Nutlin-3 down-regulates retinoblastoma protein expression and inhibits muscle cell differentiation

MDM2 as a Rational Target for Intervention in CDK4/6 Inhibitor Resistant, Hormone Receptor Positive Breast Cancer

With the adoption of inhibitors of cyclin dependent kinases 4 and 6 (CDK4/6i) in combination with endocrine therapy as standard of care for the treatment of advanced and metastatic estrogen receptor positive (ER+) breast cancer, the search is now on for novel therapeutic options to manage the disease after the inevitable development of resistance to CDK4/6i. In this review we will consider the integral role that the p53/MDM2 axis plays in the interactions between CDK4/6, ERα, and inhibitors of these molecules, the current preclinical evidence for the efficacy of MDM2 inhibitors in ER+ breast cancer, and discuss the possibility of targeting the p53/MDM2 via inhibition of MDM2 in the CDK4/6i resistance setting.

Small-molecule MDM2 inhibitor LQFM030-induced apoptosis in p53-null K562 chronic myeloid leukemia cells

Our group designed and synthesized the N-phenyl-piperazine LQFM030 [1-(4-((1-(4-chlorophenyl)-1H-pyrazol-4-yl)methyl) piperazin-1-yl) ethanone], a small molecule derived from molecular simplification of the Nutlin-1, an inhibitor of the human homologue of murine double minute 2 (MDM2) protein that is expressed in several types of cancer. To better investigate the effects of LQFM030 regarding the p53 mutation status, this study investigated the antiproliferative activity of LQFM030 against the p53-null K562 leukemia cells as well as the cell death pathways involved. In addition, the effects of LQFM030 on the levels of the p53/MDM2 complex were also carried out using 3T3 cells as a p53 wild-type model. Our data suggest that LQFM030 triggered apoptosis in K562 cells via different mechanisms including cell cycle arrest, caspase activation, reduction of mitochondrial activity, decrease in MDM2 expression, and transcriptional modulation of MDMX, p73, MYC, and NF-ĸB. Additionally, it promoted effects in p53/MDM2 binding in p53 wild-type 3T3 cells. Therefore, LQFM030 has antiproliferative effects in cancer cells by a p53 mutation status-independent manner with different signaling pathways. These findings open new perspectives to the treatment of leukemic cells considering the resistance development associated with cancer treatment with conventional cytotoxic drugs.

An evaluation in vitro of the efficacy of nutlin-3 and topotecan in combination with 177Lu-DOTATATE for the treatment of neuroblastoma

Targeted radiotherapy of metastatic neuroblastoma using the somatostatin receptor (SSTR)-targeted octreotide analogue DOTATATE radiolabelled with lutetium-177 (¹⁷⁷Lu-DOTATATE) is a promising strategy. This study evaluates whether its effectiveness may be enhanced by combination with radiosensitising drugs. The growth rate of multicellular tumour spheroids, derived from the neuroblastoma cell lines SK-N-BE(2c), CHLA-15 and CHLA-20, was evaluated following treatment with ¹⁷⁷Lu-DOTATATE, nutlin-3 and topotecan alone or in combination. Immunoblotting, immunostaining and flow cytometric analyses were used to determine activation of p53 signalling and cell death. Exposure to ¹⁷⁷Lu-DOTATATE resulted in a significant growth delay in CHLA-15 and CHLA-20 spheroids, but not in SK-N-BE(2c) spheroids. Nutlin-3 enhanced the spheroid growth delay induced by topotecan in CHLA-15 and CHLA-20 spheroids, but not in SK-N-BE(2c) spheroids. Importantly, the combination of nutlin-3 with topotecan enhanced the spheroid growth delay induced by X-irradiation or by exposure to ¹⁷⁷Lu-DOTATATE. The efficacy of the combination treatments was p53-dependent. These results indicate that targeted radiotherapy of high risk neuroblastoma with ¹⁷⁷Lu-DOTATATE may be improved by combination with the radiosensitising drugs nutlin-3 and topotecan.

Aberrant Caspase Activation in Laminin-α2-Deficient Human Myogenic Cells is Mediated by p53 and Sirtuin Activity

Background:

Mutations in the LAMA2 gene encoding laminin-α2 cause congenital muscular dystrophy Type 1A (MDC1A), a severe recessive disease with no effective treatment. Previous studies have shown that aberrant activation of caspases and cell death through a pathway regulated by BAX and KU70 is a significant contributor to pathogenesis in laminin-α2-deficiency.

Objectives:

To identify mechanisms of pathogenesis in MDC1A.

Methods:

We used immunocytochemical and molecular studies of human myogenic cells and mouse muscles—comparing laminin-α2-deficient vs. healthy controls—to identify mechanisms that regulate pathological activation of caspase in laminin-α2-deficiency.

Results:

In cultures of myogenic cells from MDC1A donors, p53 accumulated in a subset of nuclei and aberrant caspase activation was inhibited by the p53 inhibitor pifithrin-alpha. Also, the p53 target BBC3 (PUMA) was upregulated in both MDC1A myogenic cells and Lama2–/– mouse muscles. In addition, studies with sirtuin inhibitors and SIRT1 overexpression showed that caspase activation in MDC1A myotubes was inversely related to sirtuin deacetylase activity. Caspase activation in laminin-α2-deficiency was, however, not associated with increased phosphorylation of p38 MAPK.

Conclusions:

Aberrant caspase activation in MDC1A cells was mediated both by sirtuin deacetylase activity and by p53. Interventions that inhibit aberrant caspase activation by targeting sirtuin or p53 function could potentially be useful in ameliorating MDC1A.

The Satellite Cell Niche Regulates the Balance between Myoblast Differentiation and Self-Renewal via p53

Satellite cells are adult muscle stem cells residing in a specialized niche that regulates their homeostasis. How niche-generated signals integrate to regulate gene expression in satellite cell-derived myoblasts is poorly understood. We undertook an unbiased approach to study the effect of the satellite cell niche on satellite cell-derived myoblast transcriptional regulation and identified the tumor suppressor p53 as a key player in the regulation of myoblast quiescence. After activation and proliferation, a subpopulation of myoblasts cultured in the presence of the niche upregulates p53 and fails to differentiate. When satellite cell self-renewal is modeled ex vivo in a reserve cell assay, myoblasts treated with Nutlin-3, which increases p53 levels in the cell, fail to differentiate and instead become quiescent. Since both these Nutlin-3 effects are rescued by small interfering RNA-mediated p53 knockdown, we conclude that a tight control of p53 levels in myoblasts regulates the balance between differentiation and return to quiescence.

Roles of pRB in the Regulation of Nucleosome and Chromatin Structures

Retinoblastoma protein (pRB) interacts with E2F and other protein factors to play a pivotal role in regulating the expression of target genes that induce cell cycle arrest, apoptosis, and differentiation. pRB controls the local promoter activity and has the ability to change the structure of nucleosomes and/or chromosomes via histone modification, epigenetic changes, chromatin remodeling, and chromosome organization. Functional inactivation of pRB perturbs these cellular events and causes dysregulated cell growth and chromosome instability, which are hallmarks of cancer cells. The role of pRB in regulation of nucleosome/chromatin structures has been shown to link to tumor suppression. This review focuses on the ability of pRB to control nucleosome/chromatin structures via physical interactions with histone modifiers and chromatin factors and describes cancer therapies based on targeting these protein factors.