Biomedical subjects

David A Boothman

Publications and source records attributed to David A Boothman.

22 records · Page 2Linked to original sources

PubMed2003

Enhancement of solubility and bioavailability of beta-lapachone using cyclodextrin inclusion complexes.

PURPOSE: To explore the use of cyclodextrins (CD) to form inclusion complexes with beta-lapachone (beta-lap) to overcome solubility and bioavailability problems previously noted with this drug. METHODS: Inclusion complexes between beta-lap and four cyclodextrins (alpha-, beta-, gamma-, and HPbeta-CD) in aqueous solution were investigated by phase solubility studies, fluorescence, and 1H-NMR spectroscopy. Biologic activity and bioavailability of beta-lap inclusion complexes were investigated by in vitro cytotoxicity studies with MCF-7 cells and by in vivo lethality studies with C57Blk/6 mice (18-20 g). RESULTS: Phase solubility studies showed that beta-lap solubility increased in a linear fashion as a function of alpha-, beta-, or HPbeta-CD concentrations but not gamma-CD. Maximum solubility of beta-lap was achieved at 16.0 mg/ml or 66.0 mM with HPbeta-CD. Fluorescence and 1H-NMR spectroscopy proved the formation of 1:1 inclusion complexes between beta-CD and HPbeta-CD with beta-lap. Cytotoxicity assays with MCF-7 cells showed similar biologic activities of beta-lap in beta-CD or HPbeta-CD inclusion complexes (TD50 = 2.1 microM). Animal studies in mice showed that the LD50 value of beta-lap in an HPbeta-CD inclusion complex is between 50 and 60 mg/kg. CONCLUSIONS: Complexation of beta-lap with HPbeta-CD offers a major improvement in drug solubility and bioavailability.

2-Hydroxypropyl-beta-cyclodextrin↗

PubMed2003

Ku70 suppresses the apoptotic translocation of Bax to mitochondria.

Bax induces mitochondrial-dependent cell death signals in mammalian cells. However, the mechanism of how Bax is kept inactive has remained unclear. Yeast-based functional screening of Bax inhibitors from mammalian cDNA libraries identified Ku70 as a new Bax suppressor. Bax-mediated apoptosis was suppressed by overexpression of Ku70 in mammalian cells, but enhanced by downregulation of Ku70. We found that Ku70 interacts with Bax, and that the carboxyl terminus of Ku70 and the amino terminus of Bax are required for this interaction. Bax is known to translocate from the cytosol to mitochondria when cells receive apoptotic stimuli. We found that Ku70 blocks the mitochondrial translocation of Bax. These results suggest that in addition to its previously recognized DNA repair activity in the nucleus, Ku70 has a cytoprotective function in the cytosol that controls the localization of Bax.

Animals↗

PubMedDate not supplied

Mu-calpain activation in beta-lapachone-mediated apoptosis.

Beta-lapachone (beta-Lap) triggers apoptosis in a number of human breast and prostate cancer cell lines through a unique apoptotic pathway that is dependent upon NQO1, a two-electron reductase. Recently, our laboratory showed that beta-lap-exposed MCF-7 cells exhibited an early increase in intracellular cytosolic Ca(2+) from endoplasmic reticulum stores, and that BAPTA-AM (an intracellular Ca(2+) chelator) blocked these early increases and partially inhibited all aspects of beta-lap-induced apoptosis. We now show that exposure of NQO1-expressing breast cancer cells to beta-lap stimulates a unique proteolytic apoptotic pathway involving mu-calpain activation. No apparent activation of m-calpain was noted. Upon activation, mu-calpain translocated to the nucleus concomitant with specific nuclear proteolytic events. Apoptotic responses in beta-lap-exposed NQO1-expressing cells were significantly delayed and survival enhanced by exogenous over-expression of calpastatin, a natural inhibitor of mu- and m-calpains. Furthermore, purified mu-calpain cleaved PARP to a unique fragment (approximately 60 kDa), not previously reported for calpains. We provide evidence that beta-lap-induced, mu-calpain-stimulated apoptosis does not involve any known apoptotic caspases; the activated fragments of caspases were not observed after beta-lap exposures, nor were there any changes in the pro-enzyme forms as measured by Western blot analyses. The ability of beta-lap to trigger an apparently novel, p53-independent, calpain-mediated apoptotic cell death further support the development of this drug for improved breast cancer therapy.

Antibiotics, Antineoplastic↗

PubMedDate not supplied

Repression of IR-inducible clusterin expression by the p53 tumor suppressor protein.

The clusterin (CLU) protein has been reported to have both cytoprotective and cytotoxic activities. Previous data from our lab suggest that the secretory form of CLU (sCLU) is cytoprotective and induced after very low, nontoxic doses of ionizing radiation (IR: >0.02 Gy), while a nuclear form is cytotoxic. Cells must presumably suppress sCLU to stimulate cell death, however, factors regulating the stress-inducible expression of sCLU have not been elucidated. Here we demonstrate that p53 can suppress sCLU induction responses. A variety of cytotoxic agents stimulated sCLU expression and DNA damage was sufficient but not necessary for induction. IR-stimulated CLU promoter activity, with concomitant increases in CLU mRNA and protein, showed that CLU induction was delayed with maximal expression observed 48-96 h post-treatment. Expression of the human papillomavirus E6 protein in MCF-7 breast or RKO colon cancer cells enhanced basal CLU levels. Isogenically matched HCT116 colon cancer cell lines that differed only in p53 or p21 status, confirmed a role for p53 in the transcriptional repression of sCLU. Loss of functional p53 in HCT116:p53(-/-) cells augmented CLU de novo synthesis after IR exposure. Repression of sCLU protein levels by p53 may be important for the cascade of p53-mediated events leading to cell death after IR or other cytotoxic agent exposure.

Antineoplastic Agents↗