Several vascular diseases including coronary artery disease, hypertension, stroke, and abdominal aortic aneurysm, have significant genetic underpinnings. Genome-wide association studies have unveiled many genetic loci associated with one or more of these diseases. However, the causative genes at most of these loci are yet to be determined, which hampers the translation of the genetic findings into a better understanding of the disease mechanisms and the identification of new therapeutic targets. Here, in an integrative functional genomics analysis of these loci, we identify a panel of likely causal genes, some of which are pleiotropic for more than one of these vascular diseases. Pooled CRISPR knockout screen analyses of these likely causal genes indicate that many of them influence vascular smooth muscle cell behaviour, and validation experiments of selected genes confirm that FES, BCAR1, CARF and SMARCA4 exert such effects. Further functional experiments focusing on FES, a pleiotropic gene for both coronary artery disease and hypertension, show that it modulates the expression of genes involved in vascular remodeling and that Fes knockout in mice promotes atherosclerosis as well as raises blood pressure. These findings provide an insight into the genetic basis of vascular diseases and inform targets for therapeutic development.

Abstract In recent years, immunotherapy of patients with higher-risk non-muscle invasive bladder cancer (NMIBC) in North America has relied on the use of the TICE strain of BCG. However, limitations in the supply chain have warranted investigation of the therapeutic benefit of other strains of BCG, such as BCG-Russia. Trained immunity, a form of innate immune memory, is now widely believed to be an important component of the therapeutic benefit of BCG. Therefore, in the present study we compared the effects of BCG-TICE and BCG-Russia on the acquisition of trained immunity and related secondary immune responses. C57BL/6 mice received a single intravenous injection of BCG-Russia or BCG-TICE. Four weeks later, bone marrow was collected for flow cytometric analysis of hematopoietic stem and progenitor cell (HSPC) populations, generation of bone marrow-derived macrophages, functional assessment of trained immunity, and transcriptomic profiling. Compared with BCG-Russia, BCG-TICE elicited stronger levels of trained immunity, characterized by higher production of several proinflammatory cytokines upon secondary activation. BCG promoted the expansion of HSPCs independent of strain. BCG-TICE was linked to upregulation of key inflammation-related genes and enrichment of functionally relevant pathways. The results of this study reveal strain-dependent differences in the ability of BCG to induce innate immune memory and inflammatory pathways that could ultimately determine efficacy of immunotherapy of patients with NMIBC.

The standard-of-care for patients with higher-risk non-muscle invasive bladder cancer (NMIBC) after tumour resection is intravesical administration of Bacillus Calmette-Guérin (BCG). While this form of adjuvant immunotherapy has improved recurrence-free and progression-free survival, a large proportion of patients experience recurrences within a year of diagnosis. The reasons for this high rate of early recurrence following BCG therapy remain unclear; however, inadequate activation of systemic immunity may be a contributing factor. To address this, we analysed the transcriptomic and chromatin accessibility profiles of peripheral blood mononuclear cells obtained from patients with NMIBC at single-cell resolution before BCG immunotherapy and after five induction doses of BCG. Monocytes from patients who experienced disease recurrence within a year of initiation of BCG therapy (BCG non-responders) exhibited a pro-inflammatory phenotype consistent with age-related immunosenescence prior to BCG immunotherapy. Moreover, inflammation-associated pathways that were active before initiation of BCG therapy in the BCG non-responders were down-regulated after five instillations of BCG. In contrast, these pathways were quiescent before BCG therapy in patients who remained disease-free for at least a year but were markedly up-regulated after five doses of BCG. Genomic regions with accessible chromatin were enriched in activator protein 1 (AP-1) binding sequences in monocytes from BCG-non-responders prior to BCG therapy. AP-1 is a central regulator of the inflammatory phenotype associated with immunosenescence. Our findings indicate that a pre-existing state of innate immunosenescence underlies early disease recurrence following BCG. Patients unlikely to benefit from BCG may be offered alternative therapies early in their disease journey.

Calpains are a family of 15 calcium-activated cysteine proteases that have emerged as potential antimetastatic targets in breast cancer. Calpain-1 and calpain-2 are ubiquitously expressed heterodimers composed of unique catalytic subunits (encoded by Capn1 and Capn2 , respectively) and a common regulatory subunit (encoded by Capns1 ). Genetic disruption of Capns1 abolishes calpain-1 and calpain-2 activity. Using CRISPR-Cas9 mediated Capns1 knockout, we validated calpains-1/2 as promising therapeutic targets in a mouse model of mammary carcinoma. Capns1 knockout impaired cell invasion by 53 ± 10% in vitro and reduced lung metastasis by 68 ± 12% in an orthotopic engraftment mouse model.

Calpain-1 and calpain-2 are heterodimeric proteases consisting of a common small regulatory subunit CAPNS1 and a large catalytic subunit, CAPN1 or CAPN2, respectively. These calpains have emerged as potential therapeutic targets in cancer and other diseases through their roles in cell signaling pathways affecting sensitivity to chemotherapeutic and targeted drugs and in promoting metastasis. While inhibition of calpains has the potential to provide therapeutic benefit to cancer patients, there are currently no clinically approved active site-directed drugs that specifically and effectively inhibit them. However, the structures of calpain-1 and calpain-2 make them susceptible to allosteric inhibition aimed at interfering with heterodimerization of the catalytic and regulatory subunits, which is necessary for stability and proteolytic activity. Split-Nanoluciferase biosensors were generated to quantify the protein-protein interactions between the calcium-binding penta-EF-hand domains of CAPN1 or CAPN2 and CAPNS1. These biosensors were used to quantify the heterodimer dissociation constants (KD) of calpain-1 and calpain-2, estimated at 185 nM and 509 nM, respectively, in the presence of 5 mM Ca2+; and 362 nM and 1651 nM, respectively, in the presence of Mg2+. The half-maximal Ca2+ concentrations supporting these protein-protein interactions for calpain-1 and calpain-2 were 59.9 μM and 940.8 μM, respectively. Molecular modeling, based on the crystal structure of calpain-2, was used to predict 20 residues of the penta-EF-hand domains that contribute to heterodimerization. Individual point mutation of CAPNS1 at Q263 reduced the catalytic activity of calpain-2 to 51.0 ± 6.4% in live cells.

Dysregulated calpain-1 and calpain-2 protease activity linked to several diseases has encouraged efforts to explore inhibiting calpain to provide therapeutic benefits. However, there are currently no clinically approved drugs that specifically target calpain functionality. To address this unmet need, we carried out in silico drug discovery efforts to identify small molecules capable of modulating calpain activity. Our approach is based on the observation that heterodimer formation of the calpain-2 catalytic (CAPN2) and regulatory (CAPNS1) subunits is needed for both proteolytic activity and CAPN2 stability. In recognition of this obligate protein-protein interaction (PPI), the CAPN2-CAPNS1 interface was targeted with nearly 3.6 million small molecules to find candidates that bind at the interface with high affinity and introduce steric clashes capable of altering heterodimerization or the conformation of CAPN2, thereby modulating proteolytic activity. Twenty small molecules predicted to disrupt the most hydrogen bonds at the CAPN2-CAPNS1 interface were validated experimentally. Five small molecules inhibited calpain activity by 53.6 ± 4.1, 36.8 ± 38.3, 31.1 ± 17.5, 69.8 ± 27.3, and 47.1 ± 18.5%, while two enhanced protease activity by 163.0 ± 41.9 and 129.2 ± 11.9%. Unexpectedly, the effects of these seven molecules on the CAPN2-CAPNS1 PPI assay did not correlate with their effects on protease activity. Molecular simulation showed that small molecules that modulate calpain activity without abolishing heterodimerization do so by altering the conformational changes needed for the activity. This apparent allosteric mechanism paves the way for developing novel therapeutic solutions for modulating the calpain activity in various diseases associated with calpain dysregulation.

Bone morphogenetic protein-9 (BMP9) has been implicated as a regulator of metastasis and tumor angiogenesis, with contrasting studies demonstrating both pro- and antiangiogenic roles for BMP9 across different cancer cell lines and animal models. However, these works have yet to define the contribution of the type-II BMP receptor (BMPR-II) to these processes, or assess whether the effects of BMP9 are mediated via actions on the endothelium, the tumor, or its microenvironment. Here, we demonstrate that the heterozygous (Bmpr2EC+/-) or homozygous (Bmpr2EC-/-) deletion of BMPR-II in the pulmonary endothelium is associated with increased overall burden and vascularization of metastases in the lungs of mice subjected to the EO771 orthotopic engraftment model of metastatic breast cancer. These increases, relative to Bmpr2EC+/+ littermates, were observed despite equivalent primary mammary tumor growth across mice of all genotypes. In vitro, secreted factors or extracellular matrix components from BMPR-II-silenced human pulmonary arterial endothelial cells (HPAECs) did not alter EO771 proliferation relative to controls. However, endothelial BMPR-II depletion did eliminate the capacity of BMP9 to suppress both HPAEC migration to VEGF165 and EO771 transmigration across an HPAEC monolayer. In a tail vein injection model, the short-term establishment of EO771 cell metastatic lesions was equivalent in the lungs of female Bmpr2EC+/- and Bmpr2EC-/- mice, relative to Bmpr2EC+/+ controls, suggesting that the enhanced lung tumor burden observed in orthotopically implanted mice with endothelial Bmpr2 deletion is likely a consequence of enhanced tumor vascularization, rather than altered lung retention and engraftment. Our findings identify an important role for endothelial BMPR-II signaling in regulating the vascularization of metastatic lesions in the lungs.

Representative immune profiling flow plots and splenic and tumor immune profiling.

Homeostatic immunoregulatory mechanisms that prevent adverse effects of immune overaction can serve as barriers to successful anticancer immunity, representing attractive targets to improve cancer immunotherapy. Here, we demonstrated the role of the nonreceptor tyrosine kinase Fes, abundantly expressed in immune cells, as an innate intracellular immune checkpoint. Host Fes deficiency delayed tumor onset in a gene dose-dependent manner and improved tumor control, survival, doxorubicin efficacy, and sensitized tumors to anti-PD-1 therapy in murine triple-negative breast cancer and melanoma models. These effects were associated with a shift to an antitumorigenic immune microenvironment. Fes-deficient macrophages displayed increased Toll-like receptor signaling, proinflammatory cytokine production, and antigen presentation to and activation of T cells, leading to increased cancer cell killing in vitro and tumor control in vivo. This study highlights Fes as an innate immune checkpoint with potential as a therapeutic target and a predictive biomarker to guide immune checkpoint inhibitor treatment.Significance: Fes activity modulates the inflammatory cytokine presentation and T-cell priming capabilities of macrophages, supporting the potential of Fes as a target for developing therapeutic and biomarker strategies to improve cancer immunotherapy.

In breast cancer, progression from localized stage I to distant metastatic stage IV disease is associated with a reduction of 5-year survival from nearly 100% to 23.2%. Expression of the calcium-activated protease isoforms calpain-1 and calpain-2 has been correlated with cell migration and invasion in vitro, metastatic potential in preclinical mouse models of cancer, and breast cancer prognosis in patients. It is unclear which of these two calpain isoforms is responsible for the apparent metastatic potential of cancer cells. Here, we demonstrate that while individual CRISPR-Cas9 knockouts of either CAPN1 or CAPN2 genes (encoding the catalytic subunits of calpain-1 and -2, respectively) reduce in vitro migration and marginally suppress in vivo metastasis, genetic disruption of both calpain-1 and calpain-2 through knockout of the CAPNS1 gene (encoding the common regulatory subunit of calpain-1 and -2) diminishes metastasis by 83.4 ± 13.6% in a mouse xenograft model of human triple-negative breast cancer. The effect of calpain-1/2 deficiency was replicated in vitro with a modified cell-permeable calpastatin (CAST)-based peptide inhibitor (cell migration reduced to 53.5 ± 11.0% of vehicle control). However, this peptide inhibitor was not effective in vivo at reducing metastasis under the conditions used (vehicle vs. CAST, 1.12 ± 1.35 lung metastases per mm2 vs. 0.34 ± 0.20 metastases per mm2), likely due to rapid clearance, as indicated by the short serum half-life. This work demonstrates that calpain-1/2 disruption effectively abrogates metastasis and provides rationale for development of effective calpain inhibitors.

Immunotherapy is a powerful pillar of cancer therapy that still faces barriers due to cancer-mediated immunosuppression. Immunogenic cell death recruits and activates antigen-presenting cells (APCs) through engagement of pattern recognition receptors (PRRs), leading to pro-inflammatory Signal 3 cytokine production required for full activation of adaptive immune cells, including cytotoxic T lymphocytes (CTLs). The Fes tyrosine kinase suppresses innate immune responses in APCs by inhibiting PRR signaling and regulating cytokine trafficking. In non-cancer contexts, Fes may guard against consequences of overactive innate immunity, such as endotoxic shock or autoimmunity. However, this inhibitory effect on APCs may serve as a checkpoint to suppress successful anti-cancer immunotherapy by obstructing efficient priming of cancer specific CTLs. We hypothesize that Fes inhibition in APCs will improve Signal 3 cytokine signaling, resulting in greater adaptive immunity and tumor control. Using bone marrow derived macrophages (BMDMs) from wildtype (WT) or Fes knockout (fes-/-) mice, we assessed LPS-induced PRR signalling by immunoblot analysis, production of key Signal 3 cytokines by multiplex ELISA, and the level of cell-associated cytokines by flow cytometry. The ability of BMDMs to prime CTLs was assessed in antigen cross-presentation co-cultures with OT-1 T cells. Using E0771 and B16F10 syngeneic orthotopic mouse engraftment models, we compared the efficacy of doxorubicin and anti-PD-1 to control tumor growth and prolong survival in WT and fes-/- mice. Tumors and spleen immune profiles were analyzed by flow cytometry. WT or fes-/- BMDMs were adoptively transferred into E0771 and B16F10 tumours to directly assess their relative ability to control tumour growth. fes-/- BMDMs displayed improved PRR signaling, increased IFNβ, IL-12, and TNFα secretion, and greater levels of internal and cell-surface IL-12 following LPS stimulation. In antigen cross-presentation assays, LPS stimulated fes-/- BMDMs had improved CTL priming. Tumor control and survival were greater in fes-/- mice in both the E0771 and B16F10 engraftment models. Doxorubicin and the combination of doxorubicin and anti-PD-1 were more effective in fes-/-. This was especially striking in the B16F10 model, which is known to be resistant to PD-1 therapy. Immune profiling of tumors showed increased CTL and NK cell activation and PD-1 positivity, and a shift from predominately M2- to M1-polarized tumor associated macrophages in fes-/- mice. Intratumorally injected M1-polarized fes-/- BMDMs were better able to control tumor growth in both E0771 and B16F10 models. Fes acts as an innate immune checkpoint whose inhibition may enhance anti-cancer immunotherapy. We believe this effect is due to an increase in inflammatory signalling, and improved signal 3 cytokine signalling in fes-/- APCs. Brian J. Laight, Danielle Harper, Natasha Dmytryk, Connie S. Zhang, Changnian Shi, Sameh Basta, Madhuri Koti, Peter A. Greer. The Fes kinase plays an innate immune checkpoint role to suppress CD8+ T cell mediated anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6132.

Abstract Immunotherapies are a promising emerging pillar of cancer treatment, but they still face many barriers due to the immunosuppressive nature of cancer. Cancer immunotherapy relies on the interplay between innate and adaptive immune responses. One way of stimulating such responses, known as immunogenic cell death (ICD), involves the release of tumour-associated antigens and damage associated molecular patterns (DAMPs). These DAMPs function to recruit and activate innate immune cells, including antigen-presenting cells (APCs), through engagement of pattern recognition receptors (PRRs), subsequently leading to production of the pro-inflammatory Signal 3 cytokines required for activation of adaptive immune cells (e.g., cytotoxic T lymphocytes [CTLs] and natural killer [NK] cells). The tyrosine kinase Fes suppresses innate immune responses in APCs by inhibiting components of the PRR signaling cascade. In non-cancer contexts, the negative regulation of APCs by Fes may guard against consequences of overactive innate immunity, including endotoxic shock or autoimmune disease. However, this same inhibitory effect on APC function may also serve as a checkpoint to successful anti-cancer immunotherapy, by obstructing efficient priming of cancer specific CTLs by APCs. Therefore, by inhibiting Fes, we hypothesize there will be greater Signal 3 cytokine production, resulting in greater CTL activation, and therefore improved tumor control. Using bone marrow derived APCs, including macrophages (BMDMs) and dendritic cells (BMDCs), from wildtype (WT) or Fes knockout (fes-/-) mice, we have shown through both Western blotting and flow cytometry analysis, that PRR signal transduction cascades are suppressed by Fes and increase levels of Signal 3 cytokines produced by fes-/- APCs. This includes higher levels of cell associated IL-12 in fes-/- APCs. Using syngeneic orthotopic mouse engraftment models of triple negative breast cancer (EO771) and melanoma (B16-F10) we showed that treatment with doxorubicin (which induces ICD) or anti-PD-1 (immune checkpoint inhibitor) plus doxorubicin controls tumor growth and prolongs survival to a greater extent in fes-/- mice. Immunophenotyping of tumors and spleens from these mice showed higher levels of activated CTLs and skewing of macrophages to a M1 state in fes-/- mice. SIINFEKL peptide loaded-BMDM/BMDCs from fes-/- mice were also more effective at priming CTLs from OT-1 mice (which express a T cell receptor that recognizes the SIINFEKL peptide) in antigen cross-presentation co-culture assays. These results implicate Fes as a potential novel immune checkpoint whose inhibition may enhance anti-cancer immunotherapy by suppressing its role in dampening inflammatory Signal 3 cytokine production by APCs. I will present recent data exploring the role of Fes in regulating the expression and trafficking of IL-12 in APCs to better understand the molecular basis of improved CTL activation by fes-/- APCs. Citation Format: Julian Simonetti, Brian J. Laight, Natasha Dmytryk, Danielle Harper, Yan Gao, Changnian Shi, Madhuri Koti, Sameh Basta, Peter A. Greer. The FES tyrosine kinase as an emerging target for cancer immunotherapy [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Optimizing Therapeutic Efficacy and Tolerability through Cancer Chemistry; 2024 Dec 9-11; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(12_Suppl):Abstract nr A017.

Background Failure of immunotherapy in high-grade serous ovarian cancer (HGSC) may be due to high levels of transforming growth factor-β (TGF-β) in ascites or tumour immune microenvironment (TIME). Here, we test whether coordinated blockade of TGF-β and PD-L1 with bintrafusp alfa (BA) can provoke anti-tumour immune responses in preclinical HGSC models. Methods BA is a first-in-class bifunctional inhibitor of TGF-β and PD-L1, and was tested for effects on overall survival and altered TIME in syngeneic HGSC models. Results Using a mouse ID8-derived HGSC syngeneic model with IFNγ-inducible PD-L1 expression, BA treatments significantly reduced ascites development and tumour burden. BA treatments depleted TGF-β and VEGF in ascites, and skewed the TIME towards cytotoxicity compared to control. In the BR5 HGSC syngeneic model, BA treatments increased tumour-infiltrating CD8 T cells with effector memory and cytotoxic markers, as well as cytolytic NK cells. Extended BA treatments in the BR5 model produced ∼50% BA-cured mice that were protected from re-challenge. These BA-cured mice had increased peritoneal T-effector memory and NK cells compared to controls. Conclusions Our preclinical studies of BA in advanced ovarian cancer models support further testing of BA as an improved immunotherapy option for patients with advanced ovarian cancer.

Activating the immune system is crucial for successful cancer immunotherapies, various proteins, such as the Fes non-receptor tyrosine kinase exist to limit activation and maintain homeostasis. However, in cancer settings, this serves as a barrier to the desired effects of immune activation following immunomodulatory treatment. Here, we demonstrate the role of Fes, a protein abundantly expressed in macrophages, as a novel innate intracellular immune checkpoint. Fes inactivity is associated with delayed tumour onset in a dose-dependent manner, and its deletion delays tumour growth, improves survival, enhances response to doxorubicin treatment, and sensitizes resistant tumours to PD-1 immune checkpoint inhibition. These effects are associated with an increase in Toll-like receptor signaling in antigen presenting cells, leading to an increase in proinflammatory cytokine production and cytotoxic T cell effector functions. Furthermore, we demonstrate a novel role for Fes in regulating the presentation of IL-12 on macrophage cell surfaces to enhance T-cell activation. Our results highlight Fes as a novel innate immune checkpoint with potential to serve as predictive biomarker to effective immune checkpoint blockade, and a potential novel therapeutic target for improved response to immunotherapy.### Competing Interest StatementThe authors have declared no competing interest.

Abstract Calpains are a family of 15 calcium-activated cysteine proteases that have emerged as potential therapeutic targets in triple negative breast cancer (TNBC). They regulate the function of their substrates via limited proteolytic processing and are involved in both pro- and anti-apoptotic signaling pathways, as well as membrane-cytoskeletal remodeling events associated with cell migration and invasion. The most well-understood members of the calpain family are the classical calpain-1 and calpain-2 isoforms, which are ubiquitously expressed heterodimers each consisting of a large catalytic subunit, encoded by the capn1 and capn2 genes, respectively, and a common small regulatory subunit encoded by capns1. Overexpression of calpain-1 and calpain-2 has been associated with shorter survival in HER2+ breast cancer and TNBC, respectively. We hypothesize that inhibition of calpain-1 and calpain-2 may be exploited to improve tumor response to cytotoxic chemotherapy and suppress metastasis. CRISPR-Cas9 mediated knockout of capns1 in AC2M2 mouse mammary carcinoma cells, which results in a loss of both calpain-1 and calpain-2 activity, disrupts migration and invasion in vitro and impedes lung metastasis in tail vein and orthotopic engraftment mouse models. Calpain knockout also sensitizes AC2M2 cells to the microtubule stabilizing drug paclitaxel, and preliminary results suggest that cancer cell intrinsic calpain depletion may prevent neoadjuvant chemotherapy-induced metastasis. To explore potential off-target effects associated with systemic calpain inhibition, we have established a novel transgenic mouse with conditional deletion of capns1 in its hematopoietic stem cell lineage. By comparing the immune profiles of wild-type and capns1 knockout mice, we aim to better understand how calpain inhibitors will affect various immune cell populations and their respective functions. We plan to extend this understanding to anticancer immunity by conducting tumor immunophenotyping experiments in syngeneic orthotopic engraftment models using wild-type and capns1 knockout mice. At present, no clinically relevant calpain inhibitors are available. However, using genetic approaches, we have validated calpain-1 and calpain-2 as relevant therapeutic targets in TNBC, providing rationale for the development of selective calpain inhibitors. Citation Format: Danielle Harper, Ivan Shapovalov, Samantha Cockburn, Jenny Min, Yan Gao, Peter A. Greer. Genetic disruption of CAPNS1 impedes triple-negative breast cancer metastasis: A case for selective calpain-1/2 inhibitors [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Optimizing Therapeutic Efficacy and Tolerability through Cancer Chemistry; 2024 Dec 9-11; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(12_Suppl):Abstract nr A009.

Abstract Calpain-1 and calpain-2 are heterodimeric calcium-dependent cysteine proteases composed of the catalytic subunits CAPN1 or CAPN2, respectively, and the common regulatory subunit CAPNS1. They are associated with cancer progression, metastasis, and treatment resistance in breast cancer. Here, we present novel insights into the therapeutic potential of calpain inhibition by combining genetic disruption and preclinical mouse tumor models and biosensor-based detection of calpain heterodimerization with ongoing efforts to discover small-molecule and peptide inhibitors. CRISPR-Cas9-mediated knockout of CAPN1, CAPN2, or CAPNS1 in MDA-MB-231 human triple-negative breast cancer (TNBC) cells revealed that disruption of both calpains, through CAPNS1 knockout, significantly reduced cell migration and inhibited spontaneous metastasis in a mouse orthotopic engraftment model by over 80%. Individual knockouts of CAPN1 or CAPN2 also reduced metastasis but to a lesser extent, highlighting the necessity of dual inhibition for optimal therapeutic effect. In parallel, we have been actively seeking small molecules and peptide inhibitors to target calpain through two approaches: inhibiting the PEF-PEF interaction that mediates heterodimerization using small molecules; and targeting the active site using a calpastatin (CAST)-based peptide. To identify small molecules capable of disrupting the PEF-PEF interaction, we conducted in silico screens of over 3.6 million compounds from several libraries. These compounds were evaluated based on their calculated binding affinity and potential to sterically hinder the conformational changes required for calpain activity. The CAST-based peptide inhibitor was designed based on the active site binding B-domain and tested on a purified calpain-2. These efforts lay the groundwork for novel therapeutic approaches targeting calpain-1 and calpain-2, which have emerged as promising targets for preventing metastasis in TNBC. We will present our progress in identifying and validating these small molecules and peptides for further development. Citation Format: Ivan Shapovalov, Pitambar Poudel, Shailesh K. Panday, Danielle Harper, Jung Yeon Min, Yan Gao, Kazem Nouri, Emil Alexov, Peter A. Greer. Targeting calpain-1 and calpain-2 for prevention of breast cancer metastasis: In vivo insights and drug discovery approaches. [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Optimizing Therapeutic Efficacy and Tolerability through Cancer Chemistry; 2024 Dec 9-11; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(12_Suppl):Abstract nr A016