Search PubMed⌕ Search

Biomedical subjects

L Q Sun

Publications and source records attributed to L Q Sun.

At least 37 records · Page 2Linked to original sources
PubMed1999

Target site selection for an RNA-cleaving catalytic DNA.

A small catalytic DNA, known as the 10-23 DNA enzyme or deoxyribozyme, has been shown to efficiently hydrolyze RNA at purine-pyrimidine (R-Y) junctions in vitro. Although these potentially cleavable junctions are ubiquitous, they are often protected from deoxyribozyme activity by RNA secondary structure. We have developed a multiplex cleavage assay for screening the entire length of a target RNA molecule for deoxyribozyme cleavage sites that are efficient, both in terms of kinetics and accessibility. This strategy allowed us to simultaneously compare the RNA cleaving activity of 80 deoxyribozymes for a model target gene (HPV16 E6), and an additional 60 deoxyribozymes against the rat c-myc target. The human papilloma virus (HPV) target was used primarily to characterize the multiplex system and determine its validity. The c-myc target, coupled with a smooth muscle cell proliferation assay, allowed us to assess the relationship between in vitro cleavage efficiency and c-myc gene suppression in cell culture. The multiplex reaction approach streamlines the process of revealing effective deoxyribozymes in a functional assay and provides accessibility data that may also be applicable to site selection for other hybridization-based agents.

Animals↗
PubMed1998

(E)-2'-deoxy-2'-(fluoromethylene) cytidine potentiates radioresponse of two human solid tumor xenografts.

Antitumor and radiosensitizing effects of (E)-2'-deoxy-2'-(fluoromethylene) cytidine (FMdC), a novel inhibitor of ribonucleotide reductase, were evaluated on nude mice bearing s.c. human C33-A cervix cancer and U-87 MG glioblastoma xenografts. FMdC given once daily has a dose-dependent antitumor effect. The maximum tolerated dose in the mice was reached with 10 daily i.p. administrations of 10 mg/kg over 12 days. In the case of radiotherapy (RT) alone (10 fractions over 12 days), the radiation dose required to produce local tumor control in 50% of the treated C33-A xenografts was 51.0 Gy. When combined with FMdC, the radiation dose required to produce local tumor control was reduced to 41.4 and 38.2 Gy, at respective doses of 5 and 10 mg/kg given i.p. 1 h before each irradiation. The corresponding enhancement ratios (ERs) were 1.2 and 1.3, respectively. In U-87 MG xenografts, when 5-20 mg/kg FMdC combined with 30 or 40 Gy of RT, the combination treatment produced a significantly increased growth delay as compared with RT alone (P < or =0.002). The ERs of 5, 10, and 20 mg/kg FMdC at a dose of 30 Gy were 2.0, 1.4, and 1.8, respectively. At the 40-Gy level, ERs of 10 and 20 mg/kg FMdC were 1.4 and 1.7. When FMdC was combined with 50 Gy of RT, an increased long-term remission rate of 80-88.9% was observed, as compared with 25% for RT alone (P <0.05). FMdC produced moderate myelosuppression in the mice bearing cervix cancer, whereas leukocytosis occurred in the mice bearing glioblastoma at a low dose. Slightly increased skin toxicity (only with U-87 MG tumor) was observed, as compared with RT alone. In conclusion, FMdC is a potent cytotoxic agent and able to modify the radiation response of C33-A and U-87 MG xenografts.

Animals↗
PubMed1998

Preclinical characterization of an anti-tat ribozyme for therapeutic application.

A hammerhead ribozyme retroviral construct, denoted RRz2, targeting the coding region of the human immunodeficiency virus type 1 (HIV-1) tat gene, has shown itself to be effective in a range of test systems. Inhibition of the replication of HIV-1 IIIB and primary drug-resistant strains in pooled transduced CEMT4 cells was consistently found to be more than 80% compared with the control-vector transduced cells, whereas a mutant RRz2 gave approximately 45% inhibition. A multiple HIV-1 passage assay showed the absence of emergence of mutations within the specific viral RNA ribozyme target sequences. This lack of generation of ribozyme "escape mutants" occurred despite the almost complete disappearance of a HIV-1 quasi-species in the testing virus. When RRz2 was tested in peripheral blood lymphocytes (PBLs) from HIV-1-infected patients, paired analysis showed that cell viability in the ribozyme-transduced HIV-1-infected PBLs was significantly higher than that in the vector-transduced cells. This difference in viability (vector versus RRz2) was not observed in PBLs from non-HIV-1-infected donors. Taken together, these results indicate that the transfer of an anti-HIV-1 ribozyme gene into human T lymphocytes could have major impact on viral replication and T cell viability in the HIV-1-infected individual.

Base Sequence↗
PubMed1998

Adenovirus-mediated delivery of a uPA/uPAR antagonist suppresses angiogenesis-dependent tumor growth and dissemination in mice.

AdmATF is a recombinant adenovirus encoding a secreted version of the amino-terminal fragment (ATF) of murine urokinase (uPA). This defective adenovirus was used in three murine models to assess the antitumoral effects associated with local or systemic delivery of ATF, a broad cell invasion inhibitor that antagonizes uPA binding to its cell surface receptor (uPAR). A single intratumoral injection of AdmATF into pre-established MDA-MB-231 human breast xenografts grown in athymic mice, or into pre-established C57/BL6 syngeneic Lewis lung carcinoma resulted in a specific arrest of tumor growth. Neovascularization within and at the vicinity of the injection site was also suppressed, suggesting that AdmATF inhibited primary tumor growth by targeting angiogenesis. AdmATF also interfered with tumor cell establishment at distant sites: (1) lung dissemination of Lewis lung carcinoma cells was significantly reduced following intratumoral injection at the primary site; and (2) systemic administration of AdmATF inhibited subsequent liver metastasis in a LS174T human colon carcinoma xenograft model. These data outline the potential of using a recombinant adenovirus directing the secretion of an antagonist of cell-associated uPA for cancer gene therapy.

Adenoviridae↗
PubMed1998

Effect of pentoxifylline on radiation-induced G2-phase delay and radiosensitivity of human colon and cervical cancer cells.

Cells of three adherent cell lines with mutated p53 (WiDr and C33-A) and disrupted p53 (C4-I) were used to investigate the effect of pentoxifylline (PTX) on radiation-induced G2-phase block and its relationship to radiosensitivity. Postirradiation exposure to 0.25-1.0 mM PTX resulted in an increase in radiosensitivity in a concentration-dependent manner as determined by a clonogenic assay. The change in radiation sensitivity was quantified by calculating the enhancement ratio (ER) at a clinically relevant dose of 2 Gy; the ER for WiDr cells was 1.23+/-0.03 and 1.39+/-0.15 for 0.5 and 1.0 mM PTX, respectively. For C33-A cells, the ER ranged from 1.04+/-0.04 to 1.99+/-0.17 for 0.25-1.0 mM PTX, whereas for C4-I cells the values were 1.29+/-0.04 and 1.76+/-0.17 for 0.25 and 0.5 mM PTX. In asynchronous WiDr, C33-A and C4-I cells, flow cytometry analysis showed a dose-dependent accumulation of cells in G2/M phase which was detectable at 6 h and peaked at 12 h after irradiation. Such a G2/M-phase block was transient at a dose of 2 Gy and persisted at 48 or 72 h after a dose of 4 or 6 Gy. At 12 h after 2 Gy, PTX significantly reduced the radiation-induced G2/M-phase block in a dose-dependent manner. After the higher doses of 4 and 6 Gy, the dose-dependent G2-phase arrest was significantly alleviated at 24 h by treatment with PTX, and the kinetics of this alleviation depended on the radiation dose. The results demonstrate that human colon and cervical cancer cells characterized by a mutated or disrupted p53 (i.e. not transfected) are radiosensitized by PTX, which alleviates the postirradiation G2/M-phase block.

Cell Cycle↗
PubMed1997

Antitumor and radiosensitizing effects of (E)-2'-deoxy-2'-(fluoromethylene) cytidine, a novel inhibitor of ribonucleoside diphosphate reductase, on human colon carcinoma xenografts in nude mice.

Antitumor and radiosensitizing effects of (E)-2'-deoxy-2'-(fluromethylene) cytidine (FMdC), a novel inhibitor of ribonucleotide reductase, were evaluated on nude mice bearing s.c. xenografts and liver metastases of a human colon carcinoma. FMdC given once daily or twice weekly has a dose-dependent antitumor effect. The maximum tolerated dose in the mice was reached with 10 mg/kg applied daily over 12 days. Twice weekly administration of FMdC reduced its toxicity but lowered the antitumor effect. Treatment of preestablished liver micrometastases obtained via intrasplenic injection of tumor cells, with 5 or 10 mg/kg FMdC, significantly prolonged the survival of the mice as compared to controls (P < 0.025 and P < 0.001, respectively). Ten mg/kg resulted in longer survival than 5 mg/kg FMdC (P < 0.05). Radiotherapy alone of s.c. xenografts (10 fractions over 12 days) yielded the radiation dose required to produce local tumor control in 50% of the treated mice (TCD50) of 43.0 Gy. When combined with FMdC, TCD50 was reduced to 22.5 and 19.0 Gy at doses of 5 and 10 mg/kg given i.p. 1 h before each irradiation, respectively. The corresponding enhancement ratios were 1.91 and 2.43, respectively. FMdC produced moderate and reversible myelosuppression. When 5 mg/kg FMdC was combined with irradiation, there was no increased skin or hematological toxicity as compared to radiotherapy or FMdC alone. At the 10 mg/kg level, however, lower leukocyte counts were observed. These results show that FMdC appears to be a potent anticancer drug and radiosensitizer.

Animals↗
PubMed1997

Timing effects of combined radioimmunotherapy and radiotherapy on a human solid tumor in nude mice.

Timing effects of radioimmunotherapy (RIT) combined with external-beam radiotherapy (RT) were assessed in human colon carcinoma xenografts. Initially, dose effects of fractionated RT and RIT were evaluated separately. Then, 30 Gy RT (10 fractions over 12 days) were combined with three weekly i.v. injections of 200 microCi of 131I-labeled anti-carcinoembryonic antigen monoclonal antibodies in four different treatment schedules. RIT was given either prior to, concurrently, immediately after, or 2 weeks after RT administration. The longest regrowth delay (RD) of 105 days was observed in mice treated by concurrent administration of RT and RIT, whereas the RDs of RT and RIT alone were 34 and 20 days, respectively. The three sequential combination treatments produced significantly shorter RDs ranging from 62 to 70 days. The tumor response represented by the minimal volume (MV) also showed that concurrent administration of RT and RIT gave the best result, with a mean MV of 4.5% as compared to MVs from 26 to 53% for the three sequential treatments. The results were confirmed in a second experiment, in which a RT of 40 Gy was combined with an identical RIT as above (three injections of 200 microCi of 131I-labeled monoclonal antibodies). At comparable toxicity levels, the maximum tolerated RT or RIT alone gave shorter RDs and less tumor shrinkage compared to simultaneous RT+ RIT. These results may be useful for designing clinical protocols of combined RIT and RT.

Animals↗
PubMed1997

Anti-HIV ribozymes.

HIV is an RNA virus that replicates intracellularly through various RNA intermediates. Several of these can be targeted by ribozymes (catalytic RNA molecules), and a number of investigators, including this group, have demonstrated the ability of ribozymes to suppress HIV replication in this way. It is argued that this gene therapy approach may be viewed as an adjunct to chemotherapeutic drugs, which may allow not just viral suppression, but also immune restoration. This can only finally be tested in clinical trials, and several are planned. The basic ribozyme unit, the potential of which was described less than 10 years ago, is about to be tested in an amunable disease state.

Acquired Immunodeficiency Syndrome↗
PubMed1996

Carcinoembryonic antigen expression, antibody localisation and immunophotodetection of human colon cancer liver metastases in nude mice: a model for radioimmunotherapy.

Colorectal cancer frequently disseminates through the portal vein into the liver. In this study, outbred Swiss nude mice were adapted to facilitate the induction of liver metastases by a pre-grafting treatment with 6 Gy total body irradiation and i.v. injection of anti-asialo GM1 antibody. One day later, cultured LS 174T human colon cancer cells were injected into the surgically exposed spleen, which was resected 3 min later. In 48 of 65 mice, a few to several hundred liver metastases were macroscopically observed at dissection 3 to 4 weeks after transplantation. Ten of 10 mice, followed-up for survival, died with multiple large confluent liver metastases. By reducing the radiation dose to 4 or 0 Gy, or omitting the anti-asialo GM1 antibody injection, only 60%, 37% or 50% of mice, respectively, had visible metastases 3 weeks after transplantation. Carcinoembryonic antigen (CEA) measured in tumour extracts was in the mean 25.6 micrograms/g in liver metastases compared with 9.2 micrograms/g in s.c. tumours. Uptake of radiolabelled anti-CEA monoclonal antibody (MAb) in the metastases 12, 24 and 48 hr after injection gave a mean value of 39% of the injected dose per gram of tissue (ID/g). In comparison, MAb uptake in s.c. and intrasplenic tumours or lung metastases gave a mean percentage ID/g of 20, 18 and 15, respectively. Laser-induced fluorescence after injection of indocyanin-MAb conjugate allowed direct visual detection of small liver metastases, including some that were not visible under normal light. Preliminary results showed that mice, pre-treated with 4 Gy irradiation and the anti-asialo GM1 injection, were tolerant to radioimmunotherapy with a total dose of 500 muCi 131I labeled anti-CEA intact MAbs given in 3 injections.

Animals↗
PubMed1995

Target sequence-specific inhibition of HIV-1 replication by ribozymes directed to tat RNA.

The structural motif formed between a hammerhead ribozyme and its substrate consists of three RNA double helices in which the sequence 5' to the XUY is termed helix I and the sequence 3' to the XUY helix III. Two hammerhead ribozymes targeted to the tat gene of HIV-1SF2 were designed to study target specificity and the potential effect of helix I mismatch on ribozyme efficacy both in vitro and in vivo. The first ribozyme (Rz1) targeted to the 5' splicing region of the tat gene was designed to cleave GUC*A. In HIV-1IIIB the A is changed to a G. The second ribozyme (Rz2) was targeted to the translational initiation region of the tat gene which is highly conserved among a variety of HIV-1 isolates, including both HIV-1SF2 and HIV-1IIIB. In vitro cleavage studies demonstrated that Rz1 efficiency cleaved HIV-1SF2 substrate RNA, but not HIV-1IIIB, presumably due to the base change from A to G. In contrast, Rz2 cleaved HIV-1SF2 or HIV-1IIIB substrate with equal efficiency. Both ribozymes were cloned into the 3' untranslated region of the neomycin gene (neo) within the pSV2neo vector and transfected into the SupT1 human CD4+ T cell line. Following selection, stable transfectants were challenged with either HIV-1SF2 or HIV-1IIIB virus. While Rz1-expressing cells were significantly protected from HIV-1SF2 infection, they exhibited no protection when infected with HIV-1IIIB virus. In contrast, Rz2 was effective in inhibiting the replication of both HIV-1SF2 and HIV-1IIIB in SupT1 cells. Expression of both ribozymes in these cells was demonstrated by Northern analysis. RT-PCR sequencing analysis confirmed the respective HIV-1 target sequence integrity. These data demonstrate the importance of the first base pair distal to the XUY within helix I of the hammerhead structure for both in vitro and in vivo ribozyme activities and imply that the effectiveness of the anti-HIV-1 ribozymes against appropriate target sequences is due to their catalytic activities rather than any antisense effect.

Base Sequence↗
PubMed1995

Resistance to human immunodeficiency virus type 1 infection conferred by transduction of human peripheral blood lymphocytes with ribozyme, antisense, or polymeric trans-activation response element constructs.

Human peripheral blood lymphocytes (PBLs) were transduced with a number of recombinant retroviruses including RRz2, an LNL6-based virus with a ribozyme targeted to the human immunodeficiency virus (HIV) tat gene transcript inserted within the 3' region of the neomycin-resistance gene; RASH5, and LNHL-based virus containing an antisense sequence to the 5' leader region of HIV-1 downstream of the human cytomegalovirus promoter; and R20TAR, an LXSN-based virus with 20 tandem copies of the HIV-1 trans-activation response element sequence driven by the Moloney murine leukemia virus long terminal repeat. After G418 selection, transduced PBLs were challenged with the HIV-1 laboratory strain IIIB and a primary clinical isolate of HIV-1, 82H. Results showed that PBLs from different donors could be transduced and that this conferred resistance to HIV-1 infection. For each of the constructs, a reduction of approximately 70% in p24 antigen level relative to the corresponding control-vector-transduced PBLs was observed. Molecular analyses showed constitutive expression of all the transduced genes from the retroviral long terminal repeat, but no detectable transcript was seen from the internal human cytomegalovirus transcript was seen from the internal human cytomegalovirus promoter for the antisense construct. Transduction of, and consequent transgene expression in, PBLs did not impact on the surface expression of either CD4+/CD8+ (measured by flow cytometry) or on cell doubling time (examined by [3H]thymidine uptake). These results indicate the potential utility of these anti-HIV-1 gene therapeutic agents and show the preclinical value of this PBL assay system.

Animals↗
PubMed1995

Combined radioimmunotherapy and radiotherapy of human colon carcinoma grafted in nude mice.

The effect of combined radioimmunotherapy (RIT) and fractionated external beam radiotherapy (RT) was assessed in two human colon cancer xenografts, Co112 and LS174T in nude mice. These tumors were selected for being resistant to RIT alone, as is usually the case in the clinical situation. Tumor-bearing mice were treated with a combination of five X-ray fractions over 5 days followed by RIT with two doses of 1.5 mCi 131I-labeled anticarcinoembryonic antigen monoclonal antibody F(ab')2. In Co112 and LS174T, RIT alone achieved a regrowth delay similar to that of fractionated RT with total doses of 28 and 26 Gy, respectively. In both tumor types, an additive therapeutic effect, measured as increased regrowth delay or local control, was observed when combining RT of different dose levels with RIT. Normal tissue responses were assessed by monitoring acute peak skin reactions and blood cell count. Bone marrow depression for the combination treatment was similar to that of RIT alone; relative to skin, at equitoxic levels, no mice bearing Co112 tumors were locally controlled with a 32 Gy RT dose alone, while this RT combined with RIT gave a local control of 100%. These studies show a therapeutic benefit when external beam RT is combined with RIT.

Animals↗
PubMed1994

Ribozyme-mediated suppression of Moloney murine leukemia virus and human immunodeficiency virus type I replication in permissive cell lines.

Several hammerhead ribozymes targeted to different sites within the retroviral packaging (psi) sequences of the Moloney murine leukemia virus (Mo-MLV) and the human immunodeficiency virus type 1 (HIV-1) were designed and shown to cleave target RNA in vitro at the chosen sites. The engineered ribozymes, as well as antisense sequence complementary to the Mo-MLV psi packaging region, were cloned into the 3' untranslated region of the neomycin-resistance gene (neo). This was coupled to the simian virus 40 early promoter within the pSV2neo vector. For the ribozymes against the Mo-MLV psi site, the constructs were transfected into Mo-MLV-infected and virus-producing mouse NIH 3T3 cells. With the exception of one of the single ribozymes (the one least effective in cutting target RNA in vitro), all of the constructs effectively (70-80%) suppressed retrovirus production. These results demonstrate a direct correlation between in vitro cleavage and in vivo ribozyme-mediated virus suppression. In addition, a ribozyme targeted to the HIV-1 psi packaging site was engineered into the same vector and transfected into the human T-cell line SupT1. The transfectants were cloned and then challenged with HIV-1. When compared to vector-transfected control cells, a significant reduction in HIV-1 production was observed as measured by p24 and syncytia formation assays. This study demonstrates a feasible approach to the suppression of retrovirus replication by targeting the psi packaging site with hammerhead ribozymes.

3T3 Cells↗
PubMed1991

Sputum occult blood screening for lung cancer. Stage II screening of 14,431 subjects.

Sputum occult blood screening (SOBS) for lung cancer was performed in outpatients with suspected lung cancer. A total of 1011 patients were seen. Among them, 604 patients were found to be negative for SOBS, and 407 were found to be positive. The false-negative rate was 3.97% (24 of 604), and the opposite positive rate was 19.65% (80 of 407). A total of 14,431 normal subjects over 40 years of age were screened by SOBS. In the series, 1942 specimens were found to be positive. Among the 1942 patients, 31 were found to have definite cancer cells.

Adult↗
PubMed1989

Purification of ovine prolactin by affinity chromatography with monoclonal antibodies.

Five monoclonal antibodies (McAbs) against ovine prolactin (oPRL) were obtained by the lymphocyte hybridoma technique. One low-affinity McAb with (2D2) was purified by hydroxylapatite chromatography. The 2D2 was immobilized on Sepharose 4B with epichlorohydrin to produce an immunosorbent column, which was used to purify oPRL from a crude preparation by a single-step procedure.

Animals↗
PubMed1985

Human uropepsinogen is a new human pepsinogen proisozyme.

The first 20 amino acid residues of human uropepsinogen has been determined to be H2N-Ile-Met-Tyr-Lys-Val-Pro-Leu-Pro-Ile-Lys-Lys-Ile-Leu-Val Val-Pro-Leu-Ile-Val-Tyr-Met. Comparison with the sequence of human stomach pepsinogen shows that these proteins are isozymes. Comparative sequence data are presented and discussed.

Amino Acid Sequence↗