Acid-Sensitive Peptide-Conjugated Doxorubicin Mediates the Lysosomal Pathway of Apoptosis and Reverses Drug Resistance in Breast Cancer

Schiff bases and their metal complexes to target and overcome (multidrug) resistance in cancer

Overcoming multidrug resistance (MDR) is one of the major challenges in cancer therapy. In this respect, Schiff base-related compounds (bearing a R1R2CNR3 bond) gained high interest during the past decades. Schiff bases are considered privileged ligands for various reasons, including the easiness of their preparation and the possibility to form complexes with almost all transition metal ions. Schiff bases and their metal complexes exhibit many types of biological activities and are used for the treatment and diagnosis of various diseases. Until now, 13 Schiff bases have been investigated in clinical trials for cancer treatment and hypoxia imaging. This review represents the first collection of Schiff bases and their complexes which demonstrated MDR-reversal activity. The areas of drug resistance covered in this article involve: 1) Modulation of ABC transporter function, 2) Targeting lysosomal ABCB1 overexpression, 3) Circumvention of ABC transporter-mediated drug efflux by alternative routes of drug uptake, 4) Selective activity against MDR cancer models (collateral sensitivity), 5) Targeting GSH-detoxifying systems, 6) Overcoming apoptosis resistance by inducing necrosis and paraptosis, 7) Reactivation of mutated p53, 8) Restoration of sensitivity to DNA-damaging anticancer therapy, and 9) Overcoming drug resistance through modulation of the immune system. Through this approach, we would like to draw attention to Schiff bases and their metal complexes representing highly interesting anticancer drug candidates with the ability to overcome MDR.

Nanomedicine in therapeutic warfront against estrogen receptor-positive breast cancer

Breast cancer (BC) is the most frequently diagnosed malignancy in women worldwide. Almost 70-80% of cases of BC are curable at the early non-metastatic stage. BC is a heterogeneous disease with different molecular subtypes. Around 70% of breast tumors exhibit estrogen-receptor (ER) expression and endocrine therapy is used for the treatment of these patients. However, there are high chances of recurrence in the endocrine therapy regimen. Though chemotherapy and radiation therapy have substantially improved survival rates and treatment outcomes in BC patients, there is an increased possibility of the development of resistance and dose-limiting toxicities. Conventional treatment approaches often suffer from low bioavailability, adverse effects due to the non-specific action of chemotherapeutics, and low antitumor efficacy. Nanomedicine has emerged as a conspicuous strategy for delivering anticancer therapeutics in BC management. It has revolutionized the area of cancer therapy by increasing the bioavailability of the therapeutics and improving their anticancer efficacy with reduced toxicities on healthy tissues. In this article, we have highlighted various mechanisms and pathways involved in the progression of ER-positive BC. Further, different nanocarriers delivering drugs, genes, and natural therapeutic agents for surmounting BC are the spotlights of this article.

The role of peptides in reversing chemoresistance of breast cancer: current facts and future prospects

Breast cancer is the first malignant tumor in women, and its incidence is also increasing year by year. Chemotherapy is one of the standard therapies for breast cancer, but the resistance of breast cancer cells to chemotherapy drugs is a huge challenge for the effective treatment of breast cancer. At present, in the study of reversing the drug resistance of solid tumors such as breast cancer, peptides have the advantages of high selectivity, high tissue penetration, and good biocompatibility. Some of the peptides that have been studied can overcome the resistance of tumor cells to chemotherapeutic drugs in the experiment, and effectively control the growth and metastasis of breast cancer cells. Here, we describe the mechanism of different peptides in reversing breast cancer resistance, including promoting cancer cell apoptosis; promoting non-apoptotic regulatory cell death of cancer cells; inhibiting the DNA repair mechanism of cancer cells; improving the tumor microenvironment; inhibiting drug efflux mechanism; and enhancing drug uptake. This review focuses on the different mechanisms of peptides in reversing breast cancer drug resistance, and these peptides are also expected to create clinical breakthroughs in promoting the therapeutic effect of chemotherapy drugs in breast cancer patients and improving the survival rate of patients.

A Novel Homodimer Peptide-Drug Conjugate Improves the Efficacy of HER2-Positive Breast Cancer Therapy

Tumor-targeting peptide-drug conjugates (PDCs) have become a focus of research in recent years. However, due to the instability of peptides and their short in vivo effective half-life, they have limited clinical application. Herein, we propose a new DOX PDC based on a homodimer HER-2-targeting peptide and acid-sensitive hydrazone bond, which could enhance the anti-tumor effect of DOX and reduce systemic toxicities. The PDC could accurately deliver DOX into HER2-positive SKBR-3 cells, with it showing 2.9 times higher cellular uptake than free DOX and enhanced cytotoxicity with respect to IC₅₀ of 140 nM (vs. 410 nM for free DOX). In vitro assays showed that the PDC had high cellular internalization efficiency and cytotoxicity. In vivo anti-tumor experiments indicated that the PDC could significantly inhibit the growth of HER2-positive breast cancer xenografts in mice and reduce the side effects of DOX. In summary, we constructed a novel PDC molecule targeting HER2-positive tumors, which may overcome some deficiencies of DOX in breast cancer therapy.

Current understandings and clinical translation of nanomedicines for breast cancer therapy

Breast cancer is one of the most frequently diagnosed cancers that is threatening women's life. Current clinical treatment regimens for breast cancer often involve neoadjuvant and adjuvant systemic therapies, which somewhat are associated with unfavorable features. Also, the heterogeneous nature of breast cancers requires precision medicine that cannot be fulfilled by a single type of systemically administered drug. Taking advantage of the nanocarriers, nanomedicines emerge as promising therapeutic agents for breast cancer that could resolve the defects of drugs and achieve precise drug delivery to almost all sites of primary and metastatic breast tumors (e.g. tumor vasculature, tumor stroma components, breast cancer cells, and some immune cells). Seven nanomedicines as represented by Doxil® have been approved for breast cancer clinical treatment so far. More nanomedicines including both non-targeting and active targeting nanomedicines are being evaluated in the clinical trials. However, we have to realize that the translation of nanomedicines, particularly the active targeting nanomedicines is not as successful as people have expected. This review provides a comprehensive landscape of the nanomedicines for breast cancer treatment, from laboratory investigations to clinical applications. We also highlight the key advances in the understanding of the biological fate and the targeting strategies of breast cancer nanomedicine and the implications to clinical translation.

CD44-targeted, indocyanine green-paclitaxel-loaded human serum albumin nanoparticles for potential image-guided drug delivery

The use of multifunctional nanomedicines for image-guided drug delivery is currently being universally evaluated as a means of efficiently managing cancers and other diseases. In this study we evaluated the potential of an indocyanine green (ICG) and paclitaxel (PTX) loaded human serum albumin (HSA) nanoparticles that was conjugated with hyaluronic acid for use in image-guided drug delivery targeted to CD44-positive non-small cell lung cancer (NSCLC). Series of NSCLC cell lines were evaluated for the expression of CD44 using both western blot analysis and qRT-PCR and compared to a normal lung fibroblast cell line (MRC-5). Using Fluorescence microscopy and photoacoustic imaging (PA), we explored the ability of these targeted nanoparticles to selectively accumulate in NSCLC cell lines in comparison to MRC-5 and their potential for biomedical imaging towards their use for theranostic application. Results obtained suggest that these targeted nanoparticles have potential for application in both imaging and treatment of NSCLC.

Peptide-drug conjugate-based novel molecular drug delivery system in cancer

Drug delivery systems are generally believed to comprise drugs and excipients. A peptide-drug conjugate is a single molecule that can simultaneously play multiple roles in a drug delivery system, such as in vivo drug distribution, targeted release, and bioactivity functions. This molecule can be regarded as an integrated drug delivery system, so it is called a molecular drug delivery system. In the context of cancer therapy, a peptide-drug conjugate comprises a tumor-targeting peptide, a payload, and a linker. Tumor-targeting peptides specifically identify membrane receptors on tumor cells, improve drug-targeted therapeutic effects, and reduce toxic and side effects. Payloads with bioactive functions connect to tumor-targeting peptides through linkers. In this review, we explored ongoing clinical work on peptide-drug conjugates targeting various receptors. We discuss the binding mechanisms of tumor-targeting peptides and related receptors, as well as the limiting factors for peptide-drug conjugate-based molecular drug delivery systems.

Novel N-Methylated Cyclodepsipeptide Prodrugs for Targeted Cancer Therapy

Coibamide A (1) is a highly N-methylated cyclodepsipeptide with low nanomolar antiproliferative activities against various cancer cell lines. In previous work, we discovered a simplified analogue, [MeAla3-MeAla6]-coibamide (1a), which exhibited the same inhibitory abilities as coibamide A. Herein, to reduce the whole-body toxicity and improve the solubility of 1a, two novel peptide-drug conjugates RGD-SS-CA (2) and RGD-VC-CA (3) were designed, synthesized, and evaluated. Composed of cyclodepsipeptide 1a, a tumor-homing RGD motif, and a conditionally labile linker, the conjugates are expected to release 1a tracelessly in specific tumor microenvironments. Compared with RGD-VC-CA (3), RGD-SS-CA (2) proved to be superior in in vitro drug release and cytotoxicity tests. Notably, intravenous injection of RGD-SS-CA (2) into mice-bearing human tumor xenografts induced significant tumor growth suppression with negligible toxicity. Therefore, as a novel prodrug of the coibamide A analogue, conjugate 2 has great potential for further exploration in cancer drug discovery.

Photo-triggered release of doxorubicin from liposomes formulated by amphiphilic phthalocyanines for combination therapy to enhance antitumor efficacy

Multidrug combination therapy based on drug delivery systems (DDSs) has great potential for cancer treatment. Stimuli-sensitive DDSs further enhance therapeutic efficacy by providing controllable drug delivery. Herein, the phospholipid compound DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) was used to construct thermosensitive liposomes to load the photosensitizer ZnPc(PEG)₄ (zinc phthalocyanine substituted by tetraethylene glycol) for molecular imaging, and photodynamic and photothermal therapy, together with doxorubicin (DOX) for chemotherapy. Interestingly, ZnPc(PEG)₄ as an amphipathic molecule was found to be important in the construction of the liposomes, and it provided liposomes with improved stability. The thus-obtained liposomes ZnPc(PEG)₄:DOX@LiPOs were demonstrated to have enhanced ROS production capacity, heat generation properties and a photo-triggered doxorubicin release effect, and, in cellular experiments, increased cytotoxicity and apoptotic cell proportions, compared to ZnPc(PEG)₄@LiPOs and DOX@LiPOs. ZnPc(PEG)₄ loaded in lipid bilayers showed stronger intracellular ROS production ability compared to free ZnPc(PEG)₄. In vivo studies indicated that ZnPc(PEG)₄:DOX@LiPOs exhibited enhanced tumor accumulation, increased anti-cancer effects and reduced liver retention. These photo-triggered liposomes constructed by the photosensitizer ZnPc(PEG)₄ can also be used to package other cargo for combined target tumor therapy and molecular imaging.

A Review on Targeting Nanoparticles for Breast Cancer

Chemotherapeutic agents have been used extensively in breast cancer remedy. However, most anticancer drugs cannot differentiate between cancer cells and normal cells, leading to toxic side effects. Also, the resulted drug resistance during chemotherapy reduces treatment efficacy. The development of targeted drug delivery offers great promise in breast cancer treatment both in clinical applications and in pharmaceutical research. Conjugation of nanocarriers with targeting ligands is an effective therapeutic strategy to treat cancer diseases. In this review, we focus on active targeting methods for breast cancer cells through the use of chemical ligands such as antibodies, peptides, aptamers, vitamins, hormones, and carbohydrates. Also, this review covers all information related to these targeting ligands, such as their subtypes, advantages, disadvantages, chemical modification methods with nanoparticles and recent published studies (from 2015 to present). We have discussed 28 different targeting methods utilized for targeted drug delivery to breast cancer cells with different nanocarriers delivering anticancer drugs to the tumors. These different targeting methods give researchers in the field of drug delivery all the information and techniques they need to develop modern drug delivery systems.

A self-assembled pH/enzyme dual-responsive prodrug with PEG deshielding for multidrug-resistant tumor therapy

Multidrug resistance (MDR) is one of the major obstacles for tumor therapy. Intake by receptor-mediated endocytosis enables molecules to bypass ABC transporter efflux, which is the primary mechanism of MDR. Here, we developed a novel pH/enzyme dual-responsive polypeptide prodrug to reverse multidrug resistance. This drug is composed of pH/MMP2-sensitive nanoparticles (MSNPs) self-assembled from mPEG-peptide-DOX. MSNPs can overcome sequential physiological barriers of multidrug resistance by prolonging the circulation time through PEGylation, enhancing tumor accumulation through passive targeting, increasing tumor penetration by enzyme-sensitive PEG deshielding, bypassing ABC transporter efflux by undergoing receptor-mediated endocytosis, and inducing sufficient DOX release from nanoparticles triggered by lysosomal pH. The reversal of MDR by MSNPs was evaluated in MCF-7/ADR cells and nude mice bearing tumors consisting of MCF-7/ADR cells. Both in vitro and in vivo studies showed that the MSNPs can effectively reverse MDR. Thus, MSNPs may constitute a potentially promising strategy for overcoming MDR in clinical applications.

Transferrin receptor-targeted redox/pH-sensitive podophyllotoxin prodrug micelles for multidrug-resistant breast cancer therapy

Podophyllotoxin (PPT), a toxic polyphenol extracted from the roots of Podophyllum species, showed remarkable activity against P-glycoprotein (P-gp) mediated multidrug resistant (MDR) cancer cells. Many PPT-prodrugs based on nano-technology have been developed for increasing aqueous solubility and reducing the side effects of PPT; however, the sensitive linkers in almost all PPT-prodrugs were ester bonds, resulting in slow and incomplete drug release. We developed a redox/pH double-sensitive and tumor active targeted drug delivery system for PPT delivery, in which PPT was covalently coupled to T7-peptide (Pep) modified polyethylene glycol (PEG) or methoxy-polyethylene glycol (mPEG) through a disulfide bond to obtain the final polymer (Pep-PEG-SS-PPT or PEG-SS-PPT). The mixed micelles (Pep-SS-NPs) were made by mixing Pep-PEG-SS-PPT with PEG-SS-PPT, and the mixed micelles showed good size uniformity and high stability in serum solution. The in vitro release experiment showed that about (81.7 ± 2.8)% PPT was released from Pep-SS-NPs in 10 mM glutathione (GSH) at pH 7.4, and also about (64.6 ± 1.7)% PPT was released from Pep-SS-NPs at pH 5.0. In vitro cytotoxicity analysis suggested that Pep-SS-NPs exhibited 57- to 270-fold lower resistance index (RI) values for different drug-resistant cancer cell lines than paclitaxel (PTX) or docetaxel (DTX). The cell uptake assay indicated that the Pep-SS-NPs could significantly enhance the intracellular level of coumarin-6 compared to that of the control group. The maximum tolerated dose (MTD) of Pep-SS-NPs was increased greatly compared to that of free PPT (5.3-fold). In vivo research showed that Pep-SS-NPs significantly enhanced antitumor efficacy against MCF-7/ADR xenograft tumors compared to the control groups. These findings suggest that mixed micelles could be a potentially successful nanomedicine for MDR breast cancer therapy.

Targeted Delivery of a Ligand-Drug Conjugate via Formyl Peptide Receptor 1 through Cholesterol-Dependent Endocytosis

G protein-coupled receptors (GPCRs) undergo ligand-induced internalization that carries the cognate ligands into intracellular compartments. The present study explores this property for the use of formyl peptide receptor 1 (FPR1), a class A GPCR that binds formylated peptides, as a potential target for drug delivery. A pH-sensitive peptide-drug conjugate consisting of doxorubicin (DOX), N-ε-maleimidocaproic acid hydrazide (EMCH), and the formyl peptide fMet-Leu-Phe-Cys (abbreviated as DEF) was prepared. DEF retained pharmacological activities of formyl peptides in binding to FPR1 and mobilization of Ca²⁺ from intracellular stores. However, the conjugated DOX was no longer cell membrane-permeable and relied on FPR1 for cellular entry. DOX was released from DEF into acidic compartments labeled with fluorescent trackers for endosomes. Treatment of cells with pharmacological inhibitors that block clathrin- or caveolae-mediated endocytosis did not abrogate FPR1-dependent DEF internalization, nor did inhibition of macropinocytosis and phagocytosis. In contrast, cholesterol depletion abrogated DEF internalization through FPR1, suggesting characteristics of cholesterol-dependent uptake mediated by a cell surface receptor. These results demonstrate the possibility of using FPR1 for targeted drug delivery.

A versatile drug delivery system targeting senescent cells

Senescent cells accumulate in multiple aging-associated diseases, and eliminating these cells has recently emerged as a promising therapeutic approach. Here, we take advantage of the high lysosomal β-galactosidase activity of senescent cells to design a drug delivery system based on the encapsulation of drugs with galacto-oligosaccharides. We show that gal-encapsulated fluorophores are preferentially released within senescent cells in mice. In a model of chemotherapy-induced senescence, gal-encapsulated cytotoxic drugs target senescent tumor cells and improve tumor xenograft regression in combination with palbociclib. Moreover, in a model of pulmonary fibrosis in mice, gal-encapsulated cytotoxics target senescent cells, reducing collagen deposition and restoring pulmonary function. Finally, gal-encapsulation reduces the toxic side effects of the cytotoxic drugs. Drug delivery into senescent cells opens new diagnostic and therapeutic applications for senescence-associated disorders.

Doxorubicin conjugated with a trastuzumab epitope and an MMP-2 sensitive peptide linker for the treatment of HER2-positive breast cancer

HER2-positive breast cancer correlates with more aggressive tumor growth, a poorer prognosis and reduced overall survival. Currently, trastuzumab (Herceptin), which is an anti-HER2 antibody, is one of the key drugs. There is evidence indicating that conjugation of trastuzumab with chemotherapy drugs, such as doxorubicin (DOX), for multiple targets could be more effective. However, incomplete penetration into tumors has been noted for those conjugates. Compared to an antibody, peptides may represent an attractive alternative. For HER2, a similar potency has been observed for a 12-amino-acid anti-HER2 peptide mimetic YCDGFYACYMDV-NH₂ (AHNP, disulfide-bridged) and full-length trastuzumab. Thus, a peptide, GPLGLAGDDYCDGFYACYMDV-NH₂, which consists of AHNP and an MMP-2 cleavable linker GPLGLAGDD, was first designed, followed by conjugation with DOX via a glycine residue at the N-terminus to form a novel DOX-peptide conjugate MAHNP-DOX. Using HER2-positive human breast cancer cells BT474 and SKBR3 as in vitro model systems and nude mice with BT474 xenografts as an in vivo model, this conjugate was comprehensively characterized, and its efficacy was evaluated and compared with that of free DOX. As a result, MAHNP-DOX demonstrated a much lower in vitro IC₅₀, and its in vivo extent of inhibition in mice was more evident. During this process, enzymatic cleavage of MAHNP-DOX is critical for its activation and cellular uptake. In addition, a synergistic response was observed after the combination of DOX and AHNP. This effect was probably due to the involvement of AHNP in the PI3K–AKT signaling pathway, which can be largely activated by DOX and leads to anti-apoptotic signals.

Albumin Binding Domain Fusing R/K-X-X-R/K Sequence for Enhancing Tumor Delivery of Doxorubicin

For the purpose of improving the tumor delivery of doxorubicin (DOX), a kind of peptide-DOXO conjugate was designed and prepared, in which the peptide composed of an albumin-binding domain (ABD) and a tumor-specific internalizing sequence (RGDK or RPARPAR) was conjugated to a (6-maleimidocaproyl) hydrazone derivative of doxorubicin (DOXO-EMCH). The doxorubicin uptake by lung cancer cell line of A549 evidenced that the conjugates are capable of being internalized through a tumor-specific sequence mediated manner, and the intracellular imaging of distribution in A549 cell demonstrated that the conjugated doxorubicin can be delivered to the cell nucleus. The A549 cell cytotoxicity of peptide-DOXO conjugates was presented with IC₅₀ values and shown in the range of about 9-11 μM. Pharmacokinetics study revealed that both conjugates exhibited nearly 5.5 times longer half-time than DOX, and about 4 times than DOXO-EMCH. The in vivo growth inhibitions of the two peptide-DOXO conjugates on BALB/c nude mice bearing A549 tumor (47.78% for ABD-RGDK-DOXO and 47.09% for ABD-RPARPAR-DOXO) were much stronger than that of doxorubicin and DOXO-EMCH (24.28% and 25.67% respectively) at a doxorubicin equivalent dose. Besides, the in vivo fluorescence imaging study confirmed that the peptide markedly increased the payload accumulation in tumor tissues and indicated that albumin binding domain fusing tumor-specific sequence effectively enhanced the tumor delivery of doxorubicin and thus improved its therapeutic potency.

Transferrin receptor-targeted pH-sensitive micellar system for diminution of drug resistance and targetable delivery in multidrug-resistant breast cancer

The emergence of drug resistance is partially associated with overproduction of transferrin receptor (TfR). To overcome multidrug resistance (MDR) and achieve tumor target delivery, we designed a novel biodegradable pH-sensitive micellar system modified with HAIYPRH, a TfR ligand (7pep). First, the polymers poly(l-histidine)-coupled polyethylene glycol-2000 (PHIS-PEG₂₀₀₀) and 7pep-modified 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-polyethylene glycol-2000 (7pep-DSPE-PEG₂₀₀₀) were synthesized, and the mixed micelles were prepared by blending of PHIS-PEG₂₀₀₀ and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-polyethylene glycol-2000 (DSPE-PEG₂₀₀₀) or 7pep-DSPE-PEG₂₀₀₀ (7-pep HD micelles). The micelles exhibited good size uniformity, high encapsulation efficiency, and a low critical micelle concentration. By changing the polymer ratio in the micellar formulation, the pH response range was specially tailored to pH ~6.0. When loaded with antitumor drug doxorubicin (DOX), the micelle showed an acid pH-triggering drug release profile. The cellular uptake and cytotoxicity study demonstrated that 7-pep HD micelles could significantly enhance the intracellular level and antitumor efficacy of DOX in multidrug-resistant cells (MCF-7/Adr), which attributed to the synergistic effect of poly(l-histidine)-triggered endolysosom escape and TfR-mediated endocytosis. Most importantly, the in vivo imaging study confirmed the target-ability of 7-pep HD micelles to MDR tumor. These findings indicated that 7-pep HD micelles would be a promising drug delivery system in the treatment of drug-resistant tumors.

Peptides and Drug Delivery

Peptides have been used as drugs to treat various health conditions, and they are also being developed as diagnostic agents. Due to their receptor selectivity, peptides have recently been utilized for drug delivery to target drug molecules to specific types of cells (i.e. cancer cells, immune cells) to lower the side effects of the drugs. In this case, the drug is conjugated to the carrier peptide for directing the drug to the target cells (e.g. cancer cells) with higher expression of a specific receptor that recognizes the carrier peptide. As a result, the drug is directed to the target diseased cells without affecting the normal cells. Peptides are also being developed for improving drug delivery through the intestinal mucosa barrier (IMB) and the blood-brain barrier (BBB). These peptides were derived from intercellular junction proteins such as occludins, claudins, and cadherins and improve drug delivery through the IMB and BBB via the paracellular pathways. It is hypothesized that the peptides modulate protein-protein interactions in the intercellular junctions of the IMB and BBB to increase the porosity of paracellular pathways of the barriers. These modulator peptides have been shown to enhance brain delivery of small molecules and medium-sized peptides as well as a large protein such as 65 kDa albumin. In the future, this method has the potential to improve oral and brain delivery of therapeutic and diagnostic peptides and proteins.

An albumin-based tumor-targeted oxaliplatin prodrug with distinctly improved anticancer activity in vivo

An oxaliplatin-based platinum(iv) drug which specifically binds to albumin after i.v. application led to several complete responses in tumor-bearing mice.

The design of targeted platinum(iv) prodrugs is a very promising approach to enhance the low selectivity of platinum(ii) drugs towards cancerous tissue in order to reduce the impact on healthy tissue and, consequently, the often severe side-effects. Herein, we report a set of mono-functionalized cis- and oxaliplatin-based platinum(iv) complexes bearing a maleimide moiety, which allows selective binding to serum albumin in the bloodstream. This leads not only to a prolonged plasma half-life by avoidance of fast renal clearance, but also to preferential accumulation of the drug in the tumor tissue due to the EPR-effect. Additionally, analogous succinimide-functionalized derivatives were prepared to verify the influence of the maleimide moiety. First experiments showed that all the maleimide compounds are stable and also possess good albumin-binding properties in whole serum. Further analytical studies on in vivo samples proved the highly increased plasma half-life, as well as tumor accumulation of the maleimide-functionalized substances. In vivo antitumor experiments with CT-26-bearing mice showed that, in contrast to the cisplatin derivatives, the oxaliplatin-based complexes had exceptionally better activity than the free drug resulting in the cure of the majority of treated mice. Subsequent analysis suggested that a distinctly faster reduction as well as reduced tumor accumulation of the cisplatin derivative might explain the worse performance compared to the oxaliplatin(iv) complexes. Taken together, a novel lead platinum(iv) complex with outstanding antitumor activity is presented, which will now be further developed towards clinical phase I trials.

Doxorubicin/heparin composite nanoparticles for caspase-activated prodrug chemotherapy

Caspase-activated prodrug chemotherapy is introduced and demonstrated using the composite nanoparticles (NPs), which deliver doxorubicin (DOX) and DEVD-S-DOX together to the tumor tissue. DEVD-S-DOX, DOX linked to a peptide moiety (DEVD), is a prodrug that is cleaved into free DOX by caspase-3 upon apoptosis. DEVD-S-DOX has no therapeutic efficacy, but it changes into free DOX with the expression of caspase-3. With the accumulation of the composite NPs in the tumor tissue by the enhanced permeation and retention (EPR) effect, a small exposure of DOX in the tumor cells initiated apoptosis in a localized area of the tumor tissue, which induced caspase-3 activation. Cleavage of DEVD-S-DOX into free DOX by caspase-3 continued with repetitive activation of caspase-3 and cleavage of DEVD-S-DOX at the tumor site. The composite NPs were characterized with transmittance electron microscopy (TEM) and particle size analyzer. We then evaluated the nanoparticle drug release, therapeutic efficacy, and in vivo biodistribution for tumor targeting using a non-invasive live animal imaging technology and the quantification of DOX with high performance liquid chromatography. DOX-induced apoptosis-targeted chemotherapy (DIATC) was verified by in vitro/in vivo DEVD-S-DOX response to free DOX and cellular uptake behavior of the composite NPs with flow cytometry analysis. Significant antitumor efficacy with minimal cardiotoxicity was also observed, which supported DIATC for improved chemotherapy.