Sildenafil citrate suppresses disease progression in patients with Waldenstrom’s macroglobulinemia

Abstract

7556 Background: Responses to sildenafil citrate (Viagra), a phosphodiesterase-5 inhibitor used to treat erectile dysfunction, have been observed in patients with Waldenstrom’s Macroglobulinemia (WM). Moreover, sildenafil citrate induces apoptosis of WM lymphoplasmacytic cells (Clin Lymphoma 5:205, 2004). We therefore conducted a prospective phase II study of sildenafil citrate in patients with slowly progressing WM who did not meet consensus eligibility for active therapy (Semin Oncol 2003; 30:116). Intended therapy was as follows: Week 1 25 mg po qD Week 2 50 mg po qD Week 3 75 mg po qD Week 4, then Months 2–24 100mg po qD or Maximum Tolerated Dose Methods: Thirty patients were enrolled, 18 of whom were previously untreated. All patients demonstrated progressing disease prior to enrollment. Median age was 66 (range 43–85 yrs), baseline BM involvement was 30% (range 5–90%), serum IgM was 3,640 (range 790–6,720 mg/dL), hematocrit was 37.1% (range 32.7–58.5%), and B2M was 2.3 (range 1.5–8.9 mg/dL). Patients were evaluable for response after 3 months of therapy. Results: At a median of 3 months, serum IgM levels declined in 19/30 (63%) patients from a median of 3,640 (range 790–6,720 mg/dL) to 2,965 (range 1,170–6,110 mg/dL). 5/30 patients (17%) demonstrated at least a minor response (≥25% IgM decrease). Two patients were taken off study for non-response to therapy. Toxicities were mild and included headaches, sinus congestion, facial flushing, dyspepsia, and generally resolved on their own with prolonged sildenafil citrate usage. Only two patients required dose modification to 25 mg and 75 mg po qD, respectively. Corollary studies to determine putative mechanisms of action for sildenafil citrate in WM were also performed and will be updated at the meeting. Conclusions: This prospective clinical trial provides preliminary evidence for activity of sildenafil citrate in patients with advancing WM. With minimal toxicity, sildenafil citrate appears to have suppressed disease progression in more than half of patients and has resulted in objective responses, thus warranting further investigation in WM and possibly other B-cell disorders. No significant financial relationships to disclose.