Evaluating near-infrared photoimmunotherapy for targeting fibroblast activation protein-α expressing cells in vitro and in vivo

Photoimmunotherapy (PIT), carried out using an Ab conjugated to the near infrared dye IRDye700DX, is achieving significant success in target-specific elimination of cells. Fibroblast activation protein alpha (FAP-α) is an important target in cancer because of its expression by cancer-associated fibroblasts (CAFs) as well as by some cancer cells. Cancer-associated fibroblasts that express FAP-α have protumorigenic and immune suppressive functions. Using immunohistochemistry of human breast cancer tissue microarrays, we identified an increase of FAP-α⁺  CAFs in invasive breast cancer tissue compared to adjacent normal tissue. We found FAP-α expression increased in fibroblasts cocultured with cancer cells. In proof-of-principle studies, we engineered human FAP-α overexpressing MDA-MB-231 and HT-1080 cancer cells and murine FAP-α overexpressing NIH-3T3 fibroblasts to evaluate several anti-FAP-α Abs and selected AF3715 based on its high binding affinity with both human and mouse FAP-α. After conjugation of AF3715 with the phthalocyanine dye IR700, the resultant Ab conjugate, FAP-α-IR700, was evaluated in cells and tumors for its specificity and effectiveness in eliminating FAP-α expressing cell populations with PIT. Fibroblast activation protein-α-IR700-PIT resulted in effective FAP-α-specific cell killing in the engineered cancer cells and in two patient-derived CAFs in a dose-dependent manner. Following an intravenous injection, FAP-α-IR700 retention was three-fold higher than IgG-IR700 in FAP-α overexpressing tumors, and two-fold higher compared to WT tumors. Fibroblast activation protein-α-IR700-PIT resulted in significant growth inhibition of tumors derived from FAP-α overexpressing human cancer cells. A reduction of endogenous FAP-α⁺  murine CAFs was identified at 7 days after FAP-α-IR700-PIT. Fibroblast activation protein-α-targeted near infrared PIT presents a promising strategy to eliminate FAP-α⁺  CAFs.

Functional roles of FAP-α in metabolism, migration and invasion of human cancer cells

Fibroblast activation protein-α (FAP-α) is a transmembrane serine protease that is attracting significant interest as it is expressed by a subgroup of cancer-associated fibroblasts that play a role in immune suppression and cancer metastasis. FAP-α is also expressed by some cancer cells, such as melanoma, colorectal and breast cancer cells. Triple negative breast cancer (TNBC) is an aggressive cancer that urgently requires identification of novel targets for therapy. To expand our understanding of the functional roles of FAP-α in TNBC we engineered a human TNBC cell line, MDA-MB-231, to stably overexpress FAP-α and characterized changes in metabolism by ¹H magnetic resonance spectroscopy, cell proliferation, migration characterized by wound healing, and invasion. FAP-α overexpression resulted in significant alterations in myoinositol, choline metabolites, creatine, and taurine, as well as a significant increase of migration and invasion, although proliferation remained unaltered. The increase of migration and invasion are consistent with the known activities of FAP-α as an exopeptidase and endopeptidase/gelatinase/collagenase in tissue remodeling and repair, and in cell migration. We additionally determined the effects of FAP-α overexpression on the human fibrosarcoma HT1080 cell line that showed increased migration, accompanied by limited changes in metabolism that identified the dependency of the metabolic changes on cell type. These metabolic data identify a previously unknown role of FAP-α in modifying cancer cell metabolism in the TNBC cell line studied here that may provide new insights into its functional roles in cancer progression.

Phototheranostics of Splenic Myeloid-Derived Suppressor Cells and Its Impact on Spleen Metabolism in Tumor-Bearing Mice

(1) Background: MDSCs play an active role in the immune surveillance escape of cancer cells. Because MDSCs in mice are CD11b⁺Gr1⁺, near-infrared photoimmunotherapy (NIR-PIT) using the NIR dye IR700 conjugated to an MDSC-binding antibody provides an opportunity for targeted elimination of MDSCs. (2) Methods: The efficacy of Gr1-IR700-mediated NIR-PIT was evaluated in vitro using magnetically separated CD11b⁺Gr1⁺ MDSCs from spleens of 4T1-luc tumor-bearing (TB) mice. For in vivo evaluation, spleens of Gr1-IR700-injected 4T1-luc TB mice were irradiated with NIR light, and splenocyte viability was determined using CCK-8 assays. Metabolic profiling of NIR-PIT-irradiated spleens was performed using ¹H MRS. (3) Results: Flow cytometric analysis confirmed a ten-fold increase in splenic MDSCs in 4T1-luc TB mice. Gr1-IR700-mediated NIR-PIT eliminated tumor-induced splenic MDSCs in culture. Ex vivo fluorescence imaging revealed an 8- and 9-fold increase in mean fluorescence intensity (MFI) in the spleen and lungs of Gr1-IR700-injected compared to IgG-IR700-injected TB mice. Splenocytes from Gr1-IR700-injected TB mice exposed in vivo to NIR-PIT demonstrated significantly lower viability compared to no light exposure or untreated control groups. Significant metabolic changes were observed in spleens following NIR-PIT. (4) Conclusions: Our data confirm the ability of NIR-PIT to eliminate splenic MDSCs, identifying its potential to eliminate MDSCs in tumors to reduce immune suppression. The metabolic changes observed may identify potential biomarkers of splenic MDSC depletion as well as potential metabolic targets of MDSCs.

Abstract 4920: FAP-α overexpression increases cancer cell migration

Fibroblast activation protein-α (FAP-α) is attracting increasing interest because of its role in immune suppression and cancer metastasis. To understand the role of FAP-α in cancer cells we engineered triple negative human breast cancer MDA-MB-231 cells and fibrosarcoma HT1080 cells to stably overexpress FAP-α and compared cell migration of parental and FAP-α overexpressing cells using wound healing analysis. We observed a significant increase of migration with FAP-α overexpression in MDA-MB-231 cells. HT1080 cells displayed similar trends on migration with FAP-α overexpression.

We developed MDA-MB-231 and HT-1080 cells overexpressing FAP-α (231-FAP and HT-1080-FAP) by transducing these cells with lentivirus encoding the gene for human FAP (Accession No. NM_004460.3) that was subcloned into lentiviral vector pMA3211. Immunoblot analysis with FAP-α antibody confirmed the overexpression of FAP-α protein. To evaluate migration, wound healing analysis was performed. Cells were seeded and incubated in DMEM without FBS for 24h before wounds were made by scratching cells with a p200 pipet. Pictures were taken immediately (0h), and at 6h, 24h, and 48h after wound formation. The wound areas were measured using ImageJ and normalized to the area (100%) at 0h. We used a cell counting kit-8 (CCK-8) to determine if cell proliferation was altered by FAP-α overexpression.

231-FAP cells exhibited significantly increased migration from 6h (66%) to 48h (0.6%) after wound formation compared to parental cells (73% at 6h and 7.6% at 48h). HT1080-FAP cells showed increased migration only at 24h (8%) and 48h (1.9%) after wound formation compared to parental cells (19% at 24h and 5.3% at 48h) although this was not statistically significant. The CCK-8 assay showed that there were no differences in cell proliferation between MDA-MB-231 cells and 231-FAP cells with or without 10% FBS. Both cell lines showed a comparably small reduction of proliferation (approximately 30%) at 48h point in FBS free medium. In contrast, both HT1080 and HT1080-FAP cell proliferation was reduced significantly (approximately 75%) at 48h point in FBS free medium. HT1080-FAP cell proliferation was slightly higher than parental cells in medium with FBS (16%) and without FBS (19%) at 48h point than parental cells.

Our data are consistent with the known activities of FAP-α as an exopeptidase and endopeptidase/gelatinase/collagenase in tissue remodeling and repair, and in cell migration. We found that FAP-α significantly increased MDA-MB-231 breast cancer cell migration but had very little effect on cell proliferation. FAP-α overexpression in HT1080 fibrosarcoma cells also increased migration but not as much as in MDA-MB-231 cells. Ongoing work with xenografts derived from these cell lines will provide further insights into tumor microenvironment changes with FAP-α overexpression.

Citation Format: Noriko Mori, Jiefu Jin, Balaji Krishnamachary, Yelena Mironchik, James D. Barnett, Zaver M. Bhujwalla. FAP-α overexpression increases cancer cell migration [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4920.

Abstract 3360: Phototheranostics of cancer associated fibroblasts by targeting fibroblast activation protein-α

Introduction: Stromal cells such as cancer associated fibroblasts (CAFs) mediate many of the aggressive characteristics of cancer1 and have an ever-replenishing supply that is largely left intact by our current therapeutic strategies.2 Fibroblast activation protein-α (FAP-α) is a target antigen that been reported to be selectively expressed in tumors by a subset of immunosuppressive stromal fibroblasts. Here, we extended our previous near-infrared photoimmunotherapy (NIR-PIT) study,3 to develop a FAP-α-targeted monoclonal antibody (mAb) photosensitizer conjugate. We developed FAP-α overexpressing MDA-MB-231 and HT-1080 cells to test the feasibility of targeting FAP-α expressing populations in cells and tumors in vivo, in terms of the specificity of the conjugate to bind to, detect, and eliminate FAP-α expressing populations.

Method: FAP-α monoclonal antibody (AF3715) and its IgG isotype control were conjugated with a NIR phthalocyanine dye, IR700, to form FAP-α-IR700 and IgG-IR700. FAP-α overexpression was achieved by transducing MDA-MB-231 and HT-1080 cells with lentivirus encoding the gene for human FAP (Accession No. NM_004460.3) that was subcloned into lentiviral vector pMA3211 to obtain 231-FAP and HT-1080-FAP cells. Cell viability was measured by using CCK-8 assay. Bilateral tumor models were established by inoculating 1×106 MDA-MB-231 cells or 1×106 231-FAP cells in 0.05 ml of Hank's balanced salt solution on either side in the mammary fat pads of athymic Balb/c (nu/nu) female mice. A similar number of HT-1080 or HT-1080-FAP cells were inoculated bilaterally in the flank. 50 μg of FAP-α-IR700 or IgG-IR700 was injected i.v., and fluorescence images of IR700 in mice were obtained over a 24-h period (n = 3 per group). At 24 h post injection, mice were euthanized, and tumors were isolated for imaging. For PIT, tumor-bearing mice (n = 4 per group) received two i.v. injections of 100 μg of FAP-α-IR700 at a one-week interval, and tumors were exposed to NIR irradiation at 200 J/cm2 at 24h p.i. Tumor diameters were measured over 2 weeks. IgG-IR700 and PBS-injected mice were used as controls.

Results and Discussion: We confirmed FAP-α overexpression in 231-FAP and HT-1080-FAP cells. FAP-α-IR700 was activated by NIR light, causing FAP-α-specific cell death. FAP-α-IR700-mediated phototoxicity was dependent on the conjugate concentration and NIR light dose; and it was inhibited by excess AF3715. We observed the preferential accumulation of FAP-α-IR700 in FAP-α-overexpressing 231-FAP and HT-1080-FAP tumors compared to their wild-type counterparts. The mean fluorescence intensity of FAP-α-IR700 in FAP-α-overexpressing tumors was approximately two to threefold higher than the wild type tumors. FAP-α-IR700 injection together with NIR light exposure resulted in the highest tumor growth delay in 231-FAP tumors and HT-1080-FAP tumors. Our results evaluate and confirm the ability of FAP-α-IR700 to target and eliminate FAP-α-overexpressing cell populations, providing novel opportunities to selectively deplete FAP-α high CAFs in cancers.

References: 1. Horimoto, Y. et al. Cell Adh Migr. 2012; 2. Eyden, B. et al. J Cell Mol Med. 2008; 3. Jin, J. et al. Sci.Rep. 2016. Supported by NIH R35 CA209960, P41 EB024495, and Emerson Collective Cancer Research Fund.

Citation Format: Jiefu Jin, James D. Barnett, Balaji Krishnamachary, Yelena Mironchik, Hisataka Kobayashi, Zaver Bhujwalla. Phototheranostics of cancer associated fibroblasts by targeting fibroblast activation protein-α [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3360.

Nanoparticle interactions with immune cells dominate tumor retention and induce T cell-mediated tumor suppression in models of breast cancer

The factors that influence nanoparticle fate in vivo following systemic delivery remain an area of intense interest. Of particular interest is whether labeling with a cancer-specific antibody ligand ("active targeting") is superior to its unlabeled counterpart ("passive targeting"). Using models of breast cancer in three immune variants of mice, we demonstrate that intratumor retention of antibody-labeled nanoparticles was determined by tumor-associated dendritic cells, neutrophils, monocytes, and macrophages and not by antibody-antigen interactions. Systemic exposure to either nanoparticle type induced an immune response leading to CD8+ T cell infiltration and tumor growth delay that was independent of antibody therapeutic activity. These results suggest that antitumor immune responses can be induced by systemic exposure to nanoparticles without requiring a therapeutic payload. We conclude that immune status of the host and microenvironment of solid tumors are critical variables for studies in cancer nanomedicine and that nanoparticle technology may harbor potential for cancer immunotherapy.

Increased uptake of doxorubicin by cells undergoing heat stress does not explain its synergistic cytotoxicity with hyperthermia

Purpose:

A proposed mechanism for the enhanced effectiveness of hyperthermia and doxorubicin (Dox) combinations is increased intracellular Dox concentrations resulting from heat-induced cell stress. The purpose of this study was to determine whether specific varied Dox and heat combinations produce measurable effects greater than the additive combination, and whether these effects can be attributed to heat-induced increases in intracellular Dox concentrations.

Methods:

HCT116, HT29 and CT26 cells were exposed to Dox and water bath heating independently. A clonogenic survival assay was used to determine cell killing and intracellular Dox concentrations were measured in HCT116 cells with mass spectrometry. Cells were exposed to heating at 42 °C (60 min) and 0.5 μg/ml of Dox at varying intervals. Synergy was determined by curve-fitting and isobologram analysis.

Results:

All cell lines displayed synergistic effects of combined heating and Dox. A maximum synergistic effect was achieved with simultaneous cell exposure to Dox and heat. For exposures at 42 ° C, the synergistic effect was most pronounced at Dox concentrations <0.5 μg/ml. Increased intracellular concentrations of Dox in HCT116 cells caused by heat-stress did not generate a concomitant thermal enhancement.

Conclusions:

Simultaneous exposure of HCT116 cells to heating and Dox is more effective than sequential exposure. Heat-induced cell responses are accompanied by increased intracellular Dox concentrations; however, clonogenic survival data do not support this as the cause for synergistic cytotoxicity.

Human Cancer Cell Membrane-Coated Biomimetic Nanoparticles Reduce Fibroblast-Mediated Invasion and Metastasis and Induce T-Cells

Biomimetic nanoparticles (NPs) combine the flexibility and reproducibility of synthetic materials with the functionality of biological materials. Here, we developed and characterized biomimetic poly(lactic- co-glycolic acid) (PLGA) NPs coated with human cancer cell membrane fractions (CCMFs) to form CCMF-coated PLGA (CCMF-PLGA) NPs. We evaluated the ability of these CCMF-PLGA NPs to disrupt cancer cell-stromal cell interactions and to induce an immune response. Western blot analysis verified the plasma membrane purity of CCMFs. Confocal fluorescence microscopy and flow cytometry confirmed the presence of intact membrane-associated proteins including CXCR4 and CD44 following membrane derivation and coating. CCMFs and CCMF-PLGA NPs were capable of inhibiting cancer cell migration toward human mammary fibroblasts. Intravenous injection of CCMF-PLGA NPs significantly reduced experimental metastasis in vivo. Following immunization of Balb/c mice, near-infrared fluorescence imaging confirmed the migration of NPs to proximal draining lymph nodes (LNs). A higher percentage of CD8⁺ and CD4⁺ cytotoxic T-lymphocyte populations was observed in spleens and LNs of CCMF-PLGA NP-immunized mice. Splenocytes isolated from CCMF-PLGA NP-immunized mice had the highest number of interferon gamma-producing T-cells as detected by the ELISpot assay. CCMF-PLGA NPs hold promise for disrupting cancer cell-stromal cell interactions and for priming the immune system in cancer immunotherapy.

Evaluating N-benzylgalactonoamidines as putative transition state analogs for β-galactoside hydrolysis

Experimental evidence is provided for p-methylbenzyl-D-galactonoamidine to function as a true transition state analog for the enzymatic hydrolysis of aryl-β-D-galactopyranosides by β-galactosidase (A. oryzae). The compound exhibits inhibition constants in the low nanomolar concentration range (12-56 nM) for a selection of substrates. Along these lines, a streamlined synthetic method based on phase-transfer catalysis was optimized to afford the required variety of new aryl-β-D-galactopyranosides. Last, the stability of the galactonoamidines under the assay conditions was confirmed.

Potential use of DNA barcodes in regulatory science: applications of the Regulatory Fish Encyclopedia

The use of a DNA-based identification system (DNA barcoding) founded on the mitochondrial gene cytochrome c oxidase subunit I (COI) was investigated for updating the U.S. Food and Drug Administration Regulatory Fish Encyclopedia (RFE; http://www.cfsan.fda.gov/-frf/rfe0.html). The RFE is a compilation of data used to identify fish species. It was compiled to help regulators identify species substitution that could result in potential adverse health consequences or could be a source of economic fraud. For each of many aquatic species commonly sold in the United States, the RFE includes high-resolution photographs of whole fish and their marketed product forms and species-specific biochemical patterns for authenticated fish species. These patterns currently include data from isoelectric focusing studies. In this article, we describe the generation of DNA barcodes for 172 individual authenticated fish representing 72 species from 27 families contained in the RFE. These barcode sequences can be used as an additional identification resource. In a blind study, 60 unknown fish muscle samples were barcoded, and the results were compared with the RFE barcode reference library. All 60 samples were correctly identified to species based on the barcoding data. Our study indicates that DNA barcoding can be a powerful tool for species identification and has broad potential applications.

Effects of on-board and dockside handling on the formation of biogenic amines in mahimahi (Coryphaena hippurus), skipjack tuna (Katsuwonus pelamis), and yellowfin tuna (Thunnus albacares)

Consumer illnesses by scombroid poisonings have been a continuing problem for many years. The intoxications follow the ingestion of fish such as tuna and mahimahi that have undergone bacterial decomposition, leading to the formation of biogenic amines. Research studies have concluded that histamine is one of the indicators of scombrotoxic fish and that other amines, such as cadaverine, could be involved in the illnesses. Guidance for the handling of fish on board fishing vessels to prevent the production of scombrotoxic fish has been limited by a lack of data addressing changes that occur in fish from the water to delivery at dockside. In this study, the changes in selected biogenic amines were determined in mahimahi and tuna, which were captured and held in seawater at 25 to 35 degrees C for incubation times up to 18 h. The fillets from the treated fish were sectioned by transverse cuts and analyzed for histamine, cadaverine, and putrescine. Results showed that at 26 degrees C, more than 12 h of incubation were required before a histamine concentration of 50 ppm was reached in mahimahi. At 35 degrees C, 50 ppm histamine formed within 9 h. Similar results were found for skipjack and yellowfin tuna. Histamine concentrations exceeded 500 ppm within an additional 3 h of incubation in mahimahi. At both temperatures, an increase in the concentration of cadaverine preceded an increase in histamine levels. Changes in putrescine concentrations in the fish were less pronounced. The study also demonstrated that histidine decarboxylase activity was retained in some frozen samples of fish and could result in further increases in histamine on thawing.

Genome-wide distribution of ORC and MCM proteins in S. cerevisiae: high-resolution mapping of replication origins

DNA replication origins are fundamental to chromosome organization and duplication, but understanding of these elements is limited because only a small fraction of these sites have been identified in eukaryotic genomes. Origin Recognition Complex (ORC) and minichromosome maintenance (MCM) proteins form prereplicative complexes at origins of replication. Using these proteins as molecular landmarks for origins, we identified ORC- and MCM-bound sites throughout the yeast genome. Four hundred twenty-nine sites in the yeast genome were predicted to contain replication origins, and approximately 80% of the loci identified on chromosome X demonstrated origin function. A substantial fraction of the predicted origins are associated with repetitive DNA sequences, including subtelomeric elements (X and Y') and transposable element-associated sequences (long terminal repeats). These findings identify the global set of yeast replication origins and open avenues of investigation into the role(s) ORC and MCM proteins play in chromosomal architecture and dynamics.

Deletion of the RNA polymerase subunit RPB4 acts as a global, not stress-specific, shut-off switch for RNA polymerase II transcription at high temperatures

We used whole genome expression analysis to investigate the changes in the mRNA profile in cells lacking the Saccharomyces cerevisiae RNA polymerase II subunit RPB4 (Delta RPB4). Our results indicated that an essentially complete shutdown of transcription occurs upon temperature shift of this conditionally lethal mutant; 98% of mRNA transcript levels decrease at least 2-fold, 96% at least 4-fold. This data was supported by in vivo experiments that revealed a rapid and greater than 5-fold decline in steady state poly(A) RNA levels after the temperature shift. Expression of several individual genes, measured by Northern analysis, was also consistent with the whole genome expression profile. Finally we demonstrated that the loss of RNA polymerase II activity causes secondary effects on RNA polymerase I, but not RNA polymerase III, transcription. The transcription phenotype of the Delta RPB4 mutant closely mirrors that of the temperature-sensitive rpb1-1 mutant frequently implemented as a tool to inactivate the RNA polymerase II in vivo. Therefore, the Delta RPB4 mutant can be used to easily design strains that enable the study of distinct post-transcriptional cellular processes in the absence of RNA polymerase II transcription.

Total Volatile Acids: Temperature Dependent Decomposition Indicator in Halibut Determined by Flow Injection Analysis

Total volatile acids (TVA) is a well known indicator for the decomposition of seafood products. A flow injection analysis (FIA) method, using a gas diffusion cell at elevated temperature, was developed for the determination of TVA in fish and applied to halibut. The FIA method is simple and rapid. The results of this study indicate that the correlation between levels of TVA and degree of decomposition is temperature dependent.

Scaling and root planing efficacy in multirooted teeth

The effect of operator experience level and root surface access on instrumentation of multirooted teeth was investigated. Fifty molars designated for extraction were randomly distributed among four operators of two different experience levels for scaling and root planing with or without surgical access. Following treatment the teeth were extracted and scored in a blind manner for residual calculus. Teeth were sectioned to allow assessment of the furcal aspects. Results show that operators of both experience levels obtained calculus-free root surfaces significantly more often with flap access than with a non-surgical approach. Additionally, operators with more experience achieved calculus-free root surfaces significantly more often than operators of lesser experience with both an open and closed procedure. However, when furcation aspects alone were assessed, it was found that the more experienced operators obtained a calculus-free surface only 68% of the time with an open approach. Results suggest that, although both surgical access and a more experienced operator significantly enhance calculus removal in molars with furcation invasion, total calculus removal in furcations utilizing conventional instrumentation may be limited.

Comparison of freeze-dried bone allograft and porous hydroxylapatite in human periodontal defects

This study was conducted to clinically compare the efficacy of freeze-dried bone allograft (FDBA) and porous hydroxylapatite granules. Nineteen pairs of intraosseous defects were grafted in seven patients. One defect of each pair was implanted with FDBA, the other with granular porous hydroxylapatite. Matching defects were treated similarly in all other aspects. Evaluations were based on both preoperative and postoperative measurements from a fixed reference point, standardized radiographs, surgical osseous measurements, and histology of degranulated tissues. Grafted sites were reentered 6 to 11 months postsurgery. Results showed a mean osseous fill of 2.1 mm for FDBA versus 1.3 mm for granular porous hydroxylapatite (P = .07). A mean clinical attachment gain of 2.2 mm for FDBA versus 1.3 mm for granular porous hydroxylapatite (P less than .05), and a mean decrease in probing depths of 3.0 mm for FDBA versus 1.4 mm for granular porous hydroxylapatite (P less than 0.5) was found. FDBA was clinically indistinguishable from host bone, whereas porous hydroxylapatite appeared to be separated from host bone by soft tissue. The data and clinical findings suggested that FDBA may have some enhanced reparative potential when compared to granular porous hydroxylapatite in the treatment of periodontal defects in humans.

System for ESR measurements at hydrostatic pressures to 60 kilobars

A single-crystal sapphire serves both as a solid microwave cavity (X band) and an anvil in a Bridgman-anvil pressure geometry. A metal gasket is used in a manner similar to its use in the diamond-anvil pressure cell, and single-crystal samples are subject to purely hydrostatic pressures. The ruby-fluorescence pressure-measurement technique is utilized. Sample size is limited to a disk approximately 0.6 mm in diameter and 0.1 mm thick. ESR data on Cr(3+) in ruby to 60 kilobars are given as an illustration of the precision and data quality. Line widths and profiles, as well as line positions, are meaningful. Very little degradation of the data is experienced at the higher pressures. The first and second derivatives of the zero-field splitting (delta) of the states in ruby with pressure are measured as ddelta/dP= (6.70+/-0.08) x 10(-4) cm(-1) kilobar(-1) and d(2)delta/dP(2)= (-2.44+/-0.30) x10(-6) cm(-1) kilobar(-2) at P=0. The gyromagnetic ratio g(11) is shown to experience a fractional change less than 2 x 10(-4) to 60 kilobars.

Pressure Measurement Made by the Utilization of Ruby Sharp-Line Luminescence

A rapid, convenient technique for precision pressure measurement in the diamond-anvil high-pressure cell, which makes use of the sharp-line (R-line) luminescence of ruby, has been developed. The observed shift is -0.77 +/-0.03 reciprocal centimeters per kilobar for R(1) and -0.84+/- 0.03 reciprocal centimeters per kilobar for R(2) to lower energy and is approximately linear in the range studied (to 22 kilobars). Line-broadening has been observed in some instances and has been tentatively identified with nonhydrostatic conditions surrounding the ruby sample.

High Pressure Polymorphism in Cesium

A new polymorph of cesium, existing over the narrow pressure range from about 42.2 to 42.7 kilobars at room temperature, has been discovered. Its crystal structure is face-centered-cubic with a = 5.800 +/- 0.007 A at 42.5 kb and 27 degrees C. Cesium-II, which exists over the pressure range 23.7 to 42.2 kb, is also face-centered-cubic with a = 5.984 +/- 0.011 A at 41 kb and 27 degrees C. An improved resistance-pressure curve and x-ray compressibility measurements for Cs are also given.

X-ray Diffraction Studies on Tin at High Pressure and High Temperature

Tin at a pressure of 39 kb and at 314 degrees C has tetragonal symmetry with an atom at each point of a body-centered tetragonal lattice. The unit cell dimensions are a equal to 3.81 A, c equal to 3.48 A, and c/ a = 0.91. The melting curve of tin was observed up to 45 kb and the boundary line between the tin I and tin II phases was observed to 70 kb by x-ray diflraction techniques.

High Pressure X-ray Diffraction Studies on Barium

Simultaneous x-ray diffraction and electrical resistance measurements on barium establish, with certainty, that Bridgman's 78-kb resistance transition is identical with his 59-kb volumetransition. During this transition, the bodycentered cubic structure changes to hexagonalclose packed. Lattice parameters for the latter structure at 62 kb (volume scale) are: a = 3.90 A, c = 6.15 A, and c/a = 1.58. Compression (AV/Vo) at 62 kb is 0.359 + 0.005 compared to 0.345 previously reported by Bridgman. Below the transition, at 49 kb, compression is 0.300 +/- 0.005 compared to Bridgman's 0.288. Bridgman's 17-kb volume transition was not detected by x-ray diffraction.

Ytterbium: Transition at High Pressure from Face-Centered Cubic to Body-Centered Cubic Structure

Pressure of 40,000 atmospheres at 25 degrees C induces a phase transformation in ytterbium metal; the face-centered cubic structure changes to body-centered cubic. The radius of the atom changes from 1.82 to 1.75 A. At the same time the atom's volume decreases by 11 percent and the volume, observed macroscopically, decreases 3.2 percent.