Design of novel bioconjugates for targeted drug delivery

Steroid and bioactive molecule conjugates: Improving therapeutic approaches in disease management

Conjugates of steroids and other natural bioactive molecules (such as amino acids or carbohydrates) have proven promising compounds with diverse biological effects. This literature review summarises the importance of steroid conjugates in a broad spectrum of therapeutic applications. Steroid conjugates exhibit improved pharmacokinetic properties, improved target specificity, and reduced side effects compared to the parent compounds. This increases their clinical usefulness. Their versatility extends to drug delivery systems, enabling precise modulation of drug release kinetics and bioavailability. Moreover, steroid conjugates are vital in treating inflammatory and neurodegenerative diseases, hormonal disorders, cancer therapy, and combating microbial infections. The review presents the current state of research on steroid conjugates, highlighting the crucial role of steroid conjugates in modern medicine and their potential to revolutionise therapeutic paradigms and improve patient outcomes. Steroid compounds are excellent for developing agents with better bioavailability and are used as drug carriers or hydrogelators.

Hydrophilic biomaterials: From crosslinked and self-assembled hydrogels to polymer-drug conjugates and drug-free macromolecular therapeutics

This "Magnum Opus" accentuates my lifelong belief that the future of science is in the interdisciplinary approach to hypotheses formulation and problem solving. Inspired by the invention of hydrogels and soft contact lenses by my mentors, my six decades of research have continuously proceeded from the synthesis of biocompatible hydrogels to the development of polymer-drug conjugates, then generation of drug-free macromolecular therapeutics (DFMT) and finally to multi-antigen T cell hybridizers (MATCH). This interdisciplinary journey was inspiring; the lifetime feeling that one is a beginner in some aspects of the research is a driving force that keeps the enthusiasm high. Also, I wanted to illustrate that systematic research in one wide area can be a life-time effort without the need to jump to areas that are temporarily en-vogue. In addition to generating general scientific knowledge, hydrogels from my laboratory have been transferred to the clinic, polymer-drug conjugates to clinical trials, and drug-free macromolecular systems have an excellent potential for personalizing patient therapies. There is a limit to life but no limit to imagination. I anticipate that systematic basic research will contribute to the expansion of our knowledge and create a foundation for the design of new paradigms based on the comprehension of mechanisms of physiological processes. The emerging novel platform technologies in biomaterial-based devices and implants as well as in personalized nanomedicines will ultimately impact clinical practice.

A Comprehensive Review on Steroidal Bioconjugates as Promising Leads in Drug Discovery

Ever increasing unmet medical requirements of the human race and the continuous fight for survival against variety of diseases give birth to novel molecules through research. As diseases evolve, different strategies are employed to counter the new challenges and to discover safer, more effective, and target-specific therapeutic agents. Among several novel approaches, bioconjugation, in which two chemical moieties are joined together to achieve noticeable results, has emerged as a simple and convenient technique for a medicinal chemist to obtain potent molecules. The steroid system has been extensively used as a privileged scaffold gifted with significantly diversified medicinal properties in the drug discovery and development process. Steroidal molecules are preferred for their rigidness and good ability to penetrate biological membranes. Slight alteration in the basic ring structure results in the formation of steroidal derivatives with a wide range of therapeutic activities. Steroids are not only active as such, conjugating them with various biologically active moieties results in increased lipophilicity, stability, and target specificity with decreased adverse effects. Thus, the steroid nucleus prominently behaves as a biological carrier for small molecules. The steroid bioconjugates offer several advantages such as synergistic activity with fewer side effects due to reduced dose and selective therapy. The steroidal bioconjugates have been widely explored for their usefulness against various disorders and have shown significant utility as anticancer, anti-inflammatory, anticoagulant, antimicrobial, insecticidal/pesticidal, antioxidant, and antiviral agents along with several other miscellaneous activities. This work provides a comprehensive review on the therapeutic progression of steroidal bioconjugates as medicinally active molecules. The review covers potential biological applications of steroidal bioconjugates and would benefit the wider scientific community in their drug discovery endeavors.

Tailored therapeutics based on 1,2,3-1H-triazoles: a mini review

Contemporary drug discovery approaches rely on library synthesis coupled with combinatorial methods and high-throughput screening to identify leads. However, due to the multitude of components involved, a majority of optimization techniques face persistent challenges related to the efficiency of synthetic processes and the purity of compound libraries. These methods have recently found an upgradation as fragment-based approaches for target-guided synthesis of lead molecules with active involvement of their biological target. The click chemistry approach serves as a promising tool for tailoring the therapeutically relevant biomolecules of interest, improving their bioavailability and bioactivity and redirecting them as efficacious drugs. 1,2,3-1H-Triazole nucleus, being a planar and biologically acceptable scaffold, plays a crucial role in the design of biomolecular mimetics and tailor-made molecules with therapeutic relevance. This versatile scaffold also forms an integral part of the current fragment-based approaches for drug design, kinetic target guided synthesis and bioorthogonal methodologies.

Stimulus-responsive nanoscale delivery systems triggered by the enzymes in the tumor microenvironment

The tumor microenvironment is the cellular environment that is also described as the "soil" for supporting tumor growth, proliferation, invasion and metastasis, as well as protecting tumor cells from immunological recognition. Notably, tumor cells can grow much faster than other normal organs and invade surrounding tissues more easily, which results in abnormal expression of enzymes in the tumor microenvironment, including matrix metalloproteinases, cathepsins, phospholipases, oxidoreductases, etc. In opposite, due to the high selectivity and catalytic activity, these enzymes can promote nanoparticles to recognize tumor tissues more accurately, and the more accumulation of drugs at primal tumor sites will enhance therapeutic efficacy with lower systemic toxicity. Therefore, one promising antitumor strategy is to design stimulus-responsive nanoscale delivery systems triggered by the enzymes with the support of various nanocarriers, such as liposomes, micelles and inorganic nanoparticles, etc. In this review, numerous facts were cited to summarize and discuss the typical types of enzyme-stimulus responsive nanoscale delivery systems. More importantly, we also focused on their recent advancements in antitumor therapy, and offered the direction for further studies.

HPMA-Copolymer Nanocarrier Targets Tumor-Associated Macrophages in Primary and Metastatic Breast Cancer

Polymeric nanocarriers such as N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers deliver drugs to solid tumors and avoid the systemic toxicity of conventional chemotherapy. Because HPMA copolymers can target sites of inflammation and accumulate within innate immune cells, we hypothesized that HPMA copolymers could target tumor-associated macrophages (TAM) in both primary and metastatic tumor microenvironments. We verified this hypothesis, first in preliminary experiments with isolated bone marrow macrophage cultures in vitro and subsequently in a spontaneously metastatic murine breast cancer model generated from a well-established, cytogenetically characterized 4T1 breast cancer cell line. Using our standardized experimental conditions, we detected primary orthotopic tumor growth at 7 days and metastatic tumors at 28 days after orthotopic transplantation of 4T1 cells into the mammary fat pad. We investigated the uptake of HPMA copolymer conjugated with Alexa Fluor 647 and folic acid (P-Alexa647-FA) and HPMA copolymer conjugated with IRDye 800CW (P-IRDye), following their retroorbital injection into the primary and metastatic tumor-bearing mice. A significant uptake of P-IRDye was observed at all primary and metastatic tumor sites in these mice, and the P-Alexa647-FA signal was found specifically within CD11b⁺ TAMs costained with pan-macrophage marker CD68. These findings demonstrate, for the first time, a novel capacity of a P-Alexa647-FA conjugate to colocalize to CD11b⁺CD68⁺ TAMs in both primary and metastatic breast tumors. This underscores the potential of this HPMA nanocarrier to deliver functional therapeutics that specifically target tumor-promoting macrophage activation and/or polarization during tumor development. Mol Cancer Ther; 16(12); 2701-10. ©2017 AACR.

Peptide-Targeted Polymer Cancerostatics

A tumor-targeting drug delivery system consists of a tumor recognition moiety and a directly linked cytotoxic agent or an agent attached to a water-soluble synthetic polymer carrier through a suitable linker. Conjugation of a drug with a polymer carrier can change its solubility, toxicity, biodistribution, blood clearance and therapeutic specificity. Increased therapeutic specificity of a polymer drug can be achieved by the attachment of a targeting moiety (e.g. a lectin, protein, antibody, or peptide) that specifically interacts with receptors on the target cells. A large number of tumor-specific peptides were described in recent years. After a short introduction, some important examples of peptide-targeted conjugates will be described and discussed.

Synthesis and Degradation Characteristics of Polyurethanes Containing AZO Derivatives of 5-Amino Salicylic Acid

New types of biodegradable and pH sensitive polyurethanes containing azo derivatives of 5-aminosalicylic acid (5-ASA) were synthesized by condensation of hexamethylene diisocyanate (HDI) with 4, 4-dihydroxy azobenzene-3, 3-dicarboxylic acid (AZO I) or 4, 4-dihydroxy 3-formyl azobenzene-3-carboxylic acid (AZO II). They contained both hydrolysable urethane bonds and enzymatically degradable azo-aromatic links. Degradation of polyurethanes (PU-AZO I and PU-AZO II) in phosphate buffer solutions was pH dependant. In basic conditions AZO I or AZO II was rapidly released over 48h. Incubation of PU-AZO I and PU-AZO II with rat cecal contents at 37°C gradually released 5-ASA, and the amount of drug released was 85% and 78% in 48h respectively. These polyurethane derivatives are being investigated for colon-specific drug delivery systems for treating inflammatory bowel disease based on the pH-dependant degradation of the polymer.

Drug-conjugated PLA-PEG-PLA copolymers: a novel approach for controlled delivery of hydrophilic drugs by micelle formation

A conjugate of the antihypertensive drug, lisinopril, with triblock poly(lactic acid)-poly(ethylene glycol)-poly(lactic acid) (PLA-PEG-PLA) copolymer was synthesized by the reaction of PLA-PEG-PLA copolymer with lisinopril in the presence of dicyclohexylcarbodiimide and dimethylaminopyridine. The conjugated copolymer was characterized in vitro by hydrogen nuclear magnetic resonance (HNMR), Fourier transform infrared (FTIR), differential scanning calorimetry (DSC) and gel permeation chromatography (GPC) techniques. Then, the lisinopril conjugated PLA-PEG-PLA were self-assembled into micelles in aqueous solution. The resulting micelles were characterized further by various techniques such as dynamic light scattering (DLS) and atomic force microscopy (AFM). The results revealed that the micelles formed by the lisinopril-conjugated PLA-PEG-PLA have spherical structure with the average size of 162 nm. The release behavior of conjugated copolymer, micelles and micelles physically loaded by lisinopril were compared in different media. In vitro release study showed that in contrast to physically loaded micelles, the release rate of micelles consisted of the conjugated copolymer was dependent on pH of media where it was higher at lower pH compared to the neutral medium. Another feature of the conjugated micelles was their more sustained release profile compared to the lisinopril-conjugated copolymer and physically loaded micelles.

Photodynamic therapy in colorectal cancer treatment--The state of the art in preclinical research

BACKGROUND

Photodynamic therapy (PDT) is used in many different oncologic fields. Also in gastroenterology, where have been a few attempts to treat both the premalignant lesion and advanced colorectal cancer (CRC). This review aims to give a general overview of preclinical photodynamic studies related to CRC cells and animal studies of photodynamic effects related to CRC treatment to emphasize their potential in study of PDT mechanism, safety and efficiency to translate these results into clinical benefit in CRC treatment.

MATERIALS AND METHOD

Literature on in vitro preclinical photodynamic studies related to CRC cells and animal studies of photodynamic effects related to CRC treatment with the fallowing medical subject headings search terms: colorectal cancer, photodynamic therapy, photosensitizer(s), in vitro, cell culture(s), in vivo, animal experiment(s). The articles were selected by their relevance to the topic.

RESULTS

The majority of preclinical studies concerning possibility of PDT application in colon and rectal cancer is focused on phototoxic action of photosensitizers toward cultured colorectal tumor cells in vitro. The purposes of animal experiments are usually elucidation of mechanisms of observed photodynamic effects in scale of organism, estimation of PDT safety and efficiency and translation of these results into clinical benefit.

CONCLUDING REMARKS

In vitro photodynamic studies and animal experiments can be useful for studies of mechanisms and efficiency of photodynamic method as a start point on PDT clinical research. The primary disadvantage of in vitro experiments is a risk of over-interpretation of their results during extrapolation to the entire CRC.

Macromolecular therapeutics

This review covers water-soluble polymer-drug conjugates and macromolecules that possess biological activity without attached low molecular weight drugs. The main design principles of traditional and backbone degradable polymer-drug conjugates as well as the development of a new paradigm in nanomedicines - (low molecular weight) drug-free macromolecular therapeutics are discussed. To address the biological features of cancer, macromolecular therapeutics directed to stem/progenitor cells and the tumor microenvironment are deliberated. Finally, the future perspectives of the field are briefly debated.

Soluble polymer conjugates for drug delivery

The use of water-soluble polymeric conjugates as drug carriers offers several possible advantages. These advantages include: (1) improved drug pharmacokinetics; (2) decreased toxicity to healthy organs; (3) possible facilitation of accumulation and preferential uptake by targeted cells; (4) programmed profile of drug release. In this review, we will consider the main types of useful polymeric conjugates and their role and effectiveness as carriers in drug delivery systems.:

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.

Combination cytotoxicity of backbone degradable HPMA copolymer gemcitabine and platinum conjugates toward human ovarian carcinoma cells

Multiblock, backbone degradable HPMA copolymer-drug conjugates containing gemcitabine and DACH platinum (mP-GEM and mP-DACH Pt), respectively were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization and subsequent chain extension by click chemistry. Using combination index analysis, the cytotoxicities of the two multiblock conjugates, as single agent and in combination, were evaluated in vitro in A2780 human ovarian cancer cells, with free drugs as controls. The greatest synergistic cytotoxic effect was observed when A2780 cells were sequentially exposed to mP-GEM for 24h and mP-DACH Pt for 48h. In addition, mechanistic studies support the rationale of the synergy between mP-GEM and mP-DACH Pt: mP-GEM pretreatment was able to enhance the platinum-DNA adduct accumulation and inhibit cell proliferation to a higher extent than single mP-DACH Pt treatment. These observations are useful for the development of combination macromolecular therapeutics for ovarian cancer based on the second-generation backbone degradable HPMA copolymers.

Passive and active hepatoma tumor targeting of new N-(2-hydroxypropyl)methacrylamide copolymer conjugates: synthesis, characterization, and evaluation in vitro and in vivo

Human hepatocellular carcinoma (HCC) is one of the major causes of death worldwide. To investigate the relative importance of active and passive targeting strategies, the synthesis, characterization, in vitro uptake, and in vivo biodistribution of specific sulfapyridine HPMA (HPMA: N-(2-hydroxypropyl methacrylamide)) copolymer (sulfapyridine: SPD) conjugates, nonspecific HPMA copolymer conjugates, and DTPA are described in this study. The poly(HPMA)-SPD-DTPA (DTPA: diethylenetriaminepentaacetic acid), poly(HPMA)-DTPA, and DTPA conjugates were radiolabeled with the radionuclide (99m)Tc and tested for uptake by cultured H22 cells. The cellular accumulation of poly(HPMA)-SPD-DTPA-(99m)Tc complex was found to be time-dependent. The poly(HPMA)-SPD-DTPA-(99m)Tc tracer exhibited rapid uptake kinetics in cell culture with a t(1/2) of ~5 min. The uptake of poly(HPMA)-SPD-DTPA-(99m)Tc was significantly higher than that of poly(HPMA)-DTPA-(99m)Tc, indicating that the uptake of the poly(HPMA)-SPD-DTPA-(99m)T was active binding. The uptake of poly(HPMA)-DTPA-(99m)Tc was significantly higher than that of DTPA-(99m)Tc, suggesting that the uptake of the poly(HPMA)-DTPA-(99m)T was passive binding. Twenty-four hour necropsy data in the hepatocellular carcinoma tumor model showed significantly higher (p < 0.001) tumor localization for poly(HPMA)-SPD-DTPA-(99m)Tc (4.98 ± 0.48%ID/g [percentage injected dose per gram tissue]) compared with poly(HPMA)-DTPA-(99m)Tc (2.69 ± 0.15% ID/g) and DTPA-(99m)Tc (0.83 ± 0.03%ID/g). Moreover, higher T/B for poly(HPMA)-SPD-DTPA-(99m)Tc indicated reduced extravazation of the targeted polymeric conjugates in normal tissues. Specific molecular targeting and nonspecific vascular permeability are both significant in the relative tumor localization of poly(HPMA)-SPD-DTPA-(99m)Tc. Extravascular leak in nonspecific organs appears to be a major factor in reducing the T/B for the sulfapyridine molecules. Thus, the poly(HPMA)-SPD-DTPA is expected to be used as the potential macromolecular targeting carrier for hepatoma carcinoma in mice.

Hyaluronic acid-based nanogel-drug conjugates with enhanced anticancer activity designed for the targeting of CD44-positive and drug-resistant tumors

Many drug-resistant tumors and cancer stem cells (CSC) express elevated levels of CD44 receptor, a cellular glycoprotein binding hyaluronic acid (HA). Here, we report the synthesis of nanogel-drug conjugates based on membranotropic cholesteryl-HA (CHA) for efficient targeting and suppression of drug-resistant tumors. These conjugates significantly increased the bioavailability of poorly soluble drugs with previously reported activity against CSC, such as etoposide, salinomycin, and curcumin. The small nanogel particles (diameter 20-40 nm) with a hydrophobic core and high drug loads (up to 20%) formed after ultrasonication and demonstrated a sustained drug release following the hydrolysis of biodegradable ester linkage. Importantly, CHA-drug nanogels demonstrated 2-7 times higher cytotoxicity in CD44-expressing drug-resistant human breast and pancreatic adenocarcinoma cells compared to that of free drugs and nonmodified HA-drug conjugates. These nanogels were efficiently internalized via CD44 receptor-mediated endocytosis and simultaneous interaction with the cancer cell membrane. Anchoring by cholesterol moieties in the cellular membrane after nanogel unfolding evidently caused more efficient drug accumulation in cancer cells compared to that in nonmodified HA-drug conjugates. CHA-drug nanogels were able to penetrate multicellular cancer spheroids and displayed a higher cytotoxic effect in the system modeling tumor environment than both free drugs and HA-drug conjugates. In conclusion, the proposed design of nanogel-drug conjugates allowed us to significantly enhance drug bioavailability, cancer cell targeting, and the treatment efficacy against drug-resistant cancer cells and multicellular spheroids.

Synthesis, characterization, and in vivo evaluation of tumor targeting N-(2-hydroxypropyl)methacrylamide copolymer conjugates containing sulfamethazine groups

Recent studies have identified that sulfadiazine derivatives can be concentrated in the hepatocellular carcinoma tissue. Herein, we report the synthesis, characterization, and evaluation of a novel sulfamethazine N-(2-hydroxypropyl)methacrylamide copolymer conjugates for tumor targeting. N-(3-Aminopropyl)methacrylamide-diethylenetriaminepentaacetic acid monomer 1, methacryloyl-sulfamethazine monomer 2, poly( N-(2-hydroxypropyl)methacrylamide)-sulfamethazine-diethylenetriaminepentaacetic acid conjugate 4, and poly( N-(2-hydroxypropyl)methacrylamide)-sulfamethazine-diethylenetriaminepentaacetic acid-99mTc were successfully synthesized and characterized. Poly( N-(2-hydroxypropyl)methacrylamide)-diethylenetriaminepentaacetic acid conjugate 3, diethylenetriaminepentaacetic acid-99mTc, and poly( N-(2-hydroxypropyl)methacrylamide)-diethylenetriaminepentaacetic acid-99mTc were also synthesized and characterized for comparison (99mTc: metastable technetium-99). A 24-h necropsy data in the hepatocellular carcinoma tumor model showed significantly higher ( p < 0.001) tumor localization for poly( N-(2-hydroxypropyl)methacrylamide)-sulfamethazine-diethylenetriaminepentaacetic acid-99mTc (4.82%ID/g ± 0.46%ID/g (percentage injected dose per gram tissue)) compared with poly( N-(2-hydroxypropyl)methacrylamide)-diethylenetriaminepentaacetic acid-99mTc (2.69%ID/g ± 0.15%ID/g) and diethylenetriaminepentaacetic acid-99mTc (0.83%ID/g ± 0.03%ID/g). Moreover, higher tumor/organ ratios for poly( N-(2-hydroxypropyl)methacrylamide)-sulfamethazine-diethylenetriaminepentaacetic acid-99mTc indicated reduced extravasation of the targeted polymeric conjugates in normal tissues. Thus, the poly( N-(2-hydroxypropyl)methacrylamide)-sulfamethazine-diethylenetriaminepentaacetic acid can potentially be used as a macromolecular targeting carrier for hepatocellular carcinoma in mice.

A glycobiology review: carbohydrates, lectins and implications in cancer therapeutics

This review is intended for general readers who would like a basic foundation in carbohydrate structure and function, lectin biology, and the implications of glycobiology in human health and disease, particularly in cancer therapeutics. These topics are among the hundreds included in the field of glycobiology and are treated here because they form the cornerstone of glycobiology or the focus of many advances in this rapidly expanding field.

Radiosynthesis, biodistribution and micro-SPECT imaging study of dendrimer-avidin conjugate

Partially acetylated generation five polyamidoamine (PAMAM) dendrimer (G5-Ac) was reacted with biotin and 2-(p-isothiocyanatobenzyl)-6-methyl-diethylenetria minepentaacetic acid (1B4M-DTPA), respectively to form the complex Bt-G5-Ac-1B4M which was further conjugated with avidin to give the conjugate Av-G5-Ac-1B4M. Then both of the conjugates were radiolabeled with technetium-99m ((99m)Tc), respectively. Their in vitro cellular uptake study shows that the conjugate of Av-G5-Ac-1B4M-(99m)Tc exhibits much higher cellular uptake in HeLa cells than that of Bt-G5-Ac-1B4M-(99m)Tc. Accordingly the following evaluation such as in vitro/in vivo stability, biodistribution and micro-SPECT imaging was observed only for the conjugate of Av-G5-Ac-1B4M-(99m)Tc.

Insertion of a lysosomal enzyme cleavage site into the sequence of a radiolabeled neuropeptide influences cell trafficking in vitro and in vivo

Radiolabeled neuropeptides are widely explored for targeting tumours for either imaging or radiotherapeutic purposes. After binding to their receptors, these peptides are rapidly internalized into lysosomes, where they are degraded by proteolytic enzymes, such as cathepsins. The aim of this study was to investigate the effect of the inclusion of specific cleavage sites for cathepsin B into the peptide sequence. The cleavage site, GFLG, together with a series of dipeptides for pharmacokinetic modification of radiometabolites, were, therefore, inserted into a peptide that binds to the gastrin/CCK2 receptor. The receptor binding of the peptides was explored in AR42J cells, rates of internalization, and externalization of the radionuclide were measured and the nature of the radiometabolites explored. The effects of the modifications on biodistribution in tumor-bearing mice was explored by high-resolution single-photon emission computed tomography imaging. Differences in rates of externalization from tumor cells in vitro and in the rates of washout from tumor and kidney in vivo were observed. These results indicate that insertion of an enzymatic cleavage site, such as that for cathepsin B, into a neuropeptide appears to have an influence on the intracellular processing, which results in a change in the rate of egress of radioactivity from target and nontarget tissues.

Therapeutic peptides for cancer therapy. Part II - cell cycle inhibitory peptides and apoptosis-inducing peptides

BACKGROUND

Therapeutic peptides have great potential as anticancer agents owing to their ease of rational design and target specificity. However, their utility in vivo is limited by low stability and poor tumor penetration.

OBJECTIVE

The authors review the development of peptide inhibitors with potential for cancer therapy. Peptides that arrest the cell cycle by mimicking CDK inhibitors or induce apoptosis directly are discussed.

METHODS

The authors searched Medline for articles concerning the development of therapeutic peptides and their delivery.

RESULTS/CONCLUSION

Inhibition of cancer cell proliferation directly using peptides that arrest the cell cycle or induce apoptosis is a promising strategy. Peptides can be designed that interact very specifically with cyclins and/or cyclin-dependent kinases and with members of apoptotic cascades. Use of these peptides is not limited by their design, as a rational approach to peptide design is much less challenging than the design of small molecule inhibitors of specific protein-protein interactions. However, the limitations of peptide therapy lie in the poor pharmacokinetic properties of these large, often charged molecules. Therefore, overcoming the drug delivery hurdles could open the door for effective peptide therapy, thus making an entirely new class of molecules useful as anticancer drugs.

Combination chemotherapy and photodynamic therapy with fab' fragment targeted HPMA copolymer conjugates in human ovarian carcinoma cells

The biological activities of sequential combinations of anticancer drugs, SOS thiophene (SOS) and mesochlorin e₆ monoethylenediamine (Mce₆), in the form of free drugs, nontargeted N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer−drug conjugates, P-GFLG-Mce₆ and P-GFLG-SOS (P is the HPMA copolymer backbone and GFLG is the glycylphenylalanylleucylglycine spacer), and Fab′-targeted HPMA copolymer−drug conjugates, P-(GFLG-Mce₆)-Fab′ and P-(GFLG-SOS)-Fab′ (Fab′ from OV-TL16 antibodies complementary to CD47), were evaluated against human ovarian carcinoma OVCAR-3 cells. Mce₆, SOS, P-GFLG-Mce₆, P-GFLG-SOS, P-(GFLG-Mce₆)-Fab′, and P-(GFLG-SOS)-Fab′, when used as single agents or in binary combination, exhibited cytotoxic activities against OVCAR-3 cells, as determined using a modified MTT assay. The binding and internalization of P-(GFLG-Mce₆)-Fab′ and P-(GFLG-SOS)-Fab′ by OVCAR-3 cells were visualized by confocal microscopy and flow cytometry. The results confirmed an enhanced biorecognition by OVCAR-3 cells of Fab′-targeted HPMA copolymer conjugates over nontargeted conjugates. The median-effect analysis and the determination of the combination index (CI) were used to describe the drug interaction and quantify the synergism, antagonism, or additivity in anticancer effects. The sequential combinations of SOS+Mce₆ and P-GFLG-SOS+P-GFLG-Mce₆ displayed very strong synergism to synergism in the entire range of cell inhibition levels (f_a = 0.5 − 0.95). The P-(GFLG-SOS)-Fab′+P-(GFLG-Mce₆)-Fab′ exhibited a strong synergism for f_a values up to about 0.85, but showed synergistic effect and nearly additive effect at f_a = 0.9 and 0.95, respectively. These observations support the continuation of in vivo investigations of these conjugates for the treatment of ovarian cancer.

Chemical modification of therapeutic drugs or drug vector systems to achieve targeted therapy: looking for the grail

Most therapeutic drugs distribute to the whole body, which results in general toxicity and poor acceptance of the treatments by patients. The targeted delivery of chemotherapeutics to defined cells, either stromal or cancer cells in cancer lesions, or defined inflammatory cells in immunological disorders, is one of the main challenges and a very active field of research in the development of treatment strategies to minimize side-effects of drugs. Disease-associated cells express molecules, including proteases, receptors, or adhesion molecules, that are different or differently expressed than their normal counterparts. Therefore one goal in the field of targeted therapies is to develop chemically derivatized drugs or drug vectors able to target defined cells via specific recognition mechanisms and also able to overcome biological barriers. This article will review the approaches which have been explored to achieve these goals and will discuss in more detail three examples (i) the use of nanostructures to take advantage of increased vascular permeability in some human diseases, (ii) the targeting of therapeutic drugs to an organ, the brain, protected against foreign molecules by the blood-brain barrier, and (iii) the use of the folate receptor to target either tumor cells or activated macrophages.

A novel polymer–paclitaxel conjugate based on amphiphilic triblock copolymer

A novel amphiphilic polymer-paclitaxel conjugate P(LGG-paclitaxel)-PEG-P(LGG-paclitaxel) has been prepared. It was derived from its parent polymer P(LGG)-PEG-P(LGG), poly{(lactic acid)-co-[(glycolic acid)-alt-(l-glutamic acid)]}-block-poly(ethylene glycol)-block-poly{(lactic acid)-co-[(glycolic acid)-alt-(l-glutamic acid)]}, which was prepared by ring-opening copolymerization of l-lactide (LLA) with (3s)-benzoxylcarbonylethyl-morpholine-2,5-dione (BEMD) in the presence of dihydroxyl PEG with molecular weight of 4600 as a macroinitiator using stannous octoate (Sn(Oct)(2)) as catalyst, and by subsequent catalytic hydrogenation. It could self-assemble into micelles in an aqueous system with P(LGG-paclitaxel) block in the core and PEG in the shell. ESEM and DLS analysis of the micelles revealed a homogeneous spherical morphology and a unimodal size distribution. In vitro release of paclitaxel from the conjugate micelles showed that its release rate depended on pH value and was higher at lower pH than in neutral condition. In vitro antitumor activity of the paclitaxel conjugate against rat brain glioma C6 cells was evaluated by MTT method. The results showed that the paclitaxel can be released from the conjugate without losing cytotoxicity.

Polycefin, a new prototype of a multifunctional nanoconjugate based on poly(beta-L-malic acid) for drug delivery

A new prototype of nanoconjugate, Polycefin, was synthesized for targeted delivery of antisense oligonucleotides and monoclonal antibodies to brain tumors. The macromolecular carrier contains: 1. biodegradable, nonimmunogenic, nontoxic beta-poly(L-malic acid) of microbial origin; 2. Morpholino antisense oligonucleotides targeting laminin alpha4 and beta1 chains of laminin-8, which is specifically overexpressed in glial brain tumors; 3. monoclonal anti-transferrin receptor antibody for specific tissue targeting; 4. oligonucleotide releasing disulfide units; 5. L-valine containing, pH-sensitive membrane disrupting unit(s), 6. protective poly(ethylene glycol); 7. a fluorescent dye (optional). Highly purified modules were conjugated directly with N-hydroxysuccinimidyl ester-activated beta-poly(L-malic acid) at pendant carboxyl groups or at thiol containing spacers via thioether and disulfide bonds. Products were chemically validated by physical, chemical, and functional tests. In vitro experiments using two human glioma cell lines U87MG and T98G demonstrated that Polycefin was delivered into the tumor cells by a receptor-mediated endocytosis mechanism and was able to inhibit the synthesis of laminin-8 alpha4 and beta1 chains at the same time. Inhibition of laminin-8 expression was in agreement with the designed endosomal membrane disruption and drug releasing activity. In vivo imaging showed the accumulation of intravenously injected Polycefin in brain tumor tissue via the antibody-targeted transferrin receptor-mediated endosomal pathway in addition to a less efficient mechanism known for high molecular mass biopolymers as enhanced permeability and retention effect. Polycefin was nontoxic to normal and tumor astrocytes in a wide range of concentrations, accumulated in brain tumor, and could be used for specific targeting of several biomarkers simultaneously.

Polymer-peptide conjugates for angiogenesis targeted tumor radiotherapy

INTRODUCTION

New methods of delivering radiotherapy to sites of occult or disseminated cancer are needed to control the disease and address the failure of conventional therapy. Because tumor cells rely on angiogenesis for survival, we assessed the effectiveness of beta-emitter radiotherapy delivered by polymer-peptide conjugates that target tumor neovasculature. This molecularly targeted radiation is intended to damage both the endothelial bed and surrounding neoplastic cells.

METHODS

N-(2-Hydroxypropyl) methacrylamide (HPMA), a biocompatible and water-soluble copolymer, was derivatized to incorporate side chains for (99m)Tc and (90)Y chelation and was further conjugated to a alpha(V)beta(3) integrin-targeting peptide (RGD4C). The HPMA copolymer-RGD4C conjugate was characterized by its side-chain contents, in vitro endothelial cell adhesion assay and its biodistribution and antitumor effectiveness in a SCID mouse xenograft model of human prostate carcinoma.

RESULTS

The conjugate contained about 16 RGD4C moieties per polymer backbone. Tumor accumulation significantly increased (P < .01) over time from 1.05 +/- 0.03 % injected dose (%ID)/g tissue at 1 h to 4.32 +/-0.32% at 72 h. The activity in major normal tissues significantly decreased (P < .05) during that period. At 21 days, the control tumors increased 442% in volume from baseline. In contrast, a 7% and a 63% decrease of tumor volume were observed for the 100- and 250-microCi (90)Y treatment groups, respectively. Histopathological examination revealed increased apoptosis in the treated tumors with no acute signs of radiation-induced toxicity to other organs.

CONCLUSION

This copolymer-peptide conjugate targets tumor angiogenic vessels and delivers sufficient radiotherapy to arrest tumor growth.