Inhibition of growth in a rabbit VX2 thigh tumor model with intraarterial infusion of carbon dioxide-saturated solution

In vivo evaluation of percutaneous carbon dioxide treatment for improving intratumoral hypoxia using 18F-fluoromisonidazole PET-CT

Carbon dioxide (CO₂) treatment is reported to have an antitumor effect owing to the improvement in intratumoral hypoxia. Previous studies were based on histological analysis alone. In the present study, the improvement in intratumoral hypoxia by percutaneous CO₂ treatment in vivo was determined using ¹⁸F-fluoromisonidazole positron emission tomography-computed tomography (¹⁸F-FMISO PET-CT) images. Twelve Japanese nude mice underwent implantation of LM8 tumor cells in the dorsal subcutaneous area 2 weeks before percutaneous CO₂ treatment and ¹⁸F-FMISO PET-CT scans. Immediately after intravenous injection of ¹⁸F-FMISO, CO₂ and room air were administered transcutaneously in the CO₂-treated group (n=6) and a control group (n=6), respectively; each treatment was performed for 10 minutes. PET-CT was performed 2 h after administration of ¹⁸F-FMISO. ¹⁸F-FMISO tumor uptake was quantitatively evaluated using the maximum standardized uptake value (SUV_max), tumor-to-liver ratio (TLR), tumor-to-muscle ratio (TMR), metabolic tumor volume (MTV) and total lesion glycolysis (TLG). Mean ± standard error of the mean (SEM) of the tumor volume was not significantly different between the two groups (CO₂-treated group, 1.178±0.450 cm³; control group, 1.368±0.295 cm3; P=0.485). Mean ± SEM of SUV_max, TLR, MTV (cm3) and TLG were significantly lower in the CO₂-treated group compared with the control group (0.880±0.095 vs. 1.253±0.071, P=0.015; 1.063±0.147361 vs. 1.455±0.078, P=0.041; 0.353±0.139 vs. 1.569±0.438, P=0.015; 0.182±0.070 vs. 1.028±0.338, P=0.015), respectively. TMR was not significantly different between the two groups (4.520±0.503 vs. 5.504±0.310; P=0.240). In conclusion, ¹⁸F-FMISO PET revealed that percutaneous CO₂ treatment improved intratumoral hypoxia in vivo. This technique enables assessment of the therapeutic effect in CO₂ treatment by imaging, and may contribute to its clinical application.

Intra-arterially infused carbon dioxide-saturated solution for sensitizing the anticancer effect of cisplatin in a rabbit VX2 liver tumor model

The present study aimed to evaluate the efficacy of an intra-arterially infused carbon dioxide (CO2)-saturated solution in sensitizing the anticancer effect of cisplatin in a rabbit VX2 liver tumor model. Forty VX2 liver tumor-bearing Japanese white rabbits were randomly divided into four groups and infused via the proper hepatic artery with a saline solution (control group), CO2-saturated solution (CO2 group), cisplatin solution (cisplatin group), or CO2-saturated solution and cisplatin solution (combined group). The tumor volume (TV) and the relative tumor volume (RTV), RTV = (TV on day 3 or 7)/(TV on day 0) x 100, were calculated using contrast-enhanced computed tomography. Hypoxia-inducible factor-1α (HIF‑1α) and carbonic anhydrase IX (CA IX) staining were used to evaluate cellular hypoxia. Cleaved caspase-3 and cleaved caspase-9 were analyzed to assess tumor apoptosis. The mean RTV on days 3 and 7 were 202.6±23.7 and 429.2±94.8%, respectively, in the control group; 172.2±38.1 and 376.5±61.1% in the CO2 group; 156.1±15.1 and 269.6±45.2% in the cisplatin group; and 118.3±28.1 and 210.3±55.1% in the combined group. RTV was significantly lower in the CO2 group than in the control group (day 3; P<0.05), and in the combined group than in the cisplatin group (days 3 and 7; P<0.05). HIF-1α and CA IX suppression, and increased cleaved caspase-3 and cleaved caspase-9 expression, were detected in the CO2 and combined groups, compared with the other two groups. An intra-arterially infused CO2-saturated solution inhibits liver VX2 tumor growth and sensitizes the anticancer effect of cisplatin.

Optimization of antitumor treatment conditions for transcutaneous CO2 application: An in vivo study

Carbon dioxide (CO2) therapy can be applied to treat a variety of disorders. We previously found that transcutaneous application of CO2 with a hydrogel decreased the tumor volume of several types of tumors and induced apoptosis via the mitochondrial pathway. However, only one condition of treatment intensity has been tested. For widespread application in clinical antitumor therapy, the conditions must be optimized. In the present study, we investigated the relationship between the duration, frequency, and treatment interval of transcutaneous CO2 application and antitumor effects in murine xenograft models. Murine xenograft models of three types of human tumors (breast cancer, osteosarcoma, and malignant fibrous histiocytoma/undifferentiated pleomorphic sarcoma) were used to assess the antitumor effects of transcutaneous CO2 application of varying durations, frequencies, and treatment intervals. In all human tumor xenografts, apoptosis was significantly induced by CO2 treatment for ≥10 min, and a significant decrease in tumor volume was observed with CO2 treatments of >5 min. The effect on tumor volume was not dependent on the frequency of CO2 application, i.e., twice or five times per week. However, treatment using 3- and 4-day intervals was more effective at decreasing tumor volume than treatment using 2- and 5-day intervals. The optimal conditions of transcutaneous CO2 application to obtain the best antitumor effect in various tumors were as follows: greater than 10 min per application, twice per week, with 3- and 4-day intervals, and application to the site of the tumor. The results suggest that this novel transcutaneous CO2 application might be useful to treat primary tumors, while mitigating some side effects, and therefore could be safe for clinical trials.