High dose intermittent sorafenib shows improved efficacy over conventional continuous dose in renal cell carcinoma

Abstract

Background: Renal cell carcinoma (RCC) responds to agents that inhibit vascular endothelial growth factor (VEGF) pathway. Sorafenib, a multikinase inhibitor of VEGF receptor, is effective at producing tumor responses and delaying median progression free survival in patients with cytokine refractory RCC. However, resistance to therapy develops at a median of 5 months. In an effort to increase efficacy, we studied the effects of increased sorafenib dose and intermittent scheduling in a murine RCC xenograft model.

Methods: Mice bearing xenografts derived from the 786-O RCC cell line were treated with sorafenib according to multiple doses and schedules: 1) Conventional dose (CD) continuous therapy; 2) high dose (HD) intermittent therapy, 3) CD intermittent therapy and 4) HD continuous therapy. Tumor diameter was measured daily. Microvessel density was assessed after 3 days to determine the early effects of therapy, and tumor perfusion was assessed serially by arterial spin labeled (ASL) MRI at day 0, 3, 7 and 10.

Results: Tumors that were treated with HD sorafenib exhibited slowed tumor growth as compared to CD using either schedule. HD intermittent therapy was superior to CD continous therapy, even though the total dose of sorafenib was essentially equivalent, and not significantly different than HD continuous therapy. The tumors exposed to HD sorafenib had lower microvessel density than the untreated or the CD groups. ASL MRI showed that tumor perfusion was reduced to a greater extent with the HD sorafenib at day 3 and at all time points thereafter relative to CD therapy. Further the intermittent schedule appeared to maintain RCC sensitivity to sorafenib as determined by changes in tumor perfusion.

Conclusions: A modification of the sorafenib dosing schedule involving higher dose intermittent treatment appeared to improve its efficacy in this xenograft model relative to conventional dosing. MRI perfusion imaging and histologic analysis suggest that this benefit is related to enhanced and protracted antiangiogenic activity. Thus, better understanding of dosing and schedule issues may lead to improved therapeutic effectiveness of VEGF directed therapy in RCC and possibly other tumors.

Figures

Figure 1

Effects of dosing and schedule of sorafenib on tumor growth. Treatment was initiated when tumors reached 12 mm in long axis (volume ~500 mm3) with the administration of vehicle or different doses and schedule of sorafenib orally as indicated. All animals were sacrificed and tumors were dissected ~36 days post treatment with the exception of vehicle treated mice which were sacrificed when tumors reached the mandated 20 mm sacrifice size (~22 days post treatment, volume ~2500 mm3). Figure 1A shows that treatment with high dose intermittent therapy inhibited tumor growth to a greater extent than conventional dose continuous and intermittent therapy. Data are presented as mean tumor volume with SEM. Figure 1B presents the tumor volume on the average day when vehicle treated tumors reached 20 mm in long axis (~22 days post treatment). The tumor volume of mice with high dose intermittent therapy is significantly smaller than that of conventional dose continuous therapy (P < 0.05) while the volume did not differ in the high dose intermittent vs high dose continuous or conventional dose intermittent vs conventional dose continuous arms (P > 0.05).

Figure 2

Microvessel density analysis of sorafenib treated tumors. Immunohistochemical analysis of CD31 (A-C) and CD34 (D-F) expression in vehicle (A, D), low dose (B, E) and high dose (C, F) at day3 are shown. The bar graph shows the average CD31 and CD34 expression in the vehicle (n = 3), conventional dose (n = 3), and high dose (n = 3) arms. As compared to vehicle treated tumors, the tumors exposed to conventional and high dose sorafenib had lower MVD (CD34 and CD31)(P < 0.01). There was a consistent trend for lower MVD in the high dose treatment as compared to the conventional dose treatment in both the CD34 and CD31 analyses.

Figure 3

Effect of dosing and schedule of sorafenib on tumor perfusion. Figure 3A shows normalized serial tumor perfusion from 3 mice at 4 time points. Conventional dose of sorafenib lowers tumor perfusion by 57% by day 3. This decrease begins to resume by day 10 of therapy. In contrast, high dose intermittent sorafenib lowers perfusion by 85% at day 3. While tumor perfusion increases slightly at day 7 after there has been a 4 day lapse in treatment, by day 10, tumor perfusion is still low (20% of pretreatment). Tumor perfusion was significantly different in two arms at day 3 (P < 0.01) and day 10 (P < 0.001) as determined by two way ANOVA followed by Bonferroni posttest. Data are presented as mean normalized tumor perfusion with SEM. Figure 3B, shows a representative set of serial tumor perfusion images from mice treated with a conventional dose (upper row) or high dose intermittent (lower row) sorafenib. The blood flow values are shown in bold text are the values obtained while the mice were on sorafenib and the values that are not in bold are from mice before or off therapy. The tumor size was measured in long and short axes (mm) and the mean blood flow (mL/100 g/minute) are shown below each image. A color bar at the bottom represents the range of perfusion values from 0 to 160 mL/100 g/minute.