Anticancer and antiangiogenic activity of HPMA copolymer-aminohexylgeldanamycin-RGDfK conjugates for prostate cancer therapy

Nanotherapeutics for prostate cancer treatment: A comprehensive review

Prostate cancer (PCa) is the most prevalent solid organ malignancy and seriously affects male health. The adverse effects of prostate cancer therapeutics can cause secondary damage to patients. Nanotherapeutics, which have special targeting abilities and controlled therapeutic release profiles, may serve as alternative agents for PCa treatment. At present, many nanotherapeutics have been developed to treat PCa and have shown better treatment effects in animals than traditional therapeutics. Although PCa nanotherapeutics are highly attractive, few successful cases have been reported in clinical practice. To help researchers design valuable nanotherapeutics for PCa treatment and avoid useless efforts, herein, we first reviewed the strategies and challenges involved in prostate cancer treatment. Subsequently, we presented a comprehensive review of nanotherapeutics for PCa treatment, including their targeting methods, controlled release strategies, therapeutic approaches and mechanisms. Finally, we proposed the future prospects of nanotherapeutics for PCa treatment.

Emerging frontiers in nanomedicine targeted therapy for prostate cancer

Prostate cancer is a prevalent cancer in men, often treated with chemotherapy. However, it tumor cells are clinically grows slowly and is heterogeneous, leading to treatment resistance and recurrence. Nanomedicines, through targeted delivery using nanocarriers, can enhance drug accumulation at the tumor site, sustain drug release, and counteract drug resistance. In addition, combination therapy using nanomedicines can target multiple cancer pathways, improving effectiveness and addressing tumor heterogeneity. The application of nanomedicine in prostate cancer treatment would be an important strategy in controlling tumor dynamic process as well as improve survival. Thus, this review highlights therapeutic nanoparticles as a solution for prostate cancer chemotherapy, exploring targeting strategies and approaches to combat drug resistance.

Recent Progress in Nanomaterial-Based Biosensors and Theranostic Nanomedicine for Bladder Cancer

Bladder cancer (BCa) is one of the most expensive and common malignancies in the urinary system due to its high progression and recurrence rate. Although there are various methods, including cystoscopy, biopsy, and cytology, that have become the standard diagnosis methods for BCa, their intrinsic invasive and inaccurate properties need to be overcome. The novel urine cancer biomarkers are assisted by nanomaterials-based biosensors, such as field-effect transistors (FETs) with high sensitivity and specificity, which may provide solutions to these problems. In addition, nanomaterials can be applied for the advancement of next-generation optical imaging techniques and the contrast agents of conventional techniques; for example, magnetic resonance imaging (MRI) for the diagnosis of BCa. Regarding BCa therapy, nanocarriers, including mucoadhesive nanoparticles and other polymeric nanoparticles, successfully overcome the disadvantages of conventional intravesical instillation and improve the efficacy and safety of intravesical chemotherapy for BCa. Aside from chemotherapy, nanomedicine-based novel therapies, including photodynamic therapy (PDT), photothermal therapy (PTT), chemodynamic therapy (CDT), sonodynamic therapy (SDT), and combination therapy, have afforded us new ways to provide BC therapy and hope, which can be translated into the clinic. In addition, nanomotors and the nanomaterials-based solid tumor disassociation strategy provide new ideas for future research. Here, the advances in BCa diagnosis and therapy mentioned above are reviewed in this paper.

Structural diversity and biological relevance of benzenoid and atypical ansamycins and their congeners

Covering: 2011 to 2021The structural division of ansamycins, including those of atypical cores and different lengths of the ansa chains, is presented. Recently discovered benzenoid and atypical ansamycin scaffolds are presented in relation to their natural source and biosynthetic routes realized in bacteria as well as their muta and semisynthetic modifications influencing biological properties. To better understand the structure-activity relationships among benzenoid ansamycins structural aspects together with mechanisms of action regarding different targets in cells, are discussed. The most promising directions for structural optimizations of benzenoid ansamycins, characterized by predominant anticancer properties, were discussed in view of their potential medical and pharmaceutical applications. The bibliography of the review covers mainly years from 2011 to 2021.

Anticancer activity and toxicity of new quaternary ammonium geldanamycin derivative salts and their mixtures with potentiators

Geldanamycin (GDM) has been modified by different type neutral/acidic/basic substituents (1–7) and by quinuclidine motif (8), transformed into ammonium salts (9–13) at C(17). These compounds have been characterised by spectroscopic and x-ray methods. Derivative 8 shows better potency than GDM in MCF-7, MDA-MB-231, A549 and HeLa (IC₅₀s = 0.09–1.06 µM). Transformation of 8 into salts 9–13 reduces toxicity (by 11-fold) at attractive potency, e.g. MCF-7 cell line (IC₅₀∼2 µM). Our studies show that higher water solubility contributes to lower toxicity of salts than GDM in healthy CCD39Lu and HDF cells. The use of 13 mixtures with potentiators PEI and DOX enhanced anticancer effects from IC₅₀∼2 µM to IC₅₀∼0.5 µM in SKBR-3, SKOV-3, and PC-3 cancer cells, relative to 13. Docking studies showed that complexes between quinuclidine-bearing 8–13 and Hsp90 are stabilised by extra hydrophobic interactions between the C(17)-arms and K58 or Y61 of Hsp90.

Enhanced nuclear delivery of H1-S6A, F8A peptide by NrTP6-modified polymeric platform

Nucleus is the central regulator of cell metabolism, growth and differentiation, which is considered as an effective target for the treatment of many diseases. To efficiently deliver drugs into nucleus, delivery systems have to bypass a number of barriers especially crossing the cell membrane and nuclear envelope. Here we report a nucleolar targeting peptide (NrTP6) modified polymeric conjugate platform based on N-(2-hydroxypropyl)-methacrylamide (HPMA) copolymers for enhanced nuclear delivery of H1-S6A, F8A peptide to hinder c-Myc from binding to DNA. On one hand, the modification of NrTP6 would promote cellular uptake and nuclear accumulation of the conjugates, and on the other hand, the conjugates can release smaller molecular weight subunits (H1-NrTP6) via cleavage of lysosomally enzyme-sensitive spacer for facilitating nucleus transport. It was found that NrTP6 modified HPMA copolymer-H1 peptide conjugates could improve internalization and nuclear accumulation of H1 peptide by 2.2 and 37.1-fold, respectively, compared to the non-NrTP6 modified ones, in HeLa cells. Moreover, the same trend was found in MDA-MB-231 cells and 4T1 cells. In addition, we found that the nuclear targeting mechanism of NrTP6 peptide mediation may be associated with the importin α/β pathway. Furthermore, the in vivo investigation revealed that NrTP6-modified polymeric platform exhibited the best therapeutic efficacy with a tumor growth inhibition rate of 77.0%. These results indicated that NrTP6 modification was a promising strategy for simultaneously realizing cellular internalization and nuclear targeting, which might provide a new path for intranuclear drug delivery.

Integrin-Mediated Delivery of Drugs and Nucleic Acids for Anti-Angiogenic Cancer Therapy: Current Landscape and Remaining Challenges

Angiogenesis, sprouting of new blood vessels from pre-existing vasculatures, plays a critical role in regulating tumor growth. Binding interactions between integrin, a heterodimeric transmembrane glycoprotein receptor, and its extracellular matrix (ECM) protein ligands govern the angiogenic potential of tumor endothelial cells. Integrin receptors are attractive targets in cancer therapy due to their overexpression on tumor endothelial cells, but not on quiescent blood vessels. These receptors are finding increasing applications in anti-angiogenic therapy via targeted delivery of chemotherapeutic drugs and nucleic acids to tumor vasculatures. The current article attempts to provide a retrospective account of the past developments, highlight important contemporary contributions and unresolved set-backs of this emerging field.

Responsive Hybrid (Poly)peptide-Polymer Conjugates

(Poly)peptide-polymer conjugates continue to garner significant interest in the production of functional materials given their composition of natural and synthetic building blocks that confer select and synergistic properties. Owing to opportunities to design predefined architectures and structures with different morphologies, these hybrid conjugates enable new approaches for producing micro- or nanomaterials. Their modular design enables the incorporation of multiple responsive properties into a single conjugate. This review presents recent advances in (poly)peptide-polymer conjugates for drug-delivery applications, with a specific focus on the utility of the (poly)peptide component in the assembly of particles and nanogels, as well as the role of the peptide in triggered drug release.

Delivery of HSP90 Inhibitor Using Water Soluble Polymeric Conjugates with High Drug Payload

PURPOSE

HSP90 (Heat shock protein 90kD) has been validated as a therapeutic target in Castrate Resistant Prostate Cancer. Unfortunately, HSP90 inhibitors suffer from dose-limiting toxicities that hinder their clinical applications. Previously developed polymeric delivery systems for HSP90 inhibitors had either low drug content or low biological activity suggesting the need for better delivery system for HSP90 inhibitors.

METHODS

We developed a simplified synthetic strategy to prepare polyethylene glycol based water-soluble polymeric system for model HSP90 inhibitor geldanamycin (GDM). We then investigated the effect of cathepsin B degradable linker and drug content in polymeric conjugates on their growth inhibitory property using DU145 (androgen independent) and LNCaP (androgen dependent) cell lines.

RESULTS

Water-soluble polymeric conjugates were synthesized with GDM content ranging from 9 to 30% wt/wt. We demonstrated the importance of cathepsin B degradable linker from the context of drug content and different prostate cancer cell lines. The most active conjugate against DU145 cells exhibited IC₅₀ value of 2.9 μM. This was similar to the IC₅₀ (2.1 μM) of small molecular drug aminohexane geldanamycin.

CONCLUSION

Water-soluble polymeric conjugate with high drug content was synthesized that exhibited in-vitro growth inhibitory activity similar to small molecular weight HSP90 inhibitor. Graphical Abstract Water soluble degradable polymeric conjugate for the delivery of Geldanamycin.

Modulating angiogenesis with integrin-targeted nanomedicines

Targeting angiogenesis-related pathologies, which include tumorigenesis and metastatic processes, has become an attractive strategy for the development of efficient guided nanomedicines. In this respect, integrins are cell-adhesion molecules involved in angiogenesis signaling pathways and are overexpressed in many angiogenic processes. Therefore, they represent specific biomarkers not only to monitor disease progression but also to rationally design targeted nanomedicines. Arginine-glycine-aspartic (RGD) containing peptides that bind to specific integrins have been widely utilized to provide ligand-mediated targeting capabilities to small molecules, peptides, proteins, and antibodies, as well as to drug/imaging agent-containing nanomedicines, with the final aim of maximizing their therapeutic index. Within this review, we aim to cover recent and relevant examples of different integrin-assisted nanosystems including polymeric nanoconstructs, liposomes, and inorganic nanoparticles applied in drug/gene therapy as well as imaging and theranostics. We will also critically address the overall benefits of integrin-targeting.

A novel αVβ3 ligand-modified HPMA copolymers for anticancer drug delivery

The integrin α_Vβ₃ receptor emerged as one of the most promising targets owing to its high expression on the surface of various malignant tumour cells and tumour angiogenesis endothelial cells, but with little expression in mature endothelial cells and the majority of normal cells. Here, we report a new targeting ligand FQSIYPpIK (FQS) with high affinity to integrin α_Vβ₃ receptor. To take the advantage of the particular interaction between FQS and integrin α_Vβ₃ receptor, FQS was linked to N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers. A model drug doxorubicin (DOX) was simultaneously conjugated to the same HPMA copolymers via pH-sensitive hydrazone linkages (FQS-HPMA-DOX). In in vitro study, FQS-HPMA-DOX could be internalised into α_Vβ₃ receptor-overexpressed B16F10 cells via a highly specific ligand - receptor pathway (5.0 times and 4.5 times higher cellular internalisation than HPMA-DOX and a scrambled peptide (s)-FQS (sequence: SYFIPKQIp)-modified copolymers ((s)-FQS-HPMA-DOX)). It is worth noting that compared with the classical α_Vβ₃ ligand cRGDfK-modified HPMA copolymers (cRGDfK-HPMA-DOX), FQS-HPMA-DOX also showed superior targeting efficiency. In in vivo study in the B16F10 melanoma bearing mice model showed the antitumour efficiency of FQS-HPMA-DOX (83.9%) were significantly higher than HPMA-DOX (44.9%) and cRGDfK-HPMA-DOX (77.5%). These results suggest that FQS peptide can act as an effective targeting ligand for the delivery of therapeutic agents.

Targeted polymer-drug conjugates: Current progress and future perspective

The combination of polymer technology and targeted drug delivery may pave the way for more effective yet safer therapeutic options for cancer therapy. Polymer-drug conjugates belonging to polymer therapeutics represent an emerging approach for drug delivery. The development of smart targeted polymer-drug conjugates that can specifically deliver drugs at a sustained rate to tumor cells may substantially improve the therapeutic index of anticancer agents. In this update, we provide an overview of the most important targeting molecules, and systemically summarize the recent advances in the development of tumor-targeted polymer-drug conjugates. Additionally, several promising approaches for the future will also be presented.

HPMA Copolymer CXCR4 Antagonist Conjugates Substantially Inhibited the Migration of Prostate Cancer Cells

A N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer–CXCR4 antagonist (BKT140) conjugate (P-BKT140) was developed and its biological activities were tested. Both free BKT140 and monomer MA-GGPLGLAG-BKT140 (MA is methacryloyl) were prepared by solid phase synthesis. P-BKT140 was prepared by reversible addition–fragmentation chain transfer (RAFT) copolymerization of monomers HPMA and MA-GGPLGLAG-BKT140. The in vitro results show that the free BKT140 and P-BKT140 have similar cytotoxicity against human prostate carcinoma PC-3 cells, indicating that conjugation of BKT140 to HPMA did not significantly impact the cytotoxicity of BKT140. Both BKT140 and P-BKT140 inhibited the CXCL12-induced migration of PC-3 prostate cancer cells, but the P-BKT140 conjugate possessed a substantially higher inhibition activity than free BKT140.

In vitro synergistic action of geldanamycin- and docetaxel-containing HPMA copolymer-RGDfK conjugates against ovarian cancer

HPMA copolymer-RGDfK (HPMA-RGDfK) conjugates bearing either aminohexylgeldanamycin (AHGDM) or docetaxel (DOC) were synthesized and characterized. In vitro stability and binding were evaluated. Cytotoxicity toward ovarian cancer cells was evaluated and the ability of the conjugates to induce cell death was assessed by combination index analysis. Conjugates bearing AHGDM were more stable and exhibited slower drug release than those bearing DOC. Both conjugates demonstrated the ability to bind to avb3 integrins. In combination, HPMA-RGDfK conjugates demonstrated marked synergism as compared to their non-targeted counterparts and free drug controls. HPMA-RGDfK conjugates bearing AHGDM and DOC induce synergistic cytotoxicity in vitro, suggesting their potential as a promising combination therapy.

Targeting prostate carcinoma by G3-C12 peptide conjugated N-(2-hydroxypropyl)methacrylamide copolymers

Prostate carcinoma is the second leading cause of cancer-related deaths. Increased expression of membrane-bound galectin-3 by prostate carcinoma cell has been found to correlate with more poorly differentiated and increased metastatic potential. In the present study, different amount of galectin-3-binding peptide, G3-C12 (the sequence ANTPCGPYTHDCPVKR), was attached to N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers as targeting moiety. The results of qPCR and competitive binding test indicated that the expression level of galectin-3 in two metastatic prostate carcinoma cell lines (PC-3 and DU145 cells) could be significantly suppressed by the addition of G3-C12-modified HPMA copolymers (PG1 and PG2), demonstrating the high affinity of PG1 and PG2 to galectin-3. Due to the multivalent effects of moieties, the uptake of copolymers was remarkably enhanced with the increasing amount of conjugated G3-C12 peptide. A higher internalization of PG1 and PG2 occurred in PC-3 cells via caveolin- and clathrin-mediated endocytosis, whereas a clathrin-mediated uptake process was involved in DU145 cells. The in vivo biodistribution and pharmacokinetics of nonmodified ((131)I-pHPMA) and G3-C12-modified ((131)I-PG1 and (131)I-PG2) copolymers were estimated on a well-established mice model bearing PC-3 xenografts by (131)I-SPECT-imaging. Higher tumor accumulation of (131)I-PG1 (1.60 ± 0.08% ID/g, p < 0.05) and (131)I-PG2 (1.54 ± 0.06% ID/g, p < 0.05) was observed compared with (131)I-pHPMA (1.19 ± 0.04% ID/g) at 2 h post-intravenous injection. Although the amount of conjugated G3-C12 peptide performed a remarkable in vitro effect on the affinity and internalization of HPMA copolymers to the galectin-3 overexpressed prostate carcinoma cells, the molecular weight and ligand modification all play important roles on their in vivo tumor accumulation.

Comparison of active and passive targeting of doxorubicin for somatostatin receptor 2 positive tumor models by octreotide-modified HPMA copolymer-doxorubicin conjugates

Somatostatin receptor 2 (SSTR2), specifically over-expressed on many tumor cells, is a potential receipt for active targeting in cancer therapy. In the present study, octreotide (Oct), which had high affinity to SSTR2, was attached to N-(2-hydroxypropyl) methacrylamide (HPMA) polymeric system to enhance the antitumor efficiency of the anticancer drug doxorubicin (DOX). Two kinds of cell lines (HepG2 and A549), which overexpress SSTR2, were chosen as cell models. Compared with non-modified conjugates, Oct-modified conjugates exhibited superior cytotoxicity and intracellular uptake on both HepG2 and A549 cell lines. This might be due to the mechanism of receptor-mediated endocytosis. Subsequently, the in vivo biodistribution and antitumor activity evaluations showed that Oct modification significantly improved the tumor accumulation and antitumor efficacy of HPMA copolymer conjugates in SSTR2 over-expressed Kunming mice bearing H22 tumor xenografts. In summary, Oct-modified HPMA polymer-DOX conjugates might be a promising system for the treatment of SSTR2 over-expressed cancers.

Tumor Targeting via Integrin Ligands

Selective and targeted delivery of drugs to tumors is a major challenge for an effective cancer therapy and also to overcome the side-effects associated with current treatments. Overexpression of various receptors on tumor cells is a characteristic structural and biochemical aspect of tumors and distinguishes them from physiologically normal cells. This abnormal feature is therefore suitable for selectively directing anticancer molecules to tumors by using ligands that can preferentially recognize such receptors. Several subtypes of integrin receptors that are crucial for cell adhesion, cell signaling, cell viability, and motility have been shown to have an upregulated expression on cancer cells. Thus, ligands that recognize specific integrin subtypes represent excellent candidates to be conjugated to drugs or drug carrier systems and be targeted to tumors. In this regard, integrins recognizing the RGD cell adhesive sequence have been extensively targeted for tumor-specific drug delivery. Here we review key recent examples on the presentation of RGD-based integrin ligands by means of distinct drug-delivery systems, and discuss the prospects of such therapies to specifically target tumor cells.

Overcoming the stromal barrier for targeted delivery of HPMA copolymers to pancreatic tumors

Delivery of macromolecules to pancreatic cancer is inhibited by a dense extracellular matrix composed of hyaluronic acid, smooth muscle actin and collagen fibers. Hyaluronic acid causes a high intratumoral fluidic pressure which prevents diffusion and penetration into the pancreatic tumor. This study involves the breaking down of hyaluronic acid by treating CAPAN-1 xenograft tumors in athymic nu/nu mice with targeted N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers radiolabeled with (111)In for single photon emission computerized tomography (SPECT) imaging. Two targeting strategies were investigated including αvβ3 integrin and HER2 receptors. HPMA copolymers were targeted to these receptors by conjugating short peptide ligands cRGDfK and KCCYSL to the side chains of the copolymer. Results demonstrate that tumor targeting can be achieved in vivo after treatment with hyaluronidase. This approach shows promise for enhanced delivery of polymer-peptide conjugates to solid tumors.

Synergistic enhancement of cancer therapy using a combination of heat shock protein targeted HPMA copolymer-drug conjugates and gold nanorod induced hyperthermia

In the field of nanomedicine, selective delivery to cancer cells is a common goal, where active targeting strategies are often employed to increase tumor accumulation. In this study, tumor hyperthermia was utilized as a means to increase the active delivery of heat shock protein (HSP) targeted N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-drug conjugates. Following hyperthermia, induced expression of cell surface heat shock protein (HSP) glucose regulated protein 78 kDa (GRP78) was utilized for targeted drug therapy. Conjugates bearing the anticancer agents aminohexylgeldanamycin (AHGDM), docetaxel (DOC), or cisplatin and the GRP78 targeting peptide WDLAWMFRLPVG were synthesized and characterized. Binding to cell surface expressed heat shock protein GRP78 on the surface of human prostate cancer DU145 cells was evaluated. HSP targeted AHGDM and DOC conjugates demonstrated active binding comparable to native targeting peptide. They were then assessed in vitro for the ability to synergistically induce cytotoxicity in combination with moderate hyperthermia (43 °C, 30 min). HSP targeted DOC conjugates exhibited high potency against DU145 cells with an IC₅₀ of 2.4 nM. HSP targeted AHGDM and DOC conjugates demonstrated synergistic effects in combination with hyperthermia with combination index values of 0.65 and 0.45 respectively. Based on these results, HSP targeted DOC conjugates were selected for in vivo evaluation. In DU145 tumor bearing mice, a single treatment of tumor hyperthermia, induced via gold nanorod mediated plasmonic photothermal therapy, and intravenous administration of HSP targeted HPMA copolymer-docetaxel at 10mg/kg resulted in maintained tumor regression for a period of 30 days. These results demonstrate the potential for tumor hyperthermia to increase the delivery of HSP targeted macromolecular chemotherapeutics.

c(RGDfK) decorated micellar drug delivery system for intravesical instilled chemotherapy of superficial bladder cancer

The aim of this work was to develop a targeted drug delivery system with potentials for intravesical instilled chemotherapy of superficial bladder cancer. The amphiphilic diblock copolymer poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) was first conjugated with the cyclic (Arginine-Glycine-Aspartic acid-d-Phenylalanine-Lysine) (c(RGDfK)) and fluorescein isothiocyannate (FITC) via the functional terminal groups of hydrophilic block, and then assembled into micelles. The interaction between micelles and various model cells was well studied by means of confocal laser scanning microscopy and flow cytometry. The c(RGDfK) on the surface of the micelle was confirmed by (1)H NMR analysis and cell affinity with human glioblastoma-astrocytoma cells (U87MG). The cell viability of bladder cancer cells (T-24 cells) after incubation with doxorubicin (DOX) loaded polymeric micelles was evaluated by in vitro cytotoxicity assay. The results revealed that c(RGDfK) modified micelles showed strong affinity to T-24 cells and strong inhibitory effect on the proliferation of T-24 cells when doxorubicin drug was loaded, indicating the high affinity of c(RGDfK) to bladder cancer cells. The c(RGDfK) modified micelles assembled from PCL-b-PEO diblock copolymers developed in this study are of great potentials as nano-scaled drug delivery system for intravesical instilled chemotherapy of superficial bladder cancer.

RGD-Binding Integrins in Prostate Cancer: Expression Patterns and Therapeutic Prospects against Bone Metastasis

Prostate cancer is the third leading cause of male cancer deaths in the developed world. The current lack of highly specific detection methods and efficient therapeutic agents for advanced disease have been identified as problems requiring further research. The integrins play a vital role in the cross-talk between the cell and extracellular matrix, enhancing the growth, migration, invasion and metastasis of cancer cells. Progression and metastasis of prostate adenocarcinoma is strongly associated with changes in integrin expression, notably abnormal expression and activation of the β₃ integrins in tumour cells, which promotes haematogenous spread and tumour growth in bone. As such, influencing integrin cell expression and function using targeted therapeutics represents a potential treatment for bone metastasis, the most common and debilitating complication of advanced prostate cancer. In this review, we highlight the multiple ways in which RGD-binding integrins contribute to prostate cancer progression and metastasis, and identify the rationale for development of multi-integrin antagonists targeting the RGD-binding subfamily as molecularly targeted agents for its treatment.

Polymeric conjugates for drug delivery

The field of polymer therapeutics has evolved over the past decade and has resulted in the development of polymer-drug conjugates with a wide variety of architectures and chemical properties. Whereas traditional non-degradable polymeric carriers such as poly(ethylene glycol) (PEG) and N-(2-hydroxypropyl methacrylamide) (HPMA) copolymers have been translated to use in the clinic, functionalized polymer-drug conjugates are increasingly being utilized to obtain biodegradable, stimuli-sensitive, and targeted systems in an attempt to further enhance localized drug delivery and ease of elimination. In addition, the study of conjugates bearing both therapeutic and diagnostic agents has resulted in multifunctional carriers with the potential to both "see and treat" patients. In this paper, the rational design of polymer-drug conjugates will be discussed followed by a review of different classes of conjugates currently under investigation. The design and chemistry used for the synthesis of various conjugates will be presented with additional comments on their potential applications and current developmental status.

Biological evaluation of RGDfK-gold nanorod conjugates for prostate cancer treatment

Selective delivery of gold nanorods (GNRs) to sites of prostate tumor angiogenesis is potentially advantageous for localized photothermal therapy. Here, we report the cellular uptake and biodistribution of GNRs surface functionalized with the cyclic RGDfK peptide. The GNRs were synthesized to have a surface plasmon resonance (SPR) peak at 800?nm and grafted with a thiolated poly(ethylene glycol) (PEG) corona with or without RGDfK. The binding and uptake of the targeted (RGDfK) and untargeted GNRs were evaluated in DU145 prostate cancer and human umbilical vein endothelial cells (HUVEC) by high-resolution dark field microscopy, inductively coupled plasma mass spectrometry (ICP-MS), and transmission electron microscopy (TEM). The biodistribution of both GNRs was then evaluated in prostate tumor bearing mice. Targeting of the RGDfK surface-modified GNRs was confirmed in vitro due to selective binding and uptake by endothelial cells. Tumor targeting was not observed in vivo, however, due to fast clearance of the RGDfK-GNRs from the blood. Further modifications of the nanoparticle?s surface properties are needed to enhance localization of the targetable system in sites of tumor angiogenesis.

Comparison of active and passive targeting of docetaxel for prostate cancer therapy by HPMA copolymer-RGDfK conjugates

N-(2-Hydroxypropyl)methacrylamide (HPMA) copolymer-docetaxel-RGDfK conjugate was synthesized, characterized, and evaluated in vitro and in vivo in comparison with untargeted low and high molecular weight HPMA copolymer-docetaxel conjugates. The targeted conjugate was designed to have a hydrodynamic diameter below renal threshold to allow elimination post treatment. All conjugates demonstrated the ability to inhibit the growth of DU145 and PC3 human prostate cancer cells and the HUVEC at low nanomolar concentrations. The targeted conjugate showed active binding to α(v)β(3) integrins in both HUVEC and DU145 cells, whereas the untargeted conjugate demonstrated no evidence of specific binding. Efficacy at two concentrations (20 mg/kg and 40 mg/kg) was evaluated in nu/nu mice bearing DU145 tumor xenografts treated with a single dose of conjugates and compared with controls. RGDfK targeted and high molecular weight nontargeted conjugates exhibited the highest antitumor efficacy as evaluated by tumor regression. These results demonstrate that α(v)β(3) integrin targeted polymeric conjugates with improved water solubility, reduced toxicity and ease of elimination post treatment in vivo are promising candidates for prostate cancer therapy.