Amy C. Peterson

PD-L1/B7H-1 Inhibits the Effector Phase of Tumor Rejection by T Cell Receptor (TCR) Transgenic CD8+ T Cells

Although increased circulating tumor antigen-specific CD8+ T cells can be achieved by vaccination or adoptive transfer, tumor progression nonetheless often occurs through resistance to effector function. To develop a model for identifying mechanisms of resistance to antigen-specific CTLs, poorly immunogenic B16-F10 melanoma was transduced to express the Kb-binding peptide SIYRYYGL as a green fluorescent protein fusion protein that should be recognized by high-affinity 2C TCR transgenic T cells. Although B16.SIY cells expressed high levels of antigen and were induced to express Kb in response to IFN-γ, they were poorly recognized by primed 2C/RAG2−/− T cells. A screen for candidate inhibitory ligands revealed elevated PD-L1/B7H-1 on IFN-γ-treated B16-F10 cells and also on eight additional mouse tumors and seven human melanoma cell lines. Primed 2C/RAG2−/−/PD-1−/− T cells showed augmented cytokine production, proliferation, and cytolytic activity against tumor cells compared with wild-type 2C cells. This effect was reproduced with anti-PD-L1 antibody present during the effector phase but not during the priming culture. Adoptive transfer of 2C/RAG2−/−/PD-1−/− T cells in vivo caused tumor rejection under conditions in which wild-type 2C cells or CTLA-4-deficient 2C cells did not reject. Our results support interfering with PD-L1/PD-1 interactions to augment the effector function of tumor antigen-specific CD8+ T cells in the tumor microenvironment.

Chemokine expression in melanoma metastases associated with CD8+ T-cell recruitment.

Despite the frequent detection of circulating tumor antigen-specific T cells, either spontaneously or following active immunization or adoptive transfer, immune-mediated cancer regression occurs only in the minority of patients. One theoretical rate-limiting step is whether effector T cells successfully migrate into metastatic tumor sites. Affymetrix gene expression profiling done on a series of metastatic melanoma biopsies revealed a major segregation of samples based on the presence or absence of T-cell-associated transcripts. The presence of lymphocytes correlated with the expression of defined chemokine genes. A subset of six chemokines (CCL2, CCL3, CCL4, CCL5, CXCL9, and CXCL10) was confirmed by protein array and/or quantitative reverse transcription-PCR to be preferentially expressed in tumors that contained T cells. Corresponding chemokine receptors were found to be up-regulated on human CD8(+) effector T cells, and transwell migration assays confirmed the ability of each of these chemokines to promote migration of CD8(+) effector cells in vitro. Screening by chemokine protein array identified a subset of melanoma cell lines that produced a similar broad array of chemokines. These melanoma cells more effectively recruited human CD8(+) effector T cells when implanted as xenografts in nonobese diabetic/severe combined immunodeficient mice in vivo. Chemokine blockade with specific antibodies inhibited migration of CD8(+) T cells. Our results suggest that lack of critical chemokines in a subset of melanoma metastases may limit the migration of activated T cells, which in turn could limit the effectiveness of antitumor immunity.

T cell anergy is reversed by active Ras and regulated by diacylglycerol kinase

T cell anergy has been correlated with defective signaling by the GTPase Ras, but causal and mechanistic data linking defective Ras activity with T cell anergy are lacking. Here we used adenoviral transduction to genetically manipulate nonproliferating T cells and show that active Ras restored interleukin 2 production and mitogen-activated protein kinase signaling in T cells that were made anergic in vitro or in vivo. Diacylglycerol kinases (DGKs), which negatively regulate Ras activity, were upregulated in anergic T cells, and a DGK inhibitor restored interleukin 2 production in anergic T cells. Both anergy and DGK-α overexpression were associated with defective translocation of the Ras guanine nucleotide–exchange factor RasGRP1 to the plasma membrane. Our data support a causal function for excess DGK activity and defective Ras signaling in T cell anergy.

Immunization with Melan-A peptide-pulsed peripheral blood mononuclear cells plus recombinant human interleukin-12 induces clinical activity and T-cell responses in advanced melanoma.

PURPOSE Preclinical studies showed that immunization with peripheral blood mononuclear cells (PBMC) loaded with tumor antigen peptides plus interleukin-12 (IL-12) induced CD8+ T-cell responses and tumor rejection. We recently determined that recombinant human (rh) IL-12 at 30 to 100 ng/kg is effective as a vaccine adjuvant in patients. A phase II study of immunization with Melan-A peptide-pulsed PBMC + rhIL-12 was conducted in 20 patients with advanced melanoma. PATIENTS AND METHODS Patients were HLA-A2-positive and had documented Melan-A expression. Immunization was performed every 3 weeks with clinical re-evaluation every three cycles. Immune responses were measured by ELISpot assay before and after treatment and through the first three cycles, and were correlated with clinical outcome. RESULTS Most patients had received prior therapy and had visceral metastases. Nonetheless, two patients achieved a complete response, five patients achieved a minor or mixed response, and four patients had stable disease. The median survival was 12.25 months for all patients and was not yet reached for those with a normal lactate dehydrogenase. There were no grade 3 or 4 toxicities. Measurement of specific CD8+ T-cell responses by direct ex vivo ELISpot revealed a significant increase in interferon gamma-producing T cells against Melan-A (P =.015) after vaccination, but not against an Epstein-Barr virus control peptide (P =.86). There was a correlation between the magnitude of the increase in Melan-A-specific cells and clinical response (P =.046). CONCLUSION This immunization approach may be more straightforward than dendritic cell strategies and seems to have clinical activity that can be correlated to a biologic end point.

Tumor progression despite massive influx of activated CD8+ T cells in a patient with malignant melanoma ascites

Although melanoma tumors usually express antigens that can be recognized by T cells, immune-mediated tumor rejection is rare. In many cases this is despite the presence of high frequencies of circulating tumor antigen-specific T cells, suggesting that tumor resistance downstream from T cell priming represents a critical barrier. Analyzing T cells directly from the melanoma tumor microenvironment, as well as the nature of the microenvironment itself, is central for understanding the key downstream mechanisms of tumor escape. In the current report we have studied tumor-associated lymphocytes from a patient with metastatic melanoma and large volume malignant ascites. The ascites fluid showed abundant tumor cells that expressed common melanoma antigens and retained expression of class I MHC and antigen processing machinery. The ascites fluid contained the chemokines CCL10, CCL15, and CCL18 which was associated with a large influx of activated T cells, including CD8+ T cells recognizing HLA-A2 tetramer complexes with peptides from Melan-A and NA17-A. However, several functional defects of these tumor antigen-specific T cells were seen, including poor production of IFN-γ in response to peptide-pulsed APC or autologous tumor cells, and lack of expression of perforin. Although these defects were T cell intrinsic, we also observed abundant CD4+CD25+FoxP3+ T cells, as well as transcripts for FoxP3, IL-10, PD-L1/B7-H1, and indoleamine-2,3-dioxygenase (IDO). Our observations suggest that, despite recruitment of large numbers of activated CD8+ T cells into the tumor microenvironment, T cell hyporesponsiveness and additional negative regulatory mechanisms can limit the effector phase of the anti-tumor immune response.

Phase II study of the Flk-1 tyrosine kinase inhibitor SU5416 in advanced melanoma.

Purpose: Vascular endothelial growth factor (VEGF) expression is prognostic in melanoma, and the activity of VEGF is mediated in part through the receptor tyrosine kinase Flk-1. A Phase II study of SU5416, a preferential inhibitor of Flk-1, was carried out in patients with metastatic melanoma to determine clinical response, tolerability, and changes in tumor vascular perfusion. Experimental Design: Patients with documented progressive disease and ≤1 prior therapy were eligible. Central nervous system metastases were allowed if stable off medication. SU5416 (145 mg/m2) was administered via a central catheter twice weekly for 8 weeks. Premedication with dexamethasone, diphenhydramine, and a H2 blocker was required because of the Cremophor vehicle. Tumor vascular perfusion was assessed before treatment and during week 8 by dynamic contrast magnetic resonance imaging, and plasma was analyzed for VEGF. Results: Thirty-one patients were enrolled. Two-thirds had received prior therapy, 21 had visceral metastasis, and 14 had an elevated lactate dehydrogenase. Mean absolute lymphocyte counts were decreased (P = 0.002), and glucose levels were increased (P = 0.001) posttherapy, presumably because of steroid premedication. Four vascular adverse events were observed. Of 26 evaluable patients, 1 experienced a partial response, 1 had stable disease, and 5 had a mixed response. Dynamic contrast magnetic resonance imaging in 5 evaluable patients showed decreased tumor perfusion at week 8 (P = 0.024), and plasma VEGF levels were elevated compared with pretherapy (P = 0.008). Conclusions: SU5146 appears to be relatively well tolerated in this population. Although the modest clinical activity and potential effects on tumor vascularity may support additional exploration of VEGF as a target in melanoma, effects from steroid premedication limit further investigation of this agent.

Bridging the Gap between Preclinical and Clinical Studies Using Pharmacokinetic–Pharmacodynamic Modeling: An Analysis of GDC-0973, a MEK Inhibitor

Purpose: GDC-0973 is a potent and selective mitogen-activated protein (MAP)/extracellular signal–regulated kinase (ERK) kinase (MEK) inhibitor. Pharmacokinetic–pharmacodynamic (PK–PD) modeling was used to relate GDC-0973 plasma and tumor concentrations, tumor pharmacodynamics and antitumor efficacy to establish pharmacokinetic endpoints and predict active doses in the clinic. Experimental Design: A PK–PD model was used to characterize GDC-0973 tumor disposition and in vivo potency in WM-266-4 xenograft mice. Simulations were conducted using the PK–PD model along with human pharmacokinetics to identify a target plasma concentration and predict active doses. In vivo potency and antitumor efficacy were characterized in A375 melanoma xenograft mice, and a population-based integrated PK–PD-efficacy model was used to relate tumor pharmacodynamics (%pERK decrease) to antitumor activity. Results: GDC-0973 showed a sustained tumor pharmacodynamic response due to longer residence in tumor than in plasma. Following single doses of GDC-0973, estimated in vivo IC50 values of %pERK decrease based on tumor concentrations in xenograft mice were 0.78 (WM-266-4) and 0.52 μmol/L (A375). Following multiple doses of GDC-0973, the estimated in vivo IC50 value in WM-266-4 increased (3.89 μmol/L). Human simulations predicted a minimum target plasma concentration of 83 nmol/L and an active dose range of 28 to 112 mg. The steep relationship between tumor pharmacodynamics (%pERK decrease) and antitumor efficacy suggests a pathway modulation threshold beyond which antitumor efficacy switches on. Conclusions: Clinical observations of %pERK decrease and antitumor activity were consistent with model predictions. This article illustrates how PK–PD modeling can improve the translation of preclinical data to humans by providing a means to integrate preclinical and early clinical data. Clin Cancer Res; 18(11); 3090–9. ©2012 AACR.

Reply to A. Soultati et al

We have read with interest the comment from Soultati et al in reference to the randomized phase II study of onartuzumab in combination with erlotinib in patients with advanced non–small-cell lung cancer (NSCLC). Soultati et al recognize that MET inhibition may not be best assessed using traditional response criteria and suggest reviewing our data to better define the pattern of disease progression. If progression was primarily due to new sites of distant disease and not growth of baseline lesions, this might potentially account for the low objective response rate observed in our study. A review of the imaging data from computed tomography scanning does not identify any differences in the proportion or patterns of disease progression between treatment arms. Since the phase II publication, the results of a recently completed phase III trial of onartuzumab and erlotinib in patients with advanced MET-positive NSCLC have been presented. Unfortunately there was no advantage for onartuzumab in terms of survival, progression-free survival, or response. Although this trial did not replicate the phase II results, targeting MET may still prove to be a useful strategy in more defined patient populations in which this is a key oncogenic driver of disease.

T cell development and function in CrkL-deficient mice.

The adapter protein CrkL has been implicated in multiple signal transduction pathways in hematopoietic cells. In T lymphocytes, the recruitment of CrkL‐C3G complexes has been correlated with hyporesponsiveness, implicating CrkL as a potential negative regulator. To test this hypothesis we examined T cell activation in CrkL‐deficient mice. The CrkL–/– genotype was partially embryonic lethal. In viable CrkL–/– mice, peripheral blood counts were normal. The thymus from CrkL–/– mice had 40% fewer cells compared to littermates, but the proportion of thymocyte subsets was comparable. There was no discernable alteration in T cell function as reflected by T cell numbers, expression of memory markers, IL‐2 production, proliferation, and differentiation into Th1/Th2 phenotypes. Immunization induced comparable levels of IgG2a and IgG1 antibodies. Chimeric mice, generated by transfer of CrkL–/– fetal liver cells into irradiated RAG2–/– recipients, also showed normal T cell function, arguing against selection via partial embryonic lethality. Our results indicate that CrkL is not absolutely required for T cell development or function, and argue against it being an essential component of a negative regulatory pathway in TCR signaling.

Enzalutamide in combination with docetaxel in men with prostate cancer (PC): Preliminary results from a phase I study.

63 Background: Enzalutamide (ENZA), a novel oral androgen receptor (AR) inhibitor, inhibits AR signaling via inhibition of androgen binding to the AR, AR nuclear translocation, and nuclear AR-DNA binding. ENZA demonstrated a survival benefit in men with metastatic castration-resistant prostate cancer (mCRPC) who had received prior docetaxel (Scher et al, NEJM 2012; 367:1187). A Phase III study in men with progressive chemotherapy-naïve disease (PREVAIL), is ongoing. Docetaxel (DOC) is the current standard first-line chemotherapy for mCRPC. CYP3A4, which plays a role in DOC clearance, is induced by ENZA. Patients (pts) eligible to receive DOC may benefit from continued AR inhibition with ENZA, provided the combination is well tolerated with no unacceptable drug-drug interactions. METHODS This study evaluated the safety and pharmacokinetics (PK) of DOC co-administered with ENZA in men with mCRPC on androgen deprivation therapy. Pts received DOC (75 mg/m2) by 1-h infusion every 3 weeks, with corticosteroids. ENZA (160 mg/d) was started 24 h after the first DOC infusion. Plasma PK samples were collected for 24 h after Cycle (C) 1 and C2 DOC infusions to enable within-subject comparisons of DOC PK ± ENZA. A sample size of 18 pts able to receive ≥ 2 full doses of DOC was specified for PK analyses. RESULTS As of 21 Sept. 2012, 22 pts have been enrolled, 3 did not complete both C1 and C2; PK and C1 and C2 safety data are currently available from 15 pts reported here. The median age was 65 (range 46-80 yrs); 11 had ECOG performance status 1 (vs 0). Prior primary therapy included surgery (n=2), radiation (n=4) or both (n=5); median PSA was 44.7ng/mL (1.9-585). ANC<1000mm3 was reported in 14 pts (1 febrile neutropenia), other adverse events in ≥4 pts included fatigue (11), dyspnea (6), alopecia (5), peripheral neuropathy (5), anemia (4) and dysgueusia (4). No seizures were reported. Preliminary PK data (n=15) show similar DOC exposure (within 20%) for DOC in combination with ENZA vs. DOC alone. CONCLUSIONS This is the first evaluation of ENZA given in combination with DOC.In mCRPC pts ENZA does not appear to affect tolerability of DOC or have a clinically meaningful impact on DOC PK. CLINICAL TRIAL INFORMATION NCT01565928.