Susan G Komen  
I've Been Diagnosed With Breast Cancer Someone I Know Was Diagnosed Share Your Story Join Us And Stay Informed Donate To End Breast Cancer
    Home > Research & Grants > Grants Program > Research Grants > Research Grants Awarded > Abstract

    Research Grants Awarded

    Targeting Death Pathways By Tumor-Targeting Sirna-Nanovectors As Novel Molecular Therapy For Primary And Metastatic Breast Cancer

    Grant Mechanism:
    Career Catalyst Research

    Scientific Abstract:
    Resistance to current therapies and metastasis severely limit the success of treatment and the major cause of death of breast cancer patients. Anti-apoptotic and anti-autophagic protein Bcl-2 is overexpressed in many cancers including breast cancer patients and contribute to tumor initiation, progression, metastasis, angiogenesis and resistance to most chemotherapeutics, hormone therapy and radiotherapy. Targeting Bcl-2 represents a promising strategy for overcoming the resistance to programmed cell death induced by current cancer therapy. Small-interfering RNA (siRNA) technology has recently emerged as a powerful tool for sequence-specific gene silencing or knock-down and holds significant potential as novel molecular therapy for cancer. However, in vivo delivery of the siRNA-based therapeutics efficiently and specifically to primary tumor and its metastases remains a great challenge. We have developed a novel neutral-charge nanovector delivery system and found that this nanoliposomal delivery system can target siRNA in vivo into tumor cells 10-fold and 30-fold more effectively than cationic liposomes and naked siRNA, respectively, resulting in a significant downregulation of the target protein in tumor tissues in animal models. Our in vivo studies showed that only three systemic (i.v.) administration of nanoliposomal siRNA targeting Bcl-2 alone significantly reduced tumor growth in nude mice bearing Bcl-2 positive highly aggressive and metastatic breast cancer xenografts. We also demonstrated for the first time that targeted knock-down of Bcl-2 by siRNA induces significant autophagic cell death (type II programmed cell death) in addition to apoptosis (type I) in vitro and in vivo breast cancer cells. The molecular mechanism by which Bcl-2 knockdown induce autophagic cell death are not well understood. Most importantly, these particular nanoliposomes were not toxic to mice and normal cells. To develop highly tumor-specific and targeted delivery system we recently created folate expressing nanovectors and found that folate receptor (FR)-targeted nanoliposomes could deliver siRNA into cancer cells about 4.5-fold more effectively than our regular nanoliposomes in vitro. FR is highly overexpressed in majority of human cancers including breast cancer cell lines and 80% of metastatic epithelial cancer cells but not in most normal tissues. Our hypothesis is that neutral-charge nanoliposomal siRNA specific for Bcl-2 can effectively reduce primary and metastatic tumor growth in in vivo human breast cancer cells by leading to targeted knock-down of Bcl-2 and, in turn, induce apoptosis and autophagic cell death and enhanced sensitivity to chemotherapy and prolong survival. We will also test the hypothesis that folate receptor-targeted nanoliposomes can enhance in vivo delivery of siRNA in tumor tissues (primary and metastatic) and provide better target silencing. The success of our novel nanovectors for systemic siRNA delivery provides a promising, non-toxic delivery system for siRNA-based therapeutics. Our long-term goal is to develop the tumor- targeting siRNA-nanovectors as novel molecular therapy targeting Bcl-2 for human cancers expressing with Bcl-2. To test our hypothesis, we propose to carry out two specific aims, Aim 1: To determine the in vivo efficacy of regular and FR-targeted nanoliposomal Bcl-2 siRNA alone and in combination with chemotherapy in xenograft mouse models of human breast cancer; Aim 2: To delineate the molecular mechanism of autophagic cell death induced by Bcl-2 downregulation in breast cancer cells. Combining siRNA-based Bcl-2 molecular therapy with conventional therapy would improve the efficacy and overcome the resistance to current cancer treatment, especially for advance and metastatic tumors, in which Bcl-2 protein is overexpressed and for which conventional therapy is not very effective. Successfully carried out, our studies will provide proof-of-concept that siRNA can be delivered by the nanovectors for tumor-targeted silencing of the genes critical for cancer progression and resistance. The results of this study will provide the basis and guide future clinical trials in humans with Bcl-2 positive tumors.

    Lay Abstract:
    Resistance to current therapies and metastasis severely limit the success of treatment and the major cause of death of breast cancer patients. Anti-apoptotic and anti-autophagic protein Bcl-2 is overexpressed in many cancers including breast cancer patients and contribute to tumor initiation, progression, metastasis, angiogenesis and resistance to most chemotherapeutics, hormone therapy and radiotherapy. Targeting Bcl-2 represents a promising strategy for overcoming the resistance to programmed cell death induced by current cancer therapy. Small-interfering RNA (siRNA) technology has recently emerged as a powerful tool for sequence-specific gene silencing or knock-down and holds significant potential as novel molecular therapy for cancer. However, in vivo delivery of the siRNA-based therapeutics efficiently and specifically to primary tumor and its metastases remains a great challenge. We have developed a novel neutral-charge nanovector delivery system and found that this nanoliposomal delivery system can target siRNA in vivo into tumor cells 10-fold and 30-fold more effectively than cationic liposomes and naked siRNA, respectively, resulting in a significant downregulation of the target protein in tumor tissues in animal models. Our in vivo studies showed that only three systemic (i.v.) administration of nanoliposomal siRNA targeting Bcl-2 alone significantly reduced tumor growth in nude mice bearing Bcl-2 positive highly aggressive and metastatic breast cancer xenografts. We also demonstrated for the first time that targeted knock-down of Bcl-2 by siRNA induces significant autophagic cell death (type II programmed cell death) in addition to apoptosis (type I) in vitro and in vivo breast cancer cells. The molecular mechanism by which Bcl-2 knockdown induce autophagic cell death are not well understood. Most importantly, these particular nanoliposomes were not toxic to mice and normal cells. To develop highly tumor-specific and targeted delivery system we recently created folate expressing nanovectors and found that folate receptor (FR)-targeted nanoliposomes could deliver siRNA into cancer cells about 4.5-fold more effectively than our regular nanoliposomes in vitro. FR is highly overexpressed in majority of human cancers including breast cancer cell lines and 80% of metastatic epithelial cancer cells but not in most normal tissues. Our hypothesis is that neutral-charge nanoliposomal siRNA specific for Bcl-2 can effectively reduce primary and metastatic tumor growth in in vivo human breast cancer cells by leading to targeted knock-down of Bcl-2 and, in turn, induce apoptosis and autophagic cell death and enhanced sensitivity to chemotherapy and prolong survival. We will also test the hypothesis that folate receptor-targeted nanoliposomes can enhance in vivo delivery of siRNA in tumor tissues (primary and metastatic) and provide better target silencing. The success of our novel nanovectors for systemic siRNA delivery provides a promising, non-toxic delivery system for siRNA-based therapeutics. Our long-term goal is to develop the tumor- targeting siRNA-nanovectors as novel molecular therapy targeting Bcl-2 for human cancers expressing with Bcl-2. To test our hypothesis, we propose to carry out two specific aims, Aim 1: To determine the in vivo efficacy of regular and FR-targeted nanoliposomal Bcl-2 siRNA alone and in combination with chemotherapy in xenograft mouse models of human breast cancer; Aim 2: To delineate the molecular mechanism of autophagic cell death induced by Bcl-2 downregulation in breast cancer cells. Combining siRNA-based Bcl-2 molecular therapy with conventional therapy would improve the efficacy and overcome the resistance to current cancer treatment, especially for advance and metastatic tumors, in which Bcl-2 protein is overexpressed and for which conventional therapy is not very effective. Successfully carried out, our studies will provide proof-of-concept that siRNA can be delivered by the nanovectors for tumor-targeted silencing of the genes critical for cancer progression and resistance. The results of this study will provide the basis and guide future clinical trials in humans with Bcl-2 positive tumors.