Checkpoint kinase inhibition in prostate cancer cells resistant to poly ADP-ribose polymerase inhibitors.

150 Background: Poly ADP-ribose polymerase inhibitors (PARPi) have shown promise in the treatment of metastatic castration-resistant prostate cancer patients with DNA damage response defects . The phase 3 PROfound trial showed olaparib delayed the time to radiographic progression or death as compared with abiraterone or enzalutamide. In addition to olaparib, three other PARPi are in Phase 3 trials in prostate cancer (PC): rucaparib, talazoparib, and niraparib. Despite responses, resistance is common and treatment options for PARPi-resistant patients are limited. In this study, we observed de novo activation of checkpoint kinases (CHEK) in talazoparib-resistant (TR) PC cells. Therefore, we hypothesized that targeting CHEK may mitigate resistance to PARPi in PC. Methods: We developed TR human prostate cancer PC3 (low BRCA2 protein due to heterozygous deletion of BRCA2) cells. We performed phosphoproteomic analysis to identify possible mechanisms of talazoparib resistance in PC3 cells and validated the results with Western blot. Results: TR-PC3 cells proliferated slower and had a significant increase in the phosphorylation of CHEK2 compared to parental (p) PC3. Treatment with a CHEK2-selective inhibitor, CCT241533, did not affect cell growth in TR-PC3 cells. Conversely, treatment with a CHEK 1/2 inhibitor, prexasertib, led to significant cell growth inhibition in TR-PC3 at a much lower IG 50% concentration compared to pPC3. RNAi-mediated knockdown validated the superior efficacy of combined CHEK1 and CHEK2 inhibition since this combination produced the greatest cell growth inhibition seen in both TR-PC3 and de novo PARPi-resistant p22RV1. Treatment of pPC-3 and p22RV1 with combinations of talazoparib and prexasertib showed greater cell growth inhibition compared to either drug alone. Conclusions: Resistance to PARPi in PC cells with deletion of BRCA2 may potentially be overcome with CHEK inhibition. Moreover, our preliminary data suggested that the effect of PARPi and CHEK inhibitors on PARPi/CHEK inhibitor-naïve PC cells was greatest when used together, indicating that patients with PC may experience greatest anti-tumor activity of the two drugs when they are used in combination.

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MnTE-2-PyP Suppresses Prostate Cancer Cell Growth via H2O2 Production

Antioxidants ◽

10.3390/antiox9060490 ◽

2020 ◽

Vol 9 (6) ◽

pp. 490

Author(s):

Yuxiang Zhu ◽

Elizabeth A. Kosmacek ◽

Arpita Chatterjee ◽

Rebecca E. Oberley-Deegan

Keyword(s):

Prostate Cancer ◽

Cell Cycle ◽

Cell Death ◽

Cell Growth ◽

Growth Inhibition ◽

Cell Cycle Progression ◽

Cell Growth Inhibition ◽

Lncap Cells ◽

Cycle Progression ◽

Pc3 Cells

Prostate cancer patients are often treated with radiotherapy. MnTE-2-PyP, a superoxide dismutase (SOD) mimic, is a known radioprotector of normal tissues. Our recent work demonstrated that MnTE-2-PyP also inhibits prostate cancer progression with radiotherapy; however, the mechanisms remain unclear. In this study, we identified that MnTE-2-PyP-induced intracellular H2O2 levels are critical in inhibiting the growth of PC3 and LNCaP cells, but the increased H2O2 levels affected the two cancer cells differently. In PC3 cells, many proteins were thiol oxidized with MnTE-2-PyP treatment, including Ser/Thr protein phosphatase 1 beta catalytic subunit (PP1CB). This resulted in reduced PP1CB activity; however, overall cell cycle progression was not altered, so this is not the main mechanism of PC3 cell growth inhibition. High H2O2 levels by MnTE-2-PyP treatment induced nuclear fragmentation, which could be synergistically enhanced with radiotherapy. In LNCaP cells, thiol oxidation by MnTE-2-PyP treatment was not observed previously and, similarly to PC3 cells, there was no effect of MnTE-2-PyP treatment on cell cycle progression. However, in LNCaP cells, MnTE-2-PyP caused an increase in low RNA population and sub-G1 population of cells, which indicates that MnTE-2-PyP treatment may cause cellular quiescence or direct cancer cell death. The protein oxidative modifications and mitotic catastrophes caused by MnTE-2-PyP may be the major contributors to cell growth inhibition in PC3 cells, while in LNCaP cells, tumor cell quiescence or cell death appears to be major factors in MnTE-2-PyP-induced growth inhibition.

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