Inclusion Criteria:

1. Age more than or equal to 18 years

2. Subjects with histologically or cytologically confirmed SCCHN that is recurrent
and/or metastatic and judged incurable by surgery and/or radiation therapy and with
zero to one line of chemotherapy for recurrent or metastatic disease at least 60 days
prior to study entry.

3. Measurable disease, defined as at least one unidimensionally measurable lesion ≥ 20
mm by conventional techniques or ≥10 mm by spiral computerized tomography (CT) scan
or magnetic resonance imaging (MRI)

4. Tumor that is accessible to biopsy

5. Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2

6. Life expectancy of at least three months

7. Hemoglobin ≥ 8.0 gm/dL

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

9. Platelet count ≥ 50,000/mm3

10. Total bilirubin ≤1.5X institutional upper limit of normal (ULN)

11. Serum AST ≤ 3X institutional ULN

12. Serum ALT ≤ 3X institutional ULN

13. Serum creatinine ≤1.5X institutional ULN

14. Ability to understand and the willingness to sign a written informed consent document
(ICD)

Exclusion Criteria:

1. Nasopharyngeal carcinoma

2. Prior treatment with P276-00 or other Cyclin dependent kinase (CDK) targeting agents

3. History of allergic reactions attributed to compounds of similar chemical composition
to P276-00

4. Subjects who have received radiotherapy, chemotherapy or biologic/targeted anticancer
agents within 60 days prior to Day 1 of study drug administration or have not
recovered from adverse effects of any prior radiotherapy, chemotherapy or
biologic/targeted agents.

5. More than one chemotherapy regimen for the recurrent or metastatic disease

6. Subjects who had received any other investigational drug within 1 month or within
five half-lives of the other investigational agent, whichever is longer prior to Day
1 of study drug administration

7. Subjects with QTc > 450 msec on 12 lead standard electrocardiogram (ECG)

8. History of unstable angina or myocardial infarction or stroke within previous 6
months

9. Subjects with uncontrolled inter-current illness including, but not limited to active
infection, symptomatic congestive heart failure, cardiac arrhythmia, or psychiatric
illness/social situations that would limit compliance with study requirements

10. Subjects known to be suffering from infection with HIV, Tuberculosis, Hepatitis C or
Hepatitis B

11. Known brain metastasis

12. History of prior malignancy except for curatively treated basal cell or squamous cell
carcinoma of skin, in situ cervical cancer, in situ breast cancer, in situ prostate
cancer or any other cancer for which the subject has been disease-free for at least 3
years

13. Women who are pregnant or lactating

14. Women of childbearing potential [defined as sexually mature women who have not
undergone hysterectomy or who have not been naturally postmenopausal for at least 24
consecutive months (i.e. who have had menses any time in the preceding 24 consecutive
months)] and men, not agreeing to use adequate contraception (e.g., hormonal or
barrier method of birth control or abstinence) prior to study entry (after signing
the ICD), during the period of study participation and for at least 4 weeks after
withdrawal from the study, unless they are surgically sterilized

15. Any condition, including laboratory abnormalities, that in the opinion of the
Investigator places the subject at an unacceptable risk or deems the subject not
suitable for participation in the study