On December 7, 2020 Actinium Pharmaceuticals, Inc. (NYSE AMERICAN: ATNM) ("Actinium" or the "Company") reported that safety data from its ongoing pivotal Phase 3 SIERRA trial of Iomab-B in patients with relapsed or refractory Acute Myeloid Leukemia (R/R AML) were presented at the 2020 American Society of Hematology (ASH) (Free ASH Whitepaper) annual meeting (Press release, Actinium Pharmaceuticals, DEC 7, 2020, View Source [SID1234572353]). The oral presentation highlighted Iomab-B’s targeting ability and corresponding safety data from 110 patients from the SIERRA trial for which detailed safety data was available. Iomab-B targets CD45, an antigen expressed on leukemia and lymphoma cancer cells and immune cells including bone marrow stem cells but not cells outside of the blood forming or hematopoietic system. This allows high amounts of radiation to be delivered to the bone marrow via Iomab-B while sparing healthy organs. As a result, statistically significant lower rates of sepsis were reported as well as lower rates of febrile neutropenia, mucositis and non-relapse transplant related mortality in patients receiving Iomab-B and bone marrow transplant (BMT) compared to patients that received salvage therapy and a BMT. In addition, patients that crossed over to receive Iomab-B and went to BMT after receiving salvage therapy but not achieving a complete response also had lower rates of sepsis, febrile neutropenia, mucositis and non-relapse transplant related mortality.

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Dr. Mark Berger, Actinium’s Chief Medical Officer, commented, "We are pleased that the engraftment and safety profile of Iomab-B remains positive and consistent with prior interim safety results at 75% of patient enrollment in SIERRA and also consistent with the large body of historical data from Iomab-B. Collectively, this data gives excitement as we approach the upcoming ad hoc interim analysis for SIERRA that will be completed by year-end and the ultimate potential of Iomab-B for patients with R/R AML and other blood cancers as a targeted conditioning regimen."

Safety data presented in ASH (Free ASH Whitepaper) oral presentation are highlighted in the table below:

ASH Oral Presentation: High Doses of Targeted Radiation with Anti-CD45 Iodine (131I) Apamistamab [Iomab-B] Do Not Correlate with Incidence of Mucositis, Febrile Neutropenia or Sepsis in the Prospective, Randomized Phase 3 Sierra Trial for Patients with Relapsed or Refractory Acute Myeloid Leukemia

Adverse Event

1 Adverse Event data available for 46 of 47 evaluable patients

2 Adverse Event data available for 27 of 30 evaluable patients

3 Iomab-B arm: 4 patients unevaluable. Conventional Care Arm: 4 patients unevaluable

Patient Group

No. of
Patients

Radiation dose delivered to
the Marrow. Median (range)

Radiation dose to GI tract.
Median (range)

Iomab-B

Vijay Reddy, Vice President, Clinical Development and Head of BMT, "The targeted nature of Iomab-B makes it highly differentiated from current BMT conditioning regimens that are largely comprised of non-targeted cytotoxic chemotherapies. These data from SIERRA showing higher rates of sepsis, neutropenia and mucositis in patients receiving chemotherapy are consistent with the literature and unfortunately what we expected but hope to address with Iomab-B. Particularly, chemotherapy’s effect on the GI tract and resulting mucositis, which we believe is leading to the higher rates of sepsis seen in the control arm. We are highly encouraged by the lower rates of adverse events and the universal engraftment reported from SIERRA and excited for the potential of targeted conditioning could have an BMT access, patient outcomes and quality of life."

About Iomab-B

Iomab-B (I-131 apamistamab) via the monoclonal antibody apamistamab, targets CD45, an antigen widely expressed on leukemia and lymphoma cancer cells, B cells and stem cells. Apamistamab is linked to the radioisotope iodine-131 (I-131) and once attached to its target cells emits energy that travels about 100 cell lengths, destroying a patient’s cancer cells and ablating their bone marrow. By carrying iodine-131 directly to the bone marrow in a targeted manner, Actinium believes Iomab-B will avoid the side effects of radiation on most healthy tissues while effectively killing the patient’s cancer and marrow cells.

Iomab-B is currently being studied in the pivotal Phase 3 SIERRA (Study of Iomab-B in Relapsed or Refractory AML) trial, a 150-patient, randomized controlled clinical trial in patients with relapsed or refractory Acute Myeloid Leukemia (AML) who are age 55 and above. The SIERRA trial is being conducted at preeminent transplant centers in the U.S. with the primary endpoint of durable Complete Remission (dCR) at six months and a secondary endpoint of overall survival at one year. Upon approval, Iomab-B is intended to prepare and condition patients for a bone marrow transplant, also referred to as a hematopoietic stem cell transplant, in a potentially safer and more efficacious manner than the non-targeted intensive chemotherapy conditioning that is the current standard of care in bone marrow transplant conditioning. A bone marrow transplant is often considered the only potential cure for patients with certain blood-borne cancers and blood disorders. Additional information on the Company’s Phase 3 clinical trial in R/R can be found at www.sierratrial.com.