Monoclonal antibodies in the treatment of malignancy: basic concepts and recent developments

CXCR4-antagonist Peptide R-liposomes for combined therapy against lung metastasis

The chemokine CXCL12 activates CXCR4, initiating multiple pathways that control immune cell trafficking, angiogenesis and embryogenesis; CXCR4 is also overexpressed in multiple tumors affecting metastatic dissemination. While there has been great enthusiasm for exploiting the CXCR4-CXCL12 axis as a target in cancer therapy, to date the promise has yet to be fulfilled. A new class of CXCR4-antagonist cyclic peptides was recently developed and the compound named Peptide R was identified as the most active. With the intent to improve the efficacy and biodistribution of Peptide R, stealth liposomes decorated with Peptide R were developed (PL-Peptide R). In vitro PL-Peptide R efficiently inhibited CXCR4-dependent migration and in vivo it significantly reduced lung metastases and increased overall survival in B16-CXCR4 injected C57BL/6 mice. To evaluate if PL-Peptide R could also be a drug delivery system for CXCR4 expressing tumors, the PL-Peptide R was loaded with doxorubicin (DOX) (PL-Peptide R-DOX). PL-Peptide R-DOX efficiently delivered DOX to CXCR4 expressing cell lines with a consequent decrease in the DOX IC50 efficient dose. In vivo, B16-CXCR4 injected C57BL/6 mice treated with PL-Peptide R-DOX developed fewer lung metastases compared to PL-DOX treated mice. This work provides the proof-of-concept to prevent metastasis by using combined nanomedicine.

The Crossroads of Geriatric Cardiology and Cardio-Oncology

Cancer and cardiovascular disease (CVD) are two major causes of mortality in older adults. With improved survival and outcomes from cancer and CVD, the role of the geriatrician is evolving. Geriatricians provide key skills to facilitate patient-centered and value-based care in the growing older population of cancer patients (and survivors). Cancer treatment in older adults is particularly injurious with respect to complications stemming from cancer therapy and as well as to CVD related to cancer therapy in the context of physiologic aging. To best meet their natural potential as caregiving leaders, geriatricians must hone skills and insights pertaining to oncologic and cardiovascular care, insights that can inform and enhance key management expertise. In this paper, we will review common chemotherapy and radiation-induced cardiovascular complications, screening recommendations, and advance the concept of a geriatric, cardiology, and oncology collaboration. We assert that geriatricians are well suited to a leadership role in the care of older cardio-oncology patients and in the education of primary care physicians and subspecialists on geriatric principles.

6-iodolactone, key mediator of antitumoral properties of iodine

An iodinated derivative of arachidonic acid, 5-hydroxy-6-iodo-8,11,14-eicosatrienoic acid, δ-lactone (6-IL) has been implicated as a possible intermediate in the autoregulation of the thyroid gland by iodine. In addition to antiproliferative and apoptotic effects observed in thyrocytes, this iodolipid could also exert similar actions in cells derived from extrathyroidal tissues like mammary gland, prostate, colon, or the nervous system. In mammary cancer (solid tumors or tumor cell lines), 6-IL has been detected after molecular iodine (I2) supplement, and is a potent activator of peroxisome proliferator-activated receptor type gamma (PPARγ). These observations led us to propose I2 supplement as a novel coadjutant therapy which, by inducing differentiation mechanisms, decreases tumor progression and prevents chemoresistance. Some kinds of tumoral cells, in contrast to normal cells, contain high concentrations of arachidonic acid, making the I2 supplement a potential "magic bullet" that enables local, specific production of 6-IL, which then exerts antineoplastic actions with minimal deleterious effects on normal tissues.

Multivalent scaffolds for affinity maturation of small molecule cell surface binders and their application to prostate tumor targeting

Adamantane scaffolds for affinity maturation of prostate cancer specific ligands of low molecular mass are described. These scaffolds are modular and can be used for conjugation of up to three ligands and an additional effector molecule by standard peptide coupling techniques. The potential of the scaffolds is demonstrated with the multimerization of GPI 1, a prostate cancer specific small molecule. A detailed study of multimerized GPI conjugates with near-infrared fluorophores and their binding properties to different prostate cancer cell lines shows the specific binding of these conjugates to cell types positive for prostate specific membrane antigen (PSMA). We demonstrate that these conjugates allow the sensitive imaging of prostate cancer cells with NIR methodology and suggest that our adamantane scaffolds might be generally useful for affinity maturation of small molecules targeting cell surface epitopes.

Glycoengineering of human IgG1-Fc through combined yeast expression and in vitro chemoenzymatic glycosylation

The presence and precise structures of the glycans attached at the Fc domain of monoclonal antibodies play an important role in determining antibodies' effector functions such as antibody-dependent cell cytotoxicity (ADCC), complement activation, and anti-inflammatory activity. This paper describes a novel approach for glycoengineering of human IgG1-Fc that combines high-yield expression of human IgG1-Fc in yeast and subsequent in vitro enzymatic glycosylation, using the endoglycosidase-catalyzed transglycosylation as the key reaction. Human IgG1-Fc was first overproduced in Pichia pastoris. Then the heterogeneous yeast glycans were removed by Endo-H treatment to give the GlcNAc-containing IgG1-Fc as a homodimer. Finally, selected homogeneous glycans were attached to the GlcNAc-primer in the IgG1-Fc through an endoglycosidase-catalyzed transglycosylation, using sugar oxazolines as the donor substrates. It was found that the enzymatic transglycosylation was efficient with native GlcNAc-containing IgG1-Fc homodimer without the need to denature the protein, and the reaction could proceed to completion to give homogeneous glycoforms of IgG1-Fc when an excess of oligosaccharide oxazolines was used as the donor substrates. The binding of the synthetic IgG1-Fc glycoforms to the FcgammaIIIa receptor was also investigated. This novel glycoengineering approach should be useful for providing various homogeneous, natural or synthetic glycoforms of IgG1-Fc for structure-function relationship studies, and for future clinical applications.

The clinical pharmacology of therapeutic monoclonal antibodies in the treatment of malignancy; have the magic bullets arrived?

Monoclonal antibodies (Mabs) are proteins in the immunoglobulin family that bind to specific protein epitope targets on cancer and stromal cells, allowing them to be successfully exploited as therapeutic agents. The prototype Mabs were produced from fusion of mouse B lymphocytes and mouse myeloma cells and were entirely murine in sequence. Subsequent advances in technology have allowed for humanized Mabs, which have different pharmacokinetic properties than murine Mabs in humans. Mabs antitumour activity is mediated through direct interaction with specific target molecules, deployment of immune cytotoxic pathways, or through chaperoning cytotoxic agents to tumour. Mabs are typically administered intravenously, are generally well tolerated and can have powerful anticancer activity. Humanized Mabs have a t(1/2) in human sera of 2-3 weeks, which determines the frequency of administration. At present, nine clinically approved Mabs are used in the treatment of human cancer, and many others are in clinical trials. We discuss the pharmacology, clinical indications, and toxicity of the currently available anticancer Mabs in this review.

The diagnosis and management of cardiovascular disease in cancer patients

Cardiovascular disease is commonly found in cancer patients. The co-existence of heart disease and cancer in a patient often complicates treatment, because therapy for one disease may negatively affect the outcome of the other disease. In addition, guidelines for the treatment of cardiovascular disease are often based on studies, which exclude patients who have cancer. In this review we will discuss the diagnosis and management of cardiovascular disease in cancer patients. We will focus on cancer-related causes of cardiovascular disease and special treatment options for cardiovascular disease in cancer patients. The cardiac complications of cancer therapy will be discussed according to common syndromes: left ventricular dysfunction, myocardial ischemia, blood pressure changes, thromboembolism, bradyarrhythmias, and prolonged QT interval.

Monoclonal antibodies as targeted therapy in hematologic malignancies in older adults

BACKGROUND

Biological agents are proving to be increasingly useful and exciting additions to the antineoplastic armamentarium, but many clinicians are unfamiliar with the properties of these types of agents.

OBJECTIVES

This review focuses on monoclonal antibodies (MAbs) that are used in the treatment of hematologic malignancies. Our goal was to provide the reader with information on trials that led to US Food and Drug Administration (FDA) approval of commonly used MAbs in hematologic malignancies, including their mechanisms of action and pharmacokinetics, with specific emphasis on use in elderly patients; we also present data on toxicities and precautions to be aware of when administering these drugs.

METHODS

Materials for this review were gathered based on a computerized literature search (English-language articles only) using the PubMed database covering the period January 1998 to December 2005. Search terms used included the following: elderly, monoclonal antibodies, and neoplasms.

RESULTS

Alemtuzumab is a recombinant DNA-derived, humanized MAb directed against the CD52 B-cell antigen. It is indicated for the treatment of B-cell chronic lymphocytic leukemia (CLL) in patients who have been treated with alkylating agents and who have failed to respond to fludarabine therapy. Gemtuzumab ozogamicin is an MAb conjugated with a cytotoxic antitumor antibiotic, calicheamicin. It has been approved for use in patients with CD33-positive acute myeloid leukemia (AML) in first relapse who are aged > or =60 years and who are not considered candidates for other cytotoxic chemotherapy. Rituximab, one of the first MAbs approved by the FDA for use in human cancers, is an antibody directed against the CD20 antigen found on the surface of normal and malignant B lymphocytes. It is extensively used in the treatment of B-cell malignancies, such as CLL, and non-Hodgkin's lymphomas (NHLs), such as follicular lymphoma and diffuse large B-cell lymphoma.

CONCLUSIONS

It is noteworthy that while there have been a number of studies using these agents in the younger population, there continues to be a paucity of clinical trials targeting the elderly patient in particular; this continues to be an area of research interest. More clinical studies of these agents--conducted specifically in elderly patients with CLL, NHL, AML, and other hematologic malignancies--are needed.

Development of peptide-targeted lipoplexes to CXCR4-expressing rat glioma cells and rat proliferating endothelial cells

A peptide analog, 4-fluorobenzoyl-RR-(L-3-(2-naphthyl)alanine)-CYEK-(L-citrulline)-PYR-(L-citrulline)-CR, covalently linked to a phospholipid, was used for targeting a lipid-based gene delivery vehicle to CXCR4(+)-cells. Characterization of transfection activity was done in vitro using a transformed rat glioma cell line (RG2) that expresses CXCR4. The substitution of the targeting lipid at increasing mole percentages in the place of helper lipids yielded a progressive increase in reporter gene expression, reaching a maximum of 2.5 times the control value at 20 mol% of ligand. The substitution of helper lipids with cysteine-derivatized phospholipid analog or phosphatidylethanolamine resulted in a progressive decrease in transfection activity, with complete inactivation of the complex occurring at 20 mol%. A DNA dose-response with 10 mol% of lipopeptide reduced the effective DNA dose at least fivefold with regard to the number of transfected cells and >20-fold with regard to the amount of gene expression. Gene transfer to rat endothelial cells was studied in the context of an arterial organ culture. Mesenteric arteries were cannulated and maintained in culture for up to 4 days. CXCR4 cell-surface expression on endothelial cells was induced after overnight incubation with vascular endothelial growth factor (VEGF). Gene transfer studies showed that only the peptide-targeted lipoplexes transfected the endothelium, and only after CXCR4 had been induced with VEGF. These results demonstrate that non-viral transfection complexes can be targeted to cells expressing CXCR4, and that gene transfer is dependent upon cell surface receptor expression levels.

Improved biochemical strategies for targeted delivery of taxoids

Paclitaxel (Taxol) and docetaxel (Taxotere) are very important anti-tumor drugs in clinical use for cancer. However, their clinical utility is limited due to systemic toxicity, low solubility and inactivity against drug resistant tumors. To improve chemotherapeutic levels of these drugs, it would be highly desirable to design strategies which bypass the above limitations. In this respect various prodrug and drug targeting strategies have been envisioned either to improve oral bioavailability or tumor specific delivery of taxoids. Abnormal properties of cancer cells with respect to normal cells have guided in designing of these protocols. This review article records the designed biochemical strategies and their biological efficacies as potential taxoid chemotherapeutics.

Multiple myeloma: monoclonal antibodies-based immunotherapeutic strategies and targeted radiotherapy

Multiple myeloma (MM) is an incurable B-cell malignancy of terminally differentiated plasma cells. Besides conventional treatments, several targeted therapies are emerging for MM. We review recent developments in monoclonal antibodies (MoAbs) and (radio)immunoconjugates-based targeted immunotherapeutic (serotherapies) strategies, as well as skeletal targeted radiotherapy (STR) in MM. MoAbs-based strategies include the targeting of cytokines and their receptors as well as toxins, drugs or radionuclide delivery to MM cells. Both targeted radioimmunotherapy (RIT) and STR have proved efficient in the treatment of radiosensitive tumours. We conclude that there is a need for more mechanistic investigations of drug action to identify novel therapeutic targets in myeloma cells, as well as in the bone marrow microenvironment.

Proapoptotic activity of cell-permeable anti-Akt single-chain antibodies

We developed anti-Akt1 single-chain antibodies (scFv) by panning a mouse phage-displayed scFv recombinant antibody library. Recombinant scFv that bound glutathione S-transferase (GST)-Akt1 were screened for their ability to inhibit Akt activity in vitro in a kinase reaction containing human recombinant Akt1 and an Akt/serum glucocorticoid-inducible kinase (SGK) substrate. Michaelis-Menten analysis of kinase inhibition by a selected scFv was consistent with scFv-mediated competition with enzyme's substrate for the catalytic site of Akt. To generate a membrane-permeable version of the anti-Akt1 scFv, the scFv gene was subcloned into a GST expression vector carrying a membrane-translocating sequence (MTS) from Kaposi fibroblast growth factor. A purified GST-anti-Akt1-MTS fusion protein accumulated intracellularly in 293T, BT-474, and PyVmT cells in a dose- and time-dependent fashion. Intracellular accumulation correlated temporally with inhibition of p-Ser(473) Akt and GSK-3alpha/beta phosphorylation, suggesting that Ser(473) is an Akt autophosphorylation site. Phosphorylated (activated) phosphoinositide-dependent kinase 1, mitogen-activated protein kinase, p38, and HER2 (erbB2) were not affected, supporting Akt kinase specificity for the inhibitory scFv. Exogenously expressed constitutively active Akt2 and Akt3 were also inhibited in vitro by the anti-Akt1 fusion protein. Furthermore, GST-anti-Akt1-MTS induced apoptosis in three cancer cell lines that express constitutively active Akt. Finally, systemic treatment with the anti-Akt scFv reduced tumor volume and neovascularization and increased apoptosis in PyVmT-expressing transgenic tumors implanted in mouse dorsal window chambers. Thus, GST-anti-Akt1-MTS is a novel cell-permeable inhibitor of Akt, which selectively inhibits Akt-mediated survival in intact cells both in vitro and in vivo.

Cardiovascular complications of cancer therapy: diagnosis, pathogenesis, and management

The cardiotoxicity of anticancer agents can lead to significant complications that can affect patients being treated for various malignancies. The severity of such toxicity depends on many factors such as the molecular site of action, the immediate and cumulative dose, the method of administration, the presence of any underlying cardiac condition, and the demographics of the patient. Moreover, toxicity can be affected by current or previous treatment with other antineoplastic agents. Cardiotoxic effects can occur immediately during administration of the drug, or they may not manifest themselves until months or years after the patient has been treated. In this article we review commonly used chemotherapy agents, including several recently approved medications, for their propensity to cause cardiotoxicity. Further research will be required to more accurately predict which patients are at risk for developing cardiotoxicity. In addition, management plans, as well as strategies to reduce cardiotoxicity, need to be developed.

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.

In vitro and in vivo activity of the maytansinoid immunoconjugate huN901-N2'-deacetyl-N2'-(3-mercapto-1-oxopropyl)-maytansine against CD56+ multiple myeloma cells

HuN901 is a humanized monoclonal antibody that binds with high affinity to CD56, the neuronal cell adhesion molecule. HuN901 conjugated with the maytansinoid N(2')-deacetyl-N(2')-(3-mercapto-1-oxopropyl)-maytansine (DM1), a potent antimicrotubular cytotoxic agent, may provide targeted delivery of the drug to CD56 expressing tumors. Based on gene expression profiles of primary multiple myeloma (MM) cells showing expression of CD56 in 10 out of 15 patients (66.6%) and flow cytometric profiles of MM (CD38(bright)CD45(lo)) cells showing CD56 expression in 22 out of 28 patients (79%), we assessed the efficacy of huN901-DM1 for the treatment of MM. We first examined the in vitro cytotoxicity and specificity of huN901-DM1 on a panel of CD56(+) and CD56(-) MM cell lines, as well as a CD56(-) Waldenstrom's macroglobulinemia cell line. HuN901-DM1 treatment selectively decreased survival of CD56(+) MM cell lines and depleted CD56(+) MM cells from mixed cultures with a CD56(-) cell line or adherent bone marrow stromal cells. In vivo antitumor activity of huN901-DM1 was then studied in a tumor xenograft model using a CD56(+) OPM2 human MM cell line in SCID mice. We observed inhibition of serum paraprotein secretion, inhibition of tumor growth, and increase in survival of mice treated with huN901-DM1. Our data therefore demonstrate that huN901-DM1 has significant in vitro and in vivo antimyeloma activity at doses that are well tolerated in a murine model. Taken together, these data provide the framework for clinical trials of this agent to improve patient outcome in MM.

Cytotoxic activity of the maytansinoid immunoconjugate B-B4-DM1 against CD138+ multiple myeloma cells

We tested the in vitro and in vivo antitumor activity of the maytansinoid DM1 (N(2')-deacetyl-N(2')-(3-mercapto-1-oxopropyl)-maytansine), a potent antimicrotubule agent, covalently linked to the murine monoclonal antibody (mAb) B-B4 targeting syndecan-1 (CD138). We evaluated the in vitro activity of B-B4-DM1 against a panel of CD138(+) and CD138(-) cell lines, as well as CD138(+) patient multiple myeloma (MM) cells. Treatment with B-B4-DM1 selectively decreased growth and survival of MM cell lines, patient MM cells, and MM cells adherent to bone marrow stromal cells. We further examined the activity of B-B4-DM1 in 3 human MM models in mice: (1) severe combined immunodeficient (SCID) mice bearing subcutaneous xenografts; (2) SCID mice bearing green fluorescent protein-positive (GFP(+)) xenografts; and (3) SCID mice implanted with human fetal bone (SCID-hu) and subsequently injected with patient MM cells. Tumor regression and inhibition of tumor growth, improvement in overall survival, and reduction in levels of circulating human paraprotein were observed in mice treated with B-B4-DM1. Although immunohistochemical analysis demonstrates restricted CD138 expression in human tissues, the lack of B-B4 reactivity with mouse tissues precludes evaluation of its toxicity in these models. In conclusion, B-B4-DM1 is a potent anti-MM agent that kills cells in an antigen-dependent manner in vitro and mediates in vivo antitumor activity at doses that are well tolerated, providing the rationale for clinical trials of this immunoconjugate in MM.

Expression and regulation of luteinizing hormone/human chorionic gonadotropin receptors in ovarian cancer and its correlation to human chorionic gonadotropin-doxorubicin sensitivity

OBJECTIVE

Ovarian cancer cell lines and tissues express gonadotropin receptors. Conjugation of cytostatics to ligands of these receptors may increase the specificity of cytotoxic drugs.

STUDY DESIGN

Toxicity of doxorubicin-human chorionic gonadotropin conjugates was determined in 4 ovarian cancer cell lines. Expression and regulation of luteinizing hormone/human chorionic gonadotropin receptors were analyzed before and after treatment with human chorionic gonadotropin, epidermal growth factor, and 8-bromo-cyclic adenosine monophosphate with a nested reverse transcriptase-polymerase chain reaction approach.

RESULTS

Toxicity of human chorionic gonadotropin-doxorubicin conjugates was increased compared with unconjugated doxorubicin in OVCAR-3 cells. However, drug conjugates failed to demonstrate increased toxicity in other cell lines, especially after preincubation with human chorionic gonadotropin. All cell lines expressed luteinizing hormone/human chorionic gonadotropin receptors. Receptor expression in OVCAR-3 cells was not effected by human chorionic gonadotropin, endothelial growth factor, or 8-bromo-cyclic adenosine monophosphate treatment. In other cell lines, receptor expression was down-regulated by these agents.

CONCLUSION

Cytotoxic activity of doxorubicin was increased specifically by conjugation to human chorionic gonadotropin. However, the regulation of luteinizing hormone/human chorionic gonadotropin receptor expression and other compounds may reduce the drug-uptake of the conjugates.

Molecular neuro-oncology and development of targeted therapeutic strategies for brain tumors. Part 1: Growth factor and Ras signaling pathways

Brain tumors are a diverse group of malignancies that remain refractory to conventional treatment approaches, including radiotherapy and cytotoxic chemotherapy. Molecular neuro-oncology has now begun to clarify the transformed phenotype of brain tumors and identify oncogenic pathways that may be amenable to targeted therapy. Growth factor signaling pathways are often upregulated in brain tumors and may contribute to oncogenesis through autocrine and paracrine mechanisms. Excessive growth factor receptor stimulation can also lead to overactivity of the Ras signaling pathway, which is frequently aberrant in brain tumors. Receptor tyrosine kinase inhibitors, antireceptor monoclonal antibodies and antisense oligonucleotides are targeted approaches under investigation as methods to regulate aberrant growth factor signaling pathways in brain tumors. Several receptor tyrosine kinase inhibitors, including imatinib mesylate (Gleevec), gefitinib (Iressa) and erlotinib (Tarceva), have entered clinical trials for high-grade glioma patients. Farnesyl transferase inhibitors, such as tipifarnib (Zarnestra), which impair processing of proRas and inhibit the Ras signaling pathway, have also entered clinical trials for patients with malignant gliomas. Further development of targeted therapies and evaluation of these new agents in clinical trials will be needed to improve survival and quality of life of patients with brain tumors.

Expression of CEA, Tag-72, and Lewis-Y antigen in primary and metastatic lesions of ovarian carcinoma

Ovarian carcinoma has a high mortality rate, because most ovarian carcinomas are detected at a late stage. Traditional therapies, such as surgical debulking and chemotherapy, have not been successful in improving the long-term survival of these patients. Alternative therapies targeting various biomarkers, such as carcinoembryonic antigen (CEA), Tag-72, and Lewis-Y antigen, have been developed to treat patients with advanced ovarian cancers. To ensure that therapies targeting these biomarkers are effective, it is imperative to determine whether there is any differential expression of these targeted biomarkers between primary and metastatic ovarian carcinomas. In the present study, primary and metastatic lesions from 68 and 58 patients, respectively, including primary and matched metastatic lesions from 31 patients, were evaluated for cytoplasmic and membranous expression of CEA (clone Col-1), Tag-72 (clone CC-49), and Lewis-Y antigen (clone BR-96) by immunohistochemistry. No significant differences were observed with cytoplasmic and membranous expression of Tag-72 (CC-49) and Lewis-Y antigen (BR-96) in the primary and metastatic, matched and unmatched lesions (Wilcoxon signed-rank test). Although there was no statistically significant difference in the scores of CEA (Col-1) between primary and metastatic lesions, 5 of 11 (45%) cases with positive staining with CEA (Col-1) demonstrated discordant results between primary and metastatic lesions. There was a moderate positive correlation of the cytoplasmic and membranous expression of Tag-72 (CC-49), as well as cytoplasmic expression of BR-96 between primary and metastatic ovarian carcinomas. There was a weak negative correlation between the membranous expression of CEA (Col-1) and that of Lewis-Y antigen (BR-96); however, the difference was not statistically significant. No correlation was observed with other combinations of biomarkers. Our findings suggest that samples from either primary or metastatic ovarian carcinomas can be used for the evaluation of the expression of Tag-72 (CC-49) and Lewis-Y antigen (BR-96) to identify targets for novel therapies in patients with disseminated ovarian carcinomas. CEA (Col-1), due to its low expression and variation in phenotypic expression between primary and metastatic lesions, should be evaluated carefully in metastatic lesions before targeting the CEA antigen with CEA (Col-1)-like antibodies.

Natural killer (NK) cell function is a strong prognostic factor in colorectal carcinoma patients treated with the monoclonal antibody 17-1A

Tumor cells might be susceptible to different effector functions of the immune system. This cytotoxic capacity has been utilized to analyze the prognostic significance of peripheral blood mononuclear cells (PBMC) in patients with metastatic colorectal carcinoma (CRC) treated with the monoclonal antibody (MAb)17-1A. Such analysis might form the basis for future patient selection and may lead to improvements in therapeutic strategies. Between 1986 and 1998, 73 patients were treated with regimens containing MAb17-1A. Prior to therapy, the lytic capability of PBMC was assayed against: K562 (4 hr assay), the CRC cell line SW948 (4 hr and 18 hr assays) and antibody-dependent cellular cytotoxicity (ADCC, 18 hr assay). Since the study was performed over 13 years, the assays were checked for time-related bias. Reproducibility over time was satisfactory. Patients exhibited a significantly higher cytotoxic capability in all 4 assays compared to healthy control donors. No correlation to clinical outcome was noted for 18 hr ADCC and 18 hr spontaneous cytotoxicity. Pretreatment natural killer (NK) cell cytotoxicity (K562) was significantly related to overall survival (OS), progression-free survival (PFS), and response rate. OS for patients with high and low NK cell cytotoxicity was 71 vs. 30 weeks, respectively (p = 0.007). NK cell cytotoxicity (K562) was an independent prognostic factor for OS (p = 0.016). Pretreatment NK cell activity is a strong prognostic factor for patients with metastatic CRC receiving MAb17-1A therapy and is a predictor for OS, PFS and response. These results should be considered when designing antibody-based therapeutic protocols.

Development of potent monoclonal antibody auristatin conjugates for cancer therapy

We describe the in vitro and in vivo properties of monoclonal antibody (mAb)-drug conjugates consisting of the potent synthetic dolastatin 10 analogs auristatin E (AE) and monomethylauristatin E (MMAE), linked to the chimeric mAbs cBR96 (specific to Lewis Y on carcinomas) and cAC10 (specific to CD30 on hematological malignancies). The linkers used for conjugate formation included an acid-labile hydrazone and protease-sensitive dipeptides, leading to uniformly substituted conjugates that efficiently released active drug in the lysosomes of antigen-positive (Ag+) tumor cells. The peptide-linked mAb-valine-citrulline-MMAE and mAb-phenylalanine-lysine-MMAE conjugates were much more stable in buffers and plasma than the conjugates of mAb and the hydrazone of 5-benzoylvaleric acid-AE ester (AEVB). As a result, the mAb-Val-Cit-MMAE conjugates exhibited greater in vitro specificity and lower in vivo toxicity than corresponding hydrazone conjugates. In vivo studies demonstrated that the peptide-linked conjugates induced regressions and cures of established tumor xenografts with therapeutic indices as high as 60-fold. These conjugates illustrate the importance of linker technology, drug potency and conjugation methodology in developing safe and efficacious mAb-drug conjugates for cancer therapy.

Selective cell targeting with light-absorbing microparticles and nanoparticles

We describe a new method for selective cell targeting based on the use of light-absorbing microparticles and nanoparticles that are heated by short laser pulses to create highly localized cell damage. The method is closely related to chromophore-assisted laser inactivation and photodynamic therapy, but is driven solely by light absorption, without the need for photochemical intermediates (particularly singlet oxygen). The mechanism of light-particle interaction was investigated by nanosecond time-resolved microscopy and by thermal modeling. The extent of light-induced damage was investigated by cell lethality, by cell membrane permeability, and by protein inactivation. Strong particle size dependence was found for these interactions. A technique based on light to target endogenous particles is already being exploited to treat pigmented cells in dermatology and ophthalmology. With exogenous particles, phamacokinetics and biodistribution studies are needed before the method can be evaluated against photodynamic therapy for cancer treatment. However, particles are unique, unlike photosensitizers, in that they can remain stable and inert in cells for extended periods. Thus they may be particularly useful for prelabeling cells in engineered tissue before implantation. Subsequent irradiation with laser pulses will allow control of the implanted cells (inactivation or modulation) in a noninvasive manner.

Retinoic acid-induced Golgi apparatus disruption in F2000 fibroblasts: a model for enhanced intracellular retrograde transport

Retinoic acid (RA) can transform the Golgi apparatus (GA) into a diffuse vacuolar aggregate and increase the toxicity of some immunotoxins that enter into cells by receptor-mediated endocytosis. An ultramorphological study of the RA-induced GA disruption was performed on F2000 fibroblasts. Cultures were treated with 0.11 to 30 microM RA for 7-180 min. The endocytosis of Limax flavus agglutinin-peroxidase conjugate (LFA), and the interactions between a phorbol ester (PMA) and RA concerning GA disruption, were examined. Exposure to 0.33 microM RA for 20 min transformed the GA into vacuolar aggregate. These vacuoles were not involved in endocytosis since they remained unstained after endocytosis of LFA. However, the lysosomes were involved in endocytosis, as they were strongly stained. Therefore, a RA-induced shift towards lysosomal routing of the entered LFA was presumed. Exposure to PMA made cells resistant to the Golgi-disturbing effects of RA, indicating that protein kinase C plays an important role in this process.

Immunomicelles: targeted pharmaceutical carriers for poorly soluble drugs

To prepare immunomicelles, new targeted carriers for poorly soluble pharmaceuticals, a procedure has been developed to chemically attach mAbs to reactive groups incorporated into the corona of polymeric micelles made of polyethylene glycol-phosphatidylethanolamine conjugates. Micelle-attached antibodies retained their ability to specifically interact with their antigens. Immunomicelles with attached antitumor mAb 2C5 effectively recognized and bound various cancer cells in vitro and showed an increased accumulation in experimental tumors in mice when compared with nontargeted micelles. Intravenous administration of tumor-specific 2C5 immunomicelles loaded with a sparingly soluble anticancer agent, taxol, into experimental mice bearing Lewis lung carcinoma resulted in an increased accumulation of taxol in the tumor compared with free taxol or taxol in nontargeted micelles and in enhanced tumor growth inhibition. This family of pharmaceutical carriers can be used for the solubilization and enhanced delivery of poorly soluble drugs to various pathological sites in the body.

Peptide and protein drug delivery to and into tumors: challenges and solutions

The potential of peptide and protein anticancer agents has yet to be realized owing to the many unresolved problems concerning their delivery to the site of a tumor and into tumor cells. However, our understanding of the mechanisms underlying the biological fate and biodistribution of protein and peptide drugs has advanced to the stage where methods that use or influence these mechanisms are now available. There are different approaches that can improve the stability, longevity and targeting of peptides and proteins in the body, such as their modification with various soluble polymers, incorporation into microparticular drug carriers, enhanced permeability and retention effect-based tumor targeting and the use of targeting moieties. Furthermore, new approaches to intracellular drug delivery, including the use of transduction proteins and peptides, are being developed. These advances promise the delivery of a new generation of anticancer drugs.

Cancer immunotherapy: an embarrassment of riches?

There is clear evidence that certain forms of immunotherapy can be successful against certain cancers. However, it would appear that cancerous cells of various origin are exceptionally adept at subverting the immune response. Consequently, it is probable that the most efficacious therapy will be one in which multiple responses of the immune system are activated. There is currently an embarrassment of riches with regard to multiple vaccine strategies in the clinic, although no single method seems to hold the solution. Here, we draw together several of the humoral- and cellular-activating strategies currently under clinical investigation.

Immunofluorescence imaging as a tool for studying the pharmacokinetics of a human monoclonal single chain fragment antibody

We have used immunofluorescence imaging to study binding of a monoclonal antibody fragment to subcutaneously implanted human melanoma cells in nude mice. The data acquired using this nontraditional approach was then analyzed using standard pharmacokinetic methods to produce estimates of k(e) (0.06h(-1)), t 1/2 (16 h), mean residency time (23.4 h) and percent exposure of the antibody to the tumor (40%). To our knowledge this is the first time standard pharmacokinetic analyzes have been conducted on immunofluorescence imaging data. The combination of this novel imaging technique and standard pharmacokinetic analytical methods should prove to be a useful tool for comparing the properties of antibody fragments in animal models.

Ligand-targeted therapeutics in anticancer therapy

Cytotoxic chemotherapy or radiotherapy of cancer is limited by serious, sometimes life-threatening, side effects that arise from toxicities to sensitive normal cells because the therapies are not selective for malignant cells. So how can selectivity be improved? One strategy is to couple the therapeutics to antibodies or other ligands that recognize tumour-associated antigens. This increases the exposure of the malignant cells, and reduces the exposure of normal cells, to the ligand-targeted therapeutics.

The development of immunotherapies for non-small cell lung cancer

Standard of care for non-small cell lung cancer (NSCLC) (surgery, chemotherapy and radiation) may enhance patient survival but the enhancement is typically transient and quite uncommon with advanced disease. Researchers and medical professionals are using new approaches to improve patient mortality and morbidity. One of these approaches, immunotherapy, seeks to stimulate antitumour immunity above a threshold level needed for tumour regression or to induce stability in the face of progression. Among the most established approaches are vaccines involving monoclonal antibodies (mAbs) or immune effector cells. These approaches stimulate the humoral and cell-mediated arms of the immune system, respectively. As the development of humanised or fully human antibodies has spurred exploration of radioimmunoconjugates and immunotoxins, mAbs have enjoyed a revival of sorts. Cell-based therapies using the tumour cell itself as a vaccine component has resulted in disease stabilisation or regression. In addition, immune cells (e.g., T-lymphocytes and dendritic cells [DCs]) are the focal point of numerous patient trials in which meaningful clinical impact was achieved. In general, there are many tactics under development for the treatment of NSCLC. This review primarily concerns immunotherapeutic cancer treatments that are either already in clinical trial or well progressed into preclinical studies.