Following are public and technical abstracts for the Renal Medullary Carcinoma project funded by the Department of Defense Kidney Cancer Research Program (KCRP) for 2017.
Principal Investigator: Pavlos Msaouel
Institution: M.D. Anderson Cancer Center, University of Texas
Funding Mechanism: Concept Award
Award Amount: $120,000
Public Abstract
Background: Renal medullary carcinoma (RMC) is a rare but deadly cancer that almost always occurs in young African-Americans, more often in the right kidney (~70% of cases) than the left. All individuals with RMC have either sickle cell disease, sickle cell trait, or other conditions associated with sickling of red blood cells. Individuals with sickle cell trait frequently have no other clinical symptoms and often learn that they harbor the sickle cell trait after being diagnosed with RMC. Less than 5% of patients with RMC will survive beyond 5 years after diagnosis, despite the best currently available therapies. We need to understand how and why RMC occurs in order to develop strategies to more effectively prevent, diagnose, and treat this highly lethal kidney malignancy.
Hypothesis and Objective: To this day, we do not know why RMC only occurs in individuals with sickle cell disease or trait, or why it arises more frequently in the right kidney. To address these questions we propose a novel, testable concept that connects these two defining characteristics of RMC. The renal inner medulla is the least oxygenated tissue in the human body. It also contains the highest concentration of salt. This high amount of salt damages the DNA of cells in the renal inner medulla and, at the same time, suppresses the repair of this damage. In addition, the low oxygen levels and high salt concentrations will force the red blood cells of individuals with sickle cell trait or disease to change their shape, a phenomenon known as “sickling.” Red blood cells that have “sickled” can obstruct the blood supply of the renal inner medulla resulting in tissue death (“microinfarcts”). These microinfarcts reduce the salt concentration in the renal inner medulla, thus activating the repair of DNA damage. However, because of the low oxygen concentration in these tissues, the repair of DNA will be suboptimal and have increased chances of introducing mutations that can lead to cancer. The physical laws governing fluid circulation stipulate that longer blood vessels will result in lower blood flow. The right kidney artery is known to be longer than the left and this may result in reduced blood flow on the right side, thus increasing the chances that microinfarcts can happen on the right renal inner medulla compared with the left.
Based on the above considerations, we propose that the microinfarcts in the renal inner medulla, resulting from sickling of red blood cells, will be more commonly found in the right kidney and will produce tissue damage that will activate a suboptimal repair of DNA, thus increasing the chances that cells will mutate to cancer. To test this concept, we propose the following experiments in mice genetically engineered to mimic human sickle cell disease or trait:
- Determine if microinfarcts are more common in the right renal inner medulla compared with the left.
- Determine if there is increased activity of suboptimal DNA repair mechanisms in the renal inner medulla of mice mimicking human sickle cell disease and trait compared with mice mimicking normal human blood circulation.
Impact: RMC most frequently occurs in a particularly vulnerable population consisting mainly of young African Americans. Following its validation by the above experiments, we intend to use the proposed model to investigate how environmental factors and genetic or epigenetic variations can increase or reduce the risk of developing RMC. These insights can help us develop strategies to effectively screen and prevent RMC.
Innovation: The concept we propose is the first to model how and why RMC happens in individuals with sickle cell trait or disease. Our proposed experiments will allow us to determine if anatomical differences in kidney blood supply can explain this laterality. After we complete this project, we plan to use our experience with these models to develop new strains of mice genetically engineered not only to mimic human sickle cell trait and disease but also to harbor the genetic mutation that is found in all RMCs, in a gene called SMARCB1. This will allow us to explore how microinfarcts due to sickle cell disease or trait interact with SMARCB1 genetic mutations, and to identify additional factors that drive the development of RMC.
Technical Abstract
Background: Renal medullary carcinoma (RMC) is a highly aggressive malignancy with a predilection towards the right kidney (~70% of cases) occurring predominantly in young African Americans (median age 28 years old). Notably, all individuals with RMC have sickle hemoglobinopathies, such as sickle cell disease or trait. The median survival of patients with RMC is approximately 13 months despite nephrectomy and currently available systemic therapies, with less than 5% of patients surviving beyond 5 years. This highlights the need to understand the etiology of RMC and develop new diagnostic, preventive, and therapeutic strategies.
Hypothesis and Objective: A key knowledge gap in RMC biology is why sickle hemoglobinopathies predispose to the development of this cancer and why RMC preferably occurs in the right kidney. We propose a testable model that connects these defining features by utilizing the following key insights: The extreme hypoxia and hypertonicity within the renal inner medulla (RIM) produce and dysregulate the repair of DNA double-strand breaks associated with carcinogenesis. Within this microenvironment, the red blood cells of individuals with sickle hemoglobinopathies will sickle, resulting in microvascular occlusions that produce regional microinfarcts within the RIM. These regional microinfarcts reduce the interstitial osmolarity in the RIM resulting in the reactivation of DNA repair pathways, with a shift towards error-prone non-homologous end joining (NHEJ) due to hypoxia-induced repression of high-fidelity homologous recombination (HR). NHEJ decreases the stability of the genome and increases the risk of carcinogenesis via chromosomal breaks and genomic rearrangements that can inactivate genes such as SMARCB1, the tumor suppressor that is lost in all RMC cases. The Hagen-Poiseuille equation, commonly used to describe blood circulation, stipulates that (assuming equal radius and pressure differences) the flow rate of blood will be inversely proportional to the length of the vessel. Thus, the longer length of the right renal artery will result in reduced blood flow in the right RIM compared with the left, further exacerbating regional microinfarcts that predispose to RMC. Therefore, we hypothesize that regional microinfarcts induced by RBC sickling are more common in the right RIM due to the longer right renal artery, and that these microinfarcts result in perturbations of RIM interstitial osmolarity that reactivate error-prone NHEJ DNA double-strand repair.
To test our hypothesis, we propose the following Specific Aims:
Specific Aim 1: Determine if regional microinfarcts are more common in the right, compared with the left, RIM of mice with humanized sickle cell disease and trait.
Specific Aim 2: Determine if the RIM of mice with humanized sickle cell disease and trait have increased NHEJ DNA repair activity compared with mice harboring wild-type human beta hemoglobin.
Study Design: The right renal artery of mice is almost twice the length (~2.9 mm) of the left renal artery (~1.5 mm) and is therefore an appropriate model to test our hypothesis. We will use established mouse models harboring humanized sickle cell disease (SS), sickle cell trait (Sß), or wild-type human ßß hemoglobin. Both kidneys will be harvested at regular intervals and examined for differences in regional microinfarcts and DNA double-strand breaks. Expression levels of Rad51 and Brca1 will be used as markers of HR, whereas Rif1 and Parp1 will be used as markers of NHEJ.
Impact: RMC predominantly occurs in a particularly vulnerable population consisting mainly of young African Americans. Our short-term goal is to use the proposed model to elucidate how environmental factors and inter-individual genetic/epigenetic variations increase or attenuate the risk of RMC. These insights will inform the development of strategies to effectively screen and prevent RMC.
Innovation: The proposed novel concept provides the first testable model of the initial steps in RMC pathogenesis. Although it is well-established that the RIM is characterized by extreme hypoxia and hypertonicity, as well as an abundance of unrepaired DNA double-strand breaks, this will be the first investigation of how these unique conditions are associated with carcinogenesis. In addition, although RMC has a known predilection towards the right kidney, this will be the first study to investigate whether differences in vascular anatomy can explain this laterality.