Inclusion Criteria:

          -  Tissue specimen available for retrospective analysis of B7-H3 and PD-L1 expression.

          -  Eastern Cooperative Oncology Group performance status of ≤2

          -  Life expectancy ≥ 12 weeks for dose escalation phase and ≥ 24 weeks for cohort
             expansion phase

          -  Measurable disease. Prostate cancer patients with bone only disease are eligible.

          -  Acceptable laboratory parameters and adequate organ reserve.

          -  Dose Escalation Phase: Patients with histologically proven, unresectable, locally
             advanced or metastatic solid tumors for whom no therapy with demonstrated clinical
             benefit is available.

        Module A Cohort Expansion:

          -  mCRPC that has progressed with one prior line of chemotherapy for metastatic disease
             and no more than two prior lines of anti-hormonal therapy.

          -  NSCLC: metastatic disease after standard cytotoxic, targeted, and biologic or
             checkpoint inhibitor therapy. No more than 2 prior lines of chemotherapy.

          -  TNBC: Locally advance or metastatic disease that has progressed following at least one
             systemic therapy.

          -  SCCHN that has progressed during or following at least one systemic therapy for
             metastatic or recurrent unresectable disease. No more than 2 prior lines of
             chemotherapy.

          -  Melanoma that has progressed during or following at least one systemic treatment for
             unresectable locally advanced or metastatic disease. Patients who are intolerant of or
             refused standard therapy are eligible.

        Exclusion Criteria:

          -  Patients with history of prior central nervous system (CNS) metastasis must have been
             treated, be asymptomatic, and not have concurrent treatment for CNS disease,
             progression of CNS metastases on MRI, CT or PET within 6 months, or history of
             leptomeningeal disease or cord compression at the time of enrollment.

          -  Prior treatment with B7-H3 targeted agents for cancer.

          -  Treatment with systemic cancer therapy, biologic agents, or anti-hormonal therapy
             (mCRPC) within 4 weeks, prior small molecule targeted or kinase inhibitors within 14
             days or 5 half-lives, prior radioligand within 6 months

          -  Clinically significant cardiovascular disease.

          -  Clinically significant pulmonary compromise or requirement for supplemental oxygen.

          -  History of clinically-significant cardiovascular disease, including but not limited to
             pericarditis or pericardial effusion.

          -  Active viral (including confirmed or presumed COVID-19), bacterial, or systemic fungal
             infection requiring parenteral treatment within 7 days of first study drug
             administration.

          -  Known history of hepatitis B or C infection or known positive test for hepatitis B
             surface antigen or core antigen, or hepatitis C polymerase chain reaction.

          -  Known positive testing for human immunodeficiency virus or history of acquired immune
             deficiency syndrome.

          -  Major trauma or major surgery within 4 weeks of first study drug administration.

          -  Clinically significant venous insufficiency.

          -  > Grade 1 peripheral neuropathy.

          -  Evidence of pleural effusion.

          -  Evidence of ascites.

          -  Serum testosterone >50 ng/dl or >1.7 nmol/L in mCRPC in Module A Cohort Expansion
             Phase