Abstract
Pentoxifylline (PENTO) has been known to improve RBC fluidity, and thus improve the flux of RBC through narrow capillaries. Additionally, PENTO also decreases the $O_2$ affinity of hemoglobin by increasing 2,3-DPG levels, thereby increasing the $O_2$ release from RBC. Nicotinamide (NA) has been reported to decrease the number of acutely hypoxic cells in tumors by temporarily increasing tumor blood flow. Therefore, the purpose of this study was to examine whether the combination of PENTO and NA (PENTO+NA) would reduce the radioresistance of the Fsall murine fibrosarcoma by oxygenating the hypoxic cells. We obsewed a significantly enhanced radiation-induced growth delay of the FSaII tumors by PENTO+NA. Thus the enhancement ratio was between 2.5 and 2.8 in growth delay assay. The $TCD_{50}$ of control tumors was about 57 Gy, but that of PENTO+NA treated tumors was about 32Gy. Thus $TCD_{50}$ was modified by a factor of 1.8. We also observed that PENTO+NA exerted no effect on the radiation-induced skin damage after the legs without bearing tumors were exposed to X-irradiation. In order to clarify radiosensitizing effects of PENTO+ NA, changes in tumor blood flow and intratumor pOf were measured using laser Doppler flowmetry and $O_2$ microelectrode methods. The tumor blood flow significantly increased at 10 min. after injection of PENTO+ NA. Furthermore, we also found that PENTO+ NA significantly increased intratumor $pO_2$ from 8 to 19 mmHg. We concluded that PENTO+MA was far more effective than NA alone or PENTO alone. The increase in the response of tumors in vivo to X-irradiation appeared to be due mainly to an increase in the tumor oxygenation. Further studies using various concentrations of PENTO alone and in combination with NA to obtain better sequencing and maximal radiosensitization are warranted.
Pentoxifylline (PENTO)는 적혈구의 유동성을 증가시켜 모세혈관의 적혈구 흐름을 증가시킨다. 또한 적혈구내 2,3-DPG를 증가시켜서 산소 친화력을 감소시켜 산소의 해리를 촉진시킨다. Nicotinamide (NA)는 종양내 혈류를 일시적으로 증가시켜서 종양내 급성 저산소 세포의 수를 감소시킨다. PENTO와 NA의 병용이 저산소 세포의 산소화에 의해서 방사선 감수성을 증가시킬 수 있는지를 확인하기 위하여 FSaII생쥐의 섬유육종을 이용하여 실험을 시행하였다. 방사선에 의한 성장 장애가 유의하게 증가하였으며, 증가율은 2.5~2.8이었다. $TCD_{50}$가 대조 종양군에서는 57Gy였으나 PENTO+NA투여 종양군에서는 32Gy로 1.8배의 $TCD_{50}$의 감소를 보였다. 정상피부의 방사선 감수성에는 영향이 없었다. PENTO+NA의 방사선 감수성의 증가를 규명하기 위하여 종양내 혈류의 변화, 종양내 산소농도를 laser Doppler flowmetry와 산소 미소전극 방법으로 측정하였다. PENTO+NA투여후 10분 경과하여 혈류가 유의하게 증가하였으며 종양내 산소 분압도 8 mmHg에서 19 mmHg로 유의하게 증가함을 관찰하였다. 따라서 PEHTO또는 NA단독보다 PENTO+NA병통이 더욱 효과적이라 사료되며 생체내 종양의 방사선 감수성의 증가는 종양내 산소의 증가로 생각되며 더욱 방사선 감수성을 증가시키기 위하여 여러 농도의 PENTO의 단독 또는 NA와의 병용등에 대한 지속적인 연구가 필요하다.