Lipid-based delivery
systems
Liposomal nanoparticles have been traditionally the most typically used
nanoparticle-based vehicles for siRNA delivery to pancreatic tumor
tissues. Despite great transfection efficiency and capacity to form
complexes with negatively charged siRNA, cationic lipids/liposomes are
extremely toxic due to the induction of reactive oxygen species (ROS)
and high intracellular calcium levels (Zahednezhad, Saadat, Valizadeh,
Zakeri-Milani, & Baradaran, 2019). Cationic lipids also have a role in
complement system activation and thus lead to their rapid removal by
reticuloendothelial system (e.g. macrophages). It was also shown that
cationic lipids also have a high toxicity to macrophages and other cells
of immune system. On the other hand, anionic liposomes are rapidly
cleared from the blood (Y. Zhu et al., 2019). As a result, precise
selection of lipids and formulation strategies may help decrease the
potential toxicities.
Arsenic trioxide (ATO) is one of the most effective compounds in the
treatment of cancer but one of the bottlenecks for its clinical use is
its toxicity to normal tissues (Aslan, Shahbazi, Ulubayram, & Ozpolat,
2018). To solve this problem Zeng et al. (Zeng et al., 2014)
designed a platform of poly (ethylene glycol)-block-poly (DL-lactide)
(PEG-PDLLA) to deliver arsenic. Moreover, a novel polymer structure,
Poly (ethylene glycol)-block-poly (L-lysine) (PEG-PLL), was introduced
to enhance antitumor activity both in vitro and in vivo,by means of the coadministration of mutant K-ras siRNA
(PEG-PLL/siK-ras). This coadministration with PEG-PLL/siK-ras seems to
reduce cell growth, migration, and invasion as well as colony formation.
Also, there was a dramatic increase in the percentage of PANC-1 cells in
the G0/G1 phase compared with S phase. In addition, the synergistic
effect of siK-ras and arsenic could downregulate Bcl-2 and K-ras protein
expression and reduced tumor growth with higher cytotoxicity.
Survivin is one of the overexpressed proteins in human pancreatic cancer
that is related to more extensive metastases, chemo/radio-resistance,
and shorter median survival. Although usage of paclitaxel can expand the
tumor interstitial space by induction of apoptosis, it can significantly
increase the survivin protein level in residual tumors. The cotreatment
of this drug and gene therapy was proven to be effective (Satoh et al.,
2001). Wang and colleagues (J. Wang et al., 2015) examined this
treatment using the paclitaxel and pegylated cationic (PCat)-siRNA
lipoplexes (PCat-siSurvivin) in human pancreatic Hs766T xenograft tumor.
Their combinational application could significantly improve the efficacy
of tumor regression and delayed tumor regrowth.
Regarding the importance of CUX1 transcription factor in the regulation
of cell proliferation and differentiation and its possible roles in
tumorigenesis and tumor progression, a study by Ripka and colleagues
(Ripka et al., 2010) showed that polyethyleneimine (PEI)-complexed siRNA
against CUX1 (siCUX1) can increase apoptosis induction in PANC1 and
ImimPC1 pancreatic cancer cell lines; via GEM and 5-FU and TRAIL
pathway. Furthermore, following intratumoral injection of PEI-siCUX1,
tumor growth in murine xenograft models was inhibited.
Induction of apoptosis is another way of eliminating pancreatic cancer
cells. miR-34a is one of the most effective options in this regard
(Kurtanich et al., 2019). Hu et al. (Q. L. Hu et al., 2013)
transferred a new form of this miRNA to different tumor cell lines and
mouse models through β-cyclodextrin-polyethyleneimine (β-PEI-CD
[PC]) vector. Subsequently, cell population in the G0/G1 phase
enhanced in comparison to G2/M and S phases which indicated the
inhibition of cell growth and tumor size reduction.
Ubiquitin ligase ITCH plays a significant role in the
proteasome-dependent degradation of p73, an important protein in cell
cycle arrest and apoptosis pathways (Rossi et al., 2005). Fuente and
colleagues (de la Fuente et al., 2015) used poly (propylenimine)
dendrimers (DAB-Am16/shSCR) to deliver ITCH targeting short hairpin RNA
(shRNA) into MIA PaCa-2 and PANC-1, HPAC and BxPC3 pancreatic cells in
addition to MIA PaCa-2 xenograft animal models of BALB/c mice and
Sprague-Dawley rats. Results indicated a decrease in the mRNA level of
target genes. IV administration of this compound with GEM could reduce
tumor volume without much change in body weight.
miR-150 is one of the tumor suppressor miRNAs which can be used as a
therapeutic goal but some of its physiochemical features, such as
anionic charge, hydrophilicity, sensitivity to nuclease degradation, and
inefficient uptake, restrict its use (Kurtanich et al., 2019).
Application of Poly (lactic-co -glycolic acid)(PLGA) and PEI to
deliver miR-150 in human pancreatic cancer cells (Colo-357 and HPAF) are
based on measurements of its target genes. This miR-150 delivery showed
decreased expression of MUC4 and MUC13 glycoproteins which play roles in
pancreatic cancer progression (Kurtanich et al., 2019). Since p53, HER2
and pAKTSer473 expression is affected by MUC13, miR-145 can be
considered as one of the treatment options through suppression of MUC13
(Khan et al., 2014). Magnetic nanoparticles formulation (MNPF) for the
delivery of miR-145(miR-145-MNPF) showed suppression of MUC13,
pAKTSer473, and HER2 expression and returned function of p53 in HPAF-II
and AsPC-1 human pancreatic cancer cell lines (Setua et al., 2017).
Recently, a novel class of nanocarriers termed “lipid–polymer hybrid
nanoparticles (LPNs)” has been designed to overcome the challenges of
both polymer- and liposome-based delivery systems. The LPNs consists of
three main components: (1) a cationic hydrophobic polymeric core in
which poorly water-soluble drugs and siRNAs can be encapsulated; (2) a
hydrophilic polymeric shell with antibiofouling properties to improve
LPNs stability and prolongin vivo systemic circulation time; (3) an inner lipid monolayer
at the interface of the core and the shell, which play significant role
in improving biocompatibility and drug retention of the polymeric core
(L. Zhang et al., 2008). There is a large extent of hypoxia in
pancreatic cancer tumors. Hypoxia-inducible factor (HIF) transcription
factor is one of the crucial factors in the survival of cancer cells in
hypoxic conditions. HIF-1α is involved in the regulation of a wide range
of genes related to cancer angiogenesis, invasion, and proliferation.
Overexpression of this factor can increase the likelihood of resistance
to the first-line chemotherapeutic drug such as GEM. Zhao et al.(X. Zhao et al., 2015) used LENPs made from cationic e-polylysine
co-polymer (ENPs) and EGylated lipid bilayer to deliver HIF-1α siRNA and
GEM into PANC-1 human PDAC cells and female BALB/c nude mice model
bearing subcutaneous human PANC-1 xenografts. Cytotoxicity and antitumor
effects of GEM were significantly increased in the simultaneous
application of Gem and HIF-1α siRNA. LENPs showed higher blood stability
than ENPs nanoparticles. Moreover, stability of drug in copolymer core,
high cellular uptake and cytoplasmic release, significant antitumor
effects of the Gem and si-HIF-1α, and immune response reduction suggest
using LENP-GEM-siHIF-1α in clinical research.