Is the Induction of Tumor Cell Senescence the Key to a Good Irradiated Tumor Vaccine?
Authors: Michael P Brown
Journal: Molecular Therapy (2012)

Along with surgery and chemotherapy, radiation therapy (RT) is a mainstay of both curative and palliative anticancer treatment. Recent US Food and Drug Administration approval of two immunotherapeutic agents brings immunotherapy into this clinical armamentarium. There is strong emerging rationale for a clinical partnership between RT and immunotherapy in cancer treatment, based primarily on advances in our understanding of the molecular basis of the activation of the innate immune system. In this context, in this issue of Molecular Therapy, Meng et al. present work that further refines our understanding of the immunological mechanisms underlying the systemic effects of RT.1Meng Y Efimova EV Hamzeh KW Darga TE Mauceri HJ Fu Y-X et al.Radiation-inducible immunotherapy for cancer: senescent tumor cells as a cancer vaccine.Mol Ther. 2012; 20: 1046-1055Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar The new work shows that RT-induced senescence is the key event driving antitumor immunity in their model system. The report corroborates other studies in preclinical animal models that demonstrate that ionizing radiation (IR) markedly alters the tumor microenvironment.2Formenti SC Demaria S Systemic effects of local radiotherapy.Lancet Oncol. 2009; 10: 718-726Abstract Full Text Full Text PDF PubMed Scopus (695) Google Scholar,3Hodge JW Guha C Neefjes J Gulley JL Synergizing radiation therapy and immunotherapy for curing incurable cancers. Opportunities and challenges.Oncology. 2008; 22: 1064-1070PubMed Google Scholar IR increases tumor cell immunogenicity by improving antigen processing and presentation as well as by engendering immunogenic tumor cell death, which, together with the production of intratumoral proinflammatory cytokines and chemokines, links innate immune system activation to the development of a broadening adaptive cellular immune response that is directed toward tumor cells outside the radiation field.2Formenti SC Demaria S Systemic effects of local radiotherapy.Lancet Oncol. 2009; 10: 718-726Abstract Full Text Full Text PDF PubMed Scopus (695) Google Scholar,3Hodge JW Guha C Neefjes J Gulley JL Synergizing radiation therapy and immunotherapy for curing incurable cancers. Opportunities and challenges.Oncology. 2008; 22: 1064-1070PubMed Google Scholar,4Hodge JW Sharp HJ Gameiro SR Abscopal regression of antigen disparate tumors by antigen cascade after systemic tumor vaccination in combination with local tumor radiation.Cancer Biother Radiopharm. 2012; 27: 12-22Crossref PubMed Scopus (89) Google Scholar RT combined with radiosensitizing chemotherapy is the standard of care for inoperable, locally advanced cancers, and it is curative in about half of cases. Because cure implies eradication of both locoregional and distant disease, the curative potential of combined-modality therapy is believed to result indirectly from improved locoregional control rates, although chemotherapy delivered at radiosensitizing doses may act directly against systemic micrometastases.5Nyati MK Morgan MA Feng FY Lawrence TS Integration of EGFR inhibitors with radiochemotherapy.Nat Rev Cancer. 2006; 6: 876-885Crossref PubMed Scopus (253) Google Scholar,6Seiwert TY Salama JK Vokes EE The concurrent chemoradiation paradigm—general principles.Nat Clin Pract Oncol. 2007; 4: 86-100Crossref PubMed Scopus (330) Google Scholar As was previously shown in human tumor cells,7Barreto-Andrade JC Afimova EV Mauceri HJ Beckett MA Sutton HG Darga TE et al.Response of human prostate cancer cells and tumors to combining PARP inhibition with ionizing radiation.Mol Cancer Ther. 2011; 10: 1185-1193Crossref PubMed Scopus (62) Google Scholar,8Efimova EV Mauceri HJ Golden DW Labay E Bindokas VP Darga TE et al.Poly(ADP-ribose) polymerase inhibitor induces accelerated senescence in irradiated breast cancer cells and tumors.Cancer Res. 2010; 70: 6277-6282Crossref PubMed Scopus (91) Google Scholar the new study by Meng et al. shows that combined treatment of B16SIY murine melanoma cells with the poly(ADP–ribose) polymerase (PARP) inhibitor, veliparib, and ionizing radiation (V+IR) induced hallmarks of cumulative DNA damage, persistent cell cycle arrest, and accelerated senescence in vitro and in vivo that were significantly greater than either treatment alone. Moreover, the combined treatment significantly slowed tumor growth in an immunocompetent syngeneic murine host, similar to what had been previously observed with human tumor cells in immunodeficient murine hosts.1Meng Y Efimova EV Hamzeh KW Darga TE Mauceri HJ Fu Y-X et al.Radiation-inducible immunotherapy for cancer: senescent tumor cells as a cancer vaccine.Mol Ther. 2012; 20: 1046-1055Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar,7Barreto-Andrade JC Afimova EV Mauceri HJ Beckett MA Sutton HG Darga TE et al.Response of human prostate cancer cells and tumors to combining PARP inhibition with ionizing radiation.Mol Cancer Ther. 2011; 10: 1185-1193Crossref PubMed Scopus (62) Google Scholar,8Efimova EV Mauceri HJ Golden DW Labay E Bindokas VP Darga TE et al.Poly(ADP-ribose) polymerase inhibitor induces accelerated senescence in irradiated breast cancer cells and tumors.Cancer Res. 2010; 70: 6277-6282Crossref PubMed Scopus (91) Google Scholar It seems that delayed tumor growth resulted from paracrine factors from senescent tumor cells (STCs), because tumor growth slowed progressively when seeded with an increasing number of admixed purified STCs. Gene expression analyses of V+IR-treated tumor cells confirmed the senescence phenotype and demonstrated significantly increased expression of cytokine and chemokine genes. This expression pattern differed from that reported as the senescence-associated secretory phenotype,9Rodier F Coppé JP Patil CK Hoeijmakers WA Muñoz DP Raza SR et al.Persistent DNA damage signalling triggers senescence-associated inflammatory cytokine secretion.Nat Cell Biol. 2009; 11: 973-979Crossref PubMed Scopus (1440) Google Scholar because interleukin-6 expression was reduced and expression of interferon-β (IFN-β) and its inducible chemokine, CXCL11, which attracts activated T cells, was significantly increased. Furthermore, intratumoral STCs were shown to express IFN-β as well as various chemokines. In this respect, the intratumoral production of IFN-β has been found to be critical for the cross-priming of tumor antigen-specific T cells.10Fuertes MB Kacha AK Kline J Woo SR Kranz DM Murphy KM et al.Host type I IFN signals are required for antitumor CD8+ T cell responses through CD8{alpha}+ dendritic cells.J Exp Med. 2011; 208: 2005-2016Crossref PubMed Scopus (787) Google Scholar That the observed gene expression pattern was immuno­stimulatory was borne out by demonstrating in vitro that V+IR-treated cells activated bone marrow–derived dendritic cells, which in turn stimulated tumor cell–experienced CD8+ T cells to proliferate and produce IFN-γ. This group had previously shown that a single 20-Gy dose of RT delivered to B16SIY tumors produced an intratumoral T-cell infiltrate that was inferred to contribute directly to tumor regression.11Lee Y Auh SL Wang Y Burnette B Wang Y Meng Y et al.Therapeutic effects of ablative radiation on local tumor require CD8+ T cells: changing strategies for cancer treatment.Blood. 2009; 114: 589-595Crossref PubMed Scopus (985) Google Scholar In the current study, V+IR treatment produced a prominent intratumoral infiltrate of IFN-γ+ CD8+ T cells. In vivo depletion studies showed that tumor control after V+IR treatment depended mainly on CD8+ T cells and the presence of intratumoral STCs. How the CD8+ T cells acted to control tumor growth remains unclear. However, T cells from tumor-draining lymph nodes of mice that had been inoculated with a V+IR-treated tumor vaccine exhibited IFN-γ secretion in response to ex vivo stimulation with the melanocyte differentiation antigen, gp100. This result suggests that a broader immune response may be generated by an “antigen cascade”4Hodge JW Sharp HJ Gameiro SR Abscopal regression of antigen disparate tumors by antigen cascade after systemic tumor vaccination in combination with local tumor radiation.Cancer Biother Radiopharm. 2012; 27: 12-22Crossref PubMed Scopus (89) Google Scholar so as to control nonsenescent tumor cells. Inoculation of mice with a B16SIY tumor vaccine comprising intact, viable, V+IR-treated STCs protected the mice against a live-tumor challenge. Although this tumor vaccine property of V+IR-treated STCs was confirmed in another tumor model, the effect depended on induction of the senescence phenotype. In a third tumor model, the lack of a senescence phenotype in the tumor vaccine after its ex vivo preparation by V+IR treatment was associated with an absence of tumor antigen-specific T-cell responses in vivo and no protection from challenge with live tumor cells. Finally, as previously described,11Lee Y Auh SL Wang Y Burnette B Wang Y Meng Y et al.Therapeutic effects of ablative radiation on local tumor require CD8+ T cells: changing strategies for cancer treatment.Blood. 2009; 114: 589-595Crossref PubMed Scopus (985) Google Scholar treatment of B16SIY tumor-bearing mice with a single 20-Gy dose of RT induced a CD8+ T-cell intratumoral infiltrate and tumor growth delay, both of which were augmented by prior inoculation with the B16SIY STC vaccine. Meng et al. have shown that PARP inhibition enhances the efficiency and immuno­genicity of RT-induced STC formation to produce antitumor immunity (Figure 1). PARPs are a family of proteins involved in a number of cellular processes involving mainly DNA repair and programmed cell death. These findings indicate two chief ways in which this approach can be adopted clinically, as either (i) “in situ autovaccination”12Formenti S Harnessing ionizing radiation to enhance immunotherapy: a paradigm shift.Oncology. 2008; 22: 1080Google Scholar or (ii) an exogenous tumor vaccine. Further investigations will be needed to determine if prior immunization with an STC vaccine is critical to the overall efficacy of this strategy or if autovaccination in situ will suffice. Nevertheless, these findings should also renew interest in the subject of whole tumor cell vaccines, which are often irradiated before inoculation. Then again, adequate quality control of autologous STC vaccine products will be needed given the demonstrated prometastatic potential of the inflammatory secretome that can originate from STC vaccines.13Ohanna M Giuliano S Bonet C Imbert V Hofman V Zangari J et al.Senescent cells develop a PARP-1 and nuclear factor-{kappa}B-associated secretome (PNAS).Genes Dev. 2011; 25: 1245-1261Crossref PubMed Scopus (180) Google Scholar As with any provocative study, several new questions are generated (Figure 1c). The first is the extent to which the effects described are generalizable. The interindividual response of human tumors to RT is highly variable. The proportions of cells dying different kinds of cell death vary, as do other responses to RT such as senescence and autophagy, which can also result in tumor cell death. It is unclear whether combining RT with PARP inhibition will produce senescence more often than apoptosis. Hence, tumor biopsies before and after treatment may yield information about cell death as well as genomic, epigenetic, proteomic, and immune-related changes, and should be incorporated in the design of future prospective clinical studies. It is also of interest to ask what patients might benefit from this treatment paradigm. A suitable clinical setting for a trial of V+IR treatment may be inoperable, locally advanced non–small cell lung cancer. Unexpected long-term survival (>5 years) was observed in approximately 1% of 3035 patients who had proven non–small cell lung cancer and who were treated with fractionated external-beam RT given at palliative doses not considered to be curative (≤36 Gy). These long-term survivors had a significantly better performance status and were significantly less likely to have distant metastases.14Mac Manus MP Matthews JP Wada M Wirth A Worotniuk V Ball CL Unexpected long-term survival after low-dose palliative radiotherapy for non-small cell lung cancer.Cancer. 2006; 106: 1110-1116Crossref PubMed Scopus (23) Google Scholar The aim of any anti­cancer treatment should be to maximize the number of patients who might ultimately benefit. Immune-checkpoint inhibitors now have an established role in the management of advanced malignancies with US Food and Drug Administration approval of ipilimumab—the monoclonal antibody specific to cytotoxic T-lymphocyte antigen 4—for the treatment of metastatic melanoma patients. Because therapy with this monoclonal antibody can result in intratumoral infiltration of activated CD8+ T cells irrespective of antitumor responses15Huang RR Jalil J Economou JS Chmielowski B Koya RC Mok S et al.CTLA4 blockade induces frequent tumor infiltration by activated lymphocytes regardless of clinical responses in humans.Clin Cancer Res. 2011; 17: 4101-4109Crossref PubMed Scopus (123) Google Scholar and is most effective in the presence of primed immune responses,16van Elsas A Hurwitz AA Allison JP Combination immunotherapy of B16 melanoma using anti-cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) and granulocyte/macrophage colony-stimulating factor (GM-CSF)-producing vaccines induces rejection of subcutaneous and metastatic tumors accompanied by autoimmune depigmentation.J Exp Med. 1999; 190: 355-366Crossref PubMed Scopus (880) Google Scholar a method such as V+IR-induced tumor senescence may serve to focus and augment a beneficial immune response while minimizing “off-target” toxicity in normal tissues. Different doses and schedules of RT combined with ipilimumab are currently being addressed in three newly opened clinical trials registered at ClinicalTrials.gov: (i) NCT01449279, a pilot study of ipilimumab in subjects with stage IV melanoma receiving palliative radiation therapy; (ii) NCT01497808, RADVAX, a stratified phase I/II dose escalation trial of stereotactic body radiation therapy followed by ipilimumab in metastatic melanoma; and (iii) NCT00861614, a randomized, double-blind, phase III trial comparing ipilimumab with placebo following radiation therapy in subjects with castration-resistant prostate cancer who have received prior treatment with docetaxel. Although RT is a local treatment, a therapeutic effect of RT on cancer deposits away from the irradiated target is described as an “abscopal effect,”2Formenti SC Demaria S Systemic effects of local radiotherapy.Lancet Oncol. 2009; 10: 718-726Abstract Full Text Full Text PDF PubMed Scopus (695) Google Scholar,3Hodge JW Guha C Neefjes J Gulley JL Synergizing radiation therapy and immunotherapy for curing incurable cancers. Opportunities and challenges.Oncology. 2008; 22: 1064-1070PubMed Google Scholar,17Persson BRR Koch CB Grafström G Ceberg C Rosenschöld PM Nittby H et al.“Abscopal” effect of radiation therapy combined with immune-therapy using IFN-γ gene transfected syngeneic tumor cells, in rats with bilateral implanted N29 tumors.ISRN Immunol. 2011; ([online], article ID 230130 doi:10.5402/2011/230130)Google Scholar and most evidence supports an immunological basis.2Formenti SC Demaria S Systemic effects of local radiotherapy.Lancet Oncol. 2009; 10: 718-726Abstract Full Text Full Text PDF PubMed Scopus (695) Google Scholar,3Hodge JW Guha C Neefjes J Gulley JL Synergizing radiation therapy and immunotherapy for curing incurable cancers. Opportunities and challenges.Oncology. 2008; 22: 1064-1070PubMed Google Scholar Notwithstanding preclinical data consistently in support of the abscopal effect,3Hodge JW Guha C Neefjes J Gulley JL Synergizing radiation therapy and immunotherapy for curing incurable cancers. Opportunities and challenges.Oncology. 2008; 22: 1064-1070PubMed Google Scholar,4Hodge JW Sharp HJ Gameiro SR Abscopal regression of antigen disparate tumors by antigen cascade after systemic tumor vaccination in combination with local tumor radiation.Cancer Biother Radiopharm. 2012; 27: 12-22Crossref PubMed Scopus (89) Google Scholar,17Persson BRR Koch CB Grafström G Ceberg C Rosenschöld PM Nittby H et al.“Abscopal” effect of radiation therapy combined with immune-therapy using IFN-γ gene transfected syngeneic tumor cells, in rats with bilateral implanted N29 tumors.ISRN Immunol. 2011; ([online], article ID 230130 doi:10.5402/2011/230130)Google Scholar,18Chakraborty M Abrams SI Colman CN Camphausen K Schlom J Hodge JW External beam radiation of tumors alters phenotype of tumor cells to render them susceptible to vaccine-mediated T-cell killing.Cancer Res. 2004; 64: 4328-4337Crossref PubMed Scopus (365) Google Scholar clinical abscopal effects have been reported infrequently.2Formenti SC Demaria S Systemic effects of local radiotherapy.Lancet Oncol. 2009; 10: 718-726Abstract Full Text Full Text PDF PubMed Scopus (695) Google Scholar However, the abscopal effect is highly desirable clinically for the reason that it represents a simple but powerful anticancer treatment. Although it is important to note that Meng et al. had not sought to demonstrate an abscopal effect, the most rigorous test of the effectiveness of an immuno­therapy is whether the antitumor immune response can operate in a less permissive tumor micro­environment unaltered by RT.17Persson BRR Koch CB Grafström G Ceberg C Rosenschöld PM Nittby H et al.“Abscopal” effect of radiation therapy combined with immune-therapy using IFN-γ gene transfected syngeneic tumor cells, in rats with bilateral implanted N29 tumors.ISRN Immunol. 2011; ([online], article ID 230130 doi:10.5402/2011/230130)Google Scholar Therefore, more clinically realistic tumor models for the investigation of RT–immunotherapy combinations would have a tumor deposit as a radiation therapy target and at least one remotely located synchronous tumor deposit as an immunotherapy target. Consequently, examination of the abscopal effect in the B16SIY tumor model would be of interest. Interestingly, the cancer patients in whom the aforementioned ipilimumab RT–clinical trial combinations are being tested have at least one metastasis. Additional challenges that face implementation of the V+IR strategy include (i) the limited availability of diagnostic tumor tissue in many human cancers, although if tumor tissue can be used to prepare an STC vaccine, that may provide an in vitro test result predictive of a response to therapy; (ii) determining whether irradiation of regional lymph nodes should be avoided; and (iii) the eventual comparison of the V+IR strategy with standard treatment for many locally advanced cancers, which is often chemoradiotherapy. The delivery of large doses of RT in a small number of fractions using new complex techniques known as stereotactic body RT is gaining popularity in clinical practice, particularly for oligometastases of lung cancer19Ball D Stereotactic radiotherapy for nonsmall cell lung cancer.Curr Opin Pulm Med. 2008; 14: 297-302Crossref PubMed Scopus (15) Google Scholar and inoperable early-stage lung cancer,20Siva S MacManus M Ball D Stereotactic radiotherapy for pulmonary oligometastases: a systematic review.J Thorac Oncol. 2010; 5: 1091-1099Abstract Full Text Full Text PDF PubMed Scopus (188) Google Scholar in which local control rates equivalent to surgery are claimed. However, no randomized clinical data on efficacy compared with conventional RT and dose exist, and schedule and techniques are not standardized. Furthermore, unlike the data presented here, other preclinical data do not favor the use of a single large fraction of RT. In a study of two tumor types hosted in syngeneic immunocompetent mice, fractionated schedules of RT rather than a single large fraction were associated with the abscopal effect.5Nyati MK Morgan MA Feng FY Lawrence TS Integration of EGFR inhibitors with radiochemotherapy.Nat Rev Cancer. 2006; 6: 876-885Crossref PubMed Scopus (253) Google Scholar In chemoradiotherapy, the principle of spatial cooperation describes the independent operation of radiation therapy and chemotherapy, each at fully active doses, to treat local (in-field) and systemic (out-of-field) disease, respectively. Consequently, nonoverlapping toxicities would be anticipated.21Steel GG Peckham MJ Exploitable mechanisms in combined radiotherapy-chemotherapy: the concept of additivity.Int J Radiat Oncol Biol Phys. 1979; 5: 85-91Abstract Full Text PDF PubMed Scopus (813) Google Scholar Once these significant preclinical data of Meng et al. can be validated clinically, a paradigm shift will truly have occurred.1Meng Y Efimova EV Hamzeh KW Darga TE Mauceri HJ Fu Y-X et al.Radiation-inducible immunotherapy for cancer: senescent tumor cells as a cancer vaccine.Mol Ther. 2012; 20: 1046-1055Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar,12Formenti S Harnessing ionizing radiation to enhance immunotherapy: a paradigm shift.Oncology. 2008; 22: 1080Google Scholar