RESUMO
Heterogeneous expression of drug target proteins within tumor sites is a major mechanism of resistance to anticancer therapies. We describe a strategy to selectively inhibit, within tumor sites, the function of a critical intracellular protein, the sarcoplasmic/endoplasmic reticulum calcium adenosine triphosphatase (SERCA) pump, whose proper function is required by all cell types for viability. To achieve targeted inhibition, we took advantage of the unique expression of the carboxypeptidase prostate-specific membrane antigen (PSMA) by tumor endothelial cells within the microenvironment of solid tumors. We generated a prodrug, G202, consisting of a PSMA-specific peptide coupled to an analog of the potent SERCA pump inhibitor thapsigargin. G202 produced substantial tumor regression against a panel of human cancer xenografts in vivo at doses that were minimally toxic to the host. On the basis of these data, a phase 1 dose-escalation clinical trial has been initiated with G202 in patients with advanced cancer.
Assuntos
Antígenos de Superfície/metabolismo , Células Endoteliais/metabolismo , Glutamato Carboxipeptidase II/metabolismo , Pró-Fármacos/uso terapêutico , Neoplasias da Próstata/tratamento farmacológico , Animais , Linhagem Celular Tumoral , Humanos , Masculino , CamundongosRESUMO
Prostate-Specific Membrane Antigen (PSMA) is a glutamate carboxypeptidase II that is highly expressed by both normal and malignant prostate epithelial cells and by the neovasculature of many tumor types but is not expressed by endothelial cells in normal tissue. PSMA possesses the hydrolytic properties of an N-acetylated alpha-linked acidic dipeptidase (NAALADase) and also functions as a pteroyl poly-gamma-glutamyl carboxypeptidase (i.e., folate hydrolase). Therefore, PSMA can be targeted for activation of peptide-based prodrugs within the extracellular fluid of prostate cancers. In this study, methotrexate-based peptide analogs were evaluated to identify PSMA selective substrates that are also stable to nonspecific hydrolysis in human and mouse plasma. These methotrexate analogs were also characterized for in vitro toxicity against PSMA and nonPSMA producing human cancer cell lines. Analogs containing gamma-linked glutamate residues were most efficiently hydrolyzed by PSMA, but were unstable in plasma. Analogs containing both alpha- and gamma-linked acidic amino acids were less efficiently hydrolyzed by PSMA but were most stable in plasma. Analogs were 5-10 fold more selectively toxic in vitro in the presence of active PSMA. These studies have identified PSMA selective, plasma stable peptide substrates that can be incorporated into prodrugs targeted for activation by PSMA within prostate cancer sites.
Assuntos
Antígenos de Superfície/metabolismo , Glutamato Carboxipeptidase II/metabolismo , Metotrexato/metabolismo , Fragmentos de Peptídeos/metabolismo , Pró-Fármacos , Neoplasias da Próstata/metabolismo , Animais , Antígenos de Superfície/genética , Ácido Aspártico/metabolismo , Western Blotting , Líquido Extracelular , Glutamato Carboxipeptidase II/genética , Ácido Glutâmico/metabolismo , Humanos , Cadeias gama de Imunoglobulina/genética , Cadeias kappa de Imunoglobulina/genética , Masculino , Camundongos , Neoplasias da Próstata/tratamento farmacológico , Neoplasias da Próstata/patologia , Proteínas Recombinantes de Fusão/metabolismo , Especificidade por Substrato , Células Tumorais Cultivadas/metabolismoRESUMO
A method for targeted delivery of the cytotoxic agent 5-fluorodeoxyuridine (FudR) (1) to sites of metastatic prostate cancer is described. The prodrug was synthesized by coupling the active drug (FudR) to the PSA-peptide via a self-cleaving diamino acid linker to produce HSSKLQ-Leu-Aib-FudR. This prodrug serves as a substrate for prostate specific antigen (PSA). This approach permitted efficient conversion of the inactive prodrug back to the active cytotoxic state by the enzymatic activity of PSA which is highly expressed by prostate cells.