Gamma delta T cells in acute myeloid leukemia: biology and emerging therapeutic strategies

γδ T cells play an important role in disease control in acute myeloid leukemia (AML) and have become an emerging area of therapeutic interest. These cells represent a minor population of T lymphocytes with intrinsic abilities to recognize antigens in a major histocompatibility complex-independent manner and functionally straddle the innate and adaptive immunity interface. AML shows high expression of phosphoantigens and UL-16 binding proteins that activate the Vδ2 and Vδ1 subtypes of γδ T cells, respectively, leading to γδ T cell-mediated cytotoxicity. Insights from murine models and clinical data in humans show improved overall survival, leukemia-free survival, reduced risk of relapse, enhanced graft-versus-leukemia effect, and decreased graft-versus-host disease in patients with AML who have higher reconstitution of γδ T cells following allogeneic hematopoietic stem cell transplantation. Clinical trials leveraging γδ T cell biology have used unmodified and modified allogeneic cells as well as bispecific engagers and monoclonal antibodies. In this review, we discuss γδ T cells' biology, roles in cancer and AML, and mechanisms of immune escape and antileukemia effect; we also discuss recent clinical advances related to γδ T cells in the field of AML therapeutics.

Abstract 5098: B7-H3 blockade in combination with natural killer cell activity enhancers including NKTR-255 and venetoclax synergistically induces cytotoxicity in B7-H3+ AML cells

Background: Acute myeloid leukemia (AML) is characterized by clonal proliferation of malignant myeloid blasts in the bone marrow. We have recently reported that blocking B7-H3 using a novel monoclonal antibody (mAB), T-1A5 enhances natural killer (NK) cell mediated cytotoxicity against AML cells. IL-15 is an essential component for NK cell activity. Recombinant human IL-15 (rIL-15), however, degrades rapidly and therefore may provide a suboptimal stimulus to NK cells. Studies have shown that BCL2 inhibitor, venetoclax (ABT-199), enhances NK cell induced antibody dependent cellular cytotoxicity (ADCC) against cancer cells. However, the combined effect of B7-H3 blocking and BCL2 inhibition remains unexplored in AML. We hypothesized that blocking B7-H3 using T-1A5 in the presence of novel investigational polymer-engineered IL-15 receptor agonist, NKTR-255, and the BCL2 inhibitor synergistically induces NK cell mediated ADCC in AML cells.

Methods: CD16 and NKG2D activation markers measured by flow cytometry in AML patient and healthy donor derived NK cells. The NKTR-255 was used to generate NK cells, and their cytotoxicity was compared to that of NK cells generated with rIL-15 using IncuCyte. To investigate these NK cells’ cytotoxic activity against AML cells, we treated B7-H3+ AML cell lines (OCI-AML3 and MV4-11) with anti-B7-H3 chimeric mAb ChT-1A5 in the presence and absence of NK cells generated using NKTR-255 or rIL-15. To assess the potential synergy of BCL2 and B7-H3 in NK cell mediated anti-leukemic activity against AML cells, we treated B7-H3+ cells with T-1A5 with or without ABT-199in the presence or absence of NK cells.

Results: The expression of NK cell activation markers were significantly lower in NK cells derived from AML patients than healthy donors. To assess the effect of NKTR-255 on NK cell activity, we generated NK cells using NKTR-255 and compared them with NK cells generated using rIL-15 using the standard 14-day culture protocol. We observed similar proliferation and NK cell numbers between NKTR-255 and rIL-15. However, NK cells stimulated with NKTR-255 showed significantly enhanced (more than 2-fold) cytolytic activity against B7-H3+ AML cell lines compared with NK cells stimulated with rIL-15. Moreover, when combined with ChT-1A5, NKTR-255 significantly enhanced NK cell mediated ADCC activity in B7-H3+ AML cells compared to rIL-15. Interestingly, we observed that the combination of T-1A5 and venetoclax synergistically induced an anti-leukemic effect in B7-H3+ AML cell lines when compared with either drug alone or isotype IgG1 in a dose-dependent manner.

Conclusion: Our data demonstrate that blockade of the immune checkpoint protein, B7-H3 with the IL-15 receptor agonist, NKTR-255, or the BCL2 inhibitor, ABT-199, synergistically induces NK cell mediated cytotoxicity against B7-H3+ AML cells.

Citation Format: Anudishi Tyagi, A. Mario Marcondes, Willem Overwijk, Venkata Lokesh Battula. B7-H3 blockade in combination with natural killer cell activity enhancers including NKTR-255 and venetoclax synergistically induces cytotoxicity in B7-H3+ AML cells. [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 5098.

Abstract 5115: Novel humanized anti-GD2 antibody inhibits GD2-mediated immunosuppression by targeting GD2+ breast cancer stem-like cells

Background: Breast cancer stem-like cells (BCSCs) are reported to be a major contributing factor for tumor growth and chemotherapy resistance in triple-negative breast cancer (TNBC). We reported that the disialoganglioside GD2 is highly expressed on BCSCs and that targeting GD2 with dinutuximab (chimeric anti-GD2 antibody) in combination with NK cells synergistically reduced tumor volumes in TNBC animal models. Here, we hypothesize that naxitamab targets GD2+ BCSCs and inhibits breast cancer (BC) growth by enhancing macrophage mediated phagocytosis and T cell mediated cytotoxicity. In addition, we explore whether addition of an investigational polymer-engineered IL-15 receptor-agonist, NKTR-255 treated NK cells, can further enhance this anti-GD2 mediated anti-cancer activity.

Methods: Naxitamab is a US FDA approved fully humanized anti-GD2 (hu3F8) monoclonal antibody for the treatment of pediatric neuroblastoma. We evaluated the effects of naxitamab treatment on macrophage mediated phagocytosis of BC cells using the live cell imaging system, IncuCyte®. Next, we compared the effects of NKTR-255 treated NK cells with recombinant human IL-15 (rIL-15) treated NK cells in naxitamab induced ADCC in GD2+ BC cells. We also performed immunohistochemistry (IHC) to examine GD2 expression and correlate it with T cell infiltration in primary TNBC patient samples with high and low GD2 levels. The effect of naxitamab treatment on T cell mediated cytotoxicity in BC cells was also observed.

Results: When compared to control, naxitamab treatment promoted macrophage mediated phagocytosis of Hs578T and HCC1395 cells in a dose dependent manner (p <0.001). Additionally, when co-cultured with healthy donor derived macrophages, we found a significant reduction in Hs578T spheroids treated with naxitamab in comparison to IgG control (p<0.001). Furthermore, we observed a significantly higher rate of apoptosis in GD2+ Hs578T and HCC1395 breast cancer cells treated with naxitamab and NK cells generated using NKTR-255, compared to rIL-15 treated NK cells (p<0.0001). Interestingly, IHC analysis showed that TNBC patients with high GD2 expression have significantly lower CD3+ T cell infiltration than patients with low GD2 expression (p<0.05). We also observed increased T cell mediated killing of BT549 and T47D cells treated with naxitamab in comparison to IgG control (p<0.001).

Conclusion: TNBC with high GD2 expression inhibits immune cell infiltration and naxitamab can inhibit BCSC growth by targeting GD2. Combination of naxitamab with macrophages induced macrophage mediated phagocytosis TNBC cells. NK cells were more stable and cytotoxic when generated with NKTR-255 vs. native IL-15, and naxitamab further enhanced NK cell mediated ADCC of GD2+ BCSCs. The increased T cell mediated killing of breast cancer cells treated with naxitamab further supports the immunomodulatory role of GD2.

Citation Format: Vivek Anand, Venkatesh Hegde, Maryam Siddiqui, Anudishi Tyagi, Bolutyfe Oderinde, Mario Marcondes, Willem Overwijk, Venkata Lokesh Battula. Novel humanized anti-GD2 antibody inhibits GD2-mediated immunosuppression by targeting GD2+ breast cancer stem-like cells. [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 5115.

Abstract P2-20-06: Anti-B7-H3 Antibody (T-1A5) Blocks Immunomodulatory Function of B7-H3 and Enhances NK and T Cell–Mediated Cytotoxicity against Breast Cancer Cells

One of the main factors contributing to breast cancer (BC) initiation and metastasis is immune suppression by tumor cells. Immune checkpoint blockade has recently been shown to overcome tumor-induced immune suppression, but a significant proportion of patients do not respond, implying that more effective cancer immunotherapies are required. B7-H3 belongs to B7 family of immune checkpoint proteins that is overexpressed in various human malignancies. Here, we hypothesize that blocking B7-H3 using monoclonal antibodies (mAbs) enhances immune cell proliferation and function. To test our hypothesis, B7-H3 expression was determined using RNA-seq data from primary and metastatic breast tumors, and adjacent normal tissues, from the TCGA and METABRIC databases. To assess B7-H3 protein expression in BC, we performed immunohistochemistry (IHC) on frozen primary tumor tissues (n=50) and adjacent normal tissues (n=23) from TNBC patients. In addition, to investigate the immunomodulatory effect of B7-H3 in BC, we performed IHC for T-cell markers in subsets of patient tissues with high and low levels of B7-H3 expression. Next, we assessed B7-H3 expression in over 13 BC cell lines, including TNBC and ER+, PR+, and HER2+ cell lines, as well as TNBC PDX-derived cells. Moreover, to determine the effect of B7-H3 knockdown on NK- and T-cell activity, we co-cultured control and B7H3–KD BC cells in the presence and absence of NK and T cells and measured the induction of apoptosis in BC cells through IncuCyte live-cell imaging system. The effect of a novel B7H3-blocking mAb (clone T-1A5, isotype IgG1) on NK-cell and T-cell-mediated cytotoxicity in BC cell lines was examined using live-cell imaging. In the TCGA and METABRIC databases, B7-H3 was found to be significantly overexpressed (P< 0.0001) in tumor tissues than in adjacent normal tissues of BC patients. A survival analysis by the log-rank test indicated that patients with B7-H3high tumors had significantly lower progression-free (P=0.01) and relapse-free (P=0.0026) survival than patients with B7-H3low tumors. Moreover, B7-H3 is significantly upregulated in all the BC subtypes including basal, luminal A, luminal B and Her2-enriched with highest expression in basal type BC. Relative mRNA quantification and flow cytometry analysis demonstrated strong B7-H3 expression in most of the BC cell lines including TNBC and ER+, PR+, and HER2+ cell lines, as well as TNBC PDX-derived cells. Furthermore, IHC analysis revealed that compared to the matched normal tissue, B7-H3 expression was substantially higher in tumor tissue (N=16, P< 0.001). Also, patients with high B7-H3 expression had significantly lower numbers of CD3+, CD4+, and CD8+ T-cell, compared to patients with low B7-H3 expression (P< 0.001), indicating immunosuppressive role of B7-H3. Furthermore, NK cell and T cell mediated killing was significantly higher in B7H3-KD BC cell lines compared to control cells. We observed a significant increase in the killing of BC cells by NK cells and T cells in the presence of anti-B7H3 mAb T-1A5 in a concentration dependent manner (P < 0.001), suggesting that anti-B7H3 antibodies suppress the immunomodulatory function of B7-H3 and enhance NK and T cell–mediated ADCC in BC. To determine the antibody-dependent cell-mediated cytotoxicity, we developed a human-mouse chimera of T-1A5 (chT-1A5) and tested in combination with NK cells. Interestingly, we found a concentration and time dependent increase in ADCC in BC cells in the presence of chT-1A5 antibody. Our data suggests that B7-H3 is overexpressed in primary BC and inhibits immune-cell infiltration. Moreover, blocking the immunomodulatory functions of B7-H3 using anti-B7H3 antibody T-1A5 enhances NK and T cell–mediated killing of BC cells.

Citation Format: Vivek Anand, Anudishi Tyagi, Venkata Lokesh Battula. Anti-B7-H3 Antibody (T-1A5) Blocks Immunomodulatory Function of B7-H3 and Enhances NK and T Cell–Mediated Cytotoxicity against Breast Cancer Cells [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-20-06.

Ganglioside GD2: a novel therapeutic target in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a heterogeneous disease characterized by lack of hormone receptor expression and is known for high rates of recurrence, distant metastases, and poor clinical outcomes. TNBC cells lack targetable receptors; hence, there is an urgent need for targetable markers for the disease. Breast cancer stem-like cells (BCSCs) are a fraction of cells in primary tumors that are associated with tumorigenesis, metastasis, and resistance to chemotherapy. Targeting BCSCs is thus an effective strategy for preventing cancer metastatic spread and sensitizing tumors to chemotherapy. The CD44^hi CD24^lo phenotype is a well-established phenotype for identification of BCSCs, but CD44 and CD24 are not targetable markers owing to their expression in normal tissues. The ganglioside GD2 has been shown to be upregulated in primary TNBC tumors compared with normal breast tissue and has been shown to identify BCSCs. In this review, we discuss GD2 as a BCSC- and tumor-specific marker in TNBC; epithelial-to-mesenchymal transition and the signaling pathways that are upstream and downstream of GD2 and the role of these pathways in tumorigenesis and metastasis in TNBC; direct and indirect approaches for targeting GD2; and ongoing clinical trials and treatments directed against GD2 as well as future directions for these strategies.

Anti-GD2 antibody dinutuximab inhibits triple-negative breast tumor growth by targeting GD2+ breast cancer stem-like cells

BACKGROUND

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype with no effective standard therapy. Breast cancer stem-like cells (BCSCs) in primary TNBCs are reported to be responsible for metastatic spread of the disease and resistance to chemotherapy, but no available therapeutic tools target BCSCs. We previously reported that the ganglioside GD2 is highly expressed on BCSCs and that inhibition of its expression hampers TNBC growth. We therefore hypothesized that the anti-GD2 antibody dinutuximab (ch14.18) targets GD2+ BCSCs and inhibits TNBC growth.

METHOD

To test our hypothesis, we first determined GD2 expression via immunohistochemistry in frozen primary tumor samples from patients with TNBC (n=89). Then, we examined the effects of dinutuximab on TNBC cell adhesion, migration, and mammosphere formation in vitro and on tumor growth in vivo using TNBC cell-line and patient-derived xenograft (PDX) models.

RESULTS

We found that GD2 was expressed in around 60% of primary TNBC tumors at variable levels and was associated with worse overall survival of patients with TNBC (p=0.002). GD2 was found to be expressed in tumors and stroma, but normal ducts and lobules in adjacent tissues have shown low or no GD2 staining, indicating that GD2 is potentially a novel biomarker for tumor and its microenvironment. Treatment with dinutuximab significantly decreased adhesion and migration of MDA-MB-231 and SUM159 TNBC cells. Moreover, dinutuximab treatment inhibited mTOR signaling, which has been shown to be regulated by GD2 in BCSCs. Dinutuximab also reduced tumor growth in nude mice bearing TNBC cell-line xenografts. Finally, dinutuximab in combination with activated natural killer cells inhibited tumor growth in a TNBC PDX model and improved overall survival of tumor-bearing mice.

CONCLUSIONS

Dinutuximab successfully eliminated GD2+ cells and reduced tumor growth in both in vivo models. Our data provide proof-of-concept for the criticality of GD2 in BCSCs and demonstrate the potential of dinutuximab as a novel therapeutic approach for TNBC.

Abstract PS16-19: Hotspot p53 mutations correlate with increased expression of stem cell markers in triple-negative breast cancer

p53 mutations occur in 80% of triple-negative breast cancer (TNBC) cases. Several types of p53 mutations have been reported, among which gain of function mutations have been associated with increased cancer stem cells, chemotherapy resistance, and disease relapse in several malignancies. Particularly, hotspot p53 mutations (mutations at amino acid location 157, 175, 248, 249, 273 predict worse overall survival in some cancer types. We have previously reported that Ganglioside GD2, a cell surface glycosphingolipid, identifies breast cancer stem cells and promotes tumorigenesis. We have also reported that GD3 synthase, a key enzyme which catalyzes the rate-limiting step of the GD2 biosynthesis pathway, is significantly upregulated in breast tumors with p53 mutations. Here, we hypothesize that mutant p53 promotes stemness in TNBC cells by regulating GD3 synthase and GD2 expression. To identify specific p53 mutations that contribute to TNBC stemness, we stratified TNBC cell lines (N=18) based on p53 mutation status including mutation type, location, and domain affected. We measured GD2 and GD3 synthase expression in the available TNBC cell lines by flow cytometry and RT-PCR, respectively. We found that GD3 synthase expression is significantly upregulated in TNBC cell lines with p53 hotspot mutations compared to cell lines with other p53 mutations (Median relative expression 0.0114 compared to 0.0003, p=0.005). Similarly, we found that GD2 expression is significantly higher in TNBC cell lines with hotspot mutations compared to non-hotspot counterparts (Median GD2+ cells 15.2% compared to 0.97%, p= 0.013) Additionally, GD2 and GD3 synthase are upregulated in basal-type TNBC cell lines and TCGA patient samples compared to other TNBC molecular subtypes. Interestingly, we also found that GD2 expression is not always directly correlated with GD3S expression, suggesting that GD2 synthase expression is also a key factor in the regulation of GD2 expression. To examine the effect of mutant p53 protein levels on TNBC stemness, we measured p53 expression in all the available TNBC cell lines by western blot, and found that p53 protein levels do not correlate with GD2 or GD3S expression. To validate these findings, we analyzed RPPA data from the MD Anderson Cancer Cell Lines Project and found similar results. These data suggest that it is the type of p53 mutation, but not the amount of p53 protein in the cells that determines GD2 and GD3 synthase expression in TNBC cells. For instance, p53 hotspot mutations involving amino acid position 248 have been shown to be strongly associated with increased cancer stemness. We found that cell lines with p53 mutations at this specific location have significantly higher GD3 synthase expression compared to other mutant p53 forms. We are currently examining the direct role of mutant p53 in the regulation of GD3S expression by stabilizing mutant p53 using MDM2 inhibitors as well as stable knockdown of p53 gene in multiple TNBC cell lines to establish a clear link between mutant p53 and stem cell marker expression in TNBC cell lines.

In conclusion, stem cell markers are highly expressed in p53 mutant TNBC cell lines compared to wild type p53 counterparts. Specifically, cell lines with hotspot p53 mutations significantly correlate with increased TNBC stemness. The type of p53 mutation, rather than level of its expression correlates with stem cell marker expression in TNBC cells.

Citation Format: Fouad El-Dana, Bin Yuan, Stanley Ly, Vivek Anand, Venkata Lokesh Battula. Hotspot p53 mutations correlate with increased expression of stem cell markers in triple-negative breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS16-19.

Bone marrow stromal cells induce an ALDH+ stem cell-like phenotype and enhance therapy resistance in AML through a TGF-β-p38-ALDH2 pathway

The bone marrow microenvironment (BME) in acute myeloid leukemia (AML) consists of various cell types that support the growth of AML cells and protect them from chemotherapy. Mesenchymal stromal cells (MSCs) in the BME have been shown to contribute immensely to leukemogenesis and chemotherapy resistance in AML cells. However, the mechanism of stroma-induced chemotherapy resistance is not known. Here, we hypothesized that stromal cells promote a stem-like phenotype in AML cells, thereby inducing tumorigenecity and therapy resistance. To test our hypothesis, we co-cultured AML cell lines and patient samples with BM-derived MSCs and determined aldehyde dehydrogenase (ALDH) activity and performed gene expression profiling by RNA sequencing. We found that the percentage of ALDH+ cells increased dramatically when AML cells were co-cultured with MSCs. However, among the 19 ALDH isoforms, ALDH2 and ALDH1L2 were the only two that were significantly upregulated in AML cells co-cultured with stromal cells compared to cells cultured alone. Mechanistic studies revealed that the transforming growth factor-β1 (TGF-β1)-regulated gene signature is activated in AML cells co-cultured with MSCs. Knockdown of TGF-β1 in BM-MSCs inhibited stroma-induced ALDH activity and ALDH2 expression in AML cells, whereas treatment with recombinant TGF-β1 induced the ALDH+ phenotype in AML cells. We also found that TGF-β1-induced ALDH2 expression in AML cells is mediated by the non-canonical pathway through the activation of p38. Interestingly, inhibition of ALDH2 with diadzin and CVT-10216 significantly inhibited MSC-induced ALDH activity in AML cells and sensitized them to chemotherapy, even in the presence of MSCs. Collectively, BM stroma induces ALDH2 activity in AML cells through the non-canonical TGF-β pathway. Inhibition of ALDH2 sensitizes AML cells to chemotherapy.

CXCR4 Inhibition Enhances Efficacy of FLT3 Inhibitors in FLT3-Mutated AML Augmented by Suppressed TGF-b Signaling

Given the proven importance of the CXCL12/CXCR4 axis in the stroma–acute myeloid leukemia (AML) interactions and the rapid emergence of resistance to FLT3 inhibitors, we investigated the efficacy and safety of a novel CXCR4 inhibitor, LY2510924, in combination with FLT3 inhibitors in preclinical models of AML with FLT3-ITD mutations (FLT3-ITD-AML). Quizartinib, a potent FLT3 inhibitor, induced apoptosis in FLT3-ITD-AML, while LY2510924 blocked surface CXCR4 without inducing apoptosis. LY2510924 significantly reversed stroma-mediated resistance against quizartinib mainly through the MAPK pathway. In mice with established FLT3-ITD-AML, LY2510924 induced durable mobilization and differentiation of leukemia cells, resulting in enhanced anti-leukemia effects when combined with quizartinib, whereas transient effects were seen on non-leukemic blood cells in immune-competent mice. Sequencing of the transcriptome of the leukemic cells surviving in vivo treatment with quizartinib and LY2510924 revealed that genes related to TGF-β signaling may confer resistance against the drug combination. In co-culture experiments of FLT3-ITD-AML and stromal cells, both silencing of TGF-β in stromal cells or TGF-β-receptor kinase inhibitor enhanced apoptosis by combined treatment. Disruption of the CXCL12/CXCR4 axis in FLT3-ITD-AML by LY2510924 and its negligible effects on normal immunocytes could safely enhance the potency of quizartinib, which may be further improved by blockade of TGF-β signaling.

Abstract P3-02-05: Targeting glutamine metabolism inhibits GD2+ breast cancer stem cell function in triple negative breast cancer

Breast cancer stem cells (BSCs) constitute a fraction of primary tumor cells that exhibit drug resistance and have metastatic potential. Ganglioside GD2 has been shown by us and others as a marker for BCSCs. Nutrient deprivation-associated metabolic stress observed during tumor progression is reportedly associated with the cancer stem cell phenotype, and we have shown that oxidative stress caused by serum deprivation induces GD2 expression in vitro and in vivo. To identify metabolic signatures associated with GD2+ cells and their potential adaptive mechanisms to oxidative stress, global metabolic profiling was performed using a mass spectroscopy-based approach. We found that metabolites associated with amino acid metabolism, particularly glutathione metabolism, to be most highly upregulated in GD2+ compared to GD2− cells. In addition, glutathione biosynthesis and oxidation to glutathione disulfide was also increased in cells undergoing oxidative stress. These data suggest that the glutathione-mediated detoxification pathways play a key role in GD2+ or basal type breast cancer cells.

As glutamine is a major precursor molecule for glutathione biosynthesis, we hypothesized that glutamine, at least in part, regulates cellular redox tone and the GD2+ phenotype in breast cancer cells. To test our hypothesis, we cultured breast cancer cell lines MDA-MB-231 and SUM159 in media containing 0%, 0.5%, 1%, 2%, or 4% of L-glutamine for 3 days. Flow cytometry analysis revealed that the percentage of GD2+ increased from 6% to 12% and from 12% to 22% in MDA-MB-231 and SUM159 cells, respectively when the cells were cultured at 0 or 4% glutamine. Glutaminase, an enzyme that converts glutamine to glutamate, which further leads to glutathione biosynthesis, has been shown to be overexpressed in basal-type breast cancer cells. To investigate the role of glutaminase on stem cell redox homeostasis and phenotype, we treated TNBC cell lines MDA-MB-231 and SUM159 cells with glutaminase inhibitors CB-839 or 968 compound for 3 days. Flow analysis revealed 70-80% reduction in GD2 expression after treatment in a dose dependent manner. In addition, treatment with CB-839 inhibited cell proliferation by over 80% in a dose-dependent manner in MDA-MB-231 cells and SUM159 cells (p<0.001). Next, to determine the effect of glutaminase inhibition on BCSC function, we cultured MDA-MB-231 and SUM-159 cells in low adherent cell culture dishes with or without glutaminase inhibitors 968 or CB-839 for 7 days. Interestingly, we observed a 40-50% reduction in mammosphere formation in both treated cell lines compared to the untreated controls, suggesting that inhibition of glutaminase is critical for BCSC function. In conclusion, the anti-oxidant glutathione is highly upregulated in GD2+ BCSCs, and this appears to be associated with the concentration of glutamine, and appears to regulate, perhaps via the regulation of redox homeostaisis, GD2 expression in BCSCs. Targeting glutaminase and redox homeostasis using CB-839 or CB968 inhibits BCSC as measured by GD2 positivity and mammosphere formation. Glutaminase inhibition in combination with chemotherapy could be a valuable future therapeutic strategy for targeting BCSCs in TNBC.

Citation Format: Stanley Ly, Khoa Nguyen, Michael Andreeff, Venkata Lokesh Battula. Targeting glutamine metabolism inhibits GD2+ breast cancer stem cell function in triple negative breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-02-05.

Abstract 2040: Acute myeloid leukemia cells induce new bone formation by expanding osteoprogenitor niche in the bone marrow

Genetic alterations in osteoprogenitor cells have been shown to induce myeloid leukemia in mouse models. We reported recently that acute myeloid leukemia (AML) cells induce osteogenic differentiation in mesenchymal stromal cells (MSC) in the bone marrow (BM) to facilitate faster AML engraftment in mice (Battula et al., JCI Insight, 2017). However, specifics of this osteogenic niche generated by AML are not known. Here, we hypothesize that AML cells induce new bone formation by expanding osteoprogenitor-rich niche in the BM. To investigate the effect of AML cells on osteoprogenitor cells and mature osteoblasts, we generated transgenic mice by crossing Osx-CreERt2 mice with Ocn-GFP; ROSA-tdTomato mice. The resulting triple transgenic mice had the genotype of Osx-CreERt2;Ocn-GFP;ROSA-tdTomato. In these mice the tdTomato (red) positive cells represented cells that originated from Osterix-expressing (Osx+) cells, whereas a GFP+ (green) cell represented an osteocalcin-expressing (Ocn+) mature osteoblast. We implanted murine AML cells with MLL-ENL fusion proteins into these mice. Three weeks after implantation of AML cells, the femurs and tibia of these mice were subjected to histological evaluation using whole-tissue fluorescence microscopy. Interestigly, in the BM of mice implanted with AML cells, we found a 3-4 fold increase in Osx+ cells compared to control animals. However, no significant difference in the number of GFP+ cells on the endosteum and trabecular bone surface was observed, suggesting that AML cells expand osteoprogenitor cells in the BM. Next, to investigate AML-induced alterations in bone, we implanted AML patient-derived xenograft (PDX) cells with the FLT3-ITD translocation into non-obese diabetic scid interleukin-2Rγnull (NSG) mice. When the percentage of AML blasts in peripheral blood increased over 95%, we performed micro-computed tomography (µCT) to analyze changes in the bone architecture. Of note, we observed a massive increase in cortical bone thickness and new medullary bone formation in the diaphysis area. Quantitative analysis revealed that the bone volume and bone mineral content in AML mouse femurs were about twofold higher than those in healthy mouse femurs. To validate these findings, we stained femurs from mice with and without AML with Masson-Goldner's trichrome reagents. Notably, staining of the femurs from mice with AML revealed massive web-like bone formation within the medullary cavity, which is usually not seen in normal BM. Also, bone that was not fully formed, but in the process of maturation, stained light blue. In conclusion, our data suggest that AML cells expand osteoprogenitor cells resulting in thickening of the cortical bone and new bone formation in mouse models. In-depth analysis of bone remodeling in AML patients could result in new insights into the pathobiology of the disease and provide novel therapeutic avenues for AML.

Citation Format: Bin Yuan, Stanley Ly, Ivo Veletic, Kiersten Maldonado, Xin Zhou, Benoit deCrombrugghe, Michael Andreeff, Venkata Lokesh Battula. Acute myeloid leukemia cells induce new bone formation by expanding osteoprogenitor niche in the bone marrow [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2040.

Abstract 3248: B7-H3, an immune checkpoint protein is overexpressed in AML and the blocking monoclonal antibodies enhance NK cell-mediated apoptosis in AML cells

Acute myeloid leukemia (AML) is the most common and aggressive acute leukemia found in adults. Immune checkpoint inhibition has led to important clinical advances in cancer therapy in recent years due to superior cure rates compared with standard therapy. We hypothesize that B7-H3 (CD276) an immune checkpoint protein is overexpressed in AML cells and targeting B7-H3 activates immune cells against AML cells. We analyzed B7-H3 expression in peripheral blood (PB) and bone marrow (BM) mononuclear cells from AML patients (n=65) and healthy donors (n=10) at MD Anderson Cancer Center. Cell surface expression analysis by flow cytometry revealed that the cells of ~60% of the patients were positive for B7-H3 and its expression was 2- to 3-fold higher in AML cells than in healthy donor cells. B7-H3 expression is relatively higher in CD34+ AML cells than in CD34- AML cells (p<0.01). In contrast, no difference was observed between CD34+ and CD34- cells from healthy donors. The Cancer Genome Atlas RNA sequencing data revealed that patients with high B7-H3 expression had significantly lower overall and disease-free survival durations than did patients with low B7-H3 expression (p=0.024). To investigate the role of B7-H3 in immunomodulation, we stably knocked down B7-H3 in OCI-AML3 and co-cultured them with or without human PB-derived NK cells at a 2:1 ratio and measured apoptosis induction in AML cells by annexin-v binding approach. We found that knockdown of B7-H3 induced NK cell-mediated apoptosis in AML cells 3-fold compared to control AML cells. These data indicate that inhibition of B7-H3 in AML cells enhances NK cell-mediated apoptosis in AML cells. To target B7-H3, we have generated four monoclonal antibodies: B1, B2, B3 and B4 (codenamed to protect IP). To investigate whether these novel anti-B7-H3 monoclonal antibodies are able to block B7-H3 immunomodulatory function and activate NK cells, we performed a co-culture experiment with GFP-expressing OCI-AML3 cells and PB-derived NK cells in the presence or absence of anti-B7-H3 antibodies. Apoptosis induction was measured by real-time annexin-v binding using IncuCyte live cell imaging system. The addition of anti-B7-H3 monoclonal antibodies, B1, B2, B3 and B4 at 25μg/ml enhanced NK cell-induced apoptosis 3-fold in OCI-AML3 cells. These data indicate that anti-B7-H3 antibodies block the immunomodulatory function of B7-H3 and induce NK cell-mediated apoptosis in AML cells. In vivo testing of these antibodies against AML-PDX models is currently ongoing. In conclusion, we found that B7-H3 is overexpressed in AML cells and its expression is associated with bad prognosis in AML patients. Knockdown or antibody-mediated blocking of B7-H3 enhanced NK cell-induced apoptosis in AML cells. These data indicated that B7-H3 is a novel immune-checkpoint protein in AML and patients could potentially benefit from anti-B7-H3 therapies.

Citation Format: Stanley Ly, Bin Yuan, Sabrina Grimm, Michael Andreeff, Hans-Jörg Bühring, Venkata Lokesh Battula. B7-H3, an immune checkpoint protein is overexpressed in AML and the blocking monoclonal antibodies enhance NK cell-mediated apoptosis in AML cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3248.

Abstract 1169: Characterization of a small molecule inhibitor for GD3 synthase (ST8SIA1), a novel target in breast cancer stem-like cells

We reported that GD2 selectively identifies breast cancer stem-like cells (BCSCs) in TNBCs and that the enzyme ST8SIA1 regulates GD2 biosynthesis. We have shown that knockout of ST8SIA1 expression in TNBC cell lines inhibits tumor growth and metastasis in vivo, whereas ST8SIA1 overexpression induces epithelial-to-mesenchymal transition, leading to metastasis of TNBC cells. Very recently we have shown that ST8SIA1 regulates focal adhesion kinase (FAK)/AKT/mammalian target of rapamycin (mTOR) signaling in GD2+ BCSCs. Here we hypothesize that inhibition of ST8SIA1 activity using small molecule inhibitors targets BCSC function. Because of a lack of a crystal structure for developing small-molecule inhibitors of ST8SIA1, we developed a homolog of ST8SIA1 using the crystal structure of ST8SIA3 (PDB ID: 5B09) as a template. ST8SIA3 shares 32% identity and 54% similarity with this crystal structure. To this model we docked GM3, the substrate for the ST8SIA1 enzyme and analyzed their interactions. Next, we used this model to dock the compound library to identify potential inhibitors of ST8SIA1. To that end, we performed structure-based virtual screening or virtual ligand screening of 10,000 compounds based on the structure of GM3 (>70% identity), which we retrieved from the ChemSpider database. Similarly, we retrieved 1500 compounds based on the parent structure of flavone (>70% identity) from the ZINC database. After further filtration and selection of these structures, we ranked these compounds on the basis of 11 different scoring functions in DS 4.5. We selected the top candidate (ZINC02886919) for further functional characterization. ZINC02886919 had a predicted binding affinity (-logKd) of 6.17, with which we calculated the predicted Kd as 0.812 μM. Visualization analysis demonstrated that ZINC02886919 is involved in both polar and hydrophobic interactions in the binding pocket. We then synthesized ZINC02886919 and pursued pharmacological and in vitro assays. Treatment of SUM159 cells with ZINC02886919 decreased the percentage of GD2+ BCSCs by 5- to 10-fold within 72h in a concentration-dependent manner (from 31% to 6%). In addition, ZINC02886919 inhibited soft agar colony and mammosphere formation for SUM159 cells by 10- to 20-fold. These data indicated that the ST8SIA1 homolog model that we developed shares structural similarity with native human ST8SIA1 protein and that ZINC02886919 is a potential inhibitor of ST8SIA1 activity and thus BCSC function. In conclusion, inhibition of ST8SIA1 expression or activity inhibits BCSC function, TNBC tumor growth, and metastasis. The ST8SIA1 inhibitor ZINC02886919 inhibits GD2 expression and mammosphere and soft agar colony formation in vitro. The effect of ZINC02886919 on tumor growth and metastasis is currently being tested in vivo.

Citation Format: Appalaraju Jappupilli, Khoa Nguyen, Stanley Ly, Michael Andreeff, Prashen Chelikani, Venkata Lokesh Battula. Characterization of a small molecule inhibitor for GD3 synthase (ST8SIA1), a novel target in breast cancer stem-like cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1169.

Abstract P2-06-22: PEA15-AA, an unphosphorylatable mutant of PEA15, as a novel therapeutic gene for triple-negative breast cancer

Background: Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer characterized by a high rate of metastatic recurrence and poor prognosis. Molecular mechanism underlying the metastatic behavior of TNBC has not been well elucidated, and newer approaches addressing drivers of metastasis are crucial to improving patient outcomes. PEA15 (Phosphoprotein enriched in astrocytes-15) regulates cell proliferation, apoptosis, and autophagy. In breast cancer, PEA15 expression inhibits invasion by binding to ERK and preventing its nuclear translocation. The biological function of PEA15 is tightly regulated by its phosphorylation at Ser104 and Ser116. However, the effect of PEA15 phosphorylation status on TNBC remains unknown. In this study, we tested the hypothesis that unphosphorylated PEA15 will prevent metastasis in TNBC through inhibition of the epithelial-to-mesenchymal transition (EMT).

Method: We established stable cells overexpressing unphosphorylatable (PEA15-AA) and phospho-mimetic (PEA15-DD) PEA15 mutants in MDA-MB-468 cells. To dissect specific Cellular Mechanisms regulated by PEA15 phosphorylation, we performed RT-PCR immune and metastasis arrays. In vivo mouse models were used to see effects of PEA15 phosphorylation on tumor growth.

Results: The clonogenic growth of PEA15-AA–expressing cells was significantly reduced by 80% compared with empty vector-transfected cells (PEA15-V). Anchorage-independent growth, an indicator of in vivo tumorigenicity, was inhibited in cells expressing PEA15-AA by 60% compared with PEA15-V. PEA15-AA upregulated the expression of E-cadherin and decreased the expression of mesenchymal markers, suggesting that PEA15-AA reverses EMT. Compared with PEA15-V, migration and invasion of cells expressing PEA15-AA were reduced by 65% and 72%, respectively. In contrast, PEA15-DD promoted migration, invasion, and expression of mesenchymal markers. To determine the in vivo effect of PEA15-AA, we injected stable PEA15 transfectants of MDA-MB-468 cells into the mammary fat pad of NOD/SCID mice. The PEA15-DD–injected group showed greater tumor volumes than PEA15-V and PEA15-AA groups, suggesting that PEA15-AA has antitumor effects both in vitro and in vivo. From the immune and metastasis arrays, we found that expression level of IL-8, which is known to induce EMT, was greatly decreased by PEA15-AA, while IL-8 was highly expressed in PEA15-DD cells. Addition of recombinant IL-8 to the cells expressing PEA15-AA partially rescued mesenchymal characteristics, increasing migration and expression of mesenchymal markers. By contrast, IL-8 knockdown in PEA15-DD–expressing cells decreased the mesenchymal phenotype. These findings indicate that IL-8 may play an important role as a mediator of phosphorylation of PEA-15 in breast cancer cell migration and invasion and suggest that PEA15-AA inhibits the expression of IL-8, thereby reversing EMT.

Conclusion: Taken together, our results show that PEA15 phosphorylation serves as an important regulator, having a dual role as an oncogene or tumor suppressor. Further studies are warranted to evaluate the impact of PEA15 phosphorylation status on metastasis in vivo. These findings support the development of PEA15-AA as a potential therapeutic strategy for TNBC.

Citation Format: Park J, Chauhan G, Cohen EN, Ueno NT, Battula VL, Tripathy D, Reuben JM, Bartholomeusz C. PEA15-AA, an unphosphorylatable mutant of PEA15, as a novel therapeutic gene for triple-negative breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-06-22.

Osteogenic niche in the regulation of normal hematopoiesis and leukemogenesis

The bone marrow microenvironment, also known as the bone marrow niche, is a complex network of cell types and acellular factors that supports normal hematopoiesis. For many years, leukemia was believed to be caused by a series of genetic hits to hematopoietic stem and progenitor cells, which transform them to preleukemic, and eventually to leukemic, cells. Recent discoveries suggest that genetic alterations in bone marrow niche cells, particularly in osteogenic cells, may also cause myeloid leukemia in mouse models. The osteogenic niche, which consists of osteoprogenitors, preosteoblasts, mature osteoblasts, osteocytes and osteoclasts, has been shown to play a critical role in the maintenance and expansion of hematopoietic stem and progenitor cells as well as in their oncogenic transformation into leukemia stem/initiating cells. We have recently shown that acute myeloid leukemia cells induce osteogenic differentiation in mesenchymal stromal cells to gain a growth advantage. In this review, we discuss the role of the osteogenic niche in the maintenance of hematopoietic stem and progenitor cells, as well as in their transformation into leukemia cells. We also discuss the signaling pathways that regulate osteogenic niche-hematopoietic stem and progenitor cells or osteogenic niche-leukemic stem/initiating cell interactions in the bone marrow, together with novel approaches for therapeutically targeting these interactions.

Abstract 1929: ST8SIA1 is a novel therapeutic target in TNBC: Regulates FAK-PI3K-AKT-mTOR signaling to promote tumor growth and metastasis

We identified ganglioside GD2 as a breast cancer stem cell (BCSC) marker and that GD3 synthase (ST8SIA1) regulates GD2 expression and BCSC function. We have reported that GD2 is up-regulated in TNBC and inhibition of its expression by knockdown of ST8SIA1 inhibits tumor growth and metastasis. Here we hypothesize that ST8SIA1 is overexpressed in TNBC and regulates cell signaling downstream of GD2 to promote tumor growth and metastasis. RNA sequencing data analysis of TCGA dataset with over 1100 primary and metastatic breast tumors revealed that ST8SIA1 was overexpressed in around 10% of all breast cancer patients. Basal type tumors expressed the highest levels of ST8SIA1 compared to luminal-A, luminal-B, and HER2-enriched (p<0.01) tumors. In addition, TNBC, (n=115) had 4.63-fold higher expression of ST8SIA1 than did hormone receptor-positive tumors, including ER+, PR+, and HER2+ tumors (n=852, p<0.001). Further analysis of ST8SIA1 expression in different TNBC subtypes revealed that the mesenchymal-subtype of TNBC had the highest expression (p<0.001) among the 7 TNBC subtypes. A survival analysis by univariant analysis indicated that patients with ST8SIA1high tumors had significantly lower overall and disease-free survival rates than did patients with ST8SIA1low tumors (p=0.0148 and p=0.0109, respectively with 60months follow-up). To investigate the mechanism of the ST8ISA1-mediated regulation of tumor growth and metastasis, we performed a proteomic analysis of GD2+ and GD2- SUM159 and MDA-MB-231 cells using antibody micro-arrays (Kinexus). After systematic data analysis and functional validation by western blotting, we found that FAK, PI3K, AKT, ERK, mTOR, and 4EBP1 were highly phosphorylated in GD2+ compared to in GD2- SUM159 cells. As it is known that GD2 acts as a co-receptor on the cell surface and activates downstream signaling, we hypothesized that ST8SIA1 regulates PI3K-AKT-mTOR signaling in BCSCs through GD2. To test our hypothesis, we knocked out ST8SIA1 in SUM159 cells using CRISPR-Cas9 approach. As expected knockout (KO) of ST8SIA1 reduced percentage of GD2+ cells from 20±5% to <1% in SUM159 cells. In addition, ST8SIA1-KO cells did not induce tumor growth or cause metastases in-vivo. Interestingly, we found that lack of ST8SIA1 led to inhibition of FAK, AKT, ERK, 4EBP1, and mTOR phosphorylation, suggesting that this signaling axis is regulated by ST8SIA1 in TNBC cells. Conclusion: ST8SIA1 is up-regulated in basal-like and mesenchymal subsets of TNBC tumors and is associated with poor prognosis in TNBC patients. Furthermore, we found that ST8SIA1 tightly regulates PI3K-AKT-mTOR signaling pathway downstream of GD2. Targeting ST8SIA1 could be a novel therapeutic strategy in TNBC therapy.

Citation Format: Khoa Nguyen, Bin Yuan, Yuanqing Yan, Kim-Anh Do, Naoto T. Ueno, Michael Andreeff, Venkata Lokesh Battula. ST8SIA1 is a novel therapeutic target in TNBC: Regulates FAK-PI3K-AKT-mTOR signaling to promote tumor growth and metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1929.

Abstract 1766: Dinutuximab targets GD2+ breast cancer stem cells and inhibits TNBC tumor growth

Breast cancer stem-like cells (BCSCs), also known as breast cancer initiating cells, are a fraction of cells in the primary tumor that are highly tumorigenic, chemotherapy resistant, and are able to cause metastases. Therefore, targeting BCSCs is an important strategy that could complement standard chemotherapy for breast cancer. We have identified that ganglioside GD2 as an important maker for BCSCs and that ST8SIA1 (GD3-synthase) is an enzyme that regulates GD2 expression in BCSCs (Battula et al., JCI, 2012). GD2 is over expressed in triple negative breast cancer (TNBC) compared to non-TNBC. Inhibition of GD2 expression by knockdown of ST8SIA1 completely inhibited tumor growth and metastases in xenograft models. Therefore, we hypothesize that targeting GD2+ BCSCs will inhibit TNBC tumor growth. To test our hypothesis, we used the chimeric anti-GD2 monoclonal antibody (Dinutuximab) that has been FDA approved for the treatment of neuroblastoma in children. The main mode of action for dinutuximab is antibody dependent cell-mediated cytotoxicity (ADCC). To test the activity of dinutuximab against GD2+ BCSCs, we treated MDA-MB-231 and SUM159 breast cancer cells with dinutuximab alone at different concentrations (1, 12.5, 25, 50, and 100µg/ml) for 24, 48, and, 72hrs or in combination with IL-21 activated NK cells. As control, cells were treated with rituximab (anti-CD20 antibody) and NK cells. Although only a moderate effect was observed on GD2+ cells when treated with dinutuximab alone, we found a dramatic decrease in the number of live (annexin-vneg and DAPIneg) GD2+ cells when treated with dinutuximab in combination with NK-cells. This combination decreased the percentage of GD2+ cells from 20.1±0.3% to 5.8±0.2% (p<0.001). No significant effect on GD2+ cells was observed in the rituximab + NK cell group, indicating that the dinutuximab + NK-cell combination is most affective in inducing cytolysis of GD2+ cells. Next, to investigate the effect of dinutuximab on in-vivo tumor growth, we implanted firefly luciferase expressing MDA-MB-231 cells into nude mice (these mice were chosen because of the presence of NK cells). When palpable tumors were formed (tumor volume 25-30mm3), the mice were treated with dinutuximab or rituximab at 1.4mg/kg twice a week for 6 weeks. Tumor growth was measured weekly by bioluminescence imaging as well as by calipers. We found a >10 fold decrease in tumor growth in mice treated with dinutuximab compared to control. In contrast, tumor volumes reached up to 250mm3 within 10 weeks of tumor implantation in the rituximab treated group (p<0.001). Conclusion: Our data suggest that dinutuximab targets GD2+ BCSCs with the help of NK cells by ADCC and inhibits tumor growth. We are currently in the process of developing a phase I/II clinical trial using dinutuximab in patients with TNBC. In addition, preclinical testing of dinutuximab in combination with NK cells using TNBC PDX models is underway.

Citation Format: Venkata Lokesh Battula, Khoa Nguyen, Anitha Somanchi, Hong Mu, Naoto T. Ueno, Dean Lee, Michael Andreeff. Dinutuximab targets GD2+ breast cancer stem cells and inhibits TNBC tumor growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1766.

IKK inhibition by BMS-345541 suppresses breast tumorigenesis and metastases by targeting GD2+ cancer stem cells

We have identified that the ganglioside GD2 is a marker for breast cancer stem cells (BCSCs), and that targeting the enzyme GD3 synthase (GD3S, which regulates GD2 biosynthesis) reduces breast tumorigenesis. The pathways regulating GD2 expression, and their anomalous functions in BCSC, are unclear. Proteomic analysis of GD2⁺ and GD2^- cells from breast cancer cell lines revealed the activation of NFκB signaling in GD2⁺ cells. Dose- and time-dependent suppression of NFκB signaling by the small molecule inhibitor BMS-345541 reduced GD2⁺ cells by > 90%. Likewise, BMS-345541 inhibited BCSC GD3S expression, mammosphere formation, and cell migration/invasion in vitro. Breast tumor-bearing mice treated with BMS-345541 showed a statistically significant decrease in tumor volume and exhibited prolonged survival compared to control mice, with a median survival of 78 d for the BMS-345541-treated group vs. 58 d for the controls. Moreover, in an experimental metastases model, treatment with BMS-345541 reduced the lung metastases by > 5-fold. These data suggest that GD2 expression and function, and NFκB signaling, are related, and they control BCSCs tumorigenic characteristics. Thus, the suppression of NFκB signaling by BMS-345541 is a potentially important advance in controlling breast cancer growth and metastases.

Expression of ganglioside GD2, reprogram the lipid metabolism and EMT phenotype in bladder cancer

High-grade Bladder Cancer (BLCA) represents the most aggressive and treatment-resistant cancer that renders the patients with poor survival. However, only a few biomarkers have been identified for the detection and treatment of BLCA. Recent studies show that ganglioside GD2 can be used as cancer biomarker and/or therapeutic target for various cancers. Despite its potential relevance in cancer diagnosis and therapeutics, the role of GD2 is unknown in BLCA. Here, we report for the first time that high-grade BLCA tissues and cell lines have higher expression of GD2 compared to low-grade by high-resolution Mass Spectrometry. The muscle invasive UMUC3 cell line showed high GD2, mesenchymal phenotype, and cell proliferation. Besides, we have shown the cancer stem cells (CSC) property (CD44hiCD24lo) of GD2+ UMUC3 and J82 cells. Also, the evaluation of lipid metabolism in GD2+ BLCA cell lines revealed higher levels of Phosphatidylinositol (PI), Phosphatidic acid (PA), Cardiolipin (CL) and lower levels of Phosphatidylserine (PS), plasmenyl-phosphatidylethanolamines (pPE), plasmenyl-phosphocholines (pPC), sphingomyelins (SM), triglycerides (TGs) and N-Acetylneuraminic acid. These findings are significantly correlated with the tissues of BLCA patients. Based on this evidence, we propose that GD2 may be used as an effective diagnostic and therapeutic target for aggressive BLCA.

Abstract P5-07-03: GD2-mediated FAK signaling regulates breast cancer stem cell function in triple negative breast cancer

Ganglioside GD2 identifies breast cancer stem cells (BCSCs, Battula et al., JCI, 2012) and expression of GD2 is tightly regulated by GD3 synthase (GD3S). GD3S is highly expressed in GD2+ cells and inhibition of GD3S inhibits tumor formation and metastasis of breast cancer cells. However, the mechanism of GD2-mediated regulation of BCSC function is not known. Here we hypothesize that GD2 regulates signaling pathways involved in cell adhesion, migration and invasion of breast cancer cells. To identify these signaling pathways, antibody micro-arrays were used with 850 validated antibodies specific to total or phosphorylated proteins. Interestingly, focal adhesion kinase (FAK) was the most significantly phosphorylated protein in GD2+ compared to GD2- cells (S910 and S722). In addition, expression of FAK downstream mediators including Csk, PKCq, PKCl/I, Pyk2, and p38MAPK, was up-regulated in GD2+ compared to GD2- cells. Western blot analysis of FACS sorted SUM159 cells also revealed increased phosphorylation of FAK >80% at Y397 and >25% at Y861 in GD2+ compared to GD2- cells. FAK downstream targets including paxillin, p130 Cas, pERK were also up-regulated in GD2+ cells compared to GD2- cells indicating definitive activation of FAK signaling in GD2+ BCSCs. To investigate the functional role of GD2 in FAK mediated functions, we genetically deleted GD3S using the CRISPR knock-out system in SUM159 cells. only <1% GD2expression compared to >20% in parental cells was observed. GD3S-KO cells grew 5-10% slower in cell culture mostly because of the reduction (15±5%) in adherence. Trans-well assays revealed 3-5 fold reduction in migration and invasion of GD3S-KO compared to parental cells. These data indicate that GD2 and GD3S are not only the markers of BCSCs but also regulators of their function. Finally, we tested the effect of FAK inhibitor (PF-573228) against GD2+ BCSCs and GD3S-KO SUM159 cells. PF-573228 treatment decreased the number of mammospheres generated by GD2+ cells 3-4 fold in a dose dependent manner (100nM-1µm). In addition, treatment of PF-573228, inhibited migration and invasion of GD2+ cells 2 and 3 fold, respectively. However, treatment with PF-573228 on GD3S-KO cells further reduced their ability to migrate and invade by over 70% compared to untreated cells. In addition, GD3S-KO cells failed to form any mammospheres when cultured under low adherence conditions (p<0.00001), whereas the parental cells formed 15-20 mammospheres per 1,000 cells plated. In conclusion, our data demonstrate that FAK signaling is activated in GD2+ cells but that FAK inhibition alone may not be sufficient to inhibit BCSC function. Combined FAK and GD3S inhibition may exert highly synergistic effects against BCSCs.

Citation Format: Nguyen K, Sun JC, Hortobagyi GN, Andreeff M, Battula VL. GD2-mediated FAK signaling regulates breast cancer stem cell function in triple negative breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P5-07-03.

Abstract P5-07-02: ST8SIA1 regulates tumorigenesis in triple negative breast cancer

Recurrence in breast cancer is mainly due to metastases and drug resistance in a fraction of primary tumors cells which are also known as cancer stem cells or tumor initiating cells. We found that Ganglioside GD2 identifies breast cancer stem cell (BCSCs) in triple negative breast cancer (TNBC) and that GD2 biosynthesis is tightly regulated by enzyme ST8SIA1 (GD3 synthase) in GD2+ cells. We have reported that ST8SIA1 is highly expressed in TNBC and its expression is highly correlated with p53 mutations primary tumors (Yan et al, SABCS abstract 2016). Here we hypothesize that ST8SIA1 has a functional role in BCSC mediated tumorigenesis in TNBC. To test the hypothesis, we deleted ST8SIA1 in SUM159 cells using CRISPR-Cas9 technology. As expected, deletion of ST8SIA1 in SUM159 cells reduced GD2+ cells from 17±1.5% to 0.3±0.1%. However, cell proliferation assay revealed no significant difference between ST8SIA1-KO and Cas9 control cells. In contrast, in-vitro tumorigenesis by soft-agar assays revealed a complete loss of colony formation in ST8SIA1-KO cells, whereas Cas9 control cells produced 30±10 colonies out of 1000 cells plated. To investigate tumor initiation potential, ST8SIA1-KO- or Cas9 control- SUM159 cells were transplanted in mammary fat pad of NSG mice. Cas9 control cells produced tumors within 1-2 weeks and reached the maximum allowed size by IACUC (1.5cm) within 3-4 weeks. In contrast, ST8SIA1-KO cells failed to produce any tumors even 15 weeks after injections. In addition, survival analysis by log-rank test revealed that most of the cas9 control cell injected mice died within 4 weeks after cell implantation whereas no deaths were observed in ST8SIA1-KO cells injected mice even 100 days after tumor implantation. These data indicate that loss of ST8SIA1 in TNBC cells depletes GD2+ BCSCs and inhibits in-vitro and in-vivo tumorigenesis.

To investigate gene expression changes due to loss of ST8SIA1 in CRISPR knockout cells, we analyzed mRNA expression in ST8SIA1-KO- and Cas9 control- SUM159 cells by RNAseq analysis (done in triplicates for each cell type). At p<0.05 and fold change >2, we found 1502 genes down-regulated and 842 genes up-regulated in ST8SIA1-KO- compared to cas9 control- cells. Ingenuity pathway analysis revealed that several stem cell associated signaling pathway including, wnt, stat3, NFκB, nanog and IL8 whereas tumor suppressor PTEN and p38 MAPK signaling were activated in ST8SIA1-KO- compared to cas9 control- cells. In specific, proteins associated with stem cell function including NOTCH3, PDGFRB, PDGFRA, VCAM1, CXCR4, CXCL12, SOX2, wnt5a were down regulated in ST8SIA1-KO cells whereas DKK1 which acts as an antagonist for wnt-β-catenin signaling, was up-regulated in ST8SIA1-KO cells. These findings were validated by flow cytometry and western blot analysis using specific antibodies. In conclusion, our data suggests that deletion of ST8SIA1 in TNBC cells depletes BCSCs and inhibits tumorigenesis in-vitro and in-vivo. Development of specific inhibitors of ST8SIA1 could be of potential therapeutic value for patients with TNBC.

Citation Format: Battula VL, Nguyen K, Sun JC, Dasgupta A, Bartholomeusz C, Andreeff M. ST8SIA1 regulates tumorigenesis in triple negative breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P5-07-02.

Abstract P6-02-01: Metabolic stress induces GD2 expression and cancer stem cell phenotype in triple negative breast cancer

Breast cancer stem cells (BCSCs) have been characterized as a fraction of cells in primary tumors that are drug resistant and have metastatic potential. Ganglioside GD2 has been shown by us and others as a marker for BCSCs. Furthermore, nutrient deprivation associated metabolic stress seen during tumor progression is reportedly associated with the cancer stem cell phenotype. We hypothesized that metabolic stress could induce spontaneous generation of GD2+ BCSCs during tumor progression. To test our hypothesis, we cultured breast cancer cell lines MDA-MB-231 and SUM159 at low seeding density and measured percentage and absolute number of GD2+ cells daily. Flow cytometry analysis revealed that the percentage of GD2+ cells increased from 4.5 ± 2.5 on day 2 to 15 ± 3.8% on day 5 in MDA MB-231 cells and from 8.5 ± 2.8% on day2 to 28 ± 6.2% on day 5 in SUM159 cells (both designated as triple-negative breast cancer, TNBC). To investigate this phenomenon in-vivo, we injected GFP+ MDA-MB-231 cells in NSG mice mammary fat pads and examined GD2 expression in the implanted tumors weekly. Interestingly, we noticed that the percentage of GD2+ also increased from 12 ± 1.5% on week 1 to 30 ± 2.5% on week 6. Next, SUM159 cells were cultured in either nutrient rich (NR, i.e., 10% serum) or nutrient deprived (ND, 1% serum) for 4 days. We found that the percentage of GD2+ cells in NR medium at the end of 4 day culture was ~20% of the total cell population, whereas in ND medium was almost 50%. We then tested the effects of nutrient rich environment on GD2 expression by refreshing the media daily. Interestingly, cells that received fresh media had lower number of GD2+ cells (15 ± 1.5%) compared to cells cultured in the same medium for 4 days (33 ± 2.5%). Our data suggests that nutrient deprivation induces a stem cell phenotype in TNBC cells.

Next, we performed global metabolic profiling (i.e., for a total of 300 biochemical metabolites) using a mass spectroscopy-based approach. We profiled SUM159 cells cultured with NR vs. ND medium (set-1); GD2+ vs GD2- SUM159 cells (set -2); GD2+ vs GD2- MDA-MB-231 cell (set-3). Metabolites associated with amino acid metabolism, in particular glutathione metabolism, including glutamyl-alanine, 5-oxy-proline, proline, glutamine, and glutathione itself were found to be most highly up-regulated in GD2+ compared to GD2- cells and also in cells cultured in serum starved compared to serum rich conditions. Further analysis of these metabolites and their association with GD2+ cell signature raveled that gamma-glutamyl transferase (GGT5), was one of the most highly up-regulated (>150-fold) gene across all the groups. GGT is expressed on cell surface and transfers glutamyl group to amino acids, which then get transported across the membrane. In cancer, cells expressing GGT has been shown to be resistant to chemotherapeutic agents including cisplatin. Targeting glutathione metabolism could be future therapeutic strategy to inhibit BCSC growth in TNBC.

Citation Format: Battula VL, Piyaranthna B, Nguyen K, Sun JC, Jin F, Coarfa C, Nagireddy P, Andreeff M. Metabolic stress induces GD2 expression and cancer stem cell phenotype in triple negative breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-02-01.

Abstract P1-06-03: Epithelial to mesenchymal transition (EMT) regulates the spontaneous generation of GD2+ breast cancer stem-like cells through NFκB activation

Breast cancer recurrence may be a consequence of persistent breast cancer stem-like cells (BCSCs) that survive chemo- or hormonal therapy. Therefore, targeting BCSCs could complement standard chemotherapy. We discovered that the ganglioside GD2 is expressed on and defines BCSCs (Battula et al., JCI, 2012), as consequence of activation of the enzyme GD3 synthase (GD3S). Inhibition of GD3S expression inhibited breast cancer metastasis to lung. We also observed that GD2- breast cancer cells spontaneously generate GD2+ cells in vitro. As induction of EMT generates a stem cell–like phenotype, we hypothesized that EMT regulates the generation of GD2+ breast cancer cells. To test this hypothesis, MDA-MB-231and SUM159 cells were cultured in vitro and the percentage of GD2+ cells was measured over time. Interestingly, the percentage and absolute number of GD2+ cells increased in a time-dependent manner, suggesting the spontaneous generation of GD2+ cells. Concomitantly, mesenchymal-related markers including vimentin, N-cadherin, and twist increased 3 to 6 - fold. To further investigate whether this process is operational in vivo, GFP+ MDA-MB-231 cells were transplanted into mammary fat pads of NOD/SCID mice. Each week, a group of mice was sacrificed, tumors were extracted and the number of GFP+GD2+ cells was determined by flow cytometry. In line with our in vitro results, we observed significant increases in GD2+ BCSCs with increasing tumor volume from 15.1%±4.6% to 37%±8.7% over a 6 week period, suggesting that breast cancer cells spontaneously undergo EMT during tumor progression and generate GD2+ BCSCs.

To identify possible targets to inhibit EMT in breast cancer cells, proteomic analysis using Kinexus® antibody arrays revealed activation of NFκB and focal adhesion kinase (FAK) signaling in GD2+ breast cancer cells. The activation of NFκB (phospho p65) in GD2+ cells was validated by CyTOF mass cytometry using metal tagged antibodies. These data suggest that inhibition of NFκB signaling may inhibit GD2+ BCSC growth. Indeed, the IKK inhibitor BMS345541 reduced GD2+ cells by >95% and inhibited GD3S expression (determined by qRT-PCR) in a dose- and time-dependent fashion. In contrast, treatment with doxorubicin increased the percentage of GD2+ cells, from 13.5±2.5% to 21±2.6% in MDA-MB-231 cells, suggesting that GD2+ cells are resistant to doxorubicin. In addition, treatment with BMS345541 inhibited the ability of breast cancer cells to form mammospheres by >90% in vitro. In-vivo tumorigenesis assay demonstrated that BMS345541 induced a significant decrease (p <0.01) in tumor volume, and increased survival of tumor bearing mice: median survival was 78 days for BMS345541-treated mice vs. 58 days for controls (p<0.002).

Conclusion: GD2+ BCSCs are spontaneously produced during tumor progression by EMT and NFκB and FAK mediated signaling might regulate this process. Inhibition of NFκB and FAK signaling pathways may inhibit the spread of BCSCs and reduce breast cancer metastases.

Citation Format: Battula VL, Sun J, Nguyen K, Hortobagyi G, Andreeff M. Epithelial to mesenchymal transition (EMT) regulates the spontaneous generation of GD2+ breast cancer stem-like cells through NFκB activation. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P1-06-03.

Abstract 5085: Acute myeloid leukemia cells induce osteogenic differentiation in mesenchymal stem cells through bone morphogenetic protein- and RUNX-2- mediated signaling

Mesenchymal stem/stromal cells (MSCs) are a critical component of the bone marrow micro-environment (BME), induce cell survival signals in normal and acute myeloid leukemia (AML) cells and protect them from chemotherapy. The mechanisms underlying BME-induced cell growth and chemo-resistance however have not been fully elucidated. Here, we hypothesize that AML cells induce functional changes in BME to gain growth advantage. We have compared age matched (40-60) bone marrow derived MSCs from AML patients (AML-MSC, n = 10) and normal (N-MSC, n = 10) individuals and analyzed their cell growth, cell surface phenotype and multi-lineage differentiation. AML-MSCs are phenotypically different with larger cell surface area and lower cell growth. The average doubling time of AML-MSCs is 52±8hrs compared to 34±6hours for N-MSCs (p<0.01). Cell surface phenotyping by flow cytometry revealed that tissue non-specific alkaline phosphatase (ALP/ALPL/TNAP), which is highly expressed in embryonic stem cells, naïve-MSCs and osteoblasts, is expressed 10-14 fold higher in AML- compared to N-MSCs. Since ALP is also an osteoblast specific marker, we compared the osteogenic differentiation potential of N- and AML-MSCs: an increase in baseline ALP activity (by BCIP/NBT substrate) was observed in AML- compared to N-MSCs. mRNA analysis by qRT-PCR revealed 5-10-fold up-regulation of osteoblast-specific genes including RUNX-2, osteopontin, TNAP and osterix in AML-MSCs compared to N-MSCs before osteogenic induction. These data indicate that AML-MSCs are primed to differentiate into osteoblasts. Adipocyte differentiation was assessed by Oil-Red O staining for lipid droplets and revealed a >95% reduction (p<0.001) in the number mature adipocytes in AML-MSCs compared to N-MSCs suggesting that AML-MSCs lack the ability to differentiate into adipocytes. To validate these observations, we co-cultured N-MSCs with OCI-AML3 cells for 3-5 days and FACS sorted the MSCs for gene expression and differentiation analysis. As expected, qRT-PCR analysis revealed that osteopontin, osterix and ALP were up-regulated 3-4 fold in N-MSCs co-cultured with OCI-AML3 cells. In addition, ALP activity was 2-3 fold higher in N-MSCs co-cultured with OCI-AMl3 cells compared to mono-cultured cells. Bone morphogenetic proteins (BMP) are the most essential factors during osteogenic differentiation and new bone formation in humans. We therefore treated MSCs with AML cell-derived condition medium, and observed a dramatic 6-8 fold increase in pSmad1/5 levels in N-MSCs in a time dependent manner. In addition, AML induced pSmad1/5 up-regulation was inhibited when MSCs were treated with BMP-type1 receptor specific inhibitor LDN-193189, in a dose dependent manner. Our data suggest that AML cells induce osteogenic differentiation in BM-MSCs and inhibition of BMP signaling may suppress AML cell growth in the BM endosteal niche.

Citation Format: Venkata Lokesh Battula, Phuong M. Le, Jeff Sun, Christopher B. Benton, Teresa Mc.Queen, Elizabeth J. Shpall, Carlos E. Bueso-Ramos, Marina Konopleva, Michael Andreeff. Acute myeloid leukemia cells induce osteogenic differentiation in mesenchymal stem cells through bone morphogenetic protein- and RUNX-2- mediated signaling. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5085. doi:10.1158/1538-7445.AM2015-5085

Abstract 1528: GD2+ breast cancer stem cell growth is dependent on NFκB signaling and suppressed by the IKK inhibitor BMS345541 in vitro and in vivo

Recurrence of breast cancer after treatment could be caused by breast cancer stem-like cells (BCSCs) or breast cancer-initiating cells. Therefore, targeting BCSCs is an important strategy that could complement standard chemotherapy. We recently reported that the ganglioside GD2 is exclusively expressed on BCSCs and that targeting its metabolic enzyme (GD3 synthase, GD3S), reduced breast tumor growth and metastasis in immuno-deficient mice (Battula et al., JCI, 2012). To identify signaling pathways that are activated in GD2+ BCSCs, we performed proteomic analysis in GD2+/- cells from breast cancer cell lines MDA-MB-231 and SUM159 cells using Kinexus® antibody arrays. Data analysis employing Ingenuity® pathway analysis revealed activation of NFκB signaling in GD2+ cells in both cell lines. To validate the array data, we tested activation of NFκB (phospho p65) by CyTOF mass cytometry using metal tagged antibodies and found that NFκB was indeed activated in GD2+ but not in GD2- cells, suggesting activation of canonical NFκB signaling in GD2+ BCSCs. Systemic phospho- and total-protein analyses by immuno blotting revealed that proteins involved in non-canonical signaling, including RelB, NFκB2, and Traf2, were also up-regulated (2-3 fold) in GD2+ compared to GD2- cells. These data suggest that both canonical and non-canonical NFκB signaling are active in GD2+ cells and that it may require inhibition of both pathways to block GD2+ BCSC growth. We found that BMS345541 (IC50 for IKKβ = 0.4μM (canonical) and IC50 for IKKα = 4μM (canonical and non-canonical) reduced GD2+ cells and inhibited GD3S expression (determined by qRT-PCR) in a dose- and time-dependent fashion. Treatment with BMS345541 at 5μM for 72hrs reduced GD2+ cell frequency from 18.5±2.5% to 1.7±0.4% (P <0.001) which is >90% reduction of GD2+ cells in a dose-dependent manner. In contrast, treatment with doxorubicin increased the percentage of GD2+ cells, from 13.5±2.5% to 21±2.6% in MDA-MB-231 cells, suggesting that GD2+ cells are resistant to doxorubicin. BCSCs generate mammospheres under low adhesion conditions. Treatment with the BMS compound inhibited the ability of breast cancer cells to form mammospheres app.12 fold in vitro. To test if BMS345541 inhibits in vivo tumor growth, NOD/SCID mice were transplanted with MDA-MB-231 cells (0.5×106) injected into the mammary fat pad. Following engraftment (2 weeks after transplantation), mice were treated with 50mg/kg of BMS345541 or with DMSO daily for only 5 days (IP, n = 5). The BMS345541-treated group showed a significant decrease (P <0.01) in tumor volume, and prolonged survival compared to the control group: median survival was 78 days for the BMS345541-treated group vs. 58 days for controls (P<0.002). Our data suggest that NFκB inhibition by BMS345541 reduces tumor growth in vivo and prolongs survival of tumor-bearing mice by inhibiting NFκB-mediated GD2+ BCSC growth.

Citation Format: Venkata Lokesh Battula, Jeffrey Sun, Gabriel N. Hortobagyi, Michael Andreeff. GD2+ breast cancer stem cell growth is dependent on NFκB signaling and suppressed by the IKK inhibitor BMS345541 in vitro and in vivo. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1528. doi:10.1158/1538-7445.AM2015-1528

GD3 synthase regulates epithelial-mesenchymal transition and metastasis in breast cancer

The epithelial-mesenchymal transition (EMT) bestows cancer cells with increased stem cell properties and metastatic potential. To date, multiple extracellular stimuli and transcription factors have been shown to regulate EMT. Many of them are not druggable and therefore it is necessary to identify targets, which can be inhibited using small molecules to prevent metastasis. Recently, we identified the ganglioside GD2 as a novel breast cancer stem cell marker. Moreover, we found that GD3 synthase (GD3S)--an enzyme involved in GD2 biosynthesis--is critical for GD2 production and could serve as a potential druggable target for inhibiting tumor initiation and metastasis. Indeed, there is a small molecule known as triptolide that has been shown to inhibit GD3S function. Accordingly, in this manuscript, we demonstrate that the inhibition of GD3S using small hairpin RNA or triptolide compromises the initiation and maintenance of EMT instigated by various signaling pathways, including Snail, Twist and transforming growth factor-β1 as well as the mesenchymal characteristics of claudin-low breast cancer cell lines (SUM159 and MDA-MB-231). Moreover, GD3S is necessary for wound healing, migration, invasion and stem cell properties in vitro. Most importantly, inhibition of GD3S in vivo prevents metastasis in experimental as well as in spontaneous syngeneic wild-type mouse models. We also demonstrate that the transcription factor FOXC2, a central downstream effector of several EMT pathways, directly regulates GD3S expression by binding to its promoter. In clinical specimens, the expression of GD3S correlates with poor prognosis in triple-negative human breast tumors. Moreover, GD3S expression correlates with activation of the c-Met signaling pathway leading to increased stem cell properties and metastatic competence. Collectively, these findings suggest that the GD3S-c-Met axis could serve as an effective target for the treatment of metastatic breast cancers.

Targeting connective tissue growth factor (CTGF) in acute lymphoblastic leukemia preclinical models: anti-CTGF monoclonal antibody attenuates leukemia growth

Connective tissue growth factor (CTGF/CCN2) is involved in extracellular matrix production, tumor cell proliferation, adhesion, migration, and metastasis. Recent studies have shown that CTGF expression is elevated in precursor B-acute lymphoblastic leukemia (ALL) and that increased expression of CTGF is associated with inferior outcome in B-ALL. In this study, we characterized the functional role and downstream signaling pathways of CTGF in ALL cells. First, we utilized lentiviral shRNA to knockdown CTGF in RS4;11 and REH ALL cells expressing high levels of CTGF mRNA. Silencing of CTGF resulted in significant suppression of leukemia cell growth compared to control vector, which was associated with AKT/mTOR inactivation and increased levels of cyclin-dependent kinase inhibitor p27. CTGF knockdown sensitized ALL cells to vincristine and methotrexate. Treatment with an anti-CTGF monoclonal antibody, FG-3019, significantly prolonged survival of mice injected with primary xenograft B-ALL cells when co-treated with conventional chemotherapy (vincristine, L-asparaginase and dexamethasone). Data suggest that CTGF represents a targetable molecular aberration in B-ALL, and blocking CTGF signaling in conjunction with administration of chemotherapy may represent a novel therapeutic approach for ALL patients.

Abstract 2606: Bone marrow microenvironment contributes to stem cell phenotype in acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous disease that originates in the bone marrow (BM). BM consists of a complex hypoxic micro-environment that includes osteoblasts, osteoclasts, and mesenchymal stromal cells (MSCs).We previously reported that co-culture with BM-derived MSCs induces anti-apoptotic and drug resistant genes in leukemic cells. As drug resistance is a characteristic of cancer stem cells (CSCs), we hypothesized that components of the micro-environment such as MSCs and hypoxia induce stem cell phenotype in leukemic cells. To test the hypothesis, AML cell lines including OCI-AML3 and KG1 cells were cultured with or without stromal cells at 1% (hypoxia) or 21% (normoxia) oxygen for 1 or 3 or 5 or 7 days and tested for stem cell related functions. Co-culture of leukemic cells with bone marrow-derived MSCs induced Aldehyde dehydrogenase (ALDH) activity in ‘attached fraction’ of OCI-AML3 cells from 5.8%±3.3% to 36.9%±4.7% in a time dependent manner. Interestingly, ALDH activity was also increased in ‘floating fraction’ of OCI-AML3 cells from 2.52%±0.9% to 38.5%±5.7% when co-cultured with MSCs in a time dependent manner, suggesting that cell to cell contact is not necessary to observe this phenotype. In addition, culture of OCI-AML3 cells in 1% oxygen alone increased ALDH+ population from 0.5%±0.1% to 25.6%±3.2% after 7 days and no-further increase was observed when co-cultured with MSCs in hypoxic conditions suggesting that stroma or hypoxia alone are sufficient for induction of stem cell activity in leukemia cells. Another well characterized property of hematopoietic stem cells is generation of side population (SP). KG1 cells, when co-cultured with MSCs, induced side population cells (from 0.2%±0.1% to 2.6%±0.8%); Similarly, OCI-AML3 cells induced SP cells (from 0.2%±0.1% to 10.2%±2.4%) when cultured under hypoxia conditions, indicating that the micro-environment induces stemness in leukemia cells. Interestingly, the size of leukemic cells was reduced from 19.5±2.3μm to 14.4±1.7μm when cultured in 1% oxygen, suggesting low metabolic activity of these cells. Cell cycle analysis revealed that hypoxia inhibited cell cycle at G0/G1 phase of the cell cycle. In case of OCI-AML3 cells, S-phase cells were decreased from 14.5%±0.1% to 5.02±0.1% and the cells in G1-phase were increased from 68.02%±3.1% to 87.62%±2.7%. In case of KG1 cells, S-phase cells were decreased from 26.24%±2.2% to 17.07±1.3% and the cells in G1-phase were increased from 68.02%±3.1% to 77.44%±4.7% indicating cells became more quiescent when cultured under micro-environmental conditions Gene expression analysis revealed that embryonic stem cell markers, including oct4, nanog and sox2, were significantly up regulated by 2-3 fold when cells were cultured at 1% oxygen. These findings indicate that components of the micro-environment induce stem cell phenotype in leukemic cells which may help their survival during chemotherapy.

Citation Format: Venkata Lokesh Battula, Ye Chen, Frank Yang, Marina Konopleva, Michael Andreeff. Bone marrow microenvironment contributes to stem cell phenotype in acute myeloid leukemia. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2606. doi:10.1158/1538-7445.AM2013-2606

Human extramedullary bone marrow in mice: a novel in vivo model of genetically controlled hematopoietic microenvironment

The interactions between hematopoietic cells and the bone marrow (BM) microenvironment play a critical role in normal and malignant hematopoiesis and drug resistance. These interactions within the BM niche are unique and could be important for developing new therapies. Here, we describe the development of extramedullary bone and bone marrow using human mesenchymal stromal cells and endothelial colony-forming cells implanted subcutaneously into immunodeficient mice. We demonstrate the engraftment of human normal and leukemic cells engraft into the human extramedullary bone marrow. When normal hematopoietic cells are engrafted into the model, only discrete areas of the BM are hypoxic, whereas leukemia engraftment results in widespread severe hypoxia, just as recently reported by us in human leukemias. Importantly, the hematopoietic cell engraftment could be altered by genetical manipulation of the bone marrow microenvironment: Extramedullary bone marrow in which hypoxia-inducible factor 1α was knocked down in mesenchymal stromal cells by lentiviral transfer of short hairpin RNA showed significant reduction (50% ± 6%; P = .0006) in human leukemic cell engraftment. These results highlight the potential of a novel in vivo model of human BM microenvironment that can be genetically modified. The model could be useful for the study of leukemia biology and for the development of novel therapeutic modalities aimed at modifying the hematopoietic microenvironment.

Ganglioside GD2 identifies breast cancer stem cells and promotes tumorigenesis

Cancer stem cells (CSCs) are a small subpopulation of cancer cells that have increased resistance to conventional therapies and are capable of establishing metastasis. However, only a few biomarkers of CSCs have been identified. Here, we report that ganglioside GD2 (a glycosphingolipid) identifies a small fraction of cells in human breast cancer cell lines and patient samples that are capable of forming mammospheres and initiating tumors with as few as 10 GD2+ cells. In addition, the majority of GD2+ cells are also CD44hiCD24lo, the previously established CSC-associated cell surface phenotype. Gene expression analysis revealed that GD3 synthase (GD3S) is highly expressed in GD2+ as well as in CD44hiCD24lo cells and that interference with GD3S expression, either by shRNA or using a pharmacological inhibitor, reduced the CSC population and CSC-associated properties. GD3S knockdown completely abrogated tumor formation in vivo. Also, induction of epithelial-mesenchymal transition (EMT) in transformed human mammary epithelial cells (HMLER cells) dramatically increased GD2 as well as GD3S expression in these cells, suggesting a role of EMT in the origin of GD2+ breast CSCs. In summary, we identified GD2 as a new CSC-specific cell surface marker and GD3S as a potential therapeutic target for CSCs, with the possibility of improving survival and cure rates in patients with breast cancer.

Abstract LB-193: Ganglioside GD2 identifies cancer stem cells and inhibition of GD2 biosynthesis by targeting GD3 synthase exerts antitumor effects

Currently, only very few markers either as single or in combination are available to identify cancer stem cells (CSCs). In this report, we identified that the ganglioside GD2, a marker known to express on mesenchymal stromal cells (MSCs) is expressed on a small fraction (5.5% ± 3.4%) of transformed human mammary epithelial cells (HMLER) and breast cancer patient tumors. FACS sorted GD2+ cells appear spindle shaped and proliferate 5 fold slower compared to GD2- cells in-vitro. Analysis of breast cancer cell lines (n=12) indicated that GD2 expression varies and that the basal breast cancer cell lines have a higher percentage of GD2+ cells (median 9%, range 1.2-17%, n=6), as compared to their luminal counterparts (median 0.2%, range 0-3%, n=6, p<0.001). Functional analysis revealed that GD2+ HMLER and MDA-MB-231 cells produced 2-5 fold more mammospheres in-vitro (p<0.003) and tumors in-vivo than GD2- cells (p<0.04). Recent reports suggest that breast tumor cells with CD44highCD24low phenotype exhibit CSCs characteristics. Interestingly, the majority (94% ± 3.5%) of GD2+ cells were characterized by the CD44highCD24low phenotype in HMLER cells. Analysis of primary breast cancer samples (n=10) revealed that GD2 is variably expressed in these samples (median 4.35%, range 0.5%-35.8%) and 95.5% ± 2.7% of GD2+ cells co-segregated with CD44highCD24lowCD45- phenotype. In contrast, only 2.4%± 0.4% of GD2- cells displayed this phenotype. Gene-chip and quantitative RT-PCR analysis revealed that GD3 synthase (GD3S), the enzyme responsible for synthesis of GD3, the precursor of GD2, was expressed 10-fold higher in GD2+ cells compared to GD2- HMLER and MDA-MB-231 cells. Analysis of GD2 expression in HMLER cells induced to undergo EMT revealed that the percentage of GD2+ cells increased 6-7 fold and the expression of GD3S > 10 fold. Moreover, we observed spontaneous generation of GD2+ from GD2- cells and vice versa in both in-vitro and in-vivo, suggesting a role of EMT in this process. Stable knock-down of GD3S in MDA-MB-231 cells using shRNA impaired in-vitro matrigel invasion by more than 10-fold and completely abolished tumor growth in-vivo. Importantly, Triptolide, an anti-inflammatory and anti-cancer drug, which was recently shown to inhibit GD3S expression in melanoma cells, also inhibited GD3S expression in MDA-MB-231 and SUM159 cells by >95% in a dose dependent manner and thereby inhibited growth of GD2+ cells in a time dependent manner. Intra-peritoneal administration of Triptolide (0.15mg/Kg/day) in NOD/SCID mice bearing MDA-MB-231 breast tumors completely eliminated tumors in 50% and reduced the tumor volume 7- to 8-fold in 25% of the mice. In conclusion, we identified GD2 as a new CSC specific cell surface marker and GD3 synthase as a potential therapeutic target for CSCs, with the potential of improving survival and cure rates of patients with breast cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-193. doi:1538-7445.AM2012-LB-193

Epithelial-mesenchymal transition-derived cells exhibit multilineage differentiation potential similar to mesenchymal stem cells

The epithelial-to-mesenchymal transition (EMT) is an embryonic process that becomes latent in most normal adult tissues. Recently, we have shown that induction of EMT endows breast epithelial cells with stem cell traits. In this report, we have further characterized the EMT-derived cells and shown that these cells are similar to mesenchymal stem cells (MSCs) with the capacity to differentiate into multiple tissue lineages. For this purpose, we induced EMT by ectopic expression of Twist, Snail, or transforming growth factor-beta in immortalized human mammary epithelial cells. We found that the EMT-derived cells and MSCs share many properties including the antigenic profile typical of MSCs, that is, CD44(+), CD24(-), and CD45(-). Conversely, MSCs express EMT-associated genes, such as Twist, Snail, and mesenchyme forkhead 1 (FOXC2). Interestingly, CD140b (platelet-derived growth factor receptor-beta), a marker for naive MSCs, is exclusively expressed in EMT-derived cells and not in their epithelial counterparts. Moreover, functional analyses revealed that EMT-derived cells but not the control cells can differentiate into alizarin red S-positive mature osteoblasts, oil red O-positive adipocytes and alcian blue-positive chondrocytes similar to MSCs. We also observed that EMT-derived cells but not the control cells invade and migrate towards MDA-MB-231 breast cancer cells similar to MSCs. In vivo wound homing assays in nude mice revealed that the EMT-derived cells home to wound sites similar to MSCs. In conclusion, we have demonstrated that the EMT-derived cells are similar to MSCs in gene expression, multilineage differentiation, and ability to migrate towards tumor cells and wound sites.

Abstract 2314: Epithelial-mesenchymal transition derived cells exhibit multi-lineage differentiation potential similar to mesenchymal stem cells

The epithelial-to-mesenchymal transition (EMT) is an embryonic process that becomes latent in most normal adult tissues. Recently, we have shown that induction of EMT endows stem cell traits to breast epithelial cells. Mesenchymal stem cells (MSC) have the capacity to self-renew and differentiate into multiple tissue lineages. We hypothesized that the activation of EMT by ectopic expression of Twist, Snail or TGF-β in immortalized human mammary epithelial cells (HMEC) will result in the generation of cells with a phenotype and functionality similar to MSC. We found that the EMT-derived cells not only showed similar morphology but also displayed the typical MSC phenotype i.e. CD44+, CD24− and CD45−. Alternatively, MSC expressed EMT inducing genes such as Twist, Snail and FOXC2. Interestingly, CD140b (PDGFR-β), a marker for naive MSC, was exclusively expressed in EMT-derived cells compared to their epithelial counterparts. Moreover, functional analysis revealed that EMT-derived but not the control cells differentiate into Alizarin Red S-positive mature osteoblasts, Oil Red O-positive adipocytes and Alcian Blue-positive chondrocytes similar to MSC. We also observed that EMT-derived but not control cells invade and migrate towards MDA-MB-231 tumor cells in-vitro similar to MSC, displaying the characteristic tropism of MSC for tumor cells as previously reported by us. In-vivo wound homing assays in nude mice revealed that the EMT-derived cells home to wound sites similar to MSC. In conclusion, we demonstrated that the EMT-derived cells are similar to MSC in gene-expression, multi-lineage differentiation, migration towards tumor cells and their ability to home to wounds. These results also suggest that EMT-derived MSC are active participants in cancer growth and invasion.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2314.

Direct evidence of mesenchymal stem cell tropism for tumor and wounding microenvironments using in vivo bioluminescent imaging

Multipotent mesenchymal stromal/stem cells (MSC) have shown potential clinical utility. However, previous assessments of MSC behavior in recipients have relied on visual detection in host tissue following sacrifice, failing to monitor in vivo MSC dispersion in a single animal and limiting the number of variables that can be observed concurrently. In this study, we used noninvasive, in vivo bioluminescent imaging to determine conditions under which MSC selectively engraft in sites of inflammation. MSC modified to express firefly luciferase (ffLuc-MSC) were injected into healthy mice or mice bearing inflammatory insults, and MSC localization was followed with bioluminescent imaging. The inflammatory insults investigated included cutaneous needle-stick and surgical incision wounds, as well as xenogeneic and syngeneic tumors. We also compared tumor models in which MSC were i.v. or i.p. delivered. Our results demonstrate that ffLuc-expressing human MSC (hMSC) systemically delivered to nontumor-bearing animals initially reside in the lungs, then egress to the liver and spleen, and decrease in signal over time. However, hMSC in wounded mice engraft and remain detectable only at injured sites. Similarly, in syngeneic and xenogeneic breast carcinoma-bearing mice, bioluminescent detection of systemically delivered MSC revealed persistent, specific colocalization with sites of tumor development. This pattern of tropism was also observed in an ovarian tumor model in which MSC were i.p. injected. In this study, we identified conditions under which MSC tropism and selective engraftment in sites of inflammation can be monitored by bioluminescent imaging over time. Importantly, these consistent findings were independent of tumor type, immunocompetence, and route of MSC delivery.

Isolation of functionally distinct mesenchymal stem cell subsets using antibodies against CD56, CD271, and mesenchymal stem cell antigen-1

BACKGROUND

Conventionally, mesenchymal stem cells are functionally isolated from primary tissue based on their capacity to adhere to a plastic surface. This isolation procedure is hampered by the unpredictable influence of co-cultured hematopoietic and/or other unrelated cells and/or by the elimination of a late adhering mesenchymal stem cells subset during removal of undesired cells. To circumvent these limitations, several antibodies have been developed to facilitate the prospective isolation of mesenchymal stem cells. Recently, we described a panel of monoclonal antibodies with superior selectivity for mesenchymal stem cells, including the monoclonal antibodies W8B2 against human mesenchymal stem cell antigen-1 (MSCA-1) and 39D5 against a CD56 epitope, which is not expressed on natural killer cells.

DESIGN AND METHODS

Bone marrow derived mesenchymal stem cells from healthy donors were analyzed and isolated by flow cytometry using a large panel of antibodies against surface antigens including CD271, MSCA-1, and CD56. The growth of mesenchymal stem cells was monitored by colony formation unit fibroblast (CFU-F) assays. The differentiation of mesenchymal stem cells into defined lineages was induced by culture in appropriate media and verified by immunostaining.

RESULTS

Multicolor cell sorting and CFU-F assays showed that mesenchymal stem cells were approximately 90-fold enriched in the MSCA-1(+)CD56(-) fraction and approximately 180-fold in the MSCA-1(+)CD56(+) fraction. Phenotype analysis revealed that the expression of CD10, CD26, CD106, and CD146 was restricted to the MSCA-1(+)CD56(-) mesenchymal stem cells subset and CD166 to MSCA-1(+)CD56(+/-) mesenchymal stem cells. Further differentiation of these subsets showed that chondrocytes and pancreatic-like islets were predominantly derived from MSCA-1(+)CD56(+/-) cells whereas adipocytes emerged exclusively from MSCA-1(+)CD56(-) cells. The culture of single sorted MSCA-1(+)CD56(+) cells resulted in the appearance of phenotypically heterogeneous clones with distinct proliferation and differentiation capacities.

CONCLUSIONS

Novel mesenchymal stem cells subsets with distinct phenotypic and functional properties were identified. Our data suggest that the MSCA-1(+)CD56(+) subset is an attractive starting population for autologous chondrocyte transplantation.

Prospective isolation and characterization of mesenchymal stem cells from human placenta using a frizzled-9-specific monoclonal antibody

We have recently shown that frizzled-9 (FZD9, CD349) is expressed on the cell surface of cultured mesenchymal stromal cells (MSC) derived from the human bone marrow (BM) and chorionic placenta (PL). To study whether FZD9 is also a marker for naive mesenchymal stem cells (MSC), we analyzed the expression pattern of FZD9 on freshly isolated PL cells and determined the clonogenic potential of isolated FZD9(+) cells using the colony-forming units-fibroblastic (CFU-F) assay. About 0.2% of isolated PL cells were positive for FZD9. Two-color analysis revealed that FZD9(+) PL cells uniformly express CD9, CD63, and CD90, but are heterogeneous for CD10, CD13, and CD26 expression. In contrast to BM-derived MSC, PL-derived MSC expressed only low levels of CD271. Colony assays of sorted cells showed that clonogenic CFU-F reside exclusively in the FZD9(+) but not in the FZD9(-) fraction. Further analysis revealed that CFU-F were enriched by 60-fold in the FZD9(+)CD10(+)CD26(+) fraction but were absent in the FZD9(+)CD10(-)CD26(-) population. Cultured FZD9(+) cells expressed the embryonic stem cell makers Oct-4 and nanog as well as SSEA-4 and TRA1-2-49/6E. In addition, they could be differentiated into functional adipocytes and osteoblasts. This report describes for the first time that FZD9 is a novel and specific marker for the prospective isolation of MSC from human term PL.

Novel markers for the prospective isolation of human MSC

The isolation of mesenchymal stem cells (MSC) from primary tissue is hampered by the limited selectivity of available markers. So far, CD271 is one of the most specific markers for bone marrow (BM)-derived MSC. In search of additional markers, monoclonal antibodies (mAbs) with specificity for immature cells were screened by flow cytometry for their specific reactivity with the rare CD271(+) population. The recognized CD271(+) populations were fractionated by fluorescence-activated cell sorting and the clonogenic capacity of the sorted cells was analyzed for their ability to give rise to CFU-F. The results showed that only the CD271(bright) but not the CD271(dim) population contained CFU-F. Two-color flow cytometry analysis revealed that only the CD271(bright) population was positive for the established MSC markers CD10, CD13, CD73, and CD105. In addition, a variety of mAbs specific for novel and partially unknown antigens selectively recognized the CD271(bright) population but no other BM cells. The new MSC-specific molecules included the platelet-derived growth factor receptor-beta (CD140b), HER-2/erbB2 (CD340), frizzled-9 (CD349), the recently described W8B2 antigen, as well as cell-surface antigens defined by the antibodies W1C3, W3D5, W4A5, W5C4, W5C5, W7C6, 9A3, 58B1, F9-3C2F1, and HEK-3D6. In conclusion, the described markers are suitable for the prospective isolation of highly purified BM-MSC. These MSC may be used as an improved starting population for transplantation in diseases like osteogenesis imperfecta, cartilage repair, and myocardial infarction.

Human placenta and bone marrow derived MSC cultured in serum-free, b-FGF-containing medium express cell surface frizzled-9 and SSEA-4 and give rise to multilineage differentiation

Conventionally, mesenchymal stem cells (MSC) are generated by plating cells from bone marrow (BM) or other sources into culture flasks and selecting plastic-adherent cells with fibroblastoid morphology. These cells express CD9, CD10, CD13, CD73, CD105, CD166, and other markers but show only a weak or no expression of the embryonic markers stage-specific embryonic antigen-4 (SSEA-4), Oct-4 and nanog-3. Using a novel protocol we prepared MSC from BM and non-amniotic placenta (PL) by culture of Ficoll-selected cells in gelatin-coated flasks in the presence of a serum-free, basic fibroblast growth factor (b-FGF)-containing medium that was originally designed for the expansion of human embryonic stem cells (ESC). MSC generated in gelatin-coated flasks in the presence of ESC medium revealed a four-to fivefold higher proliferation rate than conventionally prepared MSC which were grown in uncoated flasks in serum-containing medium. In contrast, the colony forming unit fibroblast number was only 1.5- to twofold increased in PL-MSC and not affected in BM-MSC. PL-MSC grown in ESC medium showed an increased surface expression of SSEA-4 and frizzled-9 (FZD-9), an increased Oct-4 and nestin mRNA expression, and an induced expression of nanog-3. BM-MSC showed an induced expression of FZD-9, nanog-3, and Oct-4. In contrast to PL-MSC, only BM-MSC expressed the MSC-specific W8B2 antigen. When cultured under appropriate conditions, these MSC gave rise to functional adipocytes and osteoblast-like cells (mesoderm), glucagon and insulin expressing pancreatic-like cells (endoderm), as well as cells expressing the neuronal markers neuron-specific enolase, glutamic acid decarboxylase-67 (GAD), or class III beta-tubulin, and the astrocyte marker glial fibrillary acidic protein (ectoderm). In conclusion, using a novel protocol we demonstrate that adult BM-and neonatal PL-derived MSC can be induced to express high levels of FZD-9, Oct-4, nanog-3, and nestin and are able of multi-lineage differentiation.