[Docetaxel in treatment of other solid tumors]

Pharmacokinetic profile of the microtubule stabilizer patupilone in tumor-bearing rodents and comparison of anti-cancer activity with other MTS in vitro and in vivo

INTRODUCTION

Patupilone is a microtubule stabilizer (MTS) currently in clinical development. Here, we evaluate the anti-cancer activity in vitro and in vivo in comparison to paclitaxel and describe the pharmacokinetics (PK) of patupilone in tumor-bearing nude mice and rats.

METHODS

The potency in vitro of patupilone and two other MTS, paclitaxel and ixabepilone, was determined using human colon carcinoma cell lines with low (HCT-116, HT-29, RKO) and high (HCT-15) P-glycoprotein expression (P-gp), as well as two multi-drug resistance (MDR) model cell pairs, MCF7/ADR and KB-8511 cells and their respective drug-sensitive parental counterparts. The PK of patupilone was investigated in nude mice bearing HCT-15 or HT-29 xenografts and in rats bearing s.c. pancreatic CA20498 tumors or A15 glioma tumors. Anti-cancer activity in vivo was compared to that of paclitaxel using three different human tumor colon models. The retention and efficacy of patupilone was compared in small and large HT-29 xenografts whose vascularity was determined by non-invasive magnetic resonance imaging.

RESULTS

Patupilone was highly potent in vitro against four different colon carcinoma cell lines including those showing multi-drug-resistance. In contrast, paclitaxel and ixabepilone displayed significantly reduced activity with markedly increased resistance factors. In both rats and mice, a single i.v. bolus injection of patupilone (1.5-4 mg/kg) rapidly distributed from plasma to all tissues and was slowly eliminated from muscle, liver and small intestine, but showed longer retention in tumor and brain with no apparent elimination over 24 h. Patupilone showed significant activity against three human colon tumor models in vivo, unlike paclitaxel, which only had activity against low P-gp expressing tumors. In HT-29 tumors, patupilone activity and retention were independent of tumor size, blood volume and flow.

CONCLUSIONS

The high potency of patupilone, which is not affected by P-gp expression either in vitro or in vivo, and favorable PK, independent of tumor vascularity, suggest that it should show significant activity in colorectal cancer and in other indications where high P-gp expression may compromise taxane activity.

Chemotherapy in head and neck cancer. Overview of newer agents

Several new chemotherapy agents show varying degrees of activity in head and neck cancer. The most extensively studied and most promising agents at this time are the taxanes, particularly paclitaxel. Its exact role in combination with other chemotherapeutic agents or with radiation is still being clarified in clinical testing, but it is certainly reasonable to use paclitaxel for palliation of metastatic or recurrent disease. Docetaxel is a more recently developed agent, and more information regarding its use in palliative therapy will be forthcoming as results from the international randomized trial become available. Gemcitabine has shown very modest activity when used as a single agent or in combination therapy, although further data from ongoing research have not yet been reported. It is an extraordinarily potent radiosensitizer in the head and neck, but unfortunately it appears to have a very narrow therapeutic ratio and should certainly not be used with radiation outside of a clinical trial with careful monitoring of toxicity. Topotecan does not appear to be a clinically useful single agent in treating head and neck cancer, and vinorelbine has shown minimal activity in the few clinical trials that have been conducted in head and neck cancer. Nedaplatin is a very new drug, and it is not possible to draw conclusions regarding its effectiveness until further evaluation has been completed. Continued investigation of new chemotherapeutic agents in head and neck cancer is needed.