Besides hepatic P450 (
cytochrome P450) metabolism, there is increasing interest in the possibility of intratumoral activation of oxazaphosphorines by P450. Therefore, we investigated the expression of P450 (
CYP2C8,
CYP2C9, CYP2C18, and
CYP2C19) by RT (
reverse transcriptase)-polymerase chain reaction (PCR) and of
CYP2C9 by Western blotting in 10 different
breast tumor samples. Since P450 may be down regulated by
interleukin (IL)
IL-6, the receptor (R) for
IL-6 was analyzed by RT-PCR and
IL-6 in supernatants was calculated from ELISA data. None of the
breast tumors was positive for CYP2C18 and
CYP2C19 mRNA, whereas
CYP2C8 and
CYP2C9 were detected in all 10
breast tumors. Correspondingly, all
breast tumors tested (9 of 10) revealed low, but nevertheless positive, staining of the
CYP2C9 protein. All 10 samples were positive for the
IL-6 receptor mRNA. ELISA measurement of
IL-6 cytokine in supernatants revealed that all measured samples (8 of 10) were producing
IL-6, the amounts ranging from 0.004 to 3.1 ng/g(
tumor tissue). In summary, we have demonstrated that
tumors of the breast express two out of four members of the
CYP2C family, indicating that activation of such
prodrugs as oxazaphosphorines may take place intratumorally. The presence of the
IL-6 receptor and of
IL-6 cytokine, which is produced in an autocrine manner, opens up the possibility that the well-known down regulating effect of
IL-6 also takes place in
breast tumors and might explain the weak or even absent expression of different
CYP2C members.