Cell experiment:

Cells are treated with 0.1 μM of either PF477736 or AZD7762 and Evofosfamide (TH-302) for 2 h under either normoxia (21% O2) or hypoxia (N2). Following wash, cells are cultured for additional 22 h in the presence of Chk1 inhibitor under normoxia. Cells are fixed in 75% ethanol and cell cycle distribution is determined using cell cycle reagent and Guava flow cytometry. HT-29 cells are exposed to Evofosfamide (TH-302)e (8 nM, 40 nM, 200 nM, 1 μM, and 5 μM) and 0.1 μM of AZD7762 for 2 h under either normoxia (21% O2) or hypoxia (N2). After wash, cells are continuously cultured for additional 46 h in the presence of 0.1 μM of AZD7762. Luminescence-based caspase activity assay is performed[1].

Animal experiment:

Mice[2] Female SCID mice of age 5-6 weeks are inoculated with SU.86.86, Hs766t or Mia-PaCa2 cells (5×106) subcutaneously on the left hind leg. Tumors are allowed to grow for an average of three weeks to an average size of ~150 mm3. Mice are then randomized and placed into cohorts and treated with saline (control) or Evofosfamide (TH-302) (50 mg/kg) injected intraperitoneally. A total of 34 mice underwent MR imaging studies. The SU.86.86 group consist of 5 TH-302 treated and 5 control animals; Mia-PaCa2 consist of 6 Evofosfamide treated and 5 control animals; Hs766t consist of 7 Evofosfamide treated and 6 control animals. Animals are sacrificed when tumors reach 2000 mm3. Rats[2] Syngeneic rhabdomyosarcoma R1 tumors (1 mm3) are implanted subcutaneously in the lateral flank of adult WAG/Rij rats. Experiments are started upon a mean tumor volume of 4.2 cm3(range, 2.0-8.1) to ensure a stable HF. Treatment is administered on 4 consecutive days and consist of an intraperitoneal injection (i.p.; QD×4) with either NaCl or Evofosfamide (TH-302) (25, 50, or 75 mg/kg). Before the start of treatment, a PET scan is made using [18F]HX4. Radiotherapy is applied in a single dose of 0, 4, 8, or 12 Gy on day 3 of the treatment, 3 hours after NaCl or Evofosfamide (TH-302) injection, 1 hour after oxygen modification. During both PET imaging and radiotherapy, rats are anesthetized using a mixture of ketamine/xylazine (i.p; 66.7 and 6.7 mg/kg, respectively). During the 5 days of treatment (1 day PET imaging, 4 days of injections with Evofosfamide or vehicle), animals are exposed to modified oxygen concentrations for 4 hours per day in order to alter the HF of the tumor. The combination oxygen modification of nicotinamide (i.p. 500 mg/kg) and carbogen (95% oxygen, 5% CO2; 5 L/minute) consist of a nicotinamide injection and 30 minutes later the exposure to carbogen breathing for 3.5 hours. In the middle of the nicotinamide/carbogen treatment, NaCl/Evofosfamide is administered. Reduced oxygen breathing (7%, residual N2; 2.5 L/minute) is given for 4 hours with the NaCl/Evofosfamide injection after the first 2 hours. The injection of the [18F]HX4 PET tracer [mean 18.8 MBq, range 7.1-25.1 MBq; lateral tail vein using an intravenous line (Venoflux 0.4 mm G27) flushed with 10% heparine)] is given 2 hours before the end of the oxygen modification. PET imaging is performed 3 hours after tracer injection.

TH-302 is a 2-nitroimidazole triggered hypoxia-activated prodrug of bromo-isophosphoramide mustard [1].
Hypoxia is a prevailing feature of tumors due to the abnormal aspects and structure of tumor vasculatures. It is found that hypoxic tumors usually show resistance to the traditional chemo- and radiation therapies and hypoxic tumors are more metastatic and invasive. Since the hypoxic tumors are not hyperproliferative, the traditional anti-proliferation drugs are not suitable. As a hypoxia-activated prodrug, TH-302 can release the cytotoxic agent Br-IPM and selectively deliver it the to the tumor cells under the anoxic condition [1 and 2].
The activity of TH-302 is dependent on the degree of anoxia and the exposure time of the drug under hypoxia. Higher activity requires lower oxygen concentration. Different with tirapazamine (another HAP), TH-302 needed much severer hypoxia (about 0.1%) to keep high potency. When treated in a panel of 32 kinds of tumor cells, TH-302 showed modest cytotoxicity with IC50 values all above 40 μM under the normal air condition. In contrast, TH-302 exerted elevated anti-tumor potency under the hypoxic condition. The IC50 values of it were in a range from 0.1 to 90 μM. Among these tumor cells, the non-small cell lung cancer H460 cells were most sensitive against TH-302 treatment with IC50 value of 0.1±0.03 μM. Besides that, TH-302 also showed potent efficacies in many other tumor cells, including Caki-1 (renal), SK-MEL-5 (melanoma), DU145 (prostate) and HCT116 (colon), with IC50 values of 0.4, 0.7, 0.7 and 0.8 μM, respectively [1].
In mice bearing H460 xenografts, administration of TH-302 at doses of 6.25 to 50 mg/kg dose-dependently caused tumor growth inhibition (TGI) with 43% to 89% and 50 mg/kg TH-302 administration showed no hematologic toxicity. Apart from this, TH-302 was found to induce DNA damage. TH-302 at dose of 100 mg/kg for 6 hours resulted in notable increase of γH2AX-positive cells [2].
References:
[1] Meng F, Evans J W, Bhupathi D, et al. Molecular and cellular pharmacology of the hypoxia-activated prodrug TH-302. Molecular cancer therapeutics, 2012, 11(3): 740-751.
[2] Sun J D, Liu Q, Wang J, et al. Selective tumor hypoxia targeting by hypoxia-activated prodrug TH-302 inhibits tumor growth in preclinical models of cancer. Clinical cancer research, 2012, 18(3): 758-770.