Debraj GuhaThakurta

Predictive Biomarkers of Sensitivity to the Phosphatidylinositol 3′ Kinase Inhibitor GDC-0941 in Breast Cancer Preclinical Models

Purpose: The class I phosphatidylinositol 3′ kinase (PI3K) plays a major role in proliferation and survival in a wide variety of human cancers. A key factor in successful development of drugs targeting this pathway is likely to be the identification of responsive patient populations with predictive diagnostic biomarkers. This study sought to identify candidate biomarkers of response to the selective PI3K inhibitor GDC-0941. Experimental Design: We used a large panel of breast cancer cell lines and in vivo xenograft models to identify candidate predictive biomarkers for a selective inhibitor of class I PI3K that is currently in clinical development. The approach involved pharmacogenomic profiling as well as analysis of gene expression data sets from cells profiled at baseline or after GDC-0941 treatment. Results: We found that models harboring mutations in PIK3CA, amplification of human epidermal growth factor receptor 2, or dual alterations in two pathway components were exquisitely sensitive to the antitumor effects of GDC-0941. We found that several models that do not harbor these alterations also showed sensitivity, suggesting a need for additional diagnostic markers. Gene expression studies identified a collection of genes whose expression was associated with in vitro sensitivity to GDC-0941, and expression of a subset of these genes was found to be intimately linked to signaling through the pathway. Conclusion: Pathway focused biomarkers and the gene expression signature described in this study may have utility in the identification of patients likely to benefit from therapy with a selective PI3K inhibitor. Clin Cancer Res; 16(14); 3670–83. ©2010 AACR.

Humoral Immune Response against Nontargeted Tumor Antigens after Treatment with Sipuleucel-T and Its Association with Improved Clinical Outcome

Purpose: Antitumor activity of cancer immunotherapies may elicit immune responses to nontargeted (secondary) tumor antigens, or antigen spread. We evaluated humoral antigen spread after treatment with sipuleucel-T, an immunotherapy for asymptomatic or minimally symptomatic metastatic castration-resistant prostate cancer (mCRPC), designed to target prostatic acid phosphatase (PAP; primary antigen). Experimental Design: Serum samples from patients with mCRPC enrolled in the placebo-controlled phase III IMPACT study (evaluable n = 142) were used to assess humoral antigen spread after treatment with sipuleucel-T. Immunoglobulin G (IgG) responses to self-antigens (including tumor antigens) were surveyed using protein microarrays and confirmed using Luminex xMAP. IgG responses were subsequently validated in ProACT (n = 33), an independent phase II study of sipuleucel-T. Association of IgG responses with overall survival (OS) was assessed using multivariate Cox models adjusted for baseline prostate-specific antigen (PSA) and lactate dehydrogenase levels. Results: In patients from IMPACT and ProACT, levels of IgG against multiple secondary antigens, including PSA, KLK2/hK2, K-Ras, E-Ras, LGALS8/PCTA-1/galectin-8, and LGALS3/galectin-3, were elevated after treatment with sipuleucel-T (P < 0.01), but not control. IgG responses (≥2-fold elevation posttreatment) occurred in ≥25% of patients, appeared by 2 weeks after sipuleucel-T treatment, and persisted for up to 6 months. IgG responses to PSA and LGALS3 were associated with improved OS in sipuleucel-T–treated patients from IMPACT (P ≤ 0.05). Conclusions: Sipuleucel-T induced humoral antigen spread in patients with mCRPC. IgG responses were associated with improved OS in IMPACT. The methods and results reported may identify pharmacodynamic biomarkers of clinical outcome after sipuleucel-T treatment, and help in clinical assessments of other cancer immunotherapies. Clin Cancer Res; 21(16); 3619–30. ©2015 AACR. See related commentary by Hellstrom and Hellstrom, p. 3581

A Randomized Phase II Trial of Sipuleucel-T with Concurrent versus Sequential Abiraterone Acetate plus Prednisone in Metastatic Castration-Resistant Prostate Cancer

Purpose: This phase II open-label study evaluated the effect of concurrent or sequential administration of abiraterone acetate plus prednisone (AA + P) on sipuleucel-T manufacture and immune responses in metastatic castration-resistant prostate cancer (mCRPC) patients. Experimental Design: mCRPC patients received sipuleucel-T followed by AA + P 1 day (concurrent) or 10 weeks (sequential) after the first sipuleucel-T infusion. AA + P treatment continued for 26 weeks. The primary endpoint was cumulative antigen presenting cell (APC) activation, and secondary endpoints included cumulative APC number and total nucleated cell counts. Additional endpoints included in vivo peripheral immune responses to sipuleucel-T (T-cell responses, T-cell proliferation, humoral responses, and antigen spread) as well as safety. Results: Sixty-nine mCRPC patients were enrolled, with 35 and 34 patients randomized to the concurrent and sequential arms, respectively. Ex vivo APC activation was significantly greater at the second and third infusions compared with baseline in both arms (P < 0.05), indicative of an immunologic prime-boost effect. In both arms, sipuleucel-T product parameter profiles and peripheral immune responses were consistent with previously conducted sipuleucel-T phase III trials. Antigen spread was similarly observed in both arms and consistent with the other immunologic endpoints. Conclusions: These data suggest that sipuleucel-T can be successfully manufactured during concurrent administration of AA + P without blunting immunologic effects or altering immune parameters that correlate with sipuleucel-Ts clinical benefit. Combination of these agents was well tolerated, with no new safety signals emerging. Clin Cancer Res; 21(17); 3862–9. ©2015 AACR.

Applications of systems biology in cancer immunotherapy: from target discovery to biomarkers of clinical outcome

Immunotherapies are coming to the forefront as a treatment paradigm in cancer with multiple US FDA approvals in recent years and a better understanding of their therapeutic mode of action. The control of tumor growth by the immune system is orchestrated by a complex array of cellular interactions and molecular pathways, both in the immune cells as well as the tumor. Although research over the past three decades has elucidated many aspects of tumor immunosurveillance, given the inherent complexity of the immune cell phenotypes and function, high-throughput molecular profiling (‘omics’) approaches have now become essential to support the discovery and development of new therapies. Technologies, such as DNA and protein microarrays, deep sequencing, mass spectrometry, as well as the computational methods for their analyses, are advancing the contributions of systems biology towards the development and mechanistic understanding of cancer immunotherapies. In this review, the authors illustrate this through some recently reported studies.

Induction of antigen spread after sipuleucel-T treatment and its association with improved clinical outcome

An effective cancer immunotherapy that triggers immune-mediated lysis of tumor cells, may lead to the priming of T or B lymphocytes against tumor antigens distinct from the initial target/s of the therapy. This is referred to as antigen or epitope spread. Evidence of antigen spread after treatment may not only provide insights into the mechanism of action (MoA) of cancer immunotherapies, but also provide pharmacodynamic (post-treatment) biomarkers of clinical response and outcome. Sipuleucel-T, an FDA approved autologous cellular immunotherapy for the treatment of symptomatic or minimally symptomatic, metastatic castrate-resistant prostate cancer (mCRPC), is designed to elicit immune responses to the prostate-specific antigen, Prostatic Acid Phosphatase (PAP). We sought to determine if antigen spread occurs in response to sipuleucel-T treatment.

Abstract 2542: Sipuleucel-T-induced immune response against secondary cancer antigens is associated with improved overall survival

Introduction and Objective: Tumor cell death in response to immunotherapy may lead to the release of secondary (non-targeted) cancer antigens that prime subsequent immune responses (antigen spread) 1 . This may contribute to tumor control and reveal post-treatment biomarkers of clinical outcome. Sipuleucel-T, an immunotherapy targeted towards the prostate-specific antigen, prostatic acid phosphatase, is approved in the US and EU for treatment of asymptomatic or minimally symptomatic, metastatic castration-resistant prostate cancer. We evaluated: (i) antigen spread after sipuleucel-T treatment, based on IgG antibody responses against secondary cancer antigens, and (ii) association of such IgG responses with overall survival (OS). Methods: ProtoArray®, an unbiased protein microarray platform, was used to characterize the spectrum of serum IgG responses after treatment. IgG responses against secondary antigens were confirmed using an independent platform, Luminex®, xMAP®. Pre- and post- treatment sera from two clinical trials of sipuleucel-T were analyzed: IMPACT 2 (double-blind, placebo-controlled, phase 3, NCT00065442) and ProACT (open-label, phase 2, NCT00715078). The correlations between IgG responses (≥ 2 fold elevation post-treatment) and OS were assessed in IMPACT using a Cox regression model, adjusted for baseline PSA, LDH, bone lesions, Gleason score, and prior bisphosphonate use. Results: Serum IgG responses (p -3 ) towards several secondary cancer antigens (PSA, hK2/KLK2, K-Ras, E-Ras, and LGALS8/PCTA-1) were observed after treatment with sipuleucel-T in IMPACT as well as ProACT. Across trials, the frequency of patients with IgG responses after sipuleucel-T treatment was: ≥25% for PSA, ≥33% for hK2, ≥36% for K-Ras, ≥39% for E-Ras, ≥24% for LGALS8. These IgG responses were observed as early as 2 weeks and up to 6 months after treatment with sipuleucel-T. Control arm patients in IMPACT did not show such responses (p>0.01). In the sipuleucel-T arm of IMPACT (N=140), an IgG response to PSA ≈2 weeks after treatment was positively correlated with increased OS, compared to patients with no IgG response to PSA (Cox p Conclusions: Sipuleucel-T elicited IgG responses against multiple cancer antigens. Sipuleucel-T- induced IgG response against PSA was positively correlated with improved OS. These data enhance our understanding of sipuleucel-T9s mechanism of action, and may help to identify pharmacodynamic biomarkers of clinical outcome. The methods and results presented here may also help in the characterization of antigen spread and pharmacodynamic biomarkers after treatment with other cancer immunotherapies. 1. Ribas A, et al. Trends Immunol. 24:58-61 (2003) 2. Kantoff PW, et al. N Engl J Med. 363:411-22 (2010) Citation Format: Debraj GuhaThakurta, Li-Qun Fan, Tuyen Vu, Francis Stewart, Philip Kantoff, Eric Small, Celeste Higano, Thomas Gardner, Nadeem Sheikh, James Trager. Sipuleucel-T-induced immune response against secondary cancer antigens is associated with improved overall survival. [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 2542. doi:10.1158/1538-7445.AM2014-2542