Gemcitabine-based therapy for pancreatic cancer using the squalenoyl nucleoside monophosphate nanoassemblies

Gemcitabine-Vitamin E Prodrug-Loaded Micelles for Pancreatic Cancer Therapy

Pancreatic cancer (PC) is an aggressive cancer subtype presenting unmet clinical challenges. Conventional chemotherapy, which includes antimetabolite gemcitabine (GEM), is seriously undermined by a short half-life, its lack of targeting ability, and systemic toxicity. GEM incorporation in self-assembled nanosystems is still underexplored due to GEM's hydrophilicity which hinders efficient encapsulation. We hypothesized that vitamin E succinate-GEM prodrug (VES-GEM conjugate) combines hydrophobicity and multifunctionalities that can facilitate the development of Pluronic® F68 and Pluronic® F127 micelle-based nanocarriers, improving the therapeutic potential of GEM. Pluronic® F68/VES-GEM and Pluronic® F127/VES-GEM micelles covering a wide range of molar ratios were prepared by solvent evaporation applying different purification methods, and characterized regarding size, charge, polydispersity index, morphology, and encapsulation. Moreover, the effect of sonication and ultrasonication and the influence of a co-surfactant were explored together with drug release, stability, blood compatibility, efficacy against tumour cells, and cell uptake. The VES-GEM conjugate-loaded micelles showed acceptable size and high encapsulation efficiency (>95%) following an excipient reduction rationale. Pluronic® F127/VES-GEM micelles evidenced a superior VES-GEM release profile (cumulative release > 50%, pH = 7.4), stability, cell growth inhibition (<50% cell viability for 100 µM VES-GEM), blood compatibility, and extensive cell internalization, and therefore represent a promising approach to leveraging the efficacy and safety of GEM for PC-targeted therapies.

Photochemical Internalization Using Natural Anticancer Drugs, Antimetabolites, and Nanoformulations: A Systematic Study against Breast and Pancreatic Cancer Cell Lines

Photochemical internalization (PCI) is a novel, minimally invasive drug delivery technology that facilitates the delivery of therapeutic molecules into the cytosol of cells. In this work, PCI was utilized in an effort to enhance the therapeutic index of the existing anticancer drugs as well as novel nanοformulations against breast and pancreatic cancer cells. Frontline anticancer drugs were tested with bleomycin as a benchmark PCI control; namely, three vinca alkaloids (vincristine, vinorelbine, and vinblastine), two taxanes (docetaxel and paclitaxel), two antimetabolites (gemcitabine and capecitabine), a combination of taxanes with antimetabolites, and two nano-sized formulations (squalene- and polymer-bound gemcitabine derivatives) were tested in a 3D PCI in vitro model. Strikingly, we discovered that several drug molecules exhibited remarkably augmented therapeutic activity by several orders of magnitude compared to their respective controls (without PCI technology or directly compared with bleomycin controls). Nearly all drug molecules showed enhanced therapeutic efficiency, but more interestingly, we traced several drug molecules that showed multi-fold enhancement (ranging from 5000- up to 170,000-fold enhancement) in their IC₇₀ indices. Interestingly, PCI delivery of the vinca alkaloids (especially PCI-vincristine), and some of the nanoformulations tested, was seen to perform impressively across all of the treatment outcomes of potency, efficacy, and synergy─as determined by means of a cell viability assay. The study constitutes a systematic guide for the development of future PCI-based therapeutic modalities for precision oncology.

Nucleoside transporters and immunosuppressive adenosine signaling in the tumor microenvironment: Potential therapeutic opportunities

Adenosine compartmentalization has a profound impact on immune cell function by regulating adenosine localization and, therefore, extracellular signaling capabilities, which suppresses immune cell function in the tumor microenvironment. Nucleoside transporters, responsible for the translocation and cellular compartmentalization of hydrophilic adenosine, represent an understudied yet crucial component of adenosine disposition in the tumor microenvironment. In this review article, we will summarize what is known regarding nucleoside transporter's function within the purinome in relation to currently devised points of intervention (i.e., ectonucleotidases, adenosine receptors) for cancer immunotherapy, alterations in nucleoside transporter expression reported in cancer, and potential avenues for targeting of nucleoside transporters for the desired modulation of adenosine compartmentalization and action. Further, we put forward that nucleoside transporters are an unexplored therapeutic opportunity, and modulation of nucleoside transport processes could attenuate the pathogenic buildup of immunosuppressive adenosine in solid tumors, particularly those enriched with nucleoside transport proteins.

Azacitidine Omega-3 Self-Assemblies: Synthesis, Characterization, and Potent Applications for Myelodysplastic Syndromes

5-Azacitidine, a cytidine analogue used as a hypomethylating agent, is one of the main drugs for the treatment of myelodysplastic syndromes (MDSs) and acute myeloid leukemia (AML) in the elderly. However, after administration, it exhibits several limitations, including restricted diffusion and cellular internalization due to its hydrophilicity, and a rapid enzymatic degradation by adenosine deaminase. The aim of this study was to improve the drug cell diffusion and protect it from metabolic degradation via the synthesis of amphiphilic prodrugs and their potential self-assembly. Azacitidine was conjugated to two different omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The carboxylic acid group of the omega-3 fatty acids was effectively conjugated to the amine group of the azacitidine base, yielding two amphiphilic prodrugs. Nanoprecipitation of the obtained prodrugs was performed and self-assemblies were successfully obtained for both prodrugs, with a mean diameter of 190 nm, a polydispersity index below 0.2 and a positive zeta potential. The formation of self-assemblies was confirmed using pyrene as a fluorescent dye, and the critical aggregation concentrations were determined: 400 µM for AzaEPA and 688 µM for AzaDHA. Additionally, the stability of the obtained self-assemblies was studied and after 5 days their final stable arrangement was reached. Additionally, cryo-TEM revealed that the self-assemblies attain a multilamellar vesicle supramolecular structure. Moreover, the obtained self-assemblies presented promising cytotoxicity on a leukemia human cell line, having a low IC50 value, comparable to that of free azacitidine.

Gemcitabine-loaded microbubble system for ultrasound imaging and therapy

Ultrasound imaging presents many positive attributes, including safety, real-time imaging, universal accessibility, and cost. However, inherent difficulties in discrimination between soft tissues and tumors prompted development of stabilized microbubble contrast agents. This presents the opportunity to develop agents in which drug is entrapped in the microbubble shell. We describe preparation and characterization of theranostic poly(lactide) (PLA) and pegylated PLA (PEG-PLA) shelled microbubbles that entrap gemcitabine, a commonly used drug for pancreatic cancer (PDAC). Entrapping 6 wt% gemcitabine did not significantly affect drug activity, microbubble morphology, or ultrasound contrast activity compared with unmodified microbubbles. In vitro microbubble concentrations yielding ≥ 500nM entrapped gemcitabine were needed for complete cell death in MIA PaCa-2 PDAC drug sensitivity assays, compared with 62.5 nM free gemcitabine. In vivo administration of gemcitabine-loaded microbubbles to xenograft MIA PaCa-2 PDAC tumors in athymic mice was well tolerated and provided substantial tumoral image enhancement before and after destructive ultrasound pulses. However, no significant differences in tumor growth were observed among treatment groups, in keeping with the in vitro observation that much higher doses of gemcitabine are required to mirror free gemcitabine activity. STATEMENT OF SIGNIFICANCE: The preliminary results shown here are encouraging and support further investigation into increased gemcitabine loading. Encapsulation of gemcitabine within polylactic acid (PLA) microbubbles does not damage its activity towards pancreatic cancer (pancreatic ductal adenocarcinoma, PDAC) cells. Excellent imaging and evidence of penetration into the highly desmoplastic PDAC tumors is demonstrated. Microbubble destruction was confirmed in vivo, showing that elevated mechanical index shatters the microbubbles for enhanced delivery. The potential to slow PDAC growth in vivo is shown, but higher gemcitabine concentrations are required. Current efforts are directed at increasing drug loading by inclusion of drug-carrying nanoparticles for effective in vivo treatment.

The evolution of nucleosidic analogues: self-assembly of prodrugs into nanoparticles for cancer drug delivery

Nucleoside and nucleotide analogs are essential tools in our limited arsenal in the fight against cancer. However, these structures face severe drawbacks such as rapid plasma degradation or hydrophilicity, limiting their clinical application. Here, different aspects of nucleoside and nucleotide analogs have been exposed, while providing their shortcomings. Aiming to improve their fate in the body and combating their drawbacks, two different approaches have been discussed, the prodrug and nanocarrier technologies. Finally, a novel approach called "PUFAylation" based on both the prodrug and nanocarrier technologies has been introduced, promising to be the supreme method to create a novel nucleoside or nucleotide analog based formulation, with enhanced efficacy and highly reduced toxicity.

New Nanoparticle Formulation for Cyclosporin A: In Vitro Assessment

Cyclosporin A (CsA) is a molecule with well-known immunosuppressive properties. As it also acts on the opening of mitochondrial permeability transition pore (mPTP), CsA has been evaluated for ischemic heart diseases (IHD). However, its distribution throughout the body and its physicochemical characteristics strongly limit the use of CsA for intravenous administration. In this context, nanoparticles (NPs) have emerged as an opportunity to circumvent the above-mentioned limitations. We have developed in our laboratory an innovative nanoformulation based on the covalent bond between squalene (Sq) and cyclosporin A to avoid burst release phenomena and increase drug loading. After a thorough characterization of the bioconjugate, we proceeded with a nanoprecipitation in aqueous medium in order to obtain SqCsA NPs of well-defined size. The SqCsA NPs were further characterized using dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryoTEM), and high-performance liquid chromatography (HPLC), and their cytotoxicity was evaluated. As the goal is to employ them for IHD, we evaluated the cardioprotective capacity on two cardiac cell lines. A strong cardioprotective effect was observed on cardiomyoblasts subjected to experimental hypoxia/reoxygenation. Further research is needed in order to understand the mechanisms of action of SqCsA NPs in cells. This new formulation of CsA could pave the way for possible medical application.

pH-Sensitive Nanodrug Carriers for Codelivery of ERK Inhibitor and Gemcitabine Enhance the Inhibition of Tumor Growth in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC), a metabolic disorder, remains one of the leading cancer mortality sources worldwide. An initial response to treatments, such as gemcitabine (GEM), is often followed by emergent resistance reflecting an urgent need for alternate therapies. The PDAC resistance to GEM could be due to ERK1/2 activity. However, successful ERKi therapy is hindered due to low ligand efficiency, poor drug delivery, and toxicity. In this study, to overcome these limitations, we have designed pH-responsive nanoparticles (^pHNPs) with a size range of 100-150 nm for the simultaneous delivery of ERKi (SCH 772984) and GEM with tolerable doses. These ^pHNPs are polyethylene glycol (PEG)-containing amphiphilic polycarbonate block copolymers with tertiary amine side chains. They are systemically stable and capable of improving in vitro and in vivo drug delivery at the cellular environment's acidic pH. The functional analysis indicates that the nanomolar doses of ERKi or GEM significantly decreased the 50% growth inhibition (IC₅₀) of PDAC cells when encapsulated in ^pHNPs compared to free drugs. The combination of ERKi with GEM displayed a synergistic inhibitory effect. Unexpectedly, we uncover that the minimum effective dose of ERKi significantly promotes GEM activities on PDAC cells. Furthermore, we found that ^pHNP-encapsulated combination therapy of ERKi with GEM was superior to unencapsulated combination drug therapy. Our findings, thus, reveal a simple, yet efficient, drug delivery approach to overcome the limitations of ERKi for clinical applications and present a new model of sensitization of GEM by ERKi with no or minimal toxicity.

Penetrable Nanoplatform for "Cold" Tumor Immune Microenvironment Reeducation

Lack of tumor-infiltration lymphocytes (TILs) and resistances by overexpressed immunosuppressive cells (principally, myeloid-derived suppressor cells (MDSCs)) in tumor milieu are two major challenges hindering the effectiveness of immunotherapy for "immune-cold" tumors. In addition, the natural physical barrier existing in solid cancer also limits deeper delivery of drugs. Here, a tumor-targeting and light-responsive-penetrable nanoplatform (Apt/PDGs^s@pMOF) is developed to elicit intratumoral infiltration of cytotoxic T cells (CTLs) and reeducate immunosuppressive microenvironment simultaneously. In particular, porphyrinic metal-organic framework (pMOF)-based photodynamic therapy (PDT) induces tumor immunogenic cell death (ICD) to promote CTLs intratumoral infiltration and hot "immune-cold" tumor. Upon being triggered by PDT, the nearly 10 nm adsorbed drug-loaded dendrimer de-shields from the nanoplatform and spreads into the deeper tumor, eliminating MDSCs and reversing immunosuppression, eventually reinforcing immune response. Meanwhile, the designed nanoplatform also has a systemic MDSC inhibition effect and moderate improvement of overall antitumor immune responses, resulting in effective suppression of distal tumors within less significant immune-related adverse effects (irAEs) induced.

From poly(alkyl cyanoacrylate) to squalene as core material for the design of nanomedicines

This review article covers the most important steps of the pioneering work of Patrick Couvreur and tries to shed light on his outstanding career that has been a source of inspiration for many decades. His discovery of biodegradable poly(alkyl cyanoacrylate) (PACA) nanoparticles (NPs) has opened large perspectives in nanomedicine. Indeed, NPs made from various types of alkyl cyanoacrylate monomers have been used in different applications, such as the treatment of intracellular infections or the treatment of multidrug resistant hepatocarcinoma. This latest application led to the Phase III clinical trial of Livatag^®, a PACA nanoparticulate formulation of doxorubicin. Despite the success of PACA NPs, the development of a novel type of NP with higher drug loadings and lower burst release was tackled by the discovery of squalene-based nanomedicines where the drug is covalently linked to the lipid derivative and the resulting conjugate is self-assembled into NPs. This pioneering work was accompanied by a wide range of novel applications which mainly dealt with the management of unmet medical needs (e.g. pancreatic cancer, brain ischaemia and spinal cord injury).

PEG-b-poly (carbonate)-derived nanocarrier platform with pH-responsive properties for pancreatic cancer combination therapy

A pH-responsive nanoparticle platform, based on PEG-b-poly (carbonate) block copolymers have been proposed that can respond to low pH as found in many cancer micro- and intracellular environment, including that in pancreatic cancer. The hydrophobic domain, i.e., the poly (carbonate) segment has been substituted with tertiary amine side chains, such as N, N'-dibutylethylenediamine (pK_a = 4.0, DB) and 2-pyrrolidin-1-yl-ethyl-amine (pk_a = 5.4, Py) to generate two different sets of block copolymers namely PEG-DB and PEG-PY systems. These side-chain appended amines promote disassembly of nanoparticles and activation of drug release in response to pH conditions mimicking extra- (pH 6.9-6.5) and intracellular compartments (5.5-4.5, from early endosome to lysosome) of cancer tissues respectively. A frontline chemotherapy used for pancreatic cancer, i.e., gemcitabine (GEM) and a Hedgehog inhibitor (GDC 0449) has been used as the model combination to evaluate the encapsulation and pH-dependent release efficiency of these block copolymers. We found that, depending on the tertiary amine side chains appended to the polycarbonate segment, these block copolymers self-assemble to form nanoparticles with the size range of 100-150 nm (with a critical association concentration value in the order of 10^-6 M). We also demonstrated an approach where GEM and GDC 0449-encapsulated PEG-DB and PEG-PY nanoparticles, responsive to two different pH conditions, when mixed at a 1:1 vol ratio, yielded a pH-dependent co-release of the encapsulated contents. We envision that such release behaviour can be exploited to gain spatiotemporal control over drug accumulation in pathological compartments with different pH status. The mixture of pH-responsive nanoparticles was found to suppress pancreatic cancer cell proliferation when loaded with anticancer agents in vitro. Cell-proliferation assay showed that both variants of PEG-b-polycarbonate block copolymers were inherently non-toxic. We have also immobilized iRGD peptide on intracellularly activable PEG-DB systems to augment cellular uptake. These targeted nanoparticles were found to promote selective internalization of particles in pancreatic cancer cells and tumor tissue.

A Scalable Method for Squalenoylation and Assembly of Multifunctional 64Cu-Labeled Squalenoylated Gemcitabine Nanoparticles

Squalenoylation of gemcitabine, a front-line therapy for pancreatic cancer, allows for improved cellular-level and system-wide drug delivery. The established methods to conjugate squalene to gemcitabine and to form nanoparticles (NPs) with the squalenoylated gemcitabine (SqGem) conjugate are cumbersome, time-consuming and can be difficult to reliably replicate. Further, the creation of multi-functional SqGem-based NP theranostics would facilitate characterization of in vivo pharmacokinetics and efficacy.

Methods: Squalenoylation conjugation chemistry was enhanced to improve reliability and scalability using tert-butyldimethylsilyl (TBDMS) protecting groups. We then optimized a scalable microfluidic mixing platform to produce SqGem-based NPs and evaluated the stability and morphology of select NP formulations using dynamic light scattering (DLS) and transmission electron microscopy (TEM). Cytotoxicity was evaluated in both PANC-1 and KPC (Kras^LSL-G12D/+; Trp53^LSL-R172H/+; Pdx-Cre) pancreatic cancer cell lines. A ⁶⁴Cu chelator (2-S-(4-aminobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid, NOTA) was squalenoylated and used with positron emission tomography (PET) imaging to monitor the in vivo fate of SqGem-based NPs.

Results: Squalenoylation yields of gemcitabine increased from 15% to 63%. Cholesterol-PEG-2k inclusion was required to form SqGem-based NPs using our technique, and additional cholesterol inclusion increased particle stability at room temperature; after 1 week the PDI of SqGem NPs with cholesterol was ~ 0.2 while the PDI of SqGem NPs lacking cholesterol was ~ 0.5. Similar or superior cytotoxicity was achieved for SqGem-based NPs compared to gemcitabine or Abraxane® when evaluated at a concentration of 10 µM. Squalenoylation of NOTA enabled in vivo monitoring of SqGem-based NP pharmacokinetics and biodistribution.

Conclusion: We present a scalable technique for fabricating efficacious squalenoylated-gemcitabine nanoparticles and confirm their pharmacokinetic profile using a novel multifunctional ⁶⁴Cu-SqNOTA-SqGem NP.

Overcoming tumor cell chemoresistance using nanoparticles: lysosomes are beneficial for (stearoyl) gemcitabine-incorporated solid lipid nanoparticles

Despite recent advances in targeted therapies and immunotherapies, chemotherapy using cytotoxic agents remains an indispensable modality in cancer treatment. Recently, there has been a growing emphasis in using nanomedicine in cancer chemotherapy, and several nanomedicines have already been used clinically to treat cancers. There is evidence that formulating small molecular cancer chemotherapeutic agents into nanomedicines significantly modifies their pharmacokinetics and often improves their efficacy. Importantly, cancer cells often develop resistance to chemotherapy, and formulating anticancer drugs into nanomedicines also helps overcome chemoresistance. In this review, we briefly describe the different classes of cancer chemotherapeutic agents, their mechanisms of action and resistance, and evidence of overcoming the resistance using nanomedicines. We then emphasize on gemcitabine and our experience in discovering the unique (stearoyl) gemcitabine solid lipid nanoparticles that are effective against tumor cells resistant to gemcitabine and elucidate the underlying mechanisms. It seems that lysosomes, which are an obstacle in the delivery of many drugs, are actually beneficial for our (stearoyl) gemcitabine solid lipid nanoparticles to overcome tumor cell resistance to gemcitabine.

Pancreatic Cancer Chemoresistance to Gemcitabine

Pancreatic ductal adenocarcinoma (PDAC), commonly referred to as pancreatic cancer, ranks among the leading causes of cancer-related deaths in the Western world due to disease presentation at an advanced stage, early metastasis and generally a very limited response to chemotherapy or radiotherapy. Gemcitabine remains a cornerstone of PDAC treatment in all stages of the disease despite suboptimal clinical effects primarily caused by molecular mechanisms limiting its cellular uptake and activation and overall efficacy, as well as the development of chemoresistance within weeks of treatment initiation. To circumvent gemcitabine resistance in PDAC, several novel therapeutic approaches, including chemical modifications of the gemcitabine molecule generating numerous new prodrugs, as well as new entrapment designs of gemcitabine in colloidal systems such as nanoparticles and liposomes, are currently being investigated. Many of these approaches are reported to be more efficient than the parent gemcitabine molecule when tested in cellular systems and in vivo in murine tumor model systems; however, although promising, their translation to clinical use is still in a very early phase. This review discusses gemcitabine metabolism, activation and chemoresistance entities in the gemcitabine cytotoxicity pathway and provides an overview of approaches to override chemoresistance in pancreatic cancer.

Nanotechnologies in Pancreatic Cancer Therapy

Pancreatic cancer has been classified as a cancer of unmet need. After diagnosis the patient prognosis is dismal with few surviving over 5 years. Treatment regimes are highly patient variable and often the patients are too sick to undergo surgical resection or chemotherapy. These chemotherapies are not effective often because patients are diagnosed at late stages and tumour metastasis has occurred. Nanotechnology can be used in order to formulate potent anticancer agents to improve their physicochemical properties such as poor aqueous solubility or prolong circulation times after administration resulting in improved efficacy. Studies have reported the use of nanotechnologies to improve the efficacy of gemcitabine (the current first line treatment) as well as investigating the potential of using other drug molecules which have previously shown promise but were unable to be utilised due to the inability to administer through appropriate routes-often related to solubility. Of the nanotechnologies reported, many can offer site specific targeting to the site of action as well as a plethora of other multifunctional properties such as image guidance and controlled release. This review focuses on the use of the major nanotechnologies both under pre-clinical development and those which have recently been approved for use in pancreatic cancer therapy.

Nanotechnology for delivery of gemcitabine to treat pancreatic cancer

Pancreatic cancer (PC) is one of the most deadly and quickly fatal human cancers with a 5-year mortality rate close to 100%. Its prognosis is very poor, mainly because of its hostile biological behavior and late onset of symptoms for clinical diagnosis; these bring limitations on therapeutic interventions. Factors contributing for the difficulties in treating PC include: high rate of drug resistance, fast metastasis to different organs, poor prognosis and relapse of the tumor after therapy. After being approved by US FDA 1997, Gemcitabine (Gem) is the first line and the gold standard drug for all stages of advanced PC till now. However, its efficacy is unsatisfactory, mainly due to; its chemical instability and poor cellular uptake, resulting in an extremely short half-life and low bioavailability. To solve this drawbacks and increase the therapeutic outcome important progress has been achieved in the field of nanotechnology and offers a promising and effective alternative. This review mainly focus on the most commonly investigated nanoparticle (NP) delivery systems of Gem for PC treatment and the latest progresses achieved. Novel nanocarriers with better tumor targeting efficiencies and maximum treatment outcome to treat this deadly due are given much attention.

Plasmonic nanocarrier grid-enhanced Raman sensor for studies of anticancer drug delivery

Targeted drug delivery systems using nanoparticle nanocarriers offer remarkable promise for cancer therapy by discriminating against devastating cytotoxicity of chemotherapeutic drugs to healthy cells. To aid in the development of new drug nanocarriers, we propose a novel plasmonic nanocarrier grid-enhanced Raman sensor which can be applied for studies and testing of drug loading onto the nanocarriers, attachment of targeting ligands, dynamics of drug release, assessment of nanocarrier stability in biological environment, and general capabilities of the nanocarrier. The plasmonic nanogrid sensor offers strong Raman enhancement due to the overlapping plasmonic fields emanating from the nearest-neighbor gold nanoparticle nanocarriers and creating the enhancement "hot spots". The sensor has been tested for immobilization of an anticancer drug gemcitabine (2',2'-difluoro-2'-deoxycytidine, GEM) which is used in treatment of pancreatic tumors. The drawbacks of currently applied treatment include high systemic toxicity, rapid drug decay, and low efficacy (ca. 20%). Therefore, the development of a targeted GEM delivery system is highly desired. We have demonstrated that the proposed nanocarrier SERS sensor can be utilized to investigate attachment of targeting ligands to nanocarriers (attachment of folic acid ligand recognized by folate receptors of cancer cells is described). Further testing of the nanocarrier SERS sensor involved drug release induced by lowering pH and increasing GSH levels, both occurring in cancer cells. The proposed sensor can be utilized for a variety of drugs and targeting ligands, including those which are Raman inactive, since the linkers can act as the Raman markers, as illustrated with mercaptobenzoic acid and para-aminothiophenol.

How can nanomedicines overcome cellular-based anticancer drug resistance?

This review discusses the mechanisms of anticancer drug resistance according to its cellular level of action and outlines the nanomedicine-based strategies adopted to overcome it.

Nucleic Acid Bioconjugates in Cancer Detection and Therapy

Nucleoside- and nucleotide-based chemotherapeutics have been used to treat cancer for more than 50 years. However, their inherent cytotoxicities and the emergent resistance of tumors against treatment has inspired a new wave of compounds in which the overall pharmacological profile of the bioactive nucleic acid component is improved by conjugation with delivery vectors, small-molecule drugs, and/or imaging modalities. In this manner, nucleic acid bioconjugates have the potential for targeting and effecting multiple biological processes in tumors, leading to synergistic antitumor effects. Consequently, tumor resistance and recurrence is mitigated, leading to more effective forms of cancer therapy. Bioorthogonal chemistry has led to the development of new nucleoside bioconjugates, which have served to improve treatment efficacy en route towards FDA approval. Similarly, oligonucleotide bioconjugates have shown encouraging preclinical and clinical results. The modified oligonucleotides and their pharmaceutically active formulations have addressed many weaknesses of oligonucleotide-based drugs. They have also paved the way for important advancements in cancer diagnosis and treatment. Cancer-targeting ligands such as small-molecules, peptides, and monoclonal antibody fragments have all been successfully applied in oligonucleotide bioconjugation and have shown promising anticancer effects in vitro and in vivo. Thus, the application of bioorthogonal chemistry will, in all likelihood, continue to supply a promising pipeline of nucleic acid bioconjugates for applications in cancer detection and therapy.