Therapeutic value of a BET bromodomain inhibitor in c-Jun~Fra-2hep mice
The therapeutic potential of interfering pharmacologically with c-Myc expression and activity was tested in c-Jun~Fra-2hep mice employing JQ-1, a BET bromodomain inhibitor widely used in basic research (48, 49). When c-Jun~Fra-2 was induced for 2 months prior to 4 weeks of treatment (Suppl. Figure 6A), JQ-1 decreased hepatic c-Myc protein expression (Figure 6A), while c-Jun~Fra-2 was not affected (Figure 6A, Suppl. Figure 6B). Hepatic c-myc mRNA was unchanged, when comparing JQ-1- to vehicle-treated c-Jun~Fra-2hep mice, while mRNA expression of foxm1 , ccna2 and a panel of c-Myc target genes was decreased (Suppl. Figure 6C). Serum AFP, ALT and AST were ameliorated in JQ-1 treated c-Jun~Fra-2hep mice, while ALP remained high (Suppl. Figure 6D-E). Finally, Ki67, Cyclin D1 and γH2AX indexes were reduced upon JQ1 treatment (Suppl. Figure 6F), consistent with a potential beneficial effect of JQ1 on the pre-neoplastic events occurring in c-Jun~Fra-2hep mice.
Next, 6 c-Jun~Fra-2hep mice were randomized at 9 months into 2 treatment groups and followed during 8 weeks to assess the effect of JQ1 on already established tumors (Suppl. Figure 6A). At end point necropsy, most JQ-1-treated c-Jun~Fra-2hep mice had smaller and fewer liver nodules compared to their vehicle-treated counterparts (Figure 6B). Serum AFP rapidly decreased in treated c-Jun~Fra-2hep mice and remained stable until end point, although slightly higher than controls (Figure 6C, Suppl. Table 1B). ALT and AST were still high at end point in JQ1-treated c-Jun~Fra-2hep mice, but unlike vehicle-treated counterparts, liver transaminases did not increase over time (Suppl. Figure 6G). In contrast, ALP slightly decreased, but remained comparable between treatment arms (Suppl. Figure 6G). Ultrasound follow up revealed that JQ-1 had a tumor-static effect: while tumors in vehicle-treated c-Jun~Fra-2hep mice increased in size over time, 6 out of 7 tumors in JQ-1-treated mice remained relatively stable and no new tumors were detected (Figure 6D, Suppl. Table 1B). qRT-PCR analyses comparing JQ-1-responsive to vehicle-treated tumors revealed decreased expression of c-myc, along with foxm1and other cell cycle- HCC-, immune- and fibrosis-related transcripts, while c-Jun~Fra-2 was not affected (Figure 6E, Suppl. Figure 6H). Furthermore, we combined JQ1 with Sorafenib, a receptor tyrosine kinase inhibitor widely used to treat HCC. Sorafenib alone had no noticeable effect on tumor size after 8 weeks of treatment (Figure 6F), consistent with reports indicating Sorafenib resistance in HCC with high JUN/JNK (50, 51). JQ1 also slowed liver tumor growth in c-Jun~Fra-2hep mice treated with when co-administered with Sorafenib (Figure 6F) and reduced circulating AFP and ALT at endpoint (Figure 6G). Taken together, these results indicate that BET bromodomain inhibitors should be considered for HCC therapy, particularly in patients with high AP-1/Myc expression.