In chronic myeloid leukemia (CML), BCR/ABL-mediated oncogenic signaling can be targeted with the BCR/ABL-inhibitors Imatinib, Nilotinib and Dasatinib. However, these agents may also affect anti-tumor immunity. Here, we analyzed the effects of the 3 BCR/ABL-inhibitors on natural killer (NK) cell reactivity. Exposure of CML cells (K562, Meg-01) to pharmacological concentrations of Imatinib, Nilotinib and Dasatinib diminished expression of ligands for the activating immunoreceptor NKG2D to a similar extent. This resulted in comparably reduced NK cell cytotoxicity and IFN-c production. When direct effects on NK cell responses to K562 and primary CML cells as well as activating cytokines were studied, Dasatinib was found to abrogate NK cytotoxicity and cytokine production. Nilotinib did not alter cytotoxicity but, at high levels, impaired NK cytokine production, while Imatinib had no direct influence on NK cell reactivity. Of note, Nilotinib, but not the other BCR/ABL-inhibitors increased cell death within the preferentially cytokine-secreting CD56 bright CD16 2 NK cell subset, which may, at least in part, serve to explain the effect of Nilotinib on NK cytokine production. Analysis of NK cell signaling revealed that Dasatinib inhibited proximal signaling events leading to decreased phosphorylation of PI3K and ERK that are crucial for NK cell reactivity. Imatinib and Nilotinib, in contrast, showed no relevant effect on NK cell PI3K or ERK activity. In light of the potential role of NK cells in the immunesurveillance of residual leukemia and for future combinatory immunotherapeutic approaches, our data indicate that choice and dosing of the most suitable BCR/ABL-inhibitor for a given patient require careful consideration.Chronic myeloid leukemia (CML) is a myeloproliferative disease that is characterized by the reciprocal t(9;22) translocation, the Philadelphia chromosome. The Philadelphia chromosome results in the BCR/ABL fusion protein, a protein kinase (PK) mediating the oncogenic signaling in the majority of CML patients. 1 This stimulated the development and the clinical approval of the BCR/ABL-inhibitor Imatinib (STI571, Gleevec; Novartis Pharmaceuticals, East Hannover, NJ), an orally administered compound that was shown to block proliferation and to induce apoptosis of BCR/ABL-positive CML cells. 2 To study the clinical efficacy of Imatinib in the treatment of CML patients, the open-label phase III International Randomized Study of Interferon and STI571 (IRIS) was initiated in 2000. The 7-year follow-up of the IRIS trial confirmed that patients receiving Imatinib had significantly better results with regard to complete molecular responses and progression of disease than patients receiving interferon-a (IFN-a). 3 However, some patients show disease progression under Imatinib, for example, due to point mutations causing Imatinib resistance. Thus, second generation BCR/ABL-inhibitors like Nilotinib (AMN107, Novartis Pharmaceuticals, Basel, Switzerland) and Dasatinib (BMS-354825, Bristol-Myers Squibb, Princeton, NJ)...

Sunitinib and Sorafenib are protein kinase inhibitors (PKI) approved for treatment of patients with advanced renal cell cancer (RCC). However, long-term remissions of advanced RCC have only been observed after IL-2 treatment, which underlines the importance of antitumor immune responses in RCC patients. Because PKI, besides affecting tumor cells, also may inhibit signaling in immune effector cells, we determined how Sunitinib and Sorafenib influence antitumor immunity. We found that cytotoxicity and cytokine production of resting and IL-2-activated PBMC are inhibited by pharmacological concentrations of Sorafenib but not Sunitinib. Analysis of granule-mobilization within PBMC revealed that this was due to impaired reactivity of NK cells, which substantially contribute to antitumor immunity by directly killing target cells and shaping adaptive immune responses by secreting cytokines like IFN-γ. Analyses with resting and IL-2-activated NK cells revealed that both PKI concentration dependently inhibit cytotoxicity and IFN-γ production of NK cells in response to tumor targets. This was due to impaired PI3K and ERK phosphorylation which directly controls NK cell reactivity. However, while Sorafenib inhibited NK cell effector functions and signaling at levels achieved upon recommended dosing, pharmacological concentrations of Sunitinib had no effect, and this was observed upon stimulation of NK cell reactivity by tumor target cells and upon IL-2 treatment. In light of the important role of NK cells in antitumor immunity, and because multiple approaches presently aim to combine PKI treatment with immunotherapeutic strategies, our data demonstrate that choice and dosing of the most suitable PKI in cancer treatment requires careful consideration.

Multiple approaches presently aim to combine targeted therapies using tyrosine kinase inhibitors with immunotherapy. Ex vivo-generated dendritic cells are frequently used in such strategies due to their unique ability to initiate primary T-cell immune responses. Besides governing tumor cell growth, many kinases targeted by tyrosine kinase inhibitors are involved in the development and function of dendritic cells and thus tyrosine kinase inhibitor therapy may cause immunoinhibitory side effects. We here report that exposure of developing human monocyte-derived dendritic cells to the BCR-ABL inhibitors imatinib, dasatinib, and nilotinib results in profound upregulation of the transmembrane glycoprotein osteoactivin that has recently been characterized as a negative regulator of T-cell activation. Thus, in line with osteoactivin upregulation, exposure to tyrosine kinase inhibitors resulted in significantly reduced stimulatory capacity of dendritic cells in mixed lymphocyte reactions that could be restored by the addition of blocking anti-osteoactivin antibody. Our data demonstrate that tyrosine kinase inhibitor-mediated inhibition of dendritic cell function is, at least in great part, mediated by upregulation of the immune inhibitory molecule osteoactivin.

In chronic myeloid leukemia (CML), the translocation t(9;22) results in the fusion protein BCR-ABL (breakpoint cluster region-abelson murine leukemia), a tyrosine kinase mediating oncogenic signaling which is successfully targeted by treatment with BCR-ABL inhibitors like imatinib. However, BCR-ABL inhibitors may also affect antitumor immunity. For instance, it was reported that imatinib impairs the function of dendritic cells (DCs) that play a central role in initiating and sustaining T cell responses. Meanwhile, second generation BCR-ABL inhibitors like nilotinib, which inhibits BCR-ABL with enhanced potency have become standard of treatment, at least in patients with BCR-ABL kinase domain mutations. In this study we analyzed the influence of therapeutic concentrations of nilotinib on human monocyte-derived DCs and compared its effects to imatinib. We found that both tyrosine kinase inhibitors (TKI) comparably and significantly impaired differentiation of monocytes to DCs as revealed by curtated downregulation of CD14 and reduced upregulation of CD1a and CD83. This was only partially restored after withdrawal of the TKI. Moreover, both TKI significantly reduced activation-induced IL-12p70 and C-C motif chemokine ligand (CCL) 3 secretion, while divergent TKI effects for CCL2 and CCL5 were observed. In contrast, only nilotinib significantly impaired the migratory capacity of DCs and their capacity to induce T-cell immune responses in MLRs. Our results indicate that imatinib and nilotinib may differ significantly with regard to their influence on antitumor immunity. Thus, for future combinatory approaches and particularly stop studies in CML treatment, choice of the most suitable BCR-ABL inhibitor requires careful consideration.

1733 Targeted therapies with tyrosine kinase inhibitors (TKI) have significantly improved the treatment of cancer patients. Ex vivo generated dendritic cells (DC) are commonly used in immunotherapeutic strategies due to their unique ability to initiate adaptive immune responses, and multiple approaches presently aim to combine targeted therapies with immunotherapy. However, as many kinases targeted by TKI are, besides governing tumor cell growth, also involved in the activation of DC, TKI therapy may cause immunoinhibitory side effects. Osteoactivin (GPNMB, DC-HIL) is a type I transmembrane glycoprotein that is detected abundantly in DC but not in monocytes. Its expression on antigen-presenting cells can inhibit T cell activation by binding syndecan-4 (SD-4) on T cells. Here we investigated the effect of the BCR/ABL TKI imatinib, dasatinib and nilotinib, which are approved for the treatment of CML, on the expression of osteoactivin and DC functions. DC were generated from blood monocytes by plastic adherence and exposure to GM-CSF and IL-4. Imatinib, nilotinib or dasatinib were added to the culture medium every second day starting from the first day of culture. In some experiments, toll-like receptor (TLR) ligands (L) (LPS (TLR4L), pam3Cys (TLR2L), poly I:C (TLR3L) or R848 (TLR7/8L) were added on day 6 of culture for maturation of DC. We found that DC generated in the presence of therapeutic concentrations of all three TKI displayed an altered phenotype. Imatinib caused significantly reduced expression of the typical DC markers CD1a, CD83 and the co-stimulatory molecule CD86. Nilotinib reduced the expression of CD1a, CD83, CD86 and the DC-specific C-type lectin receptor DC-SIGN (CD209). Dasatinib impaired expression of CD1a, CD83, CD86, CD80 and DC-SIGN. Most notably, we observed excessive up-regulation of osteoactivin on DC upon treatment with all three TKI. Interestingly, incubation with the immunosuppressive and anti-inflammatory cytokine IL-10 also resulted in osteoactivin over-expression. In line with osteoactivin up-regulation, exposure to TKI resulted in reduced stimulatory capacity of DC in MLR with allogenic T cells that could be restored by addition of blocking anti-osteoactivin antibody. In summary, our data demonstrate that up-regulation of osteoactivin is critically involved in the inhibition of DC function upon TKI exposure. These findings are of great importance for future combinatory approaches using TKI and DC-based immunotherapy and indicate that inhibition of osteoactivin expression or function may serve as a novel strategy to enhance the efficacy of immunotherapeutic interventions in cancer patients. Disclosures: No relevant conflicts of interest to declare.