Second Treatment Free Remission after Combination Therapy with Ruxolitinib Plus Tyrosine Kinase Inhibitors in Chronic Phase Chronic Myeloid Leukemia (CML)
Authors: Sweet Kendra , Atallah Ehab L. , Radich Jerry P. , Zhang Mei-Jie , Sahakian Eva , Mediavilla-Varela Melanie , Vistocky Alexis , Heinrich Michael C. , Thompson James E. , Mauro Michael J. , Flynn Kathryn E , Baim Arielle , Pinilla Ibarz Javier 
Published: November 2021

Abstract
Background:
Discontinuation of tyrosine kinase inhibitors (TKIs) is feasible in a subset of CML patients who have maintained a deep molecular response for at least two years. Numerous discontinuation trials have been performed and consistently show approximately 50% of patients relapse after stopping TKIs. A recent study examining rates of treatment free remission (TFR) after a second attempt at stopping TKIs found, with a median follow up time of 38.3 months, 64.3% of patients had a molecular relapse (defined as a loss of major molecular response (MMR)). At 12, 24 and 36 months, TFR rates were 48%, 42% and 35%, respectively. These data suggest some patients with a history of molecular relapse upon TKI cessation could successfully stop treatment on a subsequent attempt, yet the majority will relapse a second time. 'Complete eradication' of CML remains elusive in most patients likely as a result of minimal residual disease (MRD), which is the result of BCR-ABL independent drug resistance. More specifically, CML cells that reside in sanctuary sites such as the bone marrow adhere to fibronectin and demonstrate cell adhesion mediated drug resistance (CAM-DR). The bone marrow microenvironment contains many cytokines and growth factors capable of inducing STAT3-Y705 phosphorylation via the JAK-STAT pathway leading to protection against TKI-induced cell death. Inhibiting JAK2 and TYK2 leads to complete inhibition of pSTAT3-Y705, thereby implicating the role of activation of JAK2 and TYK2 in STAT3-Y705 phosphorylation and resistance towards BCR-ABL TKI-induced cell death. A phase I clinical trial combined ruxolitinib, which inhibits JAK2 and TYK2, plus nilotinib in chronic phase (CP) CML patients and found that ruxolitinib 15mg PO BID was safe and well tolerated with 4/10 patients achieving undetectable BCR-ABL1 transcripts by PCR.
Study Design and Methods:
This single arm phase II study (NCT03610971) will enroll 41 subjects from the H Jean Khoury Cure CML Consortium. Eligible subjects must have a confirmed diagnosis of CP-CML and have previously attempted to discontinue TKI therapy per NCCN guidelines and had molecular recurrence, defined as loss of MMR, and were restarted on TKI.
This trial combines ruxolitinib 15mg BID plus BCR-ABL TKI (imatinib, dasatinib, nilotinib or bosutinib) for 12 28-day cycles in the combination treatment phase (CTP). RQ-PCR to measure BCR-ABL transcripts will be checked at screening and every three months during the CTP. In the event that a subject experiences intolerance to a TKI, has confirmed loss of MMR, or loss of MR4.5 (&gt;0.0032% IS) on two central PCR results, or discontinues ruxolitinib, the subject will be removed from CTP and enter into long term follow-up (LTFU).
CTP phase will be followed by further RQ-PCR screening for the concurrent TFR phase. At this time ruxolitinib will be discontinued and any subject who has met the criteria for the TFR phase will be enrolled. During the TFR phase, subjects will discontinue their TKI and be monitored off treatment with RQ-PCR checked monthly for the first year, every six weeks for year two, and every 12 weeks during year three. Upon molecular recurrence, defined as loss of MMR, TKIs will be restarted.
The primary endpoint is the 12-month TFR rate subsequent to completion of 12 cycles of combination therapy; however, subjects will remain in the TFR phase for three years. Therefore, the total duration of the trial will be approximately five years (one year on CTP + three years in the TFR phase + one-year LTFU). Study statistical design was calculated to yield a one-sided type I error rate of 0.025 and power of 65% when the true one-year relapse rate is 35%.
This study will additionally assess patient-reported outcomes in conjunction with RQ-PCR testing. PROMIS and other measures will be self-administered through REDCap. Correlative studies will include comparing changes in pSTAT3 in K562 and KU812 cell lines using plasma from CML patients being treated with TKIs plus ruxolitinib, using the plasma inhibitory assay technique. Changes in pSTAT3 and pSTAT5 will be correlated with clinical response and rate of TFR. Additional correlatives include multiparameter flow-based assessment of the T-cell compartment (activity/polarization) as well as natural killer cell fractions in CML patients at various time points (TKIs alone, TKIs plus ruxolitinib and during TFR).
Thus far, 14 patients have been enrolled.

Disclosures
Sweet: Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; AROG: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Bristol Meyers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees. Atallah: Amgen: Consultancy; BMS: Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; Abbvie: Consultancy, Speakers Bureau. Radich: Amgen: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Genentech: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees. Thompson: Novartis/ Bristol-Myers Squibb: Research Funding. Mauro: Pfizer: Consultancy; Takeda: Consultancy; Bristol Myers Squibb: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Sun Pharma / SPARC: Research Funding. Pinilla Ibarz: AbbVie, Janssen, AstraZeneca, Novartis, TG Therapeutics, Takeda: Consultancy, Other: Advisory; Sellas: Other: ), patents/royalties/other intellectual property; MEI, Sunesis: Research Funding; AbbVie, Janssen, AstraZeneca, Takeda: Speakers Bureau.

OffLabel Disclosure:
Ruxolitinib is being used off-label in chronic myeloid leukemia