The number of intestinal bacteria is not critical for the enhancement of antitumor activity and reduction of intestinal toxicity of irinotecan by the Chinese herbal medicine PHY906 (KD018).

Background: The four-herb Chinese medicine PHY906(KD018) has been shown to both enhance the in vivo antitumor activity of irinotecan (CPT-11) against colon cancer tumor allografts and alleviate intestinal toxicity caused by CPT-11.

Methods: Since intestinal bacteria can metabolize CPT-11 and PHY906, we investigated whether intestinal bacteria play a critical role in the in vivo activity of PHY906 in murine Colon-38 tumor-bearing mice. Intestinal bacteria were depleted using streptomycin/neomycin for 10 days before and during treatment with PHY906 and/or CPT-11. qPCR using 16S DNA group-specific primers was used to quantify the levels of the major intestinal bacteria.

Results: Both PHY906 and antibiotic treatment changed the profile of intestinal bacteria species: Lactobacillus/Enterococcus, Bacteroides, Clostridium leptum, and E. rectale/C. coccoides. Antibiotic treatment did not alter the ability of PHY906 to enhance the antitumor activity of CPT-11. Antibiotic treatment alone partially reduced animal body weight loss in CPT-11-treated mice. However, PHY906 treatment was able to protect against the body weight loss in the CPT-11/antibiotic treatment group. H&E and PCNA staining of intestine showed that antibiotic treatment partially reduced the intestinal damage caused by CPT-11 but not as effectively as PHY906 treatment. Antibiotic treatment plus PHY906 conferred the most effective protection of intestine histological structure against damage by CPT-11. Both PHY906 and antibiotic treatment inhibited CPT-11-associated inflammatory processes, including infiltration of the intestine by neutrophils, MCP1 and TNF-alpha mRNA expression in the intestine, and expression of pro-inflammatory cytokines G-CSF and MCP1 proteins in the plasma. However, whereas antibiotic treatment suppressed the mRNA expression of two important intestinal progenitor/stem cell markers, Olfm4 and Lgr5, PHY906 treatment resulted in enhanced expression of these two stem cell markers.

Conclusions: Alterations in the population of intestinal bacteria did not affect the abilities of PHY906 to enhance CPT-11 antitumor activity or reduce the intestinal toxicity associated with CPT-11 treatment. The major species of intestinal bacteria do not appear to play a role in PHY906's enhancement of the therapeutic index of CPT-11 in tumor-bearing mice. Thus, patients with different intestinal bacterial profiles may still benefit from PHY906 treatment alongside CPT-11.