Purpose: Conventional
chemotherapy has modest efficacy in advanced
adenoid cystic carcinomas (ACC).
Tumor recurrence is a major challenge in the management of ACC patients. Here, we evaluated the antitumor effect of a novel small-molecule inhibitor of the MDM2-p53 interaction (MI-773) combined with
cisplatin in patient-derived xenograft (PDX) ACC
tumors.Experimental Design: Therapeutic strategies with
MI-773 and/or
cisplatin were evaluated in SCID mice harboring PDX ACC
tumors (UM-PDX-HACC-5) and in low passage primary human ACC cells (UM-HACC-2A, -2B, -5, -6) in vitro The effect of
therapy on the fraction of cancer stem cells (CSC) was determined by flow cytometry for ALDH activity and CD44 expression.Results: Combined
therapy with
MI-773 with
cisplatin caused p53 activation, induction of apoptosis, and regression of ACC PDX
tumors. Western blots revealed induction of MDM2, p53 and downstream p21 expression, and regulation of apoptosis-related
proteins PUMA, BAX, Bcl-2, Bcl-xL, and active
caspase-9 upon
MI-773 treatment. Both single-agent
MI-773 and
MI-773 combined with
cisplatin decreased the fraction of CSCs in PDX ACC
tumors. Notably, neoadjuvant
MI-773 and surgery eliminated
tumor recurrences during a postsurgical follow-up of more than 300 days. In contrast, 62.5% of mice that received vehicle control presented with palpable
tumor recurrences within this time period (P = 0.0097).Conclusions: Collectively, these data demonstrate that therapeutic inhibition of MDM2-p53 interaction by
MI-773 decreased the CSC fraction, sensitized ACC xenograft
tumors to
cisplatin, and eliminated
tumor recurrence. These results suggest that patients with ACC might benefit from the therapeutic inhibition of the MDM2-p53 interaction. Clin
Cancer Res; 23(4); 1036-48. ©2016 AACR.