Histone deacetylase inhibitors sensitize tumour cells for cytotoxic effects of natural killer cells

Castration resistance in human prostate cancer is conferred by a frequently occurring androgen receptor splice variant

Progression of prostate cancer following castration is associated with increased androgen receptor (AR) expression and signaling despite AR blockade. Recent studies suggest that these activities are due to the generation of constitutively active AR splice variants, but the mechanisms by which these splice variants could mediate such effects are not fully understood. Here we have identified what we believe to be a novel human AR splice variant in which exons 5, 6, and 7 are deleted (ARv567es) and demonstrated that this variant can contribute to cancer progression in human prostate cancer xenograft models in mice following castration. We determined that, in human prostate cancer cell lines, ARv567es functioned as a constitutively active receptor, increased expression of full-length AR (ARfl), and enhanced the transcriptional activity of AR. In human xenografts, human prostate cancer cells transfected with ARv567es cDNA formed tumors that were resistant to castration. Furthermore, the ratio of ARv567es to ARfl expression within the xenografts positively correlated with resistance to castration. Importantly, we also detected ARv567es frequently in human prostate cancer metastases. In summary, these data indicate that constitutively active AR splice variants can contribute to the development of castration-resistant prostate cancers and may serve as biomarkers for patients who are likely to suffer from early recurrence and are candidates for therapies directly targeting the AR rather than ligand.

Histone deacetylase inhibitors prevent activation of tumour-reactive NK cells and T cells but do not interfere with their cytolytic effector functions

Histone deacetylase inhibitors (HDIs) exert direct tumour-toxic activity and sensitise tumour cells for other therapeutic regimens as well as the cytotoxic effects of activated immune cells. However, the HDI suberoylanilide hydroxamic acid (SAHA; vorinostat) interfered with the IL-2 activation of human NK cells and the priming of human tumour-specific T cells. In contrast, NK or T cells which were activated in the absence of HDIs became resistant to their immunosuppressive action. Therefore, as a therapeutic strategy, first the patient's immune system might be stimulated and then HDIs could sensitise the tumours for the attack of the pre-activated immune effector cells.

The histone deacetylase inhibitor vorinostat induces calreticulin exposure in childhood brain tumour cells in vitro

PURPOSE

It has recently been recognised that anticancer chemotherapy can elicit an immunogenic form of apoptosis characterised by the exposure of calreticulin (CRT) on the surface of dying tumour cells, entailing an immune response that contributes to the therapeutic outcome. CRT exposure has been found to be induced by anthracyclins and oxaliplatin, but not by other proapoptotic antineoplastic agents including etoposide, camptothecin and cisplatin. In this study, we examined the histone deacetylase inhibitor vorinostat for its capability to stimulate CRT exposure in tumour cells.

METHODS

Childhood tumour cells, i.e. the brain tumour cell lines PFSK and DAOY and the Ewing's sarcoma cell line CADO-ES-1, were treated with vorinostat, and CRT exposure was determined by flow cytometric analysis of CRT immunofluorescence. Combination effects of vorinostat/TRAIL and vorinostat/bortezomib were also assessed.

RESULTS

Vorinostat treatment induced CRT exposure in PFSK and DAOY cells, but not in caspase-8-deficient CADO-ES-1 cells. CRT exposure could be prevented by the pan-caspase inhibitor z-VAD-fmk and by brefeldin A, an inhibitor of Golgi-mediated transport.

CONCLUSION

Vorinostat has the capacity to elicit CRT exposure, suggesting its usefulness as immunogenic antitumour agent.

Natural killer and gammadelta T cells in haematological malignancies: enhancing the immune effectors

Human natural killer (NK) and gamma delta (gammadelta) T cells are potent effectors involved in the destruction of abnormal cells. Accumulating clinical and experimental data point towards a key role for NK cells and gammadelta T cells in the control of most, if not all, haematological malignancies. This review focuses on the alterations in these effector cells found in patients with haematological malignancies, which might explain an escape from innate immune surveillance. We discuss new anti-cancer drugs that target these effector cells indirectly or directly. Finally, we review future strategies that offer the possibility of enhancing the effector functions of NK and gammadelta T cells against haematological malignancies.