No abstract

We report an extensive structure-activity relationship (SAR) of seventy-eight compounds active against two pancreatic cancer cell lines. Our comprehensive evaluation of these compounds utilizes SAR that allow us to evaluate which features of potent compounds play a key role in their cytotoxicity. This is the first report of 19 new second-generation structures, where these new compounds were designed from the first generation of 59 compounds. These 78 structures were tested for their cytotoxicity and this is the first report of their activity against 2 pancreatic cancer cell lines. Our results show that out of 78 compounds, three compounds are worth pursuing as leads, as they show potency of ≥55% in both cancer cell lines. These three compounds all have a common structural motif, 2 consecutive D-amino acids and an N-methyl moiety. Further, of these three compounds, two are second-generation structures, indicating that we can incorporate and utilize data from the first generation to design potency into the second generation. Finally, one analog is in the mid nanomolar range, and has the lowest IC50 of any reported San A derivative. These analogs share no structural homology to current pancreatic cancer drugs, and are cytotoxic at levels on par with existing drugs treating other cancers. Thus, we have established Sansalvamide A as an excellent lead for killing multiple pancreatic cancer cell lines.

We report the synthesis of 34 second-generation Sansalvamide A derivatives. San A derivatives have unique anticancer properties and target multiple cancers, including colon, pancreatic, breast, prostate, and melanoma. As novel templates, the derivatives described herein explore the role of stereochemistry, amide bond geometry, transannular hydrogen bonding, and polarity on antitumor potency. Testing the chemotherapeutic activity of these derivatives against multiple cancer cell lines will provide clear structural motifs and identify conformational space that is important for cytotoxicity. The 34 compounds presented are divided into six series, where five series involve the insertion of D-amino acids in conjunction with four structural features at each of the five positions of the macrocycle. The sixth series involves comparison between all L- and all D-amino acid derivatives with N-methyls placed at each position around the macrocyclic core. The four structural features explored in conjunction with D-amino acids include N-methyl amino acids, aromatic amino acids, polar amino acids, and hydrophobic alkyl amino acids.

We outline the synthesis of six novel derivatives that are based on a recently discovered HDAC inhibitor FR235222. Our work is the first report utilizing a novel binding element, guanidine, as metal coordinators in HDAC inhibitors. Further, we demonstrate that these compounds show cytotoxicity that parallels their ability to inhibit deacetylase activity, and that the most potent compounds maintain an L-Phe at position 1, and a D-Pro at position 4. Both inhibition of HDAC activity and cytotoxicity against the pancreatic cancer cell line BxPC3 are exhibited by these compounds, establishing that a guanidine unit can be utilized successfully to inhibit HDAC activity. There are already numerous HDAC inhibitors in clinical trials. 3,4 However, treating pancreatic cancers has been unsuccessful with any drug currently on the market. Given that HDACs are inappropriately up-regulated in pancreatic cancers, 5,6 HDAC inhibitors (HDACIs) have tremendous potential for treating these drug-resistant cancers. Pancreatic cancer is the fifth most deadly cancer in U.S. Only 10% of patients are eligible for surgery, 7 and less than 20% of pancreatic cancers respond to the drug of choice (Gemzar) or other drugs on the market. 8, 9The 5-year survival rate for patients with pancreatic cancers is less than 5%. 10 With such a low response rate to current chemotherapeutic treatments, there is an immediate need for new drugs that provide additional chemotherapeutic options to pancreatic cancer patients.To date, HDACIs can be divided into five chemical families: hydroxamic acid derivatives, short chain fatty acids, benzamides, electrophilic ketones, and cyclic tetrapeptides. 1,11 These five families all inhibit the activity of metal-dependent HDAC classes I and II. The There is extensive literature on derivatives containing the three moieties found in natural product metal-binding units. In addition to work exploring their potency, other non-traditional metal binding units have been published including, sulfur, 15 N-formyl hydroxylamine, 16 and phosphorous-containing compounds. 17 However, no work has been published to date on guanidines as metal-binding units in HDACIs. Guanidines represent a very important class of compounds both biologically and chemically. Their hydrophilic nature provides stabilization of protein conformations via hydrogen bonding and mediates solubility of natural products. 18 With a high pK a value of 12.5, arginine residues containing a guanidinium side chain may not be considered optimal metal-binding ligands. However, the highly acidic nature of a metal cation found in the HDAC pocket can potentially lower the pK a value of the guanidinium side chain, allowing for coordination with the metal. In fact, several recent reports document the stability of guanidine-metal interactions, 19,20 although additional studies are needed. Despite their likely metal binding capabilities, guanidines have gone unexplored in the realm of HDACI as potential metal-binding units.Here we describe the design and synthesis of HDAC...

Synthesis of nine macrocyclic peptide HDAC inhibitors and three triazole derivatives are described. HDAC inhibitory activity of these compounds against HeLa cell lysate is evaluated. The biological data demonstrates that incorporation of a triazole unit improves the HDAC inhibitory activity.During the cell cycle, post-translational modifications to the ε-amino-terminal tails of histone proteins are made by a number of different enzymes, including histone acetyl transferases (HATs) and histone deacetylases (HDACs).1 Histone tails contain ~40 lysine residues, which are acetylated by HATs. Acetylation induces a conformational change within chromatin, allowing the transcriptional machinery access to DNA thus promoting gene expression.1 , 2 HDACs repress gene expression by deacetylating the lysine tails, allowing the positively charged lysines to bind tightly to the negatively charged DNA and denying the transcriptional machinery access to genes, thereby repressing gene expression. Thus, these post-translational modifications play a key role in directing gene expression, and can create a phenotype that is unrelated to changes in DNA.3 Inappropriate up-regulation of HDACs' silence specific tumor suppressor genes, which are responsible for cell proliferation, differentiation, and apoptosis.4 , 5 Molecules that interfere with HDAC activity have shown great promise as anticancer agents as they inhibit this silencing process, and allow tumor suppressor genes to be transcribed and control the cell's growth.6 -8 With a number of HDAC inhibitors in clinical trials and suberoylanilide hydroxamic acid (SAHA, Zolinza®) recently approved by the FDA for the treatment of cutaneous T cell lymphoma (CTCL), HDAC inhibition proves to be a worthy strategy for cancer therapy.9 HDAC inhibitors consist of three components: 1) the active site metal binding unit, 2) surface recognition domain and 3) a linker that connects the two domains.10 They operate by binding the surface recognition domain located at the rim of the HDAC pocket, and placing the metal binding unit within the pocket (Fig 1).11 HDAC inhibitors can be divided into five structural categories: short chain fatty acids, hydroxamic acids, electrophilic ketones, benzamides, and cyclic peptides.12 These five structural categories are known to Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Supplementary dataSupplementary data associated with this article can be found in the online version at: inhibit the 3 classes of metal-dependent HDACs.13 There are 11 metal dependent HDACs currently known, and it is unclear which isoforms are res...