Nucleic Acid Therapeutics: State of the Art and Future Prospects

Cyclodextrins as eminent constituents in nanoarchitectonics for drug delivery systems

Cyclodextrins have been widely employed for drug delivery systems (DDSs) in which drugs are selectively delivered to a target site in the body. Recent interest has been focused on the construction of cyclodextrin-based nanoarchitectures that show sophisticated DDS functions. These nanoarchitectures are precisely fabricated based on three important features of cyclodextrins, namely (1) the preorganized three-dimensional molecular structure of nanometer size, (2) the easy chemical modification to introduce functional groups, and (3) the formation of dynamic inclusion complexes with various guests in water. With the use of photoirradiation, drugs are released from cyclodextrin-based nanoarchitectures at designated timing. Alternatively, therapeutic nucleic acids are stably protected in the nanoarchitectures and delivered to the target site. The efficient delivery of the CRISPR-Cas9 system for gene editing was also successful. Even more complicated nanoarchitectures can be designed for sophisticated DDSs. Cyclodextrin-based nanoarchitectures are highly promising for future applications in medicine, pharmaceutics, and other relevant fields.

A peptide conjugate of vitamin E succinate targets breast cancer cells with high ErbB2 expression

Overexpression of erbB2 is associated with resistance to apoptosis. We explored whether high level of erbB2 expression by cancer cells allows their targeting using an erbB2-binding peptide (LTVSPWY) attached to the proapoptotic alpha-tocopheryl succinate (alpha-TOS). Treating erbB2-low or erbB2-high cells with alpha-TOS induced similar levels of apoptosis, whereas alpha-TOS-LTVSPWY induced greater levels of apoptosis in erbB2-high cells. alpha-TOS rapidly accumulated in erbB2-high cells exposed to alpha-TOS-LTVSPWY. The extent of apoptosis induced in erbB2-high cells by alpha-TOS-LTVSPWY was suppressed by erbB2 RNA interference as well as by inhibition of either endocytotic or lysosomal function. alpha-TOS-LTVSPWY reduced erbB2-high breast carcinomas in FVB/N c-neu transgenic mice. We conclude that a conjugate of a peptide targeting alpha-TOS to erbB2-overexpressing cancer cells induces rapid apoptosis and efficiently suppresses erbB2-positive breast tumors.

A novel antisense oligonucleotide inhibiting several antiapoptotic Bcl-2 family members induces apoptosis and enhances chemosensitivity in androgen-independent human prostate cancer PC3 cells

Bcl-2 and Bcl-xL are associated with treatment resistance and progression in many cancers, including prostate cancer. The objective of this study was to determine whether a novel bispecific antisense oligonucleotide targeting both Bcl-2 and Bcl-xL induces apoptosis and enhances chemosensitivity in androgen-independent PC3 prostate cancer cells. An antisense oligonucleotide with complete sequence identity to Bcl-2 and three-base mismatches to Bcl-xL selected from five antisense oligonucleotides targeting various regions with high homology between Bcl-2 and Bcl-xL was found to be the most potent inhibitor of both Bcl-2 and Bcl-xL expression in PC3 cells. This selected Bcl-2/Bcl-xL bispecific antisense oligonucleotide reduced mRNA and protein levels in a dose-dependent manner, reducing Bcl-2 and Bcl-xL protein levels to 12% and 19%, respectively. Interestingly, Mcl-1 was down-regulated as well, although levels of Bax, Bad, or Bak were not altered after treatment with this bispecific antisense oligonucleotide. Indirect down-regulation of inhibitor of apoptosis (IAP) family, including XIAP, cIAP-1 and cIAP-2, via second mitochondria-derived activator of caspases was also observed after bispecific antisense oligonucleotide treatment. Executioner caspase-3, caspase-6, and caspase-7 were shown to be involved in apoptosis induced by bispecific antisense oligonucleotide. This Bcl-2/Bcl-xL bispecific antisense oligonucleotide also enhanced paclitaxel chemosensitivity in PC3 cells, reducing the IC50 of paclitaxel by >90%. These findings illustrate that combined suppression of antiapoptotic Bcl-2 family members using this antisense oligonucleotide could be an attractive strategy for inhibiting cancer progression through alteration of the apoptotic rheostat in androgen-independent prostate cancer.

Oblimersen sodium (Genasense bcl-2 antisense oligonucleotide): a rational therapeutic to enhance apoptosis in therapy of lung cancer

Bcl-2 protein inhibits apoptosis and confers resistance to treatment with traditional cytotoxic chemotherapy, radiotherapy, and monoclonal antibodies. Oblimersen sodium is an antisense oligonucleotide compound designed to specifically bind to human bcl-2 mRNA, resulting in catalytic degradation of bcl-2 mRNA and subsequent decrease in bcl-2 protein translation. Both small cell and non-small cell lung cancer show baseline and inducible expression of bcl-2, which may contribute to resistance to therapy. Preclinical studies have shown that combining bcl-2 antisense with chemotherapy improves antitumor response, increases apoptosis of tumor cells, and increases survival. Preliminary data from a large international randomized trial in melanoma show a trend toward increased survival and significantly improved response rates and response duration when oblimersen is added to dacarbazine. Phase I studies in small cell lung cancer patients demonstrate that oblimersen can be combined with paclitaxel or carboplatin and etoposide. The combination of docetaxel and oblimersen has been shown to be feasible in Phase I studies and is currently undergoing evaluation in comparison with docetaxel alone as first-line salvage therapy in patients refractory or relapsed after one prior chemotherapy regimen. Enhancement of the efficacy of anticancer treatments with oblimersen bcl-2 antisense therapy represents a promising new apoptosis-modulating strategy.

Myb targeted therapeutics for the treatment of human malignancies

For the past several years, we have been engaged in developing a therapeutically effective strategy for disrupting gene function with reverse complementary, or so called 'antisense', oligodeoxynucleotides (ODN). This pursuit has focused on finding appropriate diseases in which to apply this approach, and suitable gene targets. Of the genes that we have targeted for disruption using the antisense ODN strategy (Clevenger et al., 1995; Gewirtz and Calabretta, 1988; Ratajczak et al., 1992c; Small et al., 1994) one that has been of particular interest, and one where therapeutically motivated disruptions are now in clinical trial, is the myb gene (reviewed in Lyon et al., 1994). These trials involve treatment of human leukemias. These diseases are a logical choice for developing oncogene targeted therapies because of easy access to tissues, and the abundance of knowledge about the cell and molecular biology of these diseases. Nevertheless, as will be touched on below, other malignancies have also been examined as models for Myb targeted therapy with some surprisingly encouraging results. Finally, while we have focused our efforts on the ODN strategy, I will allude briefly to other strategies for disrupting Myb function with therapeutic intent.

Reassessing the role of C-MYB in tumorigenesis

Hematopoietic tumors in both humans and mice frequently up-regulate expression of the c-myb gene, but it is unclear whether this is a cause or a consequence of the leukemic state. Recent results placing super-activation of the c-Myb protein at the bottom of a kinase-activated signal transduction pathway indicate that it may be a downstream effector of transformation induced by other oncogenes. The relationship between c-Myb and the serine-threonine kinase pim-1, its immediate activator, is discussed, together with the possibility that c-Myb, like pim-1, may be able to synergize with c-Myc to induce tumors.