Cellectar Biosciences Inc (NASDAQ:CLRB) investors are overwhelmingly excited this morning after the biopharmaceutical company provided a positive update on its Phase I clinical study of CLR 131 in patients with relapsed or refractory multiple myeloma following the previously announced successful completion of its third cohort and initiation of Cohort 4 at a 31.25 mCi/m2 dose.

The objectives of the multi-center, open label, Phase I dose escalation study include the characterization of the safety and tolerability of CLR 131 administered as a single dose, 30-minute infusion in patients with relapsed or refractory multiple myeloma, and the establishment of a recommended efficacious dose for Phase II, both with and without dexamethasone, as well as an assessment of therapeutic activity.

The data from Cohort 3 show that the 25 mCi/m2 dose was safe and well tolerated, and those patients experienced a similar adverse event profile to that experienced by patients in the previous two cohorts. The average grade of adverse event by patient was 2.57 in Cohort 3, compared to Cohorts 1 and 2 with average grades of 2.05 and 2.71, respectively. Cohort 3 patients experienced an average of seven adverse events compared to Cohorts 1 and 2 with 4.75 and 4.25 events respectively. However, there were no unexpected adverse events and those adverse events experienced by patients were both predictable and manageable.

All four Cohort 3 patients achieved stable disease and continue to be followed for progression-free survival (PFS) and median overall survival (mOS). It is important to note, that similar to Cohort 2 vs. Cohort 1, patients in Cohort 3 experienced a more substantial and sustained reduction in m-protein, a surrogate marker of efficacy. The company expects to provide a more extensive efficacy data update for Cohort 3 in the near term.

While it is also premature to report survival-related efficacy data from Cohort 3, all patients in Cohorts 1 and 2 continue to experience overall survival benefit. Patients from Cohort 1, who received a single 12.5 mCi/m2 dose, have experienced, to date, mOS of 17.7 months. Cohort 2 patients, who received a single 18.75 mCi/m2 dose, have a current median overall survival of 8.4 months. Based on this data, the company has the option of using an 18.75 mCi/m2 single or multi-dose regimen as monotherapy or in combination with other agents as a therapeutic dose in future clinical studies evaluating efficacy. Importantly, median overall survival for all evaluable patients in each cohort continues to increase, and the company will continue to follow these patients to determine the full extent of the overall survival benefit of CLR 131.

In addition, all evaluable patients in the first two cohorts experienced PFS. The median PFS is 92 days for Cohort 1 and 133 days for Cohort 2, with one Cohort 2 patient continuing to experience PFS.

While no head-to-head studies have been conducted between CLR 131 and other therapies in this heavily pretreated population, a 2016 article published in the peer-reviewed journal, Bone Marrow Transplantation, showed that those patients evaluated that were refractory to both proteasome inhibitors and immunomodulatory drugs have mOS of 9 months and PFS of 5 months.[1] All patients enrolled in Cohorts 1 and 2 were previously treated with both proteasome inhibitors and immunomodulatory drugs and experienced disease progression.

“The clinical performance of CLR 131, particularly its safety, tolerability and survival benefits, continues to exceed our expectations as we begin our fourth cohort with patients receiving a 25 percent dose increase from Cohort 3.  This speaks favorably to the potential of the drug in a single or multi-dose regimen,” said Jim Caruso, president and CEO of Cellectar Biosciences.  “Based on these results, we look forward to providing a full Cohort 3 data update and the imminent initiation of our Phase II clinical trial of CLR 131 in multiple myeloma and other blood cancers, as well as the exploration of additional clinical benefits provided by a second dose midway through the Phase II trial.”

The company recently brought forward guidance for the initiation of its NCI-supported Phase II trial in multiple myeloma and other selected hematologic cancers to the first quarter of 2017. As the study is currently designed, all patients will receive, at a minimum, a single dose of CLR 131 at 25 mCi/m2 infused over approximately 30 minutes, with the option of a second 25 mCi/m2 dose 75-180 days later, based upon physician assessment. The Phase II study will be conducted in up to 15 centers across the United States and Cellectar anticipates initial efficacy data as early as the second half of 2017.

Shares of Cellectar are up nearly 14% to $2.43 in early Monday trading. CLRB has a 1-year high of $6.03 and a 1-year low of $1. The stock’s 50-day moving average is $1.76 and its 200-day moving average is $1.99.

On the ratings front, Ladenburg analyst Wangzhi Li initiated coverage with a Buy rating on CLRB and a price target of $2.70, in a report issued on December 21. The current price target implies an upside of 26% from current levels. According to TipRanks.com, Li has a yearly average loss of 3.4%, a 40% success rate, and is ranked #3362 out of 4501 analysts.

Cellectar BioSciences, Inc. operates as a biopharmaceutical company. It engages developing phospholipid drug conjugates designed to provide cancer targeted delivery of oncologic payloads to cancer stem cells.