CAR T cells targeting tumor-associated exons of glypican 2 regress neuroblastoma in mice

Targeting solid tumors must overcome several major obstacles, in particular, the identification of elusive tumor-specific antigens. Here, we devise a strategy to help identify tumor-specific epitopes. Glypican 2 (GPC2) is overexpressed in neuroblastoma. Using RNA sequencing (RNA-seq) analysis, we show that exon 3 and exons 7-10 of GPC2 are expressed in cancer but are minimally expressed in normal tissues. Accordingly, we discover a monoclonal antibody (CT3) that binds exons 3 and 10 and visualize the complex structure of CT3 and GPC2 by electron microscopy. The potential of this approach is exemplified by designing CT3-derived chimeric antigen receptor (CAR) T cells that regress neuroblastoma in mice. Genomic sequencing of T cells recovered from mice reveals the CAR integration sites that may contribute to CAR T cell proliferation and persistence. These studies demonstrate how RNA-seq data can be exploited to help identify tumor-associated exons that can be targeted by CAR T cell therapies.

Chemotherapy-Induced Upregulation of Small Extracellular Vesicle-Associated PTX3 Accelerates Breast Cancer Metastasis

Although neoadjuvant chemotherapy is a standard component of breast cancer treatment, recent evidence suggests that chemotherapeutic drugs can promote metastasis through poorly defined mechanisms. Here we utilize xenograft mouse models of triple-negative breast cancer to explore the importance of chemotherapy-induced tumor-derived small extracellular vesicles (sEV) in metastasis. Doxorubicin (DXR) enhanced tumor cell sEV secretion to accelerate pulmonary metastasis by priming the premetastatic niche. Proteomic analysis and CRISPR/Cas9 gene editing identified the inflammatory glycoprotein PTX3 enriched in DXR-elicited sEV as a critical regulator of chemotherapy-induced metastasis. Both genetic inhibition of sEV secretion from primary tumors and pharmacologic inhibition of sEV uptake in secondary organs suppressed metastasis following chemotherapy. Taken together, this research uncovers a mechanism of chemotherapy-mediated metastasis by which drug-induced upregulation of sEV secretion and PTX3 protein cargo primes the premetastatic niche and suggests that inhibition of either sEV uptake in secondary organs or secretion from primary tumor cells may be promising therapeutic strategies to suppress metastasis. SIGNIFICANCE: These findings show that chemotherapy-induced small extracellular vesicles accelerate breast cancer metastasis, and targeted inhibition of tumor-derived vesicles may be a promising therapeutic strategy to improve the efficacy of chemotherapy treatment.

Abstract 5871: Immunogenomic approaches to optimize immunotherapeutic targeting of neuroblastoma

Background: Neuroblastoma (NB) is the most common extra-cranial solid cancer in children. Although multimodal therapies with differentiating agents and immunotherapy with anti-GD2 antibody and GM-CSF have shown promising results, it remains deadly in approximately 50% of patients with high-risk disease. Chimeric antigen receptor T-cell therapies (CAR-T) have been found to be effective in treating refractory and relapsed leukemia and lymphoma, and two of them have been recently approved by the FDA. However, current CARs frequently lose efficacy due to T cell exhaustion and CARs against solid tumor antigens often lack enough specificity due to a low incidence of somatic mutations resulting in a paucity of tumor neoantigens. There have not been effective CAR-T therapies against other solid cancers to date although many clinical trials are underway. We previously identified 2 cell surface cancer-associated antigens, GPC2 (Glypican-2) and CD276 (B7-H3), both highly expressed in NB tumor cells but expressed at low or undetectable levels in normal organs. Here we attempt to develop a high throughput way of identifying optimal CART cell binders that show activation and expansion in the presence of GPC2 and CD276 but lack of exhaustion.

Methods: Binders targeting GPC2 or CD276 were cloned into CAR lentiviral constructs and then were separately transduced into T cells to develop CAR-T cells. Then we analyzed cytotoxicity of these CART cells individually. To identify the most effective GPC2 or CD276-specific targeting CAR-T cells, we utilized a combined proteomics and transcriptomics method for every single CAR-T cell to quantify RNA and protein at the same. All CAR-T cells were pooled and co-cultured with CD276/GPC2-expressing NB cancer cells (target cells) for 24 hr. Co-cultured CAR-T cells were examined for their activation, exhaustion, cytotoxicity state and distinguished different cell types by staining with CITE-seq (Cellular Indexing of Transcriptomes and Epitopes by Sequencing) antibodies, and then molecularly barcoded using 10X Genomics platform for single cell RNA-sequencing (scRNA-seq).

Results: We attempted to test the efficacy of CAR-T cells using 14 established and novel binders against GPC2 or CD276. According to cytotoxicity assay of these 14 CART cells, we found CT3 was the most effective GPC2 targeting CART cells but majority of CD276 CART cells showed high cytolytic activity in vitro.

Conclusions and Future Directions: Using the CITE-seq and RNAseq analyses, we can identify which of the CARs are enriched and have an activated T cell signature, but lack exhaustion markers. Top candidate binders for each antigen are currently being developed into “AND” or “OR” CARs that are being tested in in-vitro and in-vivo models of NB. Thus, we have developed a high throughput method to identify high affinity functional binders against tumor cell surface antigens and provide a novel immunogenomics methods of CARs optimization for development of highly effective immunotherapies against NB and other cancers.

Citation Format: Meijie Tian, Adam Tai-Chi Cheuk, Yong Song, Sivasish Sindiri, Nan Li, Christopher M. Dower, Mitchell Ho, Bradley St Croix, Javed Khan. Immunogenomic approaches to optimize immunotherapeutic targeting of neuroblastoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5871.

Abstract A13: Immunogenomic approaches to optimize immunotherapeutic targeting of neuroblastoma

Neuroblastoma (NB) is the most common extracranial solid cancer in children. Although multimodal therapies with differentiating agents and immunotherapy with anti-GD2 antibody and GM-CSF have shown promising results, it remains deadly in approximately 50% of patients with high-risk disease. Chimeric antigen receptor T-cell therapies (CAR-T) have been found to be effective in treating refractory and relapsed leukemia and lymphoma, and two of them have been recently approved by the FDA. However, current CARs frequently lose efficacy due to T-cell exhaustion, and CARs against solid tumor antigens often lack enough specificity due to a low incidence of somatic mutations resulting in a paucity of tumor neoantigens. There have not been effective CAR-T therapies against other solid cancers to date, although many clinical trials are under way. Therefore, we attempted to develop a high-throughput way of identifying optimal CART cell binders that show activation and expansion in the presence of targets but lack of exhaustion. We previously identified two cell surface cancer-associated antigens, GPC2 (Glypican-2) and CD276 (B7-H3), both highly expressed in NB tumor cells but expressed at low or undetectable levels in normal organs. 14 established binders as well as novel binders targeting these two antigens were cloned into CAR lentiviral constructs and then were separately transduced into T cells to develop 14 CAR-T cells using a 2nd-generation design. All 14 CAR-T cells were pooled and cocultured with CD276/GPC2-expressing NB cancer cells (target cells) for 24 hr. To identify the effective GPC2 or CD276-specific targeting CAR-T cells, we utilized a combined proteomics and transcriptomics method for every single CAR-T cell to quantify RNA and protein at the same. Cocultured CAR-T cells were examined for their activation, exhaustion, cytotoxicity state and distinguished different cell types by staining with CITE-seq (Cellular Indexing of Transcriptomes and Epitopes by Sequencing) antibodies, and then molecularly barcoded using 10X Genomics platform for single-cell RNA-sequencing (scRNA-seq). The data are currently being analyzed and will be presented. Using this method, we will be able to identify which of the CARs are enriched and have an activated T-cell signature, and lack exhaustion marks as determined by the CITE-seq and RNAseq analyses. Finally, top candidate binders for each antigen will be developed into “AND” or “OR” CARs and will be tested in in vitro and in vivo models of NB. Thus, we will develop a high-throughput way to identify high-affinity functional binders against tumor cell surface antigens. This study also will provide novel immunogenomics methods of CARs optimization for development of highly effective immunotherapies against NB and other cancers.

Citation Format: Meijie Tian, Adam Tai-Chi Cheuk, Jeetendra Kumar, Young K. Song, Sivasish Sindiri, Nan Li, Christopher M. Dower, Mitchell Ho, Brad St. Croix, Javed Khan. Immunogenomic approaches to optimize immunotherapeutic targeting of neuroblastoma [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr A13.

Isolation of rabbit single domain antibodies to B7-H3 via protein immunization and phage display

Single domain antibodies have certain advantages including their small size, high stability and excellent tissue penetration, making them attractive drug candidates. Rabbit antibodies can recognize diverse epitopes, including those that are poorly immunogenic in mice and humans. In the present study, we established a method to isolate rabbit VH single domain antibodies for potential cancer therapy. We immunized rabbits with recombinant human B7-H3 (CD276) protein, made a phage-displayed rabbit VH single domain library with a diversity of 7 × 10⁹, and isolated two binders (A1 and B1; also called RFA1 and RFB1) from phage panning. Both rabbit VH single domains exhibited antigen-dependent binding to B7-H3-positive tumor cell lines but not B7-H3 knockout tumor cell lines. Our study shows that protein immunization followed by phage display screening can be used to isolate rabbit single domain antibodies. The two single domain antibodies reported here may have potential applications in cancer immunotherapy.

Targeted Inhibition of ULK1 Promotes Apoptosis and Suppresses Tumor Growth and Metastasis in Neuroblastoma

Neuroblastoma is the most common extracranial solid malignancy in the pediatric population, accounting for over 9% of all cancer-related deaths in children. Autophagy is a cell self-protective mechanism that promotes tumor cell growth and survival, making it an attractive target for treating cancer. However, the role of autophagy in neuroblastoma tumor growth and metastasis is largely undefined. Here we demonstrate that targeted inhibition of an essential autophagy kinase, unc-51 like autophagy kinase 1 (ULK1), with a recently developed small-molecule inhibitor of ULK1, SBI-0206965, significantly reduces cell growth and promotes apoptosis in SK-N-AS, SH-SY5Y, and SK-N-DZ neuroblastoma cell lines. Furthermore, inhibition of ULK1 by a dominant-negative mutant of ULK1 (dnULK1^K46N) significantly reduces growth and metastatic disease and prolongs survival of mice bearing SK-N-AS xenograft tumors. We also show that SBI-0206965 sensitizes SK-N-AS cells to TRAIL treatment, but not to mTOR inhibitors (INK128, Torin1) or topoisomerase inhibitors (doxorubicin, topotecan). Collectively, these findings demonstrate that ULK1 is a viable drug target and suggest that inhibitors of ULK1 may provide a novel therapeutic option for the treatment of neuroblastoma. Mol Cancer Ther; 17(11); 2365-76. ©2018 AACR.

Mechanisms and context underlying the role of autophagy in cancer metastasis

Macroautophagy/autophagy is a fundamental cellular degradation mechanism that maintains cell homeostasis, regulates cell signaling, and promotes cell survival. Its role in promoting tumor cell survival in stress conditions is well characterized, and makes autophagy an attractive target for cancer therapy. Emerging research indicates that autophagy also influences cancer metastasis, which is the primary cause of cancer-associated mortality. However, data demonstrate that the regulatory role of autophagy in metastasis is multifaceted, and includes both metastasis-suppressing and -promoting functions. The metastasis-suppressing functions of autophagy, in particular, have important implications for autophagy-based treatments, as inhibition of autophagy may increase the risk of metastasis. In this review, we discuss the mechanisms and context underlying the role of autophagy in metastasis, which include autophagy-mediated regulation of focal adhesion dynamics, integrin signaling and trafficking, Rho GTPase-mediated cytoskeleton remodeling, anoikis resistance, extracellular matrix remodeling, epithelial-to-mesenchymal transition signaling, and tumor-stromal cell interactions. Through this, we aim to clarify the context-dependent nature of autophagy-mediated metastasis and provide direction for further research investigating the role of autophagy in cancer metastasis.

Selective Reversible Inhibition of Autophagy in Hypoxic Breast Cancer Cells Promotes Pulmonary Metastasis

Autophagy influences how cancer cells respond to nutrient deprivation and hypoxic stress, two hallmarks of the tumor microenvironment (TME). In this study, we explored the impact of autophagy on the pathophysiology of breast cancer cells using a novel hypoxia-dependent, reversible dominant-negative strategy to regulate autophagy at the cellular level within the TME. Suppression of autophagy via hypoxia-induced expression of the kinase-dead unc-51-like autophagy-activating kinase (ULK1) mutant K46N increased lung metastases in MDA-MB-231 xenograft mouse models. Consistent with this effect, expressing a dominant-negative mutant of ULK1 or ATG4b or a ULK1-targeting shRNA facilitated cell migration in vitro Functional proteomic and transcriptome analysis revealed that loss of hypoxia-regulated autophagy promotes metastasis via induction of the fibronectin integrin signaling axis. Indeed, loss of ULK1 function increased fibronectin deposition in the hypoxic TME. Together, our results indicated that hypoxia-regulated autophagy suppresses metastasis in breast cancer by preventing tumor fibrosis. These results also suggest cautions in the development of autophagy-based strategies for cancer treatment. Cancer Res; 77(3); 646-57. ©2016 AACR.

Abstract 5110: The role of autophagy in the tumor microenvironment

The tumor microenvironment (TME) is a complex and dynamic breeding ground for the selection of aggressive tumor cells with an advantage of survival and metastatic potential. Autophagy has emerged as a powerful cellular process that can greatly influence how cancer cells respond to nutrient deprivation and hypoxic stress, the hallmarks of the TME. However, the physiological importance of hypoxia-regulated autophagy remains unknown. Here, we used a novel hypoxia-dependent reversible dominant-negative strategy, which allowed for physiological regulation of autophagy at the cellular level during tumor growth and metastasis and creates a heterogeneous population comprised of autophagy-competent and autophagy-deficient tumor cells. We demonstrate that the suppression of autophagy by HIF1-α dependent ULK1 inhibition within the hypoxic tumor microenvironment enhances the metastatic potential of breast cancer cells both in vitro and in vivo. Functional proteomic and transcriptome analysis indicated that the loss of hypoxia-regulated autophagy promotes metastasis through extracellular remodeling pathways, primarily through induction of the fibronectin-integrin signaling axis, along with LOX-mediated extracellular remodeling and pre-metastatic niche formation. In this way, the role of physiological hypoxia regulated autophagy was assessed for the first time in a triple negative breast cancer model. Currently, we are exploring the interplay between autophagy-competent and autophagy-deficient tumor cells within the TME, and how it relates to metastasis. Although the importance of autophagy in tumor-stromal interactions has recently become appreciated, the role autophagy plays in tumor cell-tumor cell interactions remains unknown. Through investigation of these intra-tumor cell networks, we can elucidate the precise mechanism of how physiologically-regulated autophagy in tumor cells influences the surrounding TME and tumor progression.

Citation Format: Christopher M. Dower, Hong-Gang Wang. The role of autophagy in the tumor microenvironment. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5110.

Midwifery in the 21st century. Recommendations from the Pew Health Professions Commission/UCSF Center for the Health Professions 1998 Taskforce on Midwifery

Unprecedented changes in the delivery and financing of health care have produced angst and opportunity, criticism, and innovation. To explore the effects of these market-driven changes on midwifery, the University of California at San Francisco Center for the Health Professions convened a Taskforce on Midwifery in 1998. Consisting of eight experts from across the country, the Taskforce was charged with exploring the impact of health care system developments on midwifery, and identifying issues facing the profession and the roles midwives play in women's health care. The Taskforce answered its charge by offering 14 recommendations related to midwifery practice, regulation, education, research, and policy. The recommendations incorporate the Taskforce vision that the midwifery model of care should be embraced by, and incorporated into, the health care system in order to make it available to all women and their families. Midwives, educators, collaborators, and policymakers can use the recommendations to develop curricula, practice sites, and laws for an improved health care system that fully includes midwives and encompasses the midwifery model of care.

Changing nature of physician licensure. Implications for medical education in California

Recent upheavals within health care delivery, technological advances, and changing attitudes among consumers have challenged and changed health professions licensure. At the same time, traditional regulatory frameworks remain in place. Beginning with a comparison of California's physician regulation with other states, we explore this tension between established regulatory systems and emerging reforms. Current trends in regulatory reform across the United States and in California include efforts to standardize practice requirements, expand scopes of practice for nonphysicians, and restructure boards. Because of these trends, medical educators will be expected to prepare physicians to practice under increased scrutiny and expectations of accountability; promote interdisciplinary education, training, and practice; and step up the efforts toward uniformity in medical education, training, and practice.