Niravkumar R. Patel

Nanopreparations to overcome multidrug resistance in cancer

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 microtumor tissues in vitro are discussed in detail.

Reversal of multidrug resistance by co-delivery of tariquidar (XR9576) and paclitaxel using long-circulating liposomes.

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.

Accumulation and toxicity of antibody-targeted doxorubicin-loaded PEG-PE micelles in ovarian cancer cell spheroid model.

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.

Polyethylene glycol-phosphatidylethanolamine (PEG-PE)/vitamin E micelles for co-delivery of paclitaxel and curcumin to overcome multi-drug resistance in ovarian cancer.

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.

Mitochondria-targeted liposomes improve the apoptotic and cytotoxic action of sclareol

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.

Anti-cancer activity of anti-GLUT1 antibody-targeted polymeric micelles co-loaded with curcumin and doxorubicin.

Abstract Background: Treatment of late stage cancers has proven to be a very difficult task. Targeted therapy and combinatory drug administration may be the solution. Purpose: The study was performed to evaluate the therapeutic efficacy of PEG-PE micelles, co-loaded with curcumin (CUR) and doxorubicin (DOX), and targeted with anti-GLUT1 antibody (GLUT1) against HCT-116 human colorectal adenocarcinoma cells both in vitro and in vivo. Methods: HCT-116 cells were treated with non-targeted and GLUT1-targeted CUR and DOX micelles as a single agent or in combination. Cells were inoculated in female nude mice. Established tumors were treated with the micellar formulations at a dose of 4 mg/kg CUR and 0.4 mg/kg DOX every 2 d for a total of 7 injections. Results: CUR + DOX-loaded micelles decorated with GLUT1 had a robust killing effect even at low doses of DOX in vitro. At the doses chosen, non-targeted CUR and CUR + DOX micelles did not exhibit any significant tumor inhibition versus control. However, GLUT1-CUR and GLUT1-CUR + DOX micelles showed a significant tumor inhibition effect with an improvement in survival. Conclusion: We showed a dramatic improvement in efficacy between the non-targeted and GLUT1-targeted formulations both in vitro and in vivo. Hence, we confirmed that GLUT1-CUR + DOX micelles are effective and deserve further investigation.

Therapeutic delivery using cell-penetrating peptides

Abstract Intracellular delivery of promising therapeutic agents as well as nanocarriers presents a unique challenge. However, with the discovery of the cell-penetrating peptides (CPPs), overcoming this obstacle seems more plausible. In many cases, CPPs conjugated with therapeutic agent or therapeutic agent loaded-nanoparticles have shown promising results via increased cellular uptake. In this review, the current status of CPPs for the intracellular delivery of not just potential therapeutic small molecules but also large molecules like peptides, nucleic acids and nanocarriers is discussed. In addition, the design of ‘smart stimuli-sensitive nanocarrier’ to overcome the non-target-specificity of CPPs is also described.

Formulation development of a novel targeted theranostic nanoemulsion of docetaxel to overcome multidrug resistance in ovarian cancer

Abstract 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 < 150 nm 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®.

Cancer cell spheroids for screening of chemotherapeutics and drug-delivery systems

Over the last few decades, the most popular platform to perform high-throughput screening for viable anti-neoplastic compounds has been monolayer cell culture. However, cells in monolayer culture lose many of their in vivo characteristics. As a result, this platform provides a limited predictive value in determining the clinical outcome of the compounds of interest. Using a technique known as 3D spheroid culture, may be the answer to this conundrum. Spheroids have been shown to mimic the tissue-like properties of tumors necessary for the proper evaluation of compounds. In this review, production of cancer cell spheroids, utilization of these spheroids in understanding various therapeutic mechanisms and the potential for their use in high-throughput screening of drugs and drug-delivery systems are discussed in detail.

Design, Synthesis, and Characterization of Folate-Targeted Platinum-Loaded Theranostic Nanoemulsions for Therapy and Imaging of Ovarian Cancer

Platinum (Pt) based chemotherapy is widely used to treat many types of cancer. Pt therapy faces challenges such as dose limiting toxicities, cumulative side effects, and multidrug resistance. Nanoemulsions (NEs) have tremendous potential in overcoming these challenges as they can be designed to improve circulation time, limit non-disease tissue uptake, and enhance tumor uptake by surface modification. We designed novel synthesis of three difattyacid platins, dimyrisplatin, dipalmiplatin, and distearyplatin, suitable for encapsulation in the oil core of an NE. The dimyrisplatin, dipalmiplatin, and distearyplatin were synthesized, characterized, and loaded into the oil core of our NEs, NMI-350, NMI-351, and NMI-352 respectively. Sequestration of the difattyacid platins was accomplished through high energy microfluidization. To target the NE, FA-PEG3400-DSPE was incorporated into the surface during microfluidization. The FA-NEs selectively bind the folate receptor α (FR-α) and utilize receptor mediated endocytosis to deliver Pt past cell surface resistance mechanisms. FR-α is overexpressed in a number of oncological conditions including ovarian cancer. The difattyacid platins, lipidated Gd-DTPA, and lipidated folate were characterized by nuclear magnetic resonance (NMR), mass spectrometry (MS), and elemental analysis. NEs were synthesized using high shear microfluidization process and characterized for size, zeta-potential, and loading efficiency. In vitro cytotoxicity was determined using KB-WT (Pt-sensitive) and KBCR-1000 (Pt-resistant) cancer cells and measured by MTT assay. Pharmacokinetic profiles were studied in CD-1 mice. NEs loaded with difattyacid platins are highly stable and had size distribution in the range of ∼120 to 150 nm with low PDI. Cytotoxicity data indicates the longer the fatty acid chains, the less potent the NEs. The inclusion of C6-ceramide, an apoptosis enhancer, and surface functionalization with folate molecules significantly increased in vitro potency. Pharmacokinetic studies show that the circulation time for all three difattyacid platins encapsulated in NE remained identical, thus indicating that chain length did not influence circulation time. A stable NMI-350 family of NEs were successfully designed, formulated, and characterized. The Pt-resistance in KBCR-1000 cells was reversed with the NMI-350 family. Dimyrisplatin loaded NE (NMI-350) was most potent in vitro. The NMI-350 family demonstrated identical pharmacokinetic profiles to one another and circulated much longer than cisplatin. These data indicate that NMI-350 warrants further preclinical and clinical development as a replacement for current Pt regimens especially for those afflicted with multi drug resistant cancers.