Samir Saleh

Selective de-protection of silyl ethers

Abstract Pyridinium p -toluenesulfonate has been found to remove t -butyldimethylsilyl ethers selectively in the presence of t -butyldiphenylsilyl ethers. This methodology should find wide applicability in complex organic synthesis.

Limits of [18F]-FLT PET as a Biomarker of Proliferation in Oncology

Background Non-invasive imaging biomarkers of cellular proliferation hold great promise for quantifying response to personalized medicine in oncology. An emerging approach to assess tumor proliferation utilizes the positron emission tomography (PET) tracer 3’-deoxy-3’[18F]-fluorothymidine, [18F]-FLT. Though several studies have associated serial changes in [18F]-FLT-PET with elements of therapeutic response, the degree to which [18F]-FLT-PET quantitatively reflects proliferative index has been continuously debated for more that a decade. The goal of this study was to elucidate quantitative relationships between [18F]-FLT-PET and cellular metrics of proliferation in treatment naïve human cell line xenografts commonly employed in cancer research. Methods and Findings [18F]-FLT-PET was conducted in human cancer xenograft-bearing mice. Quantitative relationships between PET, thymidine kinase 1 (TK1) protein levels and immunostaining for proliferation markers (Ki67, TK1, PCNA) were evaluated using imaging-matched tumor specimens. Overall, we determined that [18F]-FLT-PET reflects TK1 protein levels, yet the cell cycle specificity of TK1 expression and the extent to which tumors utilize thymidine salvage for DNA synthesis decouple [18F]-FLT-PET data from standard estimates of proliferative index. Conclusions Our findings illustrate that [18F]-FLT-PET reflects tumor proliferation as a function of thymidine salvage pathway utilization. Unlike more general proliferation markers, such as Ki67, [18F]-FLT PET reflects proliferative indices to variable and potentially unreliable extents. [18F]-FLT-PET cannot discriminate moderately proliferative, thymidine salvage-driven tumors from those of high proliferative index that rely primarily upon de novo thymidine synthesis. Accordingly, the magnitude of [18F]-FLT uptake should not be considered a surrogate of proliferative index. These data rationalize the diversity of [18F]-FLT-PET correlative results previously reported and suggest future best-practices when [18F]-FLT-PET is employed in oncology.

Selective removal of phenolic and alcoholic silyl ethers

Abstract Potassium carbonate/Kriptofix 222 and pyridinium p -toluenesulfonate or BF 3 -etherate have been found to remove the tert -butyldimethylsilyl group from phenolic and alcoholic silyl ethers, respectively. This methodology should find wide applicability in complex organic synthesis.

3'-Deoxy-3'-18F-fluorothymidine PET predicts response to (V600E)BRAF-targeted therapy in preclinical models of colorectal cancer.

Selective inhibition of oncogenic targets and associated signaling pathways forms the basis of personalized cancer medicine. The clinical success of V600EBRAF inhibition in melanoma, coupled with the emergence of acquired resistance, underscores the importance of rigorously validating quantitative biomarkers of treatment response in this and similar settings. Because constitutive activation of BRAF leads to proliferation in tumors, we explored 3′-deoxy-3′-18F-fluorothymidine (18F-FLT) PET to noninvasively quantify changes in tumor proliferation that are associated with pharmacologic inhibition of V600EBRAF downstream effectors and that precede changes in tumor volume. Methods: Human colorectal cancer (CRC) cell lines expressing V600EBRAF were used to explore relationships between upregulation of p27 and phosphorylation of BRAF downstream effectors on small-molecule V600EBRAF inhibitor exposure. Athymic nude mice bearing V600EBRAF-expressing human CRC cell line xenografts were treated with a small-molecule V600EBRAF inhibitor (or vehicle) daily for 10 d. Predictive 18F-FLT PET was conducted before changes in tumor volume occurred. Correlations were evaluated among PET, inhibition of phosphorylated MEK (p-MEK) and phosphorylated-ERK (p-ERK) by Western blot, tumor proliferation by histology, and small-molecule exposure by matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS). Results: Treatment of CRC cell lines with PLX4720 reduced proliferation associated with target inhibition and upregulation of p27. In vivo, PLX4720 treatment reduced 18F-FLT uptake, but not 18F-FDG uptake, in Lim2405 xenografts before quantifiable differences in xenograft volume. Reduced 18F-FLT PET reflected a modest, yet significant, reduction of Ki67 immunoreactivity, inhibition of p-MEK and p-ERK, and elevated tumor cell p27 protein levels. Both 18F-FLT PET and 18F-FDG PET accurately reflected a lack of response in HT-29 xenografts, which MALDI imaging mass spectrometry suggested may have stemmed from limited PLX4720 exposure. Conclusion: We used preclinical models of CRC to demonstrate 18F-FLT PET as a sensitive predictor of response to V600EBRAF inhibitors. Because 18F-FLT PET predicted reduced proliferation associated with attenuation of BRAF downstream effectors, yet 18F-FDG PET did not, these data suggest that 18F-FLT PET may represent an alternative to 18F-FDG PET for quantifying clinical responses to BRAF inhibitors.

Control elements in the intramolecular diels-alder reaction: synthesis of α-eudesmol

Abstract Triene 1 undergoes cyclization with substantial 1,3 and 1,4 chiral induction to give largely trans, equatorial α-eudesmol 3 .

A Peptide-Based Positron Emission Tomography Probe for In Vivo Detection of Caspase Activity in Apoptotic Cells

Purpose: Apoptosis, or programmed cell death, can be leveraged as a surrogate measure of response to therapeutic interventions in medicine. Cysteine aspartic acid–specific proteases, or caspases, are essential determinants of apoptosis signaling cascades and represent promising targets for molecular imaging. Here, we report development and in vivo validation of [18F]4-fluorobenzylcarbonyl–Val–Ala–Asp(OMe)–fluoromethylketone ([18F]FB-VAD-FMK), a novel peptide-based molecular probe suitable for quantification of caspase activity in vivo using positron emission tomography (PET). Experimental Design: Supported by molecular modeling studies and subsequent in vitro assays suggesting probe feasibility, the labeled pan-caspase inhibitory peptide, [18F]FB-VAD-FMK, was produced in high radiochemical yield and purity using a simple two-step, radiofluorination. The biodistribution of [18F]FB-VAD-FMK in normal tissue and its efficacy to predict response to molecularly targeted therapy in tumors was evaluated using microPET imaging of mouse models of human colorectal cancer. Results: Accumulation of [18F]FB-VAD-FMK was found to agree with elevated caspase-3 activity in response to Aurora B kinase inhibition as well as a multidrug regimen that combined an inhibitor of mutant BRAF and a dual PI3K/mTOR inhibitor in V600EBRAF colon cancer. In the latter setting, [18F]FB-VAD-FMK PET was also elevated in the tumors of cohorts that exhibited reduction in size. Conclusions: These studies illuminate [18F]FB-VAD-FMK as a promising PET imaging probe to detect apoptosis in tumors and as a novel, potentially translatable biomarker for predicting response to personalized medicine. Clin Cancer Res; 20(8); 2126–35. ©2014 AACR.

Microwave-assisted, one-pot reaction of 7-azaindoles and aldehydes: a facile route to novel di-7-azaindolylmethanes

A novel and highly efficient synthetic method leveraging microwave-assisted organic synthesis (MAOS) to yield di-7-azaindolylmethanes (DAIMs) is reported. Under MAOS conditions, reaction of 7-azaindole with aldehydes resulted predominantly in DAIMs, as opposed to the expected 7-azaindole addition products that form at ambient temperature. Based upon studies of different indoles and azaindoles with various aromatic and aliphatic aldehydes, we herein propose a mechanism where rapid and efficient microwave heating promotes nucleophilicity of 7-azaindoles towards the corresponding alkylidene-azaindolene intermediate to form the DAIM. This sequence provides a versatile approach to efficiently synthesize novel DAIMs that may be useful pharmaceuticals.

Synthesis of the major urinary metabolite of prostaglandin D2

Starting from the Corey lactone (3), the total synthesis of a specific urinary metabolite of prostaglandin D2, viz., (Z)-9α,11β-dihydroxy-15-oxo-2,3,18,19-tetranorprost-5-ene-1,20-dioic acid (1) and its 5E-isomer is described. The synthetic material was isolated in a tricyclic form as the corresponding hemiacetal lactone (2). The g.c.m.s. characteristics of the methyl ester, trimethylsilyl ether derivative of this compound were identical with those previously described for the same derivative of the 11β-tetranor metabolite of PGD2.

Carboxyethyl Homologation of Lactols: Synthons For Dinorprostanoids

Abstract Synthons derived by three carbon homologation of suitably functionalized lactols are key intermediates in the preparation of dinor prostaglandin metabolites. An efficient method for the synthesis of dinor prostaglandin synthons with the desired Z-5, 6 double bond geometry is described.

A Practical Route for the Synthesis of Prostaglandin D2 Metabolites

Abstract A convenient, efficient route for the total synthesis of 9α, 11β-dihydroxy-13,14-dihydro-15-oxo-PGF2 2, a new plasma metabolite of prostaglandin D2 1 is described.