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.

The expression of ASPP2 (53BP2L), a proapoptotic member of a family of p53-binding proteins, is frequently suppressed in many human cancers. Accumulating evidence suggests that ASPP2 inhibits tumor growth; however, the mechanisms by which ASPP2 suppresses tumor formation remain to be clarified. To study this, we targeted the ASPP2 allele in a mouse by replacing exons 10 -17 with a neoR gene. ASPP2 ؊/؊ mice were not viable because of an early embryonic lethal event. Although ASPP2 ؉/؊ mice appeared developmentally normal, they displayed an increased incidence of a variety of spontaneous tumors as they aged. Moreover, ␥-irradiated 6-week-old ASPP2 ؉/؊ mice developed an increased incidence of high-grade T cell lymphomas of thymic origin compared with ASPP2 ؉/؉ mice. Primary thymocytes derived from ASPP2 ؉/؊ mice exhibited an attenuated apoptotic response to ␥-irradiation compared with ASPP2 ؉/؉ thymocytes. Additionally, ASPP2 ؉/؊ primary mouse embryonic fibroblasts demonstrated a defective G0/G1 cell cycle checkpoint after ␥-irradiation. Our results demonstrate that ASPP2 is a haploinsufficient tumor suppressor and, importantly, open new avenues for investigation into the mechanisms by which disruption of ASPP2 pathways could play a role in tumorigenesis and response to therapy.A poptosis-stimulating protein of p53-2 (ASPP2), also known as 53BP2L, encoded by TP53BP2 (1-3), enhances damage-induced apoptosis at least in part through a p53-mediated pathway (2, 4 -6). Depending on cell context and type of stress, ASPP2 levels increase via transcriptional or posttranslational mechanisms after cellular damage (4, 6). In addition to interacting with p53 (and family members) (5, 7), ASPP2 protein, and the 123-aa, amino-terminal, truncated splice isoform 53BP2/Bbp, also known as 53BP2S (3), interacts with several proteins involved in modulating apoptosis and cell growth, including Bcl-2, p65/RelA subunit of NF-B, Yesassociated protein-1, HCV core protein, APCL, and protein phosphatase-1 (8 -13). Additionally, ASPP2 is a direct E2F target gene, suggesting that it is a common link between the Rb/E2F and p53/p73 pathways (14 -16). ASPP2 expression is suppressed in many human cancers, and it has been associated with poor clinical outcome in patients with aggressive nonHodgkin's lymphoma treated with chemotherapy (2, 17-24). These findings suggest that ASPP2 is involved in important tumor suppression networks and the cellular damage response. Overexpression of ASPP2 or Bbp/53BP2S can suppress E1A and ras-mediated transformation of rat embryo fibroblasts (25,26), whereas attenuation of ASPP2 expression promotes clonogenic survival and inhibits apoptosis in cell culture (2, 4, 6) and promotes tumor formation in vivo (27). However, the mechanisms by which reduced ASPP2 expression enhances tumor formation in vivo remain to be elucidated.In this report, we targeted the ASPP2 allele in a mouse by using homologous recombination to explore the in vivo consequences of attenuated ASPP2 expression. We demonstrate that reduced ASPP2 express...

The p53 pathway is a central mediator of the apoptotic response. ASPP2/ 53BP2L (apoptosis-stimulating protein of p53 2, also known as 53BP2L) enhances apoptosis through selective stimulation of p53 transactivation of proapoptotic target genes. Although the Rb/E2F pathway regulates ASPP2/ 53BP2L transcription, the complex mechanisms controlling ASPP2/ 53BP2L levels and function remain unknown. We now report that proteasomal degradation modulates ASPP2/ 53BP2L protein levels and apoptotic function. Treatment of cells with proteasomal inhibitors, including the clinically utilized proteasomal inhibitor bortezomib, increases ASPP2/ 53BP2L protein but not RNA levels. Likewise, anthracycline-based chemotherapy, which has multiple mechanisms of action, including proteasomal inhibition, increases ASPP2/ 53BP2L protein but not RNA levels. Proteasomal inhibition or anthracycline treatment increases ASPP2/ 53BP2L protein stability and half-life. Furthermore, the central region of the ASPP2/ 53BP2L protein is ubiquitinated as would be expected for a proteasomal substrate. More importantly, small interfering RNA knockdown of ASPP2/ 53BP2L levels attenuated bortezomib-induced apoptosis, and this effect was greater in wildtype p53 cells. Because elevated levels of ASPP2/ 53BP2L are proapoptotic, these results described an important new molecular mechanism that modulates the p53-ASPP2/ 53BP2L apoptotic pathway.

Apoptosis Stimulating Protein of p53-2, ASPP2, aka 53BP2L, (encoded by TP53BP2) is a pro-apoptotic member of a family of p53 binding proteins. ASPP2 expression is frequently suppressed in human cancers and numerous studies have consistently demonstrated that ASPP2 inhibits cell growth as well as stimulates apoptosis-at least in part through a p53-mediated pathway. Two independent mouse models have shown that ASPP2 is a haplo-insufficient tumor suppressor and underscore the importance of the role of ASPP2 in human cancer. However, mounting evidence suggests that the mechanism(s) of action for ASPP2 are complex and likely extend beyond stimulation of apoptotic programs. Data highlighting this expanding spectrum of potential ASPP2-mediated pathways is summarized along with new results from recent in vivo models suggesting new avenues for investigation.

The FLT3 inhibitor tandutinib (formerly MLN518) has sequence-independent synergistic effects with cytarabine and daunorubicin , Cell Cycle, 8:16, 2621-2630 To link to this article: https://doi.org/10.4161/cc.8.16.9355 But the data also show that optimal use of tandutinib will require combination therapy with cytotoxic agents. Notably, single agent tandutinib has not been associated with myelosuppression, mucositis or cardiac toxicity-the dose limiting toxicities of AML chemotherapy.We determined the feasibility of combining tandutinib with the standard "3 + 7" induction regimen in AML and show that, in contrast to other structurally unrelated FLT3 inhibitors recently evaluated in clinical trials, the use of tandutinib displayed application sequence independent synergistic antileukemic effects in combination with cytarabine and daunorubicin. Strong synergistic antiproliferative and proapoptotic effects were thereby predominantly seen on FLT3 ITD positive blasts. Further we demonstrate, that addition of tandutinib may allow dose reduction of chemotherapy without loss of overall antileukemic activity-resulting in a potential decrease of side effects. This approach might be an interesting novel strategy especially in the treatment of elderly/comorbid patients.Our data provide a rationale for combining tandutinib with induction chemotherapy in intensified as well as in dose reduction protocols for FLT3 ITD positive AML.