BIMG-13. A NOVEL RADIOPHARMACEUTICAL ([18F]DASA-23) TO MONITOR PYRUVATE KINASE M2 INDUCED GLYCOLYTIC REPROGRAMMING IN GLIOBLASTOMA

BACKGROUND

Pyruvate kinase M2 (PKM2) catalyzes the final step in glycolysis, a key process of cancer metabolism. PKM2 is preferentially expressed by glioblastoma (GBM) cells with minimal expression in healthy brain, making it an important biomarker of cancer glycolytic re-programming. We describe the bench-to-bedside development, validation, and translation of a novel positron emission tomography (PET) tracer to study PKM2 in GBM. Specifically, we evaluated 1-((2-fluoro-6-[¹⁸F]fluorophenyl)sulfonyl)-4-((4-methoxyphenyl)sulfonyl)piperazine ([¹⁸F]DASA-23) in cell culture, mouse models of GBM, healthy human volunteers, and GBM patients.

METHODS

[¹⁸F]DASA-23 was synthesized with a molar activity of 100.47 ± 29.58 GBq/µmol and radiochemical purity >95%. We performed initial testing of [¹⁸F]DASA-23 in GBM cell culture and human GBM xenografts implanted orthotopically into mice. Next we produced [¹⁸F]DASA-23 under current Good Manufacturing Practices United States Food and Drug Administration (FDA) oversight, and evaluated it in healthy volunteers and a pilot cohort of patients with gliomas.

RESULTS

In mouse imaging studies, [¹⁸F]DASA-23 clearly delineated the U87 GBM from the surrounding healthy brain tissue and had a tumor-to-brain ratio (TBR) of 3.6 ± 0.5. In human volunteers, [¹⁸F]DASA-23 crossed the intact blood-brain barrier and was rapidly cleared. In GBM patients, [¹⁸F]DASA-23 successfully outlined tumors visible on contrast-enhanced magnetic resonance imaging (MRI). The uptake of [¹⁸F]DASA-23 was markedly elevated in GBMs compared to normal brain, and it was able to identify a metabolic non-responder within 1-week of treatment initiation.

CONCLUSION

We developed and translated [¹⁸F]DASA-23 as a promising new tracer that demonstrated the visualization of aberrantly expressed PKM2 for the first time in human subjects. These encouraging results warrant further clinical evaluation of [¹⁸F]DASA-23 to assess its utility for imaging therapy-induced normalization of aberrant cancer metabolism.

EXTH-30. PRECEDING p53 STABILIZATION USING DOXORUBICIN AUGMENTS PRIMA-1-MEDIATED p53 REFOLDING AND INCREASED CELLULAR APOPTOSIS: EVALUATION OF A SEQUENTIAL COMBINATION THERAPY AGAINST GLIOBLASTOMA

INTRODUCTION

Mutant p53 cancer cells are poorly responsive to chemotherapy. A small molecule drug, PRIMA-1, can bind to wildtype and mutant p53 to induce structural conformation that enhances p53 DNA binding. In a quest for new effective combination chemotherapies, we hypothesized that sequential treatment of GBM cells with doxorubicin then PRIMA-1 could stabilize and refold p53 to enhance chemotherapy-induced cellular apoptosis. We evaluated this combination in GBM cells engineered to express different p53 mutants and exhibiting different phenotypes.

METHODS

We constructed split reporter biosensors incorporating different structural mutants of p53 (p53Y220C, p53G245S, and p53R282W) all within p53-null Ln308 GBM cells, to evaluate PRIMA-1-mediated refolding of p53 using bioluminescence imaging. We used these cells, and other GBM cells endogenously dissimilar for p53 phenotypes (U87MG with wt-p53, and Ln229 with mutant p53 [mt-p53P98L/p14ARFdel/p16del]), to investigate the anticancer activity of doxorubicin plus PRIMA-1 by using immunoblot analysis of p53 downstream pathway proteins. We also evaluated treatment by imaging mice implanted with GBMs of different p53 phenotypes.

RESULTS

PRIMA-1 induced reporter complementation at > 80 mM in all GBM cells regardless of p53 status. Doxorubicin stabilized p53 and increased its levels significantly more than in control cells. Significant changes in apoptotic index occurred in GBM cells treated with doxorubicin (1mM) followed by PRIMA-1 (40 mM), compared to cells treated with each drug independently, or with PRIMA-1 followed by doxorubicin. There was upregulation of p53, p21, and Bax, but downregulation of Bcl2 after combination therapy. PRIMA-1 and doxorubicin acted synergistically in GBM cells, but not significantly compared to using doxorubicin followed by PRIMA-1.

CONCLUSION

Our molecular imaging biosensor is useful to detect drug-induced restoration of p53 wildtype conformation. Doxorubicin stabilizes and increases p53 levels in GBM cells for subsequent enhanced PRIMA-1-mediated p53 refolding and increased levels of cellular apoptosis—an effective anti-GBM combination treatment.

Minor histocompatibility antigens in Tunisians: could platelet endothelial cell adhesion molecule 1 marker be one of them?

Platelet endothelial cell adhesion molecule 1 (PECAM-1/CD31) is one of the human minor histocompatibility antigens that are the main targets of alloreactive T-cells after hematopoietic stem cells or solid organs transplantation. In order to investigate its polymorphism in Tunisians, three single nucleotide polymorphisms (SNPs) (rs668, rs12953 and rs1131012) were selected to perform an allele and haplotype analysis. Hundred-and-forty-two healthy and unrelated subjects were enrolled in this survey. Genomic DNAs were extracted using salting out method. SNP genotyping assays were performed with home-designed sequence-specific primers polymerase chain reaction (SSP-PCR). As a result, molecular analysis showed that PECAM-1 is one of the most polymorphic markers in the Tunisian population because minor allele frequency was 0.3, and minimum haplotype frequency was 0.03. A low linkage disequilibrium (D' = 0.45) between rs12953 and rs1131012 was noticed, although all other loci were in the Hardy-Weinberg equilibrium (minimum P value = 0.07). The frequencies were close to those reported in African-American and Caucasian groups.

Evolution of differential substrate specificities in Mu class glutathione transferases probed by DNA shuffling

A library of variant enzymes was created by combined shuffling of the DNA encoding the human Mu class glutathione transferases GST M1-1 and GST M2-2. The parental GSTs are 84 % sequence identical at the protein level, but their specific activities with the substrates aminochrome and 2-cyano-1,3-dimethyl-1-nitrosoguanidine (cyanoDMNG) differ by more than 100-fold. Aminochrome is of particular interest as an oxidation product of dopamine and of possible significance in the etiology of Parkinson's disease, and cyanoDMNG is a model for genotoxic and potentially carcinogenic nitroso compounds. GST M2-2 has at least two orders of magnitude higher catalytic activity with both of the substrates than any of the other known GSTs, including GST M1-1. The DNA library of variant Mu class GST sequences contained "mosaic" structures composed of alternating segments of both parental sequences. All clones contained the 5'-end of a GST M1-1 clone optimized for high-level expression in Escherichia coli. The remainder of the sequences derived from segments of GST M2-2 and GST M1-1 DNA. All of the clones analyzed contained between two and seven distinct DNA segments. In addition, each clone contained an average of approximately one point mutation. None of the library clones analyzed was identical with either of the two parental structures. Variant GST sequences were expressed in E. coli, and their enzymatic activities with aminochrome, cyanoDMNG, and 1-chloro-2,4-dinitrobenzene (CDNB) were determined in bacterial lysates. Such screening of more than 70 clones demonstrated a continuous range of activities covering at least two orders of magnitude for each of the substrates. For a given clone, the activities with aminochrome and cyanoDMNG, in spite of their different chemistries, were clearly correlated, whereas no strong correlation was found with CDNB. This functional correlation suggests a common structural basis for the enzymatic mechanisms for conjugation of aminochrome and denitrosation of cyanoDMNG. From an evolutionary perspective, the results show that recombination of segments from homologous proteins gives rise to a large proportion of functionally competent proteins with a range of activities. The data support the proposal that natural evolution of protein functions may involve recombination of DNA segments followed by selection for advantageous functional properties of the resulting proteins. Clearly, the same approach can be utilized in the engineering of proteins displaying novel functions by in vitro evolution.

Toxin-producing species of Penicillium and the development of mycotoxins in must and homemade wine

A number of penicillium strains belonging to the species Penicillium roqueforti, P. crustosum, P. paneum Frisvad, and P. chrysogenum were analyzed for their ability to produce the mycotoxins isofumigaclavine A, isofumigaclavine B, festuclavine, roquefortine C, and PR toxin when cultured on three different media. Some of the strongest mycotoxin-producing strains were later inoculated into samples of must (grape juice) before and after wine fermentation. After incubation at 25 degrees C for 1 and 2 weeks it was found that all except one of the penicillium strains were able to produce one or more of the toxins analyzed. However, the types of toxins as well as toxin concentrations varied a great deal, depending on culturing medium or culturing time. The media containing yeast extract normally gave higher toxin levels. From the wine experiments it was shown that isofumigaclavine A can be formed under certain circumstances in must and wine. A qualitative High Performance Liquid Chromatography (HPLC) method for simultaneous determination of isofumigaclavines A and B, roquefortine C, and PR toxin was also developed.

A nonlinear mathematical model for the development and rupture of intracranial fusiform aneurysms

Laplace's law, which describes a linear relation between the tension and the radius, is often used to characterize the mechanical response of the aneurysm wall to distending pressures. However, histopathological studies have confirmed that the wall of the fully developed aneurysm consists primarily of collagen and is subject to large increases in tension for small increases in the radius, i.e., a nonlinear relationship exists between the tension within the aneurysm wall and the radius. Thus, a nonlinear version of Laplace's law is proposed to accurately describe the development and rupture of a fusiform saccular aneurysm. The fusiform aneurysm was modelled as a thin-walled ellipsoidal shell with a major axis radius, Ra, minor axis radius, Rb, circumferential tension, S0, and meridional tension, S phi, with phi defining the angle from the surface normal. Using both linear and nonlinear models, differential expressions of the volume distensibility evaluated at 90 degrees were used to determine the critical radius of the aneurysm along the minor axis from S0 and S phi in terms of the following geometric and biophysical variables; A, elastic modulus of collagen; E, elastic modulus of the aneurysm (elastin and collagen); t, wall thickness; P, systolic pressure; and Ra. For typical physiological values of A = 2.8 MPa, E = 1.0 MPa, T = 40 microns, P = 150 mmHg, and Ra = 4Rb, the linear model yielded critical radii of 4.0 mm from S phi and 2.2 mm from S0. The resultant critical radius was 4.56 mm. Using the same values, the critical radii from the tension components of the nonlinear model were 3.5 mm from S phi and 1.9 mm from S0.(ABSTRACT TRUNCATED AT 250 WORDS)

A nonlinear mathematical model for the development and rupture of intracranial saccular aneurysms

Mathematical models of aneurysms are typically based on Laplace's law which defines a linear relation between the circumferential tension and the radius. However, since the aneurysm wall is viscoelastic, a nonlinear model was developed to characterize the development and rupture of intracranial spherical aneurysms within an arterial bifurcation and describes the aneurysm in terms of biophysical and geometric variables at static equilibrium. A comparison is made between mathematical models of a spherical aneurysm based on linear and nonlinear forms of Laplace's law. The first form is the standard Laplace's law which states that a linear relation exists between the circumferential tension, T, and the radius, R, of the aneurysm given by T = PR/2t where P is the systolic pressure. The second is a 'modified' Laplace's law which describes a nonlinear power relation between the tension and the radius defined by T = ARP/2At where A is the elastic modulus for collagen and t is the wall thickness. Differential expressions of these two relations were used to describe the critical radius or the radius prior to aneurysm rupture. Using the standard Laplace's law, the critical radius was derived to be Rc = 2Et/P where E is the elastic modulus of the aneurysm. The critical radius from the modified Laplace's law was R = [2Et/P]2At/P. Substituting typical values of E = 1.0 MPa, t = 40 microns, P = 150 mmHg, and A = 2.8 MPa, the critical radius is 4.0 mm using the standard Laplace's law and 4.8 mm for the modified Laplace's law.(ABSTRACT TRUNCATED AT 250 WORDS)