Semisynthetic neoboutomellerone derivatives as ubiquitin-proteasome pathway inhibitors.

The interesting pharmacological properties of neoboutomellerones 1 and 2 were the basis for the assembly of a small library of analogues consisting of natural products isolated from the plant Neoboutonia melleri and of semisynthetic derivatives. As the two enone systems (C23-C24a and C1-C3) and the two hydroxyls groups (C22 and C26) of neoboutomellerones are required for activity, modifications were focused on these functional groups. Biological evaluation by using a cellular assay for proteasome activity provided clues regarding the mechanism of action of these natural products and synthetic derivatives. Certain neoboutomellerone derivatives inhibited the proliferation of human WM-266-4 melanoma tumor cells at submicromolar concentration and warrant evaluation as anticancer agents.

99mTc-HYNIC-spermine for imaging polyamine transport system-positive tumours: preclinical evaluation.

PURPOSE: F14512 exploiting the polyamine transport system (PTS) for tumour cell delivery has been described as a potent antitumour agent. The optimal use of this compound will require a probe to identify tumour cells expressing a highly active PTS that might be more sensitive to the treatment. The aim of this study was to design and characterize a scintigraphic probe to evaluate its uptake in cancer cells expressing the PTS. METHODS: Three polyamines coupled to a hydrazinonicotinamide (HYNIC) moiety were synthesized and labelled with 99mTc. Their radiochemical purity was determined by HPLC. The plasma stability of the 99mTc-HYNIC-spermine probe and its capacity to accumulate into PTS-active cells were also evaluated. In vitro internalization was tested using murine melanoma B16/F10 cells and human lung carcinoma A549 cells. Biodistribution was determined in healthy mice and tumour uptake was studied in B16/F10 tumour-bearing mice. A HL-60-Luc human leukaemia model was used to confront single photon emission computed tomography (SPECT) images obtained with the 99mTc-labelled probe with those obtained by bioluminescence. RESULTS: The 99mTc-HYNIC-spermine probe was selected for its capacity to accumulate into PTS-active cells and its stability in plasma. In vitro studies demonstrated that the probe was internalized in the cells via the PTS. In vivo measurements indicated a tumour to muscle scintigraphic ratio of 7.9±2.8. The combined bioluminescence and scintigraphic analyses with the leukaemia model demonstrated that the spermine conjugate accumulates into the tumour cells. CONCLUSION: The 99mTc-HYNIC-spermine scintigraphic probe is potentially useful to characterize the PTS activity of tumours. Additional work is needed to determine if this novel conjugate may be useful to analyse the PTS status of patients with solid tumours.

Preclinical activity of F14512, designed to target tumors expressing an active polyamine transport system.

We have exploited the polyamine transport system (PTS) to deliver selectively a spermine-drug conjugate, F14512 to cancer cells. This study was aimed to define F14512 anticancer efficacy against tumor models and to investigate whether fluorophor-labeled polyamine probes could be used to identify tumors expressing a highly active PTS and that might be sensitive to F14512 treatments. Eighteen tumor models were used to assess F14512 antitumor activity. Cellular uptake of spermine-based fluorescent probes was measured by flow cytometry in cells sampled from tumor xenografts by needle biopsy. The accumulation of the fluorescent probe within B16 tumors in vivo was assessed using infrared fluorescence imaging. This study has provided evidence of a major antitumor activity for F14512. Significant responses were obtained in 67% of the tumor models evaluated, with a high level of activity recorded in 33% of the responsive models. Complete tumor regressions were observed after i.v., i.p. or oral administrations of F14512 and its antitumor activity was demonstrated over a range of 2-5 dose levels, providing evidence of its good tolerance. The level of cellular fluorescence emitted by the fluorescent probes was higher in cells sampled from tumors sensitive to F14512 treatments than from F14512-refractory tumors. We suggest that these probes could be used to identify tumors expressing a highly active PTS and guide the selection of patients that might be treated with F14512. These results emphasize the preclinical interest of this novel molecule and support its further clinical development.

Synthesis of conjugated spermine derivatives with 7-nitrobenzoxadiazole (NBD), rhodamine and bodipy as new fluorescent probes for the polyamine transport system.

The synthesis of a series of conjugated spermine derivatives with benzoxadiazole, phenylxanthene or bodipy fluorophores is described. These fluorescent probes were used to identify the activity of the polyamine transport system (PTS). N(1)-Methylspermine NBD conjugate 5 proved to have the optimal fluorescence characteristics and was used to show a selectivity for PTS-proficient CHO versus PTS-deficient CHO-MG cells. It can therefore be used as a tool for the selection of cells sensitive to cytotoxic compounds vectored through the PTS.

F14512, a potent antitumor agent targeting topoisomerase II vectored into cancer cells via the polyamine transport system.

The polyamine transport system (PTS) is an energy-dependent machinery frequently overactivated in cancer cells with a high demand for polyamines. We have exploited the PTS to selectively deliver a polyamine-containing drug to cancer cells. F14512 combines an epipodophyllotoxin core-targeting topoisomerase II with a spermine moiety introduced as a cell delivery vector. The polyamine tail supports three complementary functions: (a) facilitate formulation of a water-soluble compound, (b) increase DNA binding to reinforce topoisomerase II inhibition, and (c) facilitate selective uptake by tumor cells via the PTS. F14512 is 73-fold more cytotoxic to Chinese hamster ovary cells compared with CHO-MG cells with a reduced PTS activity. A decreased sensitivity of L1210 leukemia cells to F14512 was observed in the presence of putrescine, spermidine, and spermine. In parallel, the spermine moiety considerably enhances the drug-DNA interaction, leading to a reinforced inhibition of topoisomerase II. The spermine tail of F14512 serves as a cell delivery vehicle as well as a DNA anchor, and this property translates at the cellular level into a distinct pharmacologic profile. Twenty-nine human solid or hematologic cell lines were used to characterize the high cytotoxic potential of F14512 (median IC50 of 0.18 micromol/L). Finally, the potent antitumor activity of F14512 in vivo was evidenced with a MX1 human breast tumor xenograft model, with partial and complete tumor regressions. This work supports the clinical development of F14512 as a novel targeted cytotoxic drug and sheds light on the concept of selective delivery of drugs to tumor cells expressing the PTS.