| Summary: | The human positive coactivator 4 (PC4) was originally identified as a multi-functional cofactor capable of mediating transcription activation by diverse gene- and tissue-specific activators. Recent studies suggest that PC4 might also function as a novel cancer biomarker and therapeutic target for different types of cancers. siRNA knockdown studies indicated that down-regulation of PC4 expression could inhibit tumorigeneicity of A549 non-small cell lung cancer tumor model in nude mice. Here we show that AG-1031, a small molecule identified by high throughput screening, can inhibit the double-stranded DNA binding activity of PC4, more effectively than its single-stranded DNA binding activity. AG-1031 also specifically inhibited PC4-dependent transcriptional activation in vitro using purified transcription factors. AG-1031 inhibited proliferation of several cultured cell lines derived from non-small cell lung cancers (NSCLC) and growth of tumors that formed from A549 cell xenografts in immuno-compromised mice. Moreover, pre-injection of AG-1031 in these mice not only reduced tumor size, but also prevented tumor formation in 20% of the animals. AG-1031 treated A549 cells and tumors from AG-1031 treated animals showed a significant decrease in the levels of both PC4 and VEGFC, a key mediator of angiogenesis in cancer. On the other hand, all tested mice remained constant weight during animal trials. These results demonstrated that AG-1031 could be a potential therapy for PC4-positive NSCLC.
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