Clinical Trial: Phase 1b/3 Targeted Alpha-Emitter PRRT RYZ101 (Ac225)


What is Alpha-emitter PRRT? 

Substitution of an alpha emitter (e.g. ²¹²Pb) for the beta emitters currently being used (i.e., 177Lu or 90Y) will provide significantly higher Linear Energy Transfer (LET) and a shorter path length. Higher LET particles should cause more tumour cell death. Shorter path length should result in less collateral damage of the normal tissue and therefore less side effects for subjects receiving the drug.

What is RYZ101?

RYZ101 is an investigational targeted alpha-emitter radiopharmaceutical therapy, designed to deliver a highly potent radioisotope, Actinium-225 (Ac225), to tumors expressing SSTR2. RYZ101 is being evaluated in clinical studies for patients with SSTR+ GEP-NETs who have previously been treated with Lu177-based somatostatin therapies.  There is also a plan to trial the drug in patients with extensive stage (ES) small cell lung cancer (SCLC), a type of lung Neuroendocrine Carcinoma.

Where did this news come from?

RayzeBio, Inc., a targeted radiopharmaceutical company developing an innovative pipeline against validated solid tumor targets, today announced significant progress in the clinical development of its lead product candidate, RYZ101. RYZ101 is an investigational, targeted radiopharmaceutical drug designed to deliver Actinium-225 (Ac225), a highly potent alpha-emitting radioisotope, to solid tumors expressing the somatostatin receptor (SSTR).

Headlines points for busy people:

— The company is enrolling in ACTION-1 study, a Phase 1b/3 trial of RYZ101, for treatment of neuroendocrine tumors (see details below)

— The RayzeBio received Investigational New Drug Application (IND) clearance from the U.S. Food and Drug Administration (FDA) to investigate RYZ101 for first-line treatment of patients with SSTR+ extensive-stage small cell lung cancer (ES-SCLC) in combination with standard of care.  This is a type of Lung Neuroendocrine Carcinoma

— The company say that RYZ101 is positioned to be the first approved Actinium-225 radiopharmaceutical therapy for the industry. 

The Company is enrolling patients in the Phase 1b portion of the ACTION-1 Phase 1b/3 trial of RYZ101 (NCT05477576). Safety, tolerability, and pharmacokinetics of RYZ101 will be evaluated in patients SSTR+ gastroenteropancreatic neuroendocrine tumors (GEP-NETs) who have progressed on Lu-177 labelled somatostatin analogue therapy. Enrollment is progressing as planned and RayzeBio expects to announce data from the trial in 2023.

A statement from the company and leading US nuclear radiologists

“Clinicians and patients are very excited about the mechanism of action of RYZ101 and the advantages it offers. Significant interest is growing to explore Ac225, a highly potent radioisotope, for treatment of solid tumors. We believe RYZ101 has strong scientific rationale for treatment of both GEP-NETs and small cell lung cancer. We are very encouraged with the level of interest we have seen in the program and look forward to reporting results from RYZ101 in due course,” said Susan Moran, M.D., M.S.C.E., Chief Medical Officer of RayzeBio.

“Ac225 has the potential to provided increased efficacy compared to existing beta particle therapy, and we are excited to see the first randomized phase 3 trial evaluating an actinium labeled compound (RYZ101). ACTION-1 will study this treatment in patients with advanced neuroendocrine tumors of the GI tract and pancreas, who have limited effective treatment options. This trial will be the next step forward in improving treatment of these patients,” said Dr. Thomas Hope, M.D., Vice Chair of Clinical Operations and Strategy in the Department of Radiology. Dr. Hope is the chair of the steering committee for the phase 3 portion of ACTION-1 study.

As referenced in another press release issued today, RayzeBio has raised $418 million in equity capital since inception in 2020, including $160 million raised in a Series D financing, to advance targeted radiopharmaceutical therapies for cancer.

Who is RayzeBio?

RayzeBio is a biotechnology company focused on improving outcomes for people with cancer by harnessing the power of targeted radioisotopes. With a focus on clinically validated solid tumor targets, RayzeBio is developing novel drug conjugates to deliver potent therapeutic radioisotopes such as Actinium-225, an alpha-emitter. The company is backed by a syndicate of sophisticated healthcare investors and was established in 2020. For additional information, please visit

Sources used in the compilation of this post

  1. RayzeBio news – click here
  2. RayzeBio website – click here
  3. The clinical trial document for the ALPHA1 trial:  NCT05477576 (click here) (As at 8th Jan 2022, only 7 trial centres in USA are listed)
  4. The clinical trial document for the Small Cell Lung Cancer trial – click here

Targeted Alpha-Emitter Therapy

Read my general Alpha-emitter PRRT blog post here or click on the picture below:

Click to read

Other trials for Alpha-Emitter PRRT

The industry has settled on two different radionuclides so far, AC225 and Pb212.  This blog post covers AC225 but 212Pb has been around longer and the biggest trial is contained in this post below.  Click here or on the picture to read more.

Click the picture to read more

General Clinical Trials Disclaimer

Choosing to participate in a study is an important personal decision. Talk with your doctor and family members or friends about deciding to join a study. To learn more about this study, you or your doctor may contact the study research staff using the contacts provided in the clinical trials document. It’s very important to check the trial inclusion and exclusion criteria before making any contact.  If you need questions, the articles here is very useful Questions to Ask About Clinical Trials | Cancer.Net

The inclusion of any trial within this blog should not be taken as a recommendation by Ronny Allan. 



I am not a doctor or any form of medical professional, practitioner or counsellor. None of the information on my website, or linked to my website(s), or conveyed by me on any social media or presentation, should be interpreted as medical advice given or advised by me.  Neither should any post or comment made by a follower or member of my private group be assumed to be medical advice, even if that person is a healthcare professional as they are not members of the private group or followers of my sites in any official capacity.  Please also note that mention of a clinical service, trial/study or therapy does not constitute an endorsement of that service, trial/study or therapy by Ronny Allan, the information is provided for education and awareness purposes and/or related to Ronny Allan’s own patient experience. This element of the disclaimer includes any complementary medicine, non-prescription over the counter drugs and supplements such as vitamins and minerals.


Whenever I post about a trial or study, some people get excited without understanding that these new treatments and capabilities can very often take years to come to fruition and it’s also possible that clinical trials can be halted, or that national approval agencies will not approve the final product.  Plus, not everyone will be eligible, so always check the exclusion and inclusion criteria in the relevant clinical trials document  Please bear that in mind when reading studies/clinical trials posted on RonnyAllan.NET

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