Emerging targets to monitor and overcome docetaxel resistance in castration resistant prostate cancer (review).

Drug development for castration resistant prostate cancer (CRPC) is challenging, since this cancer is still associated with high mortality and limited therapeutic options. In 2004, docetaxel became the first-line chemotherapy for CRPC improving survival by a few months and remains the standard of care in CRPC patients. However, existing or developing resistance to docetaxel in patients is the main limitation of its efficacy. The present review presents the molecular mechanisms involved in docetaxel toxicity and in docetaxel resistance in prostate cancer cells. We outlined the endogenous mechanisms of resistance and the role of tumor microenvironment in the resistance of CRPC to docetaxel. This has led us to focus on molecules associated with resistance, such as the molecular chaperones heat shock proteins (HSPs) and clusterin (CLU), and the cytokines interleukin-6 (IL-6) and the divergent member of the tumor growth factor family MIC-1 (macrophage inhibitory cytokine-1 also named GDF-15). We discuss their interest as blood-based markers to monitor docetaxel resistance. Finally, new therapies intended to overcome docetaxel resistance of CRPC targeted on these molecular resistance pathways are present.

IAP-targeted therapies for cancer.

DNA damage, chromosomal abnormalities, oncogene activation, viral infection, substrate detachment and hypoxia can all trigger apoptosis in normal cells. However, cancer cells acquire mutations that allow them to survive these threats that are part and parcel of the transformation process or that may affect the growth and dissemination of the tumor. Eventually, cancer cells accumulate further mutations that make them resistant to apoptosis mediated by standard cytotoxic chemotherapy or radiotherapy. The inhibitor of apoptosis (IAP) family members, defined by the presence of a baculovirus IAP repeat (BIR) protein domain, are key regulators of cytokinesis, apoptosis and signal transduction. Specific IAPs regulate either cell division, caspase activity or survival pathways mediated through binding to their BIR domains, and/or through their ubiquitin-ligase RING domain activity. These protein-protein interactions and post-translational modifications are the subject of intense investigations that shed light on how these proteins contribute to oncogenesis and resistance to therapy. In the past several years, we have seen multiple approaches of IAP antagonism enter the clinic, and the rewards of such strategies are about to reap benefit. Significantly, small molecule pan-IAP antagonists that mimic an endogenous inhibitor of the IAPs, called Smac, have demonstrated an unexpected ability to sensitize cancer cells to tumor necrosis factor-alpha and to promote autocrine or paracrine production of this cytokine by the tumor cell and possibly, other cells too. This review will focus on these and other developmental therapeutics that target the IAPs in cancer.

Both cIAP1 and cIAP2 regulate TNFalpha-mediated NF-kappaB activation.

The cellular inhibitor of apoptosis 1 and 2 (cIAP1 and cIAP2) proteins have been implicated in the activation of NF-kappaB by TNFalpha; however, genetic deletion of either cIAP1 or 2 did not support a physiologically relevant role, perhaps because of functional redundancy. To address this, we used combined genetic and siRNA knockdown approaches and report that cIAP1 and 2 are indeed critical, yet redundant, regulators of NF-kappaB activation upon TNFalpha treatment. Whereas NF-kappaB was properly activated by TNFalpha in cultured and primary cells deficient in either cIAP1 or 2, removal of both cIAPs severely blunted its activation. After treatment with TNFalpha, cIAP1 and 2 were rapidly recruited to the TNF receptor 1, along with the adapter protein TNF receptor associated factor 2. Importantly, either cIAP1 or 2 was required for proper TNF receptor 1 signalosome function. In their combined absence, polyubiquitination of receptor interacting protein 1, an upstream event necessary for NF-kappaB signaling, was attenuated. As a result, phosphorylation of the inhibitor of kappaB kinase beta was diminished, and signal transduction was severely blunted. Consequently, cells missing both cIAP1 and 2 were sensitized to TNFalpha-mediated apoptosis. Collectively, these data demonstrate that either cIAP1 or 2 is required for proper Rip1 polyubiquitination and NF-kappaB activation upon TNFalpha treatment.

Cellular localisation of survivin: impact on the prognosis in colorectal cancer.

PURPOSE: The present study was designed to determine whether the nuclear or cytoplasmic expression of survivin, was related to clinicopathological parameters and survival in sporadic colon carcinomas. METHODS: Western blotting of cell fractions and immunocytochemical methodology were used in five human colon cancer cell lines. Immunohistochemical study was performed in formalin-fixed paraffin-embedded section from 46 patients with sporadic colorectal adenocarcinomas with a polyclonal antibody directed against survivin. Apoptotic index was evaluated by using the M30 antibody. Survival rates were estimated by the Kaplan-Meier method and compared using the log-rank test. Multivariate survival analysis was performed by the Cox proportional hazards model. RESULTS: Western blotting and immunocytochemistry analyses confirmed that survivin could be detected both in the nucleus and the cytoplasm. Immunohistochemical analysis demonstrated that 39% of tumours expressed survivin in the nucleus and 41% in the cytoplasm. No relationship was observed between survivin expression and clinicopathological features. Unexpectedly, the apoptotic index appeared to be linked with high survivin nuclear expression. Overall, 3-year observed survival rate was 73% in patients with cytoplasmic survivin expression versus 48% for negative expression (P = 0.14). Survival was 72% versus 50% for positive nuclear survivin expression versus negative (P = 0.16). After adjustment for age and stage, cytoplasmic survivin expression was a significant prognostic factor. A high level of expression was associated to a better survival: RR = 0.35 [0.13-0.98], P = 0.045. CONCLUSION: These results indicate that the analysis of the subcellular expression of survivin is a determining factor to define the prognostic value. Its evaluation, using a polyclonal antibody, might help clinicians in the stratification of patients with colorectal cancer.

Early increase in DcR2 expression and late activation of caspases in the platelet storage lesion.

Platelet transfusion is widely used to prevent bleeding in patients with severe thrombocytopenia. The maximal storage duration of platelet concentrates is usually 5 days, due to the platelet storage lesion that impairs their functions when stored for longer times. Some of the morphological and biochemical changes that characterize this storage lesion are reminiscent of cell death by apoptosis. The present study analyzed whether proteins involved in nucleated cell apoptosis could play a role in the platelet storage lesion. Storage of leukocyte-depleted platelets obtained by apheresis is associated with a late and limited activation of caspases, mainly caspase-3. This event correlates with an increased expression of the pro-apoptotic BH3-only protein Bim in the particulate fraction and a slight and late release of the pro-apoptotic mitochondrial protein Diablo/Smac in the cytosol. Platelets do not express the death receptors Fas, DR4 and DR5 on their plasma membrane, while the expression of the decoy receptor DcR2 increases progressively during platelet storage. Addition of low concentrations of the cryoprotector dimethylsulfoxide accelerates platelet caspase activation during storage, an effect that is partially prevented by the caspase inhibitor z-VAD-fmk. Altogether, DcR2 expression on the plasma membrane is an early event while caspase activation is a late event during platelet storage. These observations suggest that caspases are unlikely to account for the platelet storage lesion. As a consequence, addition of caspase inhibitors may not improve the quality of platelet concentrates stored in standard conditions.

Mitochondria-targeting drugs arsenic trioxide and lonidamine bypass the resistance of TPA-differentiated leukemic cells to apoptosis.

Exposure of U937 human leukemic cells to the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) induces their differentiation into monocyte/macrophage-like cells. This terminal differentiation is associated with a resistant phenotype to apoptosis induced by the topoisomerase II inhibitor etoposide. The inhibition occurs upstream of the mitochondrial release of cytochrome c and the activation of procaspase-2, -3, -6, -7, -8, and -9. By using cell-free systems, it was demonstrated that the mitochondrial pathway to cell death that involves mitochondrial membrane depolarization, cytochrome c release and cytosolic activation of procaspases by cytochrome c/dATP remains functional in TPA-differentiated U937 cells. Accordingly, 2 drugs recently shown to target the mitochondria, namely lonidamine and arsenic trioxide, bypass the resistance of TPA-differentiated U937 cells to classical anticancer drugs. Cell death induced by the 2 compounds is associated with mitochondrial membrane depolarization, release of cytochrome c and Smac/Diablo from the mitochondria, activation of caspases, poly(ADP-ribose) polymerase cleavage and internucleosomal DNA fragmentation. Moreover, the decreased glutathione content associated with the differentiation process amplifies the ability of arsenic trioxide to activate the mitochondrial pathway to cell death. Similar results were obtained by comparing undifferentiated and TPA-differentiated human HL60 leukemic cells. These data demonstrate that mitochondria-targeting agents bypass the resistance to classical anticancer drugs induced by TPA-mediated leukemic cell differentiation. (Blood. 2001;97:3931-3940)

Modulation of apoptotic pathways triggered by cytotoxic agents.

Anticancer drugs can induce tumour cell death by apoptosis. The main pathway from specific damage induced by the drug to apoptosis involves activation of caspases in the cytosol by pro-apoptotic molecules such as cytochrome c released from the mitochondria. At least in some cell types, anticancer drugs also upregulate the expression of death receptors and sensitize tumour cells to their cognate ligands, which could be used to amplify the response to cytotoxic drugs. The Bcl-2 family of proteins, which includes anti- and pro-apoptotic molecules, regulates cell sensitivity at the mitochondrial level. Chemotherapeutic drugs modulate their expression (e.g. through p53-dependent gene transcription), their activity (e.g. by phosphorylation) and their subcellular localization (e.g. by translocation of pro-apoptotic proteins from the cytosol to the mitochondria). When interacting with tumour cells, anticancer drugs also activate lipid- and kinase-dependent signalling pathways that modulate the death response to specific damage. Protective pathways include activation of NF kappa B transcription factor, accumulation of heat shock proteins and activation of proteins involved in cell cycle regulation. The recent identification on these pathways to cell death has suggested several new strategies to improve the therapeutic efficacy of currently used anticancer drug regimens.