BI-2536 and BI-6727, dual Polo-like kinase/bromodomain inhibitors, effectively reactivate latent HIV-1

Abstract

HIV-1 latent reservoirs harbouring silenced but replication-competent proviruses are a major obstacle against viral eradication in infected patients. The “shock and kill” strategy aims to reactivate latent provirus with latency reversing agents (LRAs) in the presence of antiretroviral drugs, necessitating the development of effective and efficient LRAs. We screened a chemical library for potential LRAs and identified two dual Polo-like kinase (PLK)/bromodomain inhibitors, BI-2536 and BI-6727 (volasertib), which are currently undergoing clinical trials against various cancers. BI-2536 and BI-6727 significantly reactivated silenced HIV-1 provirus at both the mRNA and protein level in two latently infected model cell lines (ACH2 and U1). BI-2536 dramatically reactivated transcription of latent HIV-1 provirus in peripheral blood mononuclear cells derived from infected patients. Long terminal repeat activation by the inhibitors was associated with bromodomain rather than PLK inhibition. We also found that BI-2536 synergistically activates the latent provirus in combination with SAHA, a histone deacetylase inhibitor, or the non-tumour-promoting phorbol ester prostratin. Our findings strongly suggest that BI-2536 and BI-6727 are potent LRAs for the “shock and kill” HIV-1 eradication strategy.

In Depth Analysis of Kinase Cross Screening Data to Identify CAMKK2 Inhibitory Scaffolds

“…In the literature, BI2536 was reported as a potent PLK1, PLK2 and PLK3 inhibitor, with Kd's < 10 nM [102]. In addition to the collateral PLK inhibition, BI2536 has been shown to be a potent inhibitor of BRD4, which is a critical regulator of cell division and confounds its use as a selective kinase inhibitor probe [103]. OTSSP167 is an extremely potent but promiscuous kinase inhibitor, with an S 10 at 1 µM of 0.66.…”

Diversity of small molecule HIV‐1 latency reversing agents identified in low‐ and high‐throughput small molecule screens

“…Several additional BRD4/BET inhibitors have been identified as LRAs, namely BI‐2536 and BI‐6727 (Figure , BETi; Figure ; and Table ) . Both of these compounds have pteridine groups (Figure ), and were identified in screens of protein kinase inhibitors using latently infected monocytic THP‐1 cells (Tables and ) . BI‐2536 was initially identified as an inhibitor of polo‐like kinase 1 (PLK1), which has a key regulatory function for mitotic progression .…”

“…More recently, BI‐2536 was also shown to bind BDs, and structural analyses revealed specific interactions of BI‐2536 with the BRD4 hydrophobic cavity . The latency reversing activity of BI‐2536 and BI‐6727 are likely associated with inhibition of BRD4, rather than an inhibitory effect on protein kinases; accordingly, other PLK inhibitors were unable to cause significant activation of HIV‐1 transcription in the same HIV‐1 reporter cell lines utilized for the initial screen . Furthermore, ChIP analyses indicates that treatment with either BI compound causes reduction in BRD4 recruitment to the HIV‐1 promoter, similar to the effect of JQ1, a previously identified LRA with known BRD4 inhibitory function …”

In depth analysis of kinase cross screening data to identify CAMKK2 inhibitory scaffolds

“…In addition to the collateral PLK inhibition, BI2536 has been shown to be a potent inhibitor of BRD4, which is a critical regulator of cell division and confounds its use as a selective kinase inhibitor probe. [134] OTSSP167 is an extremely potent but promiscuous kinase inhibitor, with an S10 at 1 µM of 0.66. Neither CDK1/2 inhibitor III or JAK3 inhibitor VI can be considered selective, even at a lower concentration of 0.5 µM, they have S10 values of 0.278 and 0.163 respectively.…”