Christopher Pavlik

Santacruzamate A, a Potent and Selective Histone Deacetylase Inhibitor from the Panamanian Marine Cyanobacterium cf. Symploca sp.

A dark brown tuft-forming cyanobacterium, morphologically resembling the genus Symploca, was collected during an expedition to the Coiba National Park, a UNESCO World Heritage Site on the Pacific coast of Panama. Phylogenetic analysis of its 16S rRNA gene sequence indicated that it is 4.5% divergent from the type strain for Symploca and thus is likely a new genus. Fractionation of the crude extract led to the isolation of a new cytotoxin, designated santacruzamate A (1), which has several structural features in common with suberoylanilide hydroxamic acid [(2), SAHA, trade name Vorinostat], a clinically approved histone deacetylase (HDAC) inhibitor used to treat refractory cutaneous T-cell lymphoma. Recognition of the structural similarly of 1 and SAHA led to the characterization of santacruzamate A as a picomolar level selective inhibitor of HDAC2, a Class I HDAC, with relatively little inhibition of HDAC4 or HDAC6, both Class II HDACs. As a result, chemical syntheses of santacruzamate A as well as a structurally intriguing hybrid molecule, which blends aspects of both agents (1 and 2), were achieved and evaluated for their HDAC activity and specificity.

Imaging tumor hypoxia by near-infrared fluorescence tomography

We have developed a novel nitroimidazole indocyanine dye conjugate for tumor-targeted hypoxia fluorescence tomography. The hypoxia probe has been evaluated in vitro using tumor cell lines and in vivo with tumor targeting in mice. The in vitro cell studies were performed to assess fluorescence labeling differences between hypoxia and normoxia conditions. When treated with the hypoxia probe, a fluorescence emission ratio of 2.5-fold was found between the cells incubated under hypoxia compared to the cells in normoxia condition. Hypoxia specificity was also confirmed by comparing the cells treated with indocyanine dye alone. In vivo tumor targeting in mice showed that the fluorescence signals measured at the tumor site were twice those at the normal site after 150 min post-injection of the hypoxia probe. On the other hand, the fluorescence signals measured after injection of indocyanine dye were the same at tumor and normal sites. In vivo fluorescence tomography images of mice injected with the hypoxia probe showed that the probe remained for more than 5 to 7 h in the tumors, however, the images of mice injected with indocyanine only dye confirmed that the unbound dye washed out in less than 3 h. These findings are supported with fluorescence images of histological sections of tumor samples using a Li-COR scanner and immunohistochemistry technique for tumor hypoxia.

Synthesis of 3-guaninyl- and 3-adeninyl-5-hydroxymethyl-2-pyrrolidinone nucleosides.

L- and D-glutamic acids, as well as trans-4-hydroxy-L-proline, are converted to the corresponding 3-guaninyl-5-hydroxymethyl-2-pyrrolidinone (4) or 3-adeninyl-5-hydroxymethyl-2-pyrrolidinone (5) nucleoside analog. The protecting group used to block the lactam nitrogen in key intermediates has a significant effect on the diastereoselectivity of the coupling reaction with adenine or guanine.

An Unexpectedly Facile Cyclization of Polyhydric Alcohols

Contrary to previous reports in the literature, the reaction of polyhydric alcohols such as sorbitol or mannitol gives good yields of the tetrahydroxyoxepane derivative in the presence of an acid catalyst, in refluxing toluene, with complete retention of stereochemistry.

Polymer-mediated cyclodehydration of alditols and ketohexoses

The polymer PEDOT(+) (1 or 2) mediates a cyclodehydration reaction with alditols 3, 5, 7, 9, in hydrocarbon solvents, to give cyclic ethers 4, 6, 8, or 10, respectively, in high yield with a trivial isolation protocol. Polymers 1 or 2 also mediate the cyclodehydration of ketohexoses such as d-fructose, but not aldohexoses, to the important industrial intermediate 5-hydroxymethylfurfural (17), under milder conditions when compared to reactions mediated by mineral acids. A cascade reaction with ketohexoses is observed in toluene via cyclodehydration followed by Friedel-Crafts alkylation of the initially formed benzylic alcohol to give 16.

Synthesis and biological evaluation of santacruzamate A analogues for anti-proliferative and immunomodulatory activity

Santacruzamate A (SCA) is a natural product isolated from a Panamanian marine cyanobacterium, previously reported to have potent and selective histone deacetylase (HDAC) activity. To optimize the enzymatic and cellular activity, 40 SCA analogues were synthesized in a systematic exploration of the zinc-binding group (ZBG), cap terminus, and linker region. Two cap group analogues inhibited proliferation of MCF-7 breast cancer cells, with analogous increased degranulation of cytotoxic T cells (CTLs), while one cap group analogue reduced CTL degranulation, indicative of suppression of the immune response. Additional testing of these analogues resulted in reevaluation of the previously reported SCA mechanism of action. These analogues and the resulting structure-activity relationships will be of interest for future studies on cell proliferation and immune modulation.

Hypoxia targeted carbon nanotubes as a sensitive contrast agent for photoacoustic imaging of tumors

Development of new and efficient contrast agents is of fundamental importance to improve detection sensitivity of smaller lesions. Within the family of nanomaterials, carbon nanotubes (CNT) not only have emerged as a new alternative and efficient transporter and translocater of therapeutic molecules but also as a photoacoustic molecular imaging agent owing to its strong optical absorption in the near-infrared region. Drugs, Antibodies and nucleic acids could functionalize the CNT and prepare an appropriate system for delivering the cargos to cells and organs. In this work, we present a novel photoacoustic contrast agent which is based on a unique hypoxic marker in the near infrared region, 2-nitroimidazole -bis carboxylic acid derivative of Indocyanine Green conjugated to single walled carbon nanotube (SWCNT-2nitroimidazole-ICG). The 2-nitroimidazole-ICG has an absorption peak at 755 nm and an extinction coefficient of 20,5222 M-1cm-1. The conjugation of this marker with SWCNT shows more than 25 times enhancement of optical absorption of carbon nanotubes in the near infrared region. This new conjugate has been optically evaluated and shows promising results for high contrast photoacoustic imaging of deeply located tumors. The conjugate specifically targets tumor hypoxia, an important indicator of tumor metabolism and tumor therapeutic response. The detection sensitivity of the new contrast agent has been evaluated in-vitro cell lines and with in-vivo tumors in mice.

Tumor hypoxia fluorescence imaging using 2-nitroimidazole bis-carboxylic acid indocyanine dye conjugate

We present tumor hypoxia mapping by diffuse optical fluorescence tomography. A novel 2-nitroimidazole bis-carboxylic acid indocyanine dye conjugate has been developed for tumor-targeted hypoxia fluorescence imaging. The hypoxia probe has been evaluated in-vitro using 4T1 tumor cell lines and in-vivo tumor targeting in mice. In-vivo tumor targeting in six mice demonstrated that a measured half-life of 2-nitroimidazole-indocyanine dye wash out in the tumor was significantly longer (112±32.37 minutes) than that of bis-carboxylic acid indocyanine dye (69.75±14.01 minutes). The bis-carboxylic acid indocyanine dye was completely washed out from the tumor site within 3-5 hours post-injection, but 2-nitroimidazole-ICG remained for up to 21 hours in the tumor site. Near infrared fluorescence images of mice tumors showed a 2.6-fold contrast of dye uptake with hypoxic conjugate injection (7.46±1.68 μM) compared to that with indocyanine dye injection (2.9±0.60 μM). The in-vitro cell studies were performed to assess fluorescence labeling comparing hypoxia to normoxia conditions. A fluorescence emission ratio of 2.5-fold was found between the cells treated with the 2-nitroimidazole-indocyanine dye and incubated under hypoxia compared to the cells in normoxia condition. Hypoxia specificity was also confirmed when compared to cells treated with unconjugated indocyanine dye alone. Fluorescence images acquired using a Li-COR scanner from harvested tumor samples support the in vivo monitoring and imaging results.

Nitroimidazole-Indocynine Green Conjugates for Breast Cancer Hypoxia Imaging

We present the optical properties of new nucleophilic imidazole compounds synthesized for tumor hypoxia imaging. The photophysical and hypoxic properties of these new molecules are evaluated and targeted for imaging breast cancer hypoxia.