Novel Cytosine Deaminase Fusion Gene Enhances the Effect of Radiation on Breast Cancer in Bone by Reducing Tumor Burden, Osteolysis, and Skeletal Fracture

Product release mechanism and the complete enzyme catalysis cycle in yeast cytosine deaminase (yCD): A computational study

Yeast cytosine deaminase (yCD) is critical in gene-directed enzyme prodrug therapy as it catalyzes the hydrolytic deamination of cytosine. The product (uracil) release process is considered as rate-limiting in the whole enzymatic catalysis and includes the cleavage of the uracil-metal bond and the delivery of free uracil out of the reactive site. Herein extensive combined random acceleration molecular dynamics (RAMD) and molecular dynamics (MD) simulations coupled with the umbrella sampling technique have been performed to study the product transport mechanism. Five channels have been identified, and the thermodynamic and dynamic characterizations for the two most favorable channels have been determined and analyzed. The free energy barrier for the most beneficial pathway is about 13kcal/mol and mainly results from the cleavage of hydrogen bonds between the ligand uracil and surrounding residues Asn51, Glu64, and Asp155. The conjugated rings of Phe114 and Trp152 play gating and guiding roles in the product delivery via π⋯π van der Waals interactions with the product. Finally, the full cycle of the enzymatic catalysis has been determined, making the whole process computationally more precise.

Adenoviral-mediated imaging of gene transfer using a somatostatin receptor-cytosine deaminase fusion protein

Suicide gene therapy is a process by which cells are administered a gene that encodes a protein capable of converting a nontoxic prodrug into an active toxin. Cytosine deaminase (CD) has been widely investigated as a means of suicide gene therapy due to the enzyme’s ability to convert the prodrug 5-fluorocytosine (5-FC) into the toxic compound 5-fluorouracil (5-FU). However, the extent of gene transfer is a limiting factor in predicting therapeutic outcome. The ability to monitor gene transfer, non-invasively, would strengthen the efficiency of therapy. In this regard, we have constructed and evaluated a replication-deficient adenovirus (Ad) containing the human somatostatin receptor subtype 2 (SSTR2) fused with a C-terminal yeast CD gene for the non-invasive monitoring of gene transfer and therapy. The resulting Ad (AdSSTR2-yCD) was evaluated in vitro in breast cancer cells to determine the function of the fusion protein. These studies demonstrated that the both the SSTR2 and yCD were functional in binding assays, conversion assays, and cytotoxicity assays. In vivo studies similarly demonstrated the functionality using conversion assays, biodistribution studies, and small animal positron-emission tomography (PET) imaging studies. In conclusion, the fusion protein has been validated as useful for the non-invasive imaging of yCD expression and will be evaluated in the future for monitoring yCD-based therapy.

Development of inhibitor-directed enzyme prodrug therapy (IDEPT) for prostate cancer

Prostate cancer (PCa) is the second most common cause of cancer death among American men after lung cancer. Unfortunately, current therapies do not provide effective treatments for patients with advanced, metastatic, or hormone refractory disease. Therefore, we seek to generate therapeutic agents for a novel PCa treatment strategy by delivering a suicide enzyme (yCD_triple) to a cell membrane bound biomarker found on PCa cells (prostate-specific membrane antigen (PSMA)). This approach has resulted in a new PCa treatment strategy reported here as inhibitor-directed enzyme prodrug therapy (IDEPT). The therapeutic agents described were generated using a click chemistry reaction between the unnatural amino acid (p-azidophenylalanine (pAzF)) incorporated into yCD_triple and the dibenzylcyclooctyne moiety of our PSMA targeting agent (DBCO-PEG₄-AH₂-TG97). After characterization of the therapeutic agents, we demonstrate significant PCa cell killing of PSMA-positive cells. Importantly, we demonstrate that this click chemistry approach can be used to efficiently couple a therapeutic protein to a targeting agent and may be applicable to the ablation of other types of cancers and/or malignancies.

Novel mouse mammary cell lines for in vivo bioluminescence imaging (BLI) of bone metastasis

BACKGROUND

Tumor cell lines that can be tracked in vivo during tumorigenesis and metastasis provide vital tools for studying the specific cellular mechanisms that mediate these processes as well as investigating therapeutic targets to inhibit them. The goal of this study was to engineer imageable mouse mammary tumor cell lines with discrete propensities to metastasize to bone in vivo. Two novel luciferase expressing cell lines were developed and characterized for use in the study of breast cancer metastasis to bone in a syngeneic mouse model.

RESULTS

The 4 T1.2 luc3 and 66c14 luc2 cell lines were shown to have high levels of bioluminescence intensity in vitro and in vivo after orthotopic injection into mouse mammary fat pads. The 4 T1.2 luc3 cell line was found to closely model the sites of metastases seen in human patients including lung, liver, and bone. Specifically, 4 T1.2 luc3 cells demonstrated a high incidence of metastasis to spine, with an ex-vivo BLI intensity three orders of magnitude above the commercially available 4 T1 luc2 cells. 66c14 luc2 cells also demonstrated metastasis to spine, which was lower than that of 4 T1.2 luc3 cells but higher than 4 T1 luc2 cells, in addition to previously unreported metastases in the liver. High osteolytic activity of the 4 T1.2 luc3 cells in vivo in the bone microenvironment was also detected.

CONCLUSIONS

The engineered 4 T1.2 luc3 and 66c14 luc2 cell lines described in this study are valuable tools for studying the cellular events moderating the metastasis of breast tumor cells to bone.

Response to multiple radiation doses of fibroblasts over-expressing dominant negative Ku70

PURPOSE

To evaluate the response of cells over-expressing dominant negative (DN) Ku70 to single and multiple small radiation doses.

METHODS AND MATERIALS

Clones of fibroblasts over-expressing DNKu70, DNKu70-7, DNKu70-11, and parental Rat-1 cells were irradiated under oxic or hypoxic conditions with single or multiple doses. Cells were trypsinized 0 or 6 h after irradiation to determine surviving fraction (SF).

RESULTS

Oxic DNKu70-7 or -11 cells trypsinized 6 h after irradiation were 1.52 or 1.25 and 1.28 or 1.15 times more sensitive than oxic Rat-1 at SF of 0.5 and 0.1, respectively. Hypoxic DNKu70-7 or -11 cells trypsinized 6 h after irradiation were 1.44 or 1.70 and 1.33 or 1.51 times more sensitive than hypoxic Rat-1 at SF of 0.5 and 0.1, respectively. To the multiple doses, oxic and hypoxic DNKu70-7 or -11 cells were 1.35 or 1.37 and 2.23 or 4.61 times more sensitive than oxic and hypoxic Rat-1, respectively, resulting in very small oxygen enhancement ratios. Namely, enhancement caused by DNKu70 under hypoxia after multiple doses was greater than that under oxic conditions and greater than that after single dose.

CONCLUSIONS

Over-expression of DNKu70 enhances cells' response to radiation given as a single dose and as multiple small doses. The enhancement after multiple doses was stronger under hypoxic than under oxic conditions. These results encourage the use of DNKu70 fragment in a gene-radiotherapy.

Evaluating distant metastases in breast cancer: from biology to outcomes

There is an urgent need to understand distant metastases in breast cancer as they are the most lethal form of recurrence and a major cause of mortality in patients. Some predictors for distant metastases, including nodal status, tumor grade, and hormonal status, are useful in identifying patients at increased risk for distant metastases. Adjuvant endocrine therapy has been the treatment of choice for postmenopausal women with hormone-sensitive breast cancer, and some therapies have shown significant reductions in the risk of distant metastases. Skeletal metastases in breast cancer are treated with bisphosphonates with a certain level of success. With more new agents undergoing clinical trials, a thorough review of the specific and long-term safety of these agents is essential, as is a better understanding of the deterioration in the quality of life and cost concerns of patients who develop distant metastases. Gene-expression profiling is a new entrant in the field of distant metastases diagnosis, which is largely successful in defining gene signatures that predict the development of distant metastases. This review will discuss the biology and the impact of distant metastases on outcomes for patients with breast cancer; it also encompasses the current status, emerging focus, and future perspectives in treatment of skeletal metastases in patients with breast cancer.

Effects of a monoclonal antibody raised against nerve growth factor on skeletal pain and bone healing after fracture of the C57BL/6J mouse femur

A closed femur fracture pain model was developed in the C57BL/6J mouse. One day after fracture, a monoclonal antibody raised against nerve growth factor (anti-NGF) was delivered intraperitoneally and resulted in a reduction in fracture pain-related behaviors of approximately 50%. Anti-NGF therapy did not interfere with bone healing as assessed by mechanical testing and histomorphometric analysis.

INTRODUCTION

Current therapies to treat skeletal fracture pain are limited. This is because of the side effect profile of available analgesics and the scarcity of animal models that can be used to understand the mechanisms that drive this pain. Whereas previous studies have shown that mineralized bone, marrow, and periosteum are innervated by sensory and sympathetic fibers, it is not understood how skeletal pain is generated and maintained even in common conditions such as osteoarthritis, low back pain, or fracture.

MATERIALS AND METHODS

In this study, we characterized the pain-related behaviors after a closed femur fracture in the C57BL/6J mouse. Additionally, we assessed the effect of a monoclonal antibody that binds to and sequesters nerve growth factor (anti-NGF) on pain-related behaviors and bone healing (mechanical properties and histomorphometric analysis) after fracture.

RESULTS

Administration of anti-NGF therapy (10 mg/kg, days 1, 6, and 11 after fracture) resulted in a reduction of fracture pain-related behaviors of approximately 50%. Attenuation of fracture pain was evident as early as 24 h after the initial dosing and remained efficacious throughout the course of fracture pain. Anti-NGF therapy did not modify biomechanical properties of the femur or histomorphometric indices of bone healing.

CONCLUSIONS

These findings suggest that therapies that target NGF or its cognate receptor(s) may be effective in attenuating nonmalignant fracture pain without interfering with bone healing.

Osteoclasts direct bystander killing of bone cancer

Primary and metastatic bone cancers are difficult to eradicate and novel approaches are needed to improve treatment and extend life. As bone cancer grows, osteoclasts, the principal bone-resorbing cells of the body, are recruited to and activated at sites of cancer. In this investigation, we determined if osteoclast lineage cells could function as a cell-based gene delivery system to bone cancers. We used the cytosine deaminase (CD) 5-fluorocytosine (5-FC) enzyme/prodrug system and studied bone marrow and bones from transgenic mice expressing a novel CD gene regulated by the osteoclast tartrate-resistant acid phosphatase (TRAP) gene promoter (Tg/NCD). DsRed2-labeled 2472 sarcoma cells were placed in Tg/NCD osteoclastogenic cultures and treated with 5-FC. 5-FC treatment resulted in profound bystander killing (90%; P < 0.05). The effect of 5-FC treatment on osteoclast lineage cells was most dramatic when administered at the beginning of the 7-day cultures, suggesting that mature osteoclasts are less sensitive to 5-FC. Evaluation of osteoclast-directed bystander killing in vivo revealed dramatic killing of bone cancer with only a modest effect on osteoclast number. Specifically, 5-FC treatment of tumor-bearing Tg/NCD mice or Tg/NCD bone marrow transplanted C3H mice (Tg/NCD-C3H) resulted in 92% and 44% reductions in tumor area, respectively (P < 0.05). Eight of ten 5-FC-treated Tg/NCD mice had complete bone tumor killing and five of six 5-FC-treated Tg/NCD-C3H mice had reduced tumor compared with controls. In addition, Tg/NCD osteoclasts were resistant to 5-FC treatment in vivo, a very important feature, as it identifies osteoclasts as an ideal CD gene delivery system.