Radiotherapy-induced Immune Response Enhanced by Selective HDAC6 Inhibition

Radiotherapy is a curative cancer treatment modality that imparts damage to cellular DNA, induces immunogenic cell death, and activates antitumor immunity. Despite the radiotherapy-induced direct antitumor effect seen within the treated volume, accumulating evidence indicates activation of innate antitumor immunity. Acute proinflammatory responses mediated by anticancer M1 macrophages are observed in the immediate aftermath following radiotherapy. However, after a few days, these M1 macrophages are converted to anti-inflammatory and pro-cancer M2 phenotype, leading to cancer resistance and underlying potential tumor relapse. Histone deacetylase 6 (HDAC6) plays a crucial role in regulating macrophage polarization and innate immune responses. Here, we report targeting HDAC6 function with a novel selective inhibitor (SP-2-225) as a potential therapeutic candidate for combination therapy with radiotherapy. This resulted in decreased tumor growth and enhanced M1/M2 ratio of infiltrating macrophages within tumors. These observations support the use of selective HDAC6 inhibitors to improve antitumor immune responses and prevent tumor relapse after radiotherapy.

Abstract 5180: Profiling signaling pathways in chronic lymphocytic leukemia using reverse phase protein array

Chronic lymphocytic leukemia (CLL), the most common adult leukemia remains incurable despite advancements in treatment regimens over the past decades. B-cell receptor (BCR) mediated signaling is well recognized for its central role in the pathogenesis of CLL. Small molecular inhibitors targeting BCR signaling pathway and its downstream PI3K/AKT pathway are currently investigated in clinical trials because of their ability to induce apoptosis or block protein interactions in CLL cells. However, variability in pathological conditions and genetic aberrations render these small molecule inhibitors not equally effective in all CLL patients and highlights the need for individualized treatment options. In this pilot study, we analyzed differential protein expression of 18 CLL patient and 6 normal B-cell samples using reverse phase protein array (RPPA). RPPA enables us to study the proteome as well as phospho-proteome of CLL samples. When probed with 167 monoclonal antibodies RPPA revealed distinct protein expression patterns between CLL and normal B-cells. RPPA data was analyzed by unsupervised hierarchical clustering and CLL patient samples were clearly separated from normal B-cell samples. Proteins of BCR and downstream PI3K/AKT pathway such as SYK, LCK, PDK1, AKT, RICTOR, mTOR, TSC1, TSC2 and p70S6K were all upregulated in CLL samples. Harvesting the full potential of RPPA to study phosphorylation changes, we observed an increase in PI3K pathway activating signals such as PDK1-pS241, p70S6K-pT389, 4EBP1-pS65 and 4EBP1-pT70 suggesting a cell proliferative mechanism. There was also decrease in inhibitory signals such as RICTOR-pT1135. Pro-apoptotic factors BID, BAX, Caspase 7-cleaved and ANXA1 were poorly expressed in CLL samples compared to normal B-cells suggesting a defect in apoptosis mechanism is predominant in CLL samples. As previously reported, we have seen overexpression of anti-apoptotic factor BCL2. BIM isoforms, BIM-EL and BIM-L were overexpressed in CLL compared to normal samples; however the ratio of BIM-EL to BIM-L was higher in normal B cells compared to CLL cells. For the first time, we generated a comprehensive BCR protein and phospho-protein expression profiles in primary CLL samples. Our results reveal novel anti-apoptosis and cell proliferative mechanisms in CLL and potentially identified new therapeutic targets in CLL.

Citation Format: Satish Kumar R. Noonepalle, Austin Shull, Farrukh T. Awan, Leah Pei, Zhiyong Ding, Huidong Shi. Profiling signaling pathways in chronic lymphocytic leukemia using reverse phase protein array. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5180. doi:10.1158/1538-7445.AM2014-5180