Potent GCN2 Inhibitor Capable of Reversing MDSC-Driven T Cell Suppression Demonstrates In Vivo Efficacy as a Single Agent and in Combination with Anti-Angiogenesis Therapy

General control nonderepressible 2 (GCN2) protein kinase is a cellular stress sensor within the tumor microenvironment (TME), whose signaling cascade has been proposed to contribute to immune escape in tumors. Herein, we report the discovery of cell-potent GCN2 inhibitors with excellent selectivity against its closely related Integrated Stress Response (ISR) family members heme-regulated inhibitor kinase (HRI), protein kinase R (PKR), and (PKR)-like endoplasmic reticulum kinase (PERK), as well as good kinome-wide selectivity and favorable PK. In mice, compound 39 engages GCN2 at levels ≥80% with an oral dose of 15 mg/kg BID. We also demonstrate the ability of compound 39 to alleviate MDSC-related T cell suppression and restore T cell proliferation, similar to the effect seen in MDSCs from GCN2 knockout mice. In the LL2 syngeneic mouse model, compound 39 demonstrates significant tumor growth inhibition (TGI) as a single agent. Furthermore, TGI mediated by anti-VEGFR was enhanced by treatment with compound 39 demonstrating the complementarity of these two mechanisms.

Abstract 3153: Targeting the stress response kinase GCN2 to restore immunity in the tumor microenvironment

Recent advances in cancer metabolism suggest that targeting amino acid metabolism represents a promising strategy for the development of novel therapeutic agents. Tumor, stromal and myeloid-derived suppressor cells (MDSC) within the tumor microenvironment (TME) create a nutrient-poor environment that inhibit immune function and support tumor growth. GCN2 (general control nonderepressible 2), a stress response kinase, plays a key role in maintaining cellular homeostasis under a wide range of stressors. Phosphorylation of GCN2 (pGCN2) in response to stress leads to inhibition of global protein synthesis and subsequently leads to 1) T cell anergy and apoptosis, 2) enhanced MDSC-dependent immune suppression and 3) tumor cell survival. Collectively, these roles suggest that GCN2 inhibition could have both a direct anticancer and an immune-activating effect. Treating nutrient-deprived T cells in vitro with a RAPT GCN2 inhibitor (RPT-GCN2i) rescued CD4+ and CD8+ T cell proliferation and effector functions. The RPT-GCN2i also reversed T cell suppression mediated by MDSCs derived from healthy donors or cancer patients. Using syngeneic mouse tumor models, we demonstrated that translational induction of activating transcription factor 4 (ATF4) is a strong marker of GCN2 pathway activation in vivo. Oral administration of an RPT-GCN2i exhibited notable drug-target occupancy and potently inhibited GCN2 kinase and ATF4 in the TME. RPT-GCN2i as a single agent and in combination with checkpoint blockade or angiogenesis inhibitor (anti-VEGFR) led to delays in tumor growth rate in various syngeneic tumor models. In addition, GCN2 inhibition redirected MDSC within the TME from a suppressive to inflammatory phenotype through downregulation of Arg1 and iNOS. Our results show that inhibition of GCN2 is an attractive approach for enhancing antitumor immune response and therefore GCN2 is a promising therapeutic target for the treatment of cancer.

Citation Format: Lisa Marshall, Buvana Ravishankar, Urvi Kolhatkar, Mengshu Xu, Lavanya Adusumilli, Deepa Pookot, Thant Zaw, Chandru Ramana, Raashi Sreenivasan, Mikhail Zibinsky, Jeffrey Jackson, Grant Shibuya, Paul Leger, Omar Robles, Anqi Ma, Andrew Ng, Anton Shakhmin, Justy Guagua, Scott Jacobson, Steve Wong, Delia Bradford, Tracy L. McGaha, M Teresa Ciudad, James E. Talmadge, Holly C. Britton, George Katibah, Gene Cutler, David Wustrow, Paul D. Kassner, Dirk G. Brockstedt. Targeting the stress response kinase GCN2 to restore immunity in the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3153.

Abstract 1646: Development of small-molecule HPK1 inhibitors to unleash tumor-specific T cell responses

Hematopoietic progenitor kinase 1 (HPK1) is an intracellular protein kinase that negatively regulates T cell signaling and proliferation. Upon T cell receptor (TCR) activation, active HPK1 phosphorylates the adaptor protein SLP76 in the TCR complex, recruiting the negative regulator 14-3-3 and targeting components of the TCR signaling complex for degradation. HPK1 thus limits the TCR signaling important for mounting an effective immune response against tumor cells. We are employing structure-guided drug design to develop potent small-molecule inhibitors of HPK1. Our compounds potently inhibit HPK1 in biochemical assays, reduce levels of phosphorylated SLP76 and concomitantly increase IL-2 production by Jurkat T cells. Importantly, our HPK1 inhibitors enhance cytokine production by human and mouse primary T cells above that observed with TCR activation alone. Treatment of mice with orally available HPK1 inhibitors results in increased activation of antigen-specific CD8+ T cells in vivo and decreased tumor growth as single agent and in combination with clinically relevant checkpoint inhibitor antibodies. Our work confirms the importance of HPK1 for T cell function and supports HPK1 as a promising next generation immuno-oncology target.

Citation Format: George Katibah, Yamini Ohol, Cyril Bucher, Lavanya Adusumilli, Deepika Kaveri, Omar Robles, Michael Sun, Cynthia Cho, Heather Milestone, Rachel Ames, Scott Jacobson, Dan Nebalasca, Justy Gomez- Guagua, Jerick Sanchez, Molly Grandcolas, Steve Wong, Martin Brovarney, Chandru Ramana, Thant Zaw, Lan Nguyen, Parcharee Tivitmahaisoon, Andrew Ng, Anqi Ma, Blanca Gomez, Michelle Ko, Paul Leger, Jeffrey Jackson, Grant Shibuya, Anton Shakhmin, Delia Bradford, Mengshu Xu, Mikhail Zibinsky, Daniel Poon, David Wustrow, Paul Kassner, Dirk Brockstedt. Development of small-molecule HPK1 inhibitors to unleash tumor-specific T cell responses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1646.

Flying solo in Myanmar: case study on challenges and important lessons learned by an early career psychiatrist in a district setting

The transition from trainee early career psychiatrist (ECP) to independent practitioner can be challenging. Upon completion of training in well-equipped academic settings, an ECP from Myanmar is required to serve in a divisional hospital for at least 3 years. Significant challenges are faced by ECPs practising solo in divisional hospitals, including inexperience in administrative aspects, lack of future-proof training, scarcity of resources and facilities, struggles in the provision of holistic biopsychosocial treatment, work–life imbalance, and limited career advancement and access to continuous training. The solutions tried thus far include the incorporation of information and communication technology in training, gathering support and distant supervision from both local and international settings, and task shifting. Bigger challenges are often rewarded by faster growth, and difficult times stimulate creative solutions. The sacrifice of these solo ECPs has significantly improved the mental health service of Myanmar district regions.

Burnout among house officers in Myanmar: A cross-sectional study

Background

Burnout can result in a serious negative impact on a doctor's life, the quality of patient care, and the healthcare organization. This study aims to determine the prevalence of burnout and factors affecting burnout among the house officers in Myanmar.

Materials and methods

An exploratory cross-sectional quantitative survey study was conducted using a self-administered, web-based survey. House officers working in any of the government hospitals in Myanmar were invited to participate in the study. The survey link was distributed online via Facebook. To measure burnout, we utilised a non-proprietary single-item measure, validated to serve as a reliable substitute for the Maslach Burnout Inventory Emotional Exhaustion (MBI:EE). To measure global life satisfaction, the validated Satisfaction with Life Scale (SWLS) was used. The questions for the scales regarding the psychosocial environment were extracted from the long version of the validated Copenhagen Psychosocial Questionnaire (COPSOQ II). The scales selected were "possibilities for the development", "meaning of work", "commitment to workplace", "recognition", "social support from colleagues" and "social support from supervisors". Multiple logistic regression method was applied to determine the factors associated with burnout.

Results

Regarding the prevalence of burnout, out of 159 participants, 42.8% (n = 68) of the participants had no symptoms of burnout. 57.2% (n = 91) had one or more symptoms of burnout. Multivariate analysis showed that the only significant factor associated with burnout was "recognition" (OR 0.96, 95% CI: 0.94-0.97, P < 0.001).

Conclusion

From this study, we have determined the relatively high burnout prevalence and that recognition is the only preventive factor; increase in recognition will decrease the odds of burnout. Hence, urgent interventions are recommended to prevent undesirable effects on both health professionals and patients. Recognition for work done should always be in the heart of the health authorities and medical community in Myanmar.