Abstract
2081 Background: Disruption of Hsp90-client protein heterocomplexes leads to degradation of a variety of oncoproteins. KOS-1022, an Hsp90 inhibitor and water-soluble geldanamycin derivative, is in trials in patients with solid tumors. Compared to a prior geldanamycin derivative (17-AAG), KOS-1022 is ∼3–5 fold more potent (comparing in vitro cytotoxicity or the MTD in toxicology studies on the same schedule). Primary study objectives: establish safety and MTD of KOS-1022 in patients with advanced hematologic malignancies; characterize PK and PD. Methods: Escalating doses of KOS-1022 are given IV over 1 h twice weekly for 2 out of 3 weeks. Plasma KOS-1022 concentrations (1st and 4th infusion, Cycle 1) are quantitated by LC/MS/MS. Pre and on-study CD34+ bone marrow and peripheral blasts undergo flow cytometry to quantify Hsp70/90, pAKT/total AKT, markers of apoptosis and proliferation. Response in AML pts used IWG criteria. Results: 13 pts have been enrolled at doses of 8 (n=4), 16 (n=6), 24 (n=1) and 32 mg/m2 (n=2). All were AML (except 1 CML). Most (n=11) patients had 2–3 prior induction regimens. DLT was seen in 2 pts at 32 mg/m2 (acute myocardial infarction and elevation of troponin). Both patients had significant co-morbidity, including (1) prior myocardial infarction and (2) progressive AML with a similar troponin elevation during induction chemotherapy prior to study. Common drug-related toxicities (all Grade 1–2): fatigue, nausea, diarrhea and arthralgias. From 8 to 32 mg/m2, approximately linear PK was observed. Mean terminal half-lives varied from 13.0–31.2 hours. Day 1 clearance for 8, 16 and 32 mg/m2 was 5.6, 9.7 and 10.8 L/hr/m2; mean Vz (L/m2) for these groups were 238, 433 and 489. Although pre-infusion drug was quantifiable on Day 11 in most patients, Day 11/Day 1 AUC0–25h ratio was 0.96. Activity in AML: 2 CRi and 1 SD x 9 cycles were observed. Comparing BMAs taken at Day 8 and Day 15 to baseline: decreased Hsp90 (41% to 13%), increased Hsp70 (8% to 84%) with decreased pAKT (Ser), pAKT (Thr) and total AKT in CD34+ cells. Conclusions: KOS-1022 appears to be well tolerated, with preliminary signs of clinical and biologic activity in refractory leukemia. MTD has not been defined. Plasma PK is linear over this dose range. [Table: see text]
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