Third-Generation Anticancer Photodynamic Therapy Systems Based on Star-like Anionic Polyacrylamide Polymer, Gold Nanoparticles, and Temoporfin Photosensitizer

Photodynamic therapy (PDT) is a non-invasive anticancer treatment that uses special photosensitizer molecules (PS) to generate singlet oxygen and other reactive oxygen species (ROS) in a tissue under excitation with red or infrared light. Though the method has been known for decades, it has become more popular recently with the development of new efficient organic dyes and LED light sources. Here we introduce a ternary nanocomposite: water-soluble star-like polymer/gold nanoparticles (AuNP)/temoporfin PS, which can be considered as a third-generation PDT system. AuNPs were synthesized in situ inside the polymer molecules, and the latter were then loaded with PS molecules in an aqueous solution. The applied method of synthesis allows precise control of the size and architecture of polymer nanoparticles as well as the concentration of the components. Dynamic light scattering confirmed the formation of isolated particles (120 nm diameter) with AuNPs and PS molecules incorporated inside the polymer shell. Absorption and photoluminescence spectroscopies revealed optimal concentrations of the components that can simultaneously reduce the side effects of dark toxicity and enhance singlet oxygen generation to increase cancer cell mortality. Here, we report on the optical properties of the system and detailed mechanisms of the observed enhancement of the phototherapeutic effect. Combinations of organic dyes with gold nanoparticles allow significant enhancement of the effect of ROS generation due to surface plasmonic resonance in the latter, while the application of a biocompatible star-like polymer vehicle with a dextran core and anionic polyacrylamide arms allows better local integration of the components and targeted delivery of the PS molecules to cancer cells. In this study, we demonstrate, as proof of concept, a successful application of the developed PDT system for in vitro treatment of triple-negative breast cancer cells under irradiation with a low-power LED lamp (660 nm). We consider the developed nanocomposite to be a promising PDT system for application to other types of cancer.

Optimization of tumor-treating field therapy for triple-negative breast cancer cells in vitro via frequency modulation

PURPOSE

Currently, tumor-treating field (TTField) therapy utilizes a single "optimal" frequency of electric fields to achieve maximal cell death in a targeted population of cells. However, because of differences in cell size, shape, and ploidy during mitosis, optimal electric field characteristics for universal maximal cell death may not exist. This study investigated the anti-mitotic effects of modulating electric field frequency as opposed to utilizing uniform electric fields.

METHODS

We developed and validated a custom device that delivers a wide variety of electric field and treatment parameters including frequency modulation. We investigated the efficacy of frequency modulating tumor-treating fields on triple-negative breast cancer cells compared to human breast epithelial cells.

RESULTS

We show that frequency-modulated (FM) TTFields are as selective at treating triple-negative breast cancer (TNBC) as uniform TTFields while having a greater efficacy for combating TNBC cell growth. TTField treatment at a mean frequency of 150 kHz with a frequency range of ± 10 kHz induced apoptosis in a greater number of TNBC cells after 24 h as compared to unmodulated treatment which led to further decreased cell viability after 48 h. Furthermore, all TNBC cells died after 72 h of FM treatment while cells that received unmodulated treatment were able to recover to cell number equivalent to the control.

CONCLUSION

TTFields were highly efficacious against TNBC growth, FM TTFields showed minimal effects on epithelial cells similar to unmodulated treatment.

Efficacy and selectivity of tumor-treating field therapy for triple-negative breast cancer cells via in-house delivery device

PURPOSE

Triple-negative breast cancer continues to be one of the leading causes of death in women, making up 7% of all cancer deaths. Tumor-treating electric fields are low-energy, low-frequency oscillating electric fields that induce an anti-proliferative effect on mitotic cells in glioblastoma multiforme, non-small cell lung cancer, and ovarian cancer. Little is known about effects of tumor-treating fields on triple-negative breast cancer and known research for tumor-treating fields only utilizes low (< 3 V/cm) electric field intensities.

METHODS

We have developed an in-house field delivery device capable of high levels of customization to explore a much wider variety of electric field and treatment parameters. Furthermore, we investigated the selectivity of tumor-treating field treatment between triple-negative breast cancer and human breast epithelial cells.

RESULTS

Tumor-treating fields show greatest efficacy against triple-negative breast cancer cell lines between 1 and 3 V/cm electric field intensities while having little effect on epithelial cells.

CONCLUSION

These results provide a clear therapeutic window for tumor-treating field delivery to triple-negative breast cancer.

The Influence of the Normal Mammary Microenvironment on Breast Cancer Cells

The tumor microenvironment is recognized as performing a critical role in tumor initiation, progression, and metastasis of many cancers, including breast cancer. The breast cancer microenvironment is a complex mixture of cells consisting of tumor cells, immune cells, fibroblasts, and vascular cells, as well as noncellular components, such as extracellular matrix and soluble products. The interactions between the tumor cells and the tumor microenvironment modulate tumor behavior and affect the responses of cancer patients to therapies. The interactions between tumor cells and the surrounding environment can include direct cell-to-cell contact or through intercellular signals over short and long distances. The intricate functions of the tumor microenvironment in breast cancer have led to increased research into the tumor microenvironment as a possible therapeutic target of breast cancer. Though expanded research has shown the clear importance of the tumor microenvironment, there is little focus on how normal mammary epithelial cells can affect breast cancer cells. Previous studies have shown the normal breast microenvironment can manipulate non-mammary stem cells and tumor-derived cancer stem cells to participate in normal mammary gland development. The tumorigenic cells lose their tumor-forming capacity and are "redirected" to divide into "normal", non-tumorigenic cells. This cellular behavior is "cancer cell redirection". This review will summarize the current literature on cancer cell redirection and the normal mammary microenvironment's influence on breast cancer cells.

Abstract 2536: Investigating the mechanisms of HER2+ breast cancer cell redirection

Introduction: Breast cancer research has advanced understanding of breast cancer development and progression greatly over the past few decades. Despite progress in research, breast cancer is the second leading cause of cancer death in North America and is the most frequent type of cancer for women. Better treatments and diagnostic tools have increased breast cancer survival rates, but there is still a fundamental lack of understanding in tumor progression. Previous studies show the normal mammary microenvironment can influence non-mammary cells and tumor-derived cancer cells to participate in normal mammary gland development. The tumorigenic cells lose their tumor-forming capabilities and are “redirected” into phenotypically normal, non-tumorigenic cells. The purpose of this study is to obtain knowledge of the mechanisms that play a role in cancer cell redirection and therefore be able manipulate those mechanisms for therapeutic treatment in a clinical setting. Our hypothesis is that microenvironmental elements control whether a tumorigenic cell will enter a redirected state. We have developed and validated an in vitro model to mimic the mammary microenvironment to study cancer cell redirection. We found that when cancer cells that overexpress HER2+ are redirected in our cancer redirection model, phospho-HER2+ is silenced. We use HER2+ phosphorylation as a marker for cancer cell redirection though not a mechanism for cancer cell redirection.

Materials and Methods: HER2+ breast cancer cells and normal breast epithelial cells (BECs) were co-cultured in ratios of 1:1 or 1:50. Monocultures of breast cancer cells and BECs were used as controls. Western analysis and immunostaining was used to assess attenuation of HER2+ and phospho-HER2+ receptors and RNAseq was used for pathway analyses. Images were taken using a Leica confocal microscope. For comparison of 2 or more groups, a one-way analysis of variance was performed. A p-value of less than 0.05 was considered significant.

Results and Discussion: We found that the redirected cells underwent a phenotype shift in which the redirected cells adopted a normal mammary epithelial phenotype based on gene expression profiles. Furthermore, when HER2+ breast cancer cells were redirected in vitro they lost their tumor-forming potential in vivo. Signal pathway analyses revealed that redirected cancer cells are adopting a normal phenotype compared to breast cancer cells.

Conclusions: These results indicate that epithelial cells provide signals that influence HER2+ breast cancer cells to undergo a shift in phenotype. The phenotypic shift in cancer cell redirection includes multiple intracellular signaling pathways that may be the key towards effective cancer treatment.

Acknowledgements: This research was supported by South Carolina Idea Networks of Biomedical Research Excellence (SC INBRE).

Citation Format: Caroline J. Campbell, Brian W. Booth. Investigating the mechanisms of HER2+ breast cancer cell redirection [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2536.

Biomedical applications of tannic acid

Tannic Acid (TA) is a naturally occurring antioxidant polyphenol that has gained popularity over the past decade in the field of biomedical research for its unique biochemical properties. Tannic acid, typically extracted from oak tree galls, has been used in many important historical applications. TA is a key component in vegetable tanning of leather, iron gall ink, red wines, and as a traditional medicine to treat a variety of maladies. The basis of TA utility is derived from its many hydroxyl groups and its affinity for forming hydrogen bonds with proteins and other biomolecules. Today, the study of TA has led to the development of many new pharmaceutical and biomedical applications. TA has been shown to reduce inflammation as an antioxidant, act as an antibiotic in common pathogenic bacterium, and induce apoptosis in several cancer types. TA has also displayed antiviral and antifungal activity. At certain concentrations, TA can be used to treat gastrointestinal disorders such as hemorrhoids and diarrhea, severe burns, and protect against neurodegenerative diseases. TA has also been utilized in biomaterials research as a natural crosslinking agent to improve mechanical properties of natural and synthetic hydrogels and polymers, while also imparting anti-inflammatory, antibacterial, and anticancer activity to the materials. TA has also been used to develop thin film coatings and nanoparticles for drug delivery. In all, TA is fascinating molecule with a wide variety of potential uses in pharmaceuticals, biomaterials applications, and drug delivery strategies.

Degradation and release of tannic acid from an injectable tissue regeneration bead matrix in vivo

The development of multifunctional biomaterials as both tissue regeneration and drug delivery devices is currently a major focus in biomedical research. Tannic Acid (TA), a naturally occurring plant polyphenol, displays unique medicinal abilities as an antioxidant, an antibiotic, and as an anticancer agent. TA has applications in biomaterials acting as a crosslinker in polymer hydrogels improving thermal stability and mechanical properties. We have developed injectable cell seeded collagen beads crosslinked with TA for breast reconstruction and anticancer activity following lumpectomy. This study determined the longevity of the bead implants by establishing a degradation time line and TA release profile in vivo. Beads crosslinked with 0.1% TA and 1% TA were compared to observe the differences in TA concentration on degradation and release. We found collagen/TA beads degrade at similar rates in vivo, yet are resistant to complete degradation after 16 weeks. TA is released over time in vivo through diffusion and cellular activity. Changes in mechanical properties in collagen/TA beads before implantation to after 8 weeks in vivo also indicate loss of TA over a longer period of time. Elastic moduli decreased uniformly in both 0.1% and 1% TA beads. This study establishes that collagen/TA materials can act as a drug delivery system, rapidly releasing TA within the first week following implantation. However, the beads retain TA long term allowing them to resist degradation and remain in situ acting as a cell scaffold and tissue filler. This confirms its potential use as an anticancer and minimally invasive breast reconstructive device following lumpectomy.

Asymmetric cell division of mammary stem cells

Somatic stem cells are distinguished by their capacity to regenerate themselves and also to produce daughter cells that will differentiate. Self-renewal is achieved through the process of asymmetric cell division which helps to sustain tissue morphogenesis as well as maintain homeostasis. Asymmetric cell division results in the development of two daughter cells with different fates after a single mitosis. Only one daughter cell maintains "stemness" while the other differentiates and achieves a non-stem cell fate. Stem cells also have the capacity to undergo symmetric division of cells that results in the development of two daughter cells which are identical. Symmetric division results in the expansion of the stem cell population. Imbalances and deregulations in these processes can result in diseases such as cancer. Adult mammary stem cells (MaSCs) are a group of cells that play a critical role in the expansion of the mammary gland during puberty and any subsequent pregnancies. Furthermore, given the relatively long lifespans and their capability to undergo self-renewal, adult stem cells have been suggested as ideal candidates for transformation events that lead to the development of cancer. With the possibility that MaSCs can act as the source cells for distinct breast cancer types; understanding their regulation is an important field of research. In this review, we discuss asymmetric cell division in breast/mammary stem cells and implications on further research. We focus on the background history of asymmetric cell division, asymmetric cell division monitoring techniques, identified molecular mechanisms of asymmetric stem cell division, and the role asymmetric cell division may play in breast cancer.

Characterization of collagen type I/tannic acid beads as a cell scaffold

Breast cancer is the most commonly diagnosed cancer among women worldwide. Surgical removal of tumors is often necessary and many patients suffer complications due to subsequent breast reconstruction. A safe and effective breast reconstructive material is needed for patients recovering from surgical removal of small breast cancer tumors. Our lab has developed injectable collagen/tannic acid beads seeded with patient-derived preadipocytes for regeneration of healthy breast tissue in patients post-lumpectomy. Previous research indicates that the inclusion of tannic acid in the matrix imparts an anticancer property. This research seeks to determine the variables needed to control collagen/tannic acid bead diameter and seeded cell attachment, which are essential to proper bead implantation and function. We found that as tannic acid concentration increases within the beads, cell attachment decreases. Bead diameter is controlled by bead generator voltage, solution osmolality, the degree of cell attachment, and tannic acid concentrations. Higher voltages resulted in significant decrease in bead diameter. Collagen/tannic acid beads decreased in diameter when placed in solutions of increasing osmolality. Higher degrees of cell attachment across the surface of the beads were associated with a significant decrease in diameter. In beads made with high concentrations of tannic acid, bead diameter was found to decrease. Collagen/TA beads are a promising subdermal tissue regenerative matrix with anticancer activity as an alternative to simple lipofilling in breast reconstructive procedures. This study was conducted to better understand the properties of collagen/TA beads in order to improve injection efficacy and tissue regenerative activity.

Induction of phenotypic changes in HER2-postive breast cancer cells in vivo and in vitro

The influence of breast cancer cells on normal cells of the microenvironment, such as fibroblasts and macrophages, has been heavily studied but the influence of normal epithelial cells on breast cancer cells has not. Here using in vivo and in vitro models we demonstrate the impact epithelial cells and the mammary microenvironment can exert on breast cancer cells. Under specific conditions, signals that originate in epithelial cells can induce phenotypic and genotypic changes in cancer cells. We have termed this phenomenon "cancer cell redirection." Once breast cancer cells are redirected, either in vivo or in vitro, they lose their tumor forming capacity and undergo a genetic expression profile shift away from one that supports a cancer profile towards one that supports a non-tumorigenic epithelial profile. These findings indicate that epithelial cells and the normal microenvironment influence breast cancer cells and that under certain circumstances restrict proliferation of tumorigenic cells.

Redirecting Normal and Cancer Stem Cells to a Mammary Epithelial Cell Fate

Tissue microenvironments, also known as stem cell niches, influence not only resident cells but also cells in surrounding tissues. Physical and biochemical intercellular signals originating from resident stem cells or non-stem cells participate in the homeostasis of the tissue regulating cell proliferation, differentiation, wound healing, tissue remodeling, and tumorigenesis. In recent publications it has been demonstrated that the normal mouse mammary microenvironment can provide development and differentiation guidance to not only resident mammary cells but also cells of non-mammary origin including tumor-derived cells. When placed in reforming mammary stem cell niches the non-mammary cells proliferate and differentiate along mammary epithelial cell lineages and contribute progeny to reforming mammary gland outgrowths. The tumor-derived cells that are redirected to assume mammary epithelial phenotypes lose their cancer-forming capacity and shift their gene expression profiles from a cancer profile towards a normal mammary epithelial expression profile. This review summarizes the recent discoveries regarding the ability of the normal mouse mammary microenvironment to dictate the cell fates of non-mammary cells introduced into mammary stem cell niches.

Abstract 3092: Redirection of human HER2-positive breast cancer cells

Breast cancer is the most common form of cancer among women, affecting one eigth of the female population. While advances in clinical management and therapeutic modalities have been achieved, serious limitations in the improvement of outcomes after the diagnosis remain, largely due to the complexity of the underlying biology. Studying the mechanism that makes cancer cells tumorigenic and how they can lose the ability to cause malignant formations is the first step towards understanding complex mechanisms of this disease. The normal mammary microenvironment can redirect cells to assume a normal mammary epithelial phenotype. This phenomenon also applies to tumorigenic cells; cancer cells lose their tumor-forming capacity and differentiate, assuming a normal, non-tumorigenic phenotype. This phenomenon has been termed “cancer cell redirection.” Comparing cells that went through this transformation with original cancer cells, features that identify tumorigenic activity can be acknowledged. We have established an in vitro model of cancer cell redirection, in which HER2+ breast cancer cells are grown alone or in co-culture with normal human breast epithelial cells. The ratios of cells used in co-cultures, 1:1 and 1:50 (cancer: normal) were previously established through in vivo and in vitro studies. Redirection was confirmed by immunostaining. The metric used to determine cancer cell redirection was the absence of receptor tyrosine kinase phosphorylation without a change in surface expression of the receptor. HER2 and P-HER2 expression were both present in the HER2+ cancer cells and in the: MCF10A and 1:1 co-cultures. However, HER2 expression was observed in 1:50 co-cultures, but an absence of P-HER2 was noted. Based on attenuation of receptor phosphorylation in the 1:50 co-cultures we can confirm the breast cancer cell redirection, which matches our previous results. Furthermore, alteration of HER2 dimerization patterns in redirected cells were investigated. The capacity of cancer and redirected cells to form tumors was examined with use of mammosphere assay. Formation of mammospheres has correlated to stem cell function and tumor-initiation capacity. The HER2+ breast cancer cell lines formed significantly higher numbers of spheres compared to the non-tumorigenic breast epithelial cells. Mammosphere formation is decreased in redirected cancer cells. Breast cancer stem cells are HER2+ regardless of pathological or genetic classification. This suggests that HER2 expression is not only a target in HER2+ breast cancer but should be targeted in all breast cancers to prevent breast cancer stem cells from recapitulating tumors following treatment. Our data demonstrates that by attenuating activity of HER2 theses cancer cells lose the capacity to form tumors in vivo and lose their cancer phenotype in vitro.

Citation Format: Anastasia Frank-Kamenetskii, Julia M. Mook, Brian W. Booth. Redirection of human HER2-positive breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3092.

HER2+ breast cancer cells undergo apoptosis upon exposure to tannic acid released from remodeled cross-linked collagen type I

Tannic acid (TA) is a naturally occurring polyphenol that cross-links collagen type I and possesses anticancer potential. In previous studies, we demonstrated the increased sensitivity of estrogen receptor-positive (ER⁺ ) breast cancer cells to TA as opposed to triple negative breast cancer cells and normal human breast epithelial cells. In the current study, human pre-adipocytes and HER2+ breast cancer cells were grown on TA cross-linked collagen type I beads. Cell attachment, growth, and proliferation of the cells result in remodeling of the collagen matrix and release of the cross-linking TA. TA concentrations in the conditioned media were determined. Induced apoptosis of cells grown on the TA cross-linked collagen type I beads was imaged and quantified. Viability of HER2⁺ breast cancer cells and normal breast epithelial cells after exposure TA released from bead remodeling was quantified. Caspase gene expression and protein expression were evaluated. HER2⁺ breast cancer cells underwent caspase-mediated apoptosis in response to TA exposure. TA-induced apoptosis in a concentration- and time-dependent manner, with HER2⁺ breast cancer cells demonstrating an increased sensitivity to the TA effects. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 26-32, 2018.

Abstract 2186: Incorporation of natural compounds into biomaterials to prevent breast cancer recurrence

Numerous studies have demonstrated that naturally occurring phytochemicals such as Tannic acid (TA) possess anti-cancer properties. Apoptotic activity is increased in breast cancer and prostate cancer cells in response to exposure to tannin extracts. Collagen type I is a biomaterial routinely used for cosmetic and reconstructive surgeries, including breast reconstruction following breast cancer mandated surgeries. TA functions as a collagen crosslinking agent through both hydrogen bonding and hydrophobic effects. Thus, if TA-crosslinked collagen type I is used for breast reconstruction procedures, the crosslinked collagen will be remodeled by growing breast epithelial cells and adipocytes where the incorporated TA will be released killing nearby residual cancer cells preventing recurrence. When adipocytes are grown on TA-crosslinked collagen beads the measureable released TA induces caspase-mediated apoptosis in ER+ and HER2+ breast cancer cells but has no effect on triple negative breast cancer cells and reduced apoptotic-inducing activity in normal breast epithelial cells. We are developing an injectable matrix comprised of TA-crosslinked collagen beads and adipocytes to serve as a tissue regeneration platform in patients post-lumpectomy. Variables such as collagen temperature, syringe pump rate, and drop distance have been studied to determine ideal method for producing beads of the desired size and shape. These promising results will lead to the construction of a matrix designed to not only promote tissue regeneration but also simultaneously help to prevent tumor recurrence. This matrix provides protection in breast cancer patients and holds promise for patients suffering from other soft tissue cancers.

Citation Format: Lauren Jordan, Bailey-Jean Walker, Christopher Moody, Brian W. Booth. Incorporation of natural compounds into biomaterials to prevent breast cancer recurrence. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2186.

Remodeling of tannic acid crosslinked collagen type I induces apoptosis in ER+ breast cancer cells

BACKGROUND

The naturally-occurring phytochemical tannic acid (TA) has anticancer properties. We have demonstrated that estrogen receptor-positive (ER+) breast cancer cells are more sensitive to effects of TA than triple-negative breast cancer cells and normal breast epithelial cells. In the present study, cells were grown on TA-crosslinked collagen beads. Growing cells remodel collagen and release TA, which affects attached cells.

MATERIALS AND METHODS

The ER+ breast cancer cell line MCF7 and the normal breast epithelial cell line MCF10A were grown on TA-crosslinked collagen beads in roller bottles. Concentrations of TA in conditioned media were determined. Induced apoptosis was imaged and quantified. Caspase gene expression was calculated by real-time polymerase chain reaction (PCR).

RESULTS

Both cell lines attached and grew on TA-crosslinked collagen beads where they remodeled collagen and released TA into surrounding medium. Released TA induced caspase-mediated apoptosis.

CONCLUSION

TA induced apoptosis in a concentration-dependent manner, with ER+ MCF7 cells displaying more sensitivity to effects of TA.

Evaluation of normal and metastatic mammary cells grown in different biomaterial matrices: establishing potential tissue test systems

The in vitro growth and differentiation of normal mammalian cells is quite different than the growth of cells derived from tumors. Additionally, cells of the same origin (tissue) behave differently depending on the biomaterial matrix in or on which they are grown in vitro. We examined both Matrigel(TM) and a collagen/agarose blend and demonstrated that two murine mammary derived cells lines, 4T1 and NMuMG, derived from a metastatic mammary tumor or a normal mammary gland, respectively, exhibit different growth and differentiation patterns depending on the three-dimensional matrix in which they are grown. The shape and size of the colonies that formed were matrix dependent. The two cell lines produced different levels of growth factors and metalloproteinases, and expressed differentiation markers specific to a matrix. Through the classification of different cell behaviors in different growth matrices, we will be able to intelligently design and tune tissue test systems to ask and answer specific challenging scientific questions.

Differential gene expression in nuclear label-retaining cells in the developing mouse mammary gland

The immortal strand theory postulates stem cells protect themselves from DNA replication-associated mutations and subsequent cancer risk through selective segregation of template DNA strands. Stem cells self-renew by asymmetric cellular division. During asymmetric division, stem cells maintain their template DNA strands, while the newly synthesized DNA strands segregate to newly formed daughter cells. Previous studies have demonstrated that self-renewing mammary stem cells originate in the expanding mammary ducts during puberty-associated allometric growth. In this study, we labeled newly forming mammary stem cells with the thymidine analog 5-ethynl-2'-deoxyuridine for 2 weeks during allometric ductal expansion. Cells that incorporate and retain the nuclear label following extended chase periods are termed label-retaining cells (LRCs). A second nuclear label, 5-bromodeoxyuridine, was administered before euthanasia to identify cells traversing the cell cycle. Mammary cells collected following euthanasia were sorted based on nuclear label retention. Members of the Notch and Wnt signaling pathways were found differentially expressed by mammary LRCs. These pathways are involved in the regulation of stem cells in the mouse mammary gland. Upon further analysis, we found that in contrast to non-LRCs, Notch1 and Notch2 are expressed and localized in the nuclei of the LRCs. Expression of Notch-inducible genes, Hes1 and Hey2, was elevated in LRCs. Inhibition of Notch1 by shRNA reduced colony forming potential and label retention by mammary epithelial cells in vitro. These results indicate that genes are differentially regulated in the LRC population of mammary glands and Notch1 mediates asymmetric cell division of mammary progenitor cells.

Cell settling effects on a thermal inkjet bioprinter

This paper seeks to quantify cell settling in the print media reservoir of a bioprinter in order to determine its effect on consistent cell delivery per printed drop. The bioprinter studied here is based on the thermal inkjet HP26A cartridge, but any system that dispenses controlled volumes of fluid may be affected similarly. A simple model based on Stokes' law suggests that the cell concentration in the bottom of the reservoir should increase linearly up to some maximum and that the cell concentration in the printed drops should follow this trend. The results show that cell output initially followed the predicted increasing trend, but then peaked and decreased. The timing and rate of the decrease related to the number of use cycles for the cartridges. The results provide guidance for modifications to the printing process to ensure consistent printing of cells.

Post-bioprinting processing methods to improve cell viability and pattern fidelity in heterogeneous tissue test systems

Bioprinted tissue test systems show promise as a powerful tool for studying cell-cell interaction in heterogeneous, tissue-like co-culture. Several challenges were encountered while attempting to consistently fabricate samples with high viability and pattern fidelity. This paper evaluates four methods for processing samples after bioprinting but prior to adding media for incubation. These methods, composed of various combinations of three techniques meant to promote cell hydration, are evaluated with respect to sample viability and pattern preservation. In the best performing method, Hank's Balanced Salt Solution was applied immediately after fabrication and a collagen overlayer was applied one hour thereafter. The success of this method highlights the ability of the collagen substrate to absorb moisture, which promotes cell health without disturbing the cell's printed location. An addendum to the main study is an investigation of the limits of an HP26 print cartridge to deposit cells at a faster rate for the purpose of creating cell layers with densities that approach confluence.

The normal mammary microenvironment suppresses the tumorigenic phenotype of mouse mammary tumor virus-neu-transformed mammary tumor cells

The microenvironment of the mammary gland has been shown to exert a deterministic control over cells from different normal organs during murine mammary gland regeneration in transplantation studies. When mouse mammary tumor virus (MMTV)-neu-induced tumor cells were mixed with normal mammary epithelial cells (MECs) in a dilution series and inoculated into epithelium-free mammary fat pads, they were redirected to non-carcinogenic cell fates by interaction with untransformed MECs during regenerative growth. In the presence of non-transformed MECs (50:1), tumor cells interacted with MECs to generate functional chimeric outgrowths. When injected alone, tumor cells invariably produced tumors. Here, the normal microenvironment redirects MMTV-neu-transformed tumorigenic cells to participate in the regeneration of a normal, functional mammary gland. In addition, the redirected tumor cells show the capacity to differentiate into normal mammary cell types, including luminal, myoepithelial and secretory. The results indicate that signals emanating from a normal mammary microenvironment, comprised of stromal, epithelial and host-mediated signals, combine to suppress the cancer phenotype during glandular regeneration. Clarification of these signals offers improved therapeutic possibilities for the control of mammary cancer growth.

The normal microenvironment directs mammary gland development

Normal development of the mammary gland is a multidimensional process that is controlled in part by its mammary microenvironment. The mammary microenvironment is a defined location that encompasses mammary somatic stem cells, neighboring signaling cells, the basement membrane and extracellular matrix, mammary fibroblasts as well as the intercellular signals produced and received by these cells. These dynamic signals take numerous forms including growth factors, steroids, cell-cell or cell-basement membrane physical interactions. Cellular growth and differentiation of the mammary gland throughout the developmental stages are regulated by changes in these signals and interactions. The purpose of this review is to summarize current information and research regarding the role of the mammary microenvironment during normal glandular development.

Reprogramming human cancer cells in the mouse mammary gland

The tissue microenvironment directs stem/progenitor cell behavior. Cancer cells are also influenced by the microenvironment. It has been shown that, when placed into blastocysts, cancer cells respond to embryonic cues and differentiate according to the tissue type encountered during ontological development. Previously, we showed that the mouse mammary gland was capable of redirecting adult mouse testicular and neural stem/progenitor cells toward a mammary epithelial cell fate during gland regeneration. Here, we report that human embryonal carcinoma cells proliferate and produce differentiated mammary epithelial cell progeny when mixed with mouse mammary epithelial cells and inoculated into the epithelium-free mammary fat pads of athymic nude mice. Fluorescence in situ hybridization confirmed the presence of human cell progeny in the mammary outgrowths for human centromeric DNA, as well as immunochemistry for human-specific breast epithelial cytokeratins and human-specific milk proteins in impregnated transplant hosts. It was found that the number of human cells increased by 66- to 660-fold during mammary epithelial growth and expansion as determined by human cytokeratin expression. All features found in primary outgrowths were recapitulated in the secondary outgrowths from chimeric implants. These results show that human embryonal carcinoma-derived progeny interact with mouse mammary cells during mammary gland regeneration and are directed to differentiate into cells that exhibit diverse mammary epithelial cell phenotypes. This is the first demonstration that human cells are capable of recognizing the signals generated by the mouse mammary gland microenvironment present during gland regeneration in vivo.

ErbB/EGF signaling and EMT in mammary development and breast cancer

Activation of the ErbB family of receptor tyrosine kinases via cognate Epidermal Growth Factor (EGF)-like peptide ligands constitutes a major group of related signaling pathways that control proliferation, survival, angiogenesis and metastasis of breast cancer. In this respect, clinical trials with various ErbB receptor blocking antibodies and specific tyrosine kinase inhibitors have proven to be partially efficacious in the treatment of this heterogeneous disease. Induction of an embryonic program of epithelial-to-mesenchymal transition (EMT) in breast cancer, whereupon epithelial tumor cells convert to a more mesenchymal-like phenotype, facilitates the migration, intravasation, and extravasation of tumor cells during metastasis. Breast cancers which exhibit properties of EMT are highly aggressive and resistant to therapy. Activation of ErbB signaling can regulate EMT-associated invasion and migration in normal and malignant mammary epithelial cells, as well as modulating discrete stages of mammary gland development. The purpose of this review is to summarize current information regarding the role of ErbB signaling in aspects of EMT that influence epithelial cell plasticity during mammary gland development and tumorigenesis. How this information may contribute to the improvement of therapeutic approaches in breast cancer will also be addressed.

Stem cells and the mammary microenvironment

An entire mammary epithelial outgrowth, capable of full secretory differentiation, may comprise the progeny of a single cellular antecedent. This conclusion is based upon the maintenance of retroviral insertion sites within the somatic DNA of successive transplant generations derived from a single mammary fragment. In addition, dissociation of these clonal dominant glands and implantation of dispersed cells at limiting dilution demonstrated that both duct-limited and lobule-limited outgrowths were developed as well as complete, fully differentiated glands. Thus, transplantation has revealed three distinct mammary epithelial progenitors in the mouse. Recently, using cre-lox conditional activation of reporter genes, the lobule-limited progenitor was lineally marked by lacZ expression. In situ, these cells were shown to regenerate secretory lobules upon successive pregnancies. In transplant studies, they demonstrated the capacity for self- renewal and contributed to the new generation of all of the epithelial cell types among mammary secretory lobules. Using this conditional activation model, cells isolated from other tissues of the WAP-Cre/Rosa26/lacZReporter mice, co-mingled with normal wild type mammary epithelial cells and transplanted into epithelium-divested mammary fat pads, were shown to be amenable to redirection of their cell fate by interaction with the mammary microenvironment in vivo. This suggests the ascendancy of the microenvironment over the intrinsic nature of somatic stem cells.

Selective segregation of DNA strands persists in long-label-retaining mammary cells during pregnancy

Introduction

During pregnancy the mammary epithelial compartment undergoes extreme proliferation and differentiation, facilitated by stem/progenitor cells. Mouse mammary epithelium in nonpregnant mice contains long label-retaining epithelial cells (LREC) that divide asymmetrically and retain their template DNA strands. The role of LREC during alveogenesis has not been determined.

Methods

We performed immunohistochemistry and autoradiography on murine mammary glands that had been labeled with 5-bromodeoxyuridine (5BrdU) during allometric ductal growth to investigate the co-expression of DNA label retention and estrogen receptor-α or progesterone receptor during pregnancy. A second DNA label ([³H]-thymidine) was administered during pregnancy to identify label-retaining cells (LRC), which subsequently enter the cell cycle. Use of this methodology allowed us to investigate the co-localization of 5BrdU with smooth muscle actin, CD31, cytokeratin, and desmin in periductal or peri-acinar LRC in mammary tissue from pregnant mice subsequent to a long chase period in order to identify LRC.

Results

Estrogen receptor-α positive and progesterone receptor positive cells represented approximately 30% to 40% of the LREC, which is under 1.0% of the epithelial subpopulation. Pregnancy altered the percentage of LREC expressing estrogen receptor-α. LRC situated in periductal or peri-acinar positions throughout the gland do not express epithelial, endothelial, or myoepithelial markers, and these undefined LRCs persist throughout pregnancy. Additionally, new cycling LREC ([³H]-thymidine retaining) appear during alveologenesis, and LRC found in other tissue types (for example, endothelium and nerve) within the mammary fat pad become double labeled during pregnancy, which indicates that they may also divide asymmetrically.

Conclusions

Our findings support the premise that there is a subpopulation of LREC in the mouse mammary gland that persists during alveologenesis. These cells react to hormonal cues during pregnancy and enter the cell cycle while continuing to retain, selectively, their original template DNA. In addition, nonepithelial LRC are found in periductal or peri-acinar positions. These LRC also enter the cell cycle during pregnancy. During alveologenesis, newly created label-retaining ([³H]-thymidine) epithelial cells appear within the expanding alveoli and continue to cycle and retain their original template DNA ([³H]-thymidine) strands, as determined by a second pulse of 5BrdU.

The mammary microenvironment alters the differentiation repertoire of neural stem cells

A fundamental issue in stem cell biology is whether adult somatic stem cells are capable of accessing alternate tissue sites and continue functioning as stem cells in the new microenvironment. To address this issue relative to neurogenic stem cells in the mouse mammary gland microenvironment, we mixed wild-type mammary epithelial cells (MECs) with bona fide neural stem cells (NSCs) isolated from WAP-Cre/Rosa26R mice and inoculated them into cleared fat pads of immunocompromised females. Hosts were bred 6-8 weeks later and examined postinvolution. This allowed for mammary tissue growth, transient activation of the WAP-Cre gene, recombination, and constitutive expression of LacZ. The NSCs and their progeny contributed to mammary epithelial growth during ductal morphogenesis, and the Rosa26-LacZ reporter gene was activated by WAP-Cre expression during pregnancy. Some NSC-derived LacZ(+) cells expressed mammary-specific functions, including milk protein synthesis, whereas others adopted myoepithelial cell fates. Thus, NSCs and their progeny enter mammary epithelium-specific niches and adopt the function of similarly endowed mammary cells. This result supports the conclusion that tissue-specific signals emanating from the stroma and from the differentiated somatic cells of the mouse mammary gland can redirect the NSCs to produce cellular progeny committed to MEC fates.

Netrin-1 can affect morphogenesis and differentiation of the mouse mammary gland

Netrin-1 has been shown to regulate the function of the EGF-like protein Cripto-1 (Cr-1) and affect mammary gland development. Since Cr-1 is a target gene of Nanog and Oct4, we investigated the relationship between Netrin-1 and Cr-1, Nanog and Oct4 during different stages of development in the mouse mammary gland. Results from histological analysis show that exogenous Netrin-1 was able to induce formation of alveolar-like structures within the mammary gland terminal end buds of virgin transgenic Cripto-1 mice and enhance mammary gland alveologenesis in early pregnant FVB/N mice. Results from immunostaining and Western blot analysis show that Netrin-1, Nanog and Oct4 are expressed in the mouse embryonic mammary anlage epithelium while Cripto-1 is predominantly expressed outside this structure in the surrounding mesenchyme. We find that in lactating mammary glands of postnatal FVB/N mice, Netrin-1 expression is highest while Cripto-1 and Nanog levels are lowest indicating that Netrin-1 may perform a role in the mammary gland during lactation. HC-11 mouse mammary epithelial cells stimulated with lactogenic hormones and exogenous soluble Netrin-1 showed increased beta-casein expression as compared to control thus supporting the potential role for Netrin-1 during functional differentiation of mouse mammary epithelial cells. Finally, mouse ES cells treated with exogenous soluble Netrin-1 showed reduced levels of Nanog and Cripto-1 and higher levels of beta-III tubulin during differentiation. These results suggest that Netrin-1 may facilitate functional differentiation of mammary epithelial cells and possibly affect the expression of Nanog and/or Cripto-1 in multipotent cells that may reside in the mammary gland.

Roles of transforming growth factor-alpha in mammary development and disease

Transforming growth factor-alpha (TGFalpha) is a member of the epidermal growth factor (EGF) family. Expression of TGFalpha is highly regulated in response to exogenous cellular signals including cytokines and other growth factors. The growth factor has been found to be indispensable for proper development of many tissues and organs. TGFalpha has also been implicated in numerous disease states including forms of breast cancer. This minireview summarizes the basic biology of TGFalpha and its actions during normal and pathogenic development of the mammary epithelium.

IL-13-induced proliferation of airway epithelial cells: mediation by intracellular growth factor mobilization and ADAM17

BACKGROUND

The pleiotrophic cytokine interleukin (IL)-13 features prominently in allergic and inflammatory diseases. In allergic asthma, IL-13 is well established as an inducer of airway inflammation and tissue remodeling. We demonstrated previously that IL-13 induces release of transforming growth factor-alpha (TGFalpha) from human bronchial epithelial cells, with proliferation of these cells mediated by the autocrine/paracrine action of this growth factor. TGFalpha exists as an integral membrane protein and requires proteolytic processing to its mature form, with a disintegrin and metalloproteinase (ADAM)17 responsible for this processing in a variety of tissues.

METHODS

In this study, normal human bronchial epithelial (NHBE) cells grown in air/liquid interface (ALI) culture were used to examine the mechanisms whereby IL-13 induces release of TGFalpha and cellular proliferation. Inhibitors and antisense RNA were used to examine the role of ADAM17 in these processes, while IL-13-induced changes in the intracellular expression of TGFalpha and ADAM17 were visualized by confocal microscopy.

RESULTS

IL-13 was found to induce proliferation of NHBE cells, and release of TGFalpha, in an ADAM17-dependent manner; however, this IL-13-induced proliferation did not appear to result solely from ADAM17 activation. Rather, IL-13 induced a change in the location of TGFalpha expression from intracellular to apical regions of the NHBE cells. The apical region was also found to be a site of significant ADAM17 expression, even prior to IL-13 stimulation.

CONCLUSION

Results from this study indicate that ADAM17 mediates IL-13-induced proliferation and TGFalpha shedding in NHBE cells. Furthermore, they provide the first example wherein a cytokine (IL-13) induces a change in the intracellular expression pattern of a growth factor, apparently inducing redistribution of intracellular stores of TGFalpha to the apical region of NHBE cells where expression of ADAM17 is prominent. Thus, IL-13-induced, ADAM17-mediated release of TGFalpha, and subsequent epithelial cell proliferation, could contribute to the epithelial hypertrophy, as well as other features, associated with airway remodeling in allergic asthma.

Interaction with the mammary microenvironment redirects spermatogenic cell fate in vivo

Previously, we characterized a parity-induced mammary epithelial cell population that possessed the properties of pluripotency and self-renewal upon transplantation. These cells were lineally marked by the expression of beta-galactosidase (LacZ) as a result of mammary-specific activation of a reporter gene through Cre-lox recombination during pregnancy. We used this experimental model to determine whether testicular cells would alter their cell fate upon interaction with the mammary gland microenvironment during pregnancy, lactation, and involution. Adult testicular cells, isolated from seminiferous tubules, were mixed with limiting dilutions of dispersed mammary epithelial cells and injected into epithelium-divested mammary fat pads. The host mice were bred 6-8 weeks later and examined 20-30 days postinvolution. This approach allowed for the growth of mammary tissue from the injected cells and transient activation of the whey acidic protein promoter-Cre gene during pregnancy and lactation, leading to Cre-lox recombination and constitutive expression of LacZ from its promoter. Here we show that cells from adult seminiferous tubules interact with mammary epithelial cells during regeneration of the gland. They adopt mammary epithelial progenitor cell properties, including self-renewal and the production of cell progeny, which differentiate into functional mammary epithelial cells. Our results provide evidence for the ascendancy of the tissue microenvironment over the intrinsic nature of cells from an alternative adult tissue.

Estrogen receptor-alpha and progesterone receptor are expressed in label-retaining mammary epithelial cells that divide asymmetrically and retain their template DNA strands

Introduction

Stem cells of somatic tissues are hypothesized to protect themselves from mutation and cancer risk through a process of selective segregation of their template DNA strands during asymmetric division. Mouse mammary epithelium contains label-retaining epithelial cells that divide asymmetrically and retain their template DNA.

Method

Immunohistochemistry was used in murine mammary glands that had been labeled with [³H]thymidine during allometric growth to investigate the co-expression of DNA label retention and estrogen receptor (ER)-α or progesterone receptor (PR). Using the same methods, we investigated the co-localization of [³H]thymidine and ER-α or PR in mammary tissue from mice that had received treatment with estrogen, progesterone, and prolactin subsequent to a long chase period to identify label-retaining cells.

Results

Label-retaining epithelial cells (LRECs) comprised approximately 2.0% of the entire mammary epithelium. ER-α-positive and PR-positive cells represented about 30–40% of the LREC subpopulation. Administration of estrogen, progesterone, and prolactin altered the percentage of LRECs expressing ER-α.

Conclusion

The results presented here support the premise that there is a subpopulation of LRECs in the murine mammary gland that is positive for ER-α and/or PR. This suggests that certain mammary LRECs (potentially stem cells) remain stably positive for these receptors, raising the possibility that LRECs comprise a hierarchy of asymmetrically cycling mammary stem/progenitor cells that are distinguished by the presence or absence of nuclear steroid receptor expression.

Alveolar progenitor cells develop in mouse mammary glands independent of pregnancy and lactation

We have previously described pluripotent, parity-induced mammary epithelial cells (PI-MEC) marked by Rosa26-lacZ expression in the mammary glands of parous females. PI-MEC act as lobule-limited epithelial stem/progenitor cells. To determine whether parity is necessary to generate PI-MEC, we incubated mammary explant cultures from virgin mice in vitro with insulin alone (I), hydrocortisone alone (H), prolactin alone (Prl), or a combination of these lactogenic hormones (IHPrl). Insulin alone activated the WAP-Cre gene. Hydrocortisone and prolactin alone did not. Any combination of hormones that included insulin was effective. Only I, H and Prl together were able to induce secretory differentiation and milk protein synthesis. In addition, EGF, IGF-2 and IGF-1 added individually produced activated (lacZ(+)) PI-MEC in explant cultures. Neither estrogen nor progesterone induced WAP-Cre expression in the explants. None of these positive initiators of WAP-Cre expression in PI-MEC were effective in mammospheres or two-dimensional cultures of mammary epithelium, indicating the indispensability of epithelial-stromal interaction in PI-MEC activation. Like PI-MEC, lacZ(+) cells from virgin explants proliferated and contributed progeny to mammospheres in vitro and to epithelial outgrowths in vivo after transplantation. LacZ(+) cells induced in virgin mouse mammary explants were multipotent (like PI-MEC) in impregnated hosts producing lacZ(+) mammary alveolar structures comprised of both myoepithelial and luminal progeny. These data demonstrate PI-MEC, a mammary epithelial sub-population of lobule-limited progenitor cells, are present in nulliparous female mice before parity and, like the PI-MEC observed following parity, are capable of proliferation, self-renewal and the capacity to produce progeny of diverse epithelial cell fates.

TGFβ1 and TGFα contrarily affect alveolar survival and tumorigenesis in mouse mammary epithelium

Growth factors and hormones are responsible for development of the mammary gland and can contribute to mammary carcinogenesis. The transforming growth factors (TGF) alpha and beta1 demonstrate opposing effects on the mammary epithelium. TGFalpha is a mitogen and survival factor for mammary secretory cells and is often upregulated in cancer, while TGFbeta1 may act as a growth suppressor and has been shown to inhibit alveolar development and lactogenesis. To examine the contradistinct effects of TGFalpha and TGFbeta1 on normal mammary epithelium, we crossed MT-TGFalpha mice with WAP-TGFbeta1 transgenic mice. The newly generated bitransgenic mice failed to nurse their pups and were resistant to mammary tumorigenesis (0% at 12 months of age), compared to single transgenic MT-TGFalpha in which the majority (65% at 12 months of age) of the mice developed hyperplastic alveolar mammary lesions. Transplantation studies showed that bitransgenic tissue was highly resistant to tumor formation even after multiple pregnancies. WAP-TGFbeta1 mammary transplants often failed to grow and fully fill cleared mammary fat pads upon transplantation. This repression of growth was completely reversed in the bitransgenic implants, which grew as well as normal epithelium upon transplantation. In addition, TGF and bitransgenic TGFalpha/TGFbeta1 mice had reduced rates of apoptosis during involution as compared to wild type and TGFbeta1. These data demonstrate that TGFbeta1 and TGFalpha exhibit opposing effects upon the proliferation and survival of mammary epithelium when expressed alone but when expressed together result in reciprocally suppressive effects upon one another in the context of mammary development and tumorigenesis.

Interleukin-13 induces proliferation of human airway epithelial cells in vitro via a mechanism mediated by transforming growth factor-alpha

Remodeling of the airways, as occurs in asthmatic patients, is associated with the continual presence of inflammatory mediators and Th2 cytokines, especially interleukin (IL)-13, during cycles of epithelial injury and repair. In this study, we examined the effect of IL-13 on well-differentiated normal human bronchial epithelial (NHBE) cells maintained in air-liquid interface culture. IL-13 induced proliferation of NHBE cells after 24 h exposure, as reflected by [(3)H]thymidine uptake and cell counts. The effects of IL-13 were mediated through the epidermal growth factor receptor (EGFR), as proliferation was attenuated by AG1478, an EGFR tyrosine kinase inhibitor. Proliferation appeared to be mediated by transforming growth factor (TGF)-alpha, a potent ligand for EGFR, which was released rapidly from NHBE cells in response to IL-13. Neutralizing antibody to TGF-alpha, but not antibodies against other potentially important growth factors (EGF, heparin binding epidermal growth factor-like growth factor [HB-EGF], platelet-derived growth factor [PDGF]), inhibited the mitogenic response to IL-13. This study provides the first experimental evidence that IL-13 can initiate a proliferative response of human airway epithelium in the absence of inflammatory cells or other cell types. The results are consistent with a mechanism whereby IL-13 induces release of TGF-alpha from the epithelial cells, which in turn binds via an autocrine/paracrine-type action to the EGFR, initiating proliferation. IL-13-induced airway remodeling in vivo may involve this epithelium-driven response.

Hypertrophic pulmonary osteoarthropathy and breast cancer

Hypertrophic pulmonary osteoarthropathy is an uncommon, poorly understood syndrome usually seen with bronchogenic carcinomas, and rarely with tumors metastatic to the lungs or mediastinum. In a review of the literature, we have found only 140 cases associated with nonbronchogenic intrathoracic tumors. We have reported a case associated with metastatic breast carcinoma in which surgical resection led to rapid disappearance of the syndrome and prolonged palliation for the patient.

An epizootic of measles in captive silvered leaf-monkeys (Presbytis cristatus) in Malaysia

An epizootic of measles occurred in a group of 31 silvered leaf-monkeys (Presbytis cristatus) that had been in captivity for 4-12 months. Twenty-four of the monkeys exhibited a maculopapular rash that persisted for 6-9 days. A serous to mucopurulent nasal discharge and conjunctivitis were seen in some animals. Eight monkeys died during the epizootic; however, their deaths could not be directly attributed to measles. Serum samples from the surviving monkeys collected 1-2 months prior to, and 5 weeks after, the epizootic were examined by the complement-fixation and hemagglutination-inhibition tests for antibodies to measles virus. The preepizootic complement-fixation titers were all less than 1:4 and hemagglutination-inhibition titers, less than 1:10. The postepizootic complement-fixation titers in 21 of 23 surviving monkeys ranged from 1:8 to 1:128, and hemagglutination-inhibition titers in 22 of 23 monkeys ranged from 1:40 to 1:80 or greater.

Enhancement of infectivity of encephalomyocarditis virus RNA by amphotericin B methyl ester

The methyl ester of amphotericin B (AmBME), a macrolide polyene antibiotic, enhanced the infectivity of encephalomyocarditis (EMC) virus RNA for L929 cells. AmBME alone (100 microgram/ml) resulted in increases in EMC virus RNA infectivity of 10- to 100-fold. Addition of DEAE dextran at concentrations (5 microgram/ml), which alone slightly suppressed EMC virus RNA infectivity, further augmented the effects of AmBME (augmentation in infectivity up to 750-fold). AmBME did not inhibit RNase, did not enhance EMC virus infectivity and increased infectivity of EMC virus RNA which was already cell-associated. The polyenes are probably acting by increasing intracellular penetration of polyribonucleotides.

Increase by calcium in production of interferon by L929 cells induced with polyriboinosinate-polyribocytidylate complex

Calcium chloride (5 to 20 mM) potentiated interferon production induced by rIn:rCn in L929 mouse fibroblasts up to a thousand-fold. Higher concentrations of calcium (20 to 65 mM) mixed with rIn:rCn were associated with increased cytotoxicity and a more acidic medium, but were effective in enhancing interferon production if preparations were adjusted to a uniform pH. Although calcium increased cellular binding of 3H-rCn:rIn, only a partial correlation between binding and interferon production was observed.