A phase II study of UCN-01 in combination with irinotecan in patients with metastatic triple negative breast cancer

Abstract

Mutations in TP53 lead to a defective G1 checkpoint and the dependence on checkpoint kinase 1 (Chk1) for G2 or S phase arrest in response to DNA damage. In preclinical studies, Chk1 inhibition resulted in enhanced cytotoxicity of several chemotherapeutic agents. The high frequency of TP53 mutations in triple negative breast cancer (TNBC: negative for estrogen receptor, progesterone receptor, and HER2) make Chk1 an attractive therapeutic target. UCN-01, a non-selective Chk1 inhibitor, combined with irinotecan demonstrated activity in advanced TNBC in our Phase I study. The goal of this trial was to further evaluate this treatment in women with TNBC. Patients with metastatic TNBC previously treated with anthracyclines and taxanes received irinotecan (100-125 mg/m(2) IV days 1, 8, 15, 22) and UCN-01 (70 mg/m(2) IV day 2, 35 mg/m(2) day 23 and subsequent doses) every 42-day cycle. Peripheral blood mononuclear cells (PBMC) and tumor specimens were collected. Twenty five patients were enrolled. The overall response (complete response (CR) + partial response (PR)) rate was 4 %. The clinical benefit rate (CR + PR + stable disease ≥6 months) was 12 %. Since UCN-01 inhibits PDK1, phosphorylated ribosomal protein S6 (pS6) in PBMC was assessed. Although reduced 24 h post UCN-01, pS6 levels rose to baseline by day 8, indicating loss of UCN-01 bioavailability. Immunostains of γH2AX and pChk1(S296) on serial tumor biopsies from four patients demonstrated an induction of DNA damage and Chk1 activation following irinotecan. However, Chk1 inhibition by UCN-01 was not observed in all tumors. Most tumors were basal-like (69 %), and carried mutations in TP53 (53 %). Median overall survival in patients with TP53 mutant tumors was poor compared to wild type (5.5 vs. 20.3 months, p = 0.004). This regimen had limited activity in TNBC. Inconsistent Chk1 inhibition was likely due to the pharmacokinetics of UCN-01. TP53 mutations were associated with a poor prognosis in metastatic TNBC.

Fig. 1

Patient outcome. Kaplan–Meier survival curves on time to treatment failure (TTF) (a) and OS (b) for all patients and Kaplan–Meier survival curves on TTF (c) and OS (d) by tumor TP53 mutation status

Fig. 2

Pharmacodynamic effects of UCN-01 on PBMC (a, b) and tumor tissue (c–h). PBMC were collected at baseline (BL), 24 h post irinotecan but prior to UCN-01 on day 2 (D2), 24 h post UCN-01 on day 3 (D3), and on day 8 (D8) prior to the second irinotecan treatment during cycle 1. PBMC were lysed and analyzed by western blotting with antibodies specific for total and phosphorylated forms of S6 ribosomal protein (S6), AKT, and GSK3ß with actin as a loading control. Representative western blots from two patients (4 and 11) are shown (a). The ratio of pS6 to total S6 protein level was plotted at each time point (b). Optional serial tumor biopsies were collected before study drug therapy at baseline (BL), 24 h post irinotecan but prior to UCN-01 on day 2 (D2), and 24 h post UCN-01 on day 3 (D3) from 4 patients (1, 4, 6, and 11). Representative immunofluorescent (IF) staining images on tumors from patient 11 are shown in (c). The quantitation of the IF analysis on the γH2AX (d), pChk1^S296 (e), phistone H3 (f), cleaved caspase 3 (g), and pS6 (h), for each patient is shown in the lower panels. CC3 cleaved caspase 3