UCSF

Research & Projects

Research in the Kroetz Lab is focused on pharmacogenomics and ABC transporter pharmacology. Jump below to:

Pharmacogenomics research projects

Our pharmacogenomics research uses a combination of genomic tools, including candidate gene and genome-wide association studies, exome sequencing, complex trait analyses, comparative genomics, and cell and model organism studies for identification of genetic biomarkers of drug response. The results from these human genetics studies can also direct investigations into novel strategies to prevent or treat drug-induced toxicity. Specific phenotypes being studied are:

Chemotherapy-induced sensory peripheral neuropathy

One of the most common toxicities associated with cancer chemotherapy treatment is sensory peripheral neuropathy, resulting from damage to the peripheral nerves in the hands and feet. Symptoms of peripheral neuropathy include pain, numbness, tingling, or burning in the hands and feet, loss of function of the fingers, and increased temperature sensitivity. In most cases chemotherapy-induced peripheral neuropathy is associated with a reduced quality of life. While several clinical factors increase a patient’s likelihood of developing this toxicity, there is increasing evidence that interindividual variation in DNA sequence also contributes to a patient’s risk. To this end, we are using genome-wide genotyping and sequencing approaches to identify genetic markers of chemotherapy-induced sensory peripheral neuropathy and to identify novel genes implicated in the mechanism of this toxicity. Functional studies in induced pluripotent stem cell-derived sensory neurons (iPSC-SNs) in culture are used to understand the molecular basis for the involvement of specific genes and variants in this toxicity.

paclitaxel graph

A SNP associated with expression of the sphingosine receptor S1PR1 increases the risk of developing paclitaxel-induced peripheral neuropathy in breast cancer patients.

Paclitaxel treatment

Paclitaxel treatment of iPSC-SNs causes growth cone collapse and neurite degeneration.

 

Post-operative delirium in older patients

A common problem following major surgery in elderly patients is the development of postoperative neurological symptoms. Patients who develop postoperative delirium have longer hospital stays, an increased risk of post-discharge decline in functional and cognitive status and increased long-term mortality. Opioid treatment for pain is one contributor to these postoperative neurological problems. In collaboration with Jacqueline Leung in the Department of Anesthesia and Perioperative Care, we are testing for an association between genetic variants and the phenotypes of postoperative delirium, subsyndromal delirium and opioid toxicities. This genome-wide association study leverages several existing patient cohorts of over 2000 older patients who have undergone major non-cardiac surgery at three university medical centers and a prospectively collected validation cohort. The identification of genetic risk factors for postoperative neurological complications could facilitate personalized postoperative pain and symptom management.

 

ABC Transporter Research Projects

Cryo-EM studies of MRP4

The multidrug resistance associated protein 4 (MRP4) transports structurally diverse xenobiotics and endogenous molecules. Its localization to the apical membrane of renal epithelial cells makes it a key player in the renal secretion of drug substrates and MRP4 on capillary endothelial cells at the blood-brain barrier provides protection against neurotoxic adverse effects. In recent years there has been increased attention to the transport of endogenous molecules by MRP4, including eicosanoids, cyclic nucleotides, sulfated steroids and bile salts. Disruption of MRP4-mediated efflux of these signaling molecules has been associated with multiple pathophysiologic conditions, including pulmonary hypertension, platelet dysfunction and CFTR-mediated secretory diarrhea. As a result, MRP4 is an attractive drug target. The development of potent and selective inhibitors of MRP4 would be greatly facilitated by an understanding of its molecular structure and the relationship between structure and transport function. To this end, we are using cryogenic electron microscopy (cryo-EM) to determine the MRP4 structure in a native membrane environment. In collaboration with Drs. Robert Stroud, Yifan Cheng and Charles Craik in the Departments of Biochemistry and Pharmaceutical Chemistry, the bovine MRP4 transporter has been expressed in baculovirus and reconstituted into nanodiscs for cryo-EM. We have recently solved structures in both the nucleotide-free and nucleotide-bound conformations that will guide the development of inhibitors and studies of structure-function.

MRP4

MRP4 is a transmembrane transporter with two transmembrane domains and two nucleotide binding domains.

MRP4 and immunoresistance

In recent years, the introduction of immunotherapy has extended the lives of many cancer patients. However, there remains a large fraction of these patients who do not have a favorable response to immune based therapies. The ABC transporter MRP4 is responsible for the efflux of prostaglandin E2 (PGE2) from the tumor cell and high levels of this eicosanoid in the tumor microenvironment can promote immunoresistance. Targeting MRP4 function may be a novel approach to preventing this resistance.

 

However, basic questions regarding the contributions of MRP4 in the control of PGE2 levels in the tumor microenvironment remain unanswered (pictured). Ongoing studies are testing whether inhibition of MRP4-mediated PGE2 secretion can improve the immunosensitivity of the tumor microenvironment and the response to anti-PD1 therapy in mouse models of colorectal cancer.

PGE2 synthesis, secretion and immunomodulatory effects