Targeted inhibition of mitochondrial Hsp90 suppresses localised and metastatic prostate cancer growth in a genetic mouse model of disease.

BACKGROUND: The molecular chaperone heat shock protein-90 (Hsp90) is a promising cancer drug target, but current Hsp90-based therapy has so far shown limited activity in the clinic. METHODS: We tested the efficacy of a novel mitochondrial-targeted, small-molecule Hsp90 inhibitor, Gamitrinib (GA mitochondrial matrix inhibitor), in the Transgenic Adenocarcinoma of the Mouse Prostate (TRAMP) model. The TRAMP mice receiving 3-week or 5-week systemic treatment with Gamitrinib were evaluated for localised or metastatic prostate cancer, prostatic intraepithelial neoplasia (PIN) or localised inflammation using magnetic resonance imaging, histology and immunohistochemistry. Treatment safety was assessed histologically in organs collected at the end of treatment. The effect of Gamitrinib on mitochondrial dysfunction was studied in RM1 cells isolated from TRAMP tumours. RESULTS: Systemic administration of Gamitrinib to TRAMP mice inhibited the formation of localised prostate tumours of neuroendocrine or adenocarcinoma origin, as well as metastatic prostate cancer to abdominal lymph nodes and liver. The Gamitrinib treatment had no effect on PIN or prostatic inflammation, and caused no significant animal weight loss or organ toxicity. Mechanistically, Gamitrinib triggered acute mitochondrial dysfunction in RM1 cells, with loss of organelle inner membrane potential and release of cytochrome-c in the cytosol. CONCLUSIONS: The Gamitrinib has pre-clinical activity and favourable tolerability in a genetic model of localised and metastatic prostate cancer in immunocompetent mice. Selective targeting of mitochondrial Hsp90 could provide novel molecular therapy for patients with advanced prostate cancer.

The expression of the DeltaNp73beta isoform of p73 leads to tetraploidy.

The p73 locus gene has a complex structure encoding a plethora of isoforms. The different DeltaN truncated isoforms of p73 may exert different activities depending on the cellular context. The beta isoform of DeltaNp73 seems to have a particular pattern of action even if its role in cell cycle and mitosis is still under investigation. To gain further knowledge of DeltaNp73beta's function, we investigated the effects of its over-expression in tumour cellular models, using the tetracycline-inducible expression system. In the human lung carcinoma cell line H1299, DeltaNp73beta over-expression resulted in suppression of cell growth and in cell death. Surprisingly stable over-expression of DeltaNp73beta impaired the genomic stability of tumour cells, leading to the formation of tetraploid cells. The cells become enlarged and multinucleate, with incorrect mitotic figures, and died by apoptotic-independent pathways. Our data suggest that DeltaNp73beta-induced aberrant mitosis evades the control of the mitotic spindle assay checkpoint, leading to tetraploidy and cell death through mitotic catastrophe rather than apoptosis. The various C-terminal regions of DeltaNp73 may influence the final cellular phenotype and we assume that the beta one in particular could be important in both cell growth control and regulation of mitosis.

Role of homologous recombination in trabectedin-induced DNA damage.

Trabectedin (ET-743, Yondelis) is a natural marine compound with antitumour activity currently undergoing phase II/III clinical trials. The mechanism of the drug's action is still to be defined, even though it has been clearly demonstrated the key role of Nucleotide Excision Repair (NER). To get further insights into the drug's mode of action, we studied the involvement of the DNA-double strand break repair (DNA-DSB) pathways: homologous and non-homologous recombination, both in budding yeasts and in mammalian cells and the possible cross-talk between NER and these repair pathways. Budding yeasts and mammalian cells deficient in the non-homologous end-joining pathway were moderately sensitive to trabectedin, while systems deficient in the homologous recombination pathway were extremely sensitive to the drug, with a 100-fold decrease in the IC50, suggesting that trabectedin-induced lesions are repaired by this pathway. The induction of Rad51 foci and the appearance of gamma-H2AX were chosen as putative markers for DNA-DSBs and were studied at different time points after trabectedin treatment in NER proficient and deficient systems. Both were clearly detected only in the presence of an active NER, suggesting that the DSBs are not directly caused by the drug, but are formed during the processing/repair of the drug- induced lesions.

Dynamics of cell cycle phase perturbations by trabectedin (ET-743) in nucleotide excision repair (NER)-deficient and NER-proficient cells, unravelled by a novel mathematical simulation approach.

OBJECTIVES: Trabectedin (ET-743, Yondelis) is a natural marine product, with antitumour activity, currently in phase II/III clinical trials. Previous studies have shown that cells hypersensitive to ultraviolet (UV)-rays because of nucleotide excision repair (NER) deficiency, were resistant to trabectedin. The purpose of this study was to investigate whether this resistance was associated with different drug-induced cell cycle perturbations. MATERIALS AND METHODS: An isogenic NER-proficient cellular system (CHO-AA8) and a NER-deficient one (CHO-UV-96), lacking functional ERCC-1, were studied. Flow cytometric assays showed progressive accumulation of cells in G2 + M phase in NER-proficient but not in NER-deficient cells. Applying a computer simulation method, we realized that the dynamics of the cell cycle perturbations in all phases were complex. RESULTS: Cells exposed to trabectedin during G1 and G2 + M first experienced a G1 block, while those exposed in S phase were delayed in S and G2 + M phases but eventually divided. In the presence of functional NER, exit from the G1 block was faster; then, cells progressed slowly through S phase and were subsequently blocked in G2 + M phase. This G2 + M processing of trabectedin-induced damage in NER-proficient cells was unable to restore cell cycling, suggesting a difficulty in repairing the damage. CONCLUSIONS: This might be due either to important damage left unrepaired by previous G1 repair, or that NER activity itself caused DNA damage, or both. We speculate that in UV-96 cells repair mechanisms other than NER are activated both in G1 and G2 + M phases.

Modulation of gene transcription by natural products--a viable anticancer strategy.

Drug design based on the structure of specific enzymes playing a role in carcinogenesis, e.g. tyrosine kinases, has been successful at identifying novel effective anticancer drugs. In contrast, no success has been achieved in drug design attempts, in which transcription factors or DNA-transcription factor complexes involved in the pathogenesis of human neoplasms were targeted. This failure is likely to be due to the fact that the mechanism of transcription regulation is probably too complex and still too inadequately understood to be a suitable target for drug design. It seems plausible that the high selectivity of some human tumors to some DNA-interactive anticancer drugs, e.g. cisplatin, is related to an effect on the transcription of genes that are crucial for those tumors. In this article we propose that some natural products have evolutionarily evolved to exert highly specialized functions, including modulation of the transcriptional regulation of specific genes. We discuss in detail the marine natural product Yondelis (Trabectedin, ET-743) that is effective against some soft tissue sarcoma, possibly because it interferes with the aberrant transcription mechanism in these tumors. In addition we highlight the existing evidence that many different natural products are effective inhibitors of NF-kB, a transcription factor that plays a crucial role in inflammation and cancer, indicating that some of these compounds might possess antitumor properties. We propose that large-scale characterization of natural products acting as potential modulators of gene transcription is a realistic and attractive approach to discover compounds therapeutically effective against neoplastic diseases characterized by specific aberrations of transcriptional regulation.

New drugs from the sea.

This paper illustrates some biochemical and pharmacological properties of two natural marine products such as trabectedin (ET-743, Yondelis) and aplidine. Trabectedin has shown clinical antitumor activity in refractory soft tissue sarcoma and ovarian cancer. The lack of cross resistance of trabectedin with other chemotherapeutic drugs is presumably related to its peculiar mode of action, that seems to be related to a promoter-dependent transcription modulation. Aplidine is a potent pro-apoptotic inducer in human leukemia and has antiangiogenic properties. These examples support the view that more research should be carried out to investigate new natural marine products since there are compounds among them with antitumor properties. Some of them appear to act by mechanisms different from those of conventional chemotherapeutic drugs and thus may be effective against tumors for which no active drugs are available.