B-cell lymphoma 2 (Bcl-2) is an antiapoptotic
protein that is overexpressed in
head and neck squamous cell carcinomas, which has been implicated in development of radio- and chemoresistance. Small molecule inhibitors such as
AT-101 (a BH3-mimetic
drug) have been developed to inhibit the antiapoptotic activity of Bcl-2
proteins, which proved effective in restoring radio- and chemo-sensitivity in
head and neck cancer cells. However, high doses of
AT-101 are associated with gastrointestinal, hepatic, and fertility side effects, which prompted the search for other Bcl-2 inhibitors.
Short interfering RNA (
siRNA) proved to inhibit antiapoptotic Bcl-2
protein expression and trigger
cancer cell death. However, transforming
siRNA molecules into a viable
therapy remains a challenge due to the lack of efficient and biocompatible carriers. We report the development of degradable star-shaped
polymers that proved to condense anti-Bcl-2
siRNA into "smart" pH-sensitive and membrane-destabilizing particles that shuttle their cargo past the endosomal membrane and into the cytoplasm of
head and neck cancer cells. Results show that "smart" anti-Bcl-2 particles reduced the
mRNA and
protein levels of antiapoptotic Bcl-2
protein in UM-SCC-17B
cancer cells by 50-60% and 65-75%, respectively. Results also show that combining "smart" anti-Bcl-2 particles with the IC25 of
AT-101 (inhibitory concentration responsible for killing 25% of the cells) synergistically inhibits
cancer cell proliferation and increases cell apoptosis, which reduce the survival of UM-SCC-17B
cancer cells compared to treatment with
AT-101 alone. Results indicate the therapeutic benefit of combining
siRNA-mediated knockdown of antiapoptotic Bcl-2
protein expression with low doses of
AT-101 for inhibiting the growth of
head and neck cancer cells.