In-Vivo Activation Of STAT3 In Angioimmunoblastic T Cell Lymphoma, PTCL Not Otherwise Specified, and ALK Negative Anaplastic Large Cell Lymphoma: Implications For Therapy

T cell lymphoma (TCL) is a heterogeneous group of malignant lymphomas and is subdivided in three major subgroups, (i) cutaneous (mycosis fungoides (MF), sezary syndrome (SS) and primary CTCL), (ii) nodal (peripheral T-cell lymphoma, PTCL NOS, anaplastic large cell lymphoma (ALCL), angioimmunoblastic (AITL)) (iii) and extranodal. Because of this broad morphological spectrum and immunophenotypic variation the pathogenesis of most of the TCL is poorly understood. Constitutive STAT3 signaling provides growth-promoting signals in many forms of malignancy; however in-vivo activation of phosphorylated STAT3 and its clinical correlation in subtypes of TCLs has not been extensively studied. In this study we examined constitutive STAT3 activation in various subtypes of TCL tumors and performed pre-clinical testing to determine whether STAT3 inhibitors will be effective.

First, we assessed the STAT3 activation (pSTAT3^Tyr705) by immunohistochemistry (IHC) on a tissue microarray (TMA) from 169 untreated TCL patient samples. Using a cutoff of ≥30% pSTAT3 nuclear staining, 38% (64/169) of TCL tumors were pSTAT3+. Interestingly, pSTAT3 was differentially expressed among the various TCL subgroups. 27% (16/59) PTCL NOS, 29% (11/38) AITL, 93% (14/15) ALK+ ALCL, 57% (13/28) ALK- ALCL, 50% (6/12) extranodal NK/T cell tumors and 17% (1/6) primary cutaneous showed pSTAT3 positivity. Using either a 30% or 80% cut-off, pSTAT3 positivity was associated with inferior event free survival for AITL, PTCL NOS and ALK neg ALCLs TCLs. Due to small sample size within each group statistical significance (p=0.03) was met only for ALK neg ALCL (80% cutoff). Further analysis in the human TCL cell lines and normal control T-cells also revealed differential expression of pSTATs. ALCL cell lines, Karpas 299 and SR786 were pSTAT3 positive but pSTAT5 negative. Both the CTCL (SS) cell lines HuT78 and SeAx were pSTAT3 negative, however MyLa a cell line of MF origin was strongly pSTAT3+ and pSTAT5+. The normal control CD4 T-cells was pSTAT3- and pSTAT5+. These data clearly suggest that pSTAT3 is differentially expressed among the TCL tumors and is a potential therapeutic target. Potential mechanisms for STAT3 activation could be aberrant secretion of cytokines/chemokines produced by the tumor itself or the tumor microenvironment. We compared the cytokine profile of the culture supernatant from pSTAT3 positive SUDHL1 and pSTAT3 negative HuT78 TCL cell lines using a 30-plex ELISA. The most significantly different cytokines among these 2 cell lines were interleukin -10 (IL-10) and soluble interleukin-2 receptor alpha (sIL-2Ra). The SUDHL1 was found to secrete a very high level (1700 pg/ml) of IL-10, in contrast to only 167 pg/mL in the HuT78 supernatant. Moreover, SUDHL1 secretes 3.5 times more sIL-2Ra (6600 pg/ml) than the pSTAT3 negative cell line HuT78 (1800 pg/ml). In-vitro exposure to IL-10 but not sIL-2Ra was able to further upregulate pSTAT3 in SUDHL1 and Karpas 299. Overall, these data suggest that autocrine secretion of IL-10 but not sIL-2Ra is important for STAT3 activation in ALCL TCLs. Next we compared the cytokine profile of 2 pSTAT3 positive cells from different origin; SUDHL1 (ALCL) and MyLa (MF). In contrast to SUDHL1 (which produce high level of IL-10), MyLa was producing very little IL-10 (18pg/ml). The other most significantly different cytokines between these cells was RANTES with MyLa producing a very high level (28897 pg/ml) and SUDHL1 a very low level (8pg/ml). We also noticed differential level of IL-13 between these cells; MyLa producing 113pg/ml while SUDHL1 only 13 pg/ml. SAR302 (Sanofi, Cambridge, MA), a selective JAK2 inhibitor currently in clinical trial for myeloproliferative neoplasms was able to inhibit autocrine secretion of IL-10 but not sIL-2Ra in a dose-dependent manner followed by STAT3 dephosphorylation and decreased lymphoma cell survival.

In summary, our data provide first evidence of in-vivo STAT3 activation in AITL, PTCL NOS, ALK negative ALCL TCLs using TMA from patient samples. Comprehensive cytokine analysis determined IL-10 as an autocrine factor driving STAT3 activation in ALCLTCLs, while RANTES and IL-13 might be important drivers for STAT3 activation in MF TCLs. Finally our data provide a mechanistic basis of selecting and targeting TCL tumor cells with high IL-10 levels and/or constitutive STAT3 activity with potent and novel JAK2 inhibitors such as SAR302 or other STAT3 inhibitors.