Cancer cell
Cancer cell

Results from the ongoing phase II trial of XL184 demonstrates substantial activity in patients with previously treated progressive or recurrent glioblastoma multiforme (study XL184-201). Data of the ongoing trial was presented during the 45th annual meeting of the American Society of Clinical Oncology (ASCO). XL184 has exhibited dose-dependent tumor growth inhibition and tumor regression in a variety of tumor models, including breast cancer, colon cancer, medullary thyroid cancer , non-small cell lung cancer, and glioblastoma. Additional research now shows that treatment with XL184 at a dose of 175 mg PO qd results in potent inhibition of glioblastoma multiforme (GBM).

XL184 (BMS-907351) is a potent, orally administered, small molecule inhibitor of receptor tyrosine kinases. The compound also inhibits MET, a receptor tyrosine kinase that plays a key role in cellular proliferation, migration, and angiogenesis. MET is mutationally activated in some tumor types, such as hereditary and sporadic papillary renal cell carcinoma and some head and neck cancers. More frequently, MET is either over-expressed or activated in the absence of mutation in glioblastomas, breast carcinomas, some gastric cancers, and other solid tumors. MET amplification has been demonstrated in some NSCLCs.

Overexpression of MET and vascular endothelial growth factor receptor-2 (VEGFR-2), as well as the ligands which activate these receptors, has been shown to correlate with poor prognosis in glioblastoma multiforme, which is the most common and most aggressive form of brain tumor in humans, accounting for 52% of all primary brain tumor cases and 20% of all intracranial tumors, and occurs in only 2?3 cases per 100,000 people in Europe and North America.

In addition, phosphorylated RET has been described in some cases of glioblastoma multiforme. Expression of VEGF has been observed in a variety of cancers and has been associated with prognostic significance. Targeting the VEGF receptor has been recognized as a potential anti-cancer strategy in multiple tumors. Dual targeting of MET and VEGFR2 blocks two of the major mechanisms tumors use to overcome hypoxia. Activated RET is involved in cell signaling cascades that regulate cell proliferation, migration, differentiation, and survival. RET is mutationally activated in papillary thyroid cancer (PTC) and in both familial and sporadic forms of medullary thyroid cancer (MTC).

Development of XL184
Exelixis Inc. (210 East Grand Avenue, P.O. Box 511, South San Francisco, CA 94083-0511 phone (650) 837-7000,fax (650) 837-8300), a biotechnology company focusing on the development of compounds targeting multiple receptor tyrosine kinases simultaneously as well as components of key components of downstream signaling pathways that play important roles in cancer and metabolic diseases, develops XL184 with Bristol-Myers Squibb Company (BMS), a global biopharmaceutical company.The companies are currently conducting multiple clinical studies for XL184, in glioblastoma multiforme (GBM) and medullary thyroid cancer (MTC). John De Groot, MD, of The MD Anderson Cancer Center, and an investigator on the Phase 2 glioblastoma-trial, presented data during a poster session during the ASCO meeting.

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The exploratory study evaluated the safety, tolerability and clinical activity of XL184 at a continuous daily dose of 175 mg in patients with previously treated glioblastoma multiforme. To date, 46 patients who make up the intent to treat (ITT) population have been enrolled in the trial, including 30 (65%) in first relapse and 16 (35%) in second or third relapse. Importantly, the trial did not exclude patients previously treated with an antiangiogenic agent.The tumor response, as determined by an independent radiology facility (IRF), using MacDonald criteria were reported. By ITT analysis, 7 of 35 (20%) of the antiangiogenic na?ve patients had a confirmed partial response. The overall rate of response in all patients, including the refractory population of previously treated patients with an antiangiogenic therapy, was 15%. The median duration of response by IRF was 2.9 months (range = 1.9-8.6 months). In an exploratory analysis, among 35 patients with at least one post baseline MRI scan, 12 (34%) had tumor shrinkage ?50% as their best response as determined by investigator, including 1 patient who had received prior antiangiogenic therapy.

The efficacy evaluable population was defined as patients having received at least 1 dose of XL184 and either had at least 1 post-baseline tumor assessment per investigator or failed to return for any tumor assessments because of death or clinical determination of progression. In the anti-angiogenic na?ve population, 7 of 31 (23%) of efficacy evaluable patients had a confirmed partial response by IRF. The 6-month progression-free survival (PFS) rate in patients receiving no prior antiangiogenic therapy was 23%, with 10 patients censored for PFS at the time of analysis, and the median PFS interval was 3.6 months.

?These initial data from our ongoing glioblastoma multiforme (GBM) program are encouraging, and suggest that XL184 could have utility in this underserved indication,? said Michael M. Morrissey, Ph.D., president of research and development at Exelixis. ?We believe that these data support continued evaluation of XL184 in patients with GBM, and we intend to enroll additional patients in this study to better assess the compound?s anti-tumor activity and safety profile in this difficult to treat patient population.?

As of January 6, 2009 all 46 patients were evaluated for safety. At least 1 post-baseline tumor assessment at 4 weeks was available for 26 pts. Of these, 17 pts had not received prior therapy with an anti-angiogenic agent, whereas 9 pts had received prior therapy with bevacizumab (n = 6), vandetanib (n = 2), or VEGF-TRAP (n = 1). Most adverse events were of Grade 1 or 2 severity. The most frequently occurring Grade 3 and Grade 4 adverse events were: fatigue (30%), alanine aminotransferase increase (9%), confusional state (9%), lipase increase (9%), lymphopenia (9%), convulsion (7%), headache (7%), and hypophosphatemia (7%). Adverse events of special interest were: hypertension (all incidences, 39%; Grade 3/4, 7%), palmar-plantar erythrodysesthesia (30%; 7%), bleeding events (28%; 9%), proteinuria (26%; 0%), pulmonary embolism (9%; 7%) and craniotomy wound dehiscence (4%; 2%).

In the study, 87% of patients had a dose interruption of XL184, median average daily dose was 122 mg/day. XL184 will be evaluated at a lower dose of 125 mg daily in order to provide continuous and sustained exposure to the drug in this previously treated glioblastoma population.

Other studies with XL184
Correlative tumor profiling and biomarker evaluation and vascular imaging data from this trial was also presented in two additional posters in the same poster session. Abstract 2048, entitled ?Neurovascular imaging in GBM patients quantifies early physiologic changes after treatment with XL184, an inhibitor of multiple receptor tyrosine kinases: results from a Phase II study? was presented by Gregory Sorensen, MD, from the Massachusetts General Hospital, Boston, MA, and abstract 2049, entitled “Correlative tumor molecular profiling and plasma biomarker analysis in a phase 2 study of XL184 in patients with progressive or recurrent glioblastoma multiforme” was presented by Samuel DePrimo, PhD, Exelixis Inc, South San Francisco, CA.

Medullary Thyroid Cancer
The American Cancer Society estimates that Medullary Thyroid Cancer (MTC) accounts for aproximately5% of all thyroid cancers. Medullary thyroid carcinoma (MTC) is a rare calcitonin-producing neuroendocrine tumour that originates from the parafollicular C-cells of the thyroid gland. The RET proto-oncogene encodes the RET receptor tyrosine kinase, which has essential roles in cell survival, differentiation and proliferation.

The disease occurs in sporadic and inherited forms (approximately 80% and 20% of MTC, respectively). Patients with the inherited form of medullary thyroid carcinoma (MTC) invariably have an activating mutation in RET in their germline DNA. Activating mutations in RET are also present in the tumor DNA of up to 50% of sporadic MTC patients with no familial history of thyroid cancer. MTC may metastasize to lymph nodes or other organs before it is ever diagnosed. Additionally, MTC does not take up radioactive iodine, which is commonly used to treat other types of thyroid cancers and to diagnose metastases. As a result, MTC is more difficult to treat than other thyroid cancers.

So far, there are no approved therapies for MTC; however, common treatments for MTC include surgery to remove malignant tissue, radiation therapy, and chemotherapy, all of which are associated with potential side effects, some of which may be long-term.During 2008 annual meeting of the American Society of Clinical Oncology (ASCO) safety and clinical activity data were presented from an ongoing phase 1 trial of XL184 in 69 patients with various solid tumors, including 17 MTC patients evaluable for response. These data showed a disease control rate (percentage of patients with partial responses or prolonged stable disease greater than 3 months) of 100% in the evaluable MTC patients, with 53% of those patients (9 of 17) experiencing partial responses. In this trial, the median duration of partial responses and stable disease for patients with MTC had not yet been reached. Most of the MTC patients in the trial had previously failed other treatments, including tyrosine kinase inhibitors with anti-RET activity, including vandetanib (AstraZeneca, Zactima?, also known as ZD6474), sorafenib (Nexavar?, Bayer/Onyx), or motesanib (Amgen/Takeda) chemotherapeutic agents, immunotherapy, radioactive iodine, and radiotherapy. Patients are now recruited to participate in new and ongoing trials.

Last editorial review: June 29, 2009.

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