Research

The KeyHunt Laboratory is focused on identifying novel therapeutic strategies and prognostic markers based on the alteration in the G1/S and G2/M checkpoint in tumor cells focusing on solid tumors such as breast, sarcoma, pancreatic and lung cancers.  We are currently involved in five areas of research, which fall into translational and basic research categories:

1) Inhibition of LMW forms of cyclin E as a therapeutic target in combination therapy for triple negative breast cancer.

2) Delineation of how the alteration of cyclin E, a G1 cyclin, could lead to the tumorigenic phenotype and determination of the oncogenic potential of the altered forms of cyclin E in breast cancer. 

3) Determination of the mechanism of action of intracellular elastase and its inhibitor elafin in tumorigenesis and subsequent metastasis.

4) Examination of mechanisms of action and resistance to CDK4/6 inhibitors in ER positive breast cancer patients.

5) Identification of novel treatment strategies, targeting the cell cycle, for soft-tissue sarcomas.

The translation of these research directions into clinical trials is the main focus of our laboratory. Below, we provide examples of projects that can take our findings from bench to the clinic. 

The KeyHunt Laboratory was the first to discover that the cyclin E, a key regulator in the G1/S transition is altered in breast cancer through the generation of low molecular weight (LMW) isoforms, a result of post-translational cleavage by the elastase class of serine proteases.  Specifically, they have developed in vivo models to examine the role of LMW-E in oncogenesis and discovered that the LMW-E isoforms are potent oncogenes that act early in the etiology of breast cancer (1-4).  They are also using these unique genetically engineered mouse models to interrogate the secondary oncogenic events induced by cyclin E early on in the neoplastic process (5,6). Through the molecular analysis of the inducible murine transgenic model of LMW-E mediated tumorigenesis, they have mapped some of the early events in the pre-neoplastic mammary gland that gives rise to aggressive tumors with high metastatic potential. These events include induction of DNA damage, upregulation of several genes involved in unregulated DNA replication and G2/M transition. They then went on to elucidate the mechanism of LMW-E mediated oncogenicity through identification and characterization of novel binding proteins and substrates for LMW-E. Protein microarray analysis identified the histone acetyltransferase (HAT) Hbo1 as a novel cyclin E/CDK2 substrate that mediates the cancer-stem-cell like phenotype. Other studies revealed that: Cyclin E is a downstream oncogenic target of PKCiota, and that activation of PKCiota by PI3K would further activate the signaling between PKCiota and cyclin E (7); LMW-E is a mediator of HER-2 action in breast cancer and renders letrozole therapy ineffective in breast cancer cells that express both aromatase and ER (8,9). Lastly, they identified ATP-citrate lyase (ACLY) as a novel interacting protein of LMW-E in the cytoplasm  (10). LMW-E upregulates ACLY enzymatic activity and ACLY is required for LMW-E mediated transformation, migration and invasion in vitro, as well as tumor growth in vivo.

Their research in this area has been funded by several R01 grants R01CA087548 (renewed successfully for 15 years), R01CA087548 (renewed successfully for 15 years), R01CA152228 (which funded a clinical trial that stemmed from cyclin E work - NCT01624441) and R01CA223772, whose aim is to interrogate if and how the expression of LMW-E early in the pre-invasive breast cancer (i.e. ductal carcinoma in situ) results in induction of genomic alteration leading to an invasive carcinoma. To this end they are currently examining the role of cytoplasmic cyclin E in differentiating indolent versus high-risk ductal carcinoma in situ (DCIS) in patients, and in cyclin E inducible cell lines and mouse models.  The successful completion of these studies will delineate those early oncogenic events in patients diagnosed with DCIS and provide the rationale to use LMW-E as a biomarker to identify the DCIS cases who could benefit from aggressive treatment, versus those (with no cytoplasmic cyclin E) who can be monitored without the need for aggressive intervention.

This figure is taken from: PMID:30194068.

The unique biochemical activities of LMW-E versus FL cyclin E and their consequences. (A) (i) Cyclin E (FL 50 kDa) is an activating subunit of CDK2 that promotes kinase activity (small yellow star) during the G1-S-phase transition. Tumor-specific LMW-E isoforms are generated by (ii) alternative translation from methionine 46 (40 kDa) and (iii) NE-mediated cleavage of full-length cyclin E at two N-terminal sites (45/44 kDa and 35/33 kDa; doublets due to phosphorylation events). LMW-E isoforms demonstrate higher binding affinity for CDK2, promoting hyperactivation of the kinase (large yellow star). (iv) In western blot analysis of normal (N) and tumor (T) tissue (using a C-terminally-directed antibody), LMW-E isoforms characteristically resolve as five distinct bands beneath FL cyclin E. In half of LMW-E-expressing breast tumors, cyclin E is also overexpressed; in the other half, however, LMW-E is expressed in the absence of full-length cyclin E (B). (i) When the pRb pathway is unaltered by oncogenic events, hypophosphorylated pRb binds to and sequesters E2F family transcription factors in G0-phase. (ii) FL cyclin E activates CDK2, leading to the hyperphosphorylation and inactivation of pRb, thereby releasing E2Fs to activate S-phase gene expression and progression. (iii) However, CDK inhibitors (e.g. p27) can inhibit the FL cyclin E-CDK2 complex (even if FL cyclin E is overexpressed) and prevent S-phase progression. (iv) Hyperactive LMW-E-CDK2 complexes can localize to the nucleus and hyperphosphorylate pRB; (v) even in the presence of CDK inhibitors, thereby promoting insensitivity to negative growth signals. (C) Hyperactive LMW-E-CDK2 complexes have other consequences. (i) FL Cyclin E-CDK2 can phosphorylate the substrate HBO-1; however, (ii) only constitutive hyperphosphorylation by LMW-E-CDK2 can promote HBO-1-dependant EMT and stemness properties, suggesting that cell cycle context-independent phosphorylation of HBO-1 alters its histone acetyltransferase activity in a pro-tumorigenic manner. (D) The proper timing of DNA replication and mitosis is essential to genome integrity. (i) One mechanism to ensure the fidelity of this process is feedback control through CDC25c, which promotes the proper timing of mitotic entry and exit through the activation of cyclin B-CDK1 and PLK1. (ii) Overexpression of FL cyclin E results in the improper phosphorylation of CDC25c and premature mitotic entry, but maintains the phosphorylation of CDC25c, delaying mitotic progression to cytokinesis and thereby largely preventing genomic instability. (iii) LMW-E overexpression also initiates premature mitotic entry; however unlike FL cyclin E, LMW-E cannot sustain CDC25c phosphorylation, resulting in faster mitotic exit and genomic instability. (iv) Genomic instability is further promoted by centrosome amplification induced by both FL cyclin E and LMW-E overexpression. (E) (i) FL cyclin E is largely restricted to the nucleus and therefore has limited opportunities to interact with cytoplasmic proteins. (ii) In contrast, LMW-E lacks an N-terminal nuclear localization signal promoting its accumulation in the cytoplasm where it can interact with novel binding partners including ACLY. LMW-E-CDK2 enhances ACLY activity (independent of phosphorylation), thereby promoting intracellular lipid accumulation and pro-tumorigenic phenotypes, including migration and invasion.

Publications & Clinical Trials Resulting From This Project

1.  Akli S, Van Pelt CS, Bui T, Multani AS, Chang S, Johnson D, Tucker S, Keyomarsi K. Overexpression of the low molecular weight cyclin E in transgenic mice induces metastatic mammary carcinomas through the disruption of the ARF-p53 pathway. Cancer Res. 2007;67(15):7212-22. PMID: 17671189

2. Bagheri-Yarmand R, Biernacka A, Hunt KK, Keyomarsi K. Low molecular weight cyclin E overexpression shortens mitosis, leading to chromosome missegregation and centrosome amplification. Cancer Res. 2010;70(12):5074-84. doi: 10.1158/0008-5472.CAN-09-4094. PMID: 20530685

3. Bagheri-Yarmand R, Nanos-Webb A, Biernacka A, Bui T, Keyomarsi K. Cyclin E deregulation impairs mitotic progression through premature activation of Cdc25C. Cancer Res. 2010;70(12):5085-95. doi: 10.1158/0008-5472.CAN-09-4095. PMID: 20530684

4. Akli S, Van Pelt CS, Bui T, Meijer L, Keyomarsi K. Cdk2 is required for breast cancer mediated by the low-molecular-weight isoform of cyclin E. Cancer Res. 2011;71(9):3377-86. doi: 10.1158/0008-5472.CAN-10-4086. PMID: 21385896

5. Duong MT, Akli S, Wei C, Wingate HF, Liu W, Lu Y, Yi M, Mills GB, Hunt KK, Keyomarsi K. LMW-E/CDK2 deregulates acinar morphogenesis, induces tumorigenesis, and associates with the activated b-Raf-ERK1/2-mTOR pathway in breast cancer patients. PLoS Genet. 2012;8(3):e1002538. doi: 10.1371/journal.pgen.1002538. PMID: 22479189

6. Duong MT, Akli S, Macalou S, Biernacka A, Debeb BG, Yi M, Hunt KK, Keyomarsi K. Hbo1 is a cyclin E/CDK2 substrate that enriches breast cancer stem-like cells. Cancer Res. 2013;73(17):5556-68. doi: 10.1158/0008-5472.CAN-13-0013. PMID: 23955388

7. Nanos-Webb A, Bui T, Karakas C, Zhang D, Carey JP, Mills GB, Hunt KK, Keyomarsi K. PKCiota promotes ovarian tumor progression through deregulation of cyclin E. Oncogene. 2016;35(19);2428-40. doi:10.1038/onc.2015.301. PMID:26279297

8. Mittendorf EA, Liu Y, Tucker SL, McKenzie T, Qiao N, Akli S, Biernacka A, Liu Y, Meijer L, Keyomarsi K, Hunt KK. A novel interaction between HER2/neu and cyclin E in breast cancer. Oncogene. 2010;29(27):3896-907. doi:10.1038/onc2010.151. PMID:20453888

9. Doostan I, Karakas C, Kohansal M, Low KH, Ellis MJ, Olson JA Jr.  Cytoplasmic Cyclin E Mediates Resistance to Aromatase Inhibitors in Breast Cancer. Clinical Cancer Research, 2017; 23(23):7288-7300. PMID: 28947566

10. Lucenay KS, Doostan I, Karakas C, Bui T, Ding Z, Mills GB, Hunt KK, Keyomarsi K. Cyclin E Associates with the Lipogenic Enzyme ATP-Citrate Lyase to Enable Malignant Growth of Breast Cancer Cells. Cancer Research. 2016; 76(8):2406-18.  PMID: 26928812

The Key/Hunt laboratory have shown that the LMW forms of cyclin E are prognostically relevant in breast cancer patients and their activity can be targeted. Early on, Dr. Keyomarsi established the overexpression of the LMW-E to be a strong predictor of poor survival in breast cancer using western blot analysis (1). Next, they set out to decipher if the cellular localization of the LMW-E was different than full length cyclin E. Their group discovered that through elastase mediated cleavage of full length cyclin E at two distinct sites in the amino terminus of the protein, the nuclear localization signal is lost in the LMW forms. Since cyclin E can only be degraded through its anchoring by FBW7 to the proteasome in the nucleus, they showed that not only do the LMW-E reside in the cytoplasm, but that they are much more stable than full length cyclin E, which is only found in the nucleus and subject to degradation (2). Based on this finding, they hypothesized that through immunohistochemistry, they can differentiate if a tumor is expressing full length cyclin E (nuclear) or LMW-E (cytoplasmic). As a result of this finding, they then developed a novel immunohistochemical (IHC) assay and scoring system for both LMW-E and p-CDK2 and evaluated their expression in 1676 breast carcinoma patients and show that cytoplasmic cyclin E correlated strongly with cytoplasmic p-CDK2 (P < 0.0001), high tumor grade, ER/PR negative, and HER-2 positive status (all P < 0.0001). In multivariable analysis, LMW-E and p-CDK2 predicted breast cancer recurrence-free and overall survival, suggesting that these two markers of G1/S transition be used as biomarkers for aggressive breast (3)and bladder cancer (4). Most recently, they expanded these analyses and evaluated the subcellular localization of cyclin E in breast cancer specimens from 2,494 patients from 4 different cohorts and show that in multivariable analysis, cytoplasmic cyclin E staining was associated with the greatest risk of recurrence compared with other prognostic factors across all subtypes in all cohorts (5). They also show cytoplasmic cyclin E staining outperformed Ki67 and all other variables as prognostic factors (6). Collectively, their studies suggest that cytoplasmic cyclin E is likely to identify patients with the highest likelihood of recurrence consistently across different patient cohorts and subtypes (7). These patients may benefit from alternative therapies targeting the oncogenic isoforms of cyclin E. One such therapy is based on their findings on the mechanism of action of LMW-E through alteration in DNA damage response and repair pathways identified Wee1 kinase as suitable target for LMW-E expressing tumors (8). A clinical trial (NCT03253679 in collaboration with Dr. Siqing Fu and Dr. Funda Meric-Bernstam) which uses AZD1775-a Wee1 kinase inhibitor as a function of cyclin E status, has been recently approved and sponsored by both AstraZeneca and CTEP is currently accruing patients. Current studies are aimed at using cyclin E IHC as a method to stratify patients into different treatment strategies targeting either cyclin E pathway itself or pathways that are altered due to cyclin E expression. Moreover, mechanistic studies on the role of full length versus LMW-E in inducing replicative stress, mitotic defects and bypassing DNA damage are ongoing.

Publications & Clinical Trials Resulting From This Project

1. Keyomarsi K, Tucker SL, Buchholz TA, Callister M, Ding Y, Hortobagyi GN, Bedrosian I, Knickerbocker C, Toyofuku W, Lowe M, Herliczek TW, Bacus SS. Cyclin E and survival in patients with breast cancer. N Engl J Med. 2002;347(20):1566-75. Erratum in: N Engl J Med 2003 Jan 9;348(2):186. PMID: 12432043

2. Delk NA, Hunt KK, Keyomarsi K. Altered subcellular localization of tumor-specific cyclin E isoforms affects cyclin-dependent kinase 2 complex formation and proteasomal regulation. Cancer Res. 2009;69(7):2817-25. doi: 10.1158/0008-5472.CAN-08-4182. PMID: 19318554

3. Karakas C, Biernacka A, Bui T, Sahin AA, Yi M, Akli S, Schafer J, Alexander A, Adjapong O, Hunt KK, Keyomarsi K. Cytoplasmic Cyclin E and Phospho-Cyclin-Dependent Kinase 2 Are Biomarkers of Aggressive Breast Cancer. Am J Pathol. 2016;186(7):1900-1912. doi: 10.1016/j.ajpath.2016.02.024. PMID: 27182644

4. Akli S, Zhang XQ, Bondaruk J, Tucker SL, Czerniak PB, Benedict WF, Keyomarsi K. Low molecular weight cyclin E is associated with p27-resistant, high-grade, high-stage and invasive bladder cancer. Cell Cycle. 2012;11(7):1468-76. doi: 10.4161/cc.19882. PMID: 22441703

5. Hunt KK, Karakas C, Ha MJ, Biernacka A, Yi M, Sahin AA, Adjapong O, Hortobagyi GN, Bondy M, Thompson P, Cheung KL, Ellis IO, Bacus S, Symmans WF, Do KA, Keyomarsi K. Cytoplasmic Cyclin E Predicts Recurrence in Patients with Breast Cancer. Clin Cancer Res. 2017;23(12):2991-3002. doi: 10.1158/1078-0432.CCR-16-2217. PMID: 27881578

6. Doostan I, Karakas C, Kohansal M, Low KH, Ellis MJ, Olson JA Jr, Suman VJ, Hunt KK, Moulder SL, Keyomarsi K. Cytoplasmic Cyclin E Mediates Resistance to Aromatase Inhibitors in Breast Cancer. Clin Cancer Res. 2017;23(23):7288-7300. doi: 10.1158/1078-0432.CCR-17-1544. PMID:28947566

7. Caruso JA, Duong MT, Carey JPW, Hunt KK, Keyomarsi K. Low-Molecular-Weight Cyclin E in Human Cancer: Cellular Consequences and Opportunities for Targeted Therapies. Cancer Res. 2018;78(19):5481-5491. Review. doi: 10.1158/0008-5472.CAN-18-1235. PMID:30194068

8. Chen X, Low KH, Alexander A, Jiang Y, Karakas C, Hess KR, Carey JPW, Bui TN, Vijayaraghavan S, Evans KW, Yi M, Ellis DC, Cheung KL, Ellis IO, Fu S, Meric-Bernstam F, Hunt KK, Keyomarsi K. Cyclin E Overexpression Sensitizes Triple-Negative Breast Cancer to Wee1 Kinase Inhibition. Clin Cancer Res. 2018 15;24(24):6594-6610. doi: 10.1158/1078-0432.CCR-18-1446. PMID:30181387

Mechanisms of Action of CDK4/6 Inhibitors. 
Deregulation of the CDK4/6-Cyclin D pathway in tumorigenesis has led to the development and FDA approval (palbociclib) of CDK4/6 inhibitors for the treatment of advanced estrogen receptor positive breast cancer. However, two major clinical challenges remain: i) adverse events leading to discontinuation of therapy and ii) lack of a reliable biomarker to predict response. The KeyHunt laboratory has recently discovered that breast cancer cells activate autophagy in response to palbociclib, and that the combination of autophagy and CDK4/6 inhibitors induces irreversible growth inhibition and senescence in vitro, and diminishes growth of cell line and patient derived xenograft tumors in vivo. Furthermore, intact G1/S transition (Rb positive and LMW-E negative) is necessary and predictive of preclinical sensitivity to this drug combination and predictive of clinical response to palbociclib. Furthermore, combined inhibition of CDK4/6 and autophagy was also synergistic in other solid tumor types with an intact G1/S checkpoint, providing a novel and promising biomarker-driven combination therapeutic strategy to treat breast and other solid tumors. These studies (1,2)resulted in funding by a CPRIT grant(and also the activation of a clinical trial (NCT03774472 in collaboration with Dr. Debu Tripathy) examining the synergistic activity of an autophagy inhibitor.

Mechanisms of Resistance to CDK4/6 Inhibitors. Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors are currently used in combination with endocrine therapy to treat advanced hormone receptor–positive, HER2-negative breast cancer. Although this treatment doubles time to progression compared with endocrine therapy alone, about 25%–35% of patients do not respond, and almost all patients eventually acquire resistance. Discerning the mechanisms of resistance to CDK4/6 inhibition is crucial in devising alternative treatment strategies. The Key/Hunt team have recently examined mechanisms of resistance to palbociclib and they reported (1)that ER-positive breast cancer cells acquire resistance to palbociclib by downregulation of ER protein and DNA repair machinery and upregulation of the IL6/STA3 pathway, which is overcome by treatment with STAT3 and PARP inhibitors. Matched biopsies from patients with breast cancer who progressed on palbociclib showed downregulation in DNA repair, ER, and IL6/STAT3 as compared with their pretreatment biopsy samples. By identifying and validating these mediators (or drivers of palbociclib resistance, a novel treatment strategy with clinically available inhibitors to STAT3 and DNA repair is currently being designed by Keyomarsi and colleagues (Dr. Debu Tripathy and Dr. David Tweardy) to circumvent resistance and improve clinical outcomes. This study was also recently funded by CPRIT through a Multi-Investigator Research Grant (MIRA) from CPRIT where Dr. Keyomarsi and Dr. Kelly Hunt are the Co-PIs of the entire MIRA.

Publications & Clinical Trials Resulting From This Project

Hydroxychloroquine, Palbociclib, and Letrozole Before Surgery in Treating Participants With Estrogen Receptor Positive, HER2 Negative Breast Cancer. Clinical Trials Identifier: NCT03774472

1. Vijayaraghavan S, Karakas C, Doostan I, Chen X, Bui T, Yi M, Raghavendra AS, Zhao Y, Bashour SI, Ibrahim NK, Karuturi M, Wang J, Winkler JD, Amaravadi RK, Hunt KK, Tripathy D, Keyomarsi K. CDK4/6 and autophagy inhibitors synergistically induce senescence in Rb positive cytoplasmic cyclin E negative cancers. Nature Communications, 2017;8:15916. PMID: 28653662

2. Vijayaraghavan S, Moulder S, Keyomarsi K, Layman RM. Inhibiting CDK in Cancer Therapy: Current Evidence and Future Directions. Target Oncol. 2018;13(1):21-38. Review. doi: 10.1007/s11523-017-0541-2. PMID: 29218622

3. Kettner NM, Vijayaraghavan S, Durak MG, Bui T, Kohansal M, Ha MJ, Liu B, Rao X, Wang J, Yi M, Carey JPW, Chen X, Eckols TK, Raghavendra AS, Ibrahim NK, Karuturi MS, Watowich SS, Sahin A, Tweardy DJ, Hunt KK, Tripathy D, Keyomarsi K. Combined Inhibition of STAT3 and DNA Repair in Palbociclib-Resistant ER-Positive Breast Cancer. Clinical Cancer Research 2019;25(13):3996-4013. doi:10.1158/1078-0432.CCR-18-3274. PMID: 30867218

The KeyHunt observations that LMW-E could be generated from full length-cyclin E by the serine protease neutrophil elastase (NE) was an unexpected finding. Their laboratory followed up on this finding and made the novel observation that elafin, a direct inhibitor of elastase, is regulated differentially in normal versus tumor cells thorough its transcriptional downregulation by C/EBPbeta (1). These studies revealed that elafin overexpression in tumor, but not normal cells, results in the preferential induction of apoptosis in the tumor cells and elafin can eradicate xenograft tumor growth in vivo. Moreover, they reported that downregulation of elafin sensitizes human mammary epithelial cells to exogenous NE-induced proliferation, suggesting that elafin is a counterbalance against the mitogenic effects of NE, including the intracellular generation of LMW-E (2,3). These studies have set the foundation for their recent work where they found that in patients with breast cancer, high levels of NE is prognostic for poor overall, metastasis-free, and disease-specific survival (4). Moreover, they shown that genetic ablation of ELANE (gene encoding for NE) or inhibition of NE by a small molecule inhibitor has the benefit of diminishing metastasis in in vivopre-clinical models of breast cancer. In collaboration with Dr. Stephanie Watowich (Immunology) they have established a direct molecular link between tumor associated neutrophils (TANs), tumor progression and metastasis mediated by NE and, significantly, highlight a targetable pathway via NE inhibition (NE inhibitor AZD9668) for therapeutic intervention in metastatic breast cancer. This project, which will address major gaps in our understanding of how TANs enhance breast cancer growth and metastasis has recently been funding by a CPRIT grant in collaboration with Dr. Watowich, whose expertise in innate signaling and immunology is complimentary to the expertise in the KeyHunt laboratory in breast cancer biology and therapeutic targeting.

Publications & Clinical Trials Resulting From This Project:

1. Yokota T, Bui T, Liu Y, Yi M, Hunt KK, Keyomarsi K. Differential regulation of elafin in normal and tumor-derived mammary epithelial cells is mediated by CCAAT/enhancer binding protein beta. Cancer Res. 2007;67(23):11272-83. PMID: 18056453

2. Caruso JA, Hunt KK, Keyomarsi K. The neutrophil elastase inhibitor elafin triggers rb-mediated growth arrest and caspase-dependent apoptosis in breast cancer. Cancer Res. 2010;70(18):7125-36. doi: 10.1158/0008-5472.CAN-10-1547. PMID: 20823156

3. Caruso JA, Akli S, Pageon L, Hunt KK, Keyomarsi K. The serine protease inhibitor elafin maintains normal growth control by opposing the mitogenic effects of neutrophil elastase. Oncogene. 2015;34(27):3556-67. doi:10.1038/onc.2014.284. PMID:25195861

4. Caruso JA, Karakas C, Zhang J, Yi M, Albarracin C, Sahin A, Bondy M, Liu J, Hunt KK, Keyomarsi K. Elafin is downregulated during breast and ovarian tumorigenesis but its residual expression predicts recurrence. Breast Cancer Res. 2014;16(6):3417. doi:10.1186/s13058-014-0497-4. PMID: 25551582. Erratum in: Breast Cancer Res. 2015;17:87. PMID: 26108797

Sarcomas are a rare group of heterogeneous neoplasms arising from mesenchymal cells. Soft tissue sarcomas (STS) can occur in any part of the body and have a high propensity to metastasize. Conventional cytotoxic chemotherapy has failed to substantially improve disease-specific survival rates for most sarcomas with current 2-year survival rates being approximately 50% for high grade metastatic STS. The field of sarcoma presents a clear need for new rational therapeutics, and discoveries in recent years regarding the molecular and genetic basis of sarcoma have revealed new targets that deserve consideration. In earlier studies, we identified a novel role for autophagy to enhance cytotoxicity by cell cycle inhibition after genotoxic injury (1,2). More recently we have focused on the alterations in the retinoblastoma (Rb) pathway found in various STS. Loss of Rb function causes unabated cell proliferation, through overexpression of cyclin D1 and/or CDK4 and has been detected in ~50% of STS (including leiomyosarcomas and liposarcomas). Our overall hypothesis is that STS expressing wild-type Rb will be sensitive to combination therapy targeting different phases of the cell cycle. Our recent studies that have begun to test this hypothesis in vivo reveal that sequential treatment with CDK4/6 inhibitor followed by DNA damaging agents synergistically leads to significant reduction in tumor burden as compared to single agents in both cell line and patient derived xenograft (PDX) models (3).

However, a key knowledge gap is the absence of functional imaging and biomarkers to determine the efficacy the suppression of cell cycle progression in mouse models and patients undergoing such treatment strategies. We are currently using different imaging techniques as surrogates of cell proliferation to in both cell lines and PDX models. Molecular profiling of all LMS PDX models are also being performed in order to identify signatures or response to our novel treatment strategies. These studies will address how best to target the cell cycle in combination treatment and will also provide the much-needed pre-clinical rationale allowing for effective translation of this research to clinical trials in advanced STS patients. 

Lambert L, Keyomarsi K. Cell cycle deregulation in breast cancer: insurmountable chemoresistance or Achilles' heel? Adv Exp Med Biol. 2007;608:52-69. Review. PMID: 17993232

Lambert LA, Qiao N, Hunt KK, Lambert DH, Mills GB, Meijer L, Keyomarsi K. Autophagy: a novel mechanism of synergistic cytotoxicity between doxorubicin and roscovitine in a sarcoma model. Cancer Res. 2008;68(19):7966-74. PMID: 18829554

Francis AM, Alexander A, Liu Y, Vijayaraghavan S, Low KH, Yang D, Bui T, Somaiah N, Ravi V, Keyomarsi K, Hunt KK. CDK4/6 Inhibitors Sensitize Rb-positive Sarcoma Cells to Wee1 Kinase Inhibition through Reversible Cell-Cycle Arrest. Mol Cancer Ther. 2017;16(9):1751-1764. doi: 10.1158/1535-7163.MCT-17-0040. PMID: 28619757