A novel extracellular matrix-based leukemia model supports leukemia cells with stem cell-like characteristics

Acute myeloid leukemia (AML) relapse results from the survival of chemotherapy-resistant and quiescent leukemia stem cells (LSC). These LSCs reside in the bone marrow microenvironment, comprised of other cells and extracellular matrix (ECM), which facilitates LSC quiescence through expression of cell adhesion molecules. We used decellularized Wharton's jelly matrix (DWJM), the gelatinous material in the umbilical cord, as a scaffolding material to culture leukemia cells, because it contains many components of the bone marrow extracellular matrix, including collagen, fibronectin, lumican, and hyaluronic acid (HA). Leukemia cells cultured in DWJM demonstrated decreased proliferation without undergoing significant differentiation. After culture in DWJM, these cells also exhibited changes in morphology, acquiring a spindle-shaped appearance, and an increase in the ALDH⁺ cell population. When treated with a high-dose of doxorubicin, leukemia cells in DWJM demonstrated less apoptosis compared with cells in suspension. Serial colony forming unit (CFU) assays indicated that leukemia cells cultured in DWJM showed increased colony-forming ability after both primary and secondary plating. Leukemia cell culture in DWJM was associated with increased N-cadherin expression by flow cytometry. Our data suggest that DWJM could serve as an ECM-based model to study AML stem cell-like cell behavior and chemotherapy sensitivity.

Disc-shaped fossils resembling porpitids or eldonids from the early Cambrian (Series 2: Stage 4) of western USA

The morphology and affinities of newly discovered disc-shaped, soft-bodied fossils from the early Cambrian (Series 2: Stage 4, Dyeran) Carrara Formation are discussed. These specimens show some similarity to the Ordovician DiscophyllumHall, 1847; traditionally this taxon had been treated as a fossil porpitid. However, recently it has instead been referred to as another clade, the eldonids, which includes the enigmatic EldoniaWalcott, 1911 that was originally described from the Cambrian Burgess Shale. The status of various Proterozoic and Phanerozoic taxa previously referred to porpitids and eldonids is also briefly considered. To help ascertain that the specimens were not dubio- or pseudofossils, elemental mapping using energy dispersive X-ray spectroscopy (EDS) was conducted. This, in conjunction with the morphology of the specimens, indicated that the fossils were not hematite, iron sulfide, pyrolusite, or other abiologic mineral precipitates. Instead, their status as biologic structures and thus actual fossils is supported. Enrichment in the element carbon, and also possibly to some extent the elements magnesium and iron, seems to be playing some role in the preservation process.

Comparative Toxicity and Metabolism of N-Acyl Homologues of Acetaminophen and Its Isomer 3'-Hydroxyacetanilide

The hepatotoxicity of acetaminophen (APAP) is generally attributed to the formation of a reactive quinoneimine metabolite (NAPQI) that depletes glutathione and covalently binds to hepatocellular proteins. To explore the importance of the N-acyl group in APAP metabolism and toxicity, we synthesized 12 acyl side chain homologues of acetaminophen (APAP) and its 3'-regioisomer (AMAP), including the respective N-(4-pentynoyl) analogues PYPAP and PYMAP. Rat hepatocytes converted APAP, AMAP, PYPAP, and PYMAP extensively to O-glucuronide and O-sulfate conjugates in varying proportions, whereas glutathione or cysteine conjugates were observed only for APAP and PYPAP. PYPAP and PYMAP also underwent N-deacylation followed by O-sulfation and/or N-acetylation to a modest extent. The overall rates of metabolism in hepatocytes varied approximately 2-fold in the order APAP < AMAP ≈ PYPAP < PYMAP. Rat liver microsomes supplemented with NADPH and GSH converted APAP and PYPAP to their respective glutathione conjugates (formed via a reactive quinoneimine intermediate). With PYPAP only, a hydroxylated GSH conjugate was also observed. Thus, differences in biotransformation among these analogues were modest and mostly quantitative in nature. Cytotoxicity was evaluated in cultured hepatocytes by monitoring cell death using time-lapse photomicrography coupled with Hoechst 33342 and CellTox Green dyes to facilitate counting live cells vs dead cells, respectively. Progress curves for cell death and the areas under those curves showed that toxicity was markedly dependent on compound, concentration, and time. AMAP was essentially equipotent with APAP. Homologating the acyl side chain from C-2 to C-5 led to progressive increases in toxicity up to 80-fold in the para series. In conclusion, whereas N- or ring-substitution on APAP decrease metabolism and toxicity, homologating the N-acyl side chain increases metabolism about 2-fold, preserves the chemical reactivity of quinoneimine metabolites, and increases toxicity by up to 80-fold.

Antigen-Specific Binding of Multivalent Soluble Antigen Arrays Induces Receptor Clustering and Impedes B Cell Receptor Mediated Signaling

A pressing need exists for autoimmune disease therapies that act in an antigen-specific manner while avoiding global immunosuppression. Multivalent soluble antigen arrays (SAgAPLP:LABL), designed to induce tolerance to a specific multiple sclerosis autoantigen, consist of a flexible hyaluronic acid (HA) polymer backbone cografted with multiple copies of autoantigen peptide (PLP) and cell adhesion inhibitor peptide (LABL). Previous in vivo studies revealed copresentation of both signals on HA was necessary for therapeutic efficacy. To elucidate therapeutic cellular mechanisms, in vitro studies were performed in a model B cell system to evaluate binding and specificity. Compared to HA and HA arrays containing only grafted PLP or LABL, SAgAPLP:LABL displaying both PLP and LABL exhibited greatly enhanced B cell binding. Furthermore, the binding avidity of SAgAPLP:LABL was primarily driven by the PLP antigen, determined via flow cytometry competitive dissociation studies. Fluorescence microscopy showed SAgAPLP:LABL induced mature receptor clustering that was faster than other HA arrays with only one type of grafted peptide. SAgAPLP:LABL molecules also reduced and inhibited IgM-stimulated signaling as discerned by a calcium flux assay. The molecular mechanisms of enhanced antigen-specific binding, mature receptor clustering, and dampened signaling observed in B cells may contribute to SAgAPLP:LABL therapeutic efficacy.

Utilization of I-domain of LFA-1 to Target Drug and Marker Molecules to Leukocytes

The long-term objective of this project is to utilize the I-domain protein for the α-subunit of LFA-1 to target drugs to lymphocytes by binding to ICAM receptors on the cell surface. The short-term goal is to provide proof-of-concept that I-domain conjugated to small molecules can still bind to and uptake by ICAM-1 on the surface of lymphocytes (i.e., Raji cells). To accomplish this goal, the I-domain protein was labeled with FITC at several lysine residues to produce the FITC-I-domain and CD spectroscopy showed that the FITC-I-domain has a secondary structure similar to that of the parent I-domain. The FITC-I-domain was taken up by Raji cells via receptor-mediated endocytosis and its uptake can be blocked by anti-I-domain mAb but not by its isotype control. Antibodies to ICAM-1 enhance the binding of I-domain to ICAM-1, suggesting it binds to ICAM-1 at different sites than the antibodies. The results indicate that fluorophore modification does not alter the binding and uptake properties of the I-domain protein. Thus, I-domain could be useful as a carrier of drug to target ICAM-1-expressing lymphocytes.