Evofosfamide and Gemcitabine Act Synergistically in Pancreatic Cancer Xenografts by Dual Action on Tumor Vasculature and Inhibition of Homologous Recombination DNA Repair

Aims: Pancreatic ductal adenocarcinomas (PDACs) form hypovascular and hypoxic tumors, which are difficult to treat with current chemotherapy regimens. Gemcitabine (GEM) is often used as a first-line treatment for PDACs but has issues with chemoresistance and penetration in the interior of the tumor. Evofosfamide, a hypoxia-activated prodrug, has been shown to be effective in combination with GEM, although the mechanism of each drug on the other has not been established. We used mouse xenografts from two cell lines (MIA Paca-2 and SU.86.86) with different tumor microenvironmental characteristics to probe the action of each drug on the other. Results: GEM treatment enhanced survival times in mice with SU.86.86 leg xenografts (hazard ratio [HR] = 0.35, p = 0.03) but had no effect on MIA Paca-2 mice (HR = 0.91, 95% confidence interval = 0.37-2.25, p = 0.84). Conversely, evofosfamide did not improve survival times in SU.86.86 mice to a statistically significant degree (HR = 0.57, p = 0.22). Electron paramagnetic resonance imaging showed that oxygenation worsened in MIA Paca-2 tumors when treated with GEM, providing a direct mechanism for the activation of the hypoxia-activated prodrug evofosfamide by GEM. Sublethal amounts of either treatment enhanced the toxicity of other treatment in vitro in SU.86.86 but not in MIA Paca-2. By the biomarker γH2AX, combination treatment increased the number of double-stranded DNA lesions in vitro for SU.86.86 but not MIA Paca-2. Innovation and Conclusion: The synergy between GEM and evofosfamide appears to stem from the dual action of GEMs effect on tumor vasculature and inhibition by GEM of the homologous recombination DNA repair process. Antioxid. Redox Signal. 39, 432-444.

Hypoxia-Activated Prodrug Evofosfamide Treatment in Pancreatic Ductal Adenocarcinoma Xenografts Alters the Tumor Redox Status to Potentiate Radiotherapy

Aims: In hypoxic tumor microenvironments, the strongly reducing redox environment reduces evofosfamide (TH-302) to release a cytotoxic bromo-isophosphoramide (Br-IPM) moiety. This drug therefore preferentially attacks hypoxic regions in tumors where other standard anticancer treatments such as chemotherapy and radiation therapy are often ineffective. Various combination therapies with evofosfamide have been proposed and tested in preclinical and clinical settings. However, the treatment effect of evofosfamide monotherapy on tumor hypoxia has not been fully understood, partly due to the lack of quantitative methods to assess tumor pO₂in vivo. Here, we use quantitative pO₂ imaging by electron paramagnetic resonance (EPR) to evaluate the change in tumor hypoxia in response to evofosfamide treatment using two pancreatic ductal adenocarcinoma xenograft models: MIA Paca-2 tumors responding to evofosfamide and Su.86.86 tumors that do not respond. Results: EPR imaging showed that oxygenation improved globally after evofosfamide treatment in hypoxic MIA Paca-2 tumors, in agreement with the ex vivo results obtained from hypoxia staining by pimonidazole and in apparent contrast to the decrease in K^trans observed in dynamic contrast-enhanced magnetic resonance imaging (DCE MRI). Innovations: The observation that evofosfamide not only kills the hypoxic region of the tumor but also improves oxygenation in the residual tumor regions provides a rationale for combination therapies using radiation and antiproliferatives post evofosfamide for improved outcomes. Conclusion: This study suggests that reoxygenation after evofosfamide treatment is due to decreased oxygen demand rather than improved perfusion. Following the change in pO₂ after treatment may therefore yield a way of monitoring treatment response. Antioxid. Redox Signal. 35, 904-915.

Targeting Hypoxia Using Evofosfamide and Companion Hypoxia Imaging of FMISO-PET in Advanced Biliary Tract Cancer

Purpose

Hypoxia is widely known as one of the mechanisms of chemoresistance and as an environmental condition which triggers invasion and metastasis of cancer. Evofosfamide is a hypoxia-activated prodrug of the cytotoxin bromo-isophosphoramide mustard conjugated with 2-nitroimidazole. Biliary tract cancer (BTC) is known to contain large hypoxic area. This study evaluated the efficacy and safety of evofosfamide as a second-line treatment of advanced BTC.

Materials and Methods

Patients received evofosfamide at a dose of 340 mg/m² on days 1, 8, and 15 of every 28-day cycle. Primary end-point was progression-free survival (PFS) rate at 4-months (4m-PFSR). Secondary end-points included overall survival (OS), PFS, disease control rate (DCR), metabolic response by ¹⁸F-fluorodeoxyglucose positron emission tomography (PET), hypoxic parameters evaluated by ¹⁸F-fluoromisonidazole (FMISO) PET and toxicity.

Results

Twenty patients were treated with evofosfamide, with 16 response-evaluable patients. There was no objective response; stable disease was observed in nine patients, with a DCR of 56.25%. 4m-PFSR was 40.6%. Median PFS was 3.60 months (95% confidence interval [CI], 1.68 to 5.52). Median OS was 6.37 months (95% CI, 3.94 to 8.79). Reduction of tumor metabolic activity was observed in eight of 15 patients (53.3%). High baseline hypoxic parameters were associated with poor PFS. Change of hypoxic parameters between pretreatment and post-treatment reflected hypoxic-activated drug response. There was no treatment-related death.

Conclusion

Evofosfamide as second-line treatment of advanced BTC showed acceptable safety and comparable efficacy to other agents. Changes in volumetric parameters measured with FMISO PET, showing the degree of tumor hypoxia, reflected the response to evofosfamide based on the mode of action.

Hypoxia-activated prodrug enhances therapeutic effect of sunitinib in melanoma

Angiogenesis is a critical step during tumor progression. Anti-angiogenic therapy has only provided modest benefits in delaying tumor progression despite its early promise in cancer treatment. It has been postulated that anti-angiogenic therapy may promote the emergence of a more aggressive cancer cell phenotype by generating increased tumor hypoxia—a well-recognized promoter of tumor progression. TH-302 is a 2-nitroimidazole triggered hypoxia-activated prodrug (HAP) which has been shown to selectively target the hypoxic tumor compartment and reduce tumor volume. Here, we show that melanoma cells grown under hypoxic conditions exhibit increased resistance to a wide variety of therapeutic agents in vitro and generate larger and more aggressive tumors in vivo than melanoma cells grown under normoxic conditions. However, hypoxic melanoma cells exhibit a pronounced sensitivity to TH-302 which is further enhanced by the addition of sunitinib. Short term sunitinib treatment fails to prolong the survival of melanoma bearing genetically engineered mice (Tyr::CreER; BRaf^CA;Pten^lox/lox) but increases tumor hypoxia. Long term TH-302 alone modestly prolongs the overall survival of melanoma bearing mice. Combination therapy of TH-302 with sunitinib further increases the survival of treated mice. These studies provide a translational rationale for combining hypoxic tumor cell targeted therapies with anti-angiogenics for treatment of melanoma.