EFFECTS OF INTRAVITREAL BEVACIZUMAB THERAPY ON GLOMERULAR FILTRATION RATES IN PATIENTS TREATED FOR PROLIFERATIVE DIABETIC RETINOPATHY.

PURPOSE: To assess whether the repeated use of intravitreal bevacizumab injections in treatment of proliferative diabetic retinopathy is associated with a long-term decline in the glomerular filtration rate (GFR). METHODS: Three hundred charts were retrospectively reviewed, of which 60 patients met the criteria for inclusion. The criteria were as follows: reception of at least one bevacizumab injection, baseline GFR before initial bevacizumab injection, and end GFR 6 to 24 months after baseline. Analysis controlled for time between baseline and end GFR measurements, blood pressure, hemoglobin A1C, race, sex, age, and use of an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker. Significance testing was performed with step-wise multiple linear regression. The significance threshold was 5%, and all tests were two-sided. RESULTS: Patients received a range of 1 to 17 injections (average 3.6). The average baseline GFR was 76 ± 38 mL/minute, and the end GFR was 63 ± 39 mL/min. The number of injections patients received was not associated with end GFR ( P = 0.72), GFR reduction ( P = 0.88), or percent GFR reduction ( P = 0.49). CONCLUSION: Increased number of intravitreal bevacizumab injections at therapeutic dosage was not associated with reduced GFR in patients with proliferative diabetic retinopathy. This study supports that intravitreal antivascular endothelial growth factor agents are renally safe.

Assessment of patient follow-up from student-run free eye clinic to county ophthalmology clinic.

The Ophthalmology Student Interest Group at Indiana University School of Medicine provides a free student-run eye screening clinic for an underserved community in Indianapolis. Patients with abnormal findings are referred to the ophthalmology service of the local county hospital for further evaluation. This retrospective chart review studied 180 patients referred from our free eye clinic to follow up at the ophthalmology service of a local county hospital from October 2013 to February 2020. This study investigated factors impacting follow-up of patients by analyzing demographics, medical history, insurance coverage, and final diagnoses at follow-up. Thirty-five (19.4%) of 180 patients successfully followed up at the local county hospital with an average time to follow-up of 14.4 (± 15.9) months. Mean patient age was 51 (± 13.6) with nearly equal numbers of males and females. The most common diagnoses at follow-up included refractive error (51.4%), cataract (45.7%), and glaucoma (28.6%). Patients with diabetes diagnoses or Healthy Indiana Plan insurance coverage had increased probability of follow-up. This study reveals gaps in timely follow-up to the local county hospital, demonstrating the current limitations of our free clinic in connecting patients to more definitive care and the need for an improved referral process.

A seven-year analysis of the role and impact of a free community eye clinic.

BACKGROUND: The Indiana University Student Outreach Clinic (IUSOC) Eye Clinic is a monthly student-run eye clinic that provides free visual screening to the Near East Side community of Indianapolis, IN, USA. Screening includes assessments of visual acuity, intraocular pressure, peripheral visual fields, refraction, and non-mydriatic fundus photography. METHODS: This is a retrospective chart review of 875 patients seen at the IUSOC Eye Clinic from October 2013 to February 2020. Data on demographics, insurance coverage, ocular history, physical examination, suspected diagnosis, referral status, and glasses provided were collected and analyzed. RESULTS: 875 patients were seen at the IUSOC Eye Clinic from October 2013 to February 2020. 39.2% of the patients seen at the clinic reported being uninsured. 61.4% of patients were found to have visual acuity of 20/40 or worse, while 51.3% of patients were found to have a near visual acuity of 20/40 or worse. 20.3% of patients were referred to the local county hospital for further evaluation by an ophthalmologist, 14.4% of patients received free glasses prescriptions, and 27.9% of patients received free reading glasses. Common reasons for referral for further ophthalmology evaluation included glaucoma, decreased visual acuity, and diabetic retinopathy. An estimated value of services provided over the seven years of the clinic was 1271 relative value units. CONCLUSION: The IUSOC Eye Clinic fills an important role in advancing ocular health and preventing irreversible blindness in an underserved Indianapolis community. Additionally, the clinic demonstrates an educational model for involving medical student volunteers.

Ocular motility and diplopia measurements following orbital floor fracture repair.

PURPOSE: Diplopia and ocular motility restriction following orbital fracture repair are common complications. The reported rates in the literature differ greatly, in part due to varying definitions of diplopia and methods of measurement. The purpose of this study is to describe a practical and efficient in-office method for examining ocular motility and diplopia in orbital trauma patients and to report the outcomes in a series of patients who underwent orbital floor fracture repair. MATERIALS AND METHODS: A retrospective chart review from 2012 to 2019 was conducted in patients who underwent isolated orbital floor fracture repair within 3 weeks of trauma. All patients had examinations to assess extraocular motility and subjective diplopia using the described techniques. RESULTS: Ninety-three patients underwent orbital floor fracture repair and had adequate follow-up. Preoperatively, 71 (76%) patients had some restriction in motility and 59 (63%) patients complained of diplopia. Postoperatively, only 1 patient (1.09%) had clinically significant diplopia. Five (5.4%) additional patients demonstrated mild restriction in supraduction upon detailed ophthalmic examination that was not discovered upon subjective history. No patients had worsening of diplopia or motility after surgery. CONCLUSIONS: Diplopia and motility restriction following orbital fracture repair can be a persistent problem for some patients. It is important to perform a careful ophthalmic examination to detect motility deficits and diplopia that can be significant to the patient. The true rate of restriction and diplopia may be higher using detailed ophthalmic diagnostic techniques compared to subjective patient history.

Wide-Field (15â€Š× 9 mm) Swept-Source Optical Coherence Tomography Angiography Following Plaque Radiotherapy of Choroidal Melanoma: An Analysis of 105 eyes.

PURPOSE: The aim of this study was to evaluate retinal microvascular abnormalities following plaque radiotherapy of choroidal melanoma (CM) using wide-field swept-source optical coherence tomography angiography (OCTA). DESIGN: Single-centre retrospective review. METHODS: Retrospective case series of 105 CM patients treated with I-125 plaque radiotherapy and imaged with wide-field (15 × 9 mm) SS-OCTA from March 2018 to August 2018 at the Ocular Oncology Service, Wills Eye Hospital (Philadelphia, PA). RESULTS: At mean follow-up of 49 months (range 4-297) after plaque radiotherapy, there were 52 eyes (50%) with clinically evident radiation retinopathy (CERR) and 53 eyes (50%) without CERR. Comparison (CERR vs controls) revealed foveal avascular zone enlargement (1.7 vs 0.23 mm, P = 0.03) and reduction of capillary vascular density (CVD) in the superficial and deep plexus in the total wide-field (43% vs 47%, P < 0.001, and 46% vs 48%, P = 0.001, respectively), peripapillary region (66% vs 77%, P < 0.001, and 66% vs 72%, P = 0.001, respectively), and papillomacular bundle (60% vs 68%, P < 0.001, and 61% vs 64%, P = 0.03, respectively). Comparison (no CERR vs controls) revealed nonsignificant foveal avascular zone enlargement (1.20 vs 0.23 mm, P = 0.16) and reduction of CVD in the superficial plexus (46% vs 47%, P = 0.008), and not the deep plexus (48% vs 48%, P = 0.42) of the total wide-field. Comparison of irradiated eyes (CERR vs no CERR) showed reduction of CVD in the superficial and deep plexus of the total wide-field (43% vs 46%, P < 0.006, and 46% vs 48% P < 0.02, respectively), peripapillary region (66% vs 74%, P < 0.001, and 66% vs 72% P < 0.01, respectively), and superficial plexus in the papillomacular bundle (60% vs 65%, P = 0.03). CONCLUSIONS: Following plaque radiotherapy for choroidal melanoma, wide-field swept-source optical coherence tomography angiography demonstrates retinal microvascular abnormalities in the CVD in eyes with and without CERR. These findings are important in early detection and monitoring of radiation retinopathy.

Outcomes of neonatal retinoblastoma in pre-chemotherapy and chemotherapy eras.

Purpose: To quantify outcomes for neonatal retinoblastoma patients treated during the pre-chemotherapy (1980-1994) and chemotherapy (1995-2018) eras. Methods: Retrospective review of retinoblastoma patients diagnosed within the first 28 days of life between 1/1/1980 and 11/30/2018. Student's t-test, Chi-square, and Fisher's exact test were performed to compare treatments and outcomes by era. Results: There were 68 patients with neonatal retinoblastoma (12% unilateral and 88% bilateral). According to era (pre-chemotherapy vs. chemotherapy), the number of treated patients was 26 (38%) vs. 42 (62%). Primary treatment was external beam radiotherapy (50% vs. 1%,P < 0.001), plaque radiotherapy (17% vs. 0%,P < 0.001), focal treatment (transpupillary thermotherapy or cryotherapy) only (21% vs. 14%,P= 0.33), intravenous chemotherapy (0% vs. 81%,P < 0.001), enucleation (10% vs. 4%,P= 0.26), or exenteration (2% vs. 0%,P= 0.37). Outcomes included tumor control (79% vs. 94%,P= 0.02), globe salvage (75% vs. 91%,P= 0.02), final gross visual acuity for salvaged eyes 20/200 or better (66% vs. 89%,P < 0.01), and death (19% vs. 0%,P < 0.01). Conclusion: Chemotherapy advancements for neonatal retinoblastoma have improved tumor control, globe salvage, visual acuity, and patient survival.

Heterochromia following intravitreal chemotherapy in two cases.

Intravitreal chemotherapy is recognized as an effective treatment for retinoblastoma with vitreous (and occasionally subretinal) seeding refractory to intravenous or intra-arterial chemotherapy. However, this treatment carries with it the risk of toxicity to both the posterior and anterior segments of the eye, including retinal pigment epithelial mottling, ischemic/hemorrhagic retinopathy, posterior synechia, cataract, scleral necrosis, and focal iris depigmentation. We report 2 cases of iris heterochromia secondary to profound iris stromal depigmentation following intravitreal melphalan and topotecan injections.

Effects of image brightness and contrast dynamic altering stimuli (DAS) when viewing video content on ocular blood flow.

BACKGROUND/AIM: Blood flow deficiencies of the retinal and retrobulbar circulations have been previously reported in open-angle glaucoma (OAG) and other eye diseases. Herein we investigated the effects of image brightness and contrast dynamic altering stimuli (DAS) when viewing a video content on ocular blood flow, intraocular pressure (IOP) and ocular perfusion pressure (OPP) in OAG and healthy subjects. METHODS: Thirty-five subjects, 25 with OAG (mild to moderate) and 10 healthy controls, were evaluated for blood pressure, IOP, OPP and retinal capillary blood flow before, immediately after, 30 min after and 60 min after using ReviView (a dichoptic video goggles device), which stimulates one eye with a DAS video image that is brighter and with greater contrast than the fellow eye (duration of exposure 30 min). Differences between each subject's eyes and between OAG and healthy subjects were evaluated using repeated-measures analysis of variance with p<0.05 considered statistically significant. RESULTS: All subjects demonstrated a significant increase in OPP in both eyes immediately following viewing. In all DAS eyes, retinal capillary blood flow rose immediately after stimulation and remained elevated for an hour postviewing. Viewing DAS increased retinal blood flow compared with control eyes (p=0.0014, 0.0135 superiorly and p=0.0094, 0.0001 inferiorly, at 30 and 60 min, respectively). OAG eyes had a significant reduction in the number of dormant retinal capillaries (p=0.0174), while healthy eyes demonstrated a larger increase in retinal capillary blood flow (p=0.0006 and p=0.0093 at 60 min, superior and inferior, respectively) following DAS viewing. CONCLUSION: Viewing DAS video for 30 min using ReviView increased retina blood flow both in healthy subjects and in patients with OAG. TRIAL REGISTRATION NUMBER: NCT02959593.

Glaucoma secondary to intraocular tumors: mechanisms and management.

PURPOSE OF REVIEW: Glaucoma secondary to intraocular tumors is important to consider in eyes with a known tumor and those with unilateral or refractory glaucoma. The purpose of this review is to discuss the mechanisms and management of intraocular tumors with related secondary glaucoma. RECENT FINDINGS: Several intraocular tumors can lead to glaucoma, including iris melanoma, iris metastasis, iris lymphoma, trabecular meshwork melanoma, choroidal melanoma, choroidal metastasis, retinoblastoma, and medulloepithelioma. The mechanisms for glaucoma include solid tumor invasion into the angle, tumor seeding into the angle, angle closure, and iris neovascularization. Management of the tumor can lead to resolution of glaucoma. Management of the secondary glaucoma may involve medical therapy, transscleral cyclophotocoagulation, laser trabeculoplasty, and potentially antivascular endothelial growth factor therapy. Minimally invasive glaucoma surgery (MIGS) can be considered for eyes with treated, regressed posterior segment malignancies if there is no iris or ciliary body involvement. Importantly, avoidance of MIGS, filtering, or shunting surgery in eyes with active malignancies is emphasized. SUMMARY: Intraocular tumors can produce secondary glaucoma. Treatment of the primary tumor can sometimes resolve the glaucoma. Topical, oral, or laser therapies can be considered. Avoidance of MIGS, filtering, or shunting surgery is advised until the malignancy is completely regressed.

LC-SRM-Based Targeted Quantification of Urinary Protein Biomarkers.

Liquid chromatography (LC)-selected reaction monitoring (SRM) is a powerful protein quantification technique in terms of sensitivity, reproducibility, and multiplexing capability. LC-SRM can accurately measure the concentrations of surrogate proteotypic peptides for targeted proteins in complex biological samples by using their stable heavy isotope-labeled counterparts as internal standards. Herein, we describe a step-by-step protocol of the application of LC-SRM to quantify candidate protein biomarkers in human urine.

Quantification of mutant SPOP proteins in prostate cancer using mass spectrometry-based targeted proteomics.

BACKGROUND: Speckle-type POZ protein (SPOP) is an E3 ubiquitin ligase adaptor protein that functions as a potential tumor suppressor, and SPOP mutations have been identified in ~10% of human prostate cancers. However, it remains unclear if mutant SPOP proteins can be utilized as biomarkers for early detection, diagnosis, prognosis or targeted therapy of prostate cancer. Moreover, the SPOP mutation sites are distributed in a relatively short region with multiple lysine residues, posing significant challenges for bottom-up proteomics analysis of the SPOP mutations. METHODS: To address this issue, PRISM (high-pressure, high-resolution separations coupled with intelligent selection and multiplexing)-SRM (selected reaction monitoring) mass spectrometry assays have been developed for quantifying wild-type SPOP protein and 11 prostate cancer-derived SPOP mutations. RESULTS: Despite inherent limitations due to amino acid sequence constraints, all the PRISM-SRM assays developed using Arg-C digestion showed a linear dynamic range of at least two orders of magnitude, with limits of quantification ranged from 0.1 to 1 fmol/µg of total protein in the cell lysate. Applying these SRM assays to analyze HEK293T cells with and without expression of the three most frequent SPOP mutations in prostate cancer (Y87N, F102C or F133V) led to confident detection of all three SPOP mutations in corresponding positive cell lines but not in the negative cell lines. Expression of the F133V mutation and wild-type SPOP was at much lower levels compared to that of F102C and Y87N mutations; however, at present, it is unknown if this also affects the biological activity of the SPOP protein. CONCLUSIONS: In summary, PRISM-SRM enables multiplexed, isoform-specific detection of mutant SPOP proteins in cell lysates, providing significant potential in biomarker development for prostate cancer.

Mining the human urine proteome for monitoring renal transplant injury.

The human urinary proteome provides an assessment of kidney injury with specific biomarkers for different kidney injury phenotypes. In an effort to fully map and decipher changes in the urine proteome and peptidome after kidney transplantation, renal allograft biopsy matched urine samples were collected from 396 kidney transplant recipients. Centralized and blinded histology data from paired graft biopsies was used to classify urine samples into diagnostic categories of acute rejection, chronic allograft nephropathy, BK virus nephritis, and stable graft. A total of 245 urine samples were analyzed by liquid chromatography-mass spectrometry using isobaric Tags for Relative and Absolute Quantitation (iTRAQ) reagents. From a group of over 900 proteins identified in transplant injury, a set of 131 peptides were assessed by selected reaction monitoring for their significance in accurately segregating organ injury causation and pathology in an independent cohort of 151 urine samples. Ultimately, a minimal set of 35 proteins were identified for their ability to segregate the 3 major transplant injury clinical groups, comprising the final panel of 11 urinary peptides for acute rejection (93% area under the curve [AUC]), 12 urinary peptides for chronic allograft nephropathy (99% AUC), and 12 urinary peptides for BK virus nephritis (83% AUC). Thus, urinary proteome discovery and targeted validation can identify urine protein panels for rapid and noninvasive differentiation of different causes of kidney transplant injury, without the requirement of an invasive biopsy.

The clinical impact of recent advances in LC-MS for cancer biomarker discovery and verification.

Mass spectrometry (MS) -based proteomics has become an indispensable tool with broad applications in systems biology and biomedical research. With recent advances in liquid chromatography (LC) and MS instrumentation, LC-MS is making increasingly significant contributions to clinical applications, especially in the area of cancer biomarker discovery and verification. To overcome challenges associated with analyses of clinical samples (for example, a wide dynamic range of protein concentrations in bodily fluids and the need to perform high throughput and accurate quantification of candidate biomarker proteins), significant efforts have been devoted to improve the overall performance of LC-MS-based clinical proteomics platforms. Reviewed here are the recent advances in LC-MS and its applications in cancer biomarker discovery and quantification, along with the potentials, limitations and future perspectives.

Quantitative Profiling of Protein S-Glutathionylation Reveals Redox-Dependent Regulation of Macrophage Function during Nanoparticle-Induced Oxidative Stress.

Engineered nanoparticles (ENPs) are increasingly utilized for commercial and medical applications; thus, understanding their potential adverse effects is an important societal issue. Herein, we investigated protein S-glutathionylation (SSG) as an underlying regulatory mechanism by which ENPs may alter macrophage innate immune functions, using a quantitative redox proteomics approach for site-specific measurement of SSG modifications. Three high-volume production ENPs (SiO2, Fe3O4, and CoO) were selected as representatives which induce low, moderate, and high propensity, respectively, to stimulate cellular reactive oxygen species (ROS) and disrupt macrophage function. The SSG modifications identified highlighted a broad set of redox sensitive proteins and specific Cys residues which correlated well with the overall level of cellular redox stress and impairment of macrophage phagocytic function (CoO > Fe3O4 ≫ SiO2). Moreover, our data revealed pathway-specific differences in susceptibility to SSG between ENPs which induce moderate versus high levels of ROS. Pathways regulating protein translation and protein stability indicative of ER stress responses and proteins involved in phagocytosis were among the most sensitive to SSG in response to ENPs that induce subcytoxic levels of redox stress. At higher levels of redox stress, the pattern of SSG modifications displayed reduced specificity and a broader set pathways involving classical stress responses and mitochondrial energetics (e.g., glycolysis) associated with apoptotic mechanisms. An important role for SSG in regulation of macrophage innate immune function was also confirmed by RNA silencing of glutaredoxin, a major enzyme which reverses SSG modifications. Our results provide unique insights into the protein signatures and pathways that serve as ROS sensors and may facilitate cellular adaption to ENPs, versus intracellular targets of ENP-induced oxidative stress that are linked to irreversible cell outcomes.

Compensatory Islet Response to Insulin Resistance Revealed by Quantitative Proteomics.

Compensatory islet response is a distinct feature of the prediabetic insulin-resistant state in humans and rodents. To identify alterations in the islet proteome that characterize the adaptive response, we analyzed islets from 5 month old male control, high-fat diet fed (HFD), or obese ob/ob mice by LC-MS/MS and quantified ~1100 islet proteins (at least two peptides) with a false discovery rate < 1%. Significant alterations in abundance were observed for ~350 proteins among groups. The majority of alterations were common to both models, and the changes of a subset of ~40 proteins and 12 proteins were verified by targeted quantification using selected reaction monitoring and western blots, respectively. The insulin-resistant islets in both groups exhibited reduced expression of proteins controlling energy metabolism, oxidative phosphorylation, hormone processing, and secretory pathways. Conversely, an increased expression of molecules involved in protein synthesis and folding suggested effects in endoplasmic reticulum stress response, cell survival, and proliferation in both insulin-resistant models. In summary, we report a unique comparison of the islet proteome that is focused on the compensatory response in two insulin-resistant rodent models that are not overtly diabetic. These data provide a valuable resource of candidate proteins to the scientific community to undertake further studies aimed at enhancing ß-cell mass in patients with diabetes. The data are available via the MassIVE repository, under accession no. MSV000079093.

A practical Java tool for small-molecule compound appraisal.

BACKGROUND: The increased use of small-molecule compound screening by new users from a variety of different academic backgrounds calls for adequate software to administer, appraise, analyse and exchange information obtained from screening experiments. While software and spreadsheet solutions exist, there is a need for software that can be easily deployed and is convenient to use. RESULTS: The Java application cApp addresses this need and aids in the handling and storage of information on small-molecule compounds. The software is intended for the appraisal of compounds with respect to their physico-chemical properties, analysis in relation to adherence to likeness rules as well as recognition of pan-assay interference components and cross-linking with identical entries in the PubChem Compound Database. Results are displayed in a tabular form in a graphical interface, but can also be written in an HTML or PDF format. The output of data in ASCII format allows for further processing of data using other suitable programs. Other features include similarity searches against user-provided compound libraries and the PubChem Compound Database, as well as compound clustering based on a MaxMin algorithm. CONCLUSIONS: cApp is a personal database solution for small-molecule compounds which can handle all major chemical formats. Being a standalone software, it has no other dependency than the Java virtual machine and is thus conveniently deployed. It streamlines the analysis of molecules with respect to physico-chemical properties and drug discovery criteria; cApp is distributed under the GNU Affero General Public License version 3 and available from http://www.structuralchemistry.org/pcsb/. To download cApp, users will be asked for their name, institution and email address. A detailed manual can also be downloaded from this site, and online tutorials are available at http://www.structuralchemistry.org/pcsb/capp.php.

Analysis of Physicochemical Properties for Drugs of Natural Origin.

The impact of time, therapy area, and route of administration on 13 physicochemical properties calculated for 664 drugs developed from a natural prototype was investigated. The mean values for the majority of properties sampled over five periods from pre-1900 to 2013 were found to change in a statistically significant manner. In contrast, lipophilicity and aromatic ring count remained relatively constant, suggesting that these parameters are the most important for successful prosecution of a natural product drug discovery program if the route of administration is not focused exclusively on oral availability. An examination by therapy area revealed that anti-infective agents had the most differences in physicochemical property profiles compared with other areas, particularly with respect to lipophilicity. However, when this group was removed, the variation between the mean values for lipophilicity and aromatic ring count across the remaining therapy areas was again found not to change in a meaningful manner, further highlighting the importance of these two parameters. The vast majority of drugs with a natural progenitor were formulated for either oral and/or injectable administration. Injectables were, on average, larger and more polar than drugs developed for oral, topical, and inhalation routes.

Analytical platform evaluation for quantification of ERG in prostate cancer using protein and mRNA detection methods.

BACKGROUND: The established methods for detecting prostate cancer (CaP) are based on tests using PSA (blood), PCA3 (urine), and AMACR (tissue) as biomarkers in patient samples. The demonstration of ERG oncoprotein overexpression due to gene fusion in CaP has thus provided ERG as an additional biomarker. Based on this, we hypothesized that ERG protein quantification methods can be of use in the diagnosis of prostate cancer. METHODS: An antibody-free assay for ERG3 protein detection was developed based on PRISM (high-pressure high-resolution separations with intelligent selection and multiplexing)-SRM (selected reaction monitoring) mass spectrometry. We utilized TMPRSS2-ERG positive VCaP and TMPRSS2-ERG negative LNCaP cells to simulate three different sample types (cells, tissue, and post-DRE urine sediment). Enzyme-linked immunosorbent assay (ELISA), western blot, NanoString, and qRT-PCR were also used in the analysis of these samples. RESULTS: Recombinant ERG3 protein spiked into LNCaP cell lysates could be detected at levels as low as 20 pg by PRISM-SRM analysis. The sensitivity of the PRISM-SRM assay was approximately 10,000 VCaP cells in a mixed cell population model of VCaP and LNCaP cells. Interestingly, ERG protein could be detected in as few as 600 VCaP cells spiked into female urine. The sensitivity of the in-house ELISA was similar to the PRISM-SRM assay, with detection of 30 pg of purified recombinant ERG3 protein and 10,000 VCaP cells. On the other hand, qRT-PCR exhibited a higher sensitivity, as TMPRSS2-ERG transcripts were detected in as few as 100 VCaP cells, in comparison to NanoString methodologies which detected ERG from 10,000 cells. CONCLUSIONS: Based on this data, we propose that the detection of both ERG transcriptional products with RNA-based assays, as well as protein products of ERG using PRISM-SRM assays, may be of clinical value in developing diagnostic and prognostic assays for prostate cancer given their sensitivity, specificity, and reproducibility.

Sensitive targeted quantification of ERK phosphorylation dynamics and stoichiometry in human cells without affinity enrichment.

Targeted mass spectrometry is a promising technology for site-specific quantification of posttranslational modifications. However, a major constraint is the limited sensitivity for quantifying low-abundance PTMs, requiring the use of affinity reagents for enrichment. Herein, we demonstrate the direct site-specific quantification of ERK phosphorylation isoforms (pT, pY, pTpY) and their relative stoichiometry using a sensitive targeted MS approach termed high-pressure, high-resolution separations with intelligent selection, and multiplexing (PRISM). PRISM provides effective enrichment of target peptides into a given fraction from complex mixture, followed by selected reaction monitoring quantification. Direct quantification of ERK phosphorylation in human mammary epithelial cells (HMEC) was demonstrated from as little as 25 µg tryptic peptides from whole cell lysates. Compared to immobilized metal-ion affinity chromatography, PRISM provided ∼10-fold higher signal intensities, presumably due to the better peptide recovery of PRISM. This approach was applied to quantify ERK phosphorylation dynamics in HMEC treated by different doses of epidermal growth factor at both the peak activation (10 min) and steady state (2 h). The maximal ERK activation was observed with 0.3 and 3 ng/mL doses for 10 min and 2 h time points, respectively. The dose-response profiles of individual phosphorylated isoforms showed that singly phosphorylated pT-ERK never increases significantly, while the increase of pY-ERK paralleled that of pTpY-ERK. This data supports for a processive, rather than distributed model of ERK phosphorylation. The PRISM-SRM quantification of protein phosphorylation illustrates the potential for simultaneous quantification of multiple PTMs.