Safety and Tolerability of ²¹²Pb-DOTAM-GRPR1 in Adult Subjects With Recurrent or Metastatic GRPR-expressing Tumors

1. Adult participants (age ≥ 18 years old) with any of the following advanced or metastatic solid tumors (documented history of histologically confirmed diagnosis): 1. Metastatic castration-resistant prostate cancer (mCRPC) including neuroendocrine prostate cancer (NEPC) (enrolled only in SAD and MAD Q6W) 2. HR+/HER2- breast cancer (estrogen receptor/ER expression \>10% of tumor cell nuclei stain, regardless of progesterone receptor/PgR expression); HER2-negative including HER2-low (as per relevant ASCO/CAP guidelines) 3. Colorectal cancer 4. Cervical cancer 5. Non-small-cell lung cancer (NSCLC) 6. Recurrent glioblastoma (only enrolled in MAD Q4W cohorts) with evidence of recurrent disease (RD) demonstrated by disease progression using modified Response Assessment in Neuro-Oncology (RANO 2.0) criteria. Note: If surgery is performed for GBM recurrence, pre-surgery MRI will be used for confirmation of RD and residual and measurable disease post-surgery is not required but surgery must have confirmed the recurrence diagnosis by MRI. 2. Capable of giving signed informed consent 3. All participants must have progressed on at least 2 prior systemic therapies, except for recurrent GB 4. For participants with mCRPC: Prior orchiectomy and/or ongoing androgen deprivation therapy and a castrate level of serum testosterone (\<50 ng/dL or \<1.7 nmol/L) 5. Presence of at least 1 measurable lesion per RECIST 1.1 as assessed by the Investigator (not applicable for GBM). At…