At the bedside:Profiling and treating patients with CXCR4-expressing cancers

The chemokine receptor, C-X-C chemokine receptor type 4 (CXCR4) and its ligand, C-X-C motif chemokine 12, are key mediators of hematopoietic cell trafficking. Their roles in the proliferation and metastasis of tumor cells, induction of angiogenesis, and invasive tumor growth have been recognized for over 2 decades. CXCR4 is a promising target for imaging and therapy of both hematologic and solid tumors. To date, Sanofi Genzyme's plerixafor is the only marketed CXCR4 inhibitor (i.e., Food and Drug Administration-approved in 2008 for stem cell mobilization). However, several new CXCR4 inhibitors are now being investigated as potential therapies for a variety of fluid and solid tumors. These small molecules, peptides, and Abs include balixafortide (POL6326, Polyphor), mavorixafor (X4P-001, X4 Pharmaceuticals), motixafortide (BL-8040, BioLineRx), LY2510924 (Eli Lilly), and ulocuplumab (Bristol-Myers Squibb). Early clinical evidence has been encouraging, for example, with motixafortide and balixafortide, and the CXCR4 inhibitors appear to be generally safe and well tolerated. Molecular imaging is increasingly being used for effective patient selection before, or early during CXCR4 inhibitor treatment. The use of radiolabeled theranostics that combine diagnostics and therapeutics is an additional intriguing approach. The current status and future directions for radioimaging and treating patients with CXCR4-expressing hematologic and solid malignancies are reviewed. See related review - At the Bench: Pre-Clinical Evidence for Multiple Functions of CXCR4 in Cancer. J. Leukoc. Biol. xx: xx-xx; 2020

Regulation and targeting of antiapoptotic XIAP in acute myeloid leukemia

: XIAP is a member of the inhibitors-of-apoptosis family of proteins, which inhibit caspases and block cell death, with prognostic importance in AML. Here we demonstrate that cytokines regulate the expression of XIAP in leukemic cell lines and primary AML blasts. Inhibition of phosphatidylinositol-3 kinase (PI3K) with LY294002 and of the mitogen-activated protein kinase (MAPK) cascade by PD98059 resulted in decreased XIAP levels (34+/-8.7 and 23+/-5.7%, respectively). We then generated OCI-AML3 cells with constitutively phosphorylated Akt (p473-Akt) by retroviral gene transfer. Neither these nor Akt inhibitor-treated OCI-AML3 cells showed changes in XIAP levels, suggesting that XIAP expression is regulated by PI3K downstream effectors other than Akt. The induction of XIAP expression by cytokines through PI3K/MAPK pathways is consistent with its role in cell survival. Exposure of leukemic cells to chemotherapeutic agents decreased XIAP protein levels by caspase-dependent XIAP cleavage. Targeting XIAP by XIAP antisense oligonucleotide resulted in downregulation of XIAP, activation of caspases and cell death, and sensitized HL-60 cells to Ara-C. Our results suggest that XIAP is regulated by cytokines through PI3K, and to a lesser degree through MAPK pathways. Selective downregulation of XIAP expression might be of therapeutic benefit to leukemic patients

C-MYC Targeting by Degradation: Novel Dual c-Myc/GSPT1 Degrader GT19715 Exerts Profound Cell Kill in vitro and in vivo in Acute Myeloid Leukemia and Lymphomas

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Structural analysis of MDM2 RING separates degradation from regulation of p53 transcription activity

MDM2–MDMX complexes bind the p53 tumor-suppressor protein, inhibiting p53's transcriptional activity and targeting p53 for proteasomal degradation. Inhibitors that disrupt binding between p53 and MDM2 efficiently activate a p53 response, but their use in the treatment of cancers that retain wild-type p53 may be limited by on-target toxicities due to p53 activation in normal tissue. Guided by a novel crystal structure of the MDM2–MDMX–E2(UbcH5B)–ubiquitin complex, we designed MDM2 mutants that prevent E2–ubiquitin binding without altering the RING-domain structure. These mutants lack MDM2's E3 activity but retain the ability to limit p53′s transcriptional activity and allow cell proliferation. Cells expressing these mutants respond more quickly to cellular stress than cells expressing wild-type MDM2, but basal p53 control is maintained. Targeting the MDM2 E3-ligase activity could therefore widen the therapeutic window of p53 activation in tumors

Therapeutic potential of MEK inhibition in acute myelogenous leukemia: rationale for "vertical" and "lateral" combination strategies

: In hematological malignancies, constitutive activation of the RAF/MEK/ERK pathway is frequently observed, conveys a poor prognosis, and constitutes a promising target for therapeutic intervention. Here, we investigated the molecular and functional effects of pharmacological MEK inhibition in cell line models of acute myeloid leukemia (AML) and freshly isolated primary AML samples. The small-molecule, ATP-non-competitive, MEK inhibitor PD0325901 markedly inhibited ERK phosphorylation and growth of several AML cell lines and approximately 70 % of primary AML samples. Growth inhibition was due to G(1)-phase arrest and induction of apoptosis. Transformation by constitutively active upstream pathway elements (HRAS, RAF-1, and MEK) rendered FDC-P1 cells exquisitely prone to PD0325901-induced apoptosis. Gene and protein expression profiling revealed a selective effect of PD0325901 on ERK phosphorylation and compensatory upregulation of the RAF/MEK and AKT/p70( S6K ) kinase modules, potentially mediating resistance to drug-induced growth inhibition. Consequently, in appropriate cellular contexts, both "vertical" (i.e., inhibition of RAF and MEK along the MAPK pathway) and "lateral" (i.e., simultaneous inhibition of the MEK/ERK and mTOR pathways) combination strategies may result in synergistic anti-leukemic effects. Overall, MEK inhibition exerts potent growth inhibitory and proapoptotic activity in preclinical models of AML, particularly in combination with other pathway inhibitors. Deeper understanding of the molecular mechanisms of action of MEK inhibitors will likely translate into more effective targeted strategies for the treatment of AML

Enhanced TP53 reactivation disrupts MYC transcriptional program and overcomes venetoclax resistance in acute myeloid leukemias

The tumor suppressor TP53 is frequently inactivated in a mutation-independent manner in cancers and is reactivated by inhibiting its negative regulators. We here cotarget MDM2 and the nuclear exporter XPO1 to maximize transcriptional activity of p53. MDM2/XPO1 inhibition accumulated nuclear p53 and elicited a 25- to 60-fold increase of its transcriptional targets. TP53 regulates MYC, and MDM2/XPO1 inhibition disrupted the c-MYC-regulated transcriptome, resulting in the synergistic induction of apoptosis in acute myeloid leukemia (AML). Unexpectedly, venetoclax-resistant AMLs express high levels of c-MYC and are vulnerable to MDM2/XPO1 inhibition in vivo. However, AML cells persisting after MDM2/XPO1 inhibition exhibit a quiescence- and stress response-associated phenotype. Venetoclax overcomes that resistance, as shown by single-cell mass cytometry. The triple inhibition of MDM2, XPO1, and BCL2 was highly effective against venetoclax-resistant AML in vivo. Our results propose a novel, highly translatable therapeutic approach leveraging p53 reactivation to overcome nongenetic, stress-adapted venetoclax resistance

Enhanced TP53 Reactivation Disrupts MYC Transcriptional Program and Overcomes Venetoclax Resistance in Acute Myeloid Leukemias

View full abstracthttps://openworks.mdanderson.org/leading-edge/1019/thumbnail.jp

Early Detection of t(8;21) Chromosomal Translocations During Treatment of PML-RARA Positive Acute Promyelocytic Leukemia: A Case Study

Here we describe a female patient who developed acute promyelocytic leukemia (APL) characterized by t(l5;17) translocation at diagnosis. The patient began treatment with all-trans retinoic acid (ATRA) + chemotherapy. During follow up, the patient was found to be negative for the t(15;17) transcript after 3 months of therapy which remained undetectable, thereafter. However, the emergence of a small clone with a t(8;21) abnormality was observed in the bone marrow and peripheral blood (PB) cells between 3 and 18 months following treatment initiation. The abnormal translocation observed in PB cells obtained at 3 months was detected after the second cycle of consolidation therapy and reappeared at 15 months during maintenance treatment, a period without ATRA. Although based on a single case, we conclude that genetic screening of multiple translocations in AML patients should be requested to allow early identification of other emerging clones during therapy that may manifest clinically following treatment

Selective depletion of a minor subpopulation of B-chronic lymphocytic leukemia cells is followed by a delayed but progressive loss of bulk tumor cells and disease regression

Cancer precursor/progenitor cells may initiate and sustain the growth of tumors, but evidence for their existence in human disease is indirect, relying on their it in vitro it properties and animal models. More directly, specific elimination of these rare cells from cancer patients should produce a delayed but progressive disappearance of differentiated malignant progeny. Here, we describe selective eradication of a putative precursor population in a patient with B-cell chronic lymphocytic leukemia, followed 6 months later by a progressive loss of mature tumor cells without further treatment. This outcome supports the presence of a rare population of precursor/progenitor cells in human malignancies, and suggests benefit from their removal

Anti-tumour activity in vitro and in vivo of selective differentiating agents containing hydroxamate

A series of hydroxamates, which are not metalloprotease inhibitors, have been found to be selectively toxic to a range of transformed and human tumour cells without killing normal cells (fibroblasts, melanocytes) at the same concentrations. Within 24 h of treatment, drug action is characterized by morphological reversion of tumour cells to a more normal phenotype (dendritic morphology), and rapid and reversible acetylation of histone H4 in both tumour and normal cells. Two; hydroxamates inhibited growth of xenografts of human melanoma cells in nude mice; resistance did not develop in vivo or in vitro. A third hydroxamate, trichostatin A, was active in vitro but became inactivated and had no anti-tumour activity in vivo. Development of dendritic morphology was found to be dependent upon phosphatase activity, RNA and protein synthesis. Proliferating hybrid clones of sensitive and resistant cells remained sensitive to ABHA, indicating a dominant-negative mechanism of sensitivity. Histone H4 hyperacetylation suggests that these agents act at the chromatin level. This work may lead to new drugs that are potent, and selective anti-tumour agents with low toxicity to normal Cells