Inclusion Criteria:

- Males and females Histologically confirmed GBM (Patients with gliosarcoma are also
eligible)

- Assessable or measurable disease by MRI

- Progression after prior treatment that includes radiation, temozolomide and
bevacizumab.

-> 4 weeks since prior chemotherapy, bevacizumab and other systemic treatment and > 3
weeks from prior radiation.

- age >18 years

- Weight < 150 kg.

- Karnofsky performance score > 60

- Life expectancy >12 weeks

- Brain MRI within 21 days prior to registration

- Laboratory results requirements

- Absolute neutrophil count (ANC) ≥ 1000/mm3.

- Platelets (Plt) ≥ 100,000/mm3

- Hemoglobin (Hgb) ≥ 8.0 g/dL

- Total bilirubin ≤ 2.0 mg/dL

- Serum alanine transferase/ Serum aspartate transaminase (ALT/AST) ≤ 2.5x the
upper limit of normal (ULN)

- Serum creatinine ≤ 2.0 mg/dL

- Pancreatic Amylase (p-amylase) ≤ the ULN

- Negative serum pregnancy test for women of child-bearing potential

- Stable corticosteroid dose at least 14 days prior to registration

- Women of childbearing potential must have a negative pregnancy test.

- Men and women of childbearing potential must be willing to consent to using effective
contraception while on treatment and for at least 3 months thereafter.

- Patients must not be on enzyme-inducing anti-epileptic drugs (EIAED). Patients may
be on non-enzyme inducing anti-epileptic drugs (NEIAED) or may not be taking any
anti-epileptic drugs. A list of AED that cause modest or no induction of hepatic
metabolic enzymes will be discussed

Exclusion Criteria:

- Non-GBM primary invasive malignant neoplasm within the five years prior to screening
except for:

- keratinocyte (non-melanoma) (i.e., basal cell, squamous cell) carcinoma of the
skin; or low-grade papillary superficial transitional cell carcinoma of the
bladder.However, patients with stage 1 cancers not requiring cancer therapy
including chemotherapy or hormone therapy, for which a lifespan of greater than
3 years without treatment is expected (such as early stage prostate cancer) may
be enrolled.

- Clinically significant cardiac disease (New York Heart Association Class III/ IV or
severe debilitating pulmonary disease

- Subjects with QTc>500 msec (either Bazzett's or Fridericia's method)

- Radiation therapy, cytotoxic chemotherapy, bevacizumab or other treatment for GBM
within previous three weeks

- Evidence of an active infection requiring ongoing intravenous antibiotic therapy

- Any toxicity ≥ grade 2 (non-laboratory) (NCI CTCAE, Version 4.03) prior to first dose
of study drug

- Prior treatment with PSMA ADC or other therapies targeting PSMA, or other anti-body
drug conjugate (ADC) products that contain monomethyl auristatin E (MMAE) (e.g.,
brentuximab vedotin, glembatumumab vedotin, ASG-5ME)

- Known hypersensitivity reactions to PSMA ADC or any of its components.

- Any medical condition that in the opinion of the Investigator may interfere with a
subject's participation in or compliance with the study

- Patients with a prior history of pancreatitis