Mark L. McLaughlin

Synthesis of a water-soluble chiral N-acylcalix(4)arene amino acid derivative

Abstract The synthesis of a novel water-soluble chiral N -acylcalix(4)arene amino acid derivative has been achieved. The chiral calix(4)arene is in a “cone” conformation according to NMR spectroscopy. We report preliminary results using this chiral calixarene derivative as a mobile phase additive in capillary electrophoresis.

Discovery of a novel proteasome inhibitor selective for cancer cells over non-transformed cells

Numerous proteins controlling cell cycle progression, apoptosis, and angiogenesis are degraded by the ubiquitin/proteasome system, which has become the subject for intense investigations for cancer therapeutics. Therefore, we used in silico and experimental approaches to screen compounds from the NCI chemical libraries for inhibitors against the chymotrypsin-like (CT-L) activity of the proteasome and discovered PI-083. Molecular docking indicates that PI-083 interacts with the Thr21, Gly47 and Ala49 residues of the β5 subunit and Asp114 of the β6 subunit of the proteasome. PI-083 inhibits CT-L activity and cell proliferation and induces apoptosis selectively in cancer cells (ovarian T80-Hras, pancreatic C7-Kras and breast MCF-7) as compared to their normal/immortalized counterparts (T80, C7 and MCF-10A, respectively). In contrast, Bortezomib, the only proteasome inhibitor approved by the Food and Drug Administration (FDA), did not exhibit this selectivity for cancer over non-transformed cells. In addition, in all cancer cells tested, including Multiple Myeloma (MM), breast, pancreatic, ovarian, lung, prostate cancer cell lines as well as fresh MM cells from patients, PI-083 required less time than Bortezomib to induce its antitumor effects. Furthermore, in nude mouse xenografts in vivo, PI-083, but not Bortezomib, suppressed the growth of human breast and lung tumors. Finally, following in vivo treatment of mice, PI-083 inhibited tumor, but not hepatic liver CT-L activity, whereas Bortezomib inhibited both tumor and liver CT-L activities. These results suggest that PI-083 is more selective for cancer cells and may have broader antitumor activity and therefore warrants further advanced preclinical studies.

Identification of a disruptor of the MDM2-p53 protein–protein interaction facilitated by high-throughput in silico docking

NSC 333003 has been identified from the NCI Diversity Set as an inhibitor of the MDM2-p53 protein-protein interaction by in silico docking (virtual screening). Its potency and chemical characteristics render it well suited for lead optimization studies that can result in more potent analogs with improved drug-like properties. Its synthesis was achieved using an acid catalyzed condensation reaction from commercially available benzothiazole hydrazine and pyridyl phenyl ketone in refluxing methanol. Stereochemical implications for this compound are described.

Acquisition of resistance toward HYD1 correlates with a reduction in cleaved α4 integrin expression and a compromised CAM-DR phenotype.

We recently reported that the β1 integrin antagonist, referred to as HYD1, induces necrotic cell death in myeloma cell lines as a single agent using in vitro and in vivo models. In this article, we sought to delineate the determinants of sensitivity and resistance toward HYD1-induced cell death. To this end, we developed an HYD1 isogenic resistant myeloma cell line by chronically exposing H929 myeloma cells to increasing concentrations of HYD1. Our data indicate that the acquisition of resistance toward HYD1 correlates with reduced levels of the cleaved α4 integrin subunit. Consistent with reduced VLA-4 (α4β1) expression, the resistant variant showed ablated functional binding to fibronectin, VCAM-1, and the bone marrow stroma cell line HS-5. The reduction in binding of the resistant cell line to HS-5 cells translated to a compromised cell adhesion-mediated drug resistant phenotype as shown by increased sensitivity to melphalan- and bortezomib-induced cell death in the bone marrow stroma coculture model of drug resistance. Importantly, we show that HYD1 is more potent in relapsed myeloma specimens than newly diagnosed patients, a finding that correlated with α4 integrin expression. Collectively, these data indicate that this novel d-amino acid peptide may represent a good candidate for pursuing clinical trials in relapsed myeloma and in particular patients with high levels of α4 integrin. Moreover, our data provide further rationale for continued preclinical development of HYD1 and analogues of HYD1 for the treatment of multiple myeloma and potentially other tumors that home and/or metastasize to the bone. Mol Cancer Ther; 10(12); 2257–66. ©2011 AACR.

Synthesis of a series of polar, orthogonally protected, α,α-disubstituted amino acids

Abstract The synthesis of four novel, “cationic”, α,α-disubstituted amino acids is described. The new amino acids use an orthogonal protection scheme making them suitable for incorporation via solid-phase peptide synthesis.

Stereoselectivity in the synthesis of tetramethylethano-bridged 3,3′-di-tert-butyltitanocene dichloride

Abstract Racemic and meso ansa-(2,3-dimethyl-2,3-butano)-3,3′-bis(1,1′-dimethylethyl)cyclopenta-1,3-dien-5-yl)titanium dichloride (5 and 4) were prepared in a 1:4 to 1:2 ratio by the addition of TiCl3·3THF to 2,3-bis[3-(1,1-dimethylethyl)-1,3-cyclopentadien-5-yl]2,3-dimethylbutanedilithium (3) in THF with subsequent oxidation by HCl in a 44% yield. A 30% yield of the 1:1 racemic:meso ratio resulted when 3 was treated with titanocene dichloride in THF followed by carbon tetrachloride oxidation. In the attempts to synthesize the desired anti isomer, 3 was treated with in-situ generated racemic dichloro-1,1′-bi-2-naphtholatetitanium(IV) to give ansa-(2,3-dimethyl-2,3-butano)-anti-3,3′-bis(1,1-dimethy lethyl)cyclopenta-1,3-dien-5-yl)titanium 1,1′-bi-2-naphtholate (6) in a 10–15% yield. 6 crystallized in a monoclinic space group P21/c with a = 10.084(2) A, b = 29.312(7) A, c = 12.190(2) A, β = 99.37(2)°, V = 355(2) A3, and Z = 4. Refinement of 425 least squares variables converged to R = 0.044 and Rw = 0.046 for 4153 observed reflections with I > 2δ(I). The molecule contains an approximate C2 axis of symmetry with the t-butyl groups anti to each other. The C(Cp)C(t-butyl) bonds are displaced from the plane defined by the cyclopentadienyls by about 10°.

Benz[f]tryptophan, a bathochromic analog of tryptophan, synthesis of its N-α-t-boc derivative

Abstract The recently reported anionic cyclization of N,N-diallylaminobenzene derivatives to indolines is readily extended to the synthesis of a naphthalene derivative which is taken on to the first synthesis of a benz[ f ]tryptophan derivative.

Tandem reverse-electron-demand diels-alder reactions of 1,5-cyclooctadiene.

Abstract Hexachlorocyclopentadiene and 5,5-dimethoxy-1,2,3,4-tetrachlorocyclopenta-2,4-diene react with 1,5-cyclooctadiene to produce a 1:4 syn to anti mixture of diadducts in good yield. The stereochemistry of the diastereomers is examined using X my and molecular mechanics calculations are used to explore some of the potential causes for the observed diastereoselectivity.

A facile stereospecific synthesis of α-hydrazino esters

Abstract A convenient route to make α-hydrazino esters from their corresponding α-amino esters is reported. A key step is selective nitrosamine reduction using activated Zn, conc. HCl, and methanol at low temperatures giving nearly quantitative yields of the pure α-hydrazino esters

MTI-101 (cyclized HYD1) binds a CD44 containing complex and induces necrotic cell death in multiple myeloma

Our laboratory recently reported that treatment with the d-amino acid containing peptide HYD1 induces necrotic cell death in multiple myeloma cell lines. Because of the intriguing biological activity and promising in vivo activity of HYD1, we pursued strategies for increasing the therapeutic efficacy of the linear peptide. These efforts led to a cyclized peptidomimetic, MTI-101, with increased in vitro activity and robust in vivo activity as a single agent using two myeloma models that consider the bone marrow microenvironment. MTI-101 treatment similar to HYD1 induced reactive oxygen species, depleted ATP levels, and failed to activate caspase-3. Moreover, MTI-101 is cross-resistant in H929 cells selected for acquired resistance to HYD1. Here, we pursued an unbiased chemical biology approach using biotinylated peptide affinity purification and liquid chromatography/tandem mass spectrometry analysis to identify binding partners of MTI-101. Using this approach, CD44 was identified as a predominant binding partner. Reducing the expression of CD44 was sufficient to induce cell death in multiple myeloma cell lines, indicating that multiple myeloma cells require CD44 expression for survival. Ectopic expression of CD44s correlated with increased binding of the FAM-conjugated peptide. However, ectopic expression of CD44s was not sufficient to increase the sensitivity to MTI-101–induced cell death. Mechanistically, we show that MTI-101–induced cell death occurs via a Rip1-, Rip3-, or Drp1-dependent and -independent pathway. Finally, we show that MTI-101 has robust activity as a single agent in the SCID-Hu bone implant and 5TGM1 in vivo model of multiple myeloma. Mol Cancer Ther; 12(11); 2446–58. ©2013 AACR.