Rational Design and Development of Nanodelivery Systems and Combination Treatments for Overcoming Chemoresistance in Solid Tumors

• Author / Creator

  Soleymani Abyaneh, Hoda

• The long term goal of this research is to develop drug delivery systems and combination treatments that can overcome chemoresistance in breast cancer. Here, we attempted two different approaches: First, we tried development of polymeric micelles capable of enhanced drug delivery to tumor, while avoiding nonspecific drug distribution to healthy organs. Special attention was paid to the effect of core stereoregularity and chemical structure in di- as well as tri-block copolymers in the development of polymeric micellar carriers with enhanced thermodynamic and kinetic stability, high drug loading and slowed drug release. Such nano-carriers are expected to achieve improved accumulation in solid tumors through enhanced permeation and retention (EPR) effect. Synthesis of block copolymers of poly(ethylene oxide)-poly(lactide) (PEO-PLA) with different tacticity in the PLA block was pursued using either bulk or solution polymerization. This was followed by block copolymer self-assembly and micellar characterization. In diblock copolymer micelles, a positive correlation between stereoactivity of the core-forming block and degree of core-crystallinity as well as micellar kinetic and thermodynamic stability was observed. Nonetheless, the improved micellar stability neither translated to a reduced rate of drug release nor increased level of drug loading using nimodipine as a model lipophilic drug. Triblock copolymer micelles with a drug miscible inner core (evidenced by a low Flory Huggins interaction parameter); i.e., poly(ε-caprolactone) (PCL) or poly(α-benzyl carboxylate-ε-caprolactone) (PBCL), and drug immiscible outer core, i.e., PLA, improved nimodipine loading content while inhibiting its burst release from the nano-carrier. In the second part of this thesis, we investigated application of actively targeted polymeric micelles with and without modulators of relevant mechanisms of hypoxia induced chemoresistance (HICR) to cisplatin to overcome drug resistance in breast cancer at a cellular level. This study was aimed to potentiate cytotoxic effects of free and polymeric micellar cisplatin in MDA-MB-231 cells and its two subpopulations with distinct tumorigenic features. The peptide ligand of epidermal growth factor receptor (EGFR), GE11 (YHWYGYTPQNVI), was conjugated to the acetal-PEO end of acetal-PEO-Poly(α-carboxyl-ε-caprolactone) (acetal-PEO-PCCL). The polymer then formed a complex with cisplatin through its pendent COOH groups self-assembling to polymeric micelles during the process. GE11-peptide increased cellular uptake of polymeric micellar cisplatin by MDA-MB-231 cells under hypoxic condition, however the cytotoxicity of GE11-cisplatin micelles was not significantly different from plain micellar cisplatin. We then investigated the combination of free and micellar cisplatin with inhibitors of cellular pathways involved in HICR in MDA-MB-231 cells. Our results pointed to a major role for signal transducer and activator of transcription 3 (STAT3) in addition to hypoxia inducing factor-1α (HIF-1α), in the appearance of stem-cell markers and resistance to cisplatin in MDA-MB-231 cells. Hypoxia was also shown to actively convert the low tumorigenic/stem-like subpopulations of MDA-MB-231, separated based on their unresponsiveness to a Sox2 reporter (abbreviated as RU cells), to the more tumorigenic/stem-like subpopulation (abbreviated as RR cells). Evidence for the major role of STAT3 activation as responsible factors for this conversion was also revealed. The use of pharmacological inhibitors of STAT3 and HIF-1α with free, as well as polymeric micellar cisplatin (plain and GE11 modified) substantially enhanced the cisplatin toxicity and showed success in partial reversal of HICR to cisplatin. Overall, the results of our studies show the chemical structure of block copolymer based nano-carriers has the required flexibility for the development of delivery systems for certain application needs. We have shown this towards development of stable nano-carriers capable of high drug loading and slow drug release by manipulating the stereochemistry and structure of di- as well as triblock copolymer micelles. Nano-delivery systems developed to enhance drug delivery to tumor tissue may not be able to overcome chemoresistance at the cellular level, particularly since they are designed to slow down drug release and have low interaction with cells because of their hydrophilic surfaces. Our results show, the potency of conventional and nano-chemotherapeutics can be enhanced once major cellular and molecular players of chemoresistance are identified and appropriate inhibitors of the identified pathway are used in combination with the anti-cancer agent. We have shown this through identification of major players in the hypoxia-induced tumorigenic conversion and chemoresistance against cisplatin (STAT3 and HIF-1α followed by the use of genetic silencers as well as pharmacological inhibitors of the mentioned pathways in combination with free and micellar cisplatin formulations, in MDA-MB-231 cells.

• Subjects / Keywords

  • Stemness
  • Hypoxia-induced chemoresistance
  • Cisplatin
  • Triple negative breast cancer
  • STAT3
  • Polymeric micelles
  • Stereoregularity
  • ABC triblock copolymer
  • Stereoactivity
  • EGFR targeted micelles
  • Hypoxia
  • Chemoresistance
  • HIF-1 alpha
  • Micellar stability

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3M61C407

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.