Therapeutic Eradication of Cancer Stem Cells
Cancer is a leading cause of death in California. Research has found that many cancers can spread throughout the body and resist current anti-cancer therapies because of cancer stem cells, or CSC. CSC can be considered the seeds of cancer; they can resist being killed by anti-cancer drugs and can lay dormant, sometimes for long periods, before growing into active cancers at the original tumor site, or at distant sites throughout the body. Required are therapies that can kill CSC while not harming normal stem cells, which are needed for making blood and other cells that must be replenished. We have discovered a protein on the surface of CSC that is not present on normal cells of healthy adults. This protein, called ROR1, ordinarily is found only on cells during early development in the embryo. CSC have co-opted the use of ROR1 to promote their survival, proliferation, and spread throughout the body. We have developed a monoclonal antibody that is specific for ROR1 and that can inhibit these functions, which are vital for CSC. Because this antibody does not bind to normal cells, it can serve as the “magic bullet” to deliver a specific hit to CSC. We will conduct clinical trials with the antibody, first in patients with chronic lymphocytic leukemia to define the safety and best dose to use. Then we plan to conduct clinical trials involving patients with other types of cancer. To prepare for such clinical trials, we will use our state-of-the-art model systems to investigate the best way to eradicate CSC of other intractable leukemias and solid tumors. Finally, we will investigate the potential for using this antibody to deliver toxins selectively to CSC. This selective delivery could be very active in killing CSC without harming normal cells in the body because they lack expression of ROR1. With this antibody we can develop curative stem-cell-directed therapy for patients with any one of many different types of currently intractable cancers.
The proposal aims to develop a novel anti-cancer-stem-cell (CSC) targeted therapy for patients with intractable malignancies. This therapy involves use of a fully humanized monoclonal antibody specific for a newly identified, CSC antigen called ROR1. This antibody was developed under the auspices of a CIRM disease team I award and is being readied for phase I clinical testing involving patients with chronic lymphocytic leukemia (CLL). Our research has revealed that the antibody specifically reacts with CSC of other leukemias and many solid-tumor cancers, but does not bind to normal adult tissues. Moreover, it has functional activity in blocking the growth and survival of CSC, making it ideal for directing therapy intended to eradicate CSC of many different cancer types, without affecting normal adult stem cells or other normal tissues. As such, treatment could avoid the devastating physical and financial adverse effects associated with many standard anti-cancer therapies. Also, because this therapy attacks the CSC, it might prove to be a curative treatment for California patients with any one of a variety different types of currently intractable cancers.
Beyond the significant benefit to the patients and families that are dealing with cancer, this project will also strengthen the position of the California Institute of Regenerative Medicine as a leader in cancer stem cell biology, and will deliver intellectual property to the state of California that may then be licensed to pharmaceutical companies.
In summary, the benefits to the citizens of California from the CIRM disease team 3 grant are:
(1) Direct benefit to the thousands of patients with cancer
(2) Financial savings through definitive treatment that obviates costly maintenance or salvage therapies for patients with intractable cancers
(3) Potential for an anti-cancer therapy with a high therapeutic index
(4) Intellectual property of a broadly active uniquely targeted anti-CSC therapeutic agent.
Dormant cancer stem cells (CSC) evade therapies that target dividing cells and promote drug-resistance, relapse, and metastasis. Despite advances in molecularly targeted therapy, therapeutic resistance and relapse, driven by self-renewing CSC, remain major therapeutic challenges in common hematologic malignancies like chronic lymphocytic leukemia (CLL). As a result of a CIRM HALT leukemia disease team grant, we were able to pre-clinically inhibit CSC survival in CLL and a broad array of other advanced malignancy models by developing a monoclonal antibody, cirmtuzumab (UC-961), which targets the Wnt5A receptor, ROR1. Cirmtuzumab is a humanized monoclonal antibody (mAb) that binds with high-affinity to a proprietary, extracellular epitope of ROR1, which we defined as an onco-embryonic antigen. While ROR1 is not expressed on adult hematopoietic stem cells or other normal post-partum tissues, it is highly expressed on the cell-surface of CSC in CLL. Cirmtuzumab does not bind to normal adult tissues, but has unique functional activity against CSC by targeting ROR1, which acts in a niche-dependent fashion. In preclinical models, shRNA-silencing of ROR1 was shown to impair activation of phospho-AKT/CREB, increases spontaneous apoptosis, and inhibit the proliferation, migration, and metastatic potential of CSC in a manner similar to cirmtuzumab. In addition, cirmtuzumab inhibits the capacity of CSC to to propagate CLL in immune-deficient mice. Finally, cirmtuzumab induced rapid internalization of ROR1, thereby inhibiting CSC survival. Based on these unique features, we proceeded with the cirmtuzumab clinical development plan under the auspices of the CIRM disease team 3 grant.
Over the last year, this CIRM Disease team grant has enabled filing and FDA approval of an investigational new drug application (IND) for cirmtuzumab as well as the implementation and administration of an ongoing first-in-human Phase 1A clinical trial to assess safety and tolerability in patients with CLL who are not amenable to standard therapy. In keeping with the FDA IND-approved intra-patient dose escalation schema and related cirmtuzumab administration timeline, our team has enrolled 8 patients to the Phase lA clinical trial at UC San Diego for patients with relapsed or refractory CLL since 8/29/15. In particular, we have now completed enrollment of the first and second dose cohorts (doses: 15 mcg/kg and 30 mcg/kg for cohort 1; 60 mcg/kg, 120 mcg/kg, and 240 mcg/kg for cohort 2). There have been no observed grade 2 or higher adverse events attributed to cirmtuzumab. Two patients have now enrolled and initiated therapy in the third dose cohort (planned doses 500 mcg/kg and 1 mg/kg). While durable clinical responses have not been observed at these low doses, there has been evidence of biological activity and clinical benefit with stabilization of disease in some patients. This has prompted the development of a Phase 1B clinical trial, currently under review at our IRB and at CIRM, to allow patients that have derived some benefit from cirmtuzumab treatment to receive additional doses and to determine if longer term treatment provides for enhanced clinical benefit while retaining an excellent safety profile.
Correlative biomarkers include flow cytometric analyses that address disease heterogeneity and are suggestive of decreased ROR1 expression in the more recent dosing cohorts that may be used in the future to predict clinical outcome. In cohorts that demonstrate signs of sustained clinical responses, we will examine the activity of cirmtuzumab-based treatments in eradicating ROR1+ CSC by flow cytometry. Pharmacokinetic assessments are ongoing but cirmtuzumab plasma levels appear to correlate with response in the more recent higher dose cohort. In addition, we will examine the activity and anticipated therapeutic index (TI) of cirmtuzumab in relapsed/refactory CLL. If one or more of these tests meet milestones, then clinical studies of regimens with the highest apparent TI will be conducted in years 3-4. Upon completion of our program, we will deliver a cirmtuzumab-based therapeutic that will be suitable for registration and/or pivotal clinical trials and facilitate commercialization of this novel cancer stem-cell targeted therapy for Californians with cancer.