Potentiation of the antitumor effect of doxorubicin by correcting extracellular acidosis with sodium bicarbonate in vitro and in vivo in the CT26 murine colon adenocarcinoma model

Objective. To evaluate the effect of extracellular acidosis correction with sodium bicarbonate (NaHCO3
) on the antitumor 
efficacy of doxorubicin in vitro and in vivo in the CT26 murine colon adenocarcinoma model.
Materials and methods. Doxorubicin cytotoxicity (0.001–50 µM, 24 h) against CT26 cells was assessed by the MTT 
assay in RPMI-1640 medium with standard (0.024 M; pH 7.32) or elevated (0.035 M; pH 7.51) NaHCO3
concentrations; IC50 
values were determined using a four-parameter logistic model. In vivo, BALB/c mice bearing subcutaneous CT26 allografts 
were randomized into four groups (n = 5): control; doxorubicin 8 mg/kg i.p., single dose; 4% NaHCO3
0.4 mL i.p. for 5 days; 
and their combination. Tumor growth dynamics and overall survival were evaluated.
Results. Medium alkalinization enhanced doxorubicin cytotoxicity in the 0.05–1 µM range and decreased its IC50 from 
0.22±0.05 to 0.11±0.02 µM (2-fold; p 0.01), consistent with an increase in the lipophilic non-ionized drug fraction from 
11.6% to 17.0% (Henderson – Hasselbalch equation) and the ion-trapping mechanism. In vivo, doxorubicin and NaHCO3
monotherapies inhibited tumor growth by 37% (p<0.001) and 34% (p<0.01), respectively, whereas the combination achieved 
76% inhibition (p<0.001), significantly surpassing both monotherapies. Median survival was 38 days in controls, 49 days 
with alkalinization (p<0.01), and 45 days with combination therapy (p < 0.05).
Conclusion. Correction of extracellular acidosis with sodium bicarbonate potentiates doxorubicin activity via the 
ion-trapping mechanism and exerts independent antitumor effects, supporting buffer therapy as an accessible adjunct to 
chemotherapy that requires optimization of the cytostatic dosing regimen.