Abstract 2540: Immune modulation by the TLR8 agonist VTX-2337; a comparison of the pharmacodynamic response in cancer patients and healthy volunteers

Immunotherapy has proven to be a successful treatment approach for some cancer patients. One promising paradigm in immunotherapy is targeting pathogen-associated molecule pattern receptors (PAMPS) such as the toll-like receptors (TLRs) to activate the innate immune system and enhance the development of tumor-directed adaptive immune responses. However, an ongoing concern in the application of immunotherapeutics is the potential for the immune response in cancer patients to be less robust than in healthy individuals, due to the underlying advanced neoplastic disease or due to previous regimens of cytotoxic drugs. To address this concern in relation to the response to TLR8 stimulation, we compared the pharmacokinetic and pharmacodynamic (PK/PD) relationship defined in a phase 1 clinical trial of the selective small molecule TLR8 agonist VTX-2337 in oncology patients to the response in healthy volunteers.

A phase 1 dose-escalation clinical trial (A101) in subjects with advanced solid tumors (n=33) demonstrated that plasma levels of multiple biomarkers of immune activation, including G-CSF, MCP-1, MIP1-β and TNFα, increased in a dose-dependent manner and correlated with increasing plasma levels of VTX-2337. The PK/PD relationship defined in the initial clinical trial was closely aligned with predictions from both in vitro assays and preclinical studies conducted in cynomolgus monkeys. A subsequent phase 1 trial (A105) was conducted as a single-center, open-label, two-period, randomized, crossover, phase 1 study in normal volunteers (n=10). The objective of this study was to compare the PK/PD profiles and local tolerance of two formulations of VTX-2337. In this study, the two preparations of VTX-2337 demonstrated comparable PK profiles and PD responses.

At comparable dose levels, the PK profile and overall exposure (AUC) to VTX-2337 was similar for oncology patients and healthy volunteers. VTX-2337 induced the same repertoire of circulating cytokines and chemokines, indicative of TLR8 activation, in both populations. The magnitude of the mediator response in oncology patients was also highly comparable to the response in healthy volunteers that received a similar dose. This comparison demonstrates that the immune system of cancer patients with advanced disease remains highly responsive to TLR8 activation by VTX-2337.

In summary, advanced neoplastic disease or a prior treatment history with cytotoxic agents that can negatively impact immune cell function did not appear to moderate the response to VTX-2337 based on the PK/PD relationship using predictive biomarkers.

Citation Format: Greg Dietsch, Donald Northfelt, Ramesh Ramanathan, Peter Cohen, Kristi Manjarrez, Mona Newkirk, James Kyle Bryan, Robert Hershberg. Immune modulation by the TLR8 agonist VTX-2337; a comparison of the pharmacodynamic response in cancer patients and healthy volunteers. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2540. doi:10.1158/1538-7445.AM2014-2540

Personalized approach to growth hormone treatment: clinical use of growth prediction models

The goal of growth hormone (GH) treatment in a short child is to attain a fast catch-up growth toward the target height (TH) standard deviation score (SDS), followed by a maintenance phase, a proper pubertal height gain, and an adult height close to TH. The short-term response variable of GH treatment, first-year height velocity (HV) (cm/year or change in height SDS), can either be compared with GH response charts for diagnosis, age and gender, or with predicted HV based on prediction models. Three types of prediction models have been described: the Kabi International Growth Hormone Study models, the Gothenburg models and the Cologne model. With these models, 50-80% of the variance could be explained. When used prospectively, individualized dosing reduces the variation in growth response in comparison with a fixed dose per body weight. Insulin-like growth factor-I-based dose titration also led to a decrease in the variation. It is uncertain whether adding biochemical, genetic or proteomic markers may improve the accuracy of the prediction. Prediction models may lead to a more evidence-based approach to determine the GH dose regimen and may reduce the drug costs for GH treatment. There is a need for user-friendly software programs to make prediction models easily available in the clinic.

The cytoprotective peptide humanin is induced and neutralizes Bax after pro-apoptotic stress in the rat testis

We have previously demonstrated that the mitochondria-derived cytoprotective peptide humanin (HN), when administered intratesticularly to rats, rescues germ cells from apoptosis secondary to testicular stress of hormonal deprivation induced by gonadotropin-releasing hormone antagonist (GnRH-A). To decipher the cellular mechanisms of HN action in the amelioration of GnRH-A-induced germ cell apoptosis, adult male rats received the following treatments for 5 days: (i) daily intratesticular (IT) injections with saline (control); (ii) a single subcutaneous injection of GnRH-A on Day 1 and daily IT injection of saline; (iii) daily IT injection of synthetic HN; and (iv) GnRH-A injection on Day 1 and daily IT injection of HN (GnRH-A+HN). HN alone had no effect on germ cell apoptosis. GnRH-A increased germ cell apoptosis and BAX in the testicular mitochondrial fractions. Synthetic HN decreased germ cell apoptosis induced by GnRH-A and BAX in the mitochondria. We deduced that the cytoprotective action of synthetic HN on GnRH-A-induced germ cell apoptosis was mediated by attenuating p38 mitogen-activated protein kinase activity and increasing STAT3 phosphorylation. The effect of synthetic HN on the expression of endogenous rat HN in the testis was studied using rat HN specific antibody. GnRH-A treatment increased, but concomitant treatment with synthetic HN reduced endogenous rat HN expression in both cytosolic and mitochondrial fractions in testis. Co-immunoprecipitation experiments demonstrated that the increased rat HN was physically associated with BAX in the cytosolic testicular fractions after GnRH-A treatment. Double-immunofluorescence staining confirmed the co-localization of BAX and rat HN in the cytoplasm of Leydig cells and spermatocytes after GnRH-A treatment. We conclude that the cytoprotective effect of exogenously administered synthetic HN is mediated by interactions of endogenous rat HN with BAX in the cytoplasm preventing the entry of BAX to the mitochondria to govern the fate of germ cell survival or death during pro-apoptotic stress to the testis in rats.

Aging subverts immune function by dictating alternative STAT responses to cytokine signaling (P5078)

Chronic inflammation in the aged closely resembles tumor-induced immune suppression, manifested as a progressive T1→T2 shift and an increased presence of MDSCs. We hypothesize that reversing these age-related phenomena should reduce the elderly’s heightened susceptibility to malignancy. We have now optimized real-time analyses of phosphorylated STATs in murine T cells and MDSCs in order to correlate STAT activation with immune suppression. Both young and old T cells responded to IL-4 stimulation with STAT6 activation and to IFN-γ stimulation with STAT1 activation. Uniquely, however, young T cells also phosphorylated STAT1, STAT3 and STAT5 in response to IL-4, and responded to IL-6 with STAT3 activation, all consistent with a greater susceptibility to T1/T17 differentiation. Regarding MDSCs, both old and young displayed constitutive STAT3 activation which could be enhanced by G-CSF or IL-6 treatment. Both young and old MDSCs activated STAT1 briskly in response to IFN-γ, STAT5 in response to GM-CSF and STAT6 in response to IL-4. However, younger MDSCs, like younger T cells, displayed more diverse responsiveness to IL-4, activating not only STAT6 but also STAT1 and STAT3. While chronic in vivo exposure to T2 cytokines may explain the decreased responsiveness of older MDSCs and T cells to IL-4, paradoxically IL-4 still robustly activated STAT6 in these cells. Such selective responsiveness may be required to preserve the immune suppressive potential of older MDSCs.

Global targeting of MDSC escape mechanisms cures advanced 4T1 breast tumors (P2062)

4T1 is a metastatic breast cancer model with fulminant accumulation of MDSCs. Survival and function of MDSCs is often reported as STAT3-dependent, and STAT3 inhibitors such as sunitinib dramatically deplete 4T1 splenic MDSCs. Paradoxically, sunitinib fails to eradicate 4T1 intratumoral MDSCs or prevent tumor progression. We hypothesized that STAT3 activation is a consistent feature of splenic but not intratumoral MDSCs. PhosphoSTAT analyses of 4T1-bearers confirmed that splenic MDSCs of all Gr1 intensities were solely pSTAT3pos. In remarkable contrast, intratumoral Gr1high MDSCs largely lacked any pSTAT activation, and intratumoral Gr1dim MDSC precursors displayed varied expression of pSTAT5 and pSTAT1 in addition to pSTAT3. We therefore sought global means to target MDSCs. We determined that 4T1 and other tumor models could be cured by repetitive administration of cyclophosphamide alternating with TLR agonists such as CpG ODN1826. While cure required participation of host CD4+ and CD8+ T cells, global targeting of MDSCs was also observed: (1) as with sunitinib, pSTAT3pos splenic MDSCs were eradicated; (2) pSTAT expression by intratumoral MDSCs was fully abolished; (3) the remaining intratumoral MDSCs, all pSTATneg, outsurvived all other cells, and were likely induced to serve as the final mediators of tumor rejection. In conclusion, strategies which globally target MDSCs and promote the endogenous anti-tumor T cell response can cure advanced metastatic tumors.

Culture conditions promoting innate immunity and homeostatic proliferation generate highly enriched, MUC1- or HER2/neu-specific CD4+ and CD8+ T cells (P4419)

Although tumors from melanoma patients can often provide a source of therapeutically active T cells for adoptive therapy, it has historically proved challenging to employ peripheral blood as the T cell source for any type of cancer. We have observed nonetheless that HER2-specific T cells can be Ag-driven and enriched in culture when PBMCs from HER2-vaccinated breast cancer patients are treated with exogenous IL12. We hypothesized that stimulating innate immunity could further improve PBMC cultures by activating the DC subpopulation more effectively than adding exogenous rIL12. Bulk PBMC exposure to optimized TLR agonists produced vast quantities of IL12 and IL23, and upregulated HLA-DR, B7.1 and CD40 in the DC subpopulation, effects not produced by exogenous IL12. Subsequent IL7 exposure emulated homeostatic proliferation, selectively causing the Ag-driven T cell subset both to proliferate faster and to strongly resist apoptosis. Ag-specificity within two weeks approached 80-100% of both CD4+ and CD8+ T cells for recall Ags and 1-15% for a wide array of MUC1- and HER2-derived peptides, including the ability to distinguish glycoforms. Culture-expanded T cells retained a young CD28+/CD56- phenotype, uniformly expressed ROR-γ during culture, variably produced IL-2 and/or IL-17, and uniformly expressed T-bet and secreted IFN-γ when reexposed to Ag. Such T1/T17 bipotency may be ideal for anti-tumor adoptive therapy and highly efficient for use in Ag discovery.

Pharmacodynamic impacts of chemotherapy and immunotherapy upon adipose tissue (P2054)

Recent guidelines by the American Society of Clinical Oncologists recommend that obese individuals receive chemotherapy based on their actual body weight (ABW) without dose reduction. Contrary to prior reports, our own data demonstrate that ABW-dosed chemotherapy or immunotherapy is as effective and well tolerated by obese mice as by lean mice. Nonetheless, obese mice develop significantly greater weight loss in a dose-dependent manner during the entire period that they receive therapy, with corresponding quantifiable reductions in visceral fat depots. This disparity is not explained by altered food intake, as both lean and obese mice experience less than a week of anorexia which does not recur after Cycle 1 of treatment. Furthermore, malabsorption is absent. These observations are relevant to multiple classes of chemo agents. Altered pharmacokinetics of chemotherapy agents in adipose tissue have been reported, yet the pharmacodynamics of obesity remain speculative. Fasting blood glucose monitoring demonstrates glucose level variances which are temporally linked to treatment, rendering it likely that chemotherapy and immunotherapy provoke adipose tissue lipolysis, or alternatively cytoreduction or immunomodulation of adipocyte progenitor cells. Understanding these effects could contribute to improved treatment regimens in the setting of obesity.

IL-9 strategy to perturb Treg function and enhance anti-tumor immunity (P4273)

IL-9 is a cytokine that is primarily associated with mast cells and airway inflammation, however it also plays a role in T regulatory cell (Treg) survival and recruitment to tumors. We previously reported that 4-1BB treatment of Tregs inhibits both Treg function and IL-9 secretion. Neutralization of IL-9 with an anti-IL-9 antibody inhibits the suppressive function of Tregs without affecting the function of CD4+ and CD8+ T effector cells. Furthermore, the combination of intra-tumoral CpG and anti-IL-9 induced tumor rejection in BALB-neuT and MUC1 tolerant transgenic mice. Here we show that the lack of IL-9 inhibits Treg suppression of T cell proliferation, using IL-9 knockout (IL-9ko) mice. Phenotypic analysis of Treg markers showed that tumor draining lymph nodes of 4T1 bearing mice contain fewer CTLA-4+ and CD103+ Tregs, and that these also have reduced of CTLA-4 and CD103 expression. We also observed that IL-9ko mice spontaneously reject TUBO and 4T1 mammary carcinoma cells and that rejection is abrogated by CD8+ T cell depletion. Finally, preliminary studies of human CD4+ T cell proliferation revealed that IL-9 neutralization led to greater proliferation than isotype control treated cells. Taken together our results suggest that IL-9 can have an immunosuppressive function that comes into play in the tumor microenvironment, and that the blockade of IL-9 could serve as a novel strategy to perturb the function of Tregs to enhance the antitumor effect of tumor vaccines.