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Although TP53 mutations are rare in acute myeloid leukemia (AML), wild type p53 function is habitually annulled through overexpression of MDM2 or through various mechanisms including epigenetic silencing by histone deacetylases (HDACs). We hypothesized that co-inhibition of MDM2 and HDACs, with nutlin-3 and valproic acid (VPA) would additively inhibit growth in leukemic cells expressing wild type TP53 and induce p53-mediated apoptosis. In vitro studies with the combination demonstrated synergistic induction of apoptosis in AML cell lines and patient cells. Nutlin-3 and VPA co-treatment resulted in massive induction of p53, acetylated p53 and p53 target genes in comparison with either agent alone, followed by p53 dependent cell death with autophagic features. In primary AML cells, inhibition of proliferation by the combination therapy correlated with the CD34 expression level of AML blasts. To evaluate the combination in vivo, we developed an orthotopic, NOD/SCID IL2rγ(null) xenograft model of MOLM-13 (AML FAB M5a; wild type TP53) expressing firefly luciferase. Survival analysis and bioluminescent imaging demonstrated the superior in vivo efficacy of the dual inhibition of MDM2 and HDAC in comparison with controls. Our results suggest the concomitant targeting of MDM2-p53 and HDAC inhibition, may be an effective therapeutic strategy for the treatment of AML.

From the early inception of the transplant models through to contemporary genetic and xenograft models, evolution of murine leukaemic model systems have been critical to our general comprehension and treatment of cancer, and, more specifically, disease states such as acute myelogenous leukaemia (AML). However, even with modern advances in therapeutics and molecular diagnostics, the majority of AML patients die from their disease. Thus, in the absence of definitive in vitro models which precisely recapitulate the in vivo setting of human AMLs and failure of significant numbers of new drugs late in clinical trials, it is essential that murine AML models are developed to exploit more specific, targeted therapeutics. While various model systems are described and discussed in the literature from initial transplant models such as BNML and spontaneous murine leukaemia virus models, to the more definitive genetic and clinically significant NOD/SCID xenograft models, there exists no single compendium which directly assesses, reviews or compares the relevance of these models. Thus, the function of this article is to provide clinicians and experimentalists a chronological, comprehensive appraisal of all AML model systems, critical discussion on the elucidation of their roles in our understanding of AML and consideration to their efficacy in the development of AML chemotherapeutics.

Both clinical and experimental evidence indicate that T lymphocytes can mediate antileukemic effects in acute myelogenous leukemia (AML). These antileukemic effects can be either nonspecific cytotoxicity (killer cell activity) or reactivity against leukemia-specific antigenic peptides presented by self-HLA molecules. The antigen-specific T cell activation requires recognition of specific peptides together with costimulatory signalling. For most patients the AML blasts express both HLA class I and class II molecules for antigenic presentation, but patients are heterogeneous with regard to: (1) expression of costimulatory binding molecules; (2) expression of receptors/counterreceptors involved in induction of apoptosis; (3) constitutive release of immunomodulatory soluble mediators. This heterogeneity suggests that the ability of AML blasts to initiate an antileukemic T cell response will differ between individual patients. Thus, clinical approaches for immunotherapy in AML have to overcome three major problems. First, the therapy should reduce the patient heterogeneity so that therapeutic effects become more predictable; or alternatively one should define patient subsets which are likely to benefit from immunotherapy. Second, immunotherapy should enhance antileukemic T cell reactivity or blast susceptibility to immune attacks. Third, the therapeutic procedures must be safe and suitable for routine use. All three problems probably have to be solved before immunotherapy can become a routine treatment.

Blast cells derived from patients with acute myelogenous leukemia (AML) were cultured in the presence of interleukin-13 (IL-13). IL-13 did not cause statistically significant alterations of AML blast proliferation when cells were cultured in medium alone or together with IL-4, granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor. In contrast, IL-13 inhibited constitutive AML blast secretion of IL-1 alpha, IL-1 beta, IL-6, tumor necrosis factor alpha, granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor. IL-4 caused a similar inhibition of constitutive cytokine secretion as IL-13, but IL-13 caused no additive inhibition in the presence of IL-4. In contrast to IL-4 which increased AML blast release of IL-1 receptor antagonist, IL-13 caused no significant alteration of blast release of the receptor antagonist. IL-13 inhibited cytokine secretion also in the presence of neutralizing IL-4 and IL-10 antibodies and when AML blasts were cultures in serum-free conditions. We conclude that IL-13 has a direct and nontoxic inhibitory effect on constitutive AML blast cytokine secretion.

The effect of interleukin 10 (IL-10) on proliferation and cytokine secretion by acute myelogenous leukemia (AML) blast cells was investigated in vitro. IL-10 inhibited spontaneous AML blast proliferation for a majority of patients, whereas in the presence of exogenous growth factors (granulocyte-stimulating factor, G-CSF; granulocyte-macrophage colony-stimulating factor, GM-CSF; interleukin 3) the IL-10 effect on blast proliferation showed a wide variation depending on the individual AML patient. IL-10 seemed to cause an irreversible inhibitory effect on AML blasts, as inhibition could also be demonstrated when IL-10 was present only during the initial preincubation of the leukemia cells. IL-10 also inhibited AML blast colony formation. However, independent of the effect on AML blast proliferation, IL-10 decrease cytokine secretion from AML blast cells for all patients, as demonstrated for IL-1 alpha, IL-1 beta, tumor necrosis factor-alpha, GM-CSF and interleukin 6. IL-10 did not inhibit development of apoptosis in AML blasts cultured in vitro. Expression of complement receptors and capability to adhere and internalize bacteria by AML blasts were not altered by IL-10.