ACNU耐性グリオーマの治療

POSSIBILITY OF OVERCOMING OF ACNU RESISTANCE IN AN ACNU-RESISTANT SUBLINE OF C 6 RAT GLIOMA

　抄録　悪性グリオーマの化学療法における抗癌剤耐性の克服の可能性について，in vitroとin vivoの実験系を用いて検討した。ラットC6グリオーマおよびこれより分離したACNU耐性（C6／ACNU）グリオーマ細胞における〔¹⁴C〕ACNUの細胞内uptakeおよびretentionに対し，reserpine，カルシウム拮抗剤（nicardipine, verapamil），カルモジュリン阻害剤（trifluoperazine）等のmembrane-modifying agentsが及ぼす影響を調べた。さらにこれらの薬剤が，ACNUのcytotoxic actionに及ぼす効果を調べると同時に，in vivo脳腫瘍モデル（meningeal gliomatosis model）を用いてこれら薬剤とACNU併用による延命効果を検討した。その結果，上記薬剤はC6およびC6／ACNU細胞におけるACNUのuptakeおよびretentionを増加させると共に，ACNUのこれらの細胞に対するcytotoxic actionを増強することが認められた。invivoモデルにおいても，これら薬剤とACNUの併用により，著明な延命効果が得られた。このことから，in vitroおよびin vivoにおける上記薬剤によるACNUの増強効果は，これらの薬剤により細胞内uptakeおよびretentionが増加したために，細胞内ACNU量が増加することにより発現するものと考えられ，これらの薬剤とACNUの併用によるACNU耐性の克服の可能性が示唆された。

Membrane-modifying agents such as reserpine, calcium antagonists (nicardipine, verapamil) and calmodulin inhibitor (trifluoperazine) were found to enhance the cytotoxicity of ACNU in vitro and in vivo in ACNU-resistant C 6 (C 6/ACNU) glioma.

In in vitro experiments, uptake and retention studies with 〔¹⁴C〕 ACNU revealed that intracel-lular uptake and retention of ACNU in C 6 cells were larger than those in C 6/ACNU cells, and that these membrane-modifying agents increased the cellular uptake and retention of ACNU in C 6, especially in C 6/ACNU cells. The amount of ACNU in C 6/ACNU cells reached the same level as that detected in C 6/ACNU cells. When these drugs were added along with ACNU at the con-centration of 10 to 20 μM to the culture in vitro, ACNU resistance was completely overcome.

In in vivo experiments, reserpine, nicardipine, verapamil and trifluoperazine in doses 250 to 500 μg/kg intrathecally administered with 1 mg/kg ACNU 1 day after the tumor inoculation signifi-cantly enhanced the chemotherapeutic effect of ACNU in C 6/ACNU bearing (C 6/ACNU-MG) rats.

It might be concluded that the mechanism of enhancement of ACNU cytotoxicity presented in in vitro and in vivo is explained by the enhanced accumulation of ACNU by these membrane-modify-ing agents in C 6, especially in ACNU-resistant (C 6/ACNU) cells, and, furthermore, that combina-tion chemotherapy with ACNU and such mem-brane interacting drugs as reserpine, calcium an-tagonists (nicardipine, verapamil) and calmodulin inhibitor (trifluoperazine) could lead to the capa-bility of overcoming resistance to ACNU in glioma.

The abbreviations used are: T/C, mean survival time of treated group of rats devided by mean survival time of control group; C 6/ACNU, C E glioma cells resistant to ACNU.