Phase I Study of XK469R (NSC 698215), a Quinoxaline Phenoxypropionic Acid Derivative, in Patients with Refractory Hematological Malignancies.

XK469R is a quinoxaline phenoxypropionic acid derivative which possesses broad activity against murine and human tumors (including leukemia) and high activity against multidrug-resistant tumors. COMPARE analysis of cytotoxicity data from the NCI cell line screen suggested a unique mechanism. Phase I studies in patients with advanced solid tumors indicated that the dose-limiting toxicity (DLT) was myelosuppression, without other significant toxicities noted, at a fixed dose of 1400 mg/dose when given on a day 1,3,5 schedule every 21 days. Therefore, we conducted a phase I study to establish the DLT and maximally tolerated dose (MTD) of XK469R in patients with refractory hematologic malignancies, as well as to study the pharmacokinetics of XK469R in this patient population. XK469R was given as a straight dose as an IV infusion over 30 minutes-1 hour on days 1, 3, and 5 of a 21 day cycle. Because significant interpatient variability in drug clearance (associated with toxicity) was noted in prior studies, each dose cohort included a minimum of six patients. The dose levels studied were 1400 mg (n=6), 1750 mg (n=12), 2200 mg (n=14), and 2750mg (n=14). A total of 46 patients with relapsed/refractory leukemia have been treated and are evaluable for toxicity; 41 patients with AML, 4 ALL, and 1 CML-BC. The group consists of 26 males and 20 females with a median age of 53 (range 20–85). ECOG PS included 0 (n=19), 1 (n=21), and 2 (n=6). Median number of cycles received was 1; 10 patients received 2 cycles and 2 patients received 3 cycles. DLT was defined as any clinically significant grade 3 or 4 adverse nonhematologic toxicity other than prolonged myelosuppression, as defined by NCI criteria specific for leukemia. DLTs of colitis and mucositis were observed at the 2200 mg dose level, and mucositis and elevated bilirubin at the 2750 mg dose level. Other possibly related grade 1 and 2 toxicities noted were SGOT/PT elevations, nausea/vomiting, diarrhea, anorexia, indigestion, rash, and alopecia. The MTD, defined as the dose level at which <2/6 patients experience a DLT, was 2200 mg. Forty-two patients were evaluable for response and include CR (n=1, in 1750 mg cohort), HI (n=5), SD (n=21), and PD (n=15). Preliminary pharmacokinetic analysis revealed that plasma concentrations of XK469R decline in a biphasic manner. Half-life was long with a mean value of 48 h. Mean clearance was 206 ml/h with a coefficient of variation of 32%. Patients with lower clearance did not appear to be at greater risk of DLT. In conclusion, the recommended phase II dose of XK469R in patients with advanced leukemia is 1750 mg (day 1,3,5). Due to its novel mechanism of action, reasonable toxicity profile, and clinical activity in these high-risk patients, further exploration of XK469R, possibly in combination with other established agents, is warranted in patients with relapsed/refractory acute leukemia.