Comparison of hypoxia-activated prodrug evofosfamide (TH-302) and ifosfamide in preclinical non-small cell lung cancer models

Abstract

Evofosfamide (TH-302) is a hypoxia-activated prodrug of the cytotoxin bromo-isophosphoramide. In hypoxic conditions Br-IPM is released and alkylates DNA. Ifosfamide is a chloro-isophosphoramide prodrug activated by hepatic Cytochrome P450 enzymes. Both compounds are used for the treatment of cancer. Ifosfamide has been approved by the FDA while evofosfamide is currently in the late stage of clinical development. The purpose of this study is to compare efficacy and safety profile of evofosfamide and ifosfamide in preclinical non-small cell lung cancer H460 xenograft models. Immunocompetent CD-1 mice and H460 tumor-bearing immunocompromised nude mice were used to investigate the safety profile. The efficacy of evofosfamide or ifosfamide, alone, and in combination with docetaxel or sunitinib was compared in ectopic and intrapleural othortopic H460 xenograft models in animals exposed to ambient air or different oxygen concentration breathing conditions. At an equal body weight loss level, evofosfamide showed greater or comparable efficacy in both ectopic and orthotopic H460 xenograft models. Evofosfamide, but not ifosfamide, exhibited controlled oxygen concentration breathing condition-dependent antitumor activity. However, at an equal body weight loss level, ifosfamide yielded severe hematologic toxicity when compared to evofosfamide, both in monotherapy and in combination with docetaxel. At an equal hematoxicity level, evofosfamide showed superior antitumor activity. These results indicate that evofosfamide shows superior or comparable efficacy and a favorable safety profile when compared to ifosfamide in preclinical human lung carcinoma models. This finding is consistent with multiple clinical trials of evofosfamide as a single agent, or in combination therapy, which demonstrated both anti-tumor activity and safety profile without severe myelosuppression.

Keywords: Evofosfamide; hypoxia; hypoxia-activated prodrug; ifosfamide; non-small cell lung cancer; xenograft.

Figure 1.

(A) Metabolism of byproducts of ifosfamide induced toxicity (B) Mechanism of action of evofosfamide.

Figure 2.

Antitumor activity of evofosfamide or ifosfamide in combination with docetaxel in the metastatic H460 intrapleural model. A, metastasis progression and tumor hypoxia characterization on 4 days, 8 days, and 12 d after H460 cells inoculation. Top panel, H & E staining; middle panel, enlarged images of inserts; and bottom panel, immunofluorescence staining of pimonidazole, a marker of hypoxia, on the consecutive sections of middle panel; green, hypoxia; blue, Hoechst 33342; and red, propidium iodide; B, Kaplan-Meier plot analysis of evofosfamide or ifosfamide as monotherapy. C, Kaplan-Meier plot analysis of evofosfamide or ifosfamide in combination with docetaxel.

Figure 3.

Antitumor efficacy and safety profile of evofosfamide or ifosfamide in combination with docetaxel in the ectopic H460 xenograft model. A and B, tumor growth of evofosfamide or ifosfamide alone (A), or in combination with docetaxel (B). C and D, body weight change induced by evofosfamide or ifosfamide alone (C), or in combination with docetaxel (D). Animals were monitored daily and tumor growth was quantified twice a week. Data are expressed as Mean ± SEM of 10 animals per group. Evo, evofosfamide; Ifo, ifosfamide; Doc, docetaxel.

Figure 4.

Evofosfamide, but not ifosfamide, exhibits controlled oxygen concentration breathing condition-dependent antitumor activity in the ectopic H460 xenograft model. A and C, antitumor activity; B and D, body weight change as a readout of toxicity. Data are expressed as Mean ± SEM of 10 animals per group. Evo, evofosfamide; Ifo, ifosfamide; Doc, docetaxel. (A and C are from Reference ¹²).

Figure 5.

Effect of evofosfamide or ifosfamide on hematologic change in CD1 and H460 tumor bearing nude mice. The means and standard errors from the 5–6 mice per group are presented. A, blood samples were collected 4 hrs after the last treatment from non-tumor bearing CD-1 mice. B, blood samples were collected 3 d after the last treatment from H460 bearing nude mice; *, p < 0.05 as compared to Vehicle.

Figure 6.

At an equivalent hematoxicity level, antitumor activity of evofosfamide and ifosfamide in the H460 ectopic xenograft models. Evo, was given at 50 mg/kg, ip, and Ifo was given at 30 mg/kg ip at a regimen of QDx5/wk × 2 wks; A, antitumor activity as monotherapy. B, sunitinib was given at 80 mg/kg, QDx19, oral. Evo or Ifo was given 7 d after the initiation of sunitinib treatment. Data are expressed as Mean ± SEM of 10 animals per group.