Real-world comparative effectiveness of acalabrutinib and ibrutinib in patients with chronic lymphocytic leukemia.

Novel agents, including Bruton tyrosine kinase inhibitors (BTKis), have become the standard of care for patients with chronic lymphocytic leukemia (CLL). We conducted a real-world retrospective analysis of patients with CLL treated with acalabrutinib vs ibrutinib using the Flatiron Health database. Patients with CLL were included if they initiated acalabrutinib or ibrutinib between 1 January 2018 and 28 February 2021. The primary outcome of interest was time to treatment discontinuation (TTD). Kaplan-Meier analysis was used to estimate unweighted and weighted median TTD. A weighted Cox proportional hazards model was used to compare the TTD between cohorts. Of the 2509 patients included in the analysis, 89.6% received ibrutinib, and 14.1% received acalabrutinib. TTD was not significantly different between cohorts in the unweighted analysis. After weighting, the cohorts were balanced on all baseline characteristics except cardiovascular risk factors and baseline medications use. The median (95% confidence interval [CI]) TTD was not reached (NR; 95% CI, 25.1 to NR) for the acalabrutinib cohort and was 23.4 months (95% CI, 18.1-28.7) for the ibrutinib cohort. The discontinuation rate at 12 months was 22% for the weighted acalabrutinib cohort vs 31% for the weighted ibrutinib cohort (P = .005). After additional adjustment for prior BTKi use, the acalabrutinib cohort had a 41% lower risk of discontinuation vs ibrutinib (hazard ratio, 0.59; 95% CI, 0.43-0.81; P = .001). In the largest available study comparing BTKis, patients with CLL receiving acalabrutinib demonstrated lower rates of discontinuation and a prolonged time to discontinuation vs those receiving ibrutinib.

The mTOR Complex Controls HIV Latency.

A population of CD4 T lymphocytes harboring latent HIV genomes can persist in patients on antiretroviral therapy, posing a barrier to HIV eradication. To examine cellular complexes controlling HIV latency, we conducted a genome-wide screen with a pooled ultracomplex shRNA library and in vitro system modeling HIV latency and identified the mTOR complex as a modulator of HIV latency. Knockdown of mTOR complex subunits or pharmacological inhibition of mTOR activity suppresses reversal of latency in various HIV-1 latency models and HIV-infected patient cells. mTOR inhibitors suppress HIV transcription both through the viral transactivator Tat and via Tat-independent mechanisms. This inhibition occurs at least in part via blocking the phosphorylation of CDK9, a p-TEFb complex member that serves as a cofactor for Tat-mediated transcription. The control of HIV latency by mTOR signaling identifies a pathway that may have significant therapeutic opportunities.

HIV latency: experimental systems and molecular models.

Highly active antiretroviral therapy (HAART) has shown great efficacy in increasing the survival of HIV infected individuals. However, HAART does not lead to the full eradication of infection and therefore has to be continued for life. HIV persists in a transcriptionally inactive form in resting T cells in HAART-treated patients and can be reactivated following T-cell activation. These latently infected cells allow the virus to persist in the presence of HAART. Here, we review recent advances in the study of the molecular mechanisms of HIV latency. We also review experimental models in which latency is currently studied. We focus on the epigenetic mechanisms controlling HIV transcription and on the role of chromatin and its post-translational modifications. We discuss how small molecule inhibitors that target epigenetic regulators, such as HDAC (histone deacetylase) inhibitors, are being tested for their ability to reactivate latent HIV. Finally, we discuss the clinical potential of these drugs to flush out latently infected cells from HIV-infected patients and to eradicate the virus.

Opposing functions of TFII-I spliced isoforms in growth factor-induced gene expression.

Multifunctional transcription factor TFII-I has two spliced isoforms (Delta and beta) in murine fibroblasts. Here we show that these isoforms have distinct subcellular localization and mutually exclusive transcription functions in the context of growth factor signaling. In the absence of signaling, TFII-Ibeta is nuclear and recruited to the c-fos promoter in vivo. But upon growth factor stimulation, the promoter recruitment is abolished and it is exported out of the nucleus. Moreover, isoform-specific silencing of TFII-Ibeta results in transcriptional activation of the c-fos gene. In contrast, TFII-IDelta is largely cytoplasmic in the resting state but translocates to the nucleus upon growth factor signaling, undergoes signal-induced recruitment to the same site on the c-fos promoter, and activates the gene. Importantly, activated TFII-IDelta interacts with Erk1/2 (MAPK) kinase in the cell cytoplasm and imports the Erk1/2 to the nucleus, thereby transducing growth factor signaling. Our results identify a unique growth factor signaling pathway controlled by opposing activities of two TFII-I spliced isoforms.

An FF domain-dependent protein interaction mediates a signaling pathway for growth factor-induced gene expression.

FF domains are poorly understood protein motifs found in all eukaryotes but in a very small number of proteins. They typically occur in tandem arrays and appear predominantly in splicing and transcription factors. Curiously, they are also present in the p190 family of cytoplasmic Rho GTPase activating proteins (GAPs). We identified the serum-responsive transcriptional regulator TFII-I as a specific interactor with the p190 RhoGAP FF domains. p190 sequesters TFII-I in the cytoplasm via the FF domains, but upon PDGF receptor-mediated phosphorylation of an FF domain, TFII-I is released from p190 and translocates to the nucleus where it can activate transcription of serum-inducible genes including c-fos. These findings reveal a pathway by which mitogens promote gene transcription and indicate a role for FF domains in phosphorylation-mediated signal transduction.