Non-Hodgkin's lymphoma (NHL) is a malignant cancer originating in the lymphatic system with a 25-30% mortality rate. CHOP, consisting of cyclophosphamide (CPA), doxorubicin, vincristine, and prednisone, is a first-generation chemotherapy extensively used to treat NHL. However, poor survival rates among patients in advanced stages of NHL shows a need to improve this standard of care treatment. CPA, an integral component of CHOP, is a prodrug that requires CYP2B6-mediated bioactivation to 4-hydroxy-CPA (4-OH-CPA). The expression of CYP2B6 is transcriptionally regulated by the constitutive androstane receptor (CAR, NRi13). We have previously demonstrated that the induction of hepatic CYP2B6 by CITCO, a selective human CAR (hCAR) agonist, results in CHOP's enhanced antineoplastic effects in vitro. Here, we investigate the in vivo potential of CITCO as an adjuvant of CPA-based NHL treatment in a hCAR-transgenic mouse line. Our results demonstrate that the addition of CITCO to the CHOP regimen leads to significant suppression of the growth of EL-4 xenografts in hCAR-transgenic mice accompanied by reduced expression of cyclin-D1, ki67, Pcna, and increased caspase 3 fragmentation in tumor tissues. CITCO robustly induced the expression of cyp2b10 (murine ortholog of CYP2B6) through hCAR activation and increased plasma concentrations of 4-OH-CPA. Comparing to intraperitoneal injection, oral gavage of CITCO results in optimal hepatic cyp2b10 induction. Our in vivo studies have collectively uncovered CITCO as an effective facilitator for CPA-based NHL treatment with a pharmacokinetic profile favoring oral administration, promoting CITCO as a promising adjuvant candidate for CPA-based regimens.
Keywords: CAR; CITCO; CYP2B6/cyp2b10; cyclophosphamide; lymphoma; prodrug.