BCL-2 is dispensable for thrombopoiesis and platelet survival.

Navitoclax (ABT-263), an inhibitor of the pro-survival BCL-2 family proteins BCL-2, BCL-XL and BCL-W, has shown clinical efficacy in certain BCL-2-dependent haematological cancers, but causes dose-limiting thrombocytopaenia. The latter effect is caused by Navitoclax directly inducing the apoptotic death of platelets, which are dependent on BCL-XL for survival. Recently, ABT-199, a selective BCL-2 antagonist, was developed. It has shown promising anti-leukaemia activity in patients whilst sparing platelets, suggesting that the megakaryocyte lineage does not require BCL-2. In order to elucidate the role of BCL-2 in megakaryocyte and platelet survival, we generated mice with a lineage-specific deletion of Bcl2, alone or in combination with loss of Mcl1 or Bclx. Platelet production and platelet survival were analysed. Additionally, we made use of BH3 mimetics that selectively inhibit BCL-2 or BCL-XL. We show that the deletion of BCL-2, on its own or in concert with MCL-1, does not affect platelet production or platelet lifespan. Thrombocytopaenia in Bclx-deficient mice was not affected by additional genetic loss or pharmacological inhibition of BCL-2. Thus, BCL-2 is dispensable for thrombopoiesis and platelet survival in mice.

Phase II study of paclitaxel and vinorelbine (Pacl-Vin) in hormone-refractory metastatic prostate cancer: double tubulin targeting.

BACKGROUND: Androgen ablation is the standard treatment for advanced prostate cancer. However, most patients will eventually develop progressive hormone-refractory prostate cancer (HRPC). The aim of the Pacl-Vin study was to determine the efficacy and safety of paclitaxel in combination with vinorelbine in patients with HRPC, following from a phase I trial. METHODS: Thirty castrate patients with progressive, metastatic prostate cancer were enrolled. Patients were treated with paclitaxel 40 mg/m2, vinorelbine 20 mg/m2 intravenously on day 1 and day 8 of a 21-day cycle. RESULTS: Two patients demonstrated a partial response and seven patients had stable disease from a cohort of 10 patients with measurable disease. Of 30 patients assessable for prostate-specific antigen (PSA) response, 19 showed stable disease, which was maintained for at least 4 weeks, while six (20%) experienced>or=50% decline in PSA levels. Median overall survival was 7.3 months (interquartile range (IQR): 4.7-9.9 months). Median progression-free survival was 3.3 months (IQR: 2.5-7.0 months). Improvement in quality of life measures was noted after three cycles of therapy. Grade 3 and 4 toxicities were: neutropenia 8%, febrile neutropenia 4%, infection 2%, anaemia 3%, lethargy 1% and somnolescence 1%. One patient died as a result of neutropenic sepsis. CONCLUSION: In a poor prognostic cohort of patients paclitaxel and vinorelbine is a tolerable regimen, with a 20% PSA and objective response rate. The majority of patients achieved PSA stability. Furthermore, quality of life parameters, such as pain, were improved. However, the low level of activity of this regimen precludes its further testing.