SMAC Mimetic/IAP Inhibitor Birinapant Enhances Radiosensitivity of Glioblastoma Multiforme.

Birinapant is a novel SMAC peptidomimetic molecule in clinical development. It suppresses the inhibitor of apoptosis proteins (IAPs) and promotes cytochrome-C/Apaf-1/caspase-9 activation to induce effective apoptosis. Because IAP inhibition has been shown to enhance the sensitivity of cancer cells to radiation, we investigated the role of birinapant in radiosensitization of glioblastoma cells in vitro and in vivo. Two glioblastoma cell lines, U-251 and U-87, were used to analyze radiosensitization in vitro with 7-AAD cell death/apoptosis and clonogenic assays. Subcutaneous flank (U-251 and U-87) and intracranial orthotopic (U-251) xenografts in nude mice were used to evaluate radiosensitization in vivo. TNF-α levels in media and serum were measured using electrochemiluminescence. Radiosensitization in vitro was more prominent for U-251 cells than for U-87 cells. In vivo, in both tumor models, significant tumor growth delay was observed with combination treatment compared to radiation alone. There was a survival benefit with combination treatment in the orthotopic U-251 model. TNF-α levels in media correlated directly with radiation dose in vitro. These findings show that birinapant can enhance the radiosensitivity of glioblastoma cell lines in cell-based assays and tumor models via radiation-induced TNF-α. Further study into the use of birinapant with radiation therapy is warranted.

Using Lean Six Sigma to improve rates of day of surgery admission in a national thoracic surgery department.

OBJECTIVE: The aim of this study is to improve rates of day of surgery admission (DOSA) for all suitable elective thoracic surgery patients. DESIGN: Lean Six Sigma (LSS) methods were used to enable improvements to both the operational process and the organizational working of the department over a period of 19 months. SETTING: A national thoracic surgery department in a large teaching hospital in Ireland. PARTICIPANTS: Thoracic surgery staff, patients and quality improvement staff at the hospital. INTERVENTION(S): LSS methods were employed to identify and remove the non-value-add in the patient's journey and achieve higher levels of DOSA. A pre-surgery checklist and Thoracic Planning Meeting were introduced to support a multidisciplinary approach to enhanced recovery after surgery (ERAS), reduce rework, improve list efficiency and optimize bed management. MAIN OUTCOME MEASURE(S): To achieve DOSA for all suitable elective thoracic surgery patients in line with the National Key Performance Indicator of 75%. A secondary outcome would be to further decrease overall length of stay by 1 day. RESULTS: Over a 19 month period, DOSA has increased from 10 to 75%. Duplication of preoperative tests reduced from 83 to <2%. Staff and patient surveys show increased satisfaction and improved understanding of ERAS. CONCLUSIONS: Using LSS methods to improve both operational process efficiency and organizational clinical processes led to the successful achievement of increasing rates of DOSA in line with national targets.

Caution Needed: Molecular Diagnosis of Pediatric Group A Streptococcal Pharyngitis.

Among throat swabs processed in the microbiology laboratory as back-up for negative rapid antigen detection test results, we found a significant increase in the proportion that tested positive for group A streptococci after changing from throat culture to a molecular test.For group A streptococcus testing, our hospital laboratory replaced throat cultures with a stand-alone molecular diagnostic test that takes no more than 1 hour to perform. The prevalence of positive laboratory test results increased significantly (P < .0001) after the change to molecular testing, probably because of the extreme sensitivity of the molecular test.

Impact of a Healthcare Provider Educational Intervention on Frequency of Clostridium difficile Polymerase Chain Reaction Testing in Children: A Segmented Regression Analysis.

BACKGROUND.: Although Clostridium difficile infections (CDIs) are increasingly diagnosed in children, many children diagnosed with CDI lack classic risk factors. Frequent use of highly sensitive tcdB polymerase chain reaction (PCR) testing in low-risk patients leads to CDI misdiagnosis and unnecessary CDI antibiotic use in children with C difficile carriage. METHODS.: For this quasi-experimental study, we developed and implemented an educational intervention (EI) to inform healthcare providers (HCPs) about tcdB PCR test limitations. We provided HCP didactic education and built an electronic notification into the tcdB PCR test order that describes scenarios in which carriage is more likely than CDI. Segmented regression analysis assessed changes in level (ie, overall rates) and trend of C difficile testing rate ([TR] number of tests performed per 1000 patient encounters) and test positivity rate ([PR] number of positive tests per 1000 patient encounters) between the pre- (August 2009-August 2013) and postintervention (February 2014-July 2015) periods. RESULTS.: Hospital-wide, absolute TR reduction was 0.71 (P[level] = .0067; P[trend] = .0042) and absolute PR reduction was 0.14 (P[level] = .22; P[trend] = .018). In the outpatient setting, absolute TR reduction was 0.30 (P[level] = .0015; P[trend] < .001) and absolute PR reduction was 0.09 (P[level] = .0069; P[trend] = .046). The incidence density of healthcare facility-associated CDI did not significantly change after the EI. The EI was associated with avoidance of 574 tests and 113 positive tests (and subsequent antibiotic courses) during the postintervention period, which saved approximately $250 000 in patient charges related to CDI testing and treatment. CONCLUSIONS.: Healthcare provider education can cost-effectively reduce the frequency of C difficile testing and CDI misdiagnosis by improving test utilization among low-risk children.

Rapid identification of pathogens from pediatric blood cultures by use of the FilmArray blood culture identification panel.

The performance of the FilmArray blood culture identification (BCID) panel has been studied in adult patients. We describe here an evaluation of this assay for the rapid identification of pathogens in Bactec Peds Plus/F and Bactec standard anaerobic/F bottles that contained blood samples from pediatric patients at a tertiary care children's hospital.

Detection of Streptococcus pyogenes by use of Illumigene group A Streptococcus assay.

The performance of the Illumigene group A Streptococcus assay was evaluated by comparing it to culture using 437 consecutive throat swabs. The Illumigene assay was also directly compared to PCR with 161 samples. This Illumigene assay is rapid and easy to perform. The assay also has high sensitivity (100%) compared to culture or PCR and high specificity (99.2%) compared to PCR. A total of 8.8% of the isolates were erythromycin resistant, and 6.9% were clindamycin resistant.

Molecular profiling indicates orthotopic xenograft of glioma cell lines simulate a subclass of human glioblastoma.

Cell line models have been widely used to investigate glioblastoma multiforme (GBM) pathobiology and in the development of targeted therapies. However, GBM tumours are molecularly heterogeneous and how cell lines can best model that diversity is unknown. In this report, we investigated gene expression profiles of three preclinical growth models of glioma cell lines, in vitro and in vivo as subcutaneous and intracerebral xenografts to examine which cell line model most resembles the clinical samples. Whole genome DNA microarrays were used to profile gene expression in a collection of 25 high-grade glioblastomas, and comparisons were made to profiles of cell lines under three different growth models. Hierarchical clustering revealed three molecular subtypes of the glioblastoma patient samples. Supervised learning algorithm, trained on glioma subtypes predicted the intracerebral cell line model with one glioma subtype (r = 0.68; 95% bootstrap CI -0.41, 0.46). Survival analysis of enriched gene sets (P < 0.05) revealed 19 biological categories (146 genes) belonging to neuronal, signal transduction, apoptosis- and glutamate-mediated neurotransmitter activation signals that are associated with poor prognosis in this glioma subclass. We validated the expression profiles of these gene categories in an independent cohort of patients from 'The Cancer Genome Atlas' project (r = 0.62, 95% bootstrap CI: -0.42, 0.43). We then used these data to select and inhibit a novel target (glutamate receptor) and showed that LY341595, a glutamate receptor specific antagonist, could prolong survival in intracerebral tumour-implanted mice in combination with irradiation, providing an in vivo cell line system of preclinical studies.

Septal elicitation of hippocampal theta rhythm did not repair cognitive and emotional deficits resulting from vestibular lesions.

Bilateral vestibular lesions cause atrophy of the hippocampus in humans and subsequent deficits in spatial memory and the processing of emotional stimuli in both rats and humans. Vestibular lesions also impair hippocampal theta rhythm in rats. The aim of the present study was to investigate whether restoring theta rhythm to the hippocampus of a rat, via stimulation of the medial septum, would repair the deficits caused by vestibular lesions. It was hypothesized that the restoration of theta would repair the deficits and the vestibular rats would exhibit behavior and EEG similar to that of the sham rats. Rats were given either sham surgery or bilateral vestibular deafferentation (BVD) followed in a later operation by electrode implants. Half of the lesioned rats received stimulation. Subjects were tested in open field, elevated T-maze and spatial nonmatching to sample tests. BVD caused a deficit in hippocampal theta rhythm. Stimulation restored theta power at a higher frequency in the vestibular-lesioned rats, however, the stimulation did not repair the cognitive and emotional deficits caused by the lesions. It was concluded that stimulation, at least in the form used here, would not be a viable treatment option for vestibular damaged humans.

A prospective study of an aggressive warfarin dosing algorithm to reach and maintain INR 2 to 3 after heart valve surgery.

Good anticoagulation control in patients during the first months after heart valve surgery is important to prevent thrombotic complications. This is difficult to achieve, partly because the sensitivity to warfarin decreases progressively during approximately three months after valve surgery. A recently developed, simple but aggressive algorithm might improve anticoagulation control in this patient group. It was the objective of this study to evaluate the level of anticoagulation control when a specialised anticoagulation clinic changed from empirical dosing to the use of this new algorithm. In a before-and-after design, a cohort of consecutive patients managed with a new, aggressive dosing algorithm ('Algorithm cohort') was compared to a 'Retrospective cohort' of similar patients dosed empirically. Primary endpoint was individual time in therapeutic range (ITTR) during the first three months of warfarin therapy. Secondary endpoints included proportion of extreme International Normalised Ratio (INR) results, thrombotic and bleeding complications. Ninety-eight patients were included in the Algorithm cohort, 94 of whom were warfarin-naïve. Two hundred patients were included in the Retrospective cohort. Mean ITTR was 60.1% in the Algorithm cohort versus 48.7% in the Retrospective cohort (p <0.001). Patients in the Algorithm cohort spent 0.5% of time at an INR >5, versus 0.2 % in the Retrospective cohort. There was no major bleeding in either cohort; one patient in each cohort had a thrombotic complication. We demonstrate an improvement of the level of anticoagulation control with the use of a condition-specific, aggressive algorithm, as compared to standard dosing, in patients after heart valve surgery.

Vorinostat enhances the radiosensitivity of a breast cancer brain metastatic cell line grown in vitro and as intracranial xenografts.

Vorinostat (suberoylanilide hydroxamic acid), a histone deacetylase inhibitor, is currently undergoing clinical evaluation as therapy for cancer. We investigated the effects of vorinostat on tumor cell radiosensitivity in a breast cancer brain metastasis model using MDA-MB-231-BR cells. In vitro radiosensitivity was evaluated using clonogenic assay. Cell cycle distribution and apoptosis was measured using flow cytometry. DNA damage and repair was evaluated using gammaH2AX. Mitotic catastrophe was measured by immunostaining. Growth delay and intracranial xenograft models were used to evaluate the in vivo tumor radiosensitivity. Cells exposed to vorinostat for 16 hours before and maintained in the medium after irradiation had an increase in radiosensitivity with a dose enhancement factor of 1.57. gammaH2AX, as an indicator of double-strand breaks, had significantly more foci per cell in the vorinostat plus irradiation group. Mitotic catastrophe, measured at 72 hours, was significantly increased in cells receiving vorinostat plus irradiation. Irradiation of s.c. MDA-MB-231-BR tumors in mice treated with vorinostat resulted in an increase in radiation-induced tumor growth delay. Most importantly, animals with intracranial tumor implants lived the longest after combination treatment. These results indicate that vorinostat enhances tumor cell radiosensitivity in vitro and in vivo. There was a greater than additive improvement in survival in our intracranial model. Combining vorinostat with radiation may be a potential treatment option for patients with breast cancer who develop brain metastases.

In vitro and in vivo radiosensitization with AZD6244 (ARRY-142886), an inhibitor of mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 kinase.

PURPOSE: The mitogen-activated protein (MAP) kinase pathway is important for cell proliferation, survival, and differentiation, and is frequently up-regulated in cancers. The MAP kinase pathway is also activated after exposure to ionizing radiation. We investigated the effects of AZD6244 (ARRY-142886), an inhibitor of MAP kinase/extracellular signal-regulated kinase 1/2, on radiation response. EXPERIMENTAL DESIGN: The effects of AZD6244 on the in vitro radiosensitivity of human cancer cell lines (A549, MiaPaCa2, and DU145) were evaluated using clonogenic assays. DNA damage repair was evaluated using gammaH2AX, and mitotic catastrophe was measured using nuclear fragmentation. Cell cycle effects were measured with flow cytometry. Growth delay was used to evaluate the effects of AZD6244 on in vivo tumor radiosensitivity. RESULTS: Exposure of each cell line to AZD6244 before irradiation resulted in an increase in radiosensitivity with dose enhancement factors at a surviving fraction of 0.1, ranging from 1.16 to 2.0. No effects of AZD6244 on radiation-induced apoptosis or persistence of gammaH2AX foci after irradiation were detected. Cells treated with AZD6244 had an increased mitotic index and decreased Chk1 phosphorylation at 1 and 2 hours after irradiation. Mitotic catastrophe was increased in cells receiving AZD6244 and irradiation compared with the single treatments. In vivo studies revealed that AZD6244 administration to mice bearing A549 tumor xenografts resulted in a greater than additive increase in radiation-induced tumor growth delay (dose enhancement factor of 3.38). CONCLUSIONS: These results indicate that AZD6244 can enhance tumor cell radiosensitivity in vitro and in vivo and suggest that this effect involves an increase in mitotic catastrophe.

In vitro and in vivo radiosensitization of glioblastoma cells by the poly (ADP-ribose) polymerase inhibitor E7016.

PURPOSE: Poly (ADP-ribose) polymerase (PARP) inhibitors are undergoing clinical evaluation for cancer therapy. Because PARP inhibition has been shown to enhance tumor cell sensitivity to radiation, we investigated the in vitro and in vivo effects of the novel PARP inhibitor E7016. EXPERIMENTAL DESIGN: The effect of E7016 on the in vitro radiosensitivity of tumor cell lines was evaluated using clonogenic survival. DNA damage and repair were measured using gammaH2AX foci and neutral comet assay. Mitotic catastrophe was determined by immunostaining. Tumor growth delay was evaluated in mice for the effect of E7016 on in vivo (U251) tumor radiosensitivity. RESULTS: Cell lines exposed to E7016 preirradiation yielded an increase in radiosensitivity with dose enhancement factors at a surviving fraction of 0.1 from 1.4 to 1.7. To assess DNA double-strand breaks repair, gammaH2AX measured at 24 hours postirradiation had significantly more foci per cell in the E7016/irradiation group versus irradiation alone. Neutral comet assay further suggested unrepaired double-strand breaks with significantly greater DNA damage at 6 hours postirradiation in the combination group versus irradiation alone. Mitotic catastrophe staining revealed a significantly greater number of cells staining positive at 24 hours postirradiation in the combination group. In vivo, mice treated with E7016/irradiation/temozolomide had an additional growth delay of six days compared with the combination of temozolomide and irradiation. CONCLUSIONS: These results indicate that E7016 can enhance tumor cell radiosensitivity in vitro and in vivo through the inhibition of DNA repair. Moreover, enhanced growth delay with the addition of E7016 to temozolomide and radiotherapy in a glioma mouse model suggests a potential role for this drug in the treatment of glioblastoma multiforme.

In vitro and in vivo radiosensitization induced by the DNA methylating agent temozolomide.

PURPOSE: Temozolomide, a DNA methylating agent, is currently undergoing clinical evaluation for cancer therapy. Because temozolomide has been shown to increase survival rates of patients with malignant gliomas when given combined with radiation, and there is conflicting preclinical data concerning the radiosensitizing effects of temozolomide, we further investigated the possible temozolomide-induced enhancement of radiosensitivity. EXPERIMENTAL DESIGN: The effects of temozolomide on the in vitro radiosensitivity of U251 (a human glioma) and MDA-MB231BR (a brain-seeking variant of a human breast tumor) cell lines was evaluated using clonogenic assay. DNA damage and repair were evaluated using phosphorylated histone H2AX (gammaH2AX), and mitotic catastrophe was measured using nuclear fragmentation. Growth delay was used to evaluate the effects of temozolomide on in vivo (U251) tumor radiosensitivity. RESULTS: Exposure of each cell line to temozolomide for 1 h before irradiation resulted in an increase in radiosensitivity with dose enhancement factors at a surviving fraction of 0.1 ranging from 1.30 to 1.32. Temozolomide had no effect on radiation-induced apoptosis or on the activation of the G(2) cell cycle checkpoint. As a measure of DNA double strand breaks, gammaH2AX foci were determined as a function of time after the temozolomide + irradiation combination. The number of gammaH2AX foci per cell was significantly greater at 24 h after the combined modality compared with the individual treatments. Mitotic catastrophe, measured at 72 h, was also significantly increased in cells receiving the temozolomide + irradiation combination compared with the single treatments. In vivo studies revealed that temozolomide administration to mice bearing U251 tumor xenografts resulted in a greater than additive increase in radiation-induced tumor growth delay with a dose enhancement factor of 2.8. CONCLUSIONS: These results indicate that temozolomide can enhance tumor cell radiosensitivity in vitro and in vivo and suggest that this effect involves an inhibition of DNA repair leading to an increase in mitotic catastrophe.

Inhibition of Akt by the alkylphospholipid perifosine does not enhance the radiosensitivity of human glioma cells.

Akt has been implicated as a molecular determinant of cellular radiosensitivity. Because it is often constitutively activated or overexpressed in malignant gliomas, it has been suggested as a target for brain tumor radiosensitization. To evaluate the role of Akt in glioma radioresponse, we have determined the effects of perifosine, a clinically relevant alkylphospholipid that inhibits Akt activation, on the radiosensitivity of three human glioma cell lines (U87, U251, and LN229). Each of the glioma cell lines expressed clearly detectable levels of phosphorylated Akt indicative of constitutive Akt activity. Exposure to a perifosine concentration that reduced survival by approximately 50% significantly reduced the level of phosphorylated Akt as well as Akt activity. Cell survival analysis using a clonogenic assay, however, revealed that this Akt-inhibiting perifosine treatment did not enhance the radiosensitivity of the glioma cell lines. This evaluation was then extended to an in vivo model using U251 xenografts. Perifosine delivered to mice bearing U251 xenografts substantially reduced tumor phosphorylated Akt levels and inhibited tumor growth rate. However, the combination of perifosine and radiation resulted in a less than additive increase in tumor growth delay. Thus, in vitro and in vivo data indicate that the perifosine-mediated decrease in Akt activity does not enhance the radiosensitivity of three genetically disparate glioma cell lines. These results suggest that, although Akt may influence the radiosensitivity of other tumor types, it does not seem to be a target for glioma cell radiosensitization.

In vitro and in vivo radiosensitization induced by the ribonucleotide reductase inhibitor Triapine (3-aminopyridine-2-carboxaldehyde-thiosemicarbazone).

PURPOSE: Because ribonucleotide reductase (RR) plays a role in DNA repair, it may serve as a molecular target for radiosensitization. Unlike previously investigated RR inhibitors, Triapine potently inhibits both RR holoenzymes. Therefore, the effects of Triapine on tumor cell radiosensitivity were investigated. EXPERIMENTAL DESIGN: The effects of Triapine on the in vitro radiosensitivity of three human tumor cell lines and one normal cell line were evaluated using a clonogenic assay. Growth delay was used to evaluate the effects of Triapine on in vivo tumor radiosensitivity. The levels of the RR subunits were determined using immunoblot analysis and DNA damage and repair were evaluated using gammaH2AX foci. RESULTS: Exposure of the tumor cell lines to Triapine before or immediately after irradiation resulted in an increase in radiosensitivity. In contrast, Triapine enhanced the radiosensitivity of the normal fibroblast cell line only when the exposure was before irradiation. There were no consistent differences between cell lines with respect to the expression of the RR subunits. Whereas Triapine had no effect on radiation-induced gammaH2AX foci at 1 hour, the number of gammaH2AX foci per cell was significantly greater in the Triapine-treated cells at 24 hours after irradiation, suggesting the presence of unrepaired DNA damage. Triapine administration to mice bearing tumor xenografts immediately after irradiation resulted in a greater than additive increase in radiation-induced tumor growth delay. CONCLUSIONS: These results indicate that Triapine can enhance tumor cell radiosensitivity in vitro and in vivo and suggest that this effect involves an inhibition of DNA repair.

Inactive nurses: a source for alleviating the nursing shortage?

OBJECTIVE: This study seeks to provide an understanding of why inactive registered nurses chose to become inactive and what they would require for them to return to nursing. BACKGROUND: In 2000, a shortage of 110,000 (6%) registered nurses existed in the United States. If the current trends continue, the shortage is projected to grow to 29% by 2020. One solution to the nursing shortage may be attracting nurses with inactive licenses back into employment. METHODS: This study used a quantitative, cross-sectional survey design. Data analysis included descriptive and inferential statistics. RESULTS: Inactive nurses (N = 428) younger than 60 years in 1 Southern state were surveyed. A major portion (27.6%) of these nurses left nursing because of a conflict between parenting duties and scheduling requirements (13.5%) at work and indicated that they would return to nursing if given the opportunity to work part-time, especially if shifts were flexible and shorter. CONCLUSION: Although the group of registered nurses younger than 60 years do not constitute a large percentage of nurses in this country, they are a potential source of alleviating, to some extent, the critical nursing shortage. Employers can encourage many of these nurses to return to work by providing more flexible work schedules, including part-time and shorter shifts, as well as decreased workloads.

Enhancement of in vitro and in vivo tumor cell radiosensitivity by the DNA methylation inhibitor zebularine.

Aberrant DNA hypermethylation is a frequent finding in tumor cells, which has suggested that inhibition of DNA methylation may be an effective cancer treatment strategy. Because DNA methylation affects gene expression and chromatin structure, parameters considered to influence radioresponse, we investigated the effects of the DNA methylation inhibitor zebularine on the radiosensitivity of human tumor cells. Three human tumor cell lines were used in this study (MiaPaCa, DU145, and U251) and the methylation status of three genes frequently hypermethylated in tumor cells (RASSF1A, HIC-1, and 14-3-3sigma) was determined as a function of zebularine exposure. Zebularine resulted in DNA demethylation in a time-dependent manner, with the maximum loss of methylation detected by 48 hours. Treatment of cells with zebularine for 48 hours also resulted in an increase in radiosensitivity with dose enhancement factors of >1.5. As a measure of radiation-induced DNA damage, gammaH2AX expression was determined. Whereas zebularine had no effect on radiation-induced gammaH2AX foci at 1 hour, the number of gammaH2AX foci per cell was significantly greater in the zebularine-treated cells at 24 hours after irradiation, suggesting the presence of unrepaired DNA damage. Zebularine administration to mice reactivated gene expression in U251 xenografts; irradiation of U251 tumors in mice treated with zebularine resulted in an increase in radiation-induced tumor growth delay. These results indicate that zebularine can enhance tumor cell radiosensitivity in vitro and in vivo and suggest that this effect may involve an inhibition of DNA repair.

Enhanced tumor cell radiosensitivity and abrogation of G2 and S phase arrest by the Hsp90 inhibitor 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin.

PURPOSE: Because of the potential for affecting multiple signaling pathways, inhibition of Hsp90 may provide a strategy for enhancing tumor cell radiosensitivity. Therefore, we have investigated the effects of the orally bioavailable Hsp90 inhibitor 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG) on the radiosensitivity of human tumor cells in vitro and grown as tumor xenografts. EXPERIMENTAL DESIGN: The effect of 17-DMAG on the levels of three proteins (Raf-1, ErbB2, and Akt) previously implicated in the regulation of radiosensitivity was determined in three human solid tumor cell lines. A clonogenic assay was then used to evaluate cell survival after exposure to 17-DMAG followed by irradiation. For mechanistic insight, the G(2)- and S-phase checkpoints were evaluated in 17-DMAG-treated cells. Finally, the effect of in vivo administration of 17-DMAG in combination with radiation on the growth rate of xenograft tumors was determined. RESULTS: 17-DMAG exposure reduced the levels of the three radiosensitivity-associated proteins in a cell line-specific manner with ErbB2 being the most susceptible. Corresponding concentrations of 17-DMAG enhanced the radiosensitivity of each of the tumor cell lines. This sensitization seemed to be the result of a 17-DMAG-mediated abrogation of the G(2)- and S-phase cell cycle checkpoints. The oral administration of 17-DMAG to mice bearing tumor xenografts followed by irradiation resulted in a greater than additive increase in tumor growth delay. CONCLUSIONS: These data indicate that 17-DMAG enhances the in vitro and in vivo radiosensitivity of human tumor cells. The mechanism responsible seems to involve the abrogation of radiation-induced G(2)- and S-phase arrest.

Estimation of human corneal oxygen consumption by noninvasive measurement of tear oxygen tension while wearing hydrogel lenses.

PURPOSE: To devise a procedure for direct estimation of corneal oxygen consumption in human subjects. METHODS: Tear oxygen tension (PO2) was measured at the posterior surface of two standard hydrogel contact lenses (38% water, 0.2 and 0.06 mm thick, oxygen transmissibility [Dk/t] = 4.2 and 14 x 10(-9) cm x mL O2/mL x sec x torr) and one newly available hydrogel-silicone polymer lens (Dk/t = 99 x 10(-9)). The oxygen-sensitive dye, Pd-meso-tetra (4-carboxyphenyl) porphine, bound to bovine serum albumin, was incubated with the lenses overnight. The lenses, coated with the protein-dye complex, were placed on four subjects' eyes, and tear PO2 was measured in the open eye and after 5 minutes of eye closure, using a time-domain phosphorescence measurement system. Given the tear PO2, lens Dk/t, and corneal thickness, oxygen consumption (Q(C), in mL O2/cm(3) x sec) could be calculated from established oxygen diffusion models. RESULTS: Protein-dye complex bound to the lens surface enabled reporting of tear PO2 for long periods. As expected, estimated tear PO2 was higher in subjects wearing lenses with higher Dk/t: mean open-eye PO2 = 30.6 +/- 3.1 and 8.1 +/- 1.3 torr for the thin and thick hydrogel lenses, respectively, and 97.6 +/- 22.9 torr for the hydrogel-silicone lens. After 5 minutes of eye closure, tear PO2 was significantly reduced and reached a new steady state in approximately 20 seconds after eye opening. Fitting a single exponential model to the data and extrapolating to t = 0 provided an estimate of PO2 under the closed lid for the thin hydrogel (PO2 = 7 +/- 2.3 torr) and the hydrogel-silicone lens (PO2 = 22.6 +/- 4 torr). After 5 minutes of eye closure with the thick hydrogel lens, tear PO2 remained constant for approximately 10 seconds after eye opening (mean PO2 = 3.9 +/- 0.7) before increasing to a new steady state. This delay could be accounted for by the time needed for oxygen to diffuse to the posterior surface of the lens. Calculated Q(C) ranged from 2.2 x 10(-4) to 3.7 x 10(-6) mL O2/cm(3) x sec) at the highest and lowest PO2s, respectively, and is comparable to previous in vitro and in vivo estimates. CONCLUSIONS: Tear PO2 behind hydrogel lenses can be measured in human subjects using the phosphorescence of the porphyrin-protein complex bound to the lens surface. The method is simple, fast, reliable, and noninvasive, allowing quick and direct estimates of Q(C). In addition to contact lens wear, this method should be useful for examining the effects of disease, surgery, or topical drugs on the corneal oxygen consumption rate.