Macrophage migration inhibitory factor (MIF), originally identified as a proinflammatory cytokine, is highly elevated in many human cancer types, independent of their histological origin. MIF's ...tumour promoting activities correlate with tumour aggressiveness and poor clinical prognosis. Genetic depletion of MIF in mouse cancer models results in significant inhibition of cell proliferation and induction of apoptosis, making it an attractive target for anticancer therapies. Here, we summarize the current possibilities to inhibit MIF function in cancer.
All known small molecule MIF inhibitors antagonize MIF's enzymatic function. However, a recent knockin mouse model suggested that protein interactions play a bigger biological role in tumour cell growth regulation than MIF's enzymatic activity. Thus, alternative strategies are important for targeting MIF. Recently, we identified that MIF in cancer cells is highly stabilized through the heat shock protein 90 machinery (HSP90). Thus, MIF is an HSP90 client. Pharmacological inhibition of the Hsp90 ATPase activity results in MIF degradation in several types of cancer cells. This provides a new way to inhibit MIF function independent of its enzymatic activity.
Targeting the HSP90 machinery is a promising way to inhibit MIF function in cancer. Along with MIF and dependent on the molecular make-up of the tumour, a large number of other critical tumourigenic proteins are also destabilized by HSP90 inhibition, overall resulting in a profound block of tumour growth.
TP 53-mutant acute myeloid leukemia (AML) remains the ultimate therapeutic challenge. Epichaperomes, formed in malignant cells, consist of heat shock protein 90 (HSP90) and associated proteins that ...support the maturation, activity, and stability of oncogenic kinases and transcription factors including mutant p53. High-throughput drug screening identified HSP90 inhibitors as top hits in isogenic TP53-wild-type (WT) and -mutant AML cells. We detected epichaperomes in AML cells and stem/progenitor cells with TP53 mutations but not in healthy bone marrow (BM) cells. Hence, we investigated the therapeutic potential of specifically targeting epichaperomes with PU-H71 in TP53-mutant AML based on its preferred binding to HSP90 within epichaperomes. PU-H71 effectively suppressed cell intrinsic stress responses and killed AML cells, primarily by inducing apoptosis; targeted TP53-mutant stem/progenitor cells; and prolonged survival of TP53-mutant AML xenograft and patient-derived xenograft models, but it had minimal effects on healthy human BM CD34+ cells or on murine hematopoiesis. PU-H71 decreased MCL-1 and multiple signal proteins, increased proapoptotic Bcl-2-like protein 11 levels, and synergized with BCL-2 inhibitor venetoclax in TP53-mutant AML. Notably, PU-H71 effectively killed TP53-WT and -mutant cells in isogenic TP53-WT/TP53-R248W Molm13 cell mixtures, whereas MDM2 or BCL-2 inhibition only reduced TP53-WT but favored the outgrowth of TP53-mutant cells. Venetoclax enhanced the killing of both TP53-WT and -mutant cells by PU-H71 in a xenograft model. Our data suggest that epichaperome function is essential for TP53-mutant AML growth and survival and that its inhibition targets mutant AML and stem/progenitor cells, enhances venetoclax activity, and prevents the outgrowth of venetoclax-resistant TP53-mutant AML clones. These concepts warrant clinical evaluation.
In contrast to p53-mediated cell cycle arrest, the mechanisms of p53-mediated apoptosis in response to cellular stresses such as DNA damage, hypoxia and oncogenic signals still remain poorly ...understood. Elucidating these pathways is all the more pressing since there is good evidence that the activation of apoptosis rather than cell cycle arrest is crucial in p53 tumor suppression. Moreover, the therapeutic interest in p53 as the molecular target of anticancer intervention rests mainly on its powerful apoptotic capability. This puzzling elusiveness suggests that p53 not only engages a plethora of downstream pathways but itself might possess a biochemical flexibility that goes beyond its role as a mere transcription factor. Recent evidence of a direct pro-apoptotic role of p53 protein at mitochondria suggests a synergistic effect with its transcriptional activation function and brings an unexpected new level of complexity into p53 apoptotic pathways.
The DNA-alkylating cytotoxic agent cyclophosphamide (CTX) is commonly used in the clinic to treat hematological malignancies like lymphomas and leukemias as well as solid tumors, but shows ...dose-dependent potentially life-threatening toxicities and can induce secondary malignancies. Thus, the clinical utility of CTX would be improved if a companion drug could be identified that allows lowering the CTX dose, while maintaining or even increasing its antineoplastic therapeutic efficacy. In mouse models, high-dose CTX (300 mg/kg) is effective in treating T-lymphomas, while low dose (defined here as 100 mg/kg) is ineffective. We previously showed that the HSP90 inhibitor ganetespib potently suppresses T-lymphoma initiation and progression and extends overall survival (OS) in hotspot knockin mice expressing the p53 gain-of-function mutants R175H and R248Q (mutp53) by 30-59%. Here we asked whether ganetespib could potentiate the effect of low-dose CTX (100 mg/kg) in the autochthonous T-lymphoma-bearing mutp53 R248Q mouse model. Indeed, combinatorial CTX/ganetespib synergistically suppresses growth of autochthonous T-lymphomas in R248Q (p53Q/-) but not p53-/- control mice by reducing mutp53 levels and triggering apoptosis. Combinatorial treatment extends progression-free (PFS) and OS in p53Q/- mice significantly longer than in p53-/- mice. Specifically, PFS of p53Q/- mice improves 8.9-fold over CTX alone versus 3.6-fold in p53-/- mice. Likewise, OS of R248Q/- mice improves 3.6-fold, but worsens in p53-/- mice (0.85-fold) over CTX alone. Moreover, half of the p53Q/- mice on combinatorial treatment lived over 60 days, and one animal reached 121 days. In contrast, p53Q/- mice on single-drug treatment and p53-/- mice on any treatment lived less than 24 days. In sum, ganetespib synergizes with a sub-effective dose of CTX in mutp53 T-lymphomas by suppressing tumor growth and extending survival. Our results provide a potential strategy to reduce the effective clinical dose of CTX in mutant p53-bearing malignancies and attenuate CTX toxicity.
The tumor suppressor p53 is a transcription factor that is frequently inactivated in human tumors. Therefore, restoring its function has been considered an attractive approach to restrain cancer. ...Typically, p53-dependent growth arrest, senescence and apoptosis of tumor cells have been attributed to transcriptional activity of nuclear p53. Notably, wild-type p53 gain-of-function enhances cancer resistance in the mouse, but it also accelerates aging in some models, possibly due to altered p53 activity. Therefore, the emerging evidence of mitochondrial transcription-independent activities of p53 has raised high expectations. Here, we review new developments in transcription-dependent and transcription-independent p53 functions, recent advances in targeting p53 for cancer treatment and the pitfalls of moving from the laboratory research to the clinical setting.
p53 ubiquitination at C-terminal lysines by MDM2 and other E3 ligases had been considered a straightforward negative regulation of p53 with only one function, that is marking the protein for ...proteasomal degradation. In this review, we will focus on the recently uncovered activating role of ubiquitination in the transcription-independent direct mitochondrial death program of p53.
The transcription-independent p53-mediated apoptotic response has obtained a solid mechanistic basis in recent years. A fraction of stress-induced wild type p53 protein rapidly translocates to ...mitochondria in response to genotoxic, hypoxic, and oxidative stresses in established cell lines and primary cells, as well as in physiological and pathophysiologic stress responses in the animal. While the groundwork of mechanisms and kinetics of direct mitochondrial p53 activities is laid out, the quantitative contribution of this pathway to total p53-mediated apoptosis and tumor suppression in vivo remains to be elucidated. An update on these efforts is given here.
ABSTRACT
The response of the skin to harmful environmental agents is shaped decisively by the status of the immune system. Keratinocytes constitutively express and secrete the chemokine‐like ...mediator, macrophage migration inhibitory factor (MIF), more strongly than dermal fibroblasts, thereby creating a MIF gradient in skin. By using global and epidermis‐restricted Mif‐knockout (Mif-/- and K14‐Cre+/tg; Miffl/fl) mice, we found that MIF both recruits and maintains antigen‐presenting cells in the dermis/epidermis. The reduced presence of antigen‐presenting cells in the absence of MIF was associated with accelerated and increased formation of nonmelanoma skin tumors during chemical carcinogenesis. Our results demonstrate that MIF is essential for maintaining innate immunity in skin. Loss of keratinocyte‐derived MIF leads to a loss of control of epithelial skin tumor formation in chemical skin carcinogenesis, which highlights an unexpected tumor‐suppressive activity of MIF in murine skin.—Brocks, T., Fedorchenko, O., Schliermann, N., Stein, A., Moll, U. M., Seegobin, S., Dewor, M., Hallek, M., Marquardt, Y., Fietkau, K., Heise, R., Huth, S., Pfister, H., Bernhagen, J., Bucala, R., Baron, J. M., Fingerle‐Rowson, G. Macrophage migration inhibitory factor protects from nonmelanoma epidermal tumors by regulating the number of antigen‐presenting cells in skin. FASEB J. 31, 526–543 (2017). http://www.fasebj.org
The protease HAUSP is a critical component of the p53-Mdm2 pathway and acts as a specific deubiquitinase for both p53 and Mdm2 and thus is important for p53 regulation. In knock-down and knock-out ...cellular systems it was observed that ablation of HAUSP induces profound stabilization of p53 due to enhanced degradation of Mdm2. Thus, inhibiting HAUSP by small compound interference has been proposed as a rational therapeutic strategy to activate p53 in p53 wild type tumors. However, HAUSP-mediated effects in the p53-Mdm2 axis are highly complex and non-linear and to date the role of HAUSP in tumor suppression in vivo remains unexplored. Here we investigate the effect of HAUSP up- and downregulation on cell proliferation, apoptosis and tumor growth in vitro and in a xenograft model in vivo, using an inducible isogenic human colon carcinoma cell system. Importantly, in the absence of stress, both HAUSP up- and downregulation inhibit cell proliferation in vitro and tumor growth in vivo due to constitutively elevated p53 levels. Moreover, tumors with HAUSP up- and downregulation respond to radiotherapy with further growth inhibition. However, HAUSP downregulation causes resistance to Camptothecin- and irradiation-induced apoptosis, which correlates with suppressed mitochondrial translocation of p53. Our data suggest that changes in HAUSP modulate tumor growth and apoptotic sensitivity in vivo.
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