Low-dose (12 Gy) TSEBT+Vorinostat Versus Low-dose TSEBT Monotherapy in Mycosis Fungoides

Vorinostat is a histone deacetylase inhibitor (HDAC) that is FDA-approved for treatment of mycosis fungoides (MF), and has shown activity as a radiation-sensitizer in preclinical studies. Treatment of various cell lines \[glioblastoma multiforme (GBM), non-small cell lung cancer (NSCLC), melanoma\] has shown that pretreatment with vorinostat had a significant effect on radiation kill. This effect is believed to be secondary to multiple mechanisms that may involve antiproliferative growth inhibition and effects on DNA repair after exposure to radiation. A histone deacetylase inhibitor such as vorinostat may act as a radiosensitizer by modulating the expression of single- and double-strand DNA repair proteins such as KU67, KU86, H2AX, and Rad50. These DNA repair proteins are enzymes of that repair radiation-induced damage. The decrease in these DNA repair enzymes is thought to be the key mechanism of sensitization. Down-regulation of several key proteins involved in the nonhomologous end joining pathway is thought to generate a G2/M checkpoint blockade. Vorinostat may also cause an "open chromatin" structure increasing the effect of radiation damage to DNA. This is exemplified by the finding that there is a prolonged H2AX phosphorylation and H2AX foci formation. The mechanism producing this prolongation of H2AX foci is thought to contribute to the damage, and thus killing effect of the radiation. In the pivotal phase 2 trial of vorinostat, an overall response rate of nearly 30% was reported. The median time to progression was 4.9 months overall, and 9.8 months for MF stage IIB or higher responders. Through hyperacetylation of both histone and non-histone proteins, vorinostat is felt to exert its anti-tumor activity via several mechanisms, including cell cycle arrest, induction of apoptosis, reactive oxygen species generation, cell differentiation, and angiogenesis inhibition. Importantly, a number of pre-clinical studies have reported on the potential of vorinostat to enhance radiosensitivity of several different human tumor cell lines. The rational for clinical trial investigating combination of vorinostat and TSEBT not only comes from their underlying mechanism for potential synergy as suggested by prior in-vitro studies but also due to general therapeutic advantage derived from their non-overlapping toxicities. Recent results from a phase 1 dose-escalation trial combining palliative pelvic radiation (30 Gy in 3 Gy fractions over 2 weeks) and vorinostat in study participants with histologically-confirmed intrapelvic gastrointestinal carcinoma. Sixteen participants were enrolled into cohorts of escalating vorinostat dose (100 mg, 200 mg, 300 mg, and 400 mg daily). The most common adverse events were grade 1 and 2, among which fatigue and gastrointestinal events were most common. Grade 3 adverse events included fatigue (n = 5), hyponatremia (n = 1), hypokalemia (n = 1), and acneiform rash (n = 1). Of these, treatment related grade 3 events \[ie, dose limiting toxicities (DLT)\] were observed in 1 of 6 participants at vorinostat 300 mg daily (fatigue and anorexia), and in 2 of 6 participants at the 400 mg daily dose. As a result, the maximum tolerated dose of vorinostat in combination with palliative radiotherapy was determined to be 300mg daily. The study concluded that vorinostat can be safely combined with short term palliative radiotherapy. It should be noted that the adverse events observed in the combination trial overlap with the toxicity profile of vorinostat listed in the package insert. Anecdotal experience in a patient who was failing standard course of TSEBT is relevant and is described here. This patient's skin lesions were progressing towards the latter half of his TSEBT course, thus, vorinostat was initiated and overlapped with TSEBT in the last 2 weeks. The patient tolerated the combination well without any worsening skin reactions and his skin lesions cleared completely. At one year follow-up, his skin is still in complete remission. Another patient received a combination of romidepsin, another (HDAC) inhibitor, and low-dose (12 Gy) TSEBT. He had CR after the addition of TSEBT, while his skin lesions were stable on romidepsin alone. Based on preclinical, early clinical data and anecdotal experience, it is anticipated that vorinostat in combination with TSEBT can be administered safely and will be tolerated in participants with MF. In addition, within the recognized limits of a phase 1-2 clinical trial, this study may provide an assessment of the anti-tumor activity of vorinostat in combination with TSEBT in participants with MF and thus allow us to evaluate the radiation-enhancing potential of vorinostat. This study is a multicenter phase 1-2, randomized, 2-arm trail exploring the efficacy of TSEBT 12 Gy alone vs TSEBT 12 Gy + vorinostat. 12 Gy was selected for this study because it is effective as a rapid debulking agent (with overall response rates of near 100% in the retrospective study and ongoing clinical trial) and can be administered conveniently over 3 weeks. Because of the diminished clinical CR rates associated with TSEBT doses \< 30 Gy, it is proposed that combining TSEBT 12 Gy with vorinostat will lead to significantly higher complete response (CR) rates, longer time-to-progression (TTP), and improved quality of life as compared to TSEBT 12 Gy alone. Based on the retrospective study and preliminary experience in the ongoing 12 Gy TSEBT trial, it is hypothesized that 12 Gy is an adequate dose to achieve clinically meaningful outcomes and that the vorinostat may enhance its clinical efficacy while minimizing radiation-associated toxicities due to the shortened treatment duration. Participants are stratified by MF stage as follows. * Stage IB: \~10 % skin involvement, with up to 1000/mm3 clone+ Sezary cells in blood. * Stage IIA: Up to 10 % skin involvement, with up to 1000/mm3 clone+ Sezary cells in blood and clinically abnormal peripheral lymph nodes. * Stage IIB: One or more tumors 1 cm in diameter, with up to 1000/mm3 clone+ Sezary cells in blood and clinically abnormal peripheral lymph nodes. * Stage IIIB: Skin erythema \>80 % body surface area, with up to 1000/mm3 clone+ Sezary cells in blood and clinically abnormal peripheral lymph nodes. For detailed staging information, see References: Olsen E, et al. Blood. 2007;110:1713-1722. PMID: 17540844