SCIENTIFIC DISCUSSION This module reflects the initial scientific discussion for the approval of Hycamtin. This scientific discussion has been updated until 1 September 2004. For information on changes after this date please refer to module 8B. 1. Introduction Ovarian cancer is the fourth most common cause of cancer death in women. At time of diagnosis, the cancer has spread outside the pelvis in at least 60% of the patients. At the time of the evaluation, overall five-year survival was about 20%. The treatment of advanced ovarian carcinoma generally consisted of surgery followed by chemotherapy. Commonly used chemotherapy regimens have been platinum-based and cyclophosamide/cisplatin was a widely used combination regimen at the time of the evaluation. Paclitaxel in combination with cisplatin had shown promising results as first-line therapy. Although the response rate to first-line chemotherapy is relatively high, the disease will relapse in the majority of patients. Ovarian carcinoma, which fails first-line therapy, is not curable. Topotecan is a semisynthetic structure analogue of the natural alkaloid camptothecin. It is water soluble with an intact lactone ring. The lactone ring may open in a reversible pH-dependent reaction, forming a carboxylate derivative. Only the lactone form is pharmacologically active, inhibiting topoisomerase 1. This nuclear enzyme is crucial for DNA replication, i.e. proliferation, DNA repair and transcription. Topoisomerase 1 inhibitors bind only to the DNA-enzyme complex. This binding is rapidly reversible, allowing religation within 30 min. after drug removal. Following prolonged drug exposure, DNA fragmentation occurs leading to apoptotic cell death. The proposed indication is treatment of metastatic carcinoma of the ovary after failure of first-line or subsequent therapy. The proposed dosage is 1.5 mg/m2/day administered intravenously during 30 min. for 5 consecutive days every 3 weeks. 2. Chemical, pharmaceutical and biological aspects Hycamtin is presented as powder for solution for infusion. Each vial contains topotecan hydrochloride equivalent to 4 mg of topotecan. The product should be reconstituted with 4 ml of water for injection and diluted with 0.9% sodium chloride or 5% glucose intravenous infusion. It contains mannitol as bulking agent, tartaric acid as a stabiliser as well as hydrochloric acid and sodium hydroxide to adjust the pH to 2.5-3.5. Hycamtin is packaged in 5 ml vials of Type I flint glass (Ph. Eur.) with grey siliconised butyl rubber stoppers with aluminium flip-off seals. Topotecan hydrochloride is hygroscopic with a low solubility in organic solvents except methanol. Its aqueous solubility decreases with increasing pH. In aqueous solution it can undergo pH-dependent reversible opening of the lactone ring (below pH 4 no open form is present, above pH 9 more than 95% is hydrolysed). Topotecan is light and heat sensitive. The purpose of the pharmaceutical development was to produce a product stable enough for intravenous injection. The lyophilised form was chosen due to the stability problems arising from the above-mentioned properties of the drug substance. Topotecan is semisynthetically manufactured from the plant-derived alkaloid camptothecin. The starting material may be obtained from two natural sources - Chinese (Acuminata) and Indian (Mappia). Purification of the crude extract from either source is required. The main steps in the synthesis involve reduction and selective oxidation of the quinoline moiety of camptothecin, followed by the introduction of an N,N-dimethylaminomethyl side-chain. The structure of topotecan is proved by elementary analysis, interpreted ultra violet-, infrared-, nuclear magnetic resonance-, and mass- spectrometry spectra. Serial batch analyses confirmed the consistency of the manufacturing process, using tests which were sufficiently validated. Topotecan is chiral and contains one stereogenic (asymmetric) centre with the S configuration. The molecule is homochiral to camptothecin, for which the stereochemical purity is ascertained by chiral chromatography. The antipode has not been found in any batch and there is no known mechanism to 1/10 EMEA 2005 racemise camptothecin under the conditions applied during the synthesis of topotecan. Thus, the stereochemical purity is considered to be under control. Five impurities have been qualified at their specification levels. Owing to the limited number of batches manufactured, the limits for impurities should be reassessed when more experience is gained. Also with respect to the finished product, limits for impurities and degradation products will be reassessed when more experience is gained. With respect to other ingredients, mannitol, tartaric acid, hydrochloric acid, sodium hydroxide and water for injection were claimed to follow the requirements of the Ph. Eur. To show conformance with the Ph. Eur., certificates of analyses should be submitted when available. Limits for microbial purity of water for injection were confirmed not to exceed 10 CFU/100 ml and of topotecan hydrochloride, mannitol and tartaric acid not to exceed 102 CFU/g. The finished product is manufactured by aseptic processing. Due to equipment-related graphite contamination of the drug solution, a pre-filtration using 0.45µm filter is included before two consecutive sterile filtrations using 0.2µm filters to assure sterility. Thereafter, the solution is aseptically filled into vials before lyophilisation. The manufacturing process is satisfactory validated and relevant in-process controls are performed. Bioburen is included as a periodic in-process test. Although topotecan degrades under stressed conditions, it appears to be stable in long-term stability studies. The proposed shelf life of 24 months below 30°C can be accepted. Chemical stability of reconstituted as well as diluted solution has been demonstrated, but from a microbiological point of view, immediate use is required. If reconstituted under strict aseptic conditions (e.g. in a LAF-bench), 12 h in room temperature or 24 hours at 2-8°C can be accepted from the first breaking of the vial until the infusion to the patient is completed. Due to its light sensitivity, it must be protected from light during long-term storage. The initial shelf life at the time of the Marketing Authorisation was 24 months. The Marketing Authorisation Holder applied for an extension of the shelf life to 3 years through a Type I variation. The stability data provided demonstrated that the specifications are all met and that a shelf life of 3 years is acceptable. Additional presentations of a 1 mg vial in packs of 3 and 5 vials were approved following a Type II variation. The formulation of the bulk solution is identical to the formulation for the already approved 4 mg vials. The difference between the 1 and 4 mg vials is the fill weight and vial size. The 1 mg lyophile will be reconstituted to the same concentration as the 4 mg lyophile i.e. 1 mg/ml. However, the 1 mg vial contains a 10 % filling overage to ensure that 1 mg can be withdrawn from each vial, in line with European Pharmacopoeial recommendations for extractable volumes. 3. Toxico-pharmacological aspects Pharmacodynamics The mechanism of action of topotecan has been delineated in tumour cell lines and cell free systems, and is, in comparison with many other anti-cancer drugs, well characterised. It includes the depicted interaction with the target enzyme topoisomerase 1 and the dependency of DNA replication for the cytotoxic effect. Topoisomerase 1 is involved in the cleavage and religation of the DNA ahead of the replication fork and is therefore crucial in DNA replication, DNA repair as well as transcription. Topotecan selectively inhibits the religation step, which stabilises the enzyme-cleaved DNA complex leading to the formation of single strand breaks. Although single strand breaks are not sufficient to produce cell death, the drug-enzyme-DNA complex ultimately results in double strand breaks underlying the cytotoxic effects of topotecan. Cytotoxicity appears to be time and concentration dependent. IC50 values ranging from about 1-800 nM were obtained with various cell lines in vitro. However, no ‘in vivo mechanistic studies’, e.g. relationships between drug exposure and single strand breaks, cytotoxicity or reversibility, were carried out. Studies designed to elucidate schedule dependent activity indicated that prolonged exposure is associated with increased cytotoxic effect. Thus, the proposed schedule for licensing, a 30-min infusion each day for 5 days is, at least partly, supported by preclinical data. 2/10 EMEA 2005 Cell lines with low topoisomerase 1 level or with altered or reduced binding of topotecan to topoisomerase 1 was shown to be resistant to its cytotoxic activity. Topotecan also seems to be a substrate, albeit rather poor, for the multidrug resistance associated P-glycoprotein “drug extrusion pump”. In general, cisplatin resistant sublines were not resistant to the activity of topotecan. However, the level of in vitro cross-resistance with topotecan in tumour samples from patients with clinical, cisplatin- or paclitaxel-resistant disease was not investigated. It is generally accepted that activity against specific cell lines in vitro and in vivo poorly predicts activity against corresponding tumour types in patients. In vitro systems, using fresh tumour samples and various techniques and endpoints, may confer a good correlation with clinical activity, both with respect to diagnostic groups and in individual