Bioreduction activated prodrugs of camptothecin: molecular design, synthesis, activation mechanism and hypoxia selective cytotoxicity

Theranostic Fluorescent Probes

The ability to gain spatiotemporal information, and in some cases achieve spatiotemporal control, in the context of drug delivery makes theranostic fluorescent probes an attractive and intensely investigated research topic. This interest is reflected in the steep rise in publications on the topic that have appeared over the past decade. Theranostic fluorescent probes, in their various incarnations, generally comprise a fluorophore linked to a masked drug, in which the drug is released as the result of certain stimuli, with both intrinsic and extrinsic stimuli being reported. This release is then signaled by the emergence of a fluorescent signal. Importantly, the use of appropriate fluorophores has enabled not only this emerging fluorescence as a spatiotemporal marker for drug delivery but also has provided modalities useful in photodynamic, photothermal, and sonodynamic therapeutic applications. In this review we highlight recent work on theranostic fluorescent probes with a particular focus on probes that are activated in tumor microenvironments. We also summarize efforts to develop probes for other applications, such as neurodegenerative diseases and antibacterials. This review celebrates the diversity of designs reported to date, from discrete small-molecule systems to nanomaterials. Our aim is to provide insights into the potential clinical impact of this still-emerging research direction.

Stimuli-Responsive Prodrug Chemistries for Cancer Therapy

Prodrugs are pharmacologically inactive, chemically modified derivatives of active drugs, which, following in vivo administration, are converted to the parent drugs through chemical or enzymatic cleavage. The prodrug approach holds tremendous potential to create the enhanced version of an existing pharmacological agent and leverage those improvements to augment the drug molecules' bioavailability, targeting ability, therapeutic efficacy, safety, and marketability. Especially in cancer therapy, prodrug application has received substantial attention. A prodrug can effectively broaden the therapeutic window of its parent drug by enhancing its release at targeted tumor sites while reducing its access to healthy cells. The spatiotemporally controlled release can be achieved by manipulating the chemical, physical, or biological stimuli present at the targeted tumor site. The critical strategy comprises drug-carrier linkages that respond to physiological or biochemical stimuli in the tumor milieu to yield the active drug form. This review will focus on the recent advancements in the development of various fluorophore-drug conjugates that are widely used for real-time monitoring of drug delivery. The use of different stimuli-cleavable linkers and the mechanisms of linker cleavage will be discussed. Finally, the review will conclude with a critical discussion of the prospects and challenges that might impede the future development of such prodrugs.

Research advances in NQO1-responsive prodrugs and nanocarriers for cancer treatment

NAD(P)H: quinine oxidoreductase (NQO1) is a class of flavoprotein enzymes commonly expressed in eukaryotic cells. It actively participates in the metabolism of various quinones and their in vivo bioactivation through electron reduction reactions. The expression level of NQO1 is highly upregulated in many solid tumor cells compared with that in normal cells. NQO1 has been considered a candidate molecular target because of its overexpression and bioactivity in different tumors. NQO1-responsive prodrugs and nanocarriers have recently been identified as effective objectives for achieving controlled drug release, reducing adverse reactions and improving clinical efficacy. This review systematically introduces the research advances in applying NQO1-responsive prodrugs and nanocarriers to cancer treatment. It also discusses the existing problems and the developmental prospects of these two antitumor drug delivery systems.

Enzyme-activated Prodrugs and Their Release Mechanisms for Treatment of Cancer

Enzyme-activated prodrugs have received a lot of attention in recent years. These prodrugs have low toxicity to cells before they are activated, and when they interact with specific enzymes, they...

Stimulus-cleavable chemistry in the field of controlled drug delivery

This review comprehensively summarises stimulus-cleavable linkers from various research areas and their cleavage mechanisms, thus provides an insightful guideline to extend their potential applications to controlled drug release from nanomaterials.

An Activatable Photosensitizer Targeting Human NAD(P)H: Quinone Oxidoreductase 1

Human NAD(P)H: Quinone Oxidoreductase 1 (hNQO1) is an attractive enzyme for cancer therapeutics due to its significant overexpression in tumors compared to healthy tissues. Its unique catalytic mechanism involving the two-electron reduction of quinone-based compounds has made it a useful target to exploit in the design of hNQO1 fluorescent chemosensors and hNQO1-activatable-prodrugs. In this work, hNQO1 is exploited for an optical therapeutic. The probe uses the photosensitizer, phenalenone, which is initially quenched via photo-induced electron transfer by the attached quinone. Native phenalenone is liberated in the presence of hNQO1 resulting in the production of cytotoxic singlet oxygen upon irradiation. hNQO1-mediated activation in A549 lung cancer cells containing high levels of hNQO1 induces a dose-dependent photo-cytotoxic response after irradiation. In contrast, no photo-cytotoxicity was observed in the normal lung cell line, MRC9. By targeting hNQO1, this scaffold can be used to enhance the cancer selectivity of photodynamic therapy.

Development of a platform for activatable fluorescent substrates of glucose transporters (GLUTs)

We have developed a platform for activatable fluorescent substrates of glucose transporters (GLUTs). We firstly conjugated fluorescein to glucosamine via an amide or methylene linker at the C-2 position of d-glucosamine, but the resulting compounds, FLG1 and FLG2, showed no uptake into MIN6 cells. So, we changed the fluorophore moiety to a fluorescein analogue, 2-Me TokyoGreen, which is less negatively charged. TokyoGreen-conjugated glucosamines TGG1 and TGG2 were successfully taken up into cells via GLUT. We further derivatized TGG1 and TGG2, and among the synthesized compounds, 2-Me-4-OMe TGG showed weak fluorescence under the acidic conditions of the extracellular environment inside tumors and in gastric cancers, and strong fluorescence at the intracellular physiological pH, under the control of a photoinduced electron transfer (PeT) process. This fluorogenic platform should be useful for developing a range of activatable fluorescent substrates targeting GLUTs, as well as derivatives that would be fluorescently activated by various intracellular enzymes, such as esterases, β-galactosidase and bioreductases.

Hypoxia-targeted drug delivery

Hypoxia is a state of low oxygen tension found in numerous solid tumours. It is typically associated with abnormal vasculature, which results in a reduced supply of oxygen and nutrients, as well as impaired delivery of drugs. The hypoxic nature of tumours often leads to the development of localized heterogeneous environments characterized by variable oxygen concentrations, relatively low pH, and increased levels of reactive oxygen species (ROS). The hypoxic heterogeneity promotes tumour invasiveness, metastasis, angiogenesis, and an increase in multidrug-resistant proteins. These factors decrease the therapeutic efficacy of anticancer drugs and can provide a barrier to advancing drug leads beyond the early stages of preclinical development. This review highlights various hypoxia-targeted and activated design strategies for the formulation of drugs or prodrugs and their mechanism of action for tumour diagnosis and treatment.

Microfluidic co-culture devices to assess penetration of nanoparticles into cancer cell mass

In vitro and in vivo assessment of safety and efficacy are the essential first steps in developing nanoparticle-based therapeutic systems. However, it is often challenging to use the knowledge gained from in vitro studies to predict the outcome of in vivo studies since the complexity of the in vivo environment, including the existence of flow and a multicellular environment, is often lacking in traditional in vitro models. Here, we describe a microfluidic co-culture model comprising 4T1 breast cancer cells and EA.hy926 endothelial cells under physiological flow conditions and its utilization to assess the penetration of therapeutic nanoparticles from the vascular compartment into a cancerous cell mass. Camptothecin nanocrystals (∼310 nm in length), surface-functionalized with PEG or folic acid, were used as a test nanocarrier. Camptothecin nanocrystals exhibited only superficial penetration into the cancerous cell mass under fluidic conditions, but exhibited cytotoxicity throughout the cancerous cell mass. This likely suggests that superficially penetrated nanocrystals dissolve at the periphery and lead to diffusion of molecular camptothecin deep into the cancerous cell mass. The results indicate the potential of microfluidic co-culture devices to assess nanoparticle-cancerous cell interactions, which are otherwise difficult to study using standard in vitro cultures.

Prodrugs in medicinal chemistry and enzyme prodrug therapies

Prodrugs are cunning derivatives of therapeutic agents designed to improve the pharmacokinetics profile of the drug. Within a prodrug, pharmacological activity of the drug is masked and is recovered within the human body upon bioconversion of the prodrug, a process that is typically mediated by enzymes. This concept is highly successful and a significant fraction of marketed therapeutic formulations is based on prodrugs. An advanced subset of prodrugs can be engineered such as to achieve site-specific bioconversion of the prodrug - to comprise the highly advantageous "enzyme prodrug therapy", EPT. Design of prodrugs for EPT is similar to the prodrugs in general medicinal use in that the pharmacological activity of the drug is masked, but differs significantly in that site-specific bioconversion is a prime consideration, and the enzymes typically used for EPT are non-mammalian and/or with low systemic abundance in the human body. This review focuses on the design of prodrugs for EPT in terms of the choice of an enzyme and the corresponding prodrug for bioconversion. We also discuss the recent success of "self immolative linkers" which significantly empower and diversify the prodrug design, and present methodologies for the design of prodrugs with extended blood residence time. The review aims to be of specific interest for medicinal chemists, biomedical engineers, and pharmaceutical scientists.

Synthesis and biological evaluation of hypoxia-activated prodrugs of SN-38

We designed new hypoxia-activated prodrugs by conjugating (1-methyl-2-nitro-1H-imidazol-5-yl)methanol with 7-ethyl-10-hydroxy camptothecin (SN-38). Initially, we improved the method of multi-gram scale synthesis of (1-methyl-2-nitro-1H-imidazol-5-yl)methanol, which increased the yield to 42% compared to 8% by the original synthesis method. The improved method was used to synthesize evofosfamide (TH-302) and hypoxia-activated prodrugs of SN-38. Two different linkages between (1-methyl-2-nitro-1H-imidazol-5-yl)methanol and SN-38 were evaluated that afforded different hypoxia-selectivity and toxicity. Compound 16 (IOS), containing an ether linkage, was considered to be a promising hypoxia-selective antitumor agent.

Design, synthesis and evaluation of molecularly targeted hypoxia-activated prodrugs

Regions of insufficient oxygen supply-hypoxia-occur in diverse contexts across biology in both healthy and diseased organisms. The difference in the chemical environment between a hypoxic biological system and one with normal oxygen levels provides an opportunity for targeting compound delivery to hypoxic regions by using bioreductive prodrugs. Here we detail a protocol for the efficient synthesis of (1-methyl-2-nitro-1H-imidazol-5-yl)methanol, which is a key intermediate that can be converted into a range of 1-methyl-2-nitro-1H-imidazole-based precursors of bioreductive prodrugs. We outline methods for attaching the bioreductive group to a range of functionalities, and we discuss the strategy for positioning of the group on the biologically active parent compound. We have used two parent checkpoint kinase 1 (Chk1) inhibitors to exemplify the protocol. The PROCEDURE also describes a suite of reduction assays, of increasing biological relevance, to validate the bioreductive prodrug. These assays are applied to an exemplar compound, CH-01, which is a bioreductive Chk1 inhibitor. This protocol has broad applications to the development of hypoxia-targeted compounds.

Bioreductive deprotection of 4-nitrobenzyl group on thymine base in oligonucleotides for the activation of duplex formation

Oligonucleotides containing 4-O-(4-NO2-benzyl)thymine residues were synthesized to assess potential prodrug-type action against hypoxic cells. These modified oligonucleotides were incapable of stable duplex formation under non-hypoxic conditions. However, following deprotection of the thymine residues under bioreductive conditions, the deprotected oligonucleotides were able to form stable duplexes with target oligonucleotides.

Antitumour indolequinones: synthesis and activity against human pancreatic cancer cells

An important determinant of the growth inhibitory activity of indolequinones against pancreatic cancer cells is substitution on the 2-position with 2-unsubstituted derivatives being markedly more potent. A series of indolequinones bearing a range of substituents on nitrogen and at the indolylcarbinyl position was prepared by copper(II)-mediated reaction of bromoquinones and enamines, followed by functional group interconversions. The compounds were then assayed for their ability to inhibit the growth of pancreatic cancer cells. The pKa of the leaving group at the 3-position was shown to influence growth inhibitory activity that is consistent with the proposed mechanism of action of reduction, loss of leaving group and formation of a reactive iminium species. Substitutions on the indole nitrogen were well tolerated with little influence on growth inhibitory activity while substitutions at the 5- and 6-positions larger than methoxy led to decreased activity. The studies presented define the range of substitutions of 2-unsubstituted indolequinones required for optimal growth inhibitory activity.

Synthesis, antitumor activity, and mechanism of action of 6-acrylic phenethyl ester-2-pyranone derivatives

Based on the scaffolds of caffeic acid phenethyl ester (CAPE) as well as bioactive lactone-containing compounds, 6-acrylic phenethyl ester-2-pyranone derivatives were synthesized and evaluated against five tumor cell lines (HeLa, C6, MCF-7, A549, and HSC-2). Most of the new derivatives exhibited moderate to potent cytotoxic activity. Moreover, HeLa cell lines showed higher sensitivity to these compounds. In particular, compound showed potent cytotoxic activity (IC50 = 0.50-3.45 μM) against the five cell lines. Further investigation on the mechanism of action showed that induced apoptosis, arrested the cell cycle at G2/M phases in HeLa cells, and inhibited migration through disruption of the actin cytoskeleton. In addition, ADMET properties were also calculated in silico, and compound showed good ADMET properties with good absorption, low hepatotoxicity, and good solubility, and thus, could easily be bound to carrier proteins, without inhibition of CYP2D6. A structure-activity relationship (SAR) analysis indicated that compounds with ortho-substitution on the benzene ring exhibited obviously increased cytotoxic potency. This study indicated that compound is a promising compound as an antitumor agent.

Organic carbamates in drug design and medicinal chemistry

The carbamate group is a key structural motif in many approved drugs and prodrugs. There is an increasing use of carbamates in medicinal chemistry and many derivatives are specifically designed to make drug-target interactions through their carbamate moiety. In this Perspective, we present properties and stabilities of carbamates, reagents and chemical methodologies for the synthesis of carbamates, and recent applications of carbamates in drug design and medicinal chemistry.

Site-directed delivery of nitric oxide to cancers

Nitric oxide (NO) is a reactive gaseous free radical which mediates numerous biological processes. At elevated levels, NO is found to be toxic to cancers and hence, a number of strategies for site-directed delivery of NO to cancers are in development during the past two decades. More recently, the focus of research has been to, in conjunction with other cancer drugs deliver NO to cancers for its secondary effects including inhibition of cellular drug efflux pumps. Among the various approaches toward site-selective delivery of exogenous NO sources, enzyme activated nitric oxide donors belonging to the diazeniumdiolate category afford unique advantages including exquisite control of rates of NO generation and selectivity of NO production. For this prodrug approach, enzymes including esterase, glutathione/glutathione S-transferase, DT-diaphorase, and nitroreductase are utilized. Here, we review the design and development of various approaches to enzymatic site-directed delivery of NO to cancers and their potential.

"Switch off/switch on" regulation of drug cytotoxicity by conjugation to a cell targeting peptide

Bi-nuclear amino acid platforms loaded with various drugs for conjugation to a peptide carrier were synthesized using simple and convenient orthogonally protective solid-phase organic synthesis (SPOS). Each arm of the platform carries a different anticancer agent linked through the same or different functional group, providing discrete chemo- and bio-release profiles for each drug, and also enabling "switch off/switch on" regulation of drug cytotoxicity by conjugation to the platform and to a cell targeting peptide. The versatility of this approach enables efficient production of drug-loaded platforms and determination of favorable drug combinations/modes of linkage for subsequent conjugation to a carrier moiety for targeted cancer cell therapy. The results presented here potentiate the application of amino acid platforms for targeted drug delivery (TDD).

Bexarotene prodrugs: targeting through cleavage by NQO1 (DT-diaphorase)

Bexarotene, a retinoid X receptor (RXR) agonist, is being tested as a potential disease modifying treatment for neurodegenerative conditions. To limit the peripheral exposure of bexarotene and release it only in the affected areas of the brain, we designed a prodrug strategy based on the enzyme NAD(P)H/quinone oxidoreductase (NQO1) that is elevated in neurodegenerative diseases. A series of indolequinones (known substrates of NQO1) was synthesized and coupled to bexarotene. Bexarotene-3-(hydroxymethyl)-5-methoxy-1,2-dimethyl-1H-indole-4,7-dione ester 7a was cleaved best by NQO1. The prodrugs are not cleaved by esterase.

CH-01 is a hypoxia-activated prodrug that sensitizes cells to hypoxia/reoxygenation through inhibition of Chk1 and Aurora A

The increased resistance of hypoxic cells to all forms of cancer therapy presents a major barrier to the successful treatment of most solid tumors. Inhibition of the essential kinase Checkpoint kinase 1 (Chk1) has been described as a promising cancer therapy for tumors with high levels of hypoxia-induced replication stress. However, as inhibition of Chk1 affects normal replication and induces DNA damage, these agents also have the potential to induce genomic instability and contribute to tumorigenesis. To overcome this problem, we have developed a bioreductive prodrug, which functions as a Chk1/Aurora A inhibitor specifically in hypoxic conditions. To achieve this activity, a key functionality on the Chk1 inhibitor (CH-01) is masked by a bioreductive group, rendering the compound inactive as a Chk1/Aurora A inhibitor. Reduction of the bioreductive group nitro moiety, under hypoxic conditions, reveals an electron-donating substituent that leads to fragmentation of the molecule, affording the active inhibitor. Most importantly, we show a significant loss of viability in cancer cell lines exposed to hypoxia in the presence of CH-01. This novel approach targets the most aggressive and therapy-resistant tumor fraction while protecting normal tissue from therapy-induced genomic instability.

Copper(II)-Mediated Synthesis of Indolequinones from Bromoquinones and Enamines

The reaction of enamines and bromoquinones in the presence of copper(II) acetate and potassium carbonate results in a regiospecific synthesis of indolequinones. The reaction is broad in scope and scalable and provides a route to the core structure that is present in several biologically interesting natural and synthetic compounds.

Challenges and opportunities in developing novel drugs for TB

Mycobacterium tuberculosis is a difficult pathogen to combat and the first-line drugs currently in use are 40-60 years old. The need for new TB drugs is urgent, but the time to identify, develop and ultimately advance new drug regimens onto the market has been excruciatingly slow. On the other hand, the drugs currently in clinical development, and the recent gains in knowledge of the pathogen and the disease itself give us hope for finding new drug targets and new drug leads. In this article we highlight the unique biology of the pathogen and several possible ways to identify new TB chemical leads. The Global Alliance for TB Drug Development (TB Alliance) is a not-for-profit organization whose mission is to accelerate the discovery and development of new TB drugs. The organization carries out research and development in collaboration with many academic laboratories and pharmaceutical companies around the world. In this perspective we will focus on the early discovery phases of drug development and try to provide snapshots of both the current status and future prospects.

Mechanism-based inhibition of quinone reductase 2 (NQO2): selectivity for NQO2 over NQO1 and structural basis for flavoprotein inhibition

A role for the flavoprotein NRH:quinone oxidoreductase 2 (NQO2, QR2) in human diseases such as malaria, leukemia and neurodegeneration has been proposed. In order to explore the potential of NQO2 as a therapeutic target, we have developed potent and selective mechanism-based inhibitors centered on the indolequinone pharmacophore. The compounds show remarkable selectivity for NQO2 over the closely related flavoprotein NQO1, with small structural changes defining selectivity. Biochemical studies confirmed the mechanism-based inhibition, whereas X-ray crystallography and mass spectrometry revealed the nature of the inhibitor interaction with the protein. These indolequinones represent the first mechanism-based inhibitors of NQO2, and their novel mode of action involving alkylation of the flavin cofactor, provides significant advantages over existing competitive inhibitors in terms of potency and irreversibility, and will open new opportunities to define the role of NQO2 in disease.

Synthesis of 3-substituted indoles via reactive alkylideneindolenine intermediates

Elimination of suitable leaving groups from 3-substituted indoles under basic or acidic conditions readily provides alkylideneindolenine intermediates that may react with a large variety of nucleophilic reagents. This article highlights some recent developments of this synthetic approach for the preparation of functionalized indole derivatives.

Design of anticancer prodrugs for reductive activation

Anticancer prodrugs designed to target specifically tumor cells should increase therapeutic effectiveness and decrease systemic side effects in the treatment of cancer. Over the last 20 years, significant advances have been made in the development of anticancer prodrugs through the incorporation of triggers for reductive activation. Reductively activated prodrugs have been designed to target hypoxic tumor tissues, which are known to overexpress several endogenous reductive enzymes. In addition, exogenous reductive enzymes can be delivered to tumor cells through fusion with tumor-specific antibodies or overexpressed in tumor cells through gene delivery approaches. Many anticancer prodrugs have been designed to use both the endogenous and exogenous reductive enzymes for target-specific activation and these prodrugs often contain functional groups such as quinones, nitroaromatics, N-oxides, and metal complexes. Although no new agents have been approved for clinical use, several reductively activated prodrugs are in various stages of clinical trial. This review mainly focuses on the medicinal chemistry aspects of various classes of reductively activated prodrugs including design principles, structure-activity relationships, and mechanisms of activation and release of active drug molecules.

Emission under hypoxia: one-electron reduction and fluorescence characteristics of an indolequinone-coumarin conjugate

A characteristic feature of the reactivity of indolequinone derivatives, substituents of which can be removed by one-electron reduction under hypoxic conditions, was applied to the development of a new class of fluorescent probes for disease-relevant hypoxia. A reducing indolequinone parent molecule conjugated with fluorescent coumarin chromophores could suppress efficiently the fluorescence emission of the coumarin moieties by an intramolecular electron-transfer quenching mechanism and a conventional internal-filter effect. Under hypoxic conditions, however, the conjugate, denoted IQ-Cou, underwent a one-electron reduction triggered by X irradiation or the action of a reduction enzyme to release a fluorescent coumarin chromophore, whereupon an intense fluorescence emission with a maximum intensity at 420 nm was observed. The one-electron reduction of IQ-Cou was suppressed by molecular oxygen under aerobic conditions. IQ-Cou also showed intense fluorescence in a hypoxia-selective manner upon incubation with a cell lysate of the human fibrosarcoma cell line HT-1080. The IQ-Cou conjugate has several unique properties that are favorable for a fluorescent probe of hypoxia-specific imaging.

Natural and synthetic quinones and their reduction by the quinone reductase enzyme NQO1: from synthetic organic chemistry to compounds with anticancer potential

The quinone reductase enzyme NAD(P)H: quinone oxidoreductase 1 (NQO1) is a ubiquitous flavoenzyme that catalyzes the two-electron reduction of quinones. This Perspective briefly reviews the structure and mechanism, physiological role, and upregulation and induction of the enzyme, but focuses on the synthesis of new heterocyclic quinones and their metabolism by recombinant human NQO1. Thus a range of indolequinones, some of which are novel analogues of mitomycin C, benzimidazolequinones, benzothiazolequinones and quinolinequinones have been prepared and evaluated, leading to detailed knowledge of the structural requirements for efficient metabolism by the enzyme. Potent mechanism-based inhibitors (suicide substrates) of NQO1 have also been developed. These indolequinones irreversibly alkylate the protein, preventing its function both in standard enzyme assays and also in cells. Some of these quinones are also potent inhibitors of growth of human pancreatic cancer cells, suggesting a potential role for such compounds as therapeutic agents.

Synthesis of substituted 4-azaisoindoles — New tacrine analogues

The regioselective Friedländer reaction of 3-amino-4-cyanopyrroles with a series of cyclic ketones has enabled the first reported synthesis of substituted 4-azaisoindoles. Structurally, this new class of compounds stands for the first reported 4-azaisoindole tacrine analogues. A reaction mechanism for the formation of the reported 4-azaisoindoles is proposed.Key words: 4-azaisoindoles, tacrine, Friedländer reaction, pyrroles, mechanism.

Molecular Targeting of BCL2 and BCLXL Proteins by Synthetic BCL2 Homology 3 Domain Peptide Enhances the Efficacy of Chemotherapy

Chemotherapeutic agents are known to induce programmed cell death or apoptosis. The activation of cellular antiapoptotic defense that prevents the translation of drug-induced damage into cell death is the key factor in cellular antiapoptotic resistance that decreases the chemotherapeutic effectiveness of a broad spectrum of anticancer drugs. A novel proapoptotic anticancer drug delivery system (DDS) was designed to simultaneously induce apoptosis and suppress antiapoptotic cellular defense. The system includes three main components: 1) anticancer drug camptothecin (CPT) as an apoptosis inducer, 2) synthetic BCL2 homology 3 domain (BH3) peptide as a suppressor of cellular antiapoptotic defense, and 3) poly(ethylene glycol) (PEG) polymer as a carrier. The above DDS was studied in vitro using A2780 human ovarian carcinoma cells and in vivo on nude mice bearing xenografts of human ovarian tumor. The results obtained in both series of experiments corroborate each other. They show that the designed DDS provided intracellular delivery of active components and suppressed cellular antiapoptotic defense, leading to the more pronounced induction of caspase-dependent signaling pathway of apoptosis compared with CPT alone and simple CPT-PEG conjugate. Including BH3 peptide in complex DDS decreased apoptotic cellular defense, substantially increased toxicity of the whole complex, and provided high antitumor activity. Therefore, the proposed novel multicomponent proapoptotic anticancer drug delivery system has high potential to enhance the efficacy of chemotherapy.