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Glaviano A, Wander SA, Baird RD, Yap KCH, Lam HY, Toi M, Carbone D, Geoerger B, Serra V, Jones RH, Ngeow J, Toska E, Stebbing J, Crasta K, Finn RS, Diana P, Vuina K, de Bruin RAM, Surana U, Bardia A, Kumar AP. Mechanisms of sensitivity and resistance to CDK4/CDK6 inhibitors in hormone receptor-positive breast cancer treatment. Drug Resist Updat 2024; 76:101103. [PMID: 38943828 DOI: 10.1016/j.drup.2024.101103] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2024] [Revised: 05/17/2024] [Accepted: 06/10/2024] [Indexed: 07/01/2024]
Abstract
Cell cycle dysregulation is a hallmark of cancer that promotes eccessive cell division. Cyclin-dependent kinase 4 (CDK4) and cyclin-dependent kinase 6 (CDK6) are key molecules in the G1-to-S phase cell cycle transition and are crucial for the onset, survival, and progression of breast cancer (BC). Small-molecule CDK4/CDK6 inhibitors (CDK4/6i) block phosphorylation of tumor suppressor Rb and thus restrain susceptible BC cells in G1 phase. Three CDK4/6i are approved for the first-line treatment of patients with advanced/metastatic hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) BC in combination with endocrine therapy (ET). Though this has improved the clinical outcomes for survival of BC patients, there is no established standard next-line treatment to tackle drug resistance. Recent studies suggest that CDK4/6i can modulate other distinct effects in both BC and breast stromal compartments, which may provide new insights into aspects of their clinical activity. This review describes the biochemistry of the CDK4/6-Rb-E2F pathway in HR+ BC, then discusses how CDK4/6i can trigger other effects in BC/breast stromal compartments, and finally outlines the mechanisms of CDK4/6i resistance that have emerged in recent preclinical studies and clinical cohorts, emphasizing the impact of these findings on novel therapeutic opportunities in BC.
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Affiliation(s)
- Antonino Glaviano
- Department of Biological, Chemical and Pharmaceutical Sciences and Technologies, University of Palermo, Palermo 90123, Italy
| | - Seth A Wander
- Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA
| | - Richard D Baird
- Cancer Research UK Cambridge Centre, Hills Road, Cambridge CB2 0QQ, UK
| | - Kenneth C-H Yap
- Department of Pharmacology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117600, Singapore; NUS Center for Cancer Research, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119077, Singapore
| | - Hiu Yan Lam
- Department of Pharmacology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117600, Singapore; NUS Center for Cancer Research, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119077, Singapore
| | - Masakazu Toi
- School of Medicine, Kyoto University, Kyoto, Japan
| | - Daniela Carbone
- Department of Biological, Chemical and Pharmaceutical Sciences and Technologies, University of Palermo, Palermo 90123, Italy
| | - Birgit Geoerger
- Gustave Roussy Cancer Center, Department of Pediatric and Adolescent Oncology, Inserm U1015, Université Paris-Saclay, Villejuif, France
| | - Violeta Serra
- Experimental Therapeutics Group, Vall d'Hebron Institute of Oncology, Barcelona, Spain
| | - Robert H Jones
- Cardiff University and Velindre Cancer Centre, Museum Avenue, Cardiff CF10 3AX, UK
| | - Joanne Ngeow
- Lee Kong Chian School of Medicine (LKCMedicine), Nanyang Technological University, Experimental Medicine Building, 636921, Singapore; Cancer Genetics Service (CGS), National Cancer Centre Singapore, 168583, Singapore
| | - Eneda Toska
- Department of Biochemistry and Molecular Biology, Johns Hopkins School of Public Health, Baltimore, MD, USA
| | - Justin Stebbing
- School of Life Sciences, Anglia Ruskin University, Cambridge, UK; Division of Cancer, Imperial College London, Hammersmith Campus, London, UK
| | - Karen Crasta
- NUS Center for Cancer Research, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119077, Singapore; Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, 117593, Singapore; Healthy Longetivity Translational Program, Yong Loo Lin School of Medicine, National University of Singapore, 117456, Singapore
| | - Richard S Finn
- Department of Oncology, Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | - Patrizia Diana
- Department of Biological, Chemical and Pharmaceutical Sciences and Technologies, University of Palermo, Palermo 90123, Italy
| | - Karla Vuina
- MRC Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK
| | - Robertus A M de Bruin
- MRC Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK
| | - Uttam Surana
- Department of Pharmacology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117600, Singapore; SiNOPSEE Therapeutics Pte Ltd, A⁎STARTCentral, 139955, Singapore
| | - Aditya Bardia
- Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA
| | - Alan Prem Kumar
- Department of Pharmacology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117600, Singapore; NUS Center for Cancer Research, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119077, Singapore.
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Tian Y, Liu K, Wu D, Wu L, Xu Q, Wei W, Li Z, Du Q, Bian J. The discovery of potent USP2/USP8 dual-target inhibitors for the treatment of breast cancer via structure guided optimization of ML364. Eur J Med Chem 2024; 268:116275. [PMID: 38452725 DOI: 10.1016/j.ejmech.2024.116275] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2024] [Revised: 02/09/2024] [Accepted: 02/20/2024] [Indexed: 03/09/2024]
Abstract
USP2 and USP8 are crucial in the development and progression of breast cancer, primarily through the stabilization of protein substrates such as Her2 and ERα. The dual-target inhibitor ML364, targeting both USP2 and USP8, has garnered significant interest in recent research. In this study, we developed a series of ML364 derivatives using ligand-based drug design strategies. The standout compound, LLK203, demonstrated enhanced inhibitory activity, showing a 4-fold increase against USP2 and a 9-fold increase against USP8, compared to the parent molecule. In MCF-7 breast cancer cells, LLK203 effectively degraded key proteins involved in cancer progression and notably inhibited cell proliferation. Moreover, LLK203 exhibited potent in vivo efficacy in the 4T1 homograft model, while maintaining a low toxicity profile. These results underscore the potential of LLK203 as a promising dual-target inhibitor of USP2/USP8 for breast cancer treatment.
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Affiliation(s)
- Yucheng Tian
- Jiangsu Key Laboratory of Drug Design and Optimization, Department of Medicinal Chemistry, School of Pharmacy, China Pharmaceutical University, Nanjing, 210009, PR China
| | - Kang Liu
- Jiangsu Key Laboratory of Drug Design and Optimization, Department of Medicinal Chemistry, School of Pharmacy, China Pharmaceutical University, Nanjing, 210009, PR China
| | - Dongdong Wu
- Jiangsu Key Laboratory of Drug Design and Optimization, Department of Medicinal Chemistry, School of Pharmacy, China Pharmaceutical University, Nanjing, 210009, PR China
| | - Liuyi Wu
- Jiangsu Key Laboratory of Drug Design and Optimization, Department of Medicinal Chemistry, School of Pharmacy, China Pharmaceutical University, Nanjing, 210009, PR China
| | - Qianqian Xu
- Jiangsu Key Laboratory of Drug Design and Optimization, Department of Medicinal Chemistry, School of Pharmacy, China Pharmaceutical University, Nanjing, 210009, PR China
| | - Wei Wei
- Jiangsu Key Laboratory of Drug Design and Optimization, Department of Medicinal Chemistry, School of Pharmacy, China Pharmaceutical University, Nanjing, 210009, PR China
| | - Zhiyu Li
- Jiangsu Key Laboratory of Drug Design and Optimization, Department of Medicinal Chemistry, School of Pharmacy, China Pharmaceutical University, Nanjing, 210009, PR China.
| | - Qianming Du
- General Clinical Research Center, Nanjing First Hospital, Nanjing Medical University, Nanjing, 210006, PR China; School of Basic Medicine & Clinical Pharmacy, China Pharmaceutical University, Nanjing, 210009, PR China.
| | - Jinlei Bian
- Jiangsu Key Laboratory of Drug Design and Optimization, Department of Medicinal Chemistry, School of Pharmacy, China Pharmaceutical University, Nanjing, 210009, PR China.
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Zhang C, Zhou F, Zou J, Fang Y, Liu Y, Li L, Hou J, Wang G, Wang H, Lai X, Xie L, Jiang J, Yang C, Huang Y, Chen Y, Zhang H, Li Y. Clinical considerations of CDK4/6 inhibitors in HER2 positive breast cancer. Front Oncol 2024; 13:1322078. [PMID: 38293701 PMCID: PMC10824891 DOI: 10.3389/fonc.2023.1322078] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2023] [Accepted: 12/28/2023] [Indexed: 02/01/2024] Open
Abstract
Deregulation of cell cycles can result in a variety of cancers, including breast cancer (BC). In fact, abnormal regulation of cell cycle pathways is often observed in breast cancer, leading to malignant cell proliferation. CDK4/6 inhibitors (CDK4/6i) can block the G1 cell cycle through the cyclin D-cyclin dependent kinase 4/6-inhibitor of CDK4-retinoblastoma (cyclinD-CDK4/6-INK4-RB) pathway, thus blocking the proliferation of invasive cells, showing great therapeutic potential to inhibit the spread of BC. So far, three FDA-approved drugs have been shown to be effective in the management of advanced hormone receptor positive (HR+) BC: palbociclib, abemaciclib, and ribociclib. The combination strategy of CDK4/6i and endocrine therapy (ET) has become the standard therapeutic regimen and is increasingly applied to advanced BC patients. The present study aims to clarify whether CDK4/6i can also achieve a certain therapeutic effect on Human epidermal growth factor receptor 2 positive (HER2+) BC. Studies of CDK4/6i are not limited to patients with estrogen receptor positive/human epidermal growth factor receptor 2 negative (ER+/HER2-) advanced BC, but have also expanded to other types of BC. Several pre-clinical and clinical trials have demonstrated the potential of CDK4/6i in treating HER2+ BC. Therefore, this review summarizes the current knowledge and recent findings on the use of CDK4/6i in this type of BC, and provides ideas for the discovery of new treatment modalities.
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Affiliation(s)
- Cui Zhang
- Zunyi Medical University, Zunyi, China
| | - Fulin Zhou
- Maternal and Child Health Care Hospital of Guiyang City, Guiyang, China
| | - Jiali Zou
- Maternal and Child Health Care Hospital of Guiyang City, Guiyang, China
| | - Yanman Fang
- Maternal and Child Health Care Hospital of Guiyang City, Guiyang, China
| | - Yuncong Liu
- Department of Oncology, Guizhou Provincial People’s Hospital, Guiyang, China
| | - Libo Li
- Department of Oncology, Guizhou Provincial People’s Hospital, Guiyang, China
| | - Jing Hou
- Department of Breast Surgery, Guizhou Provincial People’s Hospital, Guiyang, China
| | - Guanghui Wang
- Department of Breast Surgery, Guizhou Provincial People’s Hospital, Guiyang, China
| | - Hua Wang
- Department of Breast Surgery, Guizhou Provincial People’s Hospital, Guiyang, China
| | - Xiaolian Lai
- Department of Digestive, People’s Hospital of Songtao Miao Autonomous County, Tongren, China
| | - Lu Xie
- Guizhou University of Traditional Chinese Medicine, Guiyang, China
| | - Jia Jiang
- Guizhou University of Traditional Chinese Medicine, Guiyang, China
| | - Can Yang
- Guizhou University of Traditional Chinese Medicine, Guiyang, China
| | | | | | - Hanqun Zhang
- Department of Oncology, Guizhou Provincial People’s Hospital, Guiyang, China
| | - Yong Li
- Department of Oncology, Guizhou Provincial People’s Hospital, Guiyang, China
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Shagisultanova E, Gradishar W, Brown-Glaberman U, Chalasani P, Brenner AJ, Stopeck A, Parris H, Gao D, McSpadden T, Mayordomo J, Diamond JR, Kabos P, Borges VF. Safety and Efficacy of Tucatinib, Letrozole, and Palbociclib in Patients with Previously Treated HR+/HER2+ Breast Cancer. Clin Cancer Res 2023; 29:5021-5030. [PMID: 37363965 PMCID: PMC10722138 DOI: 10.1158/1078-0432.ccr-23-0117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2023] [Revised: 04/08/2023] [Accepted: 06/20/2023] [Indexed: 06/28/2023]
Abstract
PURPOSE To overcome resistance to antihormonal and HER2-targeted agents mediated by cyclin D1-CDK4/6 complex, we proposed an oral combination of the HER2 inhibitor tucatinib, aromatase inhibitor letrozole, and CDK4/6 inhibitor palbociclib (TLP combination) for treatment of HR+/HER2+ metastatic breast cancer (MBC). PATIENTS AND METHODS Phase Ib/II TLP trial (NCT03054363) enrolled patients with HR+/HER2+ MBC treated with ≥2 HER2-targeted agents. The phase Ib primary endpoint was safety of the regimen evaluated by NCI CTCAE version 4.3. The phase II primary endpoint was efficacy by median progression-free survival (mPFS). RESULTS Forty-two women ages 22 to 81 years were enrolled. Patients received a median of two lines of therapy in the metastatic setting, 71.4% had visceral disease, 35.7% had CNS disease. The most common treatment-emergent adverse events (AE) of grade ≥3 were neutropenia (64.3%), leukopenia (23.8%), diarrhea (19.0%), and fatigue (14.3%). Tucatinib increased AUC10-19 hours of palbociclib 1.7-fold, requiring palbociclib dose reduction from 125 to 75 mg daily. In 40 response-evaluable patients, mPFS was 8.4 months, with similar mPFS in non-CNS and CNS cohorts (10.0 months vs. 8.2 months; P = 0.9). Overall response rate was 44.5%, median duration of response was 13.9 months, and clinical benefit rate was 70.4%; 60% of patients were on treatment for ≥6 months, 25% for ≥1 year, and 10% for ≥2 years. In the CNS cohort, 26.6% of patients remained on study for ≥1 year. CONCLUSIONS TLP combination was safe and tolerable. AEs were expected and manageable with supportive therapy and dose reductions. TLP showed excellent efficacy for an all-oral chemotherapy-free regimen warranting further testing. See related commentary by Huppert and Rugo, p. 4993.
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Affiliation(s)
- Elena Shagisultanova
- Young Women's Breast Cancer Translational Program, University of Colorado Cancer Center, Aurora, Colorado
- Division of Medical Oncology, University of Colorado Cancer Center, Aurora, Colorado
| | | | | | | | | | - Alison Stopeck
- Stony Brook University Cancer Center, Stony Brook, New York
| | - Hannah Parris
- Young Women's Breast Cancer Translational Program, University of Colorado Cancer Center, Aurora, Colorado
| | - Dexiang Gao
- Department of Bioinformatics and Biostatistics, University of Colorado Denver, Aurora, Colorado
| | - Tessa McSpadden
- OCRST, University of Colorado Cancer Center, Aurora, Colorado
| | - Jose Mayordomo
- Division of Medical Oncology, University of Colorado Cancer Center, Aurora, Colorado
| | - Jennifer R. Diamond
- Division of Medical Oncology, University of Colorado Cancer Center, Aurora, Colorado
| | - Peter Kabos
- Division of Medical Oncology, University of Colorado Cancer Center, Aurora, Colorado
| | - Virginia F. Borges
- Young Women's Breast Cancer Translational Program, University of Colorado Cancer Center, Aurora, Colorado
- Division of Medical Oncology, University of Colorado Cancer Center, Aurora, Colorado
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5
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Bahnassy S, Stires H, Jin L, Tam S, Mobin D, Balachandran M, Podar M, McCoy MD, Beckman RA, Riggins RB. Unraveling Vulnerabilities in Endocrine Therapy-Resistant HER2+/ER+ Breast Cancer. Endocrinology 2023; 164:bqad159. [PMID: 37897495 PMCID: PMC10651073 DOI: 10.1210/endocr/bqad159] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Revised: 10/01/2023] [Accepted: 10/26/2023] [Indexed: 10/30/2023]
Abstract
Breast tumors overexpressing human epidermal growth factor receptor (HER2) confer intrinsic resistance to endocrine therapy (ET), and patients with HER2/estrogen receptor-positive (HER2+/ER+) breast cancer (BCa) are less responsive to ET than HER2-/ER+. However, real-world evidence reveals that a large subset of patients with HER2+/ER+ receive ET as monotherapy, positioning this treatment pattern as a clinical challenge. In the present study, we developed and characterized 2 in vitro models of ET-resistant (ETR) HER2+/ER+ BCa to identify possible therapeutic vulnerabilities. To mimic ETR to aromatase inhibitors (AIs), we developed 2 long-term estrogen deprivation (LTED) cell lines from BT-474 (BT474) and MDA-MB-361 (MM361). Growth assays, PAM50 subtyping, and genomic and transcriptomic analyses, followed by validation and functional studies, were used to identify targetable differences between ET-responsive parental and ETR-LTED HER2+/ER+ cells. Compared to their parental cells, MM361 LTEDs grew faster, lost ER, and increased HER2 expression, whereas BT474 LTEDs grew slower and maintained ER and HER2 expression. Both LTED variants had reduced responsiveness to fulvestrant. Whole-genome sequencing of aggressive MM361 LTEDs identified mutations in genes encoding transcription factors and chromatin modifiers. Single-cell RNA sequencing demonstrated a shift towards non-luminal phenotypes, and revealed metabolic remodeling of MM361 LTEDs, with upregulated lipid metabolism and ferroptosis-associated antioxidant genes, including GPX4. Combining a GPX4 inhibitor with anti-HER2 agents induced significant cell death in both MM361 and BT474 LTEDs. The BT474 and MM361 AI-resistant models capture distinct phenotypes of HER2+/ER+ BCa and identify altered lipid metabolism and ferroptosis remodeling as vulnerabilities of this type of ETR BCa.
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Affiliation(s)
- Shaymaa Bahnassy
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC 20057, USA
| | | | - Lu Jin
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC 20057, USA
| | - Stanley Tam
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC 20057, USA
| | - Dua Mobin
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC 20057, USA
| | - Manasi Balachandran
- Department of Medicine, University of Tennessee Medical Center, Knoxville, TN 37920, USA
| | - Mircea Podar
- Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
| | - Matthew D McCoy
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC 20057, USA
| | - Robert A Beckman
- Department of Oncology and of Biostatistics, Bioinformatics, and Biomathematics, Georgetown University Medical Center, Washington, DC 20007, USA
- Lombardi Comprehensive Cancer Center and Innovation Center for Biomedical Informatics, Georgetown University Medical Center, Washington, DC 20007, USA
| | - Rebecca B Riggins
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC 20057, USA
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Bahnassy S, Stires H, Jin L, Tam S, Mobin D, Balachandran M, Podar M, McCoy MD, Beckman RA, Riggins RB. Unraveling Vulnerabilities in Endocrine Therapy-Resistant HER2+/ER+ Breast Cancer. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.08.21.554116. [PMID: 37662291 PMCID: PMC10473676 DOI: 10.1101/2023.08.21.554116] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/05/2023]
Abstract
Background Breast tumors overexpressing human epidermal growth factor receptor (HER2) confer intrinsic resistance to endocrine therapy (ET), and patients with HER2/ estrogen receptor-positive (HER2+/HR+) breast cancer (BCa) are less responsive to ET than HER2-/ER+. However, real-world evidence reveals that a large subset of HER2+/ER+ patients receive ET as monotherapy, positioning this treatment pattern as a clinical challenge. In the present study, we developed and characterized two distinct in vitro models of ET-resistant (ETR) HER2+/ER+ BCa to identify possible therapeutic vulnerabilities. Methods To mimic ETR to aromatase inhibitors (AI), we developed two long-term estrogen-deprived (LTED) cell lines from BT-474 (BT474) and MDA-MB-361 (MM361). Growth assays, PAM50 molecular subtyping, genomic and transcriptomic analyses, followed by validation and functional studies, were used to identify targetable differences between ET-responsive parental and ETR-LTED HER2+/ER+ cells. Results Compared to their parental cells, MM361 LTEDs grew faster, lost ER, and increased HER2 expression, whereas BT474 LTEDs grew slower and maintained ER and HER2 expression. Both LTED variants had reduced responsiveness to fulvestrant. Whole-genome sequencing of the more aggressive MM361 LTED model system identified exonic mutations in genes encoding transcription factors and chromatin modifiers. Single-cell RNA sequencing demonstrated a shift towards non-luminal phenotypes, and revealed metabolic remodeling of MM361 LTEDs, with upregulated lipid metabolism and antioxidant genes associated with ferroptosis, including GPX4. Combining the GPX4 inhibitor RSL3 with anti-HER2 agents induced significant cell death in both the MM361 and BT474 LTEDs. Conclusions The BT474 and MM361 AI-resistant models capture distinct phenotypes of HER2+/ER+ BCa and identify altered lipid metabolism and ferroptosis remodeling as vulnerabilities of this type of ETR BCa.
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Affiliation(s)
- Shaymaa Bahnassy
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC
| | | | - Lu Jin
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC
| | - Stanley Tam
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC
| | - Dua Mobin
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC
| | - Manasi Balachandran
- Department of Medicine, University of Tennessee Medical Center, Knoxville, TN
| | | | - Matthew D. McCoy
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC
| | - Robert A. Beckman
- Departments of Oncology and of Biostatistics, Bioinformatics, and Biomathematics, Lombardi Comprehensive Cancer Center and Innovation Center for Biomedical Informatics, Georgetown University Medical Center, Washington, DC
| | - Rebecca B. Riggins
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC
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