Ex vivo analysis of topotecan: advancing the application of laboratory-based clinical therapeutics

Abstract

Topotecan is currently approved for relapsed small-cell lung cancer and ovarian cancer. Topotecan's efficacy in the second-line setting and novel mechanism of action suggest broad antitumour activity. We utilised a clinically validated, cell-death, ex vivo assay in human tumour explants to examine the activity profile of topotecan alone and in combination with other antitumour agents. Serial dilutions of topotecan alone and in combination with other cytotoxic agents were applied to biopsy specimens of non-small-cell lung cancer (NSCLC) and breast, colon, and prostate cancers. Dose -response curves were interpolated to provide 50% lethal concentrations (LC 50 ). The degree of synergy (by median effect) and normalised Z-scores (raw scores converted to relative activity distributed around the mean) were then computed. Single-agent activity was observed for topotecan in all four tumour types. In 57 chemotherapy-naive specimens, NSCLC revealed the highest activity, demonstrated by the lowest LC 50 value (0.2670.06 mg ml À1 ; P ¼ 0.002). Overall, previously treated and chemotherapy-naive specimens revealed no significant differences in mean LC 50 's. Synergy was observed for several combinations, including topotecan plus cisplatin in prostate and for topotecan plus 5-fluorouracil in breast cancers. The Z-score analyses conducted suggest activity for previously unexplored drug regimens, including topotecan plus 5-fluorouracil, vinorelbine, and mitomycin-C in NSCLC and breast cancer. Phase II studies are underway to determine the degree to which these ex vivo findings will translate into improved clinical results. Topotecan, a semisynthetic, water-soluble derivative of camptothecin, is an inhibitor of topoisomerase I (Kingsbury et al, 1991). This derivative is more stable, has increased solubility, a shorter half-life, and decreased toxicity compared with its parent compound (Verweij et al, 1993;Burke and Mi, 1994;Rothenberg, 1997). Topoisomerase I is a nuclear enzyme that relieves torsional strain on supercoiled DNA and creates single-strand breaks during DNA replication. Topotecan prevents topoisomerase I from repairing the cleaved DNA, which results in double-stranded DNA breaks and eventually apoptosis. The unique mechanism of action of topotecan and lack of clinical crossresistance with other antineoplastic compounds suggest that topotecan has the potential for broad antitumour activity.The activity of topotecan has been demonstrated in several open-label, randomised phase II and III trials. Currently, topotecan is approved for the treatment of relapsed small-cell lung cancer (SCLC) (Eckardt et

Topotecan in the Treatment of Recurrent Small Cell Lung Cancer: An Update

“…In a patient population with a poor prognosis and potential comorbidities, there is a clear need for noncross-resistant therapeutic options. It's reversible, nonoverlapping nonhematologic toxicities and in vitro antitumor synergy with platinum agents, taxanes, and topoisomerase II inhibitors may make topotecan an ideal candidate for use in combination with other chemotherapy agents [44][45][46].…”

Capsaicin synergizes with camptothecin to induce increased apoptosis in human small cell lung cancers via the calpain pathway

“…During DNA replication and repair, the enzyme topoisomerase 1 creates single strand breaks in the DNA. Camptothecin forms a tertiary complex with topoisomerase 1 and the cleaved DNA, thereby blocking the annealing of DNA sister strands [4, 30]. This camptothecin-DNA-Topoisomerase 1 complex causes DNA damage and eventually leads to cellular apoptosis.…”

“…Patient-oriented studies show that camptothecin is active against brain metastases in SCLC [4, 30]. The clinic profile of camptothecin, its broad-spectrum anti-tumor activity, and its lack of cross resistance with other anti-cancer agents has prompted clinical studies investigating the feasibility of camptothecin being used in a first-line setting for SCLC patients [4, 5, 31].…”

Ex vivo programmed cell death and the prediction of response to chemotherapy

“…It has been shown that cells committed to death will overcome exposure to potent caspase inhibitors to die via pathways that mimic necrosis [7••]. Fresh explants of human tumors in culture have provided significant insights, including the first observation of activity for chlorodeoxyadenosine in hairy cell leukemia, synergy between purines and mustard alkylators in lymphoid malignancies [8], the activity and synergy for platins plus gemcitabine in breast and ovarian cancers [9,10], characterization of topotecan combinations [11], and the accurate selection of disease targets for gefitinib [12,13], all of which have been subsequently confirmed in clinical trials. By measuring cell death in primary culture spheroids, the cumulative effect of all of the operative survival and death cascades can be gauged at once.…”