Development of drug conjugates in cancer therapy and evaluation of dual siRNA silencing effect on breast cancer growth and invasion
Abstract
The objective of this dissertation is to present various approaches for treatment cancer,
which is the leading cause of death worldwide. Compared to other disease, cancer has many
unique biological characteristics that can be exploited for its therapy. In chapter 1 and 2, its
molecular characteristics and microenvironments, as well as the corresponding therapeutic
strategies, are summarized. In chapter 3, we developed a peptide drug conjugate to specifically deliver TGX-221 to
HER2 overexpressed prostate cancer cells. TGX-221 is a highly potent phosphoinositide 3-
kinases β (PI3Kβ) inhibitor that holds great promise as a novel chemotherapy agent for prostate
cancer. However, poor solubility and lack of targetability limit its therapeutic applications. The
peptide drug conjugate was proven to be gradually cleaved by PSA to release TGX-D1 (TGX-
221 analogue). Both the peptide drug conjugate and its cleaved products demonstrate a
comparable activity to the parent drug, TGX-D1. Moreover, cellular uptake of the peptide drug
conjugate and its cleaved product SL-TGX were significantly higher in prostate cancer cells
compared to the parent drug. The high cellular uptake of dipeptide drug conjugate SL-TGX
might be mediated by peptide transporters in prostate cancer cells. However, the expression of peptide transporters in prostate cancer cell lines has not been reported before. Therefore, in
Chapter 4, the expression profile and functional activity of peptide transporters were investigated
in the prostate cancer cell lines LNCaP, PC-3 and DU145. Peptide transporter 1 (PEPT1) is
found overexpressed in PC-3 cells, and peptide transporter 2 (PEPT2) is upregulated in LNCaP
cells. We also developed another approach to enhance water solubility and targetability of
hydrophobic drugs. In Chapter 5, we developed a polymer-rapamycin conjugate using a novel,
linear and PEG based multiblock copolymer (Mw ~ 32 kDa). Rapamycin has demonstrated
potent anti-tumor activity in preclinical and clinical studies. However, the clinical development
of its formulations has been hampered due to its poor solubility and undesirable distribution in
vivo. The polymer-rapamycin conjugate provided enhanced solubility in water compared with
free rapamycin and shows a profound activity against a panel of human cancer cell lines. This
polymer-rapamycin conjugate also presented high drug loading capacity (wt% ~ 28%) when
GlyGlyGly was used as a linker. The uptake study further indicated that the lysosome is the
major site of intracellular localization of polymer drug conjugate. Thus, these preclinical data
suggested that polymer rapamycin conjugate is a novel anti-cancer agent that holds great
promising for treatment of a wide variety of tumors. Macromolecules such as siRNA can also be used as anticancer drugs. In chapter 6, we
designed nine HER2 siRNAs and ten VEGF siRNAs and identified potent siRNA that can
silence the target gene up to 75-83%. The most potent HER2 and VEGF siRNAs were used to
conduct functional studies in HER2 positive breast cancer cells. Combination of HER2 and
VEGF siRNAs demonstrated synergistic silencing effect on VEGF. Both HER2 siRNA and VEGF siRNA showed significant inhibition on cell migration and proliferation. HER2 siRNA
also demonstrated dramatic suppression of cell spreading and adhesion to ECM, as well as
induction of apoptosis. Dual silencing of HER2 and VEGF led to significant cell morphology
change and substantial suppression on migration, spreading, cell adhesion, and proliferation.
Table of Contents
Introduction -- Review of literature -- Development of a peptide drug conjugate for prostate cancer therapy -- Expression profile and functional activity of peptide transporters in prostate cancer cell lines -- Design and synthesis of a rapamycin conjugate using a novel poly(ethylene glycol) multiblock copolymer -- Inhibition of breast cancer cell growth and invasion by dual silencing of her2 and vegf -- Letters of permission
Degree
Ph.D.