Downregulation of the FOXM1 transcription factor by dual nitric oxide-/ hydrogen sulfide-donors: preliminary structure-activity relationships

  • Author / Creator
    Rodriguez Dimitrescu, Alexandra
  • In recent decades, the Forkhead Box (FOX) family of transcription factors (e.g. FOXM1) has attracted the attention of the scientific community due to its significant role in cancer initiation and progression. Furthermore, the abnormal or deregulated expression of FOXM1 has been associated with chemotherapeutic resistance. FOXM1 plays important roles in the induction of cell cycle progression, differentiation, proliferation, DNA repair, induction of angiogenesis and suppression of apoptosis. FOXM1 has been regarded as the “Achilles’ heel of cancer”, and it represents one of the most promising therapeutic targets for the development of novel anticancer agents. Inactivation of the FOXM1 signaling pathway is emerging as a novel approach in cancer therapy, because by targeting its expression and its transcriptional activity it may significantly impact on multiple facets of tumorigenesis and drug resistance. Several therapeutic strategies have been reported in the literature to downregulate FOXM1 in cancer cells. These include; (a) siRNA, (b) inhibition of the proteasome system (stabilizes an endogenous FOXM1 inhibitor), (c) cyclin-dependent kinase inhibitors (inhibit FOXM1 phosphorylation and translocation from the cytoplasm to the nucleus), (d) modulators of the structurally related FOXO3a transcription factor (upstream modulator of FOXM1), (e) modulation of the NF-B pathway, and, more recently, (f) dual nitric oxide-/hydrogen sulfide-releasing salicylate known as NOSH compounds. Literature reports have shown that NOSH compounds have potent cell proliferation inhibitory properties, by promoting cell cycle arrest and apoptosis in eleven different cancer cell lines from six different tissue origins. These compounds have been shown to be potent inhibitors of cell proliferation (IC50: 48-280 nM range). The observed chemical similarities between the NOSH compounds and some thiazole antibiotics, known to downregulate the expression of FOXM1, have provided a rationale for the unexpected and highly significant in vitro potency of NOSH compounds. Preliminary studies from our collaborators (Dr. Khosrow Kashfi, at the City University of New York, NY, USA), have shown that NOSH compounds are able to inhibit the expression of FOXM1 in vitro, and have provided the basis for the current study. The NOSH compounds possess three main chemical moieties: (1) a salicylic acid group, (2) a nitric oxide-releasing group, and (3) a hydrogen sulfide-releasing group. It is not known if these three moieties are essential for NOSH compounds to exert downregulation of FOXM1, or if only one or two of them are needed to modulate this transcription factor. Consequently, the objectives of this thesis were: 1. To design and synthesize a series of NOSH derivatives containing two out of three components present in the parent NOSH compound; namely a) Salicylate and a H2S-releasing moiety. b) Salicylate and a NO-releasing moiety. c) NO- and a H2S-releasing moiety. d) H2S-releasing moiety alone. 2. To determine the specific role of each of the three components present in the NOSH scaffold in: a) Cell viability assays in three cancer lines of different tissue origin [colon (HT-29), liver (HepG2) and breast (SKBR-3)]. b) The downregulation of the FOXM1 protein in HT-29 and SKBR-3 cells. Based on the results obtained during the course of this investigation, it is possible to conclude that: a) The inhibitory effect exerted by NOSH derivatives on cancer cell viability is largely due to the presence of the 1,2-dithiole-3-thione (ADT-OH) group. b) The second H2S-releasing group tested, thiobenzamide (TBZ), seems to be not essential to inhibit viability of cancer cells. c) The organic nitrate (-ONO2) moiety present in the parent NOSH-1 compound is not essential to inhibit cancer cell viability. d) The salicylate moiety present in the parent NOSH-compounds seems to be not essential for the inhibition of cancer cell viability or the inhibition of FOXM1 expression. e) The FOXM1 protein levels determined in HT-29 cells were not modulated by the parent drug NOSH-1, or any NOSH-derivative tested. This effect was only observed with ADT-OH. f) The protein levels of FOXM1 in SKBR-3 cells were decreased, in a concentration-dependent manner, only by compounds containing the ADT-OH moiety. g) The protein levels of FOXM1 in SKBR-3 cells were not affected by any derivative possessing the –ONO2 or the thiobenzamide group. h) The design of future FOXM1 modulators derived from NOSH-compounds will have to be based on the ADT-OH moiety, and not on the other two groups reported for these molecules

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    Master of Science
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