Epichaperome inhibition targets TP53-mutant AML and AML stem/progenitor cells

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.

Nucleus-mitochondria positive feedback loop formed by ERK5 S496 phosphorylation-mediated poly (ADP-ribose) polymerase activation provokes persistent pro-inflammatory senescent phenotype and accelerates coronary atherosclerosis after chemo-radiation

The incidence of cardiovascular disease (CVD) is higher in cancer survivors than in the general population. Several cancer treatments are recognized as risk factors for CVD, but specific therapies are unavailable. Many cancer treatments activate shared signaling events, which reprogram myeloid cells (MCs) towards persistent senescence-associated secretory phenotype (SASP) and consequently CVD, but the exact mechanisms remain unclear. This study aimed to provide mechanistic insights and potential treatments by investigating how chemo-radiation can induce persistent SASP. We generated ERK5 S496A knock-in mice and determined SASP in myeloid cells (MCs) by evaluating their efferocytotic ability, antioxidation-related molecule expression, telomere length, and inflammatory gene expression. Candidate SASP inducers were identified by high-throughput screening, using the ERK5 transcriptional activity reporter cell system. Various chemotherapy agents and ionizing radiation (IR) up-regulated p90RSK-mediated ERK5 S496 phosphorylation. Doxorubicin and IR caused metabolic changes with nicotinamide adenine dinucleotide depletion and ensuing mitochondrial stunning (reversible mitochondria dysfunction without showing any cell death under ATP depletion) via p90RSK-ERK5 modulation and poly (ADP-ribose) polymerase (PARP) activation, which formed a nucleus-mitochondria positive feedback loop. This feedback loop reprogramed MCs to induce a sustained SASP state, and ultimately primed MCs to be more sensitive to reactive oxygen species. This priming was also detected in circulating monocytes from cancer patients after IR. When PARP activity was transiently inhibited at the time of IR, mitochondrial stunning, priming, macrophage infiltration, and coronary atherosclerosis were all eradicated. The p90RSK-ERK5 module plays a crucial role in SASP-mediated mitochondrial stunning via regulating PARP activation. Our data show for the first time that the nucleus-mitochondria positive feedback loop formed by p90RSK-ERK5 S496 phosphorylation-mediated PARP activation plays a crucial role of persistent SASP state, and also provide preclinical evidence supporting that transient inhibition of PARP activation only at the time of radiation therapy can prevent future CVD in cancer survivors.

Tet2 Inactivation Enhances the Antitumor Activity of Tumor-Infiltrating Lymphocytes

Inactivation of tumor-infiltrating lymphocytes (TIL) is one of the mechanisms mitigating antitumor immunity during tumor onset and progression. Epigenetic abnormalities are regarded as a major culprit contributing to the dysfunction of TILs within tumor microenvironments. In this study, we used a murine model of melanoma to discover that Tet2 inactivation significantly enhances the antitumor activity of TILs with an efficacy comparable to immune checkpoint inhibition imposed by anti-PD-L1 treatment. Single-cell RNA-sequencing analysis suggested that Tet2-deficient TILs exhibit effector-like features. Transcriptomic and ATAC-sequencing analysis showed that Tet2 ablation reshapes chromatin accessibility and favors binding of transcription factors geared toward CD8⁺ T-cell activation. Furthermore, the ETS family of transcription factors contributed to augmented CD8⁺ T-cell function following Tet2 depletion. Overall, our study establishes that Tet2 constitutes one of the epigenetic barriers that account for dysfunction of TILs and that Tet2 inactivation could promote antitumor immunity to suppress tumor growth. SIGNIFICANCE: This study suggests that ablation of TET2⁺ from TILs could promote their antitumor function by reshaping chromatin accessibility for key transcription factors and enhancing the transcription of genes essential for antitumor activity.

Abstract 3761: Regulation of metastasis by CD8 T lymphocytes

Metastatic breast cancer is the most dreadful malignant disease that accounts for the majority of cancer-related deaths worldwide among women. A number of studies have shown that the tumor microenvironment (TME) plays a crucial role in regulating metastasis. It is therefore imperative to understand the dynamic interactions between cancer cells and their microenvironment to examine the molecular interaction and to effectively target cancer cells. TME comprises a variety of cells including immune cells which can influence tumor survival, growth and metastasis. Tumor-infiltrating lymphocytes (TILs), in particular, the CD8 T lymphocytes, has emerged as a promising prognostic marker for immunotherapy in a variety of cancers. However, the key molecular factors that regulate the cross-talk between tumor cells and CD8 T lymphocytes and its impact on metastatic traits in breast cancer is still inconclusive. Platelets are crucial components of the tumor microenvironment that are known to modulate tumor promotion and metastasis. The contribution of platelets and platelet secreted molecules are also carefully examined in metastasis of various cancers. The primary objective of this study is to investigate the role of CD8 T lymphocytes and platelets in breast tumor progression using isogenic tumor lines that form identical primary tumors but differ in their ability to develop metastasis.

Citation Format: Robiya Joseph, Rama Soundararajan, Suhas Vasaikar, Fei Yang, Sevinj Isgandarova, Lin Tian, Monika Haemmerle, Barbara Mino, Tieling Zhou, Geraldine Vidhya Raja, Esmeralda Ramirez Pena, Petra Den Hollander, Neeraja Bhangre, Crystal Shin, Melisa Martinez, Jaime Rodriguez Canales, Jeffrey Chang, Anil Sood, Ignacio Ivan Wistuba, Don L. Gibbons, Jeffrey M. Rosen, Ghanashyam Acharya, Navin Varadarajan, Xiang H. Zhang, Sendurai A. Mani. Regulation of metastasis by CD8 T lymphocytes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3761.

Mutations in 5-methylcytosine oxidase TET2 and RhoA cooperatively disrupt T cell homeostasis

Angioimmunoblastic T cell lymphoma (AITL) represents a distinct, aggressive form of peripheral T cell lymphoma with a dismal prognosis. Recent exome sequencing in patients with AITL has revealed the frequent coexistence of somatic mutations in the Rho GTPase RhoA (RhoAG17V) and loss-of-function mutations in the 5-methylcytosine oxidase TET2. Here, we have demonstrated that TET2 loss and RhoAG17V expression in mature murine T cells cooperatively cause abnormal CD4+ T cell proliferation and differentiation by perturbing FoxO1 gene expression, phosphorylation, and subcellular localization, an abnormality that is also detected in human primary AITL tumor samples. Reexpression of FoxO1 attenuated aberrant immune responses induced in mouse models adoptively transferred with T cells and bearing genetic lesions in both TET2 and RhoA. Our findings suggest a mutational cooperativity between epigenetic factors and GTPases in adult CD4+ T cells that may account for immunoinflammatory responses associated with AITL patients.