The clinically active PARP inhibitor AG014699 ameliorates cardiotoxicity but does not enhance the efficacy of doxorubicin, despite improving tumor perfusion and radiation response in mice.

AG014699 was the first inhibitor of the DNA repair enzyme PARP-1 to enter clinical trial in cancer patients. In addition to enhancing the cytotoxic effect of DNA-damaging chemotherapies, we have previously shown that AG014699 is vasoactive, thereby having the potential to improve drug biodistribution. The effectiveness of the clinical agent doxorubicin is confounded both by poor tumor penetration and cardiotoxicity elicited via PARP hyperactivation. In this study, we analyzed the impact of AG014699 on doxorubicin tolerance and response in breast (MDA-MB-231) and colorectal (SW620, LoVo) tumor models in vitro and in vivo. As anticipated, AG014699 did not potentiate the response to doxorubicin in vitro. In vivo, AG014699 did not influence the pharmacokinetics of doxorubicin; however, it did ameliorate cardiotoxicity. Both toxicity and extent of amelioration were more pronounced in male than in female mice. AG014699 improved vessel perfusion in both MDA-MB-231 and SW620 tumors; however, this neither led to improved tumor-accumulation of doxorubicin nor enhanced therapeutic response. In contrast, when combined with radiotherapy, AG014699 significantly enhanced response both in vitro and in vivo. Real-time assessment of tumor vessel function and companion histologic studies indicate that doxorubicin causes a profound antivascular effect that counters the positive effect of AG014699 on perfusion. These data indicate that although AG014699 can enhance response to some chemotherapeutic drugs via improved delivery, this does not apply to doxorubicin. PARP inhibitors may still be of use to counter doxorubicin toxicity, and if the gender effect translates from rodents to humans, this would have greater effect in males.

The mitogen-activated protein/extracellular signal-regulated kinase kinase 1/2 inhibitor AZD6244 (ARRY-142886) enhances the radiation responsiveness of lung and colorectal tumor xenografts.

PURPOSE: Novel molecularly targeted agents, given in combination with radiotherapy, have the potential to increase tumor response rates and the survival of patients with lung cancer. AZD6244 is a potent and selective inhibitor of mitogen-activated protein kinase (MAPK) kinase 1/2 (MEK1/2), a critical enzyme within the MAPK/extracellular signal-regulated kinase (ERK) signaling pathway that regulates the proliferation and survival of tumor cells. EXPERIMENTAL DESIGN: This study examined the potential benefit of combining AZD6244 with fractionated radiotherapy using human lung and colon carcinoma xenograft models. RESULTS: AZD6244 reduced ERK phosphorylation in Calu-6 lung cancer cells in vitro. Administration of AZD6244 for 10 days (25 mg/kg twice daily p.o.) inhibited the tumor growth of Calu-6 xenografts, with regrowth occurring on cessation of drug treatment. When fractionated tumor-localized radiotherapy (5 x 2 Gy) was combined with AZD6244 treatment, the tumor growth delay was enhanced significantly when compared with either modality alone, and this effect was also seen in a colon tumor model. We examined the effect of inhibiting MEK1/2 on the molecular responses to hypoxia, a potential interaction that could contribute to radioresponsiveness. AZD6244 reduced hypoxia-inducible factor-specific transactivation in vivo, shown using Calu-6 dual clone cells that stably express a Firefly luciferase gene under the control of a hypoxia-driven promoter. Furthermore, hypoxia-inducible factor-1 alpha, GLUT-1, and vascular endothelial growth factor levels were reduced by AZD6244, and there was a significant decrease in vascular perfusion in the tumors given combination treatment when compared with the other treatment groups. CONCLUSIONS: These data provide support for the clinical development of AZD6244 in combination with radiotherapy and indicate a potential role for AZD6244 in inhibiting the tumor hypoxia response.