Biomedical subjects

Mai Johnson

Publications and source records attributed to Mai Johnson.

11 recordsLinked to original sources

PubMed2006

Differential biodistribution of adenoviral vector in vivo as monitored by bioluminescence imaging and quantitative polymerase chain reaction.

A better understanding of the in vivo biodistribution of adenoviral vectors would enable the researcher to anticipate potential side effects due to off-targeted site of transduction, and aid in the strategic design of gene therapy. We combined real-time polymerase chain reaction with in vivo optical imaging to examine viral transduction in liver, lung, spleen, kidney, prostate, and lymph nodes. A replication-deficient serotype 5 adenoviral vector expressing the firefly luciferase gene under the control of a constitutive cytomegalovirus promoter was administered in vivo via different routes. Intravenous and intraperitoneal injections resulted in greatest gene expression and viral DNA in the liver, whereas intraperitoneal injections led to a greater extent of gene delivery to the prostate. Although prostate-directed injection resulted in dominant gene expression in the targeted site, leakage of the vector to other organs was also observed. Vector injection into the lymphatic-rich paw tissue or the subcutaneous tissue of shoulder or chest followed the expected lymphatic drainage pattern, resulting in the accumulation of viral vector in ipsilateral brachial and axillary lymph nodes. Collectively, this study demonstrates that each tissue retains various amounts of adenoviral vector, depending on the route of administration. This knowledge is useful in the strategic design and implementation of adenovirus-mediated gene therapies.

Adenoviridae↗

PubMed2006

Specific targeting of gene therapy to prostate cancer using a two-step transcriptional amplification system.

Significant advances in gene therapy have been made as a result of the improvement of gene delivery systems, discovery of new therapeutic genes, better understanding of mechanisms of disease progression, exploration and improvement of tissue-specific gene regulatory sequences, and development of better prodrug/enzyme systems. This review discusses adenoviral-based and prostate-specific cancer gene therapy--emphasizing tissue-specific promoter choices to increase gene therapy safety and specificity--and the development of prostate-targeted vectors, with a focus on the two-step transactivation system for amplifying gene expression, specifically in prostate cancer cells. Several examples will be discussed for the scientific basis and therapeutic applications. In addition, prostate cancer gene therapy clinical trials and future directions in this field will also be described briefly.

Animals↗

PubMed2005

Functionality of androgen receptor-based gene expression imaging in hormone refractory prostate cancer.

PURPOSE: A highly augmented, prostate-specific two-step transcriptional amplification (TSTA) method was developed with the ultimate goal of delivering an effective and safe gene-based treatment to prostate cancer patients. Because very limited treatment options are available for recurrent hormone refractory prostate cancer (HRPC), it is imperative to assess whether the prostate-specific antigen (PSA) promoter-based TSTA gene therapy will be functional in HRPC. EXPERIMENTAL DESIGN: We tested the TSTA-driven adenovirus vector on three androgen-dependent and six HRPC models. Real-time gene expression was monitored by both optical imaging and the combined modality of positron emission tomography (PET) and computed tomography. RESULTS: The TSTA-driven firefly luciferase expressing adenoviral vector was active in all androgen receptor (AR)-expressing HRPC models, but inactive in AR- and PSA-negative lines. Interestingly, the TSTA-mediated gene expression was induced by hydrocortisone in MDA PCa 2b, a cell line with mutated AR that possesses altered ligand specificity. In animal models, the TSTA-mediated optical signal was more robust in the HRPC than androgen-dependent tumors. In a parallel trend, a TSTA vector that expresses the herpes simplex virus thymidine kinase PET reporter gene also displayed more robust PET signal in the HRPC tumor. CONCLUSIONS: The activity of TSTA system is AR dependent and it recapitulates the functional status of endogenous AR. These data support the conclusion that AR function is activated in HRPC despite castrated levels of androgen. Together with the fact that majority of recurrent prostate cancers express AR and PSA, we foresee that the TSTA approach can be a promising gene therapy strategy for the advanced stages of prostate cancer.

Adenoviridae↗

PubMed2005

Lentiviral vector retargeting to P-glycoprotein on metastatic melanoma through intravenous injection.

Targeted gene transduction to specific tissues and organs through intravenous injection would be the ultimate preferred method of gene delivery. Here, we report successful targeting in a living animal through intravenous injection of a lentiviral vector pseudotyped with a modified chimeric Sindbis virus envelope (termed m168). m168 pseudotypes have high titer and high targeting specificity and, unlike other retroviral pseudotypes, have low nonspecific infectivity in liver and spleen. A mouse cancer model of metastatic melanoma was used to test intravenous targeting with m168. Human P-glycoprotein was ectopically expressed on the surface of melanoma cells and targeted by the m168 pseudotyped lentiviral vector conjugated with antibody specific for P-glycoprotein. m168 pseudotypes successfully targeted metastatic melanoma cells growing in the lung after systemic administration by tail vein injection. Further development of this targeting technology should result in applications not only for cancers but also for genetic, infectious and immune diseases.

Animals↗

PubMed2005

Applications of molecular imaging in cancer gene therapy.

Gene-based therapy is a promising and flexible therapeutic approach to manage diverse types of cancer. The lack of convincing therapeutic success of current gene therapy protocols in part, can be attributed to the inability to monitor gene expression at the targeted site in the living subject. Linking molecular imaging to gene therapy will enable real-time assessment of the therapeutic process and the refinement of treatment protocols. This review will cover two common imaging modalities, positron emission tomography (PET) and bioluminescence imaging (BLI), used in pre-clinical and clinical gene therapy applications. Strategies to develop more specific and robust cancer gene therapy and imaging approaches will be discussed. Coupling PET to gene therapy of cancer has already been implemented in several clinical studies. This approach would help to improve the efficacy and safety of future gene therapy clinical trials.

Gene Expression↗

PubMed2003

Interrogating androgen receptor function in recurrent prostate cancer.

The early androgen-dependent (AD) phase of prostate cancer is dependent on the androgen receptor (AR). However, it is unclear whether AR is fully functional in recurrent prostate cancer after androgen withdrawal. To address this issue we interrogated AR signaling in AD and recurrent prostate cancer xenografts using molecular imaging, chromatin immunoprecipitation, and immunohistochemistry. In the imaging experiments, an adenovirus bearing a two-step transcriptional activation cassette, which amplifies AR-dependent firefly luciferase reporter gene activity, was injected into tumors implanted into severe combined immunodeficiency mice. A charge-coupled device optical imaging system detected the initial loss and then resumption of AR transcriptional activity in D-luciferin-injected mice as tumors transitioned from AD to recurrent growth. The results of chromatin immunoprecipitation and immunohistochemical localization experiments correlated with the Ad two-step transcriptional activation imaging signal. AR localized to the nucleus and bound to the endogenous prostate-specific antigen enhancer in AD tumors but exited the nucleus and dissociated from the enhancer upon castration. However, AR reentered the nucleus and rebound the prostate-specific antigen enhancer as the cancer transitioned into the recurrent phase. Surprisingly, RNA polymerase II and the general factor TFIIB remained bound to the gene throughout the transition. Our data support the concept that AR is fully functional in recurrent cancer and suggest a model by which a poised but largely inactive transcription complex facilitates reactivation by AR at castrate levels of ligand.

Adenoviridae↗

PubMed2003

Reversal of cycloheximide-induced memory disruption by AIT-082 (Neotrofin) is modulated by, but not dependent on, adrenal hormones.

RATIONALE: AIT-082 (Neotrofin), a hypoxanthine derivative, has been shown to improve memory in both animals and humans. In animals, adrenal hormones modulate the efficacy of many memory-enhancing compounds, including piracetam and tacrine (Cognex). OBJECTIVE: To investigate the role of adrenal hormones in the memory-enhancing action of AIT-082. METHODS: Plasma levels of adrenal hormones (corticosterone and aldosterone) in mice were significantly reduced by surgical or chemical (aminoglutethimide) adrenalectomy or significantly elevated by oral administration of corticosterone. The effects of these hormone level manipulations on the memory-enhancing activity of AIT-082 and piracetam were evaluated using a cycloheximide-induced amnesia/passive avoidance model. RESULTS: As previously reported by others, the memory enhancing action of piracetam was abolished by adrenalectomy. In contrast, the memory enhancement by 60 mg/kg AIT-082 (IP) was unaffected. However, a sub-threshold dose of AIT-082 (0.1 mg/kg, IP) that did not improve memory in control animals did improve memory in adrenalectomized animals. These data suggested that, similar to piracetam and tacrine, the memory enhancing action of AIT-082 might be inhibited by high levels of adrenal hormones. As expected, corticosterone (30 and 100 mg/kg) inhibited the action of piracetam, however no dose up to 100 mg/kg corticosterone inhibited the activity of AIT-082. CONCLUSIONS: These data suggest that while AIT-082 function is not dependent on adrenal hormones, it is modulated by them. That memory enhancement by AIT-082 was not inhibited by high plasma corticosterone levels may have positive implications for its clinical utility, given that many Alzheimer's disease patients have elevated plasma cortisol levels.

Adrenalectomy↗

PubMed2003

Transcriptionally targeted gene therapy to detect and treat cancer.

The greatest challenge in cancer treatment is to achieve the highest levels of specificity and efficacy. Cancer gene therapy could be designed specifically to express therapeutic genes to induce cancer cell destruction. Cancer-specific promoters are useful tools to accomplish targeted expression; however, high levels of gene expression are needed to achieve therapeutic efficacy. Incorporating an imaging reporter gene in tandem with the therapeutic gene will allow tangible proof of principle that gene expression occurs at the correct location and at a sufficient level. Gene-based imaging can advance cancer detection and diagnosis. By combining the cancer-targeted imaging and therapeutic strategies, the exciting prospect of a 'one-two punch' to find hidden, disseminated cancer cells and destroy them simultaneously can potentially be realized.

Animals↗

PubMed2003

Optimization of adenoviral vectors to direct highly amplified prostate-specific expression for imaging and gene therapy.

Gene expression-based imaging coupled to gene therapy will permit the prediction of therapeutic outcome. A significant challenge for successful gene therapy is to achieve a high-level of specific gene expression; however, tissue-specific promoters are weak. We postulate that if the weak activity of tissue-specific promoters can be amplified to the levels of strong viral promoters, which have been successful in preclinical scenarios, while retaining specificity, the therapeutic index of gene therapy can be greatly augmented. With this in mind, we developed a two-step transcriptional activation (TSTA) system. In this two-tiered system, a modified prostate-specific antigen promoter was employed to drive a potent synthetic transcriptional activator, GAL4-VP2. This, in turn, activated the expression of a GAL4-dependent reporter or therapeutic gene. Here we demonstrate that recombinant adenoviral vectors (Ads) in which we have incorporated prostate-targeted TSTA expression cassettes retain cell specificity and androgen responsiveness in cell culture and in animal models, as measured by noninvasive optical bioluminescence imaging. We investigated the mechanism of TSTA in different adenoviral configurations. In one configuration, both the activator and the reporter components are inserted into a single Ad (AdTSTA-FL). The activity of AdTSTA-FL exceeds that of a cytomegalovirus promoter-driven vector (AdCMV-FL), while maintaining tissue specificity. When the activator and reporter components are placed in two separate Ads, androgen induction is more robust than for the single AdTSTA-FL. Based on these findings, we hope to refine the TSTA Ads further to improve the efficacy and safety of prostate cancer gene therapy.

Adenoviridae↗

PubMed2002

Visualization of advanced human prostate cancer lesions in living mice by a targeted gene transfer vector and optical imaging.

Non-invasive imaging and transcriptional targeting can improve the safety of therapeutic approaches in cancer. Here we demonstrate the ability to identify metastases in a human-prostate cancer model, employing a prostate-specific adenovirus vector (AdPSE-BC-luc) and a charge-coupled device-imaging system. AdPSE-BC-luc, which expresses firefly luciferase from an enhanced prostate-specific antigen promoter, restricted expression in the liver but produced robust signals in prostate tumors. In fact, expression was higher in advanced, androgen-independent tumors than in androgen-dependent lesions. Repetitive imaging over a three-week period after AdPSE-BC-luc injection into tumor-bearing mice revealed that the virus could locate and illuminate metastases in the lung and spine. Systemic injection of low doses of AdPSE-BC-luc illuminated lung metastasis. These results demonstrate the potential use of a non-invasive imaging modality in therapeutic and diagnostic strategies to manage prostate cancer.

Animals↗

PubMedDate not supplied

Micro-PET/CT monitoring of herpes thymidine kinase suicide gene therapy in a prostate cancer xenograft: the advantage of a cell-specific transcriptional targeting approach.

Cancer gene therapy based on tissue-restricted expression of cytotoxic gene should achieve superior therapeutic index over an unrestricted method. This study compared the therapeutic effects of a highly augmented, prostate-specific gene expression method to a strong constitutive promoter-driven approach. Molecular imaging was coupled to gene therapy to ascertain real-time therapeutic activity. The imaging reporter gene (luciferase) and the cytotoxic gene (herpes simplex thymidine kinase) were delivered by adenoviral vectors injected directly into human prostate tumors grafted in SCID mice. Serial bioluminescence imaging, positron emission tomography, and computed tomography revealed restriction of gene expression to the tumors when prostate-specific vector was employed. In contrast, administration of constitutive active vector resulted in strong signals in the liver. Liver serology, tissue histology, and frail condition of animals confirmed liver toxicity suffered by the constitutive active cohorts, whereas the prostate-targeted group was unaffected. The extent of tumor killing was analyzed by apoptotic staining and human prostate marker (prostate-specific antigen). Overall, the augmented prostate-specific expression system was superior to the constitutive approach in safeguarding against systemic toxicity, while achieving effective tumor killing. Integrating noninvasive imaging into cytotoxic gene therapy will provide a useful strategy to monitor gene expression and therapeutic efficacy in future clinical protocols.

Animals↗