RESUMO
Antiestrogen therapy resistance remains a huge stumbling block in the treatment of breast cancer. We have found significant elevation of O(6) methylguanine DNA methyl transferase (MGMT) expression in a small sample of consecutive patients who have failed tamoxifen treatment. Here, we show that tamoxifen resistance is accompanied by upregulation of MGMT. Further we show that administration of the MGMT inhibitor, O(6)-benzylguanine (BG), at nontoxic doses, leads to restoration of a favorable estrogen receptor alpha (ERα) phosphorylation phenotype (high p-ERα Ser167/low p-ERα Ser118), which has been reported to correlate with sensitivity to endocrine therapy and improved survival. We also show BG to be a dual inhibitor of MGMT and ERα. In tamoxifen-resistant breast cancer cells, BG alone or in combination with antiestrogen (tamoxifen [TAM]/ICI 182,780 [fulvestrant, Faslodex]) therapy enhances p53 upregulated modulator of apoptosis (PUMA) expression, cytochrome C release and poly (ADP-ribose) polymerase (PARP) cleavage, all indicative of apoptosis. In addition, BG increases the expression of p21(cip1/waf1). We also show that BG, alone or in combination therapy, curtails the growth of tamoxifen-resistant breast cancer in vitro and in vivo. In tamoxifen-resistant MCF7 breast cancer xenografts, BG alone or in combination treatment causes significant delay in tumor growth. Immunohistochemistry confirms that BG increases p21(cip1/waf1) and p-ERα Ser167 expression and inhibits MGMT, ERα, p-ERα Ser118 and ki-67 expression. Collectively, our results suggest that MGMT inhibition leads to growth inhibition of tamoxifen-resistant breast cancer in vitro and in vivo and resensitizes tamoxifen-resistant breast cancer cells to antiestrogen therapy. These findings suggest that MGMT inhibition may provide a novel therapeutic strategy for overcoming antiestrogen resistance.
Assuntos
Neoplasias da Mama/tratamento farmacológico , Neoplasias da Mama/enzimologia , Metilases de Modificação do DNA/antagonistas & inibidores , Enzimas Reparadoras do DNA/antagonistas & inibidores , Antagonistas de Estrogênios/uso terapêutico , Receptor alfa de Estrogênio/metabolismo , Proteínas Supressoras de Tumor/antagonistas & inibidores , Animais , Antineoplásicos/farmacologia , Antineoplásicos/uso terapêutico , Apoptose/efeitos dos fármacos , Apoptose/genética , Neoplasias da Mama/genética , Neoplasias da Mama/patologia , Pontos de Checagem do Ciclo Celular/efeitos dos fármacos , Pontos de Checagem do Ciclo Celular/genética , Linhagem Celular Tumoral , Inibidor de Quinase Dependente de Ciclina p21/genética , Inibidor de Quinase Dependente de Ciclina p21/metabolismo , Metilases de Modificação do DNA/metabolismo , Enzimas Reparadoras do DNA/metabolismo , Resistencia a Medicamentos Antineoplásicos/efeitos dos fármacos , Resistencia a Medicamentos Antineoplásicos/genética , Inibidores Enzimáticos/farmacologia , Inibidores Enzimáticos/uso terapêutico , Antagonistas de Estrogênios/farmacologia , Feminino , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Guanina/análogos & derivados , Guanina/farmacologia , Guanina/uso terapêutico , Humanos , Imuno-Histoquímica , Camundongos , Camundongos Nus , Fosforilação/efeitos dos fármacos , Fosfosserina/metabolismo , Regiões Promotoras Genéticas/genética , Ligação Proteica/efeitos dos fármacos , Ligação Proteica/genética , Tamoxifeno/uso terapêutico , Transcrição Gênica/efeitos dos fármacos , Proteína Supressora de Tumor p53/metabolismo , Proteínas Supressoras de Tumor/metabolismoAssuntos
Neoplasias Brônquicas/patologia , Melanoma Amelanótico/secundário , Neoplasias Cutâneas/secundário , Idoso , Neoplasias Brônquicas/cirurgia , Feminino , Humanos , Melanoma Amelanótico/cirurgia , Tomografia por Emissão de Pósitrons , Neoplasias Cutâneas/cirurgia , Tomografia Computadorizada por Raios X , Resultado do TratamentoRESUMO
PURPOSE: Mapatumumab and lexatumumab are fully humanized, high-affinity immunoglobulin G(1 lambda) monoclonal antibodies (mAb) that target/activate the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor 1 (TRAIL-R1) and receptor 2 (TRAIL-R2), respectively, triggering the extrinsic apoptotic pathway. Theoretically, synergistic antitumor activity should be observed by combining TRAIL-R mAbs with agents (e.g., rituximab) that activate the intrinsic apoptotic pathway. EXPERIMENTAL DESIGN: To this end, targeted antigen expression in a NHL-cell panel was evaluated by flow cytometry. NHL cells were exposed to mapatumumab or lexatumumab followed by rituximab, isotype, or RPMI. DNA synthesis was quantified by [(3)H]-thymidine incorporation assays. Induction of apoptosis was detected by flow-cytometric analysis. For antibody-dependent cellular cytotoxicity (ADCC) and complement-mediated cytotoxicity (CMC) studies, standardized (51)Cr-release assays were done. We inoculated severe combined immunodeficiency (SCID) mouse with Raji cells i.v. The animals then were treated with various combinations of rituximab, mapatumumab, lexatumumab, and isotype alone or in combination. RESULTS: In vitro exposure to mapatumumab resulted in significant apoptosis (30-50%) and decreased DNA synthesis in sensitive lymphoma cells. Mapatumumab/rituximab combination resulted in a significant inhibition of cell proliferation (90% reduction) when compared with mapatumumab (60% reduction) or rituximab (5% reduction). In vivo, the median survival time of animals treated with mapatumumab and rituximab was longer (not reached) than those treated with rituximab monotherapy [33 days (95% confidence interval, 29-37), log-rank test, P = 0.05]. CONCLUSIONS: Mapatumumab induces apoptosis, cell growth arrest, ADCC, and CMC. The combination of mapatumumab plus rituximab is more effective in controlling lymphoma growth in vivo than either antibody. Rituximab and mapatumumab warrant further evaluation against B-cell lymphoma.
