Mass Spectrometry\nQuantification of Anticancer Drug\nUptake in Single Multicellular Tumor Spheroids

Although most advanced-stage ovarian cancers initially\nrespond\nto platinum- and taxane-based chemotherapy, the majority of them will\nrecur and eventually develop chemoresistance. Among all drug resistance\nmechanisms, reduced drug uptake in tumors is regarded as an important\npathway acquired by drug-resistant cancer cells. For patients with\novarian cancer, chemoresistant cells can develop into multicellular\nspheroids and spread through ascite fluid that accumulates in their\nabdomen. These spheroids consist of 3D structures that are highly\nheterogeneous with different shapes, sizes, and compositions of cell\ntypes. Thus, studying drug uptake at the single spheroid level is\nimportant for understanding chemosensitivity and chemoresistance;\nhowever, drug-uptake studies in single spheroids have not been previously\nreported due to the lack of a suitable analytical technique. In this\nstudy, we cultured spheroids using the ovarian cancer cell line (OVCAR-8)\nand treated them using paclitaxel or OSW-1, a natural compound with\nanticancer properties. We then developed a method of quantifying drug\nuptake in single spheroids using LC/MS measurements and then normalized\nthe drug amount in each spheroid to its size and total protein content.\nOur method can be used in translational studies of drug development,\ntreatment, and prediction of drug efficacy prior to chemotherapy.