Targeted therapeutic agents for colorectal cancer

The treatment of colorectal cancer (CRC) has evolved substantially during the past decade with the advent of molecular targeted therapies. Inhibitors to the vascular endothelial growth factor and epidermal growth factor receptor (EGFR) pathways have been shown to enhance the efficacy of cytotoxic chemotherapy in patients with advanced CRC, and anti-EGFR antibodies demonstrate modest activity as monotherapeutic agents. These biologic agents have improved patient outcomes and survival and have been incorporated into routine clinical practice establishing a new standard of care. Molecular markers have recently been adopted into clinical practice with the finding that the KRAS oncogene is a predictive biomarker for anti-EGFR therapy, whereby the therapeutic benefit of anti-EGFR treatment is restricted to tumors with wild-type KRAS. The use of molecular targeted agents has fewer yet more specific toxicities compared with conventional cytotoxic drugs and enables a more personalized approach to cancer therapy. In contrast to the results for advanced CRC, targeted therapies have not shown a benefit in the adjuvant setting for patients with resected colon cancer. The goal of this review is to provide an update on the medical management of CRC, with a focus on the use of targeted therapy.

Panitumumab: a new frontier of target therapy for the treatment of metastatic colorectal cancer

Panitumumab is a fully human monoclonal IgG(2) antibody targeting the EGF receptor (EGFR). This agent represents a new class of drug owing to its fully human nature, and no need for premedication and loading dose. Panitumumab selectively binds to EGFR, blocking the extracellular domain of the receptor, and has not been associated with the formation of any antibodies directed against it. The drug is indicated as monotherapy for the treatment of patients with EGFR-expressing metastatic colorectal carcinoma with non-mutated (wild-type) KRAS after failure of fluoropyrimidine-, oxaliplatin- and irinotecan-containing chemotherapy regimens. The safety profile is favorable and is generally well tolerated; the most common toxicities are skin rashes and diarrhea. Therefore, panitumumab's hypersensitivity reaction rate is lower when compared with a chimeric monoclonal antibody such as cetuximab. Panitumumab increases the clinician's repertoire of agents to treat metastatic colorectal carcinoma. The available clinical data are the most promising for a single-agent anti-EGFR monoclonal antibody in this disease at the present time. These new data open different clinical scenarios in metastatic colorectal carcinoma patients and encourage clinicians and basic researchers to investigate new therapeutic approaches for this patient subset.

Improving disease control in advanced colorectal cancer: Panitumumab and cetuximab

Colorectal cancer remains a major public health concern in Europe and North America. It is responsible for one million new cases and half a million deaths per year worldwide. During the past few years new effective treatments have evolved improving the outcome of patients with this disease. Several alternatives are currently available for advanced colorectal cancer patients including different chemotherapeutic regimens (fluoropyrimidines, irinotecan and oxaliplatin) and targeted therapies such as bevacizumab and cetuximab. Different combinations achieve a median survival of over 2 years. Intense efforts focus on identifying agents targeting growth factor receptors, signal transduction pathways or angiogenesis mediators. One of the last available drugs for the management of advanced colorectal cancer is panitumumab, a well-tolerated and effective anti-EGFR monoclonal antibody approved as a single agent in chemotherapy refractory patients. We discuss the current evidence supporting panitumumab for metastatic colorectal cancer treatment, potential predictive biomarkers and ongoing clinical trials with different combinations including panitumumab.

Broad antitumor activity in breast cancer xenografts by motesanib, a highly selective, oral inhibitor of vascular endothelial growth factor, platelet-derived growth factor, and Kit receptors

PURPOSE

Angiogenesis plays a critical role in breast cancer development and progression. Vascular endothelial growth factor (VEGF) is a potent angiogenic factor that regulates endothelial cell proliferation and survival. We investigated the effects of motesanib, a novel, oral inhibitor of VEGF receptors 1, 2, and 3; platelet-derived growth factor receptor; and Kit receptor, on the growth of xenografts representing various human breast cancer subtypes.

EXPERIMENTAL DESIGN

Athymic nude mice were implanted with MCF-7 (luminal) or MDA-MB-231 (mesenchymal) tumor fragments or Cal-51 (mixed/progenitor) tumor cells. Once tumors were established, animals were randomized to receive increasing doses of motesanib alone or motesanib plus cytotoxic chemotherapy (docetaxel, doxorubicin, or tamoxifen).

RESULTS

Across all three xenograft models, motesanib treatment resulted in significant dose-dependent reductions in tumor growth, compared with vehicle-treated controls, and in marked reductions in viable tumor fraction and blood vessel density. No significant effect on body weight was observed with compound treatment compared with control-treated animals. Motesanib did not affect the proliferation of tumor cells in vitro. There was a significantly greater reduction in xenograft tumor growth when motesanib was combined with docetaxel (MDA-MB-231 tumors) or with the estrogen receptor modulator tamoxifen (MCF-7 tumors), compared with either treatment alone, but not when combined with doxorubicin (Cal-51 tumors).

CONCLUSIONS

Treatment with motesanib alone or in combination with chemotherapy inhibits tumor growth in vivo in various models of human breast cancer. These data suggest that motesanib may have broad utility in the treatment of human breast cancer.

Current situation of Panitumumab, Matuzumab, Nimotuzumab and Zalutumumab

EGFR overexpression usually correlates with a more advanced disease stage, a poorer prognosis and a worse chemotherapy response. EGFR expression increase has been observed in many tumours. For all the aforementioned reasons, EGFR inhibition can be considered an attractive approach in cancer treatment. One strategy has been receptor inhibition of extracellular domain using monoclonal antibodies. Cetuximab is the most developed one and there is plenty information on the literature about its current status. In this review we focus on other EGFR monoclonal antibodies under clinical development. The more developed one is Panitumumab. Its clinical development is taking place very quickly and it has mainly been studied in colorectal cancer showing promising results. There are also other interesting drugs such as Matuzumab, Nimotuzumab and Zalutumumab.

Effect of coadministration of ketoconazole, a strong CYP3A4 inhibitor, on pharmacokinetics and tolerability of motesanib diphosphate (AMG 706) in patients with advanced solid tumors

Motesanib diphosphate is a novel angiogenesis inhibitor selectively targeting vascular endothelial growth factor receptors 1, 2, and 3; platelet-derived growth factor receptor and stem cell factor receptor. The purpose of this phase 1b, drug-drug interaction study was to investigate the effect of ketoconazole, a strong inhibitor of the cytochrome P450 3A4 isoenzyme, on the pharmacokinetics and tolerability of motesanib diphosphate. Fourteen patients with advanced solid tumors refractory to standard treatment were enrolled and received motesanib diphosphate 50 mg once daily from day 1 through 15. Patients were randomized to receive a single oral dose of ketoconazole 400 mg either on day 8 (Sequence 1; n = 7) or day 15 (Sequence 2; n = 7), while pharmacokinetic samples were collected. After completion of this part (day 16), 13 patients received an escalated once-daily dose of motesanib diphosphate 125 mg. Evaluable pharmacokinetic data (n = 12) suggest that ketoconazole modestly increased motesanib exposure. The motesanib area under the concentration-time curve (AUC) from 0 to 24 h increased by 86% (90% CI, 1.50-2.29; P < 0.001) and the maximum plasma concentration (C (max)) by 35% (90% CI, 1.12-1.64; P = 0.02), compared with motesanib diphosphate administration alone. The tolerability profile (with or without ketoconazole coadministration) was consistent with that from other motesanib diphosphate monotherapy studies. Treatment-related adverse events were mild to moderate and commonly included fatigue (50% of patients), hypertension (43%), diarrhea (21%), dizziness (14%), paresthesia (14%), and vomiting (14%). Hypertension was the most common related grade 3 event (21%). No grade 4 or 5 treatment-related adverse events occurred.