Enhancement of thermal effect in virally infected mammalian cells in vitro and its modification by chlorpromazine.

NIH/3T3 cells chronically infected with Moloney murine leukemia virus (M-MuLV) were more thermosensitive than uninfected cells. Cells upregulated by a primary dose of heat formed giant colonies and had an altered response to a second dose of heat. Thermosensitivity depended upon the time elapsed between heat treatments. Heating the cells at either 42 degrees or 42.5 degrees C yielded biphasic survival curves, indicating a mixed population of productively infected and quiescent cells. Hyperthermia at 43 degrees C abolished this effect. Thermal sensitivity of infected cells was correlated with the expression of a viral reporter protein. Chlorpromazine (CPZ), a membrane active drug potentiated the heat effect in both uninfected and virally infected cells. The drug also abolished the biphasic effect of heat in infected cells, suggesting that heat sensitivity of both productively and quiescent cells is membrane mediated. The combined effect of heat at 42.5 degrees C and CPZ was equivalent to the effect of heat alone at 43.5 degrees C. These observations indicate that heat can selectively be lethal to productively infected cells and the membrane active drugs could further amplify this hyperthermic effect.

Suppression of multidrug resistance via inhibition of heat shock factor by quercetin in MDR cells

MDR1 promoter has been shown to contain heat shock elements (HSE), and it has been reported that FM3A/M and P388/M MDR cells show a constitutively activated heat shock factor (HSF), suggesting that HSF might be an important target for reversing the multidrug resistance. Therefore, it was examined whether quercetin, which has been shown to interfere with the formation of the complex between HSE and HSF, and to downregulate the level of HSF1, can sensitize MDR cells against anticancer drugs by inhibition of HSF DNA-binding activity. In this study, quercetin appeared to inhibit the constitutive HSF DNA-binding activity and the sodium arsenite-induced HSF DNA-binding activity in the MDR cells. The basal and sodium arsenite-induced MDRCAT activities were remarkably suppressed by the treatment of quercetin. These results were well consistent with the finding that the treatment of quercetin decreased the expression level of P-gp, MDR1 gene product, in dose-dependent manner, and markedly increased the sensitivity of MDR cells to vincristine or vinblastine. These results suggest that quercetin can decrease the expression of P-gp via inhibition of HSF DNA-binding activity, and might be useful as a chemosensitizer in MDR cells.

Anti-retroviral effect of chlorophyll derivatives (CpD-D) by photosensitization

A new photosensitizer, CpD(chlorophyll derivatives), previously reported as a promising agent for tumor therapy, was studied to determine its inhibitory effects on Gross leukemia virus(GLV), a mouse retrovirus isolated from the GLV-producing TGV cell line, and the cytocidal effect on the GLV infected cells in vitro, following photodynamic treatment with CpD-D and red light, the viral inactivation and infectivity were examined by measuring the reverse transcriptase(RT) activity of the virus itself and that in cell-free culture supernatant of freshly GLV-infected secondary mouse embryo cells respectively. The cytocidal activity was measured by trypan blue exclusion test. Inhibition of GLV associated RT activity resulted from CpD-D and red light treatment. The RT inhibition effect was immediate and the infectivity of these photodynamically treated GLV to mouse embryo cells was also inhibited. However, specific cytotoxicity of GLV infected cells was not found. Thus, it is concluded that CpD-D may be used as an effective antiviral agent.

Effects of cimetidine combination with cyclophosphamide in transplanted murine tumors.

Studies were carried out on the combination of Cimetidine (CMTD) with Cytoxan (CTX) in three murine tumors. While the combination significantly potentiated the anticancer effect of CTX in L1210 leukemia, the results with P388 leukemia were not significantly different. The results with Lewis Lung Carcinoma showed a consistent reduction in the number of metastases. However, there was no consistent concomitant prolongation in survival. The host strain, biology of the tumour and the drug used in combination with CMTD might be some of the factors responsible for the varied response.

Inability of amphotericin B(Fungizone) or of sodium deoxycholate to alter natural drug resistance or sensitivity of transplanted murine leukemias.

The ability of Amphotericin B ('Fungizone') to alter the natural resistance of leukemia L1210 to vincristine was studied in BDF1 mice Neither Fungizone nor the "solubilizing agent" sodium deoxycholate, when used in combination with vincristine potentiated the activity of the drug against L1210. There was no change in the activity pattern of 5-fluorouracil against L1210 or vincristine against P388 lymphocytic leukemia respectively, which are sensitive to these drugs. Thus, both Fungizone and sodium deoxycholate failed to improve the activity of the drugs in either a naturally resistant or sensitive murine leukemia in vivo.