A multicenter phase II study of belotecan, a new camptothecin analogue, in elderly patients with previously untreated, extensive-stage small cell lung cancer

Enhanced Liver Targeting of Camptothecin via Conjugation with Deoxycholic Acid

Camptothecin (CPT) shows potent anticancer activity through inhibition of topoisomerase I. However, its water insolubility and severe toxicity limit its clinical application. Coupling with bile acid moieties is a promising method for liver-targeted drug delivery, which takes advantage of the bile acid receptors on hepatocytes. In this study, we evaluated the potential liver targeting and stability of a deoxycholic acid-CPT conjugate (G2). The competitive inhibition of antitumor activity experiment based on bile acid transporters was performed using the MTT method. The effects of deoxycholic acid on uptake of G2 and CPT were assessed in 2D and 3D HepG2 cell models. The stability of G2 and CPT was evaluated in vitro (in simulated gastric fluid, simulated intestinal fluid, and fresh rat plasma). Finally, biodistribution of G2 and CPT was investigated in Kunming mice following oral administration. The results showed that deoxycholic acid pretreatment could significantly reduce the antitumor activity and cellular uptake of G2 in HepG2 cells, but had no distinct effects on CPT. Meanwhile, G2 exhibited better stability compared with CPT. More importantly, biodistribution study in mice demonstrated that the liver targeting index of G2 increased 1.67-fold than that of CPT. Overall, the study suggests that conjugation with deoxycholic acid is a feasible method to achieve liver targeting delivery of CPT.

Topoisomerase 1B poisons: Over a half-century of drug leads, clinical candidates, and serendipitous discoveries

Topoisomerases are DNA processing enzymes that relieve supercoiling (torsional strain) in DNA, are necessary for normal cellular division, and act by nicking (and then religating) DNA strands. Type 1B topoisomerase (Top1) is overexpressed in certain tumors, and the enzyme has been extensively investigated as a target for cancer chemotherapy. Various chemical agents can act as "poisons" of the enzyme's religation step, leading to Top1-DNA lesions, DNA breakage, and eventual cellular death. In this review, agents that poison Top1 (and have thus been investigated for their anticancer properties) are surveyed, including natural products (such as camptothecins and indolocarbazoles), semisynthetic camptothecin and luotonin derivatives, and synthetic compounds (such as benzonaphthyridines, aromathecins, and indenoisoquinolines), as well as targeted therapies and conjugates. Top1 has also been investigated as a therapeutic target in certain viral and parasitic infections, as well as autoimmune, inflammatory, and neurological disorders, and a summary of literature describing alternative indications is also provided. This review should provide both a reference for the medicinal chemist and potentially offer clues to aid in the development of new Top1 poisons.

Camptothecin inhibits the progression of NPC by regulating TGF-β-induced activation of the PI3K/AKT signaling pathway

Nasopharyngeal carcinoma (NPC) is a type of cancer that is characterized by increased invasiveness, metastatic potential and tumor recurrence. Camptothecin has been demonstrated to exhibit anticancer activity. However, the potential underlying molecular mechanisms mediated by camptothecin in NPC cells remain elusive. In the present study, the efficacy of camptothecin for NPC was investigated in vitro and in vivo. Additionally, the potential signaling pathway mediated by camptothecin in NPC cells was also examined. The results indicated that the viability and aggressiveness of NPC cells were suppressed by camptothecin treatment in a dose-dependent manner. Camptothecin administration downregulated the expression levels of cell-cycle-associated proteins including cyclin 1, cyclin-dependent kinase (CDK)1 and CDK2 in NPC cells. Expression levels of migration-associated proteins including vimentin, fibronectin and epithelial cadherin were regulated by camptothecin treatment in NPC cells. Additionally, camptothecin inhibited the expression of transforming growth factor-β (TGF-β), phosphoinositide 3-kinase (PI3K) and protein kinase B (AKT), whereas TGF-β overexpression abrogated camptothecin-mediated inhibition of PI3K and AKT expression and camptothecin-mediated inhibition of the viability and aggressiveness of NPC cells. Camptothecin significantly inhibited tumor growth and increased survival times in a mouse model of cancer. In conclusion, these results indicate that camptothecin treatment may inhibit the viability of NPC cells and aggressiveness by regulating the TGF-β-induced PI3K/AKT signaling pathways, which in turn may be a potential molecular target for the treatment of NPC.

Real-time investigation of human topoisomerase I reaction kinetics using an optical sensor: a fast method for drug screening and determination of active enzyme concentrations

Human DNA topoisomerase I (hTopI) is a nuclear enzyme that catalyzes relaxation of super helical tension that arises in the genome during essential DNA metabolic processes. This is accomplished through a common reaction mechanism shared among the type IB topoisomerase enzymes, including eukaryotic and poxvirus topoisomerase I. The mechanism of hTopI is specifically targeted in cancer treatment using camptothecin derivatives. These drugs convert the hTopI activity into a cellular poison, and hence the cytotoxic effects of camptothecin derivatives correlate with the hTopI activity. Therefore, fast and reliable techniques for high throughput measurements of hTopI activity are of high clinical interest. Here we demonstrate potential applications of a fluorophore-quencher based DNA sensor designed for measurement of hTopI cleavage-ligation activities, which are the catalytic steps affected by camptothecin. The kinetic analysis of the hTopI reaction with the DNA sensor exhibits a characteristic burst profile. This is the result of a two-step ping-pong reaction mechanism, where a fast first reaction, the one creating the signal, is followed by a slower second reaction necessary for completion of the catalytic cycle. Hence, the burst profile holds information about two reactions in the enzymatic mechanism. Moreover, it allows the amount of active enzyme in the reaction to be determined. The presented results pave the way for future high throughput drug screening and the potential of measuring active hTopI concentrations in clinical samples for individualized treatment.