Mechanism of butyrate binding to histone deacetylase[HDAC] correlation with chemopreventive effects and ligand selectivity

Sodium butyrate [SB] is a natural cytodifferentiating and cancer preventive agent. These actions are largely triggered by inhibition of the HDAC enzyme, thereby inducing hyperacetylation/ transcription of certain genes. Unlike the prototype HDAC inhibitor, trichostatin-A [TSA], SB offers higher selectivity on cancer cells, with a lower affinity to HDAC. The mechanisms underlying these distinct biological profiles for SB remain undefined. We currently propose for, and attempt to identify differences in the binding of SB and TSA to the HDAC binding pocket. The lowest energy conformer of SB was prepositioned on TSA binding site of HDAC. Following minimization of the best-docked S8-HDAC complex, binding profiles, conformational changes and energy calculations have been derived. TSA elicited 4 hydrogen bonds with 3 key enzyme pocket residues [His131, His132 and Tyr297; bidentated]. SB missed a hydrogen bond with Tyr297 and caused more disruption of the pocket amino acid residues His131, His132 [RMS deviation value difference of up to 0.40 A]. Besides, a looser binding to the pivotal zinc atom of HDAC was evident with SB [1 vs. 2 bonds in case of TSA]. Likewise, SB was far loosely packed in the HDAC's binding tunnel as compared to TSA. Moreover, energy computations indicated that SB had a lower binding affinity than that of TSA [-27.8 vs. -66.3 Kcal/mol]. Detailed binding differences for both ligands are described. These studies demonstrate that SB binding to HDAC confers unique catalytic, conformational and computational characteristics consistent with a lower binding affinity to HDAC and a higher selectivity on cancer cells than TSA. These newly defined binding properties of SB can further state a framework strategy for the rational development of SB-like anticancer drugs with enhanced biological and safety profiles

Resveratrol activates the kinase-G system in human coronary smooth muscle cells via a nongenomic, estrogen-independant mechanism

Resveratrol [RSVL], a polyphenolic phytoestrogen in grapes, confers multifaceted cardiovascular benefits. The cellular and molecular basis of RSVL actions has been largely undefined. Currently, in human coronary smooth muscle cells [HCSMCs], RSVL markedly [3.2 fold] enhanced cGMP formation [t1/2: 6.3 min, EC 50: 1.8 microM] and stimulated kinase-G activity [4 fold]. By contrast, RSVL had no effect on cAMP or PKA activity in these cells. The RSVL-enhanced cGMP/kinase-G activity was not abrogated by either of the phosphodiesterase-inhibitors [zaprinast, 10 microM, IBMX, 0.5mM], the nitric oxide synthase-inhibitor [L-NMMA, 10 microM], or the soluble guanylyl cyclase [sGC]-inhibitor [ODQ, 10 microM].In membrane preparations from HCSMCs, RSVL activated GC in the particulate-, but not in the soluble- membrane fraction. Similar effects were due to the specific particulate-GC [pGC] agonist atrial natriuretic peptide [ANP, 0.1-1 microM]. By contrast, the nitric oxide donor, SNAP [1-10 microM] stimulated GC only in the soluble fraction. Responses to RSVL were insensitive to the estrogen receptor blockers, tamoxifen and ICI-182,780. Conversely, pretreatment with the PKC activator, PMA [0.1 microM], a known desensitizer of pGC, markedly blunted the RSVL-enhanced GC-activity. These findings demonstrate that RSVL triggers a pGC-mediated stimulation of protein kinase-G in human coronary smooth muscle cells. This pathway appears to be independent of the conventional estrogen machinery and supports both vasodilatory and anti-atherogenic actions for RSVL

Antineoplastons: major players in the biochemical defensive system against cancer

Antineoplastons are naturally occurring peptides and amino acid derivatives that were originally isolated from human urine. They possess a broad-spectrum antitumor activity and seem to be much safer and specific than many of the available chemotherapeutic agents. Their selectivity is likely entailed to preferential interaction with cellular components or signaling mechanisms that predominate in cancer cells. Our studies on breast cancer- cell lines and -patients indicated the efficacy of antineoplaston-A10 and its derivatives as antimitotic, immunemodulator and cytodifferentiating agents. Moreover, phase-I and phase-II clinical trials implied the utility of antineoplastons in treating neoplasms of various origins. Combination with lower doses of known chemotherapeutic agents or in conjunction with radiotherapy was a promising therapeutic strategy. Such regimens were likewise effective in cases with recurrent or drug-resistant neoplasms. Intensive research is continuing to reveal more on antineoplastons and their biologic characteristics