Stimuli-Responsive Polymeric Nanomedicine For Highly Efficient Tumor Targeting Chemotherapy

Doxilò(liposome-encapsulated doxorubicin) is the first nanomedicine approved by FDA in 1995 for the treatment of HIV-related Kaposi’s sarcoma, ovarian cancer and multiple myeloma. Last decade has witnessed the booming of polymeric nanomedicines since Genexol-PMò(paclitaxel formulation based on PEG-PLA micelles) was approved in South Korea for the treatment of breast cancer, lung cancer and ovarian cancer. Many polymeric nanomedicines including NC-6004, NK-911 and BIND-014 have advanced in different phases of clinical trials with various success. The results from clinical trials point out that these polymeric nanocarriers could significantly enhance the solubility of anticancer drugs, extend half-life time of drugs in blood circulation, as well as improve drug’s biodistribution and therapeutic index. However, nanomedicines encounter several challenges, including(i) poor in vivo stability due to extensive dilution and interactions with blood proteins, which often leads to dissociation or aggregation, premature drug release and low tumor-targetability;(ii) inefficient uptake by tumor cells due to surface shielding by PEG or dextran; or(iii) slow/inadequate intracellular drug release following uptake by tumor cells. Chapter 1 presented a brief literature overview on nanomedicines used in cancer therapy, the current status and obstacles, and recent advances in the design of ideal nanomedicines for cancer therapy.To obtain nanomedicines with high therapeutic index and low/no side-effects, each chapter of this thesis deals with one or more of above obstacles. Various strategies have been adopted in this thesis to design biodegradable nanocarriers, including: stimuli-responsive nanomedicines which allow fast intracellular drug release thus high antitumor activity, tumor specific targeting nanomedicines which promote efficient cellular uptake and thus high drug concentration, and robust nanomedicines which support long blood circulation ensuring low side-effects and high targetability.It is well known that cytosol and cell nuclei are reductive with glutathione concentration of 2-10 m M as compared to that of 2-20 mM in body fluid and extracellular matrix. Glutathione concentration in tumor tissues is at least 4 times higher than that of normal tissue. In chapter 2, to promote cellular uptake by tumor cells and fast intracellular drug release, we have designed galactose coupled, reduction-sensitive shell-sheddable biodegradable micellar nanomedicine based on poly(ethylene glycol)-SSpoly(e-caprolactone)(PEG-SS-PCL). The DOX loaded micelles were small(58 nm), and displayed remarkable reduction sensitivity. Cell experiments showed that the nanomedicine exhibited apparent targetability to asialoglycoprotein receptor-overexpressing hepatoma cancer cells Hep G2, and quickly delivered DOX into the cell nuclei, inducing superb in vitro antitumor effects.It has been reported that 85% cancer originated from chronic inflammation. A variety of cytokines and reactive oxygen species produced by inflammatory cells can result in repeated cell necrosis, regeneration, deterioration and tumorgenesis. In order to extend the application of the reduction-sensitive shell-sheddable micellar nanomedicine, in chapter 3 we have developed inflammation targeting, shell-sheddable micellar nanomedicine based on dendritic polyglycerol sulfate-SS-PCL(d PGS-SS-PCL) for efficient treatment of inflammation-related tumors(e.g. human breast cancer MCF-7 xenografts). The d PGS molecules housing many anions are non-toxic, and have high affinity to L-selectin and thus high anti-inflammatory capability. The obtained d PGS-SS-PCL nanomedicine was small(65 nm) and displayed apparent reduction sensitivity in terms of drug release. Notably, the nanomedicine had a long blood circulation time(half-life of elimination phase t1/2 = 2.83 h vs. 0.19 h for free DOX), and could accumulate in tumor much more efficiently after 10 h following i.v. injection via tail vein than the non-reductive control d PGS-PCL. In MCF-7 tumor bearing nude mice, DOX loaded d PGS-SS-PCL effectively inhibited tumor growth without weight loss and obvious damage to liver and heart. Moreover, the maximum tolerated dose(MTD) was determined to be more than 30 mg/kg. From the two examples, we conclude that the tumor targeting, reduction-sensitive shell-sheddable biodegradable micellar nanomedicine have high potential in targeted cancer therapy.It is reported that cell endosome/lysome(p H 4.0-6.0) as well as tumor tissues(p H 6.5-7.2) are acidic as compared to normal body fluid(p H 7.4). Chapter 4 takes advantage of this feature to realize quick drug release inside tumor cells. We have designed endosomal p H-responsive paclitaxel(PTX) prodrug micelles based on hyaluronic acid-b-dendritic polyglycerol-g-PTX(HA-d PG-PTX-M) for active targeting and effective treatment of CD44 receptor-overexpressing MCF-7 xenografts in nude mice. Here PTX was coupled to d PG via a p H-liable acetal bond. HA is a water-soluble natural polysaccharide showing high affinity to CD44 receptors which over-express on the surface of many tumor cells and tumor stem cells. HA-d PG-PTX-M nanomedicine with HA as hydrophilic shell had high drug contents(20.3 wt.%), small size(155 nm) and prominent endosomal p H triggered PTX release capacity. Moreover, the in vivo studies in nude mice displayed that HA-d PG-PTX-M had a prolonged circulation time(t1/2 = 4.32 h vs. 0.23 h for Taxol) and a high PTX accumulation in MCF-7 tumor(6.19 %ID/g) at 12 h post injection. Interestingly, HA-d PG-PTX-M could completely inhibit MCF-7 tumor growth with little side-effects, and a 100 % survival rate at 55 days was observed. Furthermore, the MTD was over 100 mg/kg in contrast to that of Taxol of 20 mg/kg. Thus, this endosomal p H sensitive prodrug nanomedicine with HA as hydrophilic shell represents a route to treating CD44 overexpressing tumors.In order to further investigate the applications of HA based nanomedicines in other CD44 receptor overexpressed tumors, in chapter 5 we have explored reduction-sensitive reversibly crosslinked robust HA nanomedicines in nude mice for the treatment of subcutaneous drug-resistant MCF-7/ADR tumor(sub-MCF-7/ADR), orthotopic MCF-7 tumor(orth-MCF-7), subcutaneous acute myeloid leukemia AML-2 tumor(sub-AML-2), and subcutaneous multiple myeloma LP1 tumor(sub-LP1). The nanomedicine is based on HA-Lys-LA conjugates composed of all natural materials. Interestingly, the in vivo studies in MCF-7/ADR tumor xenografts in nude mice showed that DOX-loaded crosslinked HA-Lys-LA10 nanoparticles(X-NP-DOX) had a long circulation time(t1/2 = 4.83 h) and an extraordinarily high DOX accumulation in the tumor(12.71 %ID/g). Remarkably, X-NP-DOX could inhibit even shrunk tumor growth in sub-MCF-7/ADR tumor-bearing mice. Importantly, it caused very low side-effects and promoted the longest life-span of the mice as compared with free DOX and PBS with 100% survival rate over 44 days. Furthermore, X-NP-DOX nanomedicine demonstrated potent antitumor efficacies, low side-effects and long survival rates in all tested CD44 receptor overexpressed orth-MCF-7, sub-AML-2 and sub-LP1 tumors. The present nanomedicine elegantly combines the high targetability of HA with the circulation stability and fast intracellular drug release provided by LA, and thus is extremely appealing in cancer therapy.Near infrared(NIR) can penetrate into the tissues up to 10 cm with negligible damage to normal cells, and it allows precise control over drug release temporally and spatially. In chapter 6, we have designed NIR responsive biodegradable micellar nanomedicine using lipoylated PEG-PCL(PEG-PCL-LA) block copolymer coated gold nanorods(Au NRs). Au NRs show strong NIR-induced photothermal effect and specific interaction with sulfur atoms thus they can serve as crosslinking agent for PEG-PCL-LA. The obtained DOX loaded nanomedicines(Au NR-M-DOX) had uniform sizes and excellent colloidal stability, and NIR-responsive DOX release. MTT assays showed that Au NR-M-DOX combined with mild NIR irradiation significantly boosted the antitumor activity to MCF-7 cells(comparable level to free DOX) as well as to drug-resistant MCF-7/ADR cells. Based on chapter 6, in chapter 7 we investigated c RGD-directed NIR-responsive Au NR/PEG-PCL hybrid nanoparticles(c RGD-HNs) for targeted chemotherapy of U87 MG xenografts in mice. The in vivo studies illustrated that c RGD-HN-DOX had much longer circulation time than free DOX(half-life of elimination phase t1/2: 5.67 h vs. 0.21 h), when combined with NIR irradiation it could completely inhibit tumor growth with much lower side-effects than free DOX. Thus tumor specific ligand-directed Au NR/PEG-PCL hybrid nanoparticles with superior spatiotemporal and rate control over drug release can serve as an important platform for cancer chemotherapy.Finally, chapter 8 gives a summary of this thesis, and a future perspective in this field is provided.