Abstract 2006: A novel macromolecular platinum drug with potent efficacy to overcome cross-resistance in cancer therapy

Background: Small molecular platinum (Pt)-based drugs such as cisplatin, carboplatin, and oxaliplatin have achieved great success in clinic over 40 years in cancer therapy. However, lack of tumor specificity leads to severe side effects. In addition, cancer cells frequently develop resistance to treatment through overexpressing cell surface multi-drug resistant proteins (MDRs). Therefore, it is desirable to develop novel Pt-based drugs with excellent anti-cancer efficacy and a minimal toxicity profile, as well as the capability to overcome drug resistance. We have previously demonstrated that poly(amino acid)-conjugated drugs can reduce toxicity and improve pharmacokinetics of chemotherapeutics and also overcome drug resistance by bypassing MDRs. Here we would like to apply this strategy on Pt drug development.

Method: To address this question, we synthesized a L-aspartic acid-chelated Pt moieties (Asp-Pt), and then conjugated it to poly(L-glutamic acid/L-aspartic acid) to generate a polymeric-Pt macromolecule, namely carrier-platin. We next applied this drug on cancer cell lines including the therapeutic-resistant cancer cells in vitro, and tumor bearing murine models in vivo to evaluate its efficacy and toxicity.

Result: We first tested the cytotoxicity of carrier-platin and compared with a current first-line chemotherapeutic oxaliplatin on colorectal cancer cell CT26 in vitro. Surprisingly, we found that carrier-platin effectively killed the CT26 cancer cells with hours while oxaliplatin slowly induced cell death after days. Importantly, carrier-platin was well-tolerated by non-cancerous cells. Furthermore, carrier-platin killed cancer cells that resistant to current chemotherapeutics in clinic, including cisplatin, oxaliplatin, doxorubicin and docetaxel, as effective as their parental cells. Next, we found that carrier-platin showed prolonged circulation time and high tumor accumulation compared with Pt-equivalent dosage of oxaliplatin. Treatment with 8 mg Pt/kg oxaliplatin caused severe body weight loss and intolerable hematotoxicity in mice, but even higher dose of carrier-platin (12 mg Pt/kg) can be tolerated by mice with stable body weight and did not induce any clinical symptoms. Finally, we revealed that carrier-platin potently inhibited mouse colorectal (CT26) and human ovarian (A2780) tumor growth over Pt-equivalent dosage of oxaliplatin. More importantly, carrier-platin was almost as effective on the cisplatin-resistant A2780 tumors (A2780-Cis) as on the parental A2780 tumors in vivo.

Conclusion: We developed a novel macromolecular drug carrier-platin that overcome shortages of current small molecular Pt drugs. It displayed a satisfactory toxicity profile accompanied with excellent anti-tumor efficacy in vivo. Moreover, carrier-platin overcomes the cross-resistance problem of cancer cells to current chemotherapeutic drugs.

Citation Format: Yongbin Liu, Dongfang Yu, Junhua Mai, Ping-Ying Pan, Shu-Hsia Chen, Haifa Shen. A novel macromolecular platinum drug with potent efficacy to overcome cross-resistance in cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2006.

Abstract 6799: A porous silicon particle based particulate anti-cancer vaccine for immunotherapy

Background: Anti-cancer vaccine is a widely-studied strategy that activates innate and adaptive host immunity via its adjuvant components and tumor antigens against cancer. Unfortunately, its response rate in clinical trials was not promising. On the vaccine part, sufficient stimulation of strong and long-lasting local and systemic immunity and efficient promotion of intratumoral infiltration of cytotoxic T lymphocytes are among the critical issues determining the therapeutic efficacy of cancer vaccines in addition to the innate features of tumor. Our project aims to develop a porous silicon particle based particulate vaccine against cancer, and investigate the therapeutic mechanism and combinational effects with current first-line strategies.

Method: We first screened the combinations of ligands of Toll-like receptors (TLRs) expressing on antigen presenting cells (APCs) and selected the most powerful combo for immune stimulation. We then loaded the identified adjuvants in addition to antigen peptides to produce vaccine particles. Stimulation and licensing of APCs were tested in vitro, and its therapeutic efficacies were evaluated on multiple orthotopic and systemic metastasis cancer murine models of breast and colon cancers. Furthermore, we investigated the vaccine’s synergistic effects and impacts on tumor microenviroment (TME) with an immunogenic chemotherapeutic oxaliplatin on a CT26 colon cancer model.

Result: According to the adjuvant screening assays, we identified a capable combination of CpG1826 (CpG) and 2’3’-cGAMP (cGAMP), which extensively stimulated the activation, maturation and type-I interferon secretion of APCs. A µGCVax formulation composed by these two adjuvants and antigen peptides was then applied on primary and metastatic HER2+ breast cancer TUBO bearing mice. µGCVax potently promoted the activation and lymph node migration of CD8+ and CD103+ dendritic cells in vivo. Distal metastatic tumor nodules in all different tissues vanished after two vaccinations. Functional cure of cancer and extension of animal survival were achieved. Moreover, oxaliplatin treatment on colon cancer caused immunogenic cell death and generated an immune favorable TME in a subcutaneous CT26 colon cancer model. The combination of µGCVax with the oxaliplatin effectively blocked the progression of large tumor mass. We finally revealed that the reprogramming of TME and the promotion of efficacy were mostly achieved from diminishing myeloid-derived suppressor cells (MDSCs) in tumor.

Conclusion: µGCVax is an effective and board-spectrum formulation for cancer immunotherapy. It effectively induces APC activation and licensing, and stimulates the innate and adaptive immunity against multiple cancers. The combination with oxaliplatin further promotes the therapeutic efficacy of µGCVax by decreasing tumor MDSCs.

Citation Format: Junhua Mai, Yongbin Liu, Dongfang Yu, Haifa Shen. A porous silicon particle based particulate anti-cancer vaccine for immunotherapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6799.

An mRNA vaccine elicits STING-dependent antitumor immune responses

Lipid-formulated RNA vaccines have been widely used for disease prevention and treatment, yet their mechanism of action and individual components contributing to such actions remain to be delineated. Here, we show that a therapeutic cancer vaccine composed of a protamine/mRNA core and a lipid shell is highly potent in promoting cytotoxic CD8⁺ T cell responses and mediating anti-tumor immunity. Mechanistically, both the mRNA core and lipid shell are needed to fully stimulate the expression of type I interferons and inflammatory cytokines in dendritic cells. Stimulation of interferon-β expression is exclusively dependent on STING, and antitumor activity from the mRNA vaccine is significantly compromised in mice with a defective Sting gene. Thus, the mRNA vaccine elicits STING-dependent antitumor immunity.

A modified porous silicon microparticle potentiates protective systemic and mucosal immunity for SARS-CoV-2 subunit vaccine

Development of optimal SARS-CoV-2 vaccines to induce potent, long-lasting immunity and provide cross-reactive protection against emerging variants remains a high priority. Here, we report that a modified porous silicon microparticle (mPSM) adjuvant to SARS-CoV-2 receptor-binding domain (RBD) vaccine activated dendritic cells and generated more potent and durable systemic humoral and type 1 helper T (Th) cell- mediated immune responses than alum-formulated RBD following parenteral vaccination, and protected mice from SARS-CoV-2 and Beta variant challenge. Notably, mPSM facilitated the uptake of SARS-CoV-2 RBD antigens by nasal and airway epithelial cells. Parenteral and intranasal prime and boost vaccinations with mPSM-RBD elicited stronger lung resident T and B cells and IgA responses compared to parenteral vaccination alone, which led to markedly diminished viral loads and inflammation in the lung following SARS-CoV-2 Delta variant challenge. Overall, our results suggest that mPSM is effective adjuvant for SARS-CoV-2 subunit vaccine in both systemic and mucosal vaccinations.

Identification of an Aptamer With Binding Specificity to Tumor-Homing Myeloid-Derived Suppressor Cells

Myeloid-derived suppressor cells (MDSCs) play a critical role in tumor growth and metastasis. Since they constantly infiltrate into the tumor tissue, these cells are considered as an ideal carrier for tumor-targeted drug delivery. We recently identified a DNA-based thioaptamer (T1) with tumor accumulating activity, demonstrated its potential on tumor targeting and drug delivery. In the current study, we have carried out structure-activity relationship analysis to further optimize the aptamer. In the process, we have identified a sequence-modified aptamer (M1) that shows an enhanced binding affinity to MDSCs over the parental T1 aptamer. In addition, M1 can penetrate into the tumor tissue more effectively by hitchhiking on MDSCs. Taken together, we have identified a new reagent for enhanced tumor-targeted drug delivery.

Rad51 Silencing with siRNA Delivered by Porous Silicon-Based Microparticle Enhances the Anti-Cancer Effect of Doxorubicin in Triple-Negative Breast Cancer

Due to its high heterogeneity and aggressiveness, cytotoxic chemotherapy is still a mainstay treatment for triple negative breast cancer. Unfortunately, the above mentioned has not significantly ameliorated TNBC patients and induces drug resistance. Exploring the mechanisms underlying the chemotherapy sensitivity of TNBC and developing novel sensitization strategies are promising approaches for improving the prognosis of patients. Rad51, a key regulator of DNA damage response pathway, repairs DNA damage caused by genotoxic agents through "homologous recombination repair." Therefore, Rad51 inhibition may increase TNBC cell sensitivity to anticancer agents. Based on these findings, we first designed Rad51 siRNA to inhibit the Rad51 protein expression in vitro and evaluated the sensitivity of TNBC cells to doxorubicin. Subsequently, we constructed discoidal porous silicon microparticles (pSi) and encapsulated discoidal 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) liposomes/siRad51 (PS-DOPC/siRad51) to explore the synergistic antitumor effects of siRad51 and doxorubicin on two mouse models of TNBC in vivo. Our in vitro studies indicated that siRad51 enhanced the efficacy of DOX chemotherapy and significantly suppressed TNBC cell proliferation and metastasis. This effect was related to apoptosis induction and epithelial to mesenchymal transition (EMT) inhibition. siRad51 altered the expression of apoptosis- and EMT-related proteins. In orthotopic and lung metastasis xenograft models, the administration of PS-DOPC/siRad51 in combination with DOX significantly alleviated the primary tumor burden and lung metastasis, respectively. Our current studies present an efficient strategy to surmount chemotherapy resistance in TNBC through microvector delivery of siRad51.

A modified porous silicon microparticle promotes mucosal delivery of SARS-CoV-2 antigen and induction of potent and durable systemic and mucosal T helper 1 skewed protective immunity

Development of optimal SARS-CoV-2 vaccines to induce potent, long-lasting immunity and provide cross-reactive protection against emerging variants remains a high priority. Here, we report that a modified porous silicon microparticle (mPSM)-adjuvanted SARS-CoV-2 receptor-binding domain (RBD) vaccine activated dendritic cells and generated more potent and durable SARS-CoV-2-specific systemic humoral and type 1 helper T (Th) cell-mediated immune responses than alum-formulated RBD following parenteral vaccination, and protected mice from SARS-CoV-2 and Beta variant infection. mPSM facilitated the uptake of SARS-CoV-2 RBD antigens by nasal and airway epithelial cells. Parenteral and intranasal prime and boost vaccinations with mPSM-RBD elicited potent systemic and lung resident memory T and B cells and SARS-CoV-2 specific IgA responses, and markedly diminished viral loads and inflammation in the lung following SARS-CoV-2 Delta variant infection. Our results suggest that mPSM can serve as potent adjuvant for SARS-CoV-2 subunit vaccine which is effective for systemic and mucosal vaccination.

A heparan-sulfate-bearing syndecan-1 glycoform is a distinct surface marker for intra-tumoral myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) infiltrate cancer tissue, promote tumor growth, and are associated with resistance to cancer therapies. However, there is no practical approach available to distinguish MDSCs from mature counterparts inside tumors. Here, we show that a recently isolated thioaptamer probe (T1) binds to MDSC subsets in colorectal and pancreatic tumors with high specificity. Whole transcriptome and functional analysis revealed that T1-binding cells contain polymorphonuclear (PMN)-MDSCs characterized by several immunosuppression pathways, ROS production, and T cell suppression activity, whereas T1-non-binding PMNs were mature and nonsuppressive. We identified syndecan-1 as the T1-interacting protein on MDSCs and chronic myelogenous leukemia K562 cell line. Heparan sulfate chains were essential in T1-binding. Inside tumors PMN-MDSCs expressed heparan sulfate biogenesis enzymes at higher levels. Tumor-cell-derived soluble factor(s) enhanced MDSCs' affinity for T1. Overall, we uncovered heparan-sulfate-dependent MDSC modulation in the tumor microenvironment and identified T1 as tool preferentially targeting tumor-promoting myeloid cell subsets.

The Sympathetic Nervous System Modulates Cancer Vaccine Activity through Monocyte-Derived Cells

The sympathetic nervous system (SNS) is an important regulator of immune cell function during homeostasis and states of inflammation. Recently, the SNS has been found to bolster tumor growth and impair the development of antitumor immunity. However, it is unclear whether the SNS can modulate APC function. Here, we investigated the effects of SNS signaling in murine monocyte-derived macrophages (moMФ) and dendritic cells (DCs) and further combined the nonspecific β-blocker propranolol with a peptide cancer vaccine for the treatment of melanoma in mice. We report that norepinephrine treatment dramatically altered moMФ cytokine production, whereas DCs were unresponsive to norepinephrine and critically lack β₂-adrenergic receptor expression. In addition, we show that propranolol plus cancer vaccine enhanced peripheral DC maturation, increased the intratumor proportion of effector CD8⁺ T cells, and decreased the presence of intratumor PD-L1⁺ myeloid-derived suppressor cells. Furthermore, this combination dramatically reduced tumor growth compared with vaccination alone. Taken together, these results offer insights into the cell-specific manner by which the SNS regulates the APC immune compartment and provide strong support for the use of propranolol in combination with cancer vaccines to improve patient response rates and survival.

Virus-Mimic mRNA Vaccine for Cancer Treatment

An effective therapeutic cancer vaccine should be empowered with the capacity to overcome the immunosuppressive tumor microenvironment. Here, the authors describe a mRNA virus-mimicking vaccine platform that is comprised of a phospholipid bilayer encapsulated with a protein-nucleotide core consisting of antigen-encoding mRNA molecules, unmethylated CpG oligonucleotides and positively charged proteins. In cell culture, VLVP potently stimulated bone marrow-derived dendritic cells (BMDCs) to express inflammatory cytokines that facilitated dendritic cell (DC) maturation and promoted antigen processing and presentation. In tumor-bearing mice, VLVP treatment stimulated proliferation of antigen-specific CD8+T cells in the lymphatic organs and T cell infiltration into the tumor bed, resulting in potent anti-tumor immunity. Cytometry by time of flight (CyTOF) analysis revealed that VLVP treatment stimulated a 5-fold increase in tumor-associated CD8+DCs and a 4-fold increase in tumorinfiltrated CD8+T cells, with concurrent decreases in tumor-associated bone marrow-derived suppressor cells and arginase 1- expressing suppressive DCs. Finally, CpG oligonucleotide is an essential adjuvant for vaccine activity. Inclusion of CpG not only maximized vaccine activity but also prevented PD-1 expression in T cells, serving the dual roles as a potent adjuvant and a checkpoint blockade agent.

Synergistic Activation of Antitumor Immunity by a Particulate Therapeutic Vaccine

Success in anticancer immune therapy relies on stimulation of tumor antigen-specific T lymphocytes and effective infiltration of the T cells into tumor tissue. Here, a therapeutic vaccine that promotes proliferation and tumor infiltration of antigen-specific T cells in both inflamed and noninflamed tumor types is described. The vaccine consists of STING agonist 2'3'-cGAMP, TLR9 ligand CpG, and tumor antigen peptides that are loaded into nanoporous microparticles (μGCVax). μGCVax is effective in inhibiting lung metastatic melanoma, primary breast cancer, and subcutaneous colorectal cancer in their respective murine models, including functional cure of HER2-positive breast cancer. Mechanistically, μGCVax potently stimulates type I interferon expression in dendritic cells, and promotes CD8+ and CD103+ dendritic cell maturation and migration to lymph nodes and other lymphatic tissues. Antitumor responses are dependent on TLR9 and interferon α/β receptor signaling, and to a less extent on STING signaling. These results demonstrate a high potential for μGCVax in mediating antitumor immunity in personalized cancer therapy.

Seed- and Soil-Dependent Differences in Murine Breast Tumor Microenvironments Dictate Anti-PD-L1 IgG Delivery and Therapeutic Efficacy

We sought to determine if Stephen Paget’s “seed and soil” hypothesis of organ-preference patterns of cancer metastasis can explain the development of heterogeneity in a tumor microenvironment (TME) as well as immunotherapeutic delivery and efficacy. We established single-cell-derived clones (clones 1 and 16) from parental 4T1 murine breast cancer cells to create orthotopic primary and liver metastasis models to deconvolute polyclonal complexity cancer cells and the difference in TME-derived heterogeneities. Tumor-bearing mice were treated with anti-PD-L1 IgG or a control antibody, and immunofluorescent imaging and quantification were then performed to evaluate the therapeutic efficacy on tumor growth, the delivery of therapy to tumors, the development of blood vessels, the expression of PD-L1, the accumulation of immune cells, and the amount of coagulation inside tumors. The quantification showed an inverse correlation between the amount of delivered therapy and therapeutic efficacy in parental-cell-derived tumors. In contrast, tumors originating from clone 16 cells accumulated a significantly greater amount of therapy and responded better than clone-1-derived tumors. This difference was greater when tumors grew in the liver than the primary site. A similar trend was found in PD-L1 expression and immune cell accumulation. However, the change in the number of blood vessels was not significant. In addition, the amount of coagulation was more abundant in clone-1-derived tumors when compared to others. Thus, our findings reconfirmed the seed- and soil-dependent differences in PD-L1 expression, therapeutic delivery, immune cell accumulation, and tumor coagulation, which can constitute a heterogeneous delivery and response of immunotherapy in polyclonal tumors growing in different organs.

Tumor derived UBR5 promotes ovarian cancer growth and metastasis through inducing immunosuppressive macrophages

Immunosuppressive tumor microenvironment (TME) and ascites-derived spheroids in ovarian cancer (OC) facilitate tumor growth and progression, and also pose major obstacles for cancer therapy. The molecular pathways involved in the OC-TME interactions, how the crosstalk impinges on OC aggression and chemoresistance are not well-characterized. Here, we demonstrate that tumor-derived UBR5, an E3 ligase overexpressed in human OC associated with poor prognosis, is essential for OC progression principally by promoting tumor-associated macrophage recruitment and activation via key chemokines and cytokines. UBR5 is also required to sustain cell-intrinsic β-catenin-mediated signaling to promote cellular adhesion/colonization and organoid formation by controlling the p53 protein level. OC-specific targeting of UBR5 strongly augments the survival benefit of conventional chemotherapy and immunotherapies. This work provides mechanistic insights into the novel oncogene-like functions of UBR5 in regulating the OC-TME crosstalk and suggests that UBR5 is a potential therapeutic target in OC treatment for modulating the TME and cancer stemness.

Reimaging biological barriers affecting distribution and extravasation of PEG/peptide- modified liposomes in xenograft SMMC7721 tumor

Liposomes, as one of the most successful nanotherapeutics, have a major impact on many biomedical areas. In this study, we performed laser scanning confocal microscope (LSCM) and immunohistochemistry (IHC) assays to investigate the intra-tumor transport and antitumor mechanism of GE11 peptide-conjugated active targeting liposomes (GE11-TLs) in SMMC7721 xenograft model. According to classification of individual cell types in high resolution images, biodistribution of macrophages, tumor cells, cells with high epidermal growth factor receptor (EGFR) expression and interstitial matrix in tumor microenvironment, in addition, their impacts on intra-tumor penetration of GE11-TLs were estimated. Type I collagen fibers and macrophage flooded in the whole SMMC7721 tumor xenografts. Tumor angiogenesis was of great heterogeneity from the periphery to the center region. However, the receptor-binding site barriers were supposed to be the leading cause of poor penetration of GE11-TLs. We anticipate these images can give a deep reconsideration for rational design of target nanoparticles for overcoming biological barriers to drug delivery.

Abstract P4-14-11: Prolonged survival of mice bearing HER2 positive breast cancer with a therapeutic cancer vaccine via intra-reconstructed abdominal flap administration

Background: Previously we reported a porous silicon micro-particle based cancer vaccine, which stimulated robust CD8+ T cell-dependent anti-tumor immunity in mice bearing HER2-positive breast cancer. In this study we evaluated the efficacy of the vaccine via single injection into reconstructed abdominal flap after primary tumor mastectomy. Method: To generate murine model of HER2 positive breast cancer murine, 1 × 105 TUBO/luciferase cells were injectedinto both mammary gland fat pad and left ventricle of each 6-8 weeks old female Balb/c mice. Primary and systemic metastatic tumor growth were monitored with a IVIS-200 imaging system. Four days after tumor inoculation, mammary gland fat pad with primary tumor was resected by mastectomy, and superficial inferior epigastric(SIE) vessels based abdominal flap was used for abdominal reconstruction. During the surgery, mice also received one of the three treatments below: 1) negative control without treatments; 2) single intra-flap vaccination of cancer vaccine; and 3) single injection of cancer vaccine via footpad injection. Therapeutic efficacy were monitored with IVIS system weekly. To analyze immune response, popliteal and inguinal lymph nodes were collected one day and seven days post vaccination, and activation of dendritic cells and T cells was evaluated with a flow cytometry. HER2 specific T cells in splenocytes which highly expressed interferon-gamma (IFNγ) were counted by ELISpot. CD3+ T cell infiltration in brain metastatic nodules were analyzed by immunohistochemical assay. Result: Prolonged survival of mice bearing HER2-positive breast cancer was achieved by both intra-flap and intra-dermal vaccination of cancer vaccine. Mice vaccinated via intra-flap injection extended median survival by 9 days (p=0.025), although not as long as intra-dermal treatment (15 days, p=0.034), comparing to control group. In lymph nodes, activated dendritic cells increased in both two vaccinated groups. Interestingly, intra-flap vaccination induced higher response in inguinal lymph node, which considered as the major draining lymph node of this route. Meanwhile, intra-dermal vaccination raised higher immune response in popliteal lymph node. In ELISpot assay, IFNγ secreted T cells were found abundant in splenocytes from both two vaccination groups. Furthermore, efficient infiltration of T cells inside the brain metastatic nodules was found in intra-dermal injection group, which provided potential protection from distal recurrence after mastectomy. Conclusion: Cancer vaccine administrated via intra-flap injection effectively stimulated systemic immune response, and slowed down tumor progression in murine HER2 positive breast cancer model.

Citation Format: Xiaoling Liu, Junhua Mai, Chaoyang Meng, Wei Wei, Haifa Shen. Prolonged survival of mice bearing HER2 positive breast cancer with a therapeutic cancer vaccine via intra-reconstructed abdominal flap administration [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-14-11.

Systematic comparison of methods for determining the in vivo biodistribution of porous nanostructured injectable inorganic particles

With a wide variety of biodistribution measurement techniques reported in the literature, it is important to perform side-by-side comparisons of results obtained with different methods on the same particle platform, to determine differences across methods, highlight advantages and disadvantages, and inform methods selection according to specific applications. Inorganic nanostructured particles (INPs) have gained a central role in the development of injectable delivery vectors thanks to their controllable design, biocompatibility, and favorable degradation kinetic. Thus, accurate determination of in vivo biodistribution of INPs is a key aspect of developing and optimizing this class of delivery vectors. In this study, a systematic comparison of spectroscopy (inductively coupled plasma optical emission spectroscopy), fluorescence (in vivo imaging system, confocal microscopy, and plate reader), and radiolabeling (gamma counter)-based techniques is performed to assess the accuracy and sensitivity of biodistribution measurements in mice. Each method is evaluated on porous silicon particles, an established and versatile injectable delivery platform. Biodistribution is evaluated in all major organs and compared in terms of absolute results (%ID/g and %ID/organ when possible) and sensitivity (σ_%). Finally, we discuss how these results can be extended to inform method selection for other platforms and specific applications, with an outlook to potential benefit for pre-clinical and clinical studies. Overall, this study presents a new practical guide for selection of in vivo biodistribution methods that yield quantitative results. STATEMENT OF SIGNIFICANCE: The significance of this work lies in the use of a single platform to test performances of different biodistribution methods in vivo, with a strict quantitative metric. These results, united with the qualitative comparison of advantages and disadvantages of each technique, are aimed at supporting the rational choice of each different method according to the specific application, to improve the quantitative description of biodistribution results that will be published by others in the future.

Tracking Biodistribution of Myeloid-Derived Cells in Murine Models of Breast Cancer

A growing tumor is constantly secreting inflammatory chemokines and cytokines that induce release of immature myeloid cells, including myeloid-derived suppressor cells (MDSCs) and macrophages, from the bone marrow. These cells not only promote tumor growth, but also prepare distant organs for tumor metastasis. On the other hand, the myeloid-derived cells also have phagocytic potential, and can serve as vehicles for drug delivery. We have previously identified thioaptamers that bind a subset of MDSCs with high affinity and specificity. In the current study, we applied one of the thioaptamers as a probe to track myeloid cell distribution in the bone, liver, spleen and tumor in multiple murine models of breast cancer including the 4T1 syngeneic model and MDA-MB-231 and SUM159 xenograft models. Information generated from this study will facilitate further understanding of tumor growth and metastasis, and predict biodistribution patterns of cell-mediated drug delivery.

PTGER3 induces ovary tumorigenesis and confers resistance to cisplatin therapy through up-regulation Ras-MAPK/Erk-ETS1-ELK1/CFTR1 axis

Background

Inflammatory mediator prostaglandin E2–prostaglandin E2 receptor EP3 (PTGER3) signaling is critical for tumor-associated angiogenesis, tumor growth, and chemoresistance. However, the mechanism underlying these effects in ovarian cancer is not known.

Methods

An association between higher tumoral expression of PTGER3 and shorter patient survival in the ovarian cancer dataset of The Cancer Genome Atlas prompted investigation of the antitumor effects of PTGER3 downmodulation. PTGER3 mRNA and protein levels were higher in cisplatin-resistant ovarian cancer cells than in their cisplatin-sensitive counterparts.

Findings

Silencing of PTGER3 via siRNA in cancer cells was associated with decreased cell growth and less invasiveness, as well as cell-cycle arrest and increased apoptosis, mediated through the Ras-MAPK/Erk-ETS1-ELK1/CFTR1 axis. Furthermore, sustained PTGER3 silencing with multistage vector and liposomal 2’-F-phosphorodithioate-siRNA–mediated silencing of PTGER3 combined with cisplatin resulted in robust antitumor effects in cisplatin-resistant ovarian cancer models.

Interpretation

These findings identify PTGER3 as a potential therapeutic target in chemoresistant ovarian cancers expressing high levels of this oncogenic protein.

Fund

National Institutes of Health/National Cancer Institute, USA.

Abstract 4811: Inhibition of PLK1 abrogates side population and increases radiation-induced DNA damage in human glioblastoma

Glioblastoma multiforme (GBM), a highly malignant form of brain tumor has limited treatment modalities with poor patient survival. Expression of CD133, a marker of cancer stem cells (CSCs), has been linked to GBM recurrence, metastasis and radiation/drug resistance. The GBM CSCs exhibit high level of ABC transporters, DNA repair enzymes and anti-apoptotic proteins. The side population (SP) phenotype of CSCs with high levels of ABC transporters is associated with chemo-resistance. Overexpression of Polo-like kinase-1 (PLK1), a key cell cycle regulator, has been linked to poor prognosis of various cancers. However, the role of PLK1 in radio/chemo-resistance of GBM is poorly understood. In this study, we explored the use of PLK1 inhibitor Volasertib in combination with temozolomide (TMZ) followed by radiation to overcome resistance in GBM, both in vitro and in vivo.

Our results revealed that Volasertib and TMZ act synergistically at a sub-lethal dose to inhibit cell proliferation and induce apoptosis. Both Volasertib and TMZ strongly induce reactive oxygen species (ROS) which may cause cell death by reducing repair capacity. Combined treatment with TMZ and Volasertib followed by radiation showed persistent DNA damage after removal of drugs for 24 hrs. In contrast to earlier reports, significant decrease in the side population was also observed, even after radiation treatment.

We also observed that Volasertib alone or in combination with TMZ activated STAT1 pathways and inhibited MAPK/AKT activation. As the latter pathway promotes apoptosis, our results suggest higher tumor growth inhibitory effect of combinatorial treatment compared to single agents in xenograft mouse model.

In summary, while Volasertib can be used alone or in the combination with radiation, Volasertib combined with TMZ may be useful to inhibit recurrence of GBM after radiation therapy. Furthermore, increased STAT1 expression may modulate the tumor-microenvironment and improve immunotherapy by MHC class 1 upregulation.

Citation Format: Arvind Pandey, Junhua Mai, Satyendra C. Tripathi, Samir M. Hanash, Haifa Shen, Sankar Mitra. Inhibition of PLK1 abrogates side population and increases radiation-induced DNA damage in human glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4811.

Chemotherapy Sensitizes Therapy-Resistant Cells to Mild Hyperthermia by Suppressing Heat Shock Protein 27 Expression in Triple-Negative Breast Cancer

Purpose: Triple-negative breast cancer (TNBC) is a clinically aggressive disease with poor prognosis. Conventional chemotherapeutics are generally able to shrink the tumor mass, but often fail to completely eradicate cancer stem-like cells (CSCs) that are responsible for high risk of relapse and frequent metastases. In this study, we examined thermal sensibility of CSCs, developed an approach that enabled concurrent elimination of both the bulk of cancer cells and CSCs, and investigated the underlying mechanism.Experimental Design: We designed a platform consisting of gold nanoparticle-coated porous silicon microparticle (AuPSM) that was also loaded with docetaxel micelles (mDTXs) to enable concurrent killing of the bulk of cancer cells by released mDTX and CSCs by mild hyperthermia upon stimulation of AuPSM with near infrared. In addition, we examined the role of heat shock proteins in sensitizing CSC killing. Finally, we applied mDTX-loaded AuPSM to treat mice with SUM159 and 4T1 orthotopic tumors and evaluated tumor growth and tumor metastasis.Results: MDA-MB-231 and SUM159 TNBC cells treated with mDTX-loaded AuPSM and mild hyperthermia displayed significantly reduced efficiencies in mammosphere formation than those treated with mDTX alone or mild hyperthermia alone. Combination treatment also completely inhibited SUM159 orthotopic tumor growth and 4T1 tumor metastasis. Mechanistically, DTX treatment suppressed expression of heat shock protein 27 in cancer cells including the CSCs, rendering cells sensitive to mild hyperthermia.Conclusions: Our results indicate that chemotherapy sensitizes CSC to mild hyperthermia. We have developed an effective therapeutic approach to eliminate therapy-resistant cells in TNBC. Clin Cancer Res; 24(19); 4900-12. ©2018 AACR.

DNA Thioaptamer with Homing Specificity to Lymphoma Bone Marrow Involvement

Selective drug accumulation in the malignant tissue is a prerequisite for effective cancer treatment. However, most drug molecules and their formulated particles are blocked en route to the destiny tissue due to the existence of multiple biological and physical barriers including the tumor microvessel endothelium. Since the endothelial cells on the surface of the microvessel wall can be modulated by inflammatory cytokines and chemokines secreted by the tumor or stromal cells, an effective drug delivery approach is to enhance interaction between the drug particles and the unique spectrum of surface proteins on the tumor endothelium. In this study, we performed in vivo screening for thioaptamers that bind to the bone marrow endothelium with specificity in a murine model of lymphoma with bone marrow involvement (BMI). The R1 thioaptamer was isolated based on its high homing potency to bones with BMI, and 40-60% less efficiency in accumulation to healthy bones. In cell culture, R1 binds to human umbilical vein endothelial cells (HUVEC) with a high affinity ( Kd ≈ 3 nM), and the binding affinity can be further enhanced when cells were treated with a mixture of lymphoma cell and bone marrow cell conditioned media. Cellular uptake of R1 is through clathrin-mediated endocytosis. Conjugating R1 on to the surface of liposomal doxorubicin nanoparticles resulted in 2-3-fold increase in drug accumulation in lymphoma BMI. Taking together, we have successfully identified a thioaptamer that preferentially binds to the endothelium of lymphoma BMI. It can serve as an affinity moiety for targeted delivery of drug particles to the disease organ.

SMAD4 Gene Mutation Renders Pancreatic Cancer Resistance to Radiotherapy through Promotion of Autophagy

Purpose: Understanding the mechanism of radioresistance could help develop strategies to improve therapeutic response of patients with PDAC. The SMAD4 gene is frequently mutated in pancreatic cancer. In this study, we investigated the role of SMAD4 deficiency in pancreatic cancer cells' response to radiotherapy.Experimental Design: We downregulated SMAD4 expression with SMAD4 siRNA or SMAD4 shRNA and overexpressed SMAD4 in SMAD4 mutant pancreatic cancer cells followed by clonogenic survival assay to evaluate their effects on cell radioresistance. To study the mechanism of radioresistance, the effects of SMAD4 loss on reactive oxygen species (ROS) and autophagy were determined by flow cytometry and immunoblot analysis, respectively. Furthermore, we measured radioresistance by clonogenic survival assay after treatment with autophagy inhibitor (Chloroquine) and ROS inhibitor (N-acetyl-l-cysteine) in SMAD4-depleted pancreatic cancer cells. Finally, the effects of SMAD4 on radioresistance were also confirmed in an orthotopic tumor model derived from SMAD4-depleted Panc-1 cells.Results:SMAD4-depleted pancreatic cancer cells were more resistant to radiotherapy based on clonogenic survival assay. Overexpression of wild-type SMAD4 in SMAD4-mutant cells rescued their radiosensitivity. Radioresistance mediated by SMAD4 depletion was associated with persistently higher levels of ROS and radiation-induced autophagy. Finally, SMAD4 depletion induced in vivo radioresistance in Panc-1-derived orthotopic tumor model (P = 0.038). More interestingly, we observed that the protein level of SMAD4 is inversely correlated with autophagy in orthotopic tumor tissue samples.Conclusions: Our results demonstrate that defective SMAD4 is responsible for radioresistance in pancreatic cancer through induction of ROS and increased level of radiation-induced autophagy. Clin Cancer Res; 24(13); 3176-85. ©2018 AACR.

A Novel DNA Aptamer for Dual Targeting of Polymorphonuclear Myeloid-derived Suppressor Cells and Tumor Cells

Aptamers have the potential to be used as targeting ligands for cancer treatment as they form unique spatial structures. Methods: In this study, a DNA aptamer (T1) that accumulates in the tumor microenvironment was identified through in vivo selection and validation in breast cancer models. The use of T1 as a targeting ligand was evaluated by conjugating the aptamer to liposomal doxorubicin. Results: T1 exhibited a high affinity for both tumor cells and polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs). Treatment with T1 targeted doxorubicin liposomes triggered apoptosis of breast cancer cells and PMN-MDSCs. Suppression of PMN-MDSCs, which serve an immunosuppressive function, leads to increased intratumoral infiltration of cytotoxic T cells. Conclusion: The cytotoxic and immunomodulatory effects of T1-liposomes resulted in superior therapeutic efficacy compared to treatment with untargeted liposomes, highlighting the promise of T1 as a targeting ligand in cancer therapy.

A Liposome Encapsulated Ruthenium Polypyridine Complex as a Theranostic Platform for Triple-Negative Breast Cancer

Ruthenium coordination complexes have the potential to serve as novel theranostic agents for cancer. However, a major limitation in their clinical implementation is effective tumor accumulation. In this study, we have developed a liposome-based theranostic nanodelivery system for [Ru(phen)2dppz](ClO4)2 (Lipo-Ru). This ruthenium polypyridine complex emits a strong fluorescent signal when incorporated in the hydrophobic lipid bilayer of the delivery vehicle or in the DNA helix, enabling visualization of the therapeutic agent in tumor tissues. Incubation of MDA-MB-231 breast cancer cells with Lipo-Ru induced double-strand DNA breaks and triggers apoptosis. In a mouse model of triple-negative breast cancer, treatment with Lipo-Ru dramatically reduced tumor growth. Biodistribution studies of Lipo-Ru revealed that more than 20% of the injected dose accumulated in the tumor. These results suggest that Lipo-Ru could serve as a promising theranostic platform for cancer.

Targeting Autocrine CCL5-CCR5 Axis Reprograms Immunosuppressive Myeloid Cells and Reinvigorates Antitumor Immunity

The tumor-promoting potential of CCL5 has been proposed but remains poorly understood. We demonstrate here that an autocrine CCL5-CCR5 axis is a major regulator of immunosuppressive myeloid cells (IMC) of both monocytic and granulocytic lineages. The absence of the autocrine CCL5 abrogated the generation of granulocytic myeloid-derived suppressor cells and tumor-associated macrophages. In parallel, enhanced maturation of intratumoral neutrophils and macrophages occurred in spite of tumor-derived CCL5. The refractory nature of ccl5-null myeloid precursors to tumor-derived CCL5 was attributable to their persistent lack of membrane-bound CCR5. The changes in the ccl5-null myeloid compartment subsequently resulted in increased tumor-infiltrating cytotoxic CD8⁺ T cells and decreased regulatory T cells in tumor-draining lymph nodes. An analysis of human triple-negative breast cancer specimens demonstrated an inverse correlation between "immune CCR5" levels and the maturation status of tumor-infiltrating neutrophils as well as 5-year-survival rates. Targeting the host CCL5 in bone marrow via nanoparticle-delivered expression silencing, in combination with the CCR5 inhibitor Maraviroc, resulted in strong reductions of IMC and robust antitumor immunities. Our study suggests that the myeloid CCL5-CCR5 axis is an excellent target for cancer immunotherapy. Cancer Res; 77(11); 2857-68. ©2017 AACR.

Lipopolyplex potentiates anti-tumor immunity of mRNA-based vaccination

mRNA-based vaccines have the benefit of triggering robust anti-cancer immunity without the potential danger of genome integration from DNA vaccines or the limitation of antigen selection from peptide vaccines. Yet, a conventional mRNA vaccine comprising of condensed mRNA molecules in a positively charged protein core structure is not effectively internalized by the antigen-presenting cells. It cannot offer sufficient protection for mRNA molecules from degradation by plasma and tissue enzymes either. Here, we have developed a lipopolyplex mRNA vaccine that consists of a poly-(β-amino ester) polymer mRNA core encapsulated into a 1,2-dioleoyl-sn-glycero-3-ethylphosphocholine/1,2-dioleoyl-sn-glycero-3-phosphatidyl-ethanolamine/1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-2000 (EDOPC/DOPE/DSPE-PEG) lipid shell. This core-shell structured mRNA vaccine enters dendritic cells through macropinocytosis. It displayed intrinsic adjuvant activity by potently stimulating interferon-β and interleukin-12 expression in dendritic cells through Toll-like receptor 7/8 signaling. Dendritic cells treated with the mRNA vaccine displayed enhanced antigen presentation capability. Mice bearing lung metastatic B16-OVA tumors expressing the ovalbumin antigen were treated with the lipopolyplex mRNA, and over 90% reduction of tumor nodules was observed. Collectively, this core-shell structure offers a promising platform for mRNA vaccine development.

Abstract P3-06-06: Development of iNPG-pDox for metastatic breast cancer treatment

This abstract was not presented at the symposium.

Abstract 4668: Silencing PTGER3 enhances chemotherapeutic responses

Inflammation is involved in the pathogenesis of cancer and inflammatory mediators such as prostaglandins (PGs) are abundantly present in the tumor microenvironment. Prostaglandin E(2) (PGE(2))-prostaglandin E2 receptor (EP)3 (PTGER3) signaling appears critical for tumor-associated angiogenesis, tumor growth and chemoresistance. However, the precise mechanism of this phenomenon in ovarian cancer remains unknown. In this study we hypothesized that down modulation of PTGER3 regulates drug resistance through the regulation of Ras-MAPK/Erk-Est-ELK1 axis in OC cells, resulting in decreased migration, proliferation and increased apoptosis. We analyzed a PTGER3 data set of OC patients from the Cancer Genome Atlas. Furthermore, the analysis of a panel of ovarian cancer cell lines showed that PTGER3 at mRNA and protein levels were higher in cisplatin-resistant cells when compared with their cisplatin sensitive counterparts. In vitro cell viability, growth, cell-cycle progression, migration, invasion and apoptosis, as well as in vivo therapeutic effectiveness in murine xenograft models, were also assessed following siRNA-mediated PTGER3 silencing in cisplatin-resistant ovarian cancer cells. The experimental validation identifies PTGER3 associated with OC survival. Significant inhibition of cell growth and viability, cell-cycle arrest, and activation of apoptosis were observed upon siRNA-mediated PTGER3 suppression. Furthermore, combination treatment with MSV/DOPC-siRNA-PTGER3 and cisplatin inhibited growth of A2780-CP20 tumors, which were otherwise resistant to cisplatin treatment. These findings identify PTGER3 as a potential therapeutic target in ovarian chemo-resistant cancers expressing high levels of this oncogenic protein.

Citation Format: Emine Bayraktar, Cristian Rodriguez-Aguayo, Junhua Mai, Cristina Ivan, Cristina Ivan, Arturo Chavez-Reyes, Anil K. Sood, Mauro Ferrari, Haifa Shen, Gabriel Lopez-Berestein. Silencing PTGER3 enhances chemotherapeutic responses. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4668.

An injectable nanoparticle generator enhances delivery of cancer therapeutics

The efficacy of cancer drugs is often limited because only a small fraction of the administered dose accumulates in tumors. Here we report an injectable nanoparticle generator (iNPG) that overcomes multiple biological barriers to cancer drug delivery. The iNPG is a discoidal micrometer-sized particle that can be loaded with chemotherapeutics. We conjugate doxorubicin to poly(L-glutamic acid) by means of a pH-sensitive cleavable linker, and load the polymeric drug (pDox) into iNPG to assemble iNPG-pDox. Once released from iNPG, pDox spontaneously forms nanometer-sized particles in aqueous solution. Intravenously injected iNPG-pDox accumulates at tumors due to natural tropism and enhanced vascular dynamics and releases pDox nanoparticles that are internalized by tumor cells. Intracellularly, pDox nanoparticles are transported to the perinuclear region and cleaved into Dox, thereby avoiding excretion by drug efflux pumps. Compared to its individual components or current therapeutic formulations, iNPG-pDox shows enhanced efficacy in MDA-MB-231 and 4T1 mouse models of metastatic breast cancer, including functional cures in 40-50% of treated mice.

Prevalence and associated factors of myopia among primary and middle school-aged students: a school-based study in Guangzhou

PurposeTo estimate the prevalence of myopia among primary and middle school-aged students in Guangzhou and to explore the potentially contributing factors to myopia.MethodsThis cross-sectional study was based on a sample of students in grades 1-6 and grades 7-9. Data were collected from refractive error measurements and a structured questionnaire.ResultsA total of 3055 participants were involved in this analysis, and the overall prevalence of myopia was 47.4% (95% confidence interval (CI)= 45.6-49.2%). The prevalence of myopia in students increased along with the growth of grade level; the prevalence of myopia in students in grade 1 was only 0.2%, as it increased to 38.8% in students in grade 3, and the rate was the highest (68.4%) in students in grade 9. Girls were at a higher risk of myopia than boys (adjusted odds ratio=1.22, 95% CI=1.04-1.44). Both male and female students whose distance of reading was longer than 25 cm were less likely to have myopia and who have one or two myopic parents were at a higher risk of myopia. In addition, reading for pleasure more than 2 h per day (adjusted odds ratio=1.84, 95% CI=1.09-3.12) was only positively associated with myopia in boys and spending time watching television per week was only positively associated with myopia in girls.ConclusionMyopia in students is a significant public health problem in Guangzhou. Female gender, higher grade, longer time spent for near work, shorter distance of near work, and parental myopia were shown to be associated with the increasing risk of myopia in children.

Effective Concentration of a Multikinase Inhibitor within Bone Marrow Correlates with In Vitro Cell Killing in Therapy-Resistant Chronic Myeloid Leukemia

Leukemia cells escape BCR-ABL-targeted therapy by developing mutations, such as T315I, in the p210(BCR-ABL) fusion protein in Philadelphia chromosome-positive chronic myeloid leukemia (CML). Although most effort has been focused on development of new tyrosine kinase inhibitors, enrichment of these small-molecule inhibitors in the tumor tissue can also have a profound impact on treatment outcomes. Here, we report that a 2-hour exposure of the T315I-mutant CML cells to 10 μmol/L of the multikinase inhibitor TG101209 suppressed BCR-ABL-independent signaling and caused cell-cycle arrest at G2-M. Further increase in drug concentration to 17.5 μmol/L blocked phosphorylation of the mutant BCR-ABL kinase and its downstream JAK2 and STAT5. The effective dosage to overcome therapy resistance identified in an in vitro setting serves as a guidance to develop the proper drug formulation for in vivo efficacy. A targeted formulation was developed to achieve sustained bone marrow TG101209 concentration at or above 17.5 μmol/L for effective killing of CML cells in vivo Potent inhibition of leukemia cell growth and extended survival were observed in two murine models of CML treated with 40 mg/kg intravenously administered targeted TG101209, but not with the untargeted drug at the same dosage. Our finding provides a unique approach to develop treatments for therapy-resistant CML. Mol Cancer Ther; 15(5); 899-910. ©2016 AACR.

Porous silicon microparticle potentiates anti-tumor immunity by enhancing cross-presentation and inducing type I interferon response

Micro- and nanometer-size particles have become popular candidates for cancer vaccine adjuvants. However, the mechanism by which such particles enhance immune responses remains unclear. Here, we report a porous silicon microparticle (PSM)-based cancer vaccine that greatly enhances cross-presentation and activates type I interferon (IFN-I) response in dendritic cells (DCs). PSM-loaded antigen exhibited prolonged early endosome localization and enhanced cross-presentation through both proteasome- and lysosome-dependent pathways. Phagocytosis of PSM by DCs induced IFN-I responses through a TRIF- and MAVS-dependent pathway. DCs primed with PSM-loaded HER2 antigen produced robust CD8 T cell-dependent anti-tumor immunity in mice bearing HER2+ mammary gland tumors. Importantly, this vaccination activated the tumor immune microenvironment with elevated levels of intra-tumor IFN-I and MHCII expression, abundant CD11c+ DC infiltration, and tumor-specific cytotoxic T cell responses. These findings highlight the potential of PSM as an immune adjuvant to potentiate DC-based cancer immunotherapy.

Recent Advances in Discovering the Role of CCL5 in Metastatic Breast Cancer

A variety of therapeutic strategies are currently under investigation to inhibit factors that promote tumor invasion, as metastasis is the most common cause of mortality for cancer patients. Notably, considerable emphasis has been placed on studying metastasis as a dynamic process that is highly dependent on the tumor microenvironment. In regards to breast cancer, chemokine C-C motif ligand 5 (CCL5), which is produced by tumor-associated stromal cells, has been established as an important contributor to metastatic disease. This review summarizes recent discoveries uncovering the role of this chemokine in breast cancer metastasis, including conditions that increase the generation of CCL5 and effects induced by this signaling pathway. In particular, CCL-5-mediated cancer cell migration and invasion are discussed in the context of intertwined feedback loops between breast cancer cells and stromal cells. Moreover, the potential use of CCL5 and its receptor chemokine C-C motif receptor 5 (CCR5) as targets for preventing breast cancer metastasis is also reviewed.

Multifunctional gold nanorods for siRNA gene silencing and photothermal therapy

Cancer is a complex disease that usually requires several treatment modalities. A multifunctional nanotherapeutic system is designed, incorporating small interfering RNA (siRNA) and gold nanorods (Au NRs) for photothermal therapy. Surface-engineered Au NRs with polyethylenimine are synthesized using a layer-by-layer assembly and siRNA is absorbed on the surface. The siRNA is efficiently delivered into breast cancer cells, resulting in subsequent gene silencing. Cells are then irradiated with near-infrared (NIR) light, causing heat-induced anticancer activity. The combination of gene silencing and photothermal therapy results in effective inhibition of cell proliferation.

Bone marrow endothelium-targeted therapeutics for metastatic breast cancer

Effective treatment of cancer metastasis to the bone relies on bone marrow drug accumulation. The surface proteins in the bone marrow vascular endothelium provide docking sites for targeted drug delivery. We have developed a thioaptamer that specifically binds to E-selectin that is overexpressed in the vasculature of tumor and inflammatory tissues. In this study, we tested targeted delivery of therapeutic siRNA loaded in the E-selectin thioaptamer-conjugated multistage vector (ESTA-MSV) drug carrier to bone marrow for the treatment of breast cancer bone metastasis. We evaluated tumor type- and tumor growth stage-dependent targeting in mice bearing metastatic breast cancer in the bone, and carried out studies to identify factors that determine targeting efficiency. In a subsequent study, we delivered siRNA to knock down expression of the human STAT3 gene in murine xenograft models of human MDA-MB-231 breast tumor, and assessed therapeutic efficacy. Our studies revealed that the CD31(+)E-selectin(+) population accounted for 20.8%, 26.4% and 29.9% of total endothelial cells respectively inside the femur of mice bearing early, middle and late stage metastatic MDA-MB-231 tumors. In comparison, the double positive cells remained at a basal level in mice with early stage MCF-7 tumors, and jumped to 23.9% and 28.2% when tumor growth progressed to middle and late stages. Accumulation of ESTA-MSV inside the bone marrow correlated with the E-selectin expression pattern. There was up to 5-fold enrichment of the targeted MSV in the bone marrow of mice bearing early or late stage MDA-MB-231 tumors and of mice with late stage, but not early stage, MCF-7 tumors. Targeted delivery of STAT3 siRNA in ESTA-MSV resulted in knockdown of STAT3 expression in 48.7% of cancer cells inside the bone marrow. Weekly systemic administration of ESTA-MSV/STAT3 siRNA significantly extended survival of mice with MDA-MB-231 bone metastasis. In conclusion, targeting the overexpressed E-selectin provides an effective approach for tissue-specific drug delivery to the bone marrow. Tumor growth in the bone can be effectively inhibited by blockage of the STAT3 signaling.

Cyclodextrin and polyethylenimine functionalized mesoporous silica nanoparticles for delivery of siRNA cancer therapeutics

Effective delivery holds the key to successful in vivo application of therapeutic small interfering RNA (siRNA). In this work, we have developed a universal siRNA carrier consisting of a mesoporous silica nanoparticle (MSNP) functionalized with cyclodextrin-grafted polyethylenimine (CP). CP provides positive charge for loading of siRNA through electrostatic interaction and enables effective endosomal escape of siRNA. Using intravital microscopy we were able to monitor tumor enrichment of CP-MSNP/siRNA particles in live mice bearing orthotopic MDA-MB-231 xenograft tumors. CP-MSNP delivery of siRNA targeting the M2 isoform of the glycolytic enzyme pyruvate kinase (PKM2) resulted in effective knockdown of gene expression in vitro and in vivo. Suppression of PKM2 led to inhibition of tumor cell growth, invasion, and migration.

High capacity nanoporous silicon carrier for systemic delivery of gene silencing therapeutics

Gene silencing agents such as small interfering RNA (siRNA) and microRNA offer the promise to modulate expression of almost every gene for the treatment of human diseases including cancer. However, lack of vehicles for effective systemic delivery to the disease organs has greatly limited their in vivo applications. In this study, we developed a high capacity polycation-functionalized nanoporous silicon (PCPS) platform comprised of nanoporous silicon microparticles functionalized with arginine-polyethyleneimine inside the nanopores for effective delivery of gene silencing agents. Incubation of MDA-MB-231 human breast cancer cells with PCPS loaded with STAT3 siRNA (PCPS/STAT3) or GRP78 siRNA (PCPS/GRP78) resulted in 91 and 83% reduction of STAT3 and GRP78 gene expression in vitro. Treatment of cells with a microRNA-18a mimic in PCPS (PCPS/miR-18) knocked down 90% expression of the microRNA-18a target gene ATM. Systemic delivery of PCPS/STAT3 siRNA in murine model of MDA-MB-231 breast cancer enriched particles in tumor tissues and reduced STAT3 expression in cancer cells, causing significant reduction of cancer stem cells in the residual tumor tissue. At the therapeutic dosage, PCPS/STAT3 siRNA did not trigger acute immune response in FVB mice, including changes in serum cytokines, chemokines, and colony-stimulating factors. In addition, weekly dosing of PCPS/STAT3 siRNA for four weeks did not cause signs of subacute toxicity based on changes in body weight, hematology, blood chemistry, and major organ histology. Collectively, the results suggest that we have developed a safe vehicle for effective delivery of gene silencing agents.

Abstract CN06-02: Breast cancer stem cells

Even though recent trends suggest a turn downward in both incidence and mortality, breast cancer remains the most common female cancer in the industrialized world. Development of resistance to a wide variety of drugs and metastatic spread of cancer cells to distant organs pose major challenge in successful treatment of breast cancer. Virtually all the roughly 40,000 annual breast cancer related deaths in the United States can be said to have occurred because the conventional therapy has failed. It is the second-leading cause of deaths from cancer in women. The survival rate for those with advanced, metastatic breast cancer has not changed significantly for decades. Recent robust evidence indicates that treatment resistance and metastasis arise from a subpopulation with stem-like properties within a heterogeneous primary cancer. These observations are consistent with subpopulations of chemoresistant cancer stem cells within the bulk tumor cells having the potential for self-renewal and metastases through different adaptive mechanisms. Thus despite apparently successful chemotherapy, the persistence of this unique sub-population of cancer stem cells may undergo epithelial-mesenchymal transition and can serve to re-initiate tumor growth and seed metastases.

Breast cancer stem cells (BCSCs) constitute a subpopulation of tumor cells that express stem cell-associated markers and have a high capacity for tumor generation in vivo. Identification of BCSCs from tumor samples or breast cancer cell lines has been based mainly on CD44+/CD24−/low or ALDH+ phenotypes. BCSCs isolation has allowed the analysis of the molecular mechanisms involved in their origin, self-renewal, differentiation into tumor cells, resistance to radiation therapy and chemotherapy, invasiveness and metastatic ability. Over the past few years, candidate cancer stem cells have been identified in a variety of human malignancies including leukemias and a number of solid tumors such as glioblastomas, medulloblastomas and carcinomas. Breast cancer is the first human carcinoma for which a putative cancer stem cell subpopulation has been isolated (Al-Hajj et. al, PNAS, 2003). Using in vitro-separated tumorigenic cells from malignant human breast cancer-derived pleural effusions, Al Hajj and colleagues isolated a cell population characterized by high CD44 expression and low or undetectable levels of CD24 (CD44+CD24−/low). These cells were highly tumorigenic when injected into immunocompromised NOD/SCID mice and shared classic features of normal stem cells, including the capacity for self-renewal and generation of heterogeneous progeny. The stem/progenitor cell phenotype of these cells was further refined by the Daidone group, who were able to grow mammospheres from single-cell suspensions obtained from the dissociation of primary breast tumors. Mammospheres are non-adherent spherical cell clusters obtained in selective culture conditions, which have been shown to be enriched in mammary stem/progenitor cells. The vast majority of cells in culture were CD44+CD24−/low, and 10 to 20% of these retained the ability to self-renew. Recently, three groups have independently provided unequivocal direct and functional evidence for the presence of cancer stem cells by lineage tracing experiments in glioblastomas (GBM), squamous skin tumors, and intestinal adenomas, suggesting the hierarchical nature of cancer (Chen J et.al, Nature, 2012, Schepers AG et. al, Science 2012; Driessens G et. al, Nature 2012). By genetic “lineage retracing," these independent groups confirm that only a fraction of cells within the bulk tumor had clonogenic potential, giving rise to the hierarchical growth of the tumor. In the GBM model, this restricted subpopulation responsible for tumor initiation was intrinsically resistant to chemotherapy.

To combat the impact of this common cancer among women and the disparities of ouotcomes observed, efforts have been directed towards the development of new approaches to early detection, chemotherapeutics, surgical and radiation treatments with promising results. We are one of the first groups to describe the breast cancer stem cells are intrinsically resistant to conventional therapy (Li X et. al. J Natl Cancer Inst, 2008; Creighton CJ et. al, PNAS, 2009). Since these initial observations, other groups have confirmed these findings following conventional chemotherapy or radiation therapy, and have supported our findings that an increase in these BCSCs is associated with poorer prognosis. This CSC model has fundamental clinical implications. The current development of cancer therapeutics is largely based on identifying agents with the ability to cause tumor regression in animal models or in clinical trials. Since tumor stem cells comprise only a small percent of the tumor bulk, focus on tumor regression may have produced agents capable of killing actively cycling or fully differentiated cells while sparing the tumor stem cell population. Thus, targeting BCSCs in combination with chemotherapy will be necessary to eliminate the heterogeneous populations within a tumor, particularly the fraction capable of tumor initiation and metastasis.

We previously published a tumorigenic signature derived from patient biopsies (Creighton CJ et. al, PNAS, 2009). Subsequently, we used a functional approach to identify novel targets for cancer stem cells. This screen was performed by shRNA knockdown of the 477 genes in our tumorigenic signature using high-throughput mammosphere formation efficiency (MSFE) assay. We identified top candidates that significantly reduced MSFE. This stringent screening yielded two potential candidates, namely RPL39 and MLF2, as the top candidate genes that affect BCSC self-renewal. Selective siRNA knockdown of RPL39 and MLF2 in patient-derived breast tumorgrafts showed reduced tumor volume and lung metastases with a concomitant decrease in BCSC markers. Thus, targeting BCSCs in combination with chemotherapy should eliminate the heterogeneous populations within a tumor. Additionally, next generation RNA-deep sequencing confirmed mutations in RPL39 and MLF2 in approximately 40% of lung metastases from breast cancer patients (n=53). Allele specific PCR confirmed damaging mutations in RPL39 and MLF2. Gain-of-function of these mutations was demonstrated by increase in proliferation, invasion, and self-renewal assays. In vitro and in vivo siRNA knockdown of RPL39 and MLF2 showed decrease in nitric oxide synthase, suggesting that these genes are driven by nitric oxide signaling. Because of the effect of RPL39 and MLF2 siRNA in reducing lung metastases in vivo, we tested the possibility that BCSC may have escaped the primary cancer to evolve in distant metastatic sites. The presence of these damaging mutations was found only in the stem cell (CD44+/CD24 low/−) subpopulation but not in non-BCSCs. These gain-of-function mutations in RPL39 (AV14) and MLF2 (R158W and D12H) were present in both ERα-positive and ERα-negative tumors, suggesting that BCSCs with these mutations may be capable of multilineage differentiation. Most importantly, the presence of these mutations was significantly associated with worse relapse-free survival and a shorter median time to relapse.

The role of BCSCs in the clinical outcome of breast cancer patients has been analyzed using different strategies, including targeting of membrane markers and transporters, interruption of intracellular signaling pathways, and alteration of the BCSCs microenvironment. Despite the success of some of those therapies in preclinical models; toxicology and pharmacokinetic studies are still required before human tests. We have shown for the first time in human breast cancer patients that residual tumors after chemotherapy are 1) enriched for the tumorigenic CD44+/CD24−/low population, 2) show enhanced mammosphere-forming efficiency (MSFE), and 3) display an increase in outgrowths in xenograft transplants in immunocompromised SCID/Beige mice, thus suggesting their increased tumorigenicity. The preclinical data showed that pharmacological inhibition of the Notch pathway with gamma secretase inhibitors (GSI) reduced the breast cancer stem cells in breast tumorgraft models. GSI enhanced the efficacy of docetaxel in preclinical studies. The clinical trial on 30 patients with advanced breast cancer showed feasibility of the combination of GSI and chemotherapy (Schott AF et. al, Clin Cancer Res., 2013).

In conclusion, the identification of breast cancer stem cell markers and an improved understanding of the molecular mechanism of BCSC phenotypes should lead to progress in cancer therapy and improved prognoses for patients with advanced breast cancer. Such emerging picture of the biological properties of BCSCs would contribute for devising innovative therapies for breast cancer, targeting the intrinsic and extrinsic factors that maintain the BCSCs.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):CN06-02.

Citation Format: Jenny C. Chang, Bhuvanesh Dave, Sergio Granados-Principal, Junhua Mai, Steven Gross, Haifa Shen, Vivek Mittal, Mauro Ferrari. Breast cancer stem cells. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr CN06-02.

Multistage vectored siRNA targeting ataxia-telangiectasia mutated for breast cancer therapy

The ataxia-telangiectasia mutated (ATM) protein plays a central role in DNA damage response and cell cycle checkpoints, and may be a promising target for cancer therapy if normal tissue toxicity could be avoided. The strategy presented here to target ATM for breast cancer therapy involves the use of liposomal-encapsulated, gene-specific ATM siRNA delivered with a well-characterized porous silicon-based multistage vector (MSV) delivery system (MSV/ATM). Biweekly treatment of MSV/ATM suppressed ATM expression in tumor tissues, and consequently inhibited growth of MDA-MB-231 orthotopic tumor in nude mice. At the therapeutic dosage, neither free liposomal ATM siRNA nor MSV/ATM triggered an acute immune response in BALB/c mice, including changes in serum cytokines, chemokines or colony-stimulating factors. Weekly treatments of mice with free liposomal ATM siRNA or MSV/ATM for 4 weeks did not cause significant changes in body weight, hematology, blood biochemistry, or major organ histology. These results indicate that MSV/ATM is biocompatible and efficacious in inhibiting tumor growth, and that further preclinical evaluation is warranted for the development of MSV/ATM as a potential therapeutic agent.

Short noncoding DNA fragment improve efficiencies of in vivo electroporation-mediated gene transfer

BACKGROUND

A major obstacle to the application of gene therapy methods in experimental and clinical practice is the lack of safe and efficient gene delivery systems. Electroporation has been shown to an effective physical delivery method. A variety of factors have been shown to affect the electroporation-mediated gene delivery efficiency. In the present study, we assessed the usefulness of noncoding short-fragment DNA (sf-DNA) for facilitating electroporation-mediated gene transfer.

METHODS

The plasmid pGL3-control encoding firefly luciferase was injected into tissues together with or without sf-DNA. Immediately after injection, the tissues were electroporated and the level of luciferase activity was assessed 24 h later. Different types of DNA fragments with different molecular weights, structures and doses were compared. The transfection efficiencies of sf-DNA-mediated electroporation in different tissues or with different electric field strengths were examined.

RESULTS

Plasmid DNA formulated with 300-bp sf-DNA resulted in a significant improvement in electroporation-mediated gene transfer efficiency. The effect is dose-dependent and is also affected by DNA fragment length and structure. It was useful for intramuscular electroporation application, as well as intratumoral application with various pulse voltage parameters.

CONCLUSIONS

The data obtained in the present study indicate that sf-DNA can be used as a helper molecule to improve electroporation-mediated gene transfection efficiency.

Abstract 2712: Identification of tumor initiating genes RPL39 and MLF2 that mediate lung metastasis through nitric oxide signaling and mesenchymal to epithelial transition

Triple negative breast cancer (TNBC) is the most aggressive and lethal form of cancer characterized by lack of estrogen, progesterone and Her2 receptors. It is prevalent in women of African American descent, often present in younger and premenopausal women. It shows high risk of recurrence and frequently metastasizes to lungs and brain, resulting in poor overall prognosis. There is no targeted therapy for TNBC as it does not respond to hormonal therapy and is intrinsically resistance to conventional chemotherapy. It is therefore imperative to understand the mechanism of survival of these cancers and unravel its biological pathways and modes of progression. We have previously described breast cancer stem cells (BCSC) to be intrinsically resistant to treatment which is further confirmed by recent publications by other groups that describe direct functional evidence for the same. Using genomic assays, we traced a BCSC gene signature comprising of 477 genes derived from patient biopsies. On selective shRNA knockdown of these genes we identified RPL39 and MLF2 as the top two candidates that affect BCSC self-renewal. Selective siRNA knockdown of RPL39 and MLF2 in human cancer xenografts, showed reduced tumor volume and lung metastases with a concomitant decrease in BCSC markers. Thus, targeting BCSCs in combination with chemotherapy should eliminate the heterogeneous populations within a tumor. Additionally, next generation RNA-seq confirmed mutations in RPL39 and MLF2 in 50% of lung metastases from breast cancer patients. In vitro and in vivo siRNA knockdown of RPL39 and MLF2 showed decrease in nitric oxide synthase, suggesting that these genes are driven by nitric oxide signaling. In conclusion this study reveals novel tumor initiating genes, RPL39 and MLF2 that target the breast cancer stem cells and also show impact on lung metastasis. Our findings enhance the understanding of treatment resistant breast cancer stem cells, the mutations that cause metastases and also lay foundation for developing new therapies for such cancers with poor prognosis.

Citation Format: Bhuvanesh Dave, Sergio Granados, Junhua Mai, Dong Soon Choi, Ding Cheng Gao, Sucharita Mitra, Haifa Shen, Senthil Muthuswamy, Vivek Mittal, Mauro Ferrari, Jenny Chang. Identification of tumor initiating genes RPL39 and MLF2 that mediate lung metastasis through nitric oxide signaling and mesenchymal to epithelial transition. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2712. doi:10.1158/1538-7445.AM2013-2712

Enhancing chemotherapy response with sustained EphA2 silencing using multistage vector delivery

PURPOSE

RNA interference has the potential to specifically knockdown the expression of target genes and thereby transform cancer therapy. However, lack of effective delivery of siRNA has dramatically limited its in vivo applications. We have developed a multistage vector (MSV) system, composed of discoidal porous silicon particles loaded with nanotherapeutics, that directs effective delivery and sustained release of siRNA in tumor tissues. In this study, we evaluated therapeutic efficacy of MSV-loaded EphA2 siRNA (MSV/EphA2) with murine orthotopic models of metastatic ovarian cancers as a first step toward development of a new class of nanotherapeutics for the treatment of ovarian cancer.

EXPERIMENTAL DESIGN

Tumor accumulation of MSV/EphA2 and sustained release of siRNA from MSV were analyzed after intravenous administration of MSV/siRNA. Nude mice with metastatic SKOV3ip2 tumors were treated with MSV/EphA2 and paclitaxel, and therapeutic efficacy was assessed. Mice with chemotherapy-resistant HeyA8 ovarian tumors were treated with a combination of MSV/EphA2 and docetaxel, and enhanced therapeutic efficacy was evaluated.

RESULTS

Treatment of SKOV3ip2 tumor mice with MSV/EphA2 biweekly for 6 weeks resulted in dose-dependent (5, 10, and 15 μg/mice) reduction of tumor weight (36%, 64%, and 83%) and number of tumor nodules compared with the control groups. In addition, tumor growth was completely inhibited when mice were treated with MSV/EphA2 in combination with paclitaxel. Furthermore, combination treatment with MSV/EphA2 and docetaxel inhibited growth of HeyA8-MDR tumors, which were otherwise resistant to docetaxel treatment.

CONCLUSION

These findings indicate that MSV/EphA2 merits further development as a novel therapeutic agent for ovarian cancer.