-regulating kinase 1 to retinoblastoma protein: novel links between apoptotic signaling and cell cycle machinery.

The retinoblastoma protein Rb has antiproliferative and antiapoptotic functions. Our previous studies have shown that certain apoptotic signals can inactivate Rb via the p38 pathway. Here we show that Rb associates with the apoptosis signal-regulating kinase ASK1 in response to specific apoptotic signals. An LXCXE motif on ASK1 was required for Rb binding; this correlated with increased E2F1 transcriptional activity and up-regulation of the proapoptotic protein p73. Overexpression of Rb inhibited ASK1-induced apoptosis; in addition, an ASK1 mutant incapable of binding Rb could not induce apoptosis, indicating that ASK1 has to overcome the antiapoptotic properties of Rb to kill cells. Chromatin immunoprecipitation assays show that in asynchronous cells the p73P1 promoter is occupied predominantly by E2F3; upon tumor necrosis factor (TNF)-alpha stimulation, E2F3 is dissociated from the promoter and replaced by E2F1. At the same time, TNF-alpha stimulation causes Rb to dissociate from the p73P1 promoter. These are promoter-specific events because Rb binds to the mitogenic cdc25A promoter upon TNF-alpha stimulation. These studies suggest that Rb acts as a link between apoptotic and proliferative pathways by interacting with distinct kinases and occupying different promoters.

Prohibitin induces the transcriptional activity of p53 and is exported from the nucleus upon apoptotic signaling.

Prohibitin, a potential tumor suppressor protein, has been shown to inhibit cell proliferation and repress E2F transcriptional activity. Though prohibitin has potent transcriptional functions in the nucleus, a mitochondrial role for prohibitin has also been proposed. Here we show that prohibitin is predominantly nuclear in two breast cancer cell lines where it co-localizes with E2F1 and p53. Upon apoptotic stimulation by camptothecin, prohibitin is exported to perinuclear regions where it localizes to mitochondria. The data presented here also show that prohibitin is capable of physically interacting with p53 in vivo and in vitro. Prohibitin was found to enhance p53-mediated transcriptional activity and cotransfection of an antisense prohibitin construct reduces p53-mediated transcriptional activation. Prohibitin appears to induce p53-mediated transcription by enhancing its recruitment to promoters, as detected by chromatin immunoprecipitation assays. These results suggest that prohibitin is capable of modulating Rb/E2F as well as p53 regulatory pathways.

A novel approach to study the activity and stoichiometry simultaneously for microsomal pentoxyresorufin-O-dealkylase reaction.

A simple approach to study the activity and stoichiometry of cytochrome P-450 IIB1-catalyzed metabolism of pentoxyresorufin (PRF) has been investigated. It involves the continuous spectral analysis of reaction mixture containing PRF, microsomes from phenobarbital-induced rats and NADPH. The kinetics of NADPH consumption, PRF utilization, NADP and resorufin formation was monitored at lambda(max) of 338, 484, 260 and 572 nm, respectively. The stoichiometry of the enzyme reaction tabulated either by specific activity or by V(max) value showed that 10 molecules of NADPH were required for the conversion of one molecule of PRF to one molecule of resorufin along with 10 molecules of NADP. Further, it was observed that almost six molecules of NADPH are consumed in the incubation mixture devoid of PRF indicating the possibility of metabolism of endogenous substrates. Interestingly, the stoichiometry ratio of 1:1 for PRF and resorufin was established even in the presence of P-450 inhibitors with a lower rate of metabolism. However, the ratio of NADPH to PRF was altered in the presence of inhibitors, suggesting that the simultaneous monitoring of the substrate, electron donor and the products could be useful in understanding the modifications of stoichiometry of electron donor and substrate/product.

A spectrophotometric method to monitor the catalytic activity of microsomal cytochrome P-450 IIB1/2: comparison with fluorometric assay.

A simple spectrophotometric method to monitor the catalytic activity of microsomal cytochrome P-450 IIB1/2 has been developed. The method employs measurement of utilization of NADPH, consumption of the substrate, pentoxyresorufin (PRF) and formation of the product, resorufin (RF) in the same reaction mixture containing hepatic microsomes from phenobarbital treated rats. The velocity of NADPH utilization (16.36 nmole/min/nmole P-450), PRF consumption (1.58 nmole/min/nmole P-450) and RF formation (1.57 nmole/min/nmole P-450) suggested a stoichiometry of 1:1 between the substrate and the product alongwith utilization of 10 molecules of NADPH. However, the Km for the enzyme activity (nmole RF formed/min/nmole P-450) using varying concentrations of PRF and NADPH as substrates were found to be 11.6 and 20.2 microM, respectively. The spectrophotometric method was compared with fluorometric method in terms of linearity with time, P-450 content and Vmax, Km values observed for the reaction. Inhibition studies with metyrapone and SKF 525A in the utilization of NADPH, consumption of PRF and formation of RF suggested that the method could be useful in monitoring the effect of various inhibitors on the P-450 IIB1/2 reaction.