Christine M. Walko

Genotype-Guided Tamoxifen Dosing Increases Active Metabolite Exposure in Women With Reduced CYP2D6 Metabolism: A Multicenter Study

PURPOSE We examined the feasibility of using CYP2D6 genotyping to determine optimal tamoxifen dose and investigated whether the key active tamoxifen metabolite, endoxifen, could be increased by genotype-guided tamoxifen dosing in patients with intermediate CYP2D6 metabolism. PATIENTS AND METHODS One hundred nineteen patients on tamoxifen 20 mg daily ≥ 4 months and not on any strong CYP2D6 inhibiting medications were assayed for CYP2D6 genotype and plasma tamoxifen metabolite concentrations. Patients found to be CYP2D6 extensive metabolizers (EM) remained on 20 mg and those found to be intermediate (IM) or poor (PM) metabolizers were increased to 40 mg daily. Eighty-nine evaluable patients had tamoxifen metabolite measurements repeated 4 months later. RESULTS As expected, the median baseline endoxifen concentration was higher in EM (34.3 ng/mL) compared with either IM (18.5 ng/mL; P = .0045) or PM (4.2 ng/mL; P < .001). When the dose was increased from 20 mg to 40 mg in IM and PM patients, the endoxifen concentration rose significantly; in IM there was a median intrapatient change from baseline of +7.6 ng/mL (-0.6 to 23.9; P < .001), and in PM there was a change of +6.1 ng/mL (2.6 to 12.5; P = .020). After the dose increase, there was no longer a significant difference in endoxifen concentrations between EM and IM patients (P = .84); however, the PM endoxifen concentration was still significantly lower. CONCLUSION This study demonstrates the feasibility of genotype-driven tamoxifen dosing and demonstrates that doubling the tamoxifen dose can increase endoxifen concentrations in IM and PM patients.

Aprepitant: drug–drug interactions in perspective

The implications of chemotherapeutic drug-drug interactions can be serious and thus need to be addressed. This review concerns the potential interactions of the antiemetic aprepitant, a neurokinin-1 receptor antagonist indicated for use (in Europe) in highly emetogenic chemotherapy and moderately emetogenic chemotherapy (MEC) in combination with a 5-hydroxytryptamine-3 (5-HT3) receptor antagonist and corticosteroids and (in the United States) in combination with other antiemetic agents, for the prevention of acute and delayed nausea and vomiting associated with initial and repeat courses of highly emetogenic cancer chemotherapy including high-dose cisplatin. When considering use of aprepitant for prevention of chemotherapy-induced nausea and vomiting, its potential drug-drug interaction profile as a moderate inhibitor of cytochrome P-450 isoenzyme 3A4 (CYP3A4) has been a source of concern for some physicians and other health care professionals. We explore in this paper how real those concerns are. Our conclusion is that either no interaction or no clinically relevant interaction exists with chemotherapeutic agents (intravenous cyclophosphamide, docetaxel, intravenous vinorelbine) or 5-HT3 antagonists (granisetron, ondansetron, palonosetron). For relevant interactions, appropriate measures, such as corticosteroid dose modifications and extended International Normalized Ratio monitoring of patients on warfarin therapy, can be taken to effectively manage them. Therefore, the concern of negative interactions remains largely theoretical but needs to be verified with new agents extensively metabolized through the 3A4 pathway.

Pharmacogenomic progress in individualized dosing of key drugs for cancer patients

Determining the correct dosage for the majority of traditional chemotherapeutic agents presents a challenge because most drugs have a narrow therapeutic index, which results in a fine balance between doses that cause significant drug toxicity and loss of efficacy. Dosing calculations for most agents use the patients body surface area, a method that correlates poorly with drug pharmacokinetics. Genetic differences in drug-metabolizing enzymes are being evaluated in an effort to explain the pharmacokinetic and pharmacodynamic variability seen with many chemotherapeutic agents. Elucidation of the underlying reasons for this variability will enable individualization of therapy to minimize toxicity and maximize efficacy, and thus improve control over the narrow therapeutic index of these agents. Such investigations have led to Clinical Pharmacology FDA Subcommittee recommendations for changes to drug package instructions. This Review discusses the current limitations of body-surface-area-based dosing, examples of successful pharmacogenomic investigations that have used drug-metabolizing enzymes to decrease drug toxicity and/or improve efficacy, and the future promises of pharmacogenomic-directed pharmacotherapy.

Integration of a clinical pharmacist into the hematology–oncology clinics at an academic medical center

PURPOSE The development, implementation, and early experience with a program providing clinical pharmacist services at the hematology-oncology clinics of a university teaching hospital are described. SUMMARY With funding from a university research grant and other sources, a pharmacist was hired to launch a new program addressing four goals identified in a needs assessment: (1) improved management of supportive care, (2) enhanced education of patients receiving complicated chemotherapy regimens, (3) improved efficiency in the chemotherapy infusion unit, and (4) development of an experiential learning opportunity for pharmacy students and residents. The pharmacist hired to lead the ongoing program was a state-approved clinical pharmacist practitioner (CPP) who had authority to prescribe with physician oversight under established protocols. EXPERIENCE An oncology supportive care consultation service implemented by the CPP in collaboration with a nurse and a physician served 89 new patients in its first 18 months of operation; during that period the CPP made 186 interventions and wrote 136 prescriptions. The CPP also established a chemotherapy counseling service that provided more than 900 bill-able patient education sessions over 18 months. In addition, the CPP launched an effort to increase use of a rituximab rapid-infusion protocol among eligible patients. The creation of the new oncology pharmacist position has given dozens of pharmacy students and residents a new opportunity for interaction with oncology clinic patients and other health care team members. CONCLUSION Integration of the services of a CPP into the hematology-oncology clinics has helped achieve goals set by physician, nursing, and pharmacy leaders.

Treatment of Vancomycin-Resistant Enterococcus with Quinupristin/Dalfopristin and High-Dose Ampicillin

OBJECTIVE: To report the successful treatment of vancomycin-resistant Enterococcus (VRE) bacteremia using the combination of quinupristin/dalfopristin and high-dose ampicillin. CASE SUMMARY: A 38-year-old African American woman with relapsed acute myeloid leukemia and neutropenic fever developed VRE bacteremia following 3 successive courses of vancomycin for methicillin-resistant staphylococcal infections. Treatment with linezolid was initiated; however, after 9 days of therapy, blood cultures continued to reveal VRE and the patient became febrile. The patient was subsequently switched to quinupristin/dalfopristin and high-dose ampicillin. The fever resolved and all subsequent blood cultures were negative after the initiation of combination therapy. DISCUSSION: The emergence of VRE infections presents a treatment challenge in immunocompromised patients. When treating VRE infections in this patient population, the effectiveness of linezolid and quinupristin/dalfopristin is limited by their bacteriostatic activity when used as monotherapy. Recent in vitro data suggest synergistic activity with quinupristin/dalfopristin when used in combination with other antimicrobials in selected isolates of VRE. CONCLUSIONS: Persistent VRE bacteremia was successfully treated in this neutropenic patient using the combination of high-dose ampicillin and quinupristin/dalfopristin. Case reports and in vitro data suggest that concomitant therapy with high-dose ampicillin may be an effective treatment alternative for VRE infections not responding to standard therapy.

Rates of Renal Toxicity in Cancer Patients Receiving Cisplatin With and Without Mannitol

Background: Cisplatin is a widely used antineoplastic. One of the major complications of cisplatin use is dose-limiting nephrotoxicity. There are many strategies to prevent this toxicity, including the use of mannitol as a nephroprotectant in combination with hydration. Objective: We aimed to evaluate the rates of cisplatin-induced nephrotoxicity in cancer patients receiving single-agent cisplatin with and without mannitol. Methods: This single-center retrospective analysis was a quasi experiment created by the national mannitol shortage. Data were collected on adult cancer patients receiving single-agent cisplatin as an outpatient from January 2011 to September 2012. The primary outcome was acute kidney injury (AKI). Results: We evaluated 143 patients who received single-agent cisplatin; 97.2% of patients had head and neck cancer as their primary malignancy. Patients who did not receive mannitol were more likely to develop nephrotoxicity: odds ratio [OR] = 2.646 (95% CI = 1.008, 6.944; P = 0.048). Patients who received the 100 mg/m2 dosing and patients who had a history of hypertension also had a higher likelihood of developing nephrotoxicity: OR = 11.494 (95% CI = 4.149, 32.258; P < 0.0001) and OR = 3.219 (95% CI = 1.228, 8.439; P = 0.017), respectively. Conclusions: When limited quantities of mannitol are available, it should preferentially be given to patients at particularly high risk of nephrotoxicity. Our analysis suggests that those patients receiving the dosing schedule of 100 mg/m2 cisplatin every 3 weeks and those with hypertension are at the greatest risk of nephrotoxicity and would benefit from the addition of mannitol.

Incidence of cetuximab-related infusion reactions in oncology patients treated at the University of North Carolina Cancer Hospital

Purpose The primary purpose of this study was to determine the rate of infusion reactions to cetuximab in oncology patients treated at the University of North Carolina Cancer Hospital. Secondarily, we sought to evaluate predictors of grade 3–4 hypersensitivity, including geography. Methods Data were collected by retrospective chart review for patients treated with cetuximab at the University of North Carolina Cancer Hospital between 15 November 2006 and 31 December 2010. Data were analyzed for occurrence of hypersensitivity reaction in 125 patients with various cancer types. Results Of the 125 subjects, 31 (24.8%) experienced an infusion reaction of any grade. Of 125, 18 (14.4%) experienced a grade 3 or 4 reaction. The odds ratio for patients with an allergy history having a grade 3 or 4 reaction was 2.57 (95% CI 0.93 to 7.09, p = 0.07). Pretreatment with steroids was associated with absence of grade 3 or 4 reaction with an odds ratio of 0.21 (95% CI 0.05 to 0.83, p = 0.04). Mapping of reaction rates by county revealed higher rates in some of the more rural counties of North Carolina, however, statistical power was lacking. Conclusions Rates of hypersensitivity reaction at UNC are similar to rates seen in other areas of the southeastern United States and higher than in other regions of the United States and Europe. Rates of both hypersensitivity reactions and grade 3 to 4 hypersensitivity reactions have not substantially changed over time. Geography, allergy history, and perhaps smoking or cancer type may help predict who will react to cetuximab. Steroids should be strongly considered as premedication in addition to diphenhydramine.

Personalizing Medicine in Geriatric Oncology

Minimizing toxicity while maximizing efficacy is a common goal in the treatment of any condition but its importance is underscored in the discipline of oncology because of the serious nature of many chemotherapeutic toxicities and the risk of cancer recurrence or disease progression. The challenge of achieving an optimal therapeutic index is especially augmented in the elderly population because of age-related metabolism changes and interacting concurrent medications. Additional factors, such as germline mutations in drug-metabolizing enzymes and other pharmacogenomic alterations, may have more pronounced effects in elderly patients, given their predisposition to altered pharmacokinetics and pharmacodynamics with resulting increased risk of toxicity. Examples of the possible interplay of these factors will be discussed using tamoxifen, paclitaxel, codeine, and fluorouracil as starting points. Limited participation of the elderly in many cancer trials, especially trials assessing drug exposure, makes much knowledge on the interaction of these patient and environmental factors speculative in nature but presents an opportunity for future research to achieve better optimization of chemotherapeutic agents in the elderly.

Regorafenib: A Novel Multitargeted Tyrosine Kinase Inhibitor for Colorectal Cancer and Gastrointestinal Stromal Tumors

OBJECTIVE To review currently available literature on the oral multikinase inhibitor regorafenib and its role in the treatment of metastatic colorectal cancer (mCRC), and imatinib- and sunitinib-resistant gastrointestinal stromal tumors (GISTs). DATA SOURCES A comprehensive literature search was performed of PubMed/MEDLINE and American Society of Clinical Oncology (ASCO) abstracts (through August 2013). STUDY SELECTION/DATA EXTRACTION Preclinical pharmacological and phase I to III trials data analyzing regorafenib efficacy and safety in mCRC or imatinib- and sunitinib-resistant GIST patients were evaluated. All available English-language, peer-reviewed articles and ASCO abstracts with relevant information were reviewed. DATA SYNTHESIS Regorafenib was approved for mCRC in September 2012 and for imatinib- and sunitinib-resistant GISTs in February 2013. Regorafenib is an inhibitor of stromal, angiogenic, and oncogenic receptor tyrosine kinases, as well as the RAF/MEK/ERK signaling pathway. Phase III CORRECT (Regorafenib Monotherapy for Previously Treated Metastatic Colorectal Cancer) trial data demonstrated an overall survival benefit for mCRC patients treated with regorafenib (6.4 vs 5.0 months; P = .0052). Phase III GRID (Gastrointestinal Stromal Tumors After Failure of Imatinib and Sunitinib) trial data revealed a progression-free survival benefit in imatinib- and sunitinib-resistant GIST patients (4.8 vs 0.9 months; P < .0001). Its adverse event (AE) profile is comparable to that of other multikinase inhibitors. The most commonly observed grade ≥3 AEs included hypertension, hand-foot skin reaction, rash, diarrhea, and fatigue. CONCLUSIONS Regorafenib is a novel oral multikinase inhibitor that has shown promising results for patients with advanced, unresectable or metastatic treatment-refractory CRCs or imatinib- and sunitinib-resistant GISTs.Objective: To review currently available literature on the oral multikinase inhibitor regorafenib and its role in the treatment of metastatic colorectal cancer (mCRC), and imatinib- and sunitinib-resistant gastrointestinal stromal tumors (GISTs). Data Sources: A comprehensive literature search was performed of PubMed/MEDLINE and American Society of Clinical Oncology (ASCO) abstracts (through August 2013). Study Selection/Data Extraction: Preclinical pharmacological and phase I to III trials data analyzing regorafenib efficacy and safety in mCRC or imatinib- and sunitinib-resistant GIST patients were evaluated. All available English-language, peer-reviewed articles and ASCO abstracts with relevant information were reviewed. Data Synthesis: Regorafenib was approved for mCRC in September 2012 and for imatinib- and sunitinib-resistant GISTs in February 2013. Regorafenib is an inhibitor of stromal, angiogenic, and oncogenic receptor tyrosine kinases, as well as the RAF/MEK/ERK signaling pathway. Phase III CORRECT (Regorafenib Monotherapy for Previously Treated Metastatic Colorectal Cancer) trial data demonstrated an overall survival benefit for mCRC patients treated with regorafenib (6.4 vs 5.0 months; P = .0052). Phase III GRID (Gastrointestinal Stromal Tumors After Failure of Imatinib and Sunitinib) trial data revealed a progression-free survival benefit in imatinib- and sunitinib-resistant GIST patients (4.8 vs 0.9 months; P < .0001). Its adverse event (AE) profile is comparable to that of other multikinase inhibitors. The most commonly observed grade ≥3 AEs included hypertension, hand-foot skin reaction, rash, diarrhea, and fatigue. Conclusions: Regorafenib is a novel oral multikinase inhibitor that has shown promising results for patients with advanced, unresectable or metastatic treatment-refractory CRCs or imatinib- and sunitinib-resistant GISTs.

Amplification of thymidylate synthetase in metastatic colorectal cancer patients pretreated with 5-fluorouracil-based chemotherapy

Resistance to 5-fluorouracil (5-FU) represents a major contributor to cancer-related mortality in advanced colorectal cancer patients. Genetic variations and expression alterations in genes involved in 5-FU metabolism and effect have been shown to modulate 5-FU sensitivity in vitro, however these alterations do not fully explain clinical resistance to 5-FU-based chemotherapy. To determine if alterations of DNA copy number in genes involved in 5-FU metabolism-impacted clinical resistance to 5-FU-based chemotherapy, we assessed thymidylate synthetase (TYMS) and thymidine phosphorylase (TYMP) copy number in colorectal liver metastases. DNA copy number of TYMS and TYMP was evaluated using real time quantitative PCR in frozen colorectal liver metastases procured from 62 patients who were pretreated with 5-FU-based chemotherapy prior to surgical resection (5-FU exposed) and from 51 patients who received no pretreatment (unexposed). Gain of TYMS DNA copy number was observed in 18% of the 5-FU exposed metastases, while only 4% of the unexposed metastases exhibited TYMS copy gain (p = 0.036). No significant differences were noted in TYMP copy number alterations between 5-FU-exposed and -unexposed metastases. Median survival time was similar in 5-FU-exposed patients with metastases containing TYMS amplification and those with no amplification. However, TYMS amplification was associated with shorter median survival in patients receiving post-resection chemotherapy (hazard ratio = 2.7, 95% confidence interval = 1.1-6.6; p = 0.027). These results suggest amplification of TYMS amplification as a putative mechanism for clinical resistance to 5-FU-based chemotherapy and may have important ramifications for the post-resection chemotherapy choices for metastatic colorectal cancer.