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Biomedical subjects

L H Li

Publications and source records attributed to L H Li.

At least 73 records · Page 4Linked to original sources
PubMed1987

Drug sensitivity of ten human tumor cell lines compared to mouse leukemia (L1210) cells.

L1210 leukemia cells, because of their rapid growth rate in suspension culture and high growth fraction, are ideally suited to screen in vitro for cytotoxic compounds. Although L1210 cells may mimic rapidly growing tumors, they have not been effective in selecting agents active against slow growing solid tumors. We expected that cell lines originating from human solid tumors, because of their slower growth rate and lower S phase fraction, would be more drug resistant than L1210. Therefore, we compared ten human tumor cell lines (5 melanomas, 4 colon carcinomas and 1 small cell lung carcinoma) to L1210 growth inhibition by 9 antitumor drugs. Not one human tumor cell line was consistently more resistant to all nine drugs than L1210 when the cells were exposed to drugs for about 2 doubling times. The drug sensitivity of 2 cell lines (L1210 and SK MEL 28) was again determined after a short term (2 hr) exposure and using growth inhibition and cell survival as end points. For both end points these two cell lines exhibited a random pattern of sensitivity to the drugs tested. Cell kill showed an order of sensitivity different than growth inhibition. The implication of these findings for drug-screening is discussed.

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PubMed1987

Effect of mouse hepatitis virus infection on combination therapy of P388 leukemia with cyclophosphamide and pyrimidinones.

At least three marked differences were noted in the results compared from two parallel experiments using identical protocols with virus-free mice and mouse hepatitis virus (MHV) infected mice inoculated with P388 leukemia. First, the therapeutic effect of cyclophosphamide (CY), a cytotoxic antitumor drug, was apparently augmented in MHV-infected mice. A 162% increase of life span (ILS) was obtained in MHV-infected mice compared to a 100% ILS in uninfected mice. Second, the experimental error in terms of the range of animal survival time was much larger with MHV-infected mice than with uninfected mice. In MHV-infected mice, the therapeutic effect of the combination treatment with CY and pyrimidinone was not statistically different from that of the treatment with CY alone. In uninfected mice, the effects of the combination therapy at all doses of pyrimidinone were statistically more effective than that of CY treatment alone.

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PubMed1987

Antitumor activity of pyrimidinones, a class of small-molecule biological response modifiers.

This study was undertaken in an attempt to evaluate the structure-activity relationship of pyrimidinones. Of 20 pyrimidinones tested, only those with a monohalogen substitution at the ortho- or meta-position of the phenyl moiety of the 2-amino-5-halo-6-phenyl-4(3H)-pyrimidinone and ABPP showed statistically significant synergism with cyclophosphamide (CY) against P388 leukemia. Therefore, ABMFPP, AIMFPP, and ABPP were selected for detailed therapeutic evaluation. The pyrimidinone alone had small but significant activity against B16 melanoma with slightly more than a 25% increase in lifespan (ILS); however, when used in combination with CY, ABPP or ABMFPP did not yield an effect greater than treatment with CY alone. Only AIMFPP appeared to produce a more or less additive effect with CY. Although none of these pyrimidinones alone had any significant activity against M5076 tumor, the combination with CY (100 mg/kg) produced a range of 102 to 123% ILS and six to nine of 10 mice per group survived greater than 45 days, whereas the treatment with CY alone yielded only a 48% ILS and none survived greater than 45 days. The synergism of the combination therapy was statistically significant (p less than 0.01). The combination used against L1210 leukemia also appeared to be superior to the treatment with CY alone and produced 25 to 50% long-term survivors (greater than 30 days). The significance of these findings is discussed in terms of its clinical implications.

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PubMed1986

Cell cycle effects of prostaglandins A1, A2, and D2 in human and murine melanoma cells in culture.

Our interest in prostaglandins (PGs) as antitumor agents stemmed from the report of Bregman and Meyskens (Cancer Res., 43: 1642-1645, 1983) that PGA1, PGA2, and PGD2 inhibited colony formation by human melanoma cells obtained from fresh biopsies of melanoma patients. We tested several PGs and found that PGA1, PGA2, and PGD2 were the most cytotoxic to L1210 cells in culture. Therefore, we studied these PGs for their effects on growth, cell survival, and cell progression of murine (B16) and human (RPMI7932,SK Mel 28) melanoma cells in culture. Although the three PGs equally inhibited the growth of B16 cells, PGD2 was more inhibitory to RPMI 7932 or SK Mel 28 than PGA1 or PGA2. Similarly the three PGs were almost equally active in inhibiting colony formation by B16 cells. However, against human melanoma cells, PGD2 was much more active than PGA1, whereas PGA2 was inactive. Towards the end of our study, we obtained PGJ2 and found that it was as cytotoxic as PGD2 for L1210 cells but was more lethal for human melanoma cells. The primary effect of all three PGs was to block cell progression from G1 to S. At 2.5 micrograms of PGD2 per ml, the blockade of cells in G1 and normal progression through the other phases resulted in accumulation of 80-90% of the cells in G1. At this dose, there was no inhibition of DNA synthesis, and cells in S progressed apparently normally through S, until all cells were blocked in G1. DNA synthesis was inhibited at 5 micrograms/ml which slowed cell progression through S and accumulated cells in G1. The partial synchronization of cells in G1 may be useful in devising new combinations of PGD2 with antitumor drugs.

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PubMed1985

Mechanism of antitumor action of pyrimidinones in the treatment of B16 melanoma and P388 leukemia.

This study was undertaken in an attempt to understand the mechanism of antitumor action of pyrimidinones alone and in combination with cyclophosphamide (CY). Pyrimidinones such as 2-amino-5-bromo-6-(3-fluorophenyl)-4(3H)pyrimidinone (ABMFPP) were relatively nontoxic toward murine L1210 leukemia cell growth in vitro with the concentration of drug required for a 50% inhibition of cell growth being greater than 50 micrograms/ml. In contrast, ABMFPP showed anti-B16 melanoma activity in vivo which was sensitive to X-irradiation of the hosts. These results collectively suggest that pyrimidinones may act differently from conventional cytotoxic antitumor agents. Multiple i.p. injections of ABMFPP (125 mg/kg/injection) significantly augmented the cytotoxicity of both natural killer cells and macrophages in peritoneal exudates. The augmentation of both effector cell populations was delayed, but was more pronounced when animals received a dose of CY (100 mg/kg) prior to ABMFPP injections. The combination of CY and ABMFPP also showed a synergistic anti-P388 leukemia effect which appeared to be related to the initial reduction of the tumor burden by CY and the marked augmentation of the cytotoxicity of both natural killer cells and macrophages by ABMFPP. The antitumor activity of ABMFPP against B16 melanoma was almost completely eliminated when animals received a dose of 400 rads X-irradiation 5 days prior to tumor inoculation or a dose of 200 rads X-irradiation followed by several injections of anti-asialo monosialoganglioside antibody. The administration of anti-asialo monosialoganglioside alone also markedly reduced the anti-B16 melanoma activity of ABMFPP. The magnitude of reduction of the antitumor effect of ABMFPP by radiation and/or anti-asialo monosialoganglioside antibody directly correlated with the inhibition of the ABMFPP-mediated augmentation of immune responses. These results strongly suggest that the antitumor effect of ABMFPP alone or in combination with CY is at least in part mediated through its augmentation of natural killer cell and/or macrophage activities.

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PubMed1984

Mechanism of action of didemnin B, a depsipeptide from the sea.

With the brush border membrane vesicles prepared from the rat kidney cortex, didemnin B and its parent compound, didemnin A function neither as a K+-specific ionophore nor as an ionophore for Na+ ions while other depsipeptide antibiotics such as valinomycin and gramicidin promote transmembrane movement of K+ and Na+ ions, respectively. Didemnin B inhibits protein synthesis and DNA synthesis much more than RNA synthesis and is in general more potent than didemnin A. Time course studies reveal that the action of didemnin B is rapid and cannot be reversed after 2 h in contact with the cells. The inhibition of protein synthesis is almost superimposable to that of L1210 cells growth. DNA synthesis is also markedly inhibited. These results collectively suggest that didemnin B acts differently, at least in part, from other depsipeptide antibiotics and its biological effect is primarily mediated through its inhibition of protein synthesis and to a lesser extent its inhibition of DNA synthesis.

Animals↗
PubMed1984

Biochemical and cellular effects of didemnins A and B.

Didemnins are a new class of cyclic depsipeptides in which didemnin A is the major component, didemnin B the minor component, and a trace of didemnin C is present. Didemnin B was more potent than was didemnin A against B16 melanoma and P388 leukemia in vivo, and B was also approximately 20 times more cytotoxic than was didemnin A in vitro. Therefore, didemnin B was studied in greater detail for its biochemical and cellular effects. Didemnin B inhibited the in vitro growth of B16 greater than L1210 greater than V-79 cells = human foreskin fibroblast = 9L greater than Chinese hamster ovary cells. Didemnin B was more lethal to exponentially growing B16 cells (50% lethal dose for a 2-hr exposure, 17.5 ng/ml) than to plateau-phase cells (50% lethal dose for a 2-hr exposure, 100 ng/ml). After a 24-hr exposure, the 50% lethal dose for exponential- and plateau-phase B16 cells was 8.8 and 59.6 ng/ml, respectively. Chinese hamster ovary cells were not killed even at 25,000 ng/ml. Mitotic cells were the least sensitive to didemnin B, and cells became more sensitive as they progressed into G1 and S phase. However, since cells in all phases were killed, didemnin B cannot be considered a phase-specific agent. Didemnin B inhibited the synthesis of protein more than that of DNA, with much less inhibition of RNA synthesis. Cell progression studies showed that high doses (300 ng/ml for 2 hr or 100 ng/ml for 24 hr) of didemnin B "froze" the cells in their respective phases with complete inhibition of cell progression or growth. At low doses (10 ng/ml for 2 hr or 3 ng/ml for 24 hr), the cells were blocked at the G1-S border thereby increasing the percentage of G1 cells and decreasing the percentage of S-phase cells. Cells continued to progress from S phase to G2 + M and from G2 + M to G1. The cytotoxicity to different cell lines and inhibition of macromolecule synthesis by didemnin A is also reported.

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PubMed1984

Chemoimmunotherapy of B 16 melanoma and P388 leukemia with cyclophosphamide and pyrimidinones.

Since increasing evidence indicates that combination modality of cancer treatment is preferable, and a series of 5-halo-6- phenylpyrimidinones has been found to induce interferon production and to stimulate a variety of immune responses, several were tested alone or in combination with cyclophosphamide (CY) against B 16 melanoma and P388 leukemia. Thus far, 2-amino-5-bromo-6-(3-fluorophenyl)-4(3H)pyrimidinone ( ABMFPP ) and its sister compound 2-amino-5-bromo-6-(2-fluorophenyl)-4(3H)pyrimidinone ( ABOFPP ) were found to be superior to other pyrimidinones including 2-amino-5-bromo-6-(6-phenyl)-4-pyrimidinone which is currently under clinical investigation. Neither ABMFPP nor ABOFPP alone had any significant activity against P388 leukemia. However, a marked synergistic effect was observed when a single i.p. injection of CY at 24 hr after tumor inoculation (10(6) cells/mouse) was followed by multiple i.p. injections of either ABMFPP or ABOFPP . For instance, the increase of life span was about 180% when animals received both CY (150 mg/kg) and ABMFPP (125 mg/kg/injection) as compared to 100% increased life span when animals received CY alone, and 0% increased life span when animals received ABMFPP alone. Also, 80% of the animals were long-term survivors (greater than 30 days) when animals received the combination therapy as compared to 20% survivors when animals received CY alone. The synergistic effect exhibited by ABMFPP or ABOFPP correlated positively to the initial reduction of tumor burden by CY. The optimal gap between CY and pyrimidinone administration was one day. The best therapeutic response was observed when pyrimidinone was given every 4 days for a total of 7 injections; however, other schedules and dosing frequencies also gave significant responses. The synergistic effect was also observed with B 16 melanoma when animals received the combination therapy. The significance of these findings, in terms of theoretical consideration as well as drug development, is discussed.

Animals↗
PubMed1983

Antiviral and antitumor compounds from tunicates.

Tunicates provide a rich source of biologically active compounds with potentially useful medicinal properties. The most interesting compounds identified thus far are the didemnins, depsipeptides from a Caribbean Trididemnum species, which are potent inhibitors of L1210 leukemia cells in vitro and are also active in vivo against P388 leukemia and B16 melanoma. In addition the didemnins inhibit growth of a variety of RNA and DNA viruses in vitro and protect mice infected intravaginally with herpes simplex virus type 2. Didemnin B, a derivative of didemnin A, is far more active than A, which argues for the likelihood of further useful chemical modifications in the series.

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PubMed1982

CC-1065 (NSC 298223), a novel antitumor agent that interacts strongly with double-stranded DNA.

CC-1065, a novel antibiotic produced by Streptomyces zelensis, was active against several experimental tumors in vivo and a broad spectrum of human tumor cells in vitro. This report describes its biological and biochemical effects of L1210 leukemia cells. CC-1065 is one of the most cytotoxic agents known. The concentrations required for a 50 and 90% inhibition of cell growth are 0.02 and 0.05 ng/ml, respectively. It is about 400 times more cytotoxic than was Adriamycin. The action of CC-1065 is rapid and is dose and time dependent. CC-1065 inhibits DNA synthesis much more than it inhibits RNA and protein synthesis. The concentrations required for a 50% inhibition of DNA synthesis and RNA synthesis are 4 to 6 and 45 to 60 ng/ml, respectively. Although the drug inhibition of DNA synthesis cannot completely account for its cytotoxic effects on L1210 cells, these results, along with those generated by other investigators, suggest that the inhibition of DNA synthesis represents a major mode of action of CC-1065. CC-1065 inhibited both thymidine kinase and DNA polymerase alpha activities, but the effect on highly purified DNA polymerase alpha was more pronounced. At 1 microgram/ml, CC-1065 inhibited more than 70% of the enzyme activity. In order to elucidate the mechanism of inhibition of DNA polymerase alpha, the interaction between CC-1065 and DNA was investigated. The studies with thermal melting of DNA and difference circular dichroism measurement indicate that CC-1065 is one of the strongest DNA-binding agents. It induced an increase in thermal melting temperature of calf thymus DNA by at least 31 degrees. The circular dichroism studies also reveal that CC-1065 binds only to double-stranded DNA but not to heat-denatured DNA or yeast RNA. These observations were supported by those obtained with two other experimental approaches. CC-1065 also appeared to interact with proteins, but the interaction was weak and reversible.

Animals↗
PubMed1982

Mechanism of interaction of CC-1065 (NSC 298223) with DNA.

CC-1065 (NSC 298223), a potent new antitumor antibiotic produced by Streptomyces zelensis, interacts strongly with double-stranded DNA and appears to exert its cytotoxic effects through disruption of DNA synthesis. We undertook this study to elucidate the sites and mechanisms of CC-1065 interaction with DNA. The binding of CC-1065 to synthetic and native DNA was examined by differential circular dichroism or by Sephadex chromatography with photometric detection. The binding of CC-1065 with calf thymus DNA was rapid, being complete within 2 hr, and saturated at 1 drug per 7 to 11 base pairs. The interaction of CC-1065 with synthetic DNA polymers indicated a specificity for adenine- and thymine-rich sites. Agarose gel electrophoresis of CC-1065-treated supercoiled DNA showed that CC-1065 did not intercalate. Site exclusion studies using substitutions in the DNA grooves showed CC-1065 to bind primarily in the minor groove. CC-1065 did not cause DNA breaks; it inhibited susceptibility of DNA to nuclease S1 digestion. It raised the thermal melting temperature of DNA, and it inhibited the ethidium-induced unwinding of DNA. Thus, in contrast to many antitumor agents, CC-1065 stabilized the DNA helix. DNA helix overstabilization may be relevant to the mechanism of action of CC-1065.

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PubMed1981

Didemnins: antiviral and antitumor depsipeptides from a caribbean tunicate.

Extracts of samples of a Caribbean tunicate (ascidian, sea squirt) of the family Didemnidae inhibit in vitro at low concentrations the growth of DNA and RNA viruses as well as L1210 leukemic cells. The active compounds isolated from the tunicate, didemnins A, B, and C, are depsipeptides, and didemnin B (a derivative of didemnin A) is the component active at the lowest concentration in inhibiting viral replication in vitro and P388 leukemia in vivo.

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