Safety and pharmacokinetics of bivatuzumab mertansine in patients with CD44v6-positive metastatic breast cancer: final results of a phase I study

Concise Review: Emerging Role of CD44 in Cancer Stem Cells: A Promising Biomarker and Therapeutic Target

The reception and integration of the plethora of signals a cell receives from its microenvironment determines the cell's fate. CD44 functions as a receptor for hyaluronan and many other extracellular matrix components, as well as a cofactor for growth factors and cytokines, and thus, CD44 is a signaling platform that integrates cellular microenvironmental cues with growth factor and cytokine signals and transduces signals to membrane-associated cytoskeletal proteins or to the nucleus to regulate a variety of gene expression levels related to cell-matrix adhesion, cell migration, proliferation, differentiation, and survival. Accumulating evidence indicates that CD44, especially CD44v isoforms, are cancer stem cell (CSC) markers and critical players in regulating the properties of CSCs, including self-renewal, tumor initiation, metastasis, and chemoradioresistance. Furthermore, there is ample evidence that CD44, especially CD44v isoforms, are valuable prognostic markers in various types of tumors. Therefore, therapies that target CD44 may destroy the CSC population, and this holds great promise for the cure of life-threatening cancers. However, many challenges remain to determining how best to use CD44 as a biomarker and therapeutic target. Here we summarize the current findings concerning the critical role of CD44/CD44v in the regulation of cancer stemness and the research status of CD44/CD44v as biomarkers and therapeutic targets in cancer. We also discuss the current challenges and future directions that may lead to the best use of CD44/CD44v for clinical applications.

SIGNIFICANCE

Mounting evidence indicates that cancer stem cells (CSCs) are mainly responsible for cancer aggressiveness, drug resistance, and tumor relapse. CD44, especially CD44v isoforms, have been identified as CSC surface markers for isolating and enriching CSCs in different types of cancers. The current findings concerning the critical role of CD44/CD44v in regulation of cancer stemness and the research status of CD44/CD44v as biomarkers and therapeutic targets in cancer are summarized. The current challenges and future directions that may lead to best use of CD44/CD44v for clinical applications are also discussed.

Advances and advantages of nanomedicine in the pharmacological targeting of hyaluronan-CD44 interactions and signaling in cancer

Extensive experimental evidence in cell and animal tumor models show that hyaluronan-CD44 interactions are crucial in both malignancy and resistance to cancer therapy. Because of the intimate relationship between the hyaluronan-CD44 system and tumor cell survival and growth, it is an increasingly investigated area for applications to anticancer chemotherapeutics. Interference with the hyaluronan-CD44 interaction by targeting drugs to CD44, targeting drugs to the hyaluronan matrix, or interfering with hyaluronan matrix/tumor cell-associated CD44 interactions is a viable strategy for cancer treatment. Many of these methods can decrease tumor burden in animal models but have yet to show significant clinical utility. Recent advances in nanomedicine have offered new valuable tools for cancer detection, prevention, and treatment. The enhanced permeability and retention effect has served as key rationale for using nanoparticles to treat solid tumors. However, the targeted and uniform delivery of these particles to all regions of tumors in sufficient quantities requires optimization. An ideal nanocarrier should be equipped with selective ligands that are highly or exclusively expressed on target cells and thus endow the carriers with specific targeting capabilities. In this review, we describe how the hyaluronan-CD44 system may provide such an alternative in tumors expressing specific CD44 variants.

Fragment-based identification of an inducible binding site on cell surface receptor CD44 for the design of protein-carbohydrate interaction inhibitors

Selective inhibitors of hyaluronan (HA) binding to the cell surface receptor CD44 will have value as probes of CD44-mediated signaling and have potential as therapeutic agents in chronic inflammation, cardiovascular disease, and cancer. Using biophysical binding assays, fragment screening, and crystallographic characterization of complexes with the CD44 HA binding domain, we have discovered an inducible pocket adjacent to the HA binding groove into which small molecules may bind. Iterations of fragment combination and structure-driven design have allowed identification of a series of 1,2,3,4-tetrahydroisoquinolines as the first nonglycosidic inhibitors of the CD44-HA interaction. The affinity of these molecules for the CD44 HA binding domain parallels their ability to interfere with CD44 binding to polymeric HA in vitro. X-ray crystallographic complexes of lead compounds are described and compared to a new complex with a short HA tetrasaccharide, to establish the tetrahydroisoquinoline pharmacophore as an attractive starting point for lead optimization.

CD44 is prognostic for overall survival in the NCI randomized trial on breast conservation with 25 year follow-up

CD44 is a transmembrane glycoprotein involved in numerous cellular functions, including cell adhesion and extracellular matrix interactions. It is known to be functionally diverse, with alternative splice variants increasingly implicated as a marker for tumor-initiating stem cells associated with poor prognosis. Here, we evaluate CD44 as a potential marker of long-term breast cancer outcomes. Tissue specimens from patients treated on the National Cancer Institute 79-C-0111 randomized trial of breast conservation versus mastectomy between 1979 and 1987 were collected, and immunohistochemistry was performed using the standard isoform of CD44. Specimens were correlated with patient characteristics and outcomes. Survival analysis was performed using the log rank test. Fifty-one patients had evaluable tumor sections and available long-term clinical follow up data at a median follow up of 25.7 years. Significant predictors of OS were tumor size (median OFS 25.4 years for ≤2 cm vs. 7.5 years for >2 cm, p = 0.001), nodal status (median OS 17.2 years for node-negative patients vs. 6.7 years for node positive patients, p = 0.017), and CD44 expression (median OS 18.9 years for CD44 positive patients vs. 8.6 years for CD44 negative patients, p = 0.049). There was a trend toward increased PFS for patients with CD44 positive tumors (median PFS 17.9 vs. 4.3 years, p = 0.17), but this did not reach statistical significance. These findings illustrate the potential utility of CD44 as a prognostic marker for early stage breast cancer. Subgroup analysis in patients with lymph node involvement revealed CD44 positivity to be most strongly associated with increased survival, suggesting a potential role of CD44 in decision making for axillary management. As there is increasing interest in CD44 as a therapeutic target in ongoing clinical trials, the results of this study suggest additional investigation regarding the role CD44 in breast cancer is warranted.

Acute myeloid leukemia and novel biological treatments: monoclonal antibodies and cell-based gene-modified immune effectors

In the context of acute myeloid leukemia (AML) treatment, the interface between chemotherapy and immunotherapy is at present getting closer as never before. Scientific research is oriented in overcoming the main limits of actual chemotherapeutic regimens against AML, which still accounts for a considerable number of relapsed or resistant forms. A lot of investments have been done in the use of monoclonal antibodies (mAbs) and recently gene-modified immune cells have been considered as an alternative approach whenever chemotherapy fails to eradicate the disease. In this sense, AML is a potential suitable target for immunotherapeutic approaches, due to overexpression of several tumor antigens. Here we describe the state of the art of mAbs and cellular therapies employing engineered immune effectors, developed against specific AML antigens, in a window embracing preclinical research and translational studies to the clinical setting.

Pharmacokinetics and ADME characterizations of antibody-drug conjugates

Pharmacokinetic and absorption, distribution, metabolism, and excretion (ADME) characterization of antibody-drug conjugates (ADCs) reflects the dynamic interactions between the biological system and ADC, and provides critical assessments in lead selection, optimization, and clinical development. Understanding the pharmacokinetics (PK), ADME properties and consequently the pharmacokinetic-pharmacodynamic properties of ADCs is critical for their successful development. This chapter discusses the PK properties of ADCs, types of PK and ADME studies in supporting different stages of development, general design of PK/ADME studies with a focus on ADC-specific characteristics, and interpretation of PK parameters.

Antibody-drug conjugates: using monoclonal antibodies for delivery of cytotoxic payloads to cancer cells

One approach to improving activity of anticancer drugs is to conjugate them to antibodies that recognize tumor-associated, cell-surface antigens. The antibody-drug conjugate concept evolved following major advances, first, in the development of humanized and fully human antibodies; second, in the discoveries of highly cytotoxic compounds ('drugs) linkable to antibodies; and finally, in the optimization of linkers that couple the drug to the antibody and provide sufficient stability of the antibody-drug conjugate in the circulation, optimal activation of the drug in the tumor, and the ability of the activated drug to overcome multidrug resistance. In this article, we will review the considerations for selecting a target antigen, the design of the conjugate, and the pre-clinical and clinical experiences with the current generation of antibody-drug conjugates.

Immunological treatment options for locoregionally advanced head and neck squamous cell carcinoma

Patients with squamous cell carcinoma of the head and neck (HNSCC) are usually treated by a multimodal approach with surgery and/or radiochemotherapy as the mainstay of local-regional treatment in cases with advanced disease. Both chemotherapy and radiation therapy have the disadvantage of causing severe side effects, while the clinical outcome of patients diagnosed with HNSCC has remained essentially unchanged over the last decade. The potential of immunotherapy is still largely unexplored. Here the authors review the current status of the art and discuss the future challenges in HNSCC treatment and prevention.

Therapeutic potential of hyaluronan oligosaccharides for bone metastasis of breast cancer

Hyaluronan (HA) oligosaccharides were reported to have suppressive effects on various malignant tumors via disruption of receptor HA interactions. However, no studies have focused on the effects of HA oligosaccharides on bone metastasis of breast cancer. In this study, we clarified the effective size of HA oligosaccharides required to inhibit cell growth in the highly invasive breast cancer cell line, MDA-MB-231 cells. Based on the results of cell growth assay, we subsequently analyzed the effects of HA tetrasaccharides, HA decasaccharides, and high molecular weight HA on the other breast cancer cell behaviors in vitro and breast cancer bone metastasis in vivo. HA decasaccharides significantly inhibited cell growth, motility, and invasion, whereas tetrasaccharides did not. HAS2 mRNA expression was altered after the treatment with both tetrasaccharides and decasaccharides. Phosphorylation of Akt was suppressed after 1 h treatment with HA decasaccharides, and the effect was partially reversed by anti-CD44 monoclonal antibody. In vivo, local application of HA decasaccharides inhibited the expansion of osteolytic lesions in tibia on soft X-rays using mouse bone metastasis model of breast cancer. Histological analysis revealed HA accumulation in bone metastatic lesions was perturbed by decasaccharides. These results suggest that HA oligosaccharides suppressed progression of bone metastasis in breast cancer via interruption of endogenous HA-CD44 interaction, and as such, can be a novel therapeutic candidate to limit bone metastasis of breast cancer.

Targeted therapy in head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) of multi-factorial etiopathogenesis is rising worldwide. Treatment-associated toxicity problems and treatment failure in advanced disease stages with conventional therapies have necessitated a focus on alternative strategies. Molecular targeted therapy, with the potential for increased selectivity and fewer adverse effects, hold promise in the treatment of HNSCC. In an attempt to improve outcomes in HNSCC, targeted therapeutic strategies have been developed. These strategies are focusing on the molecular biology of HNSCC in an attempt to target selected pathways involved in carcinogenesis. Inhibiting tumor growth and metastasis by focusing on specific protein or signal transduction pathways or by targeting the tumor microenvironment or vasculature are some of the new approaches. Targeted agents for HNSCC expected to improve the effectiveness of current therapy include EGFR inhibitors (Cetuximab, Panitumumab, Zalutumumab), EGFR tyrosine kinase inhibitors (Gefitinib, Erloitinib), VEGFR inhibitors (Bevacizumab, Vandetanib), and various inhibitors of, e.g., Src-family kinase, PARP, proteasome, mTOR, COX, and heat shock protein. Moreover, targeted molecular therapy can also act as a complement to other existing cancer therapies. Several studies have demonstrated that the combination of targeting techniques with conventional current treatment protocols may improve the treatment outcome and disease control, without exacerbating the treatment related toxicities. Some of the targeted approaches have been proved as promising therapeutic potentials and are already in use, whereas remainder exhibits mixed result and necessitates further studies. Identification of predictive biomarkers of resistance or sensitivity to these therapies remains a fundamental challenge in the optimal selection of patients most likely to benefit from targeted treatment.

The Role of CD44 in the Pathogenesis, Diagnosis, and Therapy of Gastric Cancer

CD44 is a transmembrane glycoprotein and surface receptor for hyaluronan that is involved in the response of cells to their microenvironment. CD44 splice variants play roles in carcinogenesis, differentiation, and lymph node metastasis and are predictive of the prognosis for various carcinomas, including gastric cancer. Current data suggest that gastric tissue stem cells and gastric cancer stem cells both express the splice variant, CD44v9. Overall, the data regarding the alterations that occur in CD44 and its splice variants in response to acute and chronic infection with Helicobacter pylori are scant and poorly elucidated in terms of possible changes in expression that occur in gastric cancer precursor lesions, such as chronic atrophic gastritis, pyloric metaplasia and intestinal metaplasia. In this study, we discuss the available data and suggest which new data would likely be useful in clinical practice. We also discuss the potential for CD44-targeted therapeutic strategies in gastric cancer. CD44 and its splice variants are positively associated with the initiation and progression of gastric cancer and may also play important roles in diagnosis, therapy and prognosis. CD44 research has been active but fragmented, and it may offer new therapeutic approaches to gastric cancer.

The Role of CD44 in the Pathogenesis, Diagnosis, and Therapy of Gastric Cancer

CD44 is a transmembrane glycoprotein and surface receptor for hyaluronan that is involved in the response of cells to their microenvironment. CD44 splice variants play roles in carcinogenesis, differentiation, and lymph node metastasis and are predictive of the prognosis for various carcinomas, including gastric cancer. Current data suggest that gastric tissue stem cells and gastric cancer stem cells both express the splice variant, CD44v9. Overall, the data regarding the alterations that occur in CD44 and its splice variants in response to acute and chronic infection with Helicobacter pylori are scant and poorly elucidated in terms of possible changes in expression that occur in gastric cancer precursor lesions, such as chronic atrophic gastritis, pyloric metaplasia and intestinal metaplasia. In this study, we discuss the available data and suggest which new data would likely be useful in clinical practice. We also discuss the potential for CD44-targeted therapeutic strategies in gastric cancer. CD44 and its splice variants are positively associated with the initiation and progression of gastric cancer and may also play important roles in diagnosis, therapy and prognosis. CD44 research has been active but fragmented, and it may offer new therapeutic approaches to gastric cancer.

CD44: can a cancer-initiating cell profit from an abundantly expressed molecule?

Can an abundantly expressed molecule be a reliable marker for the cancer-initiating cells (CICs; also known as cancer stem cells), which constitute the minority of cells within the mass of a tumour? CD44 has been implicated as a CIC marker in several malignancies of haematopoietic and epithelial origin. Is this a fortuitous coincidence owing to the widespread expression of the molecule or is CD44 expression advantageous as it fulfils some of the special properties that are displayed by CICs, such as self-renewal, niche preparation, epithelial-mesenchymal transition and resistance to apoptosis?

Cancer stem cells: the development of new cancer therapeutics

INTRODUCTION

Cancer stem cells (CSCs) are a subpopulation of tumor cells with indefinite proliferative potential that drive the growth of tumors. CSCs seem to provide a suitable explanation for several intriguing aspects of cancer pathophysiology.

AREAS COVERED

An explosion of therapeutic options for cancer treatment that selectively target CSCs has been recorded in the recent years. These include the targeting of cell-surface proteins, various activated signalling pathways, different molecules of the stem cell niche and various drug resistance mechanisms. Importantly, approaching cancer research by investigating the pathogenesis of these intriguing cancer cells is increasing the knowledge of the pathophysiology of the disease, emphasizing certain molecular mechanisms that have been partially neglected.

EXPERT OPINION

The characterization of the molecular phenotype of these cancer stem-like cells, associated with an accurate definition of their typical derangement in cell differentiation, can represent a fundamental advance in terms of diagnosis and therapy of cancer. Preliminary results seem to be promising but further studies are required to define the therapeutic index of this new anticancer treatment. Moreover, understanding the pathogenetic mechanisms of CSCs can expand the therapeutic applications of normal adult stem cells by reducing the risk of uncontrolled tumorigenic stem cell differentiation.

Germline polymorphisms in genes involved in the CD44 signaling pathway are associated with clinical outcome in localized gastric adenocarcinoma

The cluster of differentiation 44 (CD44) signaling pathway is crucial in cancer-cell growth, invasion, proliferation and metastasis. CD44 is a transmembrane receptor for hyaluronan and osteopontin, and has recently attracted attention as a gastric cancer stem cell marker. Previous studies showed that polymorphisms in the CD44 gene can influence both human cancer survival and determine cellular response to cytotoxic chemotherapeutics. In addition, CD44 protein overexpression has been associated with poor prognosis in gastric adenocarcinoma (GA). We tested the hypothesis whether polymorphisms involved in the CD44 pathway will predict clinical outcome in patients with localized GA. Either blood or formalin-fixed paraffin-embedded (FFPE) tissues were obtained from 137 patients with localized GA at University of Southern California and Memorial Sloan-Kettering Cancer Center medical facilities. DNA was isolated and polymorphisms within the CD44 pathway were determined by PCR-RFLP technique. In univariate analysis CD44 rs187116 and CD44 rs7116432 were significantly associated with time to tumor recurrence (TTR) and overall survival (OS). After adjusting for covariates, patients harboring at least one G allele of CD44 rs187116 remained significantly associated with TTR (adjusted p=0.009) and OS (adjusted p=0.045). Further, patients harboring CD44 T-A haplotype were at the lowest risk of developing tumor recurrence (HR: 0.255; 95% CI: 0.11-0.591; adjusted p=0.001) and death (HR 0.198; 95% CI: 0.07-0.563; adjusted p=0.002). These results provide the first evidence that CD44 polymorphisms predict clinical outcome in patients with localized GA. This may help to identify localized GA patients at high risk for tumor recurrence.

Adhesion molecules--The lifelines of multiple myeloma cells

Multiple myeloma is an incurable hematological malignancy of terminally differentiated immunoglobulin-producing plasma cells. As a common presentation of the disease, the malignant plasma cells accumulate and proliferate in the bone marrow, where they disrupt normal hematopoiesis and bone physiology. Multiple myeloma cells and the bone marrow microenvironment are linked by a composite network of interactions mediated by soluble factors and adhesion molecules. Integrins and syndecan-1/CD138 are the principal multiple myeloma receptor systems of extracellular matrix components, as well as of surface molecules of stromal cells. CD44 and RHAMM are the major hyaluronan receptors of multiple myeloma cells. The SDF-1/CXCR4 axis is a key factor in the homing of multiple myeloma cells to the bone marrow. The levels of expression and activity of these adhesion molecules are controlled by cytoplasmic operating mechanisms, as well as by extracellular factors including enzymes, growth factors and microenvironmental conditions. Several signaling responses are activated by adhesive interactions of multiple myeloma cells, and their outcomes affect the survival, proliferation and migration of these cells, and in many cases generate a drug-resistant phenotype. Hence, the adhesion systems of multiple myeloma cells are attractive potential therapeutic targets. Several approaches are being developed to disrupt the activities of adhesion molecules in multiple myeloma cells, including small antagonist molecules, direct targeting by immunoconjugates, stimulation of immune responses against these molecules, and signal transduction inhibitors. These potential novel therapeutics may be incorporated into current treatment schemes, or directed against minimal residual malignant cells during remission.

Hyaluronan-CD44 Interactions in Cancer: Paradoxes and Possibilities

Hyaluronan is a prominent component of the micro-environment in most malignant tumors and can be prognostic for tumor progression. Extensive experimental evidence in animal models implicates hyaluronan interactions in tumor growth and metastasis, but it is also evident that a balance of synthesis and turnover by hyaluronidases is critical. CD44, a major hyaluronan receptor, is commonly but not uniformly associated with malignancy, and is frequently used as a marker for cancer stem cells in human carcinomas. Multivalent interactions of hyaluronan with CD44 collaborate in driving numerous tumor-promoting signaling pathways and transporter activities. It is widely accepted that hyaluronan-CD44 interactions are crucial in both malignancy and resistance to therapy, but major challenges for future research in the field are the mechanism of activation of hyaluronan-CD44 signaling in cancer cells, the relative importance of variant forms of CD44 and other hyaluronan receptors, e.g., Rhamm, in different tumor contexts, and the role of stromal versus tumor cell production and turnover of hyaluronan. Despite these caveats, it is clear that hyaluronan-CD44 interactions are an important target for translation into the clinic. Among the approaches that show promise are antibodies and vaccines to specific variants of CD44 that are uniquely expressed at critical stages of progression of a particular cancer, hyaluronidase-mediated reduction of barriers to drug access, and small hyaluronan oligosaccharides that attenuate constitutive hyaluronan-receptor signaling and enhance chemosensitivity. In addition, hyaluronan is being used to tag drugs and delivery vehicles for targeting of anticancer agents to CD44-expressing tumor cells. (Clin Cancer Res 2009;15(24):7462-8).

Alternative splicing of pre-mRNA in cancer: focus on G protein-coupled peptide hormone receptors

Through alternative splicing, multiple different transcripts can be generated from a single gene. Alternative splicing represents an important molecular mechanism of gene regulation in physiological processes such as developmental programming as well as in disease. In cancer, splicing is significantly altered. Tumors express a different collection of alternative spliceoforms than normal tissues. Many tumor-associated splice variants arise from genes with an established role in carcinogenesis or tumor progression, and their functions can be oncogenic. This raises the possibility that products of alternative splicing play a pathogenic role in cancer. Moreover, cancer-associated spliceoforms represent potential diagnostic biomarkers and therapeutic targets. G protein-coupled peptide hormone receptors provide a good illustration of alternative splicing in cancer. The wild-type forms of these receptors have long been known to be expressed in cancer and to modulate tumor cell functions. They are also recognized as attractive clinical targets. Recently, splice variants of these receptors have been increasingly identified in various types of cancer. In particular, alternative cholecystokinin type 2, secretin, and growth hormone-releasing hormone receptor spliceoforms are expressed in tumors. Peptide hormone receptor splice variants can fundamentally differ from their wild-type receptor counterparts in pharmacological and functional characteristics, in their distribution in normal and malignant tissues, and in their potential use for clinical applications.

Expression of 24,426 human alternative splicing events and predicted cis regulation in 48 tissues and cell lines

Alternative pre–messenger RNA splicing impacts development, physiology, and disease, but its regulation in humans is not well understood, partially due to the limited scale to which the expression of specific splicing events has been measured. We generated the first genome-scale expression compendium of human alternative splicing events using custom whole-transcript microarrays monitoring expression of 24,426 alternative splicing events in 48 diverse human samples. Over 11,700 genes and 9,500 splicing events were differentially expressed, providing a rich resource for studying splicing regulation. An unbiased, systematic screen of 21,760 4-mer to 7-mer words for cis-regulatory motifs identified 143 RNA 'words' enriched near regulated cassette exons, including six clusters of motifs represented by UCUCU, UGCAUG, UGCU, UGUGU, UUUU, and AGGG, which map to trans-acting regulators PTB, Fox, Muscleblind, CELF/CUG-BP, TIA-1, and hnRNP F/H, respectively. Each cluster showed a distinct pattern of genomic location and tissue specificity. For example, UCUCU occurs 110 to 35 nucleotides preceding cassette exons upregulated in brain and striated muscle but depleted in other tissues. UCUCU and UGCAUG appear to have similar function but independent action, occurring 5' and 3', respectively, of 33% of the cassette exons upregulated in skeletal muscle but co-occurring for only 2%.

Anticancer therapeutics: targeting macromolecules and nanocarriers to hyaluronan or CD44, a hyaluronan receptor

The complex system involved in the synthesis, degradation and binding of the high molecular weight glycosaminoglycan hyaluronic acid (hyaluronan or HA) provides a variety of structures that can be exploited for targeted cancer therapy. In many cancers of epithelial origin there is an upregulation of CD44, a receptor that binds HA. In other cancers, HA in the tumor matrix is overexpressed. Both CD44 on cancer cells and HA in the matrix have been targets for anticancer therapy. Even though CD44 is expressed in normal epithelial cells and HA is part of the matrix of normal tissues, selective targeting to cancer is possible. This is because macromolecular carriers predominantly extravasate into the tumor and not normal tissue; thus CD44-HA targeted carriers administered intravenously localize preferentially into tumors. Anti-CD44 antibodies have been used in patients to deliver radioisotopes or mertansine for treatment of CD44 expressing tumors. In early phase clinical trials, patients with breast or head and neck tumors treated with anti-CD44 conjugates experienced stabilized disease. A dose-limiting toxicity was associated with distribution of the antibody-drug conjugate to the skin, a site in the body with a high level of CD44. HA has been used as a drug carrier and a ligand on liposomes or nanoparticles to target drugs to CD44 overexpressing cells. Drugs can be attached to HA via the carboxylate on the glucuronic acid residue, the hydroxyl on the N-acetylglucosamine or the reducing end which are located on a repeating disaccharide. Drugs delivered in HA-modified liposomes exhibited excellent antitumor activity both in vitro and in murine tumor models. The HA matrix is also a potential target for anticancer therapies. By manipulating the interaction of HA with cell surface receptors, either by degrading it with hyaluronidase or by interfering with CD44-HA interactions using soluble CD44 proteins, tumor progression was blocked. Finally, cytotoxic drugs or prodrug converting enzymes can be attached to the HA matrix to generate a cytotoxic fence around the tumor. This review describes how the complex interplay among cancer biology, the CD44-HA interaction, drug carriers and drug targeting has been used to improve anticancer therapies. As these approaches evolve, they hold forth the prospect of significantly improved targeted anticancer treatments.