Fredric A. Gorin - US grants

Brain glycogenolysis plays a critical role in meeting the acute energy requirements of the central nervous system during hypoxic-ischemic events, hypoglycemia, and seizures. Recent evidence suggests that brain glycogen phosphorylase has important regulatory differences from the isoenzymes expressed by skeletal muscle and liver. These regulatory differences, in particular inhibition of brain phosphorylase by glucose, has important implications into understanding control of brain glycogenolysis during acute alterations in cellular metabolism of brain tissue. We propose to identify and determine the amino sequence of brain glycogen phosphorylase in rabbit using recombinant DNA techniques. Our laboratory has determined the x-ray crystallographic structure of rabbit muscle phosphorylase a to 2.1 Angstrom resolution. We have co-crystallized regulatory ligands with the enzyme, identified five regulatory sites for this enzyme, and have elucidated many of the molecular mechanisms governing their allosteric control. We will compare the amino acid sequence of rabbit brain phosphorylase with the known sequence and tertiary structure of the rabbit muscle isoenzyme. This should allow us by comparison to account for the maintenance or alteration of regulatory sites for the brain isoenzyme. We will partially purify brain phosphorylase in rabbit from the other phosphorylase isoenzymes and examine the regulatory properties of purine compounds, AMP, ATP, as well as selective gluconeogenic substrates. DNA probes encoding for fragments of brain and skeletal muscle glycogen phosphorylase will be used for in situ hybridization to regions of the neocortex to localize these isoenzymes to neuronal and glial elements within the central nervous system.

DESCRIPTION: High grade astrocytomas (, malignant gliomas) are the most commonly occurring type of lethal adult brain-tumor with an individual's average life expectancy being less than 2 years from the time of diagnosis. Neither radiation therapy nor chemotherapy has significantly improved quality or length of survival. Since Warburg's initial observation, it has been recognized that most transformed tumor cells have high rates of glycolytic metabolism and consequent H+ production. Given the optimal alkaline pH dependence of key glycolytic enzymes, such as phosphofructokinase and hexokinase, it is essential that tumor cells employ an effective means of removing free cytosolic H+ to maintain metabolism. We have determined that intracellular pH in rat and human gliomas are significantly above that of normal astrocytes (0.2-0.6 pH units) despite the tumor's high rates of metabolic H+ production. This intracellular alkalosis appears to result from persistent activation of the type 1 isoform of the Na+-H+ exchanger (NHE 1). Our preliminary investigations have determined that this altered regulation of NHE 1 is most probably posttranslational and does not result from alterations of the NHE1 gene or proteins expressed in these highly malignant astrocytomas. Unexpectedly, we found that inhibition of NHE I in rat and human glioma cell lines with the diuretic drug, amiloride, or with its derivatives, HOE 694 and EIPA, cause a 70-100 percent cell death within 48-72 hours. By, contrast, primary astrocyte cultures were unaffected by NIHE 1 inhibition. Cell culture and in vivo analyses indicate that glioma death following NHE 1 inhibition appears to be predominantly non-apoptotic and independent of preceding caspase activation. Rat C6 gliomas were implanted into rat brains and allowed to establish for 4 days. Amiloride infusion into the cerebrospinal fluid for 8 days produced a 73 percent reduction in tumor volume. Amiloride is an oral diuretic that is approved for human use. Preliminarily, this novel intrathecal administration of amiloride in rats does not appear to cause behavioral or neuropathological alterations. Amiloride produced a dose-dependent decrease in intracellular pH in malignant gliomas, but not astrocytes. We have pilot data indicating that this ApHi initiates the selective tumor death. We propose to (1) identify the intracellular mechanisms mediating glioma death; (2) use brain implanted tumor models to more thoroughly delineate selective glioma death by NIlE I inhibitors; and (3) study the pharmacological and H+ regulatory properties of surviving gliomas. NHE I inhibitors may represent a new class of pharmacological agents that are useful for treatment of these highly aggressive and lethal brain tumors.

DESCRIPTION (provided by applicant): High grade malignant gliomas are the most frequent type of lethal adult brain tumor, and there is no current effective treatment. Amiloride is an FDA-approved diuretic that inhibits the proliferation of malignant glioma cells and, at high concentrations, selectively kills human glioma cells. Intracranial infusion of amiloride significantly decreased the rate of tumor growth of intracerebral human glioma xenografts in athymic rats, and killed glioma cells in poorly vascularized tumor regions. A primary objective of this application is to identify the cellular mechanisms by which amiloride selectively kills malignant glioma cells. Recently published data indicate that glioma cytotoxicity could arise from amiloride's dual inhibition of the sodium calcium exchanger (NCX) and of the type 1 sodium proton exchanger (NHE1). Nonspecific cellular toxicities of the more potent, lipophilic amiloride derivatives correspond with their intracellular permeation. We hypothesize that conjugating amino acids or peptides to the C (5) position and to the C(2) guanidine moiety of amiloride can generate novel hydrophilic amiloride derivatives, and limit drug activities to cell surface transporters. C (2) amiloride glycine conjugate inhibits NCX>NHE1, and is at least 50-fold more potent than amiloride in selectively killing glioma cells. C (5) amiloride glycine conjugate inhibits NHE1"NCX, and when coupled to an opioid-like pentapeptide created an inactive prodrug. This prodrug liberates bioactive C (5)-Am-Gly when incubated with enkephalinase. In a similar fashion, we envision that glioma-specific peptidases, such as metalloproteinases, could regionally activate amiloride-peptide prodrugs. The investigator proposes to further analyze the cellular mechanisms by which inhibitors of NCX and NHE1 selectively kill glioma cells. Syntheses of novel amiloride amino acid and peptide conjugates will be guided by these mechanistic studies, by their inhibitory activities on NCX and NHE1, and by screening their anti-cancer properties in a panel of human glioma cell lines and primary astrocytes. The most selective and efficacious of these novel amiloride derivatives will be infused intracranial into human glioma xenografts implanted intracerebrally into athymic rats. The pharmacokinetics, neurotoxicities, and neuropathology of these compounds also will be evaluated.

1. Abstract. We synthesized a novel set of non-toxic compounds that kill proliferating and nonproliferating glioma cells residing in perinecrotic tumor microenvironments. These hypoxic glioma populations have increased resistance to conventional radiation therapy coupled with alkylating agents such that cancer recurs in greater than 90% of individuals with high grade gliomas. The design and syntheses of these novel compounds were derived from our recent demonstration that urokinase plasminogen activator (uPA) becomes enzymatically activated intracellularly in hypoxic and acidotic high grade human gliomas. Amiloride is an FDA-approved drug that selectively inhibits uPA, but not other proteases. We synthesized and evaluated a series of amiloride-based compounds that inhibit either total or extracellular uPA activity in human glioma cells. Interestingly, forms of the drugs excluded from the cell interior and act only on surface uPA are cytostatic. Significantly, congeners that permeate the plasma membrane and also inhibit intracellular uPA trigger glioma cell death, yet do not affect normal brain cell types. Our pharmacological findings are consistent with RNA interference experiments demonstrating that inhibition of uPA mRNA initiates apoptosis of glioma cells by unknown cellular mechanisms. These observations point to the novel notion that infiltrative, hypoxic tumor cells can become reliant on intracellular uPA for their survival. Since intracellular uPA activation is not observed in normal tissue cell types or in normal adult brain, these observations suggest that intracellular uPA may represent an important drug target of malignant glioma cells that survive and recur in hypoxic-ischemic microenvironments. The selective anti-glioma cytotoxicities and absence of CNS toxicities of our lead compounds in rat orthotopic glioma xenografts are encouraging given the extremely poor outcome of most individuals having high grade gliomas. Aim 1 will investigate the in vivo efficacies of the lead compounds in a NOD/SCID-gamma murine intracerebral glioma xenograft model. We will investigate the efficacies of our lead compounds on {1} primary glial tumor growth kinetics and on {2} recurrent glioma following radiation therapy and temozolamide (TMZ) treatment. Because uPA inhibition impedes glioma neovascularization, we will also investigate {3} the potential synergism of our lead compounds to prevent or retard the previously described disseminated intracerebral growth of VEGF-depleted glioma cells in mice. Aim 2 will utilize these novel small molecule uPA inhibitors to identify the intracellular mechanisms contributing to their selective anti-glioma cytotoxicity. We will also target total uPA using RNA interference and compare resultant glioma cell death pathways to those identified using our small molecule inhibitors.

Abstract Alzheimer?s disease (AD) affects an estimated 5.7 million Americans, a number expected to reach 14 million by 2050. Despite several decades of research, the initiation and progression of AD continues to be poorly understood, indicating the need for novel therapeutic strategies. There is mounting evidence that neuroinflammation plays an important role in the progression of AD. We are proposing to investigate Cmpd 10357, a novel UCD small molecule originally developed as a highly selective anti-cancer agent, for treatment of AD. Cmpd 10357 selectively targets intracellular protein complexes containing the serine protease inhibitor, plasminogen activator inhibitor-1 (PAI-1). PAI-1 functions as the primary inhibitor of tissue plasminogen activator (tPA) and urokinase (uPA). PAI-1 is not expressed in the normal brain, but its expression is markedly increased in cytokine-activated microglia and astrocytes, and increased PAI-1 expression has been demonstrated in AD patients and AD animal models. High levels of PAI-1 expression and secretion by activated microglia and astrocytes inhibits plasmin activation by serine proteases and has been demonstrated to decrease A? protein degradation, thereby promoting plaque formation. We hypothesize that Cmpd 10357 will selectively target and kill activated microglia and astrocytes in the AD brain that express PAI-1, thereby slowing or preventing progression of AD via potentially two mechanisms: (i) reducing neuroinflammation; and/or (ii) improving A? clearance from the brain. To test this hypothesis, we will investigate the drug?s impact on neuroinflammatory status, AD pathology, and cognitive dysfunction in the transgenic TgF344-AD rat model. The objectives are to determine whether weekly intraperitoneal administration of Cmpd 10357 attenuates neuroinflammatory changes and plaque formation in the TgF344-AD rat and assess the impacts of these changes on the progression of AD pathology and cognitive decline. This project leverages an ongoing collaboration between the PIs that has resulted in publications characterizing the anti-inflammatory properties and novel drug mechanisms of action of two new classes of small molecules. Consistent with the goals of the R21 funding mechanism, this project is high risk, but if successful, high payoff in that it will generate proof-of- concept data for a novel therapeutic candidate for AD that potentially works via both A?-independent and dependent mechanisms. Findings from these studies may also validate Cmpd 10357 as a potential therapeutic approach for other neurological diseases with a predominant neuroinflammatory component, as well as a tool compound for addressing the controversy regarding the neuroprotective vs. neurotoxic role of microglia and astrocytes in AD by enabling the selective death of PA1-expressing glia at specific stages in the progression of AD in preclinical models.