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.