Biotech Tracker: New Results May Resurrect SGN-15 Program

Biotech Tracker: New Results May Resurrect SGN-15 Program

August 12, 2003 Seattle Genetics’ (NASDAQ: SGEN) phase II clinical trial of SGN-15 plus Taxotere in non-small cell lung cancer (NSCLC) has generated encouraging preliminary data. The final data analysis, due in “early 2004,” will determine whether the SGN-15 program will be resurrected. That final data set, slated to address quality of life parameters, hopefully will include the application of additional analytic methodologies.

Interim data presented at the 10th World Conference on Lung Cancer in Vancouver show that 62 study subjects were enrolled. Two thirds of the subjects were randomized to receive SGN-15 plus Taxotere, while one third received Taxotere alone. Advantages of the combination regimen included:

median survival – 11.4 months versus 5.1 months (modified intent to treat methodology)
median progression-free survival – 14.9 weeks versus 7.9 weeks (modified intent to treat methodology)
disease control (sum of complete responses, partial responses, and stable disease) rate – 61% versus 39%.
The SGN-15 dose range of 200 to 350 mg/m2 was well tolerated.

Prior to obtaining these data, Seattle Genetics had abandoned SGN-15 development in combination with Taxotere for patients with breast cancer. In colorectal cancer, results were not strong enough to merit further study, although Seattle Genetics will look at SGN-15 in combination with chemotherapeutics other than Taxotere. Hormone refractory prostate carcinoma results looked more promising at this past May’s ASCO meeting, but were preliminary.

SGN-15 is a lipid-binding monoclonal antibody conjugated to the chemotherapeutic doxorubicin. The antigen targeted by SGN-15 is enriched on cancer cells. Doxorubicin has significant adverse effects when administered systemically. These adverse effects include cardiotoxicity, bone marrow suppression, hair loss, nausea and vomiting, sun sensitivity, flushing, sore throat, bruising, bleeding, and fatigue. Minimization of these adverse effects in phase II and III trials of SGN-15 will be a key driver for the construct. So far, SGN-15 has shown some GI toxicity due to binding of the cells in the gut, but otherwise has avoided much of the toxicity associated with systemic administration of doxorubicin.

Companies such as Alza (a subsidiary of Johnson & Johnson, NYSE: JNJ) and Schering-Plough (NYSE: SGP) have taken alternative approaches to maximizing doxorubicin’s therapeutic effects while minimizing adversities. SGN-15 remains far from providing these products with competition, mainly because its magnitude of treatment effect remains suspect. Our modeling estimates the probability of SGN-15’s FDA approval at 20-30%.

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