Synergistic molecular vulnerabilities enhancing hypomethylating agents in myeloid malignancies have remained elusive. RNA-interference drug modifier screens identified antiapoptotic BCL-2 family members as potent 5-Azacytidine-sensitizing targets. In further dissecting BCL-XL, BCL-2 and MCL-1 contribution to 5-Azacytidine activity, siRNA silencing of BCL-XL and MCL-1, but not BCL-2, exhibited variable synergy with 5-Azacytidine in vitro. The BCL-XL, BCL-2 and BCL-w inhibitor ABT-737 sensitized most cell lines more potently compared with the selective BCL-2 inhibitor ABT-199, which synergized with 5-Azacytidine mostly at higher doses. Ex vivo, ABT-737 enhanced 5-Azacytidine activity across primary AML, MDS and MPN specimens. Protein levels of BCL-XL, BCL-2 and MCL-1 in 577 AML patient samples showed overlapping expression across AML FAB subtypes and heterogeneous expression within subtypes, further supporting a concept of dual/multiple BCL-2 family member targeting consistent with RNAi and pharmacologic results. Consequently, silencing of MCL-1 and BCL-XL increased the activity of ABT-199. Functional interrogation of BCL-2 family proteins by BH3 profiling performed on patient samples significantly discriminated clinical response versus resistance to 5-Azacytidine-based therapies. On the basis of these results, we propose a clinical trial of navitoclax (clinical-grade ABT-737) combined with 5-Azacytidine in myeloid malignancies, as well as to prospectively validate BH3 profiling in predicting 5-Azacytidine response.

No abstract

Summary. Background: Adenoviral-based methods of gene therapy have been ineffective at providing sustained factor (F)VIII expression in outbred populations of large animal hemophilic models primarily due to the immunogenicity of these vectors. Improvements have been made in vector design leading to the development of the helper-dependent adenoviral (HD) system. Unfortunately, it remains unclear whether these modi®cations are suf®cient to circumvent the induction of inhibitor formation associated with adenoviral gene transfer. Objective: To develop an HD vector capable of mediating sustained FVIII expression and to determine the variables that in¯uence inhibitor development. Methods: HD vectors were constructed encoding the canine FVIII B-domain deleted transgene under the control of either the cytomegalovirus (CMV) promoter or a tissue-restricted hybrid element consisting of ®ve HNF-1 binding sites, located upstream of the human FVIII proximal promoter. Inbred and outbred populations of hemophilic mice were treated, and monitored for vector-induced toxicity, therapeutic ef®cacy, and inhibitor formation. Results: When HD vectors utilizing the CMV promoter were administered, all hemophilic mice developed high levels of FVIII inhibitors. In contrast, vectors under the control of the HNF/FVIII element were capable of achieving sustained elevations of FVIII for over 6 months. Strain-speci®c differences were also observed, with outbred animals showing a greater propensity towards inhibitor development in response to treatment. Conclusions: HD vectors can be used to provide long-term FVIII expression in hemophilic animals, but treatment outcome and the induction of inhibitors is dependent on a number of variables including the transgene promoter, the vector dose, and the genetic background of the host.

The ability to target specific tissues is important in many applications of gene therapy. In this respect, a disadvantage of adenoviral vectors is the relative lack of specificity with which they transduce cells. One approach to overcome this is to express the therapeutic gene under the control of a tissue-specific promoter. However, the specificity and activity of these promoters may be altered by adenoviral sequences in the vector backbone. In contrast, helper-dependent adenoviral (HDAd) vectors [Parks, R.J., Chen, L., Anton, M., Sankar, U., Rudnicki, M.A., and Graham, F.L. (1996). Proc. Natl. Acad. Sci. U.S.A. 93, 13565-13570] are almost completely devoid of adenovirus sequences, and this may preserve the specificity of these heterologous promoters. We have compared HDAd and first-generation adenoviral (FGAd) vectors with respect to tissue-specific expression from prostate-specific antigen (PSA) or tyrosinase promoters/enhancers. A PSA-positive cell line (LNCaP) and a panel of PSA-negative cell lines were infected with HDAd vectors expressing luciferase under the control of three different kinds of PSA promoter/enhancer constructs. The results showed that these PSA promoter/enhancer cassettes in HDAd vectors maintained strict tissue-specific expression, but lost specificity when expressed from FGAd vectors. Similar results were observed with tyrosinase promoter-carrying vectors, except that the tyrosinase promoter retained a small degree of tissue specificity in FGAd vectors. Insertion of a murine cytomegalovirus immediate-early gene promoter-beta-galactosidase (MCMV-lacZ)-expressing cassette into a second site in the HDAd vector backbone significantly impaired the tissue specificity of the PSA and tyrosinase promoters. These results indicate that HDAd vectors are superior to FGAd vectors in their ability to maintain high levels of tissue-specific expression from PSA and tyrosinase promoters/enhancers. They also suggest that tissue-specific expression can be influenced not only by Ad sequences, but also by other viral and/or strong constitutive promoter/enhancers (such as the MCMV promoter) in the vector backbone.

Expression of secretoglobin family 2A member 2 (SCGB2A2, also known as mammaglobin-1) has been detected in a high percentage of primary and metastatic breast tumors, to a lesser extent in normal breast, but not in other normal tissues. Plasmid transfection studies in our lab and others, however, were unable to identify the genetic elements regulating this specificity. Here we demonstrate that a 25-kb DNA fragment derived from the human SCGB2A2 gene upstream of the protein coding sequence was highly active and preferentially expressed in breast cancer cells when introduced via a helper-dependent adenoviral (HDAd) vector. HDAd delivery was selected for its high cloning capacity, its high efficiency of gene transfer, and the absence of cis-acting viral sequences that can potentially interfere with specificity of the inserted promoters. A series of vectors with deletions in the 25-kb fragment was constructed to identify important regulatory regions of the SCGB2A2 promoter. We have determined that elements controlling the specificity of expression reside within the first 345 bp upstream of the coding sequence. In addition, we identified a strong enhancer several kilobases upstream of this minimal promoter. We suggest that the SCGB2A2 promoter/enhancer should be particularly advantageous for gene therapy protocols involving oncolytic viruses or toxic gene transfer via adenovectors to mammary tumors.