Boosting anticancer immunotherapy through androgen receptor blockade

Immune checkpoint inhibitors (ICIs) have limited activity in patients with castration-resistant prostate cancer (CRPC). A Nature article demonstrates that androgen receptor (AR) negatively modulates CD8+ T cell-driven antitumor immune response and that androgen-axis blockade is a promising therapeutic strategy to improve ICI activity in CRPC. Immune checkpoint inhibitors (ICIs) have limited activity in patients with castration-resistant prostate cancer (CRPC). A Nature article demonstrates that androgen receptor (AR) negatively modulates CD8+ T cell-driven antitumor immune response and that androgen-axis blockade is a promising therapeutic strategy to improve ICI activity in CRPC. A male bias in incidence and mortality from several cancers of non-reproductive organs is well known (Klein and Flanagan, 2016Klein S.L. Flanagan K.L. Sex differences in immune responses.Nat. Rev. Immunol. 2016; 16: 626-638https://doi.org/10.1038/nri.2016.90Crossref PubMed Scopus (2516) Google Scholar). Among potential explanations, paramount differences in the molecular and cellular mechanisms of spontaneous anticancer immune response between man and women have been put forward (Klein and Flanagan, 2016Klein S.L. Flanagan K.L. Sex differences in immune responses.Nat. Rev. Immunol. 2016; 16: 626-638https://doi.org/10.1038/nri.2016.90Crossref PubMed Scopus (2516) Google Scholar). Recently, retrospective evidence also raised the hypothesis that the efficacy of immunotherapy through anti-CTLA4 and anti-PD(L)1 drugs can be significantly affected by sex of patients with several advanced solid tumors (Conforti et al., 2018Conforti F. Pala L. Bagnardi V. De Pas T. Martinetti M. Viale G. Gelber R.D. Goldhirsch A. Cancer immunotherapy efficacy and patients' sex: a systematic review and meta-analysis.Lancet Oncol. 2018; 19: 737-746https://doi.org/10.1016/s1470-2045(18)30261-4Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar; Litchfield et al., 2021Litchfield K. Reading J.L. Puttick C. Thakkar K. Abbosh C. Bentham R. Watkins T.B. Rosenthal R. Biswas D. Rowan A. et al.Meta-analysis of tumor- and T cell-intrinsic mechanisms of sensitization to checkpoint inhibition.Cell. 2021; 184: 596-614.e14https://doi.org/10.1016/j.cell.2021.01.002Abstract Full Text Full Text PDF PubMed Scopus (272) Google Scholar). Such sex-based dimorphism of spontaneous anticancer immune response and efficacy of immune checkpoint inhibitors (ICI) in turn reflects complex interactions between genes, behaviors, and hormones (Klein and Flanagan, 2016Klein S.L. Flanagan K.L. Sex differences in immune responses.Nat. Rev. Immunol. 2016; 16: 626-638https://doi.org/10.1038/nri.2016.90Crossref PubMed Scopus (2516) Google Scholar). The X chromosome contains numerous immune-related genes that are involved in the regulation of both innate and adaptive immunity. Immune-related genes encoded on the X chromosome may escape X inactivation, resulting in higher expression levels by both immune and cancer cells of female patients than males (Markle and Fish, 2014Markle J.G. Fish E.N. SeXX matters in immunity.Trends Immunol. 2014; 35: 97-104https://doi.org/10.1016/j.it.2013.10.006Abstract Full Text Full Text PDF PubMed Scopus (224) Google Scholar). Different behaviors and exposure to environmental factors clearly play a role in this context. Indeed, men are more often exposed to factors contributing to chronic inflammation and immune suppressive status of tissue microenvironment, such as smoking habits and obesity, explaining higher incidence of tumors but also higher response to ICI (Klein and Flanagan, 2016Klein S.L. Flanagan K.L. Sex differences in immune responses.Nat. Rev. Immunol. 2016; 16: 626-638https://doi.org/10.1038/nri.2016.90Crossref PubMed Scopus (2516) Google Scholar). Finally, sex hormones are known to shape development and function of the immune system, although their specific role in anticancer immune response is poorly investigated (Klein and Flanagan, 2016Klein S.L. Flanagan K.L. Sex differences in immune responses.Nat. Rev. Immunol. 2016; 16: 626-638https://doi.org/10.1038/nri.2016.90Crossref PubMed Scopus (2516) Google Scholar). In an article recently published in Nature, Guan et al. reported preclinical and clinical evidence shedding light on androgen receptor (AR) as a negative modulator of CD8+ T cells response to anti-PD(L)1 treatment (Guan et al., 2022Guan X. Polesso F. Wang C. Sehrawat A. Hawkins R.M. Murray S.E. Thomas G.V. Caruso B. Thompson R.F. Wood M.A. et al.Androgen receptor activity in T cells limits checkpoint blockade efficacy.Nature. 2022; https://doi.org/10.1038/s41586-022-04522-6Crossref Scopus (66) Google Scholar). They took advantage of the strategic setting represented by advanced, castration-resistant prostate cancer (CRPC), since ICI treatment has been reported as poorly active for these patients (Sandhu et al., 2021Sandhu S. Moore C.M. Chiong E. Beltran H. Bristow R.G. Williams S.G. Prostate cancer.Lancet. 2021; 398: 1075-1090https://doi.org/10.1016/s0140-6736(21)00950-8Abstract Full Text Full Text PDF PubMed Google Scholar). Metastatic tumor lesions from men with CRPC, who experienced response or not to anti-PD(L)1, were comparatively analyzed to identify features of the intratumor immune infiltrate associated with response and/or resistance to treatment, in the context of a retrospective case-control study (Figure 1A). Single-cell RNA-sequencing of sorted intratumor CD8+ T cells was performed and led to the identification of two transcriptomic states significantly associated with response and resistance to anti-PD(L)1, respectively. Computational analysis of differentially expressed genes between these two CD8+ T cells states suggested that AR downregulation was significantly enriched in T cells from responders and correlated with improved T cell function. Mechanistically, this was due to AR-mediated suppression of genes whose expression in CD8+ T cells is essential to coordinate a functional antitumor response, such as TNF, granzyme B, and IFNγ (Guan et al., 2022Guan X. Polesso F. Wang C. Sehrawat A. Hawkins R.M. Murray S.E. Thomas G.V. Caruso B. Thompson R.F. Wood M.A. et al.Androgen receptor activity in T cells limits checkpoint blockade efficacy.Nature. 2022; https://doi.org/10.1038/s41586-022-04522-6Crossref Scopus (66) Google Scholar). Finally, the authors demonstrated that this insight could inform new therapeutic approaches to overcome resistance to anti-PD(L)1 treatment (Figure 1B). They showed that in a CRPC mouse model with full de novo resistance to anti-PD(L)1 treatment, the combination of androgen deprivation treatment (ADT), plus the AR antagonist enzalutamide and an anti-PD(L)1 (hereafter called "triple combination"), exerted a remarkable antitumor effect. The results confirmed a restored production of granzyme B, IFNγ, and TNF by CD8+ T cells from treated mice, suggesting that AR signaling inhibition, through ADT plus enzalutamide, could establish a CD8+ T cell state permissive to re-invigoration through PD(L)1 blockade (Guan et al., 2022Guan X. Polesso F. Wang C. Sehrawat A. Hawkins R.M. Murray S.E. Thomas G.V. Caruso B. Thompson R.F. Wood M.A. et al.Androgen receptor activity in T cells limits checkpoint blockade efficacy.Nature. 2022; https://doi.org/10.1038/s41586-022-04522-6Crossref Scopus (66) Google Scholar). This paper has several strengths, particularly for in vivo preclinical studies. This includes the utilization of the CRPC mouse model, previously shown to be strongly representative of human disease in terms of genetic aberrations harbored by cancer cells, features of intratumor immune infiltrate, and tumor sensitivity to treatments (Lu et al., 2017Lu X. Horner J.W. Paul E. Shang X. Troncoso P. Deng P. Jiang S. Chang Q. Spring D.J. Sharma P. et al.Effective combinatorial immunotherapy for castration-resistant prostate cancer.Nature. 2017; 543: 728-732https://doi.org/10.1038/nature21676Crossref PubMed Scopus (350) Google Scholar). Furthermore, in vivo treatment effects observed from testing the triple combination were striking on both tumor growth and mice survival, and mice follow-ups were remarkable long (up to 150 days). By contrast, a weakness is the relatively small size of the cohort of human tumor samples analyzed (only eight patients were included), a limit often shared by similar studies performed on fresh metastatic tumor samples. This precluded the possibility to explore the potential heterogeneity of AR transcriptional activity, and thus effect on T cell function, in specific subgroups, such as patients' race and age, since racial ancestry, as well as variations of sex-hormones levels with aging, could influence hormone receptor biology (Rayford et al., 2021Rayford W. Beksac A.T. Alger J. Alshalalfa M. Ahmed M. Khan I. Falagario U.G. Liu Y. Davicioni E. Spratt D.E. et al.Comparative analysis of 1152 African-American and European-American men with prostate cancer identifies distinct genomic and immunological differences.Commun. Biol. 2021; 4: 670https://doi.org/10.1038/s42003-021-02140-yCrossref PubMed Scopus (29) Google Scholar). Notably, this also hampered the possibility of exploring the association of AR expression and activity with other variables that in turn are related to ICI response, such as tumor PD(L)1 expression levels, whose importance will be discussed below. Taken together, the results reported by Guan et al. have several relevant implications and raise open questions that warrant future investigation. First, the synergistic effect of the triple combination should be confirmed in patients with CRPC in the context of a prospective randomized trial, pursuing a fruitful "from bedside to bench and back again" approach. Indeed, several prospective trials showed overwhelming de novo resistance to ICI as monotherapy in this setting, motivating an intense search for new therapeutic approaches that overcome this resistance (Sandhu et al., 2021Sandhu S. Moore C.M. Chiong E. Beltran H. Bristow R.G. Williams S.G. Prostate cancer.Lancet. 2021; 398: 1075-1090https://doi.org/10.1016/s0140-6736(21)00950-8Abstract Full Text Full Text PDF PubMed Google Scholar). As compared to the other treatment options currently under investigation, such as the combination of different ICI or ICI plus targeted therapy, the strategy proposed by Guan et al. has the potential advantages of a more favorable toxicity profile and a promising cost-to-benefit ratio. It should be noted that in a large randomized control trial (RCT), IMbassador250, the addition of atezolizumab (an anti-PD-(L)1 drug) to enzalutamide in patients with advanced CRPC failed to demonstrate significant improvement of patients' survival (Powles et al., 2022Powles T. Yuen K.C. Gillessen S. Kadel E.E. Rathkopf D. Matsubara N. Drake C.G. Fizazi K. Piulats J.M. Wysocki P.J. et al.Atezolizumab with enzalutamide versus enzalutamide alone in metastatic castration-resistant prostate cancer: a randomized phase 3 trial.Nat. Med. 2022; 28: 144-153https://doi.org/10.1038/s41591-021-01600-6Crossref PubMed Scopus (41) Google Scholar). However, preplanned and exploratory subgroup analyses showed longer progression-free survival with atezolizumab for patients with "hot" tumors, identified by high expression levels of PD(L)1, CD8, and CXCL9 as well as established immune gene signatures (Powles et al., 2022Powles T. Yuen K.C. Gillessen S. Kadel E.E. Rathkopf D. Matsubara N. Drake C.G. Fizazi K. Piulats J.M. Wysocki P.J. et al.Atezolizumab with enzalutamide versus enzalutamide alone in metastatic castration-resistant prostate cancer: a randomized phase 3 trial.Nat. Med. 2022; 28: 144-153https://doi.org/10.1038/s41591-021-01600-6Crossref PubMed Scopus (41) Google Scholar). Furthermore, data reported by Guan et al. showed that therapy with anti-PD(L)1 plus enzalutamide without ADT was not as effective as the triple combination, suggesting that the full androgen-axis blockade was critical for optimal antitumor effect (Guan et al., 2022Guan X. Polesso F. Wang C. Sehrawat A. Hawkins R.M. Murray S.E. Thomas G.V. Caruso B. Thompson R.F. Wood M.A. et al.Androgen receptor activity in T cells limits checkpoint blockade efficacy.Nature. 2022; https://doi.org/10.1038/s41586-022-04522-6Crossref Scopus (66) Google Scholar). All this supports the need to further explore the efficacy of the triple combination, especially in a biomarker-selected patient population. Currently, ongoing trials are evaluating the triple combination in patients with metastatic hormone-sensitive PC (KEYNOTE-991) and also in the neoadjuvant setting for patients with high-risk localized PC (NCT03753243). Second, since the synergistic effect of the triple combination was exclusively due to a direct effect on T cells and not on prostate cancer cells, this raises the hypothesis that such a treatment option may be effective across a large spectrum of tumors. In their work, Guan et al. provided intriguing preliminary results showing the efficacy of the triple combination also in a sarcoma mouse model refractory to both anti-PD(L)1 and AR inhibition (Guan et al., 2022Guan X. Polesso F. Wang C. Sehrawat A. Hawkins R.M. Murray S.E. Thomas G.V. Caruso B. Thompson R.F. Wood M.A. et al.Androgen receptor activity in T cells limits checkpoint blockade efficacy.Nature. 2022; https://doi.org/10.1038/s41586-022-04522-6Crossref Scopus (66) Google Scholar). Another nested hypothesis is that androgen-axis blockade may also enhance the efficacy of immunotherapy approaches other than anti-PD(L)1 as monotherapy. Again, the authors showed that enzalutamide may significantly foster the activity of adoptive T cell therapy (Guan et al., 2022Guan X. Polesso F. Wang C. Sehrawat A. Hawkins R.M. Murray S.E. Thomas G.V. Caruso B. Thompson R.F. Wood M.A. et al.Androgen receptor activity in T cells limits checkpoint blockade efficacy.Nature. 2022; https://doi.org/10.1038/s41586-022-04522-6Crossref Scopus (66) Google Scholar). The interaction between androgen-axis blockade and the efficacy of each specific immunotherapy approach should be carefully evaluated. Indeed, we previously reported that the direction of sex-based dimorphism of immunotherapy efficacy can be the opposite for different therapeutic approaches: data analysis of RCTs showed that while men with advanced NSCLC had significantly larger survival benefit than women when treated with anti-PD(L)1 as monotherapy, the effect was the opposite when they were treated with the combination of anti-PD(L)1 plus chemotherapy (Conforti et al., 2019Conforti F. Pala L. Bagnardi V. Viale G. De Pas T. Pagan E. Pennacchioli E. Cocorocchio E. Ferrucci P.F. De Marinis F. et al.Sex-based heterogeneity in response to Lung cancer immunotherapy: a systematic review and meta-analysis.J. Natl. Cancer Inst. 2019; 111: 772-781https://doi.org/10.1093/jnci/djz094Crossref PubMed Scopus (100) Google Scholar). Furthermore, the effect of the combination of androgen-axis blockade and ICI should also be explored in females with solid tumors. Obviously, the majority of the experiments reported by Guan et al. were conducted only in male mice; however, there is a strong rationale to speculate that androgen-axis blockade can improve ICI efficacy in females as well. Finally, other correlated and unresolved issues are the characterization of the effects of AR and of its manipulation on the other innate and adaptive immune cells involved in anticancer immune response, as well as the poorly explored role of estrogens and their receptor in this context. In conclusion, Guan et al. clearly demonstrated that AR negatively affects CD8+ T cell-driven antitumor immune response and that androgen-axis blockade improves the efficacy of ICI, in the specific context of CRPC. A broad characterization of the effects of AR and of its modulation on different tumors and on immunotherapy strategies other than anti-PD(L)1 monotherapy should be rapidly assessed by future research. The authors declare no conflicts of interest.