RESUMO
The phosphoinositide 3-kinase (PI3K) pathway is activated in most advanced prostate cancers, yet so far treatments with PI3K inhibitors have been at best tumorostatic in preclinical cancer models and do not show significant antitumor efficacy in clinical trials. Results from tissue culture experiments in prostate cancer cells suggest that PI3K inhibitors should be combined with other cytotoxic agents; however, the general toxicity of such combinations prevents translating these experimental data into preclinical and clinical models. We investigated the emerging concept of tumor-targeted synthetic lethality in prostate cancer cells by using the pan-PI3K inhibitor ZSTK474 and the immunotoxin J591PE, a protein chimera between the single-chain variable fragment of the monoclonal antibody J591 against the prostate-specific membrane antigen (PSMA) and the truncated form of the Pseudomonas aeruginosa exotoxin A (PE38QQR). The combination of ZSTK474 and J591PE increased apoptosis within 6 hours and cell death (monitored at 24-48 hours) in the PSMA-expressing cells LNCaP, C4-2, and C4-2Luc but not in control cells that do not express PSMA (PC3 and BT549 cells). Mechanistic analysis suggested that induction of apoptosis requires Bcl-2-associated death promoter (BAD) dephosphorylation and decreased expression of myeloid leukemia cell differentiation protein 1 (MCL-1). A single injection of ZSTK474 and J591PE into engrafted prostate cancer C4-2Luc cells led to consistent and stable reduction of luminescence within 6 days. These results suggest that the combination of a PI3K inhibitor and a PSMA-targeted protein synthesis inhibitor toxin represents a promising novel strategy for advanced prostate cancer therapy that should be further investigated.
Assuntos
ADP Ribose Transferases/imunologia , Antígenos de Superfície/imunologia , Apoptose , Toxinas Bacterianas/imunologia , Exotoxinas/imunologia , Glutamato Carboxipeptidase II/imunologia , Imunotoxinas/imunologia , Inibidores de Fosfoinositídeo-3 Quinase , Neoplasias da Próstata/terapia , Proteínas Recombinantes de Fusão/farmacologia , Triazinas/farmacologia , Fatores de Virulência/imunologia , ADP Ribose Transferases/genética , Animais , Anticorpos Monoclonais/genética , Anticorpos Monoclonais/imunologia , Toxinas Bacterianas/genética , Linhagem Celular Tumoral , Exotoxinas/genética , Xenoenxertos , Humanos , Imunotoxinas/genética , Masculino , Camundongos Endogâmicos BALB C , Proteína de Sequência 1 de Leucemia de Células Mieloides/metabolismo , Neoplasias da Próstata/imunologia , Neoplasias da Próstata/patologia , Pseudomonas aeruginosa , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/imunologia , Anticorpos de Cadeia Única/genética , Anticorpos de Cadeia Única/imunologia , Fatores de Virulência/genética , Exotoxina A de Pseudomonas aeruginosaRESUMO
PTEN loss and constitutive activation of the PI3K signaling pathway have been associated with advanced androgen-independent prostate cancer. PTEN-deficient prostate cancer C42Luc cells survive in serum-free media and show relative resistance to apoptosis even in the presence of the PI3K inhibitor ZSTK474. Yet, when ZSTK474 is combined with the translation inhibitor cycloheximide, C42Luc cells undergo apoptosis within 6 hours. We identified dephosphorylation of BAD (Bcl2-associated death promoter) as a main apoptosis-regulatory molecule downstream from PI3K, and loss of MCL-1 (Myeloid cell leukemia -1) as a major target of cycloheximide. The combination of MCL-1 knockdown and expression of phosphorylation-deficient mutant BAD2SA is sufficient to trigger rapid apoptosis in prostate cancer cells. These results establish the mechanism for the synergistic induction of apoptosis by the combination of a PI3K inhibitor and of a protein synthesis inhibitor in PTEN-deficient prostate cancer cells.
Assuntos
Resistencia a Medicamentos Antineoplásicos/efeitos dos fármacos , Regulação Neoplásica da Expressão Gênica , Proteína de Sequência 1 de Leucemia de Células Mieloides/antagonistas & inibidores , PTEN Fosfo-Hidrolase/genética , Proteína de Morte Celular Associada a bcl/metabolismo , Apoptose/efeitos dos fármacos , Linhagem Celular Tumoral , Meios de Cultura Livres de Soro/química , Cicloeximida/farmacologia , Resistencia a Medicamentos Antineoplásicos/genética , Sinergismo Farmacológico , Humanos , Masculino , Proteína de Sequência 1 de Leucemia de Células Mieloides/genética , Proteína de Sequência 1 de Leucemia de Células Mieloides/metabolismo , PTEN Fosfo-Hidrolase/deficiência , Fosfatidilinositol 3-Quinases/genética , Fosfatidilinositol 3-Quinases/metabolismo , Inibidores de Fosfoinositídeo-3 Quinase , Fosforilação , Inibidores de Proteínas Quinases/farmacologia , Inibidores da Síntese de Proteínas/farmacologia , Transdução de Sinais , Triazinas/farmacologia , Proteína de Morte Celular Associada a bcl/genéticaRESUMO
Prostate cancer patients have increased levels of stress and anxiety. Conversely, men who take beta blockers, which interfere with signaling from the stress hormones adrenaline and noradrenaline, have a lower incidence of prostate cancer; however, the mechanisms underlying stress-prostate cancer interactions are unknown. Here, we report that stress promotes prostate carcinogenesis in mice in an adrenaline-dependent manner. Behavioral stress inhibited apoptosis and delayed prostate tumor involution both in phosphatase and tensin homolog-deficient (PTEN-deficient) prostate cancer xenografts treated with PI3K inhibitor and in prostate tumors of mice with prostate-restricted expression of c-MYC (Hi-Myc mice) subjected to androgen ablation therapy with bicalutamide. Additionally, stress accelerated prostate cancer development in Hi-Myc mice. The effects of stress were prevented by treatment with the selective ß2-adrenergic receptor (ADRB2) antagonist ICI118,551 or by inducible expression of PKA inhibitor (PKI) or of BCL2-associated death promoter (BAD) with a mutated PKA phosphorylation site (BADS112A) in xenograft tumors. Effects of stress were also blocked in Hi-Myc mice expressing phosphorylation-deficient BAD (BAD3SA). These results demonstrate interactions between prostate tumors and the psychosocial environment mediated by activation of an adrenaline/ADRB2/PKA/BAD antiapoptotic signaling pathway. Our findings could be used to identify prostate cancer patients who could benefit from stress reduction or from pharmacological inhibition of stress-induced signaling.
