Tissue-specific promoters active in CD44+CD24-/low breast cancer cells.

It has been proposed that human tumors contain stem cells that have a central role in tumor initiation and posttreatment relapse. Putative breast cancer stem cells may reside in the CD44(+)CD24(-/low) population. Oncolytic adenoviruses are attractive for killing of these cells because they enter through infection and are therefore not susceptible to active and passive mechanisms that render stem cells resistant to many drugs. Although adenoviruses have been quite safe in cancer trials, preclinical work suggests that toxicity may eventually be possible with more active agents. Therefore, restriction of virus replication to target tissues with tissues-specific promoters is appealing for improving safety and can be achieved without loss of efficacy. We extracted CD44(+)CD24(-/low) cells from pleural effusions of breast cancer patients and found that modification of adenovirus type 5 tropism with the serotype 3 knob increased gene delivery to CD44(+)CD24(-/low) cells. alpha-Lactalbumin, cyclo-oxygenase 2, telomerase, and multidrug resistance protein promoters were studied for activity in CD44(+)CD24(-/low) cells, and a panel of oncolytic viruses was subsequently constructed. Each virus featured 5/3 chimerism of the fiber and a promoter controlling expression of E1A, which was also deleted in the Rb binding domain for additional tumor selectivity. Cell killing assays identified Ad5/3-cox2L-d24 and Ad5/3-mdr-d24 as the most active agents, and these viruses were able to completely eradicate CD44(+)CD24(-/low) cells in vitro. In vivo, these viruses had significant antitumor activity in CD44(+)CD24(-/low)-derived tumors. These findings may have relevance for elimination of cancer stem cells in humans.

Combining high selectivity of replication via CXCR4 promoter with fiber chimerism for effective adenoviral oncolysis in breast cancer.

Conditionally replicative adenoviruses (CRAds) represent novel therapeutic agents that have been recently applied in the context of breast cancer therapy. However, deficiencies in the ability of the adenovirus to infect target tumor cells and to specifically replicate within the tumor target represent key deficiencies preventing the realization of the full potential of this therapeutic approach. Minimal expression of the adenovirus serotype 5 (Ad5) receptor CAR (coxsackie and adenovirus receptor) on breast cancer cells represents a major limitation for Ad5-based virotherapy. Genetic fiber chimerism is a method to alter the tropism of Ad5-based CRAds to achieve CAR-independent infectivity of tumor cells. Here, we describe the use of a CRAd with cancer specific transcriptional control of the essential Ad5 E1A gene using the human CXCR4 gene promoter. We further modified the fiber protein of this agent by switching the knob domain with that of the adenovirus serotype 3. The oncolytic activity of this 5/3 fiber-modified CRAd was studied in breast cancer cell lines, primary breast cancer and human liver tissue slices from patients, and in a xenograft breast cancer mouse model. This infectivity enhanced CRAd agent showed improved replication and killing in breast cancer cells in vitro and in vivo with a remarkable specificity profile that was strongly attenuated in nonbreast cancer cells, as well as in normal human breast and liver tissues. In conclusion, utilization of a CRAd that combined infectivity enhancement strategies and transcriptional targeting improved the CRAd-based antineoplastic effects for breast cancer therapy.

Triple-targeted oncolytic adenoviruses featuring the cox2 promoter, E1A transcomplementation, and serotype chimerism for enhanced selectivity for ovarian cancer cells.

Conditionally replicating adenoviruses (CRAd's) feature selective replication in and killing of tumor cells. Initial clinical studies with relatively attenuated early generation agents have resulted in promising safety and efficacy data. Nevertheless, increased specificity may be advantageous for an emerging generation of infectivity-enhanced CRAd's. Further, increased specificity could translate into a larger tolerated dose. An approach for increasing specificity is dual control of E1A expression. We constructed six CRAd's featuring two variants of the cyclo-oxygenase 2 (cox2) promoter, combined with three versions of E1A. Transcriptional targeting was supplemented with transductional targeting utilizing the serotype 3 knob. In vivo and in vitro results suggest that cox2 can be utilized for enhancing the specificity of E1A deletion mutants and that combination with the Delta24 mutation increases specificity without reducing potency. Combination with Delta2-Delta24 was specific but somewhat attenuated. The promoter variants behaved similarly, although the longer 1,554-bp version displayed a trend for improved specificity. Transcriptional modifications were compatible with transductional targeting and resulted in up to 100,000-fold increase in the therapeutic window for Ad5/3cox2Ld24 vs wild-type adenovirus. Thus, the proposed triple-targeting strategy may be useful for increasing the safety and efficacy of adenoviral gene therapy for ovarian cancer.

A new targeting approach for breast cancer gene therapy using the heparanase promoter.

Gene therapy with adenoviral (Ad) vectors is a promising new approach in the treatment of cancer. Strategies to restrict adenoviral-mediated transgene expression are important to avoid gene transfer into normal cells. Heparanase (HPR) is overexpressed in breast cancer but downregulated in differentiated normal tissue. Expression of the HPR gene was evaluated in breast cancer cells. Biodistribution and liver tropism was evaluated in a mouse model. HPR is highly expressed in breast cancer tissue. The HPR promoter retained its fidelity in an adenovirus context and was activated in breast cancer cells but showed low activity in normal breast cells and the murine liver. We conclude that the HPR pathway is a promising target for the development of breast cancer directed gene therapy strategies.

In vivo cervical cancer growth inhibition by genetically engineered cytotoxic T cells.

PURPOSE: The CD44 v7/8 splice variant that is frequently expressed in cervical carcinoma and rarely expressed in normal tissues displays promising properties as a target antigen for cancer immune therapy. In this study, cytotoxic T lymphocytes (CTLs) were genetically engineered to gain CD44v7/8 target specificity. METHODS: Clone 96 (Cl96), an established murine cytotoxic T-cell line, and naïve murine T cells were retrovirally transduced with a fusion gene construct encoding for the single chain fragment scFv of the monoclonal antibody VFF17 and for the zeta chain of the T-cell receptor (TCR). The therapeutic potential of genetically engineered T cells was tested in vitro and in vivo. RESULTS: Surface expression of the chimeric TCR on infected Cl96 and naïve T cells was shown by FACS analysis. CD44v7/8-positive target cells were efficiently lysed by transduced Cl96 and naïve T cells, demonstrating the functionality and specificity of the chimeric TCR. In a xenograft BALB/c mouse model, efficient growth retardation of CD44v7/8-positive tumours was mediated by genetically engineered Cl96(VFF17)cyYZ cells. CONCLUSIONS: We were able to reprogramme the target specificity of recombinant Cl96 and naïve CTLs resulting in efficient cytolysis of CD44v7/8-positive cervical cancer cells. High transduction rates and the specific cytolysis of CD44v7/8-redirected CTLs are promising tools for an immune gene therapy approach for advanced cervical cancer.

Evaluation of a selectively oncolytic adenovirus for local and systemic treatment of cervical cancer.

Treatment options for disseminated cervical cancer remain inadequate. Here, we investigated a strategy featuring Ad5-Delta 24 RGD, an oncolytic adenovirus replication-competent selectively in cells defective in the Rb-p16 pathway, such as most cervical cancer cells. The viral fiber contains an alpha(v)beta(3) and alpha(v)beta(5) integrin-binding RGD-4C motif, allowing coxsackie-adenovirus receptor-independent infection. These integrins have been reported to be frequently upregulated in cervical cancer. Oncolysis of cervical cancer cells was similar to a wild-type control in vitro. In an animal model of cervical cancer, the therapeutic efficacy of Ad5-Delta 24 RGD could be demonstrated for both intratumoral and intravenous application routes. Biodistribution was determined following intravenous administration to mice. Further preclinical safety data were obtained by demonstrating lack of replication of the agent in human peripheral blood mononuclear cells. These results suggest that Ad5-Delta 24 RGD could be useful for local or systemic treatment of cervical cancer in patients with disease resistant to currently available modalities.