Multidrug resistance is the most widely exploited phenomenon by which cancer eludes chemotherapy. Broad variety of factors, ranging from the cellular ones, such as over-expression of efflux transporters, defective apoptotic machineries, and altered molecular targets, to the physiological factors such as higher interstitial fluid pressure, low extracellular pH, and formation of irregular tumor vasculature are responsible for multidrug resistance. A combination of various undesirable factors associated with biological surroundings together with poor solubility and instability of many potential therapeutic small & large molecules within the biological systems and systemic toxicity of chemotherapeutic agents has necessitated the need for nano-preparations to optimize drug delivery. The physiology of solid tumors presents numerous challenges for successful therapy. However, it also offers unique opportunities for the use of nanotechnology. Nanoparticles, up to 400 nm in size, have shown great promise for carrying, protecting and delivering potential therapeutic molecules with diverse physiological properties. In this review, various factors responsible for the MDR and the use of nanotechnology to overcome the MDR, the use of spheroid culture as well as the current technique of producing micro tumor tissues in vitro are discussed in detail.

One of the major obstacles to the success of cancer chemotherapy is the multidrug resistance (MDR) often resulting due to the overexpression of drug efflux transporter pumps such as P-glycoprotein (P-gp). Highly efficacious third generation P-gp inhibitors, like tariquidar, have shown promising results in overcoming the MDR. However, P-gp is also expressed in normal tissues like blood brain barrier, gastrointestinal track, liver, spleen and kidney. To maximize the efficacy of P-gp inhibitor and reduce the systemic toxicity, it is important to limit the exposure of P-gp inhibitors and the anticancer drugs to normal tissues and increase their co-localization with tumor cells. In this study, we have investigated the co-delivery of the P-gp inhibitor, tariquidar, and cytotoxic drug, paclitaxel, into tumor cells to reverse the MDR using long-circulating liposomes. Tariquidar- and paclitaxel-loaded long-circulating liposomes showed significant resensitization of the resistant variant for paclitaxel, which could be correlated with an increased accumulation of paclitaxel in tumor cells. These results suggest that the co-delivery of the P-gp inhibitor, tariquidar, and the cytotoxicity inducer, paclitaxel, looks like a promising approach to overcome the MDR.

We describe the evaluation of doxorubicin-loaded PEG-PE micelles targeting using an ovarian cancer cell spheroid model. Most ovarian cancer patients present at an advanced clinical stage and develop resistance to standard of care platinum/taxane therapy. Doxorubicin is also approved for ovarian cancer but had limited benefits in refractory patients. In this study, we used drug-resistant spheroid cultures of ovarian carcinoma to evaluate the uptake and cytotoxicity of an antibody-targeted doxorubicin formulation. Doxorubicin was encapsulated in polyethylene glycol-phosphatidyl ethanolamine (PEG-PE) conjugated micelles. The doxorubicin-loaded PEG-PE micelles (MDOX) were further decorated with a cancer cell-specific monoclonal 2C5 antibody to obtain doxorubicin-loaded immunomicelles (2C5-MDOX). Targeting and resulting toxicity of doxorubicin-loaded PEG-PE micelles were evaluated in three dimensional cancer cell spheroids. Superior accumulation of 2C5-MDOX compared to free doxorubicin or untargeted MDOX in spheroids was evidenced both by flow cytometry, fluorescence and confocal microscopy. Interestingly, even higher toxicity was measured by lactate dehydrogenase release and terminal deoxynucleotidyl transferase dUTP nick end labeling of targeted doxorubicin micelles in Bcl-2 overexpressing adriamycin-resistant spheroids. Overall, these results support use of spheroids to evaluate tumor targeted drug delivery.

The therapeutic potential of mixed micelles, made of PEG-PE and vitamin E co-loaded with curcumin and paclitaxel, was investigated against SK-OV-3 human ovarian adenocarcinoma along with its multi-drug resistant version SK-OV-3-paclitaxel-resistant (TR) cells in vitro and in vivo. The addition of curcumin at various concentrations did not significantly enhance the cytotoxicity of paclitaxel against SK-OV-3 in vitro. However, a clear synergistic effect was observed with the combination treatment against SK-OV-3TR in vitro. In vivo, this combination treatment produced a three-fold tumor inhibition with each of these cell lines. Our results indicate that such co-loaded mixed micelles could have significant clinical advantages for the treatment of resistant ovarian cancer.

Purpose Platinum-based chemotherapy is the treatment of choice for malignant epithelial ovarian cancers, but generalized toxicity and platinum resistance limits its use. Theranostic nanoemulsion with a novel platinum prodrug, myrisplatin, and the pro-apoptotic agent, C6-ceramide, were designed to overcome these limitations. Methods The nanoemulsions, including ones with an EGFR binding peptide and gadolinium, were made using generally regarded as safe grade excipients and a high shear microfluidization process. Efficacy was evaluated in ovarian cancer cells, SKOV3, A2780 and A2780CP. Results The nanoemulsion with particle size <150 nm were stable in plasma and parenteral fluids for 24 h. Ovarian cancer cells in vitro efficiently took up the non-targeted and EGFR-targeted nanoemulsions; improved cytotoxicity was observed for the these nanoemulsions with the latter showing a 50-fold drop in the IC50 in SKOV3 cells as compared to cisplatin alone. The addition of gadolinium did not affect cell viability in vitro, but showed relaxation times comparable to Magnevist®. Conclusion The myrisplatin/C6-ceramide nanoemulsion synergistically enhanced in vitro cytotoxicity. An EGFR binding peptide addition further increased in vitro cytotoxicity in EGFR positive cancer cells. The diagnostic version showed MR imaging similar to the clinically relevant Magnevist® and may be suitable as a theranostic for ovarian cancer.

Current efforts toward improving the effectiveness of drug therapy are increasingly relying on drug-targeting strategies to effectively deliver bioactive molecules to their molecular targets. Pharmaceutical nanocarriers represent a major tool toward this aim, and our efforts have been directed toward achieving nanocarrier-mediated subcellular delivery of drug molecules with mitochondria as the primary subcellular target. Meeting the need for specific subcellular delivery is essential to realizing the full potential of many poorly soluble anticancer drugs. In this article, we report that mitochondria-targeted liposomes significantly improve the apoptotic and cytotoxic action of sclareol, a poorly soluble potential anticancer drug. The results support the broad applicability of our nanocarrier-mediated subcellular targeting approach as a means to improve the effectiveness of certain anticancer therapeutics.

Objective Ovarian cancer is a highly lethal disease in which the majority of patients eventually demonstrate multidrug resistance. Develop a novel active targeted theranostic nanomedicine designed to overcome drug efflux mechanisms, using a Generally Regarded As Safe (GRAS) grade nanoemulsion (NE) as a clinically relevant platform. Materials and methods The NEs surface-functionalized with folate and gadolinium, were made using GRAS grade excipients and a high-shear microfluidization process. Efficacy was evaluated in ovarian cancer cells, SKOV3 and SKOV3TR. The NE accumulation in tumors was evaluated in SKOV3 tumor-bearing mice by magnetic resonance imaging (MRI). Results and discussion The NE with particle size <150nm were stable in plasma and parenteral fluids for 24 h. Ovarian cancer cells in vitro efficiently took up the non-targeted and folate-targeted NEs; improved cytotoxicity was observed for the folate-targeted NEs showing a 270- fold drop in the IC50 in SKOV3TR cells as compared to docetaxel alone. The addition of gadolinium did not affect cell viability in vitro, but showed relaxation times comparable to Magnevist®. Folate-targeted NEs accumulated in tumors for prolonged period of time compared to Magnevist® and showed enhanced contrast compared to non-targeted NEs with MRI in SKOV3 tumor-bearing mice suggesting active targeting of NEs due to folate modification. Conclusions A folate-targeted, theranostic NE delivers docetaxel by receptor mediated endocytosis that shows enhanced cytotoxicity capable of overcoming ABC transporter mediated taxane resistance. The diagnostic capability of the targeted nanomedicine showed enhanced contrast in tumors compared to clinically relevant MRI contrast agent Magnevist®.

Purpose Platinum-based therapies are the first line treatments for most types of cancer including ovarian cancer. However, their use is associated with dose-limiting toxicities and resistance. We report initial translational studies of a theranostic nanoemulsion loaded with a cisplatin derivative, myrisplatin and pro-apoptotic agent, C6-ceramide. Methods The surface of the nanoemulsion is annotated with an endothelial growth factor receptor (EGFR) binding peptide to improve targeting ability and gadolinium to provide diagnostic capability for image-guided therapy of EGFR overexpressing ovarian cancers. A high shear microfludization process was employed to produce the formulation with particle size below 150 nm. Results Pharmacokinetic study showed a prolonged blood platinum and gadolinium levels with nanoemulsions in nu/nu mice. The theranostic nanoemulsions also exhibited less toxicity and enhanced the survival time of mice as compared to an equivalent cisplatin treatment. Conclusions Magnetic resonance imaging (MRI) studies indicate the theranostic nanoemulsions were effective contrast agents and could be used to track accumulation in a tumor. The MRI study additionally indicate that significantly more EGFR-targeted theranostic nanoemulsion accumulated in a tumor than non-targeted nanoemulsuion providing the feasibility of using a targeted theranostic agent in conjunction with MRI to image disease loci and quantify the disease progression.