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Selective killing of tumor neovasculature paradoxically improves chemotherapy delivery to tumors.

ABSTRACT: Antiangiogenic therapies are frequently used with concomitantly administered cancer chemotherapy to improve outcomes, but the mechanism for the benefit of the combination is uncertain. We describe a mechanism by which a specific, cytotoxic antivascular agent causes vascular remodeling and improved chemotherapy results. By selectively killing tumor neovasculature using short-ranged ?-particles targeted to vascular endothelial (VE)-cadherin on vascular endothelial cells (by use of 225Ac-labeled E4G10 antibody) we were able both to reduce tumor growth and to increase the efficacy of chemotherapy, an effect seen only when the chemotherapy was administered several days after the vascular targeting agent, but not if the order of administration was reversed. Immunohistochemical and immunofluorescence studies showed that the vasculature of 225Ac-E4G10-treated tumors was substantially depleted; the remaining vessels appeared more mature morphologically and displayed increased pericyte density and coverage. Tumor uptake and microdistribution studies with radioactive and fluorescent small molecule drugs showed better accumulation and more homogenous distribution of the drugs within 225Ac-E4G10-treated tumors. These results show that 225Ac-E4G10 treatment leads to ablation and improvement of the tumor vascular architecture, and also show that the resulting vascular remodeling can increase tumor delivery of small molecules, thus providing a process for the improved outcomes observed after combining antivascular therapy and chemotherapy. This study directly shows evidence for what has long been a speculated mechanism for antiangiogenic therapies. Moreover, targeting the vessel for killing provides an alternative mode of improving chemotherapy delivery and efficacy, potentially avoiding some of the drawbacks of targeting a highly redundant angiogenic pathway.

SUBMITTER: Escorcia FE

PROVIDER: S-EPMC3058681 | biostudies-literature | 2010 Nov

REPOSITORIES: biostudies-literature

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Selective killing of tumor neovasculature paradoxically improves chemotherapy delivery to tumors.

Escorcia Freddy E FE Henke Erik E McDevitt Michael R MR Villa Carlos H CH Smith-Jones Peter P Blasberg Ronald G RG Benezra Robert R Scheinberg David A DA

Cancer research 20101102 22

Antiangiogenic therapies are frequently used with concomitantly administered cancer chemotherapy to improve outcomes, but the mechanism for the benefit of the combination is uncertain. We describe a mechanism by which a specific, cytotoxic antivascular agent causes vascular remodeling and improved chemotherapy results. By selectively killing tumor neovasculature using short-ranged α-particles targeted to vascular endothelial (VE)-cadherin on vascular endothelial cells (by use of 225Ac-labeled E4 ...[more]

PMID: 21045141

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Project description:The gene for methylthioadenosine phosphorylase (MTAP) lies on 9p21, close to the gene CDKN2A that encodes the tumor suppressor proteins p16 and p14ARF. MTAP and CDKN2A are homozygously co-deleted, with a frequency of 35 to 70%, in lung and pancreatic cancer, glioblastoma, osteosarcoma, soft-tissue sarcoma, mesothelioma, and T-cell acute lymphoblastic leukemia. In normal cells, but not in tumor cells lacking MTAP, MTAP cleaves the natural substrate, 5'-deoxy-5'-methylthioadenosine (MTA), to adenine and 5-methylthioribose-1-phosphate (MTR-1-P), which are then converted to adenine nucleotides and methionine. This distinct difference between normal MTAP-positive cells and tumor MTAP-negative cells led to several proposals for therapy. We offer a novel strategy in which both MTA and a toxic adenine analog, such as 2,6-diaminopurine (DAP), 6-methylpurine (MeP), or 2-fluoroadenine (F-Ade), are administered. In MTAP-positive cells, abundant adenine, generated from supplied MTA, competitively blocks the conversion of an analog, by adenine phosphoribosyltransferase (APRT), to its active nucleotide form. In MTAP-negative tumor cells, the supplied MTA cannot generate adenine; hence conversion of the analog is not blocked.We show that this combination treatment--adenine analog plus MTA--kills MTAP-negative A549 lung tumor cells, while MTAP-positive human fibroblasts (HF) are protected. In co-cultures of the breast tumor cell line, MCF-7, and HF cells, MCF-7 is inhibited or killed, while HF cells proliferate robustly. 5-Fluorouracil (5-FU) and 6-thioguanine (6-TG) may also be used with our strategy. Though neither analog is activated by APRT, in MTAP-positive cells, adenine produced from supplied MTA blocks conversion of 5-FU and 6-TG to their toxic nucleotide forms by competing for 5-phosphoribosyl-1-pyrophosphate (PRPP). The combination of MTA with 5-FU or 6-TG, in the treatment of MTAP-negative tumors, may produce a significantly improved therapeutic index.We describe a selective strategy to kill tumor cells lacking MTAP.

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Selective killing of tumor neovasculature paradoxically improves chemotherapy delivery to tumors.

Publications

Selective killing of tumor neovasculature paradoxically improves chemotherapy delivery to tumors.

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