title: Selective cancer therapy by extracellular activation of a highly potent glycosidic duocarmycin analogue.
abstract: Conventional cancer chemotherapy is limited by systemic toxicity and poor selectivity. Tumor-selective activation of glucuronide prodrugs by beta-glucuronidase in the tumor microenvironment in a monotherapeutic approach is one promising way to increase cancer selectivity. Here we examined the cellular requirement for enzymatic activation as well as the in vivo toxicity and antitumor activity of a glucuronide prodrug of a potent duocarmycin analogue that is active at low picomolar concentrations. Prodrug activation by intracellular and extracellular beta-glucuronidase was investigated by measuring prodrug 2 cytotoxicity against human cancer cell lines that displayed different endogenous levels of beta-glucuronidase, as well as against beta-glucuronidase-deficient fibroblasts and newly established beta-glucuronidase knockdown cancer lines. In all cases, glucuronide prodrug 2 was 1000-5000 times less cytotoxic than the parent duocarmycin analogue regardless of intracellular levels of beta-glucuronidase. By contrast, cancer cells that displayed tethered beta-glucuronidase on their plasma membrane were 80-fold more sensitive to glucuronide prodrug 2, demonstrating that prodrug activation depended primarily on extracellular rather than intracellular beta-glucuronidase activity. Glucuronide prodrug 2 (2.5 mg/kg) displayed greater antitumor activity and less systemic toxicity in vivo than the clinically used drug carboplatin (50 mg/kg) to mice bearing human lung cancer xenografts. Intratumoral injection of an adenoviral vector expressing membrane-tethered beta-glucuronidase dramatically enhanced the in vivo antitumor activity of prodrug 2. Our data provide evidence that increasing extracellular beta-glucuronidase activity in the tumor microenvironment can boost the therapeutic index of a highly potent glucuronide prodrug.
authors: Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan.
authors: Kai-Chuan
authors: KC
authors: Chen
authors: Kianga
authors: K
authors: Schmuck
authors: Lutz F
authors: LF
authors: Tietze
authors: Steve R
authors: SR
authors: Roffler
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry / Q000378:metabolism* / Q000627:therapeutic use; D045744:Cell Line, Tumor; D000080890:Duocarmycins; D045604:Extracellular Fluid / Q000201:enzymology; D005260:Female; D005822:Genetic Vectors; D005966:Glucuronidase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D020719:Glucuronides / Q000737:chemistry / Q000378:metabolism / Q000627:therapeutic use; D006801:Humans; D007211:Indoles / Q000737:chemistry / Q000378:metabolism* / Q000627:therapeutic use; D051379:Mice; D008819:Mice, Nude; D015394:Molecular Structure; D011355:Prodrugs / Q000737:chemistry / Q000378:metabolism* / Q000627:therapeutic use; D011758:Pyrroles / Q000737:chemistry / Q000378:metabolism / Q000627:therapeutic use; D034741:RNA, Small Interfering / Q000235:genetics; D059016:Tumor Microenvironment; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D000080890:Duocarmycins; D020719:Glucuronides; D007211:Indoles; D011355:Prodrugs; D011758:Pyrroles; D034741:RNA, Small Interfering; C066098:duocarmycin SA; D005966:Glucuronidase