Novel N,N-Dimethyl-idarubicin Analogues Are Effective Cytotoxic Agents for ABCB1-Overexpressing, Doxorubicin-Resistant Cells.

Anthracyclines comprise one of the most effective anticancer drug classes. Doxorubicin, daunorubicin, epirubicin, and idarubicin have been in clinical use for decades, but their application remains complicated by treatment-related toxicities and drug resistance. We previously demonstrated that the combination of DNA damage and histone eviction exerted by doxorubicin drives its associated adverse effects. However, whether the same properties dictate drug resistance is unclear. In the present study, we evaluate a library of 40 anthracyclines on their cytotoxicity, intracellular uptake, and subcellular localization in K562 wildtype versus ABCB1-transporter-overexpressing, doxorubicin-resistant cells. We identify several highly potent cytotoxic anthracyclines. Among these, N,N-dimethyl-idarubicin and anthracycline (composed of the idarubicin aglycon and the aclarubicin trisaccharide) stand out, due to their histone eviction-mediated cytotoxicity toward doxorubicin-resistant cells. Our findings thus uncover understudied anthracycline variants warranting further investigation in the quest for safer and more effective anticancer agents that circumvent cellular export by ABCB1.

Structure-based drug repurposing to inhibit the DNA gyrase of Mycobacterium tuberculosis.

Drug repurposing is an alternative avenue for identifying new drugs to treat tuberculosis (TB). Despite the broad-range of anti-tubercular drugs, the emergence of multi-drug-resistant and extensively drug-resistant strains of Mycobacterium tuberculosis (Mtb) H37Rv, as well as the significant death toll globally, necessitates the development of new and effective drugs to treat TB. In this study, we have employed a drug repurposing approach to address this drug resistance problem by screening the drugbank database to identify novel inhibitors of the Mtb target enzyme, DNA gyrase. The compounds were screened against the ATPase domain of the gyrase B subunit (MtbGyrB47), and the docking results showed that echinacoside, doxorubicin, epirubicin, and idarubicin possess high binding affinities against MtbGyrB47. Comprehensive assessment using fluorescence spectroscopy, surface plasmon resonance spectroscopy (SPR), and circular dichroism (CD) titration studies revealed echinacoside as a potent binder of MtbGyrB47. Furthermore, ATPase, and DNA supercoiling assays exhibited an IC50 values of 2.1-4.7 µM for echinacoside, doxorubicin, epirubicin, and idarubicin. Among these compounds, the least MIC90 of 6.3 and 12 µM were observed for epirubicin and echinacoside, respectively, against Mtb. Our findings indicate that echinacoside and epirubicin targets mycobacterial DNA gyrase, inhibit its catalytic cycle, and retard mycobacterium growth. Further, these compounds exhibit potential scaffolds for optimizing novel anti-mycobacterial agents that can act on drug-resistant strains.

Idarubicin, an Anthracycline, Induces Oxidative DNA Damage in the Presence of Copper (II).

BACKGROUND/AIM: The aim of the present study was to investigate whether idarubicin (IDR) induces oxidative DNA damage in the presence of copper (II). MATERIALS AND METHODS: DNA damage was evaluated by pBR322 plasmid DNA cleavage. The formation of oxidative stress markers [O2 •- and 8-hydroxy-2'-deoxyguanosine (8-OHdG)] was analysed. RESULTS: IDR induced DNA damage and O2 •- and 8-OHdG generation in the presence of copper (II). CONCLUSION: IDR induced oxidative DNA damage in the presence of copper (II). Since it has been reported that the concentration of copper in the serum of cancer patients is higher than that in healthy groups, IDR-induced oxidative DNA damage in the presence of copper (II) may play an important role in anticancer therapeutic strategies.

The influence of charge and lipophilicity of daunorubicin and idarubicin on their penetration of model biological membranes - Langmuir monolayer and electrochemical studies.

The interactions of two selected anthracyclines, daunorubicin (DNR) and idarubicin (IDA), with phospholipid monolayers used as simple models of cell membranes, were investigated. The results of Langmuir experiments together with Brewster angle microscopy showed that both drugs strongly affect cancer cell membranes composed of 1,2-dimyristoyl-sn-glycero-3-phospho-l-serine (DMPS). Electrostatic interactions allow positively charged DNR and IDA to interact with negatively charged DMPS polar heads but increased lipophilicity of IDA allows it to penetrate the layer more effectively than DNR and prevents from its expulsion at higher surface pressures. The analysis of the thermodynamical functions of hysteresis proves the presence of the enthalpically favorable interactions within the monolayer during its compression in the presence of idarubicin, which may form aggregates with DMPS molecules. The influence of the drugs was significantly less pronounced for a healthy cell model composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) due to the lack of strong electrostatic attractions. The interactions of drugs with pre-compressed phospholipid monolayers were also examined. The physical state of the monolayer and its packing determined only to some extent the penetration of anthracyclines. Since drug molecules first approach the polar region of the monolayer, the increase in surface pressure in time was more pronounced for negatively charged DMPS monolayers than for zwitterionic DMPC. Additionally, idarubicin was able to penetrate the precompressed DMPS monolayers more effectively than daunorubicin due to increased lipophilicity. This property of the drug was also responsible for IDA better penetration of hydrocarbon chains of supported DMPS monolayers compared to DNR, as shown by electrochemical studies.

An In Vitro Evaluation of Four Types of Drug-Eluting Embolics Loaded with Idarubicin.

PURPOSE: This study compared loading, elution, and stability of drug-eluting embolic beads (DEBs) loaded with idarubicin. MATERIALS AND METHODS: DC Bead (100-300 µm), HepaSphere (30-60 µm), LifePearl (200 µm), and Tandem (100 µm) DEBs were loaded with 5 mg/mL idarubicin. Loading, elution, diameter changes, loading stability over 2 weeks in storage, and time in suspension were determined for each of the DEBs. RESULTS: Loading of more than 99% of idarubicin was achieved within 15 minutes for LifePearl, DC Bead, and Tandem beads. LifePearl, DC Bead, HepaSphere, and Tandem beads eluted 75% of the total idarubicin released in 13, 24, 42, and 91 minutes, respectively. In vitro elution was completed in 2 hours with 73% ± 3%, 74% ± 3%, 65% ± 6%, and 7% ± 0% of the loaded idarubicin eluted for LifePearl, DC Bead, HepaSphere, and Tandem, respectively. Statistically significant differences were observed at every time point between at least 2 of the products. Overall, in vitro idarubicin elution was rapid and nearly complete for LifePearl, DC Bead, and HepaSphere beads but was minimal and slow from Tandem beads. The average diameter of DEBs after loading was reduced by 5% for LifePearl, whereas it was increased by 9% and 1% for DC Bead and Tandem, respectively. After loading, time in suspension was 11 ± 4 and 10 ± 2 minutes for LifePearl and HepaSphere, respectively, whereas DC Bead and Tandem beads were held in suspension for greater than 20 minutes. CONCLUSIONS: Although all 4 DEBs loaded idarubicin within 15 minutes with minimal changes in diameter, the elution amounts, rates of release, and time in suspension varied.

Synthesis of (±)-Idarubicinone via Global Functionalization of Tetracene.

Anthracyclines are archetypal representatives of the tetracyclic type II polyketide natural products that are widely used in cancer chemotherapy. Although the synthesis of this class of compounds has been a subject of several investigations, all known approaches are based on annulations, relying on the union of properly prefunctionalized building blocks. Herein, we describe a conceptually different approach using a polynuclear arene as a starting template, ideally requiring only functional decorations to reach the desired target molecule. Specifically, tetracene was converted to (±)-idarubicinone, the aglycone of the FDA approved anthracycline idarubicin, through the judicious orchestration of Co- and Ru-catalyzed arene oxidation and arenophile-mediated dearomative hydroboration. Such a global functionalization strategy, the combination of site-selective arene and dearomative functionalization, provided the key anthracycline framework in five operations and enabled rapid and controlled access to (±)-idarubicinone.

Toward Predicting Acute Myeloid Leukemia Patient Response to 7 + 3 Induction Chemotherapy via Diagnostic Microdosing.

Acute myeloid leukemia (AML) is a rare yet deadly cancer of the blood and bone marrow. Presently, induction chemotherapy with the DNA damaging drugs cytarabine (ARA-C) and idarubicin (IDA), known as 7 + 3, is the standard of care for most AML patients. However, 7 + 3 is a relatively ineffective therapy, particularly in older patients, and has serious therapy-related toxicities. Therefore, a diagnostic test to predict which patients will respond to 7 + 3 is a critical unmet medical need. We hypothesize that a threshold level of therapy-induced 7 + 3 drug-DNA adducts determines cytotoxicity and clinical response. We further hypothesize that in vitro exposure of AML cells to nontoxic diagnostic microdoses enables prediction of the ability of AML cells to achieve that threshold during treatment. Our test involves dosing cells with very low levels of 14C-labeled drug followed by DNA isolation and quantification of drug-DNA adducts via accelerator mass spectrometry. Here, we have shown proof of principle by correlating ARA-C- and DOX-DNA adduct levels with cellular IC50 values of paired sensitive and resistant cancer cell lines and AML cell lines. Moreover, we have completed a pilot retrospective trial of diagnostic microdosing for 10 viably cryopreserved primary AML samples and observed higher ARA-C- and DOX-DNA adducts in the 7 + 3 responders than nonresponders. These initial results suggest that diagnostic microdosing may be a feasible and useful test for predicting patient response to 7 + 3 induction chemotherapy, leading to improved outcomes for AML patients and reduced treatment-related morbidity and mortality.

Idarubicin is a broad-spectrum enterovirus replication inhibitor that selectively targets the virus internal ribosomal entry site.

Enterovirus 71 (EV71) causes life-threatening diseases with neurological manifestations in young children. However, the treatment of EV71 infections remains an unmet medical need. Idarubicin (IDR) is an anthracycline compound that is used therapeutically for certain types of tumour. In this study, we identified IDR as an EV71 inhibitor, which displayed antiviral potency in the submicromolar range and substantially protected cells from the cytopathic effects and cell death caused by EV71 infections. The antiviral effects extended to several other enterovirus (EV) species, and these effects were independent of cytotoxicity or topoisomerase inhibition. Structure-activity relationship studies indicated the importance of the anthracycline scaffold for anti-EV potency. IDR effectively blocked the synthesis of viral protein and RNA, but not the viral proteolysis processes. Moreover, anthracyclines were demonstrated to suppress EV internal ribosomal entry site (IRES)-mediated translation; conversely, the cellular p53 IRES activity was not sensitive to IDR action. Inhibition of IRES-mediated translation by IDR correlated with the affinity of binding between IDR and the particular IRES. Moreover, IDR impaired binding between the EV71 IRES RNA and hnRNP A1, a known host IRES trans-acting factor. In sum, we have identified a USA FDA-approved anticancer drug with the new indication as a selective EV IRES binder and inhibitor. The finding may also provide leads for the development of novel antiviral therapies directed at the EV IRES RNA.

Pentoxifylline affects idarubicin binding to DNA.

Anticancer drug idarubicin - derivative of doxorubicin - is commonly used in treatment of numerous cancer types. However, in contrast to doxorubicin, its biophysical properties are not well established yet. Additionally, potential direct interactions of idarubicin with other biologically active aromatic compounds, such as pentoxifylline - representative of methylxanthines - were not studied at all. Potential formation of such hetero-aggregates may result in sequestration of the anticancer drug and, in consequence, reduction of its biological activity. This work provide description of the idarubicin biophysical properties as well as assess influence of pentoxifylline on idarubicin interactions with DNA. To achieve these goals we employed spectrophotometric methods coupled with analysis with the appropriate mathematical models as well as flow cytometry and Ames test. Obtained results show influence of pentoxifylline on idarubicin binding to DNA and are well in agreement with the data previously published for other aromatic ligands. Additionally it may be hypothesized that direct interactions between idarubicin and pentoxifylline may influence the anticancer drug biological activity.

Preparation, characterization and evaluation of (186) Re-idarubicin: a novel agent for diagnosis and treatment of hepatocellular carcinoma.

Hepatocellular carcinoma is a widely prevalent cancer, and hence, the development of radiopharmaceuticals for its management is an important issue. In the current investigation, the complexation of idarubicin with (186) Re was studied. Optimum labelling conditions were found to be 4 mg idarubicin, 1.5 mg stannous chloride dihydrate and ~70 MBq Re-186 at pH 7. The complex showed ~97.6% RCY value at 20 min and remained stable up to 24 h in the presence of 2.5 mg ascorbic acid. Molecular docking was performed to evaluate the complex binding to its target DNA-human topoisomerase II complex. Result of the in vivo evaluation showed that the complex tends to preferentially localize in cancerous tissues. The in vitro cell growth inhibition assay showed that the effect of the (186) Re-idarubicin was stronger than the effect of cold idarubicin, which strongly suggested that its cytotoxicity was mainly because of radiotoxicity rather than chemotherapeutic activity.

Formulation and optimization of idarubicin thermosensitive liposomes provides ultrafast triggered release at mild hyperthermia and improves tumor response.

Drug delivery through thermosensitive liposomes (TSL) in combination with hyperthermia (HT) has shown great potential. HT can be applied locally forcing TSL to release their content in the heated tumor resulting in high peak concentrations. To perform optimally the drug is ideally released fast (seconds) and taken up rapidly by tumor cells. The aim of this study was to develop a novel thermosensitive liposome formulation of the anthracycline idarubicin (IDA-TSL). The hydrophobicity of idarubicin may improve its release from liposomes and subsequently rapid cellular uptake when combined mild hyperthermia. Here, we investigated a series of parameters to optimize IDA-TSL formulation. The results show that the optimal formulation for IDA-TSL is DPPC/DSPC/DSPE-PEG (6/3.5/0.5 mol%), with ammonium EDTA of 6.5 pH as loading buffer and a size of ~85 nm. In vitro studies demonstrated minimal leakage of ~20% in FCS at 37 °C for 1h, while an ultrafast and complete triggered release of IDA was observed at 42 °C. On tumor cells IDA-TSL showed comparable cytotoxicity to free IDA at 42 °C, but low cytotoxicity at 37 °C. Intravital microscopy imaging demonstrated an efficient in vivo intravascular triggered drug release of IDA-TSL under mild hyperthermia, and a subsequent massive IDA uptake by tumor cells. In animal efficacy studies, IDA-TSL plus mild HT demonstrated prominent tumor growth inhibition and superior survival rate over free IDA with HT or a clinically used Doxil treatment. These results suggest beneficial potential of IDA-TSL combined with local mild HT.

L-Cysteine capped Mn-doped ZnS quantum dots as a room temperature phosphorescence sensor for in-vitro binding assay of idarubicin and DNA.

L-cysteine capped Mn doped ZnS quantum dots/ Idarubicin (IDA) nanohybrids were used as novel room temperature phosphorescence (RTP) sensor to detect double stranded deoxyribonucleic acid (ds-DNA)/drug interaction. IDA, anthracycline derivative anticancer drug, was adsorbed on the surface of the QDs as an electron acceptor to quench the RTP emission. The RTP intensity of QDs was quenched quickly upon addition of quencher and the reaction reached equilibrium within 2 min. The quenching mechanism of phosphorescence of Mn-doped ZnS QDs by IDA is a combined dynamic and static quenching. The static and dynamic quenching constants were found as 1.1×10(5) M(-1) and 8.7×10(4) M(-1), respectively. The addition of ds-DNA caused formation of ds-DNA/IDA complex and recovered the RTP signal of Mn-doped ZnS QDs, which allowed qualitative analysis. Under optimal conditions, RTP intensity of QDs/IDA nanohybrids increased linearly with the concentration of ds-DNA from 1.2 to 6.0 µM. This method is simple, low cost and avoids from interferences.

Polyester-idarubicin nanoparticles and a polymer-photosensitizer complex as potential drug formulations for cell-mediated drug delivery.

Cell-mediated transport of therapeutics has emerged as promising alternative to classical drug delivery approaches. To preserve viability and functions of carrier cells, encapsulation of active drugs in protective nanoparticles or the use of inducible therapeutics has been proposed. Here, we compared the effects of novel polymeric formulations of an active and a stimulus-sensitive anti-cancer drug on human T lymphocytes to identify suitable drug preparations for cell-mediated drug delivery. For the first approach, the chemotherapeutic agent idarubicin (IDA) was encapsulated in poly(lactic-co-glycolic-acid) (PLGA) and newly developed maleate-polyester (MPE) nanoparticles. PLGA- and MPE-encapsulated IDA was efficiently internalized by ex vivo activated human T lymphocytes; however, both encapsulations could not prevent premature T cell death resulting from IDA-uptake. In contrast, loading with a poly(styrene sulfonate) (PSS)-complex of the light-sensitive pharmaceutical 5,10,15,20-tetrakis(meso-hydroxyphenyl)porphyrin (mTHPP) did not affect T cell viability if upon loading the cells were kept in the dark. The photosensitizer was transferred from loaded T lymphocytes to co-cultivated carcinoma cells, and induced cancer cell death if co-cultures were exposed to light. Inducible drugs, such as photosensitizers, thus, may help to overcome the limitations of encapsulated active drugs and open up new perspectives for the use of cells as drug transporters in cancer therapy.

In vitro DNA binding studies of anticancer drug idarubicin using spectroscopic techniques.

The interaction between idarubicin and double stranded deoxyribonucleic acid (ds-DNA) was investigated by UV-VIS spectrophotometry, fluorescence and Raman spectroscopy techniques. The absorption spectra of idarubicin with ds-DNA showed a slight red shift and hypochromic effect. In the fluorescence experiments, emission peaks were decreased by adding ds-DNA. Using ethidium bromide (ETB) as a fluorescence probe, fluorescence quenching of the emission peak was observed in the ETB-DNA system when idarubicin was added. Moreover, similar results were obtained in Raman spectroscopy. Binding constants of idarubicin with ds-DNA were determined as 5.14×10(5) M(-1) and 5.8×10(5) M(-1) for UV-VIS spectrophotometry and fluorescence spectroscopy, respectively. The large binding constant indicated that idarubicin has a high affinity with ds-DNA. All the evidences indicated that the binding mode of idarubicin with DNA was an intercalative binding. Furthermore, quantitative determination of idarubicin in pharmaceutical formulation was done.

Redox mechanism of anticancer drug idarubicin and in-situ evaluation of interaction with DNA using an electrochemical biosensor.

Idarubicin (IDA), 4-demethoxydaunorubicin, is an anthracycline derivative and widely used treatment of leukemia. The electrochemical behavior of IDA was examined at a glassy carbon electrode (GCE) in different aqueous supporting electrolyte using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The oxidation process of IDA was found to be pH dependent and irreversible proceeding with a transfer of 1 proton and 1 electron under the diffusion controlled mechanism. The electroactive center is the hydroxyl group on the aromatic ring which produces a final quinonic product. The diffusion coefficient of IDA was calculated to be DIDA=7.47×10(-6) cm(2) s(-1) in pH=4.3 0.1 M acetate buffer. The interaction of IDA and double stranded deoxyribonucleic acid (ds-DNA) was investigated using electrochemical ds-DNA biosensor and incubation solution by means of DPV. The DNA damage was detected following the changes in the oxidation peaks of guanosine and adenosine residues. The results obtained showed that IDA interacts with DNA which causes the change in the DNA morphological structure. In addition to these polynucleotides, PolyG and PolyA, biosensors were also used to confirm the interaction between ds-DNA and IDA. However, no oxidation peaks of the purine base oxidation products, 8-oxoGua and 2,8-oxoAde, were observed.

Photo-physical behavior of some antitumor anthracycline in solvent media with different polarity.

Absorption and emission spectra of three antitumour anthracyclines, with various substituent and stereoisomer groups, were studied in different solvents. The solute's photo-physical behavior strongly depends on solvent-solute interactions and solvent's nature. Solvatochromic method was used to investigate dipole moments of these materials in ground and excited states. Spectral variations were analyzed via means of linear solvation energy relationships concept, proposed by Kamlet and Taft. The results explain the nature of specific and non-specific solvent-solute interactions and functional groups' reorientation of studied anthracyclines in different media.

Time-Resolved Fluorescence Resonance Energy Transfer Assay for Discovery of Small-Molecule Inhibitors of Methyl-CpG Binding Domain Protein 2.

Methylated DNA binding proteins such as Methyl-CpG Binding Domain Protein 2 (MBD2) can transduce DNA methylation alterations into a repressive signal by recruiting transcriptional co-repressor complexes. Interfering with MBD2 could lead to reactivation of tumor suppressor genes and therefore represents an attractive strategy for epigenetic therapy. We developed and compared fluorescence polarization (FP) and time-resolved fluorescence resonance energy transfer (TR-FRET)-based high-throughput screening (HTS) assays to identify small-molecule inhibitors of the interaction between the methyl binding domain of MBD2 (MBD2-MBD) and methylated DNA. Although both assays performed well in 96-well format, the TR-FRET assay (Z' factor = 0.58) emerged as a superior screening strategy compared with FP (Z' factor = 0.08) when evaluated in an HTS 384-well plate format. Using TR-FRET, we screened the Sigma LOPAC library for MBD2-MBD inhibitors and identified four compounds that also validated in a dose-response series. This included two known DNA intercalators (mitoxantrone and idarubicin) among two other inhibitory compounds (NF449 and aurintricarboxylic acid). All four compounds also inhibited the binding of SP-1, a transcription factor with a GC-rich binding sequence, to a methylated oligonucleotide, demonstrating that the activity was nonspecific. Our results provide proof of principle for using TR-FRET-based HTS to identify small-molecule inhibitors of MBD2 and other DNA-protein interactions.

Structural investigation of idarubicin-DNA interaction: spectroscopic and molecular docking study.

Mechanistic understanding of interaction of drugs with their target molecule is important for development of new drug therapy regimes. Idarubicin (IDR) is a potent chemotherapeutic agent used to treat variety of cancers. Structural and conformational studies associated with binding of IDR on DNA double helix were investigated through spectroscopic techniques and molecular docking studies. Interaction studies were done by preparing different molar ratios of IDR with constant DNA concentration under physiological conditions. FTIR spectroscopy, UV-vis spectroscopy, CD spectroscopy were used to analyze interaction between IDR and DNA. FTIR results suggest IDR binds at major groove of DNA duplex via guanine and cytosine bases. UV-vis spectroscopy result indicates IDR gets intercalated between the DNA bases. The calculated binding constant shows that IDR is a moderate binder. Slight perturbation in the native B-conformation of DNA was observed in all IDR-DNA molar ratios examined. In silico investigation of IDR binding with DNA is in agreement with our experimental results, providing structural insight into DNA binding properties of IDR.

Oxidized phospholipid based pH sensitive micelles for delivery of anthracyclines to resistant leukemia cells in vitro.

A self-assembled micelle drug delivery system was constructed with an oxidized phospholipid for anthracycline anti-cancer drug delivery. An oxidized phospholipid, 1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphocholine (PazPC), was chosen to fabricate micelles via both electrostatic and hydrophobic interactions for delivery of doxorubicin (DOX) and idarubicin (IDA). The formation of ion-pair complexes between PazPC and DOX was first investigated under different pH conditions. Drug-loaded PazPC micelles at a 5:1 molar ratio of lipid/drug at pH 7.0 were then prepared by the solvent evaporation method. The empty and drug-loaded PazPC micelles exhibited a small particle size (∼10 nm) and high encapsulation efficiency. In vitro stability and release profile indicated that the micelles were stable at physiological conditions, but exhibited pH-sensitive behavior with accelerated release of DOX or IDA in an acidic endosome environment. Finally, in vitro uptake and cytotoxicity were evaluated for leukemia P388 and its resistant subline P388/ADR. The drug-loaded PazPC micelles enhanced drug uptake and exhibited higher cytotoxicity in both leukemia cells in comparison to free drugs. In conclusion, we developed a novel pH sensitive oxidized phospholipid-based micellar formulation which could potentially be useful in delivering anthracycline anti-cancer drugs and provide a novel strategy for increasing the therapeutic index while overcoming multidrug resistance for leukemia treatment.

Polypeptide conjugates of D-penicillamine and idarubicin for anticancer therapy.

We investigated anticancer therapy with a novel combination of D-penicillamine (D-pen) and Idarubicin (Ida) in a synthetic dual drug conjugate (DDC). D-pen and Ida were covalently linked to poly(α)-L-glutamic acid (PGA) via reducible disulfide and acid-sensitive hydrazone bonds, respectively. The DDCs showed cell uptake and sustained release of the bound drugs in conditions mimicking the intracellular release media (10mM glutathione and pH 5.2). The in-vitro cytotoxicity of DDCs was comparable to unconjugated Ida in several sensitive and resistant cancer cell lines and correlated with the rate of cell uptake. In a single equivalent-dose pharmacokinetic study, DDCs enhanced the drug exposure by 7-fold and prolonged the plasma circulation half-life (t(1/2)) by 5-fold over unconjugated Ida. The therapeutic index of DDCs was 2-3-fold higher than unconjugated drugs. DDCs caused 89% tumor growth inhibition compared to 60% by unconjugated Ida alone and led to significant enhancement in the median survival (17%) of athymic nu/nu mice bearing NCI-H460 tumor xenografts.