Thermo- and pH-responsive polymers in drug delivery.

Recent observations indicate that, in several types of human cancer, only a phenotypic subset of cancer cells within each tumor is capable of initiating tumor growth. This functional subset of cancer cells is operationally defined as the “cancer stem cell” (CSC) subset. Here we developed a CSC model for the study of human colorectal cancer (CRC). Solid CRC tissues, either primary tissues collected from surgical specimens or xenografts established in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice, were disaggregated into single-cell suspensions and analyzed by flow cytometry. Surface markers that displayed intratumor heterogeneous expression among epithelial cancer cells were selected for cell sorting and tumorigenicity experiments. Individual phenotypic cancer cell subsets were purified, and their tumor-initiating properties were investigated by injection in NOD/SCID mice. Our observations indicate that, in six of six human CRC tested, the ability to engraft in vivo in immunodeficient mice was restricted to a minority subpopulation of epithelial cell adhesion molecule (EpCAM)high/CD44+ epithelial cells. Tumors originated from EpCAMhigh/CD44+ cells maintained a differentiated phenotype and reproduced the full morphologic and phenotypic heterogeneity of their parental lesions. Analysis of the surface molecule repertoire of EpCAMhigh/CD44+ cells led to the identification of CD166 as an additional differentially expressed marker, useful for CSC isolation in three of three CRC tested. These results validate the stem cell working model in human CRC and provide a highly robust surface marker profile for CRC stem cell isolation.

https://www.pnas.org/content/pnas/104/24/10158.full.pdf

Phenotypic characterization of human colorectal cancer stem cells

Polymers that can respond to external stimuli are of great interest in medicine, especially as controlled drug release vehicles. In this critical review, we consider the types of stimulus response used in therapeutic applications and the main classes of responsive materials developed to date. Particular emphasis is placed on the wide-ranging possibilities for the biomedical use of these polymers, ranging from drug delivery systems and cell adhesion mediators to controllers of enzyme function and gene expression (134 references).

Stimuli responsive polymers for biomedical applications

Since its inception just over a half century ago, the field of biomaterials has seen a consistent growth with a steady introduction of new ideas and productive branches. This review describes where we have been, the state of the art today, and where we might be in 10 or 20 years. Herein, we highlight some of the latest advancements in biomaterials that aim to control biological responses and ultimately heal. This new generation of biomaterials includes surface modification of materials to overcome nonspecific protein adsorption in vivo, precision immobilization of signaling groups on surfaces, development of synthetic materials with controlled properties for drug and cell carriers, biologically inspired materials that mimic natural processes, and design of sophisticated three-dimensional (3-D) architectures to produce well-defined patterns for diagnostics, e.g., biological microelectromechanical systems (bioMEMs), and tissue engineering.

BIOMATERIALS: Where We Have Been and Where We Are Going

Injectable hydrogels with biodegradability have in situ formability which in vitro/in vivo allows an effective and homogeneous encapsulation of drugs/cells, and convenient in vivo surgical operation in a minimally invasive way, causing smaller scar size and less pain for patients. Therefore, they have found a variety of biomedical applications, such as drug delivery, cell encapsulation, and tissue engineering. This critical review systematically summarizes the recent progresses on biodegradable and injectable hydrogels fabricated from natural polymers (chitosan, hyaluronic acid, alginates, gelatin, heparin, chondroitin sulfate, etc.) and biodegradable synthetic polymers (polypeptides, polyesters, polyphosphazenes, etc.). The review includes the novel naturally based hydrogels with high potential for biomedical applications developed in the past five years which integrate the excellent biocompatibility of natural polymers/synthetic polypeptides with structural controllability via chemical modification. The gelation and biodegradation which are two key factors to affect the cell fate or drug delivery are highlighted. A brief outlook on the future of injectable and biodegradable hydrogels is also presented (326 references).

Injectable and biodegradable hydrogels: gelation, biodegradation and biomedical applications

Because hematopoietic stem cells are rich in aldehyde dehydrogenase (ALDH) activity, we developed a fluorescent substrate for ALDH, termed BODIPY aminoacetaldehyde (BAAA), and tested its potential for isolating primitive human hematopoietic cells. A population of cells with low orthogonal light scattering and bright fluorescence intensity (SSCloALDHbr cells) could be readily fractionated from human umbilical cord blood cells costained with BAAA and the multidrug-resistance inhibitor verapamil. The SSCloALDHbr population was depleted of lineage-committed cells, 40–90% pure for CD34+CD38lo/− cells, and enriched 50- to 100-fold for primitive hematopoietic progenitors detected in short- and long-term culture analyses. Together, these observations indicate that fractionating human hematopoietic stem cells on the basis of ALDH activity using BAAA is an effective method for isolating primitive human hematopoietic progenitors. This technique may be useful for isolating stem cells from other tissues as well.

https://www.pnas.org/content/pnas/96/16/9118.full.pdf

Isolation of primitive human hematopoietic progenitors on the basis of aldehyde dehydrogenase activity.

Evaluation of an elastin-like polypeptide-doxorubicin conjugate for cancer therapy

This is primarily an overview of the spontaneous (non-enzymatic) chemistry of the metabolites of cyclophosphamide, viz., cis- and trans-4-hydroxycyclophosphamide, aldophosphamide (and its hydrate), iminophosphamide, phosphoramide mustard, acrolein, and chloroethylaziridine. A brief description of detoxification products obtained through enzyme catalyzed reactions appears. Included as the historical basis for the development of cyclophosphamide is the chemistry of nitrogen mustards. Among the topics covered are: perturbations to metabolite distributions and half-lives effected by buffer, structure, pH and nucleophiles; effects of pH on mechanism; alkylation versus P-N bond hydrolysis; the influence of nucleophiles on alkylation product distributions; the influence of substituents on alkylation rates; and preactivated forms of cyclophosphamide as metabolite precursors (4-hydroperoxycyclophosphamide and mafosfamide). A review with 66 references.

The chemistry of the metabolites of cyclophosphamide.

The Chemistry of the Metabolites of Cyclophosphamide

A series of bifunctional alkylators were tested against the genotypically and phenotypically heterogeneous continuous human medulloblastoma cell lines, TE-671, Daoy, and D283 Med in vitro and against TE-671 and Daoy growing as s.c. and intracranial xenografts in athymic mice. Drugs tested included melphalan, cyclophosphamide, iphosphamide, phenylketocyclophosphamide, thiotepa, 1,3-bis(2-chloroethyl)-1-nitrosourea (in vivo), and busulfan (in vivo). Melphalan and phenylketocyclophosphamide were the most active agents in vitro with drug doses at which there is a 90% reduction in the number of colonies in comparison to controls of 2.13, 5.29, and 4.72 microM for melphalan and 4.60, 5.01, and 4.34 microM for phenylketocyclophosphamide against TE-671, D283 Med, and Daoy, respectively. Melphalan, cyclophosphamide, iphosphamide, phenylketocyclophosphamide, and thiotepa produced significant growth delays against s.c. TE-671 and Daoy xenografts, while no activity could be demonstrated for 1,3-bis(2-chloroethyl)-1-nitrosourea or busulfan. Melphalan, cyclophosphamide, iphosphamide, and thiotepa also produced significant increases in median survival in mice bearing intracranial TE-671 and Daoy xenografts. These results extend our previous studies demonstrating the antitumor activity of nitrogen and phosphoramide mustard-based bifunctional alkylating agents in the treatment of human medulloblastoma continuous cell lines and transplantable xenografts, and support the continued use of these agents in clinical trials.

https://cancerres.aacrjournals.org/content/canres/48/15/4189.full.pdf

Susan M. Ludeman

Papers

Isolation of primitive human hematopoietic progenitors on the basis of aldehyde dehydrogenase activity.

Evaluation of an elastin-like polypeptide-doxorubicin conjugate for cancer therapy

The chemistry of the metabolites of cyclophosphamide.

The Chemistry of the Metabolites of Cyclophosphamide

Experimental chemotherapy of human medulloblastoma cell lines and transplantable xenografts with bifunctional alkylating agents.