Therapeutic trials for long COVID-19: A call to action from the interventions taskforce of the RECOVER initiative

Although most individuals recover from acute SARS-CoV-2 infection, a significant number continue to suffer from Post-Acute Sequelae of SARS-CoV-2 (PASC), including the unexplained symptoms that are frequently referred to as long COVID, which could last for weeks, months, or even years after the acute phase of illness. The National Institutes of Health is currently funding large multi-center research programs as part of its Researching COVID to Enhance Recover (RECOVER) initiative to understand why some individuals do not recover fully from COVID-19. Several ongoing pathobiology studies have provided clues to potential mechanisms contributing to this condition. These include persistence of SARS-CoV-2 antigen and/or genetic material, immune dysregulation, reactivation of other latent viral infections, microvascular dysfunction, and gut dysbiosis, among others. Although our understanding of the causes of long COVID remains incomplete, these early pathophysiologic studies suggest biological pathways that could be targeted in therapeutic trials that aim to ameliorate symptoms. Repurposed medicines and novel therapeutics deserve formal testing in clinical trial settings prior to adoption. While we endorse clinical trials, especially those that prioritize inclusion of the diverse populations most affected by COVID-19 and long COVID, we discourage off-label experimentation in uncontrolled and/or unsupervised settings. Here, we review ongoing, planned, and potential future therapeutic interventions for long COVID based on the current understanding of the pathobiological processes underlying this condition. We focus on clinical, pharmacological, and feasibility data, with the goal of informing future interventional research studies.

Gaps and opportunities in the treatment of relapsed-refractory multiple myeloma: Consensus recommendations of the NCI Multiple Myeloma Steering Committee

A wide variety of new therapeutic options for Multiple Myeloma (MM) have recently become available, extending progression-free and overall survival for patients in meaningful ways. However, these treatments are not curative, and patients eventually relapse, necessitating decisions on the appropriate choice of treatment(s) for the next phase of the disease. Additionally, an important subset of MM patients will prove to be refractory to the majority of the available treatments, requiring selection of effective therapies from the remaining options. Immunomodulatory agents (IMiDs), proteasome inhibitors, monoclonal antibodies, and alkylating agents are the major classes of MM therapies, with several options in each class. Patients who are refractory to one agent in a class may be responsive to a related compound or to a drug from a different class. However, rules for selection of alternative treatments in these situations are somewhat empirical and later phase clinical trials to inform those choices are ongoing. To address these issues the NCI Multiple Myeloma Steering Committee formed a relapsed/refractory working group to review optimal treatment choices, timing, and sequencing and provide recommendations. Additional issues considered include the role of salvage autologous stem cell transplantation, risk stratification, targeted approaches for genetic subsets of MM, appropriate clinical trial endpoints, and promising investigational agents. This report summarizes the deliberations of the working group and suggests potential avenues of research to improve the precision, timing, and durability of treatments for Myeloma.

Updated Standardized Definitions for Efficacy End Points (STEEP) in Adjuvant Breast Cancer Clinical Trials: STEEP Version 2.0

PURPOSE

The Standardized Definitions for Efficacy End Points (STEEP) criteria, established in 2007, provide standardized definitions of adjuvant breast cancer clinical trial end points. Given the evolution of breast cancer clinical trials and improvements in outcomes, a panel of experts reviewed the STEEP criteria to determine whether modifications are needed.

METHODS

We conducted systematic searches of ClinicalTrials.gov for adjuvant systemic and local-regional therapy trials for breast cancer to investigate if the primary end points reported met STEEP criteria. On the basis of common STEEP deviations, we performed a series of simulations to evaluate the effect of excluding non-breast cancer deaths and new nonbreast primary cancers from the invasive disease-free survival end point.

RESULTS

Among 11 phase III breast cancer trials with primary efficacy end points, three had primary end points that followed STEEP criteria, four used STEEP definitions but not the corresponding end point names, and four used end points that were not included in the original STEEP manuscript. Simulation modeling demonstrated that inclusion of second nonbreast primary cancer can increase the probability of incorrect inferences, can decrease power to detect clinically relevant efficacy effects, and may mask differences in recurrence rates, especially when recurrence rates are low.

CONCLUSION

We recommend an additional end point, invasive breast cancer-free survival, which includes all invasive disease-free survival events except second nonbreast primary cancers. This end point should be considered for trials in which the toxicities of agents are well-known and where the risk of second primary cancer is small. Additionally, we provide end point recommendations for local therapy trials, low-risk populations, noninferiority trials, and trials incorporating patient-reported outcomes.

Recommendations for Clinical Trial Development in Mantle Cell Lymphoma

Mantle cell lymphoma (MCL) comprises around 6% of all non-Hodgkin's lymphoma (NHL) diagnoses. In younger patients, age less than 60 to 65 years, aggressive induction often followed by consolidation with autologous stem cell transplant has suggested improved outcomes in this population. Less intensive therapies in older patients often followed by maintenance have been studied or are under active investigation. However, despite recent advances, MCL remains incurable, with a median overall survival of around five years. Patients with high-risk disease have particularly poor outcomes. Treatment varies widely across institutions, and to date no randomized trials comparing intensive vs less intensive approaches have been reported. Although recent data have highlighted the heterogeneity of MCL outcomes, patient assessment for treatment selection has largely been driven by patient age with little regard to fitness, disease biology, or disease risk. One critical advance is the finding that minimal residual disease status (MRD) after induction correlates with long-term outcomes. As such, its use as a potential end point could inform clinical trial design. In order to more rapidly improve the outcomes of MCL patients, clinical trials are needed that prospectively stratify patients on the basis of MCL biology and disease risk, incorporate novel agents, and use MRD to guide the need for additional therapy.

Recommendations for Clinical Trial Development in Follicular Lymphoma

Follicular lymphoma (FL) is the second most common lymphoid malignancy, representing 20% to 25% of all cases of non-Hodgkin's lymphoma (NHL), and the most common of the indolent NHLs. FL is considered incurable in the majority of patients with the current standard therapeutic approaches, although outcomes have improved in the last few decades with our current therapies, with a median overall survival that now exceeds 18 years. While the majority of patients with FL have improved outcomes with our current therapeutic approaches, there are patients with high-risk disease features that have inferior outcomes to these therapies. There is an urgent need to integrate novel therapeutic agents into the treatment regimens for these patients to improve outcomes with continued evaluation of biomarkers indicative of prognosis and effects of these regimens on quality of life.

Hodgkin Lymphoma: Current Status and Clinical Trial Recommendations

The National Clinical Trials Network lymphoid malignancies Clinical Trials Planning Meeting (CTPM) occurred in November of 2014. The scope of the CTPM was to prioritize across the lymphoid tumors clinically significant questions and to foster strategies leading to biologically informed and potentially practice changing clinical trials. This review from the Hodgkin lymphoma (HL) subcommittee of the CTPM discusses the ongoing clinical challenges in HL, outlines the current standard of care for HL patients from early to advanced stage, and surveys the current science with respect to biomarkers and the landscape of ongoing clinical trials. Finally, we suggest areas of unmet need in HL and elucidate promising therapeutic strategies to guide future HL clinical trials planning across the NCTN.

General Biomarker Recommendations for Lymphoma

Lymphoid malignancies are a heterogeneous group of tumors that have distinctive clinical and biological behaviors. The increasing prevalence of disease reflects both treatment advances and the fact that some of these tumors are indolent. The ability to determine treatment needs at diagnosis remains problematic for some of the tumors, such as in follicular lymphomas. Major clinical advances will likely depend on precision oncology that will enable identification of specific disease entities, prognostic determination at diagnosis, and identification of precise therapeutic targets and essential pathways. However, refinement in diagnostic evaluation is an evolving science. The ability to determine prognosis at diagnosis is variable, and for many of the lymphoid malignancies prognosis can only be made after initial treatment. Clinical trials that aim to evaluate specific features of these diseases are required in order to advance clinical practice that meaningfully addresses this important public health challenge. Herein, we describe the process and general recommendation from the National Cancer Institute (NCI) clinical trials planning meeting in November 2014 to address clinical trial design and biomarker proposals in the context of NCI-supported lymphoma clinical trials in the National Clinical Trials Network.

Beyond RCHOP: A Blueprint for Diffuse Large B Cell Lymphoma Research

Diffuse large B cell lymphoma (DLBCL) comprises multiple molecular and biological subtypes, resulting in a broad range of clinical outcomes. With standard chemoimmunotherapy, there remains an unacceptably high treatment failure rate in certain DLBCL subsets: activated B cell (ABC) DLBCL, double-hit lymphoma defined by the dual translocation of MYC and BCL2, dual protein-expressing lymphomas defined by the overexpression of MYC and BCL2, and older patients and those with central nervous system involvement. The main research challenges for DLBCL are to accurately identify molecular subsets and to determine if specific chemotherapy platforms and targeted agents offer differential benefit. The ultimate goal should be to maximize initial cure rates to improve long-term survival while minimizing toxicity. In particular, a frontline trial should focus on biologically defined risk groups not likely to be cured with cyclophosphamide, doxorubicin, vincristine, and prednisone plus rituximab (R-CHOP). An additional challenge is to develop effective and personalized strategies in the relapsed setting, for which there is no current standard other than autologous stem cell transplantation, which benefits a progressively smaller proportion of patients. Relapsed/refractory DLBCL is the ideal setting for testing novel agents and new biomarker tools and will require a national call for biopsies to optimize discovery in this setting. Accordingly, the development of tools with both prognostic and predictive utility and the individualized application of new therapies should be the main priorities. This report identifies clinical research priorities for critical areas of unmet need in this disease.

Needle-free topical electroporation improves gene expression from plasmids administered in porcine skin

Electroporation has been shown to increase the potency of DNA vaccines that have demonstrated significant potential in mice. However, there is a need to develop noninvasive or minimally invasive vaccination methods. In pigs, in vivo gene expression was assessed to compare intradermal needle injection to a needle-free dermal BioJect as a means of delivery of plasmids. Each administration method was further tested with and without surface electroporation. Experiments with plasmid DNA encoding luciferase demonstrated that needle-free administration results in higher gene expression levels than needle injection. Electroporation enhanced gene expression for both intradermal delivery methods. Needle-free plasmid injection in combination with electroporation led to a more rapid induction of immune responses compared to other methods of plasmid administration. It was concluded that needle-free topical electroporation significantly enhances gene expression, possibly by improving cellular uptake of plasmid DNA.

Intradermal immunization with novel plasmid DNA-coated nanoparticles via a needle-free injection device

A high population of dendritic cells in the skin makes intradermal (ID) immunization an attractive route. We sought to further enhance immune responses from a previously reported novel nanoparticle-based DNA vaccine delivery system by administering the system intradermally into mouse skin using Biojector 2000, a needle-free jet injection device. Two mouse studies were carried out. Balb/C mice (n=5-6) were immunized on day 0, 7, and 14 by subcutaneous injection or via the Biojector 2000 with pDNA alone (CMV-beta-galactosidase, 5 micro g), pDNA-coated nanoparticles, or beta-galactosidase protein (10 micro g) adjuvanted with 'Alum' (15 micro g). On day 28, mice were sacrificed and specific serum IgG and IgA titer, in vitro cytokine release, and cell proliferation of isolated splenocytes were determined. Similar to previous reports, in both mouse studies, SC immunization with pDNA-coated nanoparticles led to over a log increase in specific serum IgG titer as compared to immunization with pDNA alone. For pDNA alone, jet and SC injection did not result in significant differences in IgG titer. In contrast, for pDNA-coated nanoparticles, jet injection led to as high as a 20-fold enhancement in IgG titer over SC injection. In addition, jet injection of pDNA-coated nanoparticles enhanced the IgG titer by more than 200-fold over jet injection of pDNA alone. Also, jet injection of pDNA-coated nanoparticles resulted in significantly enhanced specific serum IgA titer. For in vitro cytokine release, immunization with pDNA-coated nanoparticles by jet injection enhanced IFN-gamma and IL-4 release over pDNA alone by 6- and 5-fold, respectively. SC injection of pDNA-coated nanoparticles also resulted in enhanced IFN-gamma and IL-4 release over pDNA alone although with less magnitude. Finally, immunization with pDNA-coated nanoparticles, by both jet injection and SC injection, led to improved splenocyte proliferation over pDNA alone. In conclusion, a combination of a novel cationic nanoparticle-based DNA delivery system with ID jet injection led to enhanced antibody production, Th-1/Th-2 balanced cytokine release, and enhanced splenocyte proliferation.

Analysis of the role of calmodulin binding and sequestration in neuromodulin (GAP-43) function

We demonstrated previously that forced expression of the neuronal phosphoprotein neuromodulin (also known as GAP-43, F1, B-50, and p57) in mouse anterior pituitary AtT-20 cells enhances depolarization-mediated secretion and alters cellular morphology. Here we analyze the role of calmodulin binding by neuromodulin in these responses. In cells expressing wild-type neuromodulin, a complex with calmodulin that is sensitive to intracellular calcium and phosphorylation is localized to the plasma membrane. Transfection of several mutant forms of neuromodulin shows that the effects of this protein on secretion are dependent on both calmodulin binding and association with the plasma membrane. In contrast, the morphological changes depend only on membrane association. Thus, the multitude of effects of neuromodulin noted in previous studies may result from divergent properties of this protein.

Growth-associated protein-43 (GAP-43) facilitates peptide hormone secretion in mouse anterior pituitary AtT-20 cells

The neuronal growth-associated protein (GAP)-43 (neuromodulin, B-50, F1), which is concentrated in the growth cones of elongating axons during neuronal development and in nerve terminals in restricted regions of the adult nervous system, has been implicated in the release of neurotransmitter. To study the role of GAP-43 in evoked secretion, we transfected mouse anterior pituitary AtT-20 cells with the rat GAP-43 cDNA and derived stably transfected cell lines. Depolarization-mediated beta-endorphin secretion was greatly enhanced in the GAP-43-expressing AtT-20 cells without a significant change in Ca2+ influx; in contrast, expression of GAP-43 did not alter corticotropin-releasing factor-evoked hormone secretion. The transfected cells also displayed a flattened morphology and extended processes when plated on laminin-coated substrates. These results suggest that AtT-20 cells are a useful model system for further investigations on the precise biological function(s) of GAP-43.

Recoverin, a photoreceptor-specific calcium-binding protein, is expressed by the tumor of a patient with cancer-associated retinopathy

Recoverin is a member of the EF-hand family of calcium-binding proteins involved in the transduction of light by vertebrate photoreceptors. Recoverin also was identified as an autoantigen in the degenerative disease of the retina known as cancer-associated retinopathy (CAR), a paraneoplastic syndrome whereby immunological events lead to the degeneration of photoreceptors in some individuals with cancer. In this study, we demonstrate that recoverin is expressed in the lung tumor of a CAR patient but not in similar tumors obtained from individuals without the associated retinopathy. Recoverin was identified intially by Western blot analysis of the CAR patient's biopsy tissue by using anti-recoverin antibodies generated against different regions of the recoverin molecule. In addition, cultured cells from the biopsy tissue expressed recoverin, as demonstrated by reverse transcription-PCR using RNA extracted from the cells. The immunodominant region of recoverin also was determined in this study by a solid-phase immunoassay employing overlapping heptapeptides encompassing the entire recoverin sequence. Two linear stretches of amino acids (residues 64-70, Lys-Ala-Tyr-Ala-Gln-His-Val; and 48-52, Gln-Phe-Gln-Ser-Ile) made up the major determinants. One of the same regions of the recoverin molecule (residues 64-70) also was uniquely immunopathogenic, causing photoreceptor degeneration upon immunization of Lewis rats with the corresponding peptide. These data demonstrate that the neural antigen recoverin more than likely is responsible for the immunological events associated with vision loss in some patients with cancer. These data also establish CAR as one of the few autoimmune-mediated diseases for which the specific self-antigen is known.

Regulated expression of neurofibromin in migrating neural crest cells of avian embryos

Neurofibromatosis type 1 (NF1) is a common human genetic disease involving various neural crest (NC)-derived cell types, in particular, Schwann cells and melanocytes. The gene responsible for NF1 encodes the protein neurofibromin, which contains a domain with amino acid sequence homology to the ras-guanosine triphosphatase activating protein, suggesting that neurofibromin may play a role in intracellular signaling pathways regulating cellular proliferation or differentiation, or both. To determine whether neurofibromin plays a role in NC cell development, we used antibodies raised against human neurofibromin fusion proteins in western blot and immunocytochemical studies of early avian embryos. These antibodies specifically recognized the 235 kD chicken neurofibromin protein, which was expressed in migrating trunk and cranial NC cells of early embryos (E1.5 to E2), as well as in endothelial and smooth muscle cells of blood vessels and in a subpopulation of non-NC-derived cells in the dermamyotome. At slightly later stages (E3 to E5), neurofibromin immunostaining was observed in various NC derivatives, including dorsal root ganglia and peripheral nerves, as well as non-NC-derived cell types, including heart, skeletal muscle, and kidney. At still later stages (E7 to E9), neurofibromin immunoreactivity was found in almost all tissues in vivo. To determine whether the levels of neurofibromin changed during melanocyte and Schwann cell development, tissue culture experiments were performed. Cultured NC cells were found to express neurofibromin at early time points in culture, but the levels of immunoreactivity decreased as the cells underwent pigmentation. Schwann cells, on the other hand, continued to express neurofibromin in culture. These data suggest, therefore, that neurofibromin may play a role in the development of both NC cells and a variety of non-NC-derived tissues.

Calbindin D-28K immunoreactivity of human cone cells varies with retinal position

Calbindin D-28K is a calcium-binding protein found in the cone but not rod photoreceptor cells in the retinas of a variety of species. Recent studies of the monkey retina indicated that calbindin D-28K may be expressed preferentially in non-foveal regions of the retina. In the current studies of human retinas, immunohistochemical experiments demonstrated that calbindin D-28K is reduced or absent in the fovea and parafovea, but prevalent in the perifovea and periphery. These findings were supported by the quantification of calbindin D-28K in 1-mm trephine punches obtained from different regions of the human retina. The specificity of the anti-calbindin D-28K antibodies used in these studies was confirmed by Western blot analysis using purified calbindin D-28K. The protein was purified from retinal tissue and its identity confirmed by partial amino-acid sequence analysis. The expression of calbindin D-28K did not correlate with the spectral properties of the cones, rather to their position in the retina. The study of spatially expressed genes, like the one encoding calbindin D-28K, may help explain the patterns of retinal degeneration seen in some human cone-rod dystrophies.

Purification and primary structure of Capl, an S-100-related calcium-binding protein isolated from bovine retina

Calcium protein placental homolog (Capl) is an S-100-related calcium-binding protein selectively expressed in cell lines that have been induced to grow or differentiate. In addition, the expression of Capl correlates with the induction of the metastatic phenotype in tumor cell lines and the transformation of normal cells by activated oncogenes or chemical carcinogens. Although not previously associated with the nervous system, in this study, Capl was purified from bovine neural retina by a combination of phenyl-Sepharose and organomercurial chromatography. The complete amino acid sequence of bovine Capl was established primarily by Edman degradation of peptides generated by cleavage of methionyl, lysyl, glutamyl, and aspartyl bonds. NH2-terminal methionyl and aspartyl peptides were analyzed by tandem mass spectrometry, which provided the sequence of the first 8 residues and identified the NH2-terminal blocking group as an acetyl moiety. The molecular mass of the intact protein determined by electrospray mass spectrometry (M(r) = 11,716.75 +/- 0.42) and the calculated molecular mass deduced from the amino acid composition (M(r) = 11,718) were in agreement, thus supporting the accuracy of the sequence assignment. Capl isolated from the retina was shown to be indistinguishable by mass and immunochemical properties from its counterpart in the bovine aorta, which previously was the only source of purified Capl. Northern analysis using cloned Capl cDNA revealed that Capl mRNA is present not only in the retina but the choroid as well. Further support for choroidal localization came from immunohistochemical experiments using specific anti-Capl antibodies. The physiological significance of Capl in ocular tissues and the aorta is discussed.

Regulated expression of the neurofibromin type I transcript in the developing chicken brain

Neurofibromatosis type 1 (NF-1) is among the most common inherited diseases affecting cells of the central and peripheral nervous systems. A region of the NF-1 gene is similar in sequence to the ras-GTPase activator protein (ras-GAP), and investigations have confirmed that the NF-1 gene product (now known as neurofibromin) stimulates ras-GTPase activity in vitro and in vivo. Neurofibromin modulates the ability of ras proteins to regulate cellular proliferation and/or differentiation, suggesting a possible role in normal development. An alternative form of the neurofibromin transcript with an additional 63-bp exon inserted in the GAP-related domain (GRD) has been described recently. To determine whether differential expression of the two forms of neurofibromin GRD mRNA plays a role in embryonic development, we have isolated and characterized the corresponding chicken cDNA. The predicted amino acid sequence for the inserted exon is identical between chick and human, as are the exon-intron boundaries. RNase protection and RNA-polymerase chain reaction analyses demonstrate that most tissues express predominantly type II mRNA (which contains the insert) throughout embryonic development. In contrast, whereas type II is the major form in the brain early in development, expression of the type I transcript (without the insert) in this tissue increases dramatically at later times. Analysis of primary cultures derived from chick embryo brain indicates that the type I mRNA is enriched in neurons.

Analysis of the sequence and embryonic expression of chicken neurofibromin mRNA

Neurofibromatosis type 1 (NF1) is a common inherited disorder that primarily affects tissues derived from the neural crest. Recent identification and characterization of the human NF1 gene has revealed that it encodes a protein (now called neurofibromin) that is similar in sequence to the ras-GTPase activator protein (or ras-GAP), suggesting that neurofibromin may be a component of cellular signal transduction pathways regulating cellular proliferation and/or differentiation. To initiate investigations on the role of the NF1 gene product in embryonic development, we have isolated a partial cDNA for chicken neurofibromin. Sequence analysis reveals that the predicted amino acid sequence is highly conserved between chick and human. The chicken cDNA hybridizes to a 12.5-kb transcript on RNA blots, a mol wt similar to that reported for the human and murine mRNAs. Ribonuclease protection assays indicate that NF1 mRNA is expressed in a variety of tissues in the chick embryo; this is confirmed by in situ hybridization analysis. NF1 mRNA expression is detectable as early as embryonic stage 18 in the neural plate. This pattern of expression may suggest a role for neurofibromin during normal development, including that of the nervous system.

Transient expression of GAP-43 in nonneuronal cells of the embryonic chicken limb

Growth associated protein (GAP)-43 is a membrane-bound phosphoprotein expressed in neurons and is particularly abundant during periods of axonal outgrowth in development and regeneration of the nervous system. In previous work, we cloned a full-length chicken GAP-43 cDNA and described the expression of its corresponding mRNA during early development of the chicken nervous system. We report here that the GAP-43 mRNA is also expressed transiently in developing limbs of chicken embryos, which contain axons of spinal cord and dorsal root ganglion neurons, but do not contain neuronal cell bodies. GAP-43 mRNA was first detectable by RNA blot analysis in limbs from Embryonic Day 5 (E5) embryos, reached maximal levels between E6 and E8, and diminished by E10. In situ hybridization analysis showed that the GAP-43 mRNA was localized in distal regions of developing limbs and was particularly abundant in the mesenchyme surrounding the digital cartilage. In some regions of the limb, GAP-43 immunoreactivity colocalized in cells that were also immunoreactive for meromyosin, a muscle-specific marker. These data suggest that both GAP-43 mRNA and the protein are expressed in nonneuronal cells of the developing limb, some of which may be part of the muscle cell lineage.

GAP-43 in non-neuronal cells of the embryonic chick limb: clues to function

The expression of GAP-43 in developing and regenerating neurons has been well characterized, but the function of this membrane-bound phosphoprotein is still unclear. Although GAP-43 is considered to be neuron-specific, it is also expressed in various glial cells of the peripheral and central nervous systems and in at least two populations of mesenchymal cells in the developing chick limb. GAP-43 mRNA is expressed transiently in developing limbs, which contain axons of spinal cord and dorsal root ganglion neurons, but do not contain neuronal cell bodies. This expression is correlated temporally with the in-growth of neurites and axons to the limbs, but appears to be independent of nerves. In some regions of the limb, GAP-43 immunoreactivity co-localizes in cells that are also immunoreactive for meromyosin, a muscle-specific marker. In addition, GAP-43 mRNA and protein are particularly abundant in the interdigital mesenchyme that undergoes apoptosis, or programmed cell death. GAP-43 has been postulated to mediate rapid changes in cell shape and the extension of processes in neuronal growth cones and elongating axons. We suggest here that GAP-43 may serve a similar function in glial cells, in myoblasts fusing to form myotubes, and in apoptotic and phagocytic cells of the interdigital mesenchyme.

Chicken growth-associated protein GAP-43 is tightly bound to the actin-rich neuronal membrane skeleton

We have identified the chicken equivalent of growth-associated protein GAP-43 in a detergent-resistant membrane skeleton from cultures of chick neurones and embryonic chick brain. Antisera to the membrane skeleton protein, the 3D5 antigen, precipitate the translation product of chick GAP-43 cDNA, and the 3D5 antigen is also detected by antisera against synthetic peptides from the known amino acid sequence of rat GAP-43. The chick protein and the rat GAP-43 are biochemically similar proteins that both serve as major targets of phosphorylation by endogenous protein kinase C. The detergent-resistant complex in which GAP-43 is found also contains actin (approximately 5% of the total protein) and a neurone-specific cell surface glycoprotein. We suggest that the membrane skeleton of neurones may be a primary site of action of GAP-43.

Bovine dopamine beta-hydroxylase cDNA. Complete coding sequence and expression in mammalian cells with vaccinia virus vector

We have isolated cDNA clones for bovine dopamine beta-hydroxylase from an adrenal medulla cDNA library and have determined the complete coding sequence. The largest cDNA clone isolated from the library is 2.4 kilobase pairs (kb) and contains an open reading frame of 1788 bases, coding for a protein of 597 amino acids and Mr = 66,803. The predicted amino acid sequence of the bovine cDNA contains 85% identity with human dopamine beta-hydroxylase (Lamouroux, A., Vingny, A., Faucon Biquet, N., Darmon, M. C., Franck, R., Henry, J.P., and Mallet, J. (1987) EMBO J. 6, 3931-3937; Kobayashi, K., Kurosawa, Y., Fujita, K., and Nagatsu, T. (1989) Nucleic Acids Res. 17, 1089-1102). Northern blot analysis reveals that the cDNA hybridizes to an mRNA of 2.4 kb present in bovine adrenal medulla, but not in kidney, heart, or liver. In addition, the cDNA hybridizes to a second RNA species of 5.5 kb, which is 4-fold less abundant than the 2.4-kb RNA. In vitro translation of a synthetic RNA transcribed from the 2.4-kb cDNA produces a 68-kDa protein, which is specifically immunoprecipitated by antiserum to bovine dopamine beta-hydroxylase. The 2.4-kb cDNA was cloned into a vaccinia virus vector, and the recombinant virus was used to infect the rat pheochromocytoma PC12 and monkey BSC-40 fibroblast cell lines. In both cell lines, infection with recombinant virus produces a protein of Mr = 75,000, which reacts with antiserum to bovine dopamine beta-hydroxylase. These results indicate that the 2.4-kb cDNA contains the genetic information necessary to code for the bovine dopamine beta-hydroxylase subunit.

Chicken growth-associated protein (GAP)-43: primary structure and regulated expression of mRNA during embryogenesis

Growth-associated protein (GAP)-43 is a neuron-specific phosphoprotein whose expression is associated with axonal outgrowth during neuronal development and regeneration. In order to investigate the expression of this gene product in the early developing nervous system we have isolated and sequenced a cDNA for chicken GAP-43. The predicted amino acid sequence for chicken GAP-43 displays extensive similarity to that of the mammalian protein, particularly in the amino-terminal region, to which functional domains of the protein have been assigned. The cDNA hybridizes with two RNAs of differing molecular weights on Northern blots; both appear to be regulated similarly. These RNAs first appear in the brain on embryonic day 3 (E3), suggesting that GAP-43 begins to be expressed when neuroblasts become post-mitotic. In situ hybridization analysis reveals that GAP-43 RNA is expressed by several neural structures in the chick embryo, including derivatives of the neural tube, neural crest, and neuroectodermal placodes.

Recognition of specific targets by cultured dorsal root ganglion neurons

We have assessed the effects of different target cell populations on axonally transported proteins by the use of compartmental cell culture systems that separate the soma from the growing axons of rat sensory neurons. The labeling of 3 rapidly transported proteins diminishes when the growing axon contacts spinal cord cells (which are normal in vivo targets), and remains unaffected by contact with fibroblasts or heart cells. Medium conditioned by spinal cord cells does not exert this effect. Thus, specific classes of cells may be distinguished as target tissue by sensory neurons in vitro. Such recognition is accompanied by specific molecular changes in axonally transported proteins.

Neuronal traits of clonal cell lines derived by fusion of dorsal root ganglia neurons with neuroblastoma cells

In an attempt to immortalize the gene products of single neurons, somatic cell hybrids were produced by fusion of embryonic rat dorsal root ganglion (DRG) neurons with mouse neuroblastoma cells. Embryonic day 13 rat DRGs were fused with mouse neuroblastoma cells deficient in hypoxanthine phosphoribosyltransferase (HPRT; IMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.8). The hybrid cells were selected in medium with 100 microM hypoxanthine/1 microM aminopterin/12 microM thymidine to eliminate the neuroblastoma cells and with cis-hydroxyproline to retard fibroblast growth. Of the 17 lines derived, 4 manifested neuronal properties and were cloned. These lines retain both rat and mouse chromosomes and synthesize characteristic rat and mouse isoenzymes. Neuronal gangliosides, action potentials, and extensive neurite-like processes are exhibited by these hybrid cells, properties characteristic of DRG neurons but not of the neuroblastoma parent. Each line manifests a unique combination of action-potential properties and cell-surface markers, suggesting the selective expression of subsets of DRG neuronal genes. All of these neuronal properties are expressed constitutively, without the need for chemical induction or mitotic inhibition, and stably, without diminution after at least 5 months in culture. These lines may prove useful in the identification and isolation of gene products that characterize individual or small subsets of DRG neurons.

Nerve growth factor treatment enhances nicotine-stimulated dopamine release and increases in cyclic adenosine 3':5'-monophosphate levels in PC12 cell cultures

In order to examine the relationship between cyclic AMP (cAMP) levels and evoked neurotransmitter release, experiments have been performed with cultures of clonal rat PC12 pheochromocytoma cells. Stimulation of the release of endogenous dopamine by nicotine in these cultures is calcium-dependent and blocked by d-tubocurarine, a specific nicotinic cholinergic antagonist. Similarly, nicotine causes increases in cAMP levels in PC12 cell cultures that are calcium-dependent and blocked by d-tubocurarine. Cultures treated for 6 days or longer with 2 X 10(-9) M nerve growth factor (NGF) release a 3- to 4-fold greater amount of dopamine than do control cultures in response to a maximal concentration of nicotine. Correspondingly, nicotine causes a 3-fold greater increase in cAMP levels in the NGF-treated cultures than in the controls. These results suggest that stimulation of the nicotinic cholinergic receptor in PC12 cells results in some manner in the activation of adenylate cyclase and further support the notion that cAMP is involved in the process of neurotransmitter release.

Regulation of dopamine release from PC12 pheochromocytoma cell cultures during stimulation with elevated potassium or carbachol

To examine the role of cyclic AMP in the process of catecholamine release experiments have been performed with cultures of PC12 pheochromocytoma cells. Elevated potassium (56 mM) and carbamylcholine (carbachol, 10(-4) M) cause rapid increases in cyclic AMP levels in the cultures that show a time course similar to that of evoked dopamine release. These secretogogue-induced increases in cyclic AMP levels are well correlated with release in terms of relative magnitude and calcium dependence. Forskolin (a direct activator of adenylate cyclase) causes dose-related increases in cyclic AMP levels in PC12 cell cultures that are synergistic with those caused by either elevated potassium or carbachol. At low concentrations forskolin significantly increases evoked release, whereas at higher concentrations it increases both spontaneous and evoked release. These results suggest that cyclic AMP may be involved in the process of dopamine release from PC12 cells in culture.

Description and analysis of the myotonolytic effects of phenytoin in the decerebrate cat: implications for potential utility of phenytoin in spastic disorders

Phenytoin (DPH) was evaluated for its capacity to reduce several motor manifestations of decerebrate rigidity in the cat. In doses of the order of 40 to 50 mg/kg i.v., DPH diminished the force necessary to collapse the hyperextended limbs; at about half this dose range, the drug reduced gamma-motoneuron discharges; at still lower doses the drug profoundly depressed mechanical and electromyographic responses evoked by stretch from both forelimb and hindlimb extensor muscles. Serum levels of DPH associated with substantial reduction in electrical and mechanical manifestations of the extensor hypertonus were of the same order conventionally encountered when the drug is administered to humans for acute seizure management. The data are supportive of a centrally and peripherally mediated muscle relaxing effect of the drug in states where muscle spindle involvement is a contributing factor, and may help to explain further the utility of DPH in the treatment of spasticity.

Ethanol-induced changes in tyrosine hydroxylase activity in brains of mice selectively bred for differences in sensitivity to ethanol

The effects of ethanol on tyrosine hydroxylase (TH) activity in five brain areas were analyzed in two lines of mice selectively bred for their differences in sensitivity to ethanol. Following a 4.1 g/kg dose of ethanol, intraperitoneally, short sleep (SS) mice lose their righting reflex for a duration of 20 minutes and long sleep (LS) mice fail to regain their righting reflex until 120 minutes. A significant increase in TH activity occurred in the striatum, locus coeruleus and frontal cortex in both lines of mice approximately 25 minutes following ethanol administration. A decrease in TH activity occurred in the substantia nigra of SS mice at 5 minutes following ethanol administration. However, there was no significant differences in TH activity in any of these four brain regions between LS and SS mice at any time following ethanol administration. In contrast, hypothalamic TH activity was significantly increased at 25 minutes in the SS mice and at 125 minutes in the LS mice following the administration of ethanol, times which coincided with the regaining of the righting reflex. These data suggest that activation of TH in the hypothalamus of LS and SS mice in response to ethanol is associated with arousal from ethanol induced narcosis.