Susan Goodin

Epothilones: Mechanism of Action and Biologic Activity

Drugs that target microtubules are among the most commonly prescribed anticancer therapies. Although the mechanisms by which perturbation of microtubule function leads to selective death of cancer cells remain unclear, several new microtubule-targeting compounds are undergoing clinical testing. In part, these efforts focus on overcoming some of the problems associated with taxane-based therapies, including formulation and administration difficulties and susceptibility to resistance conferred by P-glycoprotein. Epothilones have emerged from these efforts as a promising new class of anticancer drugs. Preclinical studies indicate that epothilones bind to and stabilize microtubules in a manner similar but not identical to that of paclitaxel and that epothilones are effective in paclitaxel-resistant tumor models. Clinical phase I and early phase II data are available for BMS-247550, BMS-310705, EPO906, and KOS-862. The results suggest that these compounds have a broad range of antitumor activity at doses and schedules associated with tolerable side effects.

Clinical and biologic activity of an estrogenic herbal combination (PC-SPES) in prostate cancer

Background Herbal mixtures are popular alternatives to demonstrated therapies. PC-SPES, a commercially available combination of eight herbs, is used as a nonestrogenic treatment for cancer of the prostate. Since other herbal medicines have estrogenic effects in vitro, we tested the estrogenic activity of PC-SPES in yeast and mice and in men with prostate cancer. Methods We measured the estrogenic activity of PC-SPES with transcriptional-activation assays in yeast and a biologic assay in mice. We assessed the clinical activity of PC-SPES in eight patients with hormone-sensitive prostate cancer by measuring serum prostate-specific antigen and testosterone concentrations during and after treatment. Results In complementary yeast assays, a 1:200 dilution of an ethanol extract of PC-SPES had estrogenic activity similar to that of 1 nM estradiol, and in ovariectomized CD-1 mice, the herbal mixture increased uterine weights substantially. In six of six men with prostate cancer, PC-SPES decreased serum testostero...

Lapatinib : A Dual Inhibitor of Human Epidermal Growth Factor Receptor Tyrosine Kinases

BACKGROUND Lapatinib, the first dual inhibitor of epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2) tyrosine kinases, was approved by the US Food and Drug Administration (FDA) in 2007. It is indicated for use in combination with capecitabine for the treatment of patients with advanced breast cancer or metastatic breast cancer (MBC) whose tumors overexpress HER2 (ErbB2) and who have received previous treatment that included an anthracycline, a taxane, and trastuzumab. OBJECTIVE This review summarizes the pharmacology, pharmacokinetics, clinical efficacy, and safety profile of lapatinib, and its current and potential role in the treatment of breast cancer and other malignancies. METHODS Relevant English-language publications were identified through searches of MEDLINE (1966-May 2008),the American Society of Clinical Oncology abstracts database (2000-2007), abstracts from the San Antonio Breast Cancer Symposium (2005-2007), and the FDA Web site (January 2008). Search terms included lapatinib, GW572016, HER2, EGFR, receptor tyrosine kinase, dual-receptor blockade, adverse events, and clinical trials. RESULTS The T(max) of lapatinib after oral administration is 3 to 4 hours. Dividing the dose or administering it with food, particularly a high-fat meal, increases the AUC >2-fold. Lapatinib is metabolized primarily by the cytochrome P450 3A4 isozyme, with 1 metabolite remaining active against EGFR but not HER2. Due to drug accumulation, the t(1/2) of lapatinib is 24 hours with continuous dosing. In a Phase III trial comparing lapatinib and capecitabine with capecitabine alone in women with HER2-positive, locally advanced breast cancer or MBC that had progressed after treatment with an anthracycline, a taxane, and trastuzumab, the combination of lapatinib and capecitabine was associated with a numeric improvement in response rate compared with capecitabine alone (22% vs 14%, respectively; P = NS) and a significant increase in time to progression (6.2 vs 4.3 months; hazard ratio = 0.57; 95% CI, 0.43-0.77; P < 0.001). Lapatinib has been reported to have antitumor activity in Phase II trials when used as first-line therapy for MBC, in patients with inflammatory breast cancer, and in patients with central nervous system metastases. Phase II trials in other solid tumor types found modest activity. The approved dosing of lapatinib is 1,250 mg PO QD given continuously in combination with capecitabine 2,000 mg/m(2) daily administered in 2 divided doses on days 1 to 14 of a 21-day cycle. The most common clinical toxicities of all grades associated with lapatinib used in combination with capecitabine in the pivotal clinical trial were diarrhea (65%), hand-foot syndrome (53%), nausea (44%), rash (29%), and fatigue (24%). Cardiac toxicity appears to be less frequent with lapatinib than with trastuzumab. CONCLUSIONS Lapatinib is a dual inhibitor of the EGFR and HER2 tyrosine kinases. It is approved by the FDA for use in combination with capecitabine for the treatment of HER2-positive MBC that has progressed with standard treatment. In clinical trials, this combination was associated with a significant improvement in the time to progression in patients with MBC. Lapatinibs efficacy in other malignancies that overexpress EGFR and/or HER2 is under evaluation.

Targeting tumor metabolism with 2-deoxyglucose in patients with castrate-resistant prostate cancer and advanced malignancies.

A profound difference between cancer and normal tissues is the preferential utilization of glycolysis by cancer cells. To translate this paradigm in the clinic, we completed a phase I study of 2‐deoxyglucose (2DG), and assessed 2DG uptake with fluorodeoxyglucose (FDG) positron emission tomography (PET) and the autophagy substrate p62 as a marker of 2DG resistance.

Pharmacokinetics of Cetuximab After Administration of Escalating Single Dosing and Weekly Fixed Dosing in Patients with Solid Tumors

Purpose: Previous studies of cetuximab pharmacokinetics did not fully characterize its elimination phase. The purpose of this trial was to evaluate the pharmacokinetics of cetuximab given as a single dose followed by weekly fixed repeated dosing in patients with solid tumors. Experimental Design: Patients were randomly assigned to treatment with a single 2-hour infusion of cetuximab at doses of 50, 100, 250, 400, or 500 mg/m2 followed 3 weeks later by weekly 1-hour infusions of cetuximab at a fixed dose of 250 mg/m2. Extended pharmacokinetic sampling was collected through 504 hours after the first drug administration. Trough samples were obtained before each fixed weekly dose. Single and multidose pharmacokinetic variables were correlated with clinical outcomes. Results: Forty patients were enrolled. Pharmacokinetic analysis confirmed previous reports of nonlinear pharmacokinetics for cetuximab. Modeling studies predicted a 90% saturation of clearance at a dose of 260 mg/m2. Analyses of weekly trough concentrations indicated a slight accumulation of drug concentrations following repeated weekly dosing. Correlative studies indicated a significant association between cetuximab clearance and both body surface area (P = 0.002) and weight (P = 0.002). The occurrence of rash was significantly associated with disease stability (P < 0.002) but not with cetuximab pharmacokinetic variables. Conclusions: Pharmacokinetic results support using body surface area or weight in calculating individual cetuximab doses. A weekly dose of 250 mg/m2 is predicted to nearly fully saturate cetuximab clearance and, by inference, epidermal growth factor receptors. The association between rash and disease stability supports further prospective studies of this relationship.

Phase I Clinical and Pharmacologic Study of 13-cis-Retinoic Acid, Interferon Alfa, and Paclitaxel in Patients With Prostate Cancer and Other Advanced Malignancies

PURPOSE Recent studies demonstrate that retinoids decrease expression of the anti-apoptotic protein bcl-2, enhance the effect of chemotherapy, and act synergistically with interferon alfa (IFNalpha) to inhibit tumor cell growth in vitro. A phase I trial of 13-cis-retinoic acid (CRA), IFNalpha, and paclitaxel (TAX) was conducted to determine the toxicity and recommended phase II dose of this combination. Pharmacodynamic studies were performed to determine whether CRA and IFNalpha could modulate bcl-2 expression in vitro and in patients. PATIENTS AND METHODS Twenty-two patients with prostate cancer or other advanced malignancies were treated with CRA/IFNalpha and escalating doses of TAX. The effect of CRA/IFNalpha on TAX pharmacokinetics was analyzed in both patients and human liver microsomes. The effect of CRA/IFNalpha on bcl-2 expression was assessed in vitro and in peripheral-blood mononuclear cells (PBMCs) by immunoblotting. RESULTS CRA 1 mg/kg on days 1 to 4, IFNalpha 6 MU/m(2) subcutaneously on days 1 to 4, and TAX 175 mg/m(2) on day 3 was well tolerated. Pharmacokinetic studies demonstrated that CRA/IFNalpha caused a 33% decrease in TAX clearance and a 23% decrease in the area under the concentration-time curve values of the TAX metabolite 6-alfa-hydroxytaxol (6-HT). CRA alone reduced conversion of TAX to 6-HT by 41% in human liver microsomes. CRA/IFNalpha decreased bcl-2 expression in vitro and in PBMCs. CONCLUSION CRA/IFNalpha and TAX is a well-tolerated regimen. CRA/IFNalpha increases TAX area under the concentration-time curve through an inhibitory effect of CRA on the metabolism of TAX to 6-HT. CRA/IFNalpha can modulate bcl-2 expression in vitro and demonstrates similar biologic activity in patients. Further studies will determine the activity of CRA/IFNalpha/TAX and validate the assessment of bcl-2 in PBMCs as a marker of tumor response.

Phase I Trial of Weekly Docetaxel With Concurrent Three-Dimensional Conformal Radiation Therapy in the Treatment of Unfavorable Localized Adenocarcinoma of the Prostate

PURPOSE A phase I trial was conducted to determine the maximally tolerated dose (MTD) of concurrent weekly docetaxel and three-dimensional conformal radiation therapy (3-D CRT) in unfavorable localized adenocarcinoma of the prostate. PATIENTS AND METHODS Patients with unfavorable localized adenocarcinoma of the prostate underwent daily 3-D CRT to a total dose of 70.2 Gy at 1.8 Gy/fraction and concurrent docetaxel given once a week for 8 to 9 weeks. The initial weekly docetaxel dose level was 5 mg/m(2) and the docetaxel doses were escalated as follows: 8, 12, 16, 20, and 25 mg/m(2). RESULTS Between January 2000 and August 2002, 22 men completed the chemoradiation therapy protocol. The dose-limiting toxicity was grade 3 diarrhea, which occurred in the first two patients treated at the 25 mg/m(2) docetaxel dose level. The MTD of weekly docetaxel was determined to be 20 mg/m(2). The overall incidence of grade 2 diarrhea and grade 2 dysuria was 36% and 23%, respectively. Seven (32%) and 15 (68%) patients did not experience any diarrhea or dysuria, respectively. No neutropenia or thrombocytopenia was observed. One patient required intermittent urinary catheterization 10 months postcompletion of therapy, which resolved without any surgical intervention. Seventeen patients remain in prostate-specific antigen remission. At a median follow-up interval of 8 months (range, 2 to 27 months), all patients are alive. CONCLUSION Concurrent weekly docetaxel in conjunction with 3-D CRT is well tolerated with acceptable toxicity. The MTD of weekly docetaxel was determined to be 20 mg/m(2) with concurrent 3-D CRT.

Overcoming Drug Resistance in Patients with Metastatic Breast Cancer

Metastatic breast cancer is generally considered to be incurable, with response rates and duration of response progressively declining with subsequent lines of treatment. Tumors are either intrinsically resistant to systemic therapy or acquire resistance at some point during multiple courses of therapy. Mechanisms of drug resistance are numerous and include accelerated drug efflux, drug activation and inactivation, alterations in drug target, processing of drug‐induced damage, and evasion of apoptosis. Targeted anticancer agents for the treatment of breast cancer, such as hormonal agents or the more recently approved epidermal growth factor receptor inhibitors, are also associated with intrinsic and acquired resistance. A variety of strategies have been devised to prevent or overcome resistance to systemic anticancer therapy, including drug combinations and sequential regimens. However, it appears that resistance to established cytotoxic and targeted agents is inevitable. Novel agents with reduced susceptibility to resistance may prevent or delay the emergence of resistance and improve survival in patients with common solid tumors, including metastatic breast cancer. We are hopeful that further elucidation of the cellular and molecular processes that allow tumor cells to develop resistance and the use of new agents to combat these mechanisms will improve outcomes for patients with metastatic breast cancer.

Novel cytotoxic agents: Epothilones

PURPOSE The epothilones are effective antitumor medications for patients with breast cancer, including patients who have been previously treated with or are resistant to anthracyclines or the taxanes. SUMMARY With the best currently available therapies, the median survival time for patients with metastatic breast cancer is only 2-3 years, and many patients develop resistance to taxanes or other chemotherapy drugs. The epothilones are a novel class of antitumor medications, similar to the taxanes in some respects, but that also possess several advantages. Like taxanes, epothilones are believed to produce antitumor effects by binding to and stabilizing intracellular microtubules, which are essential in DNA replication and cell division. Several in vitro and animal studies have shown that the epothilones are more potent microtubule stabilizers than the taxanes, they are effective against cancer cell lines with high levels of drug resistance, and they induce the regression of taxane-resistant human tumors. Preclinical studies also have demonstrated synergistic increases in tumor cell killing when the epothilones are combined with other antitumor medications. Epothilone B (patupilone) has been evaluated in a series of phase I and II clinical trials, which demonstrated disease stabilization or objective responses in patients with a variety of cancers, including ovarian, prostate, breast, colon, stomach, and kidney cancers. This agent is currently being evaluated in phase III clinical trials. A second epothilone, ixabepilone, was recently approved by the FDA for the treatment of metastatic breast cancer. Ixabepilone was evaluated as monotherapy for the treatment of breast cancer in phase II clinical trials of previously untreated patients and in taxane-experienced and taxane-resistant disease. A phase III clinical trial demonstrated that the combination of ixabepilone and capecitabine was superior to capecitabine alone in heavily pretreated, taxane-resistant patients. CONCLUSION Ongoing clinical trials will continue to define the role of the epothilones in cancer therapy.

Abiraterone in Prostate Cancer: A New Angle to an Old Problem

Abiraterone acetate is an orally administered potent inhibitor of cytochrome P450, family 17, subfamily A, polypeptide 1 (CYP17), which is essential for synthesis of testosterone from cholesterol. Although decreasing serum testosterone through inhibition of testicular function is the first line of treatment for men with metastatic prostate cancer, residual androgens may still be detected in patients treated with luteinizing hormone-releasing hormone agonists or antagonists. Treatment with abiraterone results in rapid, and complete, inhibition of androgen synthesis in the adrenal glands and potentially within the tumor itself. An overall survival benefit of maximal androgen suppression was recently shown in a randomized placebo-controlled phase III clinical trial of abiraterone with prednisone versus prednisone in men with metastatic castrate-resistant prostate cancer previously treated with docetaxel chemotherapy. Abiraterones efficacy shows the importance of androgen signaling in patients with castrate-resistant metastatic disease, with additional confirmation from recent studies of other novel agents such as MDV3100, an androgen receptor signaling inhibitor. These promising results now pose a new angle to an old problem about hormonal therapy and raise new questions about how resistance develops, how to best sequence therapy, and how to optimize combinations with other emerging novel agents. Clin Cancer Res; 18(7); 1848–54. ©2012 AACR.