5 research outputs found
In vitro apoptotic effects of farnesyltransferase blockade in acute myeloid leukemia cells
Farnesyltransferase inhibitors (FTIs)
are a class of oral anti-cancer drugs currently tested
in phase I-II clinical trials for treatment of
hematological malignancies. The in vitro effects of
various FTIs (alpha-hydroxyfarnesylphosphonic
acid, manumycin-A and SCH66336) were tested on
CD34+ KG1a cell line and in primary acute myeloid
leukemia (AML) cells from 64 patients. By cell
viability and clonogeneic methylcellulose assays,
FTIs showed a significant inhibitory activity in
CD34+ KG1a and primary bone marrow (BM)
leukemic cells from 56% of AML patients. FTIs also
induced activation of caspase-3 and Fas-independent
apoptosis, confirmed by the finding that inhibition of
caspase-8 was not associated with the rescue of FTItreated cells. We concluded that other cellular events
induced by FTIs may trigger activation of caspase-3
and subsequent apoptosis, but the expression of
proapoptotic molecules, as Bcl-2 and Bcl-XL, and
antiapoptotic, as Bcl-X(s), were not modified by
FTIs. By contrast, expression of inducible nitric
oxide synthase (iNOS) was increased in FTI-treated
AML cells. Our results suggest a very complex
mechanism of action of FTIs that require more
studies for a better clinical use of the drugs alone or
in combination in the treatment of hematological
malignancies
Bidirectional fluxes of spermine across the mitochondrial membrane.
The polyamine spermine is transported into the
mitochondrial matrix by an electrophoretic mechanism
having as driving force the negative electrical membrane
potential (DW). The presence of phosphate increases
spermine uptake by reducingDpH and enhancingDW. The
transport system is a specific uniporter constituted by a
protein channel exhibiting two asymmetric energy barriers
with the spermine binding site located in the energy well
between the two barriers. Although spermine transport is
electrophoretic in origin, its accumulation does not follow
the Nernst equation for the presence of an efflux pathway.
Spermine efflux may be induced by different agents, such as
FCCP, antimycin A and mersalyl, able to completely or
partially reduce theDWvalue and, consequently, suppress
or weaken the force necessary to maintain spermine in the
matrix. However this efflux may also take place in normal
conditions when the electrophoretic accumulation of the
polycationic polyamine induces a sufficient drop inDWable
to trigger the efflux pathway. The release of the polyamine
is most probably electroneutral in origin and can take place
in exchange with protons or in symport with phosphate
anion. The activity of both the uptake and efflux pathways
induces a continuous cycling of spermine across the mitochondrial membrane, the rate of which may be prominent in imposing the concentrations of spermine in the inner and
outer compartment. Thus, this event has a significant role on
mitochondrial permeability transition modulation and consequently on the triggering of intrinsic apoptosis
Spermine cycling in mitochondria is mediated by adenine nucleotide translocase activity: mechanism and pathophysiological implications
Spermine, besides to be transported in mitochondria by an energy dependent electrophoretic mechanism, can be also released by two different mechanisms. The first one is induced in deenergizing conditions by FCCP or antimycin A and it is mediated by an electroneutral exchange spermine protons. The second one takes place in energizing conditions during the activity of the adenine nucleotide translocase and is mediated by an electroneutral symport mechanism involving the efflux in co-transport of spermine and phosphate and the exchange of exogenous ADP with endogenous ATP. The triggering of this mechanism permits an alternating cycling of spermine across the mitochondrial membrane, that is spermine is transported or released by energized mitochondria in the absence or presence of ATP synthesis, respectively. The physiological implications of this cycling of spermine are related to the induction or prevention of mitochondrial permeability transition and, consequently, on apoptosis or its prevention