Patient disposition and characteristics
Sixty-seven patients received treatment until the cut-off date. A total of 21 patients (three patients for each of the 200, 300, and 450 mg cohorts, and six patients for each of the 650 and 800 mg cohorts) were treated and evaluable for DLTs in part 1. Based on DLTs in cycle 1 of part 1, six patients subsequently received 650 mg SID (MTD) in part 2. In the expansion part, 46 patients received 650 mg SID and nine CRPC patients received 450 mg SID using a 5-on/2-off schedule up to 21 days per cycle. Baseline characteristics of patients are presented in Table 1.
Table 1 Baseline characteristics of patients (N = 82) Determination of MTD and RP2D
Overall, three DLTs were reported: grade 3 rash in one patient who received 650 mg SID, and grade 3 thrombocytopenia with bleeding and grade 3 rash each in one patient receiving 800 mg SID. Therefore, the MTD was determined as 650 mg in part 1. However, all patients who received 650 mg SID required treatment interruption during cycle 1 because of AEs (hypophosphatemia, decreased appetite, fibrin D dimer increased, and rash).
When the 650 mg SID dose was repeated using a 5-on/2-off schedule with the aim of improving administration sustainability in part 2, no DLTs were reported, and no patients required treatment interruption in cycle 1. Furthermore, the median relative dose intensity improved from 58% (part 1 level 4) to 100% (part 2) for the 650 mg dose level during cycle 1. The RP2D was estimated as 650 mg 5-on/2-off for 21 days per cycle.
Pharmacokinetic profile
TAS-115 was rapidly absorbed after oral administration, with the median time to maximum concentration (tmax) of 1.0–2.0 h. The area under the curve from 0 to 24 h (AUC0–24) after single administration increased dose-proportionally over the tested range from 200 mg to 650 mg in part 1, although dose-dependent increase between 650 mg and 800 mg was not seen. The 800 mg dose is only approximately 1.2 times the 650 mg dose, and there were large variations between individual patients (Fig. 1a and Supplementary Table S2). Multiple dosing of TAS-115 for 8 days results in no accumulation in part 1 (Supplementary Table S2). In part 2, the exposure of TAS-115 after multiple administration was similar to the dose level of 650 mg in part 1 (Fig. 1b). The mean and individual PK parameters (maximum plasma concentration [Cmax], and AUC0–24) under empty stomach and fed condition were shown in Fig. 1c. The geometric mean ratios (90% CI) of the Cmax and AUC0–24 under fed condition to those under empty stomach condition were 0.545 (0.243–1.224) and 0.812 (0.414–1.593), respectively, however, there were no statistically significant differences.
Safety
The most common TRAEs were laboratory abnormalities, gastrointestinal symptoms, general disorders, and skin disorders. In part 1, grade ≥3 TRAEs were reported in 13 patients and no dose-dependent increase in the incidence and grade of TRAEs was observed (Supplementary Table S3). During part 2 and the expansion part (N = 61), the most common TRAEs occurred in more than 30% of patients were increased AST (31patients, 50.8%), fatigue (27 patients, 44.3%), nausea and decreased appetite (26 patients, 42.6% each), increased ALT (23 patients, 37.7%), neutropenia and anemia (21 patients, 34.4% each), hypophosphatemia (20 patients, 32.8%), vomiting and thrombocytopenia (19 patients, 31.1% each). Grade ≥3 TRAEs were reported in 47 patients (77.0%), with neutropenia, hypophosphatemia, anemia, thrombocytopenia, leukocytopenia occurring in ≥10% of patients (Table 2).
Table 2 Incidence of treatment-related adverse events in ≥20% of patients in part 1 or part 2 + expansion part TRAEs that led to treatment discontinuation were rash (one patient, 800 mg) in part 1, rash (two patients, 650 mg), pyrexia, peritonitis and neutropenia (one patient each, 650 mg) in part 2 and expansion part. All the patients in cohorts 650 mg and 800 mg in part 1 experienced TRAEs leading to dose interruption, while the frequency in part 2 and the expansion part was decreased (approximately 77%). Serious AEs were reported in seven patients in part 1, two patients in part 2 and thirty one patients in the expansion part. Serious TRAEs were tumor hemorrhage and decreased appetite (one patient, 650 mg each), thrombocytopenia (one patient, 800 mg) in part 1, peritonitis (one patient) in part 2, decreased appetite (three patients), nausea (two patients), interstitial lung disease, rash, enterocolitis, fatigue, thrombocytopenia, and pyrexia (one patient each) in the expansion part. AEs resulted in death were hepatic failure, disease progression and respiratory failure occurred in one patient each in the expansion part (650 mg) and this was not considered related to TAS-115. No treatment-related death was observed in any of the study parts during the treatment period or within 28 days of the last dose of TAS-115.
Antitumor effects
Of the 82 patients in all parts, the best overall response was stable disease (SD) in 31 patients (37.8%), and of these, seventeen patients (8 for osteosarcoma, 4 for prostate cancer and 1 each for bladder cancer, renal cancer, breast cancer, clear cell sarcoma, and gastrointestinal stromal tumor [GIST]), had SD lasting 12 weeks or more. Minor tumor shrinkage of target lesions was reported in four patients who were determined as having progressive disease (PD).
BSI response rate in patients with bone lesions was 56.0% (14 of 25) among the patients in whom percentage change in BSI was assessed between baseline and at least once post-scan. The primary cancer types of the responders were osteosarcoma in 6 patients, prostate cancer in five patients, epithelioid sarcoma, clear cell sarcoma, and breast cancer in one patient each. The percent change from baseline is shown in the waterfall plots (Fig. 2). The BSI analysis indicated a definite decrease in the quantitative value of primary lesions or metastases to the bone in several patients.
Figure 3 shows the representative antitumor effect of TAS-115 as observed in three patients who received 650 mg in a 5-on/2-off schedule. A marked decrease of hot spots on bone scans and reduction in fluorodesoxyglucose uptake were observed 6 weeks after the first administration in a patient with epithelioid sarcoma with multiple metastases (bone, lung, adrenal glands, and soft tissue) (Fig. 3a). In a patient who had bladder cancer with metastases in lung, pleural lymph nodes, and regional lymph nodes, administration of TAS-115 was discontinued at week 7, and the lung metastatic lesions disappeared after discontinuation of TAS-115 treatment without further antitumor treatment (Fig. 3b). In addition, a notable improvement was observed in the bone scan of a patient with CRPC with multiple bone metastases (Fig. 3c).
Pharmacodynamic profile
A significant increase of sMET in plasma was observed on Day 22 in part 1 (P = .0031) and Day 19 (pre-dose and 6 h after TAS-115 administration) in part 2 and the expansion part (P = .0015 and P = .0055, respectively). At 6 h post-dose on Day 19, an increase of VEGF and decrease of VEGFR2 were observed (P = .0844 and P = .0204 respectively), as compared with pre-dose on Day 19 (Supplementary Fig. S2). The relationship between biological changes of the protein levels and antitumor activity was not evaluated due to a limited number of patients with clinical effect.