Poly(L-glutamic acid)-paclitaxel conjugate is a potent enhancer of tumor radiocurability

Contrasting Properties of Polymeric Nanocarriers for MRI-Guided Drug Delivery

Poor pharmacokinetics and low aqueous solubility combined with rapid clearance from the circulation of drugs result in their limited effectiveness and generally high therapeutic doses. The use of nanocarriers for drug delivery can prevent the rapid degradation of the drug, leading to its increased half-life. It can also improve the solubility and stability of drugs, advance their distribution and targeting, ensure a sustained release, and reduce drug resistance by delivering multiple therapeutic agents simultaneously. Furthermore, nanotechnology enables the combination of therapeutics with biomedical imaging agents and other treatment modalities to overcome the challenges of disease diagnosis and therapy. Such an approach is referred to as "theranostics" and aims to offer a more patient-specific approach through the observation of the distribution of contrast agents that are linked to therapeutics. The purpose of this paper is to present the recent scientific reports on polymeric nanocarriers for MRI-guided drug delivery. Polymeric nanocarriers are a very broad and versatile group of materials for drug delivery, providing high loading capacities, improved pharmacokinetics, and biocompatibility. The main focus was on the contrasting properties of proposed polymeric nanocarriers, which can be categorized into three main groups: polymeric nanocarriers (1) with relaxation-type contrast agents, (2) with chemical exchange saturation transfer (CEST) properties, and (3) with direct detection contrast agents based on fluorinated compounds. The importance of this aspect tends to be downplayed, despite its being essential for the successful design of applicable theranostic nanocarriers for image-guided drug delivery. If available, cytotoxicity and therapeutic effects were also summarized.

Nanoparticles for radiooncology: Mission, vision, challenges

Cancer is one of the leading non-communicable diseases with highest mortality rates worldwide. About half of all cancer patients receive radiation treatment in the course of their disease. However, treatment outcome and curative potential of radiotherapy is often impeded by genetically and/or environmentally driven mechanisms of tumor radioresistance and normal tissue radiotoxicity. While nanomedicine-based tools for imaging, dosimetry and treatment are potential keys to the improvement of therapeutic efficacy and reducing side effects, radiotherapy is an established technique to eradicate the tumor cells. In order to progress the introduction of nanoparticles in radiooncology, due to the highly interdisciplinary nature, expertise in chemistry, radiobiology and translational research is needed. In this report recent insights and promising policies to design nanotechnology-based therapeutics for tumor radiosensitization will be discussed. An attempt is made to cover the entire field from preclinical development to clinical studies. Hence, this report illustrates (1) the radio- and tumor-biological rationales for combining nanostructures with radiotherapy, (2) tumor-site targeting strategies and mechanisms of cellular uptake, (3) biological response hypotheses for new nanomaterials of interest, and (4) challenges to translate the research findings into clinical trials.

Synthetic nanoparticles for delivery of radioisotopes and radiosensitizers in cancer therapy

Radiotherapy has been, and will continue to be, a critical modality to treat cancer. Since the discovery of radiation-induced cytotoxicity in the late 19th century, both external and internal radiation sources have provided tremendous benefits to extend the life of cancer patients. Despite the dramatic improvement of radiation techniques, however, one challenge persists to limit the anti-tumor efficacy of radiotherapy, which is to maximize the deposited dose in tumor while sparing the rest of the healthy vital organs. Nanomedicine has stepped into the spotlight of cancer diagnosis and therapy during the past decades. Nanoparticles can potentiate radiotherapy by specifically delivering radionuclides or radiosensitizers into tumors, therefore enhancing the efficacy while alleviating the toxicity of radiotherapy. This paper reviews recent advances in synthetic nanoparticles for radiotherapy and radiosensitization, with a focus on the enhancement of in vivo anti-tumor activities. We also provide a brief discussion on radiation-associated toxicities as this is an area that, up to date, has been largely missing in the literature and should be closely examined in future studies involving nanoparticle-mediated radiosensitization.

Chemically enhanced radiotherapy: visions for the future

Radiotherapy (RT) is an important part of cancer management, with more than a third of all cancer cures being attributable to RT. Despite the advances in RT over the past century, the overall outcomes in a majority of malignancies are still unsatisfactory. There has been a constant endeavor to enhance the outcome of RT, and this has been in the form of altered fractionation, oxymimetic radiosensitizers, the use of concurrent chemotherapy, anti-angiogenic therapy and anti-growth factor receptor targeted therapies. This article presents a vision for the future, with emphasis upon emerging prospects which could enhance RT outcomes. Positive speculations regarding the use of immunological aspects, the use of nanoscale technology and the adoption of metronomic concurrent chemotherapy have been presented. Also, the potential with the use of low dose hyperradiosensitivity in enhancing chemotherapy outcomes too has been discussed. In this era of evidence based clinical practise, there exists a strong obsession towards the 'present' with 'contempt towards the future'. Accepting the shortcomings of the existing modalities, there must be a strong zeal towards discovering better methodologies to enhance radiotherapeutic outcomes for the sake of a better future.

Macromolecular nanotheranostics for multimodal anticancer therapy

Macromolecular carrier materials based on N-(2-hydroxypropyl)methacrylamide (HPMA) are prototypic and well-characterized drug delivery systems that have been extensively evaluated in the past two decades, both at the preclinical and at the clinical level. Using several different imaging agents and techniques, HPMA copolymers have been shown to circulate for prolonged periods of time, and to accumulate in tumors both effectively and selectively by means of the Enhanced Permeability and Retention (EPR) effect. Because of this, HPMA-based macromolecular nanotheranostics, i.e. formulations containing both drug and imaging agents within a single formulation, have been shown to be highly effective in inducing tumor growth inhibition in animal models. In patients, however, as essentially all other tumor-targeted nanomedicines, they are generally only able to improve the therapeutic index of the attached active agent by lowering its toxicity, and they fail to improve the efficacy of the intervention. Bearing this in mind, we have recently reasoned that because of their biocompatibility and their beneficial biodistribution, nanomedicine formulations might be highly suitable systems for combination therapies. In the present manuscript, we briefly summarize several exemplary efforts undertaken in this regard in our labs in the past couple of years, and we show that long-circulating and passively tumor-targeted macromolecular nanotheranostics can be used to improve the efficacy of radiochemotherapy and of chemotherapy combinations.

Peptides: important tools for the treatment of central nervous system disorders

This review shows some classical applications of peptides and suggests there is great promise for the treatment of various central nervous system diseases. Actually, peptides are considered the new generation of biologically active tools because they are key regulators in cellular and intercellular physiological responses, which possess enormous potential for the treatment of various diseases. In spite of their clinical potential, native peptides have seen limited use due to their poor bioavailability and low stability in physiological conditions. Moreover, most peptide or protein pharmaceuticals currently in use are delivered by invasive routes such as via subcutaneous injection. Considerable efforts have been made to design new drugs based on peptides and recent developments in technology and science have provided the means and opportunity to produce a stable as well as controlled-release form of peptide and protein drugs to combat poorly controlled diseases and to increase patients' quality of life. A major challenge in this regard, however, is the delivery of peptides over the blood-brain barrier. This review gives an overview of some strategies used to improve both bioavailability and uptake of peptide drugs for delivery into the brain. Indeed, recent findings suggest that the use of peptides by conjugation to a polymer such as nanoparticles can offer tremendous hope in the treatment of brain disorders. The polymer conjugation improves pharmacokinetics by increasing the molecular mass of proteins and peptides and shielding them from proteolytic enzymes. These new strategies will create new opportunities for the future development of neurotherapeutic drugs. In the present review we have focused our attention on the peptide controlled delivery, summarizing literature reports on the use of peptides and nanotechnology for the treatment and diagnosis of brain disorders.

HPMA-based polymer therapeutics improve the efficacy of surgery, of radiotherapy and of chemotherapy combinations

To assist intravenously administered anticancer agents in achieving proper circulation times and tumor concentrations, and to thereby improve the balance between their efficacy and their toxicity, a large number of drug delivery systems have been designed and evaluated over the years. Clinically relevant examples of such nanometer-sized carrier materials are liposomes, polymers, micelles and antibodies. In the vast majority of cases, however, and especially in patients, nanomedicine formulations are only able to attenuate the toxicity of the conjugated or entrapped chemotherapeutic drug, and they generally fail to improve the efficacy of the intervention. To overcome this shortcoming, and to broaden the clinical applicability of tumor-targeted nanomedicines, in the past 5 years we have developed several concepts for using N-(2-hydroxypropyl)methacrylamide (HPMA)-based polymer therapeutics to enhance the efficacy of combined modality anticancer therapy. Regarding surgery, HPMA copolymers were shown to be able to improve the retention of intratumorally administered chemotherapeutic agents at the pathological site, and to thereby increase their therapeutic index. Regarding radiotherapy, a synergistic interaction was observed, with radiotherapy improving the tumor accumulation of the copolymers, and with copolymers improving both the efficacy and the tolerability of radiochemotherapy. Futhermore, regarding chemotherapy combinations, we have for the first time provided in vivo evidence showing that passively tumor-targeted polymeric drug carriers can be used to deliver two different drugs to tumors simultaneously. Based on these findings, and on the fact that the concepts developed are considered to be broadly applicable, we conclude that nanomedicine formulations are highly suitable systems for improving the efficacy of combined modality anticancer therapy.

Procoagulant inhibitory properties of paclitaxel poliglumex

Background

In Phase I evaluation of CT-2103 (paclitaxel poliglumex), prolongation of prothrombin time (PT) and activated thromboplastin time (aPTT) was observed, without clinical consequence, with doses 1.3–1.5 times higher than the current clinical dose of 175 mg/m². This Phase I, open-label, nonrandomized pilot study was performed to study the effect of the standard dose regimen on blood coagulation.

Methods

Seven previously treated solid tumor patients received CT-2103 175 mg/m² intravenously on day 1 of 21-day cycles for a mean of 5.4 cycles (median 4, range 2–14). Plasma samples were collected for cycle 1 predose and at hours 1, 24, 48, and 72 after the end of administration for drug levels, and for PT and aPTT assays.

Results

No coagulopathy-related adverse events were documented. Bleeding time remained normal in the six patients tested, with transient increases in PT and aPTT noted but resolving within 72 hours. Titration studies at 100 μg/mL of CT-2103 (corresponding to the standard clinical dose) prolonged PT and aPTT clotting times, produced a modest dose-dependent reduction of thrombin and factor Xa, and no significant changes in factors IXa, XIa, or XIIa. Two patients achieved stable disease for ≥10 cycles.

Conclusion

CT-2103 is associated with transient prolongation of PT and aPTT without clinical sequelae.

MMP9 but Not EGFR, MET, ERCC1, P16, and P-53 Is Associated with Response to Concomitant Radiotherapy, Cetuximab, and Weekly Cisplatin in Patients with Locally Advanced Head and Neck Cancer

Concomitant administration of radiotherapy with cisplatin or radiotherapy with cetuximab appear to be the treatment of choice for patients with locally advanced head and neck cancer. In the present retrospective analysis, we investigated the predictive role of several biomarkers in an unselected cohort of patients treated with concomitant radiotherapy, weekly cisplatin, and cetuximab (CCRT). We identified 37 patients treated with this approach, of which 13 (35%) achieved a complete response and 10 (27%) achieved a partial response. Severe side effects were mainly leucopenia, dysphagia, rash, and anemia. Tumor EGFR, MET, ERCC1, and p-53 protein and/or gene expression were not associated with treatment response. In contrast, high MMP9 mRNA expression was found to be significantly associated with objective response. In conclusion, CCRT is feasible and active. MMP9 was the only biomarker tested that appears to be of predictive value in cetuximab treated patients. However, this is a hypothesis generating study and the results should not be viewed as definitive evidence until they are validated in a larger cohort.

Image-guided and passively tumour-targeted polymeric nanomedicines for radiochemotherapy

Drug targeting systems are nanometer-sized carrier materials designed for improving the biodistribution of systemically applied (chemo-) therapeutics. Reasoning that (I) the temporal and spatial interaction between systemically applied chemotherapy and clinically relevant fractionated radiotherapy is suboptimal, and that (II) drug targeting systems are able to improve the temporal and spatial parameters of this interaction, we have here set out to evaluate the potential of 'carrier-based radiochemotherapy'. N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers were used as a model drug targeting system, doxorubicin and gemcitabine as model drugs, and the syngeneic and radio- and chemoresistant Dunning AT1 rat prostate carcinoma as a model tumour model. Using magnetic resonance imaging and gamma-scintigraphy, the polymeric drug carriers were first shown to circulate for prolonged periods of time, to localise to tumours both effectively and selectively, and to improve the tumour-directed delivery of low molecular weight agents. Subsequently, they were then shown to interact synergistically with radiotherapy, with radiotherapy increasing the tumour accumulation of the copolymers, and with the copolymers increasing the therapeutic index of radiochemotherapy (both for doxorubicin and for gemcitabine). Based on these findings, and on the fact that its principles are likely broadly applicable, we propose carrier-based radiochemotherapy as a novel concept for treating advanced solid malignancies.

Microbial Biosynthesis of Polyglutamic Acid Biopolymer and Applications in the Biopharmaceutical, Biomedical and Food Industries

This review article provides an updated critical literature review on the production and applications of Polyglutamic Acid (PGA). alpha-PGA is synthesized chemically, whereas gamma-PGA can be produced by a number of microbial species, most prominently various Bacilli. Great insight into the microbial formation of gamma-PGA has been gained thanks to the development of molecular biological techniques. Moreover, there is a great variety of applications for both isoforms of PGA, many of which have not been discovered until recently. These applications include: wastewater treatment, food products, drug delivery, medical adhesives, vaccines, PGA nanoparticles for on-site drug release in cancer chemotherapy, and tissue engineering.

Peptide-targeted polyglutamic acid doxorubicin conjugates for the treatment of alpha(v)beta(6)-positive cancers

Most chemotherapeutics exert their effects on tumor cells as well as their healthy counterparts, resulting in dose limiting side effects. Cell-specific delivery of therapeutics can increase the therapeutic window for treatment by maintaining the therapeutic efficacy while decreasing the untoward side effects. We have previously identified a peptide, named H2009.1, which binds to the integrin alpha(v)beta(6). Here, we report the synthesis of a peptide targeted polyglutamic acid polymer in which the high affinity alpha(v)beta(6)-specific tetrameric H2009.1 peptide is incorporated via a thioether at the N-terminus of a 15 amino acid polymer of glutamic acid. Doxorubicin is incorporated into the polymer via an acid-labile hydrazone bond. Payloads of four doxorubicin molecules per targeting agent are achieved. The drug is released at pH 4.0 and 5.6 but the conjugate is stable at pH 7.0. The conjugate is selectively internalized into alpha(v)beta(6) positive cells as witnessed by flow cytometric analysis and fluorescent microscopy. Cellular uptake is mediated by the H2009.1 peptide, as no internalization of the doxorubicin-PG polymer is observed when it is conjugated to a scrambled sequence control peptide. Importantly, the conjugate is more cytotoxic toward a targeted cell than a cell line that does not express the integrin.

Polymer-drug conjugates: recent development in clinical oncology

Targeted drug delivery aims to increase the therapeutic index by making more drug molecules available at the diseased sites while reducing systemic drug exposure. In this update, we provide an overview of polymer-drug conjugates that have advanced into clinical trials. These systems use synthetic water-soluble polymers as the drug carriers. The preclinical pharmacology and recent data in clinical trials with poly(l-glutamic acid)-paclitaxel (PG-TXL) are discussed. This is followed by a summary of a variety of polymeric conjugates with chemotherapeutic agents. Results from early clinical trials of these polymer-drug conjugates have demonstrated several advantages over the corresponding parent drugs, including fewer side effects, enhanced therapeutic efficacy, ease of drug administration, and improved patient compliance. Collectively, these data warrant further clinical development of polymer-drug conjugates as a new class of anticancer agents.

Design, synthesis and applications of hyaluronic acid-paclitaxel bioconjugates

Paclitaxel (1a), a well known antitumor agent adopted mainly for the treatment of breast and ovarian cancer, suffers from significant disadvantages such as low solubility, certain toxicity and specific drug-resistance of some tumor cells. To overcome these problems extensive research has been carried out. Among the various proposed strategies, the conjugation of paclitaxel (1a) to a biocompatible polymer, such as hyaluronic acid (HA, 2), has also been considered. Coupling a bioactive compound to a biocompatible polymer offers, in general, many advantages such as better drug solubilization, better stabilization, specific localization and controlled release. Hereafter the design, synthesis and applications of hyaluronic acid-paclitaxel bioconjugates are reviewed. An overview of HA-paclitaxel combinations is also given.

Paclitaxel: a review of adverse toxicities and novel delivery strategies

Better known as Taxol (Bristol-Myers Squibb), paclitaxel is the first member of the taxane family to be used in cancer chemotherapy. The taxanes exert their cytotoxic effect by arresting mitosis through microtubule stabilization, resulting in cellular apoptosis. The use of paclitaxel as a chemotherapeutic agent has become a broadly accepted option in the treatment of patients with ovarian, breast and non-small cell lung cancers, malignant brain tumors, and a variety of other solid tumors. However, significant toxicities, such as myelosuppression and peripheral neuropathy, limit the effectiveness of paclitaxel-based treatment regimens. This review addresses the toxicities associated with paclitaxel treatment and describes existing and future strategies of paclitaxel administration directed at limiting these toxicities.

Antitumor agents. 258. Syntheses and evaluation of dietary antioxidant--taxoid conjugates as novel cytotoxic agents

Various dietary antioxidants, including vitamins, flavonoids, curcumin, and a coumarin, were conjugated with paclitaxel (1) through an ester linkage. The newly synthesized compounds were evaluated for cytotoxic activity against several human tumor cell lines as well as the corresponding normal cell lines. Interestingly, most tested conjugates selectively inhibited the growth of 1A9 (ovarian) and KB (nasopharyngeal) tumor cells without activity against other cell lines. Particularly, conjugates 16 and 20 were highly active against 1A9 (ED(50) value of 0.005 microg/mL) as well as KB (ED(50) values of 0.005 and 0.14 microg/mL, respectively) cells. Compound 22b, the glycinate ester salt of vitamin E conjugated with 1, appears to be a promising lead for further development as a clinical trial candidate as it exhibited strong inhibitory activity against Panc-1 (pancreatic cancer) with less effect on the related E6E7 (normal) cell line.

Magnetic resonance imaging of therapy-induced necrosis using gadolinium-chelated polyglutamic acids

PURPOSE

Necrosis is the most common morphologic alteration found in tumors and surrounding normal tissues after radiation therapy or chemotherapy. Accurate measurement of necrosis may provide an early indication of treatment efficacy or associated toxicity. The purpose of this report is to evaluate the selective accumulation of polymeric paramagnetic magnetic resonance (MR) contrast agents--gadolinium p-aminobenzyl-diethylenetriaminepentaacetic acid-poly(glutamic acid) (L-PG-DTPA-Gd and D-PG-DTPA-Gd)--in necrotic tissue.

METHODS AND MATERIALS

Two different solid tumor models, human Colo-205 xenograft and syngeneic murine OCA-1 ovarian tumors, were used in this study. Necrotic response was induced by treatment with poly(L-glutamic acid)-paclitaxel conjugate (PG-TXL). T(1)-weighted spin-echo images were obtained immediately and up to 4 days after contrast injection and compared with corresponding histologic specimens. Two low-molecular-weight contrast agents, DTPA-Gd and oligomeric(L-glutamic acid)-DTPA-Gd, were used as nonspecific controls.

RESULTS

Initially, there was minimal tumor enhancement after injection of either L-PG-DTPA-Gd or D-PG-DTPA-Gd, but rapid enhancement after injection of low-molecular-weight agents. However, polymeric contrast agents, but not low-molecular-weight contrast agents, caused sustained enhancement in regions of tumor necrosis in both tumors treated with PG-TXL and untreated tumors. These data indicate that high molecular weight, rather than in vivo biodegradation, is necessary for the specific localization of polymeric MR contrast agents to necrotic tissue. Moreover, biotinylated L-PG-DTPA-Gd colocalized with macrophages in the tumor necrotic areas, suggesting that selective accumulation of L- and D-PG-DTPA-Gd in necrotic tissue was mediated through residing macrophages.

CONCLUSIONS

Our data suggest that MR imaging with PG-DTPA-Gd may be a useful technique for noninvasive characterization of treatment-induced necrosis.

Multifunctional polyelectrolyte multilayer films: combining mechanical resistance, biodegradability, and bioactivity

Cross-linked polyelectrolyte multilayer films (CL PEM) have an increased rigidity and are mechanically more resistant than native (e.g., uncrosslinked) films. However, they are still biodegradable, which make them interesting candidates for biomedical applications. In this study, CL PEM films have been explored for their multifunctional properties as (i) mechanically resistant, (ii) biodegradable, and (iii) bioactive films. Toward this end, we investigated drug loading into CL chitosan/hyaluronan (CHI/HA) and poly(L-lysine)/hyaluronan (PLL/HA) films by simple diffusion of the drugs. Sodium diclofenac and paclitaxel were chosen as model drugs and were successfully loaded into the films. The effect of varying the number of layers in the (CHI/HA) films as well as the cross-linker concentration on diclofenac loading were studied. Diclofenac was released from the film in about 10 h. Paclitaxel was also found to diffuse within CL films. Its activity was maintained after loading in the CL films, and cellular viability could be reduced by about 55% over 3 days. Such a simple approach may be applied to other types of cross-linked films and to other drugs. These results prove that it is possible to design multifunctional multilayer films that combine mechanical resistance, biodegradability, and bioactivity properties into a single PEM architecture.

Partial volume tolerance of the spinal cord and complications of single-dose radiosurgery

BACKGROUND

Spine radiosurgery causes a rapid dose fall-off within the spinal cord. The tolerance of partial volume of the spinal cord may determine the extent of clinical application. The study analyzed the partial volume tolerance of the human spinal cord to single fraction radiosurgery.

METHODS

A total of 230 lesions with spine metastases in 177 patients were treated with radiosurgery with single fraction of 8 to 18 Gy, prescribed to the 90% isodose line that encompassed the target volume. Spinal cord volume was defined as 6 mm above and below the radiosurgery target volume. Spinal cord dose was calculated from the radiation dose/spinal cord volume histogram and correlated with clinical/neurological status and radiographic studies. Median follow-up was 6.4 months (range, 0.5-49 months). The 1-year survival rate was 49%.

RESULTS

The average spinal cord volume defined at the treated spinal segment was 5.9 +/- 2.2 mL. The average dose to the 10% spinal cord volume was 9.8 +/- 1.5 Gy, calculated from the dose-volume histogram in the group of 18 Gy prescribed dose. The spinal cord volume that received higher than 80% of the prescribed dose was 0.07 +/- 0.10 mL, which represented 1.3 +/- 1.8% of the cord volume. Among the 86 patients who survived longer than 1 year there was 1 case of radiation-induced cord injury after 13 months of radiosurgery. There were no other cases of spinal cord sequelae.

CONCLUSIONS

Whereas the maximum spinal cord tolerance to single-dose radiation is not known, partial volume tolerance of the human spinal cord is at least 10 Gy to 10% of the spinal cord volume defined as 6 mm above and below the radiosurgery target.

Radiation Modifiers: Treatment Overview and Future Investigations

Many radiosensitizers are in current clinical use. In addition, a myriad of potential new targeted therapies, which may also interact with radiation, are in clinical development. The clinical utility of new targeted therapies, in combination with existing radiation sensitizers (chemotherapies) requires further evaluation, as does the understanding of their acute and late radiation effects. Free radical scavengers appear to show promise as radioprotectors, but data for mucoprotection are less convincing.

Phase I study of CT-2103, a polymer-conjugated paclitaxel, and carboplatin in patients with advanced solid tumors

PURPOSE

The primary objective of this study was to determine the maximum tolerated dose (MTD) of CT-2103 (poly L-glutamic acid-paclitaxel) in combination with carboplatin in patients with histologically proven solid tumors that were either refractory to conventional treatment or for which no conventional therapy was available.

PATIENTS AND METHODS

Twenty-two adult patients with advanced solid tumors were treated in this dose escalation study. Patients were treated every 21 days with CT-2103 at 175, 210, 225, or 250 mg/m2 (doses expressed as units of conjugated-paclitaxel) via 10-20 minute intravenous (IV) infusion, followed one hour later with carboplatin administered at AUC 5 or 6 via 30 minute IV infusion. No prophylaxis for hypersensitivity was administered with initial treatment. Doses were administered every 21 days until progressive disease or dose-limiting toxicity (DLT) was observed. Toxicity was evaluated using NCI Common Toxicity Criteria for Adverse Events v2.0 (CTCAE v2.0); response to treatment was evaluated using Response Criteria in Solid Tumors (RECIST).

RESULTS

The MTD was determined to be 225 mg/m2. DLTs observed at 250 mg/m2 were neutropenia and thrombocytopenia. No hypersensitivity reactions were observed. Three patients achieved partial responses (PR). Fifteen patients received at least 3 cycles of treatment without observation of progressive disease. Median survival time was 5.9 months. Patients that demonstrated partial responses were all ovarian cancer patients that had previously failed paclitaxel therapy. The only Grade 4, nonhematologic treatment-related toxicity was febrile neutropenia. Grade 4 neutropenia (9 patients) was observed across all dose groups. Twelve patients developed thrombocytopenia (Grade 3/4) while receiving combination therapy. All had resolution of thrombocytopenia with discontinuation of carboplatin, suggesting that carboplatin, and not CT-2103, contributed mainly to platelet toxicity.

CONCLUSION

CT-2103 administered at 225 mg/m2 every 21 days in combination with carboplatin administered at AUC 6 has a manageable safety profile in patients with solid tumors; further clinical investigation is recommended, especially in patients with ovarian or non-small cell lung cancer.

Novel formulations of taxanes: a review. Old wine in a new bottle?

Over the past two decades, the taxanes have played a significant role in the treatment of various malignancies. However, the poor solubility of these compounds necessitates the inclusion of surfactant vehicles in their commercial formulations. Cremophor EL and polysorbate 80 have long comprised the standard solvent system for paclitaxel and docetaxel, respectively. A number of pharmacologic and biologic effects related to both of these drug formulations have been described, including clinically relevant acute hypersensitivity reactions and peripheral neuropathy. In addition, these solvents affect the disposition of intravenously administered solubilized drugs and leach plasticizers from polyvinylchloride infusion sets. A number of strategies to develop formulations of surfactant-free taxanes have been developed. They include albumin nanoparticles, polyglutamates, taxane analogs and prodrugs, emulsions, and lipsomes. An overview of these novel formulations of taxanes, their mechanisms of action, pharmacokinetics, dose and administration, adverse effects, and clinical efficacy will be discussed.

Paclitaxel poliglumex (XYOTAX; CT-2103): an intracellularly targeted taxane

Paclitaxel poliglumex (CT-2103; XYOTAX) is an innovative macromolecular taxane designed to increase the therapeutic index of paclitaxel. This large macromolecule conjugate of paclitaxel and poly-L-glutamic acid accumulates in tumor tissues by taking advantage of the enhanced permeability of tumor vasculature and lack of lymphatic drainage. Paclitaxel poliglumex prolongs exposure to active drug and minimizes systemic exposure. Preclinical studies in animal tumor models demonstrate enhanced safety and efficacy relative to paclitaxel when administered as a single agent or in conjunction with radiation. Clinical pilot studies with paclitaxel poliglumex showed improved outcomes compared to standard taxanes and allowed a more convenient administration schedule. Human pharmacokinetic data are consistent with prolonged tumor exposure to active drug and a limited systemic exposure. Based on these results, three ongoing randomized phase III trials were initiated to test the efficacy of paclitaxel poliglumex in patients with advanced non-small cell lung carcinoma.

Synthesis and biological evaluation of novel taxoids designed for targeted delivery to tumors

The use of drug-antibody conjugates affords a method for the targeted delivery of anticancer drugs specifically to cancer cells. Monoclonal antibodies alone usually do not possess high therapeutic efficacy, however, they are capable of targeting tumor markers selectively. We have prepared taxoids with significantly higher cytotoxicity than paclitaxel and docetaxel. These taxoids now meet the high potency required for use in a targeted-delivery approach using monoclonal antibodies. The synthesis and biological evaluation of these taxoids are reported.

Paclitaxel nanoparticles for the potential treatment of brain tumors

Despite the advances in tumor therapy, patients with primary brain tumors and brain metastases have a very poor prognosis. Low responses to chemotherapy are mainly attributed to impermeability of the blood-brain barrier to cytotoxic agents. Paclitaxel has been shown to be active against gliomas and various brain metastases. However, its use in treatment of brain tumors is limited due to low blood-brain barrier permeability and serious side effects associated with administration of the paclitaxel solvent, Cremophor EL. Lack of paclitaxel brain uptake is thought to be associated with the p-glycoprotein (p-gp) efflux transporter. In this work, paclitaxel (PX) was entrapped in novel cetyl alcohol/polysorbate nanoparticles. Paclitaxel nanoparticles (PX NPs) were characterized by means of size, short-term stability, drug entrapment efficiency, and release profile. The PX NP cytotoxicity profile was monitored using two different cell lines, U-118 and HCT-15. Brain uptake of PX NPs was evaluated using an in situ rat brain perfusion model. The results suggest that entrapment of paclitaxel in nanoparticles significantly increases the drug brain uptake and its toxicity toward p-glycoprotein expressing tumor cells. It was hypothesized that PX NPs could mask paclitaxel characteristics and thus limit its binding to p-gp, which consequently would lead to higher brain and tumor cell uptake of the otherwise effluxed drug.

A site-specific polymeric drug carrier for renal disease treatment

A well-designed polymeric carrier for site-specific drug delivery in the treatment of renal disease has been reported recently. Approximately 80% of the water-soluble polymer poly(vinylpyrrolidone-co-dimethyl maleic anhydride selectively accumulated in the kidney of mice 24 h after intravenous injection. The detailed mechanism of such selective accumulation is not clear but an energy-dependent process, other than endocytosis, might be involved in the uptake of the polymer. This study is the first to report active targeting using a synthetic polymeric drug carrier.