Showing papers by "Bo Lu published in 2004"

Optimal multivariate matching before randomization.

Abstract: SUMMARY Although blocking or pairing before randomization is a basic principle of experimental design, the principle is almost invariably applied to at most one or two blocking variables. Here, we discuss the use of optimal multivariate matching prior to randomization to improve covariate balance for many variables at the same time, presenting an algorithm and a case-study of its performance. The method is useful when all subjects, or large groups of subjects, are randomized at the same time. Optimal matching divides a single group of 2n subjects into n pairs to minimize covariate differences within pairs—the so-called nonbipartite matching problem—then one subject in each pair is picked at random for treatment, the other being assigned to control. Using the baseline covariate data for 132 patients from an actual, unmatched, randomized experiment, we construct 66 pairs matching for 14 covariates. We then create 10 000 unmatched and 10 000 matched randomized experiments by repeatedly randomizing the 132 patients, and compare the covariate balance with and without matching. By every measure, every one of the 14 covariates was substantially better balanced when randomization was performed within matched pairs. Even after covariance adjustment for chance imbalances in the 14 covariates, matched randomizations provided more accurate estimates than unmatched randomizations, the increase in accuracy being equivalent to, on average, a 7% increase in sample size. In randomization tests of no treatment effect, matched randomizations using the signed rank test had substantially higher power than unmatched randomizations using the rank sum test, even when only 2 of 14 covariates were relevant to a simulated response. Unmatched randomizations experienced rare disasters which were consistently avoided by matched randomizations.

XIAP and survivin as therapeutic targets for radiation sensitization in preclinical models of lung cancer

Abstract: Survivin and XIAP are members of inhibitors of apoptosis (IAPs) family. They are upregulated in various malignancies. Inactivation of these molecules has resulted in chemosensitization. The purpose of this study was to determine whether inhibition of survivin, XIAP, or both enhances radiotherapy in a lung cancer model. Transient transfection of H460 cells with antisense oligonucleotides (ASOs) against either molecule has specifically reduced their expression, by Western analysis. Results from 3-(4,5-methylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide and clonogenic assays suggest that inhibition of survivin or XIAP greatly decreased cell survival following irradiation. A significantly increased number of apoptotic cells were detected when H460 cells were treated with either antisurvivin, anti-XIAP or both ASOs (P=0.03, 0.0003 and 0.01, respectively) plus irradiation. H460 xenografts that were treated with ASOs plus radiotherapy demonstrated growth delay beyond 15 days. Growth delay in the groups of combined treatment was greater than that in other groups. However, treatment with ASOs alone did not affect tumor growth delay in mice, but decreased the survival of H460 cells in culture. Antisense treatment did not cause any mortality or weight loss during the 32 days of study. These data suggest that inhibition of survivin or XIAP radiosensitizes H460 lung cancer cells by upregulating apoptosis and downregulating cell survival. Combination of radiotherapy and inhibition of survivin and XIAP through the antisense approach results in improved tumor control by radiotherapy in a mouse model of lung cancer.

Survivin As a Therapeutic Target for Radiation Sensitization in Lung Cancer

Abstract: Expression of survivin is elevated in most malignancies, especially in radiation-resistant cell lines. In this study, we investigated how radiation affects survivin expression in primary endothelial cells as well as in malignant cell lines. We found that 3 Gy significantly reduced survivin protein level in human umbilical vein endothelial cells (HUVECs) but not in tumor cell lines. Flow cytometry studies suggest that the down-regulation of survivin is independent of cell cycle. In addition, survivin mRNA level was also down-regulatable by irradiation. However, it was abrogated by actinomycin D-mediated inhibition of gene transcription. Luciferase reporter gene assays suggest that irradiation suppressed the survivin promoter. p53 overexpression reduced survivin expression, but overexpression of a p53 mutant failed to abolish the radiation-induced down-regulation in HUVECs. Alteration of p53 status in Val138 lung cancer cell line also failed to restore the radiation-inducible down-regulation. Overexpression of survivin in 293 cells prevented apoptosis induced by irradiation and increased cell viability after irradiation. The inhibition of survivin using antisense oligonucleotides caused a significant decrease in cell viability of irradiated H460 lung cancer cells. These data suggest that radiation transcriptionally down-regulates survivin in HUVECs. This regulatory mechanism is defective in malignancies and is not mediated by p53. Survivin overexpression may lead to resistance to radiotherapy by inhibiting apoptosis and enhancing cell viability. The inhibition of survivin results in sensitization of H460 lung cancer cells to radiation. These studies suggest that survivin may be a target for cancer therapy.

Nuclear survivin as a biomarker for non-small-cell lung cancer

Abstract: Survivin inhibits apoptosis and promotes mitosis. We determined whether nuclear or cytoplasmic localisation of survivin predicts survival of 48 patients with resected non-small-cell lung cancer (NSCLC). Patients with nuclear staining of survivin had significantly worse survival (relative risk: 3.9, P=0.02). Therefore, survivin may be a biomarker for NSCLC.

Optimal Pair Matching With Two Control Groups

Abstract: In an effort to detect hidden biases due to failure to control for an unobserved covariate, some observational or nonrandomized studies include two control groups selected to systematically vary the unobserved covariate. Comparisons of the treated group and two control groups must, of course, control for imbalances in observed covariates. Using the three groups, we form pairs optimally matched for observed covariates—that is, we optimally construct from observational data an incomplete block design. The incomplete block design may use all available data, or it may use data selectively to produce a balanced incomplete block design, or it may be the basis for constructing a matched sample when expensive outcome information is to be collected only for sampled individuals. The problem of optimal pair matching with two control groups is shown by a series of transformations to be equivalent to a particular form of optimal nonbipartite matching, a problem for which polynomial time algorithms exist. In our exampl...

Receptor tyrosine kinase inhibitors as anti-angiogenic agents.

Abstract: Receptor tyrosine kinases (RTKs) and their ligands have been implicated in angiogenesis and current data suggest that they are potential cancer therapeutic targets. Split-kinase domain RTKs, including receptors for vascular endothelial growth factor receptor, platelet-derived growth factor and fibroblast growth factor, have important roles in tumor angiogenesis. RTK inhibitors targeting tumor microvasculature have shown promising results in preclinical studies, and use of these compounds as single agents, or in combination with other cytotoxic therapies, including radiation, is an area of active clinical investigation. Preclinical and clinical data from representative anti-angiogenic RTK inhibitors will be discussed in this review.

Broad spectrum receptor tyrosine kinase inhibitor, SU6668, sensitizes radiation via targeting survival pathway of vascular endothelium.

Abstract: Purpose Recent studies have demonstrated radiosensitization by inhibiting receptor tyrosine kinases (RTKs). Irradiation activates RTKs and their downstream prosurvival molecule, Akt. In this study, we investigated the mechanism by which SU6668, an inhibitor of RTKs involved in angiogenic pathways, enhances effects of irradiation. Methods and materials Western blots were used to determine Akt phosphorylation. Clonogenic assays were performed to determine endothelial survival after combination of SU6668 and irradiation. This combination therapy was also tested in mouse models with Lewis lung carcinoma or glioblastoma multiforme (GL261) for inhibition of tumor growth and tumor vasculature by examining tumor volume, tumor vascular window, and blood flow. Results We found that SU6668 inhibited the Akt activation inducible by irradiation. Clonogenic survival of endothelial cells was decreased after the combined therapy compared with radiotherapy alone. In vivo studies demonstrated reduction of tumor vasculature and blood flow. In addition, 21 Gy in 7 fractions given concurrently with SU6668 resulted in tumor growth delay compared to either treatment alone. Conclusion These data suggest that the combination therapy was more effective in destroying tumor vasculature than either treatment alone. SU6668 augments tumor-suppressive effects of radiotherapy in Lewis lung carcinoma and GL261 xenographs, possibly through reducing the survival of tumor endothelium.

The use of antisense oligonucleotides in evaluating survivin as a therapeutic target for radiation sensitization in lung cancer

Abstract: Elucidating the mechanism of over and under expression of proteins is critical in developing a better understanding of cancer. Multiple techniques are used to examine differential expression of proteins in cells and assess changes in protein expression in response to therapies such as radiation. Reduced expression can be caused by protein inactivation, mRNA instability, or reduced transcription. The following protocol was used to determine the mechanism for the reduced expression of an antiapoptotic factor, survivin, in normal tissues in response to radiation and the defect in cancer cells that prevents this reduction. We also examined ways to overcome survivin over expression in cancer cells in order to sensitize them to radiation. We will focus on the use of antisense oligonucleotides, cell cycle analysis, and luciferase reporter genes.

The Use of Gene Therapy in Cancer Research and Treatment

Abstract: Gene therapy involves identifying a gene of interest and then manipulating the expression of this gene through a variety of techniques. Here we specifically address gene therapy's role in cancer research. This paper will encompass thoroughly investigated techniques such as cancer vaccines and suicide gene therapy and the latest advancements in and applications of these techniques. It will also cover newer techniques such as Antisense Oligonucleotides and small interfering RNAs and how these technologies are being developed and used. The use of gene therapy continues to expand in cancer research and has an integral role in the advancement of cancer treatment.

Radiation-guided drug delivery systems.

Abstract: A primary limiting factor for cancer treatment is normal tissue toxicity. Targeted cancer treatment can potentially maximize cancer cure and minimize normal tissue toxicity. Physical energy can be used to activate inert oncologic drugs. X-rays have an advantage over other forms of physical energy because tissue penetration and precise localization can be achieved. Radiation can be used to control drug delivery through radiation-inducible gene therapy. Radiation-guided drug delivery systems involve the targeting of immunoconjugates to radiation-inducible neoantigens induced by irradiation of neoplasms. Magnetic fields can compliment these technologies by drawing magnetic particles containing oncologic drugs toward an externally applied magnetic field. The field of targeted drug delivery by use of external radiation fields will ultimately bring new delivery systems into clinical trials. This review highlights radiation-guided cancer drug delivery systems, at preclinical and clinical stages of development, t...