Senolytic compounds control a distinct fate of androgen receptor agonist- and antagonist-induced cellular senescent LNCaP prostate cancer cells

Abstract

Background: The benefit of inducing cellular senescence as a tumor suppressive strategy remains questionable due to the senescence-associated secretory phenotype. Hence, studies and development of senolytic compounds that induce cell death in senescent cells have recently emerged. Senescent cells are hypothesized to exhibit different upregulated pro-survival/anti-apoptotic networks depending on the senescent inducers. This might limit the effect of a particular senolytic compound that targets rather only a specific pathway. Interestingly, cellular senescence in prostate cancer (PCa) cells can be induced by either androgen receptor (AR) agonists at supraphysiological androgen level (SAL) used in bipolar androgen therapy or by AR antagonists. This challenges to define ligand-specific senolytic compounds. Results: Here, we first induced cellular senescence by treating androgen-sensitive PCa LNCaP cells with either SAL or the AR antagonist Enzalutamide (ENZ). Subsequently, cells were incubated with the HSP90 inhibitor Ganetespib (GT), the Bcl-2 family inhibitor ABT263, or the Akt inhibitor MK2206 to analyze senolysis. GT and ABT263 are known senolytic compounds. We observed that GT exhibits senolytic activity specifically in SAL-pretreated PCa cells. Mechanistically, GT treatment results in reduction of AR, Akt, and phospho-S6 (p-S6) protein levels. Surprisingly, ABT263 lacks senolytic effect in both AR agonist-and antagonist-pretreated cells. ABT263 treatment does not affect AR, Akt, or S6 protein levels. Treatment with MK2206 does not reduce AR protein level and, as expected, potently inhibits Akt phosphorylation. However, ENZ-induced cellular senescent cells undergo apoptosis by MK2206, whereas SAL-treated cells are resistant. In line with this, we reveal that the pro-survival p-S6 level is higher in SAL-induced cellular senescent PCa cells compared to ENZ-treated cells. These data indicate a difference in the agonist-or antagonist-induced cellular senescence and suggest a novel role of MK2206 as a senolytic agent preferentially for AR antagonist-treated cells. Conclusion: Taken together, our data suggest that both AR agonist and antagonist induce cellular senescence but differentially upregulate a pro-survival signaling which preferentially sensitize androgen-sensitive PCa LNCaP cells to a specific senolytic compound.

Mechanisms of Androgen Receptor Agonist- and Antagonist-Mediated Cellular Senescence in Prostate Cancer

“…This has been observed as well in case of AR ligand-induced cellular senescence in PCa. Our recently published data indicate that the pro-survival Akt-S6 pathway is more activated by AR agonist-induced cellular senescence compared to antagonist, although both types of ligand induce cell senescence by AR [61]. In line with this, SAL treatment led to increased phosphorylation of both Akt and S6, whereas Enz treatment induced phosphorylation of Akt but not S6.…”

“…In line with this, Enz decreases cell growth and on one hand was reported to induce apoptosis [79]. On the other hand, induction of cellular senescence in both CSPC LNCaP and the CRPC C4-2 cells upon Enz treatment was also reported [61,62]. Accordingly, the expression of p16 INK4A is induced by Enz in both cell lines.…”

“…Interestingly, different senescence inducers can lead to distinct activation/upregulation of pro-survival/anti-apoptotic pathways [61,138,139]. This has been observed as well in case of AR ligand-induced cellular senescence in PCa.…”

“…Inhibition of Akt by highly selective allosteric Akt inhibitor MK2206 sensitized AR antagonist-treated cells to apoptosis, while SAL-treated cells were resistant [61]. Importantly, inhibition of Akt by MK2206 reveals that phosphorylation of S6, a downstream target of Akt, might be regulated in part by AR ligands, independent of Akt phosphorylation.…”

Interleukin-23 Represses the Level of Cell Senescence Induced by the Androgen Receptor Antagonists Enzalutamide and Darolutamide in Castration-Resistant Prostate Cancer Cells

“…Thus, reenforcing cellular senescence in malignant tumors could therefore be beneficial. Interestingly, various antagonists of AR induce the cellular pathway of senescence including atraric acid, spironolactone derivatives, compound C28, ENZ and ODM [5,6,24,25]. These findings suggest that the AR is not completely inactivated by treatment with AR antagonists but retains the senescence inducing signaling and tumor suppressive functions perhaps by non-direct DNA binding through interaction with other factors.…”