Abstract 2474: Uncovering a new therapeutic vulnerability for preventing brain metastases

INTRO: Patients with brain metastases (BM) face a 90% mortality rate within one year of their diagnosis and they lack targeted therapeutic options, particularly preventative or interceptional ones.

METHODS: The Singh lab has generated a large in-house biobank of patient-derived BM cell lines that are established from patient-derived BM from primary lung and breast cancers and melanoma. We use these BM cell lines to generate murine orthotopic xenograft models of BM and interrogate the biological processes that lead to BM. These models have successfully recapitulated all the stages of their respective metastatic cascades and allowed characterization of a “premetastatic” population of BM cells that have just seeded the brains of mice before forming mature, clinically detectable tumors. Pre-metastatic cell populations are impossible to detect in human patients but present a therapeutic window wherein metastasizing cells can be targeted and eradicated before establishing clinically detectable and difficult to treat brain tumors.

RESULTS: Targeting premetastatic BM cells is a feasible interceptional strategy to block BM, but druggable targets are still very limited. Here, we applied RNA sequencing of premetastatic BM cells to reveal a unique deregulated transcriptomic profile that is specific to premetastatic cells regardless of primary tumor origin. Subsequent Connectivity Map analysis revealed compounds that we biologically characterized in vitro for selective anti-BMIC phenotypes. This effort led us to identify a tool compound that exhibits anti-BM activity in vitro, while remaining ineffective against normal brain cell controls. Follow up preclinical studies showed that treatment with this tool compound reduces the tumor burden of mice compared to placebo, while providing a significant survival advantage. Mass spectrometry-based metabolomics and CRISPR knock-out studies directly validated our tool compound’s target, Target X, as a targetable therapeutic vulnerability in BM, where pharmacological and genetic perturbation of Target X attenuates BM cell proliferation both in vitro and in vivo. We have now begun a large-scale medicinal chemistry campaign to develop a novel, brain penetrant Target X-inhibitor with a drug-like pre-clinical profile validated by our in vivo experimental models. This advanced drug candidate will be ready for later stage preclinical development and subsequent clinical development.

CONCLUSION: This potential first-in-class anti-metastatic therapy may provide an alternative interceptional treatment strategy for patients experiencing BM that are otherwise limited to palliation. Our work provides a new model for target discovery and validation to develop more effective preventative therapeutic strategies for patients with metastatic disease.

Citation Format: Agata M. Kieliszek, Daniel Mobilio, Blessing I. Bassey-Archibong, Jarrod Johnson, Nikoo Aghaei, William Gwynne, Dillon McKenna, Minomi K. Subapanditha, Chitra Venugopal, Jakob Magolan, Sheila K. Singh. Uncovering a new therapeutic vulnerability for preventing brain metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2474.

An HLA-G/SPAG9/STAT3 axis promotes brain metastases

Brain metastases (BM) are the most common brain neoplasm in adults. Current BM therapies still offer limited efficacy and reduced survival outcomes, emphasizing the need for a better understanding of the disease. Herein, we analyzed the transcriptional profile of brain metastasis initiating cells (BMICs) at two distinct stages of the brain metastatic cascade-the "premetastatic" or early stage when they first colonize the brain and the established macrometastatic stage. RNA sequencing was used to obtain the transcriptional profiles of premetastatic and macrometastatic (non-premetastatic) lung, breast, and melanoma BMICs. We identified that lung, breast, and melanoma premetastatic BMICs share a common transcriptomic signature that is distinct from their non-premetastatic counterparts. Importantly, we show that premetastatic BMICs exhibit increased expression of HLA-G, which we further demonstrate functions in an HLA-G/SPAG9/STAT3 axis to promote the establishment of brain metastatic lesions. Our findings suggest that unraveling the molecular landscape of premetastatic BMICs allows for the identification of clinically relevant targets that can possibly inform the development of preventive and/or more efficacious BM therapies.

Abstract 3999: HLA-G, SPAG9 and STAT3 signalling: An alliance that promotes early-stage brain metastases

Brain metastases (BM) are the most common brain tumours in adults and a prominent cause of cancer-related mortality globally. Leading sources of BM are cancers of the lung, breast and melanoma, which together account for approximately 80% of all BM. Unfortunately, current clinical modalities for BM including surgery, radiation therapy and chemotherapy still offer limited efficacy and median survival times of 4 - 12 months in treated patients, emphasizing the need for more effective therapeutic strategies and generally a better understanding of the disease. We recently identified the presence of stem-like cells termed “brain metastasis-initiating cells” or BMICs in patient-derived BM from lung, breast and melanoma cancers that are able to recapitulate the complete brain metastatic cascade in pre-clinical models of BM. Through these models, we serendipitously captured lung, breast and melanoma BMICs at the “pre-metastatic” stage of BM - a stage where circulating metastatic cells have seeded the brain, but not yet formed full-blown (macro-metastatic) brain lesions. Transcriptomic analysis of pre-metastatic and macro-metastatic lung, breast and melanoma BMICs revealed a unique genetic profile in pre-metastatic BMICs that was distinct from their macro-metastatic counterparts. Further analysis identified several genes commonly up-regulated in all pre-metastatic BMIC cohorts irrespective of their primary tumour of origin. Intriguingly, we found that inhibition of the non-classical human leukocyte class I antigen-G or HLA-G gene (one of the top up-regulated genes in the pre-metastatic cohorts), reduced the ability of BMICs to form mature brain lesions. Correspondingly, HLA-G over-expression increased the capacity of BMICs to establish secondary brain tumours. Mechanistically, we discovered that over-expressing HLA-G levels in BMICs (to simulate the high levels that occurs in pre-metastatic BMICs), increased the activation of STAT3 signalling and this was mediated in part via a novel HLA-G binding partner - SPAG9. Our work thus uncovered a potential cooperative role between HLA-G, SPAG9 and STAT3 signalling during the early stages of BM. Indeed, attenuation of SPAG9 protein levels or STAT3 signalling in HLA-G over-expressing BMICs using CRISPR knockout and a STAT3 inhibitor respectively obstructed the ability of high HLA-G levels to promote mature brain lesions. This is the first study to reveal a role for an HLA-G-SPAG9-STAT3 axis in BM and highlights the potential of targeting this axis to inhibit BM, which will markedly extend patient survival.

Citation Format: Blessing I. Bassey-Archibong, Chirayu R. Chokshi, Nikoo Aghaei, Agata Kieliszek, Nazanin Tatari, Dillon McKenna, Mohini Singh, Minomi Subapanditha, Arun Parmar, Neil Savage, Yu Lu, Chitra Venugopal, Sheila Singh. HLA-G, SPAG9 and STAT3 signalling: An alliance that promotes early-stage brain metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3999.

STEM-05. FUNCTIONAL MAPPING REVEALS WIDESPREAD REMODELLING AND UNRECOGNIZED PATHWAY DEPENDENCIES IN RECURRENT GLIOBLASTOMA

Resistance to genotoxic therapies and tumor recurrence are hallmarks of glioblastoma (GBM), an aggressive brain tumor. Here, we explore the functional drivers of post-treatment recurrent GBM. By conducting genome-wide CRISPR-Cas9 screens in patient-derived GBM models, we uncover distinct genetic dependencies in recurrent tumor cells that were absent in their patient-matched primary predecessors, accompanied by increased mutational burden and differential transcript and protein expression. These analyses support parallel tumor-intrinsic mechanisms of treatment resistance which rely on acquisition of immunosuppressive capacity, including a defective mismatch repair pathway, ablation of PTEN activity, and a novel combination of de novo mutations in SWI/SNF components. We map a multilayered genetic and functional response to resist chemoradiotherapy and drive tumor recurrence, identifying protein tyrosine phosphatase 4A2 (PTP4A2) as a novel driver of self-renewal, proliferation and tumorigenicity at GBM recurrence. Mechanistically, genetic perturbation and a small molecule inhibitor of PTP4A2 repress axon guidance activity through a dephosphorylation axis with roundabout guidance receptor 1 (ROBO1) and exploit a genetic dependency on ROBO signaling. Importantly, engineered anti-ROBO1 single-domain antibodies also mimic the effects of PTP4A2 inhibition. We conclude that functional reprogramming drives tumorigenicity and present a dependence on a PTP4A2-ROBO1 signaling axis at GBM recurrence.

TMOD-01. AN IN VIVO FUNCTIONAL GENOMICS SCREEN TO IDENTIFY NOVEL DRIVERS OF LUNG-TO-BRAIN METASTASIS

INTRODUCTION

Brain metastases, the most common tumors of the central nervous system, occur in approximately 20% of primary adult cancers. In particular, 40% of patients with non-small cell lung cancer develop brain metastasis. As systemic therapies for the treatment of non-small cell lung cancer become increasingly effective at controlling primary disease, patients are ironically succumbing to their brain metastases. This highlights a large unmet need to develop novel targeted therapies for the treatment of lung-to-brain metastases (LBM). We hypothesize that an in vivo functional genomic screen can identify novel genes that drive LBM.

METHODS

To do this, we developed a patient-derived xenograft (PDX) mouse model of LBM using patient lung cancer cell lines. This PDX model of LBM enables the use of fluorescent and bioluminescent in vivo imaging to track the progression of lung tumor and brain metastases.

RESULTS

We have performed an in vivo genome-wide CRISPR activation screening to identify novel drivers of LBM. We will derive candidate genes through mouse brain and lung tissue sequencing after mice reach endpoint.

EXPECTED AREA OF FINDINGS

This platform will lead to potential therapeutic targets to prevent the formation of LBM and prolong the survival of patients with non-small cell lung cancer.

LIMITATIONS

There may be limitations in getting candidate hits that overlap in all mice in our first replicate. This can be remedied by conducting the in vivo screen in at least three biological replicates.

CONCLUSION

To the best of our knowledge, this is the first genome-wide in vivo CRISPR activation screen searching for drivers of LBM using a PDX animal model. This study can provide a framework to gain a deeper understanding of the regulators of BM formation which will hopefully lead to targeted drug discovery.

BSCI-18. Identifying novel drivers of lung-to-brain metastasis through in vivo functional genomics

Introduction

Brain metastases, the most common tumors of the central nervous system, occur in approximately 20% of primary adult cancers. In particular, 40% of patients with non-small cell lung cancer develop brain metastasis. As systemic therapies for the treatment of non-small cell lung cancer become increasingly effective at controlling primary disease, patients are ironically succumbing to their brain metastases. This highlights a large unmet need to develop novel targeted therapies for the treatment of lung-to-brain metastases (LBM). We hypothesize that an in vivo functional genomic screen can identify novel genes that drive LBM.

Methods

To do this, we developed a patient-derived xenograft (PDX) mouse model of LBM using patient lung cancer cell lines. This PDX model of LBM enables the use of fluorescent and bioluminescent in vivo imaging to track the progression of lung tumor and brain metastases.

Results

We have performed an in vivo genome-wide CRISPR activation screening to identify novel drivers of LBM. We will derive candidate genes through mouse brain and lung tissue sequencing after mice reach endpoint.

Expected Area of findings

This platform will lead to potential therapeutic targets to prevent the formation of LBM and prolong the survival of patients with non-small cell lung cancer.

Limitations

There may be limitations in getting candidate hits that overlap in all mice in our first replicate. This can be remedied by conducting the in vivo screen in at least three biological replicates.

Conclusion

To the best of our knowledge, this is the first genome-wide in vivo CRISPR activation screen searching for drivers of LBM using a PDX animal model. This study can provide a framework to gain a deeper understanding of the regulators of BM formation which will hopefully lead to targeted drug discovery.

NGMA-5. An in vivo functional genomics screen to identify novel drivers of lung-to-brain metastasis

Introduction

Brain metastases, the most common tumors of the central nervous system, occur in approximately 20% of primary adult cancers. In particular, 40% of patients with non-small cell lung cancer develop brain metastasis. As systemic therapies for the treatment of non-small cell lung cancer become increasingly effective at controlling primary disease, patients are ironically succumbing to their brain metastases. This highlights a large unmet need to develop novel targeted therapies for the treatment of lung-to-brain metastases (LBM). We hypothesize that an in vivo functional genomic screen can identify novel genes that drive LBM.

Methods

To do this, we developed a patient-derived xenograft (PDX) mouse model of LBM using patient lung cancer cell lines. This PDX model of LBM enables the use of fluorescent and bioluminescent in vivo imaging to track the progression of lung tumor and brain metastases.

Results

We have performed an in vivo genome-wide CRISPR activation screening to identify novel drivers of LBM. We will derive candidate genes through mouse brain and lung tissue sequencing after mice reach endpoint.

Expected Area of findings

This platform will lead to potential therapeutic targets to prevent the formation of LBM and prolong the survival of patients with non-small cell lung cancer.

Conclusion

To the best of our knowledge, this is the first genome-wide in vivo CRISPR activation screen searching for drivers of LBM using a PDX animal model. This study can provide a framework to gain a deeper understanding of the regulators of BM formation which will hopefully lead to targeted drug discovery.

Abstract PR009: The functional genomic landscape of recurrent glioblastoma

Glioblastoma (GBM) is a highly fatal brain cancer where mortality is predominantly caused by disease recurrence and lack of second-line therapies. Here, utilizing genome-wide CRISPR-Cas9 screening, we uncover treatment-based conditional genetic interactions modulating sensitivity to combined radiation therapy (RT) and temozolomide (TMZ), the standard of care treatment administered to over 70% of glioblastoma patients. To investigate therapy-induced changes in the functional landscape of glioblastoma stem cells (GSCs) without confounding patient-to-patient differences, we systematically mapped genetic dependencies in patient-matched pre-treatment primary and post-treatment recurrent GSCs. This comparison highlights a remodelling of genes and pathways regulating tumor cell survival at disease relapse, arming recurrent GSCs with newly acquired genetic drivers and further loss of tumor suppressors. Among these genes, we identify PTP4A2, encoding protein tyrosine phosphatase 4A2, as a major regulator of stemness and tumorigenicity in recurrent GSCs. Genetic perturbation or pharmacological inhibition of PTP4A2 influences the phosphorylation status and expression of interacting proteins belonging to axonal guidance pathways, as phosphoproteomic studies showed specific enrichment in axon guidance regulator Roundabout Guidance Receptor 1 (ROBO1) in recurrent GSCs. We therefore designed and developed efficacious Camelid biotinylated single-domain antibody (bio-sdAb) and tetrameric complexes targeting human ROBO1 (MKRo-20). Subsequently, we orthotopically engrafted recurrent GSCs into immunocompromised mice and administered local treatments of tetrameric MKRo-20. All mice treated with tetrameric MKRo-20 were rendered tumor free, suggesting that modulation of ROBO1 with bio-sdAbs presents a new immunotherapeutic strategy to target recurrent glioblastoma. Our work reveals a context-specific dependence on axonal guidance through a PTP4A2-ROBO axis in recurrent glioblastoma, highlighting new avenues of therapeutic intervention for second-line therapy in GBM.

This abstract is also being presented as PO025.

Citation Format: Chirayu Chokshi, David Tieu, Kevin Brown, Chitra Venugopal, Lina Liu, Laura Kuhlman, Katherine Chan, Amy Tong, Neil Savage, Dillon McKenna, Nikoo Aghaei, Minomi Subapanditha, Joseph M Salamoun, Martin Rossotti, Peter Wipf, Elizabeth Sharlow, John S. Lazo, Thomas Kislinger, Kevin Henry, Yu Lu, Jason Moffat, Sheila K. Singh. The functional genomic landscape of recurrent glioblastoma [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr PR009.

TAMI-03. IDENTIFICATION OF NOVEL DRIVERS OF LUNG-TO-BRAIN METASTASIS THROUGH IN VIVO FUNCTIONAL GENOMICS

Brain metastasis, the most common tumor of the central nervous system, occurs in 20-36% of primary cancers. In particular, 40% of patients with non-small cell lung cancer (NSCLC) develop brain metastases, with a dismal survival of approximately 4-11 weeks without treatment, and 16 months with treatment. This highlights a large unmet need to develop novel targeted therapies for the treatment of lung-to-brain metastases (LBM). Genomic interrogation of LBM using CRISPR technology can inform preventative therapies targeting genetic vulnerabilities in both primary and metastatic tumors. Loss-of-function studies present limitations in metastasis research, as knocking out genes essential for survival in the primary tumor cells can thwart the metastatic cascade prematurely. However, gene overexpression using CRISPR activation (CRISPRa) has the potential for overcoming dependencies of gene essentiality. We theorize that an in vivo genome-wide CRISPRa screen will identify novel genes that, when overexpressed, drive LBM. We have developed a patient-derived orthotopic murine xenograft model of LBM using primary patient-derived NSCLC cell lines (termed LTX cells) from the Swanton Lab TRACERx study. We are now poised to transduce LTX cells with a human genome-wide CRISPRa single guide RNA (sgRNA) library, and to subsequently inject the cells into the lungs of immunocompromised mice. We will then track the process of LBM using bioluminescent and MRI imaging until mice reach endpoint. Sequencing of primary lung tumors and subsequent brain metastases promises to uncover enriched sgRNAs, which may represent novel drivers of primary lung tumor formation and LBM. To the best of our knowledge, this study is the first in vivo genome-wide CRISPRa screen focused on identifying novel drivers of LBM, and can inform future preventative therapies to improve survival outcomes for NSCLC patients.

STEM-01. TARGETING BRAIN METASTASIS-INITIATING CELLS: A PREVENTATIVE APPROACH

BACKGROUND

The incidence of brain metastases (BM) is tenfold higher than primary brain tumors. BM commonly originate from primary lung, breast, and melanoma tumors with a 90% mortality rate within one year of diagnosis. Current standard of care for BM includes surgical resection with concurrent chemoradiation, but does not extend median survival past 16 months, posing a large unmet need to identify novel therapies against BM.

METHODS

From a large in-house biobank of patient-derived BM cell lines, the Singh Lab has generated murine orthotopic patient-derived xenograft (PDX) models of lung, breast, and melanoma BM that recapitulate the stages of BM progression as seen in humans. Using these three PDX models, we identified a population of “pre-metastatic” brain metastasis-initiating cells (BMICs) that are newly arrived in the brain but have yet to form detectable tumors. Pre-metastatic BMICs are not detectable in human patients but are important therapeutic targets with the potential to prevent BM in at-risk patients.

RESULTS

RNA sequencing of pre-metastatic BMICs from all three PDX primary tumor models with subsequent Connectivity Map analysis identified novel compounds that have the potential of killing all three types of BMICs. In particular, we identified two compounds that have selective killing of BMICs in vitro from all three primary tumor cohorts while sparing non-cancerous cells. We further characterized their ability to inhibit the self-renewal and proliferative properties of BMICs. Ongoing in vivo work will investigate the compounds’ preclinical utilities in preventing BM.

CONCLUSION

Identification of novel small molecules that target BMICs could prevent the formation of BM completely and dramatically improve the prognosis of at-risk cancer patients.

39. CHARACTERIZING NOVEL INHIBITORS OF BRAIN METASTASIS-INITIATING CELLS

BACKGROUND

The incidence of brain metastases (BM) is tenfold higher than primary brain tumors. BM commonly originate from primary lung, breast, and melanoma tumors with a 90% mortality rate within one year of diagnosis. Current standard of care for BM includes surgical resection with concurrent chemoradiation, but does not extend median survival past 16 months, posing a large unmet need to identify novel therapies against BM.

METHODS

From a large in-house biobank of patient-derived BM cell lines, the Singh Lab has generated murine orthotopic patient-derived xenograft (PDX) models of lung, breast, and melanoma BM that recapitulate the stages of BM progression as seen in human patients. Using these three PDX models, we identified a population of “pre-metastatic” brain metastasis-initiating cells (BMICs) that are newly arrived in the brain but have yet to form detectable tumors. Pre-metastatic BMICs are not detectable in human patients but are important therapeutic targets with the potential to prevent BM in at-risk patients.

RESULTS

RNA sequencing of pre-metastatic BMICs from all three PDX primary tumor models with subsequent Connectivity Map analysis identified novel compounds that have the potential of killing all three types of BMICs. In particular, we identified two compounds that have selective killing of BMICs in vitro from all three primary tumor cohorts while sparing non-cancerous cells. We further characterized their ability to inhibit the self-renewal and proliferative properties of BMICs. Ongoing in vivo work will investigate the compounds’ preclinical utilities in preventing BM.

CONCLUSION

Identification of novel small molecules that target BMICs could prevent the formation of BM completely and dramatically improve the prognosis of at-risk cancer patients.

47. UNCOVERING A NOVEL ROLE FOR HLA-G IN BRAIN METASTASES

Brain metastases (BM) are the most common brain tumour in adults and are ten times more likely to develop than primary brain tumours. More than 20% of patients with cancer will develop BM with the three most common sources being primary cancers of the lung, breast, and melanoma. Unfortunately, current treatment options for BM do not effectively eradicate BM, with a mere median overall survival time of 12 months in treated patients. This indicates the need for better and more effective therapies against BM. Using patient-derived cell lines established from surgically removed brain metastatic tumours of lung-, breast- and melanoma-BM patients, we generated patient-derived orthotopic murine xenograft (PDX) models of lung-, breast-, and melanoma-BM. From these PDX models, we isolated a rare population of stem-like brain metastasis initiating cells (BMICs) we termed “pre-metastatic”, that had traveled from their primary/orthotopic tumours and lodged in the brain but had not yet developed into mature BM. Transcriptomic analyses performed on pre-metastatic and non-pre-metastatic BMICs from lung, breast and melanoma PDX models of BM, identified a set of deregulated genes exclusive only to pre-metastatic BMICs. Further analysis revealed HLA-G as being commonly up-regulated only during the pre-metastatic stage of the lung-, breast-, and melanoma-BM cascade. In vitro and in vivo analyses demonstrated that HLA-G knock-down reduced the proliferation and survival of BMICs from all BM cohorts, and attenuated the establishment of mature brain metastatic tumours, implying a crucial role for HLA-G in the formation of BM. Developing a therapeutic strategy that targets HLA-G in BM may prove effective at completely eliminating brain metastatic cells at an early stage of the BM cascade, thereby turning a fatal disease into an eminently more treatable one.

37. IN VIVO FUNCTIONAL GENOMIC SCREEN TO IDENTIFY NOVEL DRIVERS OF LUNG-TO-BRAIN METASTASIS

Brain metastasis, the most common tumour of the central nervous system, occurs in 20–36% of primary cancers. In particular, 40% of patients with non-small cell lung cancer (NSCLC) develop brain metastases, with a dismal survival of approximately 4–11 weeks without treatment, and 16 months with treatment. This highlights a large unmet need to develop novel targeted therapies for the treatment of lung-to-brain metastases (LBM). Genomic interrogation of LBM using CRISPR technology can inform preventative therapies targeting genetic vulnerabilities in both primary and metastatic tumours. Loss-of-function studies present limitations in metastasis research, as knocking out genes essential for survival in the primary tumour cells can thwart the metastatic cascade prematurely. However, gene overexpression using CRISPR activation (CRISPRa) has the potential for overcoming dependencies of gene essentiality. We theorize that an in vivo genome-wide CRISPRa screen will identify novel genes that, when overexpressed, drive LBM. We have developed a patient-derived orthotopic murine xenograft model of LBM using primary patient-derived NSCLC cell lines (termed LTX cells) from the Swanton Lab TRACERx study. We are now poised to transduce LTX cells with a human genome-wide CRISPRa single guide RNA (sgRNA) library, and to subsequently inject the cells into the lungs of immunocompromised mice. We will then track the process of LBM using bioluminescent and MRI imaging until mice reach endpoint. Sequencing of primary lung tumours and subsequent brain metastases promises to uncover enriched sgRNAs, which may represent novel drivers of primary lung tumour formation and LBM. To the best of our knowledge, this study is the first in vivo genome-wide CRISPRa screen focused on identifying novel drivers of LBM, and can inform future preventative therapies to improve survival outcomes for NSCLC patients.

BSCI-20. THERAPEUTIC TARGETING OF HLA-G IN BRAIN METASTASES

Brain metastases (BM) are the most common brain tumor in adults, with an incidence ten times greater than that of primary brain tumors. The most common sources of BM in adult cancer patients include cancers of the lung, breast and melanoma, which together account for almost 80% of all BM. Current clinical modalities for BM include surgery, whole brain radiation therapy and stereotactic radiosurgery but these therapies still offer limited efficacy and reduced survival of only months in treated patients, emphasizing the need for novel BM research approaches and better therapeutic strategies. Our laboratory recently discovered that stem-like cells exist in patient-derived BM from lung, breast and melanoma cancers, which we termed “brain metastasis-initiating cells” or BMICs. Through clinically relevant human-mouse xenograft models established with these patient-derived BMICs, we captured lung, breast and melanoma BMICs at pre-metastasis – a key stage where circulating metastatic cells extravasate and initially seed the brain, prior to organization into micro-metastatic foci. Transcriptome analysis of pre-metastatic BMICs revealed a unique genetic profile and several genes commonly up-regulated among lung, breast and melanoma BM, including the non-classical human leukocyte class I antigen-G (HLA-G). Loss of HLA-G in lung, breast and melanoma BMICs using two HLA-G specific shRNAs attenuated sphere formation, migratory and tumor initiating abilities of lung, breast and melanoma BMICs compared to control BMICs. HLA-G knockdown also resulted in reduced phospho(p)-STAT3 expression in patient-derived BMICs suggesting a potential cooperative role between HLA-G and pSTAT3 in BM. Since HLA-G is highly expressed at the cell surface in control tumors, ongoing experiments are focused on developing HLA-G specific chimeric antigen receptor -T cells (CAR-Ts) and determining their efficacy in targeting lung-, breast- and melanoma-BM as blocking the brain metastatic process will markedly extend patient survival and ultimately transform a fatal systemic disease into a more treatable one.