Clinical pharmacological and translational research on novel formulations of anticancer drugs

Abstract

This thesis investigated oral administration of gemcitabine (2’,2’-difluorodeoxycytidine, dFdC) and novel paclitaxel formulations and intravenous (i.v.) administration of the camptothecin prodrug MEN 4901/T-0128 in patients with advanced cancer. Oral drug administration is convenient for patients and facilitates the use of continuous dosing regimens, which might lead to an increased antitumor activity. Gemcitabine is transported into cells by human nucleoside transporters and is intracellularly phosphorylated to its active metabolite gemcitabine triphosphate (dFdCTP). A clinical study in patients with advanced solid tumors who received oral dFdC at low dose-levels demonstrated extensive first-pass metabolism of dFdC to its main metabolite 2’,2’-difluorodeoxyuridine (dFdU). A sensitive LC-MS/MS method was developed to quantify dFdCTP in peripheral blood mononuclear cells (PBMCs) of patients. The exposure to dFdC in plasma and to dFdCTP in PBMCs was low and did not significantly increase with dose. High levels of dFdUTP, the phosphorylated metabolite of dFdU, were obtained in PBMCs. The metabolite dFdU had a long terminal half-life (t1/2) of about 4 days. Our hypothesis was that dFdU accumulated in the liver, which was possibly associated with the hepatic toxicity observed in one patient. In vitro experiments demonstrated that dFdU is a good substrate for uptake by the concentrative nucleoside transporter type 1 (hCNT1), which is highly expressed in liver and kidney. This might contribute to (re)uptake of dFdU and to the long t1/2 of dFdU. Furthermore, we found that dFdU is phosphorylated to dFdUTP and incorporated into DNA and RNA, which positively correlated with the cytotoxicity of dFdU. In addition, the extent of DNA incorporation of dFdUTP and dFdCTP in human hepatocellular carcinoma HepG2 cells were comparable at equitoxic concentrations of dFdC and dFdU, suggesting comparable intrinsic toxicity of these molecules. An in vivo study in wild-type mice confirmed accumulation of dFdUTP in the liver after multiple oral dosing of dFdC. Clinical studies with novel oral formulations of paclitaxel without Cremophor EL (CrEL) co-administered with cyclosporin A (CsA), an inhibitor of P-gp, demonstrated an increase in apparent bioavailability of paclitaxel up to a maximum of 60%. A self-microemulsifying oily formulation of paclitaxel demonstrated a desirable systemic exposure to paclitaxel after oral administration in combination with CsA. The systemic exposure to paclitaxel from a polymeric capsule formulation was increased about two-fold after co-administration with CsA. Interestingly, the novel paclitaxel analogue BMS-275183, which had a lower affinity for P-gp than paclitaxel, resulted in considerable antitumor activity in patients with non-small cell lung cancer after oral administration at a twice weekly schedule. The prodrug MEN 4901/T-0128, consisting of the new camptothecin analogue T-2513 bound to a carboxymethyldextran polymer, showed partial responses in patients with colorectal cancer and head and neck cancer after single i.v. administration once every 6 weeks. MEN 4901/T-0128 demonstrated a long t1/2 of about 4.5 days. The dose-level of 1800 mg/m2 was tolerated and resulted in promising clinical activity.