Final Report of a Phase I Study of Clofarabine Plus High Dose Melphalan as a Conditioning Regimen for Allogeneic Transplantation
Authors: Kirschbaum Mark , Stein Anthony Selwyn , Frankel Paul , Popplewell Leslie , Chen Robert w , Delioukina Maria L , Nakamura Ryotaro , Snyder David S. , Slape Cynthia , Ruel Christopher , Conrad Joel , Nademanee Auayporn , Forman Stephen 
Published: October 2019

Abstract
Abstract 528

Background:
Allogeneic Stem Cell transplantation remains the only curative treatment modality for hematologic malignancies such as AML, ALL, and MDS. Reduced intensity regimens were designed which replaced the alkylating agent cyclophosphamide with the purine nucleoside antimetabolite, fludarabine, a potent immunosuppressive with a substantially milder toxicity profile. Clofarabine is a purine nucleoside analogue designed to exploit a double halogen strategy which confers resistance to adenosine deaminase, increases stability and bioavailability and makes the drug more efficient than fludarabine at inhibiting ribonucleotide reductase (RNR) and disrupting mitochondrial function, leading to apoptosis. Clofarabine is potentially a superior antileukemic agent as compared with fludarabine, thus enhancing the activity of the conditioning regimen.

Aims:
To evaluate a novel clofarabine containing regimen as conditioning for adult fully matched allogeneic stem cell transplant.

Methods:
phase I dose escalation: clofarabine (dose level 1 = 30 mg/m2, dose level 2 and 3 =40 mg/m2) IV daily days –7 to day –3 infused over 30 minutes IV, plus Melphalan (dose level 1 and 2, 100mg/m2, dose level 3, 140 mg/m2) administered over 30 minutes IV on day –2. Related or unrelated allogeneic stem cells were infused on day 0. GVHD prophylaxis: initially cyclosporine plus mycophenolate, then tacrolimus plus sirolimus was adopted as per City of Hope standard of care. Patients (pts) age ≥ 18 years with AML, ALL, MDS in either CR1, CR2 or in relapse (up to 50% marrow blasts), not deemed eligible for standard transplant regimens by the attending physician, or at high risk for relapse, are eligible.

Results:
16 eligible pts, all with AML, have been treated thus far, 7,males, 9 females, with a median age of 63 years (30 – 66). Seven pts were in CR1, 2 pts were in CR2, 4 pts where induction failures, and 3 pts were in first relapse. Grade 3 non-hematologic toxicities included elevation of transaminases, diarrhea, and hyponatremia. No dose limiting toxicities (DLT) were seen in the 3 pts treated at dose level 1. One patient in dose level 2 died prior to engraftment due to hepatic, renal, and infectious toxicities; that dose level has been expanded to 12 patients and no further DLTs were seen. The first patient treated at dose level 3 developed multiorgan failure and died prior to engraftment. Given the excellent results seen in the two previous cohorts we opted not to dose escalate any further patients beyond clofarabine 40 mg/m2 and melphalan 100 mg/m2. Three patients with primary induction failure received an unrelated donor graft and had complete engraftment and obtained remission. The median time to ANC recovery is 14 days and to platelet recovery is 16 days (see table). Mild acute skin graft versus host disease (GvHD) was seen in five patients, mild chronic GvHD in four patients, one patient developed severe chronic GVHD of the liver and died at day 201 from CNS bleed due to tacrolimus-sirolimus related TTP-HUS. Of the 14 patients that successfully completed transplant (no DLT or engraftment difficulty), only one patient has relapsed, with median follow-up of 10.5 months (range 4–24).

Conclusion:
The combination of clofarabine and melphalan is a well tolerated reduced intensity conditioning regimen with enhanced anti-leukemia activity leading to complete engraftment of related and unrelated fully matched allogeneic stem cells. Complete engraftment with prolonged disease free survival was seen at both dose levels 1 and 2.

Disclosures:
Off Label Use: clofarabine as a component of the conditioning regimen for allogeneic transplant.