The Company leases office space under agreements classified as operating leases. The Company’s active leases as of March 31, 2021 are for office and manufacturing space in Tucson, Arizona, which expire in 2022. The Company’s leases do not include any contingent rental payments, impose any financial restrictions, or contain any residual value guarantees.

The Company amended its Tucson facility leases in December 2020 to extend the terms of the leases for one year, through January 31, 2022. The lease extensions were treated as lease modifications for accounting purposes, and allow for an additional extension of three years on the same terms and conditions of the existing amended lease agreement, except that the lease rates would be adjusted to reflect lease rates applicable to like-kind buildings within the market at the time that the Company elects to exercise the extension options, but in no event less than the last applicable rental rate. The Company has not accounted for these renewal options in the calculation of the lease liabilities and right-of-use assets as the Company is not reasonably certain to exercise the options.

In the first quarter of 2021, the Company closed its development laboratory in San Carlos, California and, as a result, $0.2 million of operating right-of-use assets related to the abandonment of the laboratory were written off to research and development expense during the three months ended March 31, 2021.

	Three Months Ended March 31,
	2021		2020
Operating leases
Operating lease cost	$	167,679	$	205,227
Variable lease cost		26,151		9,456
Operating lease expense		193,830		214,683

The table below summarizes other information related to the Company’s operating leases:

	Three Months Ended March 31,
	2021			2020
Cash paid for amounts included in measurement of operating lease liabilities	$	172,095		$	218,625
Weighted-average remaining lease term – operating leases		0.8			2.1
Weighted-average discount rate – operating leases		6.3	%		9.6	%

Remaining maturities of the Company’s operating leases, excluding short-term leases, included in operating lease liabilities – current in the condensed consolidated balance sheets as of March 31, 2021 are as follows:

2021	$	346,293
2022		38,446
Total		384,739
Less present value discount		(10,793	)
Total operating lease liabilities	$	373,946

The Company has a number of computer and copier equipment leases that are classified as financing leases. Incremental borrowing rates used to discount future lease payments in calculating lease liabilities were estimated by reference to information received by the Company from bankers regarding estimated current borrowing rates for collateralized loans with similar amount and duration as the leases. The Company does not have any material financing leases where it acts as a lessor.

	Three Months Ended March 31,
	2021		2020
Financing leases
Amortization of right-of-use assets	$	7,099	$	12,518
Interest on lease liability		1,665		2,635
Total financing lease cost	$	8,764	$	15,153

The table below summarizes other information related to the Company’s financing leases:

	Three Months Ended March 31,
	2021			2020
Weighted-average remaining lease term – financing leases		3.3			3.6
Weighted-average discount rate – financing leases		9.77	%		9.77	%

As of March 31, 2021, remaining maturities of the Company’s financing leases are as follows:

2021	$	19,785
2022		20,716
2023		18,396
2024		16,080
Total		74,977
Less present value discount		(11,208	)
Financing lease liabilities, net	$	63,769

Financing lease liabilities net of discount of $63,769, of which $20,293 and $43,476 were included in other current liabilities and other non-current liabilities, respectively, and financing right-of-use assets of $59,671, were included in property and equipment, net, in the condensed consolidated balance sheet as of March 31, 2021.