Several phase I clinical trials of vorinostat in solid and haematological tumours have been completed. In initial trials this drug was introduced intravenously and the most significant DLTs observed were leukopenia and thrombocytopenia . An oral version of vorinostat was subsequently developed and phase I trials were found to have linear pharmacokinetics from 200 to 600 mg, with an apparent half-life ranging from 91 to 127 min. and 43% oral bioavailability . Following the development of this oral form, a phase I trial was conducted in patients with mesothelioma. Similar toxicities to the original phase I trials were observed primarily fatigue, dehydration, nausea, and vomiting. Of four patients who completed greater than six cycles of therapy, two showed partial responses, which have led to a placebo-controlled, randomized phase III study of oral vorinostat for mesothelioma patients for whom treatment with pemetrexed has failed . A phase II trial of vorinostat for refractory cutaneous T-cell lymphoma (CTCL) demonstrated both partial responses and ruritus relief, with limited toxicities of fatigue, thrombocytopenia, diarrhoea and nausea , and went on for further development. Following the completion of a single-arm, open-label, multi-centre pivotal trial and 11 other trials, clinical efficacy was assessed. Vorinostat showed activity in CTCL, and skin responses were a clinical benefit, and vorinostat was subsequently approved for treatment of cutaneous manifestations of CTCL . A phase II trial of vorinostat has also been completed in patients with recurrent and/or metastatic head and neck cancer. In this trial, 12 patients received 400 mg once daily. Three patients had stable disease ranging from 9 to 26 weeks. Nine patients discontinued due to progressive disease, two withdrew consent, and one discontinued therapy for grade 3 anorexia. Overall, vorinostat was generally well tolerated but did not demonstrate efficacy as defined by tumour response . In an open centre early phase II trial of oral vorinostat, patients with measurable, relapsed or refractory breast or non-small cell lung cancer who had received >/= 1 prior therapy or colorectal cancer who had received >/= 2 prior therapies were enrolled. Oral vorinostat (200, 300 or 400 mg) was taken twice daily for 14 days, followed by a 7-day rest until disease progression or intolerable toxicity was conducted, and the response rate, safety and tolerability were evaluated. Of the 16 patients recruited no DLTs were observed at 200 mg. Disease stabilization was observed in eight patients, but there were no confirmed responses .
Phenylbutyrate is another HDi for which several clinical trials have been carried out. When taken orally, the most common toxicities observed are grade 1–2 dyspepsia and fatigue . Two phase I studies found that the DLTs included reversible neurocortical toxicity characterized by somnolence and confusion [254–256]. In a phase I study of sodium phenylbutyrate on patients with Huntington's disease, toxicities observed at the higher doses included vomiting, light-headedness, confusion and gait instability, but with no significant laboratory or electrocardiographic abnormalities .
Several trials testing phenylbutyrate on spinal muscular atrophy (SMA) have been carried out. The results of these studies found that the major side effect was a temporary stomach ache [258, 259]. Unfortunately, in a randomized, double-blind, placebo-controlled trial of phenylbutyrate in spinal muscular atrophy no significant improvements were observed . However, it must be noted that in this trial, SMA patients were treated for only 13 weeks, and this may be too short a treatment period to identify any clinical benefit from PB. However, other trials continue to show further evidence that phenylbutyrate may have efficacy in the treatment of disease. In a phase I dose-escalation study in cystic fibrosis, a statistically significant induction of chloride transport was observed, with minimal adverse reactions .
Phenylbutyrate has also been used in phase I clinical trials for solid tumours. In this trial common adverse effects included grade I nausea/vomiting, fatigue and light-headedness, and the DLTs observed were short-term memory loss, sedation, confusion, nausea and vomiting. The maximum tolerated dose (MTD) was 300 mg/kg/day, and three of the twenty-one patients enrolled achieved stable disease . A dose escalation study of oral phenylbutyrate has also been carried out in patients with recurrent malignant glioma. In agreement with the trials presented above, fatigue and somnolence were the worst toxicities observed. Of the twenty-three patients enrolled one patient had a complete response for 5 years .
VPA has also entered clinical trials as a stand-alone agent in patients with advanced refractory cancer. Dose escalation was carried out in three-patient cohorts on twenty-six pre-treated patients. The MTD of infused drug was found to be 60 mg/kg/day, and the DLT was found to be grade 3 or 4 neurological side effects occurring in 8 out of 26 patients . A phase II trial of VPA has also been completed in patients with castration-resistant prostate cancer. However, VPA was not found to be well tolerated by this cohort, and could not be administered reliably in order to achieve consistent levels or duration, and it was concluded that oral VPA is not recommended for prostate cancer .
In a phase I trial of continuous oral VPA for maintenance treatment in heavily pre-treated paediatric glioma patients, moderate tumour efficacy was observed . VPA also shows potential in the treatment of neurodegenerative conditions. In a phase I trial of VPA on patients with human T-lymphotropic virus type 1 (HTLV-1), which is responsible for HTLV-associated myelopathy/tropical spastic paraparesis, clinical efficacy was observed. 16 patients were recruited and VPA was administrated orally at a maximal dose of 20 mg/kg/day. There was a significant drop in patient viral load from month 0 to month 3, and for the first time provides evidence that VPA leads to depletion of HTLV-1-infected cells in vivo . The Project Cure SMA team has just completed the phase II CARNI-VAL clinical trial examining the effects of a combinatorial treatment of VPA and carnitine on SMA (http://www.fsma.org), but the results of this trial have yet to be disseminated to the greater scientific community.
The HDi romidepsin has completed several phase I clinical trials on cancer and has also entered/completed phase II trials. In the phase I trials the major DLTs for this drug was again thromocytopenia. However, for this drug a significant increase in reversible cardiac dysrhythmias and non-specific ECG abnormalities were observed [274–276]. In a phase I dose-escalation trial of romidepsin in paediatric solid tumours romidepsin was administered as a 4-hr infusion weekly for three consecutive weeks every 28 days at dose levels of 10, 13, 17 and 22 mg/m2. Of the 24 patients enrolled, 18 could be assessed for toxicity. In agreement with the other phase I trials non-specific reversible ECG abnormalities were observed. Of the 18 patients three achieved long-term stable disease. For phase II trails the recommended dose was determined to be the recommended phase II dose in children with solid tumours is 17 mg/m2.
A second phase I trial in patients with acute myelogenous leukaemia or advanced myelodysplastic syndromes used 18 mg/m2 intravenous on days 1 and 5 every 3 weeks. The most common grade 3/4 toxicities were febrile neutropenia/infection, neutropenia/thrombocytopenia, nausea and asymptomatic hypophosphatemia, with no clinically significant cardiac toxicity. The best responses of 11 assessed patients was one complete remission (CR) in a patient with acute myeloid leukaemia (AML), stable disease in six patients. Notably however, histone H3 and H4 acetylation levels evaluated in five patients showed no consistent changes .
Two phase II trials of romidepsin have been completed. In a trial on twenty-nine patients with refractory metastatic renal cell cancer, the most common serious toxicities were fatigue, nausea, vomiting and anaemia. However, one patient developed a grade 3 atrial fibrillation, one patient developed tachycardia, and there was 1 sudden death. Within the study group itself two patients achieved an objective response, which was insufficient to bring this agent forward for further study in the treatment of renal cell cancer . In a phase II trial on T-cell lymphoma, cardiac monitoring of 42 patients was carried out. The data obtained as part of this study indicate that the administration of romidepsin is not associated with myocardial damage or impaired cardiac function . However, in a phase II study of romidepsin in neuroendocrine tumours, the study was terminated prematurely due to an unexpected high number of serious cardiac adverse events .
MS-275 has just completed two phase I trials in solid tumours. The MTD of this drug was found to be 6 mg/m2, with a mean terminal half-life of 33.9 ± 26.2 and a T(max) ranging from 0.5 to 24 hrs. Dose-limiting grade 3 toxicities were found to be reversible and included hypophosphatemia, hypoasthenia, hyponatremia and hypoalbuminemia [282, 283] . In an earlier phase I study, the MTD was found to be 10 mg/m2 and DLTs were nausea, vomiting, anorexia and fatigue. In addition the half-life was found to be within the range 39–80 hrs . In a phase I trial of MS-275 in patients with advanced acute leukaemias, the MTD was found to be 8 mg/m2 weekly for 4 weeks every 6 weeks. DLTs included infections and neurological toxicity manifesting as unsteady gait and somnolence. Other frequent toxicities observed were fatigue, anorexia, nausea, vomiting, hypoalbuminemia and hypocalcaemia . In a trial to determine pharmacokinetic data for oral MS-275 in 64 adult patients receiving MS-275 orally (dose range, 2 to 12 mg/m2), no metabolites could be detected after incubation of MS-275 in human liver microsomes, suggesting that hepatic metabolism is a minor pathway of elimination, while the mean (±S.D.) apparent oral clearance of MS-275 was 38.5 ± 18.7 l/hr .
Most recently a phase II trial of MS-275 has been completed in patients with metastatic melanoma. The primary study end-point was objective tumour response, but among 28 patients enrolled, no objective response was detected. Seven patients in showed disease stabilizations .
This orally administered HDi has recently completed a phase I clinical trial in patients with leukaemia or myelodysplastic syndromes . This was administered orally three times weekly without interruption, in a dose-escalation study of 20, 40 and 80 mg/m2. The MTD was determined to be 60 mg/m2, with DLTs of fatigue, nausea, vomiting, and diarrhoea observed at the higher doses. Of 29 patients enrolled, 3 achieved a complete bone marrow response (blasts < or = 5%). Pharmacokinetic analyses indicated absorption of MGCD0103 within 1 hr and an elimination half-life in plasma of 9 (±2) hrs .
The poor overall response of solid tumours to HDi as single agent therapies has resulted in several trials examining their potential as adjuvant therapies in combination with other drugs.
One HDi valproate, has completed a phase II trial examining its use as a combined epigenetic therapy with hydralazine to overcome chemotherapy resistance in refractory solid tumours. In this trial 17 patients were evaluable for toxicity and 15 for response. Twelve patients were found to respond with four showing a partial response and eight demonstrating stable disease (defined as neither sufficient tumour reduction to qualify for partial response nor sufficient increase to qualify for progressive disease) . A phase I trial using a similar combination (hydralazine/valproate) plus neoadjuvant Doxorubicin Cyclophosphamide was carried out in patients with locally advanced breast cancer. 16 patients were included and received treatment. All were evaluated for clinical response and toxicity and 15 for pathological response. Treatment was well tolerated and the most common toxicity observed was patient drowsiness grades 1–2. Five (31%) patients had clinical response and eight (50%) had a partial response to give an overall response rate of 81%. There was a statistically significant decrease in both global 5-methylcytosine content and HDAC activity. The results obtained in this trial have resulted in the initiation of an ongoing randomized phase III study .
A pilot clinical trial involving phenylbutyrate and 5-azacytidine in patients with acute myeloid leukaemia or myelodysplastic syndrome has also been carried out. This combination regimen was well tolerated with common toxicities of injection site skin reaction (90% of the patients) from 5-azacytidine, and somnolence/fatigue from the sodium PB infusion (80% of the patients). Of the 10 patients in this trial, 5 patients (50%) were able to achieve a partial remission or stable disease, and 1 patient was able to proceed to allogeneic stem cell transplantation and was alive without evidence of disease 39 months later .
A phase I/II study of the combination of 5-aza-2’-deoxycytidine with VPA in patients with leukaemia was completed. In this study a group of 54 patients was recruited and treated with a fixed dose of decitabine (15 mg/m2 i.v. daily for 10 days) administered concomitantly with escalating doses of VPA orally for 10 days. The MTD of VPA was determined to be 50 mg/kg daily. Twelve (22%) patients had objective response, including 10 (19%) CRs and 2 (3%) CRs with incomplete platelet recovery (CRp). Remission duration was 7.2 months (range, 1.3–12.6+ months), while overall survival was 15.3 months (range, 4.6–20.2+ months) in responders .
Several trials involving VPA in combination with all-trans retinoic acid (ATRA) have been carried out. In one study on 26 patients with poor-risk AML VPA (5–10 mg/kg starting dose) and ATRA (45 mg/m2) were administered orally. Of 26 patients recruited, 19 completed at least 4 weeks of VPA/ATRA treatment. Seven patients were withdrawn prematurely because of rapidly progressive disease (n= 3) or unacceptable neurological and cardiovascular toxicity (n= 4). Three patients had partial responses . A larger trial was carried out on 58 patients with advanced AML who were unfit for standard intensive chemotherapy. VPA was administered to reach serum concentrations between 50 and 100 g/ml, the therapeutic range used for VPA in anti-epileptic treatment. There were two different treatment schedules for ATRA, either 80 mg/m2 each day was given in two divided doses, days 1–7, every other week, or 15 mg/m2 was given daily, starting on day 4. Both drugs were administered orally. Treatment was continued as long as neither significant side effects nor disease progression occurred. Overall, treatment was well tolerated, but it was concluded that VPA had beneficial effects but was not sufficiently active to be useful as single-agent therapy for AML . A larger phase II trial involving 75 patients with myelodysplastic syndrome and relapsed or refractory acute myeloid leukaemia, found that VPA was only clinically useful in low-risk myelodysplastic syndrome . This was subsequently followed with a phase I/II study combining 5-azacitidine (5-AZA), VPA, and ATRA in patients with acute myeloid leukaemia or high-risk myelodysplastic syndrome. In this trial 53 patients were treated. 5-AZA was administered subcutaneously at a fixed dose of 75 mg/m2 daily for 7 days. VPA was dose-escalated and given orally daily for 7 days concomitantly with 5-AZA. ATRA was given at 45 mg/m2 orally daily for 5 days, starting on day 3. The MTD of VPA in this combination was found to be 50 mg/kg daily for 7 days, and reversible neurotoxicity was the DLT Overall response rate to this treatment was 42%. The median remission duration was 26 weeks, and at the time of publication median survival had not yet been reached .
VPA has also undergone a phase I dose-escalation trial in combination with the topoisomerase II inhibitor epirubicin in advanced solid tumours. In this trial forty-eight patients were enrolled, and 44 received at least one cycle of therapy (increasing doses of VPA (days 1 through 3) followed by epirubicin (day 3) in 3-week cycles). DLTs observed were somnolence, confusion, and febrile neutropenia. The maximum-tolerated dose and recommended phase II dose identified was VPA 140 mg/kg/day for 48 hrs followed by epirubicin 100 mg/m2. In the treated patients partial responses were seen across different tumour types in nine patients (22%), and stable disease/minor responses were seen in 16 patients (39%), indicating that this combination may have potential in the treatment of solid tumours .
SAHA (vorinostat) has also completed a phase I trial in combination with Carboplatin and Paclitaxel for the treatment of advanced solid malignancies. Twenty-eight patients were enrolled into the study and separated into two arms for vorinostat treatment which was either administered orally once daily for two weeks or given twice daily for 1 week, every 3 weeks. Within each arm, the doses of vorinostat and paclitaxel were dose escalated in sequential cohorts of three patients. The DLT was determined to be 400 mg of vorinostat given once daily. Other non-DLTs included nausea, fatigue, diarrhoea and neuropathy. When patient response was evaluated, 10 of 19 (53%) of patients who had advanced chemo-naive non-small cell lung cancer (NSCLC) experienced a partial response and 4 had stable disease. In comparison, chemo-naive NSCLC patients just receiving carboplatin–paclitaxel generally achieve response rates of approximately (20–30%). These results indicate that vorinostat may enhance this therapy in NSCLC, and a phase II study randomizing advanced NSCLC patients to carboplatin-paclitaxel with either vorinostat or placebo is currently ongoing .
A phase I study combining cytotoxic-differentiation therapy with 5-fluorouracil and phenylbutyrate in patients with advanced colorectal cancer has been completed. In this study 5-flurouracil (FUra) was dose escalated (24-hr continuous intravenous infusion (2–2.3 g/m2), in combination with PB (120-hr continuous intravenous infusion at a fixed dose of 410 mg/kg/day × 5), and repeated weekly, in patients with advanced colorectal cancer. Nine patients were recruited and treated of which 8 could be assessed for toxicity. Weekly infusions of FUra followed by PB were fairly well tolerated with dose-dependent, reversible toxicities including somnolence, fatigue, confusion, hearing loss, triglyceridemia and hyperuricaema. Four patients completed eight weeks of treatment. Of these three achieved stable disease .
In a phase II randomized, double-blind, placebo-controlled, multi-centre study examining a combination of CI-994 and gemcitabine in patients with advanced pancreatic cancer. A total of 174 patients were recruited and received either a combination of CI-994/gemcitabine (CI-994 6 mg/m2/day days 1–21 plus gemcitabine 1000 mg/m2 days 1, 8 and 15 each 28-day cycle) or placebo/gemcitabine (placebo plus gemcitabine 1000 mg/m days 1, 8 and 15 of each 28-day cycle days 1–21). When the results were assessed, CI-994 offered no advantage over gemcitabine alone in the treatment of these patients, and indeed lowered their quality of life .