Abstract
The effects of N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide (H-8) and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7) on the growth of P388 and its multidrug-resistant (MDR) variants were examined with the objective of assessing the possible changes in cyclic nucleotide-dependent protein kinases and protein kinase C-mediated pathways associated with MDR. H-8, an inhibitor of cyclic nucleotide-dependent protein kinases, inhibited the growth of the parental P388 murine leukaemic cells, but not that of MDR variants up to 200 microM. However the growth of both drug-sensitive and resistant cell lines were uniformly inhibited by H-7. Both the cytotoxic and cytokinetic results revealed that the growth-inhibition by H-8 of P388 cells is mainly due to a blockade of cell-cycle progression rather than due to a killing of cells. The degree of resistance to H-8 was directly proportional to their extent of resistance to vincristine, adriamycin, and 4'-demethylepipodophyllotoxin-9-(4,6-O-ethylidene)-beta-D-gluco pyr anoside (VP-16) and to that of the expression of P-glycoprotein. These findings raised the possibility that P-glycoprotein might play a role in the cross-resistance to H-8. To test the hypothesis, we examined the effect of H-8 on the binding of 3H-vincristine to membrane fraction isolated from P388/VCR-600 cells and on the enhancement of cytotoxicity to anticancer drugs in MDR cells. H-8 did not have any influences on these reactions. Thus, the cross-resistance to H-8 may be mediated through a mechanism different from an overexpression of P-glycoprotein.(ABSTRACT TRUNCATED AT 250 WORDS)
Highlights
To determine if the resistance to H-8 observed in MDR P388 cells could be due to an overexpression of P-glycoprotein and a decreased accumulation of H-8, we assessed the effect of H-8 on the binding of 3H-vincristine to membrane fraction isolated from P388/VCR-600 cells and on the enhancement of sensitivity to anti-tumour drugs in MDR cells
Our results show that H-8 does not have any effect on these reactions, suggesting that the resistance to H-8 is mediated through a mechanism different from an overexpression of P-glycoprotein
In comparison with the parental P388 cells, P388/VCR and P388/VCR-600 cells were 14.3 and 289.6-fold resistant to vincristine, respectively. These two cell lines showed crossresistance to adriamycin and VP-16 according to their extent of resistance to vincristine
Summary
Chemicals Vincristine sulfate was purchased from Shionogi Ltd, Osaka, Japan and dissolved with methanol acidified with sulfuric acid at pH 4.3. Adriamycin was purchased from Kyowa Hakko Ltd, Tokyo, Japan. 9-(4,6-O-ethylidene)-p-D-glucopyranoside (VP-16) was purchased from Bristol Myers. H-7 and H-8 were purchased from Seikagaku Kogyo, Tokyo, Japan and dissolved with distilled water and stored at 4C at the concentration of. All these drugs were sterilised through a 0.2 ftm Corning filter. Adenosine 3':5'-cyclic monophosphate (cAMP), guanosine 3':5'-cyclic monophosphate (cGMP), Kemptide (Maller et al, 1978) were purchased from Sigma. 3H(-G)vincristine (7.4 Ci mM '), '25I-labelled F(ab') fragment of sheep anti-mouse IgG, and [j-32P]ATP (3,000 Ci mmol1'). C219 monoclonal antibody was kindly provided from Dr V. Ling (Ontario Cancer Research Institute, Toronto, Canada)
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