Thesis (Ph.D.)--University of Rochester. School of Medicine & Dentistry. Dept. of Biomedical Genetics, 2013.
A major challenge in developing effective anti-cancer agents is to identify tumorspecific
properties that are sufficiently unique to achieve eradication of malignant
cells with minimal toxicity to normal cells. Therefore, it is important to study the
mechanism-of-action of experimental agents that display selective toxicity towards
cancer. In the case of acute myeloid leukemia (AML), our lab has previously
identified parthenolide (PTL), a naturally occurring small compound, with potent
activity in eradicating both bulk and stem/progenitor populations of AML cells while
sparing normal hematopoietic cells. However, the molecular mechanism by which
this compound can achieve its selective toxicity is not well characterized, and is
therefore the aim of this thesis. Using a biotinylated analog of PTL, we performed
pull-down assays and identified 312 direct binding targets of PTL in primary human
AML cells. By correlating these binding events with PTL-induced gene expression
changes in AML cells, our analyses predicted that perturbation of redox balance and
protein folding homeostasis are two major components of PTL’s anti-leukemia
mechanism. Subsequent analyses showed that PTL strongly inhibits the glutathione
pathway, a central regulator of redox balance, by directly depleting glutathione as
well inhibiting key glutathione metabolic enzymes. In comparison to normal
hematopoietic cells, glutathione metabolism in AML cells is aberrantly regulated and
more sensitive to PTL-induced inhibition, indicating that inhibition of glutathione
metabolism is an important component of PTL’s selective toxicity towards AML cells.
In addition to redox modulation, PTL also perturbs protein folding homeostasis and
triggers endoplasmic reticulum (ER) stress. Based on these results, we proposed a
model describing the selective anti-leukemia mechanism of PTL and used it to
design PTL-based drug combinations. Our approach demonstrated that the
combination of PTL with drugs that further increase PTL’s activity in perturbing redox
balance and/or protein folding homeostasis is selectively toxic to both bulk and stem
cell populations of leukemic cells. Taken together, the findings presented in this
thesis indicate that perturbation of redox balance and protein folding homeostasis
are two important components of PTL’s anti-leukemia mechanism. Moreover, certain
unique properties of AML such as aberrant glutathione metabolism can be targeted
to selectively eradicate AML cells.
