Occurrence and significance of diastereomers of methotrexate alpha-peptides

Trapping H- Bound to the Nitrogenase FeMo-Cofactor Active Site during H2 Evolution: Characterization by ENDOR Spectroscopy

We here show that the iron-molybdenum (FeMo)-cofactor of the nitrogenase alpha-70(Ile) molybdenum-iron (MoFe) protein variant accumulates a novel S = (1)/(2) state that can be trapped during the reduction of protons to H(2). (1,2)H-ENDOR measurements disclose the presence of two protons/hydrides (H(+/)(-)) whose hyperfine tensors have been determined from two-dimensional field-frequency (1)H ENDOR plots. The two H(+/)(-) have large isotropic hyperfine couplings, A(iso)( )() approximately 23 MHz, which shows they are bound to the cofactor. The favored analysis for these plots indicates that the two H(+/)(-) have the same principal values, which indicates that they are chemically equivalent. The tensors are further related to each other by a permutation of the tensor components, which indicates an underlying symmetry of binding relative to the cofactor. At present, no model for the structure of the iron-molybdenum (FeMo)-cofactor in the S = (1)/(2) state trapped during the reduction of H(+) can be shown unequivocally to satisfy all of the constraints generated by the ENDOR analysis. The data disfavors any model that involves protonation of sulfides, and thus suggests that the intermediate instead contains two chemically equivalent bound hydrides; it appears unlikely that these are terminal monohydrides.

Efficient Intracellular Delivery of a Protein and a Low Molecular Weight Substance via Recombinant Polyomavirus-like Particles

Efficient encapsulation of foreign molecules like proteins and low molecular weight drugs into polyoma virus-like particles (capsoids) was achieved by the development of an anchoring technique based upon the specific interaction of the inner core protein VP2 with VP1 pentamers. A stretch of 49 amino acids of VP2 served as an anchor molecule, either expressed as a fusion protein with green fluorescent protein (GFP) or covalently linked to methotrexate (MTX). The loaded capsoids showed regular morphology and stability for several months. GFP and MTX were internalized into cells in vitro, as was demonstrated by the detection of GFP and VP1 fluorescence in mouse fibroblasts and the cytostatic effect of intracellularly released MTX on leukemia T cells.

Development of methotrexate alpha-peptides as prodrugs for activation by enzyme-monoclonal antibody conjugates

Selective delivery of lethal concentrations of drugs to tumors, allowing the latter to be eradicated without damage to other tissues, continues to be a major goal in cancer chemotherapy. Prodrugs (i.e. drugs that have been derivatized to prevent uptake into cells or interaction with targets), activated by enzyme-monoclonal antibody conjugates positioned at tumor sites, offer promise for achieving this objective. Methotrexate alpha-peptides (derivatives in which an amino acid is linked to the alpha-carboxyl group of the glutamate moiety) are ideal prodrugs, since they are not transported into cells and can be converted to the parent drug by carboxypeptidases. The L,L-diastereomer of MTX-alpha-Phe, synthesized in good yield by treatment of the p-nitrophenyl ester of 4-amino-4-deoxy-10-methylpteroic acid with Glu-alpha-Phe, was hydrolyzed readily by carboxypeptidase A (CP-A). Conjugate was prepared by derivatizing the enzyme and monoclonal antibody KS1/4 with linkers containing maleimide and sulfhydryl groups, respectively; interaction of these groups to form a stable thioether bond joined the proteins. When administered in vitro to UCLA-P3 human lung adenocarcinoma cells (ca. 5 x 10(4) antibody binding sites/cell) that had been pre-treated with the conjugate (whose antibody KS1/4 is targeted to these cells), and excess conjugate removed by extensive washing, MTX-Phe (ID50 = 6.3 x 10(-8) M) approached the toxicity of MTX (ID50 = 4.5 x 10(-8) M). In the absence of conjugate, MTX-Phe was much less toxic (ID50 = 2.2 x 10(-6) M).

Synthesis and biological activity of beta-glucuronyl carbamate-based prodrugs of paclitaxel as potential candidates for ADEPT

The syntheses of prodrugs of paclitaxel, which can be used in ADEPT in order to target paclitaxel towards tumor cells, are described. The prodrugs 1 and 2a, b consist of a spacer molecule connected via a carbamate linkage to a beta-glucuronic acid. The spacer molecule is also connected via an ester linkage to the 2'-OH of paclitaxel. Enzyme-catalyzed hydrolysis of the glucuronic acid moiety by human beta-glucuronidase results in the liberation of the parent drug paclitaxel via gamma or delta lactam formation with half-lives of 45 min and 2 h (1 and 2b). The prodrugs 1 and 2b are two orders of magnitude less cytotoxic than paclitaxel.

Multiple folate transport systems in L1210 cells

Biotin derivatives of methotrexate (biotin-SS-MTX) and folate (biotin-SS-folate), in which the functional components are joined by a dissociable disulfide-containing spacer, have been synthesized, purified by DEAE-Trisacryl chromatography, and characterized by HPLC, elemental analysis and mass spectrometry. These compounds provide a convenient means for the single-step purification of the folate transporters from L1210 cells. Parental L1210 murine leukemia cells, which contain only the microM transporter (the reduced folate/MTX transport protein) were treated with the N-hydroxysulfosuccinimide ester of biotin-SS-MTX, and a detergent extract of the plasma membranes was exposed to streptavidin-agarose beads to adsorb the labeled protein. Dithiothreitol cleavage of the disulfide linkage released the transporter, which migrated as a well-defined component (43 kDa) on SDS-PAGE gels; no other proteins were present. An L1210 subline (JF), obtained by adapting cells to grow on nanomolar concentrations of folate, contains both the microM transporter and the nM transporter (high-affinity folate binding protein). When these cells were treated with the N-hydroxysulfosuccimide ester of biotin-SS-folate and processed as described above, analysis on SDS-PAGE gels revealed the presence of two proteins, the microM transporter (43 kDa) and the nM transporter (39 kDa). Both transporters were characterized with respect to amino acid content; blocked N-termini precluded Edman sequencing. Treatment of the nM transporter with peptide:N-glycosidase F produced a smaller component (32 kDa); the microM transporter, conversely, was unchanged by this procedure. When the microM transporter in parental L1210 cells was labeled with fluorescein-MTX and then treated with phosphoinositol-specific phospholipase C (PI-PLC), no change in fluorescence was detected. Alternatively, when the nM transporter in the JF subline was labeled with fluorescein-folate and then treated with PI-PLC, complete loss of fluorescence was observed. These results indicate that the L1210 microM transporter is a non-glycosylated, integral membrane protein, while its nM counterpart is heavily glycosylated and anchored exofacially to the membrane by a glycosylphosphatidylinositol component.