Sentence: The calcium channel blocker verapamil has been previously shown to augment the chemosensitivity of pancreatic adenocarcinoma cell lines to doxorubicin by mechanisms other than changes in the intracellular accumulation , retention , or metabolism of doxorubicin .
Drug combination annotation:
[{'class': 'COMB', 'spans': ['verapamil', 'doxorubicin'], 'is_context_needed': True}]