A quantitative MRI-based approach to estimate the permeation and retention of nanomedicines in tumors.

Despite the potential of the enhanced permeability and retention (EPR) effect in tumor passive targeting, many nanotherapeutics have failed to produce meaningful clinical outcomes due to the variable and challenging nature of the tumor microenvironment (TME) and EPR effect. This EPR variability across tumors and inconsistent translation of nanomedicines from preclinical to clinical settings necessitates a reliable method to assess its presence in individual tumors. This study aimed to develop a reliable and non-invasive approach to estimate the EPR effect in tumors using a clinically compatible quantitative magnetic resonance imaging (qMRI) technique combined with a nano-sized MRI contrast agent. A quantitative MR imaging was developed using a dynamic contrast-enhanced (DCE) MRI protocol. Then, the permeability and retention of the nano-sized MRI contrast agent were evaluated in three different ovarian xenograft tumor models. Results showed significant differences in EPR effects among the tumor models, with tumor growth influencing the calculated parameters of permeability (Ktrans) and retention (Ve) based on Tofts pharmacokinetic (PK) modeling. Our data indicate that the developed quantitative DCE-MRI method, combined with the Tofts PK modeling, provides a robust and non-invasive approach to screen tumors for their responsiveness to nanotherapeutics. These results imply that the developed qMRI method can be beneficial for personalized cancer treatments by ensuring that nanotherapeutics are administered only to patients with tumors showing sufficient EPR levels.

Bispecific immune cell engager enhances the anticancer activity of CD16+ NK cells and macrophages in vitro, and eliminates cancer metastasis in NK humanized NOG mice.

BACKGROUND: In a prior report, we detailed the isolation and engineering of a bispecific killer cell engager, referred to as BiKE:E5C1. The BiKE:E5C1 exhibits high affinity/specificity for the CD16a activating receptor on natural killer (NK) cells and human epidermal growth factor receptor 2 (HER2) on cancer cells. In vitro studies have demonstrated that BiKE:E5C1 can activate the NK cells and induce the killing of HER2+ ovarian and breast cancer cells, surpassing the performance of the best-in-class monoclonal antibody, Trazimera (trastuzumab). To advance this BiKE technology toward clinical application, the objective of this research was to demonstrate the ability of BiKE:E5C1 to activate CD16+ immune cells such as NK cells and macrophages to kill cancer cells, and eradicate metastatic HER2+ tumors in NK humanized NOG mice. METHODS: We assessed BiKE:E5C1's potential to activate CD16-expressing peripheral blood (PB)-NK cells, laNK92 cells, and THP-1-CD16A monocyte-macrophages through flowcytometry and antibody-dependent cell-mediated cytotoxicity/phagocytosis (ADCC) assays. Subsequently, laNK92 cells were selected as effector cells and genetically modified to express the nanoluciferase gene, enabling the monitoring of their viability in NK humanized NOG mice using quantitative bioluminescent imaging (qBLI). To evaluate the functionality of BiKE:E5C1 in vivo, we introduced firefly luciferase-expressing ovarian cancer cells via intraperitoneal injection into hIL-15 and hIL-2 NOG mice, creating a model of ovarian cancer metastasis. Once tumor establishment was confirmed, we treated the mice with laNK92 cells plus BiKE:E5C1 and the response to therapy was assessed using qBLI. RESULTS: Our data demonstrate that BiKE:E5C1 activates not only laNK92 cells but also PB-NK cells and macrophages, significantly enhancing their anticancer activities. ADCC assay demonstrated that IgG1 Fc region had no impact on BiKE:E5C1's anticancer activity. In vivo results reveal that both hIL-15 and hIL-2 NOG mouse models support the viability and proliferation of laNK92 cells. Furthermore, it was observed that BiKE:E5C1 activates laNK92 cells in mice, leading to eradication of cancer metastasis in both NK humanized hIL-15 and hIL-2 NOG mouse models. CONCLUSIONS: Collectively, our in vivo findings underscore BiKE:E5C1's potential as an immune cell engager capable of activating immune cells for cancer cell elimination, thereby expanding the arsenal of available BiKEs for cancer immunotherapy.

A high affinity and specificity anti-HER2 single-domain antibody (VHH) that targets trastuzumab's epitope with versatile biochemical, biological, and medical applications.

In the past decade, various single-domain antibodies from llamas, also known as VHH or nanobody, have been discovered with applications in tumor imaging and cancer therapy. However, the potential application of anti-HER2 VHHs as a diagnostic tool suitable for ELISA, flow cytometry, cell imaging, bispecific antibody engineering, and immunohistochemistry has not been fully elucidated. To investigate this potential, HER2 antigen was expressed in HEK293 F cells, purified, and used to immunize llama. Using phage display, anti-HER2 VHHs with high affinity and specificity were isolated, sequenced, and constructed with a Histag and c-Myc tag. The constructed anti-HER2 VHHs were then expressed in E. coli, purified, and evaluated for their use in ELISA, flow cytometry, cell imaging, and immunohistochemistry. The affinities of the anti-HER2 VHHs toward the HER2 antigen were determined using biolayer interferometry. Furthermore, the binding sites of the anti-HER2 VHHs were evaluated by epitope mapping and in silico modeling and docking. Here, we report the sequence of an anti-HER2 VHH with high affinity (sub-nanomolar), specificity, and selectivity. This VHH binds to the same epitope as trastuzumab and can be utilized to generate bispecific antibodies or used as a diagnostic tool to differentiate HER2+ from HER2- antigens on plates, cells, and tissues. This discovery has broad applications in biochemical, biological, and medical sciences.

Stem cell-assisted enzyme/prodrug therapy makes drug-resistant ovarian cancer cells vulnerable to natural killer cells through upregulation of NKG2D ligands.

Cancer stem-like cells (CSCs) are believed to be responsible for cancer recurrence and metastasis. Therefore, a therapeutic approach is needed to eliminate both rapidly proliferating differentiated cancer cells and slow-growing drug-resistant CSCs. Using established ovarian cancer cells lines as well as ovarian cancer cells isolated from a patient with high-grade drug-resistant ovarian carcinoma, we demonstrate that ovarian CSCs consistently express lower levels of NKG2D ligands (MICA/B and ULBPs) on their surfaces, a mechanism by which they evade natural killer (NK) cells' surveillance. Here, we discovered that exposure of ovarian cancer (OC) cells to SN-38 followed by 5-FU not only acts synergistically to kill the OC cells, but also makes the CSCs vulnerable to NK92 cells through upregulation of NKG2D ligands. Since systemic administration of these two drugs is marred by intolerance and instability, we engineered and isolated an adipose-derived stem cell (ASC) clone, which stably expresses carboxylesterase-2 and yeast cytosine deaminase enzymes to convert irinotecan and 5-FC prodrugs into SN-38 and 5-FU cytotoxic drugs, respectively. Co-incubation of ASCs and prodrugs with drug-resistant OC cells not only led to the death of the drug-resistant OC cells but also made them significantly vulnerable to NK92 cells. This study provides proof of principle for a combined ASC-directed targeted chemotherapy with NK92-assisted immunotherapy to eradicate drug-resistant OC cells.

Bispecific killer cell engager with high affinity and specificity toward CD16a on NK cells for cancer immunotherapy.

Introduction: The Fc region of monoclonal antibodies (mAbs) interacts with the CD16a receptor on natural killer (NK) cells with "low affinity" and "low selectivity". This low affinity/selectivity interaction results in not only suboptimal anticancer activity but also induction of adverse effects. CD16a on NK cells binds to the antibody-coated cells, leading to antibody-dependent cell-mediated cytotoxicity (ADCC). Recent clinical data have shown that the increased binding affinity between mAb Fc region and CD16a receptor is responsible for significantly improved therapeutic outcomes. Therefore, the objective of this study was to develop a bispecific killer cell engager (BiKE) with high affinity and specificity/selectivity toward CD16a receptor for NK cell-based cancer immunotherapy. Methods: To engineer BiKE, a llama was immunized, then high binding anti-CD16a and anti-HER2 VHH clones were isolated using phage display. ELISA, flow cytometry, and biolayer interferometry (BLI) data showed that the isolated anti-CD16a VHH has high affinity (sub-nanomolar) toward CD16a antigen without cross-reactivity with CD16b-NA1 on neutrophils or CD32b on B cells. Similarly, the data showed that the isolated anti-HER2 VHH has high affinity/specificity toward HER2 antigen. Using a semi-flexible linker, anti-HER2 VHH was recombinantly fused with anti-CD16a VHH to create BiKE:HER2/CD16a. Then, the ability of BiKE:HER2/CD16a to activate NK cells to release cytokines and kill HER2+ cancer cells was measured. As effector cells, both high-affinity haNK92 (CD16+, V176) and low-affinity laNK92 (CD16+, F176) cells were used. Results and discussion: The data showed that the engineered BiKE:HER2/CD16a activates haNK92 and laNK92 cells to release cytokines much greater than best-in-class mAbs in the clinic. The cytotoxicity data also showed that the developed BiKE induces higher ADCC to both ovarian and breast cancer cells in comparison to Trazimera™ (trastuzumab). According to the BLI data, BiKE:HER2/CD16 recognizes a different epitope on CD16a antigen than IgG-based mAbs; thus, it provides the opportunity for not only monotherapy but also combination therapy with other antibody drugs such as checkpoint inhibitors and antibody-drug conjugates. Taken together, the data demonstrate the creation of a novel BiKE with high affinity and specificity toward CD16a on NK cells with the potential to elicit a superior therapeutic response in patients with HER2+ cancer than existing anti-HER2 mAbs.

Gadolinium-labeled affibody-XTEN recombinant vector for detection of HER2+ lesions of ovarian cancer lung metastasis using quantitative MRI.

Ovarian cancer has the highest mortality rate among all gynecologic malignancies. HER2+ ovarian cancer is a subtype that is aggressive and associated with metastasis to distant sites such as the lungs. Therefore, accurate biological characterization of metastatic lesions is vital as it helps physicians select the most effective treatment strategy. Functional imaging of ovarian cancer with PET/CT is routinely used in the clinic to detect metastatic disease and evaluate treatment response. However, this imaging method does not provide information regarding the presence or absence of cancer-specific cell surface biomarkers such as HER2. As a result, this method does not help physicians decide whether to choose immunotherapy to treat metastasis. To differentiate the HER2+ from HER2¯ lesions in ovarian cancer lung metastasis, AbX50C4:Gd vector composed of a HER2 targeting affibody and XTEN peptide was genetically engineered. It was then labeled with gadolinium (Gd) via a stable linker. The vector was characterized physicochemically and biologically to determine its purity, molecular weight, hydrodynamic size and surface charge, stability in serum, endotoxin levels, relaxivity and ability to target the HER2 antigen. Then, SCID mice were implanted with SKOV-3 (HER2+) and OVASC-1 (HER2¯) tumors in the lungs and injected with the Gd-labeled HER2 targeted AbX50C4:Gd vector. The mice were imaged using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), followed by R1-mapping and quantitative analysis of the images. Our data demonstrate that the developed HER2-targeted vector can differentiate HER2+ lung metastasis from HER2¯ lesions using DCE-MRI. The developed vector could potentially be used in conjunction with other imaging modalities to prescreen patients and identify candidates for immunotherapy while triaging those who may not be considered responsive.

MicroRNAs and lncRNAs-A New Layer of Myeloid-Derived Suppressor Cells Regulation.

Myeloid-derived suppressor cells (MDSCs) constitute an important component in regulating immune responses in several abnormal physiological conditions such as cancer. Recently, novel regulatory tumor MDSC biology modulating mechanisms, including differentiation, expansion and function, were defined. There is growing evidence that miRNAs and long non-coding RNAs (lncRNA) are involved in modulating transcriptional factors to become complex regulatory networks that regulate the MDSCs in the tumor microenvironment. It is possible that aberrant expression of miRNAs and lncRNA contributes to MDSC biological characteristics under pathophysiological conditions. This review provides an overview on miRNAs and lncRNAs epiregulation of MDSCs development and immunosuppressive functions in cancer.

Bioengineered adipose-derived stem cells for targeted enzyme-prodrug therapy of ovarian cancer intraperitoneal metastasis.

The objective of this study was to develop a stem cell-based system for targeted suicide gene therapy of recurrent, metastatic, and unresectable ovarian cancer. Malignant cells were obtained from the ascites of a patient with advanced recurrent epithelial ovarian cancer (named OVASC-1). Cancer cells were characterized to determine the percentages of drug-resistant ALDH+ cells, MDR-1/ABCG2 overexpressing cells, and cancer stem-like cells. The sensitivity and resistance of the OVASC-1 cells and spheroids to the metabolites of three different enzyme/prodrug systems were assessed, and the most effective one was selected. Adipose-derived stem cells (ASCs) were genetically engineered to express recombinant secretory human carboxylesterase-2 and nanoluciferase genes for simultaneous disease therapy and quantitative imaging. Bioluminescent imaging, magnetic resonance imaging and immuno/histochemistry results show that the engineered ASCs actively targeted and localized at both tumor stroma and necrotic regions. This created the unique opportunity to deliver drugs to not only tumor supporting cells in the stroma, but also to cancer stem-like cells in necrotic/hypoxic regions. The statistical analysis of intraperitoneal OVASC-1 tumor burden and survival rates in mice shows that the administration of the bioengineered ASCs in combination with irinotecan prodrug in the designed sequence and timeline eradicated all intraperitoneal tumors and provided survival benefits. In contrast, treatment of the drug-resistant OVASC-1 tumors with cisplatin/paclitaxel (standard-of-care) did not have any statistically significant benefit. The histopathology and hematology results do not show any toxicity to major peritoneal organs. Our toxicity data in combination with efficacy outcomes delineate a nonsurgical and targeted stem cell-based approach to overcoming drug resistance in recurrent metastatic ovarian cancer.

A novel chemotherapeutic protocol for peritoneal metastasis and inhibition of relapse in drug resistant ovarian cancer.

The majority of ovarian cancer patients are diagnosed in late stages of the disease, in which the tumor cells have leaked into the peritoneum and are present as tumorspheres. These tumorspheres are rich in cancer stem-like cells (CSCs), which are resistant to therapy and are a major source of relapse. The purpose of this research was to identify a safe therapeutic approach that could eradicate the peritoneal CSC-rich tumorspheres and inhibit relapse. Highly metastatic ascitic cells (OVASC-1) that are resistant to standard-of-care chemotherapy due to upregulation of MDR1 gene were obtained from a patient with ovarian carcinoma and recurrent disease. CSC-rich tumorspheres were generated, characterized, and treated with different chemotherapeutics. The most effective drug combination that could eradicate tumorspheres at nanomolar levels despite upregulation of MDR1 gene was identified. Luciferase-expressing OVASC-1 cells were implanted in the peritoneum of nude mice and treated with the identified drug combination. The progression of disease, response to therapy and recurrence were studied by quantitative imaging. Toxicity to abdominal tissues was studied by histopathology. Mice implanted with intraperitoneal (IP) OVASC-1 xenografts showed limited response to combination therapy with cisplatin/paclitaxel at the maximum tolerated dose. Despite overexpression of MDR1 on OVASC-1 cells, mice treated with our combination IP low-dose MMAE and SN-38 chemotherapy showed complete response without relapse. No signs of toxicity to abdominal tissues were observed. While MMAE and SN-38 are not administered as free drugs due to their high potency and potential for systemic toxicity, our low-dose localized therapy approach effectively restricted the cytotoxic effects to the tumor cells in the peritoneum. Consequently, maximum efficacy with minimal adverse effects was achieved. These remarkable results with IP low-dose combination chemotherapy encourage investigation into its potential clinical application as either first-line therapy or in cases of acquired resistance to cisplatin and paclitaxel.

Evaluation of genotoxicity and mutagenic effects of vector/DNA nanocomplexes in transfected mesenchymal stem cells by flow cytometry.

In recent years, there has been a great deal of interest in ex-vivo genetic modification of mesenchymal stem cells (MSCs) to meet various biomedical needs. Considering the self-renewal potential of MSCs, it is critically important to ensure that transfection vectors (gene carriers) do not induce genotoxicity because they could theoretically turn a single stem cell into a cancer-initiating cell. Unfortunately, there is currently no reliable, unbiased, and quantitative method to measure genotoxicity (micronuclei formation) of gene carriers directly in transfected MSCs. Consequently, it has not been possible to study the correlation of vectors' physicochemical characteristics with their impact on stem cell genome stability. To address this deficiency, a flow cytometry-based method with a specialized gating protocol was developed that not only measures micronuclei formation, but also determines the mechanism of mutagenesis (i.e., clastogenic vs. aneugenic) of each vector in transfected MSCs. This gating protocol effectively eliminates all interfering signals associated with aggregated nanoparticles (viral and non-viral), exogenous DNA, and apoptotic/necrotic bodies from the micronuclei measurement process. The presented gating protocol for flow cytometry, which is provided as a template, enables investigators in academia, industry and regulatory bodies to rapidly and reliably evaluate the genosafety profiles of gene carriers. The findings of this study also indicate that highly positively charged lipid- and polymeric-based vectors can induce genotoxicity even without manifesting substantial somatic toxicity. Thus, extreme care must be taken before implanting ex-vivo-modified MSCs back into a patient's body. STATEMENT OF SIGNIFICANCE: There is a great interest in genetic modification of stem cells (SCs) by using vectors for various biomedical needs. Considering the self-renewal potential of SCs, it is essential to ensure that such vectors do not induce genetic aberrations (genotoxicity) because they could theoretically turn a single stem cell into a cancer-initiating cell. Unfortunately, there is currently no reliable method to measure genotoxicity of vectors directly in transfected SCs. To address this deficiency, a specialized flow cytometry-based method was developed that quantitatively analyzed genotoxicity and determined the mechanism of mutagenesis that occurred in transfected SCs during the transfection process. The developed technique will enable scientists to design safer vectors for genetic modification of stem cells.

Bioengineering a non-genotoxic vector for genetic modification of mesenchymal stem cells.

Vectors used for stem cell transfection must be non-genotoxic, in addition to possessing high efficiency, because they could potentially transform normal stem cells into cancer-initiating cells. The objective of this research was to bioengineer an efficient vector that can be used for genetic modification of stem cells without any negative somatic or genetic impact. Two types of multifunctional vectors, namely targeted and non-targeted were genetically engineered and purified from E. coli. The targeted vectors were designed to enter stem cells via overexpressed receptors. The non-targeted vectors were equipped with MPG and Pep1 cell penetrating peptides. A series of commercial synthetic non-viral vectors and an adenoviral vector were used as controls. All vectors were evaluated for their efficiency and impact on metabolic activity, cell membrane integrity, chromosomal aberrations (micronuclei formation), gene dysregulation, and differentiation ability of stem cells. The results of this study showed that the bioengineered vector utilizing VEGFR-1 receptors for cellular entry could transfect mesenchymal stem cells with high efficiency without inducing genotoxicity, negative impact on gene function, or ability to differentiate. Overall, the vectors that utilized receptors as ports for cellular entry (viral and non-viral) showed considerably better somato- and genosafety profiles in comparison to those that entered through electrostatic interaction with cellular membrane. The genetically engineered vector in this study demonstrated that it can be safely and efficiently used to genetically modify stem cells with potential applications in tissue engineering and cancer therapy.

Development of a Recombinant Multifunctional Biomacromolecule for Targeted Gene Transfer to Prostate Cancer Cells.

The objective of this study was to genetically engineer a fully functional single chain fusion peptide composed of motifs from diverse biological and synthetic origins that can perform multiple tasks including DNA condensation, cell targeting, cell transfection, particle shielding from immune system and effective gene transfer to prostate tumors. To achieve the objective, a single chain biomacromolecule (vector) consisted of four repeatative units of histone H2A peptide, fusogenic peptide GALA, short elastin-like peptide, and PC-3 cell targeting peptide was designed. To examine the functionality of each motif in the vector sequence, it was characterized in terms of size and zeta potential by Zetasizer, PC-3 cell targeting and transfection by flowcytometry, IgG induction by immunogenicity assay, and PC-3 tumor transfection by quantitative live animal imaging. Overall, the results of this study showed the possibility of using genetic engineering techniques to program various functionalities into one single chain vector and create a multifunctional nonimmunogenic biomacromolecule for targeted gene transfer to prostate cancer cells. This proof-of-concept study is a significant step forward toward creating a library of vectors for targeted gene transfer to any cancer cell type at both in vitro and in vivo levels.

Production of low-expressing recombinant cationic biopolymers with high purity.

The growing complexity of recombinant biopolymers for delivery of bioactive agents requires the ability to control the biomaterial structure with high degree of precision. Genetic engineering techniques have provided this opportunity to synthesize biomaterials in an organism such as E. coli with full control over their lengths and sequences. One class of such biopolymers is recombinant cationic biopolymers with applications in gene delivery, regenerative medicine and variety of other biomedical applications. Unfortunately, due to their highly cationic nature and complex structure, their production in E. coli expression system is marred by low expression yield which in turn complicates the possibility of obtaining pure biopolymer. SlyD and ArnA endogenous E. coli proteins are considered the major culprits that copurify with the low-expressing biopolymers during the metal affinity chromatography. Here, we compared the impact of different parameters such as the choice of expression hosts as well as metal affinity columns in order to identify the most effective approach in obtaining highly pure recombinant cationic biopolymers with acceptable yield. The results of this study showed that by using E. coli BL21(DE3) LOBSTR strain and in combination with our developed stringent expression and Ni-NTA purification protocols highly pure products in one purification step (>99% purity) can be obtained. This approach could be applied to the production of other complex and potentially toxic biopolymers with wide range of applications in biomedicine.

An in vitro demonstration of overcoming drug resistance in SKOV3 TR and MCF7 ADR with targeted delivery of polymer pro-drug conjugates.

Drug resistance is a common phenomenon that occurs in cancer chemotherapy. Delivery of chemotherapeutic agents as polymer pro-drug conjugates (PPDCs) pretargeted with bispecific antibodies could circumvent drug resistance in cancer cells. To demonstrate this approach to overcome drug resistance, Paclitaxel (Ptxl)-resistant SKOV3 TR human ovarian- and doxorubicin (Dox)-resistant MCF7 ADR human mammary-carcinoma cell lines were used. Pre-targeting over-expressed biotin or HER2/neu receptors on cancer cells was conducted by biotinylated anti-DTPA or anti-HER2/neu affibody - anti-DTPA Fab bispecific antibody complexes. The targeting PPDCs are either D-Dox-PGA or D-Ptxl-PGA. Cytotoxicity studies demonstrate that the pretargeted approach increases cytotoxicity of Ptxl or Dox in SKOV3 TR or MCF7 ADR resistant cell lines by 5.4 and 27 times, respectively. Epifluorescent microscopy - used to track internalization of D-Dox-PGA and Dox in MCF7 ADR cells - shows that the pretargeted delivery of D-Dox-PGA resulted in a 2- to 4-fold increase in intracellular Dox concentration relative to treatment with free Dox. The mechanism of internalization of PPDCs is consistent with endocytosis. Enhanced drug delivery and intracellular retention following pretargeted delivery of PPDCs resulted in greater tumor cell toxicity in the current in vitro studies.

Enzyme/Prodrug Systems for Cancer Gene Therapy.

The use of enzyme/prodrug system has gained attention because it could help improve the efficacy and safety of conventional cancer chemotherapies. In this approach, cancer cells are first transfected with a gene that can express an enzyme with ability to convert a non-toxic prodrug into its active cytotoxic form. As a result, the activated prodrug could kill the transfected cancer cells. Despite the significant progress of different suicide gene therapy protocols in preclinical studies and early clinical trials, none has reached the clinic due to several shortcomings. These include slow prodrug-drug conversion rate, low transfection/transduction efficiency of the vectors and nonspecific toxicity/immunogenicity related to the delivery systems, plasmid DNA, enzymes and/or prodrugs. This mini review aims at providing an overview of the most widely used enzyme/prodrug systems with emphasis on reporting the results of the recent preclinical and clinical studies.

Progress and problems with the use of suicide genes for targeted cancer therapy.

Among various gene therapy methods for cancer, suicide gene therapy attracts a special attention because it allows selective conversion of non-toxic compounds into cytotoxic drugs inside cancer cells. As a result, therapeutic index can be increased significantly by introducing high concentrations of cytotoxic molecules to the tumor environment while minimizing impact on normal tissues. Despite significant success at the preclinical level, no cancer suicide gene therapy protocol has delivered the desirable clinical significance yet. This review gives a critical look at the six main enzyme/prodrug systems that are used in suicide gene therapy of cancer and familiarizes readers with the state-of-the-art research and practices in this field. For each enzyme/prodrug system, the mechanisms of action, protein engineering strategies to enhance enzyme stability/affinity and chemical modification techniques to increase prodrug kinetics and potency are discussed. In each category, major clinical trials that have been performed in the past decade with each enzyme/prodrug system are discussed to highlight the progress to date. Finally, shortcomings are underlined and areas that need improvement in order to produce clinical significance are delineated.

Practical Issues with the Use of Stem Cells for Cancer Gene Therapy.

Stem cell-based drug delivery for cancer therapy has steadily gained momentum in the past decade as several studies have reported stem cells' inherent tropism towards tumors. Since this science is still in its early stages and there are many factors that could significantly impact tumor tropism of stem cells, some contradictory results have been observed. This review starts by examining a number of proof-of-concept studies that demonstrate the potential application of stem cells in cancer therapy. Studies that illustrate stem cells' tumor tropism and discuss the technical difficulties that could impact the therapeutic outcome are also highlighted. The discussion also emphasizes stem cell imaging/tracking, as it plays a crucial role in performing reliable dose-response studies and evaluating the therapeutic outcome of treatment protocols. In each section, the pros and cons associated with each method are highlighted, limitations are underlined, and potential solutions are discussed. The overall intention is to familiarize the reader with important practical issues related to stem cell cancer tropism and in vivo tracking, underline the shortcomings, and emphasize critical factors that need to be considered for effective translation of this science into the clinic.

Reducing the Visibility of the Vector/DNA Nanocomplexes to the Immune System by Elastin-Like Peptides.

PURPOSE: One of the major hurdles facing nanomedicines is the antibody production against nanoparticles that subsequently results in their opsonization and clearance by macrophages. The objective of this research was to examine and identify the sequence of a low-immunogenic peptide based on recombinant elastin-like polypeptides (ELPs) that does not evoke IgG response and can potentially be used for masking the surfaces of the nanoparticles. METHODS: Biopolymers composed of a DNA condensing domain in fusion with anionic, neutral and cationic elastin-like peptides were genetically engineered. The biopolymers were used to complex with plasmid DNA and form ELP-coated nanoparticles. Then, the potential immunogenicity of nanoparticles in terms of IgM/IgG response after repeated injections was evaluated in Balb/c immunocompetent mice. RESULTS: The results revealed the sequence of a non-immunogenic ELP construct that in comparison to control group did not elicit any significant IgG response, whereas the vector/DNA complexes that were coated with polyethylene glycol (PEG) did elicit significant IgG response under the same conditions. CONCLUSIONS: The identification of the sequence of an ELP-based peptide that does not induce IgG response opens the door to more focused in-depth immunotoxicological studies which could ultimately lead to the production of safer and more effective drug/gene delivery systems such as liposomes, micelles, polymeric nanoparticles, viruses and antibodies.

Genetically engineered theranostic mesenchymal stem cells for the evaluation of the anticancer efficacy of enzyme/prodrug systems.

Over the past decade, various enzyme/prodrug systems such as thymidine kinase/ganciclovir (TK/GCV), yeast cytosine deaminase/5-fluorocytosine (yCD/5-FC) and nitroreductase/CB1954 (NTR/CB1954) have been used for stem cell mediated suicide gene therapy of cancer. Yet, no study has been conducted to compare and demonstrate the advantages and disadvantages of using one system over another. Knowing that each enzyme/prodrug system has its own strengths and weaknesses, we utilized mesenchymal stem cells (MSCs) as a medium to perform for the first time a comparative study that illustrated the impact of subtle differences among these systems on the therapeutic outcome. For therapeutic purposes, we first genetically modified MSCs to stably express a panel of four suicide genes including TK (TK007 and TK(SR39) mutants), yeast cytosine deaminase:uracil phosphoribosyltransferase (yCD:UPRT) and nitroreductase (NTR). Then, we evaluated the anticancer efficacies of the genetically engineered MSCs in vitro and in vivo by using SKOV3 cell line which is sensitive to all four enzyme/prodrug systems. In addition, all MSCs were engineered to stably express luciferase gene making them suitable for quantitative imaging and dose-response relationship studies in animals. Considering the limitations imposed by the prodrugs' bystander effects, our findings show that yCD:UPRT/5-FC is the most effective enzyme/prodrug system among the ones tested. Our findings also demonstrate that theranostic MSCs are a reliable medium for the side-by-side evaluation and screening of the enzyme/prodrug systems at the preclinical level. The results of this study could help scientists who utilize cell-based, non-viral or viral vectors for suicide gene therapy of cancer make more informed decisions when choosing enzyme/prodrug systems.

Bispecific antibody complex pre-targeting and targeted delivery of polymer drug conjugates for imaging and therapy in dual human mammary cancer xenografts: targeted polymer drug conjugates for cancer diagnosis and therapy.

INTRODUCTION: Doxorubicin, a frontline chemotherapeutic agent, limited by its cardiotoxicity and other tissue toxicities, was conjugated to N-terminal DTPA-modified polyglutamic acid (D-Dox-PGA) to produce polymer pro-drug conjugates. D-Dox-PGA or Tc-99 m labeled DTPA-succinyl-polylysine polymers (DSPL) were targeted to HER2-positive human mammary carcinoma (BT-474) in a double xenografted SCID mouse model also hosting HER2-negative human mammary carcinoma (BT-20). METHODS: After pretargeting with bispecific anti-HER2-affibody-anti-DTPA-Fab complexes (BAAC), anti-DTPA-Fab or only phosphate buffered saline, D-Dox-PGA or Tc-99 m DSPL were administered. Positive therapeutic control mice were injected with Dox alone at maximum tolerated dose (MTD). RESULTS: Only BT-474 lesions were visualized by gamma imaging with Tc-99 m-DSPL; BT-20 lesions were not. Therapeutic efficacy was equivalent in mice pretargeted with BAAC/targeted with D-Dox-PGA to mice treated only with doxorubicin. There was no total body weight (TBW) loss at three times the doxorubicin equivalent MTD with D-Dox-PGA, whereas mice treated with doxorubicin lost 10% of TBW at 2 weeks and 16% after the second MTD injection leading to death of all mice. CONCLUSIONS: Our cancer imaging and pretargeted therapeutic approaches are highly target specific, delivering very high specific activity reagents that may result in the development of a novel theranostic application. HER/2 neu specific affibody-anti-DTPA-Fab bispecific antibody pretargeting of HER2 positive human mammary xenografts enabled exquisite targeting of polymers loaded with radioisotopes for molecular imaging and doxorubicin for effective therapy without the associating non-tumor normal tissue toxicities.