Alnylam Pharmaceuticals, Inc. announced results from its Phase I clinical trial with ALN-VSP, a systemically delivered RNAi therapeutic for the treatment of advanced solid tumors with liver involvement.
In the Phase I study, ALN-VSP was generally well tolerated, demonstrated evidence for anti-tumor activity, and was found to mediate RNAi activity in both hepatic and extra-hepatic tumors.
“DCE-MRI results appear to show an anti-VEGF effect with ALN-VSP in approximately 50% of evaluable patients, including those who have been previously exposed to anti-VEGF drugs. Finally, analysis of tumor biopsy samples has demonstrated siRNA delivery and proof of RNAi mechanism in both hepatic and extra-hepatic tumors,” says Jared Gollob, MD, senior director of clinical research, Alnylam.
ALN-VSP was administered to 41 patients at doses ranging from 0.1 to 1.5 mg/kg; a total of 182 doses have been administered, including to one patient who has received 24 doses at 0.7 mg/kg over the course of more than one full year, and continues to receive treatment in the study. The most common adverse events were grade 1-2 fatigue (24% of patients), nausea (17% of patients) and fever (15% of patients), with no clear dose dependence. There were also no dose-dependent changes in liver function tests.
Grade 2 infusion-related reactions were observed in 15% of patients, or 3% of total doses administered; these reactions responded to slowing of the infusion of drug, and no patients discontinued therapy because of an infusion reaction. Dose-limiting toxicities included: liver failure and death in one patient with extensive hepatic metastases and prior splenectomy/partial hepatectomy at 0.7 mg/kg which was deemed possibly related to study drug; transient grade 3 thrombocytopenia in two patients at 1.25 mg/kg; and grade 3 hypokalemia in one patient at 1.5 mg/kg. Based on these safety data, the recommended dose for advancement of ALN-VSP into Phase II studies is 1.0 mg/kg.
ALN-VSP demonstrated evidence of anti-tumor activity in advanced malignancy patients. Patients participating in the study were heavily pre-treated, having received an average of 4.3 prior treatment regimens for their metastatic cancer, including both chemotherapy and anti-angiogenic drugs.
Fifty percent (12 of 24) of patients evaluable for response attained stable disease (SD) or better with ALN-VSP doses greater than or equal to 0.7 mg/kg, compared to only 8% (1 of 13) at doses less than or equal to 0.4 mg/kg. Results include one major ongoing response in a patient with endometrial cancer and multiple liver metastases treated at 0.7 mg/kg. This patient, whose treatment is ongoing after over one full year, has so far had a partial response (PR) with an approximately 70% reduction in tumor burden. Sixty four percent (7 of 11) of patients achieved SD at the recommended Phase II dose of 1.0 mg/kg and 45% (5 of 11) continue to receive drug on study. In addition, DCE-MRI results were suggestive of an anti-VEGF effect. In approximately 50% of evaluable patients, the average decline in Ktrans (measure of blood flow) in liver tumors where this parameter was measured was greater than or equal to 40%, an effect that is comparable to what has been observed with other anti-VEGF drugs in solid tumors.
In this study, 29 tumor biopsies were obtained voluntarily from 15 patients across multiple dose levels (from 0.4 to 1.5 mg/kg) using a CT-guided procedure; these included hepatic (liver) tumor biopsies from 11 patients and extra-hepatic tumor biopsies from four patients. The two siRNAs targeting VEGF and KSP that comprise ALN-VSP were detected in nearly all of the biopsy samples evaluable for drug levels at siRNA concentrations ranging from 0.3 to 142 ng/g tissue. These levels of siRNA are pharmacologically relevant since pre-clinical studies have shown that siRNA tissue levels of 1 ng/g are associated with 50% target gene silencing.
While there was no dose-dependence to the levels of VEGF and KSP siRNAs detected in biopsy samples, this finding was consistent with the high degree of variability in proportion of tumor, fibrotic/necrotic tissue, and normal tissue in biopsy samples, which impacts the quantitative interpretations of molecular results.
Using a highly precise polymerase chain reaction (PCR)-based technique known as 5’ rapid amplification of cDNA ends (5’ RACE), blinded analysis of human tissue samples showed proof of RNAi-mediated target mRNA cleavage. Specifically, three of 15 biopsy samples showed VEGF-derived mRNA fragments corresponding exactly to the predicted RNAi-mediated cleavage product based on the VEGF siRNA sequence in the post-treatment biopsy sample. The samples that were positive for VEGF 5’ RACE included liver tumor biopsies obtained from two patients dosed at 0.4 mg/kg and an extra-hepatic tumor biopsy from one patient dosed at 1.25 mg/kg. KSP 5’ RACE assay development is in progress, with further optimization required due to low expression of KSP mRNA in tissue samples.
Pharmacokinetic data from this study showed that Cmax (peak serum concentration of drug) and area under the curve (AUC) were dose proportional with no evidence of drug accumulation. Pre-clinical animal pharmacokinetic data were predictive for the observed results in man.
Release Date: June 4, 2011
Source: Alnylam Pharmaceuticals, Inc.
Filed Under: Drug Discovery