Epigenetic regulation by decitabine of melanoma differentiation in vitro and in vivo

High cytidine deaminase expression in the liver provides sanctuary for cancer cells from decitabine treatment effects

We document for the first time that sanctuary in an organ which expresses high levels of the enzyme cytidine deaminase (CDA) is a mechanism of cancer cell resistance to cytidine analogues. This mechanism could explain why historically, cytidine analogues have not been successful chemotherapeutics against hepatotropic cancers, despite efficacy in vitro. Importantly, this mechanism of resistance can be readily reversed, without increasing toxicity to sensitive organs, by combining cytidine analogue with an inhibitor of cytidine deaminase (tetrahydrouridine). Specifically, CDA rapidly metabolizes cytidine analogues into inactive uridine counterparts. Hence, to determine if sheltering/protection of cancer cells in organs which express high levels of CDA (e.g., liver) is a mechanism of resistance, we utilized a murine xenotransplant model of myeloid cancer that is sensitive to epigenetic therapeutic effects of the cytidine analogue decitabine in vitro and hepato-tropic in vivo. Treatment of tumor-bearing mice with decitabine (subcutaneous 0.2mg/kg 2X/week) doubled median survival and significantly decreased extra-hepatic tumor burden, but hepatic tumor burden remained substantial, to which the animals eventually succumbed. Combining a clinically-relevant inhibitor of CDA (tetrahydrouridine) with a lower dose of decitabine (subcutaneous 0.1mg/kg 2X/week) markedly decreased liver tumor burden without blood count or bone marrow evidence of myelotoxicity, and with further improvement in survival. In conclusion, sanctuary in a CDA-rich organ is a mechanism by which otherwise susceptible cancer cells can resist the effects of decitabine epigenetic therapy. This protection can be reversed without increasing myelotoxicity by combining tetrahydrouridine with a lower dose of decitabine.

Pharmacokinetic and pharmacodynamic analysis of 5-aza-2'-deoxycytidine (decitabine) in the design of its dose-schedule for cancer therapy

5-Aza-2′-deoxycytidine (5-AZA-CdR, decitabine), an epigenetic drug that inhibits DNA methylation, is currently used to treat myelodysplastic syndrome (MDS), and is under investigation for treating acute myeloid leukemia (AML) and other malignancies. 5-AZA-CdR can reactivate tumor suppressor genes silenced by aberrant DNA methylation, a frequent event in all types of cancer. Because this epigenetic change is reversible, it is a good target for 5-AZA-CdR therapy. We have reviewed the preclinical data of 5-AZA-CdR to analyze the concentrations and exposure times required to eradicate cancer stem cells. We analyzed the dose-schedules used in animal models that show potent antineoplastic activity of 5-AZA-CdR. We attempted to correlate the preclinical data with the responses obtained in clinical trials of 5-AZA-CdR in patients with cancer. The pharmacokinetics and drug distribution of 5-AZA-CdR are key parameters because adequate therapeutic drug levels are required to eliminate cancer stem cells in all anatomic compartments. The plasma half-life of 5-AZA-CdR in humans is approximately 20 minutes due to the high levels in the liver of cytidine deaminase, the enzyme that inactivates this analogue. This provides a rationale to use an inhibitor of cytidine deaminase in combination with 5-AZA-CdR. Low-dose 5-AZA-CdR is effective for MDS and AML and can induce complete remissions (CR). However, maintenance of CR with low-dose 5-AZA-CdR is difficult. Based on analyses of preclinical and clinical data, low dose 5-AZA-CdR has the potential to be an effective form of therapy in some patients with cancer. For patients who do not respond to low dose therapy we recommend dose-intensive treatment with 5-AZA-CdR. Patients who are candidates for intensive dose 5-AZA-CdR should have a good bone marrow status so as to permit adequate recovery from myelosuppression, the major toxicity of 5-AZA-CdR. Solid tumors are also interesting targets for therapy with 5-AZA-CdR. Both low dose and intensive therapy with 5-AZA-CdR can reduce the proliferative potential of tumor stem cells in animal models. We propose novel dose schedules of 5-AZA-CdR for investigation in patients with cancer. The full chemotherapeutic potential of 5-AZA-CdR to treat cancer merits further clinical investigation and can only be realized when its optimal dose-schedule is determined.

Epigenetic targeting therapies to overcome chemotherapy resistance

It is now well established that epigenetic aberrations occur early in malignant transformation, raising the possibility of identifying chemopreventive compounds or reliable diagnostic screening using epigenetic biomarkers. Combinatorial therapies effective for the reexpression of tumor suppressors, facilitating resensitization to conventional chemotherapies, hold great promise for the future therapy of cancer. This approach may also perturb cancer stem cells and thus represent an effective means for managing a number of solid tumors. We believe that in the near future, anticancer drug regimens will routinely include epigenetic therapies, possibly in conjunction with inhibitors of "stemness" signal pathways, to effectively reduce the devastating occurrence of cancer chemotherapy resistance.

Trials with 'epigenetic' drugs: an update

Epigenetic inactivation of pivotal genes involved in correct cell growth is a hallmark of human pathologies, in particular cancer. These epigenetic mechanisms, including crosstalk between DNA methylation, histone modifications and non-coding RNAs, affect gene expression and are associated with disease progression. In contrast to genetic mutations, epigenetic changes are potentially reversible. Re-expression of genes epigenetically inactivated can result in the suppression of disease state or sensitization to specific therapies. Small molecules that reverse epigenetic inactivation, so-called epi-drugs, are now undergoing clinical trials. Accordingly, the Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for cancer treatment have approved some of these drugs. Here, we focus on the biological features of epigenetic molecules, analyzing the mechanism(s) of action and their current use in clinical practice.

Differential effects of low-dose decitabine on immune effector and suppressor responses in melanoma-bearing mice

BACKGROUND

Low doses of the demethylating agent decitabine have been shown to enhance the sensitivity of tumors to immune effector cells and molecules through upregulation of tumor antigen presentation and apoptotic pathways. Effects on host immune effector and suppressor responses have not been well characterized.

METHODS

Mice bearing B16 melanoma were treated with low-dose decitabine, cytokine, interleukin-2 (IL-2), toll-like receptor 9 agonist ODN1826, and/or a viral vectored vaccine targeting the melanoma antigen Trp2. Lymphoid and myeloid effector and suppressor cells were examined both systemically and intratumorally with functional, flow cytometric, and polymerase chain reaction-based assays.

RESULTS

Enhancement of tumor growth delay was observed when decitabine was applied sequentially but not concurrently with IL-2. In contrast, complete responses and prolonged survival were observed when decitabine was applied with ODN1826 as therapy and with ODN1826 as a Trp2 vaccine adjuvant. Decitabine decreased natural killer and antigen-specific cellular immune responses when administered concurrently with IL-2 and with ODN1826; the Th1-associated transcription factor Tbet also decreased. T regulatory cells were not affected. When applied concurrently with ODN1826, decitabine increased macrophage cytotoxicity, M1 polarization, and dendritic cell activation. Myeloid-derived suppressor cells were reduced.

CONCLUSION

Low-dose decitabine promotes both anti- and pro-tumor host immune responses to immunotherapeutics in melanoma-bearing mice. Macrophage effector and dendritic cell activation increase, and myeloid suppressor cells decrease. Lymphoid effector responses, however, can be inhibited.

Treatment with the cancer drugs decitabine and doxorubicin induces human skin keratinocytes to express Oct4 and the OCT4 regulator mir-145

Previously, we showed that transient transfection with OCT4 not only produced high expression of Oct4 in skin keratinocytes, but also caused a generalized demethylation of keratinocyte DNA. We hypothesized that DNA demethylation alone might allow expression of endogenous OCT4. Here, we report that treatment with the cancer drug decitabine results in generalized DNA demethylation in skin keratinocytes, and by 48 h after treatment, 96% of keratinocytes show expression of the endogenous Oct4 protein and the OCT4 repressor mir-145. This is true for keratinocytes only, as skin fibroblasts treated similarly show no OCT4 or mir-145 expression. Decitabine-treated keratinocytes also show increased mir-302c and proliferation similar to other Oct4(+) cells. Treatment with doxorubicin, another cancer drug, induces expression of mir-145 only in cells that already express OCT4, suggesting that Oct4 regulates its own repressor. Co-treatment with decitabine and doxorubicin results first in increased OCT4 and mir-145, then a decrease in both, suggesting that OCT4 and mir-145 regulate each other. The novel strategy presented here provides a regulatable system to produce Oct4(+) cells for transformation studies and provides a unique method to study the effects of endogenous Oct4 in cancer cells and the surrounding somatic cells.

Effects of tetrahydrouridine on pharmacokinetics and pharmacodynamics of oral decitabine

The deoxycytidine analog decitabine (DAC) can deplete DNA methyl-transferase 1 (DNMT1) and thereby modify cellular epigenetics, gene expression, and differentiation. However, a barrier to efficacious and accessible DNMT1-targeted therapy is cytidine deaminase, an enzyme highly expressed in the intestine and liver that rapidly metabolizes DAC into inactive uridine counterparts, severely limiting exposure time and oral bioavailability. In the present study, the effects of tetrahydrouridine (THU), a competitive inhibitor of cytidine deaminase, on the pharmacokinetics and pharmacodynamics of oral DAC were evaluated in mice and nonhuman primates. Oral administration of THU before oral DAC extended DAC absorption time and widened the concentration-time profile, increasing the exposure time for S-phase-specific depletion of DNMT1 without the high peak DAC levels that can cause DNA damage and cytotoxicity. THU also decreased interindividual variability in pharmacokinetics seen with DAC alone. One potential clinical application of DNMT1-targeted therapy is to increase fetal hemoglobin and treat hemoglobinopathy. Oral THU-DAC at a dose that would produce peak DAC concentrations of less than 0.2μM administered 2×/wk for 8 weeks to nonhuman primates was not myelotoxic, hypomethylated DNA in the γ-globin gene promoter, and produced large cumulative increases in fetal hemoglobin. Combining oral THU with oral DAC changes DAC pharmacology in a manner that may facilitate accessible noncytotoxic DNMT1-targeted therapy.

p53-Independent, normal stem cell sparing epigenetic differentiation therapy for myeloid and other malignancies

Cytotoxic chemotherapy for acute myeloid leukemia (AML) usually produces only temporary remissions, at the cost of significant toxicity and risk for death. One fundamental reason for treatment failure is that it is designed to activate apoptosis genes (eg, TP53) that may be unavailable because of mutation or deletion. Unlike deletion of apoptosis genes, genes that mediate cell cycle exit by differentiation are present in myelodysplastic syndrome (MDS) and AML cells but are epigenetically repressed: MDS/AML cells express high levels of key lineage-specifying transcription factors. Mutations in these transcription factors (eg, CEBPA) or their cofactors (eg., RUNX1) affect transactivation function and produce epigenetic repression of late-differentiation genes that antagonize MYC. Importantly, this aberrant epigenetic repression can be redressed clinically by depleting DNA methyltransferase 1 (DNMT1, a central component of the epigenetic network that mediates transcription repression) using the deoxycytidine analogue decitabine at non-cytotoxic concentrations. The DNMT1 depletion is sufficient to trigger upregulation of late-differentiation genes and irreversible cell cycle exit by p53-independent differentiation mechanisms. Fortuitously, the same treatment maintains or increases self-renewal of normal hematopoietic stem cells, which do not express high levels of lineage-specifying transcription factors. The biological rationale for this approach to therapy appears to apply to cancers other than MDS/AML also. Decitabine or 5-azacytidine dose and schedule can be rationalized to emphasize this mechanism of action, as an alternative or complement to conventional apoptosis-based oncotherapy.

[Breath test using C-13-trioleate in the evaluation of the rate of fatty acid metabolism after parenteral feeding of premature and newborn infants]

Malignant glioma (MG) is a poor prognostic brain tumor with inevitable recurrence after multimodality treatment. Searching for more effective treatment is urgently needed. Differentiation induction via epigenetic modification has been proposed as a potential anticancer strategy. Natural products are known as fruitful sources of epigenetic modifiers with wide safety margins. We thus explored the effects of oligo-fucoidan (OF) from brown seaweed on this notion in MG cells including Grade III U87MG cells and Grade IV glioblastoma multiforme (GBM)8401 cells and compared to the immortalized astrocyte SVGp12 cells. The results showed that OF markedly suppress the proliferation of MG cells and only slightly affected that of SVGp12 cells. OF inhibited the protein expressions of DNA methyltransferases 1, 3A and 3B (DNMT1, 3A and 3B) accompanied with obvious mRNA induction of differentiation markers (MBP, OLIG2, S100β, GFAP, NeuN and MAP2) both in U87MG and GBM8401 cells. Accordingly, the methylation of p21, a DNMT3B target gene, was decreased by OF. In combination with the clinical DNMT inhibitor decitabine, OF could synergize the growth inhibition and MBP induction in U87MG cells. Appropriated clinical trials are warranted to evaluate this potential complementary approach for MG therapy after confirmation of the effects in vivo.