RESUMEN
The treatment of breast cancer that is driven by amplification and overexpression of human epidermal growth factor receptor 2 (HER2) has been drastically improved by the development of HER2-targeted therapies including trastuzumab and lapatinib. While outcomes for patients diagnosed with HER2-positive breast cancer have been greatly impacted by these therapies, treatment resistance is common and toxicity to standard regimens remains a therapeutic challenge. Trastuzumab emtansine (T-DM1) is a novel antibody drug conjugate that consists of the HER2-targeted monoclonal antibody, trastuzumab, joined via a stable linker to a derivative of maytansine, a highly potent cytotoxic chemotherapy. While other antibody drug conjugates have been developed clinically, this is the first in its class that maintains the antitumor properties of the HER2-targeted antibody, trastuzumab, and also avoids release of the chemotherapy until the molecule is taken up inside the HER2-overexpressing cancer cell. Several phase I studies have shown T-DM1 is safe, tolerable and has activity in trastuzumab- and lapatinib-pretreated breast cancer. Moreover, phase II studies are now being reported that confirm its safety and clinical efficacy in both the frontline and heavily pretreated settings. Preliminary data from phase II studies evaluating its use in combination with other cytotoxics have also been reported and several large phase III trials are underway to evaluate its use in the HER2-positive metastatic breast cancer setting. This paper aims to provide a detailed review of the preclinical and clinical evidence relating to the mechanism of action, efficacy and safety of T-DM1 for the treatment of HER2-positive breast cancer.
RESUMEN
PURPOSE: This review aims to present the preclinical and clinical data regarding efficacy and safety of lapatinib alone and in combination with other agents in the treatment of human epidermal growth factor receptor-2 (HER2)-overexpressing breast cancer. BACKGROUND: HER2-positive (HER2+) breast cancer remains a treatment challenge. It is more aggressive than other breast cancers and it is associated with a poor outcome. Targeted therapy for HER2+ breast cancer has significantly changed the clinical course of the disease. Despite advances in therapy, there remains an unmet need in the treatment of HER2+ breast cancer. Lapatinib is a novel, orally bioavailable epidermal growth factor receptor/HER2+ targeted agent. Many trials have investigated the efficacy and safety of lapatinib alone and in conjunction with other agents in the treatment of HER2+ breast cancer. METHODS AND RESULTS: Preclinical and clinical trials of lapatinib have shown that it is effective in the treatment on HER2+ breast cancer. More important, studies show that it is effective in the setting of trastuzumab resistance and in the treatment of central nervous system metastases, both of which are current treatment challenges. Furthermore, lapatinib is effective in conjunction with trastuzumab in the treatment of early breast cancer. Data regarding the safety of lapatinib show that it is generally well tolerated; however, multiple studies have shown significant (grade 3 and 4) diarrhea and rash associated with lapatinib, thereby limiting its use. Carditoxicity has not been a significant adverse event associated with the use of lapatinib. CONCLUSION: Lapatinib is effective alone and in conjunction with other agents in the treatment of HER2+ breast cancer. However, its use is limited by significant diarrhea and rash.
RESUMEN
Bovine adrenal chromaffin granule cytochrome (cyt) b561 is a transmembrane hemoprotein that plays a key role in transporting reducing equivalents from ascorbate to dopamine-beta-hydroxylase for catecholamine synthesis. We have developed procedures for expression and purification of functional bovine adrenal cyt b561 in insect and yeast cell systems. The bovine cyt b561 coding sequence, with or without a hexahistidine-tag sequence at the C-terminus, was cloned into the pVL1392 transfer vector under the control of the polyhedrin promoter to generate recombinant baculovirus for protein expression in Sf9 insect cells (approximately 0.5 mg detergent-solubilized cyt b561/L culture). For the yeast system, the cyt b561 cDNA was modified with a hexahistidine-tag sequence at the C-terminus, and inserted into the pPICZB vector under the control of the alcohol oxidase promoter. The recombinant plasmid was transformed into Pichia pastoris GS115 competent cells to give methanol-inducible cyt b561 expression (approximately 0.7 mg detergent-solubilized cyt b561/L culture). Recombinant His-tagged cyt b561 expressed in Sf9 or Pichia cells was readily solubilized from membrane fractions with dodecyl maltoside and purified to electrophoretic homogeneity by one-step chromatography on Ni-NTA affinity resin. The purified recombinant cytochrome from both systems had a heme to protein ratio close to two and was fully functional, as judged by comparison with the spectroscopic and kinetic parameters of the endogenous cytochrome from chromaffin granules. A novel procedure for isolation of chromaffin granule membranes was developed to utilize frozen adrenal glands instead of fresh tissue.