Response of resistant melanoma to a combination of weekly paclitaxel and bevacizumab

Preliminary results of the combination of bevacizumab and weekly Paclitaxel in advanced melanoma

BACKGROUND

Pretreated advanced melanoma is a poor prognosis scenario with few, if any, active therapeutic options. The antibody against vascular endothelial growth factor, bevacizumab, has demonstrated increased activity in combination with chemotherapy in many tumors. We intended to evaluate the activity of the combination of weekly paclitaxel and bevacizumab in previously treated metastatic melanoma.

PATIENTS AND METHODS

Patients with previously treated metastatic melanoma received paclitaxel 70 mg/m(2) weekly and bevacizumab 10 mg/kg biweekly for 5 consecutive weeks every 6 weeks.

RESULTS

Twelve patients were treated. Two patients (16.6%) achieved a partial response and 7 patients (58.3%) stable disease. Responses were seen in soft tissue, lung and brain metastases. Median disease-free and overall survival times were 3.7 and 7.8 months, respectively. Treatment was well tolerated. Main toxicities were grade 3 asymptomatic lymphopenia in 6 patients, grade 3 leucopenia in 2 patients, and grade 3 thrombocytopenia in 1 patient.

CONCLUSIONS

Our preliminary results suggest that the combination of bevacizumab and weekly paclitaxel is active and safe in patients with metastatic melanoma, warranting further investigation.

Retinoic acid decreases ATF-2 phosphorylation and sensitizes melanoma cells to taxol-mediated growth inhibition

Cutaneous melanoma is often resistant to chemo- and radiotherapy. This resistance has recently been demonstrated to be due, at least in part, to high activating transcription factor 2 (ATF-2) activity in these tumors. In concordance with these reports, we found that B16 mouse melanoma cells had higher levels of ATF-2 than immortalized, but non-malignant mouse melanocytes. In addition, the melanoma cells had a much higher amount of phosphorylated (active) ATF-2 than the immortalized melanocytes. In the course of determining how retinoic acid (RA) stimulates activating protein-1 (AP-1) activity in B16 melanoma, we discovered that this retinoid decreased the phosphorylation of ATF-2. It appears that this effect is mediated through p38 MAPK, because RA decreased p38 phosphorylation, and a selective inhibitor of p38 MAPK (SB203580) also inhibited the phosphorylation of ATF-2. Since ATF-2 activity appears to be involved in resistance of melanoma to chemotherapy, we tested the hypothesis that treatment of the melanoma cells with RA would sensitize them to the growth-inhibitory effect of taxol. We found that pretreatment of B16 cells with RA decreased the IC50 from 50 nM to 1 nM taxol. On the basis of these findings and our previous work on AP-1, we propose a model in which treatment of B16 cells with RA decreases the phosphorylation of ATF-2, which results in less dimer formation with Jun. The "freed-up" Jun can then form a heterodimer with Fos, resulting in the increased AP-1 activity observed in RA-treated B16 cells. Shifting the balance from predominantly ATF-2:Jun dimers to a higher amount of Jun:Fos dimers could lead a change in target gene expression that reduces resistance to chemotherapeutic drugs and contributes to the pathway by which RA arrests proliferation and induces differentiation.