Oxazaphosphorines combined with immune checkpoint blockers: dose-dependent tuning between immune and cytotoxic effects

BackgroundOxazaphosphorines (cyclophosphamide (CPA), ifosfamide (IFO)) are major alkylating agents of polychemotherapy protocols but limiting their toxicity and increasing their efficacy could be of major interest. Oxazaphosphorines are prodrugs that require an activation by cytochrome P450 (CYP). CPA is mainly metabolized (>80%) to phosphoramide mustard while only 10%–50% of IFO is transformed in the alkylating entity, isophosphoramide mustard and 50%–90% of IFO release chloroacetaldehyde, a nephrotoxic and neurotoxic metabolite. Geranyloxy-IFO (G-IFO) was reported as a preactivated IFO to circumvent the toxic pathway giving directly the isophosphoramide mustard without CYP metabolization. The similarity in structure of CPA and IFO and the similarity in metabolic balance of CPA and G-IFO have led us to explore immunomodulatory effect of these components in mice and to investigate the combination of these oxazaphosphorines with immune checkpoint blockers (ICB).MethodsThe investigation of the immunomodulatory properties of IFO and G-IFO compared with CPA has been conducted through immune cell phenotyping by flow cytometry and analysis of the cytokine profile of T cells after ex-vivo restimulation. T cell-mediated antitumor efficacy was confirmed in CD4+ and CD8+ T cell-depleted mice. A combination of oxazaphosphorines with an anti-programmed cell death 1 (PD-1) antibody has been studied in MCA205 tumor-bearing mice.ResultsStudies on a MCA205 mouse model have demonstrated a dose-dependent effect of IFO and G-IFO on T cell immunity. These components in particular favored Th1 polarization when used at low dose (150 and eq. 100 mg/kg, respectively). Antitumor activity at low dose was abolished in mice depleted in CD4+ and CD8+ T cells. G-IFO at low dose (eq. 100 mg/kg) in combination with anti-PD-1 antidody showed high synergistic antitumor efficacy compared with IFO.ConclusionOxazaphosphorines are characterized by a dual mechanism of antitumor action; low-dose schedules should be preferred in combination with ICB, and dose escalation was found to have better utility in polychemotherapy protocols where a conventional direct cytotoxic anticancer effect is needed. G-IFO, the novel oxazaphosphorine drug, has shown a better metabolic index compared with IFO as its metabolization gives mainly the alkylating mustard as CPA (and not IFO) and a best potential in combination with ICB.

TH-302 plus gemcitabine (G+T) versus gemcitabine (G) in patients with previously untreated advanced pancreatic cancer (PAC).

325 Background: TH-302 is a hypoxia-targeted drug with a hypoxia-triggered 2-nitroimidazole component designed to release the DNA alkylator, bromo-isophosphoramide mustard (Br-IPM), when reduced in severe hypoxia. A randomized Phase 2B study (NCT01144455) was conducted to assess the benefit of G+T to standard dose G as first-line therapy of PAC. Methods: An open-label multi-center study of two dose levels of TH-302 (240 mg/m2 or 340 mg/m2) in combination with G versus G alone (randomized 1:1:1). G (1,000 mg/m2) and T were administered IV over 30-60 minutes on Days 1, 8 and 15 of a 28-day cycle. Patients on the G could crossover after progression and be randomized to a G+T arm. The primary efficacy endpoint was a comparison of PFS between the combination arms and G alone (80% power to detect 50% improvement in PFS with one-sided alpha of 10%). Overall survival (OS) was a secondary endpoint. Results: 214 pts were treated; 163 (76%) Stage IV and 51 (24%) Stage IIIB. Median age 65 (range 29-86); 126 M/88 F; 38% ECOG 0/62% ECOG 1. Receiving 6 or more cycles: 32% G; 45% G+T240; 55% G+T340. Median PFS was 3.6 mo in G vs 5.6 mo in G+T240 (p=0.06) and 6.0 mo in G+T340 (p=0.01). Median OS was 6.9 mo in G vs 8.7 in G+T240 (p=0.83) vs 9.2 mo in G+T340 (p=0.80). 6-mo OS was 57% in G vs 69% in G+T240 (p=0.12) and 73% in G+340 (p=0.04); 12-mo OS was 26% in G vs 37% in G+T240 (p=0.18) and 38% in G+340 (p=0.13). RECIST best response was 10% in G vs 17% in G+T240 and 26% in G+T340. 14 and 12 pts in G crossed over to T240 and T340, respectively. Median post crossover PFS was 1.8 mo in T240 vs 2.9 mo in T340 (p=0.13). Median post crossover OS was 2.6 mo in T240 vs 13.4 mo in T340 (p=0.01). AEs leading to discontinuation were: 16% G, 17% G+T240 and 12% G+T340. Rash (47% in G+T340) and stomatitis (42% in G+T340) were greater in combination, 3 pts Grd 3 rash. Grd 3/4 thrombocytopenia were 11% G, 39% G+T240 and 63% G+T340 and Grd 3/4 neutropenia were 31% G, 56% G+T240 and 60% G+T340. Conclusions: The combination of G plus TH-302 improved the PFS of G. Skin and mucosal toxicity and myelosuppression were the most common TH-302 related AEs with no increase in treatment discontinuation. A phase 3 study of TH-302 (340 mg/m2) in combination with G is planned with OS as the primary efficacy endpoint. Clinical trial information: NCT01144455.

Final results of a phase I study of TH-302, a hypoxia-activated cytotoxic prodrug (HAP)

2573 Background: TH-302 is a 2-nitroimidazole prodrug of the DNA alkylator, bromo-isophosphoramide mustard (Br-IPM). TH-302 is essentially inactive under normoxia but in severe hypoxia and in the presence of certain reductases, it is reduced and Br-IPM is released. Methods: Eligible patients (pts) had ECOG ≤1, advanced or metastatic solid tumors, evaluable by RECIST, and acceptable hematologic, liver and renal function. A modified accelerated titration design was used. TH-302 was administered intravenously over 30–60 minutes on Day 1, 8 and 15 of a 28-day cycle. CT scans were obtained after every 2 cycles. Detailed pharmacokinetic sampling was performed on Days 1 and 15. The primary objectives of this study were to determine the dose limiting toxicity (DLT) and the maximum tolerated dose (MTD). Results: Twenty-nine pts enrolled at 3 sites at 9 dose levels from 7.5–670 mg/m2. Median age: 64y. 20 male/9 female. ECOG 0/1: 16/13. Primary tumor: prostate (8), colorectal (8), lung (5) other (8). Two of 5 pts at 670 mg/m2 had DLT: Herpes simplex perianal/rectal ulcers and dehydration due to mucositis. Reversible skin and mucosal adverse events (AE) occurred in 12 of 15 (80%) pts at ≥480 mg/m2 including grade 3 events in 3 pts. The most common TH-302-related AEs were nausea, skin lesions, vomiting and fatigue. Hematologic toxicity was mild and limited: two pts with grade 1 and one pt with grade 2 neutropenia and five pts with grade 1 thrombocytopenia. Five pts had grade 3 and one grade 4 lymphopenia. Four pts have enrolled at an intermediate dose of 575 mg/m2 with no DLT so this is likely the MTD and is well above the predicted biologic effective dose of 100 mg/m2. One pt with SCLC treated at 480 mg/m2 and one with melanoma treated at 670 mg/m2 had unconfirmed partial responses; 12 pts had stable disease (6 continuing after 4 or more cycles), 7 had PD, 4 were unevaluable and 4 are too early to assess. Cmax and AUC for TH-302 and Br-IPM increased linearly with no accumulation at Day 15. Conclusions: Weekly TH-302 has remarkably little hematologic toxicity. Skin and mucosal AEs have developed at the higher dose levels. Skin/mucosa are known to have hypoxic regions. TH-302 is the first HAP to demonstrate tumor responses in Phase I. The MTD is likely 575 mg/m2. Studies in combination with chemotherapy are ongoing. [Table: see text]

Glufosfamide (GLU) plus gemcitabine (GEM) in advanced solid tumors: Phase 1 results

14022 Background: Glufosfamide is glucose linked to isophosphoramide mustard, the active metabolite of ifosfamide. Cancer cells use glucose at a higher rate than normal cells, which may lead to preferential metabolic targeting by GLU. GLU has shown activity in patients (pts) with pancreatic cancer in Phase 1/2 studies with the dose-limiting toxicities (DLT) being nephrotoxicity and neutropenia. The MTD was 4500 mg/m2. In preclinical studies, GLU has shown additive activity when combined with GEM. The objectives of this study are to establish the maximum tolerated dose (MTD) and to evaluate the safety, efficacy and PK of GLU + GEM in advanced solid tumors. Methods: Eligible pts had Karnofsky Performance Status ≥70, no prior GEM, at least one lesion by RECIST, creatinine clearance (CrCL) ≥60 mL/min and acceptable hematologic and liver function. Cohorts of 3–6 patients were treated with GLU 1500–4500 mg/m2 IV over 4 hours on Day 1 and GEM 1000 mg/m2 IV over 30 minutes on Days 1, 8 and 15 of every 28-day cycle for up to 6 cycles. CT scans were obtained every 8 weeks. Detailed PK sampling was performed. Results: Nineteen pts with pancreatic (8), gall bladder (4) and other (7) cancers were enrolled. Two DLTs have occurred: Grade 3 fatigue at 2500 mg/m2 and Grade 4 thrombocytopenia at 4500 mg/m2. Both cohorts were expanded. No DLTs occurred in the 1500 or 3500 mg/m2 cohorts. Three pts completed all 6 cycles and 3 pts continue on study. Reasons for early discontinuation were progressive disease (10), clinical deterioration (1), AE (1) and death (1). Grade 3/4 neutropenia occurred in 7 pts (5 during Cycle 1) and Grade 3/4 thrombocytopenia in 5 pts (2 during Cycle 1). The CrCL fell below 60 mL/min in one patient. No objective tumor responses have been reported; 10 of 18 (56%) evaluable pts had stable disease (SD) at 8 weeks, including 1 pt with heavily pretreated ovarian cancer with ongoing SD after 8 months on therapy. PK analyses suggest no interaction between GLU and GEM. Conclusions: Phase 1 data indicate that full dose GLU (4500 mg/m2) can be given safely in combination with GEM. Both early and delayed Grade 3/4 thrombocytopenia and neutropenia have been observed. A Phase 2 cohort of 28 pts with pancreatic adenocarcinoma is currently enrolling. Studies with GEM/GLU in other tumor types are planned. [Table: see text]