Novel Anti-B-cell Maturation Antigen Alpha-Amanitin Antibody-drug Conjugate HDP-101 Shows Superior Activity to Belantamab Mafodotin and Enhanced Efficacy in Deletion 17p Myeloma Models

B-cell maturation antigen (BCMA) plays a pathobiologic role in myeloma and is a validated target with five BCMA-specific therapeutics having been approved for relapsed/refractory disease. However, these drugs are not curative, and responses are inferior in patients with molecularly-defined high-risk disease, including those with deletion 17p (del17p) involving the tumor suppressor TP53, supporting the need for further drug development. Del17p has been associated with reduced copy number and gene expression of RNA polymerase II subunit alpha (POLR2A) in other tumor types. We therefore studied the possibility that HDP-101, an anti-BCMA antibody drug conjugate (ADC) with the POLR2A poison α-amanitin could be an attractive agent in myeloma, especially with del17p. HDP-101 reduced viability in myeloma cell lines representing different molecular disease subtypes, and overcame adhesion-mediated and both conventional and novel drug resistance. After confirming that del17p is associated with reduced POLR2A levels in publicly available myeloma patient databases, we engineered TP53 wild-type cells with a TP53 knockout (KO), POLR2A knockdown (KD), or both, the latter to mimic del17p. HDP-101 showed potent anti-myeloma activity against all tested cell lines, and exerted enhanced efficacy against POLR2A KD and dual TP53 KO/POLR2A KD cells. Mechanistic studies showed HDP-101 up-regulated the unfolded protein response, activated apoptosis, and induced immunogenic cell death. Notably, HDP-101 impacted CD138-positive but not-negative primary cells, showed potent efficacy against aldehyde dehydrogenase-positive clonogenic cells, and eradicated myeloma in an in vivo cell line-derived xenograft (CDX). Interestingly, in the CDX model, prior treatment with HDP-101 precluded subsequent engraftment on tumor cell line rechallenge in a manner that appeared to be dependent in part on natural killer cells and macrophages. Finally, HDP-101 was superior to the BCMA-targeted ADC belantamab mafodotin against cell lines and primary myeloma cells in vitro, and in an in vivo CDX. Together, the data support the rationale for translation of HDP-101 to the clinic, where it is now undergoing Phase I trials, and suggest that it could emerge as a more potent ADC for myeloma with especially interesting activity against the high-risk del17p myeloma subtype.

LFA-1 activation enriches tumor-specific T cells in a cold tumor model and synergizes with CTLA-4 blockade

The inability of CD8⁺ effector T cells (Teffs) to reach tumor cells is an important aspect of tumor resistance to cancer immunotherapy. The recruitment of these cells to the tumor microenvironment (TME) is regulated by integrins, a family of adhesion molecules that are expressed on T cells. Here, we show that 7HP349, a small-molecule activator of lymphocyte function–associated antigen-1 (LFA-1) and very late activation antigen-4 (VLA-4) integrin cell-adhesion receptors, facilitated the preferential localization of tumor-specific T cells to the tumor and improved antitumor response. 7HP349 monotherapy had modest effects on anti–programmed death 1–resistant (anti–PD-1–resistant) tumors, whereas combinatorial treatment with anti–cytotoxic T lymphocyte–associated protein 4 (anti–CTLA-4) increased CD8⁺ Teff intratumoral sequestration and synergized in cooperation with neutrophils in inducing cancer regression. 7HP349 intratumoral CD8⁺ Teff enrichment activity depended on CXCL12. We analyzed gene expression profiles using RNA from baseline and on treatment tumor samples of 14 melanoma patients. We identified baseline CXCL12 gene expression as possibly improving the likelihood or response to anti–CTLA-4 therapies. Our results provide a proof-of-principle demonstration that LFA-1 activation could convert a T cell–exclusionary TME to a T cell–enriched TME through mechanisms involving cooperation with innate immune cells.

Intravenous Immunoglobulin G Suppresses Heat Shock Protein (HSP)-70 Expression and Enhances the Activity of HSP90 and Proteasome Inhibitors

Intravenous immunoglobulin G (IVIgG) is approved for primary immunodeficiency syndromes but may induce anti-cancer effects, and while this has been attributed to its anti-inflammatory properties, IgG against specific tumor targets may play a role. We evaluated IVIgG alone, and with a Heat shock protein (HSP)-90 or proteasome inhibitor, using multiple myeloma and mantle cell lymphoma (MCL) cells in vitro, and with the proteasome inhibitor bortezomib in vivo. IVIgG inhibited the growth of all cell lines tested, induced G₁ cell cycle arrest, and suppressed pro-tumor cytokines including Interleukin (IL)-6, IL-8, and IL-10. Genomic and proteomic studies showed that IVIgG reduced tumor cell HSP70-1 levels by suppressing the ability of extracellular HSP70-1 to stimulate endogenous HSP70-1 promoter activity, and reduced extracellular vesicle uptake. Preparations of IVIgG were found to contain high titers of anti-HSP70-1 IgG, and recombinant HSP70-1 reduced the efficacy of IVIgG to suppress HSP70-1 levels. Combining IVIgG with the HSP90 inhibitor AUY922 produced superior cell growth inhibition and correlated with HSP70-1 suppression. Also, IVIgG with bortezomib or carfilzomib was superior to each single agent, and enhanced bortezomib's activity in bortezomib-resistant myeloma cells. Moreover, IVIgG reduced transfer of extracellular vesicles (EVs) to cells, and blocked transfer of bortezomib resistance through EVs. Finally, IVIgG with bortezomib were superior to the single agents in an in vivo myeloma model. These studies support the possibility that anti-HSP70-1 IgG contained in IVIgG can inhibit myeloma and MCL growth by interfering with a novel mechanism involving uptake of exogenous HSP70-1 which then induces its own promoter.

The novel protein homeostatic modulator BTX306 is active in myeloma and overcomes bortezomib and lenalidomide resistance

Small molecules targeting the cereblon-containing E3 ubiquitin ligase including thalidomide, lenalidomide, and pomalidomide modulate turnover of downstream client proteins and demonstrate pre-clinical and clinical anti-myeloma activity. Different drugs that engage with cereblon hold the potential of unique phenotypic effects, and we therefore studied the novel protein homeostatic modulator (PHM™) BTX306 with a unique thiophene-fused scaffold bearing a substituted phenylurea and glutarimide. This agent much more potently reduced human-derived myeloma cell line viability, with median inhibitory concentrations in the single nanomolar range versus micromolar values for lenalidomide or pomalidomide, and more potently activated caspases 3/8/9. While lenalidomide and pomalidomide induced greater degradation of Ikaros and Aiolos in myeloma cells, BTX306 more potently reduced levels of GSPT1, eRF1, CK1α, MCL-1, and c-MYC. Suppression of cereblon or overexpression of Aiolos or Ikaros induced relative resistance to BTX306, and this agent did not impact viability of murine hematopoietic cells in an in vivo model, demonstrating its specificity for human cereblon. Interestingly, BTX306 did show some reduced activity in lenalidomide-resistant cell line models but nonetheless retained its nanomolar potency in vitro, overcame bortezomib resistance, and was equipotent against otherwise isogenic cell line models with either wild-type or knockout TP53. Finally, BTX306 demonstrated strong activity against primary CD138-positive plasma cells, showed enhanced anti-proliferative activity in combination with bortezomib and dexamethasone, and was effective in an in vivo systemic model of multiple myeloma. Taken together, the data support further translational studies of BTX306 and its derivatives to the clinic for patients with relapsed and/or refractory myeloma. KEY MESSAGES: BTX306 has a unique thiophene-fused scaffold bearing phenylurea and glutarimide. BTX306 is more potent against myeloma cells than lenalidomide or pomalidomide. BTX306 overcomes myeloma cell resistance to lenalidomide or bortezomib in vitro. BTX306 is active against primary myeloma cells, and shows efficacy in vivo.

Targeting Myddosome Signaling in Waldenström's Macroglobulinemia with the Interleukin-1 Receptor-Associated Kinase 1/4 Inhibitor R191

PURPOSE

Waldenström's macroglobulinemia is an incurable lymphoproliferative disorder driven by an L265P mutation in the myeloid differentiation primary response gene 88 (MYD88), which activates downstream NF-κB signaling through the Myddosome. As this pathway depends in part on activity of interleukin-1 receptor-associated kinases (IRAKs)-1 and -4, we sought to evaluate the potential of the IRAK1/4 inhibitor R191 in preclinical models.

EXPERIMENTAL DESIGN

Patient-derived cell lines and primary samples were used in both in vitro and in vivo experiments to model Waldenström's macroglobulinemia and its response to IRAK1/4 inhibitors.

RESULTS

R191 induced a dose- and time-dependent reduction in viability of BCWM.1 and MWCL-1 Waldenström's cell lines, and suppressed activation of IRAK1/4. This was associated with cell-cycle arrest at G0-G1, reduced levels of cyclin-dependent kinases 4 and 6, and induction of apoptosis in cell lines and primary patient samples. Further downstream, R191 exposure led to reduced activation of NF-κB, and of protein kinase B/Akt/mammalian target of rapamycin signaling, whereas expression of a constitutively active Akt mutant induced R191 resistance. Gene expression profiling and gene set enrichment analysis revealed a signature consistent with inhibition of c-Myc and activation of the endoplasmic reticulum stress response. In both subcutaneous and systemic murine models of Waldenström's, R191 showed antitumor activity. Finally, the activity of R191 was enhanced when it was combined with novel chemotherapeutics such as bortezomib, afuresertib, and ibrutinib.

CONCLUSIONS

Taken together, these data support the translation of R191 as an approach to target IRAK1/4 to the clinic for patients with Waldenström's macroglobulinemia.

HSP90 inhibition enhances cancer immunotherapy by upregulating interferon response genes

T-cell-based immunotherapies are promising treatments for cancer patients. Although durable responses can be achieved in some patients, many patients fail to respond to these therapies, underscoring the need for improvement with combination therapies. From a screen of 850 bioactive compounds, we identify HSP90 inhibitors as candidates for combination with immunotherapy. We show that inhibition of HSP90 with ganetespib enhances T-cell-mediated killing of patient-derived human melanoma cells by their autologous T cells in vitro and potentiates responses to anti-CTLA4 and anti-PD1 therapy in vivo. Mechanistic studies reveal that HSP90 inhibition results in upregulation of interferon response genes, which are essential for the enhanced killing of ganetespib treated melanoma cells by T cells. Taken together, these findings provide evidence that HSP90 inhibition can potentiate T-cell-mediated anti-tumor immune responses, and rationale to explore the combination of immunotherapy and HSP90 inhibitors.

Many patients fail to respond to T cell based immunotherapies. Here, the authors, through a high-throughput screening, identify HSP90 inhibitors as a class of preferred drugs for treatment combination with immunotherapy.

RNA Polymerase I Inhibition with CX-5461 as a Novel Therapeutic Strategy to Target MYC in Multiple Myeloma

Dysregulation of MYC is frequently implicated in both early and late myeloma progression events, yet its therapeutic targeting has remained a challenge. Among key MYC downstream targets is ribosomal biogenesis, enabling increases in protein translational capacity necessary to support the growth and self-renewal programmes of malignant cells. We therefore explored the selective targeting of ribosomal biogenesis with the small molecule RNA polymerase (pol) I inhibitor CX-5461 in myeloma. CX-5461 induced significant growth inhibition in wild-type (WT) and mutant TP53 myeloma cell lines and primary samples, in association with increases in downstream markers of apoptosis. Moreover, Pol I inhibition overcame adhesion-mediated drug resistance and resistance to conventional and novel agents. To probe the TP53-independent mechanisms of CX-5461, gene expression profiling was performed on isogenic TP53 WT and knockout cell lines and revealed reduction of MYC downstream targets. Mechanistic studies confirmed that CX-5461 rapidly suppressed both MYC protein and MYC mRNA levels. The latter was associated with an increased binding of the RNA-induced silencing complex (RISC) subunits TARBP2 and AGO2, the ribosomal protein RPL5, and MYC mRNA, resulting in increased MYC transcript degradation. Collectively, these studies provide a rationale for the clinical translation of CX-5461 as a novel therapeutic approach to target MYC in myeloma.

Abstract B105: HSP90 inhibitor, ganetespib, enhances responses to cancer immunotherapy through increased expression of interferon response genes

Recently, T cell based immunotherapies have moved to the forefront of cancer immunotherapy with the success of Adoptive T cell therapy (ACT) and Immune checkpoint blockade. ACT, where patients are treated with tumor infiltrating T cells (TILs), conferred a clinical response rate of ∼50%. Treatment with anti-CTLA4 therapy, Ipilimumab, conferred response rates of 10-20%, greatly improving the overall survival of patients with advanced melanoma. Despite the encouraging outcomes, there are relatively low response rates coupled with the delay of weeks to months before tumor shrinkage can be appreciated. Thus, understanding mechanisms of resistance to immune therapies, to improve response rates, shorten time to treatment effect and developing predictive biomarkers of response are vital to the care of melanoma patients. In order to identify possible resistance mechanisms to immunotherapy, a high-throughput in vitro screen with 850 different bio-active compounds (Selleckchem), was designed to search for agents that could either increase or decrease the resistance of melanoma tumor cells to T cell mediated killing. Paired patient derived human melanoma tumor samples and TILs were used to assess which compounds when used to treat the melanoma cell lines can enhance the cytotoxic activity of the TILs against the paired melanoma sample, using a flow cytometry based assay in which active caspase 3 was used as a read out of apoptosis. We identified heat shock protein 90 (HSP90) inhibitors amongst the top compounds that improved T cell mediated cytotoxicity of treated tumor cells. We show that treatment with the HSP90 inhibitor ganetespib (Synta) greatly improves T cell mediated cytotoxicity of human cancer cells lines in vitro. Furthermore, in vivo murine studies using the MC38/gp100 tumor model show that ganestespib in combination with anti-CTLA4, resulted in superior antitumor effect and survival compared to either treatment alone (Average tumor volume at day 21 of treatment: Vehicle 294.3mm3, α-CTLA4 193 mm3, Ganetespib 237.5 mm3 and Ganetespib + α-CTLA4 105.8 mm3, P < 0.0001). Microarray analysis of human cell lines treated with ganetespib in vitro revealed an increase in interferon response genes including IFIT1, IFIT2, IFIT3. We confirmed these findings with quantitative real time PCR and western blot analyses and found IFIT1, IFIT2 and IFIT3 to be consistently upregulated across multiple melanoma cell lines following treatment with ganetespib. We next sought to verify the importance of the IFIT genes in the synergy observed between ganetespib treatment and T cell killing. First, we overexpressed IFIT1, IFIT2 and IFIT3 in human melanoma cell lines to recapitulate the improved sensitivity of the human melanoma cell lines to T cell killing following treatment with ganetespib. We then co-cultured these cells with their autologous T cells and found that overexpressing IFIT1, IFIT2 and IFIT3 mimicked the effects of ganetespib by increasing the sensitivity to T cell killing over the GFP control. On the other hand, silencing IFIT1, IFIT2 and IFIT3 simultaneously, abrogated the synergy between ganetespib and T cell killing. We are further elucidating the role of these genes in lowering the apoptotic threshold of cancer cells and contributing to the synergy of ganetespib and immunotherapy. This will enable the emergence of a new combination therapy of HSP90 inhibitors and anti-CTLA4 for the treatment of melanoma patients that will increase the percentage of patients responding to immunotherapy and achieving long term responses.

Citation Format: Rina M. Mbofung, Jodi A. McKenzie, Shruti Malu, Chengwen Liu, Weiyi Peng, Isere Kuiatse, Leila Williams, Seram Devi, Zhe Wang, Trang Tieu, Tim Heffernan, Richard E. Davis, Rodabe Amaria, Patrick Hwu. HSP90 inhibitor, ganetespib, enhances responses to cancer immunotherapy through increased expression of interferon response genes [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B105.

Abstract 4360: Inhibition of HSP90 enhances T cell-mediated antitumor immune responses through expression of interferon-alpha response Genes

Recently, T cell based immunotherapies have moved to the forefront of cancer immunotherapy with the success of Adoptive T cell therapy (ACT) and Immune checkpoint blockade. ACT, where patients are treated with tumor infiltrating T cells (TILs), conferred a clinical response rate of ∼50%. Treatment with anti-CTLA4 therapy, Ipilimumab, conferred response rates of 10-20%, greatly improving the overall survival of patients with advanced melanoma. Despite the encouraging outcomes, there are relatively low response rates coupled with the delay of weeks to months before tumor shrinkage can be appreciated. Thus, understanding mechanisms of resistance to immune therapies, to improve response rates, shorten time to treatment effect and developing predictive biomarkers of response are vital to the care of melanoma patients. In order to identify possible resistance mechanisms to immunotherapy, a high-throughput in vitro screen with 850 different bio-active compounds (Selleckchem), was designed to search for agents that could either increase or decrease the resistance of melanoma tumor cells to T cell mediated killing. Paired tumor samples and TILs from melanoma patients were used to assess which compounds when used to treat the melanoma cell lines can enhance the cytotoxic activity of the TILs against the paired melanoma sample, using a flow cytometry based assay in which active caspase 3 was used as a read out of apoptosis. We identified heat shock protein 90 (HSP90) inhibitors amongst compounds that improved T cell mediated cytotoxicity. We show that treatment with the HSP90 inhibitor ganetespib (Synta) greatly improves T cell mediated cytotoxicity of both human and murine cancer cells lines in vitro. Furthermore, in vivo murine studies using the MC38/gp100 tumor model show that ganestespib in combination with anti-CTLA4, resulted in superior antitumor effect and survival compared to either treatment alone (Average tumor volume at day 21 of treatment: Vehicle 294.3mm3, α-CTLA4 193 mm3, Ganetespib 237.5 mm3 and Ganetespib + α-CTLA4 105.8 mm3, P < 0.0001). Microarray analysis of human cell lines treated with ganetespib in vitro revealed an increase in interferon alpha (IFN-α) response genes including IFIT1, IFIT2, IFIT3 and IFIH1. Silencing IFIT2 abrogated the synergy observed with ganetespib treatment and T cell mediated killing, suggesting that the IFN-α response pathway plays an important role in this combination therapy. We are further elucidating the role of these genes in the synergy observed. This will enable the emergence of a new combination therapy of HSP90 inhibitors and anti-CTLA4 for the treatment of melanoma patients that will increase the percentage of patients responding to immunotherapy and achieving long term responses.

Citation Format: Rina M. Mbofung, Jodi A. McKenzie, Shruti Malu, Chengwen Liu, Leila Williams, Weiyi Peng, Zhe Wang, Satyendra Tripathi, Trang Tieu, Shuping Zhao, Seram Devi, Isere Kuiatse, Emily Ashkin, Leah Bailey, Jason Roszik, Samir Hanash, Timothy Heffernan, Richard E. Davis, Rodabe N. Amaria, Patrick Hwu. Inhibition of HSP90 enhances T cell-mediated antitumor immune responses through expression of interferon-alpha response Genes. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4360.

Tight Junction Protein 1 Modulates Proteasome Capacity and Proteasome Inhibitor Sensitivity in Multiple Myeloma via EGFR/JAK1/STAT3 Signaling

Proteasome inhibitors have revolutionized outcomes in multiple myeloma, but they are used empirically, and primary and secondary resistance are emerging problems. We have identified TJP1 as a determinant of plasma cell proteasome inhibitor susceptibility. TJP1 suppressed expression of the catalytically active immunoproteasome subunits LMP7 and LMP2, decreased proteasome activity, and enhanced proteasome inhibitor sensitivity in vitro and in vivo. This occurred through TJP1-mediated suppression of EGFR/JAK1/STAT3 signaling, which modulated LMP7 and LMP2 levels. In the clinic, high TJP1 expression in patient myeloma cells was associated with a significantly higher likelihood of responding to bortezomib and a longer response duration, supporting the use of TJP1 as a biomarker to identify patients most likely to benefit from proteasome inhibitors.

The Nuclear Factor (Erythroid-derived 2)-like 2 and Proteasome Maturation Protein Axis Mediate Bortezomib Resistance in Multiple Myeloma

Resistance to the proteasome inhibitor bortezomib is an emerging clinical problem whose mechanisms have not been fully elucidated. We considered the possibility that this could be associated with enhanced proteasome activity in part through the action of the proteasome maturation protein (POMP). Bortezomib-resistant myeloma models were used to examine the correlation between POMP expression and bortezomib sensitivity. POMP expression was then modulated using genetic and pharmacologic approaches to determine the effects on proteasome inhibitor sensitivity in cell lines and in vivo models. Resistant cell lines were found to overexpress POMP, and while its suppression in cell lines enhanced bortezomib sensitivity, POMP overexpression in drug-naive cells conferred resistance. Overexpression of POMP was associated with increased levels of nuclear factor (erythroid-derived 2)-like (NRF2), and NRF2 was found to bind to and activate the POMP promoter. Knockdown of NRF2 in bortezomib-resistant cells reduced POMP levels and proteasome activity, whereas its overexpression in drug-naive cells increased POMP and proteasome activity. The NRF2 inhibitor all-trans-retinoic acid reduced cellular NRF2 levels and increased the anti-proliferative and pro-apoptotic activities of bortezomib in resistant cells, while decreasing proteasome capacity. Finally, the combination of all-trans-retinoic acid with bortezomib showed enhanced activity against primary patient samples and in a murine model of bortezomib-resistant myeloma. Taken together, these studies validate a role for the NRF2/POMP axis in bortezomib resistance and identify NRF2 and POMP as potentially attractive targets for chemosensitization to this proteasome inhibitor.

Targeting the Spleen Tyrosine Kinase with Fostamatinib as a Strategy against Waldenström Macroglobulinemia

PURPOSE

Waldenström macroglobulinemia (WMG) is a lymphoproliferative disorder characterized by good initial responses to standard therapeutics, but only a minority of patients achieve complete remissions, and most inevitably relapse, indicating a need for novel agents. B-cell receptor signaling has been linked to clonal evolution in WMG, and Spleen tyrosine kinase (Syk) is overexpressed in primary cells, suggesting that it could be a novel and rational target.

EXPERIMENTAL DESIGN

We studied the impact of the Syk inhibitor fostamatinib on BCWM.1 and MWCL-1 WMG-derived cell lines both in vitro and in vivo, as well as on primary patient cells.

RESULTS

In WMG-derived cell lines, fostamatinib induced a time- and dose-dependent reduction in viability, associated with activation of apoptosis. At the molecular level, fostamatinib reduced activation of Syk and Bruton's tyrosine kinase, and also downstream signaling through MAPK kinase (MEK), p44/42 MAPK, and protein kinase B/Akt. As a single agent, fostamatinib induced tumor growth delay in an in vivo model of WMG, and reduced viability of primary WMG cells, along with inhibition of p44/42 MAPK signaling. Finally, fostamatinib in combination with other agents, including dexamethasone, bortezomib, and rituximab, showed enhanced activity.

CONCLUSIONS

Taken together, these data support the translation of approaches targeting Syk with fostamatinib to the clinic for patients with relapsed and possibly even newly diagnosed WMG.

Inhibition of the MDM2 E3 Ligase induces apoptosis and autophagy in wild-type and mutant p53 models of multiple myeloma, and acts synergistically with ABT-737

Intracellular proteolytic pathways have been validated as rational targets in multiple myeloma with the approval of two proteasome inhibitors in this disease, and with the finding that immunomodulatory agents work through an E3 ubiquitin ligase containing Cereblon. Another E3 ligase that could be a rational target is the murine double minute (MDM) 2 protein, which plays a role in p53 turnover. A novel inhibitor of this complex, MI-63, was found to induce apoptosis in p53 wild-type myeloma models in association with activation of a p53-mediated cell death program. MI-63 overcame adhesion-mediated drug resistance, showed anti-tumor activity in vivo, enhanced the activity of bortezomib and lenalidomide, and also overcame lenalidomide resistance. In mutant p53 models, inhibition of MDM2 with MI-63 also activated apoptosis, albeit at higher concentrations, and this was associated with activation of autophagy. When MI-63 was combined with the BH3 mimetic ABT-737, enhanced activity was seen in both wild-type and mutant p53 models. Finally, this regimen showed efficacy against primary plasma cells from patients with newly diagnosed and relapsed/refractory myeloma. These findings support the translation of novel MDM2 inhibitors both alone, and in combination with other novel agents, to the clinic for patients with multiple myeloma.

Dynamic balance of multiple myeloma clonogenic side population cell percentages controlled by environmental conditions

Cancer stem cells are key drivers of tumor progression and disease recurrence in multiple myeloma (MM). However, little is known about the regulation of MM stem cells. Here, we show that a population of MM cells, known as the side population (SP), exhibits stem-like properties. Cells that constitute the SP in primary MM isolates are negative or seldom expressed for CD138 and CD20 markers. In addition, the SP population contains stem cells that belong to the same lineage as the mature neoplastic plasma cells. Importantly, our data indicate that the SP and nonside population (NSP) percentages in heterogeneous MM cells are balanced, and that this balance can be achieved through a prolonged in vitro culture. Furthermore, we show that SP cells, with confirmed molecular characteristics of MM stem cells, can be regenerated from purified NSP cell populations. We also show that the percentage of SP cells can be enhanced by the hypoxic stress, which is frequently observed within MM tumors. Finally, hypoxic stress enhanced the expression of transforming growth factor β1 (TGF-β1) and blocking the TGF-β1 signaling pathway inhibited the NSP dedifferentiation. Taken together, these findings indicate that the balance between MM SP and NSP is regulated by environmental factors and TGF-β1 pathway is involved in hypoxia-induced increase of SP population. Understanding the mechanisms that facilitate SP maintenance will accelerate the design of novel therapeutics aimed at controlling these cells in MM.

The novel anticancer agent JNJ-26854165 induces cell death through inhibition of cholesterol transport and degradation of ABCA1

JNJ-26854165 (serdemetan) has previously been reported to inhibit the function of the E3 ligase human double minute 2, and we initially sought to characterize its activity in models of mantle cell lymphoma (MCL) and multiple myeloma (MM). Serdemetan induced a dose-dependent inhibition of proliferation in both wild-type (wt) and mutant (mut) p53 cell lines, with IC50 values from 0.25 to 3 μM/l, in association with an S phase cell cycle arrest. Caspase-3 activation was primarily seen in wtp53-bearing cells but also occurred in mutp53-bearing cells, albeit to a lesser extent. 293T cells treated with JNJ-26854165 and serdemetan-resistant fibroblasts displayed accumulation of cholesterol within endosomes, a phenotype reminiscent of that seen in the ATP-binding cassette subfamily A member-1 (ABCA1) cholesterol transport disorder, Tangiers disease. MM and MCL cells had decreased cholesterol efflux and electron microscopy demonstrated the accumulation of lipid whorls, confirming the lysosomal storage disease phenotype. JNJ-26854165 induced induction of cholesterol regulatory genes, sterol regulatory element-binding transcription factor-1 and -2, liver X receptors α and β, along with increased expression of Niemann-Pick disease type-C1 and -C2. However, JNJ-26854165 induced enhanced ABCA1 turnover despite enhancing transcription. Finally, ABCA1 depletion resulted in enhanced sensitivity to JNJ-26854165. Overall, these findings support the hypothesis that serdemetan functions in part by inhibiting cholesterol transport and that this pathway is a potential new target for the treatment of MCL and MM.

A moderate elevation of circulating levels of IGF-I does not alter ErbB2 induced mammary tumorigenesis

Background

Epidemiological evidence suggests that moderately elevated levels of circulating insulin-like growth factor-I (IGF-I) are associated with increased risk of breast cancer in women. How circulating IGF-I may promote breast cancer incidence is unknown, however, increased IGF-I signaling is linked to trastuzumab resistance in ErbB2 positive breast cancer. Few models have directly examined the effect of moderately high levels of circulating IGF-I on breast cancer initiation and progression. The purpose of this study was to assess the ability of circulating IGF-I to independently initiate mammary tumorigenesis and/or accelerate the progression of ErbB2 mediated mammary tumor growth.

Methods

We crossed heterozygous TTR-IGF-I mice with heterozygous MMTV-ErbB2 mice to generate 4 different genotypes: TTR-IGF-I/MMTV-ErbB2 (bigenic), TTR-IGF-I only, MMTV-ErbB2 only, and wild type (wt). Virgin females were palpated twice a week and harvested when tumors reached 1000 mm³. For study of normal development, blood and tissue were harvested at 4, 6 and 9 weeks of age in TTR-IGF-I and wt mice.

Results

TTR-IGF-I and TTR-IGF-I/ErbB2 bigenic mice showed a moderate 35% increase in circulating total IGF-I compared to ErbB2 and wt control mice. Elevation of circulating IGF-I had no effect upon pubertal mammary gland development. The transgenic increase in IGF-I alone wasn't sufficient to initiate mammary tumorigenesis. Elevated circulating IGF-I had no effect upon ErbB2-induced mammary tumorigenesis or metastasis, with median time to tumor formation being 30 wks and 33 wks in TTR-IGF-I/ErbB2 bigenic and ErbB2 mice respectively (p = 0.65). Levels of IGF-I in lysates from ErbB2/TTR-IGF-I tumors compared to ErbB2 was elevated in a similar manner to the circulating IGF-I, however, there was no effect on the rate of tumor growth (p = 0.23). There were no morphological differences in tumor type (solid adenocarcinomas) between bigenic and ErbB2 mammary glands.

Conclusion

Using the first transgenic animal model to elevate circulating levels of IGF-I to those comparable to women at increased risk of breast cancer, we showed that moderately high levels of systemic IGF-I have no effect on pubertal mammary gland development, initiating mammary tumorigenesis or promoting ErbB2 driven mammary carcinogenesis. Our work suggests that ErbB2-induced mammary tumorigenesis is independent of the normal variation in circulating levels of IGF-I.

Delivery of tumor-targeted immunotoxin by tumor-specific T cells (155.19)

Immunotherapy of cancer using monoclonal antibodies and adoptive transfer of lymphocytes is showing considerable promise. Based on experience with other cancer therapeutics immunotherapeutic modalities, targeting discrete molecular components of the tumor, will prove superior to a single effector system. “Multitargeting” approaches will not only prevent tumor immune escape, they will also allow safer and potent anticancer therapies. We have engineered antigen specific T cells so that they can target tumor cells directly, and then release a potent toxin linked to a monoclonal antibody molecule thereby targeting an independent tumor antigen to the tumor reactive T cell. These engineered T cells were tested in vitro and in vivo in a xenograft model of B-lymphoma. We found that tumor antigen specific T cells retain their anti-tumor activity and tumor homing abilities even when transduced with a gene encoding a chimeric monoclonal antibody-toxin. The release of the targeted immunotoxin molecule occurs only after the T cell has engaged its tumor target. The combination of these two distinct effector systems (T cells and immunotoxin) targeting two distinct tumor antigens have superior anti-tumor activity than a single system targeting a single antigen, with no greater toxicity. By combining two highly specific and partially effective strategies for tumor destruction, we achieved selective and more effective tumor killing.

Abstract 4133: Comparative gene expression and proteomic analysis of IGF-I and insulin signaling in a large panel of breast cancer cell lines

IGF-I signaling is involved in tumor progression and drug resistance and many anti-IGF-IR therapeutic agents are currently in clinical trials. Moreover, growing evidence also suggests that insulin signaling may play an important role in cancer development and progression. However, little is known regarding similarities and difference in IGF-I and insulin signaling in cancer, and there are currently no biomarkers to predict patient response to IGF targeted therapy. To gain a better understanding of these signaling pathways in human breast cancer, we measured the levels of insulin receptor (IR) and IGF-IR, and the activity of insulin and IGF-I, in a large panel of human breast cancer cell lines. Comparative gene expression analysis was performed using publicly available gene expression data and IR and IGF-IR mRNA levels in 17 breast cancer cell lines were measured by Q-RT-PCR. IGF-IR and IR levels were found to be highly variable in breast cancer cell lines. MCF7 and MDA-MB-134 have high levels of IGF-IR expression and MDA-MB-468 and ZR-75-1 have high levels of IR expression, relative to other breast cancer cell lines. Reverse phase protein array (RPPA) analysis using 134 different antibodies was performed on MCF7 cells stimulated with increasing doses of insulin or IGF-I. One Way ANOVA was performed to identify proteins affected by insulin and/or IGF stimulation. Maximal response to insulin and IGF-I stimulation was observed at a 10nM concentration of both ligands. Therefore, we further performed RPPA on 21 breast cancer cell lines treated with 10nM of insulin and IGF-I for 6 time points (5min, 10min, 30 min, 6hrs, 24hrs, and 48hrs). Spearman rank correlation was performed on IR and IGF-IR protein levels to mRNA levels from Q-RT-PCR. There was a significant correlation between IGF-IR protein and mRNA levels (r=0.559, p=0.024), but not between IR protein and mRNA levels. Principle component analysis showed that MCF7, MDA-MB-134, T47D and ZR-75-1 are insulin and IGF-I responsive. Results from ANOVA with contrast in MCF7 cells showed that insulin and IGF-I affected similar set of proteins at 10 minute and 24 hours time points, however, there were several proteins affected only by IGF-I or insulin stimulation. For example, phospho-estrogen receptor (p-ER) was found to be increased by 10 minutes IGF-I stimulation, but not by insulin stimulation. Beta-catenin and c-Myc were significantly suppressed by IGF stimulation while PARP was significantly suppressed by insulin stimulation at the 24 hour time point. Moreover, IGF affected twice the number of proteins compared to insulin at the 48 hour time point. For instance, Bcl2 and SMAD3 were suppressed and Raf and FOXO3a were increased by IGF stimulation after 48 hours of stimulation. Further statistical and system biology analysis of the temporal activation of signaling by IGF-I and insulin in the 21 cell lines is ongoing and will be presented.

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 4133.

Abstract 5056: Signaling pathways critical for insulin receptor substrate (IRS)-mediated disruption of MCF-10A acini formation

Insulin receptor substrate (IRS)-1 and IRS-2 are important adaptor proteins in insulin-like growth factor-I receptor (IGF-IR) signaling. IRS-1 and IRS-2 are expressed during mammary gland development and also in human breast tumors. In order to study the role of IRS-1 and IRS-2 in breast tumorigenesis, we overexpressed both IRS proteins in immortalized, non-transformed human mammary epithelial MCF-10A cells. It has been shown that MCF-10A cells form uniform, empty-lumen acini in three dimensional (3D) culture. We previously showed that overexpression of either IRS-1 or IRS-2 in MCF-10A cells disrupted the acini in 3D culture and resulted in extensive proliferation and disrupted apical-basal polarity. In both IRS-1 and IRS-2 overexpressing MCF-10A cells, an increase in tyrosine phosphorylation and association with p85 of both IRS proteins indicated that IRS-mediated signaling was activated. siRNA knockdown of the overexpressed IRS proteins reversed the disruption of MCF-10A acini, confirming that this is indeed an IRS-related event. In order to identify the critical effectors in IRS-mediated disruption of MCF-10A polarity and growth, we used small molecule inhibitors to screen multiple kinase signaling pathways upstream and downstream of the IRS proteins. Inhibition of Rac or atypical PKC (aPKC) didn't affect MCF-10A cell acini formation, however it abolished the IRS-mediated disruption of MCF-10A acini formation. Consistent with this, knockdown of Rac and aPKC by siRNA suppressed IRS-mediated disruption in acini formation. Rac belongs to the family of GTPase that regulates cell motility. aPKC is a key component of the PAR polarity complex, and has previously been shown to be involved in IRS-signaling in adipocytes. While the signaling mechanism of Rac and aPKC in the IRSs-induced disruption of acini is still unknown, we found that another component in the PAR polarity complex Par3 may associate with IRS proteins and leads to dissociation of the polarity complex. Taken together, overexpression of IRS-1 and IRS-2 disrupts the MCF-10A acini in 3D culture in part through Rac and aPKC pathways.

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 5056.

Sustained c-Jun-NH2-kinase activity promotes epithelial-mesenchymal transition, invasion, and survival of breast cancer cells by regulating extracellular signal-regulated kinase activation

The c-Jun NH(2)-terminus kinase (JNK) mediates stress-induced apoptosis and the cytotoxic effect of anticancer therapies. Paradoxically, recent clinical studies indicate that elevated JNK activity in human breast cancer is associated with poor prognosis. Here, we show that overexpression of a constitutively active JNK in human breast cancer cells did not cause apoptosis, but actually induced cell migration and invasion, a morphologic change associated with epithelial-mesenchymal transition (EMT), expression of mesenchymal-specific markers vimentin and fibronectin, and activity of activator protein transcription factors. Supporting this observation, mouse mammary tumor cells that have undergone EMT showed upregulated JNK activity, and the EMT was reversed by JNK inhibition. Sustained JNK activity enhanced insulin receptor substrate-2-mediated ERK activation, which in turn increased c-Fos expression and activator protein activity. In addition, hyperactive JNK attenuated the apoptosis of breast cancer cells treated by the chemotherapy drug paclitaxel, which is in contrast to the requirement for inducible JNK activity in response to cytotoxic chemotherapy. Blockade of extracellular signal-regulated kinase activity diminished hyperactive JNK-induced cell invasion and survival. Our data suggest that the role of JNK changes when its activity is elevated persistently above the basal levels associated with cell apoptosis, and that JNK activation may serve as a marker of breast cancer progression and resistance to cytotoxic drugs.

Estrogen and IGF-I Independently Down-Regulate Critical Repressors of Breast Cancer Growth

Background: Estrogen receptor and insulin-like growth factor (IGF) signaling pathways are important for both normal mammary gland development and breast cancer pathogenesis. Despite this evidence, cross-talk between these two critical mitogenic and survival pathways remains poorly understood, particularly at the level of downstream gene transcriptional networks.Methods: We performed microarray analysis on ER-positive MCF-7 breast cancer cells following stimulation with either estradiol (10nM) or IGF-I (10nM) for 3hr or 24hr. We defined an E2-IGF gene expression signature and examined the effect of the gene signature on time to recurrence in ER+ tumors in the publicly available NKI dataset. Q-RT-PCR was used to validate the effects of IGF-I and E2 on mRNA of repressed genes. To examine gene regulation further, MCF-7 cells were incubated with various signaling inhibitors and gene expression measured.Results: We found 183 probesets to be co-regulated by E2 and IGF-I after 3hr of stimulation and 454 probesets to be co-regulated at the 24hr time point. Patients with tumors that had the same set of genes up- and down-regulated had a poor outcome (p=7.04E-07). E2-IGF co-regulated genes showed a significant enrichment for down-regulated genes (p<0.001). The top 10% of down-regulated genes contained four (BLNK, SOCS2, CCNG2, and ING4) that have previously been shown to have tumor suppressor function and/or show loss in human breast tumors. We confirmed that E2 and IGF-I indeed repressed levels of these candidate genes. Blockade of ER by ICI 182780 (ICI) completely reversed E2-mediated repression but had little or no effect on IGF-mediated repression of these genes. Similarly, blockade of IGF-IR was able to completely reverse IGF-I-mediated repression of all four genes, but had essentially no effect upon E2-mediated repression. Inhibition of the PI3K pathway with LY294002 (20μM) affected short-term (3hr) down-regulation of BLNK and SOCS2 by both E2 and IGF-I, and CCNG2 by IGF-I. By 24 hours, LY completely reversed both E2 and IGF-I mediated repression of CCNG2, and significantly reversed both E2 and IGF-I repression of BLNK and SOCS2. Blockade of MEK1/2 with U0126 (10μM) had no effect on short-term repression by E2 or IGF-I, though after 24hr it affected both E2 and IGF-I repression of BLNK and SOCS2.Conclusions: E2 and IGF-I co-regulate a set of genes that affect breast cancer outcome. E2 and IGF-I down-regulate several critical tumor suppressor genes. While the down-regulation is independent of each other at the level of ER and IGF-IR, for some genes, there is convergence on the PI3K pathway for repression.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 1126.

Expression and Activity of Both IGF and Insulin Signaling Pathways in a Large Panel of Breast Cancer Cell Lines

BACKGROUND: Insulin and insulin like growth factor-I (IGF-I) are key regulators in growth and metabolism. IGF-I signaling is known to be involved in tumor progression and drug resistance, and growing evidence also suggests that insulin signaling may play an important role in cancer. To gain a better understanding of these signaling pathways in human breast cancer, we measured the levels of IR and IGF-IR, and the activity of insulin and IGF-I, in a large panel of human breast cancer cell lines.METHODS: Comparative gene expression analysis was performed using publicly available gene expression data among a panel of 51 breast cancer cell lines. Q-RT-PCR was used to validate IR and IGF-IR expression differences in 19 breast cell lines. For 8 breast cancer cell lines we immunoblotted for total IR and IGF-IR levels, as well as p-Akt and p-Erk1/2 following insulin and IGF stimulation. Reverse phase protein array (RPPA) analysis was performed on MCF7 cells stimulated with increasing doses of insulin or IGF-I.RESULTS: IR and IGF-IR mRNA levels measured by microarray on breast cancer cell lines showed divergent levels with cells positive or negative for expression of each gene. There was no obvious correlation of levels with breast caner subtype. Q-RT-PCR results were generally consistent with the gene expression data with cell lines categorized into four groups: high IGF-IR and low IR e.g. MCF7 and MDA-MB-134; low IGF-IR and high IR e.g. ZR-75-1 and MDA-MB-468; intermediate levels of IGF-IR and IR e.g. MDA-MB-231 and HCC1954; and low IGF-IR and IR e.g. MDA-MB-415 and HS-578T. IGF-IR protein levels correlated with Q-RT-PCR (Spearman Rank Correlation r=0.93, p=0.0067) whereas IR didn't. We found significant activation of Akt in both insulin and IGF treated MCF7 and MDA-MB-134 cells as well as Akt activation in IGF stimulated MDA-MB-453. Interestingly, significant Erk1/2 activation was observed only in insulin and IGF stimulated MCF7 and insulin stimulated AU565 cells. Cell lines that didn't respond to insulin or IGF stimulation generally had constitutively high p-Akt and/or p-Erk1/2. From our preliminary RPPA analysis in MCF7, we observed an increase in phosphorylation of IGF-IR, Akt, Erk1/2 and p70S6K upon increasing dose of IGF stimulation and a similar effect was also observed following insulin stimulation.DISCUSSION: IGF-IR and IR mRNA and protein levels are divergent in a panel of breast cancer cell lines with cells expressing mRNA for both, one alone, or neither receptor. IGF-IR and IR protein levels indicated similar divergent expression. Interestingly, response to both IGF-IR and insulin stimulation was restricted to cells showing high levels of IGF-IR. To better understand insulin and IGF activities in breast cancer, we are currently performing RPPA on a large panel of 21 breast cancer cell lines.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 4168.

BMS-536924 reverses IGF-IR-induced transformation of mammary epithelial cells and causes growth inhibition and polarization of MCF7 cells

PURPOSE

This study aimed to test the ability of a new insulin-like growth factor receptor (IGF-IR) tyrosine kinase inhibitor, BMS-536924, to reverse the ability of constitutively active IGF-IR (CD8-IGF-IR) to transform MCF10A cells, and to examine the effect of the inhibitor on a range of human breast cancer cell lines.

EXPERIMENTAL DESIGN

CD8-IGF-IR-MCF10A cells were grown in monolayer culture, three-dimensional (3D) culture, and as xenografts, and treated with BMS-536924. Proliferation, cell cycle, polarity, and apoptosis were measured. Twenty-three human breast cancer cell lines were treated in monolayer culture with BMS-536924, and cell viability was measured. MCF7, MDA-MB-231, and MDA-MB-435 were treated with BMS-536924 in monolayer and 3D culture, and proliferation, migration, polarity, and apoptosis were measured.

RESULTS

Treatment of CD8-IGF-IR-MCF10A cells grown in 3D culture with BMS-536924 caused a blockade of proliferation, restoration of apical-basal polarity, and enhanced apoptosis, resulting in a partial phenotypic reversion to normal acini. In monolayer culture, BMS-536924 induced a dose-dependent inhibition of proliferation, with an accumulation of cells in G(0)/G(1,), and completely blocked CD8-IGF-IR-induced migration, invasion, and anchorage-independent growth. CD8-IGF-IR-MCF10A xenografts treated with BMS-536924 (100 mg/kg/day) showed a 76% reduction in xenograft volume. In a series of 23 human breast cancer cell lines, BMS-536924 inhibited monolayer proliferation of 16 cell lines. Most strikingly, treatment of MCF7 cells grown in 3D culture with BMS-536924 caused blockade of proliferation, and resulted in the formation of hollow polarized lumen.

CONCLUSIONS

These results show that the new small molecule BMS-536924 is an effective inhibitor of IGF-IR, causing a reversion of an IGF-IR - mediated transformed phenotype.

Novel egg white based 3D cell culture system for breast cancer research

Abstract #4060

Introduction: Over the last few years, much attention has been paid to the development and utilization of three-dimensional (3D) cell culture to replace classical two-dimensional (2D) monolayer cell culture systems grown as a flat layer on plastic. Not completely surprisingly, there are tremendous differences between cells in 2D and 3D culture. However, currently available 3D cell culture media are expensive for regular use by the majority of research laboratories and thus large scale use of 3D cell culture system is presently cost prohibited. In our search for a reliable and economically viable replacement for the expensive commercial 3D media, we hypothesized that avian egg white could be a potential alternative.
 Methods: Egg white-based chamber slide: Separated egg white from the chicken eggs and coated each wells of an eight well culture chamber with 80μl of egg white by careful heating at 600C on a heating block. After 30-60 minutes, the egg white becomes a semi-solid that adheres to the bottom of the well. The unstuck egg white is washed out by adding 500µl of growth medium and removing it slowly using a Pasteur pipette.
 Cell culture and analysis: To each well 2x103 immortalized human breast epithelial cells (MCF10A), were added in 0.5ml of appropriate culture medium. We have analyzed the growth curve of the acini, lumen formation, apoptosis and cell proliferation at different days post-culture. Apico/basal polarization of the acini was analyzed using appropriate antibodies. We have also cultured IGFR1-transformed MCF10A cells, different established human cell lines (MCF7, HEK293, HeLa, LNCaP, and Saos-2), and MMTV-PyMT transformed mouse mammary epithelial cells in their appropriate growth media. For comparative studies, we used a well-established reconstituted basement membrane matrix preparation (BM).
 Results: Our analysis shows that this simple avian egg white based system supports growth of cells in 3D, with significantly decreased cost. Specifically, the growth of MCF10A in egg white-based medium results in formation of acini with hollow lumens, apoptotic clearance of the cells in the lumen, and apico/basal polarization comparable to what has been described using established 3D culture media. There was no significant difference in MCF10A proliferation and acini size between egg white and BM. We have also observed similar morphology for different established cell lines, oncogene-transformed MCF10A, and mouse mammary epithelial cells between egg white and BM.
 Conclusion: Our data convincingly argue that egg white can be used as a suitable alternative model for 3D cell culture studies. We strongly believe that this simple and inexpensive method should allow researchers to perform 3D cell culture on a regular basis, and thus result in a dramatic increase of utilization of the 3D cell culture in research.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 4060.

Mammary tumorigenesis and metastasis caused by overexpression of insulin receptor substrate 1 (IRS-1) or IRS-2

Insulin receptor substrates (IRSs) are signaling adaptors that play a major role in the metabolic and mitogenic actions of insulin and insulin-like growth factors. Reports have recently noted increased levels, or activity, of IRSs in many human cancers, and some have linked this to poor patient prognosis. We found that overexpressed IRS-1 was constitutively phosphorylated in vitro and in vivo and that transgenic mice overexpressing IRS-1 or IRS-2 in the mammary gland showed progressive mammary hyperplasia, tumorigenesis, and metastasis. Tumors showed extensive squamous differentiation, a phenotype commonly seen with activation of the canonical beta-catenin signaling pathway. Consistent with this, IRSs were found to bind beta-catenin in vitro and in vivo. IRS-induced tumorigenesis is unique, given that the IRSs are signaling adaptors with no intrinsic kinase activity, and this supports a growing literature indicating a role for IRSs in cancer. This study defines IRSs as oncogene proteins in vivo and provides new models to develop inhibitors against IRSs for anticancer therapy.

Epidermal growth factor induces insulin receptor substrate-2 in breast cancer cells via c-Jun NH(2)-terminal kinase/activator protein-1 signaling to regulate cell migration

The epidermal growth factor (EGF) and insulin-like growth factor (IGF) signaling pathways are critically involved in cancer development and progression. However, how these two signals cross-talk with each other to regulate cancer cell growth is not clearly understood. In this study, we found that EGF remarkably induced expression of major IGF signaling components, insulin receptor substrate (IRS)-1 and IRS-2, an effect that could be blocked by EGF receptor (EGFR) tyrosine kinase inhibitors. Although both extracellular signal-regulated kinase and c-Jun NH(2)-terminal kinase (JNK) signaling pathways were involved in the EGF up-regulation of IRS-1, the IRS-2 induction by EGF was specifically mediated by JNK signaling. Consistent with this, EGF increased IRS-2 promoter activity, which was associated with recruitment of activator protein-1 (AP-1) transcription factors and was inhibited by blocking AP-1 activity. Moreover, EGF treatment enhanced IGF-I and integrin engagement-elicited tyrosine phosphorylation of IRS and their downstream signaling, such as binding to phosphatidylinositol 3'-kinase regulatory subunit p85. Finally, repressing the induction of IRS-2 levels abolished the EGF enhancement of cell motility, suggesting that increased IRS-2 is essential for the EGF regulation of breast cancer cell migration. Taken together, our results reveal a novel mechanism of cross-talk between the EGF and IGF signaling pathways, which could have implications in therapeutic applications of targeting EGFR in tumors. Because AP-1 activity is involved in breast cancer progression, our work may also suggest IRS-2 as a useful marker for aggressive breast cancer.

The growth hormone receptor antagonist pegvisomant blocks both mammary gland development and MCF-7 breast cancer xenograft growth

Mammary gland development is dependent upon the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis, this same axis has also been implicated in breast cancer progression. In this study we investigated the effect of a GH antagonist, pegvisomant (Somavert, Pfizer), on normal mammary gland development and breast cancer xenograft growth. Intraperitoneal administration of pegvisomant resulted in a 60% suppression of hepatic IGF-I mRNA levels and upto a 70-80% reduction of serum IGF-I levels. Pegvisomant administration to virgin female mice caused a significant delay of mammary ductal outgrowth that was associated with a decrease in the number of terminal end buds and reduced branching and complexity of the gland. This effect of pegvisomant was mediated by a complete inhibition of both GH and IGF-IR-mediated signaling within the gland. In breast cancer xenograft studies, pegvisomant caused shrinkage of MCF-7 xenografts, with an initial 30% reduction in tumor volume, which was associated with a 2-fold reduction in proliferation and a 2-fold induction of apoptosis. Long-term growth inhibition of MCF-7 xenografts was noted. In contrast, pegvisomant had no effect on MDA-231 or MDA-435 xenografts, consistent with primary growth of these xenografts being unresponsive to IGF-I both in vitro and in vivo. In MCF-7 xenografts that regressed, pegvisomant had only minor effects upon GHR and IGF-IR signaling. This data supports previous studies indicating a role for GH/IGF in mammary gland development, and suggests that pegvisomant maybe useful for the prevention and/or treatment of estrogen receptor positive breast cancer.