The platinum drugs cisplatin, carboplatin and oxaliplatin are highly utilized in the clinic and as a consequence are extensively studied in the laboratory setting. In this study, we examined the literature and found a significant number of studies (11 - 34%) in prominent cancer journals utilizing cisplatin dissolved in dimethylsulfoxide (DMSO). However, dissolving cisplatin in DMSO for laboratory-based studies results in ligand displacement and changes the structure of the complex. We examined the effect of DMSO on platinum complexes, including cisplatin, carboplatin and oxaliplatin, finding that DMSO reacted with the complexes, inhibited their cytotoxicity and their ability to initiate cell death. These results render a substantial portion of the literature on cisplatin uninterpretable. Raising awareness of this significant issue in the cancer biology community is critical, and we make recommendations on appropriate solvation of platinum drugs for research.

Despite early positive response to platinum-based chemotherapy, the majority of ovarian carcinomas develop resistance and progress to fatal disease. Protein phosphatase 2A (PP2A) is a ubiquitous phosphatase involved in the regulation of DNA damage response and cell cycle checkpoint pathways. Recent studies have shown that LB100, a small molecule inhibitor of PP2A, sensitizes cancer cells to radiation-mediated DNA damage. We hypothesized that LB100 could sensitize ovarian cancer cells to cisplatin treatment. We performed in vitro studies in SKOV-3, OVCAR-8, and PEO1, 4, and 6 ovarian cancer lines to assess cytotoxicity potentiation, cell-death mechanism(s), cell cycle regulation, and DNA damage response signaling. In vivo studies were conducted in an intraperitoneal metastatic mouse model using SKOV-3/f-Luc cells. LB100 sensitized ovarian carcinoma lines to cisplatin-mediated cell death. Sensitization via LB100 was mediated by abrogation of cell cycle arrest induced by cisplatin. Loss of the cisplatin-induced checkpoint correlated with decreased Wee1 expression, increased cdc2 activation, and increased mitotic entry (p-histone H3). LB100 also induced constitutive hyperphosphorylation of DNA damage response proteins (BRCA1, Chk2, γH2AX), altered the chronology and persistence of JNK activation, and modulated the expression of 14-3-3 binding sites. In vivo, cisplatin sensitization via LB100 significantly enhanced tumor growth inhibition and prevented disease progression after treatment cessation. Our results suggest that LB100 sensitizes ovarian cancer cells to cisplatin in vitro and in vivo by modulation of the DNA damage response pathway and cell cycle checkpoint abrogation.

ATP-binding cassette (ABC) transporters are a group of transmembrane proteins that maintain chemical homeostasis through efflux of compounds out of organelles and cells. Among other functions, ABC transporters play a key role in protecting the brain parenchyma by efflux of xenobiotics from capillary endothelial cells at the blood-brain barrier (BBB). They also prevent the entry of therapeutic drugs at the BBB, thereby limiting their efficacy. One of the key transporters playing this role is ABCG2. Although other ABC transporters can be studied through various imaging modalities, no specific probe exists for imaging ABCG2 function in vivo. Here we show that D-luciferin, the endogenous substrate of firefly luciferase, is a specific substrate for ABCG2. We hypothesized that ABCG2 function at the BBB could be evaluated by using bioluminescence imaging in transgenic mice expressing firefly luciferase in the brain. Bioluminescence signal in the brain of mice increased with coadministration of the ABCG2 inhibitors Ko143, gefitinib, and nilotinib, but not an ABCB1 inhibitor. This method for imaging ABCG2 function at the BBB will facilitate understanding of the function and pharmacokinetic inhibition of this transporter. P rovision of nutrients and maintenance of chemical homeostasis in the brain is performed by the endothelial cells of brain capillaries within a neurovascular unit termed the bloodbrain barrier (BBB) (1). In contrast to endothelial cells of capillaries elsewhere in the body, those in the brain are joined by tight junctions forming a physiologic barrier. Drug delivery to the brain depends on physicochemical characteristics such as lipophilicity, molecular weight, and ionic state. For many compounds, brain entry is lower than other tissues/organs because of the presence of ATP-binding cassette (ABC) efflux transporters at the apical surface of endothelial cells at the BBB (2, 3). These transporters maintain chemical homeostasis in the brain, and prevent toxins from interfering with neural processes by regulating the compounds that can enter the brain.ABC transporters contribute to the clinical challenge of drug delivery to the brain, and it has been estimated that only 2% of drug discovery compounds can cross the BBB to reach therapeutic targets (4). ABCG2 (also known as breast cancer resistance protein) and ABCB1 (also called P-glycoprotein) are the two most highly expressed efflux transporters at the BBB (5). Altered expression of ABC transporters at the BBB has been associated with a range of pathophysiological conditions (2, 6). ABC efflux transporters at the BBB also play a major role in limiting effective concentrations of chemotherapeutic agents to treat primary and metastatic tumors in the brain (7). ABCG2 has been shown to work in tandem with ABCB1 at the BBB (8, 9). However, its individual contribution is not understood.Molecular imaging allows the measurement of the individual contribution and function of transporters in vivo (10). Efflux of a substrate by transporters at the BBB is reflected by...