The relationship between multi‐drug resistance and resistance to natural‐killer‐cell and lymphokine‐activated killer‐cell lysis in human leukemic cell lines

Abstract

Results concerning a possible link between susceptibility to natural-cell-mediated immune cytolysis and the multi-drug resistance (MDR) phenotype are conflicting. We evaluated in human acute lymphocytic leukemia the relationship between acquired drug resistance and susceptibility to cytolysis mediated by endogenous, interferon-activated, and interleukin-2-activated natural cytotoxic cells. Eight human leukemia drug-resistant/sensitive cell line pairs were evaluated; drug-resistant sub-lines included those selected for primary resistance to adriamycin, etoposide, teniposide, vincristine, and vinblastine. A majority of P-glycoprotein-positive MDR sub-lines displayed slight but statistically significant resistance to endogenous and/or interferon-activated natural-killer(NK)-cell-mediated lysis, as compared with the drug-sensitive parental type. P-glycoprotein-negative sub-lines displayed variable NK susceptibility; within this group, the variants selected for primary etoposide resistance were more susceptible to NK cytolysis than parental cells. Results of cold-target-inhibition experiments suggest that altered NK susceptibility does not arise solely from modulation of NK target recognition and adherence structures. IL2-activated killer (LAK) cells lysed both drug-sensitive and drug-resistant lines. Two MDR lines selected for primary etoposide resistance displayed enhanced LAK susceptibility. In contrast, the 2 variants selected for resistance to adriamycin exhibited partial resistance to LAK-mediated killing, which could be overcome at high effector-to-target ratios. Our results support the development of interleukin-2/LAK immunotherapy for the treatment of leukemias with acquired drug resistance.

Altered conjugate formation and altered apoptosis of multidrug‐resistant human leukemia cell line affects susceptibility to killing by activated natural killer (NK) cells

“… 4 Determined by immunofluorescence using the C219 monoclonal antibody as previously reported by Treichel, Olken, 1992 10…”

“…N6/ADR was derived from the human B‐lineage ALL line NALM6 by intermittent in vitro exposure of cells to increasing concentrations of doxorubicin (Adria Labs, Columbus, OH) as described previously 10. The cell lines were maintained in RPMI 1640 supplemented with 10% FBS, penicillin (50 U/ml), streptomycin (50 μg/ml) and 10 mM HEPES (hereafter referred to as complete medium) and cultured at 37°C in a humidified atmosphere of air supplemented with 5% CO 2 .…”

“…After 4 hr incubation at 37°C plates were again centrifuged; 100 μl supernatant was placed in a vial with 2.5 ml Gammascint (National Diagnostics, Manville, NJ) and counted in a scintillation counter. Results were expressed as percent specific lysis as reported previously 10. All experiments were carried out in triplicate or quadruplicate and parental and MDR cells were always tested in parallel within the same experiment.…”

“…The growth inhibiting effects of anti‐cancer agents, cytokines and soluble cytotoxic mediators was evaluated using a modification of a soluble tetrazolium/formazan assay described previously 10. Briefly, logarithmically growing cells (25,000 or 50,000/well) were incubated with the test agent in a total volume of 200 μl complete medium without phenol red in flat bottom 96‐well microtiter plates.…”

“…Although several studies have reported that P‐gp‐positive cell line variants of solid tumors are at least as sensitive to NK/LAK‐mediated cytotoxicity as the drug‐sensitive parental lines,8, 9 it has been shown that most P‐gp‐positive leukemic lines, particularly those selected for primary resistance to anthracyclines, exhibit reduced susceptibility to NK and LAK cytotoxicity 10, 11, 12, 13. We use an ADR‐selected, MDR variant to evaluate binding, activation and lytic events in the NK cytolytic pathway to identify the alterations that are responsible for the impaired susceptibility of MDR leukemic cells to immune cytotoxicity.…”