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Background: The incidence of brain metastases (BM) in breast cancer (BC) patients (pts) has increased over the past decade. The brain is regarded as a sanctuary site for metastatic cells which are partially protected from drugs by the blood-brain barrier (BBB). 2B3-101 is a doxorubicin (DOX) liposomal formulation that uses glutathione transporters on the BBB to penetrate the brain. Non-clinical studies have shown a 5-fold enhanced delivery of DOX to the brain after IV administration of 2B3-101 compared to liposomal DOX, without signs of cardio- or neurotoxicity. Methods: This phase 1/2a open label study assessed the safety, tolerability, MTD, PK, and anti-tumor activity of single agent 2B3-101 in pts with BM of solid tumors, or high-grade gliomas. For this analyses BCBM pts (n=25) were included. These pts received 2B3-101 at a starting dose of either 40 (n=3) or 50 (n=22) mg/m2 IV every 3 weeks, until disease progression or unacceptable toxicity. Anti-tumor activity was assessed by RECIST 1.1. Patients with HER2-positive BCBM were treated with concurrent trastuzumab. Results: As of May 30, 2014, 88 cycles (median 2, range 1-10) of 2B3-101 alone or with trastuzumab were administered to 25 heavily pretreated BC pts, 3 pts are still on treatment. Median age was 47 (33–61) years and 18 (72%) pts had HER2+ disease. Pts had received a median of 7 (4–15) prior regimens; 18 (72%) had received prior radiation therapy to the brain. In phase 1, 2B3-101 alone or with trastuzumab was well tolerated up to a dose intensity of 15 mg/m2/wk. Cycle 1 MTD was not reached. Phase 2a dose of 50 mg/m2 was selected based upon tolerability after repeated dosing. The most frequent reported treatment emergent AEs are qualitatively consistent with conventional PEGylated liposomal DOX and were (≥ grade 2): neutropenia (59%), palmar plantar erythrodysesthesia (PPE) (50%), fatigue (45%), stomatitis (22%), and infusion reaction (18%). Notable Grade 3–4 AEs were neutropenia (35%) and PPE (13%). All AEs were transient and manageable with dose delays, reductions and standard medication. 57% of pts had 2B3-101 dose delays and 39% of pts required dose reductions. 2B3-101 showed no neuro- or cardiotoxicity. PK data showed non-linear exposure of 2B3-101 without signs of accumulation upon repeat dosing, a mean half-life of 69h (range 43-120h) and independent of trastuzumab co-treatment. Best overall and intracranial tumor responses of 2B3-101 in 23 evaluable BCBM pts (92% of total) are summarized in Table 1. Table 1: Anti-tumor activity results of 2B3-101 in BCBM patientsPopulationNumber of evaluable ptsOverall partial responseOverall stable diseaseIntracranial tumor response of ≥ 20%.12-weeks overall PFS rateOverall232 (9%)11 (48%)4 (17%)48%"Luminal"40 (0%)2 (50%)1 (25%)50%HER2 positive162 (13%)9 (56%)3 (19%)56%TNBC30 (0%)0 (0%)0 (0%)0% Conclusions: 2B3-101 alone or with trastuzumab is safe and well tolerated and shows intra- and extracranial anti-tumor activity in heavily pretreated BC pts. A 12-week PFS rate of 56% in HER2+ BCBM was observed, which warrants further clinical studies. An international, multicenter, randomized, controlled phase IIb study in HER2+ BCBM is being planned. NCT01386580, sponsored by to-BBB technologies BV. Citation Format: Philippe G Aftimos, Bojana Milojkovic-Kerklaan, Véronique Diéras, Sevilay Altintas, Carey Anders, Monica Arnedos, Hans Gelderblom, Patricia Soetekouw, Werner Gladdines, Pieter Gaillard, Carlos de Sousa, Agnes Jager, Myra van Linde, Ahmad Awada, Jan Schellens, Dieta Brandsma. Phase 1/2a study of glutathione PEGylated liposomal doxorubicin (2B3-101) in breast cancer patients with brain metastases [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P6-16-04.

Without active delivery across the blood-brain barrier (BBB) the efficacy of doxorubicin in brain tumors is limited. 2B3-101, glutathione PEGylated liposomal doxorubicin, has been developed as brain-targeted chemotherapy. In preclinical studies, 2B3-101 showed a 5-fold enhanced doxorubicin brain-delivery versus pegylated liposomal doxorubicin (Doxil®). Patients with either solid tumor brain metastases or recurrent malignant gliomas were treated with 2B3-101 by a 90 min IV infusion q21d to assess (1) safety, tolerability and MTD (2) pharmacokinetics (PK) and (3) preliminary anti-tumor activity of 2B3-101, determined by brain MRIs and body CTs, according to RANO or RECIST criteria. Doses were escalated in cohorts of 3-6 patients. 28 patients received 2B3-101 at doses of 5-70 mg/m2, without DLTs. 15 patients had brain metastases from solid tumors, and 13 patients had recurrent malignant gliomas WHO grade III (3) or IV (10). Twenty-three patients (82%) received ≥ 3 prior therapies before 2B3-101. No cardiac or CNS toxicity was observed. At doses of ≥ 40 mg/m2, adverse events ≥ grade II (CTCAE v.4.0) were: neutropenia (21%), thrombocytopenia (4%), mucositis (4%), and PPE (18%). Grade I-II infusion reactions were observed in 4/28 patients, being transient and manageable with standard treatments. Pharmacokinetic data showed non-linear exposure of 2B3-101 without signs of accumulation with repeat dosing. Due to one case of thrombocytopenia grade IV at 60 mg/m2, this cohort was expanded to 6 patients. 2B3-101 demonstrates preliminary antitumor activity in the brain. At doses of ≥ 40 mg/m2, 12 of 16 patients demonstrated stable disease as best outcome (brain metastases (n=4), glioblastoma (n=5) and grade III glioma (n=3)). 2B3-101 also showed responses in extracranial disease. 2B3-201 is safe and well tolerated up to 70 mg/m2 q21d in both brain metastases from solid tumors and recurrent malignant gliomas. A dose intensity of 15 mg/m2/week was sustainable over at least 4 cycles. Based on this information, the phase IIa dose expansion study is currently ongoing with treatment regimens of 50 mg/m2 every 3 weeks for patients with brain metastases and 60 mg/m2 every 4 weeks for patients with recurrent malignant glioma. ClinicalTrials.gov NCT01386580, sponsored by to-BBB technologies BV. Citation Format: Pieter J. Gaillard, Bojana Milojkovic Kerklaan, Philippe Aftimos, Sevilay Altintas, Agnes Jager, Werner Gladdines, Fredrik Lonnqvist, Patricia Soetekouw, Henk Verheul, Ahmad Awada, Jan Schellens, Dieta Brandsma. Phase I dose escalating study of 2B3-101, glutathione PEGylated liposomal doxorubicin, in patients with solid tumors and brain metastases or recurrent malignant glioma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr CT216. doi:10.1158/1538-7445.AM2014-CT216

Treatment options for brain cancer are limited and overall prognoses are poor. Glutathione pegylated liposomal doxorubicin (2B3-101) is being developed as a new treatment option for patients with brain cancer. It is essentially based on the already marketed pegylated liposomal doxorubicin (Doxil), with an additional glutathione (GSH) coating to safely enhance delivery across the blood-brain barrier. In a GLP safety study 2B3-101 was administered by intravenous bolus injection on days 1, 15 and 29 to Wistar rats at 1.75, 3.5 and 7 mg/kg. Doxil (7 mg/kg), empty GSH-PEG-liposomes, and vehicle were included, resulting in 6 groups (10 animals/sex/group). Additional animals were allowed 4 weeks of recovery or were used for toxicokinetic analysis. From observations during the in-life part of the study, as well as after histopathological investigations, no major differences were noted between 2B3-101 and Doxil at 7 mg/kg q14dx3. No treatment-related changes in the brain were observed neither after repeated 2B3-101 exposure, nor after treatment with empty GSH-PEG liposomes. In addition, 2B3-101 did not result in doxorubicin-related toxicity in heart tissue. After 1st and 3rd administration of 7 mg/kg, plasma AUC values were 10-44% higher for Doxil when compared to 2B3-101, while C0 values were considered similar for both drug substances. Apparent half-lives for Doxil were 36.1 and 32.6 hours in males and females after the 3rd administration, respectively. For 2B3-101 these values were slightly shorter at 30.0 and 28.8 hours in males and females, respectively. The doxorubicin brain/plasma ratio showed retention of both 2B3-101 and Doxil after repeated doses, where 2B3-101 resulted in significantly higher doxorubicin retention in the brain 2 weeks after the 3rd administration (p Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5687. doi:1538-7445.AM2012-5687