Biomedical subjects

Robert B Campbell

Publications and source records attributed to Robert B Campbell.

7 recordsLinked to original sources

PubMed2006

Development of 5-FU and doxorubicin-loaded cationic liposomes against human pancreatic cancer: Implications for tumor vascular targeting.

PURPOSE: Human pancreatic adenocarcinoma is a major leading cause of cancer mortality in the United States. Given that current strategies are relatively ineffective against this disease, new treatments are being developed. Liposomes possessing relatively high cationic lipid content preferentially accumulate in tumor angiogenic vessels compared to vessels in normal tissues. We therefore seek to develop cationic liposomes for targeting pancreatic tumor vessels. MATERIALS AND METHODS: We report development of 5-fluorouracil (5-FU) and doxorubicin hydrochloride (DOX) loaded in PEGylated cationic liposomes (PCLs). We evaluate cell association, intracellular fate, and cytotoxicity. Human pancreatic cancer cells HPAF-II and Capan-1, and endothelial cells HMEC-1 and HUVEC were used in this study. Intratumoral distribution of PCLs in (HPAF-II) tumors was determined by intravital microscopy. RESULTS: HUVEC and HMEC-1 were most susceptible to 5-FU after 24 and 48 h, compared to HPAF-II and Capan-1. We observed >90% incorporation of 5-FU and DOX in PCLs for 3-20 mol% preparations, with reduced incorporation for >20 mol% formulations. PCLs showed significantly higher association with human endothelial versus pancreatic cancer cells, and improved growth inhibitory properties of DOX. Intravital microscopy revealed distribution of PCLs along HPAF-II vessels. CONCLUSIONS: Targeting human pancreatic cancer with PCLs may represent a rational alternative to conventional strategies.

Adenocarcinoma↗

PubMed2006

Tumor physiology and delivery of nanopharmaceuticals.

Over the past few decades significant advances have been made in the development of nanopharmaceuticals (including phospholipid and polymer-based therapeutics) against cancer. There is still, however, room for improvement. Today, many researchers are focusing on the development of innovative approaches to selectively deliver drugs to solid tumors, while minimizing insult to healthy tissues. Unfortunately, the majority of these efforts are confronted by physiological barriers that reduce the clinical dose required to effectively manage the disease state. In an effort to develop promising nanopharmaceutical products of the future, we review the most important problems facing drug delivery experts today. We discuss here, the physiological role of solid tumors in delivery and transport of nanopharmaceutical products. The nature of tumors in terms of their unique anatomical structure and functions is also discussed. Finally, an overview of ways to overcome physiological barrier functions and exploit tumor pathogenesis for therapeutic gain is provided.

Animals↗

PubMed2005

PTEN enters the nucleus by diffusion.

Despite much evidence for phosphatidylinositol phosphate (PIP)-triggered signaling pathways in the nucleus, there is little understanding of how the levels and activities of these proteins are regulated. As a first step to elucidating this problem, we determined whether phosphatase and tensin homolog deleted on chromosome 10 (PTEN) enters the nucleus by passive diffusion or active transport. We expressed various PTEN fusion proteins in tsBN2, HeLa, LNCaP, and U87MG cells and determined that the largest PTEN fusion proteins showed little or no nuclear localization. Because diffusion through nuclear pores is limited to proteins of 60,000 Da or less, this suggests that nuclear translocation of PTEN occurs via diffusion. We examined PTEN mutants, seeking to identify a nuclear localization signal (NLS) for PTEN. Mutation of K13 and R14 decreased nuclear localization, but these amino acids do not appear to be part of an NLS. We used fluorescence recovery after photobleaching (FRAP) to demonstrate that GFP-PTEN can passively pass through nuclear pores. Diffusion in the cytoplasm is retarded for the PTEN mutants that show reduced nuclear localization. We conclude that PTEN enters the nucleus by diffusion. In addition, sequestration of PTEN in the cytoplasm likely limits PTEN nuclear translocation.

Cell Line, Tumor↗

PubMed2004

Two-photon fluorescence correlation microscopy reveals the two-phase nature of transport in tumors.

Transport parameters determine the access of drugs to tumors. However, technical difficulties preclude the measurement of these parameters deep inside living tissues. To this end, we adapted and further optimized two-photon fluorescence correlation microscopy (TPFCM) for in vivo measurement of transport parameters in tumors. TPFCM extends the detectable range of diffusion coefficients in tumors by one order of magnitude, and reveals both a fast and a slow component of diffusion. The ratio of these two components depends on molecular size and can be altered in vivo with hyaluronidase and collagenase. These studies indicate that TPFCM is a promising tool to dissect the barriers to drug delivery in tumors.

Animals↗

PubMed2003

Allosteric activation of PTEN phosphatase by phosphatidylinositol 4,5-bisphosphate.

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a tumor suppressor that is lost in many human tumors and encodes a phosphatidylinositol phosphate phosphatase specific for the 3-position of the inositol ring. Here we report a novel mechanism of PTEN regulation. Binding of di-C8-phosphatidylinositol 4,5-P2 (PI(4,5)P2) to PTEN enhances phosphatase activity for monodispersed substrates, PI(3,4,5)P3 and PI(3,4)P2. PI(5)P also is an activator, but PI(4)P, PI(3,4)P2, and PI(3,5)P2 do not activate PTEN. Activation by exogenous PI(4,5)P2 is more apparent with PI(3,4)P2 as a substrate than with PI(3,4,5)P3, probably because hydrolysis of PI(3,4)P2 yields PI(4)P, which is not an activator. In contrast, hydrolysis of PI(3,4,5)P3 yields a potent activator, PI(4,5)P2, creating a positive feedback loop. In addition, neither di-C4-PI(4,5)P2 nor inositol trisphosphate-activated PTEN. Hence, the interaction between PI(4,5)P2 and PTEN requires specific, ionic interactions with the phosphate groups on the inositol ring as well as hydrophobic interactions with the fatty acid chains, likely mimicking the physiological interactions that PTEN has with the polar surface head groups and the hydrophobic core of phospholipid membranes. Mutations of the apparent PI(4,5)P2-binding motif in the PTEN N terminus severely reduced PTEN activity. In contrast, mutation of the C2 phospholipid-binding domain had little effect on PTEN activation. These results suggest a model in which a PI(4,5)P2 monomer binds to PTEN, initiates an allosteric conformational change and, thereby, activates PTEN independent of membrane binding.

Allosteric Site↗

PubMed2002

Cationic charge determines the distribution of liposomes between the vascular and extravascular compartments of tumors.

Tumor vessels possess unique physiological features that might be exploited for improving drug delivery. In the present study, we investigate the possibility of modifying polyethylene glycol-ylated liposome cationic charge of polyethylene glycol coated liposomes to optimize delivery to tumor vessels using biodistribution studies and intravital microscopy. The majority of liposomes accumulated in the liver, and increasing charge resulted in lower retention in the spleen and blood. Although overall tumor uptake was not affected by charge in the biodistribution studies, intravital microscopy showed that increasing the charge content from 10 to 50 mol % doubled the accumulation of liposomes in tumor vessels, suggesting a change in intratumor distribution; no significant effect of charge on interstitial accumulation could be detected, possibly attributable to spatial heterogeneity. Increased vascular accumulation of cationic liposomes was similar in two different tumor types and sites. Our results suggest that optimizing physicochemical properties of liposomes that exploit physiological features of tumors and control the intratumor distribution of these drug carriers should improve vascular-specific delivery.

Adenocarcinoma↗

PubMed2002

Propofol, a general anesthetic, promotes the formation of fluid phase domains in model membranes.

The molecular site of anesthetic action remains an area of intense research interest. It is not clear whether general anesthetics act through direct binding to proteins or by perturbing the membrane properties of excitable tissues. Several studies indicate that anesthetics affect the properties of either membrane lipids or proteins. However, gaps remain in our understanding of the molecular mechanism of anesthetic action. Recent developments in membrane biology have led to the concept of small-scale domain structures in lipid and lipid--protein coupled systems. The role of such domain structures in anesthetic action has not been studied in detail. In the present study, we investigated the effect of anesthetics on lipid domain structures in model membranes using the fluorescent spectral properties of Laurdan (6-dodecanoyl-2-dimethylamino naphthalene). Propofol, a general anesthetic, promoted the formation of fluid domains in model membranes of dipalmitoyl phosphatidyl choline (DPPC) or mixtures of lipids of varying acyl chains (DPPC:DMPC dimyristoyl phosphatidyl choline 1:1). The estimated size of these domains is 20--50 A. Based on these studies, we speculate that the mechanism of anesthetic action may involve effects on protein--lipid coupled systems through alterations in small-scale lipid domain structures.

1,2-Dipalmitoylphosphatidylcholine↗