SUMMARY
Multiple myeloma (MM) is an incurable and fatal disease. Reagents such as the proteasome inhibitor,
bortezomib, have significantly extended overall survival but resistance can rapidly arise. To generate therapies
that can provide durable responses, especially in the context of refractory disease, a deeper understanding of
the genetics driving the disease and the evolution of therapy resistance is required. To this end, our team has
performed RNASeq analysis of CD138+ MM cells derived from patients across the disease spectrum (n=815)
and identified that Unc-51 Like Kinase-3 (ULK3) is highly expressed in newly diagnosed and refractory MM. Our
emerging studies demonstrate a novel role for ULK3 in regulating autophagy in MM, a key program that sustains
cell survival under times of stress and has been implicated as a major mechanism of proteasome inhibitor
resistance. Of note, MM is known to be highly dependent on autophagy. Currently, specific ULK3 inhibitors are
lacking. As a strategy to overcome resistance to single agents, our team has focused on the development of
novel inhibitors such as SG3, that target multiple kinases including ULK3 (EC50 90nM) as well bromodomain
protein 4 (BRD4)(3). BRD4 is a known driver of MYC and analysis of our patient RNASeq data again reveals
increased BRD4 expression in refractory MM. The BRD4 inhibitor, JQ1, effectively impairs the tumorigenic
potential of MM but resistance has also been noted with this reagent. Our agent SG3 inhibits BRD4 activity in
the nM range (27 nM) similar to that of JQ1 (20 nM), and consistent with our ULK3 studies, SG3 treatment rapidly
inhibits autophagy in MM cells. In vivo, we found SG3 significantly inhibits MM progression and induced bone
disease. Excitingly, our team has already developed a 2nd generation SG3 derivative coined MA9 that is just as
effective as SG3 in vitro and in vivo but has superior stability. We also show that MA9 can resensitize proteosome
inhibitor resistant MM cells to bortezomib. The central hypothesis of this proposal is that ULK3 is a key regulator
of autophagy in MM and represents a novel target for treatment of refractory disease and it will be tested
with three Aims. Aim 1 will take a genetic approach and delete ULK3 to its role in regulating autophagy in MM
as well in the progression of the disease in vivo using clinically relevant animal models. Aim 2 will interrogate
the impact of our dual ULK3/BRD4 compound, MA9, in MM progression and overall survival in vivo compared to
JQ1 and the autophagy inhibitor, chloroquine (CQ). Aim 3 will examine the efficacy of MA9 for the treatment of
CD138+ MM isolated from naïve and refractory patients using a novel ex vivo high throughput platform developed
at Moffitt. Here, we will also define the contribution of ULK3 in mediating proteasome inhibitor resistance using
bortezomib resistant MM cell lines. Importantly, in each Aim, we will also determine the role of ULK3 in MM
induced bone destruction - a clinically significant aspect of this disease. We expect our anticipated results will
provide strong rationale for the translation of our novel dual ULK3/BRD4 inhibitors to the clinic.